NEUR30003 Lecture Notes - Lecture 16: Supplementary Motor Area, Primary Motor Cortex, Premotor Cortex
18 Jun 2018
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Lecture 16
- 1. The spinal cord mediates complex aspects of motor control such as feedback control
of muscle stretch and force, and integration of reflex and rhythmic activity. More complex
motor tasks - like maintaining body posture and formulating and executing voluntary
movements - require the brain.
- 2. The entire motor control system can be considered as a hierarchy (with the cerebral
cortex at the top, brainstem in the middle and spinal cord at the base) with modulatory
side loops to basal ganglia and cerebellum. Cerebral and brainstem regions with a role
in motor control influence the spinal level by "descending" white matter tracts.
- 3. The ventral / medial tracts (tectospinal, vestibulospinal and reticulospinal) carry
information related to maintenance of posture, their activity is influenced by visual,
vestibular and proprioceptive activity (proprioceptive = "body position sense": mainly
muscle spindle activity). This information is used to make adjustments to posture - often
in a pre-emptive way so that the consequences of movements are anticipated and
postural stability is maintained.
- 4. The planning and production of voluntary movements requires the cortical motor
areas. The primary motor cortex contains somatotopically organised neurons that, when
stimulated, produce simple, contralateral movements. The motor cortex influences the
spinal cord and brainstem via the lateral tracts, principally the corticospinal tract. Most of
the corticospinal tract crosses to the contralateral side in the medulla and continues
down the spinal cord in the dorsolateral white matter, making synaptic connecting with
interneurons and also directly with motoneurons.
- 5. Although the primary motor cortex was once considered to have a precise "motor
homunculus" representation of movements, the motor cortex has been shown to be
organised into regions of functionally related movements (rather than a topographic map
of the body). Supplementary and premotor cortex encode more complex movements
and more abstract representations of motor goals. Association regions of motor and
sensory cortex contain neurons that represent complex movements - some of these
(mirror neurons) are activated by both seeing and by performing the movements.
- 6. Damaging the primary motor cortex produces weakness, whereas damage to the
supplementary motor doesn't affect muscle strength but causes problems in planning &
sequencing movements (apraxia). Motor cortex can be said to enable planning of
movements such that they are integrated with complex sensory information and
behavioral goals.
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- Upper motoneuron: anything that goes on in the brain that affect behaviour or activity of
lower motoneuron
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- Cerebellum and basal ganglia do not connect to spinal cord, don’t directly influence
motor neurons, influences them through how they dictate motor cortex and brainstem
centers
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- Forward of central sulcus - motor cortex
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- Medial pathways tend to be given signals to medial motor neurons, spinal column, pelvic
girdle, keep us upright
- Lateral pathways, axons from motor cortex, voluntary movement, distal musculature
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- Inputs from cerebral cortex come from contralateral side of body - cross projections
- Signals from brainstem travel ipsilaterally down the body - spread influence either side of
midline
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Document Summary
Lecture 16: the spinal cord mediates complex aspects of motor control such as feedback control of muscle stretch and force, and integration of reflex and rhythmic activity. The primary motor cortex contains somatotopically organised neurons that, when stimulated, produce simple, contralateral movements. The motor cortex influences the spinal cord and brainstem via the lateral tracts, principally the corticospinal tract. Supplementary and premotor cortex encode more complex movements and more abstract representations of motor goals. Motor cortex can be said to enable planning of movements such that they are integrated with complex sensory information and behavioral goals. Upper motoneuron: anything that goes on in the brain that affect behaviour or activity of lower motoneuron. Cerebellum and basal ganglia do not connect to spinal cord, don"t directly influence motor neurons, influences them through how they dictate motor cortex and brainstem centers. Medial pathways tend to be given signals to medial motor neurons, spinal column, pelvic girdle, keep us upright.
