Central Nervous System | Brain | Spinal cord

 Central nervous system

The central nervous system consists of brain and spinal cord.

Brain

1 Brain 

In animals all life activities are under the control of brain. The structure of brain is suitable perform this function. Brain is situated inside a bony cranium ( a part of skill).In side cranium brain is coverd by three layers called meninges. Meninges protect brain and also provide nutrients and oxygen to brain tissue through their capillaries.

The brain contains fluid filled ventricles that are continuous with the central canal of spinal cord. Fluid within ventricles and central canal is called cerebrospinal fluid ( CSF).

The Divisions of Brain

There are three major regions in the brain of human and other vertebrates. These are Forebrain, midbrain and hindbrain. Important parts of each of these regions are described blew:

Forebrain

Forebrain is the largest area of brain. It is most highly developed in humans. Following are the important parts of this region.

(1) thalamus lies just below cerebrum. It serves as a relay centre between various parts of brain and spinal cord . It also receives and modifies sensory impulses before they travel to cerebrum. Thalamus is also involved in pain perception and consciousness ( sleep and awakening ).

( 2 ) Hypothalamus lies above midbrain and just below thalamus. In humans it is roughly the size of an almond. One of the most important function of hypothalamus is to link nervous system and endocrine system. It controls the secretions of pituitary gland. It also controls feelings such as rage pain pleasure and sorrow.

(3) Cerebrum is the largest part of forebrain. It controls skeletal muscles thinking intelligence and emotions. It is divided into two cerebral hemispheres. The anterior parts of cerebral hemispheres are called olfactory bulbs which receive impulses from olfactory nerves and create the sensation of smell. The upper layer of cerebral cortex consists of grey masster. The grey matter of nervous system consists of cell bodies and non myelinated axons. Beneath this layer is present the white matter. The white matter of nervous system consists of myelinated axons. Cerebral cortex has a large surface area and is folded in order to fit in skull. It is divided into four lobes.

Lobe             Function

Frontal           Controls motor funcations, permits conscious control of skeletal muscles and   

                         coordinates movements involved in speech.

Parietal         Contains sensory areas that receive impulses from skin.

Occipital      Receives and analyzes visual information

Temporal     Concerned with hearing and smell           

midbrain

Midbrain lies between hindbrain and forebrain and connects the two. It receives sensory information and sends it to the appropriate part of forebrain. Midbrain also control some auditory reflexes and posture.

Hindbrain 

Hindbrain consists of three big parts.

Medulla oblongata lies on the top of spinal cord. It control breathing heart rate and blood pressure. It also control many reflexes such as vomiting coughing sneezing etc. Information that passes through medulla.

Cerebellum is behind medulla. It coordinates muscle movements.

pons is present on top of medulla. It assist medulla in controlling breathing. It also serves as a connection between cerebellum and spinal cord

2 Spinal cord  

The spinal cord is in fact a tubular bundle of nerves. It starts from brain stem and extends to lower back. Like brain spinal cord is also covered by meninges. The vertebral column surrounds and protects spinal cord.

The outer region of spinal cord made of wight matter. The central region is butterfly shaped that surrounds the central canal. It is made of grey matter.

31 pairs of spinal nerves arise along spinal cord. These are Mixed nerves because each contains axons of both sensory and motor neurons. At the point where a spinal nerve arises from spinal cord there are two roots of spinal nerve. Both roots unite and form one mixed spinal nerve.

* The dorsal root contains sensory axons and a ganglion where cell bodies are located.

* The ventral root contains axons of motor neurons.

spinal cord performs two main function:

1. It serves as a link between body parts and brain. Spinal cord transmits nerve impulses from body parts to brain and from brain to body parts.

2. spinal cord also acts as a coordinator responsible for some simple reflexes.