Flashcards in 2.6 Motor Systems Deck (42):
Anterior half of cortex, motor functions
Posterior half of cortex, sensory functions
Descending tracts or pathways in the brain and spinal cord that control effectors (muscles)
How many neurons do motor pathways use?
Upper motor neurons
Motor neurons originating in primary motor cortex: inhibitory / excitatory axon fibers synapse directly onto lower motor neurons
Upper motor neuron output is strongly influenced by what?
Premotor and prefrontal area
Lower mor=tor neurons
In ventral brainstem or anterior horn of spinal cord; always excitatory because they synapse directly onto skeletal muscle fibers
Innervate face and head
Innervate limbs & trunk
Somatic motor system effectors are...
Striated skeletal muscles
Just 1 motor neuron and all of the muscle fibers downstream of its axon that it contacts with presynaptic acetylcholine -producing terminals
(can be many thousands as it is one terminal per muscle fiber)
Multiple motor units dedicated to one major muscle (ex. bicep) or group of synergistic muscles (ex: abdominals)
Somatic muscle groups mapped onto primary motor cortex
Fine motor areas are... (motor map)
Why are fine motor areas larger on map?
1) Density: more neurons controlling more motor units
2) Specialization: fewer striated muscle fibers per neuron =>finer motor control
Pertaining to cerebrum or cerebral cortex
Direct muscle control comes from..
Primary motor cortex
Complex movement sequences come from..
Planning and visualizing come from...
Basal nuclei region of brain
Has dopamine producing that ensure movements match the intended purpose
Functions of basal nuclei
-Initiates and terminates movements via brainstem motor centers (which leas to indirect pathways.. muscles that maintain posture)
-Provide feedback to motor cortex (which leads to direct pathways.. muscles used for movement)
Additional function of basal nuclei
-Mediates habit learning where conscious motor acts are transformed or hard-wired into unconscious motor habits
(procedural memory … “practice makes perfect)
Neurodegeneration of dopaminergic neurons
Parkinson's disease, Huntington's disease and some OCDs
Most neuron dense region of the brain
Cerebellum functions (4)
-Regulates balance during movements... via motor cortex
-Learned motor coordination and timing.. "when to release the ball"
-Provides input to primary motor cortex.. coordinates fine movements, especially of eyes hands and feet
-Provides input to brainstem.. regulates muscle tone in postural muscles (via proprioreceptive vestibulospinal and excitatory reticulospinal inputs)
Direct from cortex to motor neurons, control skilled movements in face and limbs
Control posture, locomotion and habitual movements
Upper motor neurons in direct pathway
Originate in cerebral cortex; axon fibers may synapse directly to motor or interneurons in brainstem or spinal cord
Two tracts of direct pathways
Control of movements of the trunk and limbs (brain to limbs and trunk)
Control of movements in face, tongue, pharynx (head)
Most corticospinal tracts decussate in _______; descend in ______
Lateral Corticospinal tracts
-Control upper and lower distal limbs
Upper motor neuron of corticospinal tracts
Axon fibers run from motor cortex --> through pyramids of medulla
Anterior corticospinal tracts
Tracts don't cross until they reach the specific region where they exit spine
-Trunk and proximal limbs
Corticospinal tracts originate in..
Trunk and limb regions of primary motor cortex (percentile gyrus)
Corticobulbar tracts lower motor neurons
Cranial motor neurons
Where de signals of indirect pathways originate?
Brainstem, ultimately regulate target muscles in trunk and proximal limbs
Two types of indirect pathways
Vestibular nuclei in brainstem; integrate balance based on input from vestibular organs
Innervates extensor muscles in trunk & proximal lower limbs
-maintain upright posture
Originates in RAS (controls motor arousal)