Neural Control And Coordination: Neuron And Nerves

Introduction

The nervous system is a collection of cells that carry electrochemical inputs from sensory receptors to the location where a reaction is generated. In human beings, neural control and coordination guide everyday activities such as waking up, automatic activities such as movement, balance, and breathing, and complex processes such as thinking, feeling emotions etc. The nervous system is the most complex body system in an organism that coordinates its action and sensory information. It is the major controlling, regulating and command centre of the brain.

The human nervous system comprises of two parts: 

1. the central neural system (CNS), and
2. the peripheral neural system (PNS)

The job of neural control and coordination lies with the nerves. Though the nervous system is quite complex, the nervous tissue comprises mainly of only two types of cells:

1. Neurons, and
2. Glial cells

Neurons are the essential and functional unit of the neural system. They carry electrical signals called nerve impulses through the body. Glial cells provide nourishment to the neurons.

Difference Between Neurons And Nerves

Although the two may sound similar, there is a difference between the two. Nerves are the projections of neurons. The main difference between them is that the nerve is a bundle of neurons along with the connective tissue, blood vessels, and lymphatic vessels, whereas the neuron is the basic unit or, more precisely, a cell of the nervous system.

Neuron: Centre of Neural Control and Coordination

A neuron comprises of the following three important parts:

1. Cell body
2. Dendrites 
3. Axon

The cell body contains cytoplasm and certain granular bodies called Nissl’s granules, besides the essential cell organelles. Dendrites are the small fibres that branch repeatedly and stick out of the cell body. They contain Nissl’s granules. Dendrites transfer impulses to the cell body. 

An axon is a thin, long fibre with a branched distal end. Neurons terminate as a bulb-like structure called synaptic knob, which contains synaptic vesicles that contain chemicals called neurotransmitters. Axons carry nerve impulses from the cell body to a synapse or a myoneural junction, which is located further apart from the cell body. 

Axons can be of two types myelinated and unmyelinated. The myelinated axons are enveloped with Schwann cells, which form a fatty medullary sheath around the axon. The small gaps between two adjacent myelin sheaths are called nodes of Ranvier. Unmyelinated nerve fibres are widespread in autonomous and somatic neural systems, whereas myelinated nerve fibres are found in spinal and cranial nerves.

Types of Neurons

Depending on the number of axons and dendrites, the neurons are divided into three types

• Multipolar: have one axon and two or more dendrites and are found in the cerebral cortex
• Bipolar: have one axon and one dendrite and are present in the retina of the eye)
• Unipolar: have a cell body with one axon only and are found usually in the embryonic stage

Also neurons can also be classified based on the direction in which they carry nerve impulses. 

• Sensory neurons: they transmit nerve impulses from tissues and organs to the spinal cord and brain
• Motor neurons: they transmit nerve impulses from the brain and spinal cord to muscles and glands 
• Interneurons: they transmit nerve impulses back and forth between sensory and motor neurons

Nerve as the Centre of Coordination and Control

The nerve is a wire-like structure that transmits nerve impulses between the central nervous system and sense organs. A nerve is a bundle of a large number of axons and is called a fascicle. Each fascicle is surrounded by perineurium. A loose connective tissue, composed of flattened cells, basement membrane, and collagen fibres, endoneurium surrounds the perineurium. Arteries and veins are present between the fascicles and supply nutrients and gases to the neurons inside the fascicles.

Nerve Impulse: Centre of Neural Control and Coordination

A nerve impulse is transferred between two neurons at junctions called a synapse. The presynaptic neuron and a postsynaptic neuron membrane form a synapse that may or may not be divided by a gap called the synaptic cleft. The two kinds of synapses are

• Electrical synapses  
• Chemical synapses

At electrical synapses, the electrical current can flow directly between the two neurons, and therefore the impulse transmission across an electrical synapse is always faster than that of a chemical synapse. 

At chemical synapse, a fluid-filled space called synaptic cleft divides the presynaptic and postsynaptic membranes.

Conclusion

The control and coordination of the body is the key function of neurons and nerves. The functioning elements of the nervous system are called neurons. The nerve impulse conduction takes place along the axon membrane across the synapse. The synapse is formed by the membranes of a presynaptic neuron and a postsynaptic neuron. These membranes might be separated by a gap called the synaptic cleft. At chemical synapses, chemicals called neurotransmitters are involved in the transmission of impulses. The information regarding any change in the environment is received by the CNS through the nerves, which are processed and analysed.