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

2 MAJOR PATHWAYS Motor Corticospinal Pathway Somatosensory Dorsal Column (Medial Lemniscal) System Anterolateral (Spinothalamic) System

3 Motor and Sensory Pathways Blumenfeld, Fig. 7.4.

4 Lateral Pathways Corticospinal (Lateral) Rubrospinal Medial Pathways Vestibulospinal Reticulospinal – Medullary - Pontine Tectospinal Blumenfeld, Fig Motor Pathways

5 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.

6 LATERAL CORTICOSPINAL TRACT Cortex Spinal Cord

7 LATERAL CORTICOSPINAL TRACT Voluntary Motor Control

8 Forebrain Cortex Areas 4, 6, 3,1,2 & 5 Internal Capsule LATERAL CORTICOSPINAL TRACT

9 Midbrain Cerebral Peduncle (Basis Pedunculi)

10 Pons

11 Upper and Lower Medulla Medullary Pyramid Decussation of Pyramids

12 Spinal Cord (Cervical Level) Lateral Corticospinal tract Alpha motor neuron to skeletal muscle

13 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.

14 Corticospinal Tract Internal capsule  Cerebral peduncle

15 Corticospinal Tract in the Midbrain

16 Corticospinal Tract in Pons

17 Corticospinal Tract in Medulla Medullary Pyramid  Decussation of the Pyramids

18 Lateral Corticospinal Tract In the Spinal Cord (Lateral columns)

19 Lesions of Spinal Cord Pathways

20 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?

21 L R #1

22 LATERAL CORTICOSPINAL TRACT Voluntary Motor Control L R

23 L R #2

24 LATERAL CORTICOSPINAL TRACT Voluntary Motor Control L R

25 L R #3

26 LATERAL CORTICOSPINAL TRACT Voluntary Motor Control L R

27 LR #4

28 LATERAL CORTICOSPINAL TRACT Voluntary Motor Control L R

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

30 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.

31 Broad Classification of Motor Syndromes

32 Classification of Motor Disorders – Considers: 1. Ability to produce desired movements – weakness or paralysis; 2. Muscle tone Definition 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).

33 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.

34 Lower Motor Neuron Signs Muscle Spindle Dorsal Root Gang. Extensor Muscle α motor γ motor Damage of Motor Neuron – Cell Body or Axon ↓ Strength ↓ Reflexes ↓ Tone Atrophy X

35 Upper Motor Neuron Signs Muscle 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) _ Cx & Brainstem Periphery X X

36 Lower Motor Neuron Syndrome Upper Motor Neuron Syndrome Reflexes Muscle Tone Atrophy Other Signs Strength Weakness / Paralysis / Paresis Hyporeflexia Hyperreflexia Hypotonia (Flaccidity) Hypertonia (Spasticity) Atrophy of Muscles Minimal (disuse) atrophy Fibrillations & Fasciculations Extensor Plantar Response (Babinski)

37 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).

38 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.