Term
| do basal ganglia or cerbellum have direct input to the motor neuron pool? |
|
Definition
| no they modulate other higher neurons |
|
|
Term
| what is a satellite cell? |
|
Definition
|
|
Term
| define epimysium, perimysium, and endomysium. |
|
Definition
|
|
Term
| what are the thick and thin filaments? |
|
Definition
thick = myosin.
thin = actin |
|
|
Term
| what is the structure of myosin? |
|
Definition
| aligned end to end, and then stacked. each myosin head has a binding site for actin and a binding site for ATP |
|
|
Term
| what is the structure of actin? |
|
Definition
|
|
Term
|
Definition
| it is the long chain that mechanically blocks the myosin binding site on actin |
|
|
Term
|
Definition
it is the moderator molecule that binds to tropomyosin. it has three active sites T, I, and C
The T site attaches the troponin complex to tropomyosin. the I site inhibits the myosin binding site on actin, and the C site binds free calcium to produce a conformational change in tropomyosin to allow myosin to bind to actin |
|
|
Term
| what is a sarcomere? M line? i band? a band? z line? |
|
Definition
| functional unit of the muscle, repeating structure. M line is where the myosin tails are attached to each other. the I line is where there is only actin. |
|
|
Term
|
Definition
| Titin is a giant protein that functions as a molecular spring which is responsible for the passive elasticity of muscle. connects the z line to the m line. |
|
|
Term
| describe the process of the cross bridge cycle of myosin unbinding and rebinding to actin |
|
Definition
| atp binds to myosin, this dissociates the head from actin. then calcium binds to troponin. the myosin head swings forward, at the same time the troponin tropomyosin complex begins to move. once the t-t complex is out of the way, myosin binds to actin. the ATP the hydrolizes to ADP + Pi, this relase of Pi generates the power stroke. finally, the ADP unbinds, and myosin is bound to actin, ready for the next ATP |
|
|
Term
| what is a t- tubule? what is t-system transmision? |
|
Definition
| A T-tubule (or transverse tubule) is a deep invagination of the sarcolemma, which is the plasma membrane, only found in skeletal and cardiac muscle cells. These invaginations allow depolarization of the membrane to quickly penetrate to the interior of the cell. |
|
|
Term
|
Definition
| SERCA resides in the sarcoplasmic reticulum (SR) within muscle cells. It is a Ca2+ ATPase that transfers Ca2+ from the cytosol of the cell to the lumen of the SR at the expense of ATP hydrolysis during muscle relaxation. |
|
|
Term
Force of muscle contraction increased with increasing stimulus
frequency. why? |
|
Definition
This is due to the time course for the
intermuscular calcium transient caused by the muscle action
potential. Increases in Ca++ causes force generation via
cross-bridge cycling. |
|
|
Term
Stimulation at low frequencies –twitches produces summation of
twitches and tetanus
With increasing stimulation frequency produces tetanus, prolonged
stimulation results in fatigue |
|
Definition
|
|
Term
| what is potentiation (treppe)? |
|
Definition
– increase in twitch
forces with low frequency stimulation
• augmented Ca2+ release from SR
• phosphorylation of myosin light
chains |
|
|
Term
| what is the force-frequency relationship? |
|
Definition
Sigmoidal relationship
between applied
frequency and muscle
force generated
•Similar for single muscle
fibers or motor units
•Performance of motor
tasks
•Varies according to history
of contractions |
|
|
Term
| what is the length-tension relationship? |
|
Definition
Passive and active contributions to tension
•Peak active force approximately 33-50% of maximally shortened length
causes - we have optimal relationship between actin and myosin, we can increase the number of cross bridges a maximal amount.
•Passive forces gradually increase at highest length
causes - titan protein has to keep actin bound to the z-line |
|
|
Term
| Does peak active joint torque correspond to peak of L-T relationship? |
|
Definition
not really.Peak torque output varies with joint anglebecause the moment arm
changes with joint angle. The angle of peak moment arm and
muscle force generation are different |
|
|
Term
| peak active force of a muscle occurs approximately @ 33-50% ofmaximally shortened length. why? |
|
Definition
| greatest number of myosin cross bridges available with minimal actin compression or filament interaction |
|
|
Term
| passive muscle forces gradually increase at highest length. why? |
|
Definition
| titin or connexin that binds myosin to the z line is stretching (spring force) |
|
|
Term
| what is the force velocity relationship? |
|
Definition
concentric (increasing velocity with decreasing force), isometric (no change in length), eccentric (decreasing velocity and increasing torque)
what causes this? assuming same neural input.it has to do with the number of cross bridges that are attached. the quicker it comes apart the more force in an eccentric contraction. the quicker it comes apart, the LESS force in a concentric contraction. |
|
|
Term
| what are alpha, gamma and beta motoro neurons? |
|
Definition
alpha - extrafusal fibers
• Gamma - intrafusal fibers
beta - both extrafusal and intrafusal |
|
|
Term
| what are extrafusal and intrafusal fibers. |
|
Definition
| extrafusal is normal skeletal muscle, intrafusal are fibers attaches to spindles |
|
|
Term
| what is the motor nucleus (pool)? |
|
Definition
Constellation of MNs in spinal cord (brainstem) controlling a
single muscle |
|
|
Term
| what is the innervation ration? |
|
Definition
Number of muscle fibers connected to a single motoneuron • How does this vary across muscles? large muscles that produce a lot of force don't need to be graded as much (gastrocnemius, high ratio), where fine motor ones need to be vary graded,
| Muscle | Number of Motor Axons | Number of Muscle Fibers | Innervation Ratio | Reference |
|---|
| First dorsal interosseous |
119 |
40,500 |
340 |
Feinstein et al |
| Medial gastrocnemius |
579 |
1,120,000 |
1,934 |
Feinstein et al |
|
|
|
Term
| motor neuron cell bodies of proximal muscles are located medially in the spinal cord., distal is lateral. what do i mean by that? |
|
Definition
| proximal muscle cell bodies are located medially, while distal muscle cell bodes are located lateral in the spinal cord. |
|
|
Term
| roughly linear relation between synaptic current and discharge rate (rate of action potentials). what does this rate correspond to? |
|
Definition
| this rate corresponds to force output (force frequency relationship) |
|
|
Term
| what are the three basic types of motor units? |
|
Definition
| •Slow (S), Fast (fatigue) Resistance (FR), Fast Fatiguable (FF) |
|
|
Term
| what is the size of the three basic types of motor units S, FR, and FF? |
|
Definition
| they increase in size and recreuitment order from smallest to largest. S, FR, FF |
|
|
Term
| what are the three basic types of muscle fibers? |
|
Definition
I - slow
IIa - fast fatigue resistant
IIb - fast fatiguable
•Differences between types seen in metabolic and contraction
characteristics |
|
|
Term
| why are motor neurons recruitmed according to size? |
|
Definition
slow have higher resistance because it has less potassium leak channels. Smaller cells – small # of
channels – harder for
current to pass through
(larger resistance)
Assume same synaptic input
to entire motor nucleus
•Cells with largest Rgenerate
larger voltage change
•Reach recruitment threshold
first |
|
|
Term
|
Definition
| number of motor units involved |
|
|
Term
| increasing synaptic drive increases firing rate of active motor units, but what else does it do? |
|
Definition
| you are ALSO recruiting additional motor units (like FR's, and FF's) |
|
|
Term
| the first motor unit recruited, when is it de-recruited? what about the last? |
|
Definition
| first motor unit de-recruits last. the last motor unit de-recruits first. |
|
|
Term
| is the afterhyperolarization the same in all motor neurons? |
|
Definition
| no, longer in S, shorter in FF |
|
|
Term
what factors effect Axonal conduction
velocity? |
|
Definition
•reflection of axon
diameter and, hence, cell
size
•fast-conducting are FF |
|
|
Term
| are motor neurons matched to muscle fibers? |
|
Definition
| S to Slow Oxidative (I), FR to Fast Oxidative Glycolytic (IIA), FF to Fast Glycolytic (IIB) |
|
|
Term
| what are some Mechanical properties of the motorneurons/motor units? (S < FR < FF) |
|
Definition
| (S < FR < FF) •Innervation ratio •Individual muscle fiber size •Speed of contraction •Amount of force per fiber or per unit produced •Fatigability (opposite of Fatigue Resistance) |
|
|
Term
| what are some important oxidative enzymes? which muscle fibers have the most? |
|
Definition
Succinate dehydrogenase
NADH – tetrazolilum reductase
(mitochondrial)
•Converse – glycolytic enzymes |
|
|
Term
| unfused tetanus? fused tetanus? whats the difference? |
|
Definition
| this is like the muscle force contraction equivalent of spatial summation in the nervous system. |
|
|
Term
do muscle properties change when
innervated from a nerve of a
different fiber type?
Nerve supports muscle function
Mechanisms are in place for
communication between
nerve and muscle to produce
genetic level changesin
muscle function |
|
Definition
| yes. for example, when the fast twitch extensor digitorum is cross innervated from a different fiber type, it behaves more like a slow twitch muscle. (vice versa for soleus, a slow twitch muscle) This tells us that there are mechanisms in place for communication between nerve and muscle to produce genentic level changes. |
|
|
Term
| for daily muscle recruitment, which motor units do we typically use? |
|
Definition
Recruitment of S MotorUnits for most of daily activities Rare recruitment
of FF unless physical stressors demand it |
|
|
Term
| what are the excitatory neurotransmitters? what are the inhibitory ones? |
|
Definition
excitatory - glutamate (CNS), acetylcholine (NMJ)
inhibitory - glycine, GABA |
|
|
Term
| what is a non-NMDA vs an NMDA ionotropic receptors? |
|
Definition
| an NMDA ionotropic receptor has tons of binding sites for different agonists and antagonists. its just extremely complex, while a non-NMDA receptor just has the glutamate binding site. |
|
|
Term
| monoamines - norepinephrine and serotonin, where do they originate? how can they both excite motor pools. |
|
Definition
| brainstem. through either excitement of interneurons or the motor units themselves. |
|
|
Term
| how to monoamines effect motorneurons? |
|
Definition
Modulate ionic conductances
•Resting membrane potential, membrane resistance
•Generation of prolonged firing (extensors > flexors in LowerExtremetiess, flexors >
extensors in UpperExtremeties) |
|
|
Term
| what is the purpose of the increased effect of monoamines on extensors in the legs and flexors in the arms? |
|
Definition
| serotonin can act on metabotropic receptors that open long lasting calcium channels. you need easily excitable extensors in the legs to maintain upright posture, but the flexors in the arms need to be easily excitable to hang from the tree. this is just a more efficient way to recruit motor neurons. |
|
|
Term
| Rapid increase in firing rate ensures efficient motor unit recruitment |
|
Definition
| everything is more efficient |
|
|
Term
| what is the definition of a reflex? |
|
Definition
stereotyped efferent response to a
standard afferent input |
|
|
Term
|
Definition
| yes. asleep vs awake or maybe at different positions in the walking cycle can produce different responses |
|
|
Term
| proprioceptors, what are the muscle receptors, and how are they grouped? |
|
Definition
classified by size from smallest to largest. –Group Ia (A alpha) – from muscle spindles, velocity sensitive, length and muscle stretch
– Group II (A beta)– also muscle spindles, but only code for muscle length or amount of muscle stretch
–Group Ib (A gamma) from golgi tendon organs, these encode force or tension in the muscle |
|
|
Term
| what are the joint receptors? |
|
Definition
| they are mostly found in collagen and tell how much the collagen is stretched. very active at joint end range. |
|
|
Term
|
Definition
cutaneous (mechanical, thermal, noxious) receptors. group II, III,
IV (Abeta, Adelta, C)
vestibular and visual included, not in SC reflexe |
|
|
Term
|
Definition
| intrafusals are basic skeletal muscle fibers that attach the spindle to the tendon. when these fire, you get more of a signal |
|
|
Term
| what is the muscle spindle pathway? |
|
Definition
| stretching the bicep stretches the muscle spindal, which sends a signal directly to the homonymous motorneuron. this just a one synapse pathway, no interneurons. the bicep muscle spindle also sends a signal to synergists at the heteronymous motorneuron. you also send a signal to an inhibitory interneuron to the antagonist (in this case you inactivate the tricep) |
|
|
Term
The muscle spindle has two sets of
afferent axons: group Ia and group
II.
The afferent axons contact the
intrafusal fibers in the center |
|
Definition
Group Iaafferents detects
changes in muscle length and the
rate with which this occurs
velocity sensitive”
monosynpatic to MNs
roup IIafferent detects changes
in muscle length
“position sensitive”
Polysynaptic (interneurons!) to MNs |
|
|
Term
| bag fibers. static vs dynamic bag fibers. |
|
Definition
| dynamic is length and velocty. static is just length |
|
|
Term
| what do gamma motor neurons excite? |
|
Definition
|
|
Term
| when i contract my muscle, i am firing intrafusal muscle fibers, what happens to the sensitivity of the muscle spindle? |
|
Definition
| increasing the sensitivity and stretch on the spindle. |
|
|
Term
The efferent innervation
is provided by gamma
motor neurons. what happens when they fire? |
|
Definition
The two types of gamma
motor neurons (dynamic
and static)cause the
ends of the intrafusal
fibers to contract, which
stretches the central
part and thereby alters
the sensitivity of the
fibers. |
|
|
Term
The response of the muscle
spindle to a given stretch
(bottom panel) can vary.
Why is this important? |
|
Definition
| you can regulate the sensitivity of the spindles. |
|
|
Term
| what is the meaning of the cat slide? what happens when we do something "New" with respect to golgi tendon organs? |
|
Definition
| for novel environments, you want as much information as possible, so you get activation of both static AND dynamic gamma motor fibers to get spindle information. however when novelty of the environment wears off, you can down regulate firing of the dynamic |
|
|
Term
Incoming Ia input can be reduced
by presynaptic inhibition. what is the mechanism? |
|
Definition
Increased conductance of chloride
causing a hyperpolarization in the
afferent synaptic terminal
This results in antidromic
collision and a refractory
period in which Na channels
will not open.
Result: Less Ca influx, less
depolarization and less NT
release from Ia afferent.
Result: depressed potential in
the post synaptic cell
orOr, metabotropic receptors can
close Ca
2+
channels, decreasing the
influx of Ca into the Ia afferent |
|
|
Term
| H-reflex - analog of the stretch reflex |
|
Definition
electrical analogue of the
stretch reflex?’
Direct motor response
precedes reflex response
Reflex response decreases
with increasing intensity |
|
|
Term
| normal nerve pathway is orthodromic. what is the opposite? |
|
Definition
| opposite direction of propogation is antidromic. |
|
|
Term
|
Definition
| this is the direct response from our stimulus from alpha motor neuron to muscle. |
|
|
Term
|
Definition
| it is the stimulus of the sensory pathway which then activates the motor fibers. |
|
|
Term
| Ia afferents are larger than alpha motor neurons, so with artificial stimulation, which one would fire first? |
|
Definition
| the I-a's stimulate the H-wave first. the larger the neuron, the smaller the resistance, so less current is needed to stimulate an action potential |
|
|
Term
| why does the h-wave go away at high stimulus strengths? |
|
Definition
| the antidromic signal runs into the orthodromic action potential from the sensory portion and cancels it out. |
|
|
Term
| why does pre-synaptic inhibition increase as you do more dynamic fast movements? |
|
Definition
| you've moved past the point where that sensory information would be helpful to you (when running, by the time you would have a reflex response, you are probably already at a different point in the gait cycle |
|
|
Term
The GTO is encapsulated
and innervated by a single
group Ib axon. what happens when we sueeze the muscle? |
|
Definition
The axon branches into
many fine endings that
intertwine among the
braided collagen fascicles.
Contracting muscle fibers
stretch the collagen
fascicles and squeeze the
Ib afferent. |
|
|
