Chapter 14Chapter 14

The Spinal Cord and Spinal The Spinal Cord and Spinal NervesNerves

Spinal CordSpinal Cord Begins at foramen magnum extends down to Begins at foramen magnum extends down to

L1/L2.L1/L2. Contiguous with the medulla of the brain stem.Contiguous with the medulla of the brain stem. Passes through the vertebral foramen of all Passes through the vertebral foramen of all

vertebrae.vertebrae. Consists of cervical, thoracic and lumbar Consists of cervical, thoracic and lumbar

divisions same as vertebral column.divisions same as vertebral column. PNS - 31 paired spinal nerves one at each level PNS - 31 paired spinal nerves one at each level

C1-C8, T1-T12 and L1-L5, S1-S5 and Co-1.C1-C8, T1-T12 and L1-L5, S1-S5 and Co-1. Contains gray and white matter, however gray Contains gray and white matter, however gray

matter is central and white matter surrounds matter is central and white matter surrounds gray matter.gray matter.

At L1/L2 level cona medullaris tapers into cauda At L1/L2 level cona medullaris tapers into cauda equina equina

Spinal cord levels:Spinal cord levels:

C1-C8C1-C8

T1-T12T1-T12

L1-L5L1-L5

Cauda eqiunaCauda eqiuna

S1-S5 S1-S5

The MeningesThe Meninges

Consists of 3 layers around the brain and Consists of 3 layers around the brain and spinal cordspinal cord

1.1. Dura mater-Dura mater- tough outer fibrous connective tough outer fibrous connective tissue layer; two layers periosteal tissue layer; two layers periosteal (periosteum) and meningeal.(periosteum) and meningeal.

2.2. Arachnoid mater-Arachnoid mater- inner layer attached to inner layer attached to dura materdura mater - subarachnoid space between - subarachnoid space between arachnoid and pia arachnoid and pia mater filled with CSF.mater filled with CSF.

3.3. Pia mater-Pia mater- thin connective tissue layer thin connective tissue layer closely adhered to brain surface and spinal closely adhered to brain surface and spinal cord. Pia mater goes deep into the sulci cord. Pia mater goes deep into the sulci (grooves) of the brain.(grooves) of the brain.

Vertebral column (x-section)Vertebral column (x-section)

Spinal cord Spinal cord (x-section)(x-section)

Gray matter of spinal Gray matter of spinal cordcord

Shaped like a “butterfly” with central canal. Shaped like a “butterfly” with central canal. Wings contain anterior, and posterior horns.Wings contain anterior, and posterior horns. Thoracic and Lumbar levels also have lateral Thoracic and Lumbar levels also have lateral

horns.horns. Contains neuron cell bodies, unmyelinated Contains neuron cell bodies, unmyelinated

axons, dendrites and neuroglia.axons, dendrites and neuroglia. Gray commissure has fibers that Gray commissure has fibers that

communicate between right and left halves communicate between right and left halves of spinal cord.of spinal cord.

Gray matter of spinal Gray matter of spinal cordcord

White matter of spinal White matter of spinal cordcord

Contains myelinated ascending and Contains myelinated ascending and descending spinal tracts.descending spinal tracts.

Divided into columns or funiculi; each Divided into columns or funiculi; each column consists of tracts or fasciculi.column consists of tracts or fasciculi.

Also has white commissural tracts that cross Also has white commissural tracts that cross thru cordthru cord

Ascending tracts carry sensory information Ascending tracts carry sensory information from body to brainfrom body to brain

Descending tracts carry motor information Descending tracts carry motor information from brain to motor nervesfrom brain to motor nerves

Tracts named according to where they Tracts named according to where they originate and terminate e.g. Lateral originate and terminate e.g. Lateral spinothalamic tractspinothalamic tract

Tracts in white matter of Tracts in white matter of spinal cordspinal cord

Ascending spinal tractsAscending spinal tracts

Transmit sensory information from peripheral Transmit sensory information from peripheral body.body.

Receptors relay information to spinal cord via Receptors relay information to spinal cord via sensory nerve in dorsal root and may synapse in sensory nerve in dorsal root and may synapse in dorsal horn of gray matter, decussate or ascend dorsal horn of gray matter, decussate or ascend to a higher level. to a higher level.

Tracts are named according to their origin and Tracts are named according to their origin and destination, e.g. Lateral spinothalamic tracts; destination, e.g. Lateral spinothalamic tracts; anterior spinothalamic; posterior anterior spinothalamic; posterior spinalcerebellar tract, etc.spinalcerebellar tract, etc.

Ascending tractsAscending tractsThree neuron chain:Three neuron chain:First-order:First-order:Receptor to afferentReceptor to afferentnerve into spinal cord.nerve into spinal cord.

Second order: Second order: Interneuron toInterneuron to relay relaynucleus in thalamus.nucleus in thalamus.

Third order:Third order:Thalamus projectsThalamus projects

information to cortex.information to cortex.

Descending spinal tractsDescending spinal tracts

Take information from brain and descend in Take information from brain and descend in gray columns to appropriate level to a lower gray columns to appropriate level to a lower motor neuron.motor neuron.

Motor innervation is contralateral i.e. the left Motor innervation is contralateral i.e. the left side of the brain controls the right side of the side of the brain controls the right side of the body and vice versa. Cross over at pyramidal body and vice versa. Cross over at pyramidal decussation in medulla.decussation in medulla.

Tracts are named according to their origin and Tracts are named according to their origin and destination, e.g. Lateral corticospinal tract; destination, e.g. Lateral corticospinal tract; anterior corticospinal tract; reticulospinal tract, anterior corticospinal tract; reticulospinal tract, etc.etc.

Descending tractsDescending tractsTwo neuron chain:Two neuron chain:

Upper motor neuron:Upper motor neuron:From cortex or brainFrom cortex or brain

stem to LMNstem to LMN

Lower motor neuron:Lower motor neuron:From spinal cord to From spinal cord to

muscle or target organmuscle or target organ

Nerve structureNerve structure

Nerves are only in the peripheryNerves are only in the periphery Cable-like organs in PNS = cranial and spinal Cable-like organs in PNS = cranial and spinal

nervesnerves Consists of 100’s to 100,000’s of myelinated and Consists of 100’s to 100,000’s of myelinated and

unmyelinated axons (nerve fibers).unmyelinated axons (nerve fibers). EndoneuriumEndoneurium surrounds each axon (nerve fiber). surrounds each axon (nerve fiber). Axons are grouped into bundles of fasciclesAxons are grouped into bundles of fascicles PerineuriumPerineurium surrounds each fascicle surrounds each fascicle Epineurium Epineurium surrounds each nerve bundlesurrounds each nerve bundle Conduction is saltatory (i.e. jumps node to node) Conduction is saltatory (i.e. jumps node to node)

in myelinated nerves and continuous in in myelinated nerves and continuous in nonmyelinated.nonmyelinated.

Nerve anatomyNerve anatomy

Spinal NervesSpinal Nerves There are There are 31 pairs31 pairs of spinal nerves. Spinal nerves of spinal nerves. Spinal nerves

are are all mixed nerves (i.e. sensory and motor)all mixed nerves (i.e. sensory and motor).. Each forms by combining the dorsal and ventral Each forms by combining the dorsal and ventral roots at a segment of the spinal cord. roots at a segment of the spinal cord.

As spinal nerves exit vertebral foramen they As spinal nerves exit vertebral foramen they branch into a meningeal nerve and a dorsal and branch into a meningeal nerve and a dorsal and ventral ramus.ventral ramus.

The meningeal branch re-enters the spinal column The meningeal branch re-enters the spinal column to supply the meninges, spinal ligaments and to supply the meninges, spinal ligaments and vertebrae.vertebrae.

After leaving the spinal cord, After leaving the spinal cord, the ventral ramus of the ventral ramus of select nerves combine to form nerve plexuses that select nerves combine to form nerve plexuses that innervate the appendages and other parts of the innervate the appendages and other parts of the bodybody..

Dorsal and ventral ramus Dorsal and ventral ramus nervesnerves

Dorsal ramus nerves innervates the Dorsal ramus nerves innervates the ligaments, muscles and skin of the back.ligaments, muscles and skin of the back.

Ventral ramus nerves innervates the Ventral ramus nerves innervates the anterior and lateral muscles, skin and anterior and lateral muscles, skin and ligaments of the trunk. They also give ligaments of the trunk. They also give rise to the nerve plexuses that innervate rise to the nerve plexuses that innervate the appendages.the appendages.

Thoracic Thoracic levellevel

--Dorsal ramusDorsal ramus

-Ventral ramus-Ventral ramus

-Dorsal root-Dorsal root

ganglionganglion

-Sympathetic-Sympathetic

chain ganglionchain ganglion

--white and graywhite and gray

rami rami communicantecommunicantess

Spinal nerve plexuses from Spinal nerve plexuses from ventral ramus ventral ramus

- major nerves off of them.- major nerves off of them. Plexus= network of nerves Plexus= network of nerves Cervical plexusCervical plexus – – forms from C1 – C4forms from C1 – C4

-Phrenic nerve is off of cervical plexus -Phrenic nerve is off of cervical plexus C3-C5C3-C5

Brachial plexusBrachial plexus – – forms from C5 – C8, and forms from C5 – C8, and T1T1

-Axillary, radial, median, ulnar nerves-Axillary, radial, median, ulnar nerves Lumbar plexusLumbar plexus – – forms from L1 - L4forms from L1 - L4

-Femoral and obturator nerves-Femoral and obturator nerves Sacral plexusSacral plexus – – forms from L4 – S4 forms from L4 – S4

-Sciatic nerve-Sciatic nerve

Spinal nerveSpinal nerve

plexusesplexuses

Cervical plexusCervical plexus

-C1- C5-C1- C5 Phrenic nervePhrenic nerve

-C3- C5-C3- C5

Brachial Brachial plexusplexus

-C5-C8 & T1-C5-C8 & T1 Axillary Axillary

nervenerve

- C5 & C6- C5 & C6 Median Median

nervenerve

- C5-C8 & T1- C5-C8 & T1 Radial nerveRadial nerve

- C5-C8 & T1- C5-C8 & T1 Ulnar nerveUlnar nerve

- C8 & T1 - C8 & T1

Lumbar Lumbar plexusplexus

L1- L4L1- L4 Femoral Femoral

nervenerve

-L2-L4-L2-L4 Obturator Obturator

nervenerve

-L2-L4-L2-L4

Sacral Sacral plexusplexus

-L4- S4-L4- S4 Sciatic nerveSciatic nerve

-Tibial n. L4--Tibial n. L4-S3S3

-Comn -Comn fibularfibular

-L4-S2-L4-S2

DERMATOMES DERMATOMES The area of skin that carries sensory The area of skin that carries sensory

information to the CNS from all of the spinal information to the CNS from all of the spinal nerves (except C1) and cranial nerve V (facial).nerves (except C1) and cranial nerve V (facial).

Entire body surface is supplied by a peripheral Entire body surface is supplied by a peripheral nerve.nerve.

Knowing the distribution of these nerves is very Knowing the distribution of these nerves is very helpful diagnostically in determining whether a helpful diagnostically in determining whether a nerve is affected at the central or peripheral nerve is affected at the central or peripheral level and at what level the injury may be.level and at what level the injury may be.

Reflex Reflex ArcArc Consists of 1. sensory receptor, 2. Consists of 1. sensory receptor, 2.

afferent nerve, 3. interneuron, 4. efferent afferent nerve, 3. interneuron, 4. efferent nerve and 5. an effector organ (muscle or nerve and 5. an effector organ (muscle or gland).gland).

Occurs at the spinal levelOccurs at the spinal level

Mono and Polysynaptic Mono and Polysynaptic Reflexes Reflexes

Receptors: Classification by Receptors: Classification by locationlocation

1.1. Exteroceptors-Exteroceptors- receptors sensitive to receptors sensitive to changes outside of body. Are found on changes outside of body. Are found on or near the body surface: pain, pressure, or near the body surface: pain, pressure, touch, temperature and special sense touch, temperature and special sense organs (eye, ear, nose, mouth).organs (eye, ear, nose, mouth).

2.2. Interoceptors- Interoceptors- visceroceptors receive visceroceptors receive stimuli from viscera; stretch, stimuli from viscera; stretch, temperature, chemical, taste.temperature, chemical, taste.

3.3. Proprioceptors-Proprioceptors- located in skeletal located in skeletal muscles and joints, tendons, ligaments; muscles and joints, tendons, ligaments; perceive stretch in these organsperceive stretch in these organs

ProprioceptorsProprioceptors

Encapsulated Encapsulated receptors that receptors that monitor stretch monitor stretch in muscles and in muscles and tendons.tendons.

Ex. Muscle Ex. Muscle spindlesspindles

Extrafusal Extrafusal fibersfibers

IntrafusalIntrafusal

Classification by Classification by StimulusStimulus

1.1. Mechanoreceptors- respond to Mechanoreceptors- respond to mechanical forces: touch, pressure, mechanical forces: touch, pressure, stretch, vibration, and itch.stretch, vibration, and itch.

2.2. Thermoreceptors- respond to Thermoreceptors- respond to temperature changestemperature changes

3.3. Chemoreceptors- respond to chemicals Chemoreceptors- respond to chemicals in solution and blood chemistry.in solution and blood chemistry.

4.4. Photoreceptors- respond to changes in Photoreceptors- respond to changes in light-eyelight-eye

5.5. Nociceptors- respond to pain and Nociceptors- respond to pain and harmful stimuli leading to pain.harmful stimuli leading to pain.

Classification by Classification by StructureStructure

1.1. Free nerve endings- in all tissues of body; Free nerve endings- in all tissues of body; abundant in epithelial and connective tissue.abundant in epithelial and connective tissue.

- respond to pain, temperature, itch and light - respond to pain, temperature, itch and light pressurepressure

Ex.- Merckels discs, hair follicle receptorsEx.- Merckels discs, hair follicle receptors

2.2. Encapsulated nerve endings- enclosed in a Encapsulated nerve endings- enclosed in a capsule of connective tissue; vary in shape capsule of connective tissue; vary in shape and distribution.and distribution.

Ex.- Meissner’s, Pacinian and Ruffini’s Ex.- Meissner’s, Pacinian and Ruffini’s corpusclescorpuscles

Reflex ArcsReflex Arcs May be unilateral or contralateralMay be unilateral or contralateral Unilateral knee jerk: Flexors contract Unilateral knee jerk: Flexors contract

extensor relaxextensor relax

Reflex ArcsReflex Arcs Unilateral: Excess tension on tendon Unilateral: Excess tension on tendon

causes inhibition of flexor and causes inhibition of flexor and stimulation of extensorstimulation of extensor

Crossed-Extensor reflex Crossed-Extensor reflex arcarc Pain to one foot causes retraction of Pain to one foot causes retraction of

injured foot and extension of opposite injured foot and extension of opposite footfoot

PNS to CNSPNS to CNS