Chapter 14 - Brain Flashcards
Some characteristics of the brain
- most nervous tissue located here
- 99% of all neurons in body located in CNS
- 20% of body’s blood flow goes to brain
- 100 billion neurons (1,000 times more than spinal cord)
- major integration center - control centers located in brain
- high metabolic rate
Embryonic Development of brain
Primary germ layers (16 day old after fertilization) - 3 layers
- Ectoderm
- Mesoderm
- Endoderm
Ectoderm
top layer; develops into nervous tissue & part of skin (epidermis); brain, spinal cord & nerves all come from this layer
Mesoderm
middle layer; develops into most muscle tissue (skeletal); CT; forms mesenchyme
Endoderm
develops into epithelial lining of digestive, respiratory, reproductive, urinary systems; epithelial tissue comes from ALL 3 layers
Formation of the ectoderm (beginning of the brain)
a. neural tube - ectoderm forms a long tube; upper region develops into brain & lower region develops into spinal cord
b. primary brain vesicles - upper part widens @ 3 regions
1. Forebrain - top
2. Midbrain - middle
3. Hindbrain - lower
Forebrain (embryo) develops into
- Cerebrum
- Diencephalon
(of adult brain)
Midbrain (embryo) develops into
Midbrain (of adult brain)
Hindbrain (embryo) develops into
- Pons
- Medulla
- Cerebellum
(of adult brain)
4 Major regions of brain
- Cerebrum - 83% of total brain mass
- Diencephalon - 3 parts - thalamus, hypothalamus, epithalamus
- Brain stem - 3 parts - midbrain, pons, medulla
- Cerebellum - 11% of brain mass; 2nd largest part
Protections of the Brain
- Skull bones
- Meninges - 3 CT coverings–continuous from spinal cord - dura mater, arachnoid mater, pia mater
- CSF - floats brain so it’s cushioned
- Blood-brain barrier (BBB)
Layers of meninges in brain
- NO epidural space–no layer of fat
- Dura mater–periosteal layer & meningeal layer
- Subdural space
- Arachnoid mater
- Subarachnoid space - CSF
- Pia mater - touches brain
Dura mater - 2 layers
- periosteal layer - periosteum of skull bones; fused onto dura mater; why there’s no epidural space
- meningeal layer
CSF
comes from blood; made in brain
choroid plexus
forms CSF
ventricles
spaces inside brain filled w/CSF; all connected
How CSF gets into the subarachnoid space
- CSF first enters ventricles
- 3 holes - apertures - how CSF gets into subarachnoid space
- CSF is removed by arachnoid villi
arachnoid villi
folds of arachnoid mater; comes from arachnoid mater; drains CSF out of brain into a vein
Blood-brain barrier (BBB)
endothelial cells (epithelial cells) lining capillaries in brain have many tight junctions; very impermeable barrier protects the brain from harmful substances & pathogens
Substances that cannot or poorly enter brain:
- cells
- proteins
- waste products - urea, uric acid
- most antibiotic drugs
- K+ ions - pumped out of brain by active transport; if levels too high, threshold is not maintained
Substances that can enter brain:
- glucose
- some amino acids
- some ions - Na+, Ca+ (not K+ –want to keep K+ low)
- oxygen - small nonpolar molecules; by simple diffusion
- carbon dioxide
- fats
- alcohol - lipid soluble
- anesthesia
4 Main Parts of Brain
- Brain stem
- Cerebellum
- Diencephalon
- Cerebrum
Brain stem (3 parts)
- Midbrain - top inch
- Pons - middle inch
- Medulla - bottom inch
Brain stem characteristics
white & gray matter; 3 inches long; connections to cerebellum & lots of connections to PNS; connects brain to spinal cord; 10 cranial nerves exit out of brain stem
Midbrain (brain stem)
coordinates head & eye movements; substantia nigra
substantia nigra
dark pigmented region; location of neurons that don’t work in Parkinson’s; makes dopamine; located in midbrain
Pons (brain stem)
respiratory center that moderates breathing; lots of connections to cerebellum
Medulla (brain stem)
autonomic relay center; main respiratory center-sets normal pattern of breathing; cardiac center–can change heart rate; direct connections to heart; vasomotor center - direct connections to blood vessels–changes diameter of blood vessels
Medulla- crossing over of corticospinal tracts
tracts comes from left side of brain & crosses over to right side @ medulla & supplies right side of body & vice versa; right side of brain controls left side of body & vice versa
Cerebellum
looks like a little cerebrum; white & gray matter; function–subconscious coordination of body movements; does not control it but coordinates it; posture & balance affected by cerebellum; Ipsilateral - same side; 2 hemispheres - left hemisphere coordinates movements on left side
Diencephalon (3 parts)
- Thalamus
- Hypothalamus
- Epithalamus
Diencephalon
nuclei located here; tiny part; almost all gray matter; lots of cell bodies
Thalamus (Diencephalon)
gateway to the cerebral cortex; all sensations (but smell); all receptors have to be cleared thru thalamus; sorts sensory info & relays to cerebral cortex
Hypothalamus (Diencephalon)
under the thalamus; smaller than thalamus; 2-3% of brain; visceral control center; controls ANS, responsible for water balance, regulates sleep cycles; regulates hunger; responsible for body temp; homeostasis is accomplished thru here
Hypothalamus (Diencephalon) - more info
parts of limbic system - sex drive, rage, animal instincts; endocrine glands - secretes lots of hormones which affect the pituitary gland (releases hormones); oversees pituitary gland; CONTROLS
medulla receives info from hypothalamus
& carries out instructions
ANS
beating of heart, secretion from glands
Epithalamus (Diencephalon)
main structure is pineal gland which regulates sleep; pineal gland - secretes 1 hormone–melatonin; gland gets instruction from hypothalamus
Cerebrum
largest part of brain; 2 halves - cerebral hemispheres - left & right - symmetrical
convolutions
folds & creases of surface; grew rapidly; increases surface area - more blood vessels
3 types of convolutions
- gyrus - upward fold; ridge
- sulcus - groove; downward fold
- fissure - deep groove
longitudinal fissure
divides left & right cerebral hemisphere; deep fold
transverse fissure
divides cerebrum from cerebellum
central sulcus
divides frontal & parietal lobes
parieto-occipital sulcus
divides parietal & occipital lobes
lateral sulcus
divides temporal lobe from frontal & parietal lobes
5 Lobes
- Frontal
- Parietal
- Occipital
- Temporal
- Insula - deep to lateral sulcus