functional anatomy week 8

Spinal cord

vital link between brain and rest of the body

Spinal nerves

serve two important functions

2 important functions of spinal nerves

a pathway for sensory and motor impulses and responsible for reflexes (our quickest reactions to stimuli)

Gross anatomy of spinal cord

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

Spinal cord extends

from foramen magnum to L1 vertebra

How are the 5 parts of spinal cord names?

Based on the nerves that attach to them

How many parts are there in the spinal cord?

5

5 parts of spinal cord

cervical part, thoracic part, lumbar part, sacral part, and coccygeal part (listed superior to inferior)

Spinal cord and vertebral canal

spinal cord is shorter than the vertebral canal that houses it

Where is coccygeal part of spinal cord?

Is in L1 vertebra

Conus medullaris

tapering inferior end of spinal cord

Cauda equina

"horse's tail" axons that extend inferiorly from spinal cords conus modularise

Filum terminal

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

Spinal cord shape

roughly cylindrical but diameter changes along its length

Cervical enlargement of spinal cord

located in the inferior cervical part (C7) of the spinal cord and innervates the upper limbs

Lumbosacral enlargement of spinal cord

(T12-L1) extends through he lamber and sacral parts of the spinal cord and innervates the lower limbs

How many pairs of spinal nerves is the spinal cord associated with?

31 pairs

31 pairs of spinal nerves

8 cervical nerves, 12 thoracic nerves, 5 lumbar nerves, 5 sacral nerves, and 1 coccygeal nerve

Cervical nerves

C1-C8

Thoracic nerves

T1-T12

Lumbar nerves

L1-L5

Sacral nerves

S1-S5

Coccygeal nerve

Co1

Spinal cord meninges

continuous with cranial meninges

Epidural space

sits between dura and periosteum of vertebra

Epidural anesthesia

given in epidural space

Dura mater spinal cord

surrounding spinal cord consists of a single meningeal later (in contrast to double-layered dura around brain)

Dura mater spinal cord function

stabilizes spinal cord and fuses with connective tissue around spinal nerves

Subdural space

narrow and is a potential space separating dura mater from deeper arachnoid mater

Arachnoid mater

has subarachnoid space and pia mater inside it

Subarachnoid space

a real space filled with cerebrospinal fluid (CSF)

Pia mater

innermost meninx that adheres directly to spinal cord

Pia mater consists of

delicate layer of elastic and collagen fibers

Spinal cord meninges

external surface of spinal cord has two longitudinal depressions

2 longitudinal depressions spinal cord meninges

posterior median sulcus and anterior median fissure

Sectional anatomy of spinal cord

spinal cord partitioned into an inner gray matter region and an outer white matter region

Grey matter of spinal cord

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

White matter of spinal cord

myelinated axons

Grey matter distribution

is centrally located in spinal cord

Grey matter sectioned shape

resembles a butterfly

Grey matter 4 subdivisions

anterior horns, lateral horns, posterior horns, and grey commissure

Anterior horns

house somas (body) or somatic motor neurons

Lateral horns

contain somas of autonomic motor neurons

Where are lateral and anterior horns found?

Only found in the T1-L2 parts of spinal cord

Posterior horns

contain axons of sensory neurons and cell bodies of interneurons

Grey commissure

contains unmyelinated axons for communication between right and left side and houses a narrow central canal

Nuclei

found within grey matter and are functional groups of neuron cell bodies

Where are sensory nuclei located?

In posterior horns

Sensory nuclei

contain interneuron cell bodies of somatic sensory nuclei and visceral sensory nuclei

Where are motor nuclei located?

In anterior horns

Motor nuclei

contain somatic motor nuclei

Where are autonomic motor nuclei located?

in the lateral horns

White matter

external to spinal grey matter

How many regions in white matter made into?

3

Funiculus

each region of the 3 regions of white matter

3 regions of white matter

posterior funiculus, lateral funiculus, and anterior funiculus

How are anterior funiculi connected?

By white commissure

Tracts

name for smaller units that axons within each funiculus are organized into

Spinal nerves

extend from spinal cord and are made up of motor and sensory axons

How many pairs of spinal nerves?

31 pairs

What do spinal nerves contain?

Connective tissue wrapping 3 things

3 things connective tissue wraps

endoneurium, perineurium, and epineurium

Anterior rootlets (spinal nerves)

multiple arises from the spinal cord and merge to form a single anterior root

Anterior roots (spinal nerve)

contain motor axons only

Motor axons (spinal nerve)

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

Posterior rootlets (spinal nerves)

multiple derives from a single posterior root

Posterior roots (spinal nerves)

contain sensory axons only

Sensory axons (spinal nerves)

arise from cell bodies in the posterior root ganglion

Posterior root ganglion (spinal nerves)

attached to the posterior root

Anterior root and corresponding posterior root (spinal nerves)

each combo unite within the intervertebral foramen to become a spinal nerve

Spinal nerve contains

both motor and sensory axons

How are nerves numbered?

According to location of the intervertebral foramina they use to exit

First seven spinal nerves (exits)

(C1-C7) exit the intervertebral foramen above the vertebra of the same number

Eight cervical spinal nerves

(exits) (C8) exit above the first thoracic vertebra

Remaining spinal nerves (exits)

exit below the vertebra of the same number

Spinal cord length

due to it being shorter than the vertebral canal, roots of lumbar and sacral spinal nerves travel inferiorly to reach their respective intervertebral foramen

Rami

term for branches the spinal nerves split into after leaving the intervertebral foramen

Posterior ramus

innervates the deep muscles and skin of the back

Anterior ramus

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

Anterior ramus split

each split into multiple branches, and many go on to form nerve plexuses

The rami communicantes

additional rami

Rami communicantes extends

between spinal nerves and the sympathetic trunk ganglia

Dermatome

segment of skin supplied by a single spinal nerve

What is the only nerve that doesn't innervate at a segment of skin?

C1

How is skin divided?

Divided into sensory segments that form dermatome map

Anesthesia

in a region could indicate specific spinal nerve damage

Shingles

rash includes blisters along dermatome

Referred visceral pian

pian in one organ is mistakenly refer to a dermatome (potentially nowhere near the organ in pain)

Nerve plexus

network of interweaving anterior rami of spinal nerves

Plexus splits

into multiple named nerves that innervate body structures

4 major plexuses include

cervical, brachial, lumbar, and sacral plexuses

Intercostal nerves

travel in spaces between adjacent ribs

Intercostal nerves include

anterior rami of spinal nerves T1-T11

Subcostal nerve

spinal nerve T12 because it arises below the ribs

what is the only intercostal nerve forming plexuses?

T1

what does T1 form?

Brachial plexus

where is T1 found?

Lies in first intercostal space

what does T2 innervate?

Intercostal muscle of second intercostal space

what does T2 do?

Is sensory for axilla and medial surface of arm

what does T3-T6 innervate?

Intercostal muscles