Control of movement Flashcards
1
Q
4 divisions in the control of motor movement:
A
Spinal cord and brainstem circuits (lower motor neurons)
Descending Systems (upper motor neurons)
Basal Ganglia
Cerebellum
2
Q
Lower Motor Neurons
-location
A
- Lower Motor Neurons live in spinal cord or brainstem that transmit the motor message directly to the skeletal muscle (synapse is known as the neuromuscular junction)
- The lower motor neuron serves as the final common pathway for transmitting to and controlling the muscles
3
Q
α motor neurons
A
Lower Motor Neurons
4
Q
Local circuit neurons
-receive info from
A
-receive sensory information from sensory neurons and information from Upper motor neurons (cortex, brainstem)
5
Q
Organization of Lower Motor Neurons
A
- topographically arranged i think.. actually i dont think so?
- Cell bodies arranged in an orderly manner in the ventral horn of the spinal cord
*Muscles closer to your midline are controlled by motor neurons that have cell bodies closer to your midline
More distal muscles- more laterally placed cell bodies
Medial: posture/balance, Distal: doing things
*Also arranged in a top-bottom fashion (muscles near the top of the spinal cord are controlled by motor neurons closer to the top of the spinal cord…)
Each lower motor neuron innervates muscle fibers of the same muscle
All motor neurons that innervate a single muscle (motor neuron pool) are grouped together in the spinal cord
Form a rod-shaped cluster that runs parallel to the long axis of the spinal cord for 1 or more segments
*Areas of the spinal cord that are responsible for controlling more or more complex musculature have more neurons in them (CERVICAL ENLARGEMENT and
LUMBAR ENLARGEMENT)
*Medial motor neurons vs Lateral motor neurons
6
Q
Each lower motor neuron innervates _______
A
Each lower motor neuron innervates muscle fibers of the same muscle
7
Q
Areas of the spinal cord that are responsible for controlling more or more complex musculature have ____ neurons in them (2 examples)
A
Areas of the spinal cord that are responsible for controlling more or more complex musculature have more neurons in them
Cervical enlargement- arm and hand control
Lumbar enlargement- leg and foot control
8
Q
Cervical enlargement-
A
arm and hand control
9
Q
Lumbar enlargement-
A
leg and foot control
10
Q
Medial motor neurons vs lateral motor neurons
-where receive their input:
A
*Medial motor neurons receive their input from upper motor neurons in the brainstem vestibular nuclei and reticular formation
Pathways run medial down the ventral spinal cord
-Posture and balance (The ones in the middle are concerned about posture and balance)
*Lateral motor neurons receive their input from upper motor neurons in the cerebral cortex
Pathways run lateral down the ventral spinal cord
Controlling further away muscles: more deliberate actions, moving fingers I think
11
Q
Local Circuits
A
- local circuit neurons
- Mostly interneurons
- Lie primarily in the intermediate zone of the spinal cord
- Supply much of the direct input to the lower motor neurons
- motor neurons have different patterns of connection with their local circuits (since motor neurons in the medial and lateral portions of the ventral horn care about different functions)
- Medial local circuit neurons vs Lateral local circuit neurons
12
Q
distance of local circuit units
A
medial vs lateral
- both running in the ventral horn (the gray matter of the spinal cord)
- local circuits in the lateral portion of the ventral horn: short distance local circuit neurons
- local circuits in the medial portion of the ventral horn: long-distance local circuit unit
13
Q
Muscle Spindles
A
- specialized muscle fibers that do not contribute to the work
- Also known as intrafusal fibers
- Embedded within connective tissue capsules in the muscle
- Innervated by sensory axons to relay information about the length of the muscle
stretch receptors that detect changes in the length of the muscle (how much it is stretched)
Involved in the sensation of position and movement of the body (proprioception)
Stretch and Speed of Stretch
14
Q
Motor Unit
A
*The relationship between the α motor neuron and the muscle fibers it innervates
Motor units and α motor neurons vary in size
Small α motor neurons innervate fewer muscle fibers and make small motor units
15
Q
- In the adult, each α motor neuron innervates multiple muscle fibers, but each muscle fiber is only innervated by a single α motor neuron
- Why?
A
*There are more muscle fibers than α motor neurons
So, activation of one α motor neuron leads to contraction of all of the muscle fibers it innervates
16
Q
Motor Units Differ in the types of muscle fibers that are innervated: name them
A
Differ in the types of muscle fibers that are innervated
Slow (S) motor units
Fast fatigable (FF) motor units
Fast fatigue-resistant (FR) motor units
17
Q
Slow (S) motor units (size, control___ muscle fibers, force, fatigue, importance)
A
smaller motor units controlling “red” muscle fibers that contract slowly, generate small forces, and resistant to fatigue
Important for activities that require sustained contraction
18
Q
(FF) motor units (size, control, force, fatigue, importance/when used)
A
Fast fatigable
- use larger α motor neurons, control larger “pale” muscles, generate more force, and are easily fatigued
- Important for brief exertions that require a lot of force (running, jumping)
19
Q
(FR) motor units- (size, control, force, fatigue, importance)
A
- Fast fatigue-resistant
- somewhere between the Fast fatigable (FF) and Slow (S) motor units; intermediate size, intermediate speed, generate 2x the force of slow motor units, are resistant to fatigue
20
Q
What About Fast and Slow Twitch?
A
*Fast and Slow Twitch are basically the same thing, but the term mostly is referring to the muscle
Slow twitch (Type I) basically same as slow motor unit Fast twitch (Type IIa) basically same as fast fatigue-resistant motor unit Fast twitch (Type IIb) basically same as fast fatigable motor unit
21
Q
Motor Units and Contribution to Activity (standing vs walking vs jumpting)
A
(slide 25)
Standing- minimal force required, but must be sustained; mostly S motor units
Walking- more force required; recruit FR motor units
Jumping- requires full force of muscle; recruit FF motor units
22
Q
How Do Rabbits Jump a Lot Then?
A
The occurrence of muscle fibers depends on exertion, innervation, and the type of innervation.
Inside a muscle there may appear different type of muscle fibers—for instance, closer to the bones, muscles are more reddish than close to the surface.
Muscle that is exposed to constant activity (such as the muscle of a wild rabbit or thighs of chickens) is reddish, and composed of slow-twitch muscle fibers
*Muscles which are not exposed to constant exertion (muscle of a domesticated rabbit, and chicken breast) are lighter in color and are composed of fast-twitch muscle fibers.
23
Q
how is our discussion of muscles really an Oversimplification
A
Muscles posses a broader spectrum of fiber phenotypes
Vary in speed of contraction, tension generation, oxidative capacity, and endurance
These variations have corresponding variations in α motor neurons
24
Q
Motor Unit Plasticity
- def
- examples
A
*Repeated use or stimulation can change the physiological properties of the motor unit
*Example: chronic electrical stimulation of the of the nerve can change FF fibers to perform more like S fibers
α motor neuron had increased excitability and longer after-hyperpolarizations
*Exercise, and the coincident tensions exerted on the fibers and the duration of the activity, can also lead to adaptations in the motor units
–Changes in physiological properties of the α motor neurons and changes to the muscle fibers
25
Frequency of Action Potentials
- generated by :
- contributes to:
*Frequency of APs generated by α motor neurons contributes to regulation of muscle tension
*Increased force occurs following increased frequency
Muscle fibers are activated by the next AP before they can relax after the first one --> sustained contraction
Asynchronous firing of different α motor neurons provides steady level of input to muscle
26
Muscle Stretch Reflexes (the players and their roles)
*Group Ia- respond phasically to small stretches
Activity dominated by signals from dynamic nuclear bag fibers (velocity of stretch)
*Group II- signal level of sustained fiber stretch; fire tonically with frequency proportional to degree of stretch
Activity dominated by static nuclear bag fibers and nuclear chain fibers
*Sensory axons form excitatory monosynaptic connections on the α motor neurons
Also synapse on inhibitory local circuit interneurons that innervate antagonistic muscle groups
Reciprocal innervation!!!
No brain input required for the muscle stretch reflex!!!!!
27
A simple reflex arc: stretch in muscle spindle
A simple reflex arc:
Sensory response to stretch in muscle spindle --> excitatory feedback to the muscle that is being stretched
***Group Ia afferents- large diameter axons; coiled around middle of intrafusal fibers
***Group II afferents- also large; mostly contact nuclear chain fibers
Mediate fast reflex adjustments in response to stretch
28
Muscle Stretch Reflex (add weight-->)
| -also seen in...
Add weight --> increase stretch --> sensory neuron lets motor neuron know --> proportionally increase contraction in the muscle doing the work and increase relaxation in counter muscle group
Also seen in knee-jerk reflex
-Tap on tendon creates the sensory signal and it causes the motor response
29
Contribution of γ motor neurons
Control the functional characteristics of the muscle spindles by modulating their level of excitability
* Muscle stretched --> spindle is stretched --> increase in axons firing
* Muscle is relaxed --> less tension --> muscle spindle not stretched --> SENSORY AXONS DO NOT GO SILENT
*The γ motor neurons synapse on the contractile poles of the intrafusal fibers --> can cause intrafusal fiber contraction
Contraction picked up by sensory afferents --> maintain some activity
*Co-activation of α and γ motor neurons allows for muscle spindles to function at all muscle lengths
30
Spinal Cord Circuitry and Regulation of Force
*Group Ia and II: collectively provide information about stretch
*Golgi tendon organs-: provide information about tension
-Muscle contraction --> increases tension on tendon
If it reaches threshold, it send signals through Group Ib axons (!!!!)
Axons synapse on inhibitory interneurons --> inhibit α motor neuron controlling same muscle
Woah, that’s too much tension. Stop it.
Axons also synapse on excitatory interneurons that pass the message to antagonistic muscles
31
Step on a tack
*Team Work
*Sensory input --> sensory axon directly firing on α motor neurons of flexors and inhibitory interneurons of extensors to mediate withdrawal of the leg from the tack
*On the other side of the spinal cord, local circuit neurons excite the α motor neurons of extensors and inhibitory interneurons of the flexors make those relax, allowing the other leg to compensate
And behind the scenes, everything else coming together to make sure you do not over-extend or over-contract or tip over
32
more complex motor
| movements (examples)
-example of complex motor movemnts: walking, swimming
*Central pattern generators are contained in local circuits of the spinal cord
Control the timing and coordination of more complex, yet regular, patterns of movement (walking, swimming)
Limbs need to have opposing actions and work in time with each other
Flex one limb to bring it off the ground while you extend the other limb towards the ground
-Timing really matters
33
Central pattern generators
| general: location, control
- are contained in local circuits of the spinal cord
| - Control the timing and coordination of more complex, yet regular, patterns of movement (walking, swimming)
34
Central Pattern Generators
- region
- circuit (dont have to know details)
Initiation of locomotion requires the contribution of some higher brain centers, such as the mesencephalic motor region
However, the act of coordination between the limbs occurs in the spinal cord
Transection of the spinal cord at the thoracic level isolates the hindlimb segments of the cord.
Hindlimbs are still able to walk on a treadmill, and reciprocal bursts of electrical activity can be recorded from flexors during the swing phase and from extensors during the stance phase of walking.
Circuit for central pattern generation of locomotion.
Neuronal modules for flexion and extension antagonism (dashed boxes) comprise excitatory neurons and reciprocally connected Ia inhibitory interneurons (rIa-INs).
These modules receive input from excitatory rhythm-generating interneurons (E/R), which are reciprocally inhibited by different classes of interneurons
35
Damage to the lower motor neurons => (2)
* Lower Motor Neuron Syndrome
| * Amyotrophic Lateral Sclerosis (ALS)
36
Amyotrophic Lateral Sclerosis (ALS)
- type of disease, def
- how starts
- treatment
- why does it happen?
as result of damage to the lower motor neurons
* Neurogenerative disease
* Slow, but progressive, loss of α motor neurons in the spinal cord and brainstem, as well as upper motor neurons in the cortex
* Starts with progressive weakness
* Muscles waste
* Currently no effective treatment
* Why? Genetics, reactive oxygen species, pro-inflammatory interactions between neurons and microglia, mitrochondrial dysfunction…
- Leading current hypothesis is hyperexcitability in cortical networks which may lead to glutamate excitotoxicity
37
* Lower Motor Neuron Syndrome
- paralysis?
- muscle tone?
- twitch?
- atrophy?
*as result of damage to the lower motor neurons
*Results in paralysis of the affected muscles
Loss of reflexes because sensorimotor reflex arcs are disrupted
Loss of muscle tone (muscle spindles no longer linked to a lower motor neuron)
Muscles may spontaneously twitch due to changes in excitability or due to pathological activity of the motor fiber
Can lead to muscular atrophy from disuse
38
Upper Motor Neurons
Cell bodies are in “higher” centers (like the cerebral cortex and brainstem)
Axons descent to influence lower motor neurons and their circuits in the brainstem and spinal cord
- cerebral cortex upper motor neurons influencing the lower motor neurons of the lateral ventral horn
- brainstem upper motor neurons influencing the lower motor neurons of the medial ventral horn
39
Medial ventral horn**
*contains lower motor neurons that govern posture, balance, locomotion, and orienting movements of the head and neck during shifts of visual gaze.
Receive descending input from pathways that originate mainly in the BRAINSTEM, course through the anterior-medial white matter of the spinal cord, and then terminate bilaterally.
-brainstem upper motor neurons influencing the lower motor neurons of the medial ventral horn
40
Lateral ventral horn**
- controls:
- receives info from:
* contains lower motor neurons that mediate the expression of skilled voluntary movements of the distal extremities.
* Receive a major descending projection from the contralateral motor cortex via the main (lateral) division of the corticospinal tract, which runs in the lateral white matter of the spinal cord.
-cerebral cortex upper motor neurons influencing the lower motor neurons of the lateral ventral horn
41
Upper motor neurons of the cortex
- reside where?
- receive info from?
* Upper motor neurons reside in several interconnected areas of the posterior frontal lobe
- Receive regulatory input from the basal ganglia and cerebellum, by way of the ventrolateral thalamus, as well as the somatosensory cortex
-upper motor neurons are found in layer 5 of the primary motor cortex
Other adjacent areas of cortex are PREMOTOR AREAS
42
Primary motor cortex: general
* large and direct pathway to the lower motor neurons and their circuits
Low intensity of stimulation needed to evoke movement (low threshold)
Other adjacent areas of cortex are PREMOTOR AREAS
43
Primary Motor Cortex: upper motor neurons
- layer?
- cell type(s)?
* Upper motor neurons reside in LAYER 5
| * Betz cells and SMALLER, non-Betz pyramidal neurons
44
The motor tracts, in general, can be functionally divided into two major groups:
Pyramidal tracts:
Extrapyramidal tracts:
45
Pyramidal tracts:
- originate in :
- pass through:
one of the two major motor groups (divided by function)
These tracts originate in the cerebral cortex, carrying motor fibers to the spinal cord and brain stem.
* They are responsible for the VOLUNTARY control of the musculature of the body and face.
* Named after the medullary pyramids of the medulla oblongata, which they pass through.
46
Extrapyramidal tracts:
one of the two major motor groups (divided by function)
These tracts originate in the brain stem, carrying motor fibers to the spinal cord.
They are responsible for the involuntary and automatic control of all musculature, such as muscle tone, balance, posture and locomotion
47
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48
Pyramidal Tracts: Functionally, these tracts can be subdivided into two
Corticospinal tracts – supplies the musculature of the body.
| Corticobulbar tracts – supplies the musculature of the head and neck.
49
Descending Tracts (2)
*the corticobulbar (to brainstem) or corticospinal tracts
50
Corticobulbar Tract
| -explain the projections
Many of the descending fibers that want to govern the actions of the cranial nerve motor nuclei send bilateral projections onto local circuit neurons in the reticular formation and the cells of the reticular formation send their axons out to make contact with the lower motor neurons in these nuclei
Coordinate action
Why bilateral projections? Built in back-up system. Damage to fibers on one side will not result in major functional deficits.
*Note: Your textbook says most of the descending fibers synapse in the reticular formation and not the motor nuclei of the cranial nerves. I cannot fully support this statement
*Not all innervation to the cranial nerve motor nuclei or local circuit neurons in the reticular formation is symmetrical and bilateral
In these exceptions, there is a bias to favor inputs from the CONTRALATERAL MOTOR CORTEX
51
Corticobulbar Tract: Not all innervation to the cranial nerve motor nuclei or local circuit neurons in the reticular formation is symmetrical and bilateral
In these exceptions, there is a bias to favor inputs from the contralateral motor cortex
*Exceptions: (3)
* Exceptions:
- Hypoglossal nucleus: control tongue protrusion
- Trigeminal motor nucleus: governs chewing
- Part of the Facial motor nucleus:
52
Corticospinal Tracts
| -the splitting (location and names)
-at the caudal end of the medullary pyramids, mostly only have corticospinal fibers left and the tract divides into two:
LATERAL CORTICOSPINAL tract vs ANTERIOR CORTICOSPINAL tract
53
lateral corticospinal tract
- control:
- pathway:
* mostly limb control
| * Direct pathway from cortex to spinal cord
54
Anterior corticospinal tract:
| -control
* trunk and shoulders
Arises from dorsal and medial regions of the motor cortex that serve these areas
Synapse bilaterally in more medial locations in the ventral horn
55
Primary Motor Cortex- History
*Late 19th century- Fritsch and Hitzig demonstrated that electrical stimulation of the motor cortex leads to muscle contractions on the contralateral side of the body
*Late 19th century- Jackson observed motor movements during certain types of epileptic seizures and noticed that they seemed to march from one body part to another
Decided that the motor cortex contains a spatial map of the body’s muscles
Early 1900s- Sherrington used focal electrical stimulation in great apes to publish a map of the motor cortex
*1930s- Penfield, a student of Sherrington and a neurosurgeon, demonstrated that the human motor cortex also contains a map of the contralateral body
-Did this in 400 patients
-Showed that the areas were disproportional like in the somatosensory cortex
-Fine motor = more area
*1960s- introduction of intracortical microstimulation led to more detailed understanding
-Better able to target Layer V neurons
-Small stimulations lead to excitation of several muscles and suppression of others suggests that neighboring areas are connected by local circuits
*1960s- Evarts implanted microelectrodes into awake, behaving monkeys
-Trained animals on motor tasks and recorded from the motor cortex
-Found that rate of firing correlates to force generated
-Found that activity in the neurons of the motor cortex happens before the behavior is executed (control)
-Also, neuron activity related to direction of force
-Neurons get less active if the movement direction deviates from what they prefer
*1970s- introduction of spike-triggering averaging, a way to determine the influence of a single neuron on a population of lower motor neurons
-A single upper motor neuron seems to be able to control multiple lower motor neurons controlling multiple muscles
-Example- one upper motor neuron can control 2-3 muscles in the wrist
-Reinforced the idea that the upper motor neurons in the cortex control the lower motor neurons
56
T/F The motor map/homunculus that we always see is not exactly accurate for the Primary Motor Cortex
-why
TRUE
*Primary Motor Cortex
The representation of muscle movement is not exactly organized at the level of individual body parts or muscles
Distribution of muscle fields (how many lower motor neurons/muscles an upper motor neuron can control) is not spatially continuous or fixed across time
Somatosensory cortex and associated fields a little cleaner to map
Dynamic and flexible coordinate muscle groups across several joints to perform actions
Purposeful movements and precise movement patterns are achieved by upper motor neurons working together through intracortical circuitry
Don’t forget we also have coding/specialization for directionality of movement
57
Premotor Cortex
- receives inputs from:
- contains:
* Each of the divisions of the premotor cortex receive multisensory input from the parietal lobe and motivational/intentional information from the prefrontal cortex
- contains upper motor neurons
58
Premotor Cortex function
Uses information from other cortical regions to select movements appropriate to the context and goal of the action !!!!!!
59
Main differences between premotor and primary motor
*Primary motor better driver of lower motor neurons (more direct synapses, more control of distal musculature)
Primary motor cortex seems to care more about things within an arm’s length (personal space) and the premotor cortex cares more about things further away (extrapersonal space)
60
Mirror Motor Neurons
| -location
* Live in the ventrolateral premotor cortex
* Respond to the preparation for execution of a movement, but also when the same action is observed
*Grab a piece of food --> fire then make movement
See someone else grab a piece of food --> fire in same pattern
* Seem to be really interested in goal-directed behaviors
- Fake grab --> no firing
- Hide the final stage of the action (grab object but do not let see the actual grab) --> firing
* Some mirror neurons are suppressed during observation but are active during self-initiated execution
- May serve to suppress imitation
61
divisions of the lateral premotor area that are also important:
Posterior Parietal Cortex and Broca’s area- speech production
62
Dorsal (Medial) Premotor Cortex
| -lesion
(part of the premotor cortex)
- self-initiated movement/movement due to internal cues
Lesion --> fewer self-initiated movements
Active when performing motor sequences from memory
63
Brainstem Motor Control Centers function
Balance, Posture, Initiate Locomotion, Orient Gaze
Need to work in conjunction with skilled motor behaviors that involve the distal extremities
Can also direct motor activities without higher motor center (cortical) involvement
64
Brainstem Motor Control Centers function : location
- Vestibular complex
- Reticular formation
- Superior colliculus
65
Medial vestibulospinal tract originates and terminates
Medial vestibulospinal tract- originates in the medial vestibular nucleus and terminates bilaterally in medial ventral horn of the cervical spinal cord
66
Medial vestibulospinal tract function
-example
Regulates head position by reflex activation of neck muscles in response to semicircular canal information
*Example- fall forward, semicircular canals detect that unexpected downward motion of the head, medial vestibulospinal tract causes the reflexive pull-back of head and extension of arms
67
Lateral vestibulospinal tract
- originates
- terminates
originates in the lateral vestibular nucleus and sends axons through the anterior and more lateral spinal cord
Terminates ipsilaterally among medial lower motor neuron pools that govern proximal control of the limbs
When otolith organs signal that you have a problem with stable balance or upright posture, signal is sent along this tract to activate extensor muscles (antigravity) in the limbs
68
vestibular complex : Other upper motor neurons project to local circuit neurons and lower motor neurons in the cranial nerve nuclei that control eye movement
- what are these cranial nerves?
- what eye movement is produced?
Oculomotor (III)
Trochlear (IV)
Abducens (VI)
*Produces eye movements that maintain a fixed gaze while your head is moving (the vestibulo-ocular reflex)
69
Reticular Formation
| -structure
* made of lots of small neuron groups spread out through the core of the brainstem
* Descending motor control pathways terminate primarily in medial parts of the spinal cord gray matter to influence local circuit neurons that coordinate axial and proximal limb muscles
70
Reticular Formation function
Help maintain posture too, but largely under control of other motor centers (cortex, brainstem)
*Initiation of movements often requires an appropriate stabilizing response
Initiated movement under control of cortex
Counteraction in other muscle groups happens more indirectly through cortex’s connections to the reticular formation (cortico-reticulospinal pathway)
71
Direct vs Indirect
| confused!!!
Lesion direct motor pathways (corticospinal) at the level of the medulla, but leave connections from cortex to reticular formation intact
Animals can make movements and have control over their axial and proximal muscles
Animals CANNOT really control their distal musculature (hands, for example) well
72
Superior Colliculus
- role in motor pathway
- importance
Contributes to upper motor neuron pathways controlling lower motor neuron function
These connections can be direct (superior colliculus --> spinal cord) or indirect (superior colliculus --> reticular formation)
Important for controlling neck musculature to generate head movement
73
Mesencephalic locomotor region-
-a Motor Control Center in Brainstem
* involved in the initiation of locomotion
- Set of nuclei that are embedded in the reticular formation, but not technically a part of it
- Axons project to reticulospinal neurons and the reticulospinal neurons finish delivering the message via their connection with central patterns generators in the spinal cord
74
Rubrospinal tract
| -originates
*Motor Control Center in Brainstem
*originates in the red nucleus and projects to the cervical spinal cord
-Located in the lateral white matter and axons terminate in lateral regions of the ventral horn and intermediate zone where local circuits controlling distal muscles are located
- think it works with the motor cortex
Not sure what it really does in humans
Very small, lacks large neurons, and most axons seem to project to the inferior olive and not the spinal cord
75
Upper Motor Neuron Syndrome
*When you get damage to descending motor pathways anywhere where you have upper motor neurons or their axons (!!!)
*Immediate flaccidity of the muscles of the contralateral body and face
How bad based on how much is affected
Frequently involves arms and legs
Trunk musculature less affected (bilateral pathways?)
*No reflex activity on the affected side
*Referred to as SPINAL SHOCK due to decreased activity of spinal circuits due to lack of upper motor neuron communication
*After a few days, spinal cord circuits recover much of their function, as they are not physically damaged
*Believe that remaining connections are strengthened, neurons sprout to form new connections, and other things to reinforce local circuitry
* Some symptoms remain:
- BABINSKI SIGN: toes extend and spread when sole of foot stroked (should have flexion)
- Infants due this too because they pathways are incomplete and immature
76
Babinski sign:
toes extend and spread when sole of foot stroked (should have flexion)
77
Upper Motor Neuron Syndrome negative outcomes
* Loss of the ability to perform fine movements: if it involved parts of pathway controlling hands, would have a problem independently moving fingers
* Spasticity: increased muscle tone, hyperactive stretch reflexes, and clonus (oscillating contraction and relaxation of muscles in response to stretch)
* Decerebrate rigidity: spastic extensor muscles of the leg and flexor muscles of the arm
78
Decerebrate rigidity:
| -when does it occur
*Upper Motor Neuron Syndrome negative outcome
spastic extensor muscles of the leg and flexor muscles of the arm
When lesions interrupt the descending pathways in the brainstem above the vestibular nuclei and below the red nucleus
79
neuromuscular junction
where Lower Motor Neurons (live in spinal cord or brainstem) synapse at the skeletal muscle to directly transmit the motor message
80
lower motor neurons
- controlling head/neck vs bodily musculature
- location of cell bodies
* Those that control BODILY MUSCULATURE have their cell bodies in the VENTRAL HORN OF THE SPINAL CORD and send their axons out through the ventral roots to join the spinal peripheral nerves
* Those that control the HEAD and NECK have their cell bodies in the brainstem and send their axons out to join the cranial nerves
81
lower motor neurons
| -inputs
*Receive input from local circuit neurons. Local circuit neurons receive information from:
-Sensory neurons (Important for sensorimotor reflexes)
-Descending pathways from “higher” centers
(Upper motor neurons (cortex, brainstem))
The lower motor neuron serves as the final common pathway for transmitting to and controlling the muscles
82
Local circuit neurons receive information from _____ before sending the info to the lower motor neurons
Local circuit neurons receive information from:
-Sensory neurons (Important for sensorimotor reflexes)
-Descending pathways from “higher” centers
(Upper motor neurons (cortex, brainstem))
83
Medial vs Distal lower motor neurons of the spinal cord
Muscles closer to your midline are controlled by motor neurons that have cell bodies closer to your midline
More distal muscles- more laterally placed cell bodies
Medial- posture/balance, Distal- doing things
(slide 5)
84
Local circuit neurons arrangement
* topographically arranged
The medial region of the intermediate zone of the spinal cord gray matter contains the local circuit neurons that synapse with lower motor neurons in the medial part of the ventral horn
The lateral regions of the intermediate zone contain local neurons that synapse primarily with lower motor neurons in the lateral ventral horn
85
*Medial local circuit neurons
have axons that project to many spinal cord segments
-Even as far as between cervical and lumbar enlargements (help with coordinated movement of upper and lower limbs) or the entire length of the spinal cord (mediate posture)
-Many have branches that cross the midline to coordinate with axial muscle groups on the other side
Either to work in opposition or together (like breathing)
86
Lateral local circuit neurons
Lateral local circuit neurons have shorter axons (in comparison to medial) that do not extend as far
More restricted pattern of connections --> fine control of movement
Most stay ipsilateral (do not need to move left arm to move right arm)
87
***α motor neurons
: The large motor neurons that do most of the work. Innervate the striated muscle fibers
88
*****γ motor neurons (Gama)
- Innervate muscle spindles
| - Regulate the sensory input by setting the intrafusal muscle fibers to an appropriate length
89
In the adult, each α motor neuron innervates _____ muscle fiber(s),each muscle fiber is innervated by ____ α motor neuron(s)
In the adult, each α motor neuron innervates multiple muscle fibers, but each muscle fiber is only innervated by a single α motor neuron
90
T/F Muscles posses a broader spectrum of fiber phenotypes
True : muscles vary in speed of contraction, tension generation, oxidative capacity, and endurance
These variations have corresponding variations in α motor neurons
91
knee-jerk reflex
knee-jerk reflex
| -Tap on tendon creates the sensory signal and it causes the motor response
92
what allows for muscle spindles to function at all muscle lengths
*Co-activation of α and γ motor neurons allows for muscle spindles to function at all muscle lengths
93
collectively provide information about stretch
Group Ia and II- collectively provide information about stretch
94
Group Ib axons *
*Golgi tendon organs-: provide information about tension
-Muscle contraction --> increases tension on tendon
If it reaches threshold, it send signals through Group Ib axons (!!!!)
95
*Upper motor neurons reside in LAYER ____ of the _____
*Upper motor neurons reside in LAYER 5 of the primary motor cortex
96
*Betz cells:
-upper motor neurons found in the primary motor cortex
*largest bodied neurons in the human CNS
Important for activation of lower motor neurons controlling muscles of the distal extremeties
Not the ONLY upper motor neurons that are important
Only account for roughly 5% of the axons that descend from the motor cortex to the spinal cord
There is not enough of them
97
smaller, non-Betz pyramidal neurons are found
in the primary motor cortex and the premotor cortex
98
descending tracts
| path until completely seperate
* the corticobulbar (to brainstem) or corticospinal tracts
* Axons pass through the internal capsule to enter the cerebral peduncles at the base of the midbrain
* Pass through the base of the pons, where they scatter a bit
* Come back together on the ventral surface of the medulla where they form the medullary pyramids
* After coming together in the medullary pyramids, the portions that become the corticobulbar tract leave at the appropriate levels of the brainstem
* Also, the corticopontine tract breaks off from the corticobulbar tract close to the base of the pons and turns towards the CEREBELLUM
99
corticobulbar tract after leave at the appropriate levels of the brainstem, innervate the
(innervate the cranial nerve nuclei, the reticular formation, and the red nucleus)
100
T/F: For the Corticobulbar Tract, all innervation to the cranial nerve motor nuclei or local circuit neurons in the reticular formation is symmetrical and bilateral
FALSE: Corticobulbar Tract: Not all innervation to the cranial nerve motor nuclei or local circuit neurons in the reticular formation is symmetrical and bilateral
In these exceptions, there is a bias to favor inputs from the contralateral motor cortex
101
after the splitting after the caudal end of the medullary pyramids- The fibers within the LATERAL CORTICOSPINAL tract
The fibers within the LATERAL CORTICOSPINAL tract mostly cross over to the other side of the CNS.
Descend into the spinal cord, terminating in the ventral horn (at all segmental levels).
*From the VENTRAL HORN, the lower motor neurons go on to supply the muscles of the body.
102
after the splitting after the caudal end of the medullary pyramids- The fibers within the ANTERIOR CORTICOSPINAL tract
The ANTERIOR CORTICOSPINAL tract remains ipsilateral, descending into the spinal cord.
They then decussate and terminate in the ventral horn of the cervical and UPPER THORACIC segmental levels.
Does terminate bilaterally
103
Which map/homunculus that we always see is most accurate (Primary Motor Cortex, Somatosensory cortex, neither, or both)
* The motor map/homunculus that we always see is not exactly accurate for the Primary Motor Cortex
* Somatosensory cortex and associated fields a little cleaner to map
104
Premotor Cortex and behavior
* Influence behavior: directly and indirectly
- Directly: extend axons through corticospinal and corticobulbar tracts to synapse on local circuit neurons - 30% of corticospinal axons originate here
- Indirectly: by projecting to primary motor cortex
105
Posterior Parietal Cortex
(a division of the lateral premotor area )
- integration of visual and proprioceptive information
Lesion --> impair ability to perform visually-cued condition tasks
106
Broca’s area
(a division of the lateral premotor area )
- speech production
Producing speech is a motor action
107
otolith organs
each of three small oval calcareous bodies in the inner ear of vertebrates, involved in sensing gravity and movement.
108
the vestibulo-ocular reflex
-cranial nerves involved
eye movements that maintain a fixed gaze while your head is moving
Oculomotor (III)
Trochlear (IV)
Abducens (VI)
vestibular complex : Other upper motor neurons project to local circuit neurons and lower motor neurons in the cranial nerve nuclei that control eye movement
109
* Initiation of movements if under control of the cortex but often requires an appropriate stabilizing response
- this Counteraction in other muscle groups happens more indirectly through cortex’s connections to the _____
*Initiation of movements often requires an appropriate stabilizing response
Initiated movement under control of cortex
Counteraction in other muscle groups happens more indirectly through cortex’s connections to the reticular formation (cortico-reticulospinal pathway)
110
-what pathway is responsible for the counteraction that follows the initiation of movement?
cortico-reticulospinal pathway)
111
spinal shock
Upper Motor Neuron Syndrome
112
Are Local circuit neurons in the spinal cord gray matter or white matter?
gray matter
113
In the primary motor cortex, is a high or low intensity stimulation needed to evoke movement? (what threshold?)
Low intensity of stimulation needed to evoke movement (low threshold)
114
regulation of muscle tension
frequency of APs generated by α motor neurons contributes to regulation of muscle tension
*Increased force occurs following increased frequency
Muscle fibers are activated by the next AP before they can relax after the first one --> sustained contraction
Asynchronous firing of different α motor neurons provides steady level of input to muscle
115
lateral corticospinal tracts: terminates and synapse
*Primarily terminates in lateral portions of ventral horn and intermediate gray matter
*Some can synapse directly on α motor neurons (controlling forearm and hand), but most synapse on local circuit neurons
This connection from the cortex to the α motor neurons of the hand is likely responsible for our ability to make discrete movements with our fingers
-has a huge amount of crossover
116
When otolith organs signal that you have a problem with stable balance or upright posture, signal is sent along ______ tract to activate extensor muscles (antigravity) in the limbs
Lateral vestibulospinal tract
117
activation of one α motor neuron leads to contraction of
activation of one α motor neuron leads to contraction of all of the muscle fibers it innervates
118
chronic electrical stimulation of the of the nerve can change FF fibers to perform more like _____ fibers
-this is an example of ?
S fibers
| -Motor Unit Plasticity
119
rubrospinal tract *
The rubrospinal tract innervates
extrapyramidal tract
the upper cervical spinal cord to produce arm flexion
120
*Group Ia
*Group Ia
-large diameter axons
-coiled around middle of intrafusal fibers
-respond phasically to small stretches
Activity dominated by signals from dynamic nuclear bag fibers (velocity of stretch)
121
The anterolateral system (eg spinothalamic tract) lies in which portion of the brainstem?
tegmentum
122
The stretch reflex operates as a _____feedback loop to regulate muscle length.
negative
123
location of Local Circuits
Lie primarily in the intermediate zone of the spinal cord
124
Types of fibers contained within muscle spindles include....
Dynamic nuclear bag fibers
125
T/F the basal ganglia is involved in disorders such as Tourette’s syndrome and schizophrenia.
TRUE
126
Muscle force is controlled in part by...
A. Alpha-gamma coactivation
B. Intrafusal fibers
C. Rate code
D. Golgi tendon organs
E. Gamma motor neurons
C. Rate code This answer is CORRECT!
127
corticospinal neuron in primary motor cortex can do all of the following EXCEPT:
A. Project to multiple motor neuron pools in the spinal cord.
B. Participate in the initiation of movement.
C. Code for the amount of force of individual muscles.
D. Code for the direction of movement.
E. Code for the extent of movement.
C
Motor cortex neurons code for the force of individual movements, not individual muscles. Lower motor neurons (alpha motor neurons) encode the force of individual muscles.
