Lecture 3: Development of the Dorsal Columnar System

Question 1

How many spinal nerve pairs are there (name number in each division of spinal column)?

Answer 1

8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccylgeal pair

Question 2

What are the conus medullar is and caudal equina respectively

Answer 2

terminal tapered portion of the cord at level L2, caudal equine is coral and ventral ROOTs of lumbar, sacral and cooccygeal nerves

Question 3

What is meant by topographic organization of the white and gray matter

Answer 3

the body part, sensory surface or muscles innervated represent an orderly pattern, divided into layers/ groups (Lamina of Rexed)

Question 4

Name the 4 divisions of the grey matter of the spinal cord?

Answer 4

dorsal horn, ventral horn, lateral horn and commissure

Question 5

Name the areas of white matter in the spinal cord (mostly ascending and descending axons/tracts).

Answer 5

dorsal (posterior) funiculus (divided into fasiculus); lateral funiculus; ventral (anterior) funiculus

Question 6

Under the general organization of the spinal cord, neurons and interneurons are situated with ____-____ topography with cells dealing with axial musculature (medial) and distal muscles (lateral), flexors are more dorsal and extensors are more ventral.

Answer 6

medio- lateral

Question 7

What is a funiculus?

Answer 7

a large group of nerve fibers located in a particular area (also used is tract for nerve fibers in a funiculus with a similar function, origin, destination and course)

Question 8

What types of fibers/sense does the dorsal column system carry?

Answer 8

alpha beta axons of the DRG carrying touch, vibration and conscious proprioception which branch to the dorsal horn and send a funiculus to the brainstem on the same side

Question 9

What is a fasciculus?

Answer 9

a smaller group of nerve fibers with similar function or origin

Question 10

Are alpha beta axons myelinated? What is their conduction speed and diameter relatively speaking.

Answer 10

are myelinated, large diameter axons with pretty fast conduction velocity

Question 11

Name 5 types of receptors used by the dorsal column and whether they are capsulated or not.

Answer 11

unencapsulated: merkels’s, hair receptors; encapsulated: meissner’s corpuscle, pacinian corpuscle and ruffini corpuscle

Question 12

Name the depth and modality of meissner’s corpuscles

Answer 12

it is a surface receptor with rapid adaption and small receptive field, carrying info about light touch, texture low and low frequency vibes

Question 13

Name the depth and modality of merkel’s cells

Answer 13

surface receptor with slow adaption and small receptive field, relays information on light touch and pressure

Question 14

Name the depth and modality of pacinian corpuscles.

Answer 14

they are deep receptors with rapid adaption and large receptive field relaying info on deep pressure and high frequency vibes

Question 15

Name the depth and modality of ruffini endings.

Answer 15

a deep receptor with slow adaption and large receptive field relaying info about deep pressure and stretch

Question 16

Name the depth and modality of hair follicle receptors.

Answer 16

they are deep with rapid adaption and a small receptive field the relay information based on hair follicle movement

Question 17

Joint receptors that run in the dorsal column include these types of receptors

Answer 17

type 1 golgi like (position and movement); type 2 ruffini (position and velocity) and type 3 (pressure)

Question 18

Is two point discrimination greatests where meissners and merkels are concentrated or evenly spaced?

Answer 18

best where concentrated

Question 19

Which portion of the dorsal column runs along the faciculus gracilis?

Answer 19

T7 and below axions run in the faciculus

Question 20

What protion of the dorsal column runs int eh faciculus cuneatus?

Answer 20

T6 and above run in the cuneatus (more lateral)

Question 21

Cutting the the dorsal column at any spinal level will cause loss of touch, vibration, conscious proprio below the lesion on the _______ side.

Answer 21

ipsilateral side (neuron axons come in from the DRG and ascend in the column on the same side up to the brain stem)

Question 22

Fasciculus cuneatus axons synapse in the nucleus ________ and the fsciculus gracilis axons synapse in the nucleus ______

Answer 22

nucleus cuneatus and nucleus gracilis respectively

Question 23

Nucleus fibers in the dorsal column cross the midline as _____ fibers and form the ascending group of axons called the _______

Answer 23

arcuate fibers; medial lemniscus

Question 24

Medial lemniscus fibers synapse where in the thalamus?

Answer 24

ventral posteriolateral thalamic nucleus (VPL)

Question 25

VPL axons continue on to what part of the brain?

Answer 25

the somatosensory cortex

Question 26

What carries dorsal column sensory information from the head?

Answer 26

trigeminal nerve CN V

Question 27

Where does the trigeminal nerve synapse in the thalamus?

Answer 27

ventral posterior medial thalamic nucleus (then continues on to the somatosensory cortex)

Question 28

What is the basis of phantom limb sensation

Answer 28

sprouting of nearby axons into the denervated area of the cortex cause sensation input form other areas that gets mis-interpreted as sensation from missing limb

Question 29

What is a rhomberg sign

Answer 29

if you sway while standing with your eyes closed that is a positive rhomberg sign which is connected to feedback from joints and vestibular system (if you sway with your eyes open, its most likely a cerebellar or vesicular problem)

Question 30

What is a L’hermitte’s sign?

Answer 30

if you maximally bend your neck forward, a positive sign would be getting electric-like sensations in your lower extremities which can be due to ectopic firing of damaged nerves that are stretched.

Question 31

What is agraphethesia?

Answer 31

inability to recognize a form drawn on the skin

Question 32

What is asterognosia?

Answer 32

inability to recognize a familiar object simply by touch

Question 33

Where are the cell bodies of the 1st and 2nd neuron in the dorsal column system located?

Answer 33

1st (DRG) 2nd (dorsal column nuclei- nucleus gracilis or cuneatus)…. 3rd neuron is in the thalamus that runs to the primary somatosensory cortex