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The Nervous System Chapter 7. Functions of the Nervous System Master controlling and communicating system of the body Maintains body homeostasis with.

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Presentation on theme: "The Nervous System Chapter 7. Functions of the Nervous System Master controlling and communicating system of the body Maintains body homeostasis with."— Presentation transcript:

1 The Nervous System Chapter 7

2 Functions of the Nervous System Master controlling and communicating system of the body Maintains body homeostasis with electrical signals Provides for sensation, higher mental functioning, emotional response Activates muscles and glands Three overlapping functions to accomplish control : Sensory input ( stimuli ) Integration ( process and interpret ) Motor / Output ( effects a response ) Functions are integrated into a loop… keeps modifying until homeostasis is reached or environmental condition changes

3 Structural Classification Central Nervous System : brain & spinal cord ( all neurons & neuroglia within ) Occupy dorsal body cavity Integrating and command center Peripheral Nervous System : outside the CNS Consists of nerves extending from brain & spinal cord Connects CNS to rest of body Spinal nerves & cranial nerves Carry impulses from sensory receptors to CNS & CNS to effectors

4 Functional Classification Sensory ( afferent ) division : conveys impulses to the CNS from sensory receptors Motor ( efferent ) division : carries impulses from the CNS to effector organs ( muscles and glands ); effect a motor response Somatic Nervous System Voluntarily controls skeletal muscles Skeletal muscle reflexes ( involuntary ) Autonomic Nervous System Regulates events that are automatic / involuntary ( activity of smooth & cardiac muscles and glands ) Sympathetic ( stimulates ) & parasympathetic ( inhibits ) nervous system



7 Nervous Tissue : Supporting Cells Neuroglia ( a. k. a. glia or glial cells ) generally support, insulate, and protect the delicate neurons Cannot transmit nerve impulses Never lose ability to divide Brain tumor = “ glioma ” Types : Central Nervous System Astrocytes Microglia Ependymal cells Oligodendrocytes Peripheral Nervous System Schwann cells Satellite cells

8 Astrocytes Star - shaped cells (“ astro ”) Most abundant ( nearly half of neural tissue ) Braces and anchors neurons to blood capillaries Aid in exchanges between the neurons and the blood capillaries ( nutrient regulation ) Protect neurons from harmful substances in blood Help control chemical environment Form scar tissue

9 Microglia Phagocytes that monitor the health of nearby neurons Dispose of debris ( including dead brain cells & bacteria )

10 Ependymal Cells Form epithelial - like membrane that covers parts of brain and forms inner lining that encloses spaces within brain and spinal cord ( central canal ) Help with blood / brain barrier Ciliated, help circulate cerebrospinal fluid

11 Oligodendrocytes Have processes wrapped around nerve fibers that produce myelin sheaths ( fatty insulating coverings ) in brain & spinal cord Myelin is important for conducting electrical impulses !

12 Supporting Cells of the PNS Schwann Cells form myelin sheaths around nerve fibers that are found in the PNS Satellite cells Protectiv e, cushionin g cells

13 Neurons Nerve cells Specialized to receive information and transmit it to other cells ! ( electrochemical message ) Sensory / integrative / motor functions of nervous system ! Common features of neurons : Cell body Metabolic center of the neuron Contains nucleus & organelles Nissl bodies ( rough ER ) & neurofibrils ( maintain cell shape ) Processes Also called “ fibers ”, can be microscopic or 3-4 feet long Dendrites : receive incoming impulses ( can have many ) Axons : generate nerve impulses & conduct away from cell body ( each neuron only has one ) Arises from Axon hillock Neurilemma : cell membrane of neuron

14 Neuro ns

15 Myelin Sheaths Myelin : white, fatty ( lipid - protein ) material, waxy appearance Protects and insulates fibers Increases transmission rate of nerve impulses Schwann cells myelinate axons in PNS and form myelin sheath Coil of wrapped membranes enclosing axon Neurilemma : part of Schwann cell external to myelin sheath Nodes of Ranvier : gaps between myelin sheaths formed by different Schwann cells Oligodendrocytes myelinate axons in CNS Can myelinate as many as 60 different fibers, no neurilemma


17 Nodes of Ranvier Spaces between myelin sheaths Give astrocytes something to hold on to and provides easier transfer of nutrients & materials Ion transfer Impulse jumps from node to node

18 Terminology of CNS Nuclei : clusters of neuron cell bodies, well protected i. e. Caudate nucleus ( region of brain ) Tracts : bundles of nerve fibers ( neuron processes ) Each sense has own tract Sensory tracts go towards brain, motor tracts come from brain White matter : myelinated fibers ( tracts ) Gray matter : unmyelinated fibers and cell bodies ( nuclei )

19 Terminology of PNS Ganglia : small collections of cell bodies outside CNS Nerves : bundles of nerve fibers ( neuron processes )

20 Functional Classification of Neurons Grouped according to the direction the nerve impulse is traveling relative to the CNS Sensory / afferent neurons Carry impulses from sensory receptors ( in the internal organs or the skin ) to the CNS ( from environment to CNS !) Cell bodies found in ganglion outside the CNS Dendrites associated with specialized receptors Motor / efferent neurons Carry impulses from CNS to the viscera and / or muscles & glands ( tell them to do something in response to the stimuli ) Cell bodies always located in the CNS Interneurons ( association neurons ) Connect motor & sensory neurons in neural pathways Cell bodies always in the CNS

21 Path of Travel Sensory  interneurons  motor

22 Sensory Receptors Grouped by location Interoceptors ( internal environment ) Exteroceptors ( external surface of body ) Pressure, pain, temperature Proprioceptors ( muscles, tendons, & joints ) Control equilibrium, posture, and own movements Send information to brain on body position Grouped by structure Free nerve endings – dendrites sense pain, usually in skin Encapsulated – capsule / knob at end of dendrites Separate, specific cells – cell takes info and stimulates neuron i. e. photoreceptors ( rods / cones ) – cell stimulates neurons to take information to brain

23 Sensory Receptors Grouped by stimuli ( selective / specific ) Stimulus produces potential if threshold met ! mechanoreceptors ( mechanical stimuli ) Rapid adaptation : Meissner ’ s corpuscle, Lamellar corpuscle, hair root plexus ; slower adaptation : Merkel disc, Raffini corpuscle thermoreceptors ( heat ) free nerve endings nociceptors ( pain ) free nerve endings, not adaptive photoreceptors ( light ) chemoreceptors ( chemicals ) pH, ions osmoreceptors ( osmotic pressure )

24 Adaptation Receptors adapt to stimuli that they are continuously exposed to ( can be rapid or slow ) i. e. smell & temperature are quickly adapting, pain is very slow Less and less integration occurs A dog ( red line ) tracks a pheasant ( yellow line ). As the dog keeps leaving the odor to prevent receptor adaptation, it zigzags.

25 Structural Classification of Neurons Page 235, Figure 7.8 Based on number of processes extending from cell body Multipolar neuron : several processes Motor & associated neurons, most common structural type Majority of interneurons in CNS are multipolar Bipolar neuron : two processes ( axon & dendrite ) Rare, found only in some special sense organs ( eye, nose ) Act in sensory processing as receptor cells Unipolar neurons : single process emerging from cell body Sensory neurons found in PNS ganglia


27 Physiology of Nerve Impulses Two major functional properties of neurons : Irritability : ability to respond to a stimulus and convert it into a nerve impulse Conductivity : ability to transmit the impulse to other neurons, muscles, or glands Neurotransmissi on : neurons communicating with one another !

28 How does it all work? Plasma membrane of a resting ( inactive ) neuron is polarized ( resting potential ) Fewer positive ions sitting on the inside than on the outside of the membrane more negative inside = resting / inactive Positive ions inside cell : K + ( potassium ) Positive ions outside cell : Na + ( sodium ) Membrane relatively impermeable to both ions Ion channels closed when resting Neuron no longer at rest when sodium enters the cell and then potassium leaves Neuron uses energy to maintain polarization Na / K pump keeps ions where they are “ supposed ” to be when at rest Page 236, Figure 7.9 – Flow chart

29 Resting Potential Sodium Potassium Polarized Negative inside Positive outside Will continue resting until receives stimulus ( from environment or from another neuron ) Typically is a neurotransmitter If enough received, neuron will depolarize and “ fire ”

30 Action Potential 1. Stimuli excite neurons 2. Gates of sodium channels in membrane open with stimulation Na + diffuses into the cell ( high concentration  low ) Depolarization : polarity of neuron ’ s membrane reversed as sodium diffuses More negative outside, positive inside 3. If threshold potential reached, neuron activated to initiate & transmit an action potential ( nerve impulse ) all - or - none response Depolarization ( electrical impulse ) happens along the axon Nodes of Ranvier – jumps from node to node

31 Action Potential 4. Na + channels close and K + channels open K + diffuse out of neuron into tissue fluid rapidly Repolarization – restores electrical conditions at membrane to the polarized ( resting ) state Neuron cannot fire again until repolarized 5. Sodium - potassium pump restores original concentrations Sodium ( goes in ) Depolarized Potassium ( goes out ) Repolarized

32 Myelinated Axons Fibers with myelin sheaths conduct impulses much faster Nerve impulse jumps from node to node along length of fiber ( salutatory conduction ) Gaps allow ions to cross

33 Action Potential All or none response Once threshold is met, neuron will fire Some mental illnesses involve neurons firing when they shouldn ’ t or not firing when they should ( bipolar, schizophrenia ) Takes milliseconds to occur Hyperpol arizatio n Depolari zation Repolari zation

34 Transmission of Signal at Synapse Electrical impulse becomes chemical signal (“ electrochemical ” event ) – page 238, Fig 7.10 Neurotransmitter chemical crosses synapse to transmit signal from one neuron to the next 1. Action potential reaches axon terminal & electrical change opens calcium channels 2. Calcium causes vesicles containing neurotransmitter to fuse with membrane & openings form, releasing transmitter 3. Neurotransmitter molecules diffuse across synapse and bind to receptors on membrane of next neuron 4. If enough neurotransmitter released, depolarization of next neuron occurs 5. neurotransmitter is removed from the synapse ( diffusion, reuptake into axon terminal, or enzymatic breakdown )

35 Video Links on MBC


37 Neurotransmitter s chemical messengers that carry signals between neurons as well as other cells in the body released from the end of one neuron and cross the synapse to receptor sites in the next neuron or effector Certain neurotransmitters increase ion permeability ( excitatory ) Others decrease permeability ( inhibitory )

38 Small Molecule Neurotransmitter Substances Acetylcholin e ( ACh ) Dopamine ( DA ) Norepinephrin e ( NE ) Serotonin (5- HT ) HistamineEpinephrine Amino Acids Gamma - aminobutyric acid ( GABA ) Glyci ne Glutama te Aspartate Neuroactive Peptides - partial list !! bradykini n beta - endorphin bombesin calcito nin cholecyst okinin enkephali n dynorphi n insulin gastrin substance P neuroten sin glucago n secretin somatosta tin motilin vasopre ssin oxytocinprolactin thyrotro pin angiote nsin II sleep peptides galanin neuropep tide Y thyrotr opin - releasi ng hormone gonadotro pnin - releasing hormone growth hormone - releasing hormone luteiniz ing hormone vasoact ive intesti nal peptide Soluble Gases Nitric Oxide ( NO ) Carbon Monoxi de

39 Acetylcholine Abbreviated ACh most common neurotransmitter located in both the central nervous and peripheral nervous system first neurotransmitter be identified in 1914 acts on basic autonomic and muscular functions Sarin gas ( chemical warfare nerve agent ) disrupts its ability to function and often leads to death

40 Glutamate Excitatory neurotransmitter Plays a role in cognition, learning, and memory Main neurotransmitter in CNS of mammals Must be in correct balance in right place at right time ! Excess glutamate in extracellular space can damage neurons “ overexcites ” neurons and causes them to open channels, letting substances into cells that shouldn ’ t be there released with stroke & head trauma and causes damage Researching drugs to help prevent damage Malfunction of glutamate has also been associated with Alzheimer ' s Disease

41 GABA gamma - aminobutyric acid GABA is the most important and common inhibitory neurotransmitter Fine - tunes neurotransmission Stops the brain from becoming overexcited Too much may cause hallucinations Also responsible for regulation of muscle tone

42 Dopamine Generally involved in regulatory motor activity In the basal ganglia of the brain, involved in mood, drives, pleasurable feelings, sensory perception, and attention Produced when “ feeling good,” also causes addictions ( caffeine, cigarettes, drugs, etc.) With addictive substances, dopamine is increased More released Less broken down More received by receptors Drugs can mimic dopamine ( i. e. marijuana – “ dope ”)

43 Epinephrine Also known as adrenaline ( when released as hormone ) Causes the feeling of being “ revved up ” or on edge Activates a “ fight or flight ” reaction in the autonomic nervous system Excitatory neurotransmitter – stimulates nerves to fire Counteracts with norepinephrine / noradrenaline

44 Serotonin Attention and other complex cognitive functions ( drives ), such as sleep ( dreaming ), eating, mood, pain regulation Neurons which use serotonin are distributed throughout the brain, stomach and spinal cord Mood disorders Antidepressants are serotonin uptake inhibitors ( leave serotonin in synapse longer !) i. e. Prozac was first a diet aid ( limited appetite ), but also caused mood change due to its affect on serotonin. Important to understand balance ! ( for example, Prozac would not be a good antidepressant for someone with a history of anorexia.)

45 Neurotransmitter Balance Most functions in body isn ’ t just one neurotransmitter – usually a balance Have to have right amount of each – any of them off can cause mental illness hard to treat mental illness with medication because don ’ t know which is off have to use trial & error

46 Other Neurotransmitter Examples Nitric oxide : vasodilator Endorphins – stress or pain, “ runners high ”

47 Physiology : Reflexes Reflexes are rapid, predictable, and involuntary responses to stimuli Occur over reflex arcs and in both CNS and PNS structures Somatic reflexes : all reflexes that stimulate the skeletal muscles ( pulling back from hot stove ) Autonomic reflexes : regulate activity of smooth muscles, the heart, and glands ( salivary reflex, pupillary reflex ) Five elements : Sensory receptor – reacts to a stimulus Effector organ – muscle or gland eventually stimulated Sensory and motor neurons to connect the two CNS integration center - synapse or interneurons between the sensory and motor neurons Example : patellar ( knee - jerk ) reflex, pulling hand back ( Fig 7.11) Spinal reflexes – without brain involvement

48 Reflexes Figur e 7.11

49 Central Nervous System

50 Central Nervous System Brain & spinal cord 100 billion multipolar neurons First appears as simple tube during embryonic development ( neural tube ) Brain formation begins in the fourth week Functional Anatomy of the Brain Cerebral hemispheres ( cognitive function ) Diencephalon ( glands ) Brain stem ( autonomic ) Cerebellum ( coordination )

51 Cerebral Hemispheres Collectively called the cerebrum Higher brain function Gyri ( gyrus ): elevated ridges of tissue separated by shallow grooves called sulci Fissures : deeper grooves which separate large regions of the brain Cerebral hemispheres separated by longitudinal fissure Sulci and fissures divide cerebral hemispheres into lobes Frontal Parietal Temporal Three basic regions : Cortex ( gray matter ) White matter ( internal area ) Basal nuclei ( gray matter whithin white matter ) Occip ital Insul a

52 Cerebral Lobes

53 Cerebral Cortex Functions : speech, memory, logical and emotional response, consciousness, interpretation of sensation, voluntary movement Gray matter – cell bodies Highly ridged and convoluted, providing more room for thousands of neurons found here Primary somatic sensory area : parietal lobe Interprets impulses traveling from the body ’ s sensory receptors ( except for special senses ) Pain, coldness, light touch Primary motor area : frontal lobe Consciously move skeletal muscles ( voluntary ) Sends impulses down motor tracts Association areas ( throughout cerebrum ) Frontal – concentration, problem solving, planning, language comprehension, word meanings, memories, higher intellectual reasoning and socially acceptable behavior, recognizing patterns and faces, morality, planning ( Cerebral Palsy – damaged ) Parietal – compose speech, touch sensation Temporal – understand speech, reading, music, memories Occipital – visual ( photoreceptors send info here through thalamus ) Broca ’ s area – speech & vocalization

54 Association Areas of Cerebrum

55 Sensory and Motor Homunculi Shows relative amount of cortical tissue devoted to each function ( Fig 7.14, page 243) Link

56 Somatosensory Areas on Cerebral Cortex can map somatosensor y areas ( lips and hands large area, trunk and limbs small area )

57 Cerebral White Matter Fiber tracts ( commissures ) carrying impulses to, from, or within the cortex Corpus callosum : fiber tract that connects cerebral hemispheres Communication between hemispheres

58 Basal Nuclei “ islands ” of gray matter within the white matter of the cerebral hemisphere Also called basal ganglia ( caudate nucleus, putamen, globus pallidus ) Motor relay station : help regulate voluntary motor activities by modifying instructions sent to the skeletal muscles by the primary motor cortex ( particularly in relation to starting or stopping movement ) Huntington ’ s disease and Parkinson ’ s disease are examples of issues with basal nuclei – individuals are unable to carry out voluntary movements in a normal way LINK

59 Basal Nuclei ( Basal Ganglia )

60 Diencephalon Enclosed by cerebral hemispheres Three major structures : Thalamus : relay station for sensory impulses passing upward to the sensory cortex Hypothalamus : (“ under thalamus ”) – primitive brain Autonomic nervous sytem center : regulates body temperature, water / ion balance, glandular secretions, and metabolism ( maintains homeostasis ) Center for many drives and emotions Thirst, appetite, sex, pain, pleasure, sleep Regulates pituitary gland & secretes hormones Mammillary bodies : reflex centers involved in olfaction Epithalamus Pineal gland : secretes melatonin ( broken down as you sleep ) Choroid plexus : forms cerebrospinal fluid Figure 7.1, page 245

61 Diencephalon

62 Limbic System cerebral cortex interconnects with the basal ganglia, the thalamus, and the hypothalamus Center of brain “ emotional - visceral brain ” Controls emotional experience and expression ; regulates emotion Amygdyla ( negative emotions – fear ) & hippocampus ( memory ) Primitive / impuls ive Associated with functions : Fighting Fleeing Feeding Reproductive behaviors link

63 The Limbic System

64 Brain Stem Pathway for ascending and descending tracts ( white matter ) connecting cerebrum & diencephalon to spinal cord Also has small nuclei ( gray matter ) that produce autonomic behaviors necessary for survival, some associated with cranial nerves and control vital activities such as breathing and blood pressure Four main structures : Midbrain ( upper ) - reflexes Pons ( middle ) - breathing Medulla oblongata ( lower ) – heart rate, breathing, blood pressure, swallowing, vomiting Reticular formation – consciousness, awake / sleep cycle, filters sensory inputs from spinal cord ; damage results in coma ( permanent unconsciousness )

65 Cerebellum Provides the precise timing for skeletal muscle activity and controls balance and equilibrium, posture, language processing & long - term learning Provides smooth and coordinated body movements Fibers reach cerebellum from inner ear, eye, proprioceptors Monitors body position and amount of tension in various body parts and sends message to correct when necessary When damaged by head trauma or stroke, or sedated by alcohol, produces “ ataxia ” ( loss of coordination )

66 Cerebellum

67 Evolution of the Brain Lizard Brain Basic functions Mammalian Brain More complex feelings & reactions Human Brain Logic & reasoning


69 The Brain of a Zombie Zombie Traits Stagger Appetite Rage Stupidity

70 Zombie Stagger Seem clumsy, bump into things, hold out arms for balance Cerebellum : involved in coordination of movements Basal ganglia works with frontal lobe and brain stem to coordinate movement & behavior

71 Zombie Appetite Always hungry, appetite never satisfied Eat humans Hypothalamus : connects with many other regions of brain and is responsible for controlling hunger, thirst, emotions, body temperature regulation, and circadian rhythms

72 Zombie Rage Aggressive at all times Extremely violent, attack humans in enraged state Dangerous and cannot be reasoned with Amygdala : brain ’ s primal emotional center ; implicated in the experience of negative emotions like fear and rage

73 Zombie Stupidity often can ’ t figure out how to open doors and rarely, if ever, plan ahead terrible problem solvers, and seem to lack any ability to communicate except through indistinguisha ble grunts Frontal lobe : located at front of brain, associated with reasoning, motor skills, higher level cognition, expressive language Zombie Autopsies


75 Protection of CNS Control center of body – needs good protection from damage ( impact, friction, etc.) Skin / hair Bone ( skull & vertebral column ) Meninges : protective lining Dura mater – “ tough mother ”; hard, leathery, tough outer layer Arachnoid mater – “ web - like ”; middle layer, contains blood vessels Pia mater – “ tender / soft mother ”; inner layer Cerebrospinal fluid Blood - brain barrier

76 Meninges


78 Cerebrospinal Fluid provides protection, maintains proper ion concentration for the CNS, and provides a pathway to the blood for waste helps maintain homeostasis, cushioning

79 CSF Made in choroid plexus In constant motion Small drains for CSF to drain out ( constantl y made, flows, and drains ) Too much CSF increases pressure ( hydroence phalus ) Ventricle s ( openings ), canals & aqueducts

80 Blood - Brain Barrier Keep blood & CNS separate ( only certain molecules can cross into CNS ) Can cross : small molecules ( i. e. water ), some viruses ( i. e. polio, shingles ), anything lipid soluble because can go through cells ( i. e. alcohol ) Many medications have to breach the BBB somehow by attaching to something lipid soluble or mixing with higher concentration of sugar to dehydrate cells and make gaps to pass through

81 Spinal Cord Approximately 17 inches long Two - way conduction pathway to and from the brain Major reflex center ( spinal reflexes ) Enclosed within vertebral column, extends from foramen magnum of skull to first or second lumbar vertebra ( just below ribs ) Cushioned and protected by meninges ( extend beyond end of spinal cord ) 31 pairs of spinal nerves arise from cord and exit vertebral column Cauda equina – collection of spinal nerves at inferior end of vertebral canal

82 Gray Matter of Spinal Cord Dorsal ( posterior ) horns : posterior projections Contain interneurons Sensory neuron fibers enter through dorsal root ; cell bodies in dorsal root ganglion Ventral ( anterior ) horns : anterior projections Cell bodies of motor neurons of somatic nervous system ( voluntary ) Motor neuron axons exit through ventral root Dorsal & ventral roots fuse o form spinal nerves Surrounds central canal ( contains CSF )


84 White Matter of the Spinal Cord Myelinated fiber tracts Conduct impulses from brain to cord or one side of spinal cord to other Sensory ( afferent ) tracts : axons carrying sensory impulses to the brain Dorsal columns, ascending Motor ( efferent ) tracts : axons carrying impulses from the brain to the skeletal muscles Lateral & ventral tracts ( ascending and descending motor tracts )



87 Peripheral Nervous System

88 Peripheral Nervous System Nerves & scattered groups of neuronal cell bodies ( ganglia ) found outside the CNS Structure of a Nerve Nerve : bundle of neuron fibers found outside the CNS Endoneurium : CT surrounding each neuron fiber Perineurium : CT surrounding groups of fibers, forming fascicles Epineurium : CT surrounding fascicles to form nerve Classification of Nerves Mixed nerves : carry both sensory & motor fibers ( spinal nerves ) Sensory ( afferent ) nerves : carry impulses toward CNS Motor ( efferent ) nerves : carry only motor fibers

89 Nerve Structure Link

90 Cranial Nerves 12 pairs of nerves serving head & neck ( primaril y ); one pair extends to thoracic and abdominal cavities Parasympa thetic nervous system ( autonomi c ) Numbered in order Most are mixed nerves Table 7.1 page 258-259; Figure 7.24 page 260 I - Olfactory II - Optic III - Oculomotor IV - Trochlear V - Trigeminal VI - Abducens VII - Facial VIII - Auditory IX - Glossophary ngeal X - Vagus XI - Accessory XII - Hypoglassal

91 Spinal Nerves and Nerve Plexuses 31 pairs of human spinal nerves Formed from combination of ventral and dorsal roots of spinal cord Each spinal nerve divides into dorsal & ventral rami ( spinal nerves only about ½ inch long ) Rami contain both motor & sensory fibers Form plexuses : tangled networks of axons serving particular parts of the body


93 Autonomic Nervous System

94 Motor subdivision of PNS that controls body activities automatically Main input from autonomic sensory neurons ( interoceptors ); monitoring internal environment ( i. e. chemoreceptors regulating CO 2 levels ) Controlled by hypothalamus and brain stem ( integration centers ) Regulates cardiac muscle, smooth muscles, and glands Homeostasis depends largely on ANS ; lots of fine - tuning ! Also called involuntary nervous system Function somewhat even if nerve supply damaged (“ running around like a chicken with its head cut off ”) Hard to consciously control ( i. e. lie detector, yoga )

95 Somatic vs. Autonomic NS Somatic division : Effector organs : skeletal muscle Only one motor neuron Cell bodies inside CNS Axons ( in spinal nerves ) extend to skeletal muscles Neurotransmi tter used is acetylcholin e ( ACh ) ANS : Effector organs : cardiac muscle, smooth muscle, glands Chain of two motor neurons Preganglionic axon ( CNS ): leaves the CNS to synapse with the second motor neuron in a ganglion outside CNS ; myelinated ; acetylcholine Postganglioni c axon ( PNS ): extends to the organ it serves ; unmyelinated ; acetylcholine or epinephrine / no repinephrine


97 See figure 7.27, page 265

98 Divisions of the Autonomic NS Sympathetic division ( thoracolumbar division ): mobilizes body during extreme situations ( fear, exercise, rage… “ fight or flight ”) Shorter pre - ganglionic neuron synapses in sympathetic trunk ganglion or collateral ganglion ( i. e. celiac and superior and inferior mesenteric ganglia ) Parasympathetic division ( craniosacral division ): “ rest & digest,” allows body to relax and conserve energy Longer pre - ganglionic neurons, synapse close to the effector organ at terminal ganglion

99 Anatomy of Autonomic Motor Pathways Some preganglionic neurons extend to adrenal medullae ( hormones released ) – “ adrenaline rush ” Sympathetic trunk ganglia : vertical row on either side of vertebral canal Sympathetic division Innervate organs above diaphragm Prevertebral ganglia : anterior to vertebral canal Sympathetic division Innervate organs below diaphragm Terminal ganglia : close to or actually in wall of organ ( longer ) Parasympathetic division

100 Anatomy of the ANS

101 SNS pregan glioni c motor neuron s arise in the spinal cord. pass into sympat hetic gangli a which are organi zed into two chains that run parall el to and on either side of the spinal cord.

102 Parasym patheti cNS main nerve is the tenth cranial nerve, the vagus nerve. originate s in the medulla oblongata Other pregangli onic parasympa thetic neurons also extend from the brain ( cranial nerves III, VII, IX ) as well as from the lower tip of the spinal cord.

103 Autonomic Functioning Organs receive fibers from both divisions Blood vessels, skin structures, some glands, adrenal medulla – all only receive sympathetic innervation Divisions have antagonistic effects due to different neurotransmitters released Dynamic balance – both have to make fine continual adjustments Communicate using neurotransmitters Parasympathetic fibers : cholinergic fibers ( release acetylcholine ) Sympathetic postganglionic fibers : adrenergic fibers ( release norepinephrine ) All pre - ganglionic neurons release acetylcholine Agonist : neurotransmitter that activates receptors ; antagonist : neurotransmitter that blocks receptor


105 Physiological Effects of ANS Table 7.3, page 268 Autonomic tone : balance between sympathetic & parasympathetic divisions Regulated by hypothalamus Sympathetic dominates during physical or emotional stress ( rapid ATP production ); “ flight or fight : response “ E situations ” - exercise, emergency, excitement, embarrassment one sympathetic neuron can synapse with 20+ postganglionic neurons ( effect much of body simultaneously ) Hormonal effects they provoke linger ( need to “ come down ” after stressful situation ) Parasympathetic dominates “ rest and digest ” activities - conserve and restore energy SLUDD ( salivation, lacrimation, urination, digestion, defecation ) “ Housekeeping ” system of the body Preganglionic neurons synapse with only 4-5 postsynaptic neurons ( more localized response )


107 Autonomic Plexuses Tangled networks of axons from sympathetic & parasympathetic neurons Cardiac ( heart ), pulmonary ( lungs ), celiac or solar ( liver, gall bladder, stomach, pancreas, spleen, kidneys, testes, ovaries ), superior mesenteric ( small & large intestines ), inferior mesenteric ( large intestine ), renal ( kidneys & ureters ) “ wind knocke d out of you ”

108 Autonomic Reflexes controlled conditions i. e. blood pressure reflex arc : Receptor  sensory neuron  integrating center  motor neuron  effector hypothalamus is major control center

109 Autonomic Nervous System Recap What are the key things to know about the ANS? Differences between sympathetic & parasympathetic divisions ( anatomy, physiology, effects ) Anatomy of autonomic pathways & associated terminology What is a plexus? Agonist vs. antagonist ( neurotransmitters )


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