m5 + 6 lect - muscular system Flashcards
what are the functions of skeletal muscle?
primary - movement
secondary - heat, stability, posture
what are muscle cells known as?
muscle fibers
what membrane wraps around a skeletal muscle fiber?
sarcolemma membrane
- contains T-tubules —> enhance depolarization throughout cell
what are the three parts of a muscle fiber?
- sarcolemma membrane
- sarcoplasmic reticulum (smooth ER)
- myofibril
- nmj = neuromuscular junction
what does the sarcoplasmic reticulum (smooth ER) do?
stores ionic calcium within cell
what is a sarcomere?
contractile unit of a cell
what is a myofibril?
cylindrical units of protein
what are the myofilaments?
actin - thin filament
myosin - thick filament
what are the 3 layers in actin filament?
- globular actin (g-actin)
- tropomyosin
- troponin
what happens at the nmj?
connection of the nerve to the muscle cell
- acetylcholine is released = stimulates the action potential to occur
what is globular actin (g-actin)?
binding site for myosin
what is tropomyosin?
- surrounds the g-actin
- actively blocks actin and myosin from contracting
what is troponin?
- connects tropomyosin and g-actin
- attachment site for calcium
- moves tropomyosin out of the way when Ca++ attaches
stimulation: happens in what nerve system? (voluntary innervation)
somatic nerve system
motor units:
- are made of one neuron and the group of muscle fibers it innervates
- varies from 4 to hundreds of fibers to produce gross or fine motor control
stimulation: what is a twitch?
- a single stimulation and single contraction of a motor unit
- had three phases: latent, contraction, relaxation
can last from 30ms to 200ms depending on fast or slow twitch fibers
how many muscle fibers does one neuron have?
200 muscle fibers
what happens in the latent phase of a twitch stimulation?
depolarization/repolarization
last 3ms
what happens in the contraction phase of a twitch stimulation?
- calcium is available
- contraction lasts 30-200ms
what happens in the relaxation phase of a twitch stimulation?
- calcium is reabsorbed
- lasts 10-30ms
contraction: motor unit recruitment needs feedback from what receptor?
proprioceptors - receives stimuli from within the body, position/movement
contraction: what does motor unit contraction do?
- the more motor units stimulated = the stronger the muscle contraction will be
- produces coordination and strength
- this activity takes place in the cerebellum and requires dopamine
what part of the cns produces fine muscle contraction?
the primary motor cortex - frontal lobe
what neurotransmitters precipitates fine muscle contraction?
acetylcholine
what link is between electrical and mechanical?
calcium
what are the steps in the cross-bridge cycle?
step 1: cross bridging
step 2: power stroke (ADP + P)
step 3: detachment
step 4: reactivation
what happens in cross-bridging (step 1 - cross bridge cycle)?
- as calcium is released by the Sarcoplasmic Reticulum, it binds to the troponin complex
- this will move the tropomyosin and allow cross-bridging to occur between the actin and the myosin
what happens in the power stroke? (step 2 - cross bridge cycle)
- with ATP (ADP + P) as fuel, the myosin ‘head’ will grab the G-actin and slide it to the middle
- at the same time the myosin spins, allowing other ‘heads’ to reach and pull the actin closer
- this shortens the sarcomere ( twists like a screw )
what happens in the detachment? (step 3 - cross bridge cycle)
- after ATP is consumed, another ATP binds to the myosin head and this triggers the release of myosin from actin
what happens in the re-activation? (step 4 - cross bridge cycle)
- ATP is oxidized, releasing energy and this moves the myosin into the ‘cocked’ or ready position
what does rigor mortis mean?
occurs when there is no ATP left in a cell causing the filaments to fuse together
changes in frequency of tension?
- muscle fibers can be stimulated to maintain their contraction, if the frequency is increased
—— the impulses sent in succession are called wave summation - as motor units are recruited and are stimulated the time between twitches becomes less and less until the muscle acts as if relaxation never occurs (up to 50 per second)
the three types of tetanus?
1) unfused or incomplete tetanus
2) fused or complete tetanus
3) cramps
what happens during unfused or incomplete tetanus?
- if these twitches are rapid enough, the muscle begins to quiver (fasciculation - tremor) but still reflexes between twitches
- caused by a lack of dopamine in the brain stem; Parkinson’s
what happens during fused or complete tetanus?
- occurs when the twitches are so close together that all the evidence the muscle relaxation is gone
- generates by a very high frequency and a build up of calcium in the motor unit
(completely normal)
what happens during cramps?
- painful tetanus caused by dehydration (release of aldosterone - save H2O) and to a loss of K+ in the cells
- banana helps bc of potassium
what is stronger stimuli generated by in a contraction?
- generated by the weight of the resistance
what happens during motor unit recruitment in a contraction?
- as work is done, the cerebellum alternates the motor units that are stimulated
- the heavier the weight, the increased the stimulus ; and the more motor units will be needed
- stimulated through the use of proprioceptors
what happens during the treppe effect in a contraction?
- as a muscle is used, it becomes increasingly stronger to a maintained maximal stimulus
- caused by an increased efficiency of the muscle to reabsorb and release calcium and breakdown ATP (enzymes)
what is muscle tone?
- this is the way we describe the health of a muscle and its ability to carry out work
- it is firm and will be somewhat continually contracting at all times
—— individual motor units will be activated in a random order to maintain contraction
—— resting tone (burns energy even while at rest) - prevents injury
- burns fat
what is muscle growth?
- caused by adding to the filaments (protein)
- growth hormone, testosterone
what kinds of contractions stimulate muscles in exercise?
- isotonic
- isometric
what are isotonic contractions?
- muscle contractions with the muscle changing length
(concentric and eccentric types)
what are isometric contractions?
- muscle contractions in which the muscle length does not change
what is muscle fatigue?
- caused by oxygen debt and lack of ATP
—– muscles need to replenish the O2
—– removal of lactic acid caused by anaerobic respiration - ATP recovery happens quickly with the replenishment of O2 thru rest
- lactic acid removal in anaerobic respiration requires movement and plenty of water
what is produced as energy?
ATP
- energy needed for muscle contraction
- produced in the mitochondria
(red muscle cells have lots + will multiply with the body’s needs)
in what three ways can ATP be produced?
1) direct phosphorylation (1)
2) aerobic respiration (36 - slow)
3) anaerobic respiration (2)
what happens during direct phosphorylation? (1 ATP)
- as ATP is ‘burned’, it loses a phosphate and becomes ADP
- ADP then reacts with creatine phosphate in the cytoplasm, donating a P group, returning ADP to ATP
- creatine is used very quickly (15 sec) (the used creatine will then be processed and excreted in the urine as creatinine)
what happens during aerobic respiration? (32-36 ATP)
1) initiated by the oxidation of glucose
- glycolysis occurs in the cytoplasm
- producing 2 pyruvic acid, 2 ATP, 2 NADH
- now, pyruvic acid changes to acetyl coenzyme A gaining 2 more NADH, but losing 2 ATP
- acetyl Co-A is then plugged in the mitochondria
2) kreb’s cycle - 2 acetyl Co-A are run thru the cycle and produce 2 ATP and 6 NADH, and 2 FADH molecules
3) electron transport chain
- here, NADH and FADH are oxidized and 32 to 34 ATP are produced
what happens in anaerobic respiration? (2 ATP)
this process undergoes glycolysis but stops at pyruvic acid
- lacking oxygen and will only produce 2 ATP per glucose
- because this process lacks oxygen, pyruvic acid will turn into lactic acid
- only heart muscle, liver, and the kidneys can use lactic acid for energy
- in skeletal muscle, it builds up and needs to be removed
what are the types of muscle fibers?
slow oxidative - red - type 1 (aerobic)
fast oxidative - pink - hybred (produced by HIIT training)
fast glycolytic - white - type 2 (most force)
what is smooth muscle?
- found in the hollow organs, this muscle is involuntary with no visible striations
arrangement of myofilaments:
- fish net or candy cane arrangement
- dense bodies help anchor the actin filaments
- contract in a corkscrew like way
relies on extra cellular calcium (prolong contraction
- the connector is ralmodulin
what is single unit smooth muscle?
- visceral muscle found in hollow organs
- innervated by varicosities => release Ach at effectors
- contain gap junctions to allow wave-like contraction - peristalsis (functional syncytium) —- no NMJs
- little innervation and stress relaxation response
- muscle spontaneously contracts - contains varicosities
what are varicosities?
nerve-endings
what is multi-unit smooth muscle?
controlled by the SNS
richly innervated
- motor units produce control
- acts more like skeletal muscle with NMJ
- found in skin and blood vessels
