Spinal Cord 2

Question 1

where are the motornuerons found?

Answer 1

in the ventral horn

Question 2

2 kinds of motorneurons

Answer 2

• alpha

- gamma

Question 3

alpha motorneurons

Answer 3

• go to skeletal muscle
• somatic efferent fibers
• go to extrafusal fibers
• end as motor end plate

Question 4

gamma motorneurons

Answer 4

• go to intrafusal fibers (muscle spindle)

- send sensory info to tell how contracted the muscle is

Question 5

distribution of motorneurons

Answer 5

• shoulder muscles: upper cervical region
• hand muscles: low cervical/upper thoracic

*what’s the point? explains our segmental arrangement

Question 6

what is a similarity of the motorneurons in the ventral horn to the dosral horn?

Answer 6

both are arranged somatitopically

Question 7

intermediolateral column contains what?

Answer 7

visceral motor nuerons

Question 8

lateral motor column supplies:

Answer 8

muscles of the limb

Question 9

medial motor column supplies:

Answer 9

axial muscles

Question 10

describe the convergence of afferents to a ventral horn motorneuron

Answer 10

• 4 descending tracts come down to converge on the neuron (corticospinal, reticulospinal, vestibulospinal, rubrospinal and tectospinal)
• an inhibitor and excitatory spinal reflex converges on it
• the motorneuron axon extends as the final common pathway to a muscle

Question 11

lower motor neurons =

Answer 11

alpha motor neurons - arise from anterior horn cells and project to skeletal muscle

Question 12

upper motor neurons =

Answer 12

arise in the CNS, stay in CNS, and descend to act on lower motor neurons

Question 13

what would happen if there were a lesion on a lower motor neuron? and why?

Answer 13

• hyporeflexive

- reflex arc is no longer in tact

Question 14

what would happen if there were a lesion on a upper motor neuron? and why?

Answer 14

• hyperreflexive
• reflex arc still intact
• think of McNeils example of the women w/ massive stroke that kicked him in the head

Question 15

what are the afferent fibers that enter the dorsal root?

Answer 15

• group A fibers

- C fibers

Question 16

group A fibers

Answer 16

• large and myelinated
• come into dorsal column w/o synapsing and ascend
• FAST

Question 17

what do group A fibers carry?

Answer 17

• proprioception
• discriminative touch
• vibration
• 2 point sensory info

Question 18

C fibers

Answer 18

• tiny unmyelinated fibers
• from spinothalamic tract
• slower

Question 19

what do C fibers carry?

Answer 19

signals related to . . .

• pain
• temp
• poorly localized touch

Question 20

how is the group A fibers / C fibers interaction significant in real life?

Answer 20

• when you hurt yourself, there is a second where you know what happened but it doesn’t hurt, you just know the pain is coming
• the “something touched me” sense is faster than the pain sense

Question 21

where does sensory start?

Answer 21

at the sensory endings for primary afferents in the DRG

• there are specialized receptors for everything
• examples: pacinian corpuscle, ruffini endings, meissner corpuscle, etc.

Question 22

fasciculus proprius

Answer 22

• interconnects segments of SC - helps w/ reflexes
• has axons that don’t leave SC
• sends info up and down more segments

Question 23

Why is a spinal cord injury not a precise cut off?

Answer 23

• the fasciculus proprius

- the fact that dermatomes also overlap

Question 24

What are the clinically important long tract systems (note: this is repetitive)

Answer 24

SENSORY
-spinothalamic 
-dorsal column aka medial lemniscal 
-spinocerebellar 
MOTOR
-corticospinal

Question 25

spinothalamic tract

Answer 25

-transmits pain, temp and poor localization into the CNS and up to thalamus

Question 26

dorsal column aka medial lemniscal system

Answer 26

-transmits discriminative touch, proprioception, vibration, 2 pt discrimination to consciousness into the CNS and up to thalamus

Question 27

spinocerebellar projections

Answer 27

-relay info about muscle tension, limb position and spinal cord level of activity to cerebellum for planning of movements

Question 28

corticospinal projections

Answer 28

-most important of the upper motorneurons in the control of fine movement

Question 29

where are primary afferent (first order) sensory neurons?

Answer 29

in the DRG

Question 30

where do primary afferent axons synapse?

Answer 30

on the same side as the DRG cell body (ipsilateral)

Question 31

what do secondary afferent neurons (second order) receive?

Answer 31

primary afferent synapses form ipsilateral DRG cells

Question 32

secondary afferent neurons project where?

Answer 32

to the contralateral ventral thalamus to synapse on 3rd order neurons

Question 33

tertiary afferent (3rd order) neurons project where?

Answer 33

from thalamus to cerebral cortex

Question 34

spinothalamic tract - enters where? - synapses where?

Answer 34

enters and synapses in lamina 2 then crosses (decussates in cord)

Question 35

dorsal column aka medial lemniscal pathway (group A fibers) - enter? - synapse? - go where?

Answer 35

- enter and ascend on same side - synpase w/ 2nd order neuron in MEDULLA - cross there and got to VPL then cortex

Question 36

what must happen for us to be aware of these pathways?

Answer 36

they MUST reach the cortex

Question 37

if you see a pathway crossing in the white commissure, what does it tell you?

Answer 37

it's spinothalamic tract

Question 38

once the pathways reach the VPL of thalamus, where specifically do they go?

Answer 38

post central gyrus

Question 39

post central gyrus is aka

Answer 39

primary somatosensory area

Question 40

distribution of the sensory homunculus

Answer 40

- more nervous system in the post central gyrus is dedicated to face and index finger than anything else - indicates importance

Question 41

what is the origin of the corticospinal tract?

Answer 41

motor cortex aka pre central gyrus

Question 42

motor homunculus

Answer 42

-closely resembles the sensory homunculus

Question 43

blood supply of motor homunculus that supplies the face and upper extremity?

Answer 43

middle cerebral a.

Question 44

blood supply of motor homunculus that supplies the leg?

Answer 44

anterior cerebral a.

Question 45

corticospinal projections - what it provides - what happens when lost - where decussation occurs

Answer 45

- cortex provides volitional control over intended movements - w/o it, one loses fine fractionated control - pyramidal decussation occurs at the spinomedullary junction

Question 46

describe the pathway of the corticospinal projections

Answer 46

precentral gyrus --> bottom of medulla to decussate --> descend down lateral corticospinal tract --> synapse on motor nuerons --> muscle

Question 47

spinal injury above the medulla would effect what? give example

Answer 47

- upper motor neurons | - ex: stroke

Question 48

spinal injury below the medulla would effect what? give example

Answer 48

- lower motor neurons | - ex: SC injury

Question 49

UMN lesion

Answer 49

- disuse atrophy - fasciculations (quivering) - spastic paralysis - hyperreflexia

Question 50

LMN lesion

Answer 50

- atrophy - flaccid - flaccid paralysis - hyporeflexia

Question 51

syringomyelia

Answer 51

- damage around the central canal | - pressure on crossing fibers causes a loss of pain and temp to those segments on both sides

Question 52

tabes dorsalis

Answer 52

- damage to dorsal column - almost always secondary to tertiary syphilis - lose touch and proprioception - when they walk they can't feel their feet touch the ground

Question 53

in a drug deal gone bad when the bullet hits the lateral faniculus, what does it affect?

Answer 53

corticospinal and spinothalamic tracts but NOT dorsal column

Question 54

brown-sequard syndrome

Answer 54

- hemisection of SC | - causes 4 neural deficits

Question 55

what are the 4 neural deficits caused by brown-sequard syndrome?

Answer 55

1. loss of pain and temp at opposite side and below 2. loss of light tough and 2pt ipsilateral and below 3. upper motor lesion ipsilateral below level of lesion 4. lower motor lesion at level of lesion d/t injury of cells directly, not axons