The human brain constituted
about two percent of the adult body weight. It is divided into (i) Forebrain
(Cerebrum:- Telencephalon and Diencephalon -thalamus, hypothalamus,
sub-thalamus , epthalamus )(ii) Mid brain (Brain stem:- pon, medulla
oblongata)(iii) Hind brain (cerebellum)
about two percent of the adult body weight. It is divided into (i) Forebrain
(Cerebrum:- Telencephalon and Diencephalon -thalamus, hypothalamus,
sub-thalamus , epthalamus )(ii) Mid brain (Brain stem:- pon, medulla
oblongata)(iii) Hind brain (cerebellum)
Cerebrum
The cerebrum constitutes the largest part of the brain
and it occupies the anterior and middle cranial fossa. It is divided by a deep
cleft called the longitudinal cerebral fissure into two (2) distinct part known
as the (Rt) and (Lt) cerebral
hemispheres each of which contains one of the lateral ventricles. Deep within
the brain these two (2) hemispheres are connected by a mass of white matter
known as the corpus callosum.
and it occupies the anterior and middle cranial fossa. It is divided by a deep
cleft called the longitudinal cerebral fissure into two (2) distinct part known
as the (Rt) and (Lt) cerebral
hemispheres each of which contains one of the lateral ventricles. Deep within
the brain these two (2) hemispheres are connected by a mass of white matter
known as the corpus callosum.
The falxcerebri separate the two (2) hemispheres and penetrates
to the depth of the corpus callosum. The superficial of peripheral part of the
cerebrum is composed of nerve cells or grey matter forming the cerebral cortex
and the deeper layers consists of white matter or nerve fibres, Separated by
sulci/fissures are convolutions of infoldings of varying depth in the cerebral
cortex.
to the depth of the corpus callosum. The superficial of peripheral part of the
cerebrum is composed of nerve cells or grey matter forming the cerebral cortex
and the deeper layers consists of white matter or nerve fibres, Separated by
sulci/fissures are convolutions of infoldings of varying depth in the cerebral
cortex.
Each hemisphere of the cerebrum is divided for descriptive
purposes into lobes which have the names of the bones of the cranium under
which they lie:
purposes into lobes which have the names of the bones of the cranium under
which they lie:
*The frontal lobe, * The
parietal lobe, * The temporal lobe * The occipital lobes.
parietal lobe, * The temporal lobe * The occipital lobes.
In each
hemisphere there are deep fissures or sulci, some of which form
boundaries of the lobes are: * The central sulcus which separates the frontal
and parietal lobes * The lateral sulcus separates frontal and parietal from the
temporal lobe. * The parieto-occipital sulcus. separates the parietal and
temporal lobes from the occipital lobe.
hemisphere there are deep fissures or sulci, some of which form
boundaries of the lobes are: * The central sulcus which separates the frontal
and parietal lobes * The lateral sulcus separates frontal and parietal from the
temporal lobe. * The parieto-occipital sulcus. separates the parietal and
temporal lobes from the occipital lobe.
The fibres which link the different parts of the brain
and spinal cord, consists of afferent and efferent fibres known as
and spinal cord, consists of afferent and efferent fibres known as
* Arcuate (association)
fibres * commussural fibres * projection fibres
fibres * commussural fibres * projection fibres
The cerebrum consist among others the following functional areas: * The
Precentral (motor) area * The premotor *
The motor speech (Broca’s area) *Fontal area * Post central (sensory area)*
Olfactory *Taste * visual etc.
Precentral (motor) area * The premotor *
The motor speech (Broca’s area) *Fontal area * Post central (sensory area)*
Olfactory *Taste * visual etc.
Deep within the cerebral hemisphere were we have the:
The basal ganglia: Influences skeletal muscle
tone.(jerky, clumsy, uncoordinated movements).
tone.(jerky, clumsy, uncoordinated movements).
The thalamus: For pains, temperature,
pressure and touch.
pressure and touch.
The hypothalamus: For hunger, thirst,
defensive reactions (fear & rage)heart and blood vessels, hormones and
sexual behaviour.
defensive reactions (fear & rage)heart and blood vessels, hormones and
sexual behaviour.
The brain stem
The brain stem consists of
three (3) parts, the midbrain, the Pons and the medulla oblongata.
three (3) parts, the midbrain, the Pons and the medulla oblongata.
The midbrain
The midbrain is the short segment of the brain which
joins the cerebral hemisphere above to the pons verolli below. The 3rd
and 4th cranial nerves originate here. It consists of two(2) stout
stalk like bands of white matter which pass out from the base of the cerebrum
and run into the pons. The groups of nerve cells, and fibres connect the
cerebrum with the lower part of the brain and the spinal cord. The white matter
consists of motor and sensory fibres running fro and to, to the nerve centres
of the cerebral cortex and the nuclear.
joins the cerebral hemisphere above to the pons verolli below. The 3rd
and 4th cranial nerves originate here. It consists of two(2) stout
stalk like bands of white matter which pass out from the base of the cerebrum
and run into the pons. The groups of nerve cells, and fibres connect the
cerebrum with the lower part of the brain and the spinal cord. The white matter
consists of motor and sensory fibres running fro and to, to the nerve centres
of the cerebral cortex and the nuclear.
The nerve cells act as relay stations. Two (2) groups
of cells of particular note are the medial and lateral geniculate bodies. They
are for transmission of nerve impulses from the optic nerves and the vestibular
portion of the vestibulocochlear nerves to the cerebellum. These nerves play
major roles in the maintenance of balance of the body.
of cells of particular note are the medial and lateral geniculate bodies. They
are for transmission of nerve impulses from the optic nerves and the vestibular
portion of the vestibulocochlear nerves to the cerebellum. These nerves play
major roles in the maintenance of balance of the body.
The pons varolli
The pons varolli is located
in front of the cerebellum between the midbrain above and medulla oblogata
below. It consists of numerous tracts which links various parts of the brain
and serve as conduction pathways. It also contains cranial nerves (v-viii)
.i.e. Trigeminal, Abducens, facial and Auditory. Structurally, the nerve cells
lie deeply while the fibres are on the surface.
in front of the cerebellum between the midbrain above and medulla oblogata
below. It consists of numerous tracts which links various parts of the brain
and serve as conduction pathways. It also contains cranial nerves (v-viii)
.i.e. Trigeminal, Abducens, facial and Auditory. Structurally, the nerve cells
lie deeply while the fibres are on the surface.
The Medulla Oblongata
The medulla oblongata extends from the pons varolli
above and its continous with the spinal cord below. It is about one inch
(2-5cm) long. It is shaped like a pyramid with its base upwards, and lies just
within the cranium above the foramen magmum. Its anterior and posterior
surfaces are marked by central fissures.
above and its continous with the spinal cord below. It is about one inch
(2-5cm) long. It is shaped like a pyramid with its base upwards, and lies just
within the cranium above the foramen magmum. Its anterior and posterior
surfaces are marked by central fissures.
Several cranial nerves
arise from groups of cells in the medulla. Present in its deeper structure are
the following vital centres: * The
cardiac centre * The respiratory centre * The vasomotor centre * The reflex
centres of vomiting, coughing, sneezing and swallowing
arise from groups of cells in the medulla. Present in its deeper structure are
the following vital centres: * The
cardiac centre * The respiratory centre * The vasomotor centre * The reflex
centres of vomiting, coughing, sneezing and swallowing
Functions of medulla
Oblongata
Oblongata
(i) Decussation of the
pyramids (ii) Sensory decussation (iii) The cardiac centre controls the rate
and force of cardiac contraction i.e. sympathetic and parasympathetic(iv)The
respiratory centre controls the rate and depth of respiration (v) The vasomotor
centre controls the caliber of the blood vessels especially the small arteries and arterioles.(vi) Reflex centres:
When irritating substances are present in the stomach or respiratory tract,
nerve impulses pass to the medulla oblongata. These impulses stimulate the
reflex centres which initiate the reflex actions of vomiting, coughing or
sneezing.
pyramids (ii) Sensory decussation (iii) The cardiac centre controls the rate
and force of cardiac contraction i.e. sympathetic and parasympathetic(iv)The
respiratory centre controls the rate and depth of respiration (v) The vasomotor
centre controls the caliber of the blood vessels especially the small arteries and arterioles.(vi) Reflex centres:
When irritating substances are present in the stomach or respiratory tract,
nerve impulses pass to the medulla oblongata. These impulses stimulate the
reflex centres which initiate the reflex actions of vomiting, coughing or
sneezing.
Reflex arc
A stimulus (e.g hot object) is perceived by a
nerve ending (RECEPTOR) which initials an impulse. The impulse travels along
the SENSORY NERVE to the ( Spinal cord)where the impulse is relayed to the synapse then to the MOTOR NERVE, and the impulse travels along the motor nerve to
muscle. An action is produce by the stimulus. The hand is withdrawn.
nerve ending (RECEPTOR) which initials an impulse. The impulse travels along
the SENSORY NERVE to the ( Spinal cord)where the impulse is relayed to the synapse then to the MOTOR NERVE, and the impulse travels along the motor nerve to
muscle. An action is produce by the stimulus. The hand is withdrawn.
Cerebellum
The cerebellum otherwise
known as the hindbrain is situated behind the pons varolli and immediately
below the posterior portion of the cerebrum occupying the posterior cranial
fossa. It is ovoid in shape and presents two (2) hemispheres which are separated by a narrow
median strip known as the vermis. it is similar in structure with the cerebrum. There are three (3) pairs of cerebellar
stalks or peduncles joining it to the midbrain above, the pons in front and the
medulla.
known as the hindbrain is situated behind the pons varolli and immediately
below the posterior portion of the cerebrum occupying the posterior cranial
fossa. It is ovoid in shape and presents two (2) hemispheres which are separated by a narrow
median strip known as the vermis. it is similar in structure with the cerebrum. There are three (3) pairs of cerebellar
stalks or peduncles joining it to the midbrain above, the pons in front and the
medulla.
The peduncles are:
1) The superior cerebellar
peduncles ( Midbrain & cerebrum)
peduncles ( Midbrain & cerebrum)
2) The middle peduncle (pons)
3) The inferior cerebellar
peduncle (medulla oblongata & spinal cord)
peduncle (medulla oblongata & spinal cord)
Impulses passing to the cerebellum via these peduncles keep it informed
concerning the state of the muscles.
concerning the state of the muscles.
The membranes covering the
brain and the spinal cord
brain and the spinal cord
The brain and spinal cord
are completely surrounded by three (3) membranes known and called the meninges
which lied between the skull and the brain between the vertebrae and the spinal
cord. Their names are: * The Dura mater * The Arachnoid mater * Thepia mater
are completely surrounded by three (3) membranes known and called the meninges
which lied between the skull and the brain between the vertebrae and the spinal
cord. Their names are: * The Dura mater * The Arachnoid mater * Thepia mater
The Spinal Cord
The spinal cord is the
slender, elongated almost cylindrical part of the central nervous system which
lies within the vertebral canal of the vertebral column. It is continuous above
with the medulla oblongata and extends from the upper border of the atlas to
the lower extends from the upper border of the atlas to the lower border of the
first lumber vertebra. It is about 18 inches (45cm) long in an adult.
slender, elongated almost cylindrical part of the central nervous system which
lies within the vertebral canal of the vertebral column. It is continuous above
with the medulla oblongata and extends from the upper border of the atlas to
the lower extends from the upper border of the atlas to the lower border of the
first lumber vertebra. It is about 18 inches (45cm) long in an adult.
There are in all thirty-one (31) pairs of spinal
nerves corresponding to the segment of the vertebral column
nerves corresponding to the segment of the vertebral column
Vis:- 8 Cervical, 12 thoracic, 5 lumber, 5
sacral and 1cocygeal nerve
sacral and 1cocygeal nerve
Nerve roots/ Pluxus:There are five (5) large
plexus of nerves formed on each side of the vertebral column viz:
plexus of nerves formed on each side of the vertebral column viz:
·
The cervical plexus * The brachial plexus * The
lumber plexus * The sacral plexus * The
coccygeal plexus
The cervical plexus * The brachial plexus * The
lumber plexus * The sacral plexus * The
coccygeal plexus
The Cranial nerves
There are twelve (12) pairs of cranial nerves with
their cells associated with the brain. Some of them are sensory, some motor and
the others are mixed. The first two pairs are attached to the forebrain, the
rest originate from the brain stem. Other than the vagus which extend into the
abdomen, the cranial nerves serve only head and neck structures. In most cases,
the names of the cranial nerves reveal either the structures they serve or
their functions. They are numbered in Roman numerals from the most rostral to
the most caudal as follows stating their types and functions.
their cells associated with the brain. Some of them are sensory, some motor and
the others are mixed. The first two pairs are attached to the forebrain, the
rest originate from the brain stem. Other than the vagus which extend into the
abdomen, the cranial nerves serve only head and neck structures. In most cases,
the names of the cranial nerves reveal either the structures they serve or
their functions. They are numbered in Roman numerals from the most rostral to
the most caudal as follows stating their types and functions.
(i)
Olfactory nerves, sensory in function, for
smell.
Olfactory nerves, sensory in function, for
smell.
(ii)
Optic nerves, sensory in function, for sight and
balance.
Optic nerves, sensory in function, for sight and
balance.
(iii)
Occulomotor nerves, motor in function, for focus
and movement of the eyes.
Occulomotor nerves, motor in function, for focus
and movement of the eyes.
(iv)
Trochlear nerves, motor in function, for
movement of the eye ball.
Trochlear nerves, motor in function, for
movement of the eye ball.
(v)
Trigeminal nerves, mixed in function, for chewing and facial
sensation.
Trigeminal nerves, mixed in function, for chewing and facial
sensation.
(vi)
Abducens nerves, motor in function, for eye
movement.
Abducens nerves, motor in function, for eye
movement.
(vii)
Facial nerves, Mixed in function, for taste and
facial expression.
Facial nerves, Mixed in function, for taste and
facial expression.
(viii)
Auditory nerves (vestibulocochlear nerve)
sensory in function, for hearing and balance.
Auditory nerves (vestibulocochlear nerve)
sensory in function, for hearing and balance.
(ix)
Glossopharyngeal nerves, mixed in function, for
taste salvation etc.
Glossopharyngeal nerves, mixed in function, for
taste salvation etc.
(x)
Vagus nerves, mixed in function, for GIT
activities.
Vagus nerves, mixed in function, for GIT
activities.
(xi)
Accessory nerves, motor in function, for movement
of the head, shoulder.
Accessory nerves, motor in function, for movement
of the head, shoulder.
(xii)
Hypoglossal nerves, Motor in function, for
tongue movement.
Hypoglossal nerves, Motor in function, for
tongue movement.
Referred Pain
Often a person feels pains
in a part of his or her body that is considerably remote from the tissue
causing the pain. This pain is called referred pain. Pain usually is initiated
in one of the visceral organs and referred to an area of the body surface. It
may be referred to an area of the body not exactly coincident with the location
of the viscus(visceral) producing the pain.
in a part of his or her body that is considerably remote from the tissue
causing the pain. This pain is called referred pain. Pain usually is initiated
in one of the visceral organs and referred to an area of the body surface. It
may be referred to an area of the body not exactly coincident with the location
of the viscus(visceral) producing the pain.
