Synapse is the junction between neurons or between neurons and muscles or glands. It helps to regulate the speed and direction of impulses. The impulses are transmitted across the synaptic cleft only through a chemical (neurotransmitter), secreted from the synaptic knobs.
The electrical messages conducted through nerves are called impulses.
Impulse is generated as follows : The difference in the distribution of ions maintains positive charge on the outer surface and negative charge inside the plasma membrane of the receptor part of neuron. When stimulated, this ionic equilibrium (polarity) changes there and the outer surface becomes negatively charged and inner become positively charged. As a result, impulse generated. This charge difference stimulates its adjacent parts and similar changes occur there too. Thus a continuous flow of the impulse becomes possible.
Impulses transmission path
Impulse due to stimulus => dendrites => dendrons => cyton => axon => axonites=> synaptic knob => secretion of neurotransmitter to the synaptic cleft => Stimulation in the adjacent dendrites => Impulse forms.
When impulses reach at the synaptic knobs, a chemical substance, known as neurotransmitter is released in the synaptic cleft. This chemical stimulates the adjacent dendrites to form new electric impulses.
Sensory neurons - Carries impulses from different body parts to the brain and spinal cord.
Motor neurons - Carries impulses from the brain and spinal cord to various parts of body.
A nerve is a group of axons or nerve fibres, covered by connective tissue.
Sensory nerves (consists of sensory neurons) : Carry impulses from sense organs to the brain and
spinal cord.
Motor nerves (consists of motor neurons) : Carry impulses from brain and spinal cord to different
organs.
Mixed nerves (consists of sensory and motor neurons) : Carry impulses from brain and spinal cord to different organs and vise versa.
Central Nervous System : Brain , Spinal cord
Peripheral Nervous System : Cranial nerves -12 pairs , Spinal nerves -31 pairs
Brain's protections : The brain is protected inside a hard skull and is covered by a three layered membrane, called the
meninges. Cerebrospinal fluid,a fluid formed inside the meninges, also protects the brain.
The outer covering of brain and spinal cord is Meninges.
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