What is the Central Nervous System?

Central Nervous System is the most crucial unit in an organism since it is the hub or the centre that commands, instigates and coordinates information. Moreover, it directly or indirectly influences all the activities within the body. The Central Nervous System in the human body is a part of the entire nervous system responsible for the overall functioning of the body. 

The nervous system gives us the sense of taste, watching, hearing, feeling and so on. The human nervous system is the system that conducts development and improvements from the sensory receptors. The receptor comes from the brain and spinal cord and leads impulses back to different body parts. The Central Nervous System (CNS) and the most common primary central nervous system (CNS) tumour are discussed here in detail. 

What is the Central Nervous System

Brain and spinal cord develop from infolding of the neural plate of the ectoderm of the embryo immediately dorsal to the notochord.It is first formed as a hollow tube and later differentiates as the anterior wider part of the brain and long cylindrical posterior part spinal cord.Brain and spinal cord are central nervous system.

Brain (or encephalon)

It is a mass of nerve cells, enclosed within a bony case called as cranium (brain box) constituting 98% weight of CNS, i.e., about 1400 gms (in adult man) made up of two componentsGrey matter consisting of cell body (cyton) part of the neuron    

White matter the part with axon and dendron covered by myelin sheath

BRAIN MENINGES Brain is covered by three membranes of connective tissue termed as meninges or menix.

Dura Mater

This is the first and the outermost membrane which is thick, very strong and non-elastic. It is made up of collagen fibres. This membrane is attached to the innermost surface of the cranium.

Arachnoid

It is a middle, thin and delicate membrane made up of connective tissue. It is found only in mammals.

Pia Mater

It is Innermost, thin and transparent membrane, made up of connective tissue.

Cerebrospinal-Fluid (CSF)

This fluid is clear and alkaline in nature just like lymph. It has protein (Albumin, globulin), glucose, and CSF is present in the ventricle of brain, subarachnoid space of brain & spinal cord.

Human brain divided into three parts –

• Fore brain –       Cerebrum,Thalamus and Hypothalamus
• Midbrain –        Consists of many groups of nerve cells called “Nuclei”.
• Hindbrain –      pons, Cerebellum, Medulla

Cerebrum

It is the first & most developed part of the brain. It makes up 2/3 part of the total brain.

Cerebrum consists of two cerebral hemispheres on the dorsal surface. A longitudinal groove is present between two cerebral hemispheres called median fissure. Both the cerebral hemispheres are partially connected with each other by curved thick nerve fibres called corpus callosum.Many ridges & grooves are found on the dorsal surface hemisphere. Ridges are known as gyri while grooves are called sulci. These cover the 2/3 part of cerebrum.Gyri & sulci are more developed in human beings so human beings are the most intelligent living beings.

On dorsal surface of cerebral hemisphere, grey matter becomes more thick, this thick layer of grey matter is known as Cerebral cortex.It contains more motor and sensory areas and other inner  white part have not clearly sensory and motor areas act as intersensory association of memory and communication this part is called as association areas.

Each cerebral hemisphere is divided into 4 lobes –   

• Anterior – Frontal lobe for intelligence, knowledge, abstract reasoning, creative ideas, memory and also control facial expression.
• Middle- Parietal lobe for taste, writing, pain touch, pressure and controlling general consciousness.
• Lateral- Temporal lobe for language, hearing and smell.
• Posterior – Occipital lobe meant for vision

Thalamus

They act as relay stations. They first receive all sensory impulse from all parts of the body and these impulses are sent to the cerebral hemispheres.

Hypothalamus

It forms the lower lateral wall of diencephalon. A cross-like structure is found on the anterior surface of hypothalamus called optic chiasma. Pituitary body is attached to the middle part of the hypothalamus by infundibular.

Functions (i) Thermoregulation (ii) Behaviour and emotion (iii) Endocrine control (iv) Biological clock system (v) There are centres of temperature control, pain, hunger,love,hate and thirst etc. So it acts as supreme commander of endocrine gland.

Limbic System – It is visible like a wishbone, tuning fork or liplike. It is part of the hypothalamus. Limbic lobe (area of temporal Lobe)

Hippocampus + Hypothalamus including septum + Part of Thalamus + Amygdaloid complex

Functions of Limbic System

(1) Behaviour, Emotion, rage and anger (Hypothalamus, Amygdaloid body)

(2) Recent memory & short term memory converts into long term memory.(Hippocampal lobe)

Midbrain (Mesencephalon)

It is a small and contracted part of the brain. It has a centre for some involuntary activities that control the functions of involuntary muscles.vision and hearing. 

Cerebral Peduncles (Crura Cerebri)

Anterior part of the midbrain contains two longitudinal myelinated thick nerve fibres, called crura cerebral. They connect the medulla oblongata of the hindbrain to the cerebrum of the forebrain. It controls the limb muscle movement.

Optic lobes (Corpora Quadrigemina)

 On the posterior part of midbrain, four spherical projections are found, called optic lobes. Four optic lobes are collectively called corpora quadrigemina. These mainly control vision.

HindBrain (Rhombencephalon)

Pons or Pons Varolii

It is a small, spherical projection, which is situated below the midbrain and upper side of medulla oblongata. It regulates the breathing reaction.

Cerebellum

It is made up of 3 lobes (2 lateral lobes and 1 vermis). Lateral lobes are also called cerebellar hemisphere.

Function It is related to body balance & posture and voluntary muscles. It is commonly known as the tree of life.

Medulla Oblongata

It is the posterior-most, tubular and cylindrical part of the brain.

The lower end medulla extends in the from of spinal cord

Functions(i) It controls all the involuntary activities of the body. e.g.- heart beats, respiration.

It also concerned with some reflexes- coughing reflex, sneezing reflex, vomiting reflex, yawning reflex

Spinal Cord

It is a cylindrical, cord-like, extension of medulla oblongata, (42 – 45 cm long and 2 cm thick in man) that runs from neck to lumbar region through the neural canal of the vertebral column. All along its length it is of uniform diameter and ends in a thin prolongation called filum terminale. It stops growing beyond 4-5 years of age.

In the spinal cord white matter remains outside and grey matter (H-shaped) is inside. This is opposite to that of the brain.

The spinal canal with CSF is lined with ciliated ependymal cells.

In frogs the grey matter is rectangular while in mammals it is butterfly shaped.

The grey matter on each side is subdivided into regions called horn as anterior (ventral) horn and posterior (dorsal) horn.

Sensory neurons enter the dorsal root and have their cell bodies in the dorsal root ganglion, close to the spinal cord. In the dorsal horn of grey matter they synapse with interneurons.

 The interneurons synapse with motor neurons in the ventral horn of grey matter and leave the spinal cord via the ventral root.

 From the thorax region downwards, a lateral grey horn (only in thoracic, upper lumbar and sacral parts) is present between dorsal and ventral horns, this contains the cell bodies of the preganglionic autonomic neurons.

 Ascending tracts carry sensory information to the brain and descending tracts relay motor information to the spinal cord.

 It acts as a coordinating centre for reflexes like knee-jerk response, contraction of the urinary bladder etc.

Conclusion 

To sum up, the nervous system is a vital part of the human system; it consists of the nervous, spine, neurons, axon and nucleus. Further, the nervous system’s most important part is the central nervous system, which contains the human brain. 

The human brain is the most functional part of the human body and helps regulate various activities throughout the day. The brain is essential for our survival as it controls sentiments, interpretation and body movements. It also regulates the neurological, intellectual and sensory systems. We hope the concept of What is the Central Nervous System (CNS) is clear to you all.