Fundamentals of Anatomy & Physiology

Fundamentals of Anatomy & Physiology
Eleventh Edition Chapter 16 The Autonomic Nervous System and Higher-Order Functions Lecture Presentation by Lori Garrett, Parkland College

Learning Outcomes 16-1 Compare the organization of the autonomic nervous system with that of the somatic nervous system, and name the divisions and major functions of the ANS Describe the structures and functions of the sympathetic division of the autonomic nervous system Describe the types of neurotransmitters and receptors and explain their mechanisms of action Describe the structures and functions of the parasympathetic division of the autonomic nervous system Describe the mechanisms of parasympathetic neurotransmitter release and their effects on target organs and tissues.

Learning Outcomes 16-6 Compare and contrast the sympathetic and parasympathetic nervous systems Discuss the functional significance of dual innervation and autonomic tone Describe the hierarchy of interacting levels of control in the autonomic nervous system, including the significance of visceral reflexes Explain how memories are created, stored, and recalled; distinguish among the levels of consciousness and unconsciousness; and describe how neurotransmitters influence brain function Summarize the effects of aging on the nervous system and give examples of interactions between the nervous system and other organ systems.

Introduction to ANS, Higher-Order Functions
Focus for this chapter Autonomic nervous system (visceral motor system) Operates without conscious instruction Controls visceral effectors Coordinates cardiovascular, respiratory, digestive, urinary, and reproductive functions Higher-order functions Consciousness Learning Intelligence

16-1 Autonomic Nervous System
Somatic nervous system (SNS) Voluntary control of skeletal muscles Autonomic nervous system (ANS) Involuntary control of visceral effectors Smooth muscle, glands, cardiac muscle, adipocytes Hypothalamus contains integrative centers Neurons comparable to upper motor neurons in SNS Motor neurons of CNS synapse on visceral motor neurons in autonomic ganglia

Visceral motor neurons Preganglionic neurons in brainstem and spinal cord Preganglionic fibers—axons of preganglionic neurons After leaving CNS, they synapse on ganglionic neurons (postganglionic neurons) Autonomic ganglia Contain many ganglionic neurons that innervate visceral effectors Postganglionic fibers—axons of ganglionic neurons

Somatic nervous system
Figure 16–1a Comparison of the Functional Organizations of the Somatic and Autonomic Nervous Systems. Upper motor neurons in primary motor cortex Brain Somatic motor nuclei of brainstem Skeletal muscle Lower motor neurons Spinal cord Somatic motor nuclei of spinal cord Skeletal muscle a Somatic nervous system

Autonomic nervous system
Figure 16–1b Comparison of the Functional Organizations of the Somatic and Autonomic Nervous Systems. Visceral motor nuclei in hypothalamus Brain Preganglionic neuron Visceral Effectors Smooth muscle Autonomic nuclei in brainstem Glands Autonomic ganglia Cardiac muscle Ganglionic neurons Spinal cord Adipocytes Autonomic nuclei in spinal cord Preganglionic neuron b Autonomic nervous system

Two divisions of ANS Sympathetic division “Fight or flight” Prepares the body to deal with emergencies Increases alertness, metabolic rate, and muscular abilities Parasympathetic division “Rest and digest” Conserves energy and maintains resting metabolic rate

Sympathetic and parasympathetic divisions Usually have opposing effects If sympathetic division causes excitation, the parasympathetic causes inhibition May also work independently Only one division innervates some structures May work together, with each controlling one stage of a complex process

Responses to increased sympathetic activity Heightened mental alertness Increased metabolic rate Reduced digestive and urinary functions Activation of energy reserves Increased respiratory rate and dilation of respiratory passageways Increased heart rate and blood pressure Activation of sweat glands

Responses to increased parasympathetic activity Decreased metabolic rate Decreased heart rate and blood pressure Increased secretion by salivary and digestive glands Increased motility and blood flow in digestive tract Stimulation of urination and defecation

16-2 The Sympathetic Division
Sympathetic division (thoracolumbar division) Short preganglionic fibers in thoracic and lumbar segments of spinal cord Preganglionic neurons located between segments T1 and L2 Cell bodies in lateral horns Axons enter anterior roots Ganglionic neurons in ganglia near spinal cord Long postganglionic fibers to target organs

Figure 16–2a The Autonomic Nervous System.
Sympathetic Division a (Thoracolumbar Division) Eye Pons Salivary glands Medulla oblongata Sympathetic nerves Superior Middle Cervical sympathetic ganglia Heart Inferior Cardiac and pulmonary plexuses Greater splanchnic nerve Gray rami to spinal nerves Lung Celiac ganglion Superior mesenteric ganglion Liver and gallbladder Stomach Lesser splanchnic nerve Spleen Pancreas Large intestine Postganglionic fibers to spinal nerves (innervating skin, blood vessels, sweat glands, arrector pili muscles, adipose tissue) Lumbar splanchnic nerves Inferior mesenteric ganglion Small intestine Adrenal medulla Sacral splanchnic nerves Sympathetic chain ganglia Kidney Spinal cord KEY Preganglionic fibers Postganglionic fibers Uterus Ovary Penis Scrotum Urinary bladder

Ganglionic neurons synapse in three locations Sympathetic chain ganglia Collateral ganglia Adrenal medullae Sympathetic chain ganglia On both sides of vertebral column Control effectors in Body wall Thoracic cavity Head Neck Limbs

Figure 16–3a Sites of Ganglia in Sympathetic Pathways.
Sympathetic Chain Ganglia Spinal nerve Preganglionic neuron Autonomic ganglion of right sympathetic chain Autonomic ganglion of left sympathetic chain Innervates visceral effectors by spinal nerves White ramus communicans Sympathetic nerve (postganglionic fibers) Ganglionic neuron Gray ramus communicans Innervates visceral organs in thoracic cavity by sympathetic nerves KEY Preganglionic neurons Note: Both innervation patterns occur on each side of the body. Ganglionic neurons

Collateral ganglia Anterior to vertebral bodies Contain ganglionic neurons that innervate abdominopelvic tissues and viscera Collateral Ganglia Lateral horn Splanchnic nerve (preganglionic fibers) Postganglionic fibers White ramus communicans Collateral ganglion Innervates visceral organs in abdominopelvic cavity b

Adrenal medulla Center of each adrenal gland Modified sympathetic ganglion Ganglionic neurons have very short axons When stimulated, they release neurotransmitters into bloodstream (not at synapse) Function as hormones to affect target cells throughout body

Figure 16–3c Sites of Ganglia in Sympathetic Pathways.
The Adrenal Medullae Preganglionic fibers Adrenal medullae Secretes neurotransmitters into general circulation Endocrine cells (specialized ganglionic neurons)

Fibers in sympathetic division Preganglionic fibers Relatively short Ganglia located near spinal cord Postganglionic fibers Relatively long, except at adrenal medullae Sympathetic chain ganglia 3 cervical 10–12 thoracic 4–5 lumbar 4–5 sacral 1 coccygeal ganglion

Summary of sympathetic chain ganglia Cervical, inferior lumbar, and sacral chain ganglia receive preganglionic fibers from T1–L2 Only thoracic and superior lumbar ganglia (T1–L2) receive preganglionic fibers from white rami Every spinal nerve receives a gray ramus from a ganglion of the sympathetic chain

Figure 16–2a The Autonomic Nervous System.
Sympathetic Division a (Thoracolumbar Division) Eye Pons Salivary glands Medulla oblongata Sympathetic nerves Superior Middle Cervical sympathetic ganglia Heart Inferior Cardiac and pulmonary plexuses Greater splanchnic nerve Gray rami to spinal nerves Lung Celiac ganglion Superior mesenteric ganglion Liver and gallbladder Stomach Lesser splanchnic nerve Spleen Pancreas Large intestine Postganglionic fibers to spinal nerves (innervating skin, blood vessels, sweat glands, arrector pili muscles, adipose tissue) Lumbar splanchnic nerves Inferior mesenteric ganglion Small intestine Adrenal medulla Sacral splanchnic nerves Sympathetic chain ganglia Kidney Spinal cord KEY Preganglionic fibers Postganglionic fibers Uterus Ovary Penis Scrotum Urinary bladder

Collateral ganglia Originate as paired ganglia (left and right) Typically unpaired in adults due to fusion Preganglionic fibers Pass through sympathetic chain without synapsing Form splanchnic nerves In posterior wall of abdominal cavity

Collateral ganglia Postganglionic fibers Leave collateral ganglia Extend throughout abdominopelvic cavity Innervate visceral tissues and organs Function to Reduce blood flow and energy use by organs not vital to short-term survival Release stored energy

Collateral ganglia Celiac ganglion Pair of interconnected masses of gray matter located at base of celiac trunk 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 two-thirds of large intestine

Collateral ganglia Inferior mesenteric ganglion Near base of inferior mesenteric artery Postganglionic fibers provide sympathetic innervation to Kidneys Urinary bladder Terminal segments of large intestine Sex organs

Adrenal medulla Modified sympathetic ganglion at center of each adrenal gland Innervated by preganglionic fibers that synapse on cells that secrete Epinephrine (adrenaline) Norepinephrine (noradrenaline) Epinephrine makes up 75–80 percent of secretory output

Adrenal medulla Bloodstream carries neurotransmitters throughout body Causes changes in metabolic activities of different cells Including cells not innervated by sympathetic postganglionic fibers Effects last much longer than those produced by direct sympathetic innervation Hormones continue to diffuse out of bloodstream

The sympathetic division can change the activities of specific effectors Sympathetic activation Occurs during a crisis The entire division responds Controlled by sympathetic centers in hypothalamus Affects peripheral tissues and CNS activity

Changes caused by sympathetic activation Increased alertness Feelings of energy and euphoria Increased blood pressure, heart rate, breathing rate, and depth of respiration Elevation in muscle tone Mobilization of energy reserves

16-3 Sympathetic Effects Stimulation of sympathetic preganglionic neurons Releases acetylcholine (ACh) at synapses with ganglionic neurons Effect is always excitatory Ganglionic neurons Release neurotransmitters at target organs Telodendria form branching networks Each swollen segment is a varicosity Packed with neurotransmitter vesicles Membrane receptors scattered across target cells

Figure 16–4 Sympathetic Varicosities.
Preganglionic fiber (myelinated) Ganglionic neuron Postganglionic fiber (unmyelinated) Ganglion Varicosities Vesicles containing norepinephrine (NE) Mitochondrion Schwann cell cytoplasm 5 µm Smooth muscle cells Varicosities

16-3 Sympathetic Effects Most sympathetic ganglionic neurons
Release NE at varicosities Called adrenergic neurons Some ganglionic neurons release ACh Called cholinergic neurons Located in body wall, skin, brain, and skeletal muscles

16-3 Sympathetic Effects Effects of sympathetic stimulation
Result primarily from interactions of NE and E with adrenergic membrane receptors Alpha receptors Beta receptors NE stimulates alpha receptors to greater degree than it does beta receptors E stimulates both classes of receptors Both are G-protein-coupled receptors

16-3 Sympathetic Effects Majority of sympathetic postganglionic fibers release NE (adrenergic) A few release ACh (cholinergic) Stimulate sweat glands and dilate blood vessels of skeletal muscles and brain Others release nitric oxide (NO) Nitroxidergic synapses Neurons innervate smooth muscles in blood vessel walls (e.g., in skeletal muscles and brain) Produce vasodilation and increased blood flow

16-4 The Parasympathetic Division
Parasympathetic division (craniosacral division) Long preganglionic fibers in brainstem and sacral segments of spinal cord Autonomic nuclei are in all parts of brainstem and lateral horns of S2–S4 Ganglionic neurons in peripheral ganglia within or adjacent to target organs Short postganglionic fibers in or near target organs

Figure 16–2b The Autonomic Nervous System.
Parasympathetic Division b (Craniosacral Division) Pterygopalatine ganglion Oculomotor (III) Lacrimal gland Eye Pons Ciliary ganglion Facial (VII) Salivary glands Medulla oblongata Submandibular ganglion Glossopharyngeal (IX) Otic ganglion Vagus (X) Heart Lungs Autonomic plexuses (see Figure 16–6) Liver and gallbladder Stomach Spleen Pancreas Large intestine Pelvic Small intestine nerves Rectum Spinal cord Kidney KEY Preganglionic fibers Postganglionic fibers Uterus Ovary Penis Scrotum Urinary bladder

Ganglionic neurons in peripheral ganglia Terminal ganglion Near target organ Usually paired Intramural ganglion Embedded in tissues of target organ Consists of interconnected masses and clusters of ganglion cells

Organization of parasympathetic division Parasympathetic preganglionic fibers leave brain in cranial nerves III (oculomotor) VII (facial) IX (glossopharyngeal) X (vagus) Control visceral structures in head Synapse in ciliary, pterygopalatine, submandibular, and otic ganglia

Vagus nerve Provides 75 percent of all parasympathetic outflow Innervates structures in Neck Thoracic and abdominopelvic cavities including distal portion of large intestine Branches intermingle with fibers of sympathetic division

Preganglionic fibers in sacral segments of spinal cord Carry sacral parasympathetic output Do not join anterior roots of spinal nerves Form pelvic nerves Innervate intramural ganglia in kidneys, urinary bladder, portions of large intestine, and sex organs

Figure 16–2b The Autonomic Nervous System.
Parasympathetic Division b (Craniosacral Division) Pterygopalatine ganglion Oculomotor (III) Lacrimal gland Eye Pons Ciliary ganglion Facial (VII) Salivary glands Medulla oblongata Submandibular ganglion Glossopharyngeal (IX) Otic ganglion Vagus (X) Heart Lungs Autonomic plexuses (see Figure 16–6) Liver and gallbladder Stomach Spleen Pancreas Large intestine Pelvic Small intestine nerves Rectum Spinal cord Kidney KEY Preganglionic fibers Postganglionic fibers Uterus Ovary Penis Scrotum Urinary bladder

Major effects of parasympathetic division Constriction of pupils and focusing on near objects Secretion by digestive glands Absorption and use of nutrients by peripheral cells Changes associated with sexual arousal Increased smooth muscle activity in digestive tract Stimulation and coordination of defecation Contraction of urinary bladder during urination Constriction of respiratory passageways Reduction in heart rate and force of contraction

16-5 Parasympathetic Effects
All parasympathetic neurons release ACh Effects on postsynaptic cell vary widely Due to different types of receptors Or nature of second messenger involved Effects of parasympathetic stimulation of cholinergic receptors are localized and short lived Most ACh is inactivated at synapse by acetylcholinesterase (AChE) ACh that diffuses into surrounding tissues is inactivated by tissue cholinesterase

Cholinergic receptors Nicotinic receptors On ganglion cells of sympathetic and parasympathetic divisions Also occur at neuromuscular junctions of SNS Exposure to ACh causes excitation of ganglionic neuron or muscle fiber

Cholinergic receptors Muscarinic receptors At cholinergic neuromuscular or neuroglandular junctions in parasympathetic division At cholinergic junctions in sympathetic division G protein-coupled receptors Effects are longer lasting than nicotinic receptors Response is excitatory or inhibitory depending on activation or inactivation of specific enzymes

Dangerous environmental toxins Nicotine Binds to nicotinic receptors Targets autonomic ganglia and skeletal neuromuscular junctions Nicotine poisoning may result in coma or death Muscarine Produced by some poisonous mushrooms Binds to muscarinic receptors Targets parasympathetic division

16-6 Summary of ANS Divisions
Sympathetic division has widespread effects Two sets of sympathetic chain ganglia, three collateral ganglia, and two adrenal medullae Short preganglionic fibers, long postganglionic fibers Extensive divergence Preganglionic neurons release ACh; most postganglionic fibers release NE Effector response depends on second messengers

16-6 Summary of ANS Divisions
Parasympathetic division has specific effects Visceral motor nuclei are associated with cranial nerves III, VII, IX, and X, and with S2–S4 Ganglionic neurons are located in ganglia within or next to target organs Innervates regions serviced by cranial nerves and organs in thoracic and abdominopelvic cavities One-fifth the divergence of sympathetic division All neurons are cholinergic Effects are generally brief and restricted

Sympathetic Parasympathetic CNS Preganglionic neuron PNS Preganglionic
Figure 16–5 A Summary Comparison of the Sympathetic and Parasympathetic Divisions. Sympathetic Parasympathetic CNS Preganglionic neuron PNS Preganglionic fiber KEY Sympathetic ganglion Neurotransmitters Acetylcholine Norepinephrine or Epinephrine Ganglionic neurons Bloodstream Postganglionic fiber Parasympathetic ganglion TARGET

16-7 Dual Innervation Dual innervation
Most vital organs are innervated by both divisions of ANS Two divisions commonly have opposing effects Parasympathetic postganglionic fibers travel by cranial nerves to peripheral destinations Sympathetic innervation reaches same structures From superior cervical ganglia of sympathetic chain

16-7 Dual Innervation Anatomy of dual innervation Autonomic plexuses
Nerve networks in the thoracic and abdominopelvic cavities Formed by mingled sympathetic postganglionic fibers and parasympathetic preganglionic fibers Travel with blood and lymphatic vessels that supply visceral organs

16-7 Dual Innervation Cardiac plexus and pulmonary plexus
Intersecting autonomic fibers in thoracic cavity Contain Sympathetic and parasympathetic fibers for heart and lungs, respectively Parasympathetic ganglia that affect those organs Esophageal plexus Contains Descending branches of vagus nerves Splanchnic nerves leaving sympathetic chain Parasympathetic preganglionic fibers of vagus nerve enter abdominopelvic cavity with esophagus Fibers enter celiac plexus

16-7 Dual Innervation Celiac plexus (solar plexus)
Associated with smaller plexuses, such as inferior mesenteric plexus Innervates viscera within abdominal cavity Hypogastric plexus Innervates digestive, urinary, and reproductive organs of pelvic cavity Contains Parasympathetic outflow of pelvic nerves Sympathetic postganglionic fibers from inferior mesenteric ganglion Splanchnic nerves from sacral sympathetic chain

Figure 16–6 The Autonomic Plexuses and Ganglia.
Aortic arch Right vagus nerve Trachea Autonomic Plexuses and Ganglia Left vagus nerve Cardiac plexus Thoracic spinal nerves Pulmonary plexus Thoracic sympathetic chain ganglia Esophagus Esophageal plexus Splanchnic nerves Celiac plexus and ganglion Diaphragm Superior mesenteric ganglion Superior mesenteric artery Inferior mesenteric plexus and ganglia Inferior mesenteric artery Hypogastric plexus Pelvic sympathetic chain

16-7 Dual Innervation The heart receives dual innervation
Acetylcholine released by parasympathetic postganglionic fibers slows heart rate NE released by varicosities of sympathetic division accelerates heart rate Small amounts of both are released continuously, producing autonomic tone Parasympathetic division dominates at rest Crisis speeds heart rate by stimulating sympathetic and inhibiting parasympathetic nerves

16-7 Dual Innervation Some organs are innervated by only one division
Example: sympathetic control of blood vessel diameter NE is released from sympathetic fibers at smooth muscle cells in blood vessel walls Sympathetic tone keeps muscles partially contracted When more blood flow is needed, Rate of NE release decreases Sympathetic cholinergic fibers are stimulated Smooth muscle cells relax and blood vessel dilates

16-8 Regulation of Autonomic Functions
Centers involved in somatic motor control Are found in all portions of CNS Lower motor neurons of cranial and spinal reflex arcs Pyramidal motor neurons of primary motor cortex Simple reflexes based in spinal cord respond rapidly and automatically to stimuli Centers in brainstem control activity of sympathetic and parasympathetic divisions

Visceral reflexes Autonomic, polysynaptic reflexes initiated in viscera Provide automatic motor responses Can be modified, facilitated, or inhibited by higher centers, especially hypothalamus Visceral reflex arc consists of Receptor Sensory neuron Processing center (one or more interneurons) Two visceral motor neurons

Visceral reflexes Long reflexes Autonomic equivalents of polysynaptic reflexes Visceral sensory neurons deliver information to CNS along posterior roots of spinal nerves Within sensory branches of cranial nerves Within autonomic nerves that innervate visceral effectors ANS carries motor commands to visceral effectors Coordinate activities of entire organ Most important in regulating visceral activities in most organs

Visceral reflexes Short reflexes Bypass CNS entirely Involve sensory neurons and interneurons whose cell bodies lie in autonomic ganglia Interneurons synapse on postganglionic neurons Postganglionic fibers distribute motor commands Control simple motor responses with localized effects Control activity in one small part of target organ Provide most control and coordination in digestive tract and associated glands Neurons involved form enteric nervous system

Figure 16–7 Visceral Reflexes.
Receptors in peripheral tissue Afferent (sensory) fibers CENTRAL NERVOUS SYSTEM Stimulus Long reflex Short reflex Processing center in spinal cord Peripheral effector Response Autonomic ganglion (sympathetic or parasympathetic) Postganglionic neuron Preganglionic neuron

Enteric nervous system Ganglia in walls of digestive tract contain cell bodies of Visceral sensory neurons Interneurons Visceral motor neurons Axons form extensive nerve nets Capable of controlling digestive functions independent of CNS

Higher levels of autonomic control Processing centers in medulla oblongata coordinate complex reflexes Contains centers and nuclei involved in Salivation Swallowing Digestive secretions Peristalsis Urinary function Regulated by hypothalamus Integration of ANS and SNS activities Many parallels in organization and function Integration occurs at brainstem Both systems under control of higher centers

Figure 16–8 A Comparison of Somatic and Autonomic Function.
Central Nervous System Cerebral cortex Limbic system Thalamus Hypothalamus Somatosensory Visceral sensory Relay and processing centers in brainstem Somatic reflexes Long reflexes Lower motor neuron Preganglionic Peripheral Nervous System Sensory pathways neuron SNS ANS Short reflexes Ganglionic neuron Skeletal muscles Sensory receptors Visceral effectors

16-9 Higher-Order Functions
Higher-order functions share three characteristics Require the cerebral cortex Involve conscious and unconscious information processing Subject to adjustment over time Not innate, fixed behaviors

Memories Stored information gathered through experience Fact memories Specific bits of information Skill memories Learned motor behaviors Incorporated at unconscious level with repetition Brainstem stores those related to innate behaviors Complex skill memories involve integration of motor patterns in basal nuclei, cerebral cortex, cerebellum

Short-term memories Information can be recalled immediately Do not last long Contain small bits of information Repeating information allows short-term memory to be converted to long-term memory Memory consolidation Long-term memories Two types Secondary memories Fade with time and require effort to recall Tertiary memories Do not fade

Figure 16–9 Memory Storage.
Repetition promotes retention Long-Term Memory Sensory input Short-Term Memory Secondary Tertiary Consolidation Memory Memory • Cerebral cortex (fact memory) • Cerebral cortex and cerebellar cortex (skill memory) Temporary loss Permanent loss due to neural fatigue, shock, interference by other stimuli Permanent loss

Brain regions involved in memory consolidation and access Amygdaloid body and hippocampus Nucleus basalis Cerebral cortex Amygdaloid body and hippocampus Components of limbic system Essential to memory consolidation Damage to hippocampus causes Inability to convert short-term memories to new long-term memories Existing long-term memories remain intact and accessible

Nucleus basalis Cerebral nucleus near diencephalon Plays uncertain role in memory storage and retrieval Tracts connect with hippocampus, amygdaloid body, and cerebral cortex Damage changes emotional states, memory, and intellectual functions Cerebral cortex Stores most long-term memories Conscious motor and sensory memories are referred to appropriate association areas Portions of occipital and temporal lobes Crucial to memories of faces, voices, and words A specific neuron may be activated by only one word or by a specific combination of sensory stimuli

Cellular mechanisms of memory formation and storage Involves anatomical and physiological changes in neurons and synapses Increased neurotransmitter release Facilitation at synapses Formation of additional synaptic connections Increased neurotransmitter release A frequently active synapse increases amount of neurotransmitter it stores Releases more on each stimulation The more neurotransmitter released, the greater the effect on postsynaptic neuron

Facilitation at synapses A repeatedly activated neural circuit results in continuous release of neurotransmitters Neurotransmitter binds to receptors on postsynaptic membrane Produces graded depolarization that brings membrane closer to threshold Resulting facilitation affects all neurons in circuit Formation of additional synaptic connections When neurons repeatedly communicate, Axon tip branches and forms additional synapses on postsynaptic neuron As a result, presynaptic neuron has greater effect on membrane potential of postsynaptic neuron

Facilitated communication along a specific neural circuit Caused by anatomical changes Thought to be the basis of memory storage Memory engram Single circuit that corresponds to a single memory Forms as result of experience and repetition Takes at least an hour to form

Factors affecting formation of memory engrams Nature, intensity, and frequency of original stimulus Drugs that stimulate CNS (caffeine, nicotine) may enhance memory consolidation Hippocampus, through unknown mechanism Linked to NMDA (N-methyl D-aspartate) receptors Blocking these receptors prevents long-term memory formation

States of consciousness Many degrees of conscious and unconscious states Degree of wakefulness indicates level of ongoing CNS activity When CNS function is abnormal or depressed, state of wakefulness is affected Deep sleep Also called slow-wave or non-REM (NREM) sleep Entire body relaxes Cerebral cortex activity is at minimum Heart rate, blood pressure, respiratory rate, and energy use decline up to 30 percent

Rapid eye movement (REM) sleep Active dreaming occurs Changes in blood pressure and respiratory rate EEG resembles awake state Less receptive to outside stimuli than in deep sleep Muscle tone decreases markedly Intense inhibition of somatic motor neurons Eyes move rapidly

Sleep Alternate between REM and deep sleep REM periods initially average 5 minutes Increase to 20 minutes during 8-hour period Produces minor changes in physiological activities of organs and systems Protein synthesis in neurons increases Extended periods without sleep lead to disturbances in mental function

Figure 16–10a States of Sleep.
Awake REM sleep Deep (slow wave) sleep a An EEG of the various sleep states. The EEG pattern during REM sleep resembles the alpha waves typical of awake adults.

Figure 16–10b States of Sleep.
Awake REM sleep Transition period Deep sleep 10:00 P.M. Midnight 2:00 A.M. 4:00 A.M. 6:00 A.M. Time b Typical pattern of sleep stages in a healthy young adult during a single night’s sleep.

Arousal Awakening from sleep Function of the reticular formation Extensive interconnections with sensory, motor, and integrative nuclei And with pathways along brainstem Determined by complex interactions between reticular formation and cerebral cortex

Reticular activating system (RAS) Important brainstem component Diffuse network in reticular formation Extends from medulla oblongata to midbrain Output of RAS projects to thalamic nuclei that influence large areas of cerebral cortex When RAS is inactive, so is cerebral cortex Stimulation of RAS produces widespread activation of cerebral cortex

Sleep is ended by any stimulus that activates reticular formation and RAS Arousal occurs rapidly Effects of a single stimulation of RAS last less than a minute After that, consciousness is maintained by positive feedback from cerebral cortex, basal nuclei, etc.

Regulation of sleep–wake cycles Involves interplay between nuclei that use different neurotransmitters One group stimulates RAS with NE Maintains awake, alert state Another group depresses RAS with serotonin Promotes deep sleep “Dueling” nuclei located in brainstem

Figure 16–11 The Reticular Activating System (RAS).
CN II CN VIII Special sensory input Reticular formation General cranial or spinal nerve input

Brain chemistry Changes in levels of neurotransmitters can strongly affect brain function and behavior Example: Huntington’s disease Destruction of ACh-secreting and GABA-secreting neurons in basal nuclei Symptoms appear as basal nuclei and frontal lobes degenerate Difficulty controlling movements Intellectual abilities gradually decline

Serotonin Affects sensory interpretation and emotional states Compounds that enhance effects also produce hallucinations Example: lysergic acid diethylamide (LSD) Compounds that inhibit production or block action cause severe depression and anxiety Fluoxetine (Prozac) slows removal of serotonin at synapses One type of selective serotonin reuptake inhibitor

Dopamine Inadequate levels cause motor problems of Parkinson’s disease Excessive production may be associated with schizophrenia Amphetamines (“speed”) stimulate secretion Important in nuclei that control intentional movements

16-10 Effects of Aging on Nervous System
Anatomical and physiological changes begin by age 30 Accumulate over time 85 percent of people over age 65 have changes in mental performance and CNS function Common age-related anatomical changes Reduction in brain size and weight Decrease in volume of cerebral cortex Elderly people have narrower gyri, wider sulci, and larger subarachnoid space Reduction in number of neurons Brain shrinkage linked to loss of cortical neurons No neuronal loss in brainstem nuclei

Common age-related anatomical changes Decrease in blood flow to brain Fatty deposits build up in walls of blood vessels Reduces blood flow through arteries (arteriosclerosis) Increases chances of cerebrovascular accident (CVA), or stroke Changes in synaptic organization of brain Synaptic connections are lost Rate of neurotransmitter production declines

Anatomical changes lead to functional changes Memory consolidation becomes more difficult Secondary memories become harder to access Hearing, balance, vision, smell, and taste become less acute Reaction times are slowed Reflexes weaken or disappear Precision of motor control decreases Motor patterns take longer to perform

Age-related changes in CNS do not interfere with ability to function in 85 percent of elderly people Some individuals develop senile dementia (senility) Memory loss Anterograde amnesia Emotional disturbances Alzheimer’s disease is most common

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