LECUTRE 6- somatic motor system : proprioceptors and lower motor neurons Flashcards
examples of Sensory proprioceptors/muscle receptors:
• Muscle spindles
• Golgi tendon organs
example of motor neurons of the peripheral neuromuscular system
• Alpha α motor neurons
• Gamma γ motor neurons
what are the Specialized intrafusal muscle fibers with non- contractile central regions
• Dynamic nuclear bag (1a, dynamic γ)
• Static nuclear bag (Ia, II, static γ)
• Nuclear chain (Ia, II, static γ)
what originate from central regions of intrafusal
fibers
Large diameter myelinated sensory receptors (Ia &
II)
what innervate the polar contractile regions of intrafusal fibers
Small diameter myelinated motor endings (γ)
Typical muscle spindle contains ___ bag and__- chain fibers
2-3 and 5
what are Primary sensory endings for muscle spindles
la
what type of discharge is Primary sensory endings
phasic and tonic discharge
what Responds to changes in muscle length and
steady-state muscle length
Primary sensory endings
whtat type of discharge is Secondary sensory endings:
tonic discharge
what type of contracture is Secondary sensory endings:
II
what ending responds to steady state muscle length
Secondary sensory endings:
where does alpha and gamma motor neurons come off of
ventral horn/ root of SC
is alpha motor neuron extrafusal or infrafusal
extrafusal
is gamma MN infra or extra
infra
where are muscle spindles embedded inside of
muscle’s
extrafusal fibers
what does muscle spindles monitor
muscle length and prevent
over stretching
when does muscle spindles fire
Fire even when muscle is relaxed
how does muscle spindles regulate alpha motor neurons?
via
feedback mechanism (ex: stretch reflex)
When muscle is loaded, muscle lengthens/is
stretched which causes increased firing of
spindle sensory afferents, what neurons are these ?
la & ll
are alpha motor neurons efferent or afferent
efferent
how are alpha MN activated
by spindles at SC in ventral horn
how happens to the muscle spindle when muscle shortens
activity declines
which neuron is in continuum of activation while muscle is shortening
la
which MN regulate sensitivity of muscle spindles within intrafusal muscle fibers
gamma
what does the dynamic gamma MN innervate and what sensitivity does it increase
dynamic nuclear bag fibers & la
which gamma MN innervate both static nuclear bag and chain fibers
static
what dies static gamma NM increase activity of
tonic activity of la and ll
what Decreases dynamic sensitivity of Ia
static gamma MN
what happens to intrafusal fibers if gamma MN were not present?
less stretch which decreases spindle activity
what part of the intrafusal fibers do the gamma MNs innervate
polar regions ( the ends)
what afferent spindles for the intrafusal muscle fibers contain
la & ll
what ensure an appropriate length-tension
relationship during muscle contraction
Co-activation of α and γ MNs
if gamma MNs are not active during a alpha -gamma co activation what happens to the spindles
they will be slacken and its discharge rate will decrease as muscle shortens
during alpha - gamma co activation what does the gamma MNs adjust
sensitivity of muscle spindle
by Ia afferents
what does the motor controls strategy do during the alpha gamma co activation for alpha MNs
Reinforces α MN activity through
feedback mechanisms
what happens during reciprocal inhibition
When 1 muscle (agonist) contracts, its opposing
muscle (antagonist) is inhibited
during reciprocal inhibition, Muscle spindles of agonist send signal to SC that
activates:
activates:
1. Agonist
2. Interneurons that inhibit antagonist
when do reciprocal inhibition happen
voluntary and reflexive mvmts
what proprioceptors are Slender, encapsulated structure located at junction between muscle
fibers and tendon (intertwined)
golgi tendon organs
what are the golgi tendon organs innervated by
Ib sensory fibers
what are the golgi tendon organs sensitive to
changes in muscle tension ( stretch of tendon)
what are the 2 motor control strategy of golgi tendon organ
afferent signal from GTO inhibit activity of MN and results in muscle relaxation ( via neg
feedback mechanism – autogenic inhibition)
or
activates MN of its own muscle and its synergists via positive feedback
do muscle spindle and GTOs have slow or fast conducting afferent nerves fibers
fast
what are the 2 afferent nerve fibers that are fast
la and lb
what do the muscle spindle activate directly and what does it cause
alpha motor neurons and cause the muscle fibers to contract
what does the GTO provide
force feeedback , the more the muscle contracts the more GTO and afferents are activated
Efficacy of length and force feedback
can be regulated independently in
SC and via γ MNs
what are called the “final common path”
lower motor neurons
where are the motor neurons located and where do they exit
in cell bodies in ventral horn of sc and exit thru the ventral root
what are the 2 types of MNs
alpha and gamma
what are MN pools
Clusters of MNs within SC
Medially and laterally located pools innervate
M- axial and proximal limb muscles, L - distal limb
what do the ventral and dorsal located pools innervate
V- extensors and D- flexors
what are motor units
functional unit of voluntary movement
how are motor units defined as
α MN and muscle fibers it innervates
what is a group of muscles innervated by single spinal nerve
myotomes
what innverate slow twitch fibers
smaller MNs
do small MNs enervate more or less force than fast twitch fibers
less
which MN can maintain levels of force for long periods of time
Small MNs
are large or small MNs important in postural control
small
what innervates fast twitch fibers
large MNs
do the large MNs fatigue fast or slow
fast
what is an area where the motor axon divides into several fine branches
neuromuscular junction
in the neuromuscular junction, each branch forms multiple swellings called
presynaptic boutons
the presynapic boutons lay over specaialized region of muscle membrane called what
motor endplate
what is released at the motor end plate
acetylcholine released which causes depolarization of the muscle
where do motor axons synapse with muscle fibers
neuromuscular junction
steps of depolarization of muscle membrane potentials
Ach bind w receptors on muscle membrane resulting in membrane depolarization which induces depolarization of T tubes
voltage gated channels open and calcium ions are released from sarcoplasmic reticulum ‘
calcium’s ions bind to receptors on troponins, initiating muscle contraction
if you increase the firing rate of MN then there is in _____ in muscle force production
increase
what is induced by higher firing rate
force summation
what is tetanus
muscle is contracting maximally
pertaining to the time to peak-twitch force which twitch is shorter
fast twitch MNs shorter than slow twitch MNs
pertaining to contraction time which twitch is shorter
Fast twitch MNs shorter than slow twitch MNs
pertaining to peak force which twitch generated higher forces
ast twitch MNs generate higher forces than slow twitch across all frequencies
at lower frequencies what forms a better summation force
slow twitch MNs
what MNs are recruited and fire first
smaller MNS first then larger MNs
what is ohm’s law
V= IR (voltage = current x resistance)
Smaller MNs have smaller membrane surface area and few ion channels, and therefore ____
input resistance and then ____ excitatory post-synaptic potential (EPSP)
larger 2x
how much of synaptic current will be needed to cause the membrane potential of small
MN to reach firing threshold (generation of APs)
small amount
do smaller MNs have faster or slower conduction velocities
faster
each muscle fibers consist of ___ and are arranged
myofibrils and arranged parallel to long axis of muscle fiber
each myofibril consists of
sarcomeres
sarcomeres are function units of muscle containing….
contractile and structural proteins, thick and thin filaments
bounded by Z-lines (disks)
what is specialized muscle membrane
that surrounds sarcoplasmic reticulum and allows
propagations of action potentials
transverse tube ( t-tube)
in the sarcoplasmic reticulum (SR) what is released , what is stored and what does it facilitate?
Acetylcholine (Ach) released
• Storage sacs for Ca2+ ions
• Facilitates cross-bridge formation and initiates muscle
contraction
what is Fibrous, at end of each sarcomere
z line / disk
what holds together fibers at sarcomere center
M line
what Maintains actin/myosin positions to prevent sarcomere from getting pulled apart
titin
what are the structural proteins in sarcomere
z line
M line
titin
what are the contractile proteins of the sarcomere
myosin
actin
troponin
tropomyosin
what do the myosin headed bind with
active sites on actin
where are actin filaments attached to
each end of sarcomere to z-lines
within the actin , contractions occur when
actin slides relative to myosin, initiated when Ca2+ binds to troponin
what changes troponin
calcium binding to it
when calcium bind to troponin what does it cause
tropomyosin to move and uncover active sites on actin
what determines the total resistance to stretch
Active contractions, titin, and actin-myosin bonds
what is Resistance to stretch in resting muscle
muscle tone
what determines the mortal resting muscle tone
Thin/weak actin-myosin bonds and titin
the longer the immobility , what happens to the actin - myosin bond
there is a weaker bond
Healthy innervated muscles will lose sarcomeres when immobilized in shortened position for prolonged time (T or F)
T
( T/F )Healthy innervated muscles will gain sarcomeres when immobilized in lengthened position for long time
True
what can restrict movement
joint capsules and noncontractile tissues
what mvmts are small % of all mvmts
reflexive
what are spinal reflexes
nvoluntary motor response to external stimulus
what needs to be present for a reflex to occur
receptor, afferent nerve, synapse/s, efferent nerve, and muscle
can Spinal reflexes can occur without brain input?
yes
what is phasic stretch reflex
Muscle contraction in response to quick stretch (ex tendon tap)
what does fast muscle stretch activate
muscle spindles to α MNs of same muscle
what is a monosynaptic
1 synapse
what is a cutaneous withdrawal reflex
Another monosynaptic reflex in SC that occurs in response to pain
what is a painful contractions lasting sec/min due to overstimulation by sensory and motor tracts
muscle cramps
what is a Visible fast twitches of all muscle fibers in 1 motor unit
Fasciculations
Fasciculations can be
normal or pathologic
fibrillations of single muscle fibers ____ – always pathologic due neuro instability after
denervation
not visible
what is a Brief contractions of muscles or group of muscles
myoclonus
what are tremors
involuntary rhythmic mvmts
when do tremors happen
at rest or w movement
what are examples of pathologic tremors
postural , orthostatic, intention
essential tremor
parkinson’s disease
what are the signs of motor neuron lesions
• Decrease or loss of reflexes (DTRs)
• Paresis or paralysis
• Muscle atrophy
• Decrease or loss of muscle tone
• Fibrillations
what do electrodiagnostic studies differentiate between
disorders of MN , NM junction and muscle
what does a Electromyography (EMG) differentiate between
denervated muscle or myopathy
Poliomyelitis and post-polio syndrome (PPS) have what type of MN
normal
in Poliomyelitis and post-polio syndrome (PPS) there is death of selected MNs due to
acute polio
in Poliomyelitis and post-polio syndrome (PPS) there is no neuroplasticity of MNs during recovery, forming
giant
motor units
