Section 3 Lecture 1 Flashcards
Antigravity mm., extensor sor flexors?
extensors
elimination fo unwanted moves at a j:
postural fixation (necessary for useful moves)
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)
Is an agonist a flexor or extensor?
Can be either
What do diffs in the desc control of flexors and extensors reflect?
The role of the extensors in resisting gravity
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)
What parameters of m. action result solely from the structure of m.?
Force, resistance to fatigue, speed of contraction
Does fineness of control result from the structure of the m. or the pattern of innervation of m.?
both
T or F? The pattern of innervation affects the force of contraction a m. can generate.
F
T or F? The pattern of innervation affects the resistance to fatigue of a m.
F
T or F? The pattern of innervation affects the speed of contraction of a m.
F.
T or F? The pattern of innervation affect the fineness of control of a m.
T
White m., fast or slow twitch?
Fast (FF and FR)
Slow twitch, red or white meat?
red m.
Fibers that are fast, more resistant to fatigue, and create a large force:
FR fibers
Fast, fatiguable, large force, fast contraction time, fatigue readily:
FF fibers
Can you increase the number of m. fibers or change the fiber type with training?
No, properties of individual fibers are changed
Which fibers are most resistant to fatigue?
slow twitch
Antigravity mm. require higher % of what fiber type?
S fibers
T or F? Every m. is composed of a mixture of the fiber types.
T
Cell bodies of alpha MNs are located here:
ventral horn
Are a-MNs my or non-my?
My
What are the bigger and slower conducting fibers?
aMN have large axons
LMNs and spinal MNs are all:
a-MN
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).
T
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.
T
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
T
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..
T
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?
Ia
T or F? Ia fibers convey both dynamic and static info.
T
T or F? Both Ia and II fibers convey static info.
T
Which fibers form secondary or flower spray endings, Ia or II?
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
