powerpoint ® lecture slides prepared by vince austin, bluegrass technical and community college c h...

PowerPoint® Lecture Slides prepared by Vince Austin, Bluegrass Technical and Community College

C H A P T E R

Copyright © 2010 Pearson Education, Inc.

12

The Central Nervous System: Part C


Functional Brain Systems

• Networks of neurons that work together and span wide areas of the brain

• Limbic system

• Reticular formation


Limbic System

• Structures on the medial aspects of cerebral hemispheres and diencephalon

• Includes parts of the diencephalon and some cerebral structures that encircle the brain stem

Copyright © 2010 Pearson Education, Inc. Figure 12.18

Corpus callosum

Septum pellucidum

Olfactory bulb

Diencephalic structuresof the limbic system

•Anterior thalamic nuclei (flanking 3rd ventricle)•Hypothalamus•Mammillary body

Fiber tractsconnecting limbic system structures

•Fornix•Anterior commissure

Cerebral struc-tures of the limbic system

•Cingulate gyrus•Septal nuclei•Amygdala•Hippocampus•Dentate gyrus•Parahippocampal gyrus


Limbic System

• Emotional or affective brain

• Amygdala—recognizes angry or fearful facial expressions, assesses danger, and elicits the fear response

• Cingulate gyrus—plays a role in expressing emotions via gestures, and resolves mental conflict

• Puts emotional responses to odors

• Example: skunks smell bad


Limbic System: Emotion and Cognition

• The limbic system interacts with the prefrontal lobes, therefore:

• We can react emotionally to things we consciously understand to be happening

• We are consciously aware of emotional richness in our lives

• Hippocampus and amygdala—play a role in memory


Reticular Formation

• Three broad columns along the length of the brain stem

• Raphe nuclei

• Medial (large cell) group of nuclei

• Lateral (small cell) group of nuclei

• Has far-flung axonal connections with hypothalamus, thalamus, cerebral cortex, cerebellum, and spinal cord


Reticular Formation: RAS and Motor Function

• RAS (reticular activating system)

• Sends impulses to the cerebral cortex to keep it conscious and alert

• Filters out repetitive and weak stimuli (~99% of all stimuli!)

• Severe injury results in permanent unconsciousness (coma)


Reticular Formation: RAS and Motor Function

• Motor function

• Helps control coarse limb movements

• Reticular autonomic centers regulate visceral motor functions

• Vasomotor

• Cardiac

• Respiratory centers


Visualimpulses

Reticular formation

Ascending generalsensory tracts(touch, pain, temperature)

Descendingmotor projectionsto spinal cord

Auditoryimpulses

Radiationsto cerebralcortex


Electroencephalogram (EEG)

• Records electrical activity that accompanies brain function

• Measures electrical potential differences between various cortical areas

Copyright © 2010 Pearson Education, Inc. Figure 12.20a

(a) Scalp electrodes are used to record brain waveactivity (EEG).


Brain Waves

• Patterns of neuronal electrical activity

• Generated by synaptic activity in the cortex

• Each person’s brain waves are unique

• Can be grouped into four classes based on frequency measured as Hertz (Hz)


Types of Brain Waves

• Alpha waves (8–13 Hz)—regular and rhythmic, low-amplitude, synchronous waves indicating an “idling” brain

• Beta waves (14–30 Hz)—rhythmic, less regular waves occurring when mentally alert

• Theta waves (4–7 Hz)—more irregular; common in children and uncommon in adults

• Delta waves (4 Hz or less)—high-amplitude waves seen in deep sleep and when reticular activating system is damped, or during anesthesia; may indicate brain damage

Copyright © 2010 Pearson Education, Inc. Figure 12.20b

Alpha waves—awake but relaxed

Beta waves—awake, alert

Theta waves—common in children

Delta waves—deep sleep

(b) Brain waves shown in EEGs fall intofour general classes.

1-second interval


Brain Waves: State of the Brain

• Change with age, sensory stimuli, brain disease, and the chemical state of the body

• EEGs used to diagnose and localize brain lesions, tumors, infarcts, infections, abscesses, and epileptic lesions

• A flat EEG (no electrical activity) is clinical evidence of death


Epilepsy

• A victim of epilepsy may lose consciousness, fall stiffly, and have uncontrollable jerking

• Epilepsy is not associated with intellectual impairments

• Epilepsy occurs in 1% of the population


Epileptic Seizures

• Absence seizures, or petit mal

• Mild seizures seen in young children where the expression goes blank

• Tonic-clonic (grand mal) seizures

• Victim loses consciousness, bones are often broken due to intense contractions, may experience loss of bowel and bladder control, and severe biting of the tongue


Control of Epilepsy

• Anticonvulsive drugs

• Vagus nerve stimulators implanted under the skin of the chest can keep electrical activity of the brain from becoming chaotic


Consciousness

• Conscious perception of sensation

• Voluntary initiation and control of movement

• Capabilities associated with higher mental processing (memory, logic, judgment, etc.)

• Loss of consciousness (e.g., fainting or syncopy) is a signal that brain function is impaired


Consciousness

• Clinically defined on a continuum that grades behavior in response to stimuli

• Alertness

• Drowsiness (lethargy)

• Stupor

• Coma


Sleep

• State of partial unconsciousness from which a person can be aroused by stimulation

• Two major types of sleep (defined by EEG patterns)

• Nonrapid eye movement (NREM)

• Rapid eye movement (REM)


Sleep

• First two stages of NREM occur during the first 30–45 minutes of sleep

• Fourth stage is achieved in about 90 minutes, and then REM sleep begins abruptly


Awake

(a) Typical EEG patterns

REM: Skeletal muscles (except ocular muscles and diaphragm) are actively inhibited; most dreaming occurs.NREM stage 1:Relaxation begins; EEG shows alpha waves, arousal is easy.

NREM stage 2: IrregularEEG with sleep spindles (short high- amplitude bursts); arousal is more difficult.

NREM stage 3: Sleep deepens; theta and delta waves appear; vital signs decline.

NREM stage 4: EEG is dominated by delta waves; arousal is difficult; bed-wetting, night terrors, and sleepwalking may occur.


Sleep Patterns

• Alternating cycles of sleep and wakefulness reflect a natural circadian (24-hour) rhythm

• RAS activity is inhibited during, but RAS also mediates, dreaming sleep

• The suprachiasmatic and preoptic nuclei of the hypothalamus time the sleep cycle

• A typical sleep pattern alternates between REM and NREM sleep


(b) Typical progression of an adult through onenight’s sleep stages

Awake

REM

Stage 1

Stage 2NonREM Stage 3

Stage 4

Time (hrs)


Importance of Sleep

• Slow-wave sleep (NREM stages 3 and 4) is presumed to be the restorative stage

• People deprived of REM sleep become moody and depressed

• REM sleep may be a reverse learning process where superfluous information is purged from the brain

• Daily sleep requirements decline with age

• Stage 4 sleep declines steadily and may disappear after age 60


Sleep Disorders

• Narcolepsy

• Lapsing abruptly into sleep from the awake state

• Insomnia

• Chronic inability to obtain the amount or quality of sleep needed

• Sleep apnea

• Temporary cessation of breathing during sleep


Language

• Language implementation system

• Basal nuclei

• Broca’s area and Wernicke’s area (in the association cortex on the left side)

• Analyzes incoming word sounds

• Produces outgoing word sounds and grammatical structures

• Corresponding areas on the right side are involved with nonverbal language components


Memory

• Storage and retrieval of information

• Two stages of storage

• Short-term memory (STM, or working memory)—temporary holding of information; limited to seven or eight pieces of information

• Long-term memory (LTM) has limitless capacity


Outside stimuli

General and special sensory receptors

Data transferinfluenced by:

ExcitementRehearsalAssociation ofold and new data

Long-termmemory(LTM)

Data permanentlylost

Afferent inputs

Retrieval

Forget

Forget

Data selectedfor transfer

Automaticmemory

Data unretrievable

Temporary storage(buffer) in cerebral cortex

Short-termmemory (STM)


Transfer from STM to LTM

• Factors that affect transfer from STM to LTM

• Emotional state—best if alert, motivated, surprised, and aroused

• Rehearsal—repetition and practice

• Association—tying new information with old memories

• Automatic memory—subconscious information stored in LTM


Categories of Memory

1. Declarative memory (factual knowledge)

• Explicit information

• Related to our conscious thoughts and our language ability

• Stored in LTM with context in which it was learned


Categories of Memory

2. Nondeclarative memory

• Less conscious or unconscious

• Acquired through experience and repetition

• Best remembered by doing; hard to unlearn

• Includes procedural (skills) memory, motor memory, and emotional memory


Brain Structures Involved in Declarative Memory

• Hippocampus and surrounding temporal lobes function in consolidation and access to memory

• ACh from basal forebrain is necessary for memory formation and retrieval


Smell

Basal forebrain

Prefrontal cortex

Taste

Thalamus

Touch

Hearing

Vision

Hippocampus

Thalamus

Prefrontalcortex

Basalforebrain

Associationcortex

Sensoryinput

ACh ACh

Medial temporal lobe(hippocampus, etc.)

(a) Declarativememory circuits


Brain Structures Involved in Nondeclarative Memory

• Procedural memory

• Basal nuclei relay sensory and motor inputs to the thalamus and premotor cortex

• Dopamine from substantia nigra is necessary

• Motor memory—cerebellum

• Emotional memory—amygdala


Dopamine

Thalamus Premotorcortex

Substantianigra

Associationcortex

Basalnuclei

Sensory andmotor inputs

Premotorcortex

ThalamusSubstantia nigra

Basal nuclei

(b) Procedural (skills) memory circuits


Molecular Basis of Memory

• During learning:

• Altered mRNA is synthesized and moved to axons and dendrites

• Dendritic spines change shape

• Extracellular proteins are deposited at synapses involved in LTM

• Number and size of presynaptic terminals may increase

• More neurotransmitter is released by presynaptic neurons



• Increase in synaptic strength (long-term potentiation, or LTP) is crucial

• Neurotransmitter (glutamate) binds to NMDA receptors, opening calcium channels in postsynaptic terminal



• Calcium influx triggers enzymes that modify proteins of the postsynaptic terminal and presynaptic terminal (via release of retrograde messengers)

• Enzymes trigger postsynaptic gene activation for synthesis of synaptic proteins, in presence of CREB (cAMP response-element binding protein) and BDNF (brain-derived neurotrophic factor)


Protection of the Brain

• Bone (skull)

• Membranes (meninges)

•Watery cushion (cerebrospinal fluid)

• Blood-brain barrier


Meninges

• Cover and protect the CNS

• Protect blood vessels and enclose venous sinuses

• Contain cerebrospinal fluid (CSF)

• Form partitions in the skull


Meninges

• Three layers

• Dura mater

• Arachnoid mater

• Pia mater


Skin of scalpPeriosteum

Falx cerebri(in longitudinalfissure only)

Blood vesselArachnoid villusPia materArachnoid mater

Duramater Meningeal

Periosteal

Bone of skull

Superiorsagittal sinus

Subduralspace

Subarachnoidspace


Dura Mater

• Strongest meninx

• Two layers of fibrous connective tissue (around the brain) separate to form dural sinuses


Dura Mater

• Dural septa limit excessive movement of the brain

• Falx cerebri—in the longitudinal fissure; attached to crista galli

• Falx cerebelli—along the vermis of the cerebellum

• Tentorium cerebelli—horizontal dural fold over cerebellum and in the transverse fissure


Falx cerebri


Straightsinus

Crista galliof theethmoid bone

Pituitarygland

Falxcerebelli

(a) Dural septa

Tentoriumcerebelli


Arachnoid Mater

• Middle layer with weblike extensions

• Separated from the dura mater by the subdural space

• Subarachnoid space contains CSF and blood vessels

• Arachnoid villi protrude into the superior sagittal sinus and permit CSF reabsorption


Skin of scalpPeriosteum

Falx cerebri(in longitudinalfissure only)

Blood vesselArachnoid villusPia materArachnoid mater

Duramater Meningeal

Periosteal

Bone of skull


Subduralspace

Subarachnoidspace


Pia Mater

• Layer of delicate vascularized connective tissue that clings tightly to the brain


Cerebrospinal Fluid (CSF)

• Composition

• Watery solution

• Less protein and different ion concentrations than plasma

• Constant volume


Cerebrospinal Fluid (CSF)

• Functions

• Gives buoyancy to the CNS organs

• Protects the CNS from blows and other trauma

• Nourishes the brain and carries chemical signals



Arachnoid villus

Subarachnoid spaceArachnoid materMeningeal dura materPeriosteal dura mater

Right lateral ventricle(deep to cut)Choroid plexusof fourth ventricle

Central canalof spinal cord

Choroidplexus

Interventricularforamen

Third ventricle

Cerebral aqueductLateral apertureFourth ventricleMedian aperture

(a) CSF circulation

CSF is produced by thechoroid plexus of eachventricle.

1

CSF flows through theventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord.

2

CSF flows through thesubarachnoid space. 3

CSF is absorbed into the dural venoussinuses via the arachnoid villi. 4

1

2

3

4


Choroid Plexuses

• Produce CSF at a constant rate

• Hang from the roof of each ventricle

• Clusters of capillaries enclosed by pia mater and a layer of ependymal cells

• Ependymal cells use ion pumps to control the composition of the CSF and help cleanse CSF by removing wastes


Ependymalcells

Capillary

Connectivetissue ofpia mater

Wastes andunnecessarysolutes absorbed

Sectionof choroidplexus

(b) CSF formation by choroid plexuses

Cavity ofventricle

CSF forms as a filtratecontaining glucose, oxygen, vitamins, and ions(Na+, Cl–, Mg2+, etc.)


Blood-Brain Barrier

• Helps maintain a stable environment for the brain

• Separates neurons from some bloodborne substances


Blood-Brain Barrier

• Composition

• Continuous endothelium of capillary walls

• Basal lamina

• Feet of astrocytes

• Provide signal to endothelium for the formation of tight junctions


(a) Astrocytes are the most abundantCNS neuroglia.

Capillary

Neuron

Astrocyte


Blood-Brain Barrier: Functions

• Selective barrier

• Allows nutrients to move by facilitated diffusion

• Allows any fat-soluble substances to pass, including alcohol, nicotine, and anesthetics

• Absent in some areas, e.g., vomiting center and the hypothalamus, where it is necessary to monitor the chemical composition of the blood


Homeostatic Imbalances of the Brain

• Traumatic brain injuries

• Concussion—temporary alteration in function

• Contusion—permanent damage

• Subdural or subarachnoid hemorrhage—may force brain stem through the foramen magnum, resulting in death

• Cerebral edema—swelling of the brain associated with traumatic head injury



• Cerebrovascular accidents (CVAs)(strokes)

• Blood circulation is blocked and brain tissue dies, e.g., blockage of a cerebral artery by a blood clot

• Typically leads to hemiplegia, or sensory and speed deficits

• Transient ischemic attacks (TIAs)—temporary episodes of reversible cerebral ischemia

• Tissue plasminogen activator (TPA) is the only approved treatment for stroke



• Degenerative brain disorders

• Alzheimer’s disease (AD): a progressive degenerative disease of the brain that results in dementia

• Parkinson’s disease: degeneration of the dopamine-releasing neurons of the substantia nigra

• Huntington’s disease: a fatal hereditary disorder caused by accumulation of the protein huntingtin that leads to degeneration of the basal nuclei and cerebral cortex

powerpoint ® lecture slides prepared by vince austin, bluegrass technical and community college c h...

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