ch 9 nervous system

© 2013 Pearson Education, Inc.

The Central Nervous System

Chapter 9

Evolution of the Nervous System

Figure 9.1a (1 of 6)

Nerve net of jellyfish

Nervenet

Figure 9.1b (2 of 6)

The flatworm nervous system has aprimitive brain.

Primitive brain

Nerve cords

Figure 9.1c (3 of 6)

The earthworm nervous system has asimple brain and ganglia along a nerve cord.

Esophagus

Primitivebrain

Mouth

Subpharyngealganglion Ventral nerve cord

with ganglia

Figure 9.1d (4 of 6)

The fish forebrain is smallcompared to remainder of brain.

Forebrain

Figure 9.1e (5 of 6)

The goose forebrain is larger.

ForebrainCerebellum

Figure 9.1f (6 of 6)

The human forebrain dominates the brain.

Forebrain

Cerebellum

Figure 9.2a ESSENTIALS – Development of the Human Nervous System

Day 20

In the 20-day embryo (dorsal view), neural plate cells(purple) migrate toward the midline. Neural crest cellsmigrate with the neural plate cells.

Neural crest

Neural plate

Figure 9.2b ESSENTIALS – Development of the Human Nervous System

Day 23By day 23 of embryonic development, neural tube formation isalmost complete.

Anterior openingof neural tube

Posterior openingof neural tube

Neural crestbecomes peripheral

nervous system.

Neural tubebecomes CNS.

Dorsal bodysurface

Figure 9.2c ESSENTIALS – Development of the Human Nervous System

4 Weeks

A 4-week human embryo showingthe anterior end of the neural tubewhich has specialized into threebrain regions.

Forebrain Midbrain

Hindbrain

Spinalcord

Lumen of neural tube

Figure 9.2d ESSENTIALS – Development of the Human Nervous System

6 Weeks

At 6 weeks, the neural tube has differentiatedinto the brain regions present at birth. The centralcavity (lumen) shown in the cross section willbecome the ventricles of the brain (see Fig. 9.4).

Hindbrain

Forebrain

Midbrain

Medullaoblongata

Cerebellumand Pons

Diencephalon

Cerebrum

Diencephalon

Cerebrum

Eye Midbrain

Medullaoblongata

Spinalcord

Figure 9.2e ESSENTIALS – Development of the Human Nervous System

11 Weeks

By 11 weeks of embryonic development, thegrowth of the cerebrum is noticeably more rapidthan that of the other divisions of the brain.

Cerebrum

Diencephalon

Midbrain

Cerebellum

Pons

Medullaoblongata

Spinal cord

Figure 9.2f ESSENTIALS – Development of the Human Nervous System

40 Weeks

At birth, the cerebrum has coveredmost of the other brain regions.Its rapid growth withinthe rigid confines ofthe cranium forcesit to develop aconvoluted,furrowedsurface.

Cerebrum

PonsCerebellum

Medullaoblongata

Spinal cordCranialnerves

Figure 9.2g ESSENTIALS – Development of the Human Nervous System

Child

The directions “dorsal” and“ventral” are different in thebrain because of flexionin the neural tube duringdevelopment.

Dorsal (superior)

Rostral Caudal

Rostral

Caudal

Ventral(inferior)

Ventral(anterior)

Dorsal(posterior)

Figure 9.3 ANATOMY SUMMARY – The Central Nervous System

ANATOMY SUMMARY

CNS: Gray and White Matter

• Gray matter– Unmyelinated nerve cell bodies

– Clusters of cell bodies in the CNS are nuclei– Dendrites– Axon terminals

• White matter– Myelinated axons

– Axon bundles connecting CNS regions are tracts– Contains very few cell bodies


CNS: Bone and Connective Tissue

• Brain is encased in bony skull, or cranium• Spinal cord runs through vertebral column• Meninges lie between bone and tissues to stabilize neural

tissue and protect from bruising– Dura mater: thickest and most superficial – Arachnoid membrane: cobweb like, middle

– Subarachnoid space contains cerebrospinal fluid secreted by choroid plexus

– Pia mater: deepest, thin that adheres to surface of brain or spinal cord, arteries that supply blood to brain.


Figure 9.3-1 ANATOMY SUMMARY – The Central Nervous System

Posterior View of the Central Nervous System Sectional View of the Meninges of the Brain, showinghow they cushion and protect delicate neural tissue

Cranium

Cerebralhemispheres

Cerebellum

Cervical spinalnerves

Cranium

DuramaterVenous sinus

Arachnoidmembrane

Pia mater

Brain

Subduralspace

Subarachnoidspace

Moving from the cranium in,name the meninges that formthe boundaries of the venoussinus and the subdural andsubarachnoid spaces.

FIGURE QUESTION

Figure 9.3b ANATOMY SUMMARY – The Central Nervous System

ANATOMY SUMMARY

Sectional View of the Meninges of the Brain, showinghow they cushion and protect delicate neural tissue

Cranium

Duramater

Venous sinus

Arachnoidmembrane

Pia mater

Brain

Subduralspace

Subarachnoidspace

Cerebrospinal Fluid

The Ventricles of the Brain

Lateral ventricles

Third ventricle

Fourth ventricle

Cerebellum

Central canal

Spinal cordFrontal viewLateral view

The lateral ventricles consist ofthe first and second ventricles.The third and fourth ventriclesextend through the brain stemand connect to the centralcanal that runs through thespinal cord. Compare thefrontal view to the crosssection in Fig. 9.10a.

– Cerebrospinal fluid (CSF): solution secreted by choroid plexus (region on walls of ventricles)

– Choroid plexus is similar to kidney tissue (capillaries and transporting epithelium from the ependyma). Pump sodium and solutes from plasma into ventricles,creating an osmotic gradient that draw water along water along with the solutes.

– CSF flows from ventricles into subarachnoid space, flows around body and absorbed back by special villi on arachnoid membrane

– 2 purposes of CSF: physical and chemical protection

Figure 9.4b-d ANATOMY SUMMARY – Cerebrospinal Fluid

ANATOMY SUMMARY

Cerebrospinal Fluid Secretion

Cerebrospinal fluid is secreted into the ventriclesand flows throughout the subarachnoid space,where it cushions the central nervous system.

Choroid plexusof third ventricle

Pia mater

Arachnoidmembrane

Arachnoidvilli

Sinus

Spinal cord

Central canal

Subarachnoidspace

Arachnoidmembrane

Dura mater

Cerebrospinal Fluid Reabsorption

Cerebrospinal fluid is reabsorbed into the bloodat fingerlike projections of the arachnoidmembrane called villi.

Cerebrospinal fluid

Bone of skull

Dura mater

Endotheliallining

Blood invenous sinus

Fluid movementArachnoidvillus

Dura mater(inner layer)

Subduralspace

Arachnoidmembrane

Subarachnoidspace

Piamater

Cerebralcortex

FIGURE QUESTIONS

1. Physicians may extract a sample of cerebrospinal fluid when they suspect an infection in the brain. Where is the least risky and least difficult place for them to insert a needle through the meninges? (See Fig. 9.4b.)2. The aqueduct of Sylvius is the narrow passageway between the third and fourth ventricles. What happens to CSF flow if the aqueduct becomes blocked by infection or tumor, a condition known as aqueductal stenosis {stenos, narrow}? On a three-dimensional imaging study of the brain, how would you distinguish aqueductal stenosis from a blockage of CSF flow in the subarachnoid space near the frontal lobe?

Choroid plexusof fourth ventricle

Figure 9.4c ANATOMY SUMMARY – Cerebrospinal Fluid

ANATOMY SUMMARYThe Choroid Plexus

The choroid plexustransports ions andnutrients from the bloodinto the cerebrospinal fluid.

Capillary

Ependymalcells

Ions, vitamins,nutrients

WaterCerebrospinalfluid in third ventricle

FIGURE QUESTIONS

Physicians may extract a sample ofcerebrospinal fluid when they suspectan infection in the brain. Where is theleast risky and least difficult place forthem to insert a needle through themeninges? (See Fig. 9.4b.)

1.

2.The aqueduct of Sylvius is the narrowpassageway between the third and fourthventricles. What happens to CSF flowif the aqueduct becomes blocked byinfection or tumor, a condition known asaqueductal stenosis {stenos, narrow}?On a three-dimensional imaging studyof the brain, how would you distinguishaqueductal stenosis from a blockage ofCSF flow in the subarachnoid space nearthe frontal lobe?

Blood-Brain Barrier

– Blood-brain barrier serves as functional protection by protecting interstitial fluid and blood

– prevents harmful chemicals (ions, hormones, etc.) and pathogens

– endothelial cells form tight junctions with one another

– astrocyte foot processes secret substance that promote tight junctions


Astrocyte

Astrocyte foot processessecrete paracrines that

promote tightjunction formation.

Tight junction preventssolute movement

between endothelial cells.


Astrocyte foot processessecrete paracrines that

promote tightjunction formation.

Tight junction preventssolute movement

between endothelial cells.

Astrocyte footprocesses

Tightjunction

Basallamina

Capillary lumen

CNS: Neural Tissue – Metabolic Needs

• Neurons need a constant supply oxygen and glucose to make ATP for active transport of ions and neurotransmitters

• Oxygen– Passes freely across blood–brain barrier– Brain receives 15% of blood pumped by heart

• Glucose– Membrane transporters move glucose from plasma into the

brain interstitial fluid– Brain responsible for about half of body’s glucose

consumption– Progressive hypoglycemia leads to confusion,

unconsciousness, and death© 2013 Pearson Education, Inc.

Figure 9.3a ANATOMY SUMMARY – The Central Nervous System

Posterior View of the Central Nervous System

Cranium

Cerebralhemispheres

Cerebellum

Cervical spinalnerves

Thoracic spinalnerves

Lumbar spinalnerves

Sacral spinal nerves

Sectionedvertebra

Coccygealnerve


One segment of spinal cord, ventral view,showing its pair of nerves.

White matter

Gray matter

Dorsal root:carries sensory

(afferent)information

to CNS.Ventral root: carries motor (efferent)information to musclesand glands.


Gray matter consists of sensory and motor nuclei.

Visceral sensory nuclei

Dorsalroot

ganglion

Lateralhorn

Ventralroot

Ventralhorn

Dorsalhorn

Somaticsensorynuclei

Autonomicefferentnuclei

Somaticmotornuclei

Figure 9.6c-1 (4 of 5)

KEY

Ascending tractscarry sensoryinformation to the brain.

Descending tractscarry commands tomotor neurons.

White matter in the spinal cord consists of tracts ofaxons carrying information to and from the brain.

To the brain

Figure 9.6c-2 (5 of 5)

KEY

Ascending tractscarry sensoryinformation to the brain.

Descending tractscarry commands tomotor neurons.

White matter in the spinal cord consists of tracts ofaxons carrying information to and from the brain.

From the brain

Figure 9.7

SPINAL REFLEXES

In a spinal reflex, sensory information entering the spinal cord isacted on without input from the brain. However, sensoryinformation about the stimulus may be sent to the brain.

StimulusSpinalcord

Integratingcenter

Sensoryinformation

Interneuron

Response

Command tomuscles or

glandsA spinal reflex initiatesa response without input

from the brain.

Figure 9.8 ANATOMY SUMMARY – Central Nervous System

The Brain: The Brain Stem

• 11 of 12 cranial nerves originate – Cranial nerves can include sensory fibers, efferent fibers, or both

(mixed nerves)

• Many nuclei are associated with reticular formation (basic processes, sleep/wake, muscle tone, stretch reflexes, breathing, blood pressure, pain

• Medulla– Somatosensory and corticospinal tracts : convey info about cerebrum to

spinal cord– Pyramids: tracts cross– coordinates breathing, blood pressure, hiccups, swallowing, vomitting

• Pons: info transfer between cerebellum and cerebrum• Midbrain: eye movement, audio and visual reflexes


Lateral View of Brain Stem

Thalamus

Cut edge ofascending

tracts tocerebrum

Cranialnerves

Optic tract

Midbrain

Pons

Cut edgesof tracts leading tocerebellum

Medullaoblongata

Spinal cord

Functions of the Brain Stem

Midbrain

Pons

• Eye movement

• Relay station between cerebrum and cerebellum• Coordination of breathing

• Control of involuntary functions

• Arousal• Sleep• Muscle tone• Pain modulation

Medulla oblongata

Reticular formation (not shown)See Figure 9.16

Figure 9.8f ANATOMY SUMMARY – Central Nervous System

ANATOMY SUMMARY

Table 9.1 The Cranial Nerves

Cerebellum

– second largest brain structure– process sensory information– control coordination of movement– receives motor input from cerebrum

Figure 9.8a-b ANATOMY SUMMARY – Central Nervous System

Lateral view of the CNS

Cerebrum

Spinalcord

Vertebrae

Lateral View of Brain

Medulla oblongata

Pons Cerebellum

Occipitallobe

Temporallobe

Parietallobe

Frontallobe

Figure 9.9

The DIENCEPHALON

The diencephalon lies between the brain stem and the cerebrum. Itconsists of thalamus, hypothalamus, pineal gland, and pituitary gland.

Thalamus

Hypothalamus

Anteriorpituitary

Posterior pituitary

Pinealgland

Corpus callosum

Diencephalon

– thalamus: sensory gate keeper, receives sensory input (optic, ears, and spinal cord) and motor information from the spinal cord and cerebellum, it projects fibers to the cerebrum for processing

– hypothalamus: center for homeostasis, hunger, thirst– pituitary gland: anterior (endocrine gland) and

posterior pituitary (neurohormones)– pineal glands: melatonin

Table 9.2 Functions of the Hypothalamus

Figure 9.8c ANATOMY SUMMARY – Central Nervous System

ANATOMY SUMMARYMid-Sagittal View of Brain

Parietallobe

Occipitallobe

Frontallobe

Corpuscallosum

Temporallobe

Cingulate gyrus

Medulla oblongata

Cerebellum

Pons

Figure 9.10-1The cerebral cortex and basal ganglia are two of the three regions ofgray matter in the cerebrum. The third region, the limbic system, isdetailed in Figure 9.11. The frontal view shown here is similar to thesectional view obtained using modern diagnostic imaging techniques.

FIGURE QUESTIONThe section through thisbrain is a section throughthe ––––––––– plane.

(a) coronal(b) lateral(c) frontal(d) transverse(e) sagittal

Section throughthe brain showingthe basal ganglia

Basalganglia

Corpuscallosum

Lateral ventricle

Tracts ofwhite matter

Tip of lateralventricle

Gray matter ofcerebral cortex

Cerebrum– Gray matter most superficial, white matter most deep (interior)

– Largest and most distinctive part of human brain, associated with reasoning

– 2 hemispheres connected by corpus callosum (axons passing from one side of the brain to the other side (communication)

– each hemisphere divided into 4 lobes (named for cranial bones)

– sulci (groves) and gyri (ridges)

– Gray matter:1. cerebral cortex: most superficial, neurons arranged in layers

2. basal ganglia: movement

3. limbic system: link btw high cognitive functions and more primitive emotional responses (fear)

1. amygdala: memory, deacon making, emotion

2. cingulate gyrus: emotional memory

3. hippocampus: learning and memory


Cell bodies in the cerebral cortex form distinct layersand columns.

Outer surface of the cerebral cortex

1

2

3

4

5

6

Graymatter

Whitematter

Layers

Figure 9.11

THE LIMBIC SYSTEM

The limbic system includes the amygdala, hippocampus, andcingulate gyrus. Anatomically, the limbic system is part of thegray matter of the cerebrum. The thalamus is shown fororientation purposes and is not part of the limbic system.

Cingulate gyrusplays a rolein emotion.

Thalamus

Hippocampus is involved in learningand memory.

Amygdala is involved in emotionand memory.

Figure 9.12

SIMPLE AND COMPLEX PATHWAYS IN THE BRAIN

A simpleneural reflex

Behavioral state and cognitioninfluence brain output.

Sensoryinput

Sensorysystem(reflex)

Cognitivesystem

(voluntary)

CNSbehavioral

statesystem

Motorsystemoutput

Physiologicalresponse or

behavior

Integration

Output

Response

Feedback

Brain Function: Cerebral Cortex

• From a functional viewpoint, it can be divided into three specializations. Information passing along a pathway is usually processed in one or more of these areas:– Sensory areas

– Sensory input translated into perception (awareness)– Motor areas

– Direct skeletal muscle movement– Association areas

– Integrate information from sensory and motor areas– Can direct voluntary behaviors


Figure 9.13

FUNCTIONAL AREAS OF THE CEREBRAL CORTEX

The cerebral cortex contains sensory areas for perception, motor areas that direct movement,and association areas that integrate information.

FRONTAL LOBE PARIETAL LOBE

OCCIPITAL LOBE

TEMPORAL LOBE

Primary motor cortex

Motor associationarea (premolar cortex)

Skeletalmusclemovement

Prefrontalassociationarea

Coordinatesinformation fromother association

areas, controlssome behaviors

Taste

Smell

Hearing

Vision

Sensoryinformationfrom skin,musculoskeletalsystem, viscera,and taste buds

Gustatory cortex

Olfactory cortex Auditorycortex

Auditoryassociation area

Visualcortex

Visualassociationarea

Primary somatic sensory cortex

Sensory association area

http://trifini.com/mind-tricks-images.html


Figure 9.14

CEREBRAL LATERALIZATION

The distribution of functional areas in the two cerebral hemispheres is not symmetrical.

LEFT HAND RIGHT HAND

Prefrontalcortex

Speechcenter

Writing

Auditorycortex

(right ear)

Generalinterpretive center

(language andmathematical

calculation)

Visual cortex(right visual field)

Prefrontalcortex

Analysisby touch

Auditorycortex(left ear)

Spatialvisualizationand analysis

Visual cortex(left visual field)

LEFTHEMISPHERE

RIGHTHEMISPHERE

FIGURE QUESTIONS

1. What would a person see if a stroke destroyed all function in the right visual cortex?2. What is the function of the corpus callosum?3. Many famous artists, including Leonardo da Vinci and Michelangelo, were left-handed. How is this related to cerebral lateralization?

CORPUS CALLOSUM

Brain Function: Sensory Information

• Primary somatic sensory cortex (parietal lobe)– Termination point of pathways from skin, musculoskeletal

system, and viscera– Somatosensory pathways

– Touch– Temperature– Pain– Itch – Body position

– left side of brain controls right side of body, (vice versa)


Brain Function: Sensory Information

• Special senses have devoted regions– Visual cortex– Auditory cortex– Olfactory cortex– Gustatory cortex

• Neural pathways extend from sensory areas to association areas, which integrate stimuli into perception


Figure 9.15

PERCEPTION

The brain has the ability to interpret sensory information to createthe perception of (a) shapes or (b) three-dimensional objects.

What shape do you see? What is this object?

Brain Function: Motor System, Efferent Division

• Three major types– Skeletal muscle movement

– Somatic motor division– Neuroendocrine signals

– Hypothalamus and adrenal medulla– Visceral responses

– Autonomic division, smooth and cardiac muscle edocrine and exocrine glands

• Voluntary movement originate:– Primary motor cortex– Motor association areas– receive sensory input from cerebellum and basal ganglia


Brain Function: Behavioral State

• Modulator of sensory and cognitive processes• Neurons collectively known as diffuse modulatory

systems – Originate in reticular formation in brain stem– Project axons to large areas of the brain– 4 modulatory systems: noradrenergic, serotonergic,

dopaminergic, and cholinergic– influences attention, motivation, wakefulness, memory,

motor control, mood, and metabolic homeostasis

• Reticular activating system controls consciousness and a role in keeping the “conscious brain” awake


Brain Function: Sleep

• Four stages with two major phases – Slow-wave sleep (deep sleep)

– Adjusts body without conscious commands– REM sleep

– Brain activity inhibits motor neurons to skeletal muscle, paralyzing them

– Dreaming takes place

• Circadian rhythm: 24 Hour light dark cycle– Suprachiasmatic nucleus (hypothalamus)


Figure 9.18

EMOTIONS AFFECT PHYSIOLOGY

The association between stress and increased susceptibility toviruses is an example of an emotionally linked immune response.

Sensorystimuli

Cerebralcortex

Integrationoccurs within theassociationareas of thecerebral cortex

Feedback createsawareness of emotionsIntegrated information

Limbic systemcreates emotion

Hypothalamusand brain stem

KEY

Interneuron

initiate

Somaticmotor

responses

Autonomicresponses

Endocrineresponses

Immuneresponses

(both voluntaryand unconscious)

Brain Function: Motivation

• Defined as internal signals that shape voluntary behaviors• Some states known as drives• Work with autonomic and endocrine responses• Motivated behaviors stop when a person has reached a

certain level of satiety


Brain Function: Moods

• Similar to emotions but longer-lasting• Mood disorders

– Fourth leading cause of illness worldwide today– Depression

– Sleep and appetite disturbances– Alterations of mood – May affect function at school or work or in personal

relationships– Antidepressant drugs alter synaptic transmission


Brain Function: Learning and Memory

• Learning has two broad types– Associative learning: 2 things are associated with each other– Nonassociative learning: change in behavior after repeated

exposure– Habituation (decreased response to repeated stimulation) and

sensitization (enhanced response to repeated stimulation)

• Memory has several types– Short-term and long-term

– Working memory and consolidation– implicit (reflexive) and explicit (declarative)– Stored in memory traces near sensory association areas– Antrograde amnesia is inability to remember new information


Figure 9.19

MEMORY PROCESSING

New information goes into short-term memory but is lost unlessprocessed and stored in long-term memory.

Output

Long-termmemory

Locate andrecall

Short-termmemory

Informationinput

Processing(consolidation)

Table 9.3 Types of Long-Term Memory

Brain Function: Language

• Integration of spoken language involves two regions • Wernicke’s area (temporal lobe)• Broca’s area (frontal lobe)

• Sensory input from either visual or auditory• Output from Broca’s initiates spoken or written

– Damage to Broca’s area causes expressive aphasia

• Output from Wernicke’s involved in understanding– Damage to Wernicke’s area causes receptive aphasia



Speaking a written word

Motorcortex

Broca’sarea

Wernicke’sarea

Readwords

Visualcortex


Speaking a heard word

Broca’sarea

Motorcortex

Hearwords

Auditorycortex

Wernicke’sarea


PET scan of the brain at work

FIGURE QUESTIONIn the image above, the brain area activein seeing words is in the _________ lobe,and the brain area active during wordgeneration is in the _______ lobe.


Sensory Physiology

Chapter 10

Sensory Division

– Special senses: vision, hearing, taste, smell, and equilibrium

– Somatic Sense: (think of mainly our sense of “touch” or feeling)touch temperature, pain, itch, and proprioception

– Proprioception: awareness of body movement and position (conscious or unconscious), mediated by muscle and joint proprioceptors

Sensory Pathways

• Stimulus as physical energy → sensory receptor– Receptor acts as a transducer

• Intracellular signal → usually change in membrane potential

• Stimulus → threshold → action potential to CNS• Integration in CNS → cerebral cortex or acted on

subconsciously



Free nerve endings

Unmyelinatedaxon

Cell body

Stimulus

Simple receptors are neuronswith free nerve endings. Theymay have myelinated orunmyelinated axons.


Stimulus

Enclosed nerveending

Layers of connectivetissue

Myelinated axon

Cell body

Complex neural receptors have nerveendings enclosed in connective tissue capsules.This illustration shows a Pacinian corpuscle,which senses touch.


Stimulus

Myelinated axon

Cell body ofsensory neuron

Synapse

Synaptic vesicles

Specialized receptorcell (hair cell)

Most special senses receptors are cellsthat release neurotransmitter onto sensoryneurons, initiating an action potential. Thecell illustrated is a hair cell, found in the ear.

Types of Sensory Receptors

Sensory Transduction

• Transduction: stimulus energy converted into information processed by CNS– Ion channels or second messengers initiate membrane

potential change

• Adequate stimulus: Form of energy to which a receptor is most responsive (Ex. thermoreceptors are most sensitive to temperature)

• Threshold: Minimum stimulus required to active a receptor

• Change in sensory receptor membrane potential is a graded potential called a receptor potential


Convergence creates large receptive fields.

Compass with pointsseparated by 20 mm

Primarysensoryneurons

Secondarysensoryneurons

Skin surface

The receptive fields of threeprimary sensory neuronsoverlap to form one largesecondary receptive field.

Convergence of primaryneurons allows simultaneoussubthreshold stimuli to sumat the secondary sensoryneuron and initiate anaction potential.

Two stimuli that fall within the samesecondary receptive field are perceivedas a single point, because only onesignal goes to the brain. Therefore,there is no two-point discrimination.


Compass with pointsseparated by 20 mm

Primarysensoryneurons

Secondarysensoryneurons

Skin surface

Small receptive fields are found in more sensitive areas.

The two stimuli activate separatepathways to the brain. The twopoints are perceived as distinctstimuli and hence there istwo-point discrimination.

When fewer neurons converge,secondary receptive fields aremuch smaller.


ch 9 nervous system

Documents

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flatworm nervous system

human nervous system6

human forebrain