B&C: Action Flashcards
Where does the motor pathways start according to the diagram from the slides and where does it go from here? (5)
the premotor and supplementary motor cortex regions and goes to the cerebellum, motor cortex, brainstem, spinal cord and basal ganglia
Describe the pathways which aren’t coming directly from the the premotor and supplementary motor cortex regions
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.
How do these higher and lower systems differ in the movements generated
Higher systems govern it in a more abstract sense (not directly) and lower systems much more governs the movements in terms of actual demands
What is the final common pathways of all motor output and how is it demonstrated?
the ventral horn Alpha motor neuron and the stretch reflex demonstrates it
What causes this reflex?
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.
Why is it called the the final common pathways of all motor output?
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
What is meant by the dorsal and ventral root and what are they important for?
Dorsolateral part- Distal movements (fingers etc) therefore fine movements.
Ventromedial parts- proximal muscles (shoulders etc) therefore posture…
What diseases affect alpha motor neurons? (2)
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)
What is the function of the stretch reflex? How is this carried out?
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)
What are intramural muscle fibres?
Muscle fibers in the muscle spindle itself (rather than extrafusal muscles on the outside
What happens to the antagonistic muscles during this reflex?
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)
What is the crossed extensor reflex?
As one limb flexes, the other extends (walking)
What is meant by the flexor and extensor?
Flexor- muscle that flexes
Extensor- reciprocal muscle that extends or opens the joint
What is meant by central pattern generation and what is ironic about this name?
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
give other examples of other fully automatic and highly coordinated movement patterns
Swallowing, breathing, orientating
What reflex protects from overload and how?
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.
Name another reflex which prevents from damage
Withdrawal reflex (heat or pain etc)
What category do all these reflexes (and more) fall under?
Lower motor control (these do all the ‘work’ only thing that is needed is a central ‘command’ and some checks and balances)
What other structures are involved in these reflexes?
Extrapyramidal systems projecting from various areas in the brainstem
What tract contains the pyramidal system and where does it run through?
Cortico spinal- From various areas in the motor cortex, through the midbrain, through the medulla and into the spinal cord
What other tracts are contained in the extrapyramidal systems? Where do these stem from?
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)
What function do each of these tracts carry out?
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
What is the function of the pyramidal system, where does it begin and go from there?
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
Describe the two tracts within the pyramidal system (pathway and function)
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
What does damage to the corticospinal tract cause? What signs can show this
- 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
What do the names of the general structures of the brainstem come from
What they look like as it was before people knew the structures
Where do the motor nerves cross to the contralateral side?
In the spinal cord
When is the need for checks and balances highlighted?
Perturbations (outside forces, uneven terrain)
Slopes (require different balance setting between agonist and antagonist)
What difficulties in movement is found with lesions to cerebellum
difficulties in balance and therefore movement. (similar to drunks)
What does the cerebellum provide which explains this?
A subcortical-cortical loop which provides fine tuning of movements, timing of automated movement sequences and motor memory, possibly also timing in general.
Describe the processes in this loop
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.
What parts is the cerebellum divided into?
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
What is typical of cerebellar ataxia?
Endpoint tremor (fine movements such as pointing) and slurred speech
What structures of the basal ganglia are given in the slides?
Striatum (caudate nucleus and putamen)
Globus pallidus (Interna and Externa)
Substantia nigra (production of dopamine)
Subthalamic nucleus
What pathways are included in the basal ganglia? (4)
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
Is D1 and D2 inhibitory or excitatory?
D1 excitatory
D2 inhibitory
What effects do the two main pathways have?
Direct pathway inhibits GPi/ SNr so that their inhibitory effect is diminished > more activation of cortex > more movement
What role does the Globus Pallidus/ Substantia Nigra reticulus play?
GPi / SNr act as inhibitor of thalamus, so that in the end cortex and output to spinal cord (i.e. movements) are suppressed
What 2 diseases can effect these structures in different ways and how
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
What is the main cause of Huntington’s disease?
Hereditory
What medication is available for parkinsons?
L-dopa, stem cells, deep brain stimulation
Name the various cortical motor regions mentioned in the slides and their associated functions
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.
What do these abbreviations stand for?
M1 : Primary motor cortex SMA: Supplementary motor area PMC: Premotor cortex PPC: Posterior parietal cortex PFC: Pre frontal cortex
What is meant by hemiplegia and what causes it?
Half sided paralysis due to lesions of upper motor neurons coming from M1
What is meant by apraxia and what causes it?
- Loss of motor skill, not due to muscular, upper(M1) or lower motor (spinal cord) neural deficit
- Lesions to SMA. PMC, PPC
Name, describe and give the ethology of two types of apraxia
- 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)
How do neurons typically translate (encode) real life movement in the M1
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.
What do these individual neurons combine to give?
Actual movement is encoded by vector sum of population of M1 cells
What are affordances?
Sensory inputs create many potential motor responses (affordances). Depending on needs and potential payoffs, one of these has to be selected
What role does the premotor cortex play regarding vectors?
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
What else is the PMC important for regarding movement?
Specific types of movements regardless of when and where (precision vs power grip)
Give a final feature of PMC regarding actions
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
Where are mirror neurons more prevalent?
Widespread in motor cortex and parietal cortex?
What is the posterior parietal cortex responsible for in regards to movement?
Posterior Parietal Cortex (PPC): translating movement from retinal (eye-centered) to hand-, head-, or body-centered reference frames
How is this related to prosthetics
This is used to ‘read’ the planned movement from the motor cortex, and use this in prosthetics
What is meant by pattern classification and how does this apply to prosthetics?
Training a computer algorithm (classifier) to ‘recognize’ specific patterns of neural activity (combinations of activity increases and decreases of specific intentions to move)
