Ch. 10: The Motor System Flashcards
- What is a Lower Motor Neuron (LMN)?
- What does it connect?
- Is it located Superior or Inferior?
- “Peripheral” motor neurons
- Spinal cord to muscle
- Inferior
- What is an Upper Motor Neuron (UMN)?
- What does it connect?
- Is it located Superior or Inferior?
- “Central” motor neurons - “descending tracts”
- Head to spinal cord
- Superior
What is the neurotransmitter of muscle contraction?
ACh
What is the ion of muscle movement?
Calcium
Which contractile protein moves over the other: Actin or Myosin?
- Actin mvoes on myosin
- Myosin stays still
What is the M line?
Anchors Myosin
What is the Z line?
Anchors Actin
What is Titin and what is its function?
- Rubber band like sarcomere
- Stabilize muscle aginst stretch or overstretch
- Does NOT cause muscle contraction
What is Active Stiffness?
- Contraction of muscles
- Conscious/intentional = normal
- Unconscious/unintentional = pathological
What is Reflex Activity?
- Type of active stiffness
- Branches of sensory neurons can activate lower motor neurons
What is Intrinsic Stiffness?
- Weak attachments of actin and myosin (velcro)
- happens when you do not move - easily broken apart
What is Passive Stiffness?
Limits of stretching out Titin
What sarcomere length produces maximal force?
Mid length
(starting patient here is easiest for them)
What is a contracture?
Loss of muscle fibers shortens muscle
(can result from shortened immobilization)
What is Serial Casting or Chronic Stretching?
stretching the promotes the addition of sarcomeres
What is co-contraction or joint stiffness?
What are the 2 types?
Partial or full contraction of muscles on both sides of a joint or “around” a “body segment”.
- Static (stiffly lock a joint) - tightening on both sides
- Dynamic (control movement of a joint) - one side shortens, one lengthens
LMN’s:
What are the two types?
- Alpha motor neurons (A-alpha).
- Innervate extrafusal muscle fibers = contract muscle
- Gamma motor neurons (A-gamma).
- Innervate intrafusal muscle fibers = keep spindle sensitive during movement
What is a motor unit?
1 peripheral axon and the muscle FIBERS it innervates
What is the order of recruitment (Henneman’s size principle)?
Usually slow twitch first, then fast
For gross motor control, how many muscle fibers per axon?
Many
For fine motor control, how many muscle fibers per axon?
Few
What is Alpha-Gamma co-activation?
- Simultaneous activity in A-alpha and -gamma motor neurons - intra and extrafusal muscle fibers contract at the same time
- Occurs during all voluntary movement.
- Functional significance: Activity in alpha and gamma at the same time - muscle spindle sensitive to stretch during voluntary movements
- Mechanism: Every UMN, xerox message and send copy to alpha and gammas
What happens in the convergence of info on alpha motorneurons?
- Messages from brain coming down
- Messages from sensory receptors coming in
- Both converge on peripheral motor neurons
What do axons from a motor neuron pool project to?
a single muscle
How many spinal levels are included in a single pool?
could be several
But, only 1 muscle
How many dermatomes are included in a single pool?
could be several
But, only 1 muscle
What is the horizontal organization of the motor neuron pools in the spinal cord?
All in ventral horn
- Medial pools = axial (core) and proximal muscles
- Lateral pools = distal muscles
- Anterior pool = more extensors
- Posterior pool = more flexors
What is reciprocal inhibition?
Both sides of joint: muscle of interest contracted, muscle on other side is inhibited
- Connections from upper motor neurons to alpha motoneurons.
- think to move, inhibition is automatic
- Connections from muscle spindle afferents to alpha motoneurons.
- when reflexes affect your muscles, inhibition is automatic
What are muscle synergies created by?
Any or all of the following:
- Activation of multiple upper motor neurons
- multiple messages to move comes from brain
- Branching of upper motor neurons
- branches to several different motor neurons
- Interneurons networks
- small connecting neurons between other connections
What is a “normal” muscle synergy?
group of muscle work together under conscious control in any pattern for functional outcome.
What is a “abnormal” muscle synergy?
group of muscle work together NOT under conscious control in LIMITED pattern AND DON’T ACHIEVE a functional outcome.
What is the role of Golgi Tendon Organs in movement?
- Tension in a tendon or muscle
- Adjusts muscle activity based on tension in context of desired functional activity
What are stepping pattern generators?
Wiring within spinal cord between spinal cord and brain that supports automatic walking
What is a Phasic Stretch Reflex?
- Stimulus = stretch of MUSCLE SPINDLE primary endings
- Monosynaptic connection
- Response = brief facilitation or activation of alpha motorneurons in same muscle
What is a Withdrawal Reflex?
- Stimulus = activation of nociceptor –> A-delta fiber.
- Multisynaptic (vertical branching)
- Response = automatic withdrawal of limb with pain.
What is the relationship between reflexes and voluntary movement?
- Sensory input (reflexes) can modify voluntary movements.
- Voluntary activation of upper motor neurons can modify the effects of reflexes.
What motor neurons are considered the “director” tracts?
Upper Motor Neurons (UMN)
hat motor neurons are considered the “helper” tracts?
Lower Motor Neurons (LMN)
Where do UMN’s “director” tracts usually start and end?
- Start: cell bodies above the brainstem (in the precentral gyrus)
- high level of conscious control
- End: in ventral horn of spinal cord
Where does the MEDIAL division of the UMN “director” tracts project?
to LMN’s of PROXIMAL arms & legs
“move any way I want”
Where does the LATERAL division of the UMN “director” tracts project?
to LMN’s of DISTAL arms & legs
“move any way I want”
Where do UMN “helper” tracts usually start and end?
- start: have cell bodies in the brainstem
- heavy lifters - limited concious control
- end: in ventral horn
Where does the MEDIAL division of the UMN “helper” tracts project?
- to LMN’s of prox arm & leg
- to LMN’s of flexors
- “Help pick stuff up against gravity”
Where does the LATERAL division of the UMN “helper” tracts project?
- to LMN’s of distal arm & leg
- to LMN’s of extensors
- “Hold me up and balance me against gravity”
Which of the UMN’s have the highest level of conscious control?
UMN “director” tracts
Which of the UMN’s have the highest level of voluntary control?
UMN “director tracts”
What are the 2 lateral activation systems that cover both distal extremities?
- Lateral corticospinal tract - director
- Rubrospinal tract - helper
What is the Lateral Corticospinal Tract and what does it do?
- biggest director - highest level of control
- Produces fractionation of movement
- fine motor control
- Majority of finers from “primary motor cortex”
- Crosses midline at bottom of medulla
What is the Rubrospinal Tract and what does it do?
- Helper - lower level of control
- lateral division - more to extensors
- 100% crosses midline
What are the 4 descneding motor tracts (UMN’s) of the medial activation system?
-
Medial Corticospinal Tract
- Director - medial division
-
Reticulospinal Tract
- Helper - medial division - more to flexors
-
Medial Vestibulospinal Tract
- Helper - medial division - more to extensors
-
Lateral Vestibulospinal Tract
- Helper - medial division - more to extensors
What is the Reticulospinal Tract and what does it do?
- Helper - medial division - more to flexors
- Mian helper for “pick stuff up” (esp arms)
- Projects bilaterally
- Medial division helper (core & prox muscles)
- Flexor muscles
What is the Medial Corticospinal Tract and what does it do?
- Director - medial division
- ONLY director of medial core and proximal musclescore & proximal
- cortico = high level of contral
- Bliateral projects
What is the Medial Vestibulospinal Tract and what does it do?
- Helper - medial division - more to extensors
- “Keep you upright against gravity”
- Bilateral projections
- starts in vestibular nucleus
What is the Lateral Vestibulospinal Tract and what does it do?
- Helper - medial division - more to extensors
- Extend legs to keep you upringt against gravity
- Unilateral - projects to same side of body
- Starts in vestibular nucleus
- Lateral BUT part of core & prox muscle division
In the descending Motor Tracts (UMN’s) what are the 2 Nonspecific Activation Ststems?
What do they do?
- Ceruleospinal Tract
- Raphespinal Tract
Connect emotional and autonomic system (back to spinal cord) to motor neurons → inc activity of all other motor neurons/tracts
