Putting it all together-Neural integration Muse lecture #11 Ch /5/12 Copyright 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 12.6c Parietal lobe Frontal lobe Right cerebral hemisphere Occipital lobe Left cerebral hemisphere Cerebral veins and arteries covered by arachnoid mater Longitudinal fissure Posterior (c) Anterior Copyright 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Figure 12.26b Ependymal cells Capillary Connective tissue of pia mater Wastes and unnecessary solutes absorbed Section of choroid plexus (b) CSF formation by choroid plexuses Cavity of ventricle CSF forms as a filtrate containing glucose, oxygen, vitamins, and ions (Na +, Cl , Mg 2+, etc.) Sensory Information Afferent Division of the Nervous System Receptors Sensory neurons Sensory pathways Efferent Division of the Nervous System Nuclei Motor tracts Motor neurons Copyright 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Increase the learning of this chapter! Emotional statebest if alert (beta wave), motivated, surprised, and aroused. Chocolate while studying! Rehearsalrepetition and practice Associationtying new information with old memories. Connect lecture to lab. Draw!!! Automatic memorysubconscious information stored in LTM. Test yourself Get some sleep. Repeat often Sensory Information Figure 151 An Overview of Neural Integration. Sensory Information Somatic Nervous System (SNS) Motor neurons and pathways that control skeletal muscles Sensory Receptors Sensation The arriving information from these senses Perception Conscious awareness of a sensation Sensory Receptors Special Senses Olfaction (smell) Vision (sight) Gustation (taste) Equilibrium (balance) Hearing Sensory Receptors The Detection of Stimuli Receptor sensitivity Each receptor has a characteristic sensitivity Receptive field Area is monitored by a single receptor cell The larger the receptive field, the more difficult it is to localize a stimulus Sensory Receptors Figure 152 Receptors and Receptive Fields Sensory Receptors The Interpretation of Sensory Information Arriving stimulus Takes many forms: physical force (such as pressure) dissolved chemical sound light Sensory Receptors The Interpretation of Sensory Information Sensations Taste, hearing, equilibrium, and vision provided by specialized receptor cells Communicate with sensory neurons across chemical synapses Sensory Receptors Adaptation Reduction in sensitivity of a constant stimulus Your nervous system quickly adapts to stimuli that are painless and constant example smell Sensory Receptors Adaptation Tonic receptors Are always active Show little peripheral adaptation Are slow-adapting receptors Remind you of an injury long after the initial damage has occurred Sensory Receptors Adaptation Phasic receptors Are normally inactive Become active for a short time whenever a change occurs Provide information about the intensity and rate of change of a stimulus Are fast-adapting receptors Classifying Sensory Receptors Exteroceptors provide information about the external environment Proprioceptors report the positions of skeletal muscles and joints Interoceptors monitor visceral organs and functions Classifying Sensory Receptors General sensory receptors are divided into four types by the nature of the stimulus that excites them Nociceptors (pain) Thermoreceptors (temperature) Mechanoreceptors (physical distortion) Chemoreceptors (chemical concentration) Classifying Sensory Receptors Nociceptors Are free nerve endings with large receptive fields Branching tips of dendrites Not protected by accessory structures Can be stimulated by many different stimuli Two types of axons: Type A and Type C fibers Classifying Sensory Receptors Thermoreceptors Also called temperature receptors Are free nerve endings located in The dermis Skeletal muscles The liver The hypothalamus Classifying Sensory Receptors Mechanoreceptors Sensitive to stimuli that distort their plasma membranes Contain mechanically gated ion channels whose gates open or close in response to Stretching Compression Twisting Other distortions of the membrane Classifying Sensory Receptors Three Classes of Mechanoreceptors Tactile receptors provide the sensations of touch, pressure, and vibration: touch sensations provide information about shape or texture pressure sensations indicate degree of mechanical distortion vibration sensations indicate pulsing or oscillating pressure Classifying Sensory Receptors Figure 153a Tactile Receptors in the Skin Classifying Sensory Receptors Baroreceptors Monitor change in pressure Consist of free nerve endings that branch within elastic tissues in wall of distensible organ (such as a blood vessel) Respond immediately to a change in pressure, but adapt rapidly Classifying Sensory Receptors Three Major Groups of Proprioceptors Muscle spindles Monitor skeletal muscle length Trigger stretch reflexes Golgi tendon organs Located at the junction between skeletal muscle and its tendon Stimulated by tension in tendon Monitor external tension developed during muscle contraction Receptors in joint capsules Free nerve endings detect pressure, tension, movement at the joint Classifying Sensory Receptors Chemoreceptors Respond only to water-soluble and lipid- soluble substances dissolved in surrounding fluid Receptors exhibit peripheral adaptation over period of seconds; central adaptation may also occur Sensory Pathways First-Order Neuron (sensory receptor) Sensory neuron delivers sensations to the CNS Cell body of a first-order general sensory neuron is located in dorsal root ganglion or cranial nerve ganglion Second-Order Neuron (interneuron) Axon of the sensory neuron synapses on an interneuron in the CNS May be located in the spinal cord or brain stem Third-Order Neuron (brain based neuron) If the sensation is to reach our awareness, the second-order neuron synapses on a third-order neuron in the thalamus Sensory Pathways Somatic Sensory Pathways Carry sensory information from the skin and musculature of the body wall, head, neck, and limbs Three major somatic sensory pathways 1 The posterior column pathway 2 The spinothalamic pathway 3 The spinocerebellar pathway Sensory Pathways Figure 154 Sensory Pathways and Ascending Tracts in the Spinal Cord pain Fine touch, proprioreception Crude touch proprioreceptive Sensory Pathways Somatic Sensory Pathways Posterior column pathway Carries sensations of highly localized (fine) touch, pressure, vibration, and proprioception Spinal tracts involved: left and right fasciculus gracilis left and right fasciculus cuneatus Figure 155a Sensory Pathways Posterior Column Pathway Axons synapse On third-order neurons in one of the ventral nuclei of the thalamus Nuclei sort the arriving information according to: the nature of the stimulus the region of the body involved Figure 155a Sensory Pathways Posterior Column Pathway Processing in the thalamus Determines whether you perceive a given sensation as fine touch, as pressure, or as vibration Ability to determine stimulus Precisely where on the body a specific stimulus originated depends on the projection of information from the thalamus to the primary sensory cortex Figure 155a Sensory Pathways Posterior Column Pathway Sensory information From toes arrives at one end of the primary sensory cortex From the head arrives at the other: when neurons in one portion of your primary sensory cortex are stimulated, you become aware of sensations originating at a specific location Figure 155a Sensory Pathways Posterior Column Pathway Sensory homunculus Functional map of the primary sensory cortex Distortions occur because area of sensory cortex devoted to particular body region is not proportional to regions size, but to number of sensory receptors it contains Sensory Pathways Figure 155a The Posterior Column Pathway. Crossover in medulla Sensory Pathways The Spinothalamic Pathway Provides conscious sensations of poorly localized (crude) touch, pressure, pain, and temperature First-order neurons Axons of first-order sensory neurons enter spinal cord and synapse on second-order neurons within posterior gray horns Crossover in spinal cord pre-ascension Sensory Pathways The Spinothalamic Pathway Second-order neurons Cross to the opposite side of the spinal cord before ascending Ascend within the anterior or lateral spinothalamic tracts: the anterior tracts carry crude touch and pressure sensations the lateral tracts carry pain and temperature sensations Sensory Pathways The Spinothalamic Pathway Third-order neurons Synapse in ventral nucleus group of the thalamus After the sensations have been sorted and processed, they are relayed to primary sensory cortex Sensory Pathways Figure 155b The Spinothalamic Tracts of the Spinothalamic Pathway. Sensory Pathways Figure 155c The Spinothalamic Tracts of the Spinothalamic Pathway. humunculus Sensory Pathways Feeling Pain (Lateral Spinothalamic Tract) An individual can feel pain in an uninjured part of the body when pain actually originates at another location Strong visceral pain Sensations arriving at segment of spinal cord can stimulate interneurons that are part of spinothalamic pathway Activity in interneurons leads to stimulation of primary sensory cortex, so an individual feels pain in specific part of body surface: also called referred pain Sensory Pathways Figure 156 Referred Pain. Sensory Pathways The Spinocerebellar Pathway Cerebellum receives proprioceptive information about position of skeletal muscles, tendons, and joints Figure 157 Sensory Pathways The Spinocerebellar Tracts The posterior spinocerebellar tracts Contain second-order axons that do NOT cross over to the opposite side of the spinal cord: axons reach cerebellar cortex via inferior cerebellar peduncle of that side Sensory Pathways Figure 157 The Spinocerebellar Pathway. No crossover Sensory Pathways Most somatic sensory information is relayed to the thalamus for processing A small fraction of the arriving information is projected to the cerebral cortex and reaches our awareness Sensory Pathways Visceral Sensory Pathways Collected by interoceptors monitoring visceral tissues and organs, primarily within the thoracic and abdominopelvic cavities These interoceptors are not as numerous as in somatic tissues Nociceptors, thermoreceptors, tactile receptors, baroreceptors, and chemoreceptors Sensory Pathways Visceral Sensory Pathways Cranial Nerves V, VII, IX, and X Carry visceral sensory information from mouth, palate, pharynx, larynx, trachea, esophagus, and associated vessels and glands Sensory Pathways Visceral Sensory Pathways Solitary nucleus Large nucleus in the medulla oblongata Major processing and sorting center for visceral sensory information Extensive connections with the various cardiovascular and respiratory centers, reticular formation Somatic Motor Pathways SNS, or the somatic motor system, controls contractions of skeletal muscles (discussed next) ANS, or the visceral motor system, controls visceral effectors, such as smooth muscle, cardiac muscle, and glands (Ch. 16) Somatic Motor Pathways Always involve at least two motor neurons 1 Upper motor neuron Cell body lies in a CNS processing center Synapses on the lower motor neuron Innervates a single motor unit in a skeletal muscle: activity in upper motor neuron may facilitate or inhibit lower motor neuron Somatic Motor Pathways 2 Lower motor neuron Cell body lies in a nucleus of the brain stem or spinal cord Triggers a contraction in innervated muscle: only axon of lower motor neuron extends outside CNS destruction of or damage to lower motor neuron eliminates voluntary and reflex control over innervated motor unit Somatic Motor Pathways Conscious and Subconscious Motor Commands Control skeletal muscles by traveling over three integrated motor pathways Corticospinal pathway Medial pathway Lateral pathway Somatic Motor Pathways Figure 158 Descending (Motor) Tracts in the Spinal Cord. Somatic Motor Pathways The Corticospinal Pathway Motor homunculus Primary motor cortex corresponds point by point with specific regions of the body Cortical areas have been mapped out in diagrammatic form Homunculus provides indication of degree of fine motor control available: hands, face, and tongue, which are capable of varied and complex movements, appear very large, while trunk is relatively small these proportions are similar to the sensory homunculus Somatic Motor Pathways Figure 159 The Corticospinal Pathway. Crossover in medulla Somatic Motor Pathways The Medial and Lateral Pathways Several centers in cerebrum, diencephalon, and brain stem may issue somatic motor commands as result of processing performed at subconscious level These nuclei and tracts are grouped by their primary functions Components of medial pathway help control gross movements of trunk and proximal limb muscles Components of lateral pathway help control distal limb muscles that perform more precise movements Somatic Motor Pathways The Basal Nuclei and Cerebellum Responsible for coordination and feedback control over muscle contractions, whether contractions are consciously or subconsciously directed Somatic Motor Pathways The Basal Nuclei Provide background patterns of movement involved in voluntary motor activities Some axons extend to the premotor cortex, the motor association area that directs activities of the primary motor cortex: alters the pattern of instructions carried by the corticospinal tracts Other axons alter the excitatory or inhibitory output of the reticulospinal tracts Somatic Motor Pathways The Cerebellum Monitors Proprioceptive (position) sensations Visual information from the eyes Vestibular (balance) sensations from inner ear as movements are under way helps fine tune motor control Somatic Motor Pathways Levels of Processing and Motor Control All sensory and motor pathways involve a series of synapses, one after the other General pattern Spinal and cranial reflexes provide rapid, involuntary, preprogrammed responses that preserve homeostasis over short term Cranial and spinal reflexes Control the most basic motor activities Somatic Motor Pathways Levels of Processing and Motor Control Integrative centers in the brain Perform more elaborate processing As we move from medulla oblongata to cerebral cortex, motor patterns become increasingly complex and variable Primary motor cortex Most complex and variable motor activities are directed by primary motor cortex of cerebral hemispheres Somatic Motor Pathways Neurons of the primary motor cortex innervate motor neurons in the brain and spinal cord responsible for stimulating skeletal muscles Higher centers in the brain can suppress or facilitate reflex responses Reflexes can complement or increase the complexity of voluntary movements Autonomic Nervous System Figure 16-2a The Organization of the Somatic and Nervous Systems. An Introduction to the ANS Somatic Nervous System (SNS) Operates under conscious control Seldom affects long-term survival SNS controls skeletal muscles Autonomic Nervous System (ANS) Operates without conscious instruction ANS controls visceral effectors Coordinates system functions: cardiovascular, respiratory, digestive, urinary, reproductive Autonomic Nervous System Organization of the ANS Integrative centers For autonomic activity in hypothalamus Neurons comparable to upper motor neurons in SNS Autonomic Nervous System Organization of the ANS Visceral motor neurons In brain stem and spinal cord, are known as preganglionic neurons Preganglionic fibers: axons of preganglionic neurons leave CNS and synapse on ganglionic neurons Autonomic Nervous System Visceral Motor Neurons (contd) Autonomic ganglia Contain many ganglionic neurons Ganglionic neurons innervate visceral effectors: such as cardiac muscle, smooth muscle, glands, and adipose tissue Postganglionic fibers: axons of ganglionic neurons Autonomic Nervous System Figure 16-2b The Organization of the Autonomic Nervous Systems. Divisions of the ANS The autonomic nervous system Operates largely outside our awareness Has two divisions Sympathetic division gas pedal increases alertness, metabolic rate, and muscular abilities fight or flight Parasympathetic division brake reduces metabolic rate and promotes digestion Rest and digest Divisions of the ANS Two divisions may work independently Some structures innervated by only one division Two divisions may work together Each controlling one stage of a complex process Divisions of the ANS Sympathetic Division Preganglionic fibers (thoracic and superior lumbar; thoracolumbar) synapse in ganglia near spinal cord Preganglionic fibers are short Postganglionic fibers are long Prepares body for crisis, producing a fight or flight response Stimulates tissue metabolism Increases alertness Divisions of the ANS Seven Responses to Increased Sympathetic Activity Heightened mental alertness Increased metabolic rate Reduced digestive and urinary functions Energy reserves activated Increased respiratory rate and respiratory passageways dilate Increased heart rate and blood pressure Sweat glands activated Skeletal muscle Cell bodies in central nervous system Peripheral nervous systemEffect + + Effector organs ACh Smooth muscle (e.g., in gut), glands, cardiac muscle Ganglion Adrenal medullaBlood vessel ACh NE Epinephrine and norepinephrine Acetylcholine (ACh)Norepinephrine (NE) Ganglion Heavily myelinated axon Lightly myelinated preganglionic axon Lightly myelinated preganglionic axons Neuro- transmitter at effector Unmyelinated postganglionic axon Unmyelinated postganglionic axon Stimulatory or inhibitory, depending on neuro- transmitter and receptors on effector organs Single neuron from CNS to effector organs Two-neuron chain from CNS to effector organs SOMATIC NERVOUS SYSTEM AUTONOMIC NERVOUS SYSTEM PARASYMPATHETIC SYMPATHETIC Figure 14.2 Autonomic Nervous System Figure 16-2b The Organization of the Autonomic Nervous Systems. Divisions of the ANS Parasympathetic Division Preganglionic fibers originate in brain stem and sacral segments of spinal cord; craniosacral Synapse in ganglia close to (or within) target organs Preganglionic fibers are long Postganglionic fibers are short Divisions of the ANS Parasympathetic Division Rest and repose Parasympathetic division stimulates visceral activity Conserves energy and promotes sedentary activities Decreased metabolic rate, heart rate, and blood pressure Increased salivary and digestive glands secretion Increased motility and blood flow in digestive tract Urination and defecation stimulation Divisions of the ANS 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 The Sympathetic Division Preganglionic neurons located between segments T 1 and L 2 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 The Sympathetic Division Figure 163 The Organization of the Sympathetic Division of the ANS. The Sympathetic Division Ganglionic Neurons Occur in three locations Sympathetic chain ganglia Collateral ganglia Suprarenal medullae The Sympathetic Division Figure 164a Sites of Ganglia in Sympathetic Pathways The Sympathetic Division Figure 164b Sites of Ganglia in Sympathetic Pathways. The Sympathetic Division Figure 164c Sites of Ganglia in Sympathetic Pathways. Skeletal muscle Cell bodies in central nervous system Peripheral nervous systemEffect + + Effector organs ACh Smooth muscle (e.g., in gut), glands, cardiac muscle Ganglion Adrenal medullaBlood vessel ACh NE Epinephrine and norepinephrine Acetylcholine (ACh)Norepinephrine (NE) Ganglion Heavily myelinated axon Lightly myelinated preganglionic axon Lightly myelinated preganglionic axons Neuro- transmitter at effector Unmyelinated postganglionic axon Unmyelinated postganglionic axon Stimulatory or inhibitory, depending on neuro- transmitter and receptors on effector organs Single neuron from CNS to effector organs Two-neuron chain from CNS to effector organs SOMATIC NERVOUS SYSTEM AUTONOMIC NERVOUS SYSTEM PARASYMPATHETIC SYMPATHETIC Figure 14.2 The Sympathetic Division Fibers in Sympathetic Division Preganglionic fibers Are relatively short Ganglia located near spinal cord Postganglionic fibers Are relatively long, except at suprarenal medullae Various Sympathetic Neurotransmitters Sympathetic Stimulation and the Release of ACh and NO Cholinergic (ACh) sympathetic terminals Innervate sweat glands of skin and blood vessels of skeletal muscles and brain Stimulate sweat gland secretion and dilate blood vessels Various Sympathetic Neurotransmitters Sympathetic Stimulation and the Release of ACh and NO Nitroxidergic synapses Release nitric oxide (NO) as neurotransmitter Neurons innervate smooth muscles in walls of blood vessels in skeletal muscles and the brain Produce vasodilation and increased blood flow Organization and Anatomy of the Parasympathetic Division Figure 167 The Organization of the Parasympathetic Division of the ANS. Organization and Anatomy of the Parasympathetic Division Figure 168 The Distribution of Parasympathetic Innervation. Organization and Anatomy of the Parasympathetic Division Figure 168 The Distribution of Parasympathetic Innervation. The Parasympathetic Division Parasympathetic Activation Centers on relaxation, food processing, and energy absorption Localized effects, last a few seconds at most The Parasympathetic Division Major effects of parasympathetic division include Constriction of pupils Restricts light entering eyes Secretion by digestive glands Exocrine and endocrine Secretion of hormones Nutrient absorption and utilization Changes in blood flow and glandular activity Associated with sexual arousal Parasympathetic Neurons Release ACh Neuromuscular and Neuroglandular Junctions All release ACh as neurotransmitter Small, with narrow synaptic clefts Effects of stimulation are short lived Inactivated by AChE at synapse ACh is also inactivated by pseudocholinesterase (tissue cholinesterase) in surrounding tissues Parasympathetic Neurons Release ACh Membrane Receptors and Responses Nicotinic receptors On surfaces of ganglion cells (sympathetic and parasympathetic): exposure to ACh causes excitation of ganglionic neuron or muscle fiber Parasympathetic Neurons Release ACh Dual Innervation Sympathetic Widespread impact Reaches organs and tissues throughout body Parasympathetic Innervates only specific visceral structures Most vital organs receive instructions from both sympathetic and parasympathetic divisions Two divisions commonly have opposing effects Dual Innervation 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 Dual Innervation Figure 169 Summary: The Anatomical Differences between the Sympathetic and Parasympathetic Divisions. Anatomy of Dual Innervation Figure 1610 The Autonomic Plexuses. Dual Innervation The heart receives dual innervation Two divisions have opposing effects Parasympathetic division Acetylcholine released by postganglionic fibers slows heart rate Sympathetic division NE released by varicosities accelerates heart rate Balance between two divisions Autonomic tone is present Releases small amounts of both neurotransmitters continuously Higher-Order Functions Require the cerebral cortex Involve conscious and unconscious information processing Not part of programmed wiring of brain Can adjust over time Higher-Order Functions Memory Fact memories Are specific bits of information Skill memories Learned motor behaviors Incorporated at unconscious level with repetition Programmed behaviors stored in appropriate area of brain stem Complex are stored and involve motor patterns in the basal nuclei, cerebral cortex, and cerebellum Higher-Order Functions Memory Shortterm memories Information that can be recalled immediately Contain small bits of information Primary memories Long-term memories Memory consolidation: conversion from short-term to long- term memory: secondary memories fade and require effort to recall tertiary memories are with you for life Higher-Order Functions Figure 1613 Memory Storage. The limbic system Higher-Order Functions Brain Regions Involved in Memory Consolidation and Access Amygdaloid body and hippocampus Nucleus basalis Cerebral cortex Copyright 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings memory Higher-Order Functions Amygdaloid body and hippocampus Are essential to memory consolidation Damage may cause Inability to convert short-term memories to new long-term memories Existing long-term memories remain intact and accessible Copyright 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings memory Higher-Order Functions 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 Higher-Order Functions Cerebral cortex Stores long-term memories Conscious motor and sensory memories referred to association areas Occipital and temporal lobes Special portions crucial to memories of faces, voices, and words A specific neuron may be activated by combination of sensory stimuli associated with particular individual; called grandmother cells Higher-Order Functions Cerebral cortex 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 Higher-Order Functions 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 Higher-Order Functions Facilitation at Synapses Neural circuit repeatedly activated Synaptic terminals begin continuously releasing neurotransmitter Neurotransmitter binds to receptors on postsynaptic membrane Produces graded depolarization Brings membrane closer to threshold Facilitation results affect all neurons in circuit Higher-Order Functions 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 Higher-Order Functions Cellular Mechanisms of Memory Formation and Storage Basis of memory storage Processes create anatomical changes Facilitate communication along specific neural circuit Memory Engram Single circuit corresponds to single memory Forms as result of experience and repetition Higher-Order Functions Cellular Mechanisms of Memory Formation and Storage Efficient conversion of short-term memory Takes at least 1 hour Repetition crucial Factors of conversion Nature, intensity, and frequency of original stimulus Strong, repeated, and exceedingly pleasant or unpleasant events likely converted to long-term memories Higher-Order Functions Cellular Mechanisms of Memory Formation and Storage Drugs stimulate CNS Caffeine and nicotine are examples: enhance memory consolidation through facilitation 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 Higher-Order Functions States of Consciousness 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% Higher-Order Functions States of Consciousness 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 Higher-Order Functions States of Consciousness Arousal and the reticular activating system (RAS) Awakening from sleep Function of reticular formation: extensive interconnections with sensory, motor, integrative nuclei, and pathways along brain stem Determined by complex interactions between reticular formation and cerebral cortex Higher-Order Functions Reticular Activating System (RAS) Important brain stem component Diffuse network in reticular formation Extends from medulla oblongata to mesencephalon Output of RAS projects to thalamic nuclei that influence large areas of cerebral cortex When RAS inactive, so is cerebral cortex Stimulation of RAS produces widespread activation of cerebral cortex Higher-Order Functions Arousal and the Reticular Activating System Ending sleep Any stimulus activates reticular formation and RAS Arousal occurs rapidly Effects of single stimulation of RAS last less than a minute Higher-Order Functions Arousal and the Reticular Activating System Maintaining consciousness Activity in cerebral cortex, basal nuclei, and sensory and motor pathways continue to stimulate RAS: after many hours, reticular formation becomes less responsive to stimulation individual becomes less alert and more lethargic neural fatigue reduces RAS activity Higher-Order Functions Arousal and the Reticular Activating System Regulation of awakeasleep 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 Higher-Order Functions Figure 1615 The Reticular Activating System. Brain Chemistry Huntington 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 Brain Chemistry Serotonin Compounds that enhance effects also produce hallucinations (LSD) Compounds that inhibit or block action cause severe depression and anxiety Variations in levels affect sensory interpretation and emotional states Brain Chemistry Serotonin 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 Brain Chemistry Parkinson Disease Inadequate dopamine production causes motor problems 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