163 ch 08_lecture_presentation

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PowerPoint® Lecture Slidesprepared byMeg FlemmingAustin Community College

C H A P T E R 8

The Nervous System


Chapter 8 Learning Outcomes

• 8-1 • Describe the anatomical and functional divisions of the nervous

system.• 8-2

• Distinguish between neurons and neuroglia on the basis of structure and function.

• 8-3 • Describe the events involved in the generation and propagation of

an action potential.• 8-4

• Describe the structure of a synapse, and explain the mechanism of nerve impulse transmission at a synapse.

• 8-5• Describe the three meningeal layers that surround the central

nervous system.



• 8-6 • Discuss the roles of gray matter and white matter in the spinal cord.

• 8-7 • Name the major regions of the brain, and describe the locations

and functions of each.• 8-8

• Name the cranial nerves, relate each pair of cranial nerves to its principal functions, and relate the distribution pattern of spinal nerves to the regions they innervate.

• 8-9 • Describe the steps in a reflex arc.

• 8-10 • Identify the principal sensory and motor pathways, and explain how

it is possible to distinguish among sensations that originate in different areas of the body.



• 8-11• Describe the structures and functions of the sympathetic and

parasympathetic divisions of the autonomic nervous system.• 8-12

• Summarize the effects of aging on the nervous system.• 8-13

• Give examples of interactions between the nervous system and other organ systems.


The Nervous System and the Endocrine System (Introduction)

• The nervous system and endocrine system

coordinate other organ systems to maintain

homeostasis

• The nervous system is fast, short acting

• The endocrine system is slower, but longer lasting

• The nervous system is the most complex system

in the body


Functions of the Nervous System (8-1)

• Monitors the body's internal and external

environments

• Integrates sensory information

• Coordinates voluntary and involuntary responses


Divisions of the Nervous System (8-1)

• Anatomical divisions are:

• The central nervous system (CNS)

• Made up of the brain and spinal cord

• Integrates and coordinates input and output

• The peripheral nervous system (PNS)

• All the neural tissues outside of the CNS

• The connection between the CNS and the organs


Divisions of the Nervous System (8-1)

• Functional divisions are:

• The afferent division

• Includes sensory receptors and neurons that send

information to the CNS

• The efferent division

• Includes neurons that send information to the effectors,

which are the muscles and glands


Efferent Division of the Nervous System (8-1)

• Further divided into:

• The somatic nervous system (SNS)

• Controls skeletal muscle

• The autonomic nervous system (ANS)

• Controls smooth and cardiac muscle, and glands

• Has two parts

1. Sympathetic division

2. Parasympathetic division


Figure 8-1 A Functional Overview of the Nervous System.

CENTRAL NERVOUS SYSTEM

PERIPHERAL NERVOUSSYSTEM

Sensory informationwithin

afferent division

Informationprocessing

Motor commandswithin

efferent division

includes

Somaticnervoussystem

Autonomicnervous system

Parasympatheticdivision

Sympatheticdivision

Receptors Effectors

Somatic sensoryreceptors (monitorthe outside worldand our position

in it)

Visceral sensoryreceptors (monitorinternal conditions

and the statusof other organ

systems)

Skeletalmuscle

Smoothmuscle

Glands

Cardiacmuscle


Checkpoint (8-1)

1. Identify the two anatomical divisions of the

nervous system.

2. Identify the two functional divisions of the

peripheral nervous system, and describe their

primary functions.

3. What would be the effect of damage to the

afferent division of the PNS?


Neurons (8-2)

• Cells that communicate with one another and other cells

• Basic structure of a neuron includes:

• Cell body

• Dendrites

• Which receive signals

• Axons

• Which carry signals to the next cell

• Axon terminals

• Bulb-shaped endings that form a synapse with the next cell


Neurons (8-2)

• Have a very limited ability to regenerate when

damaged or destroyed

• Cell bodies contain:

• Mitochondria, free and fixed ribosomes, and rough

endoplasmic reticulum

• Free ribosomes and RER form Nissl bodies and give the

tissue a gray color (gray matter)

• The axon hillock

• Where electrical signal begins


Cell bodyMitochondrionGolgi apparatusAxon hillock

Dendrite

Nucleus

Nucleolus

Nissl bodies

Axon (may be myelinated)

CollateralAxon terminals

Nucleolus

Nucleus

Axon hillock

Nissl bodies

Nerve cell body

Nerve cell bodyLM x 1500

Figure 8-2 The Anatomy of a Representative Neuron.


Structural Classification of Neurons (8-2)

• Based on the relationship of the dendrites to the cell body

• Multipolar neurons

• Are the most common in the CNS and have two or more dendrites and

one axon

• Unipolar neurons

• Have the cell body off to one side, most abundant in the afferent

division

• Bipolar neurons

• Have one dendrite and one axon with the cell body in the middle, and

are rare


Multipolar neuron

Unipolar neuron

Bipolar neuron

Figure 8-3 A Structural Classification of Neurons.


Sensory Neurons (8-2)

• Also called afferent neurons

• Total 10 million or more

• Receive information from sensory receptors

• Somatic sensory receptors

• Detect stimuli concerning the outside world, in the form of

external receptors

• And our position in it, in the form of proprioceptors

• Visceral or internal receptors

• Monitor the internal organs


Motor Neurons (8-2)

• Also called efferent neurons

• Total about half a million in number

• Carry information to peripheral targets called

effectors

• Somatic motor neurons

• Innervate skeletal muscle

• Visceral motor neurons

• Innervate cardiac muscle, smooth muscle, and glands


Interneurons (8-2)

• Also called association neurons

• By far the most numerous type at about 20 billion

• Are located in the CNS

• Function as links between sensory and motor

processes

• Have higher functions

• Such as memory, planning, and learning


Neuroglial Cells (8-2)

• Are supportive cells and make up about half of all neural

tissue

• Four types are found in the CNS

1. Astrocytes

2. Oligodendrocytes

3. Microglia

4. Ependymal cells

• Two types in the PNS

1. Satellite cells

2. Schwann cells


Astrocytes (8-2)

• Large and numerous neuroglia in the CNS

• Maintain the blood–brain barrier


Oligodendrocytes (8-2)

• Found in the CNS

• Produce an insulating membranous wrapping

around axons called myelin

• Small gaps between the wrappings called nodes of Ranvier

• Myelinated axons constitute the white matter of

the CNS

• Where cell bodies are gray matter

• Some axons are unmyelinated


Microglia (8-2)

• The smallest and least numerous

• Phagocytic cells derived from white blood cells

• Perform essential protective functions such as

engulfing pathogens and cellular waste


Ependymal Cells (8-2)

• Line the fluid-filled central canal of the spinal cord

and the ventricles of the brain

• The endothelial lining is called the ependyma

• It is involved in producing and circulating

cerebrospinal fluid around the CNS


Gray matterWhite matter

Graymatter

Neurons

Myelinatedaxons

Ependymal cells

CENTRALCANAL

Microglialcell

Inter-node

Whitematter

AxonNode

Oligoden-drocyte

Astrocyte

CapillaryBasementmembrane

Myelin(cut)

Figure 8-4 Neuroglia in the CNS.


Neuroglial Cells in PNS (8-2)

• Satellite cells

• Surround and support neuron cell bodies

• Similar in function to the astrocytes in the CNS

• Schwann cells

• Cover every axon in PNS

• The surface is the neurilemma

• Produce myelin


Schwann cell nucleus

Axons

Neurilemma

Myelin coveringinternode

Schwann cell nucleus

Nodes

Myelinated axon

Unmyelinated axon

A myelinated axon in the PNS is covered by several Schwann cells, each of which forms a myelin sheath around a portion of the axon. This arrangement differs from the way myelin forms in the CNS; compare with Figure 8-4.

A single Schwann cell can encircle several unmy-elinated axons. Every axon in the PNS is completely enclosed by Schwann cells.

TEM x 14,048

TEM x 14,048

Figure 8-5 Schwann Cells and Peripheral Axons.


Organization of the Nervous System (8-2)

• In the PNS:

• Collections of nerve cell bodies are ganglia

• Bundled axons are nerves

• Including spinal nerves and cranial nerves

• Can have both sensory and motor components


Organization of the Nervous System (8-2)

• In the CNS:

• Collections of neuron cell bodies are found in centers,

or nuclei

• Neural cortex is a thick layer of gray matter

• White matter in the CNS is formed by bundles of axons

called tracts, and in the spinal cord, form columns

• Pathways are either sensory or ascending tracts, or

motor or descending tracts


PERIPHERAL NERVOUS SYSTEM

GRAY MATTER

GangliaCollections of neuron cell bodies in the PNS

WHITE MATTER

NervesBundles of axons in the PNS

RECEPTORS

EFFECTORS

PATHWAYSCenters and tracts that connectthe brain with other organs andsystems in the body

Ascending (sensory) pathwayDescending (motor) pathway

CENTRAL NERVOUS SYSTEM

GRAY MATTER ORGANIZATION

Neural CortexGray matter onthe surface ofthe brain

CentersCollections ofneuron cell bodiesin the CNS; eachcenter has specificprocessingfunctions Nuclei

Collections ofneuron cellbodies in theinterior of theCNS

Higher CentersThe most complexcenters in thebrain

WHITE MATTER ORGANIZATION

Tracts

Bundles of CNSaxons that share a common origin,destination, and function

ColumnsSeveral tractsthat form ananatomicallydistinct mass

Figure 8-6 The Anatomical Organization of the Nervous System.


Checkpoint (8-2)

4. Name the structural components of a typical neuron.

5. Examination of a tissue sample reveals unipolar neurons.

Are these more likely to be sensory neurons or motor

neurons?

6. Identify the neuroglia of the central nervous system.

7. Which type of glial cell would increase in number in the

brain tissue of a person with a CNS infection?

8. In the PNS, neuron cell bodies are located in ________

and surrounded by neuroglial cells called ________ cells.


The Membrane Potential (8-3)

• A membrane potential exists because of:

• Excessive positive ionic charges on the outside of the

cell

• Excessive negative charges on the inside, creating a

polarized membrane

• An undisturbed cell has a resting membrane potential

measured in the inside of the cell in millivolts

• The resting membrane potential of neurons is –70 mV


Factors Determining Membrane Potential (8-3)

• Extracellular fluid (ECF) is high in Na+ and CI–

• Intracellular fluid (ICF) is high in K+ and negatively charged

proteins (Pr –)

• Proteins are non-permeating, staying in the ICF

• Some ion channels are always open

• Called leak channels

• Some are open or closed

• Called gated channels


Factors Determining Membrane Potential (8-3)

• Na+ can leak in

• But the membrane is more permeable to K+

• Allowing K+ to leak out faster

• Na+/K+ exchange pump exchanges 3 Na+ for every

2 K+

• Moving Na+ out as fast as it leaks in

• Cell experiences a net loss of positive ions

• Resulting in a resting membrane charge of –70 mV


EXTRACELLULAR FLUID

K+ leakchannel

Sodium–potassiumexchange

pump

Na+ leakchannel

Plasmamembrane

CYTOSOL

Protein

Protein

Sodium ion (Na+)

Potassium ion (K+)

Chloride ion (Cl–)

Protein

–70 –30+30

0

mV

KEY

Figure 8-7 The Resting Potential Is the Membrane Potential of an Undisturbed Cell.


Changes in Membrane Potential (8-3)

• Stimuli alter membrane permeability to Na+ or K+

• Or alter activity of the exchange pump

• Types include:

• Cellular exposure to chemicals

• Mechanical pressure

• Temperature changes

• Changes in the ECF ion concentration

• Result is opening of a gated channel

• Increasing the movement of ions across the membrane


Changes in Membrane Potential (8-3)

• Opening of Na+ channels results in an influx of Na+

• Moving the membrane toward 0 mV, a shift called

depolarization

• Opening of K+ channels results in an efflux of K+

• Moving the membrane further away from 0 mV, a shift

called hyperpolarization

• Return to resting from depolarization: repolarizing


Graded Potentials (8-3)

• Local changes in the membrane that fade over

distance

• All cells experience graded potentials when

stimulated

• And can result in the activation of smaller cells

• Graded potentials by themselves cannot trigger

activation of large neurons and muscle fibers

• Referred to as having excitable membranes


Action Potentials (8-3)

• A change in the membrane that travels the entire

length of neurons

• A nerve impulse

• If a combination of graded potentials causes the

membrane to reach a critical point of

depolarization, it is called the threshold

• Then an action potential will occur


Action Potentials (8-3)

• Are all-or-none and will propagate down the

length of the neuron

• From the time the voltage-gated channels open

until repolarization is finished:

• The membrane cannot respond to further stimulation

• This period of time is the refractory period

• And limits the rate of response by neurons


A graded depolarization

brings an area of excitable membrane

to threshold (–60 mV).

Voltage-gated sodium channels open and sodium ions move into the cell. The membrane potential rises to +30 mV.

Potassium channels close, and both sodium

and potassium channels return to their

normal states.

Sodium channels close, voltage-gated potassium channels

open, and potassium ions move out of the cell. Repolarization begins.

D E P O L A R I Z A T I O N R E P O L A R I Z A T I O N

Restingpotential

Threshold

During the refractory period, the membrane cannot respond to further stimulation.

Axon hillock

First part of axon toreach threshold

+30

0

–40

–60–70

Mem

bra

ne

po

ten

tial

(m

V)

REFRACTORY PERIOD

Time (msec)0 21

2

3

41

The Generation of an Action PotentialSPOTLIGHTFIGURE 8-8

Closing of Potassium Channels

Inactivation of SodiumChannels and Activationof Potassium Channels

Activation of SodiumChannels and RapidDepolarization

Depolarization toThresholdResting

PotentialRestingPotential

4321

–60 mV +10 mV+30 mV

–70 mV –90 mV –70 mV

Localcurrent

The axon membranecontains both voltage-gated sodium channels and voltage-gated potassium channels that are closed when the membrane is at the resting potential.

The stimulus that begins an action potential is a graded depolarization large enough to open voltage-gated sodium channels. The opening of the channels occurs at a membrane potential known as the threshold.

When the voltage-gated sodium channels open, sodium ions rush into the cytoplasm, and rapid depolarization occurs. The inner membrane surface now contains more positive ions than negative ones, and the membrane potential has changed from –60 mVto a positive value.

As the membrane potential approaches+30 mV, voltage-gated sodium channels close. This step coincides with the opening of voltage-gated potassium channels. Positively charged potassium ions move out of the cytosol, shifting the membrane potential back toward resting levels. Repolariza-tion now begins.

The voltage-gated sodium channels remain inactivated until the membrane has repolar-ized to near threshold levels. The voltage-gated potassium channels begin closing as the membrane reaches the normal resting potential (about –70 mV). Until all have closed, potassium ions continue to leave the cell. This produces a brief hyperpolarization.

As the voltage-gated potassium channels close, the membrane potential returns to normal resting levels. The action potential is now over, and the membrane is once again at the resting potential.

= Sodium ion= Potassium ion

Figure 8-8 The Generation of an Action Potential


Sodium channels close, voltage-gated potassium channels open,

and potassium ions move out of thecell. Repolarization begins.

D E P O L A R I Z AT I O N R E P O L A R I Z AT I O N

Restingpotential

Threshold

Voltage-gated sodiumchannels open andsodium ions move intothe cell. The membranepotential rises to +30mV.

Potassium channelsclose, and both sodium

and potassium chan-nels return to their

normal states.

A gradeddepolarization bringsan area of excitable

membrane to thresh-old (–60 mV).

During the refractory period,the membrane cannotrespond to further stimulation.

REFRACTORY PERIOD

Time (msec)

Mem

bra

ne

po

ten

tial

(m

V)

+30

0

–40

–60–70 1

2

3

4

0 1 2




The axon membrane contains both voltage-gated sodium channels and voltage-gated potassium channels that are closed when the membrane is at the resting potential.

= Sodium ion= Potassium ion

–70 mV

Resting Potential

The stimulus that begins an action potential is a graded depolarization large enough to open voltage-gated sodium channels. The opening of the channels occurs at a membrane potential known as the threshold.

Localcurrent

–60 mV

Depolarization to Threshold

When the voltage-gated sodium channels open, sodium ions rush into the cytoplasm, and rapid depolarization occurs. The inner membrane surface now contains more positive ions than negative ones, and the membrane potential has changed from –60 mV to a positive value.

Activation of SodiumChannels and RapidDepolarization

+10 mV



RestingPotential

+30 mV–90 mV

–70 mV

Inactivation of SodiumChannels and Activation of Potassium Channels

As the membrane potential approaches+30 mV, voltage-gated sodium channels close. This step coincides with the opening of voltage-gated potassium channels. Positively charged potassium ions move out of the cytosol, shifting the membrane potential back toward resting levels. Repolariza-tion now begins.

Closing of Potas-sium Channels

The voltage-gated sodium channels remain inactivated until the membrane has repolar-ized to near threshold levels. The voltage-gated potassium channels begin closing as the membrane reaches the normal resting potential (about –70 mV). Until all have closed, potassium ions continue to leave the cell. This produces a brief hyperpolarization.

As the voltage-gatedpotassium channelsclose, the mem-brane potential re-turns to normal rest-ing levels. Theaction potential isnow over, and themembrane is onceagain at the restingpotential.


Propagation of an Action Potential (8-3)

• Occurs when local changes in the membrane in

one site: • Result in the activation of voltage-gated channels in the next

adjacent site of the membrane

• This causes a wave of membrane potential

changes

• Continuous propagation • Occurs in unmyelinated fibers and is relatively slow

• Saltatory propagation • Is in myelinated axons and is faster


Action potential propagation along anunmyelinated axon

Action potential propagation along amyelinated axon

Stimulusdepolarizes

membrane tothreshold

Stimulusdepolarizes

membrane tothreshold

EXTRACELLULAR FLUID

Plasma membrane CYTOSOL CYTOSOLPlasma membrane

EXTRACELLULAR FLUID

Repolarization(refractory period)

Repolarization(refractory period)

MyelinatedInternode Internode Internode

Myelinated Myelinated

MyelinatedMyelinatedMyelinatedInternode Internode Internode

InternodeInternodeInternodeMyelinated Myelinated Myelinated

Local current

Local current

Figure 8-9 The Propagation of Action Potentials over Unmyelinated and Myelinated Axons.


Checkpoint (8-3)

9. What effect would a chemical that blocks the voltage-gated

sodium channels in a neuron's plasma membrane have on the

neuron's ability to depolarize?

10. What effect would decreasing the concentration of extracellular

potassium have on the membrane potential of a neuron?

11. List the steps involved in the generation and propagation of an

action potential.

12. Two axons are tested for propagation velocities. One carries

action potentials at 50 meters per second, the other at 1 meter

per second. Which axon is myelinated?


The Synapse (8-4)

• A junction between a neuron and another cell

• Occurs because of chemical messengers called

neurotransmitters

• Communication happens in one direction only

• Between a neuron and another cell type is a neuroeffector

junction

• Such as the neuromuscular junction or neuroglandular junction


A Synapse between Two Neurons (8-4)

• Occurs:

• Between the axon terminals of the presynaptic neuron

• Across the synaptic cleft

• To the dendrite or cell body of the postsynaptic neuron

• Neurotransmitters

• Stored in vesicles of the axon terminals

• Released into the cleft and bind to receptors on the

postsynaptic membrane

PLAYPLAY ANIMATION Neurophysiology: Synapse


Axon ofpresynaptic cell

Axonterminal

Mitochondrion

Synapticvesicles

Presynapticmembrane

Postsynapticmembrane

Synapticcleft

Figure 8-10 The Structure of a Typical Synapse.


The Neurotransmitter ACh (8-4)

• Activates cholinergic synapses in four steps

1. Action potential arrives at the axon terminal

2. ACh is released and diffuses across synaptic cleft

3. ACh binds to receptors and triggers depolarization of

the postsynaptic membrane

4. ACh is removed by AChE (acetylcholinesterase)


Figure 8-11 The Events at a Cholinergic Synapse.

An action potential arrives anddepolarizes the axon terminal

Presynapticneuron

Synapticvesicles

Action potentialEXTRACELLULAR

FLUIDAxonterminal

AChE

POSTSYNAPTICNEURON

Extracellular Ca2+ enters the axonterminal, triggering the exocytosis of ACh

Ca2+

Synaptic cleftCa2+

ACh

Chemically regulatedsodium ion channels


Figure 8-11 The Events at a Cholinergic Synapse.

ACh binds to receptors and depolarizesthe postsynaptic membrane

Initiation ofaction potentialif threshold is

reached

ACh is removed by AChE

Propagation ofaction potential

(if generated)


Table 8-1 The Sequence of Events at a Typical Cholinergic Synapse


Other Important Neurotransmitters (8-4)

• Norepinephrine (NE)

• In the brain and part of the ANS, is found in adrenergic

synapses

• Dopamine, GABA, and serotonin

• Are CNS neurotransmitters

• At least 50 less-understood neurotransmitters

• NO and CO

• Are gases that act as neurotransmitters


Excitatory vs. Inhibitory Synapses (8-4)

• Usually, ACh and NE trigger depolarization

• An excitatory response

• With the potential of reaching threshold

• Usually, dopamine, GABA, and serotonin trigger

hyperpolarization

• An inhibitory response

• Making it farther from threshold


Neuronal Pools (8-4)

• Multiple presynaptic neurons can synapse with

one postsynaptic neuron

• If they all release excitatory neurotransmitters:

• Then an action potential can be triggered

• If they all release an inhibitory neurotransmitter:

• Then no action potential can occur

• If half release excitatory and half inhibitory neurotransmitters:

• They cancel, resulting in no action


Neuronal Pools (8-4)

• A term that describes the complex grouping of

neural pathways or circuits

• Divergence

• Is a pathway that spreads information from one neuron

to multiple neurons

• Convergence

• Is when several neurons synapse with a single

postsynaptic neuron


Divergence Convergence

A mechanism forspreading stimulation tomultiple neurons orneuronal pools in theCNS

A mechanism for providinginput to a single neuron frommultiple sources

Figure 8-12 Two Common Types of Neuronal Pools.


Checkpoint (8-4)

13. Describe the general structure of a synapse.

14. What effect would blocking calcium channels at

a cholinergic synapse have on synapse

function?

15. What type of neural circuit permits both

conscious and subconscious control of the same

motor neurons?


The Meninges (8-5)

• The neural tissue in the CNS is protected by

three layers of specialized membranes

1. Dura mater

2. Arachnoid

3. Pia mater


The Dura Mater (8-5)

• Is the outer, very tough covering

• The dura mater has two layers, with the outer layer

fused to the periosteum of the skull

• Dural folds contain large veins, the dural sinuses

• In the spinal cord the dura mater is separated from the

bone by the epidural space


The Arachnoid

• Is separated from the dura mater by the subdural

space

• That contains a little lymphatic fluid

• Below the epithelial layer is arachnoid space

• Created by a web of collagen fibers

• Contains cerebrospinal fluid


The Pia Mater

• Is the innermost layer

• Firmly bound to the neural tissue underneath

• Highly vascularized

• Providing needed oxygen and nutrients


Checkpoint (8-5)

16. Identify the three meninges surrounding the CNS.


Spinal Cord Structure (8-6)

• The major neural pathway between the brain and

the PNS

• Can also act as an integrator in the spinal reflexes

• Involving the 31 pairs of spinal nerves

• Consistent in diameter except for the cervical

enlargement and lumbar enlargement

• Where numerous nerves supply upper and lower limbs


Spinal Cord Structure (8-6)

• Central canal

• A narrow passage containing cerebrospinal fluid

• Surface of the spinal cord is indented by the:

• Posterior median sulcus

• Deeper anterior median fissure


31 Spinal Segments (8-6)

• Identified by a letter and number relating to the

nearby vertebrae

• Each has a pair of dorsal root ganglia

• Containing the cell bodies of sensory neurons with

axons in dorsal root

• Ventral roots contain motor neuron axons

• Roots are contained in one spinal nerve


Figure 8-14a Gross Anatomy of the Spinal Cord.

Cervicalenlargement

Posteriormedian sulcus

Lumbarenlargement

Inferior tip of spinal cord

Cauda equina

Cervical spinalnerves

Thoracicspinal

nerves

Lumbarspinal

nerves

Sacral spinalnerves

Coccygealnerve (Co1)

In this superficial view of theadult spinal cord, thedesignations to the left identifythe spiral nerves.

C1C2C3C4C5C6C7C8

T1T2T3T4T5

T6

T7

T8

T9

T10

T11

T12

L1

L2

L3

L4

L5

S5S5

S1S1

S2S2

S3S3

S4S4


Figure 8-14b Gross Anatomy of the Spinal Cord.

This cross section through thecervical region of the spinal cordshows some prominent features andthe arrangement of gray matter andwhite matter.

C3

Dorsal root

Dorsal rootganglion

Centralcanal

Spinalnerve

Ventralroot

Posterior median sulcus

White matter

Gray matter

Anterior median fissure


Sectional Anatomy of the Spinal Cord (8-6)

• The central gray matter is made up of glial cells

and nerve cell bodies

• Projections of gray matter are called horns

• Which extend out into the white matter

• White matter is myelinated and unmyelinated

axons

• The location of cell bodies in specific nuclei of the

gray matter relate to their function


Sectional Anatomy of the Spinal Cord (8-6)

• Posterior gray horns are somatic and visceral

sensory nuclei

• Lateral gray horns are visceral (ANS) motor nuclei

• The anterior gray horns are somatic motor nuclei

• White matter can be organized into three columns

• Which contain either ascending tracts to the brain, or

descending tracts from the brain to the PNS


Posterior white column

Dorsal root

ganglion

Lateralwhite

column

Posteriorgray horn

Lateralgray horn

Anteriorgray

horn

Posteriormedian sulcusPosterior graycommissure

Somatic

VisceralVisceralSomatic

Functional Organizationof Gray MatterThe cell bodies of neurons in thegray matter of the spinal cord areorganized into functional groupscalled nuclei.

Sensory nuclei

Motor nuclei

Ventral rootAnterior gray commissureAnterior white commissureAnterior median fissure

Anterior white column

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


POSTERIOR Structural Organizationof Gray Matter

The projections of gray mattertoward the outer surface of thespinal cord are called horns.

Posterior gray horn

Lateral gray horn

Anterior gray horn

Dorsalroot

Dorsal rootganglion

Ventral root

Posterior graycommissure

Dura mater

Arachnoid mater(broken)

Central canalAnterior graycommissure

Anterior medianfissure

Pia mater

A micrograph of a section through the spinal cord, showingmajor landmarks in and surrounding the cord.

ANTERIOR

Figure 8-15 Sectional Anatomy of the Spinal Cord.


Figure 8-15a Sectional Anatomy of the Spinal Cord.

Posterior white column Posteriormedian sulcus


Posteriorgray horn

Dorsal rootganglion

Lateralwhite

column

Lateralgray horn

Anteriorgray

horn

Somatic

Visceral

Visceral

Somatic

Functional Organizationof Gray Matter

The cell bodies of neurons in thegray matter of the spinal cord areorganized into functional groupscalled nuclei.

Sensory nuclei

Motor nuclei

Ventral rootAnterior gray commissureAnterior white commissureAnterior median fissure

Anterior white column

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


Figure 8-15b Sectional Anatomy of the Spinal Cord.

A micrograph of a section through the spinal cord, showingmajor landmarks in and surrounding the cord.

Pia mater

Anterior medianfissure

Anterior graycommissure

Central canal

Arachnoid mater(broken)

Dura mater


POSTERIOR

ANTERIOR


Dorsalroot

Dorsal rootganglionVentral root

Structural Organizationof Gray Matter

Posterior gray horn

Lateral gray horn

Anterior gray horn

The projections of gray mattertoward the outer surface of thespinal cord are called horns.


Checkpoint (8-6)

17. Damage to which root of a spinal nerve would

interfere with motor function?

18. A person with polio has lost the use of his leg

muscles. In which areas of his spinal cord could

you locate virus-infected neurons?

19. Why are spinal nerves also called mixed nerves?


Six Major Regions of the Brain (8-7)

1. The cerebrum

2. The diencephalon

3. The midbrain

4. The pons

5. The medulla oblongata

6. The cerebellum


Major Structures of the Brain (8-7)

• The cerebrum

• Is divided into paired cerebral hemispheres

• Deep to the cerebrum is the diencephalon

• Which is divided into the thalamus, the hypothalamus,

and the epithalamus

• The brain stem

• Contains the midbrain, pons, and medulla oblongata

• The cerebellum

• Is the most inferior/posterior part


Figure 8-16a The Brain.

Longitudinal fissure

Cerebral veins and arteriesbelow arachnoid mater

Right cerebral hemisphereLeft cerebral hemisphere

CEREBRUM

CEREBELLUM

ANTERIOR

POSTERIOR

Superior view


Figure 8-16b The Brain.

Precentral gyrus

Frontal lobe of leftcerebral hemisphere

Lateral sulcus

Temporal lobe

PONS

Central sulcus

Postcentralgyrus

Parietallobe

Occipitallobe

CEREBELLUM

MEDULLA OBLONGATA Lateral view


Figure 8-16c The Brain.

Corpuscallosum

Precentralgyrus

Centralsulcus

Postcentralgyrus

ThalamusHypothalamusPineal gland(part of epithalamus)

Parieto-occipital sulcus

CEREBELLUM

Sagittal sectionMEDULLA OBLONGATA PONSMIDBRAIN

Brain stem

Temporal lobe

Fornix

Frontal lobe

Opticchiasm

Mamillary body

DIENCEPHALON


The Ventricles of the Brain (8-7)

• Filled with cerebrospinal fluid and lined with

ependymal cells

• The two lateral ventricles within each cerebral

hemisphere drain through the:

• Interventricular foramen into the:

• Third ventricle in the diencephalon, which drains

through the cerebral aqueduct into the:

• Fourth ventricle, which drains into the central canal


Cerebralhemispheres

PonsMedulla oblongata

Spinal cord

A lateral view of the ventriclesCentral canal

Lateralventricles

Interventricularforamen

Thirdventricle

Cerebralaqueduct

Fourthventricle

Cerebral hemispheres

Central canal Cerebellum

An anterior view of the ventricles

Ventricles ofthe Brain

Figure 8-17 The Ventricles of the Brain.


Cerebrospinal Fluid (8-7)

• CSF

• Surrounds and bathes the exposed surfaces of the CNS

• Floats the brain

• Transports nutrients, chemicals, and wastes

• Is produced by the choroid plexus

• Continually secreted and replaced three times per day

• Circulation from the fourth ventricle into the

subarachnoid space into the dural sinuses


Figure 8-18a The Formation and Circulation of Cerebrospinal Fluid.

A sagittal section of the CNS. Cerebrospinal fluid, formed in the choroid plexus, circulates along the routes indicated by the red arrows.

Spinal cord

Central canal

Superiorsagittalsinus

ArachnoidgranulationsExtension of choroid

plexus intolateral ventricle

Choroid plexusof third ventricle

CerebralaqueductLateral aperture

Choroid plexus offourth ventricle

Median aperture

Arachnoid mater

Subarachnoid space

Dura mater


Figure 8-18b The Formation and Circulation of Cerebrospinal Fluid.

The relation-ship of the arachnoid granulations and dura mater.

Piamater

Subarachnoidspace

Arachnoidmater

Subduralspace

Dura mater(inner layer)

Fluidmovement

Arachnoidgranulation

Dura mater(outer layer)

CraniumSuperior

sagittal sinus

Cerebralcortex


The Cerebrum (8-7)

• Contains an outer gray matter called the cerebral

cortex

• Deep gray matter in the cerebral nuclei and white matter of

myelinated axons beneath the cortex and around the nuclei

• The surface of the cerebrum

• Folds into gyri

• Separated by depressions called sulci or deeper grooves

called fissures


The Cerebral Hemispheres (8-7)

• Are separated by the longitudinal fissure

• The central sulcus

• Extends laterally from the longitudinal fissure

• The frontal lobe

• Is anterior to the central sulcus

• Is bordered inferiorly by the lateral sulcus



• The temporal lobe

• Inferior to the lateral sulcus

• Overlaps the insula

• The parietal lobe

• Extends between the central sulcus and the parieto-

occipital sulcus



• The occipital lobe

• Located most posteriorly

• The lobes are named for the cranial bone above it

• Each lobe has sensory regions and motor regions

• Each hemisphere sends and receives information

from the opposite side of the body


Motor and Sensory Areas of the Cortex (8-7)

• Are divided by the central sulcus

• The precentral gyrus of the frontal lobe

• Contains the primary motor cortex

• The postcentral gyrus of the parietal lobe

• Contains the primary sensory cortex


Motor and Sensory Areas of Cortex (8-7)

• The visual cortex is in the occipital lobe

• The gustatory, auditory, and olfactory cortexes

are in the temporal lobe


Association Areas (8-7)

• Interpret incoming information

• Coordinate a motor response, integrating the

sensory and motor cortexes

• The somatic sensory association area

• Helps to recognize touch

• The somatic motor association area

• Is responsible for coordinating movement


Primary motor cortex(precentral gyrus)

Somatic motor associationarea (premotor cortex)

FRONTAL LOBE

Prefrontal cortex

Gustatory cortexInsula

Lateral sulcus

Olfactory cortex

TEMPORAL LOBE

Auditory cortex

Auditoryassociation area

Visual cortexOCCIPITAL LOBE

Visual associationarea

Somatic sensoryassociation area

PARIETAL LOBE

Primary sensory cortex(postcentral gyrus)

Central sulcus

Figure 8-19 The Surface of the Cerebral Hemispheres.


Cortical Connections (8-7)

• Regions of the cortex are linked by the deeper

white matter

• The left and right hemispheres are linked across

the corpus callosum

• Other axons link the cortex with:

• The diencephalon, brain stem, cerebellum, and spinal

cord


Higher-Order Centers (8-7)

• Integrative areas, usually only in the left

hemisphere

• The general interpretive area or Wernicke's area

• Integrates sensory information to form visual and auditory

memory

• The speech center or Broca's area

• Regulates breathing and vocalization, the motor skills

needed for speaking


The Prefrontal Cortex (8-7)

• In the frontal lobe

• Coordinates information from the entire cortex

• Skills such as:

• Predicting time lines

• Making judgments

• Feelings such as:

• Frustration, tension, and anxiety


Hemispheric Lateralization (8-7)

• The concept that different brain functions can and

do occur on one side of the brain

• The left hemisphere tends to be involved in language

skills, analytical tasks, and logic

• The right hemisphere tends to be involved in analyzing

sensory input and relating it to the body, as well as

analyzing emotional content


General interpretivecenter (language and

mathematical calculation)

Auditory cortex(right ear)

Writing

Speech center

Prefrontalcortex

LEFT HAND RIGHT HAND

Prefrontalcortex

Anterior commissure

Analysis by touch

Auditory cortex(left ear)

Spatial visualizationand analysis

Visual cortex(left visual field)

Visual cortex(right visual field)

CORPUSCALLOSUM

RIGHTHEMISPHERE

LEFTHEMISPHERE

Figure 8-20 Hemispheric Lateralization.


The Electroencephalogram (8-7)

• EEG

• A printed record of brain wave activity

• Can be interpreted to diagnose brain disorders

• More modern techniques

• Brain imaging, using the PET scan and MRIs, has

allowed extensive "mapping" of the brain's functional

areas


Patient being wiredfor EEG monitoring

Alpha waves are characteristic of normal resting adults

Beta waves typicallyaccompany intense concentration

Theta waves are seen in children and in frustrated adults

Delta waves occur in deep sleep and in certain pathological conditions

0 1 2 3 4Seconds

Figure 8-21 Brain Waves.


Memory (8-7)

• Fact memory

• The recall of bits of information

• Skill memory

• Learned motor skill that can become incorporated into unconscious

memory

• Short-term memory

• Doesn't last long unless rehearsed

• Converting into long-term memory through memory consolidation

• Long-term memory

• Remains for long periods, sometimes an entire lifetime

• Amnesia

• Memory loss as a result of disease or trauma


The Basal Nuclei (8-7)

• Masses of gray matter

• Caudate nucleus

• Lies anterior to the lentiform nucleus

• Which contains the medial globus pallidus and the lateral

putamen

• Inferior to the caudate and lentiform nuclei is the amygdaloid body

or amygdala

• Basal nuclei

• Subconscious control of skeletal muscle tone


Lateral view of a transparent brain, showing the relative positions of the basal nuclei

Lentiform nucleusThalamusTail of caudatenucleus

Amygdaloidbody

Head of caudatenucleus

Head ofcaudatenucleus Corpus

callosumLateral ventricle Insula

Tip of lateralventricle

AmygdaloidbodyGlobus pallidus

PutamenLentiformnucleus

Frontal section

Figure 8-22 The Basal Nuclei.


The Limbic System (8-7)

• Includes the olfactory cortex, basal nuclei, gyri, and

tracts between the cerebrum and diencephalon

• A functional grouping, rather than an anatomical one

• Establishes the emotional states

• Links the conscious with the unconscious

• Aids in long-term memory with help of the

hippocampus


Cingulate gyrus

Corpus callosum

Thalamic nuclei

Hypothalamicnuclei

Olfactory tractAmygdaloid body

Hippocampus

Fornix

Mamillary body

Figure 8-23 The Limbic System.


The Diencephalon (8-7)

• Contains switching and relay centers

• Centers integrate conscious and unconscious sensory

information and motor commands

• Surround third ventricle

• Three components

1. Epithalamus

2. Thalamus

3. Hypothalamus


The Epithalamus (8-7)

• Lies superior to the third ventricle and forms the

roof of the diencephalon

• The anterior part contains choroid plexus

• The posterior part contains the pineal gland that

is endocrine and secretes melatonin


The Thalamus (8-7)

• The left and right thalamus are separated by the

third ventricle

• The final relay point for sensory information

• Only a small part of this input is sent on to the

primary sensory cortex


The Hypothalamus (8-7)

• Lies inferior to the third ventricle

• The subconscious control of skeletal muscle

contractions is associated with strong emotion

• Adjusts the pons and medulla functions

• Coordinates the nervous and endocrine systems


The Hypothalamus (8-7)

• Secretes hormones

• Produces sensations of thirst and hunger

• Coordinates voluntary and ANS function

• Regulates body temperature

• Coordinates daily cycles


The Midbrain (8-7)

• Contains various nuclei

• Two pairs involved in visual and auditory processing, the colliculi

• Contains motor nuclei for cranial nerves III and IV

• Cerebral peduncles contain descending fibers

• Reticular formation is a network of nuclei related to the

state of wakefulness

• The substantia nigra influence muscle tone


The Pons (8-7)

• Links the cerebellum with the midbrain,

diencephalon, cerebrum, and spinal cord

• Contains sensory and motor nuclei for cranial

nerves V, VI, VII, and VIII

• Other nuclei influence rate and depth of respiration


The Cerebellum (8-7)

• An automatic processing center

• Which adjusts postural muscles to maintain balance

• Programs and fine-tunes movements

• The cerebellar peduncles

• Are tracts that link the cerebral cortex, basal nuclei, and brain stem

• Ataxia

• Is disturbance of coordination

• Can be caused by damage to the cerebellum


The Medulla Oblongata (8-7)

• Connects the brain with the spinal cord

• Contains sensory and motor nuclei for cranial nerves VIII,

IX, X, XI, and XII

• Contains reflex centers

• Cardiovascular centers

• Adjust heart rate and arteriolar diameter

• Respiratory rhythmicity centers

• Regulate respiratory rate


Figure 8-24a The Diencephalon and Brain Stem.

Cerebralpeduncle

Optic tract

Cranialnerves

ThalamusDiencephalon

Thalamic nuclei

MidbrainSuperior colliculusInferior colliculus

Cerebellar peduncles

Medullaoblongata

Spinalcord

Lateral view

Spinalnerve C2

Spinalnerve C1

N XIIN XIN X

N IX

N IIN III

N V

N IV

N VIN VII

N VIII

Pons


Figure 8-24b The Diencephalon and Brain Stem.

N IV

Choroid plexusThalamusThird ventriclePineal gland

Corpora quadrigeminaSuperior colliculi

Inferior colliculi

Cerebral peduncle

Cerebellar peduncles

Posterior view

Dorsal rootsof spinal nerves

C1 and C2

Choroid plexus in roofof fourth ventricle


Checkpoint (8-7)

20. Describe one major function of each of the six regions of

the brain.

21. The pituitary gland links the nervous and endocrine

systems. To which portion of the diencephalon is it

attached?

22. How would decreased diffusion across the arachnoid

granulations affect the volume of cerebrospinal fluid in the

ventricles?

23. Mary suffers a head injury that damages her primary

motor cortex. Where is this area located?


Checkpoint (8-7)

24. What senses would be affected by damage to the

temporal lobes of the cerebrum?

25. The thalamus acts as a relay point for all but what type of

sensory information?

26. Changes in body temperature stimulate which area of the

diencephalon?

27. The medulla oblongata is one of the smallest sections of

the brain. Why can damage to it cause death, whereas

similar damage in the cerebrum might go unnoticed?


Peripheral Nervous System (8-8)

• Links the CNS to the rest of the body through

peripheral nerves

• They include the cranial nerves and the spinal

nerves

• The cell bodies of sensory and motor neurons are

contained in the ganglia


The Cranial Nerves (8-8)

• 12 pairs, noted as Roman numerals I through XII

• Some are:

• Only motor pathways

• Only sensory pathways

• Mixed having both sensory and motor neurons

• Often remembered with a mnemonic

• "Oh, Once One Takes The Anatomy Final, Very Good

Vacations Are Heavenly"



• The olfactory nerves (N I)

• Are connected to the cerebrum

• Carry information concerning the sense of smell

• The optic nerves (N II)

• Carry visual information from the eyes, through the

optic foramina of the orbits to the optic chiasm

• Continue as the optic tracts to the nuclei of the thalamus



• The oculomotor nerves (N III)

• Motor only, arising in the midbrain

• Innervate four of six extrinsic eye muscles and the

intrinsic eye muscles that control the size of the pupil

• The trochlear nerves (N IV)

• Smallest, also arise in the midbrain

• Innervate the superior oblique extrinsic muscles of the

eyes



• The trigeminal nerves (N V) • Have nuclei in the pons, are the largest cranial nerves

• Have three branches

1. The ophthalmic

• From the orbit, sinuses, nasal cavity, skin of

forehead, nose, and eyes

2. The maxillary

• From the lower eyelid, upper lip, cheek, nose, upper

gums, and teeth

• The mandibular

• From salivary glands and tongue



• The abducens nerves (N VI)

• Innervate only the lateral rectus extrinsic eye muscle,

with the nucleus in the pons

• The facial nerves (N VII)

• Mixed, and emerge from the pons

• Sensory fibers monitor proprioception in the face

• Motor fibers provide facial expressions; control tear and

salivary glands



• The vestibulocochlear nerves (N VIII)

• Respond to sensory receptors in the inner ear

• There are two components

1. The vestibular nerve

• Conveys information about balance and position

2. The cochlear nerve

• Responds to sound waves for the sense of hearing

• Their nuclei are in the pons and medulla oblongata



• The glossopharyngeal nerves (N IX)

• Mixed nerves innervating the tongue and pharynx

• Their nuclei are in the medulla oblongata

• The sensory portion monitors taste on the posterior third

of the tongue and monitors BP and blood gases

• The motor portion controls pharyngeal muscles used in

swallowing, and fibers to salivary glands



• The vagus nerves (N X)

• Have sensory input vital to autonomic control of the

viscera

• Motor control includes the soft palate, pharynx, and

esophagus

• Are a major pathway for ANS output to cardiac muscle,

smooth muscle, and digestive glands



• The accessory nerves (N XI)

• Have fibers that originate in the medulla oblongata

• Also in the lateral gray horns of the first five cervical

segments of the spinal cord

• The hypoglossal nerves (N XII)

• Provide voluntary motor control over the tongue


Mamillarybody

Basilarartery

Olfactory bulb, terminationof olfactory nerve (I)

Olfactory tract

Optic chiasmOptic nerve (II)

Infundibulum

Oculomotor nerve(III)

Trochlear nerve(IV)

Trigeminal nerve(V)

Abducens nerve(VI)

Facial nerve (VII)

Vestibulocochlearnerve (VIII)

Glossopharyngeal nerve (IX)

Vagus nerve (X)Hypoglossal nerve

(XII)Accessory nerve (XI)

Diagrammatic view showing the attachment of the 12 pairs of cranial nerves

Spinal cordMedulla

oblongataCerebellum

Inferior view of the brain

Vertebral artery

Pons

Figure 8-25 The Cranial Nerves.


Table 8-2 The Cranial Nerves


The Spinal Nerves (8-8)

• Found in 31 pairs grouped according to the region

of the vertebral column

• 8 pairs of cervical nerves, C1–C8

• 12 pairs of thoracic nerves, T1–T12

• 5 pairs of lumbar nerves, L1–L5

• 5 pairs of sacral nerves, S1–S5

• 1 pair of coccygeal nerves, Co1


Nerve Plexuses (8-8)

• The origin of major nerve trunks of the PNS

• The cervical plexus

• Innervates the muscles of the head and neck and the

diaphragm

• The brachial plexus

• Innervates the shoulder girdle and upper limb

• The lumbar plexus and the sacral plexus

• Innervate the pelvic girdle and lower limb


Figure 8-26 Peripheral Nerves and Nerve Plexuses.

Phrenic nerve (extends to the diaphragm)

Axillary nerve

Musculocutaneousnerve

Radial nerve

Ulnar nerve Median nerve

Femoral nerve Obturator nerve

Gluteal nerves

Saphenous nerve

Sacralplexus

Lumbarplexus

Brachialplexus

Cervicalplexus

C1

Sciatic nerve

C2C3C4C5C6C7C8T1T2T3T4T5T6T7T8T9

T10T11T12

L1

L2

L3L4L5S1

S2S3S4S5

Co1


Dermatome (8-8)

• A clinically important area monitored by a specific

spinal nerve


C2–C3

C2

C2–C3

N V

C3

C4

C3

C5C4

C5

C6

C7C6

C8

C8

C7

T1T2

T3

T4

T5

T6

T7

T8

T9

T10

T11

T12

T2

T3

T4T5T6T7T8T9T10T11

T12

T2

T2

T1

T1

L1

L1L2

L2

L3L4L5

L1

L2

L3

L4

L5 L3

S2

S1 L5

S5

SS4 3

S2

S1

L4

ANTERIOR POSTERIOR

Figure 8-27 Dermatomes.


Table 8-3 Nerve Plexuses and Major Nerves


Checkpoint (8-8)

28. What signs would you associate with damage to the

abducens nerve (N VI)?

29. John is having trouble moving his tongue. His physician

tells him it is due to pressure on a cranial nerve. Which

cranial nerve is involved?

30. Injury to which nerve plexus would interfere with the

ability to breathe?


Reflexes (8-9)

• Rapid, automatic, unlearned motor response to a stimulus

• Usually removes or opposes the original stimulus

• Monosynaptic reflexes

• For example, the stretch reflex

• Which responds to muscle spindles, is the simplest with only

one synapse

• The best known stretch reflex is probably the knee jerk reflex


Simple Reflexes (8-9)

• Are wired in a reflex arc

• A stimulus activates a sensory receptor

• An action potential travels down an afferent neuron

• Information processing occurs with the interneuron

• An action potential travels down an efferent neuron

• The effector organ responds


Arrival ofstimulus andactivation ofreceptor

Activation of asensory neuron

Dorsalroot

Sensationrelayed to the brain by axon

collaterals

Informationprocessingin the CNS

REFLEXARC

ReceptorStimulusEffector

Response byeffector Ventral

root

Activation of amotor neuron

KEYSensoryneuron(stimulated)

ExcitatoryinterneuronMotor neuron(stimulated)

Figure 8-28 The Components of a Reflex Arc.


Stretching of muscle tendonstimulates muscle spindles

Muscle spindle(stretch receptor)

SpinalCord

REFLEXARC

Contraction

Stretch

Activation of motorneuron produces reflex muscle contraction

Figure 8-29 A Stretch Reflex.


Complex Reflexes (8-9)

• Polysynaptic reflexes

• With at least one interneuron

• Are slower than monosynaptic reflexes, but can activate

more than one effector

• Withdrawal reflexes

• Like the flexor reflex, move a body part away from the

stimulation

• Like touching a hot stove

• Reciprocal inhibition

• Blocks the flexor's antagonist

• To ensure that flexion is in no way interfered with


Distribution within gray horns to other segments of the spinal cord

Painful stimulus Flexors

stimulated

Extensorsinhibited

KEYSensory neuron(stimulated)

Excitatoryinterneuron

Motor neuron(stimulated)

Motor neuron(inhibited)

Inhibitoryinterneuron

Figure 8-30 The Flexor Reflex, a Type of Withdrawal Reflex.


Input to Modify Reflexes (8-9)

• Reflexes are automatic, but higher brain centers

can influence or modify them

• The Babinski sign

• Triggered by stroking an infant's sole, resulting in a

fanning of the toes

• As descending inhibitory synapses develop, an adult will

respond by curling the toes instead, called the plantar

reflex


Checkpoint (8-9)

31. Define reflex.

32. Which common reflex do physicians use to test the

general condition of the spinal cord, peripheral nerves,

and muscles?

33. Why can polysynaptic reflexes produce more involved

responses than can monosynaptic reflexes?

34. After injuring his back lifting a sofa, Tom exhibits a

positive Babinski reflex. What does this imply about

Tom's injury?


Sensory Pathways (8-10)

• Are ascending pathways

• Posterior column pathway

• Spinothalamic pathway

• Spinocerebellar pathway

• A sensory homunculus

• A mapping of the area of the cortex dedicated to the

number of sensory receptors, not the size of the body

area


Sensory homunculus ofleft cerebral hemisphere

KEYAxon of first-order neuron

Second-orderneuronThird-orderneuron

Nucleus in medulla

oblongata

Nuclei inthalamus

MIDBRAIN

MEDULLA OBLONGATA

SPINAL CORD

Dorsal rootganglion

Fine-touch, pressure, vibration, and proprio-ception sensations from right side of body

Figure 8-31 The Posterior Column Pathway.


Motor Pathways (8-10)

• Are descending pathways

• Corticospinal pathway

• Also called pyramidal system

• Medial and lateral pathways

• Also called extrapyramidal system

• A motor homunculus

• Represents the distribution of somatic and ANS motor

innervation


Motor homunculus on primary motorcortex of left cerebral

hemisphereAxon of uppermotor neuron

Lower motorneuron

To skeletalmuscles

To skeletalmuscles

Motor nucleiof cranial

nerves

MIDBRAIN

MEDULLA OBLONGATA

Lateralcorticospinal

tract

To skeletalmuscles

Anterior corticospinal tract

KEY

SPINAL CORDMotor neuron in anterior gray horn

Motor nucleiof cranial

nerves

Figure 8-32 The Corticospinal Pathway.


Table 8-4 Sensory and Motor Pathways


Checkpoint (8-10)

35. As a result of pressure on her spinal cord, Jill cannot feel

touch or pressure on her legs. What sensory pathway is

being compressed?

36. The primary motor cortex of the right cerebral hemisphere

controls motor function on which side of the body?

37. An injury to the superior portion of the motor cortex

would affect the ability to control muscles of which parts

of the body?


The Autonomic Nervous System (8-11)

• Unconscious adjustment of homeostatically essential

visceral responses

• Sympathetic division

• Parasympathetic division

• The somatic NS and ANS are anatomically different

• SNS: one neuron to skeletal muscle

• ANS: two neurons to cardiac and smooth muscle, glands, and fat

cells


Two Neuron Pathways of the ANS (8-11)

• Preganglionic neuron

• Has cell body in spinal cord, synapses at the ganglion with the

postganglionic neuron

• In sympathetic division

• Preganglionic fibers are short

• Postganglionic fibers are long

• In parasympathetic division

• Preganglionic fibers are long

• Postganglionic fibers are "short"


Upper motorneurons inPrimarymotorcortex

Somatic motor nuclei of brain stem

Skeletalmuscle

Lowermotor

neurons

BRAIN

Preganglionic neuronVisceral Effectors

Smoothmuscle

Glands

Cardiacmuscle

Adipocytes

Visceral motor nuclei inhypothalamus

BRAIN

Autonomicnuclei inbrain stem

SPINAL CORD

Autonomic nuclei in spinal cord

Preganglionicneuron

Autonomic nervous systemSomatic nervous system

Somatic motornuclei ofspinal cord

SPINALCORD

Skeletalmuscle

Autonomicganglia

Ganglionicneurons

Figure 8-33 The Organization of the Somatic and Autonomic Nervous Systems.


Neurotransmitters at Specific Synapses (8-11)

• All synapses between pre- and postganglionic fibers:

• Are cholinergic (ACh) and excitatory

• Postganglionic parasympathetic synapses

• Are cholinergic

• Some are excitatory, some inhibitory, depending on the receptor

• Most postganglionic sympathetic synapses:

• Are adrenergic (NE) and usually excitatory


The Sympathetic Division (8-11)

• Sympathetic chain

• Arises from spinal segments T1–L2

• The preganglionic fibers enter the sympathetic chain

ganglia just outside the spinal column

• Collateral ganglia are unpaired ganglia that receive

splanchnic nerves from the lower thoracic and upper

lumbar segments

• Postganglionic neurons innervate abdominopelvic cavity



• The adrenal medullae

• Are innervated by preganglionic fibers

• Are modified neural tissue that secrete E and NE into

capillaries, functioning like an endocrine gland

• The effect is nearly identical to that of the sympathetic

postganglionic stimulation of adrenergic synapses


Eye

Salivaryglands

Heart

Lung

Liver andgallbladderStomach

Pancreas

Largeintestine

Spleen

Smallintestine

AdrenalmedullaKidney

Sympatheticchain ganglia

Postganglionic fibers to spinal

nerves(innervating skin,

blood vessels,sweat glands,arrector pili

muscles,adipose tissue)

Collateralganglion

Splanchnic nerve

Coll-ateral

ganglion

Splan-chnicnerves

Collateral ganglion

Cardiac andpulmonary plexuses

Cervicalsympathetic

ganglia

Spinal nerves

Spinal cord

Urinary bladderOvaryUterus ScrotumPenis

Sympathetic nerves

PONS

L2L2

T1 T1

Figure 8-34 The Sympathetic Division.

Ganglionic neuronsPreganglionic neurons

KEY



• Also called the "fight-or-flight" division

• Effects

• Increase in alertness, metabolic rate, sweating, heart

rate, blood flow to skeletal muscle

• Dilates the respiratory bronchioles and the pupils

• Blood flow to the digestive organs is decreased

• E and NE from the adrenal medullae support and

prolong the effect


The Parasympathetic Division (8-11)

• Preganglionic neurons arise from the brain stem

and sacral spinal cord

• Include cranial nerves III, VII, IX, and X, the vagus,

a major parasympathetic nerve

• Ganglia very close to or within the target organ

• Preganglionic fibers of the sacral areas form the

pelvic nerves


The Parasympathetic Division (8-11)

• Less divergence than in the sympathetic division,

so effects are more localized

• Also called "rest-and digest" division

• Effects

• Constriction of the pupils, increase in digestive secretions,

increase in digestive tract smooth muscle activity

• Stimulates urination and defecation

• Constricts bronchioles, decreases heart rate


PONS

Terminal ganglionN III Lacrimal gland

Eye

Salivary glands

Terminal ganglionN VII

Terminal ganglion

Terminal ganglion

N IX

N X (Vagus) Heart

Lungs

Cardiac andpulmonaryplexuses

Liver and gallbladder

Stomach

SpleenPancreas

Large intestine

Small intestine

Rectum

Kidney

Urinary bladder

ScrotumPenisOvaryUterus

Spinalcord

Pelvicnerves

S2

S3

S4

Figure 8-35 The Parasympathetic Division.

KEYPreganglionic neuronsGanglionic neurons


Dual Innervation (8-11)

• Refers to both divisions affecting the same organs

• Mostly have antagonistic effects

• Some organs are innervated by only one division


Table 8-5 The Effects of the Sympathetic and Parasympathetic Divisions of the ANS on Various Body Structures(1 of 2)


Table 8-5 The Effects of the Sympathetic and Parasympathetic Divisions of the ANS on Various Body Structures(2 of 2)


Checkpoint (8-11)

38. While out for a brisk walk, Megan is suddenly confronted

by an angry dog. Which division of the ANS is responsible

for the physiological changes that occur as she turns and

runs from the animal?

39. Why is the parasympathetic division of the ANS

sometimes referred to as the anabolic system?

40. What effect would loss of sympathetic stimulation have on

the flow of air into the lungs?

41. What physiological changes would you expect in a

patient who is about to undergo a root canal procedure

and is quite anxious about it?


Aging and the Nervous System (8-12)

• Common changes

• Reduction in brain size and weight and reduction in

number of neurons

• Reduction in blood flow to the brain

• Change in synaptic organization of the brain

• Increase in intracellular deposits and extracellular

plaques

• Senility can be a result of all these changes


Checkpoint (8-12)

42. What is the major cause of age-related

shrinkage of the brain?


The nervous system is closely integrated with other body systems. Every moment of your life, billions of neurons in your nervous system are exchanging information across trillions of synapses and performing the most complex integrative functions in the body. As part of this process, the nervous system monitors all other systems and issues commands that adjust their activities. However, the impact of these commands varies greatly from one system to another. The normal functions of the muscular system, for example, simply cannot be performed without instructions from the nervous system. By contrast, the cardiovascular system is relatively independent—the nervous system merely coordinates and adjusts cardiovascular activities to meet the circulatory demands of other systems. In the final analysis, the nervous system is like the conductor of an orchestra, directing the rhythm and balancing the performances of each section to produce a symphony, instead of simply a very loud noise.

The NERVOUS System

Provides sensations of touch, pressure, pain, vibration, and temperature; hair provides some protection and insulation for skull and brain; protects peripheral nerves

Provides calcium for neural function; protects brain and spinal cord

Facial muscles express emotional state; intrinsic laryngeal muscles permit communication; muscle spindles provide proprioceptive sensations

Controls contraction of arrector pili muscles and secretion of sweat glands

Controls skeletal muscle contractions that results in bone thickening and maintenance and determine bone position

Controls skeletal muscle contractions; coordinates respiratory and cardiovascular activities

SYSTEM INTEGRATORBody System Nervous System Nervous System Body System

Inte

gu

men

tary

Ske

leta

lM

usc

ula

r

Inte

gum

enta

ry(P

age

138)

Ske

leta

l(P

age

188)

Musc

ula

r(P

age

241)

Endocr

ine

(Pag

e 37

6)C

ard

iovasc

ula

r(P

age

467)

Lym

phati

c(P

age

500)

Resp

irato

ry(P

age

532)

Dig

est

ive

(Pag

e 57

2)U

rinary

(Pag

e 63

7)R

epro

duct

ive

(Pag

e 67

1)

Figure 8-36


Checkpoint (8-13)

43. Identify the relationships between the nervous

system and the body systems studied so

far.

163 ch 08_lecture_presentation

Technology

central nervous system

complex system

pearson education

peripheral nervous system

endocrine system introduction

efferent division

cell bodies

cell body dendrites