Motor / zmultisensory

Question 1

The movement system - peculiarities

Answer 1

• Always bidirectional, but today mainly efferent
• Our usual index is changed

Question 2

General schematic of control movement

Answer 2

1. BRAIN
2. Spinal cord
   Efferent motor NEURONS
   • Upper (UMN) = Brain to spinal cord
   • Lower (LMN) = Spinal cord (anterior horn) to muscle
3. MUSCLE

Question 3

A. Primary motor Cortex (M1)

Answer 3

Located in the Precentral Gyrus
Sends signals via UMR down the spine to innervate muscles. Motor representation orderly arranged = motor homunculus.

Question 4

B. Secondary Motor Areas

Answer 4

It includes Premotor Cortex (PMC) and Supplementary Motor Area (SMA)
Involved in motor planning and motor control.
They are activated even 1s before movement → movement planning.
Affordance competition hypothesis: several motor plans are prepared in parallel and the best one will be selected later It includes Premotor Cortex (PMC) and Supplementary Motor Area (SMA)
Involved in motor planning and motor control.
They are activated even 1s before movement → movement planning.
Affordance competition hypothesis: several motor plans are prepared in parallel and the best one will be selected later

Question 5

C. Basal Ganglia

Answer 5

It involves several regions including the striatum, globus pallidus and thalamus.
Receives from cortex and projects to M1 forming a closed loop (Motor cortex → Basal ganglia → M1). Double function:
• Select motor plan and initiate the movement→Strategy of winner-takes-all (most active strategy
overpowers the rest).
• Once the strategy is selected, BG will ensure coordinated and smooth movement (activate voluntary
ms and inhibits unwated ones).

Question 6

D. Cerebellum

Answer 6

Receives input from sensorimotor cortex and projects to M1.
Instructs M1 about the direction, timing and force of movements → Ensures proper execution of planned, voluntary, multijoin movements (coordination and finesse).
Also important for sensorimotor learning .

Question 7

X. Other Motor Areas

Answer 7

Posterior Parietal Cortex
Generates the intention or urge to move, related to awareness
Broca’s Area (IFG - BA 44 & 45) Speech production and fluency
Mirror Neuron System
Fire when performing an action but also when seeing or listening to it
Important for social cognition: imitation, empathy? (understanding emotions and actions from others)→ASD?

Question 8

Corticospinal tract

Answer 8

Origin: Primary motor cortex
Through: Midbrain, Pons
Key structure: Pyramids (medulla)
- Motor fibers of the corticospinal and corticobulbar tracts

Question 9

Corticospinal tract (CST)
Key: Pyramids (medulla)

Answer 9

Key: Pyramids (medulla)
90% decussate = Lateral CST • Limb muscles
10% don’t decussate at medulla but at the action level = Anterior CST
• Axial muscles (trunk, neck)

Question 10

Corticospinal tract
Each fiber:

Answer 10

Each fiber:
Specific PreCG location – specific level of spinal cord – specific muscle
• PreCG controls contralateral movements
• Lower motor neuron leaves spinal cord
through anterior root (efferent)

Question 11

Muscle: structure

Answer 11

• Skeletal muscles connect two bones
• When contracted, insertion is brought closer to origin
• But how is that contraction done? Electrical stimuli + muscle

Question 12

Muscle: properties

Answer 12

1. Muscles always pull, never push (even in push-ups)
   • We can classify skeletal muscles into 4 functional groups depending on the movement
2. We have different types of muscle contraction
3. • •
   The same movement serves for different purposes
   Elbow flexion = biceps curl or scratch your face → how do we control force and speed? MOTOR UNITS!
   Motor Unit = group of muscle fibers that get their signal from the same motor neuron They all act together as a unit and will all contract under the same signal

Size matters! Bigger motor units = more myofibers controlled by a single motor neuron = powerful (but not delicate movements)

Motor units are recruited in an orderly fashion, from smallest to largest (small neurons are more easily excited).
Biggest can create more force but also fatigue quicker.

Time also matters:
Either small or big motor units have different contraction power
• But AP only have 1 intensity (all or nothing)
• Frequency is the only way to create a grade of force.
• 1 AP = 1 twitch
• 3 AP = more contraction (motor unit summation)
• Tetanus = contraction limit → Fatigue
Since AP don’t travel all down the axon at the same time, it helps smooth movement

Question 13

Therefore, force control depends on: (muscles properties)

Answer 13

Therefore, force control depends on:
• Recruiting more motor units (more AP = larger and more motor units)
• AP firing frequency (force created by each motor unit)

Question 14

Lesions and motor impairments
M1 lesions

Answer 14

Motor impairment of the contralateral side Hemiplegia

Question 15

Lesions and motor impairments
Secondary motor areas (PMC or SMA) lesions

Answer 15

No motor or sensory impairment but…
Apraxia
Loss of skilled movement.
Reduction of precision and ability in voluntary movements.

Question 16

Lesions and motor impairments
Huntington’s Disease

Answer 16

HD is a hereditary disease that debuts with cognitive and affective symptoms and then progresses to motor dysfunction.
Striatal damage→indirect pathway affected→ increased excitation (reduced inhibition) of the motor cortex → excessive and involuntary movements (chorea) and contorted postures.

Question 17

Lesions and motor impairments
Parkinson’s Disease

Answer 17

Mainly motor problems that include:
• Difficulty intiating voluntary movement.
• Hypokinesia: reduction or absence of voluntary movement.
• Bradykinesia: slow movement.
Loss of dopaminergic neurons in the substantia nigra → reduces direct pathway (also the indirect pathway)→ reduced excitation of the motor cortex (decreased movement).
They continue planning movements, but the ability to initiate them (go-signal) is compromised.

Question 18

Lesions and motor impairments
Cerebelar lesions

Answer 18

Ataxia
Reduction of precision and ability in voluntary movements + uncoordination→“like beeing drunk”.
—
Impairments in sensorimotor learning.

Question 19

Multisensory Integration
Why should we care about convergence of the senses?

Answer 19

Our world is multimodal → our brains are multisensory
• i.e. mechanical, chemical, and electromagnetic info correlates
Multisensory processing enhances efficiency
• Combination: complementary features (e.g., color + texture of an object)
• Integration: redundant signals (e.g., seen and felt texture of an object)
• Segregation: (e.g., loud music can interfere with vision)

Question 20

Multisensory Integration
McGurk Effect

Answer 20

Visual input can increase the perception of language by 15db

Question 21

Multisensory Integration
How do we know to inerpret the signals from different modalities as one?

Answer 21

Physical delay factors:
• Sound and light travel at different speeds
Physiological delay factors:
• Transduction times are different for visual and auditory signals
We have a temporal window for integration
• This window is adaptable
• It prefers certain stimuli combinations
• Temporal window is larger for visual then Auditory input rather than the other way around

Question 22

Plasticity
Previously big questions in Neuroscience: Do blind people have better hearing or more sensitivity in their hands?

Answer 22

Plasticity = brain’s ability to reorganize as a response to environmental, physiological or pathological conditions
• Hypertrophy of intact areas
• Increased connections and enlargement of the somatosensory cortex
• Competition in multisensory areas
• Reorganization of these areas towards the preserved modality
• Colonization of sensory cortices of deprived modalities
• Activation of the visual cortex for i.e. braille reading