Motor Cortex Flashcards
Motor cortices
Primary motor cortex
Supplementary motor area
Pre-supplementary motor area
Premotor area
Posterior parietal cortex
Brodmann areas
Area 4→ primary motor cortex
Area 6→ supplementary motor cortex and premotor area
Area 5→ post parietal cortex, imm. post to 1ª sens cortex
Areas 1, 2, 3 —> primary sensory cortex
Area 6 is composed of
2 motor areas:
- supplementary motor area (more dorso-medial)
- premotor area (ventrolateral).
1ary motor cortex is responsible for
Sending the motor order towards the anterior horn of the spinal cord
Primary motor area characteristics
Somatotopic distribution - represented by motor humunculus
Firing rate of each individual neuron correlates w/ muscle force exerted
Kinematic of the movement is coded in M1 by a neuronal population ___
Motor humunculus represents
Areas of precentral gyrus that control voluntary muscles in the body.
Sensory humunculus represents
Somatotopic distribution of info reaching the postcentral gyrus from different bodily parts
In primary motor cortex we codify
Simple movements corresponding to regions of the body, not single muscles
Direction of movement is determined by
A group of neurons (not a single one)
Vascularization of primary motor cortex
Lateral aspect (face and upper limb): middle cerebral art
Medial aspect (lower limb): anterior cerebral artery
Aneurysm in anterior cerebral artery =
problems that affect the leg
Aneurysm In the middle cerebral artery =
problems that affect face, eye, arms,..
2ary motor areas (SMA and premotor cortex) is responsible for
“Preparing” for movement (coordinated movements, tasks)
Sequence of events when we make a movement
1st we decide that we want to move (prefrontal cortex)
We chose what movement we want to perform (2ary motor, preparation)
Execute the response (1ary motor, execution)
Inputs to the cortex
1ary motor cortex: from 1ary somatosensory cortex (for reflex responses), cerebellum, post parietal areas & 2ary motor areas
2ary motor cortex: from basal ganglia, prefrontal cortex (bc before any preparation takes place, 1st we decide to move) & post parietal areas
Cortex receives input from
Thalamus and other cortical areas (EXCEPT olfaction, which goes directly to the cortex)
All projections from the cerebellum and basal ganglia go to
The cortex by first passing through the thalamus
Cerebellum helps
movements be precise (rojects mostly to 1ª motor cortex
Info from cerebellum reach the cortex by
Synapsing on thalamus (at VL and VPL nuclei)
Basal ganglia are involved in
Preparatory processes (inputs for the 2ary motor areas)
Info from cerebellum will reach basal ganglia by
Synapsing on the thalamus (in VPL and VA)
Supplementary areas participates in
Preparation of self-initiated movements (specially when movements comprise 2 body sides and are + complex).
Preparatory processes which take place in SMA give rise to
Slow potential, pre-movement potential which comes in as a wave.
Lesion to supplementary motor area
Akinesia = NO self-induced movements
(YES reflexes and stimulus-induced movements)
Premotor cortex is involved in
Stimulus-induced movements
Aiding control of proximal axial musculature and distal musculature precision movements
Premotor cortex subregions
Dorsal lateral: involved in delayed actions
Ventral lateral: adapts the hand to the shape of the object we are holding.
Posterior parietal cortex is
The interphase between visual stimuli - motor executions
Posterior parietal cortex is involved in
Stimulus-induced movements, specifically movements guided by visual info
Transforming visual information into motor responses (2ª + 1ª motor cortices —> prepare & execute them)
Pre-SMA and motor learning projects to
SMA (area very relevant for motor learning)
Once we learn a movement, we begin to use
SMA
When we learn a movement we use
pre-SMA
Once a movement is fully automated, after having done it several times→ we’ll be using
1ary motor cortex
Mirror system is activated when
One performs an action, or when they see someone else perform said action
Mirror system is involved in
Empathy
Imitation (learning to speak)
Mirror system is related to an area located in
Broca’s area
Motor tracts to spinal cord
Corticospinal tract
Rubrospinal tract
Vestibulospinal tract
Reticulospinal tract
Olivospinal tract
Tectospinal tract
Fibers in rubrospinal tract are
Mostly crossed
Tectospinal tract
Sup colliculus to spinal cord
Helps adjust head position, turn our head upon visual inputs, sound or other inputs
Olivospinal tract
Only in cervical region
Corticospinal tract
Neurons go from cortex to spinal cord, to activate ant horn motor neurons
Corticospinal tract decussates at the level of
Pyramids in the medulla of the brainstem
Pyramidal cells sypansis
Excitatory
Inhibitory
Corticospinal pathway act some neurons while inhibiting others —> to perform movements & reflexes correctly.
(in ant horn of spinal cord)
Function corticospinal pathway
Keeps the reflex movements under control and is in charge of MOVEMENT PRECISION
Lesion to corticospinal pathway
Lost of voluntary precision movements, still preserve the force of the movements.
Reflexes become heightened
Divisions of corticospinal tract
Anterior corticospinal pathway (20%)
Lateral corticospinal pathway (80%)
Pathway followed by the corticospinal tract
Neurons project from cortex - come together (int capsule) - begin to descend to spinal cord.
(Small part of int capsule is formed by corticonuclear pathway = projections from cortex that synapse at brainstem nuclei)
Midbrain: int capsule enters crus cerebri.
Pons: tract becomes scattered (pontocerebellar nuclei). But it all re-joins at the level of the medulla = pyramids
80% of tract decussat. at pyramids (pyramids decussation) = lat corticospinal pathway.
20% continue descending along ant corticospinal pathway —> decussate at corresponding level of spinal cord.
1st, upper motor neuron axon forms
Corticospinal pathway
2nd, lower motor neuron axon forms
The nerve fiber
Strength depends on
2nd motor neuron
Precision depends on
1st motor neuron
Reflexes depend on
Lower motor neuron; the control and regulation of this reflex depend on the upper motor neuron
Lesion the first motor neuron causes
Exacerbated reflexes —> clonus
Loss of precision (strength is conserved)
Increase muscle tone —> spasticity
Lesion the 2nd (lower) motor neuron
Reflexes are abolished
Loss of strength —> (eventually) muscle atonía
No basal muscle tone
Vestibulospinal tract
Direct projections from vestibular nuclei to axial muscles
Vestibulospinal tract function
Keep balance
Rubrospinal tract
Projections from the red nuclei in the midbrain to the spinal cord.
Red nucleus receives
Sup cerebellar peduncle fibres from cerebellum.
In rubrospinal tract, fibers mostly go to
Upper limb
Rubrospinal tract functions
Helps make the necessary adjustments to do movements with our hands
Reticulospinal tract
The cerebellum connects with reticular nuclei in the brainstem, and then fibres from it descend to spinal cord
Reticulospinal tract function
Involved in posture control and axial muscle adjustments
Corticonulear pathway
To nuclei of the brainstem (gives CN).
Also descends down int capsule —> synapses on brainstem.
Connections between cortex - nuclei in the brainstem = mostly bilateral (there are exceptions)
Exceptions of bilateral innervation
Projections to XI CN = only ipsilateral
Projections to soft palate & uvula = mostly contralateral
Inferior part of the face = mostly contralateral
Glossal muscle (protrudes the tongue) is innervated
by XII CN = contralateral
Lesions to the XII and X CN
Peripheral lesion: tongue (XII) deviate to SAME side, uvula (X) opposite side of lesion
Central lesion (prior to decussation, in corticonuclear tract): tongue (XII) will deviate to opposite side, uvula (X) towards side of lesion
