2.6 Motor Systems

Question 1

Frontal lobe

Answer 1

Anterior half of cortex, motor functions

Question 2

Parietal lobe

Answer 2

Posterior half of cortex, sensory functions

Question 3

Motor pathways

Answer 3

Descending tracts or pathways in the brain and spinal cord that control effectors (muscles)

Question 4

How many neurons do motor pathways use?

Answer 4

TWO

Question 5

Upper motor neurons

Answer 5

Motor neurons originating in primary motor cortex: inhibitory / excitatory axon fibers synapse directly onto lower motor neurons

Question 6

Upper motor neuron output is strongly influenced by what?

Answer 6

Premotor and prefrontal area
Basal nuclei
Cerebellar neurons

Question 7

Lower mor=tor neurons

Answer 7

In ventral brainstem or anterior horn of spinal cord; always excitatory because they synapse directly onto skeletal muscle fibers

Question 8

Cranial nerves

Answer 8

Innervate face and head

Question 9

Spinal nerves

Answer 9

Innervate limbs & trunk

Question 10

Somatic motor system effectors are…

Answer 10

Striated skeletal muscles

Question 11

Motor unit

Answer 11

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)

Question 12

Motor pools

Answer 12

Multiple motor units dedicated to one major muscle (ex. bicep) or group of synergistic muscles (ex: abdominals)

Question 13

Motor map

Answer 13

Somatic muscle groups mapped onto primary motor cortex

Question 14

Fine motor areas are… (motor map)

Answer 14

LARGER

Question 15

Why are fine motor areas larger on map?

Answer 15

1) Density: more neurons controlling more motor units

2) Specialization: fewer striated muscle fibers per neuron =>finer motor control

Question 16

Cortical

Answer 16

Pertaining to cerebrum or cerebral cortex

Question 17

Direct muscle control comes from..

Answer 17

Primary motor cortex

Question 18

Complex movement sequences come from..

Answer 18

Premotor area

Question 19

Planning and visualizing come from…

Answer 19

Prefrontal area

Question 20

Basal nuclei region of brain

Answer 20

(Corpus striatum)

Has dopamine producing that ensure movements match the intended purpose

Question 21

Functions of basal nuclei

Answer 21

• 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)

Question 22

Additional function of basal nuclei

Answer 22

-Mediates habit learning where conscious motor acts are transformed or hard-wired into unconscious motor habits
(procedural memory … “practice makes perfect)

Question 23

Neurodegeneration of dopaminergic neurons

Answer 23

Parkinson’s disease, Huntington’s disease and some OCDs

Question 24

Cerebellum

Answer 24

Most neuron dense region of the brain

Question 25

Cerebellum functions (4)

Answer 25

• 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)

Question 26

Direct pathways

Answer 26

Direct from cortex to motor neurons, control skilled movements in face and limbs

Question 27

Indirect pathways

Answer 27

Control posture, locomotion and habitual movements

Question 28

Upper motor neurons in direct pathway

Answer 28

Originate in cerebral cortex; axon fibers may synapse directly to motor or interneurons in brainstem or spinal cord

Question 29

Two tracts of direct pathways

Answer 29

• Corticospinal tract

- Corticobulbar tract

Question 30

Corticospinal tract

Answer 30

Control of movements of the trunk and limbs (brain to limbs and trunk)

Question 31

Corticobulbar tract

Answer 31

Control of movements in face, tongue, pharynx (head)

Question 32

Most corticospinal tracts decussate in _______; descend in ______

Answer 32

Medulla
Lateral Corticospinal tracts
-Control upper and lower distal limbs

Question 33

Upper motor neuron of corticospinal tracts

Answer 33

Axon fibers run from motor cortex –> through pyramids of medulla

Question 34

Anterior corticospinal tracts

Answer 34

Tracts don’t cross until they reach the specific region where they exit spine
-Trunk and proximal limbs

Question 35

Corticospinal tracts originate in..

Answer 35

Trunk and limb regions of primary motor cortex (percentile gyrus)

Question 36

Corticobulbar tracts lower motor neurons

Answer 36

Cranial motor neurons

Question 37

Where de signals of indirect pathways originate?

Answer 37

Brainstem, ultimately regulate target muscles in trunk and proximal limbs

Question 38

Two types of indirect pathways

Answer 38

• Vestibulospinal

- Reticulospinal

Question 39

Vestibulospinal origin

Answer 39

Vestibular nuclei in brainstem; integrate balance based on input from vestibular organs

Question 40

Vestibulospinal function

Answer 40

Innervates extensor muscles in trunk & proximal lower limbs
-maintain upright posture

Question 41

Reticulospinal origin

Answer 41

Originates in RAS (controls motor arousal)

Question 42

Reticulospinal function

Answer 42

Innervates ALL motor neurons, maintains muscle tone during ongoing muscle movements