Skin, then bone of skill
(3 Layers of Membrane Protect the Brain: Meninges)
Outer Most layer aka DURA MATER- leather like tissue that follow outlines of skull bones. Hard tissue.
Then, ARACHNOID LAYER- more delicate layer, looks like spider web.
Between, subarachnoid space- meaning below.
Innermost layer, aka PIA MATER- nearly transparent sticks closely to the outside of the brain
(All cover the brain and spinal cord. Only dura and pia, cover exit, called the peripheral nervous system nerves.)
Then, artery, and then brain.
Cerebrospinal fluid (CSF) circulates in the hollow spaces of brain aka ventricles. Produced by the choroid plexus- using
nearby blood supply within ventricles. CSF circulates through central canal of spinal cord and 4 in brain. New CSF made 3
times daily, old absorbed into blood at top of head. Never in direct contact with blood, but composition important for
diagnosing diseases aka spinal tap (fluid from subarachnoid space)
Hydrocephalus- water on the brain, bc of narrow sections in circulation system, occurs blockages. Blood supply is generous.
Carotid arteries- brain receives its nutrients through this. On either side of neck. And through vertebral arteries, base of
Then they break up into several arteries serving the brain.
CNS- Central Nervous System- brain and spinal cord. Covered in bone. Covered by 3 layers of meninges circulating with
PNS- Peripheral Nervous System- all the nerves that exit the brain and spinal cord, carrying sensory and motor messages
to and from the other parts of the body. (Not covered in bone.) only covered by 2 layers; dura and pia. No CSF within
Spinal Cord- nerve tissue that extends from medulla, down to vertebral column (bone in spine).
Neurons making up the spinal cord are found in the upper two thirds of vertebral column. Spinal cord is shorter than
vertebral column bc cord stops growing before the bones stop. Center of spinal cord is central canal. Spinal Cord divided into 5 segments: cervical, thoracic, lumbar, sacral, and coccygeal. But based on the points of exit, its
into 31 segments.
Starting at closest to the top (near the brain), 8 cervical nerves- serve the area of head, neck, and arms.
Below that, is 12 thoracic nerves- serve most of the torso (ex. heart, lung, chest, area).
Then 5 lumbar nerves- serve lower back and legs.
5 sacral nerves- serve backs of legs and the genitals. Single coccygeal nerve- most caudal (lowest) part of spinal nerves.
Spinal Cord appears white. White matter- nerve fibers aka axons; carries signals to other neurons to and from the brain.
(axons covered in myelin thats why it looks white. Its fat, so it doesnt stain like steak fat). Axons from sensory neurons
(carry information about touch, pain, temperature, position) travel up dorsal parts of spinal cord, and motor neurons
(movements) move up the ventral parts of spinal cord.
Gray matter- (gray butterfly, h thing from the inside part center of spinal cord) primarily made up of cell bodies bc it
absorbs some of chemicals used to preserve the tissue and stains it gray. The neurons found in the dorsal horns (the
lower h) reciece sensory input and ventral horns (top h) pass motor information on to the muscles (voluntary or spinal
Without receiving information from the brain, spinal cord neurons can do important reflexes ex. knee jerk aka patellar
reflex also they can protect us from injury ex. stepping on something hot or sharp producing withdrawal reflex (3
neurons, sensory, motor, and interneuron). (less neurons, the quicker the response)
Damage to spinal cord results in loss of sensation (skin and internal organs) and loss of voluntary movement in parts of
body served by nerves located below the damaged area but the muscles can be stimulated by not under voluntary
Cervical damage ex. Chris Reeves super man is quadriplegic (all 4 limbs dont work)
Lumbar damage- paraplegic (arms and torso work, not legs).
ALL spinal cord damage, lose bladder and bowel functions voluntary (input from brain to sphincter muscles dont occur)