Fig. 50-30 Spinal cord Motor neuron cell body Motor neuron axon Nerve Muscle Muscle fibers Synaptic terminals Tendon Motor unit 1 Motor unit 2 •All motor neurons leading to skeletal muscles have branching axons, each of which terminates in a ___________ ___________ __with a single muscle fiber. •Nerve impulses passing down a single motor neuron will thus trigger contraction in ___the muscle fibers at __________: minimum unit of contraction
24
Embed
Fig. 50-30 Spinal cord Motor neuron cell body Motor neuron axon Nerve Muscle Muscle fibers Synaptic terminals Tendon Motor unit 1 Motor unit 2 All motor.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Fig. 50-30Spinal cord
Motor neuroncell body
Motor neuronaxon
Nerve
Muscle
Muscle fibers
Synaptic terminals
Tendon
Motorunit 1
Motorunit 2
•All motor neurons leading to skeletal muscles have branching axons, each of which terminates in a ________________________with a single muscle fiber.
•Nerve impulses passing down a single motor neuron will thus trigger contraction in ___the muscle fibers at which the branches of that neuron terminate.
__________: minimum unit of contraction
Put it all together…1
ATP
2
3
4
5
7
6
ATP
Botox• Bacteria Clostridium botulinum toxin
– blocks release of _______________– botulism can be fatal muscle
Motor UnitsSize of the motor unit = ______________ • a single motor neuron triggers fewer
than 10 fibers in the muscles controlling eye movements
• the motor units of the muscles controlling the larynx are as small as 2–3 fibers per motor neuron
• In contrast, a single motor unit for a muscle like the gastrocnemius (calf) muscle may include 1000–2000 fibers (scattered uniformly through the muscle).
• _____________: skeletal muscles are in a state of partial contraction ,
• The state of activity or tension of a muscle beyond that related to its physical properties, that is, its ______ ____________ to stretch. In skeletal muscle, tonus is dependent upon efferent ________. (Stedman, 25th ed)
• is maintained by the activation of a few motor units at all times even in __________muscle. – As one set of motor units relaxes, another set takes
over.
Tension
• Force (tension) developed by a muscle progressively increases as more and ______________
• NS may alternate activation of motor units – Reducing time any one set of fibers is
contracted
Fig. 50-UN2
Sensoryreceptors
More receptorsactivated
Low frequency of action potentials
(b) Multiple receptors activated
Fewer receptorsactivated
(a) Single sensory receptor activated High frequency of action potentials
Gentlepressure
Morepressure
More pressure
Gentle pressure
Sensoryreceptor
Varying rate of muscle fiber stimulation
• 1 action potential (twitch) lasts <100msec • If another ap arrives before fiber is relaxed , the
two twitches add together = ________ _______• Further ___________ occurs as the rate of
stimulation increases• When the rate is high enough and the muscle
fiber cannot relax at all between stimuli the twitches _____ into one smooth sustained contraction called - ____________
__________________________:
Time for Ca2+ to be released from SR to bind to troponin
Why do we need this step?
_____________________________:
Repetitive power strokes
Generating force /tension
_____________________________: power strokes are decreasingLevels of Ca2+ decreasing
How is this happening?
_________: graph of twitch contraction
stimulus
Tetanus
When shocks are given at 1/sec, the muscle responds with a single twitch.
At 5/sec and 10/sec, the individual twitches begin to fuse together, a phenomenon called _________
At 50 shocks per second, the muscle goes into the smooth, sustained contraction of ____________
Clonus and tetanus are possible because the __________________ is much briefer than the time needed to complete a cycle of contraction and relaxation.
Note that the amount of contraction is greater in clonus and tetanus than in a single twitch.
As we normally use our muscles, the individual fibers go into tetanus for brief periods rather than simply undergoing single twitches.
Fig. 50-31
Summation oftwo twitches
Tetanus
Singletwitch
Time
Ten
sio
n
Pair ofaction
potentials
Actionpotential Series of action
potentials athigh frequency
HeartbeatANS does run to the heart = __________• increase or decrease
the _________ _________ • the strength of the heartbeat
Even if the nerves are destroyed (as they are in a transplanted heart), the heart continues to beat.
Gap junctions __________ = _____________
Significance: All the fibers contract in a synchronous wave that sweeps from the atria down through the ventricles and pumps blood out of the heart.
Anything that interferes with this synchronous wave (such as damage to part of the heart muscle from a heart attack) may cause the fibers of the heart to beat at random — called ________________.
Fibrillation is the __________ cause of most deaths and its reversal is the function of defibrillators that are part of the equipment in ambulances, hospital emergency rooms, and — recently — even on U.S. airlines
Does the heart go into tetanus?• The refractory period in heart muscle is ___________ than the period it
takes for the muscle to contract (systole) and relax (diastole). Thus ______________ is not possible (a good thing, too!).
• Cardiac muscle has a much richer supply of ___________ than skeletal muscle. This reflects its greater dependence on _______________ for ATP.
• _____________________________
• Cardiac muscle has little glycogen and gets little benefit from glycolysis when the supply of oxygen is limited.
– Thus anything that interrupts the flow of oxygenated blood to the heart leads quickly to damage — even death — of the affected part. This is what happens in heart attacks.
How muscles grow initiallySkeletal muscle forms by _________ of mononucleated
myoblasts to form ________ _____________.
If it tried to divide, it would have several dozen or hundreds of spindles = _____________
• Some Recent Findings• Satellite cells - Day K, Shefer G, Richardson JB,
Enikolopov G, Yablonka-Reuveni Z. Nestin-GFP reporter expression defines the quiescent state of skeletal muscle satellite cells. Dev Biol. 2006 Dec 15;
• "Repair of adult skeletal muscle depends on satellite cells, quiescent myogenic stem cells located beneath the myofiber basal lamina. ...
The number of fibers is probably fixed early in life. This is regulated by __________, a cytokine that is synthesized in muscle cells (and circulates as a hormone later in life).
Interesting note: In the mouse, at least, fibers increase in size by attracting more myoblasts to fuse with them. The fibers attract more myoblasts by releasing the cytokine interleukin 4 (IL-4). Anything that lowers the level of myostatin also leads to an increase in fiber size.