B&C: Action

Question 1

Where does the motor pathways start according to the diagram from the slides and where does it go from here? (5)

Answer 1

the premotor and supplementary motor cortex regions and goes to the cerebellum, motor cortex, brainstem, spinal cord and basal ganglia

Question 2

Describe the pathways which aren’t coming directly from the the premotor and supplementary motor cortex regions

Answer 2

From motor cortex feeds into brainstem and from there into spinal cord or directly from motor cortex.
Pathways from cerebellum and basal ganglia feed back into both the premotor and supplementary motor cortex regions and the motor cortex.

Question 3

How do these higher and lower systems differ in the movements generated

Answer 3

Higher systems govern it in a more abstract sense (not directly) and lower systems much more governs the movements in terms of actual demands

Question 4

What is the final common pathways of all motor output and how is it demonstrated?

Answer 4

the ventral horn Alpha motor neuron and the stretch reflex demonstrates it

Question 5

What causes this reflex?

Answer 5

A hammer tap stretches the quadricep (tendon_ which is sensed by the muscle spindle which activates a sensory neuron called the dorsal root to an alpha motor neuron in the ventral root which causes the muscle to contract.

Question 6

Why is it called the the final common pathways of all motor output?

Answer 6

All movement you make influences this reflex, either by diminishing it or enhancing it. This alpha motor neuron is always activated when moving a muscle

Question 7

What is meant by the dorsal and ventral root and what are they important for?

Answer 7

Dorsolateral part- Distal movements (fingers etc) therefore fine movements.
Ventromedial parts- proximal muscles (shoulders etc) therefore posture…

Question 8

What diseases affect alpha motor neurons? (2)

Answer 8

Lou Gherig’s disease (ALS)- Amyotic Lateral Sclerosis
Poliomyelitis (Polio)- viral infection that selectively attacks AMN’s (can be cured recently or prevented through vaccination)

Question 9

What is the function of the stretch reflex? How is this carried out?

Answer 9

Keeping posture- the muscle spindle senses stretching, activated the AMN which contracts muscle. Gamma motor neuron then contracts muscle spindle during voluntary movement so that they can stay short enough to sense stretching when muscles are short (inout from the pons)

Question 10

What are intramural muscle fibres?

Answer 10

Muscle fibers in the muscle spindle itself (rather than extrafusal muscles on the outside

Question 11

What happens to the antagonistic muscles during this reflex?

Answer 11

Reciprocal inhibition of the antagonistic muscles: When extensor (quadriceps) contracts, flexor relaxes (sensed through muscle neuron and the alpha neuron is inhibited by an inhibitory neuron)

Question 12

What is the crossed extensor reflex?

Answer 12

As one limb flexes, the other extends (walking)

Question 13

What is meant by the flexor and extensor?

Answer 13

Flexor- muscle that flexes

Extensor- reciprocal muscle that extends or opens the joint

Question 14

What is meant by central pattern generation and what is ironic about this name?

Answer 14

The Central Pattern Generator ‘creates’ locomotion movements all on its own. The only thing that is required is a high level ‘gait’ command (or it can be set in motion by proprioceptive feedback.) This is ironic as it can be completed using only the spinal chord

Question 15

give other examples of other fully automatic and highly coordinated movement patterns

Answer 15

Swallowing, breathing, orientating

Question 16

What reflex protects from overload and how?

Answer 16

Golgi tendon reflex by the Golgi tendon organ causing the muscle to relax (by inhibiting the motor neuron) and drop the excessively heavy load when sensing this to protect the muscle.

Question 17

Name another reflex which prevents from damage

Answer 17

Withdrawal reflex (heat or pain etc)

Question 18

What category do all these reflexes (and more) fall under?

Answer 18

Lower motor control (these do all the ‘work’ only thing that is needed is a central ‘command’ and some checks and balances)

Question 19

What other structures are involved in these reflexes?

Answer 19

Extrapyramidal systems projecting from various areas in the brainstem

Question 20

What tract contains the pyramidal system and where does it run through?

Answer 20

Cortico spinal- From various areas in the motor cortex, through the midbrain, through the medulla and into the spinal cord

Question 21

What other tracts are contained in the extrapyramidal systems? Where do these stem from?

Answer 21

Rubro spinal (From right red nucleus in midbrain)
Tecto-spinal (From superior and inferior colliculi in midbrain)
Vestibulo-Spinal (Info from vestibulococlear nerve in inner ear to vestibular nucleus in medulla)
Recticulo-spinal (from recticular formation (info from many pathways) in medulla)

Question 22

What function do each of these tracts carry out?

Answer 22

Rubro spinal: Control muscle tone and distal limb muscles that perform precise movements
Tecto-spinal: Receive visual and auditory information. Also a reflex-like orientating response: head neck and upper limbs orientate towards visual and auditory stimuli
Vestibulo-Spinal: Moniters position and movement of the head to maintain posture and balance
Recticulo-spinal: Controls many reflexes (excitability) and state of arousal

Question 23

What is the function of the pyramidal system, where does it begin and go from there?

Answer 23

Voluntary control of skeletal muscles. It begins at upper motor neurons of primary motor cortex and other cortical areas (SMA, PMC.) The axons then descend into the brainstem and spinal cord to synapse on lower (alpha) motor neurons

Question 24

Describe the two tracts within the pyramidal system (pathway and function)

Answer 24

Corticobulbar tract- goes towards the cranial nerve nuclei that move eye, jaw, face and some muscles of the neck and pharynx (throat)
Corticospinal tract- visible along ventral surface of medulla oblongata as pair of thick bands, the pyramids. It controls non-facial somatic muscles. The lateral CS tract crosses at pyramidal decussation at high level while the anterior CS tract crosses to opposite side of spinal cord at lower level in anterior white commissure

Question 25

What does damage to the corticospinal tract cause? What signs can show this

Answer 25

• Paralysis
• Spasticity/ Flaccidity: a pattern of weakness in the extensors (in upper limbs) or flexors (in lower limbs) known as pyramidal weakness
• Babinski sign can demonstrate changed reflexes: When sliding from heel to tow on sole of foot the toes will point upwards instead of downwards

Question 26

What do the names of the general structures of the brainstem come from

Answer 26

What they look like as it was before people knew the structures

Question 27

Where do the motor nerves cross to the contralateral side?

Answer 27

In the spinal cord

Question 28

When is the need for checks and balances highlighted?

Answer 28

Perturbations (outside forces, uneven terrain)

Slopes (require different balance setting between agonist and antagonist)

Question 29

What difficulties in movement is found with lesions to cerebellum

Answer 29

difficulties in balance and therefore movement. (similar to drunks)

Question 30

What does the cerebellum provide which explains this?

Answer 30

A subcortical-cortical loop which provides fine tuning of movements, timing of automated movement sequences and motor memory, possibly also timing in general.

Question 31

Describe the processes in this loop

Answer 31

The motor cortex sends action potentials to lower motor neurons in the spinal cord and inform the cerebellum ion the intended movement. These lower motor neurons then send potentials to skeletal muscles causing them to contract, proprioceptive signals from the skeletal muscles and joints to the cerebellum convey information about the status and structure being moved during contraction. The cerebellum then compares information from both signals and modifies the stimulation from the motor cortex through action potentials going to the spinal cord.

Question 32

What parts is the cerebellum divided into?

Answer 32

Vestibulocerebellum: Coordination of eye movements with body movements, VOR (vestibulo-ocular-reflex)
Spinocerebellum: Balance, Walking, Affected by alcohol use
Neocerebellum: Control of fine movements, Finger to nose test, Speech

Question 33

What is typical of cerebellar ataxia?

Answer 33

Endpoint tremor (fine movements such as pointing) and slurred speech

Question 34

What structures of the basal ganglia are given in the slides?

Answer 34

Striatum (caudate nucleus and putamen)
Globus pallidus (Interna and Externa)
Substantia nigra (production of dopamine)
Subthalamic nucleus

Question 35

What pathways are included in the basal ganglia? (4)

Answer 35

Direct pathway (from striatum to GPi/SNr)
Indirect pathway (striatum> GPe > STN > GPi/SNr )
Dopamine released by SNc (SNc to striatum)
D1, D2 receptors in striatum

Connections from GPi/SNr go to thalamus to the cortex. from the f=cortex connections can go to the striatum, brainstem and spinal cord or back in the STN

Question 36

Is D1 and D2 inhibitory or excitatory?

Answer 36

D1 excitatory

D2 inhibitory

Question 37

What effects do the two main pathways have?

Answer 37

Direct pathway inhibits GPi/ SNr so that their inhibitory effect is diminished > more activation of cortex > more movement

Question 38

What role does the Globus Pallidus/ Substantia Nigra reticulus play?

Answer 38

GPi / SNr act as inhibitor of thalamus, so that in the end cortex and output to spinal cord (i.e. movements) are suppressed

Question 39

What 2 diseases can effect these structures in different ways and how

Answer 39

Huntington’s disease- Damage to the pathway from the striate to the globes pallidus externa which causes the indirect pathway to be weaker, leading to the GP having too little inhibition causing movement “all over the place”

Parkingston’s disease- Substantia Nigra no longer produces dopamine which leads to the indirect pathway being stronger and the direct pathway will be weaker. The structure will then be too strong in inhibition and the person will have huge difficulty in movement

Question 40

What is the main cause of Huntington’s disease?

Answer 40

Hereditory

Question 41

What medication is available for parkinsons?

Answer 41

L-dopa, stem cells, deep brain stimulation

Question 42

Name the various cortical motor regions mentioned in the slides and their associated functions

Answer 42

M1: Direct motor control
PMC (with PPC): Externally guided, stimulus driven action (e.g catching a ball)
SMA (With PFC): internally guided action (e.g selecting which object to pick up.

Question 43

What do these abbreviations stand for?

Answer 43

M1 : Primary motor cortex
SMA: Supplementary motor area
PMC: Premotor cortex
PPC: Posterior parietal cortex
PFC: Pre frontal cortex

Question 44

What is meant by hemiplegia and what causes it?

Answer 44

Half sided paralysis due to lesions of upper motor neurons coming from M1

Question 45

What is meant by apraxia and what causes it?

Answer 45

• Loss of motor skill, not due to muscular, upper(M1) or lower motor (spinal cord) neural deficit
• Lesions to SMA. PMC, PPC

Question 46

Name, describe and give the ethology of two types of apraxia

Answer 46

• Ideomotor apraxia: rough idea of movement can be executed- can be very selective with some movements being roughly executed others not at all (SMA, PMC)
• Ideational apraxia: No idea what to do, uses wrong tools (PPC)

Question 47

How do neurons typically translate (encode) real life movement in the M1

Answer 47

In M1 (and PMC) neurons encode movement directions. Indicvidual motor neurons encode vector of movement, i.e are tuned for the direction of movement but this is very broad.

Question 48

What do these individual neurons combine to give?

Answer 48

Actual movement is encoded by vector sum of population of M1 cells

Question 49

What are affordances?

Answer 49

Sensory inputs create many potential motor responses (affordances). Depending on needs and potential payoffs, one of these has to be selected

Question 50

What role does the premotor cortex play regarding vectors?

Answer 50

Premotor Cortex: encodes population vectors of multiple potential actions (go to red, go to blue), until
color cue is given to perform one action and not the other. Therefore it is pretty important for selecting the relevant way

Question 51

What else is the PMC important for regarding movement?

Answer 51

Specific types of movements regardless of when and where (precision vs power grip)

Question 52

Give a final feature of PMC regarding actions

Answer 52

Another feature of PMC: Mirror Neurons: Neurons that encode an action, yet also are activated by seeing (or hearing) the same action performed by others

Question 53

Where are mirror neurons more prevalent?

Answer 53

Widespread in motor cortex and parietal cortex?

Question 54

What is the posterior parietal cortex responsible for in regards to movement?

Answer 54

Posterior Parietal Cortex (PPC): translating movement from retinal (eye-centered) to hand-, head-, or body-centered reference frames

Question 55

How is this related to prosthetics

Answer 55

This is used to ‘read’ the planned movement from the motor cortex, and use this in prosthetics

Question 56

What is meant by pattern classification and how does this apply to prosthetics?

Answer 56

Training a computer algorithm (classifier) to ‘recognize’ specific patterns of neural activity (combinations of activity increases and decreases of specific intentions to move)