Central Nervous System

What is the central nervous system? It’s a system which consists of the nerves in the brain and spinal cord. It gathers information about and reacts to internal and external stimulus.
Don’t Shoot the Messenger
Much of the CNS is made up of neurons. Each neuron has a cell body, which includes a soma with a nucleus, a nucleolus, a cytoplasm called the perikaryon, and wide branching extensions called dendrites. Dendrites are like antennae which receive signals from other neurons or body cells. Their plasma membranes and cell bodies contain many receptor sites for binding chemical messengers, or neurotransmitters. Such structures are often short, tapering, and highly branched. They forming a tree-like variety of processes extending from its soma.
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Their size ranges from 1 mm to 1 m, and each axon synapses with 1 000 to over 10 000 neurons. Every axon’s cytoplasm (or axoplasm) contains neurofibrils, neurotubules, small vesicles, lysosomes, and mitochondria. It cannot create proteins because it has no rough endoplasmic reticulum. A plasma axolemma (cell membrane) surrounds the entire axon to protect it. In a multipolar neuron, the axons’s base is attached to the soma at a thickened cone-shaped region called the axon hillock. Nerve impulses occur between the hillock and initial segment where action potentials begin (an area called the “trigger zone”). Sometimes axons have side branches called collaterals, which usually branch off at a 90 ° angle and allow a neuron to communicate with many cells at once. Each axon branch ends in a thin extension series called telodendria, which ends at the synaptic terminals.
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It develops in a sensory receptor, and causes a sensory neuron’s axon to form a nerve action potential which travels along the axon into the CNS. This causes neurotransmitters to release at the synapse with interneurons. Action potential is a large graded potential, which propagates along the axon to more than one synapse. A neurotransmitter stimulates the interneuron to form a graded potential in the dendrites, and the interneuron’s axon forms a nerve action potential. The nerve action potential travels along the axon, causing the neurotransmitter to release at the next synapse with another

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