Chapter 16: Neural Integration II: The Autonomic Nervous System and Higher-Order Functions

Chapter 16: Neural Integration II:

The Autonomic Nervous System and Higher-Order

Functions

Somatic Nervous System (SNS)

• Operates under conscious control

• Seldom affects long-term survival

Autonomic Nervous System (ANS)

• Operates without conscious instruction

• Coordinates systems functions:– cardiovascular– respiratory– digestive– urinary– reproductive

Figure 16–2

Organization Similarities of SNS and ANS

Organization Similarities of SNS and ANS

• Are efferent divisions • Carry motor commands:

– SNS controls skeletal muscles– ANS controls visceral effectors

The Organization of the Somatic and Autonomic Nervous SystemsPLAYPLAY

Figure 16–2a

The SNS

The SNS

• Motor neurons of central nervous system

• Direct control over skeletal muscles

Figure 16–2b

The ANS

The ANS

• Motor neurons synapse on visceral motor neurons in autonomic ganglia

• Ganglionic neurons control visceral effectors

Integrative Centers

• For autonomic activity in hypothalamus

• Neurons comparable to upper motor neurons in SNS

Visceral Motor Neurons

• In brain stem and spinal cord, are known as preganglionic neurons

• Part of visceral reflex arcs

Preganglionic Fibers

• Axons of preganglionic neurons

• Leave CNS and synapse on ganglionic neurons

Autonomic Ganglia

• Peripheral ganglia• Contain many ganglionic neurons• Ganglionic neurons innervate visceral

effectors: – cardiac muscle– smooth muscle– glands– adipose tissues

Postganglionic Fibers

• Axons of ganglionic neurons

• Begin at autonomic ganglia:– extend to peripheral target organs

Somatic or Visceral Sensory Information

• Trigger visceral reflexes

• Motor commands of reflexes distributed by ANS

Motor Commands

• May control activities of target organs

• May alter ongoing activity

• Changes in visceral activity: – postganglionic fibers release

neurotransmitters

Sympathetic Division

• Does not “Kick in” only during exertion, stress, or emergency (common misconception)

• Some aspects of the system are functioning in visceral reflexes for normal activity. (pupil dilation and water balance, for instance)

Parasympathetic Division

• Controls during resting conditions

• Tends to conserve energy

• Allows for “quiet functions” (e.g. digestion, defecation, etc.)

Divisions of the ANS

• 2 divisions may work independently:– some structures innervated by only 1 division

• 2 divisions may work together:– each controlling one stage of a complex

process

Sympathetic Division

• Preganglionic fibers (thoracic and superior lumbar) synapse in ganglia near spinal cord

• Preganglionic fibers are short

• Postganglionic fibers are long

Figure 16–3

ANS: Sympathetic Division

Fight or Flight

• Sympathetic division readies body for crisis

• Increase in sympathetic activity:– stimulates tissue metabolism– increases alertness

7 Responses to Increased Sympathetic Activity

1. Heightened mental alertness

2. Increased metabolic rate

3. Reduced digestive and urinary functions

4. Energy reserves activated

5. Increased respiratory rate and respiratory passageways dilate

6. Increased heart rate and blood pressure

7. Sweat glands activated

Structure of the Sympathetic Division

• Preganglionic neurons located between segments T1 and L2 of spinal cord

• Ganglionic neurons in ganglia near vertebral column

• Cell bodies of preganglionic neurons in lateral gray horns

• Axons enter ventral roots of segments

Figure 16–4

Ganglionic Neurons

• Occur in 3 locations:– sympathetic chain

ganglia– collateral ganglia– adrenal medullae

Sympathetic Chain Ganglia

• Are on both sides of vertebral column

• Control effectors:– in body wall – inside thoracic cavity – in head – in limbs

Sympathetic Chain GangliaFigure 16–4a

Collateral Ganglia

• Are anterior to vertebral bodies

• Contain ganglionic neurons that innervate tissues and organs in abdominopelvic cavity

Figure 16–4b

Collateral Ganglia

Parasympathetic Division

• Preganglionic fibers originate in brain stem and sacral segments of spinal cord

• Synapse in ganglia close to (or within) target organs

• Preganglionic fibers are long

• Postganglionic fibers are short

Rest and Repose

• Parasympathetic division stimulates visceral activity

• Conserves energy and promotes sedentary activities

Pattern of Responses to Increased Levels of Parasympathetic Activity

• Decreased: – metabolic rate– heart rate and blood pressure

• Increased: – salivary and digestive glands secretion– motility and blood flow in digestive tract

• Urination and defecation stimulation

Enteric Nervous System (ENS)

• Third division of ANS• Extensive network in digestive tract walls• Complex visceral reflexes coordinated

locally• Roughly 100 million neurons• All neurotransmitters are found in the brain

Figure 16–4c

The Adrenal Medullae

Modified Sympathetic Ganglion

• At the center of each adrenal gland in area known as adrenal medulla

• Very short axons• When stimulated, release

neurotransmitters into bloodstream (not at synapse)

• Functions as hormones affect target cells throughout body

Fibers in Sympathetic Division

• Preganglionic fibers:– are relatively short– ganglia located near spinal cord

• Postganglionic fibers:– are relatively long, except at adrenal medullae

• Ventral roots of spinal segments T1–L2 contain sympathetic preganglionic fibers

Ventral Roots

• Give rise to myelinated white ramus

• Carry myelinated preganglionic fibers into sympathetic chain ganglion

• May synapse at collateral ganglia or in adrenal medullae

Preganglionic Fibers

• 1 preganglionic fiber synapses on many ganglionic neurons

• Fibers interconnect sympathetic chain ganglia

• Each ganglion innervates particular body segment(s)

Postganglionic Fibers

• Paths of unmyelinated postganglionic fibers depend on targets

Figure 16–5

Sympathetic Innervation

The Distribution of Sympathetic InnervationPLAYPLAY

Sympathetic Chain

• 3 cervical ganglia

• 10–12 thoracic ganglia

• 4–5 lumbar ganglia

• 4–5 sacral ganglia

• 1 coccygeal ganglion

Preganglionic Neurons

• Limited to spinal cord segments T1–L2:

– white rami (myelinated preganglionic fibers)– gray rami (unmyelinated postganglionic fibers)

Rami

• Only spinal nerves T1–L2 have white rami

• Every spinal nerve has gray ramus:– that carries sympathetic postganglionic fibers

for distribution in body wall

Postganglionic Sympathetic Fibers

• In head and neck leave superior cervical sympathetic ganglia

• Supply the regions and structures innervated by cranial nerves III, VII, IX, X

Abdominopelvic Viscera

• Receive sympathetic innervation via sympathetic preganglionic fibers

• Synapse in separate collateral ganglia

Splanchnic Nerves

• Formed by preganglionic fibers that innervate collateral ganglia

• In dorsal wall of abdominal cavity

• Originate as paired ganglia (left and right)

• Usually fuse together in adults

Postganglionic Fibers

• Leave collateral ganglia

• Extend throughout abdominopelvic cavity

• Innervate variety of visceral tissues and organs

Preganglionic Fibers

• From 7 inferior thoracic segments:– end at celiac ganglion or superior mesenteric

ganglion

• Ganglia embedded in network of autonomic nerves

• From lumbar segments:– form splanchnic nerves – end at inferior mesenteric ganglion

Celiac Ganglion

• Pair of interconnected masses of gray matter

• May form single mass or many interwoven masses

• Postganglionic fibers innervate stomach, liver, gallbladder, pancreas, and spleen

Superior Mesenteric Ganglion

• Near base of superior mesenteric artery

• Postganglionic fibers innervate small intestine and proximal 2/3 of large intestine

Inferior Mesenteric Ganglion

• Near base of inferior mesenteric artery

• Postganglionic fibers provide sympathetic innervation to portions of large intestine, kidney, urinary bladder, and sex organs

Neurotransmitters of the sympathetic division

Neuroendocrine Cells of Adrenal Medullae

• Secrete neurotransmitters epinephrine (E) and norepinephrine (NE)

• Since they are carried in the blood they are actually considered hormones

Epinephrine

• Also called adrenaline

• Is 75–80% of secretory output

• Remaining is noradrenaline (NE)

Sympathetic Division

• Can change activities of tissues and organs by:– releasing NE at peripheral synapses– distributing E and NE throughout body in

bloodstream

Crisis Mode

• Entire division responds (sympathetic activation)

• Are controlled by sympathetic centers in hypothalamus

• Effects are not limited to peripheral tissues

• Alters CNS activity

5 Effects of Sympathetic Activation

1. Increased alertness

2. Feelings of energy and euphoria

3. Change in breathing

4. Elevation in muscle tone

5. Mobilization of energy reserves

Stimulation of Sympathetic Preganglionic Neurons

• Releases ACh at synapses with ganglionic neurons

Cholinergic Synapses

• Use ACh as transmitter

• Excitatory effect on ganglionic neurons

Stimulation of Ganglionic Neurons

• Releases neurotransmitters at specific target organs from telodendria

• Form branching network instead of synaptic knobs

Figure 16–6

Sympathetic Varicosities

• Resemble string of pearls

• Packed with neurotransmitter vesicles

Chains of Varicosities

• Formed from postganglionic neurons

• Pass along or near surface of effector cells

• No specialized postsynaptic membranes

• Membrane receptors on surfaces of target cells

• Release NE

Adrenergic Neurons

• Use NE as neurotransmitter

Varicosities and ACh

• Some ganglionic neurons release ACh instead of NE

• Are located in body wall, skin, brain, and skeletal muscles

NE Released by Varicosities

• Affects targets until reabsorbed or inactivated

• 50–80% of NE is reabsorbed by varicosities:– is reused or broken down by MAO

• The rest diffuses out or is broken down by enzymes

Duration of Effects on Postsynaptic Membrane

• NE persist for a few seconds

• ACh only for 20 msec

Effects of NE or E Released by Adrenal Medullae Last longer because:– bloodstream does not contain MAO or COMT– most tissues contain low concentrations

2 Classes of Sympathetic Receptors

• Alpha receptors

• Beta receptors

Norepinephrine

• Stimulates alpha receptors to greater degree than beta receptors

Epinephrine

• Stimulates both classes of receptors

Localized Sympathetic Activity

• Involves release of NE at varicosities

• Primarily affects alpha receptors near active varicosities

Generalized Sympathetic Activation

• Release of E by adrenal medulla

• Affect alpha and beta receptors throughout body

Stimulation of Alpha () Receptors

• Activates enzymes on inside of cell membrane

• Alpha-1 (1)

• Alpha-2 (2)

Alpha-1 (1)

• More common type of alpha receptor

• Releases intracellular calcium ions from reserves in endoplasmic reticulum

• Has excitatory effect on target cell

Alpha-2 (2)

• Lowers cAMP levels in cytoplasm

• Has inhibitory effect on the cell

• Helps coordinate sympathetic and parasympathetic activities

Beta () Receptors

• Affect membranes in many organs (skeletal muscles, lungs, heart, and liver)

• Trigger metabolic changes in target cell• Changes occur indirectly• Each is a G protein • Stimulation increases intracellular cAMP levels

Beta Receptors

• Two types:– Beta-1 (1) Increases metabolic activity

– Beta-2 (2) • Causes inhibition• Triggers relaxation of smooth muscles along

respiratory tract

Beta-3 (3)

• Found in adipose tissue

• Leads to lipolysis, the breakdown of triglycerides in adipocytes

• Releases fatty acids into circulation

Sympathetic Postganglionic Fibers

• Mostly adrenergic (release NE)

• A few cholinergic (release ACh)

• Innervate sweat glands of skin and blood vessels of skeletal muscles and brain

• Stimulate sweat gland secretion and dilates blood vessels

ACh

• Released by parasympathetic division

• Body wall and skeletal muscles are not innervated by parasympathetic division

• Both NE and ACh needed to regulate visceral functions

Nitroxidergic Synapses

• Release nitric oxide (NO) as neurotransmitter

• Neurons innervate smooth muscles in walls of blood vessels in skeletal muscles and the brain

• Produces vasodilation and increased blood flow

Summary of Sympathetic Division (1 of 3)

• Includes 2 sets of sympathetic chain ganglia, 1 on each side of vertebral column

• 3 collateral ganglia anterior to vertebral column

• 2 adrenal medullae• Preganglionic fibers are short because

ganglia are close to spinal cord

Summary of Sympathetic Division (2 of 3)

• Postganglionic fibers are longer and stretch to reach target organs

• Single preganglionic fiber may innervate 2 dozen or more ganglionic neurons in different ganglia

Summary of Sympathetic Division (3 of 3)

• Preganglionic neurons release ACh; most postganglionic fibers release NE, few release ACh or NO

• Effector response depends on second messengers activated when NE or E binds to alpha or beta receptors

ANS: The Parasympathetic Division

Autonomic Nuclei

• Are contained in the mesencephalon, pons, and medulla oblongata:– associated with cranial nerves III, VII, IX, X

• In lateral gray horns of spinal segments S2–S4

Ganglionic Neurons in Peripheral Ganglia

• Preganglionic fiber synapses on 6–8 ganglionic neurons:– terminal ganglion:

• near target organ• usually paired

– intramural ganglion: • embedded in tissues of target organ• interconnected masses• clusters of ganglion cells

Pattern of Parasympathetic Division

• All ganglionic neurons in same ganglion

• Postganglionic fibers influence same target organ

• Effects of parasympathetic stimulation more specific and localized

What are the mechanisms of neurotransmitter release in

the parasympathetic division?

Parasympathetic Preganglionic Fibers

• Leave brain as components of cranial nerves:– III (oculomotor)– VII (facial)– IX (glossopharyngeal)– X (vagus)

The Distribution of Parasympathetic InnervationPLAYPLAY

Oculomotor, Facial, and Glossopharyngeal Nerves

• Control visceral structures in head

• Synapse in ciliary, pterygopalatine, submandibular, and otic ganglia

• Short postganglionic fibers continue to their peripheral targets

Vagus Nerve• Preganglionic parasympathetic innervation

to structures in:– neck– thoracic and abdominopelvic cavity– distal portion of large intestine

• Provides 75% of all parasympathetic outflow

• Branches intermingle with fibers of sympathetic division

Sacral Segments of Spinal Cord

• Preganglionic fibers carry sacral parasympathetic output

• Do not join ventral roots of spinal nerves

Pelvic Nerves

• Innervate intramural ganglia in walls of:– kidneys– urinary bladder– portions of large intestine– sex organs

Parasympathetic Activation

• Centers on relaxation, food processing, and energy absorption

• Localized effects, last a few seconds at most

10 Effects of Parasympathetic Activation

1. Constriction of pupils:– restricts light entering eyes

2. Secretion by digestive glands:– exocrine and endocrine

3. Secretion of hormones

4. Changes in blood flow and glandular activity:

– associated with sexual arousal

5. Increases smooth muscle activity:– along digestive tract

6. Defecation:– stimulation and coordination

7. Contraction of urinary bladder:– during urination

8. Constriction of respiratory passageways

9. Reduction in heart rate:– and force of contraction

10. Sexual arousal:– stimulation of sexual glandsSexual arousal:– stimulation of sexual glands

Parasympathetic Neurons

• All release ACh as neurotransmitter

• Effects vary widely

• Inactivated by AChE at synapse

• Ach is also inactivated by pseudocholinesterase in surrounding tissues

2 Types of ACh Receptors on Postsynaptic Membranes

• Nicotinic receptors

• Muscarinic receptors

Nicotinic Receptors

• On surfaces of ganglion cells (sympathetic and parasympathetic)

• At neuromuscular junctions of somatic nervous system

Action of Nicotinic Receptors

• Exposure to ACh causes excitation of ganglionic neuron or muscle fiber

• Open chemically gated channels in postsynaptic membrane

Muscarinic Receptors

• At cholinergic neuromuscular or neuroglandular junctions (parasympathetic)

• At few cholinergic junctions (sympathetic)

• G proteins

Action of Muscarinic Receptors

• Effects are longer lasting than nicotinic receptors

• Response reflects activation or inactivation of specific enzymes

• Can be excitatory or inhibitory

Toxins• Produce exaggerated, uncontrolled

responses

• Nicotine:– binds to nicotinic receptors– targets autonomic ganglia and skeletal

neuromuscular junctions

• Muscarine:– binds to muscarinic receptors– targets parasympathetic neuromuscular or

neuroglandular junctions

Nicotine Poisoning

• 50 mg ingested or absorbed through skin

• Symptoms: – vomiting, diarrhea, high blood pressure, rapid

heart rate, sweating, profuse salivation, convulsions

• May result in coma or death

Muscarine Poisoning

• Symptoms: – salivation, nausea, vomiting, diarrhea,

constriction of respiratory passages, low blood pressure, slow heart rate (bradycardia)

ANS: Adrenergic and Cholinergic Receptors

Comparing Sympathetic and Parasympathetic Divisions

• Sympathetic:– widespread impact– reaches organs and tissues throughout body

• Parasympathetic:– innervates only specific visceral structures

Figure 16–9

Differences between Sympathetic and Parasympathetic Divisions

Table 16-2

Summary: Sympathetic and Parasympathetic Divisions

Dual Innervation

• Most vital organs receive instructions from both sympathetic and parasympathetic divisions

• 2 divisions commonly have opposing effects

Table 16-3 (1 of 2)

Summary: Comparing

Sympathetic and Parasympathetic

Divisions

Table 16-3 (2 of 2)

Summary: Comparing Sympathetic and

Parasympathetic Divisions

Anatomy of Dual Innervation

• Parasympathetic postganglionic fibers accompany cranial nerves to peripheral destinations

• Sympathetic innervation reaches same structures by traveling directly from superior cervical ganglia of sympathetic chain

Structure: Autonomic Plexuses

• Nerve networks in the thoracic and abdominopelvic cavities:– are formed by mingled sympathetic

postganglionic fibers and parasympathetic preganglionic fibers

• Travel with blood and lymphatic vessels that supply visceral organs

6 Autonomic Plexuses

1. Cardiac plexus

2. Pulmonary plexus

3. Esophageal plexus

4. Celiac plexus

5. Inferior mesenteric plexus

6. Hypogastric plexus

Figure 16–10

The Autonomic Plexuses

Autonomic Motor Neurons

• Maintains resting level of spontaneous activity

• Background level of activation determines autonomic tone

Autonomic Tone

• Is an important aspect of ANS function:– if nerve is inactive under normal conditions,

can only increase activity– if nerve maintains background level of activity,

can increase or decrease activity

Autonomic Tone and Dual Innervation

• Significant where dual innervation occurs:– 2 divisions have opposing effects

• More important when dual innervation does not occur

Visceral Reflexes

ANS

• Simple reflexes from spinal cord provide rapid and automatic responses

• Complex reflexes coordinated in medulla oblongata

Medulla Oblongata

• Contains centers and nuclei involved in:– salivation– swallowing– digestive secretions– peristalsis– urinary function

• Regulated by hypothalamus

Hypothalamus

• Interacts with all other portions of brain

Enteric Nervous System

• Ganglia in the walls of digestive tract contain cell bodies of:– visceral sensory neurons– interneurons– visceral motor neurons

• Axons form extensive nerve nets• Control digestive functions independent of

CNS

Characteristics of Higher-Order Functions

• Require cerebral cortex

• Involve conscious and unconscious information processing

• Not part of programmed “wiring” of brain

• Can adjust over time

MemoriesStored bits of information gathered through

experience

• Declarative memory– Facts

• Skill Memory– Learned motor behaviors– Incorporated at unconscious level with

repetition– Programmed behaviors stored in appropriate

area of brain stem

Short & Long Term Memories

Short Term

• Information that can be recalled immediately

• Contain small bits of information

Long Term

• Can last a life time

2 Types of Long-Term Memory

• Secondary memories fade and require effort to recall

• Tertiary memories are with you for life

Long-Term Memories

• Most stored in cerebral cortex

• Conscious motor and sensory memories referred to association areas

Memory Storage

Brain Structures and Memory

• Amygdaloid body and hippocampus:– are essential to memory consolidation

Damage to the Hippocampus

• Inability to convert short-term memories to new long-term memories

• Existing long-term memories remain intact and accessible

Occipital and Temporal Lobes

• Special portions crucial to memories of faces, voices, and words

“Grandmother cells”

• Specific neuron activated by combination of sensory stimuli associated with particular individual (grandmother)

Memories Stored In

• Visual association area• Auditory association area• Speech center• Frontal lobes• Related information stored in other

locations– if storage area is damaged, memory will be

incomplete

Memory Consolidation at Cellular Level

• Involves anatomical, physiological changes in neurons, synapses

Increased Neurotransmitter Release

• Frequently active synapse increases the amount of neurotransmitter it stores

• Releases more on each stimulation

• The more neurotransmitter released, the greater effect on postsynaptic neuron

Facilitation at Synapses (1 of 2)

• Neural circuit repeatedly activated

• Synaptic terminals begin continuously releasing neurotransmitter

• Neurotransmitter binds to receptors on postsynaptic membrane

Facilitation at Synapses (2 of 2)

• Produce graded depolarization

• Brings membrane closer to threshold

• Facilitation results affect all neurons in circuit

Formation of Additional Synaptic Connections

• Neurons repeatedly communicating

• Axon tip branches and forms additional synapses on postsynaptic neuron

• Presynaptic neuron has greater effect on transmembrane potential of postsynaptic neuron

Memory Engram

• Single circuit corresponds to single memory

• Form as result of experience and repetition

Factors of Conversion of short to long term memory

• Nature, intensity, and frequency of original stimulus

• Strong, repeated, and exceedingly pleasant or unpleasant events likely converted to long-term memories

NMDA (N-methyl D-aspartate) Receptors

• Linked to consolidation

• Chemically gated calcium channels

• Activated by neurotransmitter glycine

• Gates open, calcium enters cell

• Blocking NMDA receptors in hippocampus prevents long-term memory formation

States of Consciousness

• Many gradations of both states

• Degree of wakefulness indicates level of ongoing CNS activity

• When abnormal or depressed, state of wakefulness is affected

Figure 16–14a

2 types of Sleep

• Characteristic patterns of brain wave activity– deep sleep– REM

Deep Sleep

• Also called slow wave sleep

• Entire body relaxes

• Cerebral cortex activity minimal

• Heart rate, blood pressure, respiratory rate, and energy utilization decline up to 30%

Rapid Eye Movement (REM) Sleep

• Active dreaming occurs• Changes in blood pressure and respiratory rate• Less receptive to outside stimuli than in deep

sleep• Muscle tone decreases markedly• Intense inhibition of somatic motor neurons• Eyes move rapidly as dream events unfold

Nighttime Sleep Pattern

Significance of Sleep

• Has important impact on CNS

• Minor changes in physiological activities of organs and systems

• Protein synthesis in neurons increases during sleep

• Extended periods without sleep lead to disturbances in mental function

Arousal

• Awakening from sleep

• Function of reticular formation

Reticular Activating System (RAS)

• Important brain stem component

• Diffuse network in reticular formation

• Extends from medulla oblongata to mesencephalon

Figure 16–15

Reticular Activating

System (RAS)

Ending Sleep

• Any stimulus activates reticular formation and RAS

• Arousal occurs rapidly

• Effects of single stimulation of RAS last less than a minute

Regulation of Awake–Asleep Cycles

• Involves interplay between brain stem nuclei that use different neurotransmitters

• Group of nuclei stimulates RAS with NE and maintains awake, alert state

• Other group promotes deep sleep by depressing RAS activity with serotonin

• “Dueling” nuclei located in brain stem

Drugs and Clinical Considerations

Lysergic Acid Diethylamide (LSD)

• Powerful hallucinogenic drug

• Activates serotonin receptors in brain stem, hypothalamus, and limbic system

Serotonin

• Compounds that enhance effects also produce hallucinations

• Compounds that inhibit or block action cause severe depression and anxiety

• Variations in levels affect sensory interpretation and emotional states

Fluoxetine (Prozac)

• Slows removal of serotonin at synapses

• Increases serotonin concentrations at postsynaptic membrane

• Classified as selective serotonin reuptake inhibitors (SSRIs)

• Other SSRIs:– Celexa, Luvox, Paxil, and Zoloft

Parkinson’s Disease

• Inadequate dopamine production causes motor problems

Huntington’s Disease

• Destruction of ACh-secreting and GABA-secreting neurons in basal nuclei

• Symptoms appear as basal nuclei and frontal lobes slowly degenerate

• Difficulty controlling movements

• Intellectual abilities gradually decline

Dopamine

• Secretion stimulated by amphetamines, or “speed”

• Large doses can produce symptoms resembling schizophrenia

• Important in nuclei that control intentional movements

• Important in other centers of diencephalon and cerebrum

Aging

• Anatomical and physiological changes begin after maturity (age 30)

• Accumulate over time

• 85% of people over age 65 have changes in mental performance and CNS function

Reduction in Brain Size and Weight

• Decrease in volume of cerebral cortex

• Narrower gyri and wider sulci

• Larger subarachnoid space

Reduction in Number of Neurons

• Brain shrinkage linked to loss of cortical neurons

• No neuronal loss in brain stem nuclei

Decrease in Blood Flow to Brain

• Arteriosclerosis:– fatty deposits in walls of blood vessels– reduce blood flow through arteries– increase chances of rupture

• Cerebrovascular accident (CVA), or stroke:– may damage surrounding neural tissue

Intracellular and Extracellular Changes in CNS Neurons

• Neurons in brain accumulate abnormal intracellular deposits

• Including lipofuscin and neurofibrillary tangles

Incapacitation

• 85% of elderly population develops changes that do not interfere with abilities

• Some individuals become incapacitated by progressive CNS changes

Senility

• Also called senile dementia

• Degenerative changes: – memory loss– anterograde amnesia– emotional disturbances

• Alzheimer’s disease is most common

That’s it(phew!)