Motor Neurons Flashcards
(41 cards)
1
Q
Describe UMN
-
A
- Motor tracts
- cell bodies in CNS
- target/synapse in CNS
- connect with LMN
2
Q
Describe LMN
A
- cell bodies in CNS/Spinal cord
- target periphery
3
Q
Describe what occurs when we decide to move
A
- Frontal lobe makes decision to move
- motor planning areas activated
- control circuits (basal ganglia/cerebellum) regulate activity of UMN
- UMN tracts deliver signals to interneurons and LMNs
- LMNs signal skeletal muscle
4
Q
Where are the cell bodies of the LMN located
A
- ventral horn
- their axons leave the spinal cord via the ventral horn
5
Q
Classification of UMNs (motor tracts)
A
- postural/gross motor tracts: control automatic skeletal muscle activity
- fine movement tracts: fractionated movements of limbs and face
- nonspecific tracts: facilitate all other motor neurons
6
Q
Multipolar neuron
describe look
A
- cell bod with many dendrites
- axon with multiple collaterals
7
Q
Types of LMN
A
- alpha motor neurons
- gamma motor neurons
8
Q
Alpha motor neurons
A
- synpase with extrafusal muscle
- innervate skeletal muscle
- when we test when we do MMT
9
Q
Gamma Motor neuron
A
- medium myelination
- synpase with intrafusal muscle fibers in the mucsle spindle
- responsble for volume control of a muscle (reflex)
- excited by the brainstem
10
Q
muscle tone imbalance
is caused by?
A
is caused by an imbalance between alpha and gamma activation
11
Q
What is the path of a lower motor neuron
A
- Axons leave spinal cord via ventral root
- Travel through the spinal nerve
- Travel through peripheral nerve
- Skeletal muscle
12
Q
Coactivation
alpha-gamma
A
- stretch on central region of the muscle is maintained while the extrafusal fibers contract
- Alpha-gamma coactivation
13
Q
what does alpha motor neuron synapse with
A
- synpases with extrafusal muscle
- extrafusal muscle is responsible for muscle action
14
Q
What does gamma motor neurons synpase with
A
- muscle spindle/intrafusal muscle fibers
- montiors and controls muscle length
15
Q
What is a motor unit
A
- alpha motor neuron and the muscle fibers it innervates
- when an alpha motor neuron ia activated ACh is released at all the neuromuscular junctions and all muscle fibers that are innervated by the neuron contract
16
Q
Slow twitch muscle fibers
A
- twitch-innervated by smaller diameter,
- slower conducting alpha motor neurons
- postural muscles/slower contracting muscles (Ex: soleus tonically active in standing, physically active with walking)
17
Q
Fast Twitch muscle fibers
A
- innervated by larger diameter, faster conducting alpha motor neurons
- Ex: gastroc-sprinting
18
Q
Henneman’s principle
A
- Slow twitch fibers continue to contribute during faster actions, as fast twitch units are recruited.
- Order of recruitment known as Henneman’s. (LE)
- Order of recruitment is modified depending on the task and phase during walking and running
19
Q
What gives sensory input to the LMN
A
- Golgi tendon organs (GTO)
- muscle spindle
20
Q
Muscle spindle
A
- Provides information about and responds to muscle length
- 3 components
- The more delicate the movement, the higher the spindle count/More spindles in muscles that produce fine motor movement vs. larger muscles responsible for posture and gross movements
21
Q
what are the three components of a muscle spindle
A
- Intrafusal muscle fibers
- sensory endings (primary 1a and secondary type 2 afferents)
- motor endings
22
Q
Describe the intrafusal muscle fibers of the muscle spindle
A
- muscle fiber
- found on the inside
23
Q
Describe the sensory endings fibers of the muscle spindle
A
- Sensory endings respond to stretch
- change in muscle length and velocity of length change
- Stretch of the central region of intrafusal fibers is sensed by these primary and secondary endings
- sensory info conveyes to the CNS by type 1a and type 2 afferents
24
Q
Primary 1a afferents in a muscle spindle
A
- annulospiral
- discharge is phasic and tonic
- phasic = velocity of length change
- tonic = stretch over time
- responds partly to muscle length but more powerfully to changes in length
25
Seconary type 2 afferent in a muscle spindle
- discharge is tonic only
- better at registering length alone (ie static stretch)
26
Motor endings component of muscle spindle
- intrafusal fibers provided by gamma motor neurons
27
Gamma motor neuron activity
- maintain sensitivity of spindle throughout normal range of muscle lengths
- Gamma motor neurons fire, causing end of intrafusal fibers to contract and maintain sensory activity from spindle
- 2 types of intrafusal fibers: Nuclear bag fibers and Nuclear chain fibers
28
Nuclear bag fibers
- clump of nuclei
- contain info about length and velocity of length
- 1a acts on both but mostly on bag fibers
29
Nuclear Chain fibers
- nuclei arranged single file
- contains info about static length only
30
What is the gamma loop
- gamma motor neurons fire to maintain the sensitivity of the spindle throughout the normal rnage of the muscle lengths
- no activation of gamma = flaccid and extrafusal cannot contract
31
GTO
- sensory organ of a tendon near musclotendinous junction
- respond to tension in the tendons
- contraction of a muscle pulls on the collagen strands which compressess the GTO and leads to action potential generation
- info is transmitted from GTOs into the SC by type 1 b afferents
- depending on the task GTO inputs either inhibits or facilitates LMN
32
Stretch reflex
- DTR
- monosynpatic
- stimulus: muscle stretch
- stretches the spindle
- primary afferents 1a activated
- alpha motor neuron activated
- response: muscle contracts
33
Reciprocal inhibition
- used to coordinate movement
- during agonist contraction antagonist is inhibited
- allows agonist to act unopposed/prevents unwanted activity
- achieved by inhibitory interneurons in the spinal cord
34
Tendon Organ reflex
- Autogenic Inhibition?
- muscle contracts; GTO detects tension and afferent activiated stimualtes interneuron
- THEORY NO SUPPORTED BY RESEARCH
35
Recurrent inhibition
- opposite of reciprocal inhibition
- inhibits agonist + disinhibition of antagonist
- helps to isolate fine motor from gross motor
36
Withdrawal/cross extension reflex
- polysynpatic
- cutaneous reflex
- activation of muscles innervated at numerous spinal cord segments
- noxious afferent stimulation => withdrawl of limb on ipsilateral side
- activation of extensor muscles on contralateral side = crossed extension
37
Spinal cord and movement coordination
- muscle syergies: coordinated muscular action; type 2 affernet and interneurons to and from the spinal cord
- proprioceptive body schema: used to plan and adapt movements,
- reciprocal inhibition
- GTO input
- Stepping pattern generators
## Footnote
*Joint capsule and ligament receptors, muscle spindle receptors, and Golgi tendon organs (GTOs) provide the proprioceptive input required to generate the body*
38
GTO and coordination
- GTO contributes proprioception by registering tendon tension
- information is conveyed by type Ib afferents to spinal cord and stimulate interneurons that either excite or inhibit motor neurons
- Overally play a role in adjusting muscle contraciton
39
Stepping Pattern Generators/Central Pattern Generators
- adaptable networks of spinal interneurons (activate LMN)
- each LE has its own SPG
- SPGs recieve proprioceptive input
- Descending signals from the brain required to activate and coordinate SPG
- body weight support and SPGs
40
UMN lesion symptoms
Location: brain, brainstem, corticospinal tracts, SC
Diagnosis: CVA, TBI, SCI, MS, CP
tone: hypertonia
reflexes: hyperreflexia
involuntary movemens: muscle spasms
strenght: weakness/paralysis
Muscle bulk: disuse atrophy
Voluntary movements: impaired or absent
41
LMN lesion symptoms
- Location: CN nuclei/nerves, ventral horn cells, spinal roots, peripheral nerve
- Diagnosis: polio, guillain-barre, peripheral Neuropathy, radiculopathy
- tone: hypotonia
- reflexes: hyporeflexia
- involuntary movemens: with denervation: fasciculations
- strenght: ipsilateral weakness/paralysis
- Muscle bulk: neurogenic atrophy
- Voluntary movements: weak or absent
