Overview of Motor Systems

Question 1

What does it mean to say that the motor system are backwards from the sensory systems

Answer 1

The sensory systems begin in the outside world and end in the brain, whereas the motor systems begin in the brain and lead to movement of muscles in the outside world!

• Motor processing begins with internal representation of desired movement
• Programming starts in Cortex which transmits signals to the lowers levels of the CNS which via neural signals causes muscle movement/contractions (muscles are the effectors)

Question 2

Described the organization of the motor system in two words

Answer 2

hierarchical (in series) and parallel

Question 3

WHat does is mean to say that the motor system is hierarchical

Answer 3

-small, simple elements (at spinal cord) are
integrated into complex patterns at higher levels of CNS

AND

-Higher levels of brain (brainstem and cortex) specify
more complex aspects of task

so small things are integrated into patterns via the CNS. and the CNS higher levels are responsible for complex tasks (things you really have to think about)

Question 4

Describe the parallel pathways of the motor system

Answer 4

-Are parallel pathways for motor control that are somewhat redundant

• some pathways go directly from the cerebral cortex to the spinal cord motor neurons,
• some go from the cortex to the brainstem
• some go from the cortex to the basal ganglia and then to the brainstem
• and really there are just a lot of pathways

Question 5

What two things influence the “final common pathway” to cause movement

Answer 5

1. Higher motor commands in the brain

2. sensory input

Question 6

What is the final common pathway

Answer 6

LOWER motor neurons

Question 7

What are the 3 major components and levels of control of motor systems

Answer 7

1. Spinal cord (bottom)
2. Brainstem
3. Cortex (top)

Question 8

All three major components and levels of control (spinal cord, brainstem, and cortex) are modulated by what 2 independent subcortical structures

Answer 8

1. Basal Ganglia
   - caudate nucleus
   - putamen
   - globus pallidus
   - substantia nigra
   - subthalamic nucleus
2. Cerebellum

Question 9

What two pairs does the thalamus mediate communication between

Answer 9

Basal ganglia ⇒ cortex

AND

Cerebellum ⇒ cortex

Question 10

What mediates the communication between the basal ganglia and the cortex

Answer 10

thalamus

Question 11

What mediates communication between the cerebellum and the cortex

Answer 11

thalamus

Question 12

There are two types of neurons in spinal cord that are

involved in motor systems. What are they

Answer 12

Motor neurons and Interneurons

Question 13

Where are motor neurons located and what is a clinical point about them

Answer 13

motor neurons are located in the ventral horn of the spinal cord

• lower motor neurons project directly to muscles
• this causes contraction and therefore movement of limbs
• lower motor neurons are the “final common pathway” of the entire motor system

Question 14

What projects directly to muscle

Answer 14

LOWER motor neurons

-the project directly to muscle and therefore directly stimulate muscle contraction which leads to limb movement

Question 15

Where are interneurons located and what do they do

Answer 15

• in intermediate zone and they project to lower motor neurons
• Form circuits that connect and coordinate motor neurons
• ⇒ So…groups of muscles contract for specific tasks.

Question 16

what does it mean to say an interneuron is segmental

Answer 16

project within a given spinal level (short) (local)

Question 17

What does it mean to say an interneuron is Propriospinal:

Answer 17

project between multiple spinal cord levels (longer)

Question 18

Motor neurons are somatototpically organized in the spinal cord. What do medial motor neurons innervate and what are they responsible for?

Answer 18

medial motor neurons innervate proximal trunk, axial muscles
– control balance, posture, movement of trunk

Question 19

Motor neurons are somatototpically organized in the spinal cord. What do lateral motor neurons innervate and what are they responsible for?

Answer 19

Lateral motor neurons innervate limb muscles

• control movement of specific limbs and digits
• motor neurons that control proximal limbs are more medial
• motor neurons that control distal limbs and digits more lateral

Question 20

What generally modulates the action of spinal motor circuits

Answer 20

the brainstem

Question 21

What are the two types of motor neurons in the brainstem

Answer 21

1. Motor nuclei contain lower motor neurons that directly innervate muscles in head, face (Occulomotor nucleus contains MNs that control
   Extraocular muscles; Hypoglossal nucleus contains MNs that control tongue; Facial nucleus contains MNs that control facial expression)
2. Neurons that send descending axons down to spinal cord and modulate the spinal cord (lower MNs, interneurons). Upper motor neurons – send their axons into the medial and lateral descending brainstem pathways (tracts).

Question 22

how are the brainstem pathway tracts named?

Answer 22

based on origin and end points

Question 23

What are the 3 Medial brainstem pathways:

Answer 23

Reticulospinal reticular formation ⇒ spinal cord

• Vestibulospinal vestibular nuclei ⇒ spinal cord
• Tectospinal Tectum (superior colliculus) ⇒ spinal cord

Question 24

Where do the medial brainstem pathway descend and where do they terminate

Answer 24

descend in medial ventral white matter and Terminate in ventral horn on medial motor neurons.

Question 25

What are the medial brainstem pathways responsible for

Answer 25

* Influence axial, trunk, proximal muscles * Provide basic postural control system upon which cortical motor areas can organize more highly differentiated movement control

Question 26

Lateral brainstem pathways:

Answer 26

- Rubrospinal tract (main one) | Red nucleus ⇒ spinal cord

Question 27

Where does the lateral brainstem pathway descend and where does it terminate

Answer 27

Descend in contralateral dorsolateral white matter Terminate in dorsolateral ventral horn

Question 28

What is the lateral brainstem pathway responsible for

Answer 28

* Influences motor neurons that control distal muscles in limbs, digits * Modulate goal-directed movements of limbs reaching for, manipulating objects

Question 29

Function of the cerebral cortex in motor movement

Answer 29

* Modulates action of motor neurons in brainstem and spinal cord (top of hierarchy) Descending commands to motor neurons in spinal cord and brainstem. * Gives us ability to organize complex motor acts and execute fine movements with precision.

Question 30

What are the Major areas of cerebral cortex involved in motor control:

Answer 30

a) Primary motor cortex: b) Premotor cortex: c) Supplementary motor area:

Question 31

Function of the Primary motor cortex:

Answer 31

-- Executes commands to motor neurons -- Coordinates force and direction of movement -- Contains somatotopic map of body Electrical stimulation of spots causes movement of body parts on opposite side

Question 32

Function of Premotor cortex:

Answer 32

-- Integrates motor movements with sensory input (esp. visual system) -- Coordinates complex sequences of movement (motor learning)

Question 33

Function of Supplementary motor area:

Answer 33

-- Important for internally-driven, will-driven movements. Formulate intention to make a movement -- “Idea” for movement; Plan movement in advance

Question 34

Function of Primary somatosensory cortex (SI):

Answer 34

-- Regulates incoming sensory info from dorsal horn of spinal cord (coming up via medial lemniscus, anterolateral tracts)

Question 35

Function of Posterior parietal cortex:

Answer 35

-- Helps localize WHERE object is with respect to body -- Helps motor system coordinate reaching in right direction for an object

Question 36

Describe the Changes in blood flow in cortex in response to simple movements: ex: flexing your left index finger

Answer 36

You will have an increase in blood flow to the right primary motor cortex

Question 37

Describe the Changes in blood flow in cortex in response to complex movements:

Answer 37

You will experience an increase in blood flow to the contralateral primary motor cortex You will ALSO experience an increase in blood flow to the supplementary motor area bilaterally. (both sides)

Question 38

Describe the changes in blood of doing a complex task after you have rehearsed it several times

Answer 38

You will have an increase in blood flow only in the supplementary motor area, bilaterally

Question 39

What motor area is particularly is important in planning complex Internally-generated movements

Answer 39

Supplementary motor area

Question 40

Describe the cerebral cortex somatotopy for motor systems

Answer 40

feet medial face lateral. and more segmented than sensory

Question 41

Cerebral cortex acts on spinal motor neurons via two descending pathways what are they

Answer 41

- Lateral corticospinal tract: (pyramidal system) | - Ventral corticospinal tract:

Question 42

Where does the Lateral corticospinal tract: (pyramidal system) descend and terminate Also what is it responsible for

Answer 42

The lateral corticospinal tract descends in dorsolateral white matter, and terminates in the lateral ventral horn * Controls contralateral limb and digit muscles, movement of extremities. - goal-directed reaching, manipulating

Question 43

Where does the ventral corticospinal tract descend and terminate what is it responsible for

Answer 43

it descends in the ventromedial white matter and terminates in the medial ventral horn it controls neck and trunk muscles; postural control -Similar to brainstem pathways; parallel pathways give redundancy

Question 44

The higher structures are responsible for _____ | The lower structures are responsible for______

Answer 44

The higher structures are responsible for complex tasks, like deciding to and then stepping on the break at a yellow light the lower structures are good for simple motor movements like reflexes where no cognition is required

Question 45

describe the energy demand difference between cognitive motor activities and reflexes and why one would be more associated with complicated tasks

Answer 45

- - Reflexes are fast and automatic - - Cognitive motor activities take more time, energy, neural processing - - so cognitive motor activities are Preserved for more complicated tasks

Question 46

What is the value of motor systems being organized in parallel cortex ⇒ spinal cord brainstem ⇒ spinal cord

Answer 46

-Provides flexibility in control -When cortical, brainstem or spinal cord lesions occurs, alternative pathways can partly compensate. -Person may retain basic motor functions (after a lesion) ** Redundancy gives flexibility and plasticity in movements, esp. after injury.

Question 47

What are the three general types of movements

Answer 47

1. Reflex movements 2. Autonomic postural adjustments 3. Voluntary movemetns

Question 48

Describe reflexes - what are they - what do they involve - general examples

Answer 48

- Simple, involuntary, unconscious, coordinated patterns of muscle contraction and relaxation evoked by peripheral stimuli - The involve spinal cord, motor neurons, sensory neurons - general examples are withdrawing from a painful stimulus, and repetitive rhytmic motor patterns (walking, running, chewing, swallowing, breathing

Question 49

How do higher level cortical regions use reflexes

Answer 49

** Higher level cortical systems use this reflex circuitry to coordinate muscles during complex, voluntary movements. Also, saves energy expended by cortex.

Question 50

What are reflexes tested to diagnose

Answer 50

level of lesion/damage and cause

Question 51

Describe Autonomic postural adjustments - defintion - what do they involve

Answer 51

More complex, more flexible than simple reflexes | -Involve brainstem, spinal cord, motor neurons

Question 52

Describe the autonomic postural adjustment example of standing on a boat that is tipping up and down

Answer 52

- Vestibular systems conveys information to midbrain about posture - Descending motor pathways from brainstem to motor neurons make a compensatory shift in mass to maintain balance - It really depends on the context. If a person is holding onto a rail while on the boat motor pathway will induce less of a compensatory shift

Question 53

Describe voluntary movements - definition - what do they involve

Answer 53

- organized around a purposeful act and movements are goal directed and very flexible - involve cerebral cortex, brainstem , spinal cord, and motor neurons ex: - - Put on brakes when light turns red - - Rush to catch a fly ball; swing a golf club - - Play complicated piece on piano - - Handwriting - - Learn to snowboard - - Speech and language Improve with practice: nervous system learns to anticipate and correct for environmental obstacles

Question 54

Voluntary movements allow you to improve and control movement. But there is a cost to this what is it?

Answer 54

the response time for voluntary movements is much longer than for reflexes because additional processing time and energy is required by multiple inputs from higher order CNS structures. SO learning takes time, effort and energy