Lecture 11 Flashcards
Reflexes vs voluntary movement
Reflexes: 1 to 1 mapping (stimulus → response)
Voluntary movement: many things to coordinate
Upper MN circuits: limb movement & postural control
Limb movements: lateral intermediate zone (IZ)
MC & pMC →IZ → skilled voluntary movement
Postural control = medial IZ
motor control centers in brainstem → IZ → posture balance, etc
vestibular nucleus - vestibulospinal tract
reticular formation - reticulospinal tract
superiorcolliculos - colliculospinal tract
red nucleus - rubrospinal tract
Primary motor cortex (PMC)
Input: BG & cerebellum via thalamus
Location: precentral gyrus
Low threshold
Cells: Betsz cells - ONLY in PMC
> largest soma, important for distal muscles
> 5% of spinal projections
Non-Betz cells - in all motor cortex divisions
Corticospinal & corticobulbar tracts (general path, controls, cst has 2 parts)
General path: motor cortical neuronal axons → internal capsule → Midbrain → cerebral peduncle → pons → medullar → spine
Corticobulbar: axons mostly end on local circuit neurons; controls head, face, and neck muscles
Corticospinal:
- lateral corticospinal tract - DISTAL muscles (90% cross in medulla)
- >terminates in lateral ventral horn & IZ
- ventral cst - AXIAL & PROXIMAL muscles
-> from dorsal & medial cortex regions
What did they show?
- Frisch & Hitzig
- Hughlings Jackson
- Dr. Penfield
- Evarts
- Michael Graziano
Frisch & Hitzig : control is contralteral
Hughlings Jackson : body is represented somehow
Dr. Penfield : brain has a map of the body
Evarts : MN activity increases with force
inc. before force → involved in planning
Michael Graziano: mapped movements, action maps
Microstimulation
Neurons can be focally stimulated
Movements organized instead of muscles
Local circuit involvement
Upper MNs (larger V) → lower MN circuits
Spike triggered averaging
Correlates individual neuron activity w/ muscle activity
Single upper MNs contact several lower MN pools
Directional tuning
If trained t o move in one direction MN activity inc. in anticipation of the direction, dec. for other directions
can find POPULATION VECTOR on preferred direction, by averaging responses
Lateral pMC (mirror neurons)
External cues → cued movement
“closed loop tasks” → ffedback & movement modification
lateral MNs encode intention to move
ventrolateral MNs also respond to observed movement
Mirror MNs: fires when acting & observing that same action
> pMC may play a role i encoding the observed actions of others
pMC direct & indirect effects
Direct effects: from projections to corticobulbar/spinal tracts
Indirect effects: from reciprocal projections to PMC
Vestibular nuclei
Medial vestibulospinal tract
- mediates feedback: posture/stability disturbances (semicircular canal signal)
- bilateral
Lateral vestibulospinal tract → otholith organ signals
- mediates proximal muscles responses, balance/posture
-ipsilateral
Medial pMC
Internal cues
“open loop” tasks → spontaneous movement
Reticular formation
(know feedfoward vs feedback)
Reticulospinal tract, medial VH
Modulates reflexes from stereotyped movement
Feedforward adjustments from cortex/hypothalamus/brainstem input
- compensatory movement is first; pre-programmed (ie. legs tense before puling bar to help stabilize)
Feedforward: future
Feedback: past
Superior colliculus
Controls axial muscles. head orientation
Direct pathway: spinal cord; colliculospinal tract
Indirect pathway: through reticular formation to reticulospinal tract
Red nucleus
Control arm/hand movements
Rubrospinal tract
Limited to cervical level of spina cord
Terminates in lateral VH & IZ
Active before movement onset
