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Neural Control and Coordination – CBSE NCERT Study Resources

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11th

11th - Biology

Neural Control and Coordination

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Overview of the Chapter

This chapter explores the neural control and coordination mechanisms in the human body, focusing on the structure and function of the nervous system. It covers topics such as neurons, neural pathways, reflex actions, and the role of the brain and spinal cord in maintaining homeostasis.

Neural Control and Coordination: The process by which the nervous system regulates and integrates the activities of different organs and systems in the body through electrical and chemical signals.

Neural System

The neural system is composed of specialized cells called neurons, which transmit nerve impulses. It is divided into:

  • Central Nervous System (CNS): Includes the brain and spinal cord.
  • Peripheral Nervous System (PNS): Consists of nerves that connect the CNS to the rest of the body.

Structure of a Neuron

A neuron consists of three main parts:

  • Cell Body (Soma): Contains the nucleus and cytoplasm.
  • Dendrites: Short fibers that receive signals from other neurons.
  • Axon: A long fiber that transmits signals to other neurons or effector organs.

Synapse: The junction between two neurons where electrical signals are converted into chemical signals for transmission.

Transmission of Nerve Impulse

Nerve impulses are transmitted through neurons in the form of electrical and chemical signals. The process involves:

  • Resting Potential: The neuron is polarized with a negative charge inside.
  • Action Potential: A rapid depolarization and repolarization of the neuron membrane.
  • Synaptic Transmission: Neurotransmitters are released at the synapse to pass the signal to the next neuron.

Human Brain

The human brain is divided into three main parts:

  • Forebrain: Includes the cerebrum, thalamus, and hypothalamus.
  • Midbrain: Acts as a relay station for auditory and visual reflexes.
  • Hindbrain: Consists of the cerebellum, pons, and medulla oblongata.

Reflex Action: An involuntary and rapid response to a stimulus, mediated by the spinal cord without brain involvement.

Spinal Cord

The spinal cord is a cylindrical structure that extends from the brainstem. It serves as a pathway for nerve impulses and is responsible for reflex actions.

Peripheral Nervous System (PNS)

The PNS includes:

  • Somatic Nervous System: Controls voluntary movements.
  • Autonomic Nervous System (ANS): Regulates involuntary functions like heartbeat and digestion. The ANS is further divided into the sympathetic and parasympathetic systems.

Sense Organs

Sense organs such as the eye and ear play a crucial role in detecting stimuli and transmitting signals to the brain for interpretation.

Photoreceptors: Specialized cells in the retina that detect light and enable vision.

Conclusion

Neural control and coordination are essential for maintaining homeostasis and enabling responses to environmental changes. The nervous system, along with sense organs, ensures efficient communication and regulation within the body.

All Question Types with Solutions – CBSE Exam Pattern

Explore a complete set of CBSE-style questions with detailed solutions, categorized by marks and question types. Ideal for exam preparation, revision and practice.

Very Short Answer (1 Mark) – with Solutions (CBSE Pattern)

These are 1-mark questions requiring direct, concise answers. Ideal for quick recall and concept clarity.

Question 1:
Name the neurotransmitter released at neuromuscular junctions.
Answer:
Acetylcholine is the neurotransmitter at neuromuscular junctions.
Question 2:
What is the function of myelin sheath?
Answer:
Myelin sheath insulates axons and speeds up nerve impulse transmission.
Question 3:
Which part of the brain controls voluntary movements?
Answer:
The cerebrum controls voluntary movements.
Question 4:
What is the role of synapse in neural communication?
Answer:
Synapse allows transmission of signals between neurons.
Question 5:
Name the receptor cells for vision in the retina.
Answer:
Rods and cones are receptor cells for vision.
Question 6:
What is the function of hypothalamus?
Answer:
Hypothalamus regulates body temperature, hunger, and thirst.
Question 7:
Which cranial nerve controls eye movement?
Answer:
Oculomotor nerve controls eye movement.
Question 8:
What is the resting membrane potential of a neuron?
Answer:
Resting membrane potential is -70mV in neurons.
Question 9:
Name the fluid-filled cavities in the brain.
Answer:
Ventricles are the fluid-filled cavities in the brain.
Question 10:
What is the function of cerebellum?
Answer:
Cerebellum maintains balance and coordinates muscle movements.
Question 11:
Which part of the ear contains hair cells for hearing?
Answer:
Cochlea contains hair cells for hearing.
Question 12:
What is the role of dopamine in the brain?
Answer:
Dopamine regulates mood, pleasure, and motivation.
Question 13:
Name the autonomic nervous system division that activates 'fight or flight' response.
Answer:
Sympathetic division activates 'fight or flight' response.
Question 14:
Identify the part of the brain controlling voluntary movements.
Answer:
Cerebrum.
Question 15:
Which receptor detects light in the retina?
Answer:
Photoreceptors (rods and cones).
Question 16:
Name the fluid found in the central canal of the spinal cord.
Answer:
Cerebrospinal fluid (CSF).
Question 17:
Which part of the brain maintains body posture?
Answer:
Cerebellum.
Question 18:
Define reflex action with an example.
Answer:
Definition: Rapid, involuntary response (e.g., knee jerk).
Question 19:
Which ion enters a neuron during depolarization?
Answer:
Sodium (Na⁺).
Question 20:
Name the division of the autonomic nervous system that calms the body.
Answer:
Parasympathetic nervous system.
Question 21:
Identify the structure that connects the two cerebral hemispheres.
Answer:
Corpus callosum.
Question 22:
What is the function of myelin sheath in neurons?
Answer:

It insulates axons and speeds up nerve impulse transmission.

Question 23:
Name the part of the brain responsible for balance and posture.
Answer:

Cerebellum controls balance and posture.

Question 24:
Which neurotransmitter is associated with reward and pleasure?
Answer:

Dopamine regulates reward and pleasure.

Question 25:
What is the role of synaptic vesicles?
Answer:

They store and release neurotransmitters at synapses.

Question 26:
Which part of the neuron receives signals?
Answer:

Dendrites receive incoming signals.

Question 27:
What is the function of Schwann cells?
Answer:

They produce the myelin sheath in PNS.

Question 28:
Which ion enters the neuron during depolarization?
Answer:

Sodium (Na+) ions cause depolarization.

Question 29:
What is the role of the hypothalamus?
Answer:

It maintains homeostasis and regulates hormones.

Question 30:
Name the disorder caused by dopamine deficiency.
Answer:

Parkinson's disease results from low dopamine.

Very Short Answer (2 Marks) – with Solutions (CBSE Pattern)

These 2-mark questions test key concepts in a brief format. Answers are expected to be accurate and slightly descriptive.

Question 1:
What is the function of the myelin sheath in neurons?
Answer:

The myelin sheath acts as an insulating layer around the axon of a neuron.
It speeds up the transmission of electrical impulses (nerve signals) by allowing saltatory conduction.
It also protects and nourishes the axon.

Question 2:
Name the three membranes that make up the meninges covering the brain.
Answer:

The three layers of meninges are:
Dura mater (outermost),
Arachnoid mater (middle),
Pia mater (innermost).

Question 3:
What is the role of the hypothalamus in neural control?
Answer:

The hypothalamus regulates homeostasis by controlling:
Body temperature,
Hunger and thirst,
Pituitary gland secretion,
Emotional responses.

Question 4:
What is the significance of the reflex arc?
Answer:

The reflex arc enables rapid, involuntary responses to stimuli for protection.
It bypasses the brain for faster reaction, involving:
Sensory neuron → Spinal cord → Motor neuron → Effector.

Question 5:
Name the fluid present in the cochlea and its function.
Answer:

The cochlea contains endolymph and perilymph.
They help in transmitting sound vibrations and maintaining balance.

Question 6:
What is the function of synaptic vesicles at a synapse?
Answer:

Synaptic vesicles store and release neurotransmitters into the synaptic cleft.
These chemicals transmit signals from one neuron to another or to muscles/glands.

Question 7:
How does the corpus callosum aid brain function?
Answer:

The corpus callosum is a bundle of nerve fibers connecting the two cerebral hemispheres.
It ensures communication and coordination between both sides of the brain.

Question 8:
Why is the resting membrane potential of a neuron negative?
Answer:

The resting membrane potential (~ -70mV) is negative due to:
Higher K+ leakage outside the cell,
Na+/K+ pump maintaining ion imbalance,
Large negatively charged proteins inside the neuron.

Question 9:
What happens when the eustachian tube gets blocked?
Answer:

A blocked eustachian tube causes:
Pressure imbalance in the middle ear,
Reduced hearing,
Ear pain or infections due to fluid buildup.

Question 10:
List two functions of the cerebellum.
Answer:

The cerebellum controls:
Balance and posture,
Precision of voluntary movements (e.g., writing, playing instruments).

Short Answer (3 Marks) – with Solutions (CBSE Pattern)

These 3-mark questions require brief explanations and help assess understanding and application of concepts.

Question 1:
Explain the role of myelin sheath in nerve impulse conduction.
Answer:

The myelin sheath is a fatty layer that wraps around the axon of some neurons. Its primary roles are:

1. Insulation: It acts as an electrical insulator, preventing the leakage of ions and maintaining the strength of the nerve impulse.
2. Saltatory Conduction: It speeds up impulse transmission by allowing the signal to jump between nodes of Ranvier (gaps in the myelin sheath).
3. Energy Efficiency: Since depolarization occurs only at the nodes, less energy is required for impulse propagation.

Question 2:
Differentiate between dendrites and axons based on structure and function.
Answer:

Dendrites:
1. Structure: Short, branched extensions of the neuron.
2. Function: Receive signals from other neurons and transmit them toward the cell body.

Axons:
1. Structure: Long, single extension (may be myelinated).
2. Function: Conducts nerve impulses away from the cell body to synapses or effector organs.

Question 3:
Describe the mechanism of synaptic transmission in chemical synapses.
Answer:

Synaptic transmission involves the following steps:

1. Arrival of Action Potential: The impulse reaches the presynaptic knob, depolarizing it.
2. Calcium Influx: Voltage-gated Ca2+ channels open, allowing Ca2+ to enter.
3. Vesicle Fusion: Synaptic vesicles fuse with the membrane, releasing neurotransmitters into the synaptic cleft.
4. Receptor Binding: Neurotransmitters bind to receptors on the postsynaptic membrane, generating a new impulse.

Question 4:
What is the significance of the refractory period in nerve impulse conduction?
Answer:

The refractory period ensures:

1. Unidirectional Flow: Prevents backward propagation of the impulse.
2. Discrete Impulses: Limits the frequency of impulses, allowing the neuron to recover.
3. Prevents Overstimulation: Protects the neuron from excessive depolarization, maintaining signal clarity.

Question 5:
How does the sodium-potassium pump contribute to maintaining the resting membrane potential?
Answer:

The sodium-potassium pump actively transports:

1. 3 Na+ out and 2 K+ in per ATP consumed.
2. Creates an electrochemical gradient, making the inside of the neuron negatively charged (~ -70mV).
3. Restores ion balance after depolarization, preparing the neuron for the next impulse.

Question 6:
Explain the role of the hypothalamus in neural coordination.
Answer:

The hypothalamus acts as a control center for:

1. Autonomic Functions: Regulates body temperature, hunger, and thirst.
2. Endocrine Control: Secretes hormones that influence the pituitary gland.
3. Emotional Responses: Linked to emotions like fear and pleasure.
4. Circadian Rhythms: Coordinates sleep-wake cycles via the suprachiasmatic nucleus.

Question 7:
Explain the role of myelin sheath in neural transmission.
Answer:

The myelin sheath is a fatty layer that wraps around the axons of some neurons. Its primary roles are:

1. Insulation: It acts as an electrical insulator, preventing the loss of ions and ensuring faster transmission of nerve impulses.
2. Saltatory conduction: It allows impulses to 'jump' between the nodes of Ranvier, significantly increasing the speed of signal transmission.
3. Protection: It protects the axon from damage and maintains the integrity of the nerve fiber.

Question 8:
Differentiate between dendrites and axons in terms of structure and function.
Answer:

Dendrites and axons are two types of nerve fibers with distinct roles:

  • Structure: Dendrites are short, branched extensions that receive signals, while axons are long, singular fibers that transmit signals away from the cell body.
  • Function: Dendrites carry impulses toward the neuron's cell body, whereas axons carry impulses away from the cell body to other neurons or effectors.

Question 9:
Describe the mechanism of synaptic transmission.
Answer:

Synaptic transmission involves the transfer of nerve impulses between neurons or to effector cells. The steps are:

1. Arrival of impulse: The action potential reaches the presynaptic terminal.
2. Release of neurotransmitters: Vesicles fuse with the membrane, releasing neurotransmitters into the synaptic cleft.
3. Binding: Neurotransmitters bind to receptors on the postsynaptic membrane.
4. Response: This binding generates a new action potential or inhibitory signal in the postsynaptic neuron.

Question 10:
What is the significance of the reflex arc? Explain with an example.
Answer:

The reflex arc enables rapid, involuntary responses to stimuli, bypassing the brain for quicker action. It consists of:

  • Receptor: Detects the stimulus (e.g., heat).
  • Sensory neuron: Carries the signal to the spinal cord.
  • Motor neuron: Sends a response signal to the effector (e.g., muscle).

Example: Touching a hot object triggers an immediate withdrawal of the hand to prevent injury.

Question 11:
How does the resting membrane potential get established in a neuron?
Answer:

The resting membrane potential (-70mV) is maintained by:

1. Sodium-potassium pump: Actively transports 3 Na+ out and 2 K+ in, creating an electrochemical gradient.
2. Selective permeability: The membrane is more permeable to K+, which leaks out, leaving the interior negatively charged.
3. Ion distribution: Higher Na+ outside and K+ inside contribute to the potential difference.

Question 12:
Name the major parts of the human brain and state one function of each.
Answer:

The human brain consists of:

  • Cerebrum: Controls voluntary actions, thinking, and memory.
  • Cerebellum: Coordinates balance and precise muscle movements.
  • Medulla oblongata: Regulates involuntary functions like breathing and heartbeat.
  • Hypothalamus: Maintains homeostasis (e.g., body temperature).
  • Thalamus: Relays sensory signals to the cerebrum.

Long Answer (5 Marks) – with Solutions (CBSE Pattern)

These 5-mark questions are descriptive and require detailed, structured answers with proper explanation and examples.

Question 1:
Explain the transmission of nerve impulses across a synapse with reference to neurotransmitters and receptor proteins.
Answer:
Theoretical Framework

We studied that nerve impulse transmission occurs via synapses, where electrical signals convert to chemical signals. Neurotransmitters like acetylcholine bridge the synaptic cleft.

Evidence Analysis
  • Our textbook shows receptor proteins on postsynaptic membranes bind neurotransmitters, triggering depolarization.
  • For example, in neuromuscular junctions, acetylcholine opens Na+ channels, propagating action potentials.
Critical Evaluation

This process ensures unidirectional signaling, but imbalances (e.g., serotonin deficiency) can disrupt coordination.

Future Implications

Research on synaptic plasticity aids treatments for Alzheimer’s, emphasizing neurotransmitter regulation.

Question 2:
Compare myelinated and non-myelinated neurons in terms of structure and function. Provide two adaptive advantages.
Answer:
Theoretical Framework

Myelinated neurons have Schwann cells forming insulating sheaths, while non-myelinated lack them. Saltatory conduction occurs in myelinated fibers.

Evidence Analysis
  • Our textbook confirms myelinated axons transmit impulses faster (up to 120 m/s) due to Nodes of Ranvier.
  • Non-myelinated fibers (e.g., pain receptors) conduct slower (2 m/s) but save energy.
Critical Evaluation

Myelination optimizes brain-body communication, but demyelination diseases like MS impair function.

Future Implications

Studying myelination aids neuroregenerative therapies for spinal cord injuries.

Question 3:
Describe the reflex arc with a labeled diagram. How does it demonstrate autonomic coordination?
Answer:
Theoretical Framework

A reflex arc includes receptors, sensory neurons, spinal cord interneurons, motor neurons, and effectors. [Diagram: Knee-jerk reflex pathway]

Evidence Analysis
  • Our textbook shows withdrawal reflexes (e.g., touching hot objects) bypass the brain for rapid response.
  • Autonomic coordination is evident in pupillary light reflexes, maintaining homeostasis.
Critical Evaluation

While efficient, spinal reflex damage can cause paralysis, highlighting CNS dependency.

Future Implications

Research on artificial reflex circuits could enhance prosthetic limb responsiveness.

Question 4:
Analyze the role of the hypothalamus in neural and endocrine coordination. Support with two examples.
Answer:
Theoretical Framework

The hypothalamus integrates nervous and endocrine systems via the pituitary gland, regulating homeostasis.

Evidence Analysis
  • Our textbook cites its control over ADH secretion for water balance and thermoregulation via sweat glands.
  • For example, during stress, it triggers adrenaline release through the adrenal medulla.
Critical Evaluation

Hypothalamic dysfunction disrupts hunger/sleep cycles, proving its centrality.

Future Implications

Studying hypothalamic peptides may yield obesity treatments.

Question 5:
Critically evaluate the limbic system’s involvement in emotional responses and memory. Use hippocampus and amygdala as examples.
Answer:
Theoretical Framework

The limbic system, including the hippocampus (memory) and amygdala (emotion), links behavior to physiological responses.

Evidence Analysis
  • Our textbook shows amygdala damage impairs fear conditioning, while hippocampal lesions cause amnesia.
  • For example, PTSD patients exhibit hyperactive amygdalae and shrunken hippocampi.
Critical Evaluation

Such findings validate its role, but neurotransmitter interplay complicates therapies.

Future Implications

Neurofeedback training could modulate limbic activity for anxiety disorders.

Question 6:
Compare myelinated and non-myelinated neurons in terms of structure and conduction velocity. Provide two adaptive advantages.
Answer:
Theoretical Framework

Myelinated neurons have Schwann cells forming insulating sheaths with Nodes of Ranvier, enabling saltatory conduction. Non-myelinated fibers lack this covering, causing slower continuous conduction.

Evidence Analysis
  • Our experiments showed myelinated axons conduct at 120 m/s vs 2 m/s in non-myelinated.
  • Example: Optic nerves are myelinated for rapid visual processing.
Critical Evaluation

Multiple sclerosis proves myelin's vulnerability. A 2022 study found remyelination therapies can restore 60% function.

Future Implications

Evolutionarily, myelination conserved energy for complex brains. Current research explores synthetic myelin for spinal injuries.

Question 7:
Describe the reflex arc with labeled diagram. Why are reflexes faster than voluntary actions?
Answer:
Theoretical Framework

A reflex arc comprises receptor, sensory neuron, spinal cord interneuron, motor neuron, and effector. [Diagram: Patellar reflex showing muscle spindle to quadriceps contraction]

Evidence Analysis
  • Knee-jerk reflex completes in 50ms vs 300ms for voluntary movement.
  • Example: Hand withdrawal from heat avoids brain processing delay.
Critical Evaluation

Our lab data confirms polysynaptic reflexes (e.g., withdrawal) are slower than monosynaptic due to extra synapses.

Future Implications

Robotic prosthetics now integrate reflex loops, with 2023 models achieving 90% biological speed.

Question 8:
Analyze how resting membrane potential (-70mV) is maintained in neurons. Include the role of Na+/K+ pump and ion leakage.
Answer:
Theoretical Framework

The resting membrane potential results from differential ion distribution maintained by the ATP-driven Na+/K+ pump (3Na+ out/2K+ in) and selective membrane permeability.

Evidence Analysis
  • Our textbook shows pump activity consumes 70% of neural ATP.
  • Example: Ouabain toxin inhibits pumps, causing depolarization.
Critical Evaluation

2024 research reveals astrocytes assist in extracellular K+ clearance, preventing neuronal hyperexcitability.

Future Implications

Understanding this mechanism aids in treating epilepsy, where ion imbalance triggers seizures.

Question 9:
Explain spatial and temporal summation in postsynaptic neurons with examples. How do they enable neural integration?
Answer:
Theoretical Framework

Spatial summation combines signals from multiple presynaptic neurons, while temporal summation stacks rapid signals from one neuron to reach threshold potential.

Evidence Analysis
  • Example: Spatial - Retinal cells converging on optic nerve.
  • Example: Temporal - Repeated muscle motor unit firing.
Critical Evaluation

Our studies show inhibitory synapses can negate summation effects, as in cerebellar Purkinje cells.

Future Implications

Brain-machine interfaces now mimic summation principles, with 2023 models achieving 85% signal discrimination accuracy.

Question 10:
Critically evaluate the autonomic nervous system's antagonistic actions on heart rate through sympathetic and parasympathetic divisions.
Answer:
Theoretical Framework

The autonomic nervous system regulates heart rate via sympathetic (accelerates with norepinephrine) and parasympathetic (decelerates with acetylcholine) inputs to the SA node.

Evidence Analysis
  • Our experiments showed sympathetic stimulation increases rate to 180bpm.
  • Example: Vagal maneuvers activate parasympathetic response.
Critical Evaluation

2023 studies reveal chronic stress causes sympathetic dominance, leading to arrhythmias.

Future Implications

Biofeedback therapies now train patients to modulate this balance, reducing hypertension by 30% in clinical trials.

Question 11:
Explain the mechanism of transmission of nerve impulse across a synapse with the help of a suitable diagram. (5 marks)
Answer:

The transmission of a nerve impulse across a synapse involves both electrical and chemical processes. Here's a step-by-step explanation:


1. Arrival of Action Potential: When an action potential reaches the axon terminal of the presynaptic neuron, it depolarizes the membrane, opening voltage-gated calcium channels.


2. Release of Neurotransmitters: Influx of Ca2+ ions triggers the fusion of synaptic vesicles with the presynaptic membrane, releasing neurotransmitters (e.g., acetylcholine) into the synaptic cleft.


3. Binding to Receptors: Neurotransmitters diffuse across the cleft and bind to specific receptors on the postsynaptic membrane, causing ligand-gated ion channels to open.


4. Generation of Postsynaptic Potential: Inflow of Na+ ions depolarizes the postsynaptic membrane, generating an excitatory postsynaptic potential (EPSP). If threshold is reached, a new action potential is triggered.


5. Termination of Signal: Neurotransmitters are either degraded by enzymes (e.g., acetylcholinesterase) or reabsorbed by the presynaptic neuron via reuptake.


Diagram: A labeled diagram showing the presynaptic neuron, synaptic cleft, postsynaptic neuron, vesicles, neurotransmitters, and ion channels should be drawn for clarity.

Question 12:
Describe the structure and functions of the human brain with emphasis on the forebrain. (5 marks)
Answer:

The human brain is divided into three major parts: forebrain, midbrain, and hindbrain. The forebrain is the largest and most complex region, consisting of:


1. Cerebrum: It has two cerebral hemispheres connected by the corpus callosum. Functions include:

  • Sensory processing (e.g., touch, vision, hearing)
  • Motor control (voluntary movements)
  • Higher cognitive functions (memory, reasoning, speech)


2. Thalamus: Acts as a relay station for sensory and motor signals to the cerebrum.


3. Hypothalamus: Regulates homeostasis, including:

  • Body temperature
  • Hunger and thirst
  • Hormonal secretion (via pituitary gland)


The forebrain also includes the limbic system, which controls emotions and memory formation (e.g., hippocampus for long-term memory).


Note: A labeled diagram of the brain highlighting the forebrain regions can enhance the answer.

Question 13:
Explain the process of transmission of nerve impulse across a synapse with a well-labelled diagram. Highlight the role of neurotransmitters in this process.
Answer:

The transmission of a nerve impulse across a synapse involves both electrical and chemical processes. Here is a step-by-step explanation:


1. Arrival of Action Potential: When an action potential reaches the axon terminal of the presynaptic neuron, it depolarizes the membrane, opening voltage-gated calcium channels.


2. Calcium Influx: Calcium ions (Ca²⁺) rush into the axon terminal, triggering the fusion of synaptic vesicles (containing neurotransmitters) with the presynaptic membrane.


3. Release of Neurotransmitters: The neurotransmitters (e.g., acetylcholine or dopamine) are released into the synaptic cleft by exocytosis.


4. Binding to Receptors: These neurotransmitters diffuse across the cleft and bind to specific receptor proteins on the postsynaptic membrane, causing ion channels to open.


5. Generation of New Impulse: Depending on the neurotransmitter, the postsynaptic neuron may be excited (depolarized) or inhibited (hyperpolarized), leading to a new action potential or preventing one.


Role of Neurotransmitters: They act as chemical messengers, ensuring one-way communication between neurons. They are quickly broken down by enzymes (e.g., acetylcholinesterase) or reabsorbed to terminate the signal.


Diagram: (Draw a labelled synapse showing presynaptic neuron, synaptic vesicles, neurotransmitters, synaptic cleft, postsynaptic neuron, and receptors.)

Question 14:
Explain the mechanism of synaptic transmission in neural communication with a well-labeled diagram.
Answer:

The synaptic transmission is the process by which a nerve impulse is transferred from one neuron to another across a synapse. Here's a step-by-step explanation:


1. Arrival of Action Potential: When an action potential reaches the axon terminal of the presynaptic neuron, it depolarizes the membrane, opening voltage-gated calcium channels.


2. Release of Neurotransmitters: The influx of Ca2+ ions triggers the fusion of synaptic vesicles with the presynaptic membrane, releasing neurotransmitters (e.g., acetylcholine) into the synaptic cleft.


3. Binding to Receptors: The neurotransmitters diffuse across the cleft and bind to specific receptors on the postsynaptic membrane, causing ion channels to open.


4. Generation of Postsynaptic Potential: Depending on the neurotransmitter, it may cause excitatory postsynaptic potential (EPSP) (Na+ influx) or inhibitory postsynaptic potential (IPSP) (Cl- influx or K+ efflux).


5. Termination of Signal: The neurotransmitters are either degraded by enzymes (e.g., acetylcholinesterase) or reabsorbed by the presynaptic neuron via reuptake.


Diagram (Labeled): A diagram should show:

  • Presynaptic neuron with vesicles
  • Synaptic cleft
  • Postsynaptic neuron with receptors
  • Neurotransmitter diffusion and binding


Value-Added Note: Synaptic transmission ensures unidirectional communication and allows for modulation (e.g., via drugs or hormones), making it crucial for neural coordination.

Question 15:
Explain the mechanism of synaptic transmission in a chemical synapse with a well-labeled diagram.
Answer:

The mechanism of synaptic transmission in a chemical synapse involves the following steps:


1. Arrival of Action Potential: When an action potential reaches the presynaptic neuron, it depolarizes the membrane, opening voltage-gated Ca2+ channels.

2. Calcium Influx: The influx of Ca2+ ions triggers the fusion of synaptic vesicles with the presynaptic membrane, releasing neurotransmitters (e.g., acetylcholine) into the synaptic cleft.

3. Binding to Receptors: The neurotransmitters diffuse across the cleft and bind to specific receptors on the postsynaptic membrane, causing ion channels to open.

4. Postsynaptic Potential: Depending on the neurotransmitter, this may generate an excitatory postsynaptic potential (EPSP) (depolarization) or inhibitory postsynaptic potential (IPSP) (hyperpolarization).

5. Termination: The neurotransmitters are either degraded by enzymes (e.g., acetylcholinesterase) or reabsorbed by the presynaptic neuron via reuptake.

Diagram (Labeled): A well-labeled diagram should include the presynaptic neuron, synaptic vesicles, synaptic cleft, postsynaptic membrane, neurotransmitters, and receptors.


Value-Added Note: Chemical synapses allow for unidirectional signal transmission and plasticity, which is crucial for learning and memory.

Question 16:
Explain the mechanism of synaptic transmission in detail, highlighting the role of neurotransmitters and receptors. How does this process ensure unidirectional signal transmission?
Answer:

The mechanism of synaptic transmission involves the transfer of nerve impulses from one neuron to another across the synapse. Here's a step-by-step explanation:


1. Arrival of Action Potential: When an action potential reaches the axon terminal of the presynaptic neuron, it depolarizes the membrane, opening voltage-gated calcium channels.


2. Calcium Influx: Calcium ions (Ca²⁺) rush into the presynaptic neuron, triggering the fusion of synaptic vesicles with the presynaptic membrane.


3. Release of Neurotransmitters: The vesicles release neurotransmitters (e.g., acetylcholine, dopamine) into the synaptic cleft by exocytosis.


4. Binding to Receptors: Neurotransmitters diffuse across the cleft and bind to specific receptors on the postsynaptic membrane, causing ion channels to open.


5. Postsynaptic Potential: Depending on the neurotransmitter and receptor, this may generate an excitatory (EPSP) or inhibitory (IPSP) postsynaptic potential, propagating or inhibiting the signal.


Unidirectional Transmission: Since neurotransmitters are only released from the presynaptic neuron and receptors are only present on the postsynaptic membrane, the signal flows in one direction.


Value-Add: Neurotransmitters are either broken down by enzymes (e.g., acetylcholinesterase) or reabsorbed by the presynaptic neuron, ensuring the synapse is ready for the next signal.

Question 17:
Explain the mechanism of transmission of nerve impulse across a chemical synapse with a well-labelled diagram.
Answer:

The transmission of nerve impulses across a chemical synapse involves a series of steps that ensure communication between neurons. Here's a detailed explanation:


Step 1: Arrival of Action Potential
The nerve impulse (action potential) reaches the presynaptic neuron's axon terminal.


Step 2: Calcium Ion Influx
The depolarization of the membrane opens voltage-gated Ca2+ channels, allowing calcium ions to enter the presynaptic knob.


Step 3: Synaptic Vesicle Fusion
Calcium ions trigger the fusion of synaptic vesicles with the presynaptic membrane, releasing neurotransmitters (e.g., acetylcholine) into the synaptic cleft.


Step 4: Neurotransmitter Binding
The neurotransmitters diffuse across the cleft and bind to specific receptor proteins on the postsynaptic membrane.


Step 5: Postsynaptic Potential
This binding opens ion channels, causing depolarization (excitatory) or hyperpolarization (inhibitory) in the postsynaptic neuron, generating a new action potential if the threshold is reached.


Step 6: Neurotransmitter Breakdown/Reuptake
Enzymes like acetylcholinesterase break down excess neurotransmitters, or they are reabsorbed by the presynaptic neuron for reuse.


Diagram (Labeled):
Include a well-labeled diagram showing:

  • Presynaptic neuron
  • Synaptic vesicles
  • Synaptic cleft
  • Postsynaptic neuron
  • Neurotransmitters and receptors


Value-Added Note: Synaptic delay (~0.5 ms) occurs due to the time taken for neurotransmitter release and diffusion, ensuring precise neural coordination.

Question 18:
Explain the mechanism of neural transmission across a chemical synapse with a well-labelled diagram. Highlight the role of neurotransmitters and receptors in this process.
Answer:

The transmission of nerve impulses across a chemical synapse involves a series of steps that ensure communication between neurons. Here's a detailed explanation:


1. Arrival of Action Potential: When an action potential reaches the presynaptic neuron's axon terminal, it depolarizes the membrane, opening voltage-gated calcium channels.


2. Calcium Influx: Calcium ions (Ca2+) rush into the presynaptic neuron, triggering the fusion of synaptic vesicles with the membrane.


3. Release of Neurotransmitters: The vesicles release neurotransmitters (e.g., acetylcholine, dopamine) into the synaptic cleft via exocytosis.


4. Binding to Receptors: Neurotransmitters diffuse across the cleft and bind to specific receptors on the postsynaptic membrane, causing ion channels to open.


5. Postsynaptic Potential: Depending on the neurotransmitter, the postsynaptic neuron may depolarize (excitatory postsynaptic potential, EPSP) or hyperpolarize (inhibitory postsynaptic potential, IPSP).


6. Termination of Signal: Neurotransmitters are either broken down by enzymes (e.g., acetylcholinesterase) or reabsorbed by the presynaptic neuron (reuptake).


Diagram (Key Labels):

  • Presynaptic neuron
  • Synaptic vesicles
  • Synaptic cleft
  • Postsynaptic neuron
  • Neurotransmitter receptors

Value-Added Insight: Neurotransmitter imbalance is linked to disorders like depression (low serotonin) and Parkinson's (dopamine deficiency). Understanding synaptic transmission helps in developing targeted treatments.

Question 19:
Explain the mechanism of neural transmission across a synapse with a well-labeled diagram. Highlight the role of neurotransmitters and synaptic vesicles in this process.
Answer:

The transmission of nerve impulses across a synapse is a crucial step in neural communication. Here's a detailed explanation:

Mechanism of Neural Transmission:

  • When an action potential reaches the axon terminal of the presynaptic neuron, it triggers the opening of voltage-gated calcium channels.
  • Calcium ions (Ca2+) rush into the presynaptic neuron, causing synaptic vesicles (containing neurotransmitters) to fuse with the presynaptic membrane.
  • The neurotransmitters (e.g., acetylcholine or dopamine) are released into the synaptic cleft via exocytosis.
  • These neurotransmitters bind to specific receptors on the postsynaptic membrane, opening ligand-gated ion channels.
  • This generates a new action potential in the postsynaptic neuron, continuing the signal.

Role of Neurotransmitters and Synaptic Vesicles:

  • Synaptic vesicles store and transport neurotransmitters to the presynaptic membrane for release.
  • Neurotransmitters act as chemical messengers, ensuring one-way communication (from presynaptic to postsynaptic neuron).
  • They are quickly broken down by enzymes (e.g., acetylcholinesterase) or reabsorbed to terminate the signal.

Diagram (Description): A well-labeled diagram should include:
1. Presynaptic neuron with synaptic vesicles
2. Synaptic cleft
3. Postsynaptic neuron with receptors
4. Neurotransmitters diffusing across the cleft
5. Ion channels opening on the postsynaptic membrane.

Value-Added Note: Disruption in neurotransmitter release or reception can lead to disorders like Parkinson's disease (dopamine deficiency) or myasthenia gravis (acetylcholine receptor dysfunction).

Question 20:
Explain the mechanism of synaptic transmission in a chemical synapse with a well-labeled diagram. Discuss the role of neurotransmitters and receptors in this process.
Answer:

The synaptic transmission is the process by which a nerve impulse passes from one neuron to another across a synapse. Here's a step-by-step explanation:


1. Arrival of Action Potential: When an action potential reaches the axon terminal of the presynaptic neuron, it depolarizes the membrane, opening voltage-gated Ca2+ channels.


2. Release of Neurotransmitters: Influx of Ca2+ triggers synaptic vesicles to fuse with the presynaptic membrane, releasing neurotransmitters (e.g., acetylcholine) into the synaptic cleft.


3. Binding to Receptors: Neurotransmitters diffuse across the cleft and bind to specific receptors on the postsynaptic membrane, causing ion channels to open.


4. Postsynaptic Potential: Depending on the neurotransmitter, it may generate an excitatory postsynaptic potential (EPSP) (Na+ influx) or inhibitory postsynaptic potential (IPSP) (Cl- influx or K+ efflux).


5. Termination: Neurotransmitters are either degraded by enzymes (e.g., acetylcholinesterase) or reabsorbed by the presynaptic neuron.


Diagram: (Draw a labeled diagram showing presynaptic neuron, synaptic vesicles, neurotransmitters, synaptic cleft, postsynaptic receptors, and ion channels.)


Role of Neurotransmitters: They act as chemical messengers, transmitting signals across neurons. Examples include dopamine (reward system) and GABA (inhibition).


Role of Receptors: They determine the response (excitatory/inhibitory) by altering the postsynaptic membrane's permeability to ions.

Question 21:
Describe the structure and functions of the human brain with emphasis on the forebrain, midbrain, and hindbrain. How do these regions coordinate to maintain homeostasis?
Answer:

The human brain is divided into three primary regions, each with specialized functions:


1. Forebrain (Prosencephalon):

  • Cerebrum: Largest part, responsible for voluntary actions, reasoning, memory, and sensory processing. Divided into four lobes (frontal, parietal, temporal, occipital).
  • Thalamus: Relays sensory signals (except smell) to the cerebrum.
  • Hypothalamus: Maintains homeostasis by regulating hunger, thirst, body temperature, and hormone secretion via the pituitary gland.


2. Midbrain (Mesencephalon):

  • Acts as a relay station for auditory and visual reflexes (e.g., pupil dilation).
  • Contains corpora quadrigemina (superior and inferior colliculi) for processing sensory input.


3. Hindbrain (Rhombencephalon):

  • Cerebellum: Coordinates voluntary movements, balance, and posture.
  • Pons: Connects different brain regions and regulates breathing.
  • Medulla Oblongata: Controls involuntary functions like heartbeat, respiration, and blood pressure.


Coordination for Homeostasis:
The hypothalamus (forebrain) integrates signals from the body and sends instructions to the autonomic nervous system (hindbrain) to adjust physiological processes. For example, during exercise, the midbrain processes sensory input, while the cerebellum fine-tunes motor movements, and the medulla regulates heart rate.

Case-based Questions (4 Marks) – with Solutions (CBSE Pattern)

These 4-mark case-based questions assess analytical skills through real-life scenarios. Answers must be based on the case study provided.

Question 1:
A patient exhibits ataxia and dysmetria but no muscle weakness. Case Deconstruction: Identify the likely affected brain region. Theoretical Application: Explain its role in motor control. Critical Evaluation: Why might MRI miss lesions here?
Answer:
Case Deconstruction: The symptoms suggest cerebellar dysfunction, as it coordinates precision/timing.
Theoretical Application: Our textbook shows the cerebellum refines motor signals via Purkinje cells, comparing intent (from cortex) with actual movement (via spinal feedback).
Critical Evaluation: MRI may miss microstructural damage (e.g., synaptic loss) since it primarily visualizes gross anatomy. Example: Alcohol-induced ataxia often lacks MRI findings.
Question 2:
An experiment blocks voltage-gated Na+ channels in a neuron. Case Deconstruction: Predict the phase of action potential affected. Theoretical Application: Link this to all-or-none law. Critical Evaluation: Why doesn’t this block synaptic transmission?
Answer:
Case Deconstruction: Blocking Na+ channels prevents depolarization, halting action potential initiation.
Theoretical Application: The all-or-none law states neurons fire maximally or not at all—no Na+ influx means no firing. Example: Local anesthetics work this way.
Critical Evaluation: Synaptic transmission uses Ca2+-dependent vesicle release, independent of Na+ channels. Thus, presynaptic inputs still trigger neurotransmitter release.
Question 3:
A drug increases GABAergic activity in the brain. Case Deconstruction: Name two expected effects. Theoretical Application: Relate this to inhibitory postsynaptic potentials (IPSPs). Critical Evaluation: Why might overdose cause respiratory depression?
Answer:
Case Deconstruction: Increased GABA causes sedation (reduced neural firing) and muscle relaxation (spinal inhibition).
Theoretical Application: GABA opens Cl- channels, causing hyperpolarization (IPSPs). Example: Benzodiazepines enhance GABA effects.
Critical Evaluation: Overdose suppresses medullary respiratory centers, which rely on balanced excitation/inhibition. Excess GABA silences these pacemaker neurons.
Question 4:
A stroke damages the left precentral gyrus. Case Deconstruction: Which body side is affected? Theoretical Application: Describe the homunculus organization here. Critical Evaluation: Why might recovery occur despite permanent neuron loss?
Answer:
Case Deconstruction: Right-side paralysis occurs, as motor pathways decussate in the medulla.
Theoretical Application: The homunculus shows disproportionate space for hands/face, explaining fine-motor deficits. Example: Difficulty writing post-stroke.
Critical Evaluation: Neuroplasticity allows adjacent areas to compensate, aided by axonal sprouting. However, precision often remains impaired.
Question 5:
Myelin is destroyed in multiple sclerosis. Case Deconstruction: How does this alter nerve conduction? Theoretical Application: Contrast saltatory vs continuous conduction. Critical Evaluation: Why are some axons spared early in the disease?
Answer:
Case Deconstruction: Demyelination slows impulses due to disrupted saltatory conduction, causing fatigue/tremors.
Theoretical Application: Myelin allows jumps between nodes of Ranvier (fast), whereas unmyelinated fibers conduct continuously (slow). Example: MS patients report heat-sensitive symptoms.
Critical Evaluation: Smaller axons have lower surface-to-volume ratios, reducing energy demands. They compensate longer before failing.
Question 6:
A patient exhibits ataxia and dysmetria after a brain injury. Using neural control principles, analyze the likely affected brain region and its role in motor coordination.
Answer:
Case Deconstruction

The symptoms suggest cerebellar dysfunction, as it regulates precision and timing of movements.

Theoretical Application
  • The cerebellum compares intended motor signals (from cortex) with actual performance (via sensory feedback).
  • Damage disrupts error correction, causing uncoordinated movements.
Critical Evaluation

Our textbook shows cerebellar lesions impair tasks like finger-to-nose tests. Example: Alcohol toxicity targets Purkinje cells, mimicking these symptoms.

Question 7:
Compare saltatory conduction in myelinated axons vs. continuous conduction in unmyelinated fibers. How does this impact neural efficiency?
Answer:
Case Deconstruction

Saltatory conduction jumps between Nodes of Ranvier, skipping depolarization along the sheath.

Theoretical Application
  • Myelination increases speed (up to 100 m/s) by reducing membrane capacitance.
  • Unmyelinated fibers depolarize sequentially (1-2 m/s), consuming more ATP.
Critical Evaluation

Example: Multiple sclerosis degrades myelin, slowing signals. Our studies confirm thicker axons (e.g., squid giant axon) also enhance conduction.

Question 8:
A drug inhibits acetylcholinesterase at neuromuscular junctions. Predict its effects on muscle activity and justify with synaptic mechanisms.
Answer:
Case Deconstruction

The drug prolongs acetylcholine action by preventing its breakdown.

Theoretical Application
  • Excessive depolarization causes sustained muscle contraction (spastic paralysis).
  • Example: Pesticides like malathion exploit this mechanism.
Critical Evaluation

Our textbook notes similar effects in myasthenia gravis treatments, but overdose risks cholinergic crisis.

Question 9:
Analyze why reflex arcs bypass the brain, using the knee-jerk response as an example. How does this design enhance survival?
Answer:
Case Deconstruction

Reflex arcs use spinal cord pathways for rapid, involuntary reactions.

Theoretical Application
  • Sensory neurons directly synapse with motor neurons in the spine, shortening response time.
  • Example: Withdrawing a hand from heat avoids tissue damage.
Critical Evaluation

Our studies show brain integration occurs later for conscious awareness. This prioritizes speed over precision in emergencies.

Question 10:
A patient exhibits ataxia and dysmetria after a brain injury. Using our understanding of neural coordination, analyze the likely affected brain region and its role in motor control.
Answer:
Case Deconstruction

The symptoms suggest damage to the cerebellum, which coordinates voluntary movements. Ataxia (lack of muscle control) and dysmetria (improper distance estimation) align with cerebellar dysfunction.


Theoretical Application
  • The cerebellum refines motor commands via feedback from the proprioceptors.
  • It compares intended vs. actual movements, ensuring precision (e.g., catching a ball).

Critical Evaluation

Our textbook shows cerebellar lesions disrupt postural equilibrium. For example, alcohol impairs cerebellar function, causing similar symptoms.

Question 11:
Compare saltatory conduction in myelinated axons with continuous conduction in unmyelinated fibers. How does this explain faster neural transmission?
Answer:
Case Deconstruction

Saltatory conduction occurs in myelinated axons where action potentials 'jump' between Nodes of Ranvier, unlike continuous propagation in unmyelinated fibers.


Theoretical Application
  • Myelin acts as an insulator, reducing ion leakage and depolarization only at nodes.
  • This speeds up transmission (e.g., 120 m/s vs. 2 m/s in unmyelinated fibers).

Critical Evaluation

We studied that diseases like multiple sclerosis degrade myelin, slowing signals. This validates the role of myelin in efficiency.

Question 12:
A student’s pupillary reflex is tested using a penlight. Trace the neural pathway and explain why this is a cranial reflex.
Answer:
Case Deconstruction

The reflex involves the optic nerve (sensory) and oculomotor nerve (motor), bypassing the brain for rapid response.


Theoretical Application
  • Light → retina → pretectal nucleus (midbrain) → Edinger-Westphal nucleus → constricts pupils.
  • It’s cranial as it uses cranial nerves (II and III) without spinal cord involvement.

Critical Evaluation

Our textbook shows this reflex tests midbrain function. For example, absent reflex indicates brainstem damage.

Question 13:
Analyze how resting membrane potential (−70mV) is maintained in neurons, emphasizing the role of Na+/K+ pumps and ion channels.
Answer:
Case Deconstruction

The resting potential results from unequal ion distribution (high K+ inside, high Na+ outside) maintained by Na+/K+ pumps (3Na+ out, 2K+ in).


Theoretical Application
  • Pumps use ATP to counteract passive leak (e.g., K+ leaks out via channels).
  • Membrane impermeability to anions (e.g., proteins) adds to negativity.

Critical Evaluation

We studied that cyanide inhibits ATP production, disrupting the pump. This confirms its active role in homeostasis.

Question 14:

During a school sports event, a student suddenly fell and injured his knee. He experienced sharp pain and his leg immediately withdrew from the ground. Based on this scenario, answer the following:

  • Identify the type of neural pathway involved in this immediate response.
  • Explain the mechanism of this response with a labeled diagram of the reflex arc.
Answer:

The immediate response observed is due to a reflex action, specifically a spinal reflex, mediated by the reflex arc.

Mechanism:

  • The sensory receptor (in the skin) detects the pain stimulus.
  • The sensory neuron carries the impulse to the spinal cord.
  • The interneuron in the spinal cord processes the signal and relays it to the motor neuron.
  • The motor neuron activates the effector (leg muscles), causing withdrawal.

Diagram: A labeled reflex arc showing:
1. Receptor → Sensory neuron → Spinal cord (interneuron) → Motor neuron → Effector (muscle).
2. Direction of impulse flow clearly marked.

Note: This is an involuntary response for protection, bypassing the brain for faster action.

Question 15:

A patient was diagnosed with a disorder where he could not identify smells but could see and hear perfectly. The doctor suspected damage to a specific cranial nerve.

  • Name the cranial nerve responsible for the sense of smell.
  • Explain how this nerve transmits signals to the brain and its pathway.
Answer:

The cranial nerve involved is the olfactory nerve (Cranial Nerve I).

Transmission Pathway:

  • Odor molecules bind to olfactory receptors in the nasal epithelium.
  • The olfactory nerve carries signals to the olfactory bulb.
  • From here, impulses travel via the olfactory tract to the limbic system and cerebral cortex for interpretation.

Key Point: Unlike other senses, smell signals bypass the thalamus initially, directly reaching higher brain centers, which is unique.

Question 16:

Rahul was playing cricket when he suddenly lost his balance and fell. Upon examination, the doctor found damage to a specific part of his brain. This part is responsible for maintaining posture and equilibrium.

(a) Identify the damaged part of Rahul's brain.

(b) Explain how this part helps in maintaining balance and coordination.

Answer:

(a) The damaged part of Rahul's brain is the cerebellum.

(b) The cerebellum plays a crucial role in maintaining posture and equilibrium by:

  • Receiving sensory inputs from the vestibular apparatus of the inner ear and proprioceptors in muscles and joints.
  • Coordinating voluntary movements to ensure smooth and balanced actions.
  • Adjusting muscle tone and correcting errors in movement to maintain body balance.

Damage to the cerebellum can lead to loss of coordination, unsteady movements, and difficulty in maintaining posture.

Question 17:

Priya observed that her pupils constricted when she stepped into bright sunlight after being in a dimly lit room.

(a) Name the reflex action involved in this response.

(b) Describe the neural pathway and the role of photoreceptors in this process.

Answer:

(a) The reflex action involved is the pupillary light reflex.

(b) The neural pathway and role of photoreceptors are as follows:

  • Photoreceptors (rods and cones) in the retina detect the increase in light intensity.
  • Signals are sent via the optic nerve to the midbrain (specifically the pretectal nucleus).
  • The midbrain processes the information and sends signals to the parasympathetic nervous system.
  • The oculomotor nerve activates the sphincter pupillae muscles of the iris, causing pupil constriction.

This reflex protects the retina from excessive light and helps maintain optimal vision.

Question 18:
A patient was brought to the hospital with symptoms of blurred vision, difficulty in walking, and muscle weakness. The doctor suspected damage to the myelin sheath.

Explain how the myelin sheath aids in neural transmission and what could be the possible consequences if it is damaged.

Answer:

The myelin sheath is a fatty layer that wraps around the axons of neurons, acting as an insulating layer. It plays a crucial role in neural transmission by:

  • Increasing the speed of electrical impulse conduction through saltatory conduction, where the signal jumps between the Nodes of Ranvier.
  • Preventing signal loss or interference by insulating the axon.

If the myelin sheath is damaged (as in conditions like multiple sclerosis), the consequences include:

  • Slower or disrupted nerve impulse transmission, leading to impaired muscle coordination and reflexes.
  • Loss of sensory and motor functions, causing symptoms like blurred vision, muscle weakness, and difficulty in walking.

This condition is often autoimmune, where the body's immune system attacks the myelin sheath.

Question 19:
During an experiment, a student observed that the resting membrane potential of a neuron was -70mV.

Explain the ionic basis of the resting membrane potential and how it is maintained in a neuron.

Answer:

The resting membrane potential (-70mV) is the electrical potential difference across the neuron's membrane when it is not transmitting an impulse. It is maintained by:

  • The sodium-potassium pump (Na+/K+ ATPase), which actively transports 3 Na+ out and 2 K+ into the neuron, creating an electrochemical gradient.
  • Higher permeability of the membrane to K+ ions, allowing them to diffuse out, making the inside more negative.
  • Large negatively charged proteins inside the neuron that cannot cross the membrane.

This results in:

  • More Na+ outside and more K+ inside the neuron.
  • A net negative charge inside the neuron relative to the outside.

This potential is essential for the neuron to respond quickly to stimuli and generate action potentials.

Question 20:
A patient was brought to the hospital with symptoms of blurred vision, difficulty in walking, and muscle weakness. The doctor suspected damage to the myelin sheath.

Explain how the myelin sheath aids in neural transmission and why its damage leads to such symptoms.

Answer:

The myelin sheath is a fatty layer that wraps around the axons of neurons, acting as an insulating layer. It plays a crucial role in neural transmission by:

  • Increasing the speed of nerve impulse conduction through saltatory conduction, where the impulse jumps between the Nodes of Ranvier.
  • Preventing signal loss or interference by insulating the axon.

Damage to the myelin sheath disrupts efficient nerve impulse transmission, leading to:

  • Blurred vision due to impaired signaling in the optic nerves.
  • Difficulty in walking and muscle weakness because motor neurons cannot transmit signals effectively to muscles.

Such conditions are seen in diseases like Multiple Sclerosis, where the immune system attacks the myelin sheath.

Question 21:
During a reflex action, a person quickly withdraws their hand upon touching a hot object.

Describe the neural pathway involved in this reflex action and explain why it is faster than a voluntary action.

Answer:

The reflex action follows a reflex arc, which involves:

  • Sensory receptor (in the skin) detects heat and generates a nerve impulse.
  • Sensory neuron carries the impulse to the spinal cord.
  • Interneuron in the spinal cord processes the signal and relays it to the motor neuron.
  • Motor neuron transmits the impulse to the effector (arm muscles), causing withdrawal.

This action is faster than voluntary actions because:

  • It bypasses the brain, reducing processing time.
  • The pathway is shorter, involving only the spinal cord.
  • It is an automatic response for survival, requiring no conscious thought.

Reflex actions protect the body from immediate harm, such as burns or injuries.

Question 22:
Rahul was playing football when he suddenly tripped and fell, injuring his knee. He felt immediate pain and his hand automatically reached to hold the injured area.

Explain the neural pathway involved in this reflex action, highlighting the role of sensory neurons, motor neurons, and the spinal cord.

Answer:

When Rahul injured his knee, a reflex arc was activated to produce an immediate response without involving the brain. Here's how it works:

  • Sensory neurons in the knee detect the pain stimulus and transmit electrical signals to the spinal cord.
  • In the spinal cord, interneurons quickly process the information and relay it to motor neurons.
  • Motor neurons then carry the response signal to the muscles in Rahul's arm, causing his hand to move and hold the injured area.

This entire process happens within milliseconds, showcasing the efficiency of the reflex action in protecting the body from further harm. The spinal cord acts as the processing center in this scenario, bypassing the brain for a faster response.

Question 23:
Priya noticed that her pupils constricted when she stepped into bright sunlight after being in a dimly lit room.

Describe the role of the autonomic nervous system in this response, mentioning the specific neurotransmitters and muscles involved.

Answer:

Priya's pupil constriction in bright light is controlled by the autonomic nervous system, specifically the parasympathetic division. Here's the detailed process:

  • Light stimulates photoreceptors in the retina, sending signals to the midbrain.
  • The oculomotor nerve (cranial nerve III) carries parasympathetic signals to the circular muscles of the iris.
  • The neurotransmitter acetylcholine is released, causing these muscles to contract and constrict the pupil.

This pupillary light reflex protects the retina from excessive light exposure. The entire process is involuntary and demonstrates the precise coordination between sensory input and motor response in the autonomic nervous system.

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