SPINAL TRACTS

1/28/86, 20 Jan 98, 18 Jan 00, 29 Jan 03, 26 Jan 05, 30Jan08

Martini’s 6^th: 519-, 7^th: 422-447

SENSORY PATHWAYS: (p 503)

       first order neuron:                 cell body in dorsal root ganglion

       second order:                        cell body in posterior grey horn or medulla, goes to thalamus

       third order:                            cell body in thalamus, transmits to cerebrum, becomes conscious.

four types of ascending tracts: (p 504-507)

two in posterior funiculus:

       1     fasciculus gracilis (slender bundle) (p 503)    muscle position

       2     fasciculus cuneatus (wedge bundle)               fine touch localization:

upper limb and neck, upper trunk

a pair in the lateral and anterior funiculus:

       3     spinothalamic tract: (p 504)                          lateral: pain and temperature

ventral: touch and pressure

one in the lateral funiculus

       4     spinocerebellar: (507) 2 dorsal and 2 ventral:         proprioceptors to Purkinje cells in the cerebellum, do not reach cerebrum, therefore unconscious (p 486)

MOTOR PATHWAYS:

 two descending tracts:

      pyramidal:           corticospinal tracts: two branches:

lateral funiculus (p 510)

ventral funiculus

      extrapyramidal:  influence coordination, posture, balance, visual and auditory, stimulation, etc.

REFLEXES:

       Monosynaptic          patellar reflex (a postural reflex, helps maintina posture): (p 444)

tap patellar ligament, stretches muscle spindle (p 442), generates sensory impulse

Sensory neuron in DRG sends message to anterior horn cell

Anteriior horn cells transmits message to contract to quadriceps

       polysynapatic   withdrawal reflex (step on a tack): (p 445)

pain from tack generates sensory impulse

Sensory neuron in DRG sends message to internuncial cell (association)

Internuncial cell sends messages to inhibitory and motor neurons

Motor neuron (anterior horn cell) stimulates flexors

Inhibitory neuron inhibits extensors

       Babinski sign:  infant fans toes when sole is stroked, adult curls (because of inhibitory impulses) (p 446)

Fanning in adults indicate lack of inhibitory impulses, damage to CNS.