Motor Pathways

Front 1

Rubrospinal Tract

Back 1

FLEXOR
1. START
a. Red Nucleus – Midbrain
b. Receives cortical input from motor cortex; hence VOLUNTARY activity
2. END
a. Alpha and Gamma motor neurons in the cervical anterior horns
3. ROUTE
a. Cortex → Red Nucleus→ cross in midbrain→ descend in Rubrospinal Tract→
synapse on α/γ motor neurons
b. Third order motor neurons exit to reach Proximal Flexors of the Limbs
4. FUNCTION
a. Receives ipsilateral input from motor cortex and cerebellar nuclei
b. Each Red Nucleus synapses in cervical segments innervating proximal muscles of the Contralateral

Front 2

Medullary (lateral) Reticulospinal

Back 2

- FLEXOR
1. START
a. Medullary Reticular Nuclei - Midbrain
b. Receives bilateral cortical input
2. END
a. Interneurons that excite Alpha and Gamma motor neurons
3. ROUTE
a. Cortex→ Medullary Reticular Nucleus→ descent ipsilateral OR
cross in medulla then descend in Reticulospinal Tract→
synapse on interneurons→ synapse on α/γ motor neurons
4. FUNCTION
a. Receives info from cortex BILATERALLY as well as info from ALS regarding TP
b. Bilateral control of limb flexor muscles
c. Also does some inhibition of extensor muscles via interneurons synapsing on γ-motor neurons

Front 3

Pontine (medial) Reticulospinal

Back 3

EXTENSOR
1. START
a. Pontine Reticular Nucleus – Pons
b. Receives bilateral cortical input
2. END
a. Ipsilateral anterior horn on MAINLY Gamma-motor neurons (some alpha)
to innervate axial and limb extensor muscles
3. ROUTE
a. Cortex→ Pontine Reticular Nucleus→ descent ipsilateral
in Reticulospinal Tract→ synapse on ipsilateral Gamma-motor neurons
4. FUNCTION
a. Receives info from cortex BILATERALLY
b. Also receives a STRONG input of sensory information from limbs

Front 4

Spinoreticular Tract

Back 4

- SENSORY
1. START
a. Peripheral Pain and Temperature receptors
2. END
a. Pontine and Medullary Reticular Nuclei
3. ROUTE
a. TP receptor→ Ascend via ALS (hence immediate crossover)→
synapse in BOTH Reticular Nuclei→
send Efferent signals to respond to stimuli (leg lift example)
4. FUNCTION
a. Relays info to Contralateral reticular nuclei regarding TP and crude touch
in the trunks and limbs
b. The reticular nuclei will then facilitate the contraction of extensor muscles

Front 5

Lateral Vestibulospinal Tract

Back 5

- EXTENSOR
1. START
a. Lateral Vestibulospinal Nucleus
2. END
a. Synapse on excitatory interneurons of the anterior horn which
eventually synapse on alpha-motor neurons
3. ROUTE
a. Vestibular organs and cerebellum→ lateral vestibular nucleus→
descend ipsilaterally in medulla and spinal cord→
synapse on interneurons→ synapse on alpha-motor neurons
4. FUNCTION
a. Receives input from vestibular organs and cerebellum
b. Eventual excitatory influence to contract axial and limb extensor muscles
the so called “anti-gravity” muscles coordinating balance

Front 6

Medial Vestibulospinal Tract

Back 6

EXTENSOR
1. START
a. Medial Vestibulospinal Nucleus
2. END
a. Synapse alpha-motor neurons at the cervical and upper thoracic
levels of the spinal cord
3. ROUTE
a. Vestibular organs and cerebellum→ medial vestibular nucleus→
descend in ipsilateral MLF of the spinal cord→
synapse on alpha-motor neurons (cervical and thoracic)
4. FUNCTION
a. Receives input from vestibular organs and cerebellum
b. INHIBIT extensor muscles by releasing Glycine on the alpha-motor neurons
which innervate extensor muscles of the neck and back
c. Predominantly work toward stabilizing head position

Front 7

Corticospinal Tract

Back 7

Start-End-Route
a. START→ Pyramidal cells Layer-5 of Precentral Gyrus
b. END→ contralateral anterior horn of the spinal cord where the UMN synapse on α/γ-LMN’s
c. ROUTE→ coronoa radiata – internal capsule – crus cerebri – basilar pons – lateral corticospinal tract – α/γ-LMN’s
5. Roles of Primary Motor Cortex
a. Simple Finger Movements→ activate motor cortex and somatosensory cortex are activated
b. Complex Finger Movements→ Premotor cortex and supplemental motor cortex are activated
c. Rehearsed Finger Movements→ only activate the supplemental cortex (programmed from rehearsal)
6. Predominant Role of Lateral Corticospinal Tract
a. Voluntary contraction of distal flexor muscles in the limbs – REACHING AND WALKING
b. Sensory input is constantly processed by the cortex and modified by the basal ganglia and cerebellum