Unit3_Motor Systems Flashcards
Small motor unit = _____ alpha-motor neuron → innervate small number of muscle fibers → _____ force
Small motor unit = Small a-motor neuron → innervate small number of muscle fibers → small force
An alpha-neurons and the muscle fibers that innervates is called?
Motor Unit
T/F?
Muscle fibers of a motor unit are of the same fiber type.
TRUE
Each muscle fiber is only innervated by one motor NEURON
What size motor unit preferential innervates slow twitch muscle fibers?
Small motor unit
What size motor unit requires more input to drive (recruited later and with larger currents)?
Large Motor Units
what motor units preferentially innervate fast twitch glycolytic muscle fibers that are quick to fatigue?
Large motor units
______________ : population of a-motor neurons that innervate the muscle fibers within a single muscle
Motor neuron pool
Describe the size principle for the recruitment of muscles.
- Systemic recruitment of smaller to larger motor units - generates graded forces.
- Orderly recruitment of increasingly forceful motor units because small neurons have HIGH input resistances → given synaptic current induces larger voltage change in a small motor neuron compared to a large motor neuron
The following describes what type of muscle cells/fibers?
non-spiking muscle fibers, shorten extremely slowly, efficiently generate isometric tension with low fatigability.
Tonic
The following describes what type of muscle cells/fibers?
Generate APs to twitch, fatigue very slowly, high conc. of myoglobin and many mitochondria
Slow Twitch
The following describes what type of muscle cells/fibers?
activate quickly, many mitochondria, fatigue moderately slowly.
Fast Twitch Oxidative
Make up the “Fast Fatigue-Resistant” Motor units.
The following describes what type of muscle cells/fibers?
Actives quickly, fatigue rapidly, few mitochondria, depends on anaerobic glycolysis ATP generation.
Fast Twitch Glycolytic
makes up “Fast-Fagtiable” motor units
Exercise/Chronic stimulation can shift motor unit phenotype from fast to slow → slows fatigability, ________ endurance capacity
increases
What is muscle tone defined as and why is it important?
Muscle tone: defined as resistance to muscle stretch - important for walking, standing, running, etc.
The stretch reflex provided resistance to stretch resulting in what?
enhances muscle tone
______________ neuron activation → top-down regulation of muscle tone
gamma-motor neuron activation → top-down regulation of muscle tone
__________: condition of decreased muscle tone due to damage to 1a sensory afferents innervating spindles or a-motor neurons innervating muscle
Hypotonia
What is Hypotonia?
condition of decreased muscle tone d/t damage of 1a sensory afferents innervating spindles or alpha-motor neurons innervating muscles.
__________: due to damage to descending motor pathways that influence spinal cord premotor circuits
Hypertonia
What is Hypertonia?
d/t damage to descending motor pathways that influences spinal cord pre-motor circuit.
What is a muscle spindle?
aka: intrafusal muscle fiber.
proprioceptor embedded within a muscle, composed of muscle fibers.
- Preferentially signals muscle stretch
- Important for maintaining muscle tone
- Feedback system for maintaining muscle strength
What type of fibers do muscle spindles use? (intrafusal muscle fibers)
Group 1a and group 2 fibers
How do group 1a fibers work?
Ia → synapse on a-motor neurons in spinal cord → trigger muscle contraction of homonymous muscle fiber in response to stretch.
- Have a non-zero firing rate under baseline conditions → maintenance of muscle tone
- Can signal passive stretch by increasing firing rate and passive shortening by decreasing firing rate
______________ : special motor neurons that innervate intrafusal muscle fibers
gamma-motor neurons
What do alpha and gamma motor neurons do during voluntary contraction?
alpha and gamma neurons fire together!
During voluntary contraction, a and y motor neurons fire together → shorten extrafusal AND intrafusal muscle fibers together → maintains spindle sensitivity to stretch
Gamma motor neurons do not directly interact with ____ fibers→ not engaged during reflexive contractions
1a fibers.
Gamma motor neurons do not directly interact with Ia fibers→ not engaged during __________________.
reflexive contractions
______________: collagen structures at junction of muscle and tendon, made up of capsule and collagen fibrils
Golgi tendon organs
Golgi tendon organs: ?
collagen structures at junction of muscle and tendon, made up of capsule and collagen fibrils.
Important for stabilizing muscle contractions
What types of fibers are Golgi tendon organs innervated by?
1b fibers
how are GTOs connected to muscle and tendons?
In series
GTOs participate in the _______ ________ _________ of muscle tension.
GTOs Participate in negative feedback regulation of muscle tension
Are GTOs contractile?
NO!!!
GTOs are not innervated by gamma-motor neurons.
Hammer tap → stretch muscle spindle→ stimulate Ia sensory axons → activate a-motor neuron in spinal cord → con.tract stretched muscle.
What reflex does this describe?
Stretch Reflex Circuit; “Knee-Jerk” reflex
Monosynaptic
What is Reciprocal Innervation?
1a fibers also innervate other inhibitory interneurons → inhibit other motor neurons → inhibit opposing antagonist muscle
In rapid error correction in movements,
Heavier than we expect → muscle spindle stretches more than muscle fibers → increase Ia spindle firing → __________ contraction of muscle fibers via a-motor neurons.
increase
mismatch between expected and actual muscle stretch detected rapidly and used to correct errors in motor output is called what?
Rapid error correction in movements
What reflex protects musculature from over exertion by relaxing the synergistic (homonymous) muscle and contracting the antagonist.
Extensor-Flexor coupling circuit
Ib afferents innervate GTOs → GTOs directly innervate inhibitory and excitatory interneurons in spinal cord is the mechanism for what reflex?
Extensor-Flexor coupling circuit
Which reflex involves cutaneous sensory/nociceptors receptors that innervate the spinal interneuron motor network?
Crossed-Extensor reflex
→ coordinate extensor relaxation and flexor contraction on same side as stimulus and converse extensor contraction and flexor relaxation on contralateral side.
Describes what reflex?
Crossed-Extensor reflex
_____?_____: neural networks that can produce patterned, rhythmic outputs in absence of sensory or central input - coordinate complex movements
Central Pattern Generator
Where is the Central Pattern Generator (CPG) located?
Mesencephalic locomotion center
Sensory and descending input from upstream motor centers can modify CPG output, but sensory is ___ necessary for CPGs to generate organized rhythmic motor output
NOT necessary
What are the modulary functions of the motor system?
cardiovascular, respiratory control, and sensorimotor reflexes, eye movement, sleep-wake regulation, and coordination of limb/trunk movement
What are the pre-motor functions of the motor system?
- Regulate locomotor speed via Input from mesencephalic locomotor region - initiator of CPG activity.
- Anticipatory responses to voluntary movement (e.g. flex legs before lifting weight, anticipating change in center of balance).
- Important for posture, balance and anticipatory movements.
__________ tract: send axons ipsilaterally and innervate medial part of ventral horn
Reticulospinal tract
What is the Vestibular nuclei?
vestibular system (vestibulospinal tract) informs brain of head position, orientation, and motion - important for protective responses to falls
Sensory info detected by what and sent via 8th cranial nerve to vestibular nuclei
semicircular canals
Vestibular nuclei sends info via what tract that regulate eye movement?
descending projections to cranial nuclei 3, 4, 6.
Vestibular nuclei sends info via what tract that regulate head orientation and neck muscle activation?
Medial vestibulospinal tracts to medial spinal cord
Vestibular nuclei sends info via what tract that control proximal limb musculature.
Lateral Vestibulospinal tract to lateral motor pools.
What reflex produces eye movement that counter head movements to keep gaze fixed.
VOR
no VOR = brain damage
The midbrain structure responsible for orienting gaze and body position is called the?
Superior colliculus/Tectospinal tract: (aka colliculospinal tract).
Computes a map merging auditory and visual space onto body coordinates.
Descending projections of colliculospinal tract target motor neurons that control axial musculature of neck (e.g. turn head/upper torso towards siren going off)
