Essay on Human Nervous System (533 Words)
Different activities of an animal’s body are controlled and coordinated through two systems, the nervous system and endocrine system.
Nervous system is a system of highly specialised nerve cells, nerve fibres and organs (called receptors), that coordinate and control the activities of different parts of the body.
This is done by converting the internal and external stimuli of environmental changes into the form of electrical impulses (a process called transduction) and transmits them to other specialised cells called effectors (muscles and glands) to react accordingly.
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Between the receptors and effectors are the conducting cells of the nervous system, the neurons. Neurons are the structural and functional unit of nervous system that forms a complex network of communication by spreading throughout the organisms.
The nervous system consists of two main parts:
(a) Central nervous system:
It consists of brain and spinal cord. The brain is lodged in the skull while spinal cord is enclosed by the vertebral column. Three connective tissue membranes which protect the central nervous system and projections of its structure are called meninges. These are –
1. Piamater:
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It is the thinnest of all the meninges. It is vascular and pigmented sheath that lies in contact with brain. It also sheathes the roots of cranial and spinal nerves. At two places it adhered to the roof surface of brain to form choroid plexus for secreting cerebrospinal fluid (CSF).
2. Arachnoid:
It is a thin, webby and slightly vascular middle sheet. A narrow subarachnoid space is present between arachnoid and piamater.
3. Duramater:
It is the outermost double layered thick and tough non-vascular meninx. It lines the cranial cavity. A narrow subdural space occurs between duramater and arachnoid which is simply a potential space in the form of a thin film of serous fluid. Three layers of meninges.
Cerebrospinal Fluid (CSF):
It is colourless, clear, slightly alkaline (7-33 pH) fluid of 1.005 specific gravity. CSF is a blood filterate with an ionic and macromolecular composition markedly different from serum. It contains far less protein but much more Na, K and chloride. Secreted by anterior choroid plexus and posterior choroid plexus it is found inside the ventricles of the brain, the central canal of the spinal cord.
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The cerebrospinal fluid acts as a shock absorber for the brain and spinal cord and may also contribute to nourish brain tissue by transporting constant supply of food and oxygen. It also maintains a constant pressure inside the cranium inspire of variations in the pressure of blood in the cranial vessels.
(b) Peripheral nervous system:
The nerves arising from the central nervous system constitute the peripheral nervous system. This system is divided into two main parts –
Voluntary nervous system:
This system is under the control of voluntary control of brain. It consists of the nerves, originates from the brain and spinal cord and is known as cranial and spinal nerves respectively.
Autonomic nervous system:
It controls and coordinates those organs which are under involuntary control. This system is further divided into two –
(i) Sympathetic nervous system (SNS), which has mainly excitatory effects on the body.
(ii) Parasympathetic nervous system, which acts antagonistically to the CNS and has mainly calming influences.