Neurons, or nerve cells, are found in the brain, spinal cord and nerves. They control information processing muscle contractions and gland activity as well as sensation interpretation. Neurons are able to receive, process and transmit information to other cells.
Overview Of A Neuron
Different parts of the neuron are responsible for specific actions. Neurons are made up of the soma, dendrites and axon.
- Soma: the cell body where metabolic maintenance occurs.
- Dendrites: most neurons have many dendrites that extend from the soma and gather signals from other neurons and transfer them to the soma.
- Axons: most neurons have only one axon, a specialized extension that conducts signals away from the soma. At its termination, an axon divides into many branches called axon terminals. These axon terminals allow the axon to transmit signals simultaneously to many other neurons, glands or muscle fibers.
Transmission Of Neuronal Messages
Sensory neurons collect information from the outside environment or from inside the animal and send this information to other neurons. Neurons are classified into three types. These are sensory neurons, interneurons and motor neurons, sometimes called motoneurons.
- Sensory neurons: these transmit information gathered from external stimuli (which could include sound, light or a chemical change) or which would respond to stimuli inside the body such as the positioning of an arm or joint.
- Interneurons: these link other neurons within the central nervous system (CNS).
- Motor neurons: these carry signals to organs causing muscle contractions or gland cell secretions.
Action Potentials And Synapse
Axons convey information from the cell body and dendrites receive information. The point where the cells meet to relay information (between axon and dendrite) is a synapse. The information is sent from the axon of the ‘sending’ cell, to the dendrite of the ‘receiving’ cell, by transmission of chemical molecules called neurotransmitters (epinephrine or acetylcholine).
Information is sent from the nerves regarding sensations, or muscle movement from the peripheral nervous system to the brain via the spinal cord. This information is sent via electrical signals called action potentials (the change in electrical potential that occurs between the inside and outside of a nerve or muscle fiber).
Different areas of the brain are responsible for information translation and response. The peripheral nervous system controls body functions that are not under voluntary control and belong to the autonomic nervous system. The cranial nerves arise in the brain and control nerves of sense organs and spinal nerves control trunk and limbs.
Resource and further reading:
Silverthorn, D.U, 2007, ‘The Physical Basis Of Neuronal Function, in Human Physiology, ed. Benjamin Cummings, San Francisco, chap. 21.
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