Lecture 13 Flashcards
Motor unit:
1 motor neuron + all the muscle fibers innervated by it
Somatic motor neurons:
nerve cells whose cell bodies are in the brainstem & spinal cord that serve skeletal muscles
-Each nerve fiber (axon) branches out to a _______ of muscle fibers
-Muscle fibers of 1 motor unit:
-________ throughout muscle
- contract in ________
number; dispersed; unison
where a nerve fiber meets a muscle fiber _____
-swollen end of nerve fiber=____________
-gap between axon terminal & sarcolemma= __________
-surface area holding acetylcholine (Act) receptors= __________
synapse
-axon terminal
-synaptic cleft
-junctional folds of the sarcolemma
Excitation of a Muscle Fiber
1. arrival of _________ (NMJ)
2. __________ release from synaptic vesicles in response to the nerve signal ______ enters the axon terminal
3. binding of ______ to receptor
4. opening of ligand-regulated ion gate; creation of ___________
5. opening of voltage-regulated ion gates; creation of ________
- nerve signal
- acetylcholine (Ach); calcium
- Ach
- endplate potential
- action potential (AP)
Action potential (AP)
a sudden, fast, transitory, and propagating change of the resting membrane potential
At rest- in an unstimulated (resting cell):
-resting membrane potential or _____________
-inside of cell is usually ______ with respect to the outside
-excess of _____ in the ECF
-excess of _____ in the ICF
-excess of _____ in the ECF
-membrane voltage
-negative
-Na+
-K+
-Ca2+, Cl-
________ refers to the increase in positivity of mb potential
depolarization
The skeletal muscle action potential:
1. Ligand-gated sodium channels open in response to Ach, allowing for _____ influx inside the cell and depolarize cell to threshold
2. When the cell reaches threshold, voltage-gated ____ channels open, causing an action potential
3. At this high mb potential, Na+ channels close, and voltage-gated _____ channels open, repolarizing the cell
4. Time interval, after a muscle fiber has been stimulated which has to pass before the muscle cell can be stimulated to contract again
- Na+
- Na+
- K+
Hyperpolarization
refers to the increase in negativity of mb potential
Excitation-contraction coupling:
it is the connection between the _______ generated in the sarcolemma and the start of a ________ ___________
action potential; muscle contraction
Excitation-contraction coupling process:
1. AP propagates down _________
2. ____ releases from terminal cisterns
3. Binding of Ca2+ to _______
4. Shifting of _______; exposure of active sites on actin
5. Hydrolysis of ATP to _________ which causes activation & cocking of myosin head (______________)
6. formation of myosin-actin cross-bridge
7. _________; sliding of thin filament over thick filament
8. Binding of a new ATP; breaking of _________
- T-tubules
- Ca2+
- Troponin
- Tropomyosin
- ADP+Pi; recovery stroke
- Power stroke
- cross-bridge
The sliding filament model of muscle contraction:
-muscle cells shorten because their individuals ________ shorten
-_________ are pulled closer together as thick and thin filaments slide past each other
-thick and thin filaments _________ length during shortening (only the amount of overlap)
-at full contraction, the thin and thick filaments overlap completely
-sarcomeres
-z lines (z-discs)
-DO NOT
Relaxation of muscle process:
1. ACh breakdown by _____________
2. Reabsorption of _____ by sarcoplasmic reticulum
3. Loss of Ca2+ from troponin
4. return of tropomyosin to position blocking _________ of actin
acetylcholinesterase (AChE)
Ca2+
active sites
Length-tension relationship:
the amount of tension generated by a muscle depends on how ________ or _________ it was before it was stimulated
stretched or shortened
If muscle is overly shortened before stimulated, a _______ contraction results, as thick filaments just butt against z-discs
WEAK
If muscle is too stretched before stimulated, a ______ contraction results, as minimal overlap between thick & thin filaments results in minimal cross-bridge formation
WEAK
-Greatest force at optimum resting length (___-____um)
-The NS maintains __________ (partial contraction) to ensure that resting muscles are near this length
-2.0-2.25um
-muscle tone
Twitch:
a quick cycle of _________ and _________ when stimulus is at or above threshold
contraction; relaxation
the tension produced by a single twitch can be measured by a ________, which produce a graph illustrating the amount of tension produced over time
myogram
Twitch process:
1. ___________: very brief delay between stimulus & contraction; time required for excitation, excitation-coupling, and tensing of elastic components of muscle (generating _______ tension)
2. _________ phase: time when muscle generates ______ tension; force generated overcome the load & cause movement
3. ________ phase: time when tension decline to baseline; SR reabsorbs Ca2+; Myosin releases (this takes longer than contraction)
- Latent Period; internal
- Contraction; external
- Relaxation
2 main types of skeletal muscle contraction:
1.
2.
Isometric
Isotonic
Isometric contraction:
-muscles produces internal tension but external resistance causes it to _____________
Important in:
THIS OCCURS AT THE BEGINNING OF ANY MUSCLE CONTRACTION
stay the SAME length
-postural muscle function
-antagonistic muscle joint stabilization
Isotonic contraction:
-muscle changes length with no change in tension
-concentric=_______
-eccentric=________
- muscle shortens
-muscle lengthens
Even if the same voltage is delivered, different stimuli cause twitches varying strength, because:
-muscle’s _________
-muscle’s ______ after continual use
-_______ muscles’ enzymes work more quickly
-muscle cell’s ________ level influences cross-bridge formation
-Frequency of ________ delivery: increase in tension output
-starting
-fatigue
-warmer
-hydration
-stimulus
All of Nothing Theory of muscle contraction states:
if the threshold stimulus of +30mV is not reached no part of the fiber will contract; once the threshold stimulus is reached, the whole muscle fiber will contract
Size principle: weak stimuli recruit _____ units, while strong stimuli recruit _____ and _____ units for powerful movements
small; small and large
Recruitment or Multiple Motor Unit (MMU) summation
process of bringing more motor units into play with stronger stimuli
-Low stimulus frequency=__________
-Physiologically normal stimulus frequency=_________
-Unnaturally high stimulus frequency=_________
-identical twitches
-temporal summation and incomplete tetanus
-steady contraction (no relaxation!); complete tetanus
Temporal summation and incomplete tetanus:
-each new twitch rides on the previous one generation greater tension (more release of ____ which activate additional sarcomeres)
-only partial relaxation between stimuli resulting in ________, incomplete tetanus
Ca2+; fluttering
