Lecture 17

Question 1

Describe the neural arrangement before innervation of the skeletal muscle

Answer 1

Cranial nerves leave brainstem to innervate skeletal muscle
Interneurons go from motor cortex, cross midline at the pyramids in the medulla and down corticospinal tracts and synapse with motor neurons in the ventral horn

Question 2

Describe the neuromuscular junction

Answer 2

motor end plate = membrane of muscle with high concentration of Ach receptor, invaginations to increase surface area
Nicotinic receptor = mixed receptor (allows Na and K and Ca to flow)

Question 3

Describe the motor unit

define a bundle of muscle fibers

Answer 3

one neuron + all muscle fibers innervated

bundle of muscle fibers = fascicle

Question 4

Describe a muscle fiber

Answer 4

multinucleated cells
has thick (myosin) and thin (actin) filaments
lots of mitochondria
SR associated to invaginations of the sarcolemma (t-tubules)

Question 5

Describe a myofibril

Answer 5

bulk of intracellular space
made of sarcomeres = contractile unit of myofibril between Z-disks
z-disk = where actin connects
M-line = where myosin connects
A band = length of myosin filaments
I band = region of actin filament where there is no overlap
H-band = region of myosin filament where there is no overlap

Question 6

Describe the actin myosin binding complex

Answer 6

myosin has two heads, each head has one ATP, one actin binding spot
myosin has flexible head, rigid tail, and hinge joint regions
actin is globular protein, polymerizes into F-actin
each actin has one myosin binding site
thin filament = 2 intertwined f-actin strands

Question 7

What are the other four proteins in a myofibril besides actin and myosin and what is their function?

Answer 7

titin = elastic, stretches from Z-disk to M-line, helps pull sarcomere back to original length
nebulin = within actin to stabilize, only attaches to Z-disk
troponin = trimeric, binds to tropomyosin, has 2 Ca2+ binding sights
tropomyosin = dimer, lies along actin and covers up myosin binding sites