The Nervous System The Nervous System II:II:

The Spinal Cord, Spinal The Spinal Cord, Spinal Nerves and ReflexesNerves and Reflexes

Anatomy & Physiology Chapter 13

Functions of the Spinal Functions of the Spinal CordCord

conduction

◦Information highway passing information between the PNS and the brain

◦bundles of fibers passing information up and down spinal cord, connecting different levels of the trunk with each other and with the brain

reflexes

◦involuntary, stereotyped responses to stimuli

withdrawal of hand from pain

◦involves brain, spinal cord and peripheral nerves

Anatomy of The Spinal Anatomy of The Spinal CordCord

spinal cord – cylinder of nervous tissue that arises from the brainstem at the foramen magnum of the skull

◦About as thick as your finger

◦passes through the vertebral canal

◦occupies the upper two-thirds of the vertebral canal inferior margin ends at L1 or a little beyond

Surface AnatomySurface Anatomy◦segment – part of the spinal cord

supplied by each pair of spinal nerves

◦spinal cord divided into the cervical, thoracic, lumbar, and sacral regions

◦gives rise to 31 pair of spinal nerves first pair passes between the skull and first

vertebra rest pass through intervertebral foramina

Enlargements of the Spinal Cord◦Caused by:

Amount of gray matter in segment

Involvement with sensory and motor nerves of limbs

◦Cervical enlargement Nerves of shoulders and upper

limbs

◦Lumbar enlargement Nerves of pelvis and lower limbs

Cervical spinalnerves

Cervicalenlargement

Thoracic spinalnerves

Lumbar enlargement

Conus medullaris

Interior tip of spinal cord

Cauda equina

Filum terminale

Lumbar spinal

nerves

Sacral spinalnerves

Coccygealnerve (Co1)

Anatomy of the Spinal Anatomy of the Spinal CordCord

Anatomy of the Spinal Cord Anatomy of the Spinal Cord

◦The distal end Conus medullaris

Thin, conical spinal cord below lumbar

enlargement

Filum terminale Thin thread of fibrous tissue at end of conus

medullaris

Attaches to coccygeal ligament

Cauda equina Nerve roots extending below conus medullaris

Cervical spinalnerves

Cervicalenlargement

Posterior median sulcus

Thoracic spinalnerves

Lumbar enlargement

Conus medullaris

Interior tip of spinal cord

Cauda equina

Filum terminale

Lumbar spinal

nerves

Sacral spinalnerves

Coccygealnerve (Co1)

Anatomy of The Spinal CordAnatomy of The Spinal Cord

The Spinal MeningesThe Spinal Meninges

Specialized membranes isolate spinal

cord from surroundings

Functions of the spinal meninges

include:

◦Protecting spinal cord

◦Carrying blood supply

◦Continuous with cranial meninges

Meningitis

◦Viral or bacterial infection of meninges

Meninges of the Spinal CordMeninges of the Spinal Cordmeninges – three

fibrous connective tissue membranes that enclose the brain and spinal cord

separate soft tissue of central nervous system from bones of cranium and vertebral canal

from superficial to deep:◦dura mater – outer layer◦arachnoid mater –

middle layer◦and pia mater – inner

layer

Meninges:

Dura mater

Arachnoid mater

Pia mater

The Dura MaterThe Dura MaterTough and fibrous

◦Cranially Fuses with periosteum of occipital bone Is continuous with cranial dura mater

◦Caudally Tapers to dense cord of collagen fibers Joins filum terminale in coccygeal ligament

Epidural Space Between spinal dura mater and walls of

vertebral canal

Contains loose connective and adipose tissue

Anesthetic injection site

The Arachnoid MaterThe Arachnoid Mater◦Middle meningeal layer

◦Subdural space Between arachnoid mater and dura mater

◦Subarachnoid space Between arachnoid mater and pia mater

Contains collagen/elastin fiber network

Filled with cerebrospinal fluid (CSF)

◦Cerebrospinal Fluid (CSF) Carries dissolved gases, nutrients, and wastes

Lumbar puncture or spinal tap withdraws

CSF

The Pia MaterThe Pia MaterIs the innermost meningeal layerIs a mesh of collagen and elastic

fibersIs bound to underlying neural tissue

Paired denticulate ligaments

Extend from pia mater to dura mater

Stabilize side-to-side movement

Blood vessels

Along surface of spinal pia mater

Within subarachnoid space

Spinal cord

Anterior median fissure

Pia mater

Denticulateligaments

Dorsal root

Ventral root, formed byseveral “rootlets” fromone cervical segment

Arachnoid mater(reflected)

Dura mater (reflected)

Spinal blood vessel

Gray Matter and White Gray Matter and White MatterMatter

◦White matter

Is superficial

Contains myelinated and unmyelinated axons (myelin

provides whitish appearance)

◦Gray matter

Surrounds central canal of spinal cord

Contains neuron cell bodies, neuroglia, unmyelinated

axons

Has projections (anterior, posterior and lateral gray

horns)

Organization of Gray MatterOrganization of Gray Matter

The gray horns

Dorsal (posterior) horns

Contains cell bodies (nuclei) of sensory

neurons

Connect to peripheral receptors

Ventral (anterior) horns

Contains cell bodies (nuclei) of motor neurons

Connect to peripheral effectors

Lateral horns contain visceral motor (ANS) nuclei are in thoracic and lumbar segments

Gray matter: White matter:

Anterior median fissure

Posterior horn

Lateral columnGray commissure

Anterior column

Central canal

Posterior column

Posterior root ganglion

Spinal nerve

Lateral horn

Anterior horn

Pia materArachnoid mater

Meninges:

Dura mater (dural sheath)

Posterior root of spinal nerve

Posteriormedian sulcus

Anterior rootof spinal nerve

Organization of Gray MatterOrganization of Gray Matter

Gray commissure

Axons that cross from one side of cord to the

other before reaching gray matter

Spinal Nerve RootsSpinal Nerve Roots

Two branches of spinal nerves1. Ventral (anterior) root

Contains axons of motor neurons

2. Dorsal (posterior) root Contains axons of sensory neurons

◦ Dorsal (posterior) root ganglia

Contain cell bodies of sensory neurons

Spinal NervesSpinal Nerves

The Spinal Nerve

◦Each side of spine

Dorsal and ventral roots join

To form a spinal nerve

◦Mixed Nerves

Carry both afferent (sensory) and efferent

(motor) fibers

Fat in epidural space

Spinous process of vertebra

Spinal nerve

Posterior root ganglion

Spinal cord

Denticulate ligament

Subarachnoid space

Posterior

Anterior

Meninges: Dura mater (dural sheath)Arachnoid mater

Pia mater

Vertebral body

Spinal Cord, Nerve roots and Spinal Cord, Nerve roots and NervesNerves

13-21

Spinal NervesSpinal Nerves

31 pairs of spinal nerves (mixed

nerves)◦ 8 cervical (C1 – C8) C1 between skull

and atlas others exiting at intervertebral foramen

◦12 thoracic (T1 – T12)

◦ 5 lumbar (L1 – L5)

◦ 5 sacral (S1 – S5)

◦ 1 coccygeal (Co)

Organization of White Organization of White MatterMatter

Anterior, Posterior and Lateral Columns

◦Tracts In white columns

Bundles of axons

Relay same information in same direction

Ascending tracts Carry information to brain

Descending tracts Carry motor commands to spinal cord

13-23

Damage to Spinal CordDamage to Spinal Cordaccidents damage the spinal cord of

thousands of people every year

◦ paraplegia - paralysis of lower limbs

◦ quadriplegia – paralysis of all four limbs

◦ respiratory paralysis, loss of sensation or motor control

◦ disorders of bladder, bowel and sexual function

damage to spinal cord from strokes or other brain injuries

◦ hemiplegia – paralysis of one side of the body only

C2C3

C2

C3 C3

C2C3

N V

C5

C5

C4

C4

C6

C7C6

T2

T1T2T3T4

T5

T6

T7

T8T9

T10

T11

T12

T2T3

T4T5T6T7T8T9T10T11T12L1L2

L3L4L5

L1

T1

T2

C8

C7

C8

L2

L3

L4

T1L1

L2

L5

S5

S

S1

S2

4S3S2

S1

L3

L4

L5

ANTERIOR POSTERIOR

DermatomDermatomes es

A dermatome is a region of the skin supplied by a single spinal nerve.

Peripheral NeuropathyPeripheral Neuropathy

Regional loss of sensory or motor

function

Due to trauma or compression

13-26

ShinglesShingleschickenpox - common disease of early childhood

◦ caused by varicella-zoster virus◦ produces itchy rash that clears up without complications

virus remains for life in the posterior root ganglia◦ kept in check by the immune system

shingles (herpes zoster) – localized disease caused by the virus traveling down the sensory nerves by fast axonal transport when immune system is compromised◦ common after age of 50◦ painful trail of skin discoloration and fluid-filled vesicles along

path of nerve◦ usually in chest and waist on one side of the body◦ pain and itching◦ childhood chicken pox vaccinations reduce the risk of shingles

later in life

ShinglesShingles

Poliomyelitis Poliomyelitis Polio and ALS - diseases that cause

destruction of motor neurons and production of skeletal muscle atrophy from lack of innervation

caused by the poliovirus

destroys motor neurons in brainstem and anterior horn of spinal cord

signs of polio include muscle pain, weakness, and loss of some reflexes

◦followed by paralysis, muscular atrophy, and respiratory arrest

virus spreads by fecal contamination of water

13-29

Amyotrophic Lateral Amyotrophic Lateral Scerosis (ALS)Scerosis (ALS)amyotrophic lateral sclerosis (ALS) –

Lou Gehrig disease◦destruction of motor neurons and

muscular atrophy◦also sclerosis (scarring) of lateral regions

of the spinal cord◦astrocytes fail to reabsorb the

neurotransmitter glutamate from the tissue fluid accumulate to toxic levels

◦early signs – muscular weakness, difficulty speaking, swallowing, and use of hands

◦sensory and intellectual functions remain unaffected

Spinal Nerves and Spinal Nerves and PlexusesPlexusesNerve Plexuses

◦Complex, interwoven networks of nerve

fibers

◦Formed from blended fibers of ventral

rami of adjacent spinal nerves

◦Control skeletal muscles of the neck and

limbs

Spinal Nerves and Spinal Nerves and PlexusesPlexusesThe Four Major Plexuses of Ventral

Rami

1. Cervical plexus

2. Brachial plexus

3. Lumbar plexus

4. Sacral plexus

Nerve PlexusesNerve Plexuses

Cervicalplexus

Brachialplexus

Lesser occipital nerveGreat auricular nerveTransverse cervical nerve

Supraclavicular nerve

Phrenic nerve

Axillary nerve

Musculocutaneousnerve

Thoracic nerves

C1C2C3C4C5C6C7C8T1T2

T3T4

T5

T6

T7

T8

T9

T10

T11

Nerve PlexusesNerve Plexuses

Lumbarplexus

Sacralplexus

Radial nerve

Ulnar nerve

Median nerve

Iliohypogastric nerve

Ilioinguinalnerve

Lateral femoralcutaneous nerve

Genitofemoralnerve

Femoral nerve

Obturator nerve

Gluteal nervesSuperior

Inferior

Pudendal nerve

Saphenous nerve

Sciatic nerve

T12

L1

L2

L3

L4

L5

S1

S2

S3

S4

S5

Co1

The Cervical PlexusThe Cervical Plexus

Includes ventral rami of spinal

nerves C1–C5

Innervates neck, thoracic cavity,

diaphragmatic muscles

Major nerve

◦Phrenic nerve (controls diaphragm)

The Brachial PlexusThe Brachial PlexusIncludes ventral rami of spinal nerves

C5–T1

Innervates pectoral girdle and upper limbs

Major nerves◦Musculocutaneous nerve (lateral cord)

◦Median nerve (lateral and medial cords)

◦Ulnar nerve (medial cord)

◦Axillary nerve (posterior cord)

◦Radial nerve (posterior cord)

The Brachial PlexusThe Brachial PlexusTrunks of

Brachial Plexus

SuperiorMiddleInferior

Dorsal scapular nerveSuprascapular nerve

Musculocutaneous nerve

Median nerve

Ulnar nerveRadial nerve

Deep radial nerve

Ulnar nerve

Median nerve

Palmar digitalnerves

Lateral antebrachialcutaneous nerve

Superficial branchof radial nerve

C5

Spinal Nerves FormingBrachial Plexus

Major nerves originating at the right brachial plexus, anterior view

C6C7C8T1

C4

The Lumbar PlexusThe Lumbar Plexus

Includes ventral rami of spinal

nerves T12–L4

Major nerves

◦Genitofemoral nerve

◦Lateral femoral cutaneous nerve

◦Femoral nerve

The Sacral PlexusThe Sacral Plexus

Includes ventral rami of spinal nerves L4–S4

Major nerves◦ Pudendal nerve

◦ Sciatic nerve

Two branches of the sciatic nerve1.Fibular nerve

2.Tibial nerve

The Sacral PlexusesThe Sacral Plexuses

Nerves of theSacral Plexus

Lumbosacral trunk

Superior gluteal

Inferior gluteal

Sciatic

Posterior femoralcutaneous

Pudendal

Spinal NervesForming the

Sacral Plexus

L4 nerveL5 nerve

S1 nerve

S2 nerve

S3 nerve

S4 nerveS5

Co1

Sacral plexus, anterior view

Reflexes Reflexes rapid, automatic responses to

specific stimuli◦Show little variability

Preserve homeostasis by making rapid adjustments in functions of organs or organ systems

In neural reflexes:◦Sensory fibers carry information from

peripheral receptors to integration center◦Motor fibers carry motor commands to

peripheral effectorsReflex arc

◦“Wiring” of a single reflex from receptor to effector

Reflex ArcReflex Arc Components of a reflex arc (neural path)

1. Receptor—site of stimulus action2. Sensory neuron—transmits afferent

impulses to the CNS3. Interneuron – (Integration center) within

the CNS4. Motor neuron—conducts efferent impulses

from the integration center to an effector organ

5. Effector—muscle fiber or gland cell that responds to the efferent impulses by contracting or secreting

Receptor

Sensory neuron

Integration center

Motor neuron

Effector

Spinal cord(in cross section)

Interneuron

Stimulus

Skin

1

2

3

4

5

Reflex ArcReflex Arc

Numbers show the sequence of impulses through the spinal cord (solid arrows). Contraction of the biceps brachii results in flexion of the arm at the elbow.

  ZOOMING IN • Is this a somatic or an

autonomic reflex arc? What type of neuron is located between the sensory and motor neuron in the CNS?

Typical Reflex Arc Typical Reflex Arc

The Flexor (Withdrawal) The Flexor (Withdrawal) ReflexesReflexes

flexor reflex – the quick contraction of flexor muscles resulting in the withdrawal of a limb from an injurious stimulus

requires contraction of the flexors and relaxation of the extensors in that limb

polysynaptic reflex arc – pathway in which signals travel over many synapses on their way back to the muscle

Contralateralmotor neurons

to extensorexcited

2

35

6

4

1

+

+

++

+

++

+

+

+

Sensory neuronactivates multiple

interneurons

Ipsilateral motorneurons to flexor

excited

Ipsilateral flexorcontracts

Contralateralextensorcontracts

Stepping on glassstimulates pain receptors

in right foot

Extension of left leg(crossed extension reflex)

withdrawal of right leg(flexor reflex)

A Flexor ReflexA Flexor Reflex

Distribution within gray horns to other segments of the spinal cord

Painfulstimulus

Flexorsstimulated

KEYExtensorsinhibited Sensory neuron

(stimulated)

Excitatoryinterneuron

Motor neuron(stimulated)

Motor neuron(inhibited)

Inhibitoryinterneuron

The Babinski ReflexesThe Babinski Reflexes

The plantar reflex(negative Babinski

reflex), a curling of thetoes, is seen in healthy

adults.

The Babinski sign (positiveBabinski reflex) occurs in

the absence of descendinginhibition. It is normal in

infants, but pathological inadults.

Medical Procedures Medical Procedures Involving theInvolving theSpinal CordSpinal CordLumbar puncture (spinal tap)

◦Cerebrospinal fluid (CSF) removed for testing

Drug administration

◦Anesthetic (an epidural)

◦Pain medication

End of PresentationEnd of Presentation