Central Nervous system: Human Brain
Central Nervous system: Human Brain
1 position and shape .
Human Brain is a soft ,whitish, large and slightly flattened structure present in the cranial cavity of cranium ( brain box ) of skull . Brain is the centre of thinking which involves complex mechanism and neural connections which are located in the brain. Brain is also the main coordinating center of the body. Different parts of brain integrate different inputs and send different outputs.
2. Meninges.
Human brain is covered by three meninges or membranes:
1 ) pia mater -
It is inner, thin and vascular.
2). Arachnoid membrane -.
It is middle , thin and vascular.
3). Dura mater -.
It is thick , outer and fibrous.
The spaces between these meningeal membranes are filled with a lymph-like cerebrospinal fluid.the meningeal membranes protect the brain from mechanical injuries, while cerebrospinal fluid protects the brain from mechanical shocks.
3 structure
Brain is formed of three parts :
a. Fore brain ;
b. Mid brain;
C. Hind brain;
1) Fore brain -
It forms anterior two - third of brain and is the main thinking part of brain.it is formed of three parts:
1) olfactory lobes;
2) cerebrum ;and
3) diencephalon.
Olfactory lobes-
These are one pair small-sized and club- shaped. Each olfactory lobe is differentiated into anterior swollen olfactory bulb and posterior narrow olfactory stalk. These control the sense of smell.
Cerebrum-
It is the largest part of brain and forms about 80% of the weight of brain. It is differentiated into one pair of cerebral hemispheres by a median or cerebral fissure. The roof of each cerebral hemispheres is highly folded to form ridges and grooves called gyri and sulci respectively.
Each cerebral hemispheres is differentiated into four lobes by three deep fissures,each of which is concerned with scecufic functions as has specific sensory areas (to receive nerve impulses from receptors) and motor areas (to send nerve impulses to effectors I . E muscles and glands ) as listed in these areas of cerebrum are divided into three categories:
Sensory areas which recive the sensory impulses of sound ,vision, smell , taste, etc
Association areas where sensory informations are interpreted .
Motor areas which control the movement of voluntrary muscles e.g. of legs .
Cerebrum controls the voluntary activities of body and is also the seat of memory, will intelligency and learning.
Diencephalon-
It is completely covered by cerebrum and is formed of :
Thalami . These are a pair of masses of neurons and conduct the nerve impulses of pain , touch, temperature, etc to cerebrum. So these act as relay centres.
Hypothalamus. It is formed of a pair of masses of neurons present below thalami .it controls involuntary functions like hunger, thirst, sweating, sleep, sexual desire, water blance, blood pressure, temperature balance, etc.
At the floor of diencephalon ,there lies a pea - seed shaped pituitary body which segland, so is also called master gland .
So diencephalon acts as relay centre, coordinates involuntary functions of body and forms pituitary gland.
2)Mid brain-
It is formed of two parts.
1 optic lobes.
2 cerebral peduncles.
Optic lobes -
These are a pair of large size lobes .each is divided into two lobes so are four in number. These control movement of head , eyes and trunk in response to visual reflexes of slight and auditory reflexes of sound.
Central peduncles -
These are a pair of bands of nerve fibres which coordinate hind brain with fore brain .
3) Hind brain .
It is formed of three parts;
1 cerebellum
2 pons;
3 medulla oblongata.
Cerebellum
It is a large size lobe present below the occipital lobe of cerebrum. It controls equilibrium and posture of the body and coordinate the voluntary movements.
Pons
It is a thick band of transverse nerve fibres and acts as coordination center between different parts of the brain , especially between cerebellum and cerebrum. It coordinate s between the muscles of two sides of body .
Medulla oblongata.
It is the posterior- most part of the brain and continues with the spinal cord .it controls involuntary functions of visceral organs through a number of centers like cardiac centres (heartbeat), respiratory center es ( breathing), salivary centres (secretion of saliva) etc it also controls coughing, sneezing ,vomiting, urinating , defaecation, blood pressure, swallowing of food , peristalsis etc.
Spinal cord
1 position and shape-
It is long,soft, whitish and cylindrical continuation of medulla oblongata. It lies in the cavity of vertebral column. It is also covered by three meninges like those of brain.
2 structure. -.
Spinal cord has two longitudinal fissures ( deep ventral fissure and shallow dorsal fissure) and two swellings (upper cervical and lower lumber swelling). At the lower end spinal cord forms a non- nervous thread - like filum terminale.
PERIPHERAL NERVOUS SYSTEM
A cranial nerves
B spinal nerves.
A ) cranial nerve -
These nerves extend between the brain and parts of head except 10th cranial nerve which extends even upto the abdomen.in man , there are 12 pairs of cranial nerves.
B) spinal nerves -
These nerves extend between the spinal cord and the body parts. In man , there are 31 pairs of spinal nerves .
Each spinal nerve is formed of sensory dorsal root and motor ventral root , so all the spinal nerves are mixed in nature.
AUTONOMIC NERVOUS SYSTEM
It control the involuntary functions of visceral organs to maintain homeostasis inside the body so is also called visceral nervous system. It is salf - governed and auto- functioning. It is formed of two parts:
A) sympathetic nervous system
B) para - sympathetic nervous system.
Both of these supply same visceral organs like heart , gut , lungs, kidney, urinary ducts, blood vessels , gonads, genital ducts, etc, and interact to maintain homeostasis. But these are antagonistic ( opposite in action) to each other towards the functioning of visceral organs.
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