Skeletal Muscle Flashcards
what is the neuromuscular junction
where the neuron connects to the muscle
What happens at the neuromuscular junction
- The action potential reaches the terminal bouton of axon
- voltage gated calcium channels open up which stimulates the release of the neurotransmitter ACH
- ACH binds to the nicotinic cholinergic receptor, which allows for Na+ to enter the muscle cells
- this causes an action potential in the muscle fibers
What is the motor end plate
a specialized region of the muscle fibers plasma membrane with many nicotinic cholinergic receptors
What is the neurotransmitter used in the neuromuscular junction
Acetycholine, the only neurotransmitter in the somatic nervous system
what ion channels play an important role in excitation of muscle fibers
voltage gated calcium channels (release ACH) Cation channels (allow for depolarization of muscle)
What does acetylcholinesterase do
it breaks down the ACH in the synaptic cleft
Where is acetylcholinesterase located
between the invaginations of the motor end plate
Why is acetylcholinesterase important
breaking down the ACH terminates the excitatory signal and causes the muscle to relax
once an action potential is generated in muscle where does it spread
over the muscle fiber sarcolemna in all directions
what is excitation-contraction coupling
it’s the sequence of events that connects the excitation of muscle fibers to their contraction
what is a T-tubule
invaginations in the sarcolemna that extend deep into the muscle fibers and run along the myofibrils
What is the sarcoplasmic reticulum
smooth ER that stores calcium which is necessary for muscle contraction
What are the steps of Excitation-contraction coupling
- ACH is realeased from neuron which causes depolarization of the muscle fiber
- the action potential runs down the sarcolemna and dives down into the T-tubules
- in the T-Tubules the DHP receptor is activated by the action potential
- the DHP receptor pulls on the Ryanodine receptor.
- the Ryanodine receptor opens, allowing calcium to leave the sarcoplasmic reticulum
- Calcium binds to troponin exposing the myosin binding sites on actin
- crossbridge cycle leads to muscle contraction
- Ca+ is pushed back into sarcoplasmic reticulum by Ca+ ATPase pumps
- tropomyosin blocks the myosin binding sites on actin
- muscle relaxes
What is the organization of skeletal muscle from largest to smallest
- Muscle
- Fascicle
- muscle fiber (myofiber)
- myofibril
- Sarcomere
- Myosin
- Actin
What is a fascicle
A bundle of muscle fibers
what is a muscle fiber
an individual muscle cell, made up of many myofibrils
What is a myofibril
a rodlike thing in a muscle cell that houses the sarcomere and is surrounded by the sarcoplasmic reticulum
What is a sarcomere
it’s the functional unit of muscle. It’s made up of myosin and actin
What are the bands/zones/lines on the sarcomere (name and what makes them)
- A band - Where any myosin is found (DARK)
- I band - where ONLY actin is found (Light)
- H zone - Where ONLY myosin is found (Medium)
- M line - scaffolding protein holding myosin together
- Z line - scaffolding protein holding actin together
how do we define one sarcomere
area from one z line to another.
What happens to sarcomere zones/lines/bands during contraction
- A band doesn’t change
- I band shrinks
- H zone shrinks
- M line stays stationary
- z lines move closer together`
What causes muscle to look striated
the bands and zones of the sarcomere
What are the layers of connective tissue in skeletal muscle
connective tissue wraps up each muscle fiber, fascicle, and surrounds the whole muscle. When the muscle contracts it pulls on the connective tissue around it, which pulls on the tendon (where all of the connective tissue meets up) and pulls the bones closer together.
What is cross bridge cycling
its the interaction between actin and myosin and how it all works
what role does calcium play in cross bridge cycling
calcium binds to troponin which pulls tropomyosin off of myosin binding sites of actin allowing myosin heads to bind and cause contraction
What is the thick filament
Myosin
What is Myosin made of
Many myosin proteins
how many thin filaments surround one thick filament
6
Does Myosin use ATP
yes, it breaks it down and releases the energy
What is the thin filament
Actin
What is actin made up of
Many actin molecules (with myosin binding sites)
Troponin and tropomyosin proteins
What is tropomyosin
a strand-like protein that covers myosin binding sites on actin
what is troponin
a 3 complex protein, one binds calcium, one binds actin, and one binds tropomyosin
what are the steps of cross bridge cycling
- Calcium in the cytoplasm binds to troponin, which pulls tropomyosin off of myosin binding sites
- Myosin head binds to actin triggering power stroke
- Power stroke occurs as myosin pulls actin towards the middle of the sarcomere (triggers ADP and Pi are released)
- Rigor sets in as myosin ins’t cocked back and is still hooked onto actin
- ATP binds to myosin head causing it to release from Actin
- ATP is hydrolyzed to ADP and Pi, causing myosin to become cocked
- Myosin rebinds to actin and continues to do so until calcium is absent
What happens when the muscle fibers isn’t getting more action potentials
- DHP receptor closes
- Ryanodine receptor closes (no more Ca+ leaves)
- The Ca+ ATPase pumps the calcium back into the sarcoplasmic reticulum
- Calsequestrin holds on to calcium in the lateral sacs, allows for more calcium to be stored
for what reasons is ATP needed for in relaxation
- The Ca+ ATPase uses ATP to pump up Ca+
2. Myosin releasing from Actin requires ATP
What is a Muscle twitch
a quick weak contraction caused by one action potential in the muscle
What is the latent period
the delay between the start of the action potential and the start of the twitch
what determines the force production done by a single muscle fiber
- Frequency of stimulation
- Fiber Length
- Fiber diameter (Greatest indicator of force)
What about muscle twitch frequency
- They last longer than action potentials
2. if they fire in quick enough succession then they summate to complete tetanus
How does fiber length increase force by one muscle fiber
The closer that it is to normal length the stronger it is. too long means that many myosin heads don’t connect, and too short means that the thin filaments run into each other.
what is serca
The Ca+ ATPase that pumps Ca+ from cytosol into sarcoplasmic reticulum
What is a motor unit
one motor neuron and all of the muscles it innervates. (all of the muscle fibers are spaced out, not next to each other)
what determines how much force a muscle exerts
each muscle fiber only pulls with one force, so more force means more motor neurons are required.
How is motor neuron recrutement organised
The smaller motor neurons are depolarized first because its easier. smallest to largest.
what is isotonic contraction
when tension doesn’t change but the muscle shortens
what is isometric comtraction
When the length of the muscle doesn’t change but tension does
What is Myasthenia Gravis
Autoimmune attack on nicotenic receptors, can’t allow muscle cells to retire
what causes the latent period
- takes time for it all to happen
2. taughtening of the tendons
What is tetanus
when the muscle twitches are close enough together that there is not dip in Ca++ levels. steady contraction
how does fiber diameter determine force
a larger diameter = more myofibrils = more force
what is an eccentric contraction
when the muscle is contracting but lengthening
what is a concentric contraction
when a muscle is contracting and shortening
what are the two ways to classify muscle fibers
- Speed of contraction (Fast twitch or slow twitch)
2. Major pathway of ATP production (glycolyic or oxidative)
What is a fast twitch fiber
it’s muscle fiber that has a short period of time between neuron firing and peak tension
What is a slow twitch fiber
it’s a muscle fiber that has a long period of time between stimulation and peak tension
what is a glycolyic muscle fiber
a muscle fiber with few Mitochondria, therefor low ATP production. They also have more glycolytic enzymes. They are usually larger in diameter, with less blood vessels
What is a oxidative muscle fiber
a muscle fiber with many mitochondria, therefor they produce a lot of ATP. They have less glycollytic enzymes. they are usually smaller in diameter and more vasculated.
What is a type I muscle fiber and when is it recruted
its a slow-oxidative fiber, and it’s recruited for posture and endurance
What is a type IIa muscle fiber and when is it recruited
it’s a fast-oxidative fiber, and it’s recruited for endurance (walking and jogging)
What is a type IIx muscle fiber and when is it recruited
its a fast-glycolytic fiber and it’s recruited for max effort (sprint type activity)
what percentages of type I and type II fibers does the average person have
50-50
what percentages of type I and type II fibers does a sprinter have
type 1 - 30
type 2 - 70
what percentages of type I and type II fibers does a long distance runner have
type 1 - 70
type 2 - 30
can fiber type be changed with exercise training
Yes (but you can’t go from slow to fast)
can fiber type de changed when you become more sedentary
yes (can’t go from fast to slow)
in what order are the fiber types recruited
slow-oxidative - type I
fast-oxidative - type IIa
fast-glycolytic - type IIx
which types of fibers get fatigued the quickest
type IIx then type IIa then type I
how does chronic endurance exercise increase a muscle resistance to fatigue
- it increases mithochondria so that ATP can be produced more quickly
- more mithochondria = less lactate
- greater relative contribution of fat
AMPK and calcium in resistance to muscle fatigue
?
How does resistance training lead to muscle hypertrophy and increased strength
- it stimulates anabolic signaling (mTor)
- that leads to protein synthesis
- that leads to hypertrophy
also
- it activates satellite cells
- which leads to muscle hypetrophy/myogenesis
4 .the larger the muscles are the stronger they are
mTor is important for what
muscle growth
What is the role of satelite cells
they basically add onto muscle cells to make them more nucleated, they are needed for hypertrophy
what is hypertropy
increased cell size
what is hyperplasia
increased number of cells
