1 SPINAL CORD III Major Pathways of the Spinal Cord - Motor C.R. Houser

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SPINAL CORD IIIMajor Pathways of the

Spinal Cord - Motor

C.R. Houser

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MAJOR PATHWAYSMotorCorticospinal Pathway

Somatosensory• Dorsal Column

(Medial Lemniscal) System

• Anterolateral (Spinothalamic) System

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Motor and Sensory Pathways

Blumenfeld, Fig. 7.4.

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Lateral Pathways

•Corticospinal (Lateral)•Rubrospinal

Medial Pathways

•Vestibulospinal•Reticulospinal – Medullary

- Pontine•Tectospinal

Blumenfeld, Fig. 6.7.

Motor Pathways

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Corticospinal Tract• Many cell bodies are

located in the primary motor area (Area 4) of the precentral gyrus - frontal lobe.

• Specific representation of body parts – Motor homunculus.

• Face and upper limb on lateral surface.

• Lower limb on medial surface.

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LATERAL CORTICOSPINAL TRACT

Cortex

Spinal Cord

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Voluntary Motor Control

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ForebrainCortex

Areas 4, 6, 3,1,2 & 5

Internal Capsule


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Midbrain

Cerebral Peduncle

(Basis Pedunculi)

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Pons

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Upper and Lower Medulla

Medullary Pyramid

Decussation of Pyramids

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Spinal Cord (Cervical Level)

Lateral Corticospinal tract

Alpha motor neuron to skeletal muscle

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Corticospinal Tract• The majority of the corticospinal

fibers cross in the decussation of the pyramids.

• A small portion of the fibers remain ipsilateral and descend in the lateral and anterior columns.

• Many fibers in the anterior column (anterior corticospinal tract) eventually cross in the spinal cord and innervate motor neurons in the contralateral ventral horn.

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Corticospinal Tract

Internal capsule Cerebral peduncle

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Corticospinal Tract in the Midbrain

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Corticospinal Tract in Pons

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Corticospinal Tract in Medulla

Medullary Pyramid Decussation of the Pyramids

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Lateral Corticospinal Tract

In the Spinal Cord (Lateral columns)

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Lesions of Spinal Cord Pathways

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For each of the illustrated lesions -

1) Identify the region of the brainstem and the specific location of the lesion.

2) Will the clinical problem be on the Left or Right side of the body?

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L R

#1

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L R

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L R

#2

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L R

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L R

#3

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L R

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L R

#4

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L R

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This patient had a selective lesion of one pyramid. Which pyramid was damaged? What functional consequences would you expect?

Left Right

L R

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What are the functions of the Corticospinal Tract?

• Has facilitatory effects primarily on motor neurons that innervate flexor and distal muscles.

• Is necessary for isolated and skilled movements of the digits.

• Is primarily concerned with voluntary, goal-directed or skilled movements.

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Broad Classification of Motor Syndromes

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Classification of Motor Disorders – Considers:

1. Ability to produce desired movements – weakness or paralysis;

2. Muscle toneDefinition of muscle tone:• Normal resistance of a muscle to active or passive

stretch.

Can be influenced by:• Alterations in local reflexes and descending

pathways.

Clinical Terms for altered muscle tone:• Atonia, hypotonia, flaccidity – Absent or decreased

tone.• Hypertonia – increased muscle tone (spasticity or

rigidity).

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Lower Motor Neuron Signs• Result from damage of Motor Neurons –

Cell Bodies or Axons

Upper Motor Neuron Signs• Result from damage of multiple descending

motor pathways – some with excitatory effects and others with inhibitory effects on the spinal cord circuitry.

• Reflect loss of the normal balance of excitatory and inhibitory inputs to the motor neurons – in favor of increased excitability of spinal level reflexes.

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Lower Motor Neuron SignsMuscle Spindle

Dorsal Root Gang.

Extensor Muscle

α motor

γ motor

Damage of Motor Neuron – Cell Body or Axon

↓ Strength

↓ Reflexes

↓ Tone

Atrophy X

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Upper Motor Neuron SignsMuscle Spindle

Dorsal Root Gang.

Extensor Muscle

α motor

γ motor

Damage of multiple descending motor pathways, some with excitatory effects and others with inhibitory effects on spinal cord circuitry.

↓ Strength

↑ Reflexes

↑ Tone

Babinski response(Extensor plantar response)

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Cx & Brainstem

+ +

+Periphery

X X

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Lower Motor Neuron Syndrome

Upper Motor Neuron Syndrome

Reflexes

Muscle Tone

Atrophy

Other Signs

Strength Weakness / Paralysis / Paresis

Weakness / Paralysis / Paresis

Hyporeflexia Hyperreflexia

Hypotonia (Flaccidity)

Hypertonia (Spasticity)

Atrophy of Muscles

Minimal (disuse) atrophy

Fibrillations & Fasciculations

Extensor Plantar Response (Babinski)

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Spasticity – characterized by:

1. Increased sensitivity of the stretch reflex (hyperreflexia).

2. Increased muscle tone (hypertonia) with increased resistance to passive movement.

• May be greater on one side of the joint than the other (flexors of upper limb and extensors of lower limb).

• Velocity dependent.

3. Clasp-knife or lengthening reaction (may see).

4. Clonus (variable)

5. Stereotyped patterns of movement (unable to “fractionate” movements at individual joints).

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Conclusions: • Upper motor neuron signs result from

damage of multiple descending motor pathways.

• Damage of the corticospinal tract contributes primarily to weakness of distal / flexor muscles and loss of isolated and skilled movements.

• Alterations in other descending motor pathways contribute to the typical increases in reflexes and muscle tone.

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1 SPINAL CORD III Major Pathways of the Spinal Cord - Motor C.R. Houser