Brain Anatomy and Physiology

Dr. Nevo Margalit – Neurosurgery

Tel Aviv Sourasky Medical Center

Scalp

• Skin

• Connective tissue (superficial fascia)

• Epicranial aponeurosis (galea aponeurotica)

• Loose areolar tissue

• Pericranium

• Occipitofrontalis muscle

Scalp

The Skull

The Skull

The skull

The MeningsThe 3 layers covering the brain

• Dura: covers the brain and spinal cord. The venous sinuses run through the dura. 2 additional Parts of the dura are the Tentorium and the Falx Cerebri.

• Arachnoid: Transparent, thin web structure. Creates a space around the brain called the sub arachnoid space where the CSF and the main blood vessels pass.

• Pia: a very thin layer. Coats the brain and spinal cord and is inseparable from them.

Dura

Tentorium and Falx

Tentorium

Arachnoid

Arachnoid – Basal Cisterns

Parts of the Central Nervous System

• 2 hemispheres

• Brainstem

• Cerebellum

• Spinal cord

Each hemisphere has lobes:

• Frontal lobe

• Parietal lobe

• Temporal lobe

• Occipital lobe

• Insular lobe

• Limbic lobe

Lateral View

Insula

Gyruses and sulci

• Each lobe is composed of gyruses separated by sulci

• The topography can be defined by histology, anatomical relationships or function

Map Brodmann

Gyruses and Sulci

Functional areas

Function 2

Function 3

f-MRI

The Motor Strip

Fibers

Ventricles and CSF

Ventricles and CSF

• CSF is produced by the choroid plexus in the ventricles

• The circulation is from the lateral ventricles to the third through the Monroe- aqueduct- IV ventricle- sub arachnoid space in skull and spine- absorption in sss and other sinuses through arachnoid granulations

CSF Pathways

CSF Pathways

Arteries of the brain

Arteries of the brain

• Anterior circulation – internal carotid artery, from common carotid in the neck. Bifurcates to MCA and ACA

• Posterior circulation – vertebral arteries that join to form the basilar artery that will then bifurcate to 2 PCA

Circle of Willis

• Communication between 2 sides – anterior communicating (a-com)

• Communication between anterior and posterior circulation – posterior communicating (p-com)

• Many anomalies may exist

Arteries in the neck

Arteries in the subarachnoid space

Arteries of the brain

Physiology

Blood supply to the brain

• The brain gets 15% of the cardiac output and 20% of the oxygen consumption

• The brain tissue gets in average 50ml of blood per 100gr of tissue per minute. The gray matter receives about 3 to 4 times more then the white matter

• Total blood supply to the brain is about 500-600ml per minute

Factors Affecting the blood supply

• Autoregulation

• Biochemical changes – O2 and CO2

• Blood brain barrier - BBB

Autoregulation

• Maintains a regular blood supply to the brain in changing blood pressures

• The range is 50-130 mm mercury

• Possible mechanisms are the myogenic control, neurogenic and biochemichal control

CO2

• The most important and powerful mechanism that controls brain blood flow

• A change in 1mm PCO2 changes the flow in 4-5%

• PCO2 of 70 gives a maximal vasodilatation. Above that the flow is pressure dependent

Hyperventilation

• Hyperventilation lowers the PCO2

• It has a strong effect but it is limited in time

• Could be dangerous if not regulated- ischemia

• Can be regulated with a jugular bulb oximeter

BLOOD BRAIN BARRIER

• The BBB is composed of the tight junctions in the endothelium cells of the blood vessels

• Prevents passage of large molecules and even small ions like Na and Cl

• Specific substances pass the BBB like glucose and amino acids

BLOOD BRAIN BARRIER

• Because of the BBB, in the brain hydrostatic and oncotic pressures are not significant. The important parameter is the osmotic pressure

• The BBB is damages in trauma, tumor, infarct, SAH and infection

BLOOD BRAIN BARRIER

Brainstem and Cranial Nerves

Brain stem

• Has 3 parts: midbrain, pons and medulla

• Transports all the information to and from the brain

• Centers for breathing and blood pressure

• The origin or endpoint for cranial nerves

• Contains the center of consciousness

• Creates connections to the cerebellum

Nuclei in the brain stem

Cranial nerves

• 12 pairs of nerves

• All cranial nerves except I and II originate from the brainstem

• The nerves are sensory, motor or mixed

• There are nuclei in the brainstem that are the origin or the endpoint of the cranial nerves

CN 1- Olfactory Nerve

• The sensation of smell

• Pure sensory nerve

• From the nose to the forebrain

• Very developed in some animals

• Tested an odorous substance

CN 2 - Optic N

• Visual information from the eye to the brain

• Pure sensory nerve• Belongs to the CNS and is not part of

the PNS• Problems could result in field problem,

acuity problem and more• Tested with a vision chart and field

exam on confrontation

CN 3, 4, 6- occulomotor, trochlear and abbducence

• Nerves that control the movement of the eyes and the constriction of the pupil

• Pure motor nerves

• Problems result in unsynchronized eye movements and/ or dilated pupil

• Tested with the patient following a finger and with light

CN 5 – Trigeminal N

• The largest CN

• Sensory and motor

• Sensation from the face eyes, mouth, and motor for mastication muscles

• Tested with touch and pin on face

CN 7 – Facial N

• Motor nerve of the face and taste from the tongue

• Motor and sensory

• Tested with movement of the facial muscles

CN 8 – Vestibulocochlear N

• The nerves for hearing and balance

• Sensory nerves

• The most common origin of a schwanoma

• Tested by hearing test and balance function

CN 9 – Glossopharyngeal N

• Sensation from the pharynx

• Mainly sensory and small motor part

• Problems result in aspiration

• Tested with the gag reflex

CN 10 – Vagus N

• Motor to the muscles larynx and pharynx and the parasympathetic of the body

• Motor nerve

• Problems result in hoarseness

• Tested by opening mouth wide and saying “AH“

CN 11 – Accessory N

• Nerve to the trapezius and sternomastoid muscles

• Motor nerve

• Tested with shoulder raise or turning the head

CN 12 – Hypoglossal N

• Nerve to the muscle of the tongue

• Motor nerve

• Tested with movement of the tongue