Unit 19 - Nervous System pt. 2 (protective features, brain)

- Bone: skull and vertebral column

- Meninges: CT around brain and spinal cord

- Cerebrospinal fluid (CSF): surrounds brain and spinal cord

- Blood brain barrier (BBB)

- Cerebral Arterial Circle: cerebral arteries form circle at base of forebrain

- dura mater (outer)

- arachnoid mater (middle)

- pia mater (inner)

- on brain it has 2 fused layers separated in some places to form  spaces which are called venous (dural) sinuses and contain blood

- on spinal cord it has 1 layer

- deep to dura mater is subdural space filled with ISF

- superficial to dura mater is epidural space (spinal cord only) filled with fat, blood vessels, CT, etc.

- middle layer of the meninges

- avascular

- has arachnoid granulations (brain only) that project into dural sinuses

o   CSF enters granulations to return to blood

subarachnoid space:

o   contains cerebrospinal fluid

o   web-like strands of CT secure it to pia mater below

- inner layer of the meninges

- on surface of CNS (brain and spinal cord)

- vascular

- inflamation of meninges

—  surrounds brain and spinal cord

—  in brain ventricles and central canal of spinal cord

—  cushions CNS – brain buoyant

—  formed from blood plasma (similar composition)

—  produced by choroid plexuses (blood capillaries) found in each ventricle

- spaces inside brain  (filled with CSF)

- 2 lateral ventricles (1^st and 2^nd) – in cerebrum

- 3^rd ventricle = in diencephalon

- 4^th ventricle = surrounded by pons, medulla oblongata, cerebrum

- endothelial cells (of capillaries) with tight junctions

- astrocytes – foot processes wrap around endothelial cells

- selectively permeable

- allows: glucose, fat soluble material

- not toxins, antibiotics, etc.

- cerebral arteries form circle at base of forebrain

o   circles pituitary gland and optic chiasma (where optic nerves cross)

o   unites the two major blood supplies to the brain (anterior and posterior)

o   provides an alternate route for blood if  vessels blocked

limbic system and reticular formation

—  nuclei in cerebrum and diencephalon

—  regulates emotions (laughing, crying, etc.)

—  contains areas involved in memory (memories evoke emotional responses)

—  nuclei in brain stem

—  cortex, thalamus, and hypothalamus are involved (together form RAS = Reticular Activating System)

—  regulates alertness and attention

— filters stimuli, so only sends new/unusual signals to other brain areas           

—  sleep results when inhibited

—  if damaged = coma

forebrain, diencephalon, midbrain, and hindbrain

the right and left cerebral hemispheres

- named after their overlying bones:

- frontal lobe

- temporal lobe

- parietal lobe

- occipital lobe

- insula (deep to temporal lobe)

- fissures (deep grooves)

- gyri (ridges)

- sulci (shallow grooves that separate gyri)

- longitudinal fissure: separates right and left cerebral hemispheres

- transverse fissure: separates cerebellum and cerebrum

- lateral fissure: separates temporal lobe from rest of cerebrum

o   postcentral gyrus in parietal lobe

o   precentral gyrus in frontal lobe      

o   central sulcus – between frontal and parietal lobes

- cerebral cortex (2 - 4mm thick, grey matter)

- tracts (white matter)

- basal nuclei

motor areas, sensory areas, association areas, and others like memory (temporal lobes) and conscious intellect (personality, learning, ideas, etc.) in the prefrontal cortex

—  all in frontal lobe

—  control skeletal muscle movement

—  3 regions: primary motor area (precentral gyrus), premotor area, Broca’s area (motor speech)

- general sensory area (pain, touch, temp, pressure): postcentral gyrus in parietal lobe

- vision: occipital lobe

- auditory and olfaction: temporal lobe

- taste and visceral sensation (e.g. full bladder): insula

—  recognize info from memories: parietal, occipital, temporal lobes

- association tracts: from gyrus to gyrus in same hemisphere

- commissural tracts: from gyrus to gyrus in opposite hemispheres e.g. corpus callosum

- projection tracts: run vertically (brain to spinal cord / spinal cord to brain)

—  paired masses of gray matter (within white matter)

—  control skeletal muscle movement

- all grey matter

- 2 parts: thalamus and hypothalamus

—  2 lobes connected by intermediate mass (bridge through 3^rd ventricle)

—  relay station for impulses coming to cortex (from spinal cord)

—  inferior to thalamus, above pituitary

—  major regulator of the internal environment (visceral control) e.g. blood pressure, heart rate

—  connects pons and diencephalon

—  contains cerebral aqueduct

- anterior portion: cerebral peduncles (projection tracts)

- posterior portion: 4 nuclei = corpora quadrigemina

o   2 superior colliculi: visual reflexes

o   2 inferior colliculi: hearing

midbrain, pons, medulla

— part of the hindbrain

—  anterior to cerebellum

—   tracts between brain and spinal cord, and tracts to/from cerebellum

—  pontine respiratory centres

—  part of the hindbrain and inferior to pons

—  ends at foramen magnum

—  2 bulges (called pyramids) are large motor tracts (part of corticospinal tracts) just above spinal cord is the decussation (crossover) of pyramids

—  3 vital centres in medulla: cardiac, vasomotor (blood vessels), respiratory

—  several non-vital centres for swallowing, sneezing, vomiting

—  part of hindbrain and posterior to pons/medulla

—  has folds similar to gyri named folia

—  cortex is gray matter

—  arbor vitae (deep to cortex) is white matter

—  coordinates skeletal muscle contraction for balance and posture

- 2 bulges (called pyramids) are large motor tracts (part of corticospinal tracts)

- the X, just above spinal cord, is the decussation (crossover) of pyramids