Chapter 3 and 4 Single

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Fig. 1-9: Purves et al. Neuroscience, Sinauer Associates Inc: Massachusetts, 2001.

CNS Organization - Axes

Anterior (infront of;

toward the

front) Posterior

(behind;

toward the

back)

Inferior (below)Caudal

Superior (above)

Rostral

Caudal

Medial (middle)

Lateral (to the side)


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Spinal Cord Segments

Cervical 7 Thoracic 12

Lumbar 5 Sacral 5

Coccygeal 1 31 in total


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Dermatomes Area of skin supplied by a

single dorsal root.

1 pair per spinal cord

segment Left/Right

None for C1

Consecutive segmentsare next to each other

Clinical sign of wherespinal cord lesion occurs


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Myotomes Groups of muscles

innervated by a singlespinal cord segment.

1 pair perLeft/Right


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Meninges

Spinal cord is part of CNS Covered by 3 meningesPia adheres to spinal cord

Arachnoid

Dura not attached to bone.

Epidural space

CSF between arachnoid and pia.


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Cross-section Butterfly shaped

grey matter Surrounded by white

matter

Dorsal medianseptum

Ventral fissure Dorsolateral sulcus

Ventrolateral sulcus


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Delineations of Grey Matter Dorsal horn

Input from DRG

Ventral horn Motor neuron output

Intermediolateral horn Thoracic/upper lumbar

Neurons of thesympathetic nervoussystem part of autonomic

nervous system

rest & digest


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10 Laminae of Rexed

I-IV: input layers(somatosensory)

V & VI: proprioceptive

VII: relay between midbrainand cerebellum

VIII: modulate motor activity

IX: main motor area X: neuroglia


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Layer IX Architecture

Ventral horn Alpha motor neurons

Flexors dorsal Extensors ventral

Trunk medial Limbs (periphery) -

lateral


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White Matter Architecture Posterior (dorsal) funiculus

Dorsal Column-MedialLemniscus Ascending tract

Kinesthesia position sense Discriminative touch

Tests for:

Vibration sense Position sense

2-point

Touch

Form recognition


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Posterior Column: DC-ML Receptor (peripheral axon)

Soma (unipolar) in DRG Proximal axon to spinal cord

Dorsal column to medullaGracile and Cuneate nuclei

Cross-over (decussation)

Medial lemniscus to thalamus Ventral posterolateral nucleus

Primary somatosensory cortex

(S1) 3 neurons to reach here


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Spinocerebellar Tracts

Dorsal Ascending

Proprioception

Ventral Ascending

Golgi tendon organ afferents

Both terminate in cerebellum Unconscious proprioception

Unlike dorsal column-medial

lemniscus which is consciousproprioception


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Lateral Spinothalamic Tract

Pain anterior Temperature - posterior

CordotomyLesion of anterior LST

Relief of chronic pain


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Corticospinal Tract

Descending tract Primary motor cortex (M1)

Premotor cortex

Pyramidal decussation

Cross-over at medulla

Lateral corticospinal tract Anterior corticospinal tract

Skill/precision in movements

Does not initiate fine movements


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Rubrospinal Tract

Rubro red nucleus In midbrain

Ventral tegmentaldecussation

In midbrain

Corrects errors inmovements of the

corticospinal tract


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Lateral Vestibulospinal Tract

Lateral vestibulospinalnucleus

Pons

Upright posture


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Medial Vestibulospinal Tract

Medial vestibularnucleus

Medulla

Control of headposition


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Reticulospinal Tracts

Reticular FormationPons & Medulla

Modulate motor neurons

Modulate sensory input

Modulate spinothalamic

neurons in dorsal horn


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Tectospinal Tract

Superior Colliculus(optic tectum)

Orienting

Eyes

Turn head in response

to lightCombined head/eye

movements


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Spinal Reflexes

Reflexes: movements that dont need consciouscontrol

Hand in fire

Remove hand Then feel pain/heat

Circuit:

Dorsal horn input

Ventral horn output


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Stretch (Myotactic) Reflex

Doctor taps on tendonBiceps flex elbowTriceps extend elbow

Radial (wrist) flex wristKnee extend knee

Ankle flex ankle

Counteracts externalinfluences

Helps maintain posture


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Inverse Myotactic Reflex

Severe tensionactivates Golgitendon organ

Reflex relaxesmuscle

Prevents tearing oftendon


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Withdrawal (Flexor) Reflex

Remove limb from pain Activate flexor muscles

Inhibit antagonisticextensor muscles

Polysynaptic


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Crossed Extensor Reflex

When flexor reflex occurs,this occurs too

Contralateral limb does the

opposite Flexor muscle relaxes

Extensor contracts

i.e. opposite limb extends

Maintains center of gravity

Dont want to fall in the fire!


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Clinical Correlates of Spinal Cord Injury

Lesions preventinput/output

Correlates are

related to whateach tract does

normally E.g. Horners

Syndrome


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Dorsal Column Lesion

Loss or lessening ofVibration sense

Position sense

2-point discrimination

Deep touch

Ipsilateral (same side) Dermatomes at and

below lesion site


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Lateral Spinothalamic Tract

Loss or lessening of:Pain

Temperature

Contralateral (oppositeside)

Dermatomes one ortwo segments belowlesion

Due to cross-over


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Dorsal Root Lesion

Loss of lessening of:All sensory modalities

Ipsilateral

Only the dermatomesupplied by that DRG


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ALS: Amyotrophic Lateral Sclerosis

Lou Gehrigs disease Motor neuron disease

Degenerative

Anterior horn

Lateral corticospinal

tractBilateral


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SignsParalysis

Muscular atrophy

Exaggerated myotacticreflexes

Babinski sign Run pen down sole of

foot

Big toe points up

Other toes fan out


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Life expectancy: 3-5

years Locked in

Paralyzed body

Normal mind 2 deaths per 100,000

Cause unknown Familial ALS

Chromosome 21 Defect in SOD1

superoxide dismutase

Protects motor neuronsfrom free radicals


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Lou GehrigAs a first baseman for the New York Yankees baseball

team, Lou Gehrig played in 2,130 consecutive games

from 1925 to 1939, setting a major league record andhad a career batting average of .340. He once hit fourhome runs in a game.

On July 4, 1939, he stood before 60,000 fans at Yankee

Stadium and confirmed what everyone seemed to know,that the "Pride of the Yankees" had been dealt a terribleblow, diagnosed with amyotrophic lateral sclerosis (nowoften called Lou Gehrig's disease), a rare disease that

causes spinal paralysis.Less than two years later, on June 2, 1941, he died inRiverdale, N.Y.


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Lou Gehrigs SpeechFans, for the past two weeks you have been reading about a bad break I got. Yet

today I consider myself the luckiest man on the face of the earth. I have been inballparks for seventeen years and have never received anything but kindness andencouragement from you fans.

Look at these grand men. Which of you wouldn't consider it the highlight of his career

to associate with them for even one day?Sure, I'm lucky. Who wouldn't consider it an honor to have known Jacob Ruppert -

also the builder of baseball's greatest empire, Ed Barrow - to have spent the nextnine years with that wonderful little fellow Miller Huggins - then to have spent thenext nine years with that outstanding leader, that smart student of psychology - the

best manager in baseball today, Joe McCarthy!Sure, I'm lucky. When the New York Giants, a team you would give your right arm to

beat, and vice versa, sends you a gift, that's something! When everybody down tothe groundskeepers and those boys in white coats remember you with trophies,that's something.

When you have a wonderful mother-in-law who takes sides with you in squabblesagainst her own daughter, that's something. When you have a father and motherwho work all their lives so that you can have an education and build your body, it'sa blessing! When you have a wife who has been a tower of strength and shownmore courage than you dreamed existed, that's the finest I know.

So I close in saying that I might have had a tough break - but I have an awful lot to livefor!Lou Gehrig - July 4,1939

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