Explain the following processes :
(a) Polarization of the membrane of a nerve fibre.
(b) Depolarization 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
Explain the following processes :
(a) Polarization of the membrane of a nerve fibre.
(b) Depolarization 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
(a) When the resting potential of the membrane changes it becomes polarized. During resting condition, the axoplasm inside the axon contains a high concentration of K+ and negatively charged proteins and low concentration of Na+. 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 the polarization of membrane or polarized nerve.
(b) 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 in positive charge inside and negative charge outside the nerve fibre. Hence, the membrane is said to be depolarized.
(c) There are two types of nerve fibres - myelinated and non-myelinated. In myelinated nerve fibre, the impulse is conducted from node to node in a mumping manner as myelinated nerve fibre is enveloped with Schwann cells, which form a myelin sheath around the axon. The myelin sheath is impermeable to ions. As a result, the ionic exchange and depolarization of nerve fibre is not possible along the whole length of the nerve fibre. It takes place only at some point, known as nodes of Ranvier. 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) At a chemical synapse, the membranes of the pre-and post-synaptic neurons are separated by a fluid-filled space called synaptic cleft. When an impulse arrives at the axon terminal, it stimulates the movement of the synaptic vesicles towards the membrane where they fuse with the plasma membrane and release their neurotransmitters in the synaptic cleft. The released neurotransmitters bind to their specific receptors, present on the post-synaptic membrane. This binding opens ion channels allowing the entry of ions which can generate a new potential in the post-synaptic neuron. The new potential developed may be either excitatory or inhibitory.
(a) When the resting potential of the membrane changes it becomes polarized. During resting condition, the axoplasm inside the axon contains a high concentration of K+ and negatively charged proteins and low concentration of Na+. 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 the polarization of membrane or polarized nerve.
(b) 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 in positive charge inside and negative charge outside the nerve fibre. Hence, the membrane is said to be depolarized.
(c) There are two types of nerve fibres - myelinated and non-myelinated. In myelinated nerve fibre, the impulse is conducted from node to node in a mumping manner as myelinated nerve fibre is enveloped with Schwann cells, which form a myelin sheath around the axon. The myelin sheath is impermeable to ions. As a result, the ionic exchange and depolarization of nerve fibre is not possible along the whole length of the nerve fibre. It takes place only at some point, known as nodes of Ranvier. 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) At a chemical synapse, the membranes of the pre-and post-synaptic neurons are separated by a fluid-filled space called synaptic cleft. When an impulse arrives at the axon terminal, it stimulates the movement of the synaptic vesicles towards the membrane where they fuse with the plasma membrane and release their neurotransmitters in the synaptic cleft. The released neurotransmitters bind to their specific receptors, present on the post-synaptic membrane. This binding opens ion channels allowing the entry of ions which can generate a new potential in the post-synaptic neuron. The new potential developed may be either excitatory or inhibitory.
