Structure and functions of brain

Introduction

The human brain is one of the wonders of god`s creation. It is so complex, technically difficult to understand the complete underlying physiology and any condition affecting the brain is usually chronic. It is the central organ of the nervous system along with the spinal cord. Our brain is more evolved, advanced and anatomically highly different than many other species.  The brain consists of the cerebrum, cerebellum, and brainstem. It is the controlling authority for many structural, functional processes that happen within our body. Brian exerts control over all other systems directly or indirectly. Some of the activities that the brain regulates are memory, sense organ functions, speech, decision making, and all higher cognitive functions. It assists in processing, integrating, and coordinating the information that is received from the peripheral organs -sense organs. The brain is a soft curd-like substance protected by meningeal layers and the skull bones.

Table Of Contents

1. Introduction

2. Structure of brain

    2.1 Meninges

    2.2 Cerebrum

   2.2.1 Lobes of cerebrum

    2.3 Cerebral ventricles 

    2.4 CSF (Cerebrospinal fluid )

3. Cerebellum

4. The Pons veroli

5. Blood supply to the brain

6. Facts about the human brain

7. The blood-brain barrier

8. Cranial nerves

 

Structure of brain

Human brain

 

Meninges

The brain is covered with 3 meningeal layers they are known as Dura mater, arachnoid mater, and piamater. Meninges are enclosed within the bony prominence known as skull bones. Skull bones are of different types every frontal bone parietal bone occipital bone, ethmoid bone, and temporal bone.

 

Cerebrum

Lobes of cerebrum

It is the upper part of the brain arranged in the 2 hemispheres-left and right. The hemispheres are also known as the cerebral hemispheres. The cerebrum is covered with a continuous layer of grey matter spread across either side of the forebrain—the cerebral cortex. The grey matter looks wrinkled material made out of the gyrus (plural = gyri)- the ridge of one of those wrinkles, and a sulcus (plural = sulci) is the groove between two gyri. Alternate sulci and gyri makes the cerebral cortex unique. Cerebrum controls most of the conscious mental processes and it is the largest region than all other parts of the brain. The outer layer of the cerebrum is known as grey matter and the inner portion is called white matter.  The cerebral hemispheres are further divided into 4 lobes, the frontal lobe that regulates the thinking, decision making, judgments, planning, and some of the conscious emotions. Parietal Lobe help in spatial computation, body orientation, and attention. The temporal lobe is on the lateral side of the brain mainly regulate the hearing, language, and memory. The last lobe is the occipital Lobe concerned with visual processing.

Cerebral ventricles 

All the cerebral lobes are dispersed within the free spaces known as the ventricles of the brain. Ventricles are of 4 types, 1st ventricle, 2nd ventricle and the 2 lateral ventricles i,e 3d and 4th ventricles. Beneath the lateral ventricles, there is the thalamus. Hypothalamus is situated just below the thalamus. Master gland, the pituitary is found in the hypothalamic region. At the back of the thalamus is the brainstem. The basal ganglia or the basal nuclei are present deep within the hemispheres that direct the behaviour and movement. The brain is connected to the spinal cord at the base of the skull called the foramen magnum.

CSF (Cerebrospinal fluid )

Cerebrospinal fluid is a sticky liquid substance act as the shock absorber. CSF is secreted by the cells of arachnoid matter known as choroid plexus. The CSF has a constant movement across the subarachnoid space. where the cerebrospinal fluid is produced and circulated. CSF is essentially made up of glucose, proteins and some other plasm filled fluids that support the brain from injury and shock. In children, infection of meninges and brain causes issues with CSF.

 

Cerebellum

The cerebellum is the Latin word meaning little brain. It is also called the hindbrain found in all the major vertebrates. One of the major functions of cerebellum is the motor control and the balance however it also helps in some of the cognitive functions (attention, concentration, language skills). Cerebellum is also vital for regulating the emotions such as fear and pleasure responses. Although the cerebellum does not initiate movement, but it contributes to the coordination, timing as well as precision over the tasks that we do. Damage to Cerebellum can result in the disorders of fine movement, problems in equilibrium, poor posture, and motor learning deficit in humans.

 

The Pons veroli

Pons is found in front of the cerebellum. Pons helps in coordinating the activities of the cerebrum and the cerebellum through receiving and sending the impulses in and out of the brain towards the spinal cord and vice versa. The Medulla oblongata is also known as the brain stem found between the pons and the spinal cord. The brain stem is responsible for controlling some of the vital functions such as breathing and heartbeat.

 

Blood supply to the brain

The brain shares the maximum outflow from the heart. This is becasue brain works continously even at the rest. Blood flow is very important to the brain and the spinal cord. The blood that is pumped from the ascending aorta is pushed upwards through the left and right carotid arteries. From there on, it is supplied to the brain, face, and scalp. The internal carotid arteries supply blood to most of the anterior portion of the cerebrum.

 

Facts about the human brain

  1. Our brain is the largest brain among all vertebrates relative to body size. It weighs about 1.5 kilograms in the average adult

  2. The average male has a brain volume of 1,274 cubic centimetres and a female of 1,131 cubic centimetres.

  3. The human brain makes up about 2% of our total body weight, however, in children it is relatively heavier when compared to the relative bodyweight of adults.

  4. The cerebrum makes up 85 % of the total brain's weight.

  5. A normal brain has 86 billion neurons in its “grey matter." Grey matter is placed in the brain centrally, forming the cytons-cell bodies.

  6. White matter is the peripheral matter made up of axons or fibres. Axons are the long fibres connected by trillions of synapses.

 

The blood-brain barrier

Brain is highly selective in its permeability. The blood vessels are split into arteries and veins. The larger arteries are split into smaller capillaries that are deeply embedded into many neurons. As the arteries gets thinner and thinner, they form a very tight junction than any other areas of the body. Furthermore, the smallest blood vessels are lined with cells joined by tight junctions. Such an arrangement of cells do not allow the fluids seep in or leak out too quickly. Pericytes- unique cells are responsible for the formation of the tight junctions. The barrier is impermeable to toxins and few drugs. It is less permeable to larger molecules but permeable to water, carbon dioxide, oxygen, and most fat-soluble substances (including anaesthetics and alcohol).

 

Cranial nerves

The whole nervous system relies on the nerves to perform its functions. The brain sends and receives signals through the sympathetic and parasympathetic nervous system. To communicate, the brain forms a network of nerves known as the cranial nerves. There are twelve pairs of cranial nerves helo in regulating various bodily functions such as hearing, eye movement, expressions, facial sensations, Sensing taste, swallowing and movement of the face, neck, shoulder and tongue muscles originate in the brainstem. The following table provides information about all the cranial nerves and their functions.  

Nerve (Number)

Name of the nerve

Function

Cranial-I

Olfactory

smell

Cranial-II

Optic

sight

Cranial-III

Oculomotor

moves eye, pupil

Cranial-IV

Trochlear

moves eye

Cranial-V

Trigeminal

face sensation

Cranial-VI

Abducens

moves eye

Cranial-VII

Facial

moves face, salivate

Cranial-VIII

Vestibulocochlear

hearing, balance

Cranial-IX

Glossopharyngeal

taste, swallow

Cranial-X

Vagus

heart rate, digestion

Cranial-XI

Accessory

moves head

Cranial-XII

Hypoglossal

moves tongue

 

 



img-1

img-1

img-1

Course List