Skeletal Muscle Flashcards
what is the electricity from neurotransmitters (action potentials) called
bioelectricity
order of muscle fibres largest to smallest
muscle, fascicle, cells (myofibres), myofibrils, myofilaments (actin and myosin)
sarcolemma
surrounds each myofibre acting as a barrier and keeping it all together (cell membrane)
sarcomere
comprised of filaments, contractile unit
t-tubules
extensions of the sarcolemma that dive deep into the muscle
sarcomeres are _____ muscle (not meaning skeletal)
striated
is actin thin or thick filament
thin
is myosin thin or thick filament
thick
when you work at the gym what are you doing to myofibres
increasing the size of them (building more sarcomeres inside them) and building more myofibres
a motor unit is comprised of
a motor neuron and all the muscle fibres it innervates
where are the somas of the motor neurons
in the anterior part of the spinal cord
each axon innervates one or multiple
myofibres
ions require ___ and a __ to diffuse across the cell membrane
channels, gradient
RMP
-70mV, established by the Na+/K+ ATPase pump
cells establish an electrochemical gradient using
Na+/K+ ATPase pump which pumps ions against their electrochemical gradient
high Na+ concentration ___ the cell
outside
high K+ concentration ___ the cell
inside
voltage gated ion channels are ___ when the RMP is -70mV
closed
voltage gated Na+ channels open when the voltage is
-60mV
voltage gated K+ channels open when the voltage in
+30mV
early depolarisation
input into the cell causes the threshold to reach -60mV and Na+ enters the cell down its electrochemical gradient
depolarisation
Na+ enters the cell until the membrane potential reaches +30mV
repolarisation
at +30mV the voltage gated Na+ channels close and the voltage gated K+ channels open. this allows K+ to leave the cell down its electrochemical gradient
hyperpolarisation
as K+ leaves the cell, the inside of the cell becomes more negative and when the voltage reaches -40mV the voltage gated K+ channels begin to slowly close. when -80mV is reached the voltage gated K+ channels close
resting membrane potential (after hyperpolarisation)
both voltage gated Na+ and K+ channels are closed, the Na+/K+ ATPase pump re-establishes the -70mV RMP
refractory period
not able to generate another action potential during this period. the voltage gated Na+ channels are either already open (causing depolarisation) or inactive (during hyperpolarisation)
chemically gated ion channels
require neurotransmitter to bind to the receptor for it to be opened
excitatory nuerotransmitter
Na+ enters the neuron and brings the membrane potential close to threshold (depolarising)
inhibitory neurotransmitter
Na+ leaves neuron, moves the membrane potential further away form threshold (hyper polarising)
cells usually have a combination of ___ and ___ nuerotransmitters
excitatory and inhibitory
integration at the axon hillock
if the combination of excitatory and inhibitory local potentials reach the threshold an action potential will fire
local potentials use __ gated ion channels
chemically
action potentials use __ gated ion channels
voltage
myelin in the PNS is made by
Schwann cells
at the synapse, the control goes from __ at the action potential, __ at the neurotransmitter and __ at the next action potential
electrical, chemical, electrical
depolarisation of axon terminal in synaptic junction causes
voltage gated Ca2+ channels to open and Ca2+ enters axon terminal
fourth step of output of the synaptic junction, after neurotransmitter diffuses across synaptic cleft
neurotransmitter binds to its receptor (chemically gated ion channel) on the post-synaptic membrane
fifth step of output in the synaptic junction, after neurotransmitter binds to receptor (chemically gated ion channel)
Na+ enters the post-synaptic cell and depolarises it
chemically gated ion channels exist in the ___ and cause __
dendrites and soma, local potentials
voltage gated ion channels exist in the __ and cause ___
axon hillock, axon and axon terminals, action potentials
what is excitation-contraction coupling
excitation, contraction and relaxation of the muscle
first step of excitation (NMJ)
depolarisation of axon terminal causing voltage gated Ca2+ channels to open and Ca2+ enters axon terminal
second step of excitation (NMJ), after Ca2+ enters axon terminal
Ca2+ triggers neurotransmitter (ACh) release from vesicles into the synaptic cleft
third step of excitation (NMJ), after neurotransmitter release into synaptic cleft
ACh diffuses across synaptic cleft
fourth step of excitation (NMJ), after ACh diffusion across synaptic cleft
ACh binds to ACh-receptor (chemically gated Na+ channel) on the motor end plate of the myofiber
fifth step of excitation (NMJ), after ACh binding
Na+ enters the myofiber, increasing the membrane potential from -70 to -60 (depolarisation)
sixth step of excitation (NMJ), after depolarisation
action potential propagates along the sarcolemma of the myofiber
what happens after an action potential propagates along the sarcolemma
the sarcolemma dives into the t-tubule, action potential is sent here, initiating Ca2+ release from the SR
what happens after Ca2+ is released from the SR
Ca2+ from the sarcoplasm diffuses to the myofilaments initiating cross bridge cycling, sarcomere shortens and muscle contracts
what processes are involved in the relaxation of muscles
Ca2+ in the sarcoplasm diffuses away from the myofilaments and the Ca2+ is re-uptaken into the SR, this consumes ATP and stops cross bridge cycling
what occurs in the cross bridge formation of the cross bridge cycling process
Ca2+ binds to troponin, moving tropomyosin of myosin binding sites (on actin) and myosin binds to actin
what happens in the power stroke of cross bridge cycling
ADP + Pi dissociates (separates) from myosin and the myosin head flexes (power stroke) sarcomere shortens and tension is developed
what processes occur when the cross bridge detaches
ATP binds to myosin head causing it to detach from actin
what happens for the myosin head to reactivate
ATP is hydrolysed into ADP + Pi and the myosin head is ‘recocked’ into an active state
length-tension relationship, short
overlap between actin and myosin is too much and the myosin cannot effectively move the Z-lines closer together, can’t get any closer, no shortening possible
length-tension relationship, wide
myosin cannot effectively bind to actin to create cross bridges as they are too far apart
length-tension relationship, medium
all myosin heads can attach to the actin and can get maximum contraction
the amount of tension a muscle can produce is proportional to the
frequency of its stimulation
a single action potential produces a short duration of contraction
twitch
as the frequency of action potentials increases the amount of tension produced also increases, this is called
summation
force produced by a fibre at its maximum, this is called
tetanic contraction (tetanus)
when is summation created
when a fibre is stimulated causing Ca2+ to be released before the remaining Ca2+ is re-uptaken and the fibre can relax, the subsequent contraction develops a higher tension due to the extra Ca2+ present, if this keeps happening the tension will increase consecutively
what is incomplete tetanus
a muscle fibre producing maximum tension during rapid cycles of contraction and relaxation, still some Ca2+ being removed from sarcoplasm between stimuli
what is complete tetanus
when relaxation phase is eliminated by higher frequency stimuli, no time for Ca2+ to be removed from sarcoplasm between stimuli
what does activation of different motor units in turn (rotating basis) allow
recovery of some motor units, maintaining whole muscle tension and preventing muscle fatigue
a single twitch will only occur in
ocular muscles
what is an isometric contraction
muscle remains the same length while developing tension
what is an isotonic contraction
muscle length shortens or lengthens while developing tension
what is a concentric contraction
muscle length shortens while contracting
what is an eccentric contraction
muscle length lengthens while contracting
what energy source is used in the first 6 seconds of exercise
ATP storage
what energy source is used between 6-10 seconds of exercise
Creatine posphate
what energy source is used from 30-40 seconds of exercise
Anaerobic
what energy source is used for prolonged exercise
Aerobic
what are the three fibre types
fast, intermediate, slow
what is the main energy source of fast twitch fibres
anaerobic glycolysis
what is the energy source of intermediate fibres
mixture of aerobic and anaerobic energy sources
what is the protein that carries oxygen in muscle cells
myoglobin
what muscle fibre type has the most myoglobin
slow twitch
what is the main energy source of slow twitch fibres
oxidative phosphorylation
