Anatomy and Physiology of brain

Brain cells• Neurons and neuroglia

neuroglia

In CNS In PNS

Asrocytes Schwann cells

Oligodendrocytes Satellite cells

Microglia

Ependymal cells

Neuron

• Basic units of nervous tissue

• Function as electrical impulse generation and transmission.

• Cannot regenerate when damaged

Neuroglia/Glial cells

• Makes half of the volume of CNS

• Smaller than neurons and 5-50 times more numerous than neurons.

• Do not propagate nerve impulses

• Can regain after injury, highly growing.

Astrocytes • Star shaped cells, have

many processes, largest and most numerous

• Two types of astrocytes-protoplasmic and fibrous

• Processes of astrocytes make contact with blood capillaries, pia matter and neurons.

Functions of astrocytes

• strength to support neurons.• blood brain barrier.• growth and interconnection of

neurons.• chemical environment for generation

of nerve impulses by neurons.• learning and memory

Oligodendrocytes:

• These resemble astrocytes but have fewer processes and smaller in size.

• Maintain myelin sheath around the CNS axons.

• A single oligodendrocyte may myelinate several neurons.

Microglia:

• Small in size, contains spindle like projections

• Function as phagocytes and clear cell debris

Ependymal cells:

• Cuboidal to columnar cells contain cillia and microvilli.

• Lines the ventricals of brain and central canal of spinal cord.

• Produce, monitor and assist in CSF circulation.

• Form blood cerebrospinal fluid barrior.

Schwann cells:

• Form myelin sheath around the neurons.

• Single cell can line only one axon.

• Participate in axon regeneration.

Satellite cells:

• Surrounds the cell bodies of neurons in PNS ganglia.

• Exchange of materials between neuronal cell bodies and interstitial fluid.

Meninges:

CSF circulation

choroid plexus of lateral ventricles

choroid plexus of third ventricle

choroid plexus of forth ventricle

lateral ventricles

through interventricular foramina

third ventricle

through cerebral aqueduct

forth ventricle

through lateral and median aperture

subarachnoid space

arachnoid villi of dural venous sinuses

venous blood

heart and lungs

CSF

CIRCULATION

CSF composition

• Normal CSF secretion is 20 ml/hr or 480 ml/day• Total volume is 80-150 ml• Carries oxygen and nutrients• Contains glucose, protein, lactic acid, urea,

cations ( Na+, K+, Ca2+, Mg2+) and anions (Cl, HCO3

-)• Functions are mechanical support, chemical and

nutritional.

Brain stem:

• Consists of 3 parts:• Medulla ablongata• Pons• Mid brain

Medulla ablongata• contains sensory and motor

tracts extends between the brain and spinal cord.

• Contains cardiovascular centre

• Medullary rythmicity area of respiratory centre

• Responsible for vomiting, coughing, sneezing, swallowing and hiccupping.

• Sensitive to touch, vibration and proprioception.

• Contains 5 pairs of cranial nerves:

• Vestibulocochlear VIII• Glossopharyngeal IX• Vagus X• Accessory XI• Hypoglossal XII• Damage to this part cause

cranial nerve alterations at the same side and paralysis in opposite side.

Pons• contains pneumotaxic area and apneustic area

which helps in respiration.• Have 4 pairs of cranial nerves:• Trigeminal V• Abducens VI• Facial VII• Vestibulocochlear VIII

Mid brain• connects cerebrum to medulla, pons and spinal

cord.• Reflex centre for visual activities• Helps in tracking moving objects• Helps in scanning stationary objects• Eyes, head and neck movements with moving

objects• Startle reflex• Sudden movement of head with noise• Have substantia nigra which release dopamine and

also responsible for subconscious muscle activities.

RAS- reticular activating system

• brain stem consists of small clusters of neuronal cell bodies.• It maintains consciousness• Awakening from sleep• Muscle tone maintenance

cerebellum

• Skilled skeletal muscle movements

• Posture and balance• Cognition and

language processing