© 2012 Pearson Education, Inc. Figure 13-1 An Overview of Chapters 13 and 14 CHAPTER 14: The Brain...

© 2012 Pearson Education, Inc.

Figure 13-1 An Overview of Chapters 13 and 14

CHAPTER 14: The Brain

Sensoryreceptors

Sensory input over cranial nerves Reflex

centersin brain

Motor output overcranial nerves

Effectors

Muscles

CHAPTER 13: The Spinal Cord

Sensoryreceptors

Sensory input over spinal nerves

Reflexcentersin spinal

cord

Motor output overspinal nerves

Glands

Adipose tissue


An Introduction to the Spinal Cord, Spinal Nerves, and Spinal Reflexes

• Spinal Reflexes

• Rapid, automatic nerve responses triggered by

specific stimuli

• Controlled by spinal cord alone, not the brain


13-2 Spinal Cord

• Roots

• Two branches of spinal nerves

1. Ventral root

• Contains axons of motor neurons

2. Dorsal root

• Contains axons of sensory neurons

• Dorsal root ganglia

• Contain cell bodies of sensory neurons


13-2 Spinal Cord• 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


Figure 13-3a The Spinal Cord and Spinal Meninges

White matter

Ventral root

Dorsal root

A posterior view of thespinal cord, showing the meningeal layers,superficial landmarks,and distribution of graymatter and white matter

Gray matter

Dorsal rootganglion

Spinal nerve

Meninges

Pia mater

Arachnoid mater

Dura mater


Figure 13-3b The Spinal Cord and Spinal Meninges

Subarachnoidspace

Ramicommunicantes

Vertebralbody

ANTERIOR

Denticulateligament

POSTERIOR

Spinal cordAdipose tissue

in epidural spaceDorsal root

ganglion

A sectional viewthrough the spinalcord and meninges,showing theperipheraldistribution ofspinal nerves

Dorsal ramus

Ventral ramus

Ventral rootof spinalnerve

Autonomic(sympathetic)ganglion

Dura materArachnoid mater

Pia mater

Meninges


13-2 Spinal Cord

• The 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


13-2 Spinal Cord

• The Interlayer Spaces of

Arachnoid Mater

• Cerebrospinal Fluid (CSF)

•Carries dissolved gases,

nutrients, and wastes

•Lumbar puncture or spinal

tap withdraws CSF


13-3 Gray Matter and White Matter

• Sectional Anatomy of the Spinal

Cord

• White matter

• Is superficial

•Contains myelinated and unmyelinated

axons

• Gray matter

• Surrounds central canal of spinal cord

•Contains neuron cell bodies, neuroglia,

unmyelinated axons

•Has projections (gray horns)



• Organization of Gray Matter

• The gray horns

• Posterior gray horns contain somatic and visceral sensory nuclei

•Anterior gray horns contain somatic motor nuclei

• Lateral gray horns are in thoracic and lumbar segments; contain visceral motor nuclei

• Gray commissures

• Axons that cross from one side of cord to the other before reaching gray matter



• Organization of Gray Matter

• The cell bodies of neurons form functional groups

called nuclei

• Sensory nuclei

•Dorsal (posterior)

•Connect to peripheral receptors

•Motor nuclei

• Ventral (anterior)

•Connect to peripheral effectors



• Control and Location

• Sensory or motor nucleus location within the gray

matter determines which body part it controls



• Organization of White Matter

• Tracts or fasciculi

• 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


Figure 13-5a The Sectional Organization of the Spinal Cord

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

Posterior white column

Dorsal rootganglion

Lateralwhite

column

Posteriorgray horn

Lateralgray horn

Anteriorgray horn

Anterior white column


Figure 13-5a The Sectional Organization of the Spinal Cord

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

Posterior median sulcus

Posterior graycommissure

Anterior gray commissureAnterior white commissureAnterior median fissure

Somatic

Visceral

Visceral

Somatic

Sensory nuclei

Motor nuclei

Ventral root

The cell bodies of neurons in the gray matter of the spinal cord are organized into functional groupscalled nuclei.

Functional Organizationof Gray Matter


13-4 Spinal Nerves and Plexuses

• Peripheral Distribution of Spinal Nerves

• Spinal nerves

• Form lateral to intervertebral foramen

•Where dorsal and ventral roots unite

• Then branch and form pathways to destination




• Motor nerves

• The first branch

•White ramus

•Carries visceral motor fibers to sympathetic ganglion of autonomic nervous system

•Gray ramus

•Unmyelinated nerves

•Return from sympathetic ganglion to rejoin spinal nerve




• Motor nerves

• Dorsal and ventral rami

• Dorsal ramus

• Contains somatic and visceral motor fibers

• Innervates the back

• Ventral ramus

• Larger branch

• Innervates ventrolateral structures and limbs


Figure 13-7 Peripheral Distribution of Spinal Nerves

The spinal nerve forms just lateral to the intervertebral foramen, where the dorsaland ventral roots unite.

The ventral root of eachspinal nerve contains theaxons of somatic motor andvisceral motor neurons.

Visceral motor nuclei

Somatic motor nuclei

Somatic motor commandsVisceral motor commands

Postganglionic fibers to smooth muscles, glands, visceral organs in thoracic cavity

Preganglionic fibers to sympathetic ganglia innervatingabdominopelvic viscera

To skeletalmuscles ofback

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

The dorsal ramus containssomatic motor and visceral motorfibers that innervate the skin andskeletal muscles of the back.

The axons in the relativelylarge ventral ramus supplythe ventrolateral bodysurface, structures in thebody wall, and the limbs.

To skeletalmuscles of bodywall, limbs

Postganglionic fibersto smooth muscles,glands, etc., of bodywall, limbs

The white ramus is the first branch from the spinal nerve and carries visceral motor fibers to a nearby sympathetic ganglion. Because these preganglionic axons are myelinated, this branch has a light color and is therefore known as the white ramus.

The gray ramus contains postganglionicfibers that innervate glands and smoothmuscles in the body wall or limbs. These fibersare unmyelinated and have a dark gray color.

A sympathetic nervecontains preganglionicand postganglionicfibers innervatingstructures in thethoracic cavity.

Dorsal rootDorsal root

ganglion

Ramicommunicantes

Sympatheticganglion




• Sensory nerves

• In addition to motor impulses

•Dorsal, ventral, and white rami also carry sensory

information

• Dermatomes

• Bilateral region of skin

•Monitored by specific pair of spinal nerves


Figure 13-7 Peripheral Distribution of Spinal Nerves

From interoceptorsof back

The dorsal ramus carries sensory information from the skin and skeletal muscles of the back.

The ventral ramus carries sensory information from the ventrolateral body surface, structures in the body wall, and the limbs.

From exteroceptors,proprioceptors ofbody wall, limbs

From interoceptorsof body wall, limbs

SomaticsensationsVisceralsensations

From exteroceptors,proprioceptors of back The dorsal root of each

spinal nerve carriessensory information tothe spinal cord.

The sympathetic nervecarries sensory informationfrom the visceral organs.

From interoceptorsof visceral organs

Somaticsensory nuclei

Ramicommunicantes

Ventralroot

Visceralsensory nuclei

Dorsalroot

ganglion


Figure 13-8 DermatomesC2C3

C2

C3 C3

C2C3

N V

C5

C5

C4

C4

C6

C7C6

T2

T1

T2T3

T4

T5

T6

T7

T8

T9

T10

T11

T12

T2

T3

T4T5T6T7T8

T9

T10T11

T12L1L2

L3L4

L5

L1

T1

T2

C8

C7

C8

L2

L3

L4

T1L1

L2

L5

S5

S

S1

S2

4S3S2

S1

L3

L4

L5

ANTERIOR POSTERIOR



• Peripheral

Neuropathy

• Regional loss of

sensory or

motor function

• Due to trauma

or compression


Figure 13-9 Shingles


13-5 Neuronal Pools

• Functional Organization of Neurons

• Sensory neurons

• About 10 million

• Deliver information to CNS

• Motor neurons

• About 1/2 million

• Deliver commands to peripheral effectors

• Interneurons

• About 20 billion

• Interpret, plan, and coordinate signals in and out


13-6 Reflexes

• Reflexes

• Automatic responses coordinated within spinal cord

• Through interconnected sensory neurons, motor

neurons, and interneurons

• Produce simple and complex reflexes


13-6 Reflexes

• Neural Reflexes

• Rapid, automatic responses to specific stimuli

• Basic building blocks of neural function

• One neural reflex produces one motor response

• Reflex arc

• The wiring of a single reflex

• Beginning at receptor

• Ending at peripheral effector

•Generally opposes original stimulus (negative feedback)


13-6 Reflexes

• Five Steps in a Neural Reflex

• Step 1: Arrival of stimulus, activation of receptor

• Physical or chemical changes

• Step 2: Activation of sensory neuron

• Graded depolarization

• Step 3: Information processing by postsynaptic cell

• Triggered by neurotransmitters

• Step 4: Activation of motor neuron

• Action potential

• Step 5: Response of peripheral effector

• Triggered by neurotransmitters


Figure 13-15 Events in a Neural Reflex

Arrival of stimulus andactivation of receptor

Activation of asensory neuron

Dorsalroot

Sensationrelayed to thebrain by axon

collaterals

Ventralroot

Receptor

Effector

Stimulus

Response by effector

REFLEXARC

Activation of a motor neuron

Information processingin the CNS

KEYSensory neuron(stimulated)

Excitatoryinterneuron

Motor neuron(stimulated)


13-6 Reflexes

• Four Classifications of Reflexes

1. By early development

2. By type of motor response

3. By complexity of neural circuit

4. By site of information processing


13-6 Reflexes

• Development of Reflexes

• Innate reflexes

• Basic neural reflexes

• Formed before birth

• Acquired reflexes

•Rapid, automatic

• Learned motor patterns


13-6 Reflexes

• Motor Response

• Nature of resulting motor response

• Somatic reflexes

• Involuntary control of nervous system

• Superficial reflexes of skin, mucous membranes

• Stretch or deep tendon reflexes (e.g., patellar,

or “knee-jerk,” reflex)

• Visceral reflexes (autonomic reflexes)

•Control systems other than muscular system


13-6 Reflexes

• Complexity of Neural Circuit

• Monosynaptic reflex

•Sensory neuron synapses directly onto motor neuron

• Polysynaptic reflex

•At least one interneuron between sensory neuron and motor neuron


13-6 Reflexes

• Site of Information Processing

• Spinal reflexes

•Occur in spinal cord

• Cranial reflexes

•Occur in brain


Figure 13-16 The Classification of Reflexes

Reflexes

can be classified by

response complexity of circuit processing site

Spinal ReflexesSomatic ReflexesInnate Reflexes

development response

Monosynaptic

• Processing inthe spinal cord

the brain• Processing in

• One synapse

• Multiple synapse(two to severalhundred)

Cranial ReflexesPolysynapticVisceral (Autonomic) Reflexes

• Control actions of smooth andcardiac muscles, glands, andadipose tissue

• Control skeletal musclecontractions

reflexes• Include superficial and stretch

• Geneticallydetermined

• Learned

Acquired Reflexes


13-7 Spinal Reflexes

• Spinal Reflexes

• Range in increasing order of complexity

•Monosynaptic reflexes

• Polysynaptic reflexes

• Intersegmental reflex arcs

•Many segments interact

• Produce highly variable motor response



• Monosynaptic Reflexes

• A stretch reflex

• Have least delay between sensory input and motor

output

• For example, stretch reflex (such as patellar reflex)

• Completed in 20–40 msec

• Receptor is muscle spindle


Figure 13-17 A Stretch Reflex

Stretch

Stimulus

Contraction

Response

Effector

KEYSensory neuron(stimulated)Motor neuron(stimulated)

Receptor(musclespindle)

Spinal cord

REFLEXARC



• Muscle Spindles

• The receptors in stretch reflexes

• Bundles of small, specialized intrafusal muscle

fibers

• Innervated by sensory and motor neurons

• Surrounded by extrafusal muscle fibers

•Which maintain tone and contract muscle



• The Sensory Region

• Central region of intrafusal fibers

• Wound with dendrites of sensory neurons

• Sensory neuron axon enters CNS in dorsal root

• Synapses onto motor neurons (gamma motor neurons)

• In anterior gray horn of spinal cord



• Gamma Efferents

• Axons of the motor neurons

• Complete reflex arc

• Synapse back onto intrafusal fibers

• Important in voluntary muscle contractions

• Allow CNS to adjust sensitivity of muscle spindles


Extrafusalfiber

Sensoryregion

Intrafusalfiber

Musclespindle

Gammaefferent

from CNS

To CNS

Gammaefferent

from CNS

Figure 13-18 A Muscle Spindle



• Postural reflexes

• Stretch reflexes

• Maintain normal upright posture

• Stretched muscle responds by contracting

• Automatically maintain balance



• Polysynaptic Reflexes

• More complicated than monosynaptic reflexes

• Interneurons control more than one muscle group

• Produce either EPSPs or IPSPs



• The Tendon Reflex

• Prevents skeletal muscles from:

•Developing too much tension

• Tearing or breaking tendons

• Sensory receptors unlike muscle spindles or

proprioceptors



• Withdrawal Reflexes

• Move body part away from stimulus (pain or pressure)

• For example, flexor reflex

• Pulls hand away from hot stove

• Strength and extent of response

•Depend on intensity and location of stimulus


Figure 13-19 A Flexor Reflex

Distribution within gray horns to other segments of the spinal cord

Painfulstimulus

Flexorsstimulated

KEYExtensorsinhibited Sensory neuron

(stimulated)



Motor neuron(inhibited)

Inhibitoryinterneuron


Figure 13-20 The Crossed Extensor ReflexTo motor neurons in other segments of the spinal cord

Extensorsinhibited

Flexorsstimulated

Extensorsstimulated

Flexorsinhibited

KEYSensory neuron(stimulated)



Motor neuron(inhibited)

Inhibitoryinterneuron

Painfulstimulus


13-8 The Brain Can Alter Spinal Reflexes

• Integration and Control of Spinal Reflexes

• Reflex behaviors are automatic

• But processing centers in brain can facilitate or inhibit

reflex motor patterns based in spinal cord



• Voluntary Movements and Reflex Motor Patterns

• Higher centers of brain incorporate lower, reflexive

motor patterns

• Automatic reflexes

•Can be activated by brain as needed

•Use few nerve impulses to control complex motor

functions

•Walking, running, jumping



• The Babinski Reflexes

• Normal in infants

• May indicate CNS damage in adults


Figure 13-21a The Babinski Reflexes

The plantar reflex(negative Babinskireflex), a curling of thetoes, is seen in healthyadults.


Figure 13-21b The Babinski Reflexes

The Babinski sign (positiveBabinski reflex) occurs inthe absence of descendinginhibition. It is normal ininfants, but pathological inadults.

© 2012 Pearson Education, Inc. Figure 13-1 An Overview of Chapters 13 and 14 CHAPTER 14: The Brain...

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Transcript of © 2012 Pearson Education, Inc. Figure 13-1 An Overview of Chapters 13 and 14 CHAPTER 14: The Brain...