Biology Class 11 NCERT Solutions: Chapter 21 Neural Control and Coordination Part 2 (For CBSE, ICSE, IAS, NET, NRA 2022)

Glide to success with Doorsteptutor material for CBSE/Class-6 : get questions, notes, tests, video lectures and more- for all subjects of CBSE/Class-6.

Q: 2. Compare the following:

(A) Central neural system (CNS) and Peripheral neural system (PNS)

(B) Resting potential and action potential

(C) Choroid and retina

Answer:

(A) Central neural system (CNS) and Peripheral neural system (PNS)

Table of Central and Peripheral Netural System
Central neural systemPeripheral neural system
1It is the main coordinating centre of the body1It is not the main coordinating centre of the body.
2It includes brain and spinal cord.2It includes cranial and spinal nerves that connect central nervous system to different parts of the body.
3
Image Shows the Central Neural System
3
Image Shows the Peripheral Neural System

(B) Resting potential and action potential

Table of Resting and Action Potential
Resting potentialAction potential
1It is the potential difference across the nerve fibre when there is no conduction of nerve impulse.1It is the potential difference across nerve fibre when there is conduction of nerve impulse.
2The membrane is more permeable to K + ions than to ions.2The membrane is more permeable to ions than to K + ions.
Resting Potential and Action Potential

(C) Choroid and retina

Table of Choroid and Retina Potential
ChoroidRetina
1Choroid is the middle vascular layer of eye1Retina is the innermost nervous coat of eye
2It contains numerous blood vessels that provide nutrients and oxygen to retina and other tissues.2It contains photoreceptor cells, rods and cones that are associated with twilight and colour vision respectively.
3
Figure Shows the Choroid
3
Figure Shows the Retina

Q: 3. 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

(D) Transmission of a nerve impulse across a chemical synapse

Answer:

(A) Polarisation of the membrane of a nerve fibre

During resting condition, the concentration of ions is more inside the axoplasm while the concentration of ions is more outside the axoplasm. As a result, the potassium ions move faster from inside to outside as compared to sodium ions. Therefore, the membrane becomes positively charged outside and negatively charged inside. This is known as polarization of membrane or polarized nerve.

Q_3_A_Polarisation of the Memberane of Nerve Fibre

(B) Depolarisation of the membrane of a nerve fibre

When an electrical stimulus is given to a nerve fibre, an action potential is generated. The membrane becomes permeable to sodium ions than to potassium ions. This results into positive charge inside and negative charge outside the nerve fibre. Hence, the membrane is said to be depolarized.

Q_3_B_Depolarisation of the Membrane of Nerve Fibre

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

There are two types of nerve fibers – myelinated and non-myelinated. In myelinated nerve fibre, the action potential is conducted from node to node in jumping manner. This is because the myelinated nerve fibre is coated with myelin sheath. The myelin sheath is impermeable to ions. As a result, the ionic exchange and depolarisation of nerve fibre is not possible along the whole length of nerve fibre. It takes place only at some point, known as nodes of Ranvier, whereas in non-myelinated nerve fibre, the ionic exchange and depolarization of nerve fibre takes place along the whole length of the nerve fibre. Because of this ionic exchange, the depolarized area becomes repolarised and the next polarized area becomes depolarized.

(D) Transmission of a nerve impulse across a chemical synapse

Synapse is a small gap that occurs between the last portion of the axon of one neuron and the dendrite of next neuron. When an impulse reaches at the end plate of axon, vesicles consisting of chemical substance or neurotransmitter, such as acetylcholine, fuse with the plasma membrane. This chemical moves across the cleft and attaches to chemo-receptors present on the membrane of the dendrite of next neuron. This binding of chemical with chemo-receptors leads to the depolarization of membrane and generates a nerve impulse across nerve fibre.

The chemical, acetylcholine, is inactivated by enzyme acetylcholinesterase. The enzyme is present in the post synaptic membrane of the dendrite.

It hydrolyses acetylcholine and this allows the membrane to repolarise.

Q_3_D_Transmission of a Nerve Impulse Across a Chem …

Developed by: