Chapter 16 Spinal Cord and Spinal Nerves (Lecture)

Two important functions of the spinal nerves

a pathway for sensory and motor impulses

responsible for reflexes (our quickest reactions to stimuli)

What are the dimensions of the spinal cord

¾ of an inch in diameter, 16-18 inches long

extends from foramen magnum to L1 vertebra

Five parts of spinal cord named for the nerves that attach to them (superior to inferior)

cervical part

thoracic part

lumbar part

sacral part

coccygeal part

the tapering inferior end of spinal cord

conus medullaris

Cauda equina

“Horse’s tail” axons that extend inferiorly from spinal cord’s conus medullaris

Filum terminale

thin strand of pia mater within cauda equina that attaches conus medullaris to coccyx

cervical enlargement location and function

located in the inferior cervical part of the spinal cord

innervates the upper limbs

lumbosacral enlargement location and function

extends through the lumbar and sacral parts of the spinal cord and innervates the lower limbs

external surface of cord has two longitudinal depressions

posterior median sulcus

anterior median fissure

the spinal cord is associated with 31 pairs of spinal nerves. what are they ?

8 cervical nerves (C1-C8)

12 thoracic nerves (T1-T12)

5 lumbar nerves (L1-L5)

5 sacral nerves (S1-S5)

1 coccygeal nerve (Co1)

spinal cord meninges are continuous with what

cranial meninges

epidural space location. what is given here ?

sits between dura and periosteum of vertebra

epidural anesthesia

dura mater consists of what and does what

a single meningeal layer

stabilizes spinal cord and fuses with connective tissue around spinal nerves

narrow subdural space

a potential space separating dura mater from deeper arachnoid mater

subarachnoid space

a real space filled with cerebrospinal fluid

pia mater

what is it and what does it consist of

the innermost meninx that adheres directly to the spinal cord

consists of a delicate later of elastic and collagen fibers

denticulate ligaments

pia mater has this. suspends and anchors the spinal cord laterally to the dura mater

gray matter, what is it and where is it located

dendrites and cell bodies of neurons, unmyelinated axons, and glial cells

located in spinal cord

white matter

myelinated axons

Gray matter sectioned resembles a butterfly. what are the subdivisions ?

anterior horns

lateral horns

posterior horns

gray commissure

anterior horns house what

somas of somatic motor neurons

lateral horns contain what ?

it’s only found in which parts of the spinal cord

contains somas of autonomic motor neurons

only found in the T1-L2 parts of spinal cord

posterior horns contain what

axons of sensory nucleus and cell bodies of interneurons

gray commissure contains what and houses what

contains unmyelinated axons for communication between right and left side

houses a narrow central canal

nuclei

functional groups of neuron cell bodies in gray matter

sensory nuclei in posterior horns contain what

interneuron cell bodies of somatic sensory nuclei and visceral sensory nuclei

motor nuclei in the anterior horns contain what

somatic motor nuclei

where are autonomic motor nuclei

in the lateral horns

white matter is partitioned into three regions, each called a funiculus. what are these three regions?

posterior funiculus

lateral funiculus

anterior funiculus (connected by white commissure)

tracts

axons within each funiculus that are organized into smaller structural units

how many pairs of spinal nerves extend from spinal cord and what connective tissue wrappings do they contain ? what are they made up of ?

31 pairs

contain endoneurium, perineurium, and epineurium

made up of motor and sensory exons

what arises from the spinal cord and what do they merge to form

multiple anterior rootlets

anterior root

anterior roots contain what

motor axons only

where do motor axons arise from

cell bodies in the anterior and lateral horns of the spinal cord

what derives from a single posterior root

multiple posterior rootlets

posterior roots contain what

sensory axons only

sensory axons arise from what (attached to the posterior root)

cell bodies in the posterior root ganglion

Each anterior root and its corresponding posterior root unite within the intervertebral foramen to become what

a spinal nerve

what does a spinal nerve contain

both motor and sensory axons

Where do the first seven spinal nerves (C1-C7) exit

the intervertebral foramen above the vertebra of the same number

where does the eight cervical spinal nerve (C8) exit

above the first thoracic vertebra

where do the remaining spinal nerves exit

below the vertebra of the same number

after leaving the intervertebral foramen, a typical spinal nerve splits into branches called what

rami

what does the posterior ramus do

it innervates the deep muscles and skin of the back

what does the anterior ramus do

innervates the anterior and lateral portions of the trunk and the upper and lower limbs

Many of the anterior rami go on to form what

nerve plexuses

what is a dermatome and what is the exception

a segment of skin supplied by a single spinal nerve

C1 doesn’t innervate a segment of skin

Anesthesia in a region could indicate what

specific spinal nerve damage

shingles rash includes what

blisters along dermatome

what is referred visceral pain

when pain in one organ is mistakenly referred to a dermatome

what is a nerve plexus and what is their function

a network of interweaving anterior rami of spinal nerves

split into multiple named nerves that innervate body structure

what are the major plexuses

cervical

brachial

lumbar

sacral

Intercostal nerves

anterior rami of spinal nerves T1-T11 that travel in the spaces between adjacent ribs

subcostal nerve

spinal nerve T12, it arises below the ribs

with the exception of spinal nerve T1, the intercostal nerves…

do not form plexuses

What do parts of T1 help and where is it

helps form brachial plexus

lies in first intercostal space

Function of T2

innervates intercostal muscles of the second intercostal space and is sensory of axilla and medial surface of arm

Function of T3-T6

innervate intercostal muscles and are sensory for the anterior chest wall

function of T7-T12

innervate intercostal muscles, abdominal muscles, and overlying skin

Left and right cervical plexuses are formed by…

anterior rami of spinal nerves C1-C4

function of branches of the plexus

innervate anterior neck muscles, skin of the neck, and parts of the head and shoulders

what is the origin of the phrenic nerve and where does it travel to function

originated primarily from C4 and some contributing axons of C3 and C5

travels through the thoracic cavity to innervate the diaphragm

what does the ansa cervicalis innervate

geniohyoid, infrahyoid muscles (omohyoid, sternohyoid, sternothyroid, and thyrohyoid)

what are the anterior rami of the superior root

C1, C2

what are the anterior rami of the inferior root

C2, C3

What are the anterior rami of segmental branches and what do they innervate

C1-C4

anterior and middle scalenes

What are the anterior rami of the greater auricular and what does it innervate

C2, C3

skin on ear, connective tissue capsule covering parotid gland

what are the anterior rami of the lesser ocipital and what does it innervate

C2’

skin of scalp superior and posterior to ear

what are the anterior rami of the supraclavicular and what does it innervate

C3, C4, skin on superior part of chest and shoulder

what are the anterior rami of the transverse cervical and what does it innervate

C2, C3

skin on anterior part of neck

what are the left and right brachial plexuses

networks of nerves that supply the upper limbs

each plexus is formed by what

the anterior rami of spinal nerves C5-T1

each brachial plexus innervates what

the pectoral girdle and the entire upper limb of one side

What forms the roots of the brachial plexus

anterior rami of C5-T1

the roots of the brachial plexus unite to form what

superior trunk: nerves C5 and C6

middle trunk: nerve C7

inferior trunk: nerves C8 and T1

portions of each trunk divide into what

an anterior division and a posterior division

the anterior and posterior divisions converge to form what three cords

posterior cord

medial cord

lateral cord

what are the five major terminal branches that emerge from the three cords ?

axillary nerve

median nerve

musculocutaneous nerve

radial nerve

ulnar nerve

What anterior rami make up the axillary nerve, what does it innervate, and how is it formed

C5, C6

innervates the deltoid, teres minor, and superolateral arm

formed from posterior cord, posterior division of the brachial plexus

What anterior rami make up the median nerve, what does it innervate, and how is it formed

C6-T1

innervates the most anterior forearm muscles (basically the finger and palms), the thenar (thumb) muscles, the lateral 2 lumbricals, and palmar aspects and dorsal tips of some fingers

formed from medial and lateral cords, anterior division of the brachial plexus

What anterior rami make up the musculocutaneous nerve, what does it innervate, and how is it formed

C5-C7

innervates the anterior arm muscles and the lateral region of forearm

forms from the lateral cord, anterior division of the brachial plexus

What anterior rami make up the radial nerve, what does it innervate, and how is it formed

C5-T1

innervates posterior arm muscles, posterior forearm muscles, brachioradialis, posterior region of arm, posterior region of forearm, and dorsal aspect of lateral three digits

formed from the posterior cord, posterior division of the brachial plexus

What anterior rami make up the ulnar nerve, what does it innervate, and how is it formed

C8-T1

innervates anterior forearm muscles, intrinsic hand muscles, and dorsal and palmar aspects of medial digits

formed from the medial cord, anterior division of the brachial plexus

What anterior rami make up the dorsal scapular, and what does it innervate

C5

rhomboids, levator scapulae

What anterior rami make up the long thoracic, and what does it innervate

C5-C7

serratus anterior

What anterior rami make up the lateral pectoral, and what does it innervate

C5-C7

pectoralis major

What anterior rami make up the medial pectoral, and what does it innervate

C8-T1

pectoralis major

pectoralis minor

What anterior rami make up the medial cutaneous nerve of forearm, and what does it innervate

C8-T1

medial side of arm

What anterior rami make up the medial cutaneous nerve of forearm, and what does it innervate

C8-T1

medial side of forearm

What anterior rami make up the nerve to subclavius, and what does it innervate

C5-C6

subclavius

What anterior rami make up the suprascapular, and what does it innervate

C5-C6

supraspinatus

infraspinatus

What anterior rami make up the subscapular nerves, and what does it innervate

C5-C6

subscapularis and teres major

What anterior rami make up the thoracodorsal, and what does it innervate

C6-C8

latissimus dorsi

the left and right lumbar plexuses are formed from what

anterior rami of spinal nerves L1-L4

the lumbar plexus is subdivided into what

an anterior division and a posterior division

the main nerve of the posterior division is the what

femoral nerve

the main nerve of the anterior division is the what

obturator nerve

what anterior rami makes up the femoral nerve and what does it innervate

L2-L4

innervates anterior thigh muscles, anterior thigh, inferomedial thigh, medial side of leg, and most medial aspect of foot

what anterior rami makes up the obturator nerve and what does it innervate

L2-L4

innervates the medial thigh muscles and the superomedial thigh

what anterior rami makes up the Iliohypogastric and what does it innervate

L1

partial innervation to abdominal muscles, and superior lateral gluteal region and inferior abdominal wall