Lecture 17

Question 1

List the major derivatives from each subdivision. (Dermatome, Myotome, Sclerotome)

Answer 1

Dermatome: becomes the dermis

Myotome: becomes muscle

Sclerotome: becomes the skeleton

Question 2

Define “dermatome” and “myotome.”

Answer 2

Dermatome: the area of skin supplied with afferent nerve fibers by a single posterior spinal root

Myotome: all the muscles that are innervated by a single efferent anterior root

Question 3

Describe the normal arrangement of myotomes per singular muscle

Answer 3

Most muscles are composed of more than one myotome

Question 4

Describe the relationships between somites and somatic innervation.

Answer 4

Somatic innervation occurs in a “segmental” fashion, which means each somite is associated with one section of innervation (as opposed to several somites innervating the same area)

Question 5

Describe the relationships between plexuses and myotome innervations.

Answer 5

A plexus is when there are several nerves that run together or are branching off of/into one another

myotome innervations may run through a plexus

this intermingling means that most myotomes, bc of their plexus involvment, supply more than one muscle

Question 6

Where are the enlargements of the spinal cord found? ( 2 of them)

Answer 6

Has enlargements in the cervical C3-T1 region and in the lumbar L1-S2 region

Question 7

Describe the locations of the following spinal cord structures:
the conus medullaris, cauda equina, and filum terminale.

Answer 7

Conus medullaris: leads into the cauda equina, and ends at about the level of L2

Cauda equina: “horses tail” structure that bridges between the conus medullaris and the sacrum (composed of the dorsal and ventral nerve roots)

Filum terminale: thin filament of meningeal tissue extending from conus medullaris to the coccyx

Question 8

State the different subdivisions of the spinal cord, and the number of spinal nerves that are found within each subdivision

Answer 8

8 cervical

12 thoracic

5 lumbar

5 sacral

1 coccygeal

Question 9

Provide the spinal nerve numbers of the 3 plexuses that can be found in the spinal cord.

Answer 9

Cervical: C1-C4

Brachial: C5-T1

Lumbosacral: L1-S4

Question 10

Describe the cross-sectional anatomy of the spinal cord into central canal, gray matter, and white matter.

Answer 10

Central canal in the middle

Gray matter: consists of the the nuclei of the central nervous system
Appear in an “H” shape in a cross section of the spinal cord
Feature anterior and posterior horns

White matter: consists of the myelinated tracts of the CNS
Surrounds the “H” shaped gray matter
Divided into columns

Question 11

Define the “horns” of a cross sectional view of the spinal cord. describe what fibers/neurons are associated with the Posterior horns, Anterior horns, and lateral horns

Answer 11

Horns: gray matter equivalents of CNS nuclei

Posterior (dorsal) horns receive incoming sensory fibers

Anterior (ventral) horns are the site of cell bodies of alpha motor neurons to skeletal muscle fibers

Lateral horns are located only in the thoracic and upper lumbar region and they are the site of autonomic neurons

Question 12

Describe what the columns of the spinal cord consist of and list their 3 main features

Answer 12

Columns: White matter that consists of the myelinated tracts of the CNS

Has posterior (dorsal) columns, Anterior (ventral) columns, and lateral columns

Question 13

Describe the function of commissures in the spinal cord. Are commissures composed of white or gray matter?

Answer 13

Commissures: basically function to cross over from opposing sides of the spinal cord

Features white matter commissures (anterior and posterior) and Gray matter commissures (anterior and posterior)

Question 14

List the order of the strucures of a typical spinal nerve, beginning with the rootlets. (while each structure has it’s own ventral and dorsal components, just list the overall structure for this quesiton)

Answer 14

Rootlets

Primary rami

Autonomic Rami

Question 15

Describe the types of fibers carried, and ganglion associated with the Dorsal and ventral rootlets

Answer 15

Dorsal root: carries afferent fibers with dorsal root ganglion

Ventral Root: carries efferent fibers with NO associated ganglion

Question 16

Describe the musculature innervated by, and the regions of cutaneous innervation supplied by the Dorsal and Ventral Primary Rami

Answer 16

Dorsal: run to epaxial deep back musculature and skin on the dorsum of the back

Ventral: run to hypaxial musculature (includes limb muscles) and the rest of the skin

Question 17

Describe the type of fibers and where they originated from that are in the white and gray ramus communicans.

Answer 17

White Ramus communicans: carries pre-ganglionic sympathetic fibers from the lateral horns of the central gray matter of the spinal cord (thoracolumbar regions)

Gray Ramus communicans: carries post-ganglionic sympathetic fibers from the paravertebral ganglia back to the spinal nerve

Question 18

from the outside, moving inward, describe the meningeal coverings that the spaces they create while surrounding the spinal cord.

Answer 18

Epidural space

Dura matter:

Subdural space

Arachnoid layer

Subarachnoid space: contains CSF

Pia mater: delicate innermost layer

Question 19

What are the denticulate ligaments?

Answer 19

Denticulate ligaments: extensions of pia mater that anchor the spinal cord to the dura mater.

They are formed by pia mater of the spinal cord coursing in-between the dorsal and ventral nerve roots bilaterally.

as people age, these thin out and eventually break(can cause issues)