CNS vs. PNS

Question 1

CNS Overview

Answer 1

all structures enclosed in bone

+ CN I and II

Question 2

PNS Overview

- efferent vs afferent axons

Answer 2

all neural structures distal to spinal nerves (peripheral axons of sensory, motor and autonomic nerves) AND cranial nerves III - XII

Efferent axons = motor axons carry info AWAY from SC
Afferent axons = sensory axons carrying info TO the SC

Question 3

Afferent Peripheral Axons of the PNS (as the Enter the SC)

- medial vs. lateral group

Answer 3

Medial group = info that ascends immediately such as conscious touch and proprioception
- Ia/II and Alpha beta fibers

Lateral group = info that synapses in dorsal horn, crosses and then ascends up lateral column
- Alpha omega and C fibers

Question 4

Efferent Axons of the PNS (4)

- motor axons

Answer 4

1. Large myelinated = alpha motor neurons (A alpha)
   - -> extrafusal muscle fibers
2. Medium myelinated = gamma motor neurons (A gamma)
   - -> intrafusal muscle fibers
3. Small myelinated = presynaptic autonomic (B)
4. Unmyelinated = postsyaptic autonomic (C)

Question 5

Afferent axons of the PNS (3)

- sensory axons

Answer 5

1. large myelinated
   - Ia/II - muscle spindles
   - Ib - GTO
2. Small myelinated = Alpha beta fibers
   - sharp, localized pain, temp, visceral receptors
   - spinothalamic system
3. Unmyelinated = C fibers
   - DULL, slow pain & temp
   - medial pain system

Question 6

Upper Motor Neuron

• defn
• clinical sign
• disease

Answer 6

DEFN: neurons w/ axons that descend from cerebral cortex pr BS & synapse on LMN w/n the CNS

• first pathway
• begins & ends in CNS

Clinical signs: paresis, spasticity, hypertonia & hyperreflexia

Diseases: stroke, SCI, Parkinsons, TBI, MS

Question 7

Lower Motor Neuron

• defn
• clinical sign
• disease

Answer 7

DEFN: cell body in BS or ventral horn of SC and axon synapses in the periphery on muscle

• begins in CNS, ends in PNS
• secondary pathway

Clinical sign: loss of reflexes, hyporeflexia, atrophy, flaccid paralysis, fibrilations and fasciculations

Diseases: polio, peripheral nerve injury, Guillian-barre syndrome

Question 8

Rexed’s Laminae (3)

- dorsal horn

Answer 8

Substantia gelatinosa = lamina II = pain

Nucleus proprius = lamina III and IV = conscious touch & proprioception

Nucleus dorsalis = lamina VII = Clarke’s column
- unconscious touch & proprioception to cerebellum

Question 9

Reflex Arc

Answer 9

stretch reflex

quick stretch stimulates Ia afferent in muscle spindle –> Ia afferent synapses w/ alpha motor neuron in the dorsal horn –> muscle contraction

aka “monosynaptic reflex”

modulated by interneuron & UMN

• -> UMN lesion = HYPERreflexia
• -> LMN lesion = HYPOreflexia