The Nervous System the Nervous System

Essentials of Anatomy & Physiology, 4th Edition Martini / Bartholomew

PowerPoint® Lecture Outlines prepared by Alan Magid, Duke University

Slides 1 to 145

Two Organ Systems Control All the Other Organ Systems • Nervous system characteristics • Rapid response • Brief duration • Endocrine system characteristics • Slower response • Long duration

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings The Nervous System Two Anatomical Divisions • Central nervous system (CNS) •Brain • Spinal cord • Peripheral nervous system (PNS) • All the neural tissue outside CNS • Afferent division (sensory input) • Efferent division (motor output) • Somatic nervous system • Autonomic nervous system

Information Processing

PERIPHERAL Sensory information Motor commands NERVOUS SYSTEM within within afferent division efferent division

includes

Somatic Autonomic nervous nervous system system

Parasympathetic Sympathetic division division

Receptors Effectors

Smooth muscle Somatic sensory Visceral sensory Skeletal Cardiac receptors (monitor receptors (monitor muscle the outside world internal conditions muscle and our position and the status Glands in it) of other organ systems) Adipose tissue

Receptors

Somatic sensory Visceral sensory receptors (monitor receptors (monitor the outside world internal conditions and our position and the status in it) of other organ systems)

Receptors

Somatic sensory Visceral sensory receptors (monitor receptors (monitor the outside world internal conditions and our position and the status in it) of other organ systems)

Information Processing

PERIPHERAL Sensory information NERVOUS SYSTEM within afferent division

Receptors

Somatic sensory Visceral sensory receptors (monitor receptors (monitor the outside world internal conditions and our position and the status in it) of other organ systems)

Information Processing

PERIPHERAL Sensory information Motor commands NERVOUS SYSTEM within within afferent division efferent division

Receptors

Somatic sensory Visceral sensory receptors (monitor receptors (monitor the outside world internal conditions and our position and the status in it) of other organ systems)

Information Processing

PERIPHERAL Sensory information Motor commands NERVOUS SYSTEM within within afferent division efferent division

includes

Somatic nervous system

Receptors Effectors

Somatic sensory Visceral sensory Skeletal receptors (monitor receptors (monitor muscle the outside world internal conditions and our position and the status in it) of other organ systems)

Information Processing

PERIPHERAL Sensory information Motor commands NERVOUS SYSTEM within within afferent division efferent division

includes

Somatic Autonomic nervous nervous system system

Parasympathetic Sympathetic division division

Receptors Effectors

Two Classes of Neural Cells • Neurons • For information transfer, processing, and storage • Neuroglia • Supporting framework for neurons • Phagocytes

Three Classes of Neurons • Sensory neurons • Deliver information to CNS • Motor neurons • Stimulate or inhibit peripheral tissues • Interneurons (association neurons) • Located between sensory and motor neurons • Analyze inputs, coordinate outputs

Neuron Anatomy • Cell body • Nucleus • Mitochondria, RER, other organelles • Dendrites • Several branches • Signal reception (inward) • Axon • Signal propagation (outward)

Figure 8-2 Neural Tissue Organization

Structural Classes of Neurons • Unipolar • Dendrite, axon continuous • Afferent neurons • Multipolar • Many dendrites, one axon • Most common class of neuron • Bipolar • One dendrite, one axon • Very rare

Figure 8-3 Neural Tissue Organization

Key Note Neurons perform all of the communication, information processing, and control functions of the nervous system. Neuroglia outnumber neurons and have functions essential to preserving the physical and biochemical structure of neural tissue and the survival of neurons.

Anatomic Organization of CNS Neurons • Center—Collection of neurons with a shared function • Nucleus—A center with a discrete anatomical boundary • Neural cortex—Gray matter covering of brain portions • White matter—Bundles of axons (tracts) that share origins, destinations, and functions

Anatomic Organization of PNS Neurons • Ganglia—Groupings of neuron cell bodies • Nerve—Bundle of axons supported by connective tissue • Spinal nerves • To/from spinal cord • Cranial nerves • To/from brain

Nervous System Figure 8-6 Neural Tissue Organization

Pathways in the CNS • Ascending pathways Carry information from sensory receptors to processing centers in the brain • Descending pathways Carry commands from specialized CNS centers to skeletal muscles

The Membrane Potential • Resting potential • Excess negative charge inside the neuron • Created and maintained by Na-K ion pump • Negative voltage (potential) inside • -70 mV (0.07 Volts)

Figure 8-7 Neuron Function Changes in Membrane Potential • Result from changes in ion movement • Ions move in transmembrane channels • Membrane channels can open or close • If Na+ channels open  positive charges enter cell  membrane potential moves positive (depolarization) • If K+ channels open  positive charges leave cell  membrane potential moves negative (hyperpolarization)

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Neuron Function Key Note A membrane potential exists across the cell membrane because (1) the cytosol and the extracellular fluid differ in their ionic composition, and (2) the cell membrane is selectively permeable to these ions. The membrane potential can quickly change, as the ionic permeability of the cell membrane changes, in response to chemical or physical stimuli.

Generation of Action Potential • Depolarization of membrane to threshold • Rapid opening of voltage-gated Na+ channels • Na+ entry causes rapid depolarization • Voltage-gated K+ channels open • K+ exit causes rapid repolarization • Refractory period ends as membrane recovers the resting state

Sodium ions

Local current

Potassium ions

Inactivation of sodium channels and activation of voltage-regulated potassium channels

+30 DEPOLARIZATION REPOLARIZATION 3

The return to normal Threshold _60 permeability and resting state _70 1 4 Transmembrane(mV) potential Resting potential REFRACTORY PERIOD

Sodium ions

Local current

+30 DEPOLARIZATION

Threshold _60 _70 1 Transmembrane(mV) potential Resting potential

0123 Time (msec) Figure 8-8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings 2 of 5 Activation of voltage- Depolarization to threshold regulated sodium channels and rapid depolarization

Sodium ions

Local current

Potassium ions

+30 DEPOLARIZATION

Threshold _60 _70 1 Transmembrane(mV) potential Resting potential

0123 Time (msec) Figure 8-8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings 3 of 5 Activation of voltage- Depolarization to threshold regulated sodium channels and rapid depolarization

Sodium ions

Local current

Potassium ions

Inactivation of sodium channels and activation of voltage-regulated potassium channels

+30 DEPOLARIZATION REPOLARIZATION 3

Threshold _60 _70 1 Transmembrane(mV) potential Resting potential

0123 Time (msec) Figure 8-8 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings 4 of 5 Activation of voltage- Depolarization to threshold regulated sodium channels and rapid depolarization

Sodium ions

Local current

Potassium ions

Inactivation of sodium channels and activation of voltage-regulated potassium channels

+30 DEPOLARIZATION REPOLARIZATION 3

The return to normal Threshold _60 permeability and resting state _70 1 4 Transmembrane(mV) potential Resting potential REFRACTORY PERIOD

Action potential video http://www.youtube.com/watch?v=yQ- wQsEK21E&feature=player_embedded http://www.youtube.com/watch?v=ifD1YG07fB8 http://www.dnatube.com/video/1105/Action-potential Neuron Function Propagation of an Action Potential • Continuous propagation • Involves entire membrane surface • Proceeds in series of small steps (slower) • 1 m/s (2 mph) • Occurs in unmyelinated axons • Saltatory propagation • Involves patches of membrane exposed at nodes • Proceeds in series of large steps (faster) • 18-140 m/s (40-300 mph)

Figure 8-9(a) Neuron Function The Propagation of Action Potentials over Unmyelinated and Myelinated Axons

Figure 8-9(b) Neuron Function Action Potential Propagation

PLAY Neurophysiology: Continuous Saltatory Propagation

PLAY Neurophysiology: Action Potential

Key Note “Information” travels within the nervous system primarily in the form of propagated electrical signals known as action potentials. The most important information (e.g., vision, balance, movement), is carried by myelinated axons.

Synapse Basics • Intercellular communication • Axon terminal • Input to next cell • Chemical signaling • Neurotransmitter release

Structure of a Synapse • Presynaptic components • Axon terminal • Synaptic knob • Synaptic vesicles • Synaptic cleft • Postsynaptic components • Neurotransmitter receptors

The Structure of a Typical Synapse

Figure 8-10 Neural Communication

Synaptic Function and Neurotransmitters • Cholinergic synapses • Release neurotransmitter acetylcholine • Enzyme in synaptic cleft (acetylcholinesterase) breaks it down • Adrenergic synapses • Release neurotransmitter norepinephrine • Dopaminergic synapses • Release neurotransmitter dopamine

PLAY Neurophysiology: Synapse

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings An action potential arrives and Extracellular Ca2+ enters the synaptic depolarizes the synaptic knob cleft triggering the exocytosis of ACh

PRESYNAPTIC Action potential NEURON Synaptic vesicles EXTRACELLULAR ACh FLUID ER Synaptic 2+ Synaptic knob Ca cleft

Ca2+ AChE Chemically regulated POSTSYNAPTIC sodium channels NEURON CYTOSOL

ACh is removed by AChE ACh binds to receptors and depolarizes (acetylcholinesterase) the postsynaptic membrane

Initiation of action potential Propagation of if threshold action potential is reached (if generated)

PRESYNAPTIC Action potential NEURON Synaptic vesicles EXTRACELLULAR FLUID ER Synaptic knob

AChE

POSTSYNAPTIC NEURON CYTOSOL

Figure 8-11 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings 2 of 5 An action potential arrives and Extracellular Ca2+ enters the synaptic depolarizes the synaptic knob cleft triggering the exocytosis of ACh

PRESYNAPTIC Action potential NEURON Synaptic vesicles EXTRACELLULAR ACh FLUID ER Synaptic 2+ Synaptic knob Ca cleft

Ca2+ AChE Chemically regulated POSTSYNAPTIC sodium channels NEURON CYTOSOL

Figure 8-11 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings 3 of 5 An action potential arrives and Extracellular Ca2+ enters the synaptic depolarizes the synaptic knob cleft triggering the exocytosis of ACh

PRESYNAPTIC Action potential NEURON Synaptic vesicles EXTRACELLULAR ACh FLUID ER Synaptic 2+ Synaptic knob Ca cleft

Ca2+ AChE Chemically regulated POSTSYNAPTIC sodium channels NEURON CYTOSOL

ACh binds to receptors and depolarizes the postsynaptic membrane

Initiation of action potential if threshold is reached

Na2+ Receptor Na2+ 2+ 2+ Na Na2+ Na Figure 8-11 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings 4 of 5 An action potential arrives and Extracellular Ca2+ enters the synaptic depolarizes the synaptic knob cleft triggering the exocytosis of ACh

PRESYNAPTIC Action potential NEURON Synaptic vesicles EXTRACELLULAR ACh FLUID ER Synaptic 2+ Synaptic knob Ca cleft

Ca2+ AChE Chemically regulated POSTSYNAPTIC sodium channels NEURON CYTOSOL

ACh is removed by AChE ACh binds to receptors and depolarizes (acetylcholinesterase) the postsynaptic membrane

Initiation of action potential Propagation of if threshold action potential is reached (if generated)

• Neuronal pools Groups of interconnected neurons with specific functions • Divergence Spread of information from one neuron to several others • Convergence Several neurons send information to one other

Figure 8-12 Neural Communication

Key Note A synaptic terminal releases a neurotransmitter that binds to the postsynaptic cell membrane. The result is a brief, local change in the permeability of the postsynaptic cell. Many drugs affect the nervous system by stimulating neurotransmitter receptors and thus produce complex effects on perception, motor control, and emotions.

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings The Central Nervous System Meninges—Layers that surround and protect the brain and spinal cord (CNS) • Dura mater (“tough mother”) • Tough, fibrous outer layer • Epidural space above dura of spinal cord • Arachnoid (“spidery”) • Subarchnoid space • Cerebrospinal fluid • Pia mater (“delicate mother”) • Thin inner layer

Figure 8-13(a) The Central Nervous System The Meninges

Figure 8-13(b) The Central Nervous System

Spinal Cord Basics • Relays information to/from brain • Processes some information on its own • Divided into 31 segments • Each segment has a pair of: • Dorsal root ganglia • Dorsal roots • Ventral roots • Gray matter appears as horns • White matter organized into columns

Figure 8-14(a) The Central Nervous System Gross Anatomy of the Spinal Cord

Figure 8-14(b) The Central Nervous System Sectional Anatomy of the Spinal Cord

Figure 8-15(a) The Central Nervous System Sectional Anatomy of the Spinal Cord

Figure 8-15(b) The Central Nervous System Key Note The sensory and motor nuclei (gray matter) of the spinal cord surround the central canal. Sensory nuclei are dorsal, motor nuclei are ventral. A thick layer of white matter consisting of ascending and descending axons covers the gray matter. These axons are organized into columns of axon bundles with specific functions. This highly organized structure often enables predicting the impact of particular injuries.

Brain Regions • Cerebrum • Diencephalon • Midbrain • Pons • Medulla oblongata • Cerebellum

Figure 8-16(a) The Central Nervous System The Brain

Figure 8-16(b) The Central Nervous System The Brain

Figure 8-16(c) The Central Nervous System

Brain—The four hollow chambers in the center of the brain filled with cerebrospinal fluid (CSF) • CSF produced by choroid plexus • CSF circulates • From ventricles and central canal • To subarachoid space • Accessible by lumbar puncture • To blood stream

The Ventricles of the Brain

Figure 8-17 The Central Nervous System

The Formation and Circulation of Cerebrospinal Fluid

Figure 8-18(a) The Central Nervous System The Formation and Circulation of Cerebrospinal Fluid

Figure 8-18(b) The Central Nervous System

Functions of the Cerebrum • Conscious thought • Intellectual activity • Memory • Origin of complex patterns of movement

Anatomy of Cerebral Cortex • Highly folded surface • Elevated ridges (gyri) • Shallow depressions (sulci) • Cerebral Hemispheres • Longitudinal fissure • Central sulcus • Boundary between frontal and parietal lobes • Other lobes (temporal, occipital)

Functions of the Cerebral Cortex • Hemispheres serve opposite body sides • Primary motor cortex (precentral gyrus) • Directs voluntary movement • Primary sensory cortex (postcentral gyrus) • Receives somatic sensation (touch, pain, pressure, temperature) • Association areas • Interpret sensation • Coordinate movement

Figure 8-19 The Central Nervous System

Hemispheric Lateralization • Categorical hemisphere (usually left) • General interpretative and speech centers • Language-based skills • Representational Hemisphere (usually right) • Spatial relationships • Logical analysis

Hemispheric Lateralization

Figure 8-20 The Central Nervous System Brain Waves (Electroencephalogram)

Figure 8-21 The Central Nervous System

The Basal Nuclei • Lie deep within central white matter of the brain • Responsible for muscle tone • Coordinate learned movements • Coordinate rhythmic movements (e.g., walking)

Figure 8-22(a) The Central Nervous System The Basal Nuclei

Figure 8-22(b) The Central Nervous System

Functions of the Limbic System • Establish emotions and related drives • Link cerebral cortex intellectual functions to brain stem autonomic functions • Control reflexes associated with eating • Store and retrieve long-term memories

Figure 8-23 The Central Nervous System The Diencephalon • Switching and relay center • Integration of conscious and unconscious motor and sensory pathways • Components include: • Epithalamus • Choroid plexus • Pineal body • Thalamus • Hypothalamus

Figure 8-24(a) The Central Nervous System

The Diencephalon and Brain Stem

Figure 8-24(b) The Central Nervous System

Functions of the Thalamus • Relay and filter all ascending (sensory) information • Relay a small proportion to cerebral cortex (conscious perception) • Relay most to basal nuclei and brain stem centers • Coordinate voluntary and involuntary motor behavior

Functions of the Hypothalamus • Produce emotions and behavioral drives • Coordinate nervous and endocrine systems • Secrete hormones • Coordinate voluntary and autonomic functions • Regulate body temperature

Anatomy and Function of the Brain Stem • Midbrain • Process visual, auditory information • Generate involuntary movements • Pons • Links to cerebellum • Involved in control of movement • Medulla oblongata • Relay sensory information • Regulate autonomic function

Anatomy and Function of the Cerebellum • Oversees postural muscles • Stores patterns of movement • Fine tunes most movements • Links to brain stem, cerebrum, spinal cord • Communicates over cerebellar peduncles

Functions of the Medulla Oblongata • Links brain and spinal cord • Relays ascending information to cerebral cortex • Controls crucial organ systems by reflex • Cardiovascular centers • Respiratory rhythmicity centers

Key Note The brain, a large mass of neural tissue, contains internal passageways and chambers filled with CSF. The six major regions of the brain have specific functions. As you ascend from the medulla oblongata to the cerebrum, those functions become more complex and variable. Conscious thought and intelligence are provided by the cerebral cortex.

PNS Basics • Links the CNS with the body • Carries all sensory information and motor commands • Axons bundled in nerves • Cell bodies grouped into ganglia • Includes cranial and spinal nerves

The Cranial Nerves • 12 Pairs • Connect to brain not the cord • Olfactory (CN I) • Sense of smell • Optic (CN II) • Sense of vision • Oculomotor (CN III) • Eye movement

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings The Peripheral Nervous System The Cranial Nerves (continued) • Trochlear (CN IV) • Eye movement • Trigeminal (CN V) • Eye, jaws sensation/movement • Abducens (CN VI) • Eye movement • Facial (CN VII) • Face, scalp, tongue sensation/movement • Vestibulocochlear (CN VIII) • Hearing, balance

The Cranial Nerves (continued) • Glossopharyngeal (CN IX) • Taste, swallowing • Vagus (CN X) • Autonomic control of viscera • Accessory (CN XI) • Swallowing, pectoral girdle movement • Hypoglossal (CN XII) • Tongue movement

Figure 8-25(a) The Peripheral Nervous System The Cranial Nerves

Figure 8-25(b) The Peripheral Nervous System

Key Note The 12 pairs of cranial nerves are responsible for the special senses of smell, sight, and hearing/balance, and control movement of the eye, jaw, face, tongue, and muscles of the neck, back, and shoulders. They also provide sensation from the face, neck, and upper chest and autonomic innervation to thoracic and abdominopelvic organs.

The Spinal Nerves • 31 Pairs • 8 Cervical • 12 Thoracic • 5 Lumbar •5 Sacral • Dermatome—Region of the body surface monitored by a pair of spinal nerves

Nerve Plexus—A complex, interwoven network of nerves • Four Large Plexuses • Cervical plexus • Brachial plexus • Lumbar plexus • Sacral plexus

Figure 8-26 The Peripheral Nervous System Dermatomes

Figure 8-27 The Peripheral Nervous System

Reflex—An automatic involuntary motor response to a specific stimulus • The 5 steps in a reflex arc • Arrival of stimulus and activation of receptor • Activation of sensory neuron • CNS processing of information • Activation of motor neuron • Response by effector (muscle or gland)

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Dorsal Sensation Arrival of Activation of a root relayed to stimulus and sensory neuron the brain by activation of collateral receptor

REFLEX Receptor ARC Stimulus

Effector Ventral root Information processing in CNS Response Activation of a motor neuron by effector KEY Sensory neuron (stimulated) Excitatory interneuron Motor neuron (stimulated)

Stimulus

Receptor Stimulus

KEY Sensory neuron (stimulated)

Figure 8-27 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings 3 of 6 Dorsal Sensation Arrival of Activation of a root relayed to stimulus and sensory neuron the brain by activation of collateral receptor

Receptor Stimulus

Information processing in CNS

KEY Sensory neuron (stimulated) Excitatory interneuron

Figure 8-27 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings 4 of 6 Dorsal Sensation Arrival of Activation of a root relayed to stimulus and sensory neuron the brain by activation of collateral receptor

REFLEX Receptor ARC Stimulus

Ventral root Information processing in CNS Activation of a motor neuron KEY Sensory neuron (stimulated) Excitatory interneuron Motor neuron (stimulated)

Figure 8-27 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings 5 of 6 Dorsal Sensation Arrival of Activation of a root relayed to stimulus and sensory neuron the brain by activation of collateral receptor

REFLEX Receptor ARC Stimulus

Effector Ventral root Information processing in CNS Response Activation of a motor neuron by effector KEY Sensory neuron (stimulated) Excitatory interneuron Motor neuron (stimulated)

Examples of Reflexes • Monosynaptic reflex—Simplest reflex arc; sensory neuron synapses directly on motor neuron • Stretch reflex—Monosynaptic reflex to regulate muscle length and tension (example: patellar reflex) • Muscle spindle—Sensory receptor in a muscle that stimulates the stretch reflex

Spinal cord REFLEX ARC

Contraction

Activation of motor neuron produces reflex muscle contraction Figure 8-29 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings 1 of 3 Stretching of muscle tendon stimulates muscle spindles Muscle spindle (stretch receptor) Stretch

Spinal cord

Spinal cord REFLEX ARC

Contraction

Polysynaptic reflex—A reflex arc with at least one interneuron between the sensory afferent and motor efferent • Has a longer delay than a monosynaptic reflex (more synapses) • Can produce more complex response • Example: flexor reflex, a withdrawal reflex • Brain can modify spinal reflexes

Figure 8-30 The Peripheral Nervous System

Key Note Reflexes are rapid, automatic responses to stimuli that “buy time” for the planning and execution of more complex responses that are often consciously directed.

Sensory Pathway • Afferent axon signals from a sensory receptor • Posterior column pathway • Carries fine touch, pressure, proprioception • Ascending neurons synapse in medulla oblongata • Axons cross over and synapse in thalamus • Thalamus sends axons to primary sensory cortex • Organized as sensory homunculus

The Posterior Column Pathway

Figure 8-31 The Peripheral Nervous System

Motor Pathways • Corticospinal pathway (tract) • Provides conscious muscle control • Organized as motor homunculus • Medial & lateral pathways (tract) • Provide subconscious muscle control

The Corticospinal Pathway

Figure 8-32 The Peripheral Nervous System

Table 8-4 The Autonomic Nervous System

Autonomic Nervous System Branch of nervous system that coordinates cardiovascular, digestive, excretory, and reproductive functions

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings The Autonomic Nervous System Anatomy of ANS • Preganglionic neuron • Cell body resides in CNS • Axon synapses in PNS in autonomic ganglion • Postganglionic axons (postganglionic fibers) synapse on peripheral effectors • Cardiac muscle • Smooth muscle • Glands • Adipose tissues

Divisions of the ANS • Sympathetic division • Preganglionic neurons in the thoracic and lumbar segments of the spinal cord • “Fight or flight” system • Parasympathetic division • Preganglionic neurons in the brain and sacral segments • “Rest and digest” system

Key Note The two divisions of the ANS operate largely without our awareness. The sympathetic division increases alertness, metabolic rate, and muscular abilities; the parasympathetic division reduces metabolic rate and promotes visceral activities such as digestion.

The Somatic and Autonomic Nervous Systems

Figure 8-33(a) The Autonomic Nervous System The Somatic and Autonomic Nervous Systems

PLAY The Organization of the Somatic and Autonomic Nervous

System Figure 8-33(b) The Autonomic Nervous System

Sympathetic Division Organization

• Preganglionic neurons in segments T1 to L2 • Ganglia near the vertebral column • Sympathetic ganglia • Paired sympathetic chain ganglia • Unpaired collateral ganglia • Preganglionic fibers to adrenal medullae • Epinephrine (adrenalin) into blood stream

Figure 8-34 The Autonomic Nervous System

Effects of Sympathetic Activation • Generalized response in crises • Increased alertness • Feeling of euphoria and energy • Increased cardiovascular activity • Increased respiratory activity • Increased muscle tone

Parasympathetic Division Organization • Preganglionic neurons in brain stem and sacral spinal segment • Ganglionic neurons (peripheral ganglia) in or near target organ • Sacral fibers form pelvic nerves

Figure 8-35 The Autonomic Nervous System

Effects of Parasympathetic Activation • Relaxation • Food processing • Energy absorption • Brief effects at specific sites

Relationship between the Two Divisions • Sympathetic division reaches visceral and somatic structures throughout the body • Parasympathetic division reaches only visceral structures via cranial nerves or in the abdominopelvic cavity • Many organs receive dual innervation • In general, the two divisions produce opposite effects on the their target organs

Age-Related Changes • Reduction in brain size and weight • Loss of neurons • Decreased brain blood flow • Changes in synaptic organization of the brain • Intracellular and extracellular changes in CNS neurons

FIGURE 8-36 Functional Relationships Between the Nervous System and Other Systems

• Provides sensations of touch, pressure, pain, vibration, and temperature; hair provides some protection and insulation for skull and brain; protects peripheral nerves • Controls contraction of arrector pili muscles and secretion of sweat glands

• Provides calcium for neural function; protects brain and spinal cord • Controls skeletal muscle contractions that produce bone thickening and maintenance and determine bone position

• Facial muscles express emotional state; intrinsic laryngeal muscles permit communication; muscle spindles provide proprioceptive sensations • Controls skeletal muscle contractions; coordinates respiratory and cardiovascular activities

• Many hormones affect CNS neural metabolism; reproductive hormones and thyroid hormone influence CNS development • Controls pituitary gland and many other endocrine organs; secretes ADH and oxytocin

• Endothelial cells of capillaries maintain blood- brain barrier when stimulated by astrocytes; blood vessels (with ependymal cells) produce CSF • Modifies heart rate and blood pressure; astrocytes stimulate maintenance of blood-brain barrier

• Defends against infection and assists in tissue repairs • Release of neurotransmitters and hormones affects sensitivity of immune response

• Provides oxygen and eliminates carbon dioxide • Controls pace and depth of respiration

• Provides nutrients for energy production and neurotransmitter synthesis • Regulates digestive tract movement and secretion

• Eliminates metabolic wastes; regulates body fluid pH and electrolyte concentrations • Adjusts renal blood pressure; controls urination

• Sex hormones affect CNS development and sexual behaviors • Controls sexual behaviors and sexual function