Brain And Cranial Nerves

-largest body organ

-85 million neurons and 10-50 trillion neuroglia

-weights ~3lbs

-uses 20% of O2

-information can be processed as fast as 120 m/s

-centre for intellect, emotions, behaviour and memory

-continuous with spinal cord

Contains:

*midbrain

*pons

*medulla oblongata

-2nd largest

-posterior to brain stem

-superior to brain stem

Contains:

*thalamus

*hypothalamus

*pineal gland

-largest

-supported on diencephalon and brain stem

Contains

*gray matter

*white matter

DAP

-dura mater, arachnoid layer, pia mater

subarachnoid space: b/w AP

continuation of the spinal meninges

-outer

-periosteal layer (external)

-meningeal layer (internal)

-subdural space

*b/w DA

*contains interstitial fluid

*not very distinguishable unless something is wrong

-3 extensions (separate and provide extra cushioning/support):

1) Falx Cerebri (separates hemispheres of cerebrum)

2) Falx Cerebelli (separates hemispheres of cerebellum)

3) Tentorium Cerebelli (separates the cerebrum from the cerebellum)

-middle

-subarachnoid space

*b/w AP

*contains CSF

-inner

-interruption of blood flow for 1-2 min impairs neurological fxns

-total deprivation for 4 min causes permanent damage to the brain

-requires glucose in blood for energy

-tight junctions that seal together the endothelial cells of brain's blood capillaries and a thick basement membrane

-protects brain cells from harmful pathogens and toxins

-processes of astrocytes (neuroglia) press up against the capillaries and secrete chemicals that maintain permeability characteristics of tight jxn

*water-soluable substances (glucose) pass BBB by active transport where they bind to something else

*proteins, drugs do not cross BBB at all

*lipid-soluable substances (O2, CO2, alcohol and anesthetic agents) pass quiet freely

clear, colourless, primarily water

-protects brain and spinal cord from chemical and physical trauma

-carries oxygen, glucose and other chemicals from blood to neurons and neuroglia

-removes waste

-80 to 150 mL

-reabsorbed 20 mL/hour

-pressure constant

-reabsorption = production (w/in choroid plexus)

-through cavities of brain and spinal cord

-around brain and spinal cord in sub-arachnoid space

1) lateral ventricles x2

*anteriorly separated by thin membrane = septum pellucidum

2) third ventricle

*main areas of production

*midline, superior to hypothalamus

3) fourth ventricle

*b/w brain stem and anterior to cerebellum

1) Mechanical Protection

2) Homeostatic Function

3) Circulation

-shock absorption for delicate brain tissues of brain and spinal cord

-brain literally "floats" in the cranial cavity (shocker absorber)

-pH of the CSF affects pulmonary ventilation and cerebral blood flow

-CSF is a transport system for polypeptide hormones (for remote sites in brain)

-CSF is a medium for exchange of nutrients and waste products b/w blood and nervous tissue

-CSF is reabsorbed into venous blood

-gradual reabsorption through arachnoid villi

-arachnoid villi project into dura venous sinuses (superior sagittal sinus)

-absorbed at a rate of 20 mL/hr

-reabsorption = production

-abnormal CSF production

-obstruction to CSF flow

-trauma/bleeding in brain

-some people are born with it

-pressure rises

1) lateral ventricles

2) third ventricle

3) fourth ventricle

4) subarachnoid space

5) superior sagittal sinus

Contains: CSF and choroid plexus

Transports to: 3rd ventricle

Via interventricular foramen

Contains: CSF and choroid plexus

Transport to: 4th ventricle

Via cerebral aquaduct

Contains: CSF and choroid plexus

Transport to: central canal, subarachnoid space

Via direct downward flow lateral and median aperature

Contains: CSF

Transport to: superior sagittal sinus in brain and outside spinal chord

Via the arachnoid villi

Contains: venous blood

Transport to: heart and lungs

-continuation of superior part of spinal cord (inferior part of brain stem)

-extends from foramen magnum superior to pons

Pyramids

Decussation of Pyramids

Sensory tracts (ascending)

Motor tracts (descending)

Nuclei

Olives

large tracts that pass from cerebrum to spinal cord, bulges on anterior of medulla (control voluntary movements of limbs and trunk)

-superior to junction of medulla with spinal cord

-90% of axons in right pyramid cross left and vice versa = why each side of the brain controls other sides' functions

-control vital autonomic functions of cardiovascular centre (rate and force of heartbeat)

-medullary respiratory area (rhythm of breathing)

-lateral to each pyramid and it receives input from cerebral cortex, red nucleus of midbrain and spinal cord

-axons extend into cerebellum and carries signal for voluntary movements to maintain equilibrium/posture

-heartbeat

-blood vessel diameter

-normal breathing rhythm

-vomiting

-sneezing

-coughing

-hiccupping

-swallowing

Involuntary Functions

nuclei that regulate:

* touch, pressure, pain, thermal, conscious proprioception

* components of sensory pathway for taste, hearing, balance

Glossopharyngeal: nuclei relay sensory and motor impulses for taste, swallowing salivation

Vagus: motor impulses to pharynx and larynx and thoracic and abdominal viscera

Accessory: control swallowing

Hypoglossal: control tongue during speech and swallowing