11. Motor Systems

paralysis = paresis

I. Direct and Indirect

A. Corticospinal (Pyramidal) Tract

B. Indirect Corticospinal pathways (maintain posture and tone)

1. Vestibulospinal tract

2. Reticulospinal tract

3. Tectospinal tract

4. Rubrospinal tract

II. Extrapyramidal

A. Corpus Striatum

B. Substantia Nigra

C. Subthalamic Nucleus

III. Cerebellum

Thalamo-midbrain junction: subthalamic nucleus

Midbrain: III, IV, Red Nucleus, Substantia Nigra

Medulla: Inferior Olivary Nucleus, Nucleus Ambiguus, Dorsal motor nucleus of X, XII

I. Direct and Indirect Motor

A. Corticospinal (Pyramidal) Tract

- initiation of voluntary movement

- Clinical: polio, Brown-Sequard, ALS

B. Indirect Corticospinal pathways (maintain posture and tone)

- maintenance of posture and tone

1. Vestibulospinal tract

2. Reticulospinal tract

3. Tectospinal tract

- IC has no projections to spinal cord (projects through SC)

4. Rubrospinal tract

II. Extrapyramidal Motor

- does not project to spinal cord

- inhibition of appropriate muscles, execution of subconscious “motor programs” (e.g. swinging arms)

- clinical: Parkinson’s disease (dopamine: substantia nigra), Huntington’s chorea (caudate and putamen: small cells), Sydenham chorea (basal ganglia), Ballismus (subthalamic nucleus), dystonia (lentiform nucleus)

A. Corpus Striatum

1. Neostriatum

- dopaminergic terminals

- feeds back to CC via motor nuclei of thalamus via direct or indirect pathway

- Direct pathway: influences CC (motor movement) through activation (inhibition of GPi)

- Indirect pathway: influences CC (motor movement) through inhibition (excites GPi) via subthalamic nucleus

- Substantia nigra influences neostriatum directly (with dopamine)

- CC uses glutamate

2. Globus Pallidus

a. GPi

b. GPe

B. Substantia Nigra

1. Pars compacta (melanin)

2. Pars Reticularis

C. Subthalamic Nucleus

III. Cerebellum

- does not project to spinal cord (influences motor movement through feedback circuits)

- learned, skilled motor movement (timing, correction, equilibrium, posture)

- primarily a sensory structure (coordinates sensory input)

- is a timing device (synchronized Purkinje cells)

- most development is post-natal

cerebellum has 3 lobes

1. anterior

2. posterior

3. flocculonodular

cerebellum has 4 deep nuclei

1. fastigial

2. globose

3. emboliform

4. dentate

cerebellum is connected via 3 peduncles

1. ICP: inferior cerebellar peduncle (medulla)

2. MCP: middle cerebellar peduncle (pons)

3. SCP: superior cerebellar peduncle (midbrain)

Cerebellum

· output: affects LMN indirectly (via vestibular nuclei [ION], red nucleus [central, receives from cortex, basal ganglia, cerebellum], thalamus [VL])

· input: motor cortex and basal ganglia (indirect via red nucleus, pons, ION), spino-cerebellar, vestibular nuclei

Note: the only 2 pathologies that à decreased muscle tone (hypotonia) are cerebellar and LMN