comd 474 PPT 7 Neural Parhways Governing Movement

What are the five major levels of integrated motor control for Speech?

1. Cerebral cortex

2. Subcortical nuclei of the cerebrum

3. Brain stem

4. Cerebellum

5. Spinal cord

What are the three great motor subsystems?

1. Pyramidal

2. Extrapyramidal

3. Cerebellar

Extrapyramidal System

• Involuntary reflexes and movement, posture control

• Coordination

• Indirect control over the anterior/ventral horn cells

• Found in the reticular formation of the ponds and medulla

What are the three major tracks of the pyramidal system?

1. Corticospinal tract

2. Coriticobulbar/corticonuclear tract

3. Corticopontine tract

Corticalspinal tract

• Considered the primary descending motor tracts

• Has some of the longest motor axons in the central nervous system

• Monosynaptic

• This is a direct route for motor commands

• Controls skilled movements in the distal muscles of the limbs and digits

Corticalspinal tract - Origin

The motor cortex of the 2 hemispheres of the cortex 

Corticalspinal tract - Primary

The precentral gyrus

Corticalspinal tract - Secondary

• The postcentral gyrus 

• Fibers terminate on sensory relay nuclei in the brainstem and dorsal horn of the spinal cord 

  • Modulates sensory transmission 

Corticalspinal tract - Pathway 

• Bilateral Motor Cortices 

• Corona Radiata

• Internal Capsule 

Corticalspinal tract - Bilateral Motor Cortices 

This features both crossed and uncrossed pathways that coordinate single and multi-side body actions

Corticalspinal tract - Corona Radiata

This carries ascending and descending nerve fibers between the cerebral cortex and the lower brain regions

Corticalspinal tract - Internal Capsule 

Fibers split with the corticospinal tract (CS) at the posterior limb of the (IC) and the corticobulbar (CB) at the genu or bend.

Joins axons from other areas. Fibers project to and from other areas like the thalamus and the brainstem.

Corticalspinal tract - Cerebral Peduncle of the Midbrain

Pons

Medulla

Corticalspinal tract - Cerebral Peduncle of the Midbrain - Pons

This communicates back and forth with the Cerebellum

Corticalspinal tract - Cerebral Peduncle of the Midbrain - Medulla

85-90% of the corticospinal fibers cross over or decussate

The corticalspinal fibers come together to form the Pyramid = the Primary Lateral tract

A few fibers do not cross = Uncrossed Anterior CS tract

Corticonbulbar/Corticonuclear Pathway

1. Originates in the CS fibers at the cortex

2. Travels through the Corona Radiata and the internal capsule

3. Separates at the Upper Brainstem

4. Decussates at various levels

   1. Synapses at the point of decussation

5. Terminates at the motor nuclei of the cranial nerves

   1. Spinal nerves and cranial nerves are both LMN

Cortocopontine tract

This brings motor information to the cerebellum from the frontal lobe. It leaves the precentral gyrus and descends in the IC. The Axons synapse with the cells in the pons and the second order neuron synapse in the pons to the cerebellum on the middle cerebellar peduncle.

Upper Motor Neurons

These are all neurons of the anterior and lateral corticospinal tracts which have long axons for first order neurons.

NEVER leaves the neuraxis

Lower Motor Neurons

These are neurons that send motor axons into the peripheral nerves. The second order neurons start at the Brainstem or the ventral horn of the spinal cord and follow “The Great Common Pathway” Sherrington.

Paralysis

Gross limitation of movement

Paresis

Incomplete paralysis

Hemiparalysis/Hemiplegia

The complete or near complete loss on one side 

Lower motor neuron paralysis - Denervation 

• Lesions in the 

  • Cranial or peripheral nerve

  • Cell bodies of the anterior horn cell of the SC 

  • Cranial nerve axons in the brainstem

• Nerve impulse is not transmitted to the muscles

• Result: muscles become soft and flabby due to loss of muscle tone 

Lower motor neuron paralysis - Hypoflexia

Reduced reflex response

Lower motor neuron paralysis - Atrophy 

• Loss of muscle bulk

  • Fibrillations: twitching of single muscle fibers 

    • Can be seen on EMG electromyography 

  • Fasciculations: contractions of groups of muscle fibers 

    • Can be seen through the skin (eye twitch) 

Motor Unit 

1. Single anterior horn cell or cranial nerve neuron 

• Motor neuron disease:

  • Muscles become weak or atrophic 

2. Peripheral axon and branches 

• Motor neuropathy 

  • Denervation (nerve severed)

3. Myoneural junction 

• Neuromyopathy 

  • Fatigable weakness 

4. Muscle fibers  

• Myopathy or dystrophy 

  • Muscles lose strength, slow down 

Bilateral Symmetry

• Bilateral innervation for motor nuclei 

• Majority of midline speech muscles 

  • All paired muscles

  •  Work together (i.e., wrinkling forehead, smile, chew, or swallow) 

• Provides a safety valve for speech in CB lesion 

  • Swallowing is the primary function!

Contralateral and Unilateral Innervations

• Each of the cranial nuclei receives varying degrees of unilateral and contralateral innervation even though it is bilaterally supplied 

• Areas with more unilateral supply are more paralyzed if the lesion is unilateral 

Contralateral and Unilateral Innervations - Most affected 

• Lower face

• Trapezius muscles 

Contralateral and Unilateral Innervations - Intermediately affected

• Tongue 

Contralateral and Unilateral Innervations - Mildly affected diaphragm

• Ocular 

• Upper face 

• Jaw 

• Pharynx 

• Larynx 

Corticobulbar Innervation in the Cranial Nerves for Speech - V Trigeminal

Bilateral (1)

Corticobulbar Innervation in the Cranial Nerves for Speech - VII Facial 

Mixed Bilateral/Contralateral (1)

Corticobulbar Innervation in the Cranial Nerves for Speech - IX Glossopharyngeal

Bilateral (for single muscle)

Corticobulbar Innervation in the Cranial Nerves for Speech - X Vegas

Bilateral (2)

Corticobulbar Innervation in the Cranial Nerves for Speech - XI Spinal Accessory

Contralateral

Corticobulbar Innervation in the Cranial Nerves for Speech - XII Hypoglossal

Mixed Bilateral/Contralateral (2)

VII Facial Nerve 

• Mixed 

  • Ventral and dorsal component 

  • Combined bilateral and contralateral 

• Upper half of face

  •  Ventral portion 

    • More bilaterally innervated 

• Mid face

  • More equal combination of fibers 

• Lower half of face 

  • Dorsal portion 

    • More contralateral 

I Olfactory

Sensory - smell 

II Optic

Sensory - vision

III Oculomotor

Motor - eye movement and pupil constriction

IV Trochlear

Motor - superior oblique eye muscle

V Trigeminal

Mixed - facial sensation and muscles of mastication (chewing)

VI Abducens

Motor - lateral rectus eye muscle

VII Facial

Mixed - facial expressions, taste (anterior tongue), and salivary/lacrimal glands

VIII Vestibulocochlear

Sensory - hearing and balance 

IX Glossopharyngeal

Mixed - taste (posterior tongue), swallowing, and blood pressure sensing

X Vagus

Mixed - parasympathetic control of internal organs (heart, lungs, digestive tract), throat muscles, and visceral sensation

XI Spinal Accessory

Motor - sternocleidomastoid and trapezius neck muscles

XII Hypoglossal

Motor - tongue movement