Chapter The central nervous system

• Identify and explain the function of different types of neurons, and structures in the central nervous system.

• Explain the functional organization of the nervous system. • These will be measured by lecture exams and quizzes.

Outline• Organization• Protection• Overview of components

– Cortex– Basal nuclei– Thalamus– Hypothalamus– Limbic system– Cerebellum– Brain stem– Spinal cord

Fig. 5-1, p. 136Effector organs

(made up of muscle and gland tissue)

Afferent division of PNS*

Efferent division of PNS

Central nervous system

Peripheral nervous systemSmooth muscleCardiac muscleExocrine glandsSome endocrineglands

Stimuli indigestive

tractSensorystimuli

Peripheral nervoussystem (PNS)

OutputfromCNS toperiphery

Brain andspinal cord

Central nervous system (CNS)

Inputto CNSfromperiphery

Enteric nervous system*

Somatic nervous system

Autonomic nervous system

Motorneurons

Skeletalmuscles

Digestiveorgans only

Autonomicnervous system

Sympatheticnervous system

Parasympatheticnervous system

Enteric nervoussystem

Visceralstimuli

Afferentdivision

Efferentdivision

Somaticnervous system

KEY

• Central nervous system (CNS)– Consists of brain and spinal cord

• Peripheral nervous system (PNS)– Afferent division

• Carries information to the CNS

• Two branches– Sympathetic– Parasympathetic

Peripheral axon(afferent fiber)

Efferent neuron*

* Efferent autonomic nerve pathways consist of a two-neuron chain betweenthe CNS and the effector organ.

Effector organ(muscle or gland)

Axonterminals

Centralnervous system(spinal cord)

Peripheralnervous system

Cellbody

Centralaxon

Sensoryreceptor

Afferent neuron

Interneuron

Axon(efferent fiber) Axon

terminalsCellbody

Fig. 5-2, p. 137

• Afferent neurons– Inform CNS about

conditions in both the external and internal environment

• Efferent neurons– Carry instructions

from CNS to effector organs – muscles and glands

• Interneurons – Found entirely

within CNS– Responsible for

• Integrating afferent information and formulating an efferent response

• Higher mental functions associated with the “mind”

Functional Classes of Neurons

Neuroglia

• Also called glial cells• Physically, metabolically, and functionally support

interneurons• Four major types of cells

– Astrocytes– Oligodendrocytes– Microglia– Ependymal cells

• 90% of CNS cells

Neuroglia• Astrocytes

– Main “glue” of CNS – holds neurons together

– Guide neurons during fetal brain development

– Aid in establishment of blood-brain barrier

– Important in repair of brain injuries and in neural scar formation

– Play role in neurotransmitter activity

– Take up excess K+ from brain ECF

– Along with other glial cells – enhance synapse formation and modify synaptic transmission

• Microglia– Immune defense

cells of the CNS– In resting state

release low levels of growth factors that help neurons and other glial cells survive and thrive. Can move.

• Oligodendrogytes

– Form myelin sheaths around axons in CNS

• Ependymal cells

– Line internal, fluid-filled cavities of the CNS

– In ventricles of brain, help form and circulate cerebrospinal fluid

Fig. 5-3, p. 138

Microglia

Space containingcerebrospinal fluid

Ependymalcell

NeuronsBraininterstitialfluid

Oligodendrocyte

Astrocyte

Capillary

• Enclosed by hard, bony structures

• Wrapped by three protective and nourishing membranes – meninges

– Dura mater

– Arachnoid mater

– Pia mater

• Floats in cushioning fluid – cerebrospinal fluid (CSF)

– Surrounds and cushions brain and spinal cord

– Shock absorbing

– Formed primarily by choroid plexuses

• Blood-brain barrier limits access of blood-borne materials into brain tissue

Protection of CNS

2

3

4

5

Brain stem

Fourth ventricle

Arachnoid villus

Cerebrospinal fluid

Subarachnoid space of brain

Dural sinus

Subarachnoid space of spinal cord

Pia mater

Dura materSpinal meningesArachnoid mater

Arachnoid materDura mater

Cranial meninges

Third ventricleChoroid plexus of third ventricleChoroid plexus of lateral ventricle

Vein

CerebrumVenous blood

Lateral ventricle

41

Spinal cordCentral canal

Choroid plexus of fourth ventricleAperture of fourth ventricleCerebellum

Pia mater

Fig. 5-6a, p. 141

Left lateralventricle

Right lateralventricle

Central canalof spinal cord

Fourth ventricle

Thirdventricle

Front of brain

Back of brain

Fig. 5-5a, p. 139

Blood-Brain Barrier (BBB)• Protects brain from chemical fluctuations in blood• Minimizes possibility that harmful blood-borne

substances might reach central nervous tissue• Prevents certain circulating hormones that could also act

as neurotransmitters from reaching brain• Limits use of drugs for treatment of brain and spinal cord

disorders– Many drugs cannot penetrate BBB

– Keeps K+ low and Na+ High

• Cells joined by tight junctions

• an anatomic-physiologic feature of the brain thought to consist of walls of capillaries in the central nervous system and surrounding astrocytic glial membranes.

• The barrier separates the parenchyma of the central nervous system from blood.

• The blood-brain barrier prevents or slows the passage of some drugs and other chemical compounds, radioactive ions, and disease-causing organisms such as viruses from the blood into the central nervous system.

Central Nervous System• Enables you to:

– Subconsciously regulate your internal environment by neural means

– Experience emotions

– Voluntarily control your movements

– Be consciously aware of your own body and your surroundings

– Engage in other higher cognitive processes such as thought and memory

Fig. 5-7b, p. 146

Pineal gland

Corpuscallosum

(b) Brain, sagittal view

MidbrainBrainstem

Top

Cerebrum (the righthemisphere, at thelongitudinal fissurebetween it and theleft hemisphere)

Hypothalamus Thalamus

Opticchiasm

Cerebellum

MedullaPons

Frontofbrain

Cerebrum (cortex)• Highly developed• Makes up about 80% of total brain weight (largest

portion of brain)• Inner core houses basal nuclei• Outer surface is highly convoluted cerebral cortex

– Highest, most complex integrating area of the brain– Plays key role in most sophisticated neural functions

– Organized into six well-defined layers

– Layers are organized into functional vertical columns

Right cerebralhemisphere

Longitudinal fissure

Left cerebralhemisphere

– Excels in logical, analytic, sequential, and verbal tasks

• Math, language forms, philosophy

– Excels in nonlanguage skills

• Spatial perception and artistic and musical talents

Cerebral Hemispheres

Frontallobe

Central sulcus

Parietallobe

Parietooccipitalnotch

Occipitallobe

Preoccipitalnotch

CerebellumBrain stem

Temporallobe

Lateralfissure

Fig. 5-8, p. 143

Carries out initial processing Of visual input

Initial reception of sound sensation

Somatosensory processingResponsible for

Voluntary motor activitySpeaking abilityElaboration of thought

Four major lobes

Fig. 5-9b, p. 144

Fig. 5-9a, p. 144

Cerebral Cortex• Primary areas of cortical specialization for

language– Broca’s area

• Governs speaking ability

– Wernicke’s area• Concerned with language comprehension• Responsible for formulating coherent patterns of

speech

• Language disorders– Aphasias– Speech impediments– Dyslexia

Cerebral Cortex• Primary motor cortex

– Located in frontal lobe

– Confers voluntary control over movement produced by skeletal muscles

– Primarily controls muscles on the opposite side of the body

– Motor homunculus• Depicts location and relative amount of motor cortex

devoted to output to muscles of each body part

Electroencephalogram (EEG)• Record of postsynaptic activity in cortical

neurons• “Brain waves”• Three major uses

– Clinical tool in diagnosis of cerebral dysfunction• epilepsy

– Used in legal determination of brain death

– Used to distinguish various stages of sleep

Electroencephalogram (EEG)

Cerebral Cortex

Schematic Linking

of Various Regions

of the Cortex

Flow of signals

Table 5-2 (1), p. 140

Hypothalamus

Brain stem

Cerebral cortex

Thalamus(medial)

Basal nuclei(lateral to thalamus)

Cerebellum

Spinal cord

Midbrain

Pons

Medulla

Brain component

Cerebral cortex

Basal nuclei

Thalamus

Hypothalamus

Cerebellum

Brain stem(midbrain, pons,and medulla)

*

Corpus callosum

Part of hypothalamus

Basalnucleigraymatter)

Caudate nucleus

Right cerebralhemisphere

Left cerebralhemisphere

Third ventricle

Thalamus

Lateral ventricle

Cerebral cortex(gray matter)

White matter

Claustrum

Globus pallidusPutamen

Fig. 5-14a, p. 154

Basal Nuclei (ganglia)• Act by modifying ongoing activity in motor pathways• Signals from the cortex reach the basal ganglia, the

signals are processed and the output is sent back to the motor cortex

• Primary functions– Inhibiting muscle tone throughout the body– Selecting and maintaining purposeful motor activity

while suppressing useless or unwanted patterns of movement

– Helps monitor and coordinate slow, sustained contractions, especially those related to posture and support

– Links cortex and thalamus

Disorders of the basal ganglia• Parkinson’s

– tremors of the hand

– dopamine deficiency

– Increased rigidity, resting tremors, slow initiation of motor behavior

– http://www.youtube.com/watch?v=S5EE8EVv600

– http://www.youtube.com/watch?feature=fvwp&NR=1&v=xuVY7wS25rc

– http://www.youtube.com/watch?v=ECkPVTZlfP8

Huntington’s– Uncontrollable movements– http://www.youtube.com/watch?v=JzAPh2v-SCQ

Table 5-2 (1), p. 140

Hypothalamus

Brain stem

Cerebral cortex

Thalamus(medial)

Basal nuclei(lateral to thalamus)

Cerebellum

Spinal cord

Midbrain

Pons

Medulla

Brain component

Cerebral cortex

Basal nuclei

Thalamus

Hypothalamus

Cerebellum

Brain stem(midbrain, pons,and medulla)

*

Diencephalon• Houses two brain components

– Thalamus • Performs some primitive sensory processing

– Hypothalamus• Controls many homeostatic functions important in

maintaining stability of internal environment

• Part of diencephalon• Serves as “relay station” and synaptic integrating center

for processing sensory input on its way to cerebral cortex• Screens out insignificant signals and routes important

ones to the somatosensory cortex (directs attention to sensory stimuli of interest)

• Capable of crude awareness of various types of sensation but cannot distinguish their location or intensity

• Positive reinforcement of motor signals initiated by the motor cortex

Thalamus

Disorders of the thalamus• Thalamic pain syndrome• Dejerine-Roussy syndrome• http://www.youtube.com/watch?v=vEV6FompwZg

Table 5-2 (1), p. 140

Hypothalamus

Brain stem

Cerebral cortex

Thalamus(medial)

Basal nuclei(lateral to thalamus)

Cerebellum

Spinal cord

Midbrain

Pons

Medulla

Brain component

Cerebral cortex

Basal nuclei

Thalamus

Hypothalamus

Cerebellum

Brain stem(midbrain, pons,and medulla)

*

Hypothalamus • Brain area most involved in directly regulating internal

environment• Functions

– Controls body temperature

– Controls thirst and urine output

– Controls food intake

– Controls anterior pituitary hormone secretion

– Produces posterior pituitary hormones

– Controls uterine contractions and milk ejection

– Serves as a major ANS coordinating center

– Plays role in emotional and behavioral patterns

– Participates in sleep-wake cycle

Limbic System• Includes portions of the

hypothalamus and other forebrain structures that encircle brain stem

• Responsible for

– Emotion (preparing for attack, crying, laughing, joy satisfaction, pleasure, fear)

– Basic, inborn behavioral patterns related to survival and perpetuation of the species

– Plays important role in motivation and learning and memory

Memory • Storage of acquired knowledge for later recall• Memory trace

– Neural change responsible for retention or storage of knowledge

• Short-term memory– Lasts for seconds to hours

• Long-term memory– Retained for days to years

• Consolidation– Process of transferring and fixing short-term memory

traces into long-term memory stores• Working memory

– Temporarily holds and interrelates various pieces of information relevant to a current mental task

Comparison of Long-Term and Short-Term Memory

* *

Habituation (in Aplysia)Repetitious indifferent stimulus

Closing of Ca2+ channels inpresynaptic neuron

Ca2+ influx

Output of transmitter frompresynaptic neuron

Postsynaptic potential inefferent neuron

Reduced behavioral responseto indifferent stimuli

Ca2+ influx

Output of transmitter frompresynaptic neuron

Postsynaptic potential inefferent neuron

Enhanced behavioralresponse to mild stimuli

Prolongation of action potentialin presynaptic neuron

Blockage of K+ channels inpresynaptic neuron

Cyclic AMP inpresynaptic neuron

Release of serotonin fromfacilitating interneuron

Strong or noxious stimulus

Sensitization (in Aplysia)

Ca2+ channels in presynapticneuron kept open longer

Fig. 5-18, p. 160

Decreased responseto continued stimuli Increased

responseto continued stimuli

Fig. 5-19, p. 162

Long Term Potentiation

Prolonged increase in the strength of existing synapticConnections in activated pathways following brief periods of repeated stimulation

Table 5-2 (1), p. 140

Hypothalamus

Brain stem

Cerebral cortex

Thalamus(medial)

Basal nuclei(lateral to thalamus)

Cerebellum

Spinal cord

Midbrain

Pons

Medulla

Brain component

Cerebral cortex

Basal nuclei

Thalamus

Hypothalamus

Cerebellum

Brain stem(midbrain, pons,and medulla)

*RAS!

Cerebellum

Cerebellum disorders

• Ataxia (uncoordinated movement) and abnormal muscle tone• Inherited, nutritional, developmental, vascular, TBI, demylenating• Cerebellar lesions

– Incoordination of movements– Delay initiation of movements– Do not prevent their execution– Not significant unless a great portion of the cerebellum is

lesioned.– Speed effected

http://www.youtube.com/watch?v=DYP2hkkE9fQ– http://www.youtube.com/watch?v=Dox3_ox8C2U&NR=1&featur

e=endscreen– http://www.youtube.com/watch?v=5eBwn22Bnio

Table 5-2 (1), p. 140

Hypothalamus

Brain stem

Cerebral cortex

Thalamus(medial)

Basal nuclei(lateral to thalamus)

Cerebellum

Spinal cord

Midbrain

Pons

Medulla

Brain component

Cerebral cortex

Basal nuclei

Thalamus

Hypothalamus

Cerebellum

Brain stem(midbrain, pons,and medulla)*

Brain Stem

• Critical connecting link between rest of brain and spinal cord

• Consists of– Medulla

– Pons

– Midbrain

Brain Stem• Functions

– Most of cranial nerves arise from brain stem– Neuronal clusters within brain stem control heart

and blood vessel function, respiration, and many digestive functions

– Plays role in regulating muscle reflexes involved in equilibrium and posture

– Reticular formation within brain stem receives and integrates all incoming sensory synaptic input and forms the RAS which arouses the cortex.

– Centers that govern sleep are in brain stem (evidence suggests center promoting slow-wave sleep lies in hypothalamus)

1. Olfactory nerve

Mucosa ofnasal cavity

Termination of fibersof olfactory nerve

Olfactory bulb

Retina

3. Oculomotornerve

5. Trochlear nerve

Motor—muscles ofmastication

2. Opticnerve

Lateral rectus

6. Abducensnerve 4. Trigeminal

nerveSensory—faceand head

Sensory—taste buds onanterior tongue

7. Facial nerve

Motor—musclesof face andscalp; salivaryand tear glands

= Motor fibers

= Sensory fibers

Fig. 5-21, p. 165

mnemonicOn olfactoryOld opticOlympus oculomotorTowering trochlearTop trigeminalA abducensFamous facialVocal vestibulocochlearGerman glossopharyngealViewed vagusSome spinal accessoryHops hypoglossal

= Motor fibers

= Sensory fibers

12. Hypoglossalnerve

9. Glossopharyngealnerve

10. Vagus nerve 11. Accessorynerve

8. Vestibulocochelarnerve

Vestibularbranch

Cochlearbranch

Cochlea,vestibule, andsemicircularcanals ofinner ear

Motor—muscles ofpharynx; parotid gland

Sensory—taste buds onposterior tongue; receptors inpharynx and carotid sinus

Tongue muscles Muscles of larynx, pharynx,soft palate, shoulder,and neck

Motor—muscles of pharynx and larynx;thoracic and abdominal organs

Sensory—taste buds on tongue and pharynx; thoracic and abdominal organs

Fig. 5-21, p. 165

Brainstem disorders

• Locked in syndrome– Quadraplegia, lack of speech, limited movement

of the eyes

– Conscious, aware, have cognitive function

– TBI, MS, stroke, Lou Gehrig’s disease

– http://www.youtube.com/watch?v=yidjnLXZ6Hg

– http://www.youtube.com/watch?v=xWHnkFaxMxM

Spinal Cord• Extends from brain stem through vertebral canal• 31 pairs of spinal nerves emerge from spinal

cord through spaces formed between arches of adjacent vertebrae– Named for region of vertebral column from which

they emerge• 8 pairs cervical (neck) nerves

• 12 pairs thoracic (chest) nerves

• 5 pairs lumbar (abdominal) nerves

• 5 pairs sacral (pelvic) nerves

• 1 pair coccygeal (tailbone) nerves

Spinal cord

Dorsal rootganglion

Spinalnerve

Vertebra

Meninges(protectivecoverings)

Intervertebraldisk

Sympatheticganglionchain Fig. 5-24, p. 168

Axon

Myelinsheath

Connective tissuearound the axon

Connective tissuearound a fascicleConnective tissue

around the nerve

Blood vessels

Nerve fascicle(many axonsbundled inconnectivetissue)

Nerve

Fig. 5-30, p. 173

Ascending tracts Descending tracts

Dorsal surface

Gray matter

Ventral surface

Dorsal columns:1. Fasciculus gracilis2. Fasciculus cuneatus

Dorsal spinocerebellar

Ventral spinocerebellar

Lateral spinothalamic

Ventral spinothalamic

Lateral corticospinal

Rubrospinal

Ventral corticospinal

Vestibulospinal

Fig. 5-27, p. 170

Somatosensory area of cerebral cortex

Thalamus

Cerebral cortex

Midbrain

Cerebellum

PonsVentral spinocerebellar tract

Primary motor cortex

Medulla

Fasciculuscuneatus

Ventralcorticospinaltract

Lateral corticospinaltract

Pressure receptor in skin

Muscle stretch receptor

Spinal cordslice 5

Spinal cordslice 5

Spinal cordslice 6

slice 1

slice 2

slice 3

slice 3

slice 4

1

23

4

5

6

Ascending tracts Descending tracts

Fig. 5-28, p. 172

Centralcanal

Dorsal horn (cell bodies of interneuronson which afferent neurons terminate)

Lateral horn (cell bodies of autonomicefferent nerve fibers)

Ventral horn (cell bodies of somaticefferent neurons)

Fig. 5-29, p. 173

Spinal Nerves

Spinal Cord• Two vital functions

– Neuronal link between brain and PNS

– Integrating center for spinal reflexes

• Reflex – Any response that occurs automatically without conscious effort

• Two types of reflexes– Simple, or basic, reflexes

• Built-in, unlearned responses– Acquired, or conditioned, reflexes

• Result of practice and learning

• Reflex Arc• Neural pathway involved in accomplishing reflex activity• Five basic components

– Receptor– Afferent pathway– Integrating center– Efferent pathway– Effector

Stimulus

Biceps(flexor)contracts

Handwithdrawn

Triceps(extensor)relaxes

Ascending pathwayto brain

Response

Components of areflex arc

ReceptorAfferent pathwayIntegrating centerEfferent pathwayEffector organs

Integrating center(spinal cord)

Thermalpain receptor

in finger

Efferent pathway

Effectororgans

= excitatory interneuron= inhibitory interneuron= Synapse= Inhibits= Stimulates

AfferentPathway

Fig. 5-31, p. 174

Reflex arc examplewithdrawal reflex

Crossed Extensor Reflex Coupled with the Withdrawal Reflex

Strokes

Alzheimer’s disease

Sleep• Function of sleep is unclear• Sleep-wake cycle

– Normal cyclic variation in awareness of surroundings

• Active process consisting of two types of sleep characterized by different EEG patterns and different behaviors– Slow-wave sleep

– Paradoxical, or REM sleep

Comparison of Slow-Wave and Paradoxical Sleep

EEG Patterns During Different Types of Sleep