skeletal muscle Flashcards
skeletal muscle is the effector of what?
somatic subdivision of the efferent branch of the peripheral nervous system
is skeletal muscle under voluntary or involuntary control?
voluntary
define sarcolemma
cell membrane around myofilaments
define sarcoplasm
it is the cytoplasm of a muscle cell
define T-tubules
invagination of sarcolemma helps to propagate cell - rapid and efficient conduction of the wave of depolarization from sarcolemma to sarcoplasmic reticulum
define muscle fiber
are individual muscle cells
define myofilament
contractile unit (myosin and actin)
Why do muscle cells have a synapse between the motor neuron and muscle fiber?
the neuromuscular junction is required to create a contraction
what is the functional unit of muscle?
sarcomere
why is the synapse (neuromuscular junction) important
ensures directionality
what neurotransmitter is released from the motor neuron synapsing with the muscle fiber at the neuromuscular junction
acetylcholine
Once acetylcholine moves through the junction and binds to receptors on the sarcolemma, what type of channels are opened?
Na+ chemically gated channels
once Na+ chemically gated channels open, is an action potential automatic?
No, if stimulus is less than threshold = graded potential
what structure of skeletal muscle facilitates rapid and efficient propagation of the action potential from sarcolemma to the sarcoplasmic reticulum?
T-Tubules
what ion is released from the sarcoplasmic reticulum once the wave of depolarization reaches it?
Ca2+
is the movement of Ca2+ from the SR into the sarcoplasm via active transport or diffusion?
diffusion
if Ca2+ can diffuse from the SR into the sarcoplasm, what does that tell you about the difference in concentration between these two environment?
Ca2+ wants to move from high -> low concentration (more calcium in SR than sarcoplasm)
what are the three molecules that make up the actin myofibril?
- troponin
- tropomyosin
- actin
what molecule does Ca2+ bind to?
tropomyosin
which molecule moves when Ca2+ binds to expose and active myosin binding site on the actin myofilament
troponin
before myosin can bind to active actin binding site, it must be in a high energy state, what state is necessary to convert it its high energy state so that it can attach to the myosin binding site on actin?
ATP must be hydrolyzed (ADP + P)
what event must occur before the myosin head detaches from the actin binding site during relaxation?
ATP binds to myosin
what does rigor mortis occur?
No ATP is present to help re-uptake calcium back into SR and detach myosin head. Muscle contraction continues because Ca2+ is still present
define multiple motor unit summation
increasing the number of motor units contacting simultaneously
define wave summation
increasing the frequency of contraction
how many motor units are activate for a threshold stimulus?
theoretically only one is needed
how does an organism vary its strength of muscle contraction?
varying the number of motor units recruited using multiple motor unit summation
