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Term Paper on the Human Brain


Term Paper Contents:

  1. Term Paper on Introduction to the Nervous System
  2. Term Paper on Divisions of the Nervous System
  3. Term Paper on Parts of Human Brain
  4. Term Paper on Forebrain of Humans
  5. Term Paper on Blood Supply to the Human Brain


Term Paper # 1. Introduction to the Nervous System:

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The nervous system is the most complex system of the body. It controls all the activities of the body directly or indirectly that includes physical, psychological and intellectual. It is responsible for judgement, intelligence and memory. It is highly evolved at the cost of regeneration. It is the chief controlling and coordinating system of the body. It adjusts the body to the surroundings and regulates all bodily activities both voluntary and involuntary.


Term Paper # 2. Divisions of the Nervous System:

It is divided into two parts:

A. Central Nervous System (C.N.S.):

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It includes Brain and spinal cord.

B. Peripheral Nervous System (P.N.S.):

Peripheral nerves supply body wall and skeletal muscles (spinal and cranial nerves) and associated ganglions of autonomic nervous system, both sympathetic and parasympathetic system which supply smooth muscles of viscera, gland and blood vessels.

C. Autonomic Nervous System (A.N.S.):

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The nerves supplying viscera along with parts of brain and spinal cord related to them constitute A.N.S.

A.N.S. – It has two parts:

(a) Sympathetic and

(b) Para sympathetic.

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Nervous Tissues:

Two types of cells are found in nervous system:

1. Neurons:

These are specialized cells of nervous system and main cells concerned with function­ing of nervous system.

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2. Neuroglia:

This is special connective tissue present in nervous system.

Various types of neuroglial cells are:

a. Astrocytes- These are concerned with the nutrition of the nervous tissue.

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b. Microglia- These are macrophages of C.N.S.

Ependymal cells – These are columnar cells lining the cavities of C.N.S.

c. Oligodendrocytes- These myelinate the tracts. Proliferation of glial cells is called gliosis. C.N.S. lesions heal by gliosis and form scar in nervous system.

Neuron:

Each neuron is made-up of a cell body containing nissl substance, a nucleus and long and short processes. Long process is called axon and short process is called dendrite. The Nissl bodies are present in cell body and dendrites and absent in axons.

In case of injury these bodies disappear, this process is called chromatolysis. They are basophilic in nature and formed by rough endoplasmic reticulum. Functionally each neuron is specialized for sensitivity and conductivity. Impulses can flow in them with great rapidity.

Peripheral Nerves:

These are collections of nerve fibres (axon).

Synapse:

The junction between two neurons is called synapse. They are connected to each other by their process, forming long chains along which the impulses are conducted. Contacts between neurons are by contiguity and not by continuity. The impulse is transmitted across a synapse through biochemical neurotransmitters.

Axon:

Terminates by meeting another neuron in brain.

Outside the central nervous system – it may end in muscle, in gland or neuron in ganglion at peripheral region.

Types of Synapse:

It may be:

1. Axo-axonic – between two axons.

2. Axo-dendritic – between axon of one neuron and dendrite of another neuron.

3. Dendrodendritic – between two dendrites.

4. Somo-dendritic – between cell body of one neuron and dendrite of another neuron.

5. Somo-axonic – between cell body of one neuron and axon of other neuron.

6. Somo-somatic – between cell bodies of two neurons.

Grey and White Matter:

Grey Matter:

Have a darker greyish colour due to collection of nerve cells (dark stained nucleus).

Neurons present along with axon and dendrites

Axon is unmyelinated.

White Matter:

Whitish in colour.

Axons are – Myelinated fibres due to reflection of light from myelin give whitish look.


Term Paper # 3. Parts of Human Brain:

1. Cerebrum

2. Cerebellum

3. Mid Brain

4. Pons

5. Medulla.

 

Peripheral nerves attached to brain are cranial nerves.

The nerves supply body wall and limbs are called cerebrospinal nerves.

Brain is divided into three parts:

In brain grey matter lies outside and white matter lies inside while in spinal cord grey matter lies around the central canal and white matter lies at periphery


Term Paper # 4. Forebrain of Humans:

It is constituted by:

I. Cerebrum

II. Diencephalon.

I. Cerebrum:

It is made up of two large cerebral hemispheres which are incompletely separated by the median longitudinal fissure. Two hemispheres are connected to each other across the median plane by the corpus callosum. Each hemisphere has a cavity called lateral ventricle.

The presence of sulci and gyri on the surface of hemisphere increases the surface area of the brain to accommodate many neurons without increasing the size of the brain. There are specific areas on the brain for specific functions.

External Features:

Each cerebral hemisphere has three surfaces:

1. Superolateral Surface:

Is convex and related to cranial vault.

2. Medial Surface:

Is flat and vertical, falx cerebri separates it from other hemisphere.

3. Inferior Surface:

Is irregular and divided into an anterior part – orbital surface and a posterior part – tentorial surface. Two parts are separated by – a deep cleft called stem of lateral sulcus.

Borders are three:

1. Supero Medial Border:

It separates supero­lateral surface from medial surface.

2. Infero Lateral Border:

Separates superolateral surface from the inferior surface.

3. Infero Medial Border:

Infero medial border is divided into two parts:

(a) Medial Orbital Border:

Separates medial surface from orbital surface.

(b) Medial Occipital Border:

It separates medial surface from tentorial surface.

Poles are three:

1. Frontal pole – present at anterior end.

2. Occipital pole – present at posterior end.

3. Temporal pole – lies laterally at the anterior end of the temporal lobe.

The surface of the cerebrum is made into elevations and depressions. The elevations are called gyri and depressions are called sulci.

Types of Sulci:

They are classified into:

1. Limiting Sulcus:

They are separating two functionally different areas, e.g., Central sulcus – it separates sensory and motor areas.

2. Complete Sulcus:

They are deep sulci – make elevations in the floor of the lateral ventricle, e.g., Calcarine sulcus and collateral sulcus.

3. Axial Sulcus:

Develops in the long axis of a rapidly growing homogenous area, e.g., Post- calcarine sulcus.

4. Operculated Sulcus:

Separates by its lips two areas and contains a third area in the walls of the sulcus, e.g., Lunate sulcus.

Central Sulcus (The Fissure of Rolando):

It is situated in the superolateral surface. Anterior to this sulcus the motor cortex and posterior to the sulcus the sensory cortex are situated.

It commences from the supero medial border about 1 cm posterior to mid-point between frontal and occipital poles.

It is directed downwards, forwards and laterally.

It is situated in the centre of three parallel sulci.

In front of the central sulcus is the frontal lobe and behind the sulcus is the parietal lobe.

Lobulation of the Cerebrum:

It has four lobes are bounded as follows:

Lateral Sulcus (Sylvian Sulcus):

It commences in the inferior surface of the cerebrum has following parts:

1. Stem

2. Anterior ramus

3. Ascending ramus

4. Posterior ramus. 

1. Frontal Lobe:

It is situated anterior to the central sulcus.

Its features are:

(a) Anterior to central sulcus the pre central gyrus is situated. It is motor cortex of the opposite half of the body. Body is represented upside down.

(b) Anterior to pre central gyrus – pre central sulcus is situated.

(c) Infront of the pre central sulcus – superior and inferior frontal sulci are running antero posteriorly.

(d) Superior to superior frontal sulcus the superior frontal gyrus is situated.

(e) The middle frontal gyrus is found between superior and inferior frontal sulci.

(f) Below the inferior frontal sulcus the inferior frontal gyrus is found.

(g) The inferior frontal gyrus is traversed by anterior and ascending rami of lateral sulcus.

They divide the inferior frontal gyrus into three parts:

(i) Pars orbitalis is situated inferior to the anterior ramus of lateral sulcus.

(ii) Pars triangularis is situated between anterior and ascending rami of lateral sulcus.

(iii) Pars opercularis lies posterior to ascending ramus.

These three areas together form Motor speech area of Broca.

Functions of Frontal Lobe:

i. Pre central gyrus is motor cortex for opposite half of the body.

ii. Pre frontal area lies anterior to pre central gyrus is concerned with the development and mainte­nance of personality, behaviour, intelligence and adjustment with the social environment.

iii. Hindsight, insight and foresight are the functions performed by pre frontal area.

iv. Orbital surface of frontal lobe is concerned with emotion and behaviour.

v. Learning and development of memory pattern are also concerned with the frontal lobe.

vi. In the posterior part of middle frontal gyrus the area of frontal eye field is situated.

2. Parietal Lobe:

Lies posterior to central sulcus.

Its features are:

(a) Behind the central sulcus post central gyrus is situated. It is the sensory areas of the opposite half of the body. Body is repre­sented upside down.

(b) Behind the post central gyrus – post central sulcus is situated.

(c) Intra parietal sulcus arises from the middle of the post central sulcus and runs back­wards. It divides the parietal lobe into superior and inferior parietal lobule.

(d) Inferior parietal lobule is subdivided by the entry of:

(i) Posterior ramus of lateral sulcus

(ii) Superior temporal sulcus

(iii) Inferior temporal sulcus.

The part of inferior parietal lobule surrounding posterior ramus of lateral sulcus is called supra marginal gyrus.

The part surrounding the superior temporal sulcus is called angular gyrus.

The part surrounding the inferior temporal sulcus is called posterior parietal lobule.

Functions of Parietal Lobe:

1. Primary sensory cortex of the opposite half of the body.

2. Touch, pressure, temperature, joint sense and vibrations are appreciated.

3. Special recognition of the body, e.g., position and movements of the body and limbs.

4. Tactile localization and discrimination are done by this lobe.

5. The parietal speech centre – sensory speech area is formed by supra marginal and angular gyrus.

6. Parietal operculum of the insula has taste area.

7. Stereognostic function, i.e., tridiamentional memory is done in this lobe.

3. Temporal Lobe:

It is situated inferior to the posterior ramus of lateral sulcus.

Its features are:

(a) Temporal pole is turned medially to form a hook shaped process called the uncus.

(b) The lateral surface of lobe is traversed by the superior and inferior temporal sulci.

It divides the surface into three gyri:

(i) Superior temporal gyrus – lies above superior temporal sulcus.

(ii) Middle temporal gyrus – lies between superior and inferior temporal sulcus.

(iii) Inferior temporal gyrus – lies below the inferior temporal sulcus.

(c) The middle of the superior temporal gyrus and anterior transverse temporal gyri together form the principal auditory area.

(d) The audito psychic area is situated in the superior, middle and inferior temporal gyri.

Functions of Temporal Lobe:

i. Auditory area is present in superior temporal and anterior transverse gyrus. Auditory fibres project bilaterally into the cortex.

ii. Audito-psychic function.

iii. Storage of memory.

iv. Smell sensation – center lies in uncus.

v. Temporal lobe helps in the articulated speech.

4. Occipital Lobe:

It is situated posterior to an imagi­nary line between parieto occipital sulcus and pre occipital notch.

Its features are:

(a) Arcus parieto occipital is a gyrus encircling the parieto occipital sulcus.

(b) Just behind the arcus parieto occipitalis, the transverse occipital sulcus descends from supero- medial margin.

(c) The lateral occipital sulcus is antero posteriorly situated in the occipital lobe. It divides the lobe into superior and inferior occipital gyri.

(d) Lunate sulcus is semi lunar shaped, lies anterior to occipital pole.

(e) It is joined from behind by the calcarine sulcus.

(f) Lunate sulcus is an operculated sulcus – func­tionally related to the areas of visual perception. They are the areas – 17, 18 and 19.

Functions of Occipital Lobe:

1. Visual perception.

2. The optic radiation enters into the area 17 primary visual cortex and is the visuo psychic in function (area 18).

3. The area 18 and 19 are able to correlate the visual information in recognizing an object.

Medial Surface of the Cerebrum:

It lies between the infero medial border and supero medial border. In this surface there is a white band called corpus callosum is situated. It has following parts – rostrum, genu, body and splenium.

Rostrum is connected to the optic chiasma by lamina terminalis. Below the corpus callosum lateral ventricle lies. Above the corpus callosum – callosal sulcus is situated.

Cingulate sulcus commences below and anterior to corpus callosum. It runs above upwards, forwards and then backwards to corpus callo­sum. Terminal part of this sulcus passes towards supero medial border.

Cingulate gyrus lies between cingulate and callosal sulcus.

Above the cingulate sulcus median frontal gyrus lies, posterior part of the gyrus is called para central lobule.

Arterial Supply of Cerebrum:

It is supplied by:

1. Anterior cerebral artery

2. Middle cerebral artery

3. Posterior cerebral artery.

I. Arterial Supply of Supero Lateral Surface:

It is supplied by branch of anterior, middle and posterior cerebral arteries.

(a) Occipital lobe and inferior temporal gyrus are supplied by posterior cerebral artery, i.e., visual cortex mainly.

(b) Anterior cerebral artery supplies sensory and motor areas of the leg and perineum, i.e., a gyrus breadth along the supero medial border upto the parieto occipital sulcus.

(c) Middle cerebral artery supplies motor and sensory cortex of the opposite half of the body except the area of leg and perineum, motor speech area, auditory area, stereognostic area and pre frontal area.

Middle cerebral artery also supplies supero lateral surface except occipital lobe, inferior temporal gyrus and finger breadth along the superior medial border.

II. Arterial Supply of Inferior Surface of the Cerebrum:

(a) Medial part of the orbital surface is supplied by anterior cerebral artery.

(b) Lateral part of orbital surface is supplied by middle cerebral artery. It also supplies the anterior part of temporal lobe inferiorly.

(c) Posterior part of temporal lobe is supplied by posterior cerebral artery. It also supplies the inferior surface of the occipital lobe.

III. Arterial Supply of Medial Surface of Cerebrum:

(a) Posterior cerebral artery supplies – medial surface of occipital lobe and para hippo­campus.

(b) Anterior cerebral artery supplies medial surface above the corpus callosum upto parieto occipital sulcus.

(c) Middle cerebral artery supplies uncus.

Functionally:

Para central lobule controls defecation, micturition and parturition.

Posterior to the upturned part of cingulated sulcus – pre cuneus gyrus lies, which is limited posteriorly by parieto occipital sulcus. Below and behind this sulcus cuneus lies.

The calcarine sulcus is situated postero inferior to the cuneus. Anteriorly it unites with the parieto occipital sulcus.

Below the gyrus – lingual gyrus is situated.

The lingual gyrus, cuneus and floor of calcarine sulcus are having visual functional areas.

Inferior Surface:

Boundaries:

1. Laterally – Super ciliary border

2. Infero lateral border.

Medially:

1. Median orbital border

2. Median occipital border.

Parts:

It has two parts:

1. Anterior part is called orbital surface.

2. Posterior part is called tentorial surface.

1. Orbital surface is formed by frontal lobe and is concerned with emotion and behaviour.

Along the medial border of this surface lies gyrus rectus. Lateral to this gyrus is olfactory sulcus which it, lodges olfactory bulb, receiving olfactory nerves from nose.

Lateral to olfactory sulcus, a “H” shaped orbital sulcus is present which divides the surface into:

i. Anterior orbital gyrus

ii. Posterior orbital gyrus

iii. Lateral orbital gyrus

iv. Medial orbital gyrus.

Orbital surface is related to the roof of the orbit.

2. Tentorial surface is formed by occipital and temporal lobes, related to tentorium – cerebelli. There are two sulci present on this surface.

(a) Collateral sulcus

(b) Occipito temporal sulcus – lies laterally.

These two sulci divide this surface into three gyri:

i. Lateral occipito temporal gyrus

ii. Medial occipito temporal gyrus

iii. Para hippocampal gyrus

In the inferior surface just behind the orbital surface, lies the stem of the lateral sulcus. It commences from the triangular shaped area called anterior perforated substance.

Boundaries of Anterior Perforated Substance:

Anterior – Medial and lateral olfactory striae.

Posteriorly – Uncus of the temporal lobe.

Medially – Optic chiasma.

Anterior perforated substance has many openings through which central branches of the middle and anterior cerebral artery are passing.

Inter Peduncular Fossa:

On the inferior surface between the two cerebral hemispheres there is hexa­gonal shaped inter peduncular fossa.

Boundaries of Inter Peduncular Fossa:

Anteriorly – optic chiasma

Antero laterally – optic tract

Postero laterally – crus cerebri

Posteriorly – Upper border of the pons.

Floor is formed by the structures anterior to posterior.

1. Tuber cinereum

2. Infundibulum of the pituitary gland

3. Mamillary bodies

4. Posterior perforated substance.

This fossa is related to the inter peduncular cistern of subarachnoid space, lodging “circle of willis” – formed by branches of internal carotid and vertebral arteries.

Oculomotor nerve emerges into this fossa medial to crus cerebri.

Veins of cerebrum are classified into superficial and deep veins.

Characteristics of Veins:

1. Walls are devoid of muscles.

2. No valves (valveless thin walled running into subarachnoid space).

3. To maintain patency some of them open into venous sinuses, e.g., superior cerebral veins draining into superior sagittal sinus.

4. Superficial middle cerebral vein drains into cavernous sinus and at times into spheno parietal sinus. Through superior and inferior anastomatic veins it communicates with superior sagittal and transverse sinus.

5. Inferior cerebral veins – drain into cavernous sinus and superior – sagittal sinus.

6. Anterior cerebral veins and deep middle cerebral vein drains into basal vein – formed by union of anterior cerebral vein, striate veins and deep middle cerebral vein. Basal vein drains its blood into great cerebral vein.

II. Diencephalon:

It is a middle structure embedded in cerebrum and therefore hidden from the surface.

Cavity forms IIIrd ventricle.

Hypothalamic sulcus extending from inter ventricular foramen to cerebral aqueduct, divides each half of diencephalon into dorsal and ventral parts.

1. Dorsal part of diencephalon is formed by:

(a) Thalamus.

(b) Metathalamus – including medial and lateral geniculate bodies.

(c) Epithalamus – including pineal body and habenula.

2. Ventral part of diencephalon is formed by:

(a) Hypothalamus

(b) Subthalamus.


Term Paper # 5. Blood Supply to the Human Brain:

Brain requires continuous supply of blood for its normal metabolic functions.

20% of the cardiac output enters the brain.

Loss of blood supply for 4 minutes causes irreversible damage of brain tissues.

Brain cells will die, when its blood supply is lost for more than 8 minutes.

Brain receives its blood supply by internal carotid and vertebral arteries.

These arteries anastomose with each other at the base of brain to form circle of Willis.

Formation of “Circle of Willis”:

1. Vertebral arteries enter the posterior cranial fossa through foramen magnum. Both vertebral arteries unite along the lower border of pons to form basilar artery.

2. Basilar artery terminally divides into a pair of posterior cerebral arteries.

3. Internal carotid artery enters the cranium through the carotid canal – passes through the cavernous sinus after emerging from the sinus it gives anterior cerebral and middle cerebral arteries.

4. Middle cerebral and posterior cerebral arteries are connected by posterior communicating artery.

5. Two anterior cerebral arteries are communicated by anterior communicating artery.

6. Thus an arterial network – called circle of Willis is formed within the subarachnoid space present in the inter peduncular fossa at the base of brain.