The Anatomy and Physiology of

Brain Sarita Sharma Assistant

professor of pharmacology

Mumbai

Organs

CNS:BrainSpinal CordPNS:Nerves

Brain It is one of the largest organs in the body, and

coordinates most body activities. It is the center for all thought, memory, judgment,

and emotion.Each part of the brain is responsible for controlling

different body functions, such as temperature regulation and breathing.

The brain is contained in skull & weighs 1300 - 1400 g

made up of about 1000 billion neurons 7 each neuron is surrounded by about 10 glial cells (neuroglia ).

Neurons cannot multiply & many neurons are lost everyday in life but glial cells can multiply throughout the life.

Brain is also covered by “Meninges” like spinal cord---outer duramater, middle arachnoidmater & inner piamater

Cerebrum

cerebellum

Ventricles of the brainThere are certain cavities in the brain called as

“ventricles”.These ventricles are filled with CSF.There are 4 ventricles of brain

2 lateral ventricles in two hemisphere

of the brain

3rd lies between hypothalamus &

thalamus

4th between brain stem & cerebellum

& is continuous with the central

cavity of spinal cord

Parts of brain:

Cerebrum

Cerebellum

Brain stem

Diencephelon

(1)Medulla(2)Pons

(3)Mid brain

(1)Thalamus (2)Hypothalamu

s(3)Epithalamus

& Pineal gland

Right cerebral hemisp

here

Left cerebral hemisp

here

(A) Cerebrum It is the largest section of the brain It is located in the upper portion of the brain and is the

area that processes thoughts, judgment, memory, problem solving, and language, imaginations.

Cerebral cortex – the superficial layer of the cerebrum is “gray mater” & this is 2-4 mm thick called “Cerebral cortex ” contains billions neurons.

During embryonic development when the brain size increases rapidly, the gray mater of the cortex enlarges much faster than deeper white mater so as result cortical region roles & fold upon itself.

The folds are called “gyri” or “convolutions”The deepest grooves between the folds are called

“fissures”The shallower grooves between folds are called “sulci”The most prominent fissure, the longitudinal fissure,

separates the cerebrum into right & left halves called “cerebral hemispheres”. Each hemisphere has 4 lobes.

The cerebrum is subdivided into the left and right Both hemisphere are connected by a bridge of nerve fibers that relay information between 2 hemisphere called “corpus callosum”

Left hemisphere controls right side of the bodyRight hemisphere controls left side of the body

Lobes of Cerebrum

Lobes of Cerebrum1. Frontal lobe: Most anterior portion of the cerebrum

(under forehead) “central sulcus” separate frontal & perital lobe.

controls motor function, personality, and speech• Like Center of reasoning, Planning, some parts of

speech, movement, Emotions, problem solving.

Also called as “motor cortex”

2. Parietal lobe: The most superior portion of the cerebrum(top of head),

receives and interprets nerve impulses from sensory receptors and interprets language.

• Receives sensory input from the skin. (touch, pressure, temperature, & pain)

Also called as “sensory cortex”

(3) Occipital lobe: The most posterior portion of the cerebrum (back of the head),

• Receives input from the eyes & controls vision.• Also called as “visual cortex”.

4. Temporal lobe: The left and right lateral portion of the cerebrum(on the sides of your head above your ears),

controls hearing and smell

Also called “Auditory cortex”

Functions of cerebrum: (1) Motor functions like control of voluntary

movements.

(2) sensory functions like perception of pain, temparature, touch, hearing, taste, & smell.

(3) control of intelligence, speech, memory & learning etc.

(B)CerebellumSecond largest portion of the brainLocated beneath the posterior part of the cerebrumA deep groove known as “transverse fissure” separates

cerebrum to cerebellum.

Aids in coordinating voluntary body movements and maintaining balance and equilibrium

External Structure

The external surface , called cerebellar cortex, look like butterfly, constricted area called “vermis”

The lateral wings or lobes called cerebellar hemisphere that is interconnected by a narrow portion called vermis.

Each hemisphere consists of lobes separated by deep fissures.

A part of the human brain that lies in the posterior cranial fossa , inferior to occipital lobes.

10% weight of entire brain.

50% of neurons.

Divisions & layers of cerebellum

(1) Anterior lobe both regulate subconscious aspects

of skeletal muscle movements(2) Posterior lobe(3) Flocculonodular lobe – on the inferior surface maintain equilibrium and balance Superficial layer of cerebellum called ”cerebellar cortex” consist

of gray mater, series of slender & parallel folds called “folia”. Deep to gray mater white mater called “arbor vitae” resemble to

branch of tree. Even deeper white mater are”cerebellar nuclei”, region of the

gray mater having axons carrying impulses from cerebellum to other parts of brain.

Flocculonodular lobe

folia

Cerebellar peduncles:

Inferior cerebellar peduncle is a thick rope-like strand that occupies the upper part of the posterior district of the medulla oblongata

Middle cerebellar peduncles connect the cerebellum to the pons.

Superior cerebellar peduncle is a paired structure that connects the cerebellum to the midbrain.

3 paired Attach the cerebellum to brain stem

These bundles of white mater consist of axons that conduct impulses between the cerebellum & other parts of the brain

Functions of cerebellum:

(1)Coordinate contractions of skeletal muscles(2)Regulate posture & balance(3)May play a role in cognition/learning from experieces

& language processing

(C) Brain Stem Consists of: (1) Midbrain (2) Pons (3) Medulla oblongata

Superiorly continuous with

Diencephalon Inferiorly continuous with spinal cord. Posteriorly pons and medulla is separated by fourth ventricle. Midbrain, pons and medulla connected to cerebellum by

superior, middle and inferior cerebellar peduncle resp.

(1)Mid brainThe midbrain or mesencephalon e

xtends from the pons to the diencephalon & about 2.5 cm long.

It acts as a pathway for impulses to be conducted between the brain and the spinal cord.

 associated with vision, hearing, motor control, sleep/wake, arousal (alertness), and temperature regulation.

Screening of information before it reach high brain structure

Parts of mid brain:Anterior part

called “cerebral peduncles”

Posterior part called “Tectum”

Contain 4 rounded elevations/swellin

gs

2 superior elevationsSuperior colliculi

2 inferior elevationsinferior colliculi

receives input from the retina and the visual

 cortex and participates in a variety of visual

reflexes, particularly the

tracking of objects in the visual field. 

receives auditory fibres and relay nucleus of the 

thalamus.

TEGMENTUM

SUBSTANTIA NIGRA

CRUS CEREBRI

Body movemen

ts

Motor neurons

relay inhibitory

signals for

unwanted body

movements

White materFunction not clear

Functions of mid brain:The midbrain serves important functions in motor

movement, particularly movements of the eye, and in auditory and visual processing. 

 Dopamine produced in the substantia nigra and ventral tegmental area plays a role in excitation, motivation.

The midbrain helps to relay information for vision and hearing.

(2) Pons:means bridge—connects the

cerebellum to the rest of the brain. lies between midbrain above and

medulla below in front of cerebellum.Like medulla it also sensory tract

and motor tract.Contains nuclei that deals with

respiration, swallowing, bladder control, hearing, equilibrium, eye ball movements, facial expressions etc.

(3) Medulla oblongataLowermost part of the brain stem &

continuation of the superior portion of spinal cord.

Situated at the base of the skull/ starts from foramen magnum & extends to the inferior border of the pons, a distance of about 3 cm.

The ascending & descending sensory & motor white mater tracts (nerves) connecting brain to spinal cord pass through medulla oblongata.

Its very important because many “regulatory centers ” are located here

(1) The cardiovascular center: regulate the heart rate, force of heartbeat & diameter of blood vessels.

(2) The medullary rhythmicity center: responsible for maintaining basic rhythm of breathing.

(3) The vasomotor center: regulate blood pressure. (4) others: vomiting, swallowing, cough, hiccupping &

sneezing etc.5 pairs of cranial nerves originates from the nuclei

located in medulla oblongata.

(D)Diencephelon

(1) Thalamus Contain mass of nerve cells.Thalamus means “inner room” in Greek, as it sits deep in the brain

at the top of the brainstem.The thalamus is called the gateway to the cerebral cortex, as

nearly all sensory inputs pass through it to the higher levels of the brain.

It makes up 80% of diencephalon.

Important relay station for all Incoming sensory nerves from periphery/ spinal Cord with different impulses of pain,temperature, Touch, pressure are conveyed to thalamus first than Go to cerebrum.

This information is relayed from thalamus to cerebrum through thalamic nuclei:

(1)Median geniculate nucleus—related to hearing(2)lateral geniculate nucleus—related to vision(3)Ventral posterior nucleus—related to taste & somatic

sensations like touch, pain, pressure, cold, heat, vibrations etc.

(2) Hypothalamus: The hypothalamus sits under the thalamus at the top of the

brainstem. Although the hypothalamus is small, it controls many critical bodily functions:

• Controls autonomic nervous system• Center for emotional response and behavior

• Regulates body temperature• Regulates food intake(appetite)• Regulates water balance and thirst• Controls sleep-wake cycles• Controls endocrine system• Controls CVS regulation- Heart rate & BP

The hypothalamus is shaded blue. The pituitary gland extends from the hypothalamus.

(3) Epithalamus & Pineal gland:Epithalamus is a small region superior & posterior to

the thalamus. It consist of pineal glandPineal gland is about the size of the pea & protrudes

from posterior midline of the 3rd ventricle It’s a endocrine gland secrets hormone “Melatonin”.Darkness stimulates the pineal gland to secrets

melatonin—it promotes sleepiness.

The cranial nerves:The 12 pairs of cranial nerves named because they

pass through bones of cranium & arise from the brain inside the cranial cavity.

These nerves may be sensory(carrying impulse to the brain), motor (carrying impulse from the brain to periphery) or mixed (containing both sensory & motor fibers)

Thank you