Neural Control and Coordination
Generation and conduction of nerve impulse
- Nerve impulse is generated due to differential permeability of ions in neural membrane. Action potential is the other term for nerve impulse.
- Neural membrane, initially maintained under resting condition as the Na/K pump, transports 3 Na+ outwards and 2k+ inwards to the nerve cell.
- Na/K pump, before obtaining a stimulus, maintains a polarised membrane by creating a positive charge on the outside of axonal membrane and negative charge inside the axons – [resting potential = −70 mv].
- When a stimulus is applied to polarised membrane, the Na/K pump fails to work and the membrane is highly permeable to Na+ ions.
- As a result the inside charge of nerve membrane converts as positive and the outside membrane as negative. Now the membrane is said to be depolarised.
- Action potential is generated when the voltage reaches +30 ±10 mv.
- After the process of creating action potential is done, the membrane is now more permeable to K+ ions, which performs repolarization.
- In a flow, excess K+ ions flow inside the membrane to counteract Na+ ions and creates Hyper polarization.
- The time period till hyperpolarization happens is termed as Refractory period before which neurons cannot conduct another impulse.
- When an impulse travels along a myelinated neuron, it jumps from one node of vanvier to another and conducts so fast and hence named as saltatory mode of conduction.
- Speed of conduction in humans is recorded to be 100m/sec and in frogs as 30 m/sec.
- Synapse is the junction b/w 2 neurons across which impulse passes and is formed by the membranes of Pre-synaptic and post synaptic neuron, which may or may not be divided by a small gap known as synaptic cleft.
- Two types of synapse – (i) Electrical synapse, (ii) Chemical synapse.
- Electrical synapse is faster than chemical synapse as they are provided by gap junction between 2 neurons. Location: cardiac muscle fibres, intestinal fibres and the epithelial cells of lens.
- Chemical synapse happens by the breakage of synaptic vesicles in telodendria by calcium ions that releases neurotransmitters from pre synapse to post synapse and makes it get attached to the receptor, so that the neural signals are successfully passed onto the next neuron.
- Neurotransmitters are of 2 types (i) Excitatory and (ii) Inhibitory
- Excitatory examples : Acetylcholine, Epinephrine, norEpinephrine
- Inhibitory neurotransmitters → Examples : GABA, Glycine, Dopamine.
- As the acetylcholine is released from pre-synaptic knob by Ca2+ ions, it is broken down by Acetylcholinesterase (AchE) into Acetate and choline which is then fixed into the cholinergic receptors of post synaptic membrane.
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