Muscle Physiology L1: Muscle Contraction Flashcards
What are the 3 types of muscles?
- Skeletal
- Cardiac
- Smooth
What is skeletal muscle?
- Controlled by somatic NS
- Voluntary
- Striated
- Organization of contractile proteins (in cell)
Skeletal muscle is controlled by the _____ NS.
somatic
Skeletal muscle is _____ (voluntary/involuntary).
voluntary
Skeletal muscle is _____ (striated/unstriated).
striated
Skeletal muscle as a organisation of _______ proteins (in cell).
contractile
What is cardiac muscle?
- Influenced by autonomic NS
- Parasympathetic and sympathetic neurons
- Involuntary
- Striated
Cardiac muscle is influenced by the _____ NS.
autonomic sympathetic and parasympathetic
Cardiac muscle is _____ (voluntary/involuntary).
involuntary
Cardiac muscle is _____ (striated/unstriated).
striated
What is smooth muscle?
- Influenced by autonomic NS
- Parasympathetic and sympathetic neurons
- Involuntary
- Unstriated
Smooth muscle is influenced by the _____ NS.
autonomic sympathetic and parasympathetic
Smooth muscle is _____ (voluntary/involuntary).
involuntary
Smooth muscle is _____ (striated/unstriated).
unstriated
Muscle cells contain many parallel _______.
Myofibrils
Why is mitochondria important in muscle cells?
- ATP plays a massive role in contractions.
- ATP produced by power house (mitochondria)
Skeletal muscle activity is controlled the ______ motor neurons.
somatic (spinal cord/brainstem)
What is a motor unit?
One motor neuron + muscle cell (it targets/innervates)
How is an action potential generated in a muscle cell?
Step 1: Neuromuscular junction
- A type of chemical synapse
- ACh acts on nicotinic receptor –> end plate potential
- Which always triggers an AP (muscle cell)
- Voltage-gated Na2+ channels –> start in adjacent membrane
Step 2 and 3: AP enters T tubule and triggers Ca2+ release from sarcoplasmic reticulum into skeletal muscle cell
Step 2:
- AP has to travel through many layers
- To propel AP (as fast as possible) tubules
Step 3:
- Sacroplasmic reticulum sits next to myofibrils
- Myofibrils- thick and thin filaments
What is step 1 of how an action potential is generated in a muscle cell?
Step 1: Neuromuscular junction
- A type of chemical synapse
- ACh acts on nicotinic receptor –> end plate potential
- Which always triggers an AP (muscle cell)
- Voltage-gated Na2+ channels –> start in adjacent membrane
What is step 2/3 of how an action potential is generated in a muscle cell?
Step 2/3: AP enters T tubule and triggers Ca2+ release from sarcoplasmic reticulum into skeletal muscle cell
Step 2:
- AP has to travel through many layers
- To propel AP (as fast as possible) tubules
Step 3:
- Sacroplasmic reticulum sits next to myofibrils
- Myofibrils- thick and thin filaments
What is a sacromere?
Basic contractile unit in skeletal muscles
What is the sliding hypothesis in a sacromere?
- Actin slide over the myosin
- Each time this occurs, the actin moves close and closer
In a sarcomere without ATP, relaxation ____ (occurs/can’t occur)
can’t occur
- Eg. when dead –> can’t relax (rigor mortis)
What is the Z line in a sacromere?
Slightly darker bands
What is a power stroke? (How do muscles contraction?)
Calcium ions triggering actin and myosin interaction resulting in POWER STROKE.
- There is a specific sequence of events that results in the excitation contraction coupling
What are the 7 steps of a muscle contraction (power stroke)?
- Action potential enters the T-tubule
- AP then activates the sarcoplasmic reticulum to release Ca2+
- Ca2+ binds to troponin
- Troponin-Ca2+ complex pulls the tropomyosin exposing the binding sites on actin
- Myosin heads bind to actin and with the release of Pi from ADP, Myosin head bends resulting in the power stroke
- New ATP binds to Myosin head releasing the bond between Myosin and Actin
- Ca2+ is pumped back into the SR
What is step 1 of a muscle contraction (power stroke)?
- Action potential enters the T-tubule
What is step 2 of a muscle contraction (power stroke)? (After AP enters T-tubule)
- AP then activates the sarcoplasmic reticulum to release Ca2+
What is step 3 of a muscle contraction (power stroke)? (After Ca2+ is released)
- Ca2+ binds to troponin
What is step 4 of a muscle contraction (power stroke)? (After Ca2+ binds to troponin)
- Troponin-Ca2+ complex pulls the tropomyosin exposing the binding sites on actin
What is step 5 of a muscle contraction (power stroke)? (After tropomyosin exposes the binding sites on actin)
- Myosin heads bind to actin and with the release of Pi from ADP, Myosin head bends resulting in the power stroke
What is step 6 of a muscle contraction (power stroke)? (After myosin bind with actin to produce the power stroke)
- New ATP binds to Myosin head releasing the bond between Myosin and Actin
What is step 7 of a muscle contraction (power stroke)? (after the bond between actin and myosin is released )
- Ca2+ is pumped back into the SR
What is cross bridging cyling?
- 6 actin filament
- 6 array of heads (myosin) –> attach –> pull actin filament –> sarcomere shortens
What are the 4 mechanisms of neurotransmission release in the excitation-contraction coupling in skeletal muscles?
- Action potential in motor neuron
- Release of ACh at the neuromuscular junction
- ACh action at nicotinic receptors (post-synaptic membrane) triggers an end-plate potential
- AP initiated in skeletal muscle membrane
- If released threshold potential- potential that activates voltage
What are the 5 mechanisms of muscle contraction in the excitation-contraction coupling in skeletal muscles after the 4 mechanisms of neurotransmission release?
- AP enters T-tubules
- Ca2+ release from sarcoplasmic reticulum
- Ca2+ triggers crossbridge cycling
- Sarcomeres shorten
- Muscle contracts
How does cellular structure affects skeletal muscle function?
Increased contraction –> up to a point –> then starts to decrease contraction
What happens at A?
Max no. of contraction
What happens at B?
Active sites away from possible myosin heads = few interaction = decreased tension
What happens at C?
- No interaction between actin and myosin
- Eg. cardiac failure
- Actin and myosin are further away
- Hard to empty blood as decrease tension
- Heart expands more
- Cycle continues
What happens at D?
- Pushed together
- Actin sites don’t align = decreased tension
What are intrafusal fibres?
- Have stretch receptors –> stretched
- AP form a code to spinal cord
What are extrafusal fibres?
- Alpha motoneuron (shortening)
- Stretch receptors= signals to brain
What are GTO afferents?
- Sensory axons
- Interweaved collagen fibres
- Close to tendon
- Acts as a relive value when too much tension in muscle
In a muscle, the more it stretches = _____(more/less) AP
more
In a muscle, the more it relaxes = _____(more/less) AP
less
Stretch receptors are activated by _______ motor neurons.
Gamma
What is a stretch receptor reflex? (using quads- monosynaptic and polysynaptic reflex)
Monosynaptic reflex –> quad muscle contraction –> bring back to approx. length
Polysynaptic reflex –> inhibits (contraction) of semitendinosus from flexing
Both occur at the same time
How does is ATP produced in skeletal muscles?
