neuro exam 3 - motor responses

basal ganglia

collection of connected structures to coordinate movement

striatum parts

caudate nucleus + putamen

glutamate and GABA

excitatory and inhibitory

direct and indirect paths

initiate and terminate movement

direct basal ganglia pathway (cortex on)

motor cortex —> excites striatum —> inhibits globus pallidus internus/substantia nigra —> inhibits thalamus —> excitation back to motor cortex

indirect basal ganglia pathway (cortex off)

motor cortex —> excites striatum —> inhibits globus pallidus externus —> inhibits subthalamic nucleus —> excites globus pallidus (internus) and substantia nigra —> inhibit thalamus —> excites motor cortex

skeletal muscle function

voluntary movements, some involuntary (shivering, breathing, posture)

muscle fibers

bundles of fibers make up skeletal muscle

myofibrils

make up the muscle fibers which arranged by thick myosin and thin actin filaments

sarcomeres

units of contraction

neuromuscular junction

neuron can innervate multiple fibers, motor unit formed by a neuron and its fibers, and increase contraction strength

motor unit

a neuron and all the fibers it innervates

t-tubules

transverse tubules that transmit electrical impulses and enable contraction

sarcoplasmic reticulum

enclosed compartment surrounding every myofibril

purpose of Ca++ pumps in SR

maintain high calcium inside SR, storage requires energy

excitation contraction coupling

communication between electrical events occurring in the plasma membrane of skeletal muscle fibres and Ca2+ release from the SR, which leads to contraction

cross bridge formation

energized myosin heads (thick filaments) bind to actin binding sites (thin filaments), forming a physical reversable link within a sarcomere

Ca++ is dependent on

ATP

Troponin is dependent on

Ca++

Myosin is dependent on

ATP

Troponin binding sites

Ca++, Actin, Tropomyosin

tropomyosin at rest

blocks binding sites on actin

what regulates contraction

Ca++ ions, troponin, tropomyosin regulate contraction

how is inhibition that stops cross bridge formation released

when Ca++ binds to Troponin

what happens when ATP hydrolyzed to ADP and Pi

myosin head goes into cocked position

how filaments slide

Ca+ binding to troponin allows myosin heads to bind to actin, myosin heads pivot and filaments slide

sliding filament theory

muscle contraction is produced by thick and thin myofilaments sliding by one another

too much stretch

no overlap of sarcomeres produces no force

too much overlap

Z line inhibits further force

full extension of arm on chin up bar

small overlap of actin-myosin (really hard)

absence of ATP

need ATP to unbind the two proteins, rigor mortis

sliding filament hypothesis

cross bridge formation, power stroke, cross bridge detachment, reactivation of myosin head

power stroke

ADP is released and myosin head pivots causing the myofilament to slide to the center of the sarcomere

cross bridge detachment

ATP is now free to bind to the myosin head and this weakens the link between actin and myosin, myosin detaches

reactivation of myosin head

ATP hydrolyzed to ADP and Pi, released energy returns myosin head to cocked position

slow twitch muscle (red)

endurance, fatigue resistant

low ATPase activity, actin and myosin cross bridges recycle slowly

fast twitch muscle (white)

quick responses, sprinting

recycle actin and myosin cross bridges quickly via high ATPase activity

red muscle fibers

large number of mitochondria and enzymes, slow to contract, can sustain contraction

white muscle fibers

fewer mitochondria, anaerobic metabolism, contract and fatigue rapidly

fatigue-resistant fast fibers

white fibers with moderate strength and fast contractions

fast fatiguable fibers

fastest, strongest white fibers, rapidly fatiguing

slow motor units

slowly fatiguing red fibers

motor neuron pool

all the alpha motor neurons that innervate a single muscle

gamma motor neurons

innervate intrafusal fibers inside muscle spindle

stretch receptor

activated by sensory feedback from muscle spindles

gamma loop

keeps spindle taut and sensitive so it can keep firing and detecting stretch, changes set point of the stretch feedback loop, addtl. control of alpha motor neurons and muscle contraction

Ia afferent

intrafusal rapidly adapting sensory neuron sense rate of stretch

II afferents

intrafusal slowly adapting static muscle and limb position

gamma motor neurons

adjusts spindle fiber to keep it on air

alpha motor neurons

adjust muscle fibers

stretch reflex

muscle pulled, tendency to pull back

discharge rate of sensory axons

related to muscle length

reciprocal inhibition

contraction of one muscle set accompanied by relaxation of antagonist muscle

golgi tendon organs

additional proprioreceptive input, acts like strain gauge, regulates muscle tension within optimal range