Week 7 Quiz Flashcards
Includes lecture 8 and 9 (17 cards)
what are the major sections of the spinal cord?
pyramidal decussation: transition between brain stem and spinal cord
conus medullaris: the tapered lower/caudal end of the spinal cord
filum terminale: pia that anchors the base of the spinal cord to the base of the spine (coccyx)
dural sac: membrane that protects the spinal cord
how are the segments of the spine divided and where do the nerves exit?
cervical: 8
thoracic: 12
lumbar: 5
sacral: 5
coccygeal: 1
C1-7 exit above their vertebral segment
C8-Co exit below their vertebral segment
cauda equina allows nerves to reach to bottom of spine since spinal cord is shorter than the spine
which spinal segments innervate each body part?
cervical: upper arm, thumb and lateral forearm, middle and little finger
thoracic: nipple, umbilicus
lumbar: big toe
sacral: heel, back of thigh
what are the basic gray and white matter divisions of the spinal cord?
lissauer’s tract: lies above the posterior horn, top
intermediate gray: between anterior and posterior horn
ventral median fissure: split between the two anterior horns, bottom
anterior white commissure: lies along midline between two halves of spinal cord
(diagram on L8S14)
how can you tell what spinal segment you are are looking at from white and gray matter divisions?
gray matter: white
white matter: purple
as you go up the spine the white matter increases, lower down the spine corresponds to less white matter and more gray matter, lower down has larger anterior/ventral/bottom horns
what kinds of nerves does each section of the spinal cord contain?
anterior/ventral horn contains motor neurons
intermediolateral cell column contains autonomic neurons
how does the myotatic/patellar tendon reflex work?
striking patellar tendon activates muscle spindle primary endings, which then excite alpha motor neurons in ventral horn that innervate the stretched muscle
(diagram on L8S22)
how does the tendon stretch reflex work?
contraction of a muscle activates the golgi tendon organs in its attached tendon, the Ib afferents then activate inhibitory interneurons that inhibit the motor neurons to that muscle (autogenic inhibition), under other conditions, the opposite effect is noted, mediated by excitatory interneurons
(diagram on L8S23)
how does the flexor/withdrawal reflex work?
a nociceptive fiber from the area of pain enters the spinal cord at S1 and activates (through at least one interneuron) motor neurons to opposing muscle groups to move limb away from pain
(diagram on L8S24)
where do dorsal root ganglia enter the spinal cord?
small DRG enter cord laterally and join Lissauer’s tract before terminating in the substantia gelatinosa on posterior horn
larger fibers enter medial to lissauers tract and join posterior columns
how is information transmitted in the posterior/dorsal column to medial lemniscus pathway?
- primary afferents carrying tactile and proprioceptive information synapse in the posterior column nuclei of the ipsilateral medulla
- the axons of second-order cells then cross the midline, form the medial lemniscus, and ascend to the
ventral posterolateral (VPL) nucleus of the thalamus - third order fibers then project to the somatosensory cortex of the
postcentral gyrus
(diagram on L9S5)
how is information transmitted in the spinothalamic tract?
- pain, temperature, and some touch and pressure afferents end in the posterior horn
- second- or higher-order fibers cross the midline, form the spinothalamic
tract, and ascend to the ventral posterolateral (VPL) nucleus of the thalamus - thalamic cells then project to the somatosensory cortex of the postcentral gyrus and to other cortical areas
- along their course through the brainstem, spinothalamic fibers give off many collaterals to the
reticular formation
(diagram on L9S10)
how is information transmitted in the spinocerebellar and cuneocerebellar tracts?
- mechanoreceptive afferents from the lower extremity ascend through fasciculus gracilis (FG) to reach Clarke’s nucleus, whose cells give rise to the ipsilateral posterior spinocerebellar tract (PSCT), which enters the inferior cerebellar peduncle and ends ipsilaterally in the vermis of the anterior lobe
- a larger variety of afferents end on
other cells of the spinal gray matter, whose axons form the contralateral anterior spinocerebellar tract
(ASCT); this tract ascends to the pons, loops over the superior cerebellar peduncle, and recrosses in the vermis of the anterior lobe - mechanoreceptive afferents from the upper extremity ascend to the medulla in the fasciculus cuneatus (FC) and end in the lateral cuneate
nucleus - these cells give rise to the cuneocerebellar tract (CCT), which
enters the inferior cerebellar peduncle and ends ipsilaterally in the vermis of the anterior lobe
(diagram on L9S11)
how does information travel in the cortiocospinal tract?
- fibers from the precentral gyrus and
other nearby cortical areas descend
through the cerebral peduncles, pons, and medullary pyramids - most cross in the pyramidal decussation to form the lateral corticospinal tract
- those that do not cross in the pyramidal decussation form the anterior corticospinal tract; most of
these fibers cross in the anterior white commissure before ending in the spinal gray matter
(diagram on L9S13)
where are the spinal tracts located in an axial view of the spinal cord?
lateral corticospinal tract: lies above the lateral horn adjacent to the dorsal horn
posterior spinocerebellar tract: lies on the border above the lateral horn adjacent to the dorsal horn
anterior spinocerebellar tract: lies on the border below the lateral horn but adjacent to the ventral horn
spinothalamic tract: lies below the lateral horn adjacent to the ventral horn
fasciculus gracilis: on the lateral sides of the posterior column
(diagram on L9S15)
somatic vs autonomic systems
autonomic (sympathetic/parasympathetic): hypothalamus receives ascending information and acts as the source of descending pathways, transmission in the periphery involves passing through a thinly myelinated postganglionic neurons before reaching skeletal muscle, preganglionic neurons emit acetylcholine and postganglionic neurons emit norepinephrine
somatic: thalamus recieves ascending information and the cerebral cortex sends out descending information, myelinated axons of lower motor neurons synapse on muscles directly
what happens in Brown-Sequard syndrome?
damage to the cerebrospinal tract, spinothalamic tract, and the posterior column pathway on one side of the spinal cord would result in ipsilateral paralysis and loss of fine touch and proprioception and contralateral loss of pain and temperature beginning a segment below the level of damage
