Biology Class 11 Question Answer Chapter 18 Neural Control and Coordination CBSE

Q1. Briefly describe the structure of the brain.

Answer : 

The brain is the central information-processing organ of the body, protected by the skull and cranial meninges (dura mater, arachnoid, and pia mater). It has three major parts:

1. Forebrain

The forebrain is the largest and most complex part of the brain, consisting of the following:

Cerebrum:

• Structure: Divided into two hemispheres (left and right) connected by a bundle of nerve fibres called the corpus callosum.
• Cerebral Cortex: The outer layer of the cerebrum, also called grey matter, has folds to increase surface area. The inner layer is made of white matter, which contains myelinated nerve fibres.
• Functions: Responsible for sensory perception, voluntary motor actions, reasoning, memory, and emotions.

Thalamus:

• Structure: Located beneath the cerebrum.
• Function: Acts as a relay centre, processing and transmitting sensory and motor signals to the appropriate areas of the cerebrum.

Hypothalamus:

• Structure: Located at the base of the thalamus.
• Functions:
  • Regulates body temperature, hunger, thirst, and circadian rhythms.
  • Contains neurosecretory cells that produce hypothalamic hormones.
  • Plays a role in emotional responses and motivation.

2. Midbrain

The midbrain is a small region that connects the forebrain and hindbrain.

Structure: Contains a canal called the cerebral aqueduct and four rounded structures known as the corpora quadrigemina.

Functions:

• • Integrates sensory inputs (visual, auditory, and tactile).
  • Coordinates reflex movements of the head, neck, and eyes.

3. Hindbrain

The hindbrain comprises the following structures:

Cerebellum:

• Structure: Has a highly folded surface to accommodate more neurons.
• Functions: Maintains balance, posture, and coordination of voluntary movements.

Pons:

• Structure: Located between the midbrain and medulla.
• Functions: Connects various parts of the brain and helps in controlling respiration.

Medulla Oblongata:

• Structure: Connects the brain to the spinal cord.
  • Functions:
    • Controls vital reflexes such as heartbeat, breathing, and digestion.
    • Regulates involuntary actions like swallowing and sneezing.

Q2. Compare the following:

Answer :

(a) Central Neural System (CNS) vs. Peripheral Neural System (PNS):

(b) Resting potential and action potential

Q3. Explain the following processes:

(a) Polarisation of the membrane of a nerve fibre

(b) Depolarisation of the membrane of a nerve fibre

(c) Conduction of a nerve impulse along a nerve fibre

Answer :

(a) Polarisation:

• At rest, the axon membrane is more permeable to
  $K^+$ 

  K+ and impermeable to $Na^+$ 

  Na+.

• Sodium-potassium pumps actively transport
  $3 \, Na^+$ 

  3Na+ out and $2 \, K^+$ 

  2K+ in, maintaining a negative charge inside.

• This results in a resting membrane potential of approximately
  $-70 \, mV$ 

  $-70mV$.

(b) Depolarisation:

• When a stimulus reaches the membrane,
  $Na^+$ 

  Na+ channels open, and $Na^+$ 

  Na+ rushes inside.

• This reverses the polarity of the membrane (inside becomes positive, outside negative).
• This phase is called depolarisation, and it generates an action potential.

(c) Transmission across a chemical synapse:

• Action potential arrives at the presynaptic terminal, triggering
  $Ca^{2+}$ 

  Ca2+ channels to open.

• 
  $Ca^{2+}$ 

  Ca2+ influx causes synaptic vesicles to release neurotransmitters into the synaptic cleft.

• Neurotransmitters bind to receptors on the postsynaptic membrane, opening ion channels.
• Depending on the neurotransmitter, the postsynaptic neuron is either excited (action potential generated) or inhibited.

Q4. Draw labelled diagrams:

(a) Neuron

(b) Brain

Q5. Write short notes:

Answer :

(a) Neural Coordination:

• Neural coordination involves the nervous system regulating and integrating body functions through electrical signals.
• The CNS and PNS work together to maintain homeostasis and respond to internal and external stimuli.

(b) Forebrain:

• Composed of the cerebrum, thalamus, and hypothalamus.
• Controls sensory perception, voluntary actions, emotions, hunger, and body temperature.
• The cerebral cortex processes higher cognitive functions like learning and memory.

(c) Midbrain:

• Located between the forebrain and hindbrain.
• Contains the cerebral aqueduct and corpora quadrigemina.
• Integrates sensory inputs and coordinates reflex movements.

(d) Hindbrain:

• Includes the cerebellum, pons, and medulla oblongata.
• Controls balance, posture, respiration, and reflex actions like sneezing.

(e) Synapse:

• A junction where a nerve impulse is transmitted from one neuron to another.
• Includes electrical and chemical synapses, with neurotransmitters playing a key role in the latter.

Q6. Mechanism of Synaptic Transmission

Answer :

1. Presynaptic Events:
   • Action potential arrives at the axon terminal.
   • Voltage-gated
     $Ca^{2+}$ 

     Ca2+ channels open, causing an influx of $Ca^{2+}$ 

     Ca2+.

   • Synaptic vesicles release neurotransmitters into the synaptic cleft.
2. Synaptic Cleft:
   • Neurotransmitters diffuse across the cleft to the postsynaptic neuron.
3. Postsynaptic Events:
   • Neurotransmitters bind to receptors, opening ion channels.
   • Excitatory neurotransmitters generate an action potential; inhibitory ones prevent it.

Q7. Role of $Na^+$

Na+ in the Generation of Action Potential

Answer :

• At rest,
  $Na^+$ 

  Na+ is concentrated outside the axon.

• Upon stimulation,
  $Na^+$ 

  Na+ channels open, allowing $Na^+$ 

  Na+ to rush in.

• This depolarises the membrane, creating an action potential.
• The rapid influx of
  $Na^+$ 

  Na+ is essential for nerve impulse transmission.

Q8. Differentiate Between :

(a) Myelinated vs. Non-myelinated Axons:

(b) Dendrites vs. Axons:

(c) Thalamus vs. Hypothalamus:

(d) Cerebrum vs. Cerebellum:

Q9. Answer the Following

(a) Which part of the human brain is the most developed?

• The cerebrum is the most developed part of the brain.
• It handles complex processes like memory, learning, emotions, and voluntary movements.

(b) Which part of our central neural system acts as a master clock?

• The hypothalamus acts as the master clock.
• It regulates circadian rhythms, controlling sleep-wake cycles and hormone secretion.

10. Distinguish between :

(a) Afferent vs. Efferent Neurons:

(b) Impulse Conduction in Myelinated vs. Non-myelinated Fibres:

(c) Cranial vs. Spinal Nerves: