exam 6- final exam

where is the spinal cord located

vertebral canal

how many segments of the spinal cordis there?

31

what do the 31 segments do

each giving rise to a pair of spinal nerves

where does the spinal cord extend to

it extends from the foramen magnum to the first or second lumbar vertebra

what is the spinal cord protected by

bone

meninges

cerebrospinal fluid

what does the spinal cord provide

a two way conduction pathway to and from brain

spinal cord is the major center for…

major reflex center

inclusion for the meninges and spaces

epidural space

spinal dura mater

subdural space

arachnoid mater

subarachnoid space

pia mater

lumbar cistern

pia mater inclusions

denticulate ligament

denticulate ligament

extensions connecting spinal cord to dura mater meninx

lumbar cistern

space for lumbar puncture

spinal cord anatomy

enlargements

intervertebral foramen

conus medullaris

filum terminale

cauda equina

enlargements

where nerves serving upper and lower extremities arise

intervertebral foramen

exit for spinal nerves

conus medullaris

tapered end of spinal cord

filum terminale

pia mater extension to coccyx

cauda equina

lower spinal nerve roots that “chase” their exits

anatomy of the cross section of the spinal cord

ventral (anterior) median fissure

dorsal (posterior) median sulcus

gray matter

white matter

central canal

ventral (anterior) median fissure

deeper groove running length of cord

dorsal (posterior)median sulcus

shallower groove

gray matter anatomy in cross section spinal cord

inner core of cord

white matter anatomy of cross section of the spinal cord

outside layer of cord

central canal

continuous with chambers in brain

central canal inclusions

contains CSF

runs length of spinal cord

gray matter inclusions

dorsal - posterior- horns

ventral-anterior- horns

lateral horns

gray commissure

dorsal roots

dorsal root ganglion

lateral horns- in gray matter

thoracic and superior lumbar segments

gray commissure

bridge connecting masses of gray matter

encloses central canal

neurons in gray matter

neurons with a cell body in gray matter are all multipolar neurons

dorsal horns

consist of interneurons

ventral horns

have some interneurons, mainly house cell bodies of somatic motor neurons

what fuses in the ventral roots of the spinal cord

axons exit cord via ventral rootlets which fuse together into the ventral roots of the spinal cord

what does the amount of ventral gray matter indicate

it indicates the amount of skeletal muscle innervation at that level - hence the enlargements of the spinal cord

lateral horns

consist of mainly cell bodies of autonomic motor neurons to visceral effectors

neurons exit cord through ventral root

dorsal roots

formed by afferent - sensory- fibers

fan out into dorsal rootlets before entering cord

dorsal root ganglion

location of cell bodies of the sensory neurons

white matter

composed of myelinated and nonmyelinated fibers

fibers run in three directions

arranged into white columns

white matter - fibers run in three different directions

ascending tracts

descending tracts

transverse tracts

white matter- arranged into white columns

dorsal - posterior- white columns

ventral - anterior- white columns

lateral white columns

ascending tracts

up to higher centers

descending tracts

down to the cord from brain or within cord to lower levels

transverse tracts - commissural fibers

from one side of the cord to the other

peripheral nervous system

provides links to and from the outside world

contains all structures outside the CNS

cranial nerves and spinal nerves

peripheral nervous system inclusions outside the CNS

such as sensory receptors, afferent and efferent nerves and their associated ganglia and motor endings

nerve classification

most nerves are mixed nerves

mixed nerves

motor-efferent- nerves

sensory afferent nerves

mixed nerves

contain both sensory and motor nerve fibers

transmits information both to and from CNS

motor-efferent- nerve

carry impulses away from the CNS only

sensory - afferent- nerves

carry impulses toward the CNS only

nerve fiber classification

somatic efferent

somatic afferent

visceral efferent

visceral afferent

somatic efferent

motor from the brain to your muscles

somatic afferent

sensory from muscle to brain

visceral efferent

motor from brain to organs

visceral afferent

sensory from organs to brain

nerve axon regeneration inclusions

CNS axons

PNS axons

Macrophages clean debris

nerve axon regeneration

axon filaments grow through regeneration tube

axon regenerates and new myelin sheath forms

mature neurons don’t divide as a rule -rule exceptions-

CNS axons

most don’t regenerate after injury

oligodendrocytes have growth inhibiting proteins

astrocytes form scar tissue

PNS axons

when injured can regenerate successfully

regeneration rate of 1.5mm/day

greater the distance between damaged ends, less chance of recovery

Degeneration

axon filaments and myelin sheath (Wallerian degeneration)

degeneration spreads down the axon

Spinal nerves

31 pairs of mixed nerve (each contain 1000’s of nerve fibers)

how are spinal nerves connected?

connected to spinal cord by ventral and dorsal roots

different types of spinal nerve

cervical spinal nerves

thoracic spinal nerves

lumbar spinal nerves

sacral spinal nerves

coccygeal nerves

cervical spinal nerves

C1-C8

thoracic spinal nerves

T1-T12

lumbar spinal nerves

L1-L5

sacral spinal nerves

S1-S5

coccygeal nerves

Co1

spinal nerve inclusions

ventral roots

dorsal roots

dorsal ramus

ventral ramus

how is a spinal nerve formed

roots merge distal to the dorsal root ganglion to form spinal nerve

where do spinal nerves exit

spinal nerves exit through intervertebral foramen and are very short (1-2cm)

where do spinal nerves branches

branches almost immediately into dorsal ramus and ventral ramus

plus, a tiny meningeal branch

ventral roots

carry motor information - away

dorsal roots

carry sensory information (swelling) - towards

dorsal ramus

supplies skin of back and deep back muscles

ventral ramus

supplies muscles and structures of upper and lower extremities and the lateral and ventral trunk

can for a plexus

T2-T12 spinal nerves don’t form a plexus

plexus

a network of nerves

rami communicants within spinal nerves

rami communicants branch off ventral ramus and join sympathetic chain ganglion

contain autonomic (visceral) nerve fibers

what happens to nerve fibers within a plexus

fibers crisscross so each branch contains fibers from several different spinal nerves

where do fibers from ventral ramus go within a plexus

fibers from ventral ramus go to body periphery via several routes

multiple spinal nerves innervate a single muscle

different types of plexuses

cervical plexus

brachial plexus

lumbar plexus

sacral plexus

cervical plexus

deep to sternocleidomastoid

formed by ventral rami of spinal nerve C1-C4(C5)

cutaneous branches of cervical plexus

skin over back of head, ear region, anterior neck, and shoulder region

motor branches of cervical plexus

muscles of the neck: trapezius and sternocleidomastoid

diaphragm: phrenic nerve - fiber from C3-C5

brachial plexus

located in neck and axilla

formed by ventral rami of spinal nerve C5-T1

often receives fibers from C4-T2

cutaneous branches of brachial plexus

skin over shoulder region and all parts of upper extremity

motor branches of brachial plexus

muscles of shoulder and upper extremity

lumbar plexus

located within psoas major

formed by ventral rami of spinal nerves L1-L4

cutaneous branches of lumbar plexus

skin over abdomen, buttock, external genitalia, many thigh regions, medial leg and foot

motor branches of lumbar plexus

muscles of the lower abdomen, median and anterior thigh regions

sacral plexus

located along the posterolateral wall of pelvis

forme by the ventral rami of spinal nerves L4-S4

lumbosacral trunk

L4+L5 contributions that join sacral plexus

cutaneous branches of sacral plexus

skin over gluteal region, external genitalia, and lower extremity

muscular branches of sacral plexus

muscles of the lower extremity

sciatic nerve

tibial nerve+ common fibular (peroneal) nerve

where does the sciatic nerve exit

exits pelvis by passing through the greater sciatic notch

where does the sciatic nerve pass through

passes deep to gluteus maximus midway between the ischial tuberosity and greater trochanter

where does the sciatic nerve end

sheath ends just proximal to the knee and the two nerves diverge

where do the nerves wrap in the sciatic nerve?

two separate nerves wrap in a common connective tissue sheath

thoracic spinal nerves

thoracic spinal nerve T2-T12 do not form a plexus

where do most fibers of T1 go?

most fibers of T1 enter brachial plexus

ventral rami = ?

intercostal nerves

where does T12 lie

T12 lies inferior to the 12th rib - subcostal nerve