Cerebrum, Limbic system

Central Nervous System

The part of the nervous system which occupies the central axis of the body is known as Central Nervous System

It comprises of brain and the spinal cord

Brain

It weighs about 1.5 kg in adults and consists of all the structures which are intracranial (located within a hard bony skull)

It is completely surrounded by three membranes which are called the meninges. From outside to inwards the meninges are:

1. Dura mater
2. Arachnoid mater
3. Pia mater

The brain consists of the following parts

1. Two cerebral hemispheres (cerebrum)
2. Brain stem (medulla, pons, midbrain)
3. Cerebellum

Cerebrum

It is the largest part of the brain and is divided into the right and left cerebral hemispheres.

The two cerebral hemispheres are separated by a space in which the falx cerebri (dura mater) invaginates.

The two hemispheres are connected to each other by a bundle of nerve fibres called the corpus callosum.

The most superficial part of each cerebral a hemisphere is called the cerebral cortex (cerebral grey matter) and it is 2-4 mm thick.

Its total surface area is 2,200 cm2 

Underneath the cerebral cortex lies the subcortical white matter in which are located masses of the grey matter called the subcortical nuclear mass such as the basal ganglia, thalamus and hypothalamus.

These nuclear masses consist of nerve cells (soma), packed up very densely together with their axons and dendrites.

Each cerebral hemisphere has three poles: frontal pole, temporal pole and occipital pole.

The entire cerebral hemisphere is marked by elevations called gyri and depressions called sulci, which give a characteristic appearance to it.

 

The important sulci are:

1. Central sulcus: It runs from the superiomeidal border midway between midpoint of the occipital and the frontal pole
2. Lateral sulcus: It lies between the frontal and the temporal pole
3. Parieto-occipital sulcus

With reference to these major sulci, the whole of the cerebral hemisphere is divided into four lobes, which are concerned with higher mental functions:

1) Frontal lobe:

• It lies in front of the central sulcus and is concerned with motor functions, Contraction. Located in front of the frontal muscle i,e,, initiation and control of voluntary lobe is the prefrontal lobe. It is concerned with the control of higher intellectual activities, emotional affects, behaviour and social consciousness, personality, memory, sense of responsibility, thinking, reasoning, moral sense and learning, etc.

(ii) Parietal lobe:

• It lies between the central sulcus and the parieto-occipital sulcus. It is concerned with sensory functions such as the following:
• It is concerned with appreciation of the elementary sensations of touch, pain, pressure, temperature (heat and cold) and joint movements
• It is associated with a more detailed process of discrimination between the stimuli. Therefore, warm objects are distinguished from warmer, cold from colder and rough from rougher, etc.
• It helps in the recognition of common familiar objects placed in the hand without looking at them (stereognosis).

(iii) Occipital lobe: 

• It lies behind the parieto-occipital sulcus and is concerned with vision.

(iv) Temporal lobe: 

• It lies below the lateral sulcus and is concerned with hearing, language (speech) and memory functions. 8. In addition, there is a limbic lobe (i.e., cingulate gyros, hippocampus) in the temporal lobe. Limbos means a ring and the term limbic system is applied to the parts of the cortical and subcortical structures that form a ring around the brain stem. The limbic cortex is phylogenetically the oldest pan of the cerebral cortex. Histologically, it is madE up of a primitive type of cortical tissue callk allocortex.

Functions of the Limbic System

• The limbic system represents the primary area of control of autonomic functions.
• It plays an important role in
• the emotions of rage (violent anger) and fear; and
• the motivation.
• It is concerned with the behavioural aspects of hunger and sex.
• It is also concerned with olfaction and memory.

Brodmann divided each of the cerebral hemispheres into several areas called Brodmann areas. Each cerebral hemisphere contains a total of 47 such functional areas, thinking that each area has an absolutely selective function.

The typical cortex contains six layers, numbered I to VI, from the outside to the inside.