M3 L2 Flashcards
3 types of movements:
- Reflexes – Neural circuit resides in spinal cord or brain stem
- Rhythmic - includes a central component that regulates spinal cord oscillatory circuit
- Voluntary - requires ‘higher’ levels such as cortex, basal ganglia, cerebellum
what is hierarchical control?
motor systems are organized by levels
what is parallel control?
more than one pathway may be active at the same time
What is the first stage to start movement? Explain
- where?
The first is strategy
- the brain receives information based on sensations + proprioception about where the body is in space.
- cerebral neocortex
- basal ganglia
What is the second stage to start movement? Explain
*where?
The second stage is tactics where the brain decides what to do from all the info (chooses 1)
- motor areas of Cortex and cerebellum
What is the final stage to start movement? Explain
*where?
final step is executive where the muscles coordinate to produce movement
- cervical, thoracic, lumbar region + brain stem + spinal cord
Strategy, tactics, and execution
How does the brain communicate with the spinal cord to control muscles?
Through descending tracts (which are clusters of axons) which provide input to the brain and spinal cord
what is a cluster of axons called in CNS vs PNS
CNS: Tracts
PNS: Nerve
Which pathways descend from the motor cortex and act on the spinal cord?
The lateral and ventromedial pathways
What does the lateral pathway control?
involved in voluntary movement of the distal muscles under the cortex control
What does the ventromedial pathway control?
involved in the movement of axial muscles and control of posture and are under brain stem control
What tracts are in the lateral pathway? Responsibilities
corticospinal tract: (large) controls voluntary movement of the body - limbs + trunk
rubrospinal tract: (small) controls muscle tone and movement in the upper limbs
Where does the corticospinal tract originate from?
Where do its axons originate from
In the neocortex
2/3 of axons originate from areas 4 and 6 of the frontal lobe motor cortex (rest from somatosensory area of parietal lobe)
What were lesion studies and what did they teach us about monkeys?
who did the experiment
used primates and removed part of the brain to see the effect on the body
- monkeys can sit w normal posture (ventral area works ok)
- slower/less accurate voluntary movement
- unable to do fractional movement (move joints independently from one another - wrist without elbow)
- Lawrence and jumpers
What are the 3 areas in the motor cortex?
Area 6 (SMA&PMA)
* planning movement
Area 4 (M1 - primary motor cortex)
* execution of movement
What did wilder penfield do?
poked people during surgery to see what would happen.
found that weak stimulation to area 4 caused movement on the opposite side
What do SMA and PMA do?
the premotor cortex (PMA) and supplementary motor area (SMA) play a role in planning movement, especially for distal musculature (muscles farther from the body’s center, like those in the hands and fingers) - based on external sensory cues
Cells in Area 6 become active about a second before movement starts, showing that this area is involved in preparation rather than just the movement itself -internal generated movement sequences
Why do cells in area 6 start firing more electrical signals (action potentials) before the actual movement happens?
This increase in activity (discharge) is like a preparation phase, where the brain gets everything ready before sending final instructions to the muscles.
what did the Weinrich and Wise (1982) experiment show?
demonstrated that neurons in the Premotor Area (PMA) are involved in motor planning, not just movement execution.
- neurons in the PMA start firing (“discharge”) after the instruction stimulus is given – (planning before)
- The PMA neurons remain active (“set phase”) while waiting for the “go” signal – (holding onto plan until its time)
- Once movement begins, the PMA neurons stop firing – (stop after planning part is over)
what does this experiment show
this additional PMA neuron experiment showed that neurons fire both when we do things (motor info) and when we see things (sensory neurons)
What are mirror neurons
* where found
* what do they allow us
fire both when you perform an action and when you watch someone else perform the same action or mentally rehearse/imagine movement
- in PMA
- allow us to plan our own movements and understand the actions and goals of others
What is the SMA involved in?
responsible for internally-generated movement sequences
Plans and sequences movements based on memory, experience, or intention
What is the main output neuron of the primary motor cortex (M1)?
Large pyramidal neurons in cortical layer V (Betz cells)
- sends info either to excitatory or to motor neurons
What is the function of Betz cells?
They send motor commands from M1 to the spinal cord via the corticospinal tract.
What is the corticospinal tract?
A pathway that carries motor signals from the motor cortex to the spinal cord.
Where do corticospinal neurons in layer V project to and synapse?
They project to alpha motor neurons and synapse on spinal interneurons and lower motor neurons
What areas provide input to layer V of M1?
Areas 6, 3, 1, and 2, and the thalamus (VLc).
Where does M1 (primary motor cortex) send output signals?
To the brainstem and spinal cord via the corticospinal tract.
How does M1 influence movement at the spinal level?
By synapsing on inhibitory interneurons, flexor motor neuron pools, and extensor motor neuron pools.
What did recordings from M1 neurons in behaving animals reveal?
revealed that a burst of activity occurs immediately before and during a voluntary movement
What 3 things did the recording studies reveal about how M1 commands voluntary movement
1- much of the motor cortex is active for every movement
– 2- the activity of each cell represents a single “vote” for a particular direction of movement
– 3- the direction of movement is determined by a tally (and averaging) of the votes registered by each cell in the population
Does the quantity of neurons change as you practice a motion more?
Yes, the motor cortex changes as you release (maleable motor unit)
What areas make up the somatosensory cortex?
Areas 1, 2, 3a, and 3b.
What areas are part of the posterior parietal cortex?
Areas 5 and 7
Whats the malleable motor map? What does have more neurons mean?
The malleable motor map refers to the brain’s ability to adapt and learn with experience
- The more neurons dedicated to a movement, the finer the control (e.g., hands and facial muscles have a lot of neurons for precise movement).
What did Donoghue and Danes experiment with the malleable motor map find?
They severed the motor nerve that supplies the muscles of the snout and its whiskers and found that regions of M1 that had evoked whisker movements now would elicit either forelimb or eye movements
- basically neurons move to new area (switch allegiance)
finer movement = more
neurons
