Section 3 Lecture 1 Flashcards by Tedman McMahon

Antigravity mm., extensor sor flexors?

extensors

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elimination fo unwanted moves at a j:

postural fixation (necessary for useful moves)

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T or F? Rods fxn in lower light levels and mediate color vision.

F. don’t mediate color vision (they do fxn in lower light levels)

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Is an agonist a flexor or extensor?

Can be either

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What do diffs in the desc control of flexors and extensors reflect?

The role of the extensors in resisting gravity

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Parameters of m. action (diff properties of mm.):

Force, resistance to fatigue, speed of contraction, fineness of control (small changes in force, small changes in joint angle)

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What parameters of m. action result solely from the structure of m.?

Force, resistance to fatigue, speed of contraction

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Does fineness of control result from the structure of the m. or the pattern of innervation of m.?

both

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T or F? The pattern of innervation affects the force of contraction a m. can generate.

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T or F? The pattern of innervation affects the resistance to fatigue of a m.

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T or F? The pattern of innervation affects the speed of contraction of a m.

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T or F? The pattern of innervation affect the fineness of control of a m.

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White m., fast or slow twitch?

Fast (FF and FR)

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Slow twitch, red or white meat?

red m.

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Fibers that are fast, more resistant to fatigue, and create a large force:

FR fibers

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Fast, fatiguable, large force, fast contraction time, fatigue readily:

FF fibers

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Can you increase the number of m. fibers or change the fiber type with training?

No, properties of individual fibers are changed

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Which fibers are most resistant to fatigue?

slow twitch

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Antigravity mm. require higher % of what fiber type?

S fibers

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T or F? Every m. is composed of a mixture of the fiber types.

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Cell bodies of alpha MNs are located here:

ventral horn

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Are a-MNs my or non-my?

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What are the bigger and slower conducting fibers?

aMN have large axons

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LMNs and spinal MNs are all:

a-MN

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How many m. fibers does each axon innervate?

2-1000's

What determines how many fibers are inn by a MN?

The size of the MN

T or F? In any give MN pool, MN vary in size (physical size of cell).

All MN's innervating a particular m.:

the MN pool

How are the MN of a MN pool distributed?

over several cord segments

T or F? There is a direct correlation bw the size of the MN and the number of fibers it innervates.

What do MNs release?

trophic factors, needed for healthy mm., regulate the survival of neurons

Can the axon of a MN live if the MN dies?

No, death, then atrophy (Pola/ALS) bc it is no longe getting trophic or growth factors

What does ALS stand for?

Amyotrophic lateral sclerosis

Full name of polio:

poliomyelitis

What kind of infection is polio?

viral

How is polio spread?

human to human contact, highly contagious

Where in the world is polio still present?

Afghanistan, Nigeria, and Pakistan

Polio hasn't been in the US since:

about 1979

What happens in Lou Gherig's disease?

death of a-MN (spinal/lower) and death of cells in MC whose axons descend in the CST

2 symptoms of the death of LMNs:

fasciculations (spont m. twitching as parent cell is dying) and m. atrophy

How many inputs does each m. fiber get?

One and only one

T or F? A single neuron in the brain can get info from many, many inputs

Unit of action of the motor system:

motor unit

How do the m. fibers in a single MU vary?

They don't

Which has larger MUs, FF fibers or S fibers?

FF fibers

How are the m. fibers in a single MU arranged?

Scattered about in the m.

Which has smaller MUs, FF fibers or S fibers?

S (for Smaller)

4 properties of larger MN's:

more force, faster response, faster to fatigue, innervates more fibers

T or F? The MUs that innervate any given m. are all of the same size.

F. diff sizes

MU's involved in fine control are:

smaller (smaller force increment than a larger unit)

T or F? The average MU size varies among mm..

Size principle:

MUs are recruited in order of increasing size, smaller recruited first and larger recruited last

S fibers are 1st/last recruited and the 1st/last to drop out.

1st, last

What allows for optimal adjustment of force increments when using a given m.?

Size principle: slow fibers which are fatigue resistant are in use more of the time.

2 kinds of feedback information from m:

muscle force (GTO) and muscle length (m. spindle receptor)

2 types of info spindles give you:

maintained length (even when constant length) and dynamic info, the info you get when m. length is changing.

What is the freq of AP generation related to in feedback info from a m.?

the change of m. length

How are m. spindle fibers arranged in relation to extrafusal fibers?

In parallel

Are m. spindles are found in every m. of the body?

yes

What would a higher density of m. spindles indicate about a m.?

That m. is used for fine control mm.

What is a m. spindle?

a CT sheath containing 2-12 intrafusal fibers

Describe intrafusal fibers:

ends contract, centers don't

Describe extrafusal fibers:

the whole fiber contracts

2 types of intrafusal fibers:

nuclear bag fibers (all nuclei of the cell are in a central bag-like region) an nuclear chain fibers (nuclei are lined up in a straight line)

Nuclear bag fibers:

rate of change of m. length

Nuclear chain fibers:

maintained or unchanged m. length (static)

2 types of sensory fibers for axons that send info from spindles into the M system in s.c.:

cell bodies in DRG, axons run to periphery and inn. m. spindles

Group Ia afferent fibers:

muscle spindle fibers (to detect change in length)

Group II afferent fibers

nuclear chain fibers (to signal maintained or unchanged length)

T or F? Intrafusal m. fibers contract from the center of the fiber.

F. form the poles

Can conduction velocity change?

Yes, ie. with diabetic neuropathy

Every single IF fiber in the spindle, end as annulospinal endings (primary endings) and convey:

dynamic and static info

Group II fibers:

only nuc. chain, 2ndary or flower spray endings, only static info

Where are the cell bodies for all sensory fibers?

DRG

Which are both larger and faster, Group Ia or Group II?

Group Ia

Sensory fibers are classified with letters/numbers while skin fibers are classified with letters/numbers.

Number, Letter

How is diabetic neuropathy assessed?

by measuring conduction velocities

Chx pox and shingles viruses can lie dormant for decades here:

DRG

M. spindles are stretch receptors, explain how they work.

stretching leads to mechanical depolarization

What is the importance of the m. spindle being aligned in parallel with EF fibers?

if stretched, APs can be formed (check)

Primary vs Secondary sensory innervation of spindle.

both Ia and II fiber innervation vs. only II fibers innervated

Which fibers form primary or annulospiral endings, Ia or II?

T or F? Ia fibers convey both dynamic and static info.

T or F? Both Ia and II fibers convey static info.

Which fibers form secondary or flower spray endings, Ia or II?

T or F? Group II fibers convey both dynamic and static info.

F static only

What initiates cell depolarization in Group II fibers?

stretch

Spindles during contraction:

m. gets shorter, spindle does not change length, spindle goes slack, no stretch on spindle, no stimulus to depolarize sensory axons, no AP generation

Solution to m. contracting and the m. spindle remaining slack:

M innervation of contractile poles of intrafusal fibers (the poles of the spindle will contract) This allows for parallel contraction.

How to send signals to the poles:

gamma motor neurons, fusimotor

Cell bodies for gamma MNs are in:

the ventral horn

Alpha MNs innervate:

intrafusal fibers

Gamma MNs innervate:

extrafusal fibers

What fraction of gamma MN's in s.c are not alpha MNs?

1/3 (check)

Can we consciously activate g-MNs or a-MN's?

No, automatic adjustments, out of conscious control

The bodies of g-MNs lie:

in the ventral horn, same as a-MN's

What do g-MNs innervate?

the contractile poles of intrafusal fibers, both bag and chain

How does our body work in terms of a- and g-MNs?

they are co-activated

How is the GTO attached in relation to the muscle tendon?

in series

GTO:

collagen basket and there is S inn. from 1b fibers. Same gen. anatomical plan.

When is the GTO active?

over the entire range of tensions that a m. can generate, not just at the extremes

What does the M.S. respond to?

gets info about length and force of m. and uses that info to correct info going out to that m.

How would an increase in force cause the channels to open on the fibers and create an AP?

in m. the collagen F's crunch down on S axons and trigger the AP