Motor Control Flashcards
1
Q
Function of motor system
A
Control of:
- Reflexes: simple movements
- Posture: abilitiy to stand in a balanced way
- Automated movements e.g. walking, chewing
- Purposeful movements e.g. taking notes
2
Q
Hierarchy of motor control
A
3 levels:
- Level 1 is the most basic and does not need to go to the brain, mainly needs input from the spinal cord → control of reflexes
- Level 2 controls for automated movement and will require some input from the brain but mostly the brainstem
- Level 3 is for more complex movement and will require input from the basal ganglia, cerebellum, thalamus, brainstem, cortex → purposeful movement
3
Q
Reflexes
A
- Involuntary, rapid, stereotyped movement
- Organs involved: spinal cord, peripheral nerves, and muscles
- E.g. Knee-jerk
- Mechanism:
- Tap stimulates primary sensory receptors in the muscle
- Synapse with alpha motor neurons
- Stimulate muscle fibers
- Produces muscle contraction
4
Q
Balance
A
- Proprioception: sense that allows you to have an idea of where your body is in space e.g. position of muscles, balance
-
Kinesthesia: movement and learning
- e.g. when you have a sprained ankle and your foot is immobilised for a long time, you might feel you lose balance and you have to relearn how to gain balance because for some time the muscle was not exercised
- Deafferentation is the destruction of afferent connections which prevents motor feedback
- Loss of proprioception, no control of movement (case of Ian Waterman who relearnt how to gain control)
- Afferent dysgraphia: problems in the use of feedback to control graphomotor patterns. Impaired ability to utilise visual and motor feedback to control handwriting - can be induced in normal patients by reducing kinaesthetic feedback
5
Q
Rhythmic pattern generators (automated movements)
A
- E.g. walking, running, chewing → thought is required for initiation but once started it is automated
- Combines voluntary and reflexive acts
- Intention and termination: voluntary
- Once initiated: repetitive & reflexive
- Mechanism:
- Walking initiated when a steady input excites two interneurons that control flexors and extensors
- Activity alternates because they inhibit each other via interneurons
- There is cross inhibition to the opposite side of the body
6
Q
Voluntary movements
A
- E.g. writing, playing the piano or football
- purposeful, goal-directed
- learned (improve with practice)
- complex actions
7
Q
Hierarchy of movement control
A
- Strategy – goal of movement; best strategy to reach goal
- Tactics – sequence of muscle contractions arranged in space & time to smoothly and accurately achieve the strategic goal
- Execution – activation of the motor neuron and interneuron pools that generate the movement; adjustments of posture
8
Q
Prefrontal and posterior parietal cortex
A
- Movement strategy
- Posterior parietal cortex - function: generation of mental body image (position of body in space) using somatosensory, visual, & proprioceptive information
- Area 5: input from somatosensory cortex
- Area 7: higher order visual areas
- Lesion: Right hemisphere (extra-personal space area) →
abnormalities of body image and spatial relations → Neglect
9
Q
Neglect
A
People ignore part of their visual field → spatial neglect. People with that are unaware of their neglect
10
Q
Libet’s experiment
A
- Awareness of Intention - do we have free will? Do our thoughts cause our behaviour?
- Rise of RP prior to awareness of intention of moving arm
- Early brain contributors of this signal are premotor and supplementary motor areas
11
Q
Anarchic hand syndrome
A
- Reach for objects without wanting to (Della Sala et al., 1991; 1994)
- Goal-directed, well executed, but unintended
- Self-awareness of disorder (unlike utilisation behaviour)
- Majority have lesions near medial wall of frontal-lobe & SMA (=supplementary motor area)
- E.g. GP could not stop her left hand scavenging for fish bones in leftovers; she used right hand to restrain left hand
12
Q
Supplementary motor area (SMA)
A
- Ready, set, go!
- Function
- abstract thought
- decision making
- anticipation of consequences of action
- Lesion to SMA
- Apraxia - difficulties in coordinating planning of movement e.g. ideomotor apraxia, limb apraxia (problems with movements of arms, hands and fingers), apraxic agraphia (writing deficit)
- Difficulties coordinating/planning movement e.g. anarchic hand syndrome
13
Q
Premotor cortex
A
- Goal direction
- Specific movement preferences
- A mirror neuron which responds when the monkey picks up a peanut also responds to the sight of a money making a similar grasp
- But not when the money waves his hand
- Respond to the sound of the movement → Records goal not sensory stimuli
14
Q
Mirror neurons
A
- Discovered by Rizzolatti (Gallese et al., 1996; Rizzolatti et al., 2001)
- Ventral PMC neurons: active during the performance and observation of actions
- Inferior parietal lobule neurons (region of PPC): also active during the performance and observation of actions
- Mirror Neurons - play a role in imitating movements
- This discovery was very important in terms of understanding how we learn and an autism theory was that perhaps autistic people were lacking some mirror neurons preventing them from learning about empathy. This theory has now been disproved.
- Mirror neurons are particularly active when we understand the spatio-temporal sequence that will lead to a particular goal - they are goal directed
- e.g. these neurons are more active in the brain of a pianist listening to piano being played than in the brain of a nonmusician listening to piano
- e.g. ballet dancers and capoeira dancers mirror neurons in PMC most strongly active when one watches a behaviour in which one is already competent
- MNs are activated by a visual image and/or a sound that indicates a familiar action ⇒ audiovisual MNs
- It is more the understanding of the action than the specific stimulation that activates MNs.
- Link → Social Cognition / Neuroscience
- Understanding the perceptions, ideas, and intentions of others
- Learning from others by imitation / imagination of others actions
15
Q
Primary motor cortex (M1)
A
- Motor cortex neurons excite extensor motor neurons and inhibit flexor motor neurons
- Neurons in M1 code for force and direction
-
Population coding of movement:
- Direction of movement is determined by averaging “votes” from each cell
- The larger the population, the finer the control
16
Q
Basal ganglia
A
- Consists of:
- Striatum (Caudate nucleus and Putamen)
- Subthalamic nucleus
- Globus pallidus
- Substantia nigra
- We’re able to both promote and inhibit movement
- Talks to thalamus (relay station)
- Thalamus wants to excite motor cortex (think of it like an excitable child)
- Globus pallidus: inhibits thalamus (it’s the parent)
- Direct pathway: silences globus pallidus, free thalamus → facilitates movement
- Indirect pathway: stimulates globus pallidus → suppression of unwanted movements
- Substantia nigra → inhibits thalamus
- Facilitate movement by focusing activity from widespread regions onto the SMA
- Filters inappropriate movements
17
Q
Basal ganglia disorders
A
- Nigrostriatal pathway excites direct pathway and inhibits indirect pathway
- Degeneration of substantia nigra (in brain stem) & inputs to striatum
- Loss of input tips the balance toward the indirect pathway
- Parkinson’s disease:
- Slow movement
- Difficulty initiating willed movement (akinesia)
- Increased muscle tone (rigidity)
- Tremors of hands, jaw, most prominent at rest
- Cause for substantia nigra degeneration is unknown
- Huntington’s disease
- Hyperkinesia
- Chorea: spontaneous, uncontrollable and purposeless movement
- Loss of neurons in striatum decrease striatal inhibition of the indirect pathway
- Loss of inhibition over thalamus
