Nervous system 1, Motor neuron
Basic structure and function of the nervous system. Often people gloss over the 'simple' stuff, and miss areas of important understanding. The main things are the plain things, and often, the plain things are the main things. Please draw your own diagram, rather that taking the short cut of freeze faming and screen capture.
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Motor means to do with movement. When we decide we want to move part of the body a motor neurone in the brain will generate a new nerve impulse. The same neurone will then carry this impulse away from the brain towards a synapse with an other motor neurone which will then carry the impulse into the PNS.
A nerve impulse is electrical in nature and is generated in the cell body. This is an enlarged area of the cell which contains the nucleus and most of the cell organelles. From here the impulse travels away, along a fibre of the motor neurone called an axon. Any nerve fibre which carries information, in the form of an electrical nerve impulse, away from a cell body is defined as an axon.
There are also dendrites connected to the motor neurone cell body. A dendrite is defined as any nerve fibre which carries information towards a cell body. Typically a motor neurone consists of short dendrites conveying information towards the cell body and a longer axon carrying information away. Nerve fibres are essentially long thin projections of the cytoplasm. Despite being very thin, nerve fibres can be very long. For example, some motor neurone axons originate in the spinal cord and run the full length of the legs into the feet.
Because motor neurones initiate movement they often connect to skeletal muscles. When an axon approaches the muscle it supplies it divides into a number of smaller fibres which end in specialised structures called the synaptic end bulbs. These bulbs are responsible for conveying the impulse from the axon into the muscle. A muscle will only contract when it is stimulated to do so by the nerve impulse. As motor neurones carry impulses out from the CNS they are sometimes referred to as efferent neurones (remember ‘e’ for Efferent and for Exit).
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