Chapter 18: Neural Control and Coordination Long Questions | biology Class 11 CBSE

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Chapter 18: Neural Control and Coordination Long Questions | biology Class 11 CBSE | ByteNotes.in

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Question 1

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Describe the structure of a neuron with the help of a labelled diagram. How are neurons classified based on the number of processes?

A neuron has three major parts: the cell body (soma) containing cytoplasm with organelles and Nissl's granules; dendrites, which are short repeatedly branching fibres containing Nissl's granules that carry impulses towards the cell body; and the axon, a long single fibre that carries impulses away from the cell body to a synapse or neuro-muscular junction.
The axon's distal end is branched, with each branch terminating in a synaptic knob containing synaptic vesicles filled with neurotransmitters.
Based on the number of processes, neurons are classified into three types: multipolar neurons have one axon and two or more dendrites and are found in the cerebral cortex.
Bipolar neurons have one axon and one dendrite and are found in the retina of the eye.
Unipolar neurons have a cell body with only one axon and are found usually in the embryonic stage.
Axons are further classified as myelinated, enveloped by Schwann cells forming a myelin sheath with nodes of Ranvier and found in spinal and cranial nerves, and non-myelinated, lacking a myelin sheath and found in autonomous and somatic neural systems.

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Question 2

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Explain the ionic basis of resting potential in a neuron. How does the sodium-potassium pump contribute to maintaining this potential?

Resting potential is the electrical potential difference across the plasma membrane when the neuron is not conducting any impulse, with the outer surface positively charged and the inner surface negatively charged.
The axonal membrane at rest is comparatively more permeable to K+ and nearly impermeable to Na+; it is also impermeable to negatively charged proteins in the axoplasm.
Consequently, the axoplasm has high K+ and negatively charged proteins but low Na+, while the extracellular fluid has high Na+ and low K+, forming a concentration gradient.
The sodium-potassium pump actively maintains these gradients by transporting 3 Na+ outward and 2 K+ into the cell, making it an electrogenic pump.
As a result, the outer surface of the axonal membrane is positively charged and the inner surface is negatively charged, establishing the resting potential.
This polarised state is essential for the neuron's excitability, as any stimulus that disturbs this ionic balance can trigger an action potential.

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Question 3

Long Form

Trace the sequence of events from the application of a stimulus to the restoration of resting potential during nerve impulse conduction along an axon.

When a stimulus is applied at a site (e.g., point A) on the polarised membrane, the membrane at that site becomes freely permeable to Na+.
This leads to a rapid influx of Na+ followed by reversal of polarity at site A: the outer surface becomes negatively charged and the inner side becomes positively charged — this is depolarisation, and the electrical potential difference here is the action potential (nerve impulse).
At adjacent site B, the membrane still has positive charge outside and negative inside. Current flows on the inner surface from A to B and on the outer surface from B to A, completing the circuit.
This current flow causes polarity reversal at site B, generating an action potential at B. The sequence repeats along the length of the axon, propagating the impulse.
The rise in Na+ permeability is extremely short-lived and is quickly followed by an increase in K+ permeability.
Within a fraction of a second, K+ diffuses outward, restoring the positive charge on the outer membrane surface (repolarisation), and the fibre returns to its resting state, ready for further stimulation.

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Question 4

Long Form

Compare electrical synapses and chemical synapses in terms of structure, mechanism of transmission, and speed. Why are electrical synapses considered rare in the human neural system?

At electrical synapses, the pre- and post-synaptic neuronal membranes are in very close proximity, with no significant gap between them. At chemical synapses, the two membranes are separated by a fluid-filled space called the synaptic cleft.
Electrical synapses allow direct flow of electrical current from one neuron to the next without any chemical intermediary, making transmission analogous to impulse conduction along a single axon.
Chemical synapses rely on neurotransmitters: when an action potential reaches the axon terminal, synaptic vesicles fuse with the pre-synaptic membrane and release neurotransmitters into the synaptic cleft.
These neurotransmitters bind to specific receptors on the post-synaptic membrane, opening ion channels to generate a new potential that may be excitatory or inhibitory.
Impulse transmission across an electrical synapse is always faster than that across a chemical synapse because it eliminates the time needed for neurotransmitter release, diffusion, and receptor binding.
Electrical synapses are rare in the human neural system, possibly because the chemical synapse provides greater flexibility through excitatory and inhibitory modulation of the post-synaptic neuron, which is essential for complex neural integration.

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Question 5

Long Form

Describe the structure and functions of the forebrain. How does the cerebrum differ structurally and functionally from the hypothalamus?

The forebrain consists of three parts: cerebrum, thalamus, and hypothalamus. Cerebrum forms the major part of the human brain and is longitudinally divided into left and right cerebral hemispheres connected by the corpus callosum.
The outer layer of the cerebral hemisphere is the cerebral cortex (grey matter), which contains motor areas, sensory areas, and association areas responsible for intersensory associations, memory, and communication. The inner white matter consists of myelinated fibre tracts.
The thalamus, wrapped around by the cerebrum, is a major coordinating centre for sensory and motor signalling.
The hypothalamus lies at the base of the thalamus and contains centres that control body temperature, hunger, and thirst. It also has neurosecretory cells that secrete hypothalamic hormones.
Structurally, the cerebrum is the largest brain region with a highly folded cortex and two hemispheres, while the hypothalamus is a much smaller structure located at the base of the thalamus.
Functionally, the cerebrum handles higher cognitive functions, voluntary movement, sensory processing, memory, and communication, whereas the hypothalamus mainly regulates homeostatic functions such as temperature, feeding, drinking, and hormone secretion.

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Question 6

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Describe the hindbrain. Analyse how each of its three components contributes to vital body functions.

The hindbrain comprises three parts: pons, cerebellum, and medulla oblongata (medulla). Together with the midbrain, pons and medulla form the brain stem, which connects the brain to the spinal cord.
Pons consists of fibre tracts that interconnect different regions of the brain, serving as a relay station for signals travelling between the cerebrum, cerebellum, and spinal cord.
Cerebellum has a highly convoluted surface in order to accommodate additional neurons within its limited volume. This large neuron population enables precise integration of motor commands.
The cerebellum coordinates voluntary movements, maintains body balance, and integrates information from the semicircular canals of the ear and the auditory system.
The medulla oblongata is connected to the spinal cord and contains vital reflex centres that control respiration, cardiovascular reflexes, and gastric secretions — functions essential for survival.
If the medulla is damaged, breathing and heart function can fail, highlighting its critical role; similarly, cerebellar damage leads to loss of coordination and balance, demonstrating how each hindbrain component performs indispensable functions.

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Question 7

Long Form

Compare the Central Neural System (CNS) and the Peripheral Neural System (PNS) with respect to their components, subdivisions, and roles in neural coordination.

The CNS consists of the brain and the spinal cord and serves as the site of information processing and control. The PNS comprises all the nerves of the body associated with the CNS.
The CNS integrates and processes sensory inputs and formulates appropriate motor responses; the PNS acts as the communication link between the CNS and the rest of the body.
PNS nerve fibres are of two types: afferent fibres that carry impulses from tissues and organs to the CNS, and efferent fibres that carry regulatory impulses from the CNS to peripheral tissues.
The PNS is further divided into the somatic neural system, which relays impulses to skeletal muscles (voluntary), and the autonomic neural system, which transmits impulses to involuntary organs and smooth muscles.
The autonomic neural system is further classified into sympathetic and parasympathetic systems; CNS has no such functional subdivision, although it is structurally divided into brain and spinal cord.
The visceral nervous system, a component of the PNS, specifically connects the CNS to the viscera through a complex of nerves, fibres, ganglia, and plexuses, further highlighting the structural complexity of the PNS compared to the CNS.

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Question 8

Long Form

Analyse the role of Na+ in the generation and propagation of an action potential along the axon.

At rest, the axonal membrane is nearly impermeable to Na+; it is concentrated outside the axon, creating a steep electrochemical gradient directed inward.
When a stimulus is applied at a site, the membrane at that site becomes freely permeable to Na+, causing a rapid influx of Na+ into the axoplasm.
This Na+ influx causes depolarisation: the inner surface of the membrane becomes positively charged and the outer surface becomes negatively charged, reversing the resting potential and generating an action potential.
The depolarised region creates a local circuit with the adjacent polarised region: current flows inward at the depolarised site and outward at the adjacent polarised site on the outer surface.
This local current causes the adjacent membrane region to become permeable to Na+, generating an action potential there, and the process repeats sequentially along the entire length of the axon.
The rise in Na+ permeability is extremely short-lived; it is quickly followed by increased K+ permeability and outward K+ diffusion that repolarises the membrane, ensuring that impulse conduction is unidirectional and self-propagating.

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Question 9

Long Form

Describe the mechanism of synaptic transmission at a chemical synapse. How does the nature of neurotransmitters determine the outcome of transmission?

At a chemical synapse, the pre- and post-synaptic neuronal membranes are separated by a fluid-filled synaptic cleft. The axon terminals contain vesicles filled with neurotransmitters.
When an action potential arrives at the axon terminal of the pre-synaptic neuron, it stimulates the movement of synaptic vesicles towards the pre-synaptic membrane.
The synaptic vesicles fuse with the pre-synaptic plasma membrane and release their neurotransmitters into the synaptic cleft by exocytosis.
The released neurotransmitters diffuse across the synaptic cleft and bind to their specific receptors present on the post-synaptic membrane.
This binding of neurotransmitters to receptors opens specific ion channels on the post-synaptic membrane, allowing entry of ions and generating a new potential in the post-synaptic neuron.
The new potential may be excitatory, triggering an action potential in the post-synaptic neuron, or inhibitory, preventing the generation of an action potential, depending on the type of neurotransmitter released and the receptor it binds to.

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Question 10

Long Form

The human brain performs a vast range of functions from vital reflexes to complex cognition. Relate each region of the brain to the specific functions it controls as described in the chapter.

The brain is divided into forebrain (cerebrum, thalamus, hypothalamus), midbrain, and hindbrain (pons, cerebellum, medulla). The cerebrum is the site for processing vision, hearing, speech, memory, intelligence, emotions, and thoughts, and controls voluntary movements.
The cerebral cortex contains sensory areas (receive sensory input), motor areas (control voluntary movement), and association areas (responsible for intersensory associations, memory, and communication).
The thalamus acts as a major coordinating centre for sensory and motor signalling; the hypothalamus controls body temperature, hunger, thirst, circadian rhythms, and hormonal secretion through neurosecretory cells.
The limbic system (amygdala, hippocampus, inner cerebral regions) along with the hypothalamus regulates sexual behaviour, emotional reactions (excitement, pleasure, rage, fear), and motivation.
The midbrain receives and integrates visual, tactile, and auditory inputs; the cerebellum integrates information from the semicircular canals and the auditory system to maintain balance and coordinate movement.
The medulla contains centres controlling respiration, cardiovascular reflexes, and gastric secretions — vital autonomic functions; pons interconnects different brain regions.

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Chapter 18: Neural Control and Coordination | Long Questions

Describe the structure of a neuron with the help of a labelled diagram. How are neurons classified based on the number of processes?

Explain the ionic basis of resting potential in a neuron. How does the sodium-potassium pump contribute to maintaining this potential?

Trace the sequence of events from the application of a stimulus to the restoration of resting potential during nerve impulse conduction along an axon.

Compare electrical synapses and chemical synapses in terms of structure, mechanism of transmission, and speed. Why are electrical synapses considered rare in the human neural system?

Describe the structure and functions of the forebrain. How does the cerebrum differ structurally and functionally from the hypothalamus?

Describe the hindbrain. Analyse how each of its three components contributes to vital body functions.

Compare the Central Neural System (CNS) and the Peripheral Neural System (PNS) with respect to their components, subdivisions, and roles in neural coordination.

Analyse the role of Na+ in the generation and propagation of an action potential along the axon.

Describe the mechanism of synaptic transmission at a chemical synapse. How does the nature of neurotransmitters determine the outcome of transmission?

The human brain performs a vast range of functions from vital reflexes to complex cognition. Relate each region of the brain to the specific functions it controls as described in the chapter.

Unlock all Long Questions