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Functional Neuroanatomy > Problem 1 - Action > Flashcards

Problem 1 - Action Flashcards

1
Q

The motor control hierarchy can be represented by 3 distinct levels from high to low respectively.

Name them.

A
  1. Association areas of the neocortex + basal ganglia of the forebrain

–> strategy/goal of the movement

  1. Motor cortex + cerebellum

–> tactics/sequences of motor movements

  1. Brian stem + spinal cord

–> execution/activation of motor + interneuron pools

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2
Q

Role of the Lateral pathways

A

Are involved in voluntary movement of the distal musculature + reflex modulation

–> are under direct cortical control

a) Corticospinal tract
b) Rubrospinal tract

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3
Q

Role of the Ventromedial pathways

A

Are involved in the control of posture and locomotion

–> are under brain stem control

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4
Q

Corticospinal tract

Lateral pathway

A

Consists of axons that exit the cortex + directly project to the spinal cord

  • -> originates in the neocortex + is the longest and largest one
  • -> 2/3 of its axons originate in the motor cortex (area4)
  • -> the most important component of LP
  • -> also called pyramidal tract
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5
Q

Extrapyramidal tract

A

Refer to the motor pathways within the brainstem that send direct projections down the spinal cord (involuntary)

–> vestibular, reticular formation nuclei, substantia nigra

BUT: Not part of the pyramidal tract

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6
Q

Rubrospinal tract

Lateral pathway

A
  1. Originates in the red nucleus of the midbrain
  2. Then decussate from the pons to join the axons of the corticospinal tract (=indirect)

–> smaller component of the lateral pathway, that gains larger role when CST is lesioned

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7
Q

What do lesions of the lateral pathways lead to ?

A

Inability to make fractioned movements of the arms + hands

–> no independent movements of shoulders, elbows, wrists + fingers

BUT: Corticorubrospinal pathway is able over time to partially compensate for any loss of the corticospinal tract input

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8
Q

Ventromedial pathways

A

Contain 4 descending tracts that originate in the brain stem + terminate in the spinal interneurons that contain proximal + axial muscles

–> uses sensory info about balance to maintain it

a) Vestibulospinal tract
b) Tectospinal tract
c) Pontine Reticulospinal tract
d) Medullary Reticulospinal tract

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9
Q

Vestibulospinal tracts

A

Originate in the vestibular nuclei of the medulla

–> relays sensory info to the ear

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10
Q

Name the 2 components of the vestiulospinal tracts and their respective functions.

A
  1. Projects bilaterally down the spinal cord to activate cervical spinal circuits

–> guiding head movements

  1. Projects ipsilaterally to the lumbar spinal cord

–> maintaining an upright + balanced posture

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11
Q

Tectospinal tract

A

Originates in the superior colliculus of the midbrain, that receives direct input from the retina

–> creating a map of the environment

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12
Q

Where does the superior colliculus receive its inputs from ?

A
  1. Retina
  2. Visual cortex
  3. Afferent axons receiving somatosensory + auditory info

–> thus constructs a map of the world

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13
Q

Reticulospinal tract

A

Originates from the reticular formation

–> has 2 descending tracts crucial for motor control

  1. Pontine reticulospinal tract
  2. Medullary reticulospinal tract
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14
Q

Pontine reticulospinal tract

A

Enhances the antigravity reflexes of the spinal cord

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15
Q

Medullary reticulospinal tract

A

Liberates the antigravity muscles from reflex control

–> has the opposite effect to pontine RT

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16
Q

Which regions of the frontal lobe are called the motor cortex ?

A
  1. Area 4 (Primary motor cortex/M1)
    - -> lies anterior to the central sulcus, on the precentral gyrus
  2. Area 6
    - -> lies anterior to area 4
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17
Q

How did Penfield discover that there is somatotopic organization in the pre-central gyrus ?

A

By electrically stimulating these regions and discovering a twitch of the muscles in a particular region of the body on the CONTRALATERAL side

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18
Q
  1. What is area 6 specialized for ?
  2. It also includes 2 somatotopically organized motor maps.
    Name them.
A
  1. Skilled voluntary movement
    - -> desired actions are translated into how the actions will be carried out (planning)

2.

a) Premotor area (PMA)
b) Supplementary motor area (SMA)

BUT: both perform similar function but on different groups of muscles

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19
Q

Premotor area (PMA)

A

Refers to the lateral region of area 6

–> connects with reticulospinal neurons that innervate PROXIMAL motor units, visually guided movements

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20
Q

Supplementary motor area (SMA)

A

Refers to the medial region of area 6

–> connects directly with DISTAL motor units

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21
Q

Which cortical regions are involved in creating a mental image of the body in order to be able to execute movement ?

A

Inputs to the Posterior parietal cortex, especially

  1. Area 5
    - -> receive inputs from primary somatosensory areas 1,2,3,7
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22
Q

Which regions represent the highest levels of the motor control hierarchy ?

Why ?

A
  1. Regions of the anterior frontal lobes + Posterior parietal cortex
  2. Here, decisions are made about what actions to take + their likely outcome

–> both send signals that converge on area 6

23
Q

Describe the firing of the relevant neurons when planning + executing a moment.

(Ready, Set, Go)

A
  1. Ready
    - -> frontal + posterior parietal lobes
  2. Set
    - -> increased firing of SMA + PMA neurons (area 6) before the movement
  3. Go
    - -> firing of the PMA + SMA during the movement, stop when it ends
24
Q

Ventral lateral nucleus

VL

A

Refers to a nucleus of the dorsal thalamus

–> generates major subcortical input to area 6, by receiving signals from the basal ganglia

25
Q

Name the brain regions and their consecutive places in the loop of where information travels to initiate movement.

A

Info travels from

  1. Cortex
  2. Basal ganglia + Thalamus
    (Striatum, Globus P., VLo)
  3. Cortex ( esp. SMA)

–> therefore, selecting + initiating voluntary movements

26
Q

Striatum

A

Refers to the Caudate + Putamen

–> is the target of the cortical input to the basal ganglia

27
Q

Function of the Globus pallidus

A

Source of the output to the thalamus

28
Q

Motor strip

A

Refers to the full length of the precentral gyrus

29
Q

Layer 5 of M1 is heavily interconnected with SMA.

Name its Input vs Output stations.

A
  1. Has pyramidal neurons that receive their inputs from 2 sources

a) Thalamus
- -> VLc (part of VL), that relays info from cerebellum

b) Other cortical areas
- -> area 6 + areas 1,2,3 (areas adjacent to area 4)

  1. Sends outputs to
    a) Spinal cord (directly

b) Subcortical sites involved in sensorimotor processing
- -> esp. brain stem

30
Q

What does the activity of each M1 cell suggest/mean when it comes to the execution of voluntary movement ?

A

Each cell represents a single vote for a particular direction of movement (=direction vector)

–> as suggested by “Centre out task”

31
Q

What determines the direction of a particular movement ?

A

The average of the votes registered by each cell of the M1 population (=population vector)

–> the larger the population, the finer the movement

32
Q

Effector

A

Refers to a part of the body that can move

ex.: arm, hand

33
Q

Motor neurons

A
  1. Originate in the spinal cord
  2. Exit through the ventral root
  3. Terminate in the muscle fibers

–> an AP here releases a neurotransmitter, to make the muscle contract

34
Q

Spinal interneurons

A

Lie within the spinal cord and innervate motor neurons

–> intergate sensory feedback with motor commands resulting in voluntary movement

35
Q

Pyramidal tract

A

Refers to the motor neurons that travel directly from the cortex to the spinal cord

36
Q

Basal ganglia

A

Is a collection of 5 nuclei

  1. Caudate nucleus
  2. Putamen
  3. Globus pallidus
  4. Subthalamic nucleus
  5. Substantia nigra

–> plays a critical role in the selection + initiation of actions

37
Q

Damages to the posterior parietal cortex can lead to …

A
  1. Apraxia
    - -> Difficulty performing skilled movement when asked out of context
  2. Contralateral neglect
    - -> Disturbance of the ability to respond to stimuli on the side opposite to the side of the brain damage
38
Q

Posterior parietal cortex

A

Directs movement by providing spatial info (Mental body image)

–> includes:

a) Area 5
- -> input from primary somatosensory cortical areas

b) Area 7
- -> input from higher visual areas

39
Q

Alpha motor neurons

A

Innervate muscle fibers + provide the physical basis fro translating nerve signals into mechanical action

40
Q

Name the pathway of Alpha neurons.

A
  1. Spinal cord (Origin)
  2. Ventral root (Exit)
  3. Muscle fibres (Termination)
  4. ACh (Release)
  5. Contraction of the muscle
41
Q

Muscle spindles

A

Inform neurons on how stretched the muscle is

–> receptor organ

42
Q

Why do alpha motor neurons have to be inhibitory + excitatory at the same time ?

A

To overcome the stretch reflex + permit voluntary movement

43
Q

Amyothrophic lateral Sclerosis (ALS)

A

Is a disease that results in muscle weakness and atrophy

44
Q

What are the possible causes vs treatment options of ALS ?

A

1.
a) Genetic mutation affecting the enzyme superoxide dismutase

b) Excitotoxiticity
- -> elevated levels of glutamate or defective glutamate transporter resulting in cell death

  1. Using Riluzole which block glutamate release

–> only slows the progress by few months

45
Q

Duchenne Muscular Dystrophy

A

Is a disease that involves progressive weakness + detonation of muscles in boys, that is passed on by mothers

46
Q

What are possible causes vs treatment options of DMD ?

A
  1. Defective region on X chromosome encoding dystrophin

–> contributes tp cytoskeleton which lies just under the sarcolemma in muscles

  1. Gene therapy to replace the defective gene, by sending virus or transplanting stem cells
47
Q

Myasthenia Gravis

A

Is a disease that involves weakness + fatiguability of voluntary muscles

–> can be fatal when respiration is compromised

48
Q

What are possible causes vs treatment options of MG ?

A
  1. Autoimmune disease
    - -> NS generates antibodies against own receptors, thus bind + interfere with normal actions
  2. Drugs inviting the reuptake of antibodies
49
Q

Non-primary motor areas

A

Refer to all the areas in the FL that can influence motor output at the level of M1 + spinal cord

50
Q

Premotor areas

A

Have weak direct influence on spinal motor neurons

–> majority terminates in the intermediate zone of the spinal cord

51
Q

How is motor movement processed ?

Name all the necessary steps.

A
  1. Info is processed by association + higher order systems
  2. Info is communicated to non-primary motor system
  3. PM areas coordinate the output level of M1 + spinal cord
52
Q

Malleable motor map

A

The larger the population of neurons representing a type of movement, the finer there possible control

53
Q

Gamma motor neurons

A

Involved in regulating the length of the muscle fibers

–> gets signals from muscle spindles

54
Q

Extrafusal fiber vs Intrafusal fiber

A

Extrafusal
–> muscle fibers that are innervated by alpha motor neurons and generate tension by contracting

Intrafusal
–> muscle fibers that serve as specialized sensory organs that detect the amount and rate of change in length of a muscle (part of the muscle spindle)

Functional Neuroanatomy (6 decks)

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