What is a neuron?
The nervous system is made up of billions of neurons about 10 μm each that send and receive electrical and chemical impulses. The neuron is made up of several components each with a specific function. The dendrites that look like branches and receive chemical messages from other neurons, the soma (cell body) contains organelles and the nucleus. The axon is approximately 10-20 μm in diameter and its length is approximately 1m. The axon is covered by myelin sheath that acts as an insulator that carries electrical impulses ( travels at a speed of 0.6-100m/s) away from the soma, the area that connects the soma and axon is known as the axon hillock. At the end of the axon, there is a presynaptic terminal that contains vesicles that release neurotransmitters. The neurotransmitters are released into the synaptic cleft then after enter the postsynaptic terminal. The nerve impulse sent out creates an action potential which will be discussed further under electric circuits.
What are the different kinds of neurons?
- motor neuron- extends from the brain to the spinal cord and out the body, an example is the voluntary movement of the arm. They regulate the action of muscles and gland tissue.
- sensory neuron- carries an impulse to the spinal cord up to the brain,they transduce different physical stimulis to the brain such as smell, touch, sight, taste, and hearing. An example of this is touching something hot and immediately becoming startled.
- interneurons- found in the central nervous system and are in between sensory and motor neurons.
Neurons communicate in two ways;
- chemical synapse- sends nerve impulses at a slower rate than the electrical synapse because the neurotransmitters are carried by vesicles from the presynaptic terminal to the postsynaptic terminal. (Fig B)
- electrical synapse- the impulse is sent out faster because both neurons are physically connected, no synaptic cleft, and therefore send out nerve impulses faster. (Fig A)