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Lecture 11

Physiology 3120 Lecture Notes - Lecture 11: Functional Magnetic Resonance Imaging, Alpha Motor Neuron, Motor Cortex


Department
Physiology
Course Code
PHYSIO 3120
Professor
Tom Stavraky
Lecture
11

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Leg Trunk
Central sulcus
Medial Lateral
FINGERS
Arm FACE
Precentral
Gyrus
Neuro XI
Motor Cortex
Stimulation: Electrical, Magnetic, Epilepsy
Lesion: Electrical, Chemical, Stroke, Degeneration
Recording:
o Single neurons
o Evoked potentials (stimulate somewhere & record field of neurons)
o EEG
o PET (Positron Emission Tomography)
o fMRI (functional Magnetic Resonance Imaging)
Motor Cortex
Definition: Area of cortex from which low intensity electrical stimulation produces
skeletal muscle contractions which are contralateral for arm and leg
o Contralateral or bilateral in terms of face
o Contralateral (always) for limbs
Located on precentral gyrus (classic motor cortex)
Somatotopic organization
o Motor representation (representation of body map)
o Somatotopic pattern (distorted homunculus)
Somatotopic Organization Evidence
Hughlings Jackson march of epileptic motor seizure
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o i.e. epilepsy occurring in fingers will travel to hand arms body
Electrical stimulation (Penfield)
Lesions (strokes)
Recordings of neural activity
Motor Representation Muscles or Movements?
Muscle Representation
Looking at particular neurons in motor cortex (i.e. corticospinal neurons)
This projects to an alpha motor neuron that innervates an effector (i.e. biceps
muscle)
An adjacent neuron is present innervating a second alpha MN that innervates i.e.
second biceps muscle
Organized somatotopic pattern in terms of pattern in muscle cortex
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Not side by side
i.e. within the finger area, the corticospinal neurons can be dispersed
Another evidence: single cortical neuron
Same corticospinal neuron can synapse different alpha MN that innervate different
effectors (muscle fibres)
o i.e. move arm to touch face
o move biceps & wrist flexion
o single neurons can bring about set of contractions of all muscles involved
1. Wide motor cortical sites project to a single muscle
2. Single cortical neurons make MS connections with motor neurons innervating
several different muscles
3. Motor cortex micro-stimulation produces purposeful-like movements
Conclusion Movement Representation
Is Somatotopic Pattern Fixed or Modifiable (Plasticity)?
Learning new keyboard task
Experimental injury
Movement of different region of the body, results in the increased activity in a
specific region in motor cortex
Same flexion movement after practice (use-dependent) increases somatotopic size
(push into other areas)
Somatotopic pattern is modifiable plasticity!!!
Rehabilitation
Lesion in the classic hand motor area
Non-trained just show shoulder & elbow representation
Trained shoulder, elbow AND hand representation in the adjacent elbow
representation was observed (plasticity of function in an area of the motor cortex)
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