The Nervous System: Structure and Functions

In higher-order organisms, the nervous system is similar. All mammals, including human beings, are higher order organisms. The nervous system is made up of two major divisions. One of the divisions is the central nervous system, while the other is the peripheral nervous system. The central nervous system consists of the brain, spinal cord, and one peripheral part, which is the retina of the eye. On the other hand, the peripheral nervous system is made up of pathways known as the nerves, constituting neurons.

In addition, the sensory neurons are specialized cells, which pick up sensory information from the periphery. The pathways or the nerves consist of long fibers known as the axons, which are connected to each other through synaptic junctions. The sensory signal is passed across the synaptic junction through the action of chemicals known as neurotransmitters. Proper functioning of the body of an animal is realized through coordination of the central nervous system and the peripheral nervous system (Brodal, 2010).

However, the enteric nervous system can control the activities of the alimentary canal independently. Neurons within the nervous system are of two types. The sensory neurons pick up sensory signals and transmit them to the brain to facilitate certain reactions. On the other hand, the motor neurons transmit signals between the brain and the moving parts of the body to control movement. The nervous system in the bodies of animals with bilateral symmetry is divided into two physically identical parts (Abernethy & Hanrahan, 2005).

Neurons have three parts. The soma is the major body of the cell. Extensions known as the axons make up the nerve fiber and are the pathways through which signals are transmitted. The neurons have structural projections called the dendrites that branch out into a fibrous tree. Transmission of signals throughout the nervous system is done through a voltage applied to the neurons. The signal is transmitted through the axon of the neuron.

At the end of the axon, the signal is relayed to the dendrite of another neuron. The connection between the dendrite and an axon of two neurons is known as a synapse or a synaptic junction.

The brain, which is at the center of the whole system, controls the animal’s body by formulating information into electric potential. A specific configuration of the electric pulses is generated by the brain. This information is sent to specific parts of the body through a sequence of pulses known as pulse trains.

The sequential pulses sent to organs of the body may instruct the particular organs to produce hormones. In turn, the hormones are transported through the blood and produce a specific response in particular parts of the body. On the other hand, the sequential pulses may trigger a certain pattern of muscle movement leading to finely controlled physical movement (Brodal, 2010).

The spinal cord is a collection of neurons that relay sensory information to the brain and transmits signals from the brain to the rest of the body. Although the spinal cord is primarily a conduit for the transmission of signals, it also generates independent signals that cause reflex actions initiated by certain external stimuli. However, the response generated by the spinal cord is very specific and usually involuntary. The spinal cord is usually enclosed in the spinal column, which acts as a protective structure (Shepherd, 2004).

Another type of cell known as the glial cells provides support to the neurons, which participate in most of the transmission processes. These cells secrete a material that protects the axons of the neurons. In addition, the glial cells provide nutrition to the neurons. Once a neuron is expended, the glial cells remove it from the system.

The nervous system is delicate and very sensitive to foreign material. In this regard, the glial cells protect the system from attack by pathogenic microorganisms. In addition, the glial cells provide a more rigid structure to support the loosely bound neurons in the system. Myelin deposited on the axons of the neurons by the glial cells insulates the neurons from electrical interference. This is important since the signal in the axon is usually in the order of microvolt (Shepherd, 2004).

Neurotransmitters are chemicals whose action relays information across the synaptic junction. At the synaptic junction, the neurotransmitter is produced by the neuron from which the signal is transmitted. The chemicals are contained in a synaptic vesicle, which opens at the cell membrane. When the synaptic vesicle opens, the neurotransmitter is passed into the synaptic cleft. The neurotransmitter then binds to a receptor on the postsynaptic membrane, which is the cell membrane of the receptor neuron.

An identical electrical signal is produced by the neurotransmitter in the receptor neuron. However, a positive or negative response may be elicited in the receptor neuron through a different mechanism (Shepherd, 2004). The whole process of transmission of the signal from the transmitting neuron to the receptor neuron takes very little time. It is through the synapses that information is relayed to any part of the body.

References

Abernethy, B., & Hanrahan, S. J. (2005). The biophysical foundations of human movement (2nd ed.). Champaign, IL: Human Kinetics.

Brodal, P. (2010). The central nervous system: structure and function (4th ed.). New York: Oxford University Press.

Shepherd, G. M. (2004). The synaptic organization of the brain (5th ed.). Oxford: Oxford University Press.

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