Brain and Cranial Nerves

Brain

Brain Stem

Consists of…

Consists of the brain stem, diencephalon, cerebrum and cerebellum.

Medulla oblongataPonsMidbrain

Located just superior to the spinal cord, at the foramen magnum.

BrainDiencephalon

Thalamus

Hypothalamus

Cerebrum

Cerebellum

Sup and lat to the brain stem. Consists of …

Most sup and lateral to the midline

Inf and medial to the thalamus

The largest part of the brain; cognitive functions and memory reside here.

Post and inf to the cerebrum; fine motor control and coordination Q30

CoveringsCranial meninges

Dura mater

Outer- periosteal layer

Inner- meningeal layer

Similar to the spinal meningies

The cranial version has two layers

…adheres to the cranium

…sits next to the subdural space and the arachnoid.

Between the two layers is a dural sinus which contains venous blood.

CoveringsArachnoidPia mater

These layers are similar to their spinal version

Cerebrospinal fluid

VentriclesLateral (2)

Third

Fourth

Interventricular foramen

…are located within each cerebral hemisphere

Med and inf to the lat ventricles

Between the brain stem and cerebellum.

An opening which connects the lateral ventricles to the third ventricle.

CSF; fills spaces in the brain called ventricles. Makes about 500 ml/day.~150 ml in ventricles and subarachnoid

Cerebrospinal fluidCerebral aqueduct

Spinal central canal

Subarachnoid

Choroid plexuses

Passes down the middle of the cord

This spaces surrounds the cord and the brain

Found within the ventricles, these tufts of capillaries produce CSF, which is very similar to blood plasma without proteins.

Connects the third with the fourth

Cerebrospinal fluidArachnoid villi

Superior saggital sinusThis space is found between the two layers of the dura.It is filled with venous blood.CSF passes through the arachnoid villi and it mixes with the venous blood of sinus and is returned to circulation.The sinus eventually drains into jugular veins and then to the heart.

Are extensions of the subarachnoid space which project into the …

Cerebrospinal fluidFunction

Shock absorber

Nutrients delivery

Removal of wastes

The CSF surrounds the brain and the cord; it creates a watery cushion to absorb the normal shocks of everyday life.

Glucose, oxygen, some amino acids are carried in CSF and delivered to neural tissues.

Carbon dioxide and waste products of normal metabolism and cell breakdown are removed by CSF.

HydrocephalusOr “water on the brain”If there is an over production of CSF or if the CSF is not drained properly, then fluid pressure within the ventricles of the brain can increase substantially.

The increased pressure will compress neural tissue and this will lead to brain damage and, in some cases, death.Causes of hydrocephalus may include blockage of the the cerebral aqueduct, in which case the CSF accumulates in the lateral and fourth ventricles.A hydrocephalic shunt may have to be implanted to relieve the pressure.

Blood supply of the brain

Interruption

Unconsciousness

Permanent injury

The brain requires a constant and steady supply of blood (with oxygen and glucose.) It receives about 15% of the total cardiac output.

Even a short interruption can cause a loss of brain function; a drop in BP can lead to dizziness and blackouts.

If the supply is blocked for longer than 5-10 seconds, unconsciousness will follow

Can occur if there is a loss of blood for longer than about 5 mins. This may result in brain injury and perhaps death.

Blood supply of the brain

Blood brain barrier

Selective barrier

The BBB is a selective barrier which prevents certain materials from passing into the sensitive cerebral tissues.

Slightly permeable to Na+, K+, Cl-.Very permeable to oxygen, carbon dioxide, water, alcohol, and most anesthetics.Not permeable to blood proteins and non-lipid organic molecules

Brain stemMedulla oblongata ( or medulla)

Pyramids

Decussation

Lateral corticospinal tract

The most inferior part of the the brain stem; just sup to the cord.

Descending through the medulla are the pyramids, motor tracts from the cortex of the cerebrum.

These tracts continue down the cord to pass motor signals to skeletal muscles in the periphery.

As the tracts of both sides pass the junction between the medulla and the cord, they cross over (the decussation) the midline and form the…

Brain stemMedulla oblongata ( or medulla)

Nucleus gracilis and cuneatus

Reticular formation and reticular activating system (RAS)

A nucleus is a collection of somas within a nerve tract within the CNS.These nuclei relay body sensory information to the thalamus.

This group of nuclei extend into the pons.They send signals in to the cerebrum to maintain a state of consciousness.If signals are interrupted for any reason, such as a blow to the chin to direct trauma to the medulla, the person will fall into unconsciousness or a coma.

Brain stemMedulla oblongata ( or medulla)

Cardiac center

Medullary rhythmicity center

Vasomotor center

Origins of cranial nerves VIII-XII

Vestibular complex

Regulates the activity of the heart; such as the heart rate and contraction strength.

Regulates the rate of respiration

Regulates peripheral vasoconstriction and blood pressure.

Later.

Receives information from the vestibule of the inner ear, which helps maintain balance.

Brain stemPons

Origins of cranial nerves V-VIII part of VIII

Reticular formation

Pneumotaxis and apneustic areas

Later.

Continues from the medulla.

Involved in regulating respiratory activities.The former detects the amount of stretch in the lungs and regulates how much the lungs inflate.

Brain stemMidbrain (mesencephalon)

Corpora quadrigemina

Superior colliculi

Inferior colliculi

The most superior part of the brain stem.

On the posterior side of the midbrain; “four bodies”

These “bodies” regulate visual reflexes, such as pupil size and focusing.

Regulate auditory reflexes.If you are exposed to loud sounds, the inferior colliculi sends signals to the middle ear to reduce the level of sound energy transmitted into the inner ear.

Brain stemMidbrain (mesencephalon)

Substantia nigra

Carries signals from the motor cortex which are used to coordinate muscle activity (along with the cerebellum.)Damage to the substantia can lead to involuntary movement and rigidity.

Q32

DiencephalonThalamus

Intermediate relay center

Origins of voluntary motor pathways

The lobes of the thalamus are located sup and lat to the brain stem, deep within each hemisphere.

It receives all of the sensory fibers (except smell) and sends signals to the sensory part of the cerebral cortex.It may be that the thalamus is the crucial structure for the perception of some sensations, rather than the cortex, which may give fine detail to sensations.

DiencephalonThalamusBrain (cortical cycles)

Emotional expressions

Pineal gland/body

Melatonin

May have their origins here.

Considered the seat of emotions. Receives sensory input and passes in on to the cerebral cortex. Integrates sensations and emotions.

Located on the posterior surface of the mid-body of the thalamus.

A hormone produced by the pineal gland that appears to regulate the circadian rhythm; wake-sleep cycles of the brain.Exposure to bright light (such as sunlight at dawn) suppresses the release of melatonin and resets the wake cycle.Melatonin at night may stimulate sleep cycles.

DiencephalonHypothalamusHormone production

Controls hormones

FunctionsInformation processing about external/internal environment

Makes two hormones (antidiuretic hormone and oxytocin) which are transported to and released by the pituitary gland.

Makes control factors that regulate the release of hormones from the pituitary.

Next page.

Controls both divisions of the ANS; sympathetic and parasympathetic.

Part of the visceral reflex arc. Processes visceral sensory signals and, in turn, activate motor neurons which control visceral effectors.

HypothalamusControl of ANS

Process visceral sensory information

Interface between the nervous and endocrine

Mind over body

Rage/aggression

The NS can control the release of hormones to control the body. Through various techniques, such as meditation and bio-feed back, it is possible to “think” your heart slower, for example.

This is the place where the two control systems overlap and exert mutual control

Is closely linked to both the thalamus (associated with emotions) and the hypothalamus (release of hormones, such as adrenaline.)

HypothalamusBody temp

Food intake regulation

Appestat

Satiety center

Hypothalamus monitors blood as it passes the preoptic area. If varies from normal range (37°C); negative feedback to bring the temp back in range.

Feeding behavior is regulated.Associated with emotions and memory.

Detects blood glucose levels: if glucose drops, feeding behaviors are turned on.

Eaten enough? Increases in blood glucose and stomach stretchTurns off feeding

Water content of blood is monitoredAdjusts drinking behaviorsStimulates the release of ADH- anti-diuretic hormoneReduces urine outputHelps retain water in the body

HypothalamusThirst center