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HES 319 > Exam 2 > Flashcards

Exam 2 Flashcards

1
Q

what is the final common pathway

A
  • last pathway to muscle (neurons that actual connect to muscle)
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2
Q

what is the “common” part of the final common pathway

A

convergence - large number of neurons converges down onto a smaller subset of neurons to influence their behavior
- fat pathway: alpha motor neurons
- skinny pathway: gamma motor neurons

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3
Q

what is a motor unit

A

alpha motor neuron and all the muscles fibers it innervates
- axon can branch hundreds of times to innervate a lot

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4
Q

alpha motor nuclei

A

in ventral horn - but motor cell bodies for single muscle can be distributed 1-4 spinal segments

clinical significance: spinal cord injury you could still have some cells for muscle connected to brain above injury (could present as weakness or dysfunction)

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5
Q

frequency of motor unit twitches results in what?

A

produce tetanic force output of motor unit

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6
Q

force output of individual motor units which are actively firing causes what

A

larger force transmitted through connective tissue to tendon and bone

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7
Q

what are the events to activate a motor unit

A
  1. depolarization of alpha motor neuron
  2. propagation of A.P distally along axon
  3. once at axon terminals results in release of acetylcholine from pre-synaptic vesicles
  4. acetylcholine binds to motor end plate causes depolarization of sarcolemma
  5. A.P travels right and left than down t-tubules to SR
  6. Ca2+ is released from SR
  7. Ca2+ binds to actin to expose actin-mysoin sites
  8. cross bridge cycle (force production
  9. Ca2+ pumped back into SR
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8
Q

how quick are sarcolemmal action potentials compared to neural action potentials?

A

significantly slower (30-50 meters per second)
neural (80-90 meters per second)

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9
Q

what is the concentration difference of Ca2+ in the SR compared to the cytosol?

A

100 x more in the SR

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10
Q

what is the importance of the protein complex on the SR

A
  1. has voltage sensing membrane
  2. Ca2+ channel

when AP travels down T-Tubules it is sensed (has threshold) which changes the confirmation which triggers ion channel change to allow Ca2+ to flood out into cytosol

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11
Q

how long do Ca2+ ion channels stay open

A

very short amount of time (1-2 m/s)

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12
Q

what is the strong binding site for myosin ?

A

myosin has a strong affinity for the actin (attachement)

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13
Q

how do you get to weak binding for myosin

A

ATP binds to myosin head which creates lower affinity and the myosin heads pops off

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14
Q

what powers the power stroke

A

splitting of ATP

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15
Q

molecular motors (aka myosin)

A

proteins that change confirmations in response to certain stimulus to do something physical
- how things are transported (vesicle on back on molecular motor)

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16
Q

what is the enzyme used during cross-bridge

A

ATPase - splits the ATP molecule into ADP + Pi

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17
Q

how many AP take to create a muscle twitch

A

one AP = one muscle twitch

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18
Q

how does muscle work in real life (AP firing)

A

we fire a train of AP that do not give enough time to pump all Ca+ back into SR so we have a pool still in the cytosol which increases cross bridge ability

  • we sustain a tetanic force from repetitive stimulation
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19
Q

why do we have non-contractile structure proteins in muscle

A
  1. physical framework (cytoskeleton proteins) connected all over. Actin and Myosin sit within this structure
  2. connect force producing structure to the outside of the cell to provide route for force transmission.
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20
Q

what is the function of Titin protein (longest molecule you have)

A

attach to myosin and Z line. has a rubber band like structure that are important to biomechanics

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21
Q

what is the function of the costamere (focal adhesion) every couple of microns

A

anchoring point for cytoskeleton stands (at every z-line) to sarcolemma

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22
Q

integrin (trans-membrane protein)

A

outside cell attached to other molecules attached to basal lamina (extracellular matrix)

inside cell attached to proteins that create Costamere

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23
Q

Dystrophin function

A

“muscular dystrophy” most common is duchenne which is associated with screwed up dystrophin (important connection between inside and outside of cell) results in not being able to transmit force from muscle to bone

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24
Q

what is the important of focal contact proteins

A

connect proteins in extracellular matrix to allow force to be transmitted out of the muscle -> tendon -> bone

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25
what is another word for basal lamina
endomysium (connective tissue) surrounding muscle fiber
26
what is the innervation ratio
muscle fiber / number of alpha motor neurons
27
what is the importance of the innervation ratio
correlates with function of the muscle. Smaller innervation ratio is associated with fine/ precise movement
28
what is the structure that surrounds the whole muscle
epimysium (fascial sheath)
29
what structure separates skeletal muscle tissue into bundles of cells
perimysium
30
what surrounds individual muscle fibers
endomysium
31
what is the function of T-tubules?
allows sarcolemma A.P to travel deep to stimulate release of Ca2+ roughly at the same time throughout muscle fiber
32
what are the three type of motor unit fiber types
1. slow 2. fast-fatigue resistant 3. fast fatigable
33
what are some characteristics of slow-twitch fibers
force produced usually rises and falls slower in response to AP - can produce small amounts of tension for a prolonged period
34
what are some characteristics of fast-twitch fibers
rapid force produces in short amount of time - the fast fatigable produce more force in a shorter amount of time
35
define recruitment threshold
force required to initiate discharge of AP from motor unit repetitively during voluntary contraction
36
define orderly recruitment
fixed order that motor units are recruited
37
What determines force of a motor unit
Number of muscle fibers it innervated
38
Properties of motor units in one muscle
1. Innervation number 2. Twitch force (based on innervation ratio) 3. Speed of twitch (rate of force development) 4.fatiguable 5. Recruitment threshold 6. soma size of motor neuron 7. number of ion channels resistance 8. muscle fiber type that predominates motor unit
39
how much does muscle innervation number varies within a population (pool) of motor units
exponentially
40
motor units with long contraction times are what type and how much force do they exert?
slow twitch and exert a low tetanic force
41
motor units with fast contraction times exert what type of force
(fast fatigue resistant and fast fatiguable) exert a range from low to hight
42
difference in tetanic forces amoung motor units is mainly due to what?
variation in innervation ratio
43
fast twitch motor units exert large force, but they also do what?
exhibit very large range of maximal tetanic forces
44
within one motor unit, what are the muscle fiber types like (hetero or homogenous)
homogenous - but change a little in properties along continuum of motor units within a muscle
45
within a motor units pool are muscle fibers homogenous or hetero
heterogenous
46
what is the force-frequency relationship?
action potentials from motor neuron (your thought of contraction) which increases rate of discharge from motor neuron determines force produced by motor unit
47
on a force frequency graph, where is a steep increase and why?
5-20 Hz. tremendous response in force with little change in discharge frequency. This is where out motor units typically operate`
48
how does summative properties of motor units work
lower twitch start first and once hits force threshold for next motor unit to start firing, they all add together in the end
49
what is always true about recruitment threshold order
we always recruit motor units in the same order (1-120)
50
what causes motor units to fire first (think about motor neuron)
size of some for the motor neuron
51
what is the size principle
smaller motor neurons will always fire first (require less external excitation to begin firing A.P)
52
what is true of smaller motor neurons
smaller SA less ion channels
53
what is OHMs law
Vm = I (synaptic current) x R (resistance)
54
fewer ion channels is associated with what type of resistance
higher
55
more ion channels are associated with what type of resistance
lower
56
with same amount of excitation, what occurs between a small and large motor neuron
the small motor neuron will have a larger change in membrane potential and put over threshold (easier to excite) due to higher resistance
57
can you change the resistance property of motor neuron
No inherent biophysical property
58
how do you get larger motor neurons to fire in motor unit
higher synaptic input current
59
how do we use the given motor unit pools in a muscle to increase or decrease force?
1. recruitment (more or less) 2.changing discharge rate (decrease/increase firing rate)
60
a single upper motor neuron shares (common) input with how many lower alpha motor neurons
many to create shared common input also synergist muscles (common motion ie. elbow flexors) can have upper motor neuron innervation
61
what is true of common input from upper motor neurons
1. shared within alpha motor neurons for a single muscle 2. shared between synergist muscles
62
what are discrete movements
brief movements (force production) that have beginning, middle, and end. this is purposeful movement
63
what are the properties that determine recruitment threshold
size of soma -> number of ion channels -> resistance in cell. all of these properties related to the change in membrane potential and thus when a motor unit will be stimulated enough to fire
64
do humans have a consistent or fluctuating firing rate
fluctuating, we have inherent variability in the firing rate which results in variability in force production
65
what about de-recruitment of motor units?
tells brain to reduce force which reduces firing rate from upper neurons to alpha motor neurons which reduces activation of motor units (excitation declined enough so some motor units no longer hit threshold)
66
what determines the amount of force in a muscle at any given movement?
number of cross-bridges engaged at that moment
67
how does number of active motor units relate to determinants of muscle force (number of cross-bridges)
more motor units = more muscle fibers active
68
how does discharge rate of motor units relate to muscle force
higher discharge rate causes more Ca2+ release into cytosol to uncover active sites for myosin-actin binding to make cross-bridges
69
sarcomere length-tension relationship: what happens when sarcomeres are too short
less force because of mechanical blockage
70
sarcomere length-tension relationship: what happens when sarcomere are too long
actin is too far for myosin to grab
71
what did the experiments during tennis elbow show
anatomically real range of motion and sarcomere length change. sarcomeres only change a small amount of length in reality
72
force-velocity relation in muscle
during shortening contraction: slow contraction allows time to engage every cross-bridge possible. But with increased velocity you reduce the timing to create cross-bridge.
73
force-velocity relation in muscle: eccentric contraction
1. more Ca2+ is released during this type of contraction (more potential cross-bridges 2. stretching Titin in incompletely activated sarcomeres 3. more rapid re-attachment of cross-bridge
74
what is titin attached to?
Myosin and Z-line and are at every myosin interval. Acts like a spring. As you lengthen the molecule you are increasing the tension.
75
why is titin important to increased muscle force produced during muscle lengthening
when stretched they will increase tension even in non-activated sarcomeres
76
on a graph, if velocity is constant what relationship will you see?
length-tension relationship
77
on a graph, if length is constant what relationship will you see?
force-velocity relationship
78
what does a contour graph show?
shows how many potential cross-bridges can be engaged at the moment for a particular velocity and length
79
how does an isometric contraction work
no change in muscle tendon unit length (load torque = muscle torque) - because tendon is made of elastin and collagen we have a component that can stretch
80
what are the properties of tendon that allow isometric contraction
stiff spring = collagen compliant spring = elastin which illustrates changes in length are still possible. During isometric contraction the compliant portion can still shorten/lengthen in muscle
81
what does larger excursions in muscle architecture mean?
ability to change length
82
does in series fiber arrangement have higher or lower excursion ability?
higher because they are arranged almost in a line which can change length more
83
what does a higher excursion capability also mean for muscles in relation to contraction velocity?
large excursions also mean high contraction velocities
84
what are the properties of in parallel muscle architecture?
contractile units are stacked which have lower length change possible, but higher force production
85
do fusiform muscles have in series or parallel fiber arrangement?
in series
86
what is the structure of a pinnated muscle
central tendon with fibers angles out
87
are fibers in a pinnated muscle in series or parallel?
parallel, which allows more fibers to be packed together for more force production
88
what does the arrangement of fibers in a muscle differ on?
depends on the function of the muscle. If you want high force like vastus lateralis you will want pinnated (parallel) but biceps you want in series
89
what are the properties of muscle independent of the nervous system that substantially influence force output of muscle?
type of contraction (and velocity) design of muscle
90
goal-directed movements of limbs usually involve coordinated activation of what muscles?
agonist and antagonist muscles, which are usually activated sequentially
91
what is fitt's law?
faster movements are always less accurate and repeatable than slower movements. - don't have time to reactive correct movement at high speeds
92
what is biphasic activation pattern
acceleration and de-acceleration
93
what is triphasic activation pattern
fast, slow, fast correction
94
what are variations/ fluctuations in muscle force due to?
fluctuations in discharge rate of motor units
95
what causes fluctuation in motor unit discharge rate?
variability in descending command from brain
96
what is a "rock solid physiological concept" about motor unit recruitment?
very predictable amount of excitation is required to get a motor neuron to fire and resulting motor unit
97
how do we measure the firing of just one motor unit?
use fire wire electrodes and place it directly next to a motor unit. On the EMG the highest spikes correspond to that motor unit because it is closest to the recording device
98
are sarcolemmal or neural action potentials being recorded on and EMG?
sarcolemmal
99
what is the functional outcome of in series design?
greater excursion (length change ability) - lower force production
100
what is the functional outcome of in parallel muscle design?
- lower excursion - higher force
101
what occurs with NS activation to start a discrete movement?
agonist "burst" is followed by correcting activity by the antagonist & agonist
102
during what type of discrete movement do we see biphasic activation pattern?
fast movements - we dont have enough time to make a correction
103
why do we like to have more time to complete a movement?
allows time for correction - triphasic activation pattern
104
control of submaximal muscle force - what are variability in muscle force due to?
fluctuations in discharge of motor units
105
what are the neural reasons for why slower movements are more accurate or faster are not?
- larger burst of excitation for fast movements results in increased variability, and less repeatable - fewer opportunities to use sensory info when completing tasks quickly
106
why do motor units within a muscle exhibit common behavior
shared common input from upper neurons
107
firing rate of motor units is predetermined by what?
amount of excitation (descending command)
108
how is the degrees of freedom problem solved?
hierarchical scheme (brain doesn't have to worry about the lowest level of information going out or coming in)
109

HES 319 (3 decks)

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