BSC 215 Lecture Notes - Lecture 27: Endoplasmic Reticulum, Axon Hillock, Central Nervous System
11 Jun 2018
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Neurons
A neuron is a cell that transmits nerve impulses. It consists of the following parts:
• The cell body (soma or perikaryon) contains the nucleus and other cell
organelles.
• There are clusters of rough endoplasmic reticulum that are called Nissl
bodies or are sometimes referred to as chromatophilic substances.
• The dendrite is typically a short, abundantly branched, slender process
(extension) of the cell body that receives stimuli.
• The axon is typically a long, slender process of the cell body that sends
nerve impulses. It emerges from the cell body at the cone‐shaped
axon hillock. Nerve impulses arise in the trigger zone, generally
located in the initial segment, an area just outside the axon hillock.
The cytoplasm of the axon, the axoplasm, is surrounded by its plasma
membrane, the axolemma. A few axons branch along their lengths to
form axon collaterals, and these branches may return to merge with
the main axon. At its end, each axon or axon collateral usually forms
numerous branches (telodendria), with most branches terminating in
bulb‐shaped structures called synaptic knobs (synaptic end bulbs, also
called terminal boutons). The synaptic knobs contain
neurotransmitters, chemicals that transmit nerve impulses to a muscle
or another neuron.
Neurons can be classified by function or by structure. Functionally, they fall
into three groups:
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Document Summary
A neuron is a cell that transmits nerve impulses. It emerges from the cell body at the cone shaped axon hillock. Nerve impulses arise in the trigger zone, generally located in the initial segment, an area just outside the axon hillock. The cytoplasm of the axon, the axoplasm, is surrounded by its plasma membrane, the axolemma. A few axons branch along their lengths to form axon collaterals, and these branches may return to merge with the main axon. At its end, each axon or axon collateral usually forms numerous branches (telodendria), with most branches terminating in bulb shaped structures called synaptic knobs (synaptic end bulbs, also called terminal boutons). The synaptic knobs contain neurotransmitters, chemicals that transmit nerve impulses to a muscle or another neuron. Neurons can be classified by function or by structure. Effectors include muscles, sweat glands, and many other organs: association neurons (interneurons) are located in the cns and transmit impulses from sensory neurons to motor neurons.
