Physiology exam 2 skeletal muscle structure

thick, thin

muscle contraction is caused by interaction of ____ and ____ filaments

F-actin

Thin filament, two twisted rows of globular G-actin, active sites of G-actin strands bind to myosin

Tropomyosin

Thin filament, double-stranded, prevents actin-myosin interaction

Troponin

Thin filament, globular protein, binds to tropomyosin to G-actin, controlled by Ca2+

thick filaments

contain twisted myosin subunits

contain titin strands that recoil after stretching (spring)

myosin tail

part of myosin that binds to other myosin

myosin head

part of myosin that reaches the nearest thin filament

sliding-filament model

proteins do not shorten, they slide past one another

crossbridge cycle

the interaction between the myosin and action that creates tension

binding of myosin to actin

step 1 of the crossbridge cycle

power stroke

step 2 of the crossbridge cycle

Ca2+ interacts with troponin

binding sites become available when

rigor

step 3 of the crossbridge cycle

unbinding of myosin and actin

step 4 of the crossbridge cycle

ATP binding

in step 4 of the crossbridge cycle, what causes the detachment?

cocking of myosin head

step 5 of the crossbridge cycle

several

each motor neuron innervates ______ muscle cell(s)

one

each muscle fiber receives input from ____ motor neuron(s)

Acetylcholine

What is released from the synapse of the neuromuscular junction

always

Motor neuron action potential ______ creates a muscle cell action potential

no Ca2+

Describe Ca2+ in the crossbridge cycle when: troponin holds tropomyosin over active binding sites on actin, no crossbridges form between actin and myosin, and the muscle is relaxed

Ca2+ present

Describe Ca2+ in the crossbridge cycle when: binds to troponin, causing movement of troponin, causing movement of tropomyosin, exposing active binding sites on actin, crossbridges form between actin and myosin, the cycle occurs and muscle contracts

step 1

which step of excitation-contraction coupling: action potential in the sarcolemma

step 2

which step of excitation-contraction coupling: action potential down T tubules

step 3

which step of excitation-contraction coupling: DHP receptors/ryanodine (voltage-gated Ca2+ channels) of T tubules open Ca2+ channels in the lateral sacs of SR

step 4

which step of excitation-contraction coupling: Ca2+ increases in the sarcoplasm, causing Ca2+ to bind to troponin, shifting to tropomyosin

step 5

which step of excitation-contraction coupling: crossbridge cycling occurs

sarcoplasm

cytoplasm of the skeletal muscle fiber

DHP receptors and ryanodine receptors

Action potentials in the T tubules can open channels in the sarcoplasmic reticulum (SR) due to which two physically linked receptors?

T tubule membrane

Where do you find DHP receptors?

voltage sensor

DHP receptor function?

in the SR membrane

Where do you find ryanodine receptors?

calcium channels

Ryanodine receptor function?

step 6

Which step of the cross-bridge cycle is this (termination of contraction): Ca2+ is removed from the sarcoplasm (lowers concentration). Ca2+-ATPase into the SR, transports Ca2+ from the sarcoplasm into the SR (recycles), Ca2+ detaches from troponin

step 7

which step of the cross-bridge cycle is this (termination of contraction): Tropomyosin is able to cover myosin binding sites on actin

primary active transport

What kind of transport is used in step 6 of the cross-bridge cycle (termination) with Ca2+-ATPase