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Muscle Receptors
Day 4
89
Anatomy
Graduate
01/26/2015

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Term
encapuslated receptors located at musculotendinous junctions in seriese with extrafusal fibers
Definition
golgi tendon organs
Term
intertwined among these tendon fascicles are fine ________ terminal endings of large primary afferent fibers
Definition
unmyelinated
Term
intertwined among these tendon fascicles are fine unmyelinated terminal endings of ______ ______ afferent fibers
Definition
large primary
Term
intertwined among these tendon fascicles are fine unmyelinated terminal endings of large primary _________ fibers
Definition
afferent
Term
in relaxed muscle, these nerve terminals within the tendon organs are not _________ or _______
Definition
distorted, compressed
Term
What must occur for these specialized tendon fascicles to become taut
Definition
muscle contracts and develops tension
Term
What happens as a result of these specialized tendon fascicles becoming taut,
Definition
they compress afferent nerve endings causing them to discharge
Term
golgi tendon organs have _____ firing thresholds to tension caused by muscle shortenting
Definition
low
Term
golgi tendon organs have _____ firing thresholds to tension caused by muscle lengthening
Definition
higher
Term
golgi tendon organs will always fiber in response to what type of motion
Definition
muscle shortening, contraction
Term
golgi tendon organs will not always fire to this type of action
Definition
muscle lengthening/stretch
Term
The adequate stimulus for tendon organ firing is development of tension by what type of muscles
Definition
homonymous
Term
GTO's discharge frequencies are ______ to the active tension developed
Definition
proportional
Term
GTO's are referred to as ______ receptors
Definition
tension
Term
Upon entering the spinal cord, central terminations divide into many terminal branches and synapse on small _______ and _______ interneurons in the spinal gray matter
Definition
excitatory, inhibitory
Term
The GTO synapses onto the interneuron, which in turn synapse upon what
Definition
motor neurons that innervate the same (homonymous) muscle
Term
any increase in active muscle tension excites tendon organs whose signal, in turn, inhibits homonymous motoneurons whose activity caused the tension
Definition
autogenous inhibition
Term
incoming signals that are inhibitory to motoneurons of one group of muscles, are at the same time excitatory to those of antagonists
Definition
reciprocal innervation
Term
all skeletal muscle contains several....
Definition
muscle spindles
Term
muscle spindle neural input does not reach what
Definition
consciousness
Term
one of the most complex receptors in the body
Definition
muscle spindles
Term
Muscle spindles provide sensory feedback to the CNS about what depending on limb position
Definition
absolute lengths of muscles
Term
Muscle spindles provide sensory feedback to the CNS about what in regards to movement
Definition
changes in muscle lengths
Term
Muscle spindles provide sensory feedback to the CNS about what in regards to velocity of movement
Definition
rates of change in muscle length
Term
neural feedback from muscle spindles comprises a major component of the sensory input responsible for (4)
Definition
motor control, motor coordination, kinesthetic sensation, proprioceptive sensation
Term
how long are muscle spindles approximately
Definition
8 mm
Term
each end of a muscle spindle attaches to what
Definition
extrafusal muscle fibers
Term
muscle spindle end attach to extrafusal muscle fibers with which they lie in _______
Definition
parallel
Term
muscle spindles attach to extrafusal muscle fibers which means what in terms of length
Definition
when one changes length, so will the other
Term
with passive increases in muscle length, what happens to spindle firing?
Definition
increases
Term
when muscle length decreases, what happens to spindle firing
Definition
decreases
Term
which muscles tend to be more involved in precise, skilled movements
Definition
distal muscles
Term
which muscles tend to be richer in spindles
Definition
muscles involved in a precise skilled movements
Term
which muscles tend to be less rich in spindles
Definition
large proximal and trunk muscles
Term
Muscles of which groups contain the highest number of spindles? (3)
Definition
deep neck muscles, hands, feet
Term
unlike most other receptors, muscle spindle sensitivity can be _______
Definition
adjusted
Term
how are adjustments made to muscle spindle sensitivity?
Definition
motor system that functions in parallel
Term
what is important to note about the motor system that controls muscle spindle sensitivity?
Definition
independent from the motor system that controls extrafusal muscle fibers
Term
muscle spindle sensitivity is controlled by what motor neurons
Definition
gamme motoneurons/fusimotoneurons
Term
what do gamma motorneurons innervate
Definition
small muscle fibers called intrafusal muscle fibers
Term
gamma motorneurons innervate intrafusal fibers that are found at _______ ends
Definition
polar
Term
what are the 2 types of intrafusal fibers?
Definition
nuclear bag, nuclear chain intrafusal fibers
Term
how do nuclear bag and nuclear chain intrafusal fibers differ (3)
Definition
morphologically, biochemically, functionally
Term
muscle spindles have primary and secondary ________ endings
Definition
afferent
Term
muscle spindles contain two types of sensory-end organs _______ and _______ afferent endings
Definition
primary, secondary
Term
which endings make firm and intimate contact with every intrafusal fiber within the spindle?
Definition
primary afferent endings
Term
which afferent endings make intimate contact around nuclear chain fibers but little/no contact on nuclear bag fibers
Definition
secondary afferent endings
Term
which afferent endings provide the CNS with information about velocity of movements?
Definition
primary afferent endings
Term
which fibers are implicated in velocity sensitivity of the muscle spindle
Definition
nuclear bags
Term
why are nuclear bags implicated in the velocity sensitivity of the muscle spindle
Definition
primary endings interact with nuclear bags, secondary do not. primary endings provide the CNS with information about velocity of movements
Term
during passive stretch, what happens to muscle spindle discharge frequency?
Definition
increases
Term
during active shortening, what happens to muscle spindle discharge frequency
Definition
decreases
Term
even if the muscle is relaxed at resting length, which endings are continuously discharging
Definition
primary endings
Term
primary endings are ________ discharging even if the muscle is relaxed at resting length
Definition
continuously
Term
primary endings are continuously discharging even if the muscle is....
Definition
relaxed at resting length
Term
which ending does not show spontaneous activity?
Definition
secondary endings
Term
which endings decrease their discharge and show a short pause in their firing during an evoked isometric muscle twitch
Definition
both primary and secondary endings
Term
primary and secondary endings decrease their discharge and show a short pause in their firing during what
Definition
evoked isometric muscle contraction
Term
the pause that occurs during an evoked isometric muscle contraction occurs at the time that what occurs
Definition
tendon organ has reached its peak firing rate
Term
what is the adequate stimulus for primary and secondary endings?
Definition
passive stretch
Term
at resting lengths, what endings fire?
Definition
primary endings
Term
the response of the primary ending to passive stretch has what two component
Definition
dynamic/phasic, static
Term
how does the firing rate of the primary ending compare during the dynamic/phase component than during the static phase when the muscle is being held at new length
Definition
firing rate of the primary ending is higher during the dynamic/phasic component
Term
frequency of firing during the dynamic phase of the stretch is proportional to what
Definition
rate of stretch
Term
the phasic component of the response codes what information
Definition
velocity of the stretch
Term
the static component codes information about what
Definition
absolute muscle length
Term
which endings are slowly adapting receptors
Definition
primary endings
Term
which endings provide the CNS with a continual input about muscle length
Definition
the persistently active primary endings
Term
primary spindle endings make what type of connection centrally? motor or afferent?
Definition
afferent
Term
central afferent connections from primary spindle endings make ________ synapses directly upon motorneurons innervating homonymous muscles in which the spindle lies?
Definition
excitatory
Term
central afferent connections from primary spindle endings make excitatory synapses directly upon motoneurons innervating the same muscles in which the spindle lies. What is the type of circuit called?
Definition
reflex circuit
Term
The reflex circuit serves what
Definition
stretch reflex
Term
central connections from primary endings: afferents also diver to influence the _______ of other neurons at the same and distal spinal segments
Definition
excitability
Term
central connections from primary endings: afferents also diverge to influence the excitability of other neurons, such as afferents making excitatory connections with motoneurons innervating synergistic muscles and inhibtory connections with motoneurons of the antagonistic muscles through inhibitory interneurons. This is an example of what?
Definition
reciprocal inhibition
Term
In any stretch reflex, homonymous and synergistic muscles will function together unoppose because of what
Definition
reciprocal inhibition of the antagonistic muscles
Term
in addition to their spinal connections, muscle spindles project information to what else
Definition
the brain
Term
muscle spindles project information to the brain where it is integrated with information from other regions of the body to permit what
Definition
purposeful and coordinated movements
Term
spindles have cortical representation, information from them appears to have no access to consciousness. T/F
Definition
true
Term
spindle input is thought to contribute to what sense
Definition
position
Term
spindle input is thought to contribute to position sense because joint position can be sense after what happens to cutaneous and joint receptors
Definition
after they are anesthestized
Term
spindle information projects to what part of the diencephalon and its neighbor?
Definition
thalamus and cerebellum
Term
why is spindle information projection to the cerebellum considered especially importnat?
Definition
for the regulation of direction, extent, speed of movements
Term
small motor axons that terminate within the spindle capsule on the polar regions of the intrafusal muscle fibers
Definition
gamma motor system
Term
action potentials in gamma axons cause what
Definition
intrafusal muscle fibers to contract
Term
what may innervate intrafusal fibers of more than one spindle
Definition
gamma axon
Term
with any on spindle a gamma axon will terminate on what
Definition
several intrafusal fibers
Term
the brain receives information from the muscle spindle but it projects information back to the spindles via what
Definition
gamma motor system
Term
if afferent input from muscle and joint receptors is distorted or abolished through injury or disease what happens
Definition
motor abnormalities result
Term
What is the machinery that allows the nervous system to independently adjust the length sensitivity and the velocity of the muscle spindle?
Definition
gamma motor system
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