PSYC 427 Lecture Notes - Lecture 6: Alpha Motor Neuron, Premotor Cortex, Anterior Grey Column
14 May 2018
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PSYC 427 – LECTURE 6
Premotor areas on the lateral side of the hemisphere have three parts:
1. Dorsal premotor (F2 and F7)
2. Ventral premotor (F4 and F5)
3. SMA and cingulate motor areas
• Extends down into the medial wall
The arcuate sulcus in monkeys is similar to the precentral sulcus in humans.
The pre-SMA region is non-motor
• Has almost no connections to SMA proper
• Most connections go to the prefrontal cortex
The ventral premotor cortex contains mirror neurons, which are active both when the animal makes a particular movement and when it observed another animal
making the same movement.
Retrograde transneuronal transport of rabies virus from single muscles is used to identify cortico-motoneuronal (CM) cells in the primary motor cortex (m1) that
make monosynaptic connections with MNs innervating the shoulder, elbow and finger muscles.
• Retrograde: from injection site, backwards to nervous system
o The first level of transport is through the alpha motor neuron
• Able to determine cells of origin, or the cells that project to particular peripheral muscles
The primary motor cortex (M1) has two subdivisions
1. Rostral region
• Lacks CM cells
• Represets old M1 that is the stadard for ay aals
• Descending commands from the old MN must use spinal mechanisms to generate MN activity and motor output
o No direct access to alpha motor neurons; must go through intermediate machinery
2. Caudal region
• Contains shoulder, elbow and finger CM cells
• Represets e MN that is preset oly i soe higher priates and humans
• Direct access to MNs through CM cells enables new M1 to bypass spinal cord mechanisms
o Sculpts novel patterns of motor output essential for highly skilled movements
The M1 is a major source of descending motor commands for voluntary movement
These commands originate, in part, from corticospinal (CST) neurons in layer V, which have axons that descend to the spinal cord.
Two types of CST neurons
1. Axons that terminate in the intermediate zone of the spinal cord
• Connections on spinal interneurons
2. Axons that terminate in the ventral horn of the spinal cord
• Direct monosynaptic connections with MNs
• Also known as CM cells
find more resources at oneclass.com
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LATERAL CORTICOSPINAL TRACT
1. After rabies injection into the peripheral hand muscle, there is retrograde transneuronal transport from the muscle to its motor neurons (first order neurons).
2. Then, there is transneuronal transport from the infected motor neurons to neurons that make monosynaptic connections with them (second order neurons).
• The survival time from infection of second-order neurons is approximately 88 hours.
3. Post-mortem sections are processed to identify the neurons infected with rabies
Retrograde transneuronal virus in rhesus monkeys
• Survival time after injection set to allow labelling of only CM cells (second order neurons)
• The dots correspond to labelled CM output cells in the primary motor cortex, terminating monosynaptically on alpha motor neurons.
o Note that most shoulder and elbow CM cells are located medially in the CS
o Neurons that terminate on the shoulder muscles are highest up in the M1, then the elbow, then fingers.
Majority of CM cells from the SpD muscle are located in the caudal portion of the M1 on the anterior bank of the central sulcus
• Far less outputs from the rostral portion of the M1 on the precentral gyrus and area 3a (very bottom of central sulcus)
o Speculation: output neurons from the very bottom of the central sulcus (label 3a) terminate onto gamma motor neurons
• Similar findings for the ITri muscle
In sum, CM cells that innervate MNs of proximal and distal forelimb muscles are concentrated in caudal M1 buried in the CS
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Premotor areas on the lateral side of the hemisphere have three parts: dorsal premotor (f2 and f7) The arcuate sulcus in monkeys is similar to the precentral sulcus in humans. Has almost no connections to sma proper: most connections go to the prefrontal cortex. The ventral premotor cortex contains mirror neurons, which are active both when the animal makes a particular movement and when it observed another animal making the same movement. Retrograde transneuronal transport of rabies virus from single muscles is used to identify cortico-motoneuronal (cm) cells in the primary motor cortex (m1) that make monosynaptic connections with mns innervating the shoulder, elbow and finger muscles. Retrograde: from injection site, backwards to nervous system. The first level of transport is through the alpha motor neuron. Able to determine cells of origin, or the cells that project to particular peripheral muscles. The primary motor cortex (m1) has two subdivisions. Represe(cid:374)ts (cid:862)old(cid:863) m1 that is the sta(cid:374)dard for (cid:373)a(cid:374)y (cid:373)a(cid:373)(cid:373)als.
