Muscles, Unit 3 Flashcards
what distinguishes nicotinic and muscarinic receptors?
Where they are localized; the parasymp has musc, the nmj has nic
what is the physiology of an NMJ good for?
High gain system; contracts reliably; one nt, shape of synapse
what is the mechanism of action of curare and botulinum toxin
block ach release
what do glycogen depletion experiments show?
that muscle fibers innervated by the same MN are scattered uniformly through a muscle, not clustered
what are characteristics of fast fatiguing muscle fibers?
white, few capillaries, little myoglobing, but are supplied with glycolytic enzyemes
what is the histochemical profile of a red muscle fiber?
myoglobin etc, cannot metabolise, resist fatigue
which type of muscle fiber shows more variety in fatigue indexes?
White fibers
for what type of muscle is rheobase the smallest?
for s-type (red)
what is type-grouping
the clumping of type of fiber innervated by a mn after cutting and reinervatting
evidence that the mn specifies the type of muscle fiber?
after transection, type grouping occurs, and you restore the properties to the muscle fiber that it had earilier; more heterogeneous
evidence muscle can influence the mn
if a transected mn is redirected to a muscle that has no vacant end plates, mn will remain undiff, f forced to connect to s type muscle will not change muscle, mn properties change
how does exercise increase muscle size?
hypertrophy; increase in muscle size. hyperplasia does not occur
during training, how is efficiency improed?
first sign is how quickly a pluse of ach can be delivered (e stem can produce up to 30% greater muscle tension)
how does exercise effect mn types? fiber types?
mn type does not change, but proportion of muscle fiber type can
what is the arrangement/function of muscle spindles?
lie in parallel with extrafusal muscle fibers, stretch when muscle stretches
nuclear and afferent charicteristics of bag1.intrafusal fiber
nuclei are clustered in center, innervated by !A (large) fibers, which terminate near center.
bag2 and nuclear chain properties
nuclei scattered throughout, !a and II afferents, terminations more distally
What do Bag1 fibers respond best to, why?
during stretch movement, sensor is at elastic middle, affects IA (velocity detectors)
What do Bag2 fibers respond best, why
the length of muscle stretch, will affect group II fibers. (length detectors)
when a muscle is released from stretch, primary afferents will be—–, secondary afferents willl—–
be inhibited, ;fire less
what unwanted situation occurs when muscle shortening happens, and is prevented by contraction of he intrafusal muscle fibers
unloading
why does.a cut muscle have less activity in the spindle afferents?
you have removed motor drive, B mn come from sc ventral horm
What class of mn innervate each type of intrafusal fiber?
gammaD - Bag1 and gammaS -bag2 and chain.
Gogli tendons (Ib) do this?
are stimulated whe when a tendon stretch (its muscle contracts)– prevents antagonist from contracting.–smooth, not protection
what type of movement recruits a Gamma d/gammaS mn?
fast and big/slow
what does stimulation of free nerve endings in muscle cause?
exercise pressor responses
what is wrong with the gamma loop hypothesis
too fast for feedback? no accounting for load?
What is servo length hypothesis?
do not depend on load, intrafusal fibers receive feedback from muscle to maintain at optimal length
What does an Ib afferent respond to?
muscle contraction (ie tendon stretch)
why are Ib inhibitory interneurons called non-reciproal?
because they don’t affect the antagonist muscle
Type III (Agamma) nerve endings are important for what?
physiological response to exercise; metabolites from muscle contraction trigger, bring more o2 and nutrients to a muscle
why are goldi tendon organs slow to resopond to stretch?
change in length occurs mostly in the extrafusal fibers
muscle spindle lies in —- with respect to muscle fibers, golgi tendon is in —–
parallel,(fire with muscle stretch), series fire with muscle contraction)
what happens during a contraction if the ventral root is cut?
this means no gamma mn firing– so primary and secondary afferents will stop firing during muscle contraction
Describe the sc connections of Ia afferents:
heavily to to lamina IX, (terminate on MN,) agonist and inhibiotyr interneuron ie antagonist, eg myostatic reflex, passive stretch due to load
secondary afferents make this type of sc connection
barely any IX connections, intermediate grey
where do group Ib afferents connect in the sc?
intermediate gray only
define myotatic reflex?
contraction of a stretched muscle by a monosynaptic proprioceptive input ot a alpha motoneuron innervating the muscle being stretched (holding a glass that’s being filled)
reciprical inhibition?
Ia inhibitory interneurons responsible for this, turn on agonist and turn off antagonist. (reflex hammer)
role of renshaw cells?
recurrent inhibition of mn that excited them; negative feed back to stablize contractions.
what is the only type of interneuron know to receive renshaw inhibition?
type 1a inhibitory interneuron, may serve to regulate strength of receprocal inhibition to antagonist ;mn
what give input to a renshaw cell?
an alpha mn, or descending input
to make a more powerful reflex, Ia inputs can do what?
produce inhibition of mn of antagonists, this is disynaptic
many pathways provide inputs to motoneurons also send signals to Ia inhibitor interneurons. this is an example of
conserfation within the central neural circuitry
Group Ib fibers make this kind of inhibition
no reciprocal; inhibition of the muscle being stretched
what is antidromic response?
stimulating at axon, therfore anti to the direction, will pass collision test (ie cancel out)
what is orthodromic response?
stimulating across a synapse; stimulating at soma, recording across synapse at soma, will fail collision test
propriospinal neurons connect segments of the sc to integrate movement. medially —— range axons supply—– muscles, and —– range axons supply —- muscles.
long, axial; short; distal
are supraspinal structures necessary to generate locomotion?
no, in a spinalized cat, still have basic pattern–alternation of flexors and extensors;stimulating afferents by putting on a treadmil
how do supraspinal structures contribute to locomotion?
MLR (mesencephalic locomotor region) initiates and controls speed
does the MLR provide input directly to the SC?
NO! reticular formation, inputs integrated with other inputs from vestibular, cerebellar, cortical etc
what are the inputs to the MLR?
bg, limbic system, lateral hypothalamus, inhibition from STN
what happens when you stimulate MLR?
find responsive neurons in lamina VIX of the spinal cord (ventral horn)
are peripheral inputs needed for walking? how do you know?
no, cutting the DR does not abolish walking
afferent feed back is important for what in walking?
reinforcing the step cycle, and in posture
what is odd about the locomotor reflex pathway?
the convergent input of extensor muscle Ia, II and Ib spindle afferents during stance do not shut off extensor, instead, the allow extensor to stay active.
how could cutaneous stimulation be important in gait?
eg the stumble response, a prolonged swing face stimulated by sensation on the dorseum of the foot
what role do Ia inhibitory interneurons play in walking?
they ensure that flexors and extensors are not active at the same time
Features of LVST; Arises-, descends- crossed or not? role in movement?
LVN, terminates in VIII and VII travels in ventrolateral funiculus, effects neck movements may be direct, indirect to other,ipsi
MVST: how does this differ from LVST?
medial longitudinal fasciculus, and travels bilaterally, mainly in cervical sc, neck.
how does the LVST influence limbs on the opposite side?
through commisural internuerons
what is LVST good for?
can influence alpha and gamma mn on both sides, maintain posture when falling
when is LVST most likely to be activated, why?
for ear-down movement, because they receive convergent otolith and canal signals that are activated by this– think quadrupeds!
what part of the reticular formation sends fibers to the spinal cord, where?
Gigantocellular- medial, descending, mainly indirec, some direct a and g activation
where do medullary reticulospinal axons go?
lateral funiculus
where do pontine reticulopsinal axons go?
ventral funiculus
descending monoaminergic pathways originate from the—- with serotonin and —– with noradrenergic
meullary raphe, locus coeruleus
evoloution of rubrospinal tract:
most important in rats, in cats activates flexors and inhibits extensors, in primates ends at cervical
two cortical spinal pathways:
dirct-ducusssates at pyramid-direct contact w mn, indirect goes to reticular formation,
