Neuro 5-Somatic Motor System Flashcards
Alpha and gamma neurons are what kind of neurons?
Motor
What is the difference between Golgi tendon organs and Muscle Spindles
Both are sensory organs
Muscle spindle- detect stretch in muscle
GTO- Detect stretch in tendon
What are the joint kinesthetic receptors
Pacinian and ruffini corpusle
bare endings
Muscle spindles are ______ muscle fibers
Intrafusal
True or false: muscle spindles contract in their central region
False, the central region is non-contractile
Type 2 sensory fibers go to what muscle spindles?
Nuclear chain and STATIC nuclear bag fibers
(not dynamic nuclear bag)
Type 1a fibers go to what muscle spindles?
All 3
Nuclear chain, static, and dynamic nuclear bag
Static gamma neurons innervate the contractile endings of what muscle spindles?
Static nuclear bag and nuclear chain
Dynamic gamma neurons innervate the contractile endings of what muscle spindles?
dynamic nuclear bags
True or false: Sarcomeres are found inside of intrafusal muscle fibers
Sarcomeres are present in extrafusal muscle fibers and the polar regions of intrafusal fibers.
Extrafusal fibers are the standard muscle fibers responsible for muscle contraction and movement, and they contain sarcomeres throughout their entire length.
Intrafusal fibers, on the other hand, are found within muscle spindles and are involved in proprioception (sense of muscle stretch). Sarcomeres are **only present in the polar ends **of intrafusal fibers, not in the central region, which functions to detect stretch
What do gamma motor neurons innervate?
The contractile ends of muscle spindles
slide says: “polar regions of intrafusal fibers”
large? diameter Alpha motor neurons (also called lower motor neurons) innervate what?
Extrafusal skeletal muscle fibers
Large diameter 1a and 2 fibers originate from the _____ region of muscle spindles
Central regions
A typical muscle spindle contains ____ nuclear bag and ____ chain fibers
2-3 nuclear bag and 5 chain fibers
Muscle spindles measure the velocity of stretch from phasic discharge of ____ fibers
1a
Muscle spindles measure the steady state length of muscle from tonic discharge of _______ fibers
1a and 2
1a’s have both ____ and _____ discharges
whereas 2’s only have ____ discharges
1a: Phasic and tonic
2: only tonic
True or false: Muscle spindles fire even when muscle fibers are relaxing
True
Muscle spindles regulate _____________ neurons via feedback mechanism/stretch reflex
alpha motor neurons
Muscle spindles send input via sensory neurons to the spinal cord at the _________ horn and the spinal cord relays information to the muscle via alpha motor neurosn from the _______ horn
Dorsal horn (afferent)
Ventral horn (efferent)
Gamma motor neurons control the ______ of the muscle spindles
Sensitivity
Dynamic gamma motor neurons increase the dynamic sensitivity of…
1a fibers
Static gamma motor neurons increase the tonic activity of….
Type 1a and 2
Note: also decreases the dynamic sensitivity of 1a
When extrafusal fibers shorten the intrafusal fibers _______
Are slack, do not fire as much
Note: less stretch = less firing
Without the sensory afferents of muscle spindles, the CNS cannot monitor information about….
Muscle length/position
coactivation of gamma and alpha motor neurons ensure
appropriate length/tension relationship
What causes reciprocal inhibitor?
Golgi Tendon Organs OR Muscle Spindles
Muscle Spindles
How does reciprocal inhibition work?
Muscle spindles of agonist (example:quads) send signal to spinal cord
From the spinal cord a signal is sent that activates further contraction at the quads
AND it sends a signal via inter neurons to inhibit contraction of the antagonist (example:hamstrings)
True or false: reciprocal inhibition can occur voluntarily AND reflexively
True
Where are golgi tendon organs found?
At the junction between muscle fibers and tendons
What kind of neurons innervate the Golgi Tendon Organs?
1b fibers
What do Golgi tendon organs do?
Autogenic inhibition or activation
The respond to force/muscle tension at the junction between the muscle and its tendon
They can either inhibit or activate the same muscle that they’re found in.
True or false: both the Golgi tendons and the muscle spindles use fast conducting afferent nerves
True
What is the ratio of muscles to motor neuron pool?
1:1
all motor neurons within the muscle neuron pool innervate ____
a single muscle
MNs innervating the axial muscles are located where in the ventral horn? what about distal muscles?
located medially
located laterally
where are flexor muscles located in the ventral horn? extensors?
flexors located dorsally
extensors ventrally
describe a motor unit
one alpha motor neuron and all the muscle fibers it innervates
small motor units (not very many muscle fibers innervated) are used for what type of movement? what about larger motor units?
small = fine movements
large = gross movement
What determines if a muscle fiber is fast/slow twitch?
the neuron innervating the muscle
motor neurons/UNITS (both) are classified as slow twitch or fast twitch depending on speed of contraction
so “both”…. but motor neurons.
which fiber (type 1 or 2) can maintain levels of force for long periods of time?
type 1 (endurance)
which muscle fiber (type 1 or 2) has a larger axon diameter?
type 2 (fast)
larger forces but fatigue quickly
which muscle fibers are used for postural control?
endurance - type 1
What NT is released from the presynaptic neuron in the NMJ?
Ach
After being released into the NMJ, Ach binds to the muscle membrane, causing what?
Depolarization of the muscle membrane and then depolarization of the T-tubules in the muscle fiber
What happens following the depolarization of T-tubules in the muscle cell?
voltage-gated channels open, releasing Ca+ from the sarcoplasmic reticulum (SR)
To initiate a muscle contraction, ___ (what ion) binds to ___
Ca+
troponins
What is rate coding?
MN signals amount of force to be exerted by muscle
(frequency of firing determines contraction strength)
Tetanus
muscle is contracting maximally
Force summation is caused by
higher firing rate
How do slow vs fast twitch MNs compare with
time to peak-twitch force
contraction time
peak force
relative force summation
time to peak force: fast twitch have shorter time
contraction time: fast twitch have shorter twitch time
peak force: fast twitch generates higher forces
relative force summation: at lower frequencies, slower twitch form better summation
What is recruited first, smaller or larger MNs?
Why is this the case?
smaller
V = IR, smaller motor neurons have large resistance (“R”), so a smaller current (“I”) will still lead to higher V
small amount of synaptic current will be sufficient to cause the potential of small MN to reach the firing threshold
Z lines are ____ and are at the end of each sarcomere
Titin is ____ and anchors Z and M lines
fibrous
elastic
Which filament has the “head” and which one slides inwards towards M line? (thick or thin)
Myosin heads connect with actin, pulling actin towards center
What does Ca+ bind to in order to open active sites on actin?
Ca+ binds to troponin, causing tropomyosin to move off active sites
Resistance to stretch in resting muscle is
muscle tone
what determines the amount of muscle tone?
weak actin/myosin bonds at rest as well as titin
How does contraction or immobility impact muscle tone/resistance to stretch?
resistance to stretch increases for a short time after prolonged contraction or immobility
longer immobility = more weak actin-myosin bonds exist
(Think about when you exercise and feel your muscles, and how you feel stiff in the morning getting out of bed)
How are sarcomeres affected when patients are immobilized in a shortened position vs a lengthened positioned for a long time?
in a shortened position - lose sarcomeres
lengthened position - gain sarcomeres
What 3 things in your body can restrict movement?
joint capsules, noncontractile tissue and antagonist muscles (co-contraction)
T/F Cocontraction is a normal part of stabilizing a joint in function
T
Reflexive movements make up a __ (small or large) percentage of our movements. Define reflexive movements
small
involuntary motor response to an external stimulus
Spinal reflexes occur without what?
brain input
T/F: patients with SCI can have spinal reflexes after time
T
Describe the phasic stretch reflex
fast muscle stretch activates signals from the muscle spindles to alpha MNs for the same muscle causing a contraction
monosynaptic
Describe the cutaneous withdrawal reflex
monosynaptic reflex in the SC that occurs in response to pain/noxious stimuli before conscious awareness of pain
The following are examples of what?
- muscle cramps
- fasciculations
- myoclonus
- abnormal movements generated by dysfunctional basal ganglia
- fibrillations
- tremors
spontaneous involuntary muscle contractions
What causes muscle cramps?
high frequency discharges of MNs overstimulated by sensory and motor input
healthy or pathologic
What are fasciculations?
VISIBLE fast twitches of all muscle fibers in one motor unit
healthy or pathologic
What is myoclonus?
brief involuntary contraction - muscle jerks when falling asleep, hiccups
healthy or pathologic
what are fibrillations
NONVISIBLE, random, brief contraction so single muscle fibers
PATHOLOGIC
FIBRILation sounds like FIBER, single fiber
What are tremors? List the three types
involuntary rhythmic movement that can occur at rest or with movement
postural - body part maintained against gravity (usually upper limb)
orthostatic - standing, (usually lower limbs)
intention - absent at rest, worsen when target is approached
Conditions affecting the ___ ____ and ______ (what two brain structures) also present with tremor?
basal ganglia and cerebellum
List common signs of lower motor neuron lesions
hypoflexia or areflexia
paresis or paralysis
muscle atrophy
decrease or loss of muscle tone (hypotonia/flaccidity)
fibrillations
What do motor nerve conduction velocities/studies measure?
measure the speed and strength of electrical signals traveling through MNs to muscles
Why might an EMG be done for a patient with motor issues?
diagnostically differentiate between denervated muscle or myopathy
“muscle not working does not mean the neuron is not working”
What part of the nervous system does polio attack?
LMNs (at the ventral horn)
What are the affects of the polio virus and how does it lead to PPS? (post-polio syndrome)
polio causes death of selected MNs, your body then forms giant motor units from remaining MNs (neuroplasticity effect)
PPS - over time the giant MNs die off due to their excessive oxygen needs, causing fatigue, weakness and pain
