Motor control 1 + 2 Flashcards
What is the motor homunculus
A somatotopic map of the primary motor area (pre-central gyrus) showing which regions of the body are controlled by which regions of the pre-central gyrus
Which of the following structures is represented the most medially in the motor homunculus
A Eye
B Face
C Knee
D Tongue
E Wrist
C
Area 6 (premotor cortex) is subdivided into what 2 areas
Premotor area (PMA) Supplementary motor area (SMA)
The supplementary motor area (subdivision of the premotor cortex) controls distal (i.e. fingers) or proximal motor units
Distal
The premotor area (subdivision of the premotor cortex) controls distal (i.e. fingers) or proximal motor units
Proximal
Is the motor or sensory homunculus more precise
Sensory
Why is the motor homunculus not as precise as the sensory
Doesn’t represent UMNs causing a single, individual muscle movement
Microstimulation shows that stimulating the arm region of the pre-central gyrus causes
movement of the hands towards mouth
The ‘decision making neurons’ are those of area 4 (primary motor cortex) or area 6 (premotor cortex)
Area 6
DECISION MAKING NEURONS in PMA (area 6) fire APs when?
ONE SECOND BEFORE a voluntary movement occurs
Monkey sitting in front of some lights and every now and then a red warning light flashes and subsequently a blue button flashes
Monkey gets a reward for pressing the button when the blue light flashes so then trains himself for more rewards
When the red warning light flashes, what happens?
When blue button flashes, what happens?
…planning of the movement happens and there’s a big increase in PMA AP firing
…he makes the movement to touch the button; PMA firing continues throughout this
Premotor cortex also contains what kind of neurons other than decision making neurons
Mirror neurons
When do mirror neurons fire
When yourself or others perform the same specific action
/ when movement is made OR when movement is imagined (rehearsed mentally)
It’s suggested that mirror neurons underpin what
emotions and empathy (as they allow you to understand how others may be feeling if you were in that same situation)
Commands to perform precise movements are encoded in the integrated activity of large populations of neurons in what area
4 (M1) - primary motor cortex
What other mechanisms can control movement apart from decision making and mirror neurons
Feedback and feedforward mechanisms
How do feedback mechanisms correct postural instability
A change in body position initiates rapid compensatory feedback messages from brainstem vestibular nuclei to spinal cord motor neurones to correct postural instability
How do feedforward mechanisms stabilise posture
Before completely falling, brainstem reticular formation nuclei (which are controlled by the cortex) initiate feedforward anticipatory adjustments to stabilise posture
What is a ‘readiness potential’
General increase in cortical activity prior to voluntary movement
Represents electrical manifestation of the ‘idea’ for a voluntary movement
What parts of the brain process the readiness potential (general increase in cortical activity prior to voluntary movement)
Basal ganglia
Cerebellum
What is a spinal cord transection
Tear within the spinal cord as a result of significant trauma
Although, UMN lesion is characterised by spasticity (increased tone), initially there is what
SPINAL SHOCK - where there’s initial hypotonia
What is the babinski sign
+ when do you get no babinski sign
Plantar flexion should occur when you tickle the feet unless you’re a baby or have cortical damage (indicates incomplete upper control of spinal circuits)
Function of basal ganglia
Initiate voluntary movement
Basal ganglia is part of a motor loop, name the components of this motor loop (5)
cerebral cortex –> basal ganglia –> ventral lateral nucleus in the dorsal thalamus –> back to area 6 of cerebral cortex
Basal ganglia integrates all the info from…
PREFRONTAL, MOTOR & SOMATOSENSORY CORTEXES
Area 4 contains what neurons if area 6 contains the decision making neurons
functional motor neurons (“go and do it” neurons)
Components of basal ganglia (5)
caudate nucleus, putamen, globus pallidus substantia nigra (functionally) subthalamic nucleus (functionally)
What does the corpus striatum consist of (2) + is the corpus striatum the input or output zone of the basal ganglia
Caudate nucleus + putamen (INPUT ZONE)
The caudate nucleus + putamen (INPUT ZONE) receive excitatory or inhibitory inputs onto their dendrites
Excitatory (glutamatergic)
The axons of the medium spiny neurons in the putamen and caudate nucleus are excitatory or inhibitory
Inhibitory (GABAergic)
Is the following an excitatory or inhibitory pathway:
Cerebral cortex projecting to putamen
Excitatory
Is the following an excitatory or inhibitory pathway:
Putamen projecting to globus pallidus
Inhibitory
Is the following an excitatory or inhibitory pathway:
Globus pallidus projecting to VLo (ventral lateral nucleus)
Inhibitory
Is the following an excitatory or inhibitory pathway:
VLo (ventral lateral nucleus) projecting back to SMA of area 6
Excitatory
Consequence of cortical activation in the motor loop
EXCITATION because inhibiting an inhibitory pathway –> excitation
Why does cortical activation of putamen (i.e. cortex activating putamen) boost cortical excitation (4)
At rest, globus pallidus neurons are spontaneously active and inhibit VLo
So, cortical excitation:
- Excites putamen which,
- Inhibits the inhibitory globus pallidus which therefore,
- Disinhibits the VLo so other inputs can excite it,
- Activity in VLo excites UMNs in SMA
At rest, are globus pallidus neurons excitatory or inhibitory
Inhibitory
What is the direct loop/pathway through the basal ganglia
Direct - motor loop involving cerebral cortex –> basal ganglia –> ventral lateral nucleus in the dorsal thalamus –> back to area 6 of cerebral cortex, which SELECTS SPECIFIC MOTOR ACTIONS
Indirect - antagonises/balances the direct pathway
Describe how the indirect loop/pathway through the basal ganglia works
Antagonises/balances the direct pathway
Putamen inhibits the globus pallidus external (GPe) which then inhibits both globus pallidus internal (GPi) AND subthalamic nuclei (STN) - so they are disinhibited now because remember GP at rest is inhibitory so inhibiting it essentially disinhibits it
Cortex can now excite the STN –> excites the GPi –> INHIBITS THE THALAMUS
Therefore, indirect pathway is via the STN
Goal of the indirect loop/pathway through the basal ganglia
SUPRESSES INAPPROPRIATE MOTOR MOVEMENTS THAT WOULD BE STOPPING YOU FROM YOUR GOAL
Dopamine enhances cortical inputs though the direct or indirect pathway via basal ganglia
+ supresses the direct or indirect pathway via basal ganglia
Enhances via direct pathway
Suppresses the indirect pathway
Huntington’s disease is a degeneration of what
Degeneration of corpus striatum disrupts cortical control via inhibitory striatopallidal projection, releasing spontaneous activity of pallidal cells,, allowing ‘motor gibberish’’ to be transferred to motor cortex..
Huntington’s is characterised by
Hyperkinesia
- chorea (spontaneous rapid flicks and major movements with no purpose)
Why is cerebellum also involved in movement as well as primary motor cortex
Commanding contractions (with motor cortex) is not enough - skilled movements need a detailed sequence of timed contractions varying in intensity and duration
How does a cerebellar lesion affect movement
Uncoordinated inaccurate movements (ATAXIA)
What pathway is even bigger than the corticospinal tract
CORTICO-PONTO-CEREBELLAR PROJECTION - connects cortex, pontine nuclei (in pons) and cerebellum
Cerebellum essentially fines tunes what
Voluntary movements
imposes timing on sequences of contractions producing coordinated and automatic voluntary movements
What does motor learning involve + what part of the brain does it involve
Computing all of the motor movements we’ve ever done and inputs this into the cortex, essence is learning the TIMING OF CONTRACTIONS
Cerebellum
Cerebellar disorders manifest as disorders of what
Co-ordination
Parkinson’s disease is a degeneration of what
Degeneration of substantial nigra neurones removes inhibitory check on striatal inhibition of pallidum (i.e. remove inhibitory effects of corpus striatum on globus pallidum) so that voluntary commands cannot get through
