Chapter 12: Somatic NS and Skeletal Muscles

what is a motor unit

one motor neuron innervates many muscle fibers

where do the motor signals for skeletal muscle originate?

ventral horn of spinal cord

what does acetylcholinesterase do?

found in the synaptic cleft of neuromuscular junctions, it breaks down ach into acetic acid and choline

describe EPSPs

excitatory postsynaptic potential: when neurotransmitters bind to receptors it makes the membrane more permeable to positive ions which inc the possibility of an AP

describe IPSPs

inhibitory postsynaptic potential: when neurotransmitters bind to receptors it makes the membrane more permeable to negative ions which dec the possibility of an AP

describe skeletal muscle tissue

long, multinucleated, connects to nerves, striated

describe cardiac muscle tissue

shorter, uni/bi nucleated, branched, involuntary, connected via gap junctions, have intercalated discs

describe smooth muscle tissue

short, involuntary, spindle shaped, uninucleated, connected via gap junctions

what are the muscle characteristics?

contractility = ability of protein fibers within myocytes to come together
excitability = responds to stimuli
conductivity = conduct stimulus
extensibility = can be stretched 3 times its length
elasticity = ability to return to original state

define sarcoplasm

myocyte cytoplasm

define sarcolemma

myocyte plasma membrane

what is the order of muscle groups starting from the whole muscle

muscle → fascicle → myocytes → myofibrils

what are transverse tubules

extensions of the sarcolemma that are filled with extracellular fluid

what are terminal cisternae

enlarged sections of sr that are on either side of the t tubule

what are titin filaments

elastic protein that stabilize myofibril structure and resist extra stretching

what is the a band in a sarcomere?

thick and thin filaments overlap

what is the i band in a sarcomere?

includes z disc and only thin filaments plus titin

what is the h zone in a sarcomere?

only thick filaments exist

what is the m line in a sacromere

line down the middle of the h zone that anchors thick and elastic filaments

what is the contractile unit of a skeletal muscle

the sarcomere, in between z lines

which filament moves during contraction?

actin slides along myosin

what is the function of the sr in muscle contraction

specialized er, stores and releases calcium for contraction

why do skeletal muscle cells have many nuclei and mitochondria?

to meet the energy demands for muscle contraction

how does a contraction terminate?

calcium-atpase in sr transports ca back into sr

what do sodium potassium pumps do?

help regulate resting membrane potentials

what are the three phases on a contraction form curve?

latent, contraction, and relaxation

describe isometric twitch

length of muscle doesnt change, happens when load is greater than tension

describe isotonic contraction

muscle shortens and load is lifted, tension is greater than load

what are the factors that determine regulation of force of contraction?

size of motor units, frequency coding, order of recruitment, velocity of shortening

what is the order of recruitment for motor units?

small units recruited first (slow oxidative then fast oxidative fibers) then large units (fast glycolytic fibers)

describe fast and slow twitch fibers

fast: myosin with fast calcium atpase activity that can contract and relax faster
slow: myosin with slow calcium atpase activity that contractions last 10 times longer

describe glycolytic vs oxidative fibers

glycolytic: fewer mitochondria and capillaries, large diameter, quick to fatigue
oxidative: oxidative phosphorylation, many mitochondria and capillaries, small diameter, resistant to fatigue