Central nervous system

Central nervous system

It consists of brain and spinal cord. It lies inside the cranium and vertebral column. They initiate the nervous coordination.

Structure and function of human brain

Human brain has undergone evolution and that resulted in formation of hind brain, mid brain and fore brain. It lies inside the cranial cavity of cranium. Brain is composed of outer grey matter formed by cytons and inner white matter formed of nerve fibers. The three part of brain are:

Hind brain

It continuous with spinal cord and is posterior part of brain. It includes medulla oblongata, cerebellum and Pons varolli. Hind brain is also called rhombencephalon.

Medulla oblongata: It is the enlargement where the spinal cord enters the brain. It contains reflex centers for breathing, swallowing, cardiovascular function and gastric secretion. Roof of medulla oblongata is highly vascular and secrets cerebrospinal fluid. It emerges out of cranium from foramen magnum.

Cerebellum: it is second largest part of brain. It is an out growth of medulla oblongata. It coordinates motor activity associated with limb movement, maintainence of posture and body equilibrium. Inner white matter of cerebellum is connected with cerebrum and medulla oblongata. Its central part is called vermis.

Pons varolli: it lies above medulla and connects two lobes of cerebellum. It connects medulla and midbrain too.

Mid brain

Mid brain is also called mesencephalon. It lies between forebrain and midbrain. It consists of Crura cerebri and corpus quadrigemina.

Crura crebri: these are two thick cylindrical band of nerve fiber (white matter). It connects cerebrum with hind brain and spinal cord and transmits motor impulses to limb from cerebrum.

Corpora quadrigemina: it consists of 2 pairs of outgrowth.  Superior pair receives sensory neuron from eye and head and control visual reflex. The inferior pair receives sensory neuron from ear. They control auditory reflexes.

Forebrain

It is also called prosencephalon. It has two main parts:

Cerebrum: the cerebrum is the largest part of brain. It is divided into right and left hemisphere. The two cerebral hemisphere remains separated by corpus callosum.  Each lobe is further divided into frontal, parietal, temporal and occipital.

The highly folded outer layer of cerebrum is called cerebral cortex or neopalium.the ridge and depressions between them are called gyri and sulci respectively. Outer layer of cerebrum is made up of grey matter and inner by white matter.

Cerebrum is the seat of mental activities like thinking, reasoning, learning, memory and intelligence. It also controls emotion, speech, laugh and micturition (urination).it helps in sensation of various stimuli like:

Parietal lobe: heat, cold, pain and touch

Occipital lobe: vision and hearing

Temporal lobe: hearing and touch

Frontal lobe: movement, taste, smell

Diencephalon: it lies between cerebrum and midbrain. It includes thalamus and hypothalamus.

The thalamus consists of two round grey matter masses bulging in diacoel i.e.  Cavity of diencephalon. It regulates emotion and heat, cold, pain sensation.

Hypothalamus is situated below thalamus. It is linked with pituitary gland. It controls hormonal output of pituitary gland, hunger, thirst, sleep, fatigue, anger, far, heat, blood pressure and water balance. Pineal gland is also present in diencephalon that controls bio rhythms.

Brain is externally covered by meninges made up of duramater, arachnoid and piamater.

Structure and function of spinal cord

The part of central nervous system that is posterior to brain and enclosed within the vertebral column is called spinal cord. It runs through the neural canal of the vertebral column which protects it from injury. It is long, whitish and dorsoventrally compressed structute.the spinal cord is divided longitudinally into two equal halves by two deep median groove called dorsal fissure and ventral fissures. The ventral fissure is much deeper and contains blood vessels .Like brain it is externally covered by meninges made up of duramater, arachnoid and piamater. The space between these membranes is filled by cerebrospinal fluid. Unlike brain, grey matter is internal in spinal cord and white mater is external n spinal cord. Spinal cord is the main centre of reflex action. Spinal nerve arises from spinal cord.