Chapter 8 Flashcards by Yashameet brar

How many pairs of spinal nerves are there?

31 pairs (8 C, 12 T, 5 L, 5 S, 1 Co)

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At what vertebral level does the adult spinal cord end?

Around the rostral edge of L2 (or caudal edge of L1)

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What is the conus medullaris?

The tapered caudal end of the spinal cord

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Name the filament that anchors the conus to the coccyx.

Filum terminale (internum + externum)

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What is the cauda equina?

Bundle of lumbar & sacral nerve roots hanging below the cord

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Which region contains the cervical enlargement and why?

Lower C5-T1; houses neurons for the brachial plexus (upper limb control)

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Which region contains the lumbar enlargement and why?

L2-S2; neurons for the lumbosacral plexus (lower limb)

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Why is a lumbar puncture safe at L3/4 in adults?

Cord has ended; only cauda equina in the lumbar cistern

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How is a dermatome defined?

Skin area supplied by the dorsal roots of a single spinal segment

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How many adjacent dorsal roots must be cut to fully anesthetize one dermatome?

Three, due to overlap

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Dorsal horn handles which type of info?

Sensory

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Ventral horn handles which type of info?

Motor (alpha & gamma neurons)

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Which lamina is the substantia gelatinosa?

Lamina II

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Main function of lamina II?

Modulates pain & temperature inputs

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Where is the nucleus proprius?

Laminae III-IV

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Clarke’s nucleus lives in which lamina and segments?

Lamina VII, C8-L2

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What does Clarke’s nucleus give rise to?

Posterior spinocerebellar tract

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Where are sympathetic pre-ganglionic neurons?

IML column in lamina VII, T1-L2

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Where are parasympathetic pre-ganglionic neurons in cord?

Lateral gray of S2-S4 (also lamina VII)

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What inhibitory interneuron provides ‘recurrent inhibition’?

Renshaw cell (lamina VII)

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Which laminae contain alpha & gamma motor neurons?

VIII & IX

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How are flexor vs extensor motor pools arranged?

Flexors dorsal, extensors ventral within lamina IX

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How are proximal vs distal muscles arranged in ventral horn?

Proximal/axial medial, distal lateral

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What is lamina X?

Gray matter around central canal (visceral relay)

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Fasciculus gracilis carries touch/proprioception from which body part?

Lower body (below T6)

Where do dorsal column fibers cross?

In the medulla (internal arcuate fibers → medial lemniscus)

Loss of vibration sense in left leg implies a lesion where?

Left dorsal column below the medulla

Which tract carries unconscious proprioception from legs?

Posterior (dorsal) spinocerebellar

Which nucleus sends the posterior spinocerebellar tract?

Clarke’s nucleus

Which tract double-crosses before reaching cerebellum?

Anterior (ventral) spinocerebellar

Main sensory carried by the anterolateral system?

Pain, temperature, crude touch

Where do spinothalamic axons cross?

Anterior white commissure within 1-2 segments of entry

Sacral spinothalamic fibers are located where in the tract?

Dorsolateral edge (→ 'sacral sparing')

What are the three 'indirect' pain pathways?

Paleo-spinothalamic, spinoreticular, spinomesencephalic

Where do 90% of corticospinal fibers decussate?

Pyramidal decussation at cervico-medullary junction

Lateral CST lesion on right side → deficits where?

Right cord lesion → ipsilateral spastic paralysis below level

Rubrospinal tract crosses where?

Ventrolateral (ventral tegmental) decussation in midbrain

Which vestibulospinal tract is uncrossed and runs entire cord?

Lateral vestibulospinal

Main job of lateral vestibulospinal tract?

Facilitate ipsilateral extensors → posture & balance

Which reticulospinal tract inhibits extensor tone?

Medullary (lateral) reticulospinal

Which reticulospinal tract excites extensor tone?

Pontine (medial) reticulospinal

Tectospinal tract function?

Reflex head-turn to visual/auditory stimuli

Descending fibers inside the medial longitudinal fasciculus mainly influence which muscles?

Neck & upper back (head positioning)

Receptor for the stretch (myotatic) reflex?

Muscle spindle (intrafusal fibers)

Afferent fiber type for stretch reflex?

Group Ia (large, fast)

How many synapses are in the stretch reflex arc?

One (monosynaptic)

What is reciprocal inhibition?

Ia afferent also excites an interneuron that inhibits antagonist α-motor neuron

Receptor for inverse myotatic reflex?

Golgi tendon organ

Inverse myotatic reflex inhibits which neuron?

Homonymous α-motor neuron via Ib interneuron

Flexor (withdrawal) reflex afferents?

Group III & IV nociceptors

Purpose of crossed-extension reflex?

Maintain support/extension of opposite limb during withdrawal

Which spinal neurons reset spindle sensitivity?

Gamma motor neurons (γ-loop)

Which descending system turns gamma tone up?

Pontine (medial) reticulospinal

Hemisection of the cord is called what syndrome?

Brown-Séquard

Brown-Séquard: touch/proprio loss is ipsi/contra?

Ipsilateral below lesion

Brown-Séquard: pain/temp loss is ipsi/contra?

Contralateral (begins ~2 segments below)

Central canal expansion condition name?

Syringomyelia

Classic sensory pattern of syringomyelia?

Bilateral loss of pain/temp in 'cape-like' distribution

Which tract is selectively hit in Tabes dorsalis?

Fasciculus gracilis (dorsal column)

Vitamin-B12 deficiency damages which two cord areas?

Dorsal columns + lateral corticospinal tract ('combined systems')

ALS destroys which two neuron types?

Upper motor (CST) & lower motor (ventral horn)

Anterior spinal artery syndrome spares which sense?

Dorsal column modalities (position/vibration) are spared

What is spinal shock?

Immediate flaccid paralysis & areflexia below cord transection, lasting days–weeks

Main artery feeding ventral 2/3 of cord?

Anterior spinal artery

Key secondary injury mediators in SCI (name 3)?

Ischemia/edema, free radicals, glutamate excitotoxicity, apoptosis

Myelin proteins that block axon regrowth?

Nogo-A, MAG (myelin-assoc. glycoprotein)

Major inhibitory intracellular switch they activate?

Rho GTPase pathway

What molecule can digest glial-scar CSPGs?

Chondroitinase ABC

Butterfly gray center in transverse cord view

Central gray matter

Thin strip connecting right & left gray horns

Gray commissure

White matter strip crossing ventral to canal

Anterior white commissure

Sensory entry zone with fine fibers

Zone of Lissauer

Mid-thoracic lateral horn cell group

Intermediolateral column (sympathetic)

Motor neuron pool for diaphragm

Phrenic nucleus (C3-5, lamina IX)

Fibers that interconnect cord levels around gray

Fasciculus proprius

Two big 'highways' on ventral medulla

Pyramids (corticospinal)

Decussation of dorsal column system

Internal arcuate fibers (medulla)

Ascending trunk in dorsolateral medulla/pons

Medial lemniscus

Chapter 8 Flashcards

(78 cards)