Ch 14_lecture_presentation

© 2012 Pearson Education, Inc.

14The Nervous System: The Spinal Cord and Spinal Nerves

PowerPoint® Lecture Presentations prepared bySteven BassettSoutheast Community College Lincoln, Nebraska


Introduction

• The Central Nervous System (CNS) consists of:

• The spinal cord• Integrates and processes information• Can function with the brain• Can function independently of the brain

• The brain• Integrates and processes information• Can function with the spinal cord• Can function independently of the spinal cord


Gross Anatomy of the Spinal Cord

• Features of the Spinal Cord• 45 cm in length• Passes through the foramen magnum

• Extends from the brain to L1

• Consists of:• Cervical region• Thoracic region• Lumbar region• Sacral region• Coccygeal region


Figure 14.1a Gross Anatomy of the Spinal Cord

Cervical spinalnerves

Thoracicspinal

nerves

Lumbarspinal

nerves

Sacral spinalnerves

Coccygealnerve (Co1)

Filum terminale(in coccygeal ligament)

Cauda equina

Inferiortip ofspinal cord

Conusmedullaris

Lumbosacralenlargement

Posteriormedian sulcus

Cervicalenlargement

C1

C2

C3

C4

C5

C6

C7

C8

T1

T2

T3

T4

T5

T6

T7

T8

T9

T10

T11

T12

L1

L2

L3

L4

L5

S1

S2

S3

S4

S5

Superficial anatomy and orientation of the adult spinal cord. The numbers to the left identify the spinal nerves and indicate wherethe nerve roots leave the vertebral canal. The spinal cord, however,extends from the brain only to the level of vertebrae L1–L2.



• Features of the Spinal Cord• Transverse view

• White matter• Gray matter• Central canal• Dorsal root and ventral root: merge to form a spinal

nerve• Dorsal root is sensory: axons extend from the

soma within the dorsal root ganglion• Ventral root is motor


Figure 14.1d Gross Anatomy of the Spinal Cord

Inferior views of cross sectionsthrough representativesegments of the spinal cordshowing the arrangement ofgray and white matter

Posterior median sulcus

White matter

Graymatter

Anterior median fissure

Dorsal root

Spinalnerve

Ventralroot

Dorsal rootganglion

Centralcanal

C3

T3

L1

S2



• Features of the Spinal Nerves• Consist of:

• Sensory nerves (afferent nerves): transmit impulses toward the spinal cord

• Motor nerves (efferent nerves): transmit impulses away from the spinal cord


Spinal Meninges

Spinal meninges are specialized membranes that provide protection, physical stability, and shock absorption.Three meningeal layers:

The dura mater— tough and thickest, fibrous outermost layer The arachnoid mater— middle layer. Contains meshwork of elastic

fibers called arachnoid trabeculae. The Pia mater— innermost layer

Meningeal spaces: Epidural space: the space just outside the dura mater Subdural space: the space between dura and arachnoid layers. Subarachnoid space: the space between arachnoid and pia layers.

It contains CSF (Cerebro Spinal Fluid). This is space is used in spinal tap to obtain CSF.


Figure 14.2c The Spinal Cord and Spinal Meninges

Posterior view of the spinal cord showing themeningeal layers, superficial landmarks, anddistribution of gray and white matter

White matter

Ventral root

Dorsal root

Pia mater

Arachnoid mater

Gray matter

Spinal nerve

Dorsal root ganglion

Dura mater


Sectional Anatomy of the Spinal Cord

• Gray matter• Central canal• Consists of somas (cell bodies) surrounding

the central canal

• White matter• Consists of axons• Nerves are organized into tracts or columns• Located outside the gray matter area



Organization of Gray Matter Surrounds the central canal and contains cell bodies of neurons

and glial cells. This is the H shape mass in the center of spinal cord.

Groups of nuclei (sensory or motor) with specific functions Posterior gray horns contain somatic and visceral sensory

nuclei; this is the destination of dorsal root. Anterior gray horns contain somatic motor nuclei. This is the

origin of ventral root. Lateral gray horns contain visceral motor neurons. Gray commissures contain the axons of interneurons that cross

from one side of the cord to the other.


Figure 14.4b Sectional Organization of the Spinal Cord

The left half of this sectional view shows important anatomical landmarks; the right half indicates the functional organization of the gray matter in the anterior, lateral, and posterior gray horns.

Posteriorgray horn

Posterior graycommissure

Lateralgray horn

Anteriorgray horn

Anterior graycommissure

Anterior medianfissure

To ventralroot

Posterior median sulcusFrom dorsal root

Sensorynuclei

Motornuclei

Somatic

Somatic

Visceral

Visceral



Organization of White Matter Divided into 6 columns, which contain tracts

Ascending tracts relay information from spinal cord to brain

Descending tracts carry information from brain to spinal cord

The spinal nerves that extend distal to the conus medularis are collectively referred to as the cauda equina.


Figure 14.4c Sectional Organization of the Spinal Cord

The left half of this sectional view shows the major columns of white matter. The right half indicates the anatomical organization of sensory tracts in the posterior white column for comparison with the organization of motor nuclei in the anterior gray horn. Note that both sensory and motor components of the spinal cord have a definite regional organization.

Posterior whitecolumn (funiculus)

Anterior whitecolumn (funiculus)

Anterior whitecommissure

FlexorsExtensors

Lateralwhite

column(funiculus)

Leg

Hip

TrunkArm

Hand

Forearm

Arm

Shoulder

Trunk


Spinal Nerves

• There are 31 pairs of spinal nerves• 8 cervical nerves• 12 thoracic nerves• 5 lumbar nerves• 5 sacral nerves• 1 coccygeal nerve


Figure 14.1a Gross Anatomy of the Spinal Cord

Cervical spinalnerves

Thoracicspinal

nerves

Lumbarspinal

nerves

Sacral spinalnerves

Coccygealnerve (Co1)

Filum terminale(in coccygeal ligament)

Cauda equina

Inferiortip ofspinal cord

Conusmedullaris

Lumbosacralenlargement

Posteriormedian sulcus

Cervicalenlargement

C1

C2

C3

C4

C5

C6

C7

C8

T1

T2

T3

T4

T5

T6

T7

T8

T9

T10

T11

T12

L1

L2

L3

L4

L5

S1

S2

S3

S4

S5

Superficial anatomy and orientation of the adult spinal cord. The numbers to the left identify the spinal nerves and indicate wherethe nerve roots leave the vertebral canal. The spinal cord, however,extends from the brain only to the level of vertebrae L1–L2.


Spinal Nerves

• The covering of the nerve fibers from inside out is:• Endoneurium: covers the nerve fiber.• Perineurium: covers a bundle of nerve fibers

( Fascicle)• Epinerium: covers a group of fascicles.


Figure 14.5a Anatomy of a Peripheral Nerve

A typical peripheralnerve and its connectivetissue wrappings

Connective TissueLayers

Blood vessels

Fascicle

Schwann cell

Myelinatedaxon

Epineurium coveringperipheral nerve

Perineurium (aroundone fascicle)

Endoneurium


Figure 14.6a Peripheral Distribution of Spinal Nerves

Motor Commands

KEY

Postganglionic fibersto smooth muscles,glands, etc., of back

To skeletalmuscles of back

To skeletalmuscles of bodywall, limbs

Postganglionic fibers tosmooth muscles, glands, etc., of body wall, limbs

Postganglionic fibersto smooth muscles,glands, visceral organsin thoracic cavity

Preganglionic fibers tosympathetic gangliainnervating abdomino-pelvic viscera

Somatic motorcommands

Visceral motorcommands

Ramicommunicantes

Gray ramus(postganglionic)

White ramus(preganglionic)

Sympathetic nerve

Sympathetic ganglion

Spinal nerve

Ventral ramus

Dorsal ramus

Dorsal root ganglionDorsal

rootVisceralmotor

Somaticmotor

Ventralroot

The distribution of motor neurons in the spinal cord and motor fibers within the spinalnerve and its branches. Although the gray ramus is typically proximal to the white ramus,this simplified diagrammatic view makes it easier to follow the relationships betweenpreganglionic and postganglionic fibers.


Figure 14.6b Peripheral Distribution of Spinal Nerves

Sensory Information

KEY

From interoceptorsof visceral organs

From interoceptorsof back

From exteroceptors,proprioceptors of back

From exteroceptors,proprioceptors ofbody wall, limbs

From interoceptorsof body wall, limbs

Somaticsensations

Visceralsensations

Ventral ramus

Ramicommunicantes

Dorsalroot

ganglion

Dorsalroot

Somaticsensory

Visceralsensory

Ventralroot

A comparable view detailing the distribution of sensory neurons and sensory fibers

Dorsal ramus


Nerve Plexuses

• There are four nerve plexuses• Cervical plexus• Brachial plexus• Lumbar plexus• Sacral plexus

• Sometimes the lumbar and sacral are combined to form the lumbosacral plexus


Important brachial plexus nerves

• Musculocutaneous N.: • mainly for flexors of the arm like brachialis and brachioradialis.

• Radial N.: • mainly the extensors of the arm like triceps brachii and

ancuneous.• Ulnar N.:

• sense and motor of 5th and half of 4th finger and associated area of the hand.

• Median N.: • sense and motor of the rest of the hand and fingers.


Important lumbosacral plexus nerves• Sciatic nerve:

• posterior muscles of the thigh.• the largest nerve of the body.

• Femoral nerve:• Anterior muscles of the thigh.

• Obturator nerve:• Adductors of the thigh.


Figure 14.8 Peripheral Nerves and Nerve Plexuses

Lesser occipital nerveGreat auricular nerveTransverse cervical nerveSupraclavicular nerve

Phrenic nerve

Axillary nerve

Musculocutaneous nerve

Thoracic nerves

Radial nerve

Ulnar nerve

Median nerve

Iliohypogastricnerve

Ilioinguinal nerve

Genitofemoral nerve

Femoral nerve

Obturator nerve

Superior

InferiorGlutealnerves

Pudendal nerve

Sciatic nerve

Lateral femoral cutaneous nerve

Saphenous nerve

Common fibular nerve

Tibial nerve

Medial sural cutaneous nerve

Cervicalplexus

Brachialplexus

Lumbarplexus

Sacralplexus

C1C2C3C4C5C6C7C8T1T2

T3T4

T5

T6

T7

T8

T9

T10

T11

T12

L1

L2

L3

L4

L5

S1

S2

S3

S4

S5

Co1


Figure 14.9 The Cervical Plexus

Great auricular nerve

Geniohyoid muscle

Transversecervical nerveThyrohyoid muscleAnsa cervicalis

Omohyoid muscle

Phrenic nerve

Sternohyoid muscle

Sternothyroid muscle

Cranialnerves

Accessorynerve (N XI)

Hypoglossalnerve (N XII)

Lesser occipitalnerve

Nerve roots ofcervical plexus

Supraclavicularnerves

Clavicle

C1

C2

C3

C4

C5


Figure 14.10b The Brachial Plexus

Anterior view of the brachial plexus and upper limbshowing the peripheral distribution of major nerves

Anterior

Distribution ofcutaneous nerves

Median nerve

Ulnar nerve

Radial nerve

Palmar digital nerves

Superficial branch of ulnar nerve

Deep branch of ulnar nerve

Anterior interosseous nerve

Median nerve

Ulnar nerve

Deep radial nerve

Radial nerve

Median nerve

Ulnar nerve

Superficial branchof radial nerve

Lateral antebrachialcutaneous nerve

Musculocutaneousnerve

BRACHIALPLEXUS

Dorsal scapular nerve

Suprascapular nerve

Superior trunkMiddle trunk

Inferior trunk

C4

C5

C6

C7

C8

T1


Figure 14.10a The Brachial Plexus

Radial nerve

Ulnar nerve

Thoracodorsalnerve

Long thoracicnerve

INFERIORTRUNK

MIDDLETRUNK BRACHIAL

PLEXUS

The trunks and cords of the brachialplexus

KEY

Lateral cord

Posterior cord

Medial cord

C5

C6

C7

C8

T1

Median nerve

Medial antebrachialcutaneous nerve

Posterior brachialcutaneous nerve

Musculocutaneousnerve

Axillary nerve

Subscapular nerves

Medial pectoral nerve

Lateral pectoral nerve

Suprascapular nerve

SUPERIOR TRUNK

Nerve tosubclavius muscle

Dorsal scapularnerve

Firstrib

Roots (ventral rami)

Trunks

Divisions

Cords

Peripheral nerves


Figure 14.12a The Lumbar and Sacral Plexuses, Part I

The lumbar plexus, anterior view

Lumbosacraltrunk

LUMBARPLEXUS

T12

L1

L2

L3

L4

L5

Femoral branch

Genital branch

Femoral nerveObturator nerve

Branches ofgenitofemoral

nerve

Lateral femoralcutaneous nerve

Genitofemoral nerve

Ilioinguinal nerve

Iliohypogastric nerve

T12 subcostal nerve


Figure 14.12c The Lumbar and Sacral Plexuses, Part I

The lumbar and sacralplexuses, anterior view

Subcostal nerve

Iliohypogastric nerve

Ilioinguinal nerve

Genitofemoral nerve

Lateral femoralcutaneous nerve

Femoral nerve

Superior gluteal nerve

Inferior gluteal nerve

Pudendal nerve

Posterior femoralcutaneous nerve (cut)

Sciatic nerve

Saphenous nerve

Common fibularnerve

Superficial fibularnerve

Deep fibularnerve

Obturator nerve

Suralnerve

Suralnerve

Saphenousnerve

Saphenousnerve

Saphenousnerve

Suralnerve

Tibialnerve

Tibialnerve

Fibularnerve

Fibularnerve


Reflexes

A reflex is an immediate involuntary response to a specific stimulus.The neural “writing” of a single reflex is referred to as a reflex arc. Reflexes are classified according to:

Their development (innate and acquired) The site where information processing occurs (spinal

and cranial) The nature of resulting motor response (somatic and

visceral or autonomic) The complexity of the neural circuit (monosynaptic and

polysynaptic)


Figure 14.14 A Reflex Arc

Arrival of stimulus andactivation of receptor

Response by effector

Activation of asensory neuron

Activation of amotor neuron

Information processingin CNS

Stimulus

Effector

Receptor

REFLEXARC

Ventralroot

Dorsalroot

Sensationrelayed to

the brain bycollateral

KEYSensory neuron(stimulated)

Excitatoryinterneuron

Motor neuron(stimulated)


Figure 14.15 The Classification of Reflexes

Reflexes

development response

can be classified by

complexity of circuit processing site

• Processing in the spinal cord

• Processing in the brain

• One synapse

• Multiple synapses (two to several hundred)

• Genetically determined

• Learned • Control actions of smooth and cardiac muscles, glands

• Control skeletal muscle contractions• Include superficial and stretch reflexes

Innate Reflexes

Acquired Reflexes

Somatic Reflexes

Visceral (Autonomic) Reflexes

Spinal Reflexes

Cranial Reflexes

Monosynaptic

Polysynaptic


Reflexes

• Spinal reflexes can be:• Monosynaptic

• Involves a single segment of the spinal cord

• Polysynaptic • Integrates motor output from several spinal

segments


Figure 14.16 Neural Organization and Simple Reflexes

CENTRALNERVOUSSYSTEM

CENTRALNERVOUSSYSTEM

Motorneuron

Ganglion

Sensoryneuron

Sensoryreceptor(musclespindle)

Skeletal muscle

Circuit 1

A monosynaptic reflex circuit involves a peripheralsensory neuron and a central motor neuron. In thisexample, stimulation of the receptor will lead to areflexive contraction in a skeletal muscle.

A polysynaptic reflex circuit involves a sensory neuron,interneurons, and motor neurons. In this example, thestimulation of the receptor leads to the coordinatedcontractions of two different skeletal muscles.

Skeletal muscle 1

Skeletal muscle 2

Motorneurons

Circuit 2

Interneurons

Ganglion

Sensory neuron

Sensoryreceptor


Figure 14.17b Stretch Reflexes

KEY

Motor neuron(stimulated)

Sensory neuron(stimulated)

The patellar reflex is controlled by muscle spindles in the quadriceps group. Thestimulus is a reflex hammer striking the muscle tendon, stretching the spindlefibers. This results in a sudden increase in the activity of the sensory neurons,which synapse on spinal motor neurons. The response occurs upon the activationof motor units in the quadriceps group, which produces an immediate increase inmuscle tone and a reflexive kick.

Spinal cord

Stimulus

Stretch

Contraction

Effector

Receptor(musclespindle)

REFLEXARC

Response


Terminology • Hemiplegia:

• loss of sensation and motor fonction of one side of the body.

• Paraplegia: • loss of sensation and motor function of lower

limbs.

• Quadriplegia: • loss of sensation and motor function of upper

and lower limbs.

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