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Motor Systems Flashcards

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1
Q

Which tracts deal with motor commands?

A

The descending tracts of the spinal cord

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2
Q

What are the two systems of the descending tracts?

A

Upper motor neurons (UMN) - brains command and control
Lower motor neurons (LMN) - spinal cords command and control

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3
Q

What are UMN?

A

Supraspinal neurons that arise above the decussation of the pyramids
They innervate LMNs

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4
Q

What are LMNs?

A

Neurons located in the motor nuclei of the brainstem and Ant horn of the spinal cord

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5
Q

What motor functions do the descending tracts mediate?

A

Voluntary / involuntary movement
Muscle tone
Spinal reflexes
Regulation of visceral functions

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6
Q

Name the pyramidal tracts

A

Corticospinal - arise in the cerebral cortex and project to LMNs in the spinal cord
Corticobulbar (nuclear) - arise in the cerebral cortex and project to LMNs in the brainstem (cranial nerve nuclei)

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7
Q

Name the extrapyramidal tracts

A

Vestibulospinal tract
Reticulospinal tract
Rubrispinal tract
Tectospinal tract

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8
Q

Describe the vestibulospinal tract

A

Arises in the vestibular nuclei of the pons and medulla
Projects to the spinal cord

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9
Q

Describe the reticulospinal tract

A

Arises in the reticular formation of the pons and medulla
Projects to the spinal cord

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10
Q

Describe the rubrospinal tract

A

Arises in the red nucleus of the midbrain
Projects to the spinal cord

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11
Q

Describe the tectospinal tracts

A

Arise in the superior colliculus
Project to cervical levels of the spinal cord

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12
Q

Where do the Corticospinal tracts originate?

A

The primary and premotor areas of the frontal lobes and central gyri of the parietal lobes

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13
Q

Where do the corticospinal tract fibres cross?

A

85% of fibres will cross at the decussation of the pyramids to form the lateral Corticospinal tract
Descend in the contralateral white column

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14
Q

What about the Corticospinal fibres that do not cross over?

A

10-15% of the fibres will travel ipsilaterally from the anterior corticospinal tract and descend in the Ant white column

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15
Q

Where do the Corticospinal fibres travel before any of the cross over?

A

They travel with corticonuclear fibres through the corona radiate and converge in the Post limb of the internal capsule

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16
Q

Describe the lateral Corticospinal tract

A

Fibres terminate in the Ant grey column of all spinal cord segments
Target neurons in the lateral portion of the Ant horn
Innervate distal muscle groups
Allow precise movements and synergistic movement of limbs

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17
Q

Describe the Ant corticospinal tract

A

Fibres descend ipsilaterally
Cross the midline at the segmental level which they terminate
Terminate on LMNs controlling trunk and proximal musculature
Has no effect below L2
Important for bilateral postural adjustments

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18
Q

Where does the corticonuclear tract originate?

A

The lateral aspect of the primary motor cortex
Then UMNs to cranial nerve nuclei

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19
Q

Describe the corticonuclear tract

A

Descends through the corona radiata and converge in the internal capsule
Synapse directly or indirectly with cranial nerves
Most fibres Innervate neurons bilaterally (except the lower face)
Some fibres terminate in the reticular formation, superior colliculus and red nucleus

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20
Q

What are corticonuclear tracts responsible for?

A

Motor control of the face
Help coordinate cortical and brainstem motor systems

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21
Q

Where does the rubrospinal tract originate?

A

The red nucleus in the tegmentum of the midbrain

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22
Q

Where does the rubrospinal tract cross?

A

The midline in the ventral tegmentum decussation
Descends to enter the lateral white column of the spinal cord

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23
Q

What provides input to the rubrospinal tract?

A

Primary and premotor cortex and cerebellum

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24
Q

What is the rubrospinal tract responsible for?

Study These Flashcards
A

Facilitates neurons that Innervate flexor muscles of the upper limbs and inhibits extensor antigravity muscles
Back up role of integrator and relay nucleus in cerebellar circuits

25
Where does the rubrospinal tract terminate?
Along with corticospinal it lies in the lateral columns of the spinal cord and terminates on the interneurons and motor neurons that control the distal musculature of limbs
26
Where does the tectospinal tract originate?
The superior colliculus of the midbrain
27
Where does the tectospinal tract cross over?
Crosses to the contralateral side in the dorsal tegmental decussation
28
How does the tectospinal tract descend?
Through the Ant white column close to the Ant median fissure to cervical levels of the spinal cord
29
What is the tectospinal tract responsible for?
Innervating motor neurons responsible for neck movement Thought to orientate the head and neck during eye movements in response to visual stimuli that reach the superior colliculus
30
Describe the 2 reticulospinal tracts
Most primitive descending motor system Reticular formation gives rise to 2 tracts Medial / Pontine Lateral / Medullary
31
Describe the medial reticulospinal tract
Arises from large cells in the medial part of the reticular formation Descends through Ant white column to all levels of the spinal cord Facilitates voluntary or cortically controlled movements Increases motor tone Excites antigravity muscles Receive input from vestibular apparatus and cerebellum
32
Describe the lateral reticulospinal tract
Arises from cells in the medial 2/3 of the medulla oblongata Descends through lateral white column of the spinal cord Opposes the pontine reticulospinal tract Inhibits voluntary movement and decreases motor tone Receives input from rubrospinal and corticospinal tracts
33
How do the reticulospinal tracts work?
Facilitate or inhibit alpha and gamma motor neurons Influence voluntary and reflex activity
34
How do the reticulospinal tracts affect breathing?
Neurons in the reticular formation of the medulla oblongata project to the respiratory muscles Influence the motor control of breathing
35
What else can the reticulospinal tract influence?
Input from the limbic system can influence emotional motor systems
36
Where are the vesitibular nuclei found?
In the pons and medulla oblongata
37
How many tracts are included in the vestibulospinal tracts?
Medial Lateral
38
Describe the medial vestibulospinal tract
The descending medial longnitudinal fasciculus Descends bilaterally through the brainstem Travels in the Ant white column of the spinal cord to cervical and upper thoracic regions Activate LMNs associated with the spinal accessory nerve Influences rotation of the shoulder Important in changes to maintain posture and balance, keeping the head stable while walking
39
Describe the lateral vestibulospinal tract
Arises from the lateral vestibular nucleus Descends ipsilaterally Projects to all levels of spinal cord Facilitates alpha and gamma neurons that Innervate extensor muscles Inhibits activity of flexor muscles Modulated the vestibular apparatus and cerebellum Mediates postural adjustments to compensate for changes in body positions Orientates the head and body
40
What is Brodmann’s area 4?
The primary motor cortex
41
What is Brodmann’s area 6?
The Premotor and supplementary area
42
What is Brodmann’s area 5
The Post parietal cortex Receives input from primary somatosensory cortical areas 3,2,1
43
What is Brodmann’s area 7?
A target for higher order visual cortical areas
44
What is important to know about Brodmann’s area 6?
Prefrontal cortex and parietal cortex both send axons that converge on area 6 This makes it a junction where signals encoding what actions are converted into signals that specify how the actions will be carried out
45
What do LMNs receive synaptic inputs from?
Dorsal root ganglion cells UMNs in the cortex Interneurones in spinal cord
46
What are the two types of spinal cord LMNs?
Alpha - directly trigger the generation of force by muscles Gamma
47
What are the two ways the CNS controls and grades muscle contractions?
1 - Via ACh and summation at the neuromuscular junction 2 - Recruiting additional synergistic motor units with the extra tension being provided by how many muscles are in that unit
48
How are fine control muscles innervated?
With much smaller innervation ratios E.G three muscle fibres per alpha motor neuron Muscles with higher numbers of small motor units can be more finely controlled by the CNS
49
What is a muscle spindle?
A stretch receptor consisting of several specialised muscle fibres in a fibrous capsule deep within skeletal muscle
50
What are Ia axons?
Sensory axons that wrap around the muscle fibres of the spindle They enter the dorsal roots of the spinal cord, reach extensively and form excitatory synapses with interneurons and alpha neurons of the neural horn
51
What do alpha motor neurons innervate?
Extrafusal fibres
52
What do gamma motor neurons innervate?
Intrafusal fibres
53
What is the difference between muscle spindles and Golgi tendon organs?
Muscle spindles - skeletal muscle stretching, situated in parallel with muscle fibres GTO - tendon stretching, situated in series
54
Where are Golgi tendon organs found?
At the junction of the muscle and the tendon
55
What Innervates Golgi tendon organs?
Ib sensory axons that entwine among collagen fibrils
56
What other function do Golgi tendon organs have?
Provide prorioceptive inputs from the muscles as they act like sensitive strain gauges as they monitor tension and force of contraction
57
What do Ib axons do?
Enter the spinal cord Synapse with Ib inhibitory interneurons in the ventral horn
58
What do Ib interneurons do?
Form inhibitory connections with the alpha motor neurons innervating the same muscle forming a spinal reflex to prevent the muscle becoming overloaded Normal function is to regulate muscle tension with an optimal range
59
What happens when muscle tension falls/ increases?
Increase - the inhibition from the alpha motor neuron slows muscle contraction Falls - inhibition from alpha motor neurons is reduced and muscle contraction increases

Advanced Neurosciences (20 decks)

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