Chapter 8 The BRAIN

Structure: The brain and the spinal cord are surrounded by three layers of membranes called the: MENINGES WHY? Requires a lot of nutrients because of high metabolic rate Requires a constant supply of oxygen CNS tissue must be isolated from blood-borne compounds and damage from contact with surrounding bones

Meninges: FUNCTION: Provide physical stability to the CNS Act as “shock absorbers” Maintain the blood-brain barrier The 3 meningal layers are: The dura mater The arachnoid The Pia mater

3 layers:

Dura mater The dura forms the outermost covering of the CNS. It lines the skull Dura – hard (Latin)

Arachnoid This layer is separated from the dura by a subdural space (below the dura). This space is filled with fluid which reduced friction between the opposing surfaces. The cerebrospinal fluid (CSF) acts a shock absorber and transports dissolved gases, nutrients and waste products. Between the next layer is the subarachnoid space

Pia Mater This layer covers the brain - Pia – delicate (Latin) The blood vessels servicing the brain and the spinal cord run along the surface of this layer, in the subarachnoid space This is an extensive supply of blood for the brain.

Why head injuries are so dangerous: The danger with any head injury is that arteries bleed very quickly, within minutes and hours while the symptoms seem very mild at first. There is no where for the blood to go, the pressure can push down onto the brainstem, and swelling can do this too…and lead to a coma and death.

Head Injuries: A severe head injury may damage cerebral blood vessels and cause bleeding into the skull. If blood leaks out between the dura and the cranium – epidural hemorrhage. If the bleeding is in the subdural space – subdural hemorrhage. The pressure from this blood can compress and damage the brain. Remember: the skull is an enclosed space, there is really nowhere for the blood to go.

Epidural hematoma

Subdural hematoma

MRI of a head bleed:

CT scan of a brain bleed

Concussions: This occurs when a violent blow to the head causes the brain to slam against the skull beyond the ability of the CSF to cushion the impact. Getting hit in the frontal region: The shock wave passes thru the brain and bounces off the back of the skull. The concussion occurs at the opposite side from the point of impact.

Concussions:

The Cranial Nerves: The cranial nerves are part of the PNS, and not part of the brain. The 12 pairs of cranial nerves primarily serve the head and neck. Only one pair extends into the thoracic and abdominal cavity. 10 of the pairs arise from the brain stem and pass through foramina in the base of the skull to reach their destinations. (Cranial nerves I and II do not.)

Cranial Nerves

Use the graphic organizer: Number and Name: 1st column Origin and course: 2nd column Function: 3rd column sensory – no movement or activity motor: movement or activity

Cranial nerves: Olfactory: CN I Ethmoid bone to olfactory bulb synapse Purely sensory - sense of smell Optic – CNII Retina of the eye thru the optic canal of the orbit Purely sensory - vision

Oculomotor – CNIII Retina of the eye thru the optic canal of the orbit Purely sensory - vision Trochlear – CNIV From midbrain – exits superior orbital fissure Primarily motor – moves the eyeball

Trigeminal – CNV From the pons, splits into 3 divisions Sensory and motor, nerve of face, scalp, floor of mouth Abducens – CNVI Inferior pons to eye motor: Lateral rectus muscle, moves the eyeball

Facial – CNVII Pons through the temporal bone to the face Motor and sensory: muscles of face, taste, salivary glands Vestibulocochlear – CNVIII In the temporal bone, then enters the pons Purely sensory – hearing, cochlea

Glossopharyngeal – CN IX From the medulla, thru the skull to the throat Motor and sensory – taste buds, pharynx, tonsils, carotid artery Vagus – CN X From the medulla, descend through the neck into thorax/abdomen Heart and smooth muscle of abdominal viscera

Accessory – CN XI Superior aspect of spinal cord to muscles of neck and back Motor: neck/shoulder muscles, pharynx, larynx and soft palate Hypoglossal – CN XII From medulla, travel to tongue Motor: muscles of the tongue