Week 11- Movement & Muscles

Question 1

what is muscle physiology?

Answer 1

• 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

Question 2

how does a decision get to the muscle?

Answer 2

motor neurons

Question 3

what is a motor unit?

Answer 3

one motor neuron and all the muscle fibres it supplies

Question 4

what can end up on different muscle cells?

Answer 4

different synaptic end bulbs of motor nerves

Question 5

what is the neuromuscular junction?

Answer 5

the connection between a synaptic end bulb and the skeletal muscle fibres that it ends on

Question 6

what is the synaptic cleft for neuromuscular junction?

Answer 6

the space between synaptic end bub of motor neuron and skeletal muscle fibre

Question 7

what happens to the different muscle fibres when the motor neuron reaches muscle?

Answer 7

they all contract at the same time

Question 8

how do nerves conduct messages and how do muscles translate received commands into muscle contraction?

Answer 8

membrane potential

action potentials

Question 9

what are the 3 key factors for the resting membrane potential?

Answer 9

1) sodium/potassium pump
2) leaky potassium channels
3) negatively charged protein molecules that can’t leak outside

Question 10

describe the generation of a muscle action potential for motor neurons

Answer 10

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.

Question 11

describe the transfer of acetylcholine with the use of the synaptic cleft

Answer 11

• 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

Question 12

what is muscle action potential (MAPS)?

Answer 12

how the message is spread across the entire muscle cell

• function of the cell membrane (sarcolemma) that spreads acress the entires muscle cell

Question 13

what are the conditions when a muscle cell is at rest? (noMAP)

Answer 13

• 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

Question 14

describe the conditions when muscle is activated (MAPS on)

Answer 14

• 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.

Question 15

what is the mechanism of muscle contraction (sliding filament model)?

**IMPORTANT**

Answer 15

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**

Question 16

what is the mechanism of muscle relaxation?

Answer 16

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

Question 17

what are the 2 factors for muscle contraction to continue?

Answer 17

1) there’s enough calcium
2) there’s enough ATP

Question 18

what are the 3 energy systems for muscle contraction?

Answer 18

1) creatine phosphate
2) anaerobic glycolysis
3) aerobic

Question 19

what are 3 sources for ATP?

Answer 19

1) carbohydrates
2) fatty acids
3) amino acids from protein breakdown

Question 20

what is myoglobin?

Answer 20

an O2 binding protein found in muscle cells

Question 21

why is there a difference in aerobic and anaerobic respiration?

Answer 21

Aerobic: Theres oxygen

36 ATP molecules/ 1 glucose

Anaerobic: No oxygen

2 ATP molecules/ 1 glycolysis

1 lactic acid/ 1 glucose = cramping

Question 22

what is the structure of smooth muscle?

Answer 22

• single nucleus
• organized into sheets
• found in walls of hollow organs
• interchanges from longitude/ circular layers

Question 23

what are the parts of a smooth muscle?

Answer 23

1) caveolae
2) intermediate filaments
3) single nucleus
4) dense bodies
5) gap junctions

Question 24

what is the caveolae?

Answer 24

membrane going in and out of the smooth muscle that contains calcium channels

Question 25

what are intermediate fiaments?

Answer 25

lattice like network throughout the smooth muscle that is needed for contraction and to achor to actin (forms the Z discs of striated muscles)

Question 26

what are dense bodies?

Answer 26

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

Question 27

what are gap junctions?

Answer 27

channels in cells for communication

Question 28

how does smooth muscle contract?

Answer 28

sliding filament mechanism "corckscrew contraction" - contraction pulls dense bodies together - as contraction is happening, sarcolemma bulges out between intermediate filaments

Question 29

how do endings of autonomic nerves contract smooth muscles?

Answer 29

**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\*\*

Question 30

what is the mechanism of muscle contraction for smooth muscles?

Answer 30

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.

Question 31

what are the different neurotransmitters that can be released onto smooth muscle?

Answer 31

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\*\*

Question 32

what is peristalsis?

Answer 32

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

Question 33

the cardiac musce structure/contraction is the same as what other one?

Answer 33

skeletal muscle

Question 34

what are desmosomes and where are they located?

Answer 34

strong anchoring junctions between ajacent cells to prevent separation found in cardiac muscles

Question 35

where are gap junction and desmosomes located in cardiac muscles?

Answer 35

ends of cardiac muscle branches, where one cell joins to another (A-Line) AKA intercalated discs

Question 36

what are the steps for cardiac muscle conrtaction?

Answer 36

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

Question 37

what does "self excitable" mean?

Answer 37

the brached structure and intercalated discs in cardiac muscle - mucle contraction occors in sync and simultaneously when stimulates

Question 38

what is the pace maker?

Answer 38

sends out regular signals, causing depolarization

Question 39

what are atrio ventrucular nodes?

Answer 39

stimulated by pace maker, delays and transfers signal to ventricle muscle