Most physiological activities in humans, like speech, sleep and the response to stimuli, happen because of the coordinated action of nerves and hormones. All these activities are mainly regulated by two systems – the endocrine system and the nerve system. These two systems interact with each other and regulate the body’s functions.
The endocrine system functions by secreting a chemical substance called hormones. These hormones act as chemical messengers and are involved in intercellular communication or cell signalling. Not only hormones, but even hormone-like substances can also act as messengers. The organs that receive the information are called the receptors. It includes the five sense organs – the ears, eyes, tongue, nose and skin. Hence, the coordination and response in higher animals include the involvement of hormones, nerves and the sense organs.
Nerve Cells or Neurons
The coordination system involving the nerves is quicker than the other control system (endocrine system). The nervous system is made up of a primary structural and functional unit called the nerve cell or neurons. These neurons are similar to any other body cell and have the nucleus and all other organelles in the cytoplasm. Apart from that, they also have processes or branches called the dendrites and axons. The nerve cells do not have centromere, and hence they cannot undergo division. Thus it transmits as well as receives nerve impulses with the help of –
- The cell body
The connections between the nerve cells can form large networks and pathways that have a direct impact on an organism’s behaviour as well as its perception of the world.
The CNS and PNS
The system of nerves can be classified into two parts – the CNS and the PNS. The central nervous system or CNS includes the spinal cord and the brain. The spinal cord and brain structures are arranged in two layers, namely the white matter and the grey matter. The grey matter comprises the nerve cell bodies and the nearby nerve fibres that arise from the nerve cell body. At the same time, the white matter is formed by the remaining part of the nerve cells.
The other system formed by the nerve cells and their processes in all other regions of the body is called the peripheral nervous system or the PNS. It comprises the spinal nerves coming from the spinal cord and the cranial nerves arising from the brain. They can be further distinguished into the autonomic and somatic nervous systems. The somatic includes nerve supply from the skeletal muscles and is concerned with the somatic functions. The autonomic mostly includes the visceral or involuntary functions.
Reflex activity in higher animals is nothing but the response to the peripheral nervous stimulation that happens without our consciousness. It is considered a protective mechanism as it protects the body from irreversible damage. For example, when we place our hands on a hot object, it retreats immediately. Likewise, when a bright light is directly thrown into the eyes, we tend to close the eyelids. Also, the pupil is constricted to prevent damage to the retina by the entrance of excessive light into the eyes.
The anatomical reflex pathway for a reflex action is termed a reflex arc. The five components of a reflex arc are –
- The receptor organ which receives the stimulus
- The sensory nerve that transmits impulses
- The centre which receives the sensory impulses
- The motor nerve that transmits impulses from the centre to the effector organ
- The effector organ where the response to the stimuli happens
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Nervous System: Control and Coordination