BRAIN

CENTRAL NERVOUS SYSTEM (CNS): 

Central nervous system includes brain and spinal cord. It coordinates all neural functions.

Lets us study about BRAIN-

BRAIN:

                    Proportionate to the body size, shrews (tiny rat) have the highest brain to body mass ratio.The brain is present in the hard bony box like structure called CRANIUM. It is covered by three layers called the meninges. The meninges are continuous and cover the spinal cord as well. The space between the inner layers is filled with fluid called CEREBRO-SPINAL FLUID. It serves as a shock-absorbing medium and protects the brain against shocks/jerks along with meninges and cranium. Mainly the nerve cell bodies together with capillaries form a mass called GREY MATTER, while the myelinated axons or those covered by fatty sheaths form white matter. The grey matter is usually present on the periphery while white matter is present towards the center. This is mainly due to the fact that there is a small area from where the myelinated axons leave the brain.

NOTE : The functions of brain is a control center was known nearly 2000 years back by Greek Physiologists.

BRAIN HAS THE FOLLOWING DIVISIONS-

 1. FORE BRAIN - CONSISTS OF OLFACTORY LOBES, CEREBRUM,       DIENCEPHALON 

 2. MID BRAIN - CONSISTS OF OPTIC LOBES

 3. HIND BRAIN - CONSISTS OF CEREBELLUM, MEDULLA OBLONGATA

FORE BRAIN - 

OLFACTORY LOBES : 

These club shaped widely spread bodies are widely are visible from the ventral surface only.

FUNCTIONS : 

These are concerned with sense of smell.

CEREBRUM : 

It consists of two lobes called CEREBRAL HEMISPHERES. The surface of the cerebrum has many folds, they appear as elevations (GYRI) and depressions (SULCI). Sulci are very prominent and divide each hemisphere into four lobes.

FUNCTIONS : 

1. Site of Mental Abilities, Controls Thinking, Memory, Reasoning, Preception, Emotions and Speech.

2. Interprets sensations and responds to Cold, Heat, Pain and Pressure.

DIENCEPHALON : 

This Rhomboidal shaped lobe visible from inferior surface of brain. It lies between cerebrum and mid brain. It is divided into THALAMUS and HYPOTHALAMUS. 

FUNCTIONS : 

1. Relay centre for sensory impulses, such  as Pain, Temperature and Light.

2. Reflex centre for Muscular Activities.

3. Centre for certain Emotions such as Anger.

4. Centre of Water balance, Blood Pressure, Body Temperature, Sleep and Hunger.

5. The Hypothalamus controls the Pituitary Gland, Which functions as the Master Gland.

MID BRAIN : 

This is a small thick stalked portion. This connects fore brain with Cerebellum and Pons of Hind Brain.

FUNCTION: 

It relay motor impulses from the cerebral cortex to the Spinal Cord and relays Sensory Impulses from the Spinal Cord to the Thalamus, Reflexes for sight and hearing.

HIND BRAIN : 

CEREBELLUM : 

It is located below the Cerebrum and above Medulla Oblongata. It consists of two large Cerebellar Hemispheres.

FUNCTIONS : 

1. Maintains Posture, Equilibrium and Muscle Tone.

2. Coordinates Voluntary Moments initiated by Cerebrum.

MEDULLA OBLONGATA : 

It is almost Triangular shaped. Medulla Oblongata extends from Pons to Spinal Cord.

FUNCTIONS : 

1. Contains centre of Cardiac, Respiratory and Vasomotor Activities. (Vasao motor refers to actions upon a blood vessels which alter its diameter).

2. Coordinates Reflexes like Swallowing, Coughing, Sneezing and Vomiting.

NOTE :

 1. The Brain Weighs Aprroximately 1400g. Though the brain comprises little more  than 2% the body weight, it uses 20% of the whole body energy.

2. An Average Adult Male Brain Weighs about 1375g and Female 1275g.