Chapter 15 Lecture Outline

Transcription

1 Chapter 15 Lecture Outline See separate PowerPoint slides for all figures and tables preinserted into PowerPoint without notes. Copyright McGraw-Hill Education. Permission required for reproduction or display. 1

2 15.1a Functional Organization Somatic nervous system (SNS) Consciously perceived or controlled processes Somatic sensory portion detects signals from special senses (vision, hearing, equilibrium, smell, taste) and from skin and proprioceptors Somatic motor portion sends signals from CNS to skeletal muscles o Voluntary movements involve cerebrum o Reflexive movements involve brainstem and spinal cord Copyright 2016 McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education 2

3 Somatic Nervous System Figure 15.1a 3

4 15.1a Functional Organization Autonomic nervous system (ANS) Also called autonomic motor or visceral motor system Processes regulated below conscious level Transmits signals from CNS to heart, smooth muscle, glands Responds to visceral sensory inputs (e.g., from blood vessels) o Those sensory neurons are not considered part of ANS Functions to maintain homeostasis o Keeps conditions inside body within optimal ranges 4

5 Autonomic Nervous System Figure 15.1b 5

6 15.1b Lower Motor Neurons of the Somatic Versus Autonomic Nervous System Lower motor neurons of somatic nervous system A single lower motor neuron extends from CNS to skeletal muscle fibers o Cell body within brainstem or spinal cord o Myelinated axon with large diameter o Releases acetylcholine (ACh) from synaptic knob to excite muscle fiber 6

7 15.1b Lower Motor Neurons of the Somatic Versus Autonomic Nervous System Lower motor neurons of autonomic nervous system ANS uses a chain of two motor neurons to reach effector First is the preganglionic neuron o Cell body within brainstem or spinal cord o Thin, myelinated axon projects to autonomic ganglion in peripheral nervous system o Releases ACh from synaptic knob to excite second motor neuron Second is the ganglionic (postganglionic) neuron o Cell body within autonomic ganglion o Very thin, unmyelinated axon projects to cardiac muscle, smooth muscle, or gland o Releases ACh or norepinephrine (NE) from synaptic knob to either excite or inhibit the effector (effectors have a variety of receptor types) 7

8 Lower Motor Neurons of the Autonomic Nervous System Figure

9 15.1c CNS Control of the Autonomic Nervous System ANS is regulated by parts of brain and spinal cord Hypothalamus is crucial (contains nuclei controlling both divisions of the ANS) Crucial for emotional ANS processes such as fight-or-flight Can be influenced by areas of cortex, thalamus, limbic system Brainstem nuclei mediate visceral reflexes E.g., maintenance of blood pressure Spinal cord governs some ANS reflexes E.g., defecation and urination as controlled by the parasympathetic nervous system 9

10 Control of Autonomic Functions by Higher Brain Centers Figure

11 15.2a Functional Differences Parasympathetic and sympathetic divisions of ANS have complimentary functions Parasympathetic division: rest-and-digest o For conserving energy, replenishing nutrients Sympathetic division: fight-or-flight o For exercise, excitement, emergency 11

12 15.2b Anatomic Differences in Lower Motor Neurons Parasympathetic Craniosacral division Preganglionic neurons in brainstem (cranial nerves) or S2 S4 spinal cord Preganglionic axons are long, postganglionic axons are short o Ganglia are close to or within the effector organ Preganglionic axons have few branches Sympathetic Thoracolumbar division Preganglionic neuron in lateral horns of T1 L2 Preganglionic axons are short, postganglionic axons are long o Ganglia are close to spinal cord (lateral or anterior to it) Preganglionic axons have many branches 12

13 Comparison of Parasympathetic and Sympathetic Divisions Figure

14 Comparison of Parasympathetic and Sympathetic Divisions Figure

15 15.3 Parasympathetic Division Parasympathetic function: maintain homeostasis at rest Craniosacral anatomical origin Destination: Ganglia found in two types of locations Terminal ganglia located close to effector Intramural ganglia located within wall of target organ 15

16 15.3a Cranial Components Four cranial nerves convey parasympathetic signals Oculomotor, facial, glossopharyngeal, and vagus nerves Oculomotor Nerve (CN III) Preganglionic axons from cell bodies in midbrain nuclei extend to ciliary ganglion within the orbit o Postganglionic axons control ciliary muscle (lens focus for near objects) and pupil constriction (iris sphincter) Facial Nerve (CN VII) Preganglionic axons with cell bodies in pons extend to pterygopalatine and submandibular ganglia o Postganglionic axons from pterygopalatine ganglion control lacrimal glands and small glands of nose and mouth o Postganglionic axons from submandibular ganglia control submandibular and sublingual salivary glands 16

17 15.3a Cranial Components Glossopharnygeal Nerve (CN IX) Preganglionic axons from cell bodies in medulla extend to otic ganglion near ear o Postganglionic axons control parotid salivary gland Vagus Nerve (CN X) Preganglionic axons from cell bodies in medulla project extensively to a variety of ganglia in thorax and abdomen o Postganglionic axons have a variety of functions including: slowing heart rate, constricting lung bronchioles, increasing digestive secretions, storing carbohydrates 17

18 15.3b Pelvic Splanchnic Nerves Pelvic splanchnic nerves Preganglionic axons from cell bodies in lateral gray regions of S2 S4 project to ganglionic neurons in terminal or intramural ganglia Contribute to superior and inferior hypogastric plexuses Postganglionic axons go to abdominal and pelvic effectors o Effects include: smooth muscle contraction, increased secretions in urinary and digestive systems; penile, clitoral erection 18

19 Overview of Parasympathetic Pathways Figure

20 15.4 Sympathetic Division Sympathetic function: exercise and emergency Thoracolumbar anatomical origin Ganglia are close to CNS, but anatomical pathways are complex Sympathetic trunks and ganglia Left and right trunks just lateral to the vertebral column Trunk resembles a pearl necklace o String composed of axons o Pearls composed of sympathetic trunk ganglia housing cell bodies 20

21 Sympathetic Trunk Figure

22 15.4a Organization and Anatomy of the Sympathetic Division White and gray rami Connect spinal nerves to sympathetic trunk White rami communicantes o Carry myelinated preganglionic sympathetic axons from T1 L2 nerves to trunk o Entrance ramps to trunk Gray rami communicantes o Carry unmyelinated postganglionic sympathetic axons from trunk to all spinal nerves o Exit ramps from trunk 22

23 15.4a Organization and Anatomy of the Sympathetic Division Sympathetic splanchnic nerves Preganglionic sympathetic axons not synapsing in sympathetic trunk Run anteriorly from sympathetic trunk, typically terminate in prevertebral ganglia Prevertebral ganglia o Located anterior to vertebral column on surface of aorta; within abdominopelvic cavity o Include celiac, superior mesenteric, and inferior mesenteric ganglia 23

24 Clinical View: Horner Syndrome Injury of cervical sympathetic trunk or T1 trunk ganglion Ptosis Drooping of superior eyelid due to paralysis of superior tarsal muscle Miosis Constricted pupil due to paralysis of pupil dilator muscle Anhydrosis Lack of sweating because sweat glands not receiving sympathetic innervation Facial flushing Due to lack of sympathetic innervation, vasodilation results 24

25 15.4b Sympathetic Pathways Axons exit the sympathetic trunk by one of four pathways Spinal nerve pathway Postganglionic sympathetic pathway Splanchnic nerve pathway Adrenal medulla pathway 25

26 15.4b Sympathetic Pathways Spinal nerve pathway For skin effectors (e.g., sweat glands) of neck, torso and limbs Preganglionic neuron enters sympathetic trunk ganglion and synapses with ganglionic neuron Postganglionic axon travels through gray ramus at same spinal level as ganglion, joins that level s spinal nerve and extends to effector 26

27 Spinal Nerve Pathway Figure 15.8a 27

28 15.4b Sympathetic Pathways Postganglionic sympathetic nerve pathway For effectors that are internal organs of thorax and neck (e.g., heart and esophagus); skin effectors of head and neck; eyelid and dilator pupillae muscles Preganglionic neuron enters and synapses in sympathetic trunk ganglion Postganglionic axon goes directly from trunk ganglion to effector at the level above or below T1-L2 o Does not leave trunk via grey ramus 28

29 Postganglionic Sympathetic Nerve Pathway Figure 15.8b 29

30 15.4b Sympathetic Pathways Splanchnic nerve pathway For effectors in abdominal and pelvic viscera Preganglionic axons pass sympathetic trunk without synapsing o Axons travel in splanchnic nerves to prevertebral ganglia where they make synapses Postganglionic axons innervate effectors 30

31 Splanchnic Nerve Pathway Figure 15.8c 31

32 15.4b Sympathetic Pathways Adrenal medulla pathway For central region of adrenal gland (medulla) Preganglionic sympathetic axons extend through sympathetic trunk and prevertebral ganglia without synapsing in either Preganglionic cells stimulate adrenal medulla cells to release epinephrine and norepinephrine into the blood o These hormones potentiate and prolong the fight-or-flight response 32

33 Adrenal Medulla Pathway Figure 15.8d 33

34 15.5a Overview of ANS Neurotransmitters ANS uses acetylcholine (ACh) and norepinephrine (NE) Either transmitter can cause stimulation or inhibition, depending on the postsynaptic receptor Cells that release ACh are cholinergic neurons Cholinergic neurons include o All ANS preganglionic neurons o All parasympathetic ganglionic neurons o Sympathetic ganglionic neurons innervating sweat glands and blood vessels in skeletal muscle Target cells have cholinergic receptors 34

35 15.5a Overview of ANS Neurotransmitters Cells that release norepinephrine (NE) are adrenergic neurons Most sympathetic ganglionic neurons are adrenergic Target cells have adrenergic receptors 35

36 Comparison of Neurotransmitters in the Autonomic Nervous System Figure

37 15.5b Cholinergic Receptors Two main types of cholinergic receptors: nicotinic and muscarinic Nicotinic receptors (sensitive to nicotine) Found on all ganglionic neurons and adrenal medulla cells o Also on skeletal muscle cells at neuromuscular junction When ACh binds nicotinic receptor it opens cation channel o Na + moves into cell (a lesser amount of K + moves out of cell) o Cell depolarizes: excitatory postsynaptic potential produced Subtypes of nicotinic receptors o E.g., receptors at neuromuscular junction are blocked by curare but receptors on ganglionic neurons are not 37

38 15.5b Cholinergic Receptors Muscarinic receptors (sensitive to muscarine toxin) Found in all target organs of parasympathetic division and a few of sympathetic division (sweat glands and blood vessels) All muscarinic receptors use second messengers, but different subtypes of receptor have different effects o When ACh binds to muscarinic receptors of smooth muscle in GI tract it is stimulated to contract more o When ACh binds to muscarinic receptors on cardiac muscle the heart rate decreases 38

39 15.5c Adrenergic Receptors Norepinephrine and epinephrine are both catecholamines that bind to adrenergic receptors Two main types of adrenergic receptors are alpha (α) and beta (β) receptors Cells with α receptors are typically stimulated by NE o Most blood vessels, pupil dilator, ureters, uterus, arector pili, pancreas Cells with β receptors may be stimulated or inhibited by NE o β 1 receptors Primarily stimulatory in heart and kidney o β 2 receptors Primarily inhibitory in heart, lungs, uterine relaxation o β 3 receptors May be stimulatory (or inhibitory) Located in adipose (triglyceride breakdown for fuel); urinary bladder smooth muscle (relaxation 39

40 Clinical View: Epinephrine for Treatment of Asthma Asthma attacks narrow the bronchioles Bronchioles contain β 2 receptors Epinephrine binds to β 2 receptors more effectively than does norepinephrine Epinephrine is used to treat asthma attack as it is a more potent relaxant of smooth muscles in bronchioles (more dilation) 40

41 15.6b Dual Innervation Most effectors are innervated by both divisions of ANS Both continuously release neurotransmitter Generate autonomic tone Dual innervation: organ receives input from both the sympathetic and parasympathetic divisions Two divisions may have antagonistic or cooperative effects Antagonistic effects Commonly the two divisions oppose each other Drugs used to block one division and enhance opposing effect 41

42 Oculomotor nerve T1-T3 spinal segments ACh NE Muscarinic receptor Alpha one receptor Miosis Mydriasis

43 Oculomotor nerve T1-T3 spinal segments atropine ACh NE Muscarinic receptor Alpha one receptor Miosis Mydriasis

44 Atropa Belladonna Deadly Nightshade

45 Vagus nerve T1-T4 spinal segments ACh NE Muscarinic receptor Beta one receptor Slows heart rate Increase heart rate and force of contraction

46 Vagus nerve T1-T4 spinal segments ACh NE Beta blocker Muscarinic receptor Slows heart rate Increase heart rate and force of contraction

47 Vagus nerve T3-T4 spinal segments ACh NE Muscarinic receptor Beta two receptor Bronchoconstriction Bronchodilation

48 Vagus nerve T4-T9 spinal segments ACh NE Muscarinic receptor Alpha or Beta receptor Increased motility Glycogen synthesis in liver Decreased motility Glycogen breakdown in liver

49 Pelvic nerves T12-L2 spinal segments ACh NE Muscarinic receptor Alpha one or Beta two receptor Relaxation of internal sphincter (urine release) Erection Contraction of urinary sphincter (urine retention) Ejaculation

50 15.6b Dual Innervation Cooperative effects Seen when parasympathetic and sympathetic stimulation have different effects that are part of an overall response E.g., male sexual function o Penis erection due to parasympathetic activity o Ejaculation due to sympathetic activity 50

51 15.6c Systems Controlled Only by the Sympathetic Division Opposing effects can be achieved without dual innervation Blood vessels constrict with increased sympathetic activity; they dilate with decreased sympathetic activity Examples of effectors innervated only by the sympathetic division Sweat glands in the trunk Arrector pili muscles in the skin Adrenal medulla neurosecretory cells 51

52 Clinical View: Raynaud Syndrome Sudden constriction of small arteries of digits Results in loss of normal hue of distal skin Accompanied by pain Triggered by cold or emotional stress Due to exaggerated local sympathetic response More common in women 52

53 Autonomic Plexuses Figure

54 15.7b Autonomic Reflexes Autonomic reflexes (visceral reflexes) Pre-programmed response to a stimulus generated by a reflex arc o Arc includes: receptor, sensory relay to CNS, CNS integration center, motor neuron, effector o ANS effectors are cardiac muscle, smooth muscle, or glands 54

55 15.7b Autonomic Reflexes Cardiovascular reflex (blood pressure) Stretch receptors in vessel walls respond to pressure elevation Signals sent to cardiac center in medulla oblongata Inhibit sympathetic and activate parasympathetic output to heart Slow heart rate, decrease volume of blood ejected o Decrease blood pressure 55

56 15.7b Autonomic Reflexes Gastrointestinal reflex (defecation) Sensory neurons in rectum respond to stretch by fecal matter Signals sent to spinal cord Signals sent through motor neurons stimulate rectum to contract and internal anal sphincter to relax 56

57 15.7b Autonomic Reflexes Micturition reflex (urination) Stretch receptors signal when bladder fills with urine Signals sent to sacral spinal cord In infant this results in reflexive contraction of smooth muscles in bladder and relaxation of urinary sphincters o Once toilet trained, signals through the pons allow for voluntary control of the external urethral sphincter 57

58 Autonomic Reflexes Figure