Week 11- Movement & Muscles Flashcards
what is muscle physiology?
- how a muscle is stimulated
- the structure of the junction between a nerve and muscle
- how a muscle contracts
- where the energy comes from
- how a muscle relaxes
how does a decision get to the muscle?
motor neurons
what is a motor unit?
one motor neuron and all the muscle fibres it supplies
what can end up on different muscle cells?
different synaptic end bulbs of motor nerves
what is the neuromuscular junction?
the connection between a synaptic end bulb and the skeletal muscle fibres that it ends on
what is the synaptic cleft for neuromuscular junction?
the space between synaptic end bub of motor neuron and skeletal muscle fibre
what happens to the different muscle fibres when the motor neuron reaches muscle?
they all contract at the same time
how do nerves conduct messages and how do muscles translate received commands into muscle contraction?
membrane potential
action potentials
what are the 3 key factors for the resting membrane potential?
1) sodium/potassium pump
2) leaky potassium channels
3) negatively charged protein molecules that can’t leak outside
describe the generation of a muscle action potential for motor neurons
1) resting potential - all channels are closed and there’s an even amount of positive/ negative ions out/in of membrane
2) depolarizing phase- a stimulus causes the threshold to rise, making voltage-gated sodium channels to open, rushing sodium in the membrane
3) Repolarization- sodium gates close and potassium voltage-gated channels open, causing potassium to leave the inside of the membrane along the concentration gradient and bring the membrane back to the resting potential.
4) resting conditions re-established - both sodium and potassium channels close and sodium-potassium (3:2) exchange pumps move sodium out and potassium in.
describe the transfer of acetylcholine with the use of the synaptic cleft
- when the acetylcholine are released from vessicle through exocytosis, some binds to liangd-gated channels
- acetylcholine helps open liangated channels for sodium to enter causing a muscle action potential
- this leads to the release of calciu ions from the sarcoplasmic reticulum into the sarcoplasm
what is muscle action potential (MAPS)?
how the message is spread across the entire muscle cell
- function of the cell membrane (sarcolemma) that spreads acress the entires muscle cell
what are the conditions when a muscle cell is at rest? (noMAP)
- sarcolemma: cell membrane covering muscle cell/fibre
- t-tibule: extensions running through muscle cell
- sarcoplasmic reticulum: inside sarcolemma
- calcium pumps- pumps in calcium when there’s stimulus (attached to SR)
- calcium release channels: channels attached to SR that release calcium
describe the conditions when muscle is activated (MAPS on)
- calcium passes through sarcolemma and triggers calcium pumps attached to sarcoplasmic reticulum to open, realeasing calcium into sarcoplasmic reticulum
- the calcium release channels change shape and the calcium in the SR rushes out and diffuses between the myofibrils.
what is the mechanism of muscle contraction (sliding filament model)?
**IMPORTANT**
1) calcium binds to tropinin which removes the tropomyosin, exposing actin
2) ATP pushes myosin heads to bind with actin, forming a crossbridge (ATP turns into ADP)
3) ADP is released from myosin which causes it to move back, pulling actin which shortens the sarcomere
4) a new ATP molecule binds to mysin head which releases itself from actin
**repeats after these steps**
what is the mechanism of muscle relaxation?
1) Acetylcholine (ACh) is broken down by acetylcolinesterase (AChE)
2) sarcoplasmic reticulum recaptures Ca2+
3) actin is no longer covered by myosin heads (no cross bridge)
4) contraction ends, returns to resting length
what are the 2 factors for muscle contraction to continue?
1) there’s enough calcium
2) there’s enough ATP
what are the 3 energy systems for muscle contraction?
1) creatine phosphate
2) anaerobic glycolysis
3) aerobic
what are 3 sources for ATP?
1) carbohydrates
2) fatty acids
3) amino acids from protein breakdown
what is myoglobin?
an O2 binding protein found in muscle cells
why is there a difference in aerobic and anaerobic respiration?
Aerobic: Theres oxygen
36 ATP molecules/ 1 glucose
Anaerobic: No oxygen
2 ATP molecules/ 1 glycolysis
1 lactic acid/ 1 glucose = cramping
what is the structure of smooth muscle?
- single nucleus
- organized into sheets
- found in walls of hollow organs
- interchanges from longitude/ circular layers
what are the parts of a smooth muscle?
1) caveolae
2) intermediate filaments
3) single nucleus
4) dense bodies
5) gap junctions
what is the caveolae?
membrane going in and out of the smooth muscle that contains calcium channels
what are intermediate fiaments?
lattice like network throughout the smooth muscle that is needed for contraction and to achor to actin
(forms the Z discs of striated muscles)
what are dense bodies?
achoring parts for the intermediate fiaments and ties to the cell membrane
both intermediate filaments and dense bodies form a strong cable where actin an myosin can pull
what are gap junctions?
channels in cells for communication
how does smooth muscle contract?
sliding filament mechanism
“corckscrew contraction”
- contraction pulls dense bodies together
- as contraction is happening, sarcolemma bulges out between intermediate filaments
how do endings of autonomic nerves contract smooth muscles?
1) varicosites (nerve endings at end of autonomic nerves): realeases neurotransmitters in general ares
2) Diffuse Junction: neurotransmitters diffuse across wide area ans stimulates a number of cells to contract
** autonomic nerves does not touch smooth muscle**
what is the mechanism of muscle contraction for smooth muscles?
1) calcium arrives from channels in caveoli and reduced SR
2) calcium then binds to calmodulin (regulatory protein in cytoplasm)
3) activated calmodulin activates myosin kinase which using ATP to activate myosin head
4) when myosin head is active, it binds with actin and muscle starts to contract.
what are the different neurotransmitters that can be released onto smooth muscle?
1) acetycholine = contracts smooth muscle = contricts airways
2) norepinephrine = relax smooth muscles = widens airways
3) oxytocin = utuary walls contract = childbearing
**same neurotransmitters can cause opposite effect depending on what tissue it acts**
what is peristalsis?
alternating contaction and relaxationof two or three layer muscle
- rhythmic movement
- circular layer contracts, making lumen narrow
- longitudinal layer widens lumen
ex: bringing food down
the cardiac musce structure/contraction is the same as what other one?
skeletal muscle
what are desmosomes and where are they located?
strong anchoring junctions between ajacent cells to prevent separation
found in cardiac muscles
where are gap junction and desmosomes located in cardiac muscles?
ends of cardiac muscle branches, where one cell joins to another
(A-Line)
AKA intercalated discs
what are the steps for cardiac muscle conrtaction?
1) an action potential is led by contractile cardiomyocytes through gap junctions
2) action potential activates calcium channels in the T-tubules which releases calcium into the cardiomyocytes
3) calcium makes troponin detatch from actin
4) actin is then bounded to myosin which initiates contraction by myosin being pulled with ATP, contracting the muscle
what does “self excitable” mean?
the brached structure and intercalated discs in cardiac muscle
- mucle contraction occors in sync and simultaneously when stimulates
what is the pace maker?
sends out regular signals, causing depolarization
what are atrio ventrucular nodes?
stimulated by pace maker, delays and transfers signal to ventricle muscle
