There are three main functional classifications of neurons that are determined by the
direction of their nerve impulses.
- Sensory (afferent) – transmit afferent nerve impulses from receptors to the
brain and/or spinal cord. - Motor (efferent) – transmit efferent nerve impulses from the brain and/or spinal
cord to effector sites such as muscles or glands. - Interneurons (Inter) – transmit nerve impulses from one neuron to another.
The basic anatomy of the neuron:
Axon – is a cylindrical projection from the cell body that transmits nervous impulses to other
neurons or effector sites (muscles, organs, other neurons, etc.). This is the part of the neuron that
provides communication from the brain and/or spinal cord to other parts of the body.
Axon Terminals – a specialized hair like structure at the end of the axon that is used to release
neurotransmitter chemicals and communicate with target neurons, allowing conductivity into the
area.
Cell Body – the cell body of the neuron; it contains the nucleus (also called the soma), and other
organelles such as lysosomes, mitochondria and Golgi complex.
Dendrites – the branching structure of a neuron that receives messages (attached to the cell
body). It is responsible for gathering information from other structures back into the neuron.
Myelin Sheath – the fatty substance that surrounds and protects some axons; also provides for
higher conduction velocity
Node of Ranvier – one of the many gaps in the myelin sheath – this is where the action potential
(chemical mediation of a nerve impulse) occurs.
Nucleus – the organelle in the cell body of the neuron that contains the genetic material of
the cell.
Schwann Cells – are a variety of neuroglia that mainly provides myelin insulation to axons in
the PNS of jawed vertebrates. The vertebrate nervous system relies on this myelin sheath for
insulation, and as a method of decreasing membrane capacitance in the axon.
Gap Junction – where the synapse jumps from schwann cell to schwann cell over the gap junction
by conduction of the myelin sheath.
Acetylcholine (ACh) – neurotransmitter extensively found in the brain and autonomic nervous
system. It stimulates the muscle fibers to go through a series of steps that produce muscle
contractions.