Neu mod 4, lecture 29 motor cortex

descending control of pain

• certina brin centers which control emotion and atteniton will synape to periadaquetal gray

  • activate endorphins

    • which stimulate synapses between PAG neurons and medulla raphae nuclei

      • raphae: serotonin

  • Serotongeineric neurons form INHIBITORY synapses within the dorsal horn of the projection neurons

• Will inhibit info from spihinothalamic neuron which will be carrying pain information

Layer 5 or area 4 in context of motor neurns

• origination for control of movement

  • upper motor neurons (betz cells)

  • pyramidal shaped

lower motor neurons

direct connection to muscle fibers

neurotransmotter used by motor neurons

acetylcholine

Corticospinal tract

• travel thorugh midbrain and meedulla

• crosses over at pyramidald dessucation of the medulla

• first synapse onto lower motor neuron

  • in ventral horn

everything above medulla represents control over

contralateral side of body

• descending pathway

everythign below medulla represents

same side of body

• descending pathway

spinal cord injruy on one side of hte body will affect motor ability on what side

• SAME side

• after crosses over

upper motro neuron lesion signs

• initial flaccid paralysis followed by SPASTIC paralysis

• loss of voluntary movement

• hypertonia/clonus

• babinski sign (toes curl otward when damaged)

lower motor neuron lesion signs

• flaccid paralysis

• decreased reflexes, twitching

• hypotonia

Premotor and supplementary motor cortex

• More complex actions 

  • Planning and gripping in more complex way 

  • Neurons there that think and plan the action 

• Area 6 and association areas important in planning

Area 4 will only light up

Area 4 will only light up with area 6 during theACTUAL movement

Corpus callosum

• White matter which connect right and left brain 

• Communication between PMA SMA On one side and other side 

• Often a site of lesion

Apraxia

 inability to perform actions on command

• Damaged association motor cortex 

• Lesion in connections between right and left cortex

(experiment) Do M1 neurons initiate muscle movement?

• Correlation experiment (this ) 

  • If neurons controlling those muscles, then they should fire before the signal would arrive in muscle (contracts) 

  • To test → recorded from M1 neuron 

  • Action potentials, record EMG activity which looks very messy 

  • Rectifier 

    • Makes allahabad ata of APs in positive direction 

  • Spike triggered averaging 

    • Want to know how son before or after a particular event some response occurs 

    • Event we are interested in is EMG activity and when it occurs in relation to the upper motor neuron activity 

    • Hypothesis 

      • Spikes hapepn before muscle 

    • Take action potential and average 9000 of them and average EMG response before and after 

    • To get feeling of bulk activity in relation to activity of spikes 

  • Result 

    • On average, signal in muscle is happening after about 100 to 200 milliseconds after primary motor neuron 

    • First evidence that muscle is follower of the upper motor neuron 

Decoding response properties of M1 neurons