lecture 18 - spinal cord and spinal nerves

regions of vertebrae (superior to inferior)

1. cervical region

2. thoracic region

3. lumbar region

4. sacral + coccygeal regions

vertebrae are stacked onto one another to create the _________ ______

vertebral column

vertebral foramen

• an opening near the spiny processes of each vertebrae

• successive holes in each vertebrae create the vertebral canal

vertebral canal

• where the spinal cord is located

how do we keep the spinal cord in the middle of the vertebral column?

meninges (of spinal cord)

intervertebral foramina

• spaces b/w the vertebrae

• where the spinal nerves will exit the vertebral canal

the numbering of the spinal nerves is based on..

which level of the vertebral canal they exit through the intervertebral foramina

true or false: the spinal cord is longer than the vertebral canal

false: the spinal cord is shorter than the vertebral canal

why is the spinal cord shorter than the vertebral canal?

difference in speed of growth during development

the spinal cord stops growing in length around ages _-_. the vertebral column continues to elongate until early __________

4-5, adulthood

the spinal cord extends from the ________ ______ to L_

foramen magnum, 2

foramen magnum

• very large circular hole in base of skull (occipital bone)

where the ______ _______ ends at the level of the foramen magnum, the spinal cord will begin

medulla oblongata

where can you landmark L2 at?

most inferior rib

spinal cord

• slightly flat on one side

• not uniform in diameter

• has 2 enlargements

2 enlargements of spinal cord

1. cervical enlargement

2. lumbosacral enlargement

• associated with extra nervous tissue needed to supply the structures of upper/lower limbs

cervical enlargement

• enlargement on spinal cord

• occurs b/w vertebrae C4 and T1

lumbosacral enlargement

• enlargement on spinal cord

• occurs b/w vertebrae T9 and T12

conus medullaris

• inferior end of spinal cord

sacral foramina

• holes in the sacral bone that nerves lower down can exit through

cauda equina

• hair-like nature of nerves coming out of bottom of spinal cord

filum terminale

• extension of the pia mater

• anchors the spinal cord to the coccyx

• prevents movement of the spinal cord in the superior direction

what is the most superficial layer of the meninges?

dura mater

which meningeal layer is the thickest and strongest?

dura mater

what is different about the dura mater in the spinal cord compared to in the brain?

• there is a space b/w the dura mater and the periosteum (connective tissue layer on bone) called the epidural space

epidural space

• space b/w the dura matter and periosteum

• filled w/ fat, blood vessels + areolar CT

• protects spinal cord + holds it in place

epidural

anesthesia injected into the epidural space to block pain receptors

meninges superficial to deep

1. dura mater

2. arachnoid mater

3. pia mater

arachnoid mater

• deep to dura mater

• thin, avascular

• simple squamous epithelial cells

subdural space

space b/w the dura mater and arachnoid mater

• contains a little serous fluid

pia mater

• deepest layer

• tightly adheres to spinal cord

• has small extensions (denticulate ligaments) that connect itself to the dura mater

denticulate ligaments

• small extensions in the pia mater that are connected to the dura mater

• occur b/w each root that exits the spinal cord

• help anchor spinal cord laterally (prevent side-to-side movement)

subarachnoid space

b/w arachnoid and pia mater

• contains CSF

2 major portions of spinal cord

1. outer white matter

2. inner gray matter

posterior median sulcus

• narrow groove on posterior side of spinal cord

anterior median fissure

• groove on anterior side of spinal cord

the posterior median _____ and anterior median ______ partially divide the spinal cord into 2 halves

sulcus, fissure

white matter of spinal cord

• composed of myelinated axons (run the length of the spinal cord)

  • can either be ascending or descending

columns

nerve tracks (white matter) organized together

3 white matter columns

1. posterior column

2. anterior column

3. lateral column

in each white matter column, there will be groups of either _________ or __________ tracts that are bundled together because they have similar ________ or serve a similar area of the body

ascending, descending, functions

white commissures

axons that connect L and R sides of spinal cord in white matter region

• allows signals to move from one side of the body to another

3 horns of gray matter of spinal cord

1. posterior horn

2. lateral horn

3. anterior horn

the lateral horns (gray matter region of spinal cord) are found only in the ______ and ______ regions

thoracic, lumbar

lateral horn

• gray matter

• very small

• associated w/ neurons of ANS

posterior horn

• gray matter

• where axons of sensory neurons enter spinal cord

true or false: sensory nerve somas are only found in the dorsal root ganglion (outside CNS)

true

the cell bodies in the posterior horn are all the cell bodies of the __________ that are going to transmit info around in the gray matter area

interneurons

anterior horn

• gray matter

• contains cell bodies for somatic motor neurons

• largest horn

the anterior horn is also referred to as the

motor horn

gray commissure

axons that connect L and R side of spinal cord in gray matter region

rootlet

• leave or enter the spinal cord

• part of PNS

ventral root

• motor neurons exit spinal cord

dorsal root

• sensory neurons enter spinal cord

dorsal root ganglion

• contains cell bodies of sensory neurons

spinal nerve

• dorsal and ventral roots merged together

all spinal nerves have _____ function

mixed (both sensory and motor)

nerve tracts are also known as

fascicles

polio

• Degeneration of gray matter within anterior horn

• Virus attacks motor neurons

• Motor loss + paralysis

ALS (amyotrophic lateral sclerosis) or Lou Gehrig’s disease

• Degeneration of anterior horn + descending motor axons

• Loss of speech, swallowing and breathing

how many pairs of spinal nerves are there

31

where does the first pair of spinal nerves exit the vertebral column?

• b/w skull and first cervical vertebrae

the spinal nerves are typically located _____ their respective vertebrae

above (e.g. spinal nerve C1 would be above vertebrae C1)

how many cervical vertebrae are there

7

how many pairs of cervical spinal nerves are there

8

the 8th cervical nerve exits ______ vertebrae C7

below

from the 8th cervical nerve on, spinal nerves are represented by the vertebrae _________ to them

superior (e.g. above vertebrae C7 is spinal nerve C7, below it is spinal nerve C8)

(next is the vertebrae T1, with spinal nerve T1 below it)

there are _ pairs of spinal nerves that exit via the sacral foramina. the rest of the spinal nerves exit through the _____________ __________

4, intervertebral foramina

how many pairs of thoracic spinal nerves are there

12

how many pairs of lumbar spinal nerves are there

5

how many pairs of sacral spinal nerves are there

5

how many pairs of coccygeal spinal nerves are there

1

a complete cut in the cervical region of the spinal cord results in

quadriplegia (all 4 limbs)

a complete cut in the upper thoracic region results in

paraplegic (only legs)

endoneurium

• CT

• surrounds the myelinated axons

• separates axons from each other

perineurium

• CT

• surrounds bundles of myelinated axons

what surrounds the fascicles (bundles of neurons) other than the perineurium?

• arteries and veins that provide blood supply

• adipose tissue

the groups of fasicles are bound together to form a _____ _____

spinal nerve

epineurium

• CT

• surrounds spinal nerve

• continuous with the dura mater of the brain

CT layers of spinal nerve from superficial to deep

1. epineurium

2. perineurium

3. endoneurium

about how many rootlets merge to form dorsal/ventral roots?

6-8

the dorsal and ventral roots pass through the ___________ space, pierce the arachnoid mater and join to form a ______ _____

subarachnoid, spinal nerve

each dorsal root contains a _______

ganglion

rami

• split in spinal nerve shortly after the dorsal and ventral roots merge

• there is posterior and anterior rami

2 branches of rami

1. posterior ramus

2. anterior ramus

posterior ramus

• innervates deep muscles of back responsible for movements of the vertebral column (also skin + CT on back)

anterior ramus

• where these nerves go depend on where you are in the body

• from T2-T12 → form the intercostal nerves

• remaining anterior rami → roots of plexuses

  • from C1-C4 → cervical plexus

  • from C5-T1 → brachial plexus

  • from L1-L4 → lumbar plexus

  • from L4-S4 → sacral plexus

  • S5 and coccygeal nerve → coccygeal plexus

roots of plexuses

• intermingling of nerves that exit the spinal cord

• formed from remaining anterior rami (5 plexuses)

intercostal nerves

• formed by anterior ramus

• innervate the intercostal muscles (involved in breathing)

cervical plexus

• most superior plexus

• roots: C1-C4

• innervate superficial neck structures, skin of neck, posterior portion of head

• contains phrenic nerve

phrenic nerve

• part of cervical plexus

• roots: C3-C5

• innervates diaphragm

brachial plexus

• roots: C5-T1

• 3 trunks, 6 divisions, 3 cords, 5 branches

• contains axillary, radial, musculocutaneous, ulnar and median nerve

axillary nerve

• part of brachial plexus

• innervates deltoid + teres minor muscles

radial nerve

• part of brachial plexus

• innervates muscles on back of arm + forearm

musculocutaneous nerve

• part of brachial plexus

• innervates biceps brachii

median nerve

• part of brachial plexus

• innervates most of anterior forearm + some hand muscles associated w/ thumb

ulnar nerve

• part of brachial plexus

• innervates forearm + most hand muscles

lumbar plexus

• L1-L4

• contain the femoral and obturator nerves

femoral + obturator nerves

• part of lumbar plexus

• innervate lateral abdominal walls, external genitals + parts of lower limbs

sacral plexus

• L4-S4

• contain common fibular and tibial nerve (which make up sciatic nerve)