Brain Physiology

CBF

regulated, continuous blood flow that depends on arterial/ venous/ intercranial pressure, diameter, viscosity (65-140 mmHg)

autoregulation

constant CBF despite changes in perfusion pressure

MAP

drives blood into brain; dilate for more blood flow, constrict for less

ICP and mean venous pressure

oppose and regulate CBF by balance perfusion and prevent vessel rupture; inc ICP→compress vessel→dec blood flow

why the brain needs CBF

O2/glucose supply, high energy demand, waste removal, protection/regulation

clenching right hand

inc flow in left motor cortex → inc flow throughout brain

physical movements of speaking

inc flow to upper premotor → inc flow in left/ categorial hemisphere

reading

widespread inc in CBF

problem solving & reasoning

inc flow in selected premotor/ frontal cortical areas

spatial tasks (right handed)

inc flow in right hemisphere

verbal tasks (right handed)

inc flow in left hemisphere

cerebral capillaries

tight junctions between endothelial cells, selectively regulate substance movement, restrict paracellular movement

astrocytes

surround cerebral capillaries, develope and maintain endothelial tight junctions, support

circle of willis

provides limited collateral (b/w hemispheres) blood flow but does not guarantee it (after occlusion)

carotid artery occlusion

cerebral ischemia; particularly when collateral circulation is inadequate

cerebral artery occlusion

infarction (tissue death)

BBB

partnership b/w cerebral capillary tight junction endothelial cells, astrocytes and choriod plexus to control movement of substances b/w blood, brain tissue, CSF

BBB functions

maintain safe environment for CNS neurons, limit harmful substance, influence drug delivery; altered during disease or infancy

choroid plexus

epithelial tight junction controls substnaces entering CSF, barrier b/w blood and CSF

arterial blood supply to brain

2 internal carotid and 2 vertebral arteries contribute to circle of willis for cerebral circulation

carotids

supply ipsilateral cerebral hemisphere

venous drainage

dural sinuses to internal jugular

sympathetic innervation of large cerebral vessels

influences vascular tone→vasoconstrict to limit CBF and protect BBB

neurovascular coupling

active brain regions receive increased local blood flow to meet metabolic demands- regional blood flow

can easily cross BBB

water, CO2, O2, free lipid soluble steroid hormones

p-glycoprotein

pumps drugs/ peptides back into blood

circumventricular organs (CVO)

outside of BBB, fenestrated capillaries allow circulating substance to influence brain function

posterior pituitary and median eminence

hormone secretion

area postrema

blood-borne toxin detection→vomiting

organum vasculosum (OVLT)

initiate fever/ sickness response, blood monitoring→osmolarity

subfornical organ (SVO)

blood monitoring→salt

somatic motor control output

spinal a-motor neuron and motor neurons in cranial nerve nuclei are the final common pathways to skeletal muscle

major functions of motor control

voluntary movement, smooth/ precise movement, postural control

voluntary movement control

corticospinal and corticobulbar

postural control

descending brain stem and peripheral sensory info

cerebellum

receives info→compares→refines→corrects; produces smooth, accurate, coordinated movement

purkinje

inhibitory, only output from cerebellum

cerebellar circuit

mossy/ climbing fibers→cerebellar cortex→purkinje→deep cerebellar→brainstem/thalamus

planning/ organization of voluntary movement

basal ganglia and cerebrocerebellum

afferent fibers

dorsal roots/ cranial nerves (AP)

efferent fibers

ventral root/ motor cranial nerves (AP)

reflex arc

sensory receptor→afferent→CNS→efferent→effector; involuntary but can be modified by higher brain

signal processing graded potential

determines if AP occurs or not; occurs at receptor: graded receptor potential or CNS synapse: graded EPSP/ IPSP

signal processing NMJ

EPSP/IPSP graded response→muscle AP→contraction

control of voluntary movement

cortex, basal ganglia, cerebellum; plan and organize movement

plan and execute movement

brain plans, coordinates joints, compares planned vs actual

brainstem pathways

posture and coordination: rubrospinal, reticulospinal, tectospinal, vestibulospinal

spinocerebellum fibers

receives sensory feedback during movement; adjust, smooth and coordinate move

supplementary motor area (SMA)

plans; organize and sequence complex voluntary movement

premotor cortex

prepares body/ sets posture for planned movement (how do i move to get it?)

primary motor cortex (M1)

execute; final cortical commands for voluntary move, precise body map (motor homunculus), sends signals corticobulbar/spinal

posterior parietal cortex

receives and integrates sensory input; hand-eye coordination, aim hand toward object, learned movement (where is everything?)

motor cortex plasticity

motor cortical maps change w/ experience; motor learning and recovery

basal ganglia

movement-control network; receives information, process/ balance motor signals, influences motor cortex through the thalamus to help produce appropriate voluntary movement

indirect pathway

limits unwanted movement; D2→GPe→STN→GPi/ SNr→inhibition of thalamus→cortex supressed

direct pathway

promotes movement; D1→GPi/SNr→disinhibit thalamus→cortex activated

climbing fibers

strong excitation of single purkinje; correcting/ teaching

mossy fibers

weak excitation of many purkinje; information