Muscle Physiology I Flashcards
Exam 1
1
Q
What are the characteristics of muscle tissue?
A
- irritabilility/exciltability: able to receive and respond to chemical, electrical, and mechanical stimulus
- contractilicity: muscles change shape as a result of stimuli becoming shotere and thicker, and develops tension.
- relaxation: the opposite of contractibility: the giving up of tension
- extensibility: muscle can be stretched or lengthened by a force outside of the muscle itself
- elasticity: muscle tissue readily returns to normal length when a stretching force is eliminated
2
Q
What is the purpose of skeletal muscles
A
- generate movement
- arrest movement
- modify movement
Muscles actively exert force by shortening and building up tension or passively exeriting force by resisting stretch
3
Q
What are rotary and translatory movements
A
- rotary: plane that moves around an axis, (ex: add/abduction)
- translatory: moves around the whole body not just a joint
4
Q
What is the structure of a skeletal muscle?
A
- endomesium: coating around a muscle fiber (like plastic wrap), seperates one muscle fiber from the other
- fasicle: group of endomesium bundled wiyh perimesium
- perimysium: sheath that surround the muscle fasicles (bundles). [in long muscles it may be arranged chain-like and extends the length of the muscle]
- epimysium: tough outermost layer, surrounds the entire muscle tissue/belly. Helps give muscle its shape and is very resistant to stretch (think of a corset)
- tendon: receives contributions from all connective tissue layers, it develops tension when the muscle shortens or is on stretch
- periosteum: highly vascularized CT that is the outer layer of the bone; tendons and ligaments be;lnds into it. It provides nourishment
5
Q
What is actin?
A
thin, light, 2 chain-like strings of actin molecules are wound around each other. They form the I band of the sarcomere
6
Q
What is myosin?
A
The thick, dark, large molecules. Has globular head groups that swivel and attch to binding sites on actin (crossbridge). The “H” zone is central protion of the myosin filament
7
Q
Describe the A band, I band, & H zone, and M band
A
- A-band: overlapp of myosin and actin fillaments
- I-band: thin actin
- H zone: only myosin; this is the contractile region, no overlapping
- M band: the part of the h-zone that contains myosin filaments that connect to one myosin filament
8
Q
Important details about actin-myosin crossbridging
A
- during the shortening of the muscle, the actin is pulled towards the myosin–crossbridges are formed, broken, and reformed as greater overlapp occurs
- During lengthening contractions, the actin pulls away from the myosin–crossbridges are broken, reformed, and broken as graduak reduction in overlapp occurs
- The degree of overlapp is the only thing that changes, the actin/mysoin dont actually change in length
9
Q
What are the functions of connective tissue?
A
- bind muscles together
- harnesses the force of muscle contraction and transmits this force to the bony attachmnets via the tendons
- provides structure and shape
- a conduit for blood vessels and nerves
- contributes to passive tension to the muscle fiber as the muscle contracts or stretches
10
Q
What are the passive contributors to muscle tension?
A
- various tissues, just by being there, contributes **passive tension **
11
Q
What are the passive elastic components?
A
CT is associated with muscle tissue: endomysium, perimysium, epimysium, tendon; they are all interconnected
* they contribute to overall tension present in a muscle, Lengtyen or shorten when the muscle actively does these
12
Q
What are the non-connective tissue elastic components
A
- the sarcolema, nerve, and blood vessels will also contribute to tension to the overall muscle contraction by lengething and shortening as the muscle contracts and relaxes
13
Q
What is the difference between fusiform and penniform fibers of muscles?
A
- Fusiform: arranged in elongatyed/parallel fashion. Provide greatest degree of shortening, = quick muscle and good ROM
- Penniform: shorter fibers, oblique arrangement, = greater force but smaller ROM
14
Q
Describe crossbridge formation?
A
Crossbridge formation occurs when a muscle is stimulated at its motor end plate and a chemical change occurs in the sarcomere.
- an influx of Ca+ triggers the exposure of binding sites on actin
- then head groups of the myosin swivel causing the actin to be pulled along the length of the myosin (this is called “power stroking”
- As the actin slides past the myosin, a chemical reaction occurs which binds the actin to the myosin
- As crossbridges form and old ones are rebuilt, the actin is moved closer to the H zone of the sacromere, until a maximum overlap occurs (no more increase in tension can develop in the fibers)
- The fillaments do not change in length, however the sacromere (contracile unit) becomes shorter
15
Q
What is the sarcolemma, myofibril, sarcomeres, and Z-lines?
A
- Sarcolemma: singe muscle cell surrounded by a cell membrane
- Myofibril: threadlike structure runs through the muscle cell and allows the muscle to contract
- Sacromeres: a series of units that makes up the myofibril, and extends between two Z-lines
- Z-lines: located at regular intervals throughout the myofibril and act as boundaries for the sarcomere and a means of linking the actin fillaments together
16
Q
What are red (tonic fibers)?
A
- Type I, slow oxidative, slow twitch
- innervated by lower thresholds than pale fibers, so used more frequently
- fibers designed for endurance
- red, small diameter, high myogliobin (oxidative) capacity, small MU size and slow axon conduction
17
Q
What are pale (phasic fibers)?
A
- Type IIa/b, fast twitch, glycolic
- for rapid contractions, less capable of sustained contractions
- innervated by higher thresholds than red fibers
- desinged for short term bursts of energy
- white, large diameter, low myoglobin contenet (oxidative capacity), high glyocolic capacity, fast fatigue, large MU size and fast axon conduction
18
Q
What is the muscle fiber’s response to a single brief stimulus?
A
a muscle twitch
- the muscle contracts quickly and relaxes
19
Q
What are the 3 types of sensory neurons?
A
- exteroceptors: conduct electrical impulses of sensation from outside the body (touch, smell, vision)
- Proprioceptors: located in muscles, tendons, and ear that bring info about postion in space (pressure, movement, equilibrium)
- Interoreceptors: located deep in viscera and detect stimuli from internal organs and blood vessels
20
Q
What is a motor unit?
A
fibers of skeletal muscles that are organized into motor units, they vary in size. On average, there are 150 fibers in each motor unit
- motor unit: the motor nerve fiber and all the muscle fibers it serves/innervates (via the axon)
- motor units are not grouped together but are dispersed throughout the muscle
- the more motor units stimulated, the greater the contraction
21
Q
What are the 3 CNS recruitment strategies?
A
- Small cell bodies are recruited first, then if not suffciient (wants to have the smallest amount of energy expendature/conseve energy)
- Larger size MU are recruited next is needed (will generate more muscle tension and expend more energy)
- Otehr factors will be taken into consideration by the CNS are: habituation, magnitude of msucle force required, speed/timing of muscle output, type of muscle contraction recuired, type of muscle fiber needed to complete the task
22
Q
How do motor units vary in muscles that control small movements or large amounts of force vary?
A
- Muscles with large size MU have smaller number of total MU
- Muscles with smaller size MU have relatively large number of total MU
Muscles that control fine movements:
- have only a few muscle fibers in each motor unit or have a good proportion of small size motor units in their total number of motor units
- small size MU can fire *more rapidly *than large size (small size give the CNS time to modulate motor output)
Muscles which cause less refined movements but need lot of force will have *larger size *motor units
- large motor units fire with *greater force *than smaller size motor units
23
Q
Do mammals have only one one type of fiber or both in every muscle? Does heredity play a role, can can it be changed?
A
- Mammals have a mixture of phasic and tonic in every muscles, although one may be more dominant
- through heredity a person may have more of one type (those with more red have advanatge at endirance exercise, and those with pale have more explosiveness)
24
Q
Give examples of what situations FG fibers are good in and also what muscle groups typcially dominate?
A
- good for mobility, non-postural and phasic activities (quick burst), produces large amount of tension such as in lifting
- higher proprotion in shoulders and arms
- gastroc
25
Give examples of what situations SO fibers are good in and also what muscle groups typcially dominate?
* used for stability, postural, or tonic activities
* postural muscles of neck, back, and leg have higher proportion
* soleus
26
What is a muscle twitch?
* muscle fibers response to a single stimulus
* all or nothing response
* depends on the size of a motor unit being stimulated, a twitch may be strong or weak
27
What 3 periods occur duing a muscle twitch?
1. latent period: no change in fiber length; time duing which impulse is traveling along the sarcolemma, calicum is being released
2. Contraction period: tension increases (cross bridges sweiveling), shortening of fibers occurs
3. Relaxation period: contractile force is no longer generated, muscle relxes and returns to origninal length
28
What is the average number of fibers in a motor unit? And what does a motor unit consist of?
Average number of MU is 150
Consist of:
* the cell body of an alpha motor neuron
* the axon that conducts the impulses from the alpha motor neuron to the skeletal muscle fiber and its motor end plate
* the skeletal muscle fiber
29
Are muscle fibers in a motor unit dispersed or grouped in a muscle?
* they are dispersed throughot the muscle
* activation of one a few motor units will = a weak muscle contraction, but activation of more motor units will = a stronger muscle contraction
30
What are the variations between motor units?
* size of motor neruon cell body
* diameter of cell body axon (larger it is the faster conduction speed)
* # of muscle fibers the axon innervates as ut branches throughout the muscle
* types of fibers (all MU will be made up of 1 type of fiber, so FG MU, FOG, or SO MU's exist
31
What are the 5 factors that the magnitude of active tension is determined by?
1. size of motor units firing
2. # of motor units firing
3. frequency of motor units firing
4. # of crossbridges occuring
5. load on the muscle
32
Describe muscle attachments
* Origin- proximal attachment
* Insertion- distal attachment
* Line of pull: determines the type of motion produced (flex, extension, abd, and add)
- direction of fibers
- proximal and distal attachmnet
- position of msucle relative to joint
33
What is the action of a muscle?
* general location of the muscle (ant, post, med, lat)
* Muscles do not usually perform both actions that are antagonistic to each other. THEY HAVE 1 ROLE
34
What is muscle action and functional muscle groups?
* Muscle action: the development of tension/force by a muscle
* Functional muscle group: a group of muscles that are capable of causing a speciifc joint action (wrist radial deviators)
35
What is a motive VS a resistive force?
* Motive force: force causing the observed movement (agonist)
* Resistive force: force opposing the observed movement (antagonist)
You need both when performing a movement
- it is a combination of both
36
Why is the angle of pull important?
idk
37
What is an agonist or prime mover?
a muscle of group of muscles that produces teh desired motion
ex) anterior delt does shoulder flexion
38
What is the purpose of accessory/assist muscles (emergency muscles)?
* they assist the prime mover but is less effective at this motion
* ex) bicep can help produce shoulder flexion but is not the prime mover
* sometimes with stroke pt their accessory muscles take over the load from the prime mover who may be damaged
39
What is the purpose of an antagonistic muscle
* produces the opposite action of the prime mover
* (in order for the agonist to successfully shorten as it contracts, the antagonist muscle must relax and passively lengthen
40
What is a stabilizer/fixator muscle?
* Muscle contracts isometrically to hold a body part stable against the pull of another contracting muscle
* Not directly involved with moving the load but works to keep parts of the body stable so primary movers can do their job
41
What is a neutralizer muscle?
* a muscle that contracts to prevent unwanted movemnet component in another muscle (they cancel out unwanted movements)
42
What are spurt muscles?
Muscles that have a large rotary component
- the proximal attachmnet is far from the joint axis, and the distal attahmnet is close to the joint axis
- it allows for more leveage
EX) biceps brachii and brachialis
43
What are shunt muscles?
* Muscles provide mainly joint stability by providing compression due to a translatory component
* The proximal attachmnet is close to the joint, and the distal attachmnet is far from the joint (muscle belly is distal to the joint)
EX) brachioradialis
44
What are spurt-shunt muscles?
* multi-joint muscle may act as a spurt muscle in one joint and a shunt muscle on another joint
* ex) a bicep is a spurt on the elbow but a shunt for the shoulder
45
What are muscle contractions?
* muscle fiber generates tension through the action of actin and myosin cross-bridge cysling
* the development of tension is seen in the shortening of a muscle fiber
* however, while under tension, the muscle may lengthen or shorten, or remain the same
* motion at a joint can be produced by gravity or through muscle activity. If gravity will produce the desired movement, the msucles are not needed to contract.
* Only muscle actiivty can control, modify, or regulate motion
46
What is a concentric contraction?
* the muscle is shortening, and develops enoigh tension to pvercome the resistance of body part, gravity, & other forces
* decrease in joint angle (shortening)
47
What is an isometric contraction?
* the musle is held in a shortened posiion (partial or complete contraction) vs weight of body part and gravity (no motion) and possibly other external forces (resistance, weight, time)
* MAINTAINS A FIXED POSITION, no change in joint position
48
What is an eccentric contraction?
* a lengtehning contraction
* from a shortened position the muscle gradually returns to a resting length
* esures smoothness of motion
* may also occur when extrneal resistance overcomes muscle resistance, forcing return to normal length
49
What is a co-contraction?
agonist and antagonist contract simultaneously to provide stability, maintain joint in a neutral position (wrist and forearm position duing hammering)
50
