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Lecturer: Dr Lucy Patston

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1 Lecturer: Dr Lucy Patston
Week beginning Monday 9 September 2013 Lecture 13 Autonomic Nervous System Lecturer: Dr Lucy Patston

2 Reading Lundy: Chapter 9 Tortora PDF on Moodle
3x word documents of ANS systems Lundy-Ekman. Neuroscience: Fundamentals for Rehabilitation, 4th Edition. W.B. Saunders Company, 2013. Kandel et al. Principles of Neural Science, 5th Edition. McGraw Hill, Tortora & Derrickson. Principles of anatomy and physiology, 13th Edition. Wiley

3 Overview Comparison of somatic and autonomic nervous systems
Anatomy of autonomic motor pathways Anatomical Components Structure of the Sympathetic Division Structure of the Parasympathetic Division Physiology of the ANS

4 Learning Objectives Today
Understand the function of the ANS as a whole and how it differs from the somatic NS Have an idea about the types of receptors found in the ANS Understand the functions and innervations of the parasympathetic system Understand the functions and innervations of the sympathetic system Be able to compare and contrast the two systems Have an appreciation for some of the disorders associated with the ANS

5 Nervous System Overview

6 Introduction Main input to ANS comes from autonomic (visceral) sensory neurons (sensory receptors located in blood vessels, visceral organs, muscles) ANS monitors the internal environment E.g., chemoreceptors monitoring blood CO2 levels, mechanoreceptors monitoring stretch in walls of organs (bladder) Sensory signals not normally consciously perceived

7 Introduction Autonomic motor neurons regulate visceral activity by increasing OR decreasing activity in effector tissues (smooth muscle, glands) E.g., constriction of pupils, dilation of blood vessels, adjustment of rate and force of heartbeat (ANS motor responses) Most motor responses cannot be consciously altered (difficult to slow own heart) Signals from somatic/special senses via limbic system influence response of ANS (e.g., being grabbed; hearing wheels squeal)

8 Comparison of ANS and SNS Motor neurons
Somatic motor neuron: single, myelinated axon extend from CNS to skeletal muscle Autonomic motor neuron: Two neuron series with autonomic ganglion as synapse point Autonomic Ganglion (in PNS) Effector organ (in PNS) First neuron: Preganglionic neuron - myelinated Second neuron: Postganglionic neuron - unmyelinated Spinal cord (in CNS)

9 Somatic motor neurons release only acetylcholine (ACh) as their neurotransmitter
Autonomic motor neurons release either ACh or norepinephrine (NE)

10 Somatic vs Autonomic Somatic efferents: Autonomic efferents:
innervate only muscle dependent on CNS input activation usually voluntary use one neuron Autonomic efferents: innervate all other parts of the body can function independently of CNS input usually non-conscious use two neurons with a synapse outside the CNS

11 Somatic system Autonomic system


13 Dual innervation ANS has two divisions
Sympathetic division Parasympathetic division Most organs have dual innervation – they receive inputs from both sympathetic and parasympathetic neurons Innervation by one division may stimulate organ, whereas innervation by the other division may inhibit organ E.g., heart rate: sympathetic increases, parasympathetic decreases

14 Divisions of the autonomic nervous system
Divisions of the autonomic nervous system. Note that although the sympathetic pathways are separate from the parasympathetic pathways, most autonomic effectors are innervated by both pathways.

15 Sympathetic Division Known as fight-or-flight division
Sympathetic activities result in increased alertness and metabolic activities to prepare body for emergency situation Rapid heart rate; dilation of pupils; dry mouth; sweaty, cool skin; dilation of blood vessels to organs involved in combating stress (heart, skeletal); constriction of blood vessels to organs NOT involved (gut, kidneys)

16 Parasympathetic Division
Known as rest-and-digest division Parasympathetic activities conserve and restore body energy during rest times Conserves energy, replenishes nutrient stores

17 Anatomical Components Overview
Preganglionic Neurons Autonomic Ganglia Sympathetic Parasympathetic Postganglionic Neurons Autonomic Plexuses

18 Preganglionic Neurons
Preganglionic Neurons (Sympathetic) Cell bodies in spinal cord (lateral horns) in 12 thoracic segments and first 3 lumbar segments Known as thoracolumbar outflow Preganglionic Neurons (Parasympathetic) Cell bodies located in nuclei of 4 cranial nerves (III, VII, IX, X) and lateral gray matter of S2-S4 in spinal cord Known as craniosacral outflow

19 Autonomic Ganglia Sympathetic Ganglia – synapse sites between pre- and postganglionic neurons Two types of sympathetic ganglia Sympathetic trunk ganglia (aka: vertebral chain ganglia or paravertebral ganglia) Prevertebral ganglia (aka: collateral ganglia) Parasympathetic Ganglia (later)

20 Sympathetic trunk ganglia
Lie in vertical row either side of vertebral column From base of skull to coccyx Trunk ganglia in neck have specific names: Superior cervical ganglia Middle cervical ganglia Inferior cervical ganglia Postganglionic neurons from these innervate heart and head/neck/shoulders Preganglionic axons SHORT, postganglionic axons LONG

21 Prevertebral ganglia Lie anterior to vertebral column
Innervate organs below the diaphragm There are five: The celiac ganglion The superior mesenteric ganglion The inferior mesenteric ganglion The aorticorenal ganglion The renal ganglion

22 Autonomic Ganglia Parasympathetic Ganglia – pre- and postganglionic neurons in parasympathetic division synapse in terminal ganglia These ganglia located close to or in visceral organ Terminal ganglia in head have specific names: Ciliary ganglion Pterygopalatine ganglion Submandibular ganglion Otic ganglion Preganglionic axons LONG, postganglionic axons SHORT

23 Postganglionic Neurons
Sympathetic Division: Preganglionic neurons connect with postganglionic neurons in one of the following ways (see next slide for diagram): Synapse in ganglion it first reaches Ascend or descend the sympathetic chain Continue, without synapsing, to a prevertebral ganglion Continue, without synapsing, to adrenal medulla One sympathetic preganglionic neuron may have many branches and may synapse with 20+ postganglionic neurons. Projection of divergence explains why sympathetic responses can affect many effectors at once

24 Different types of connections between ganglia and postganglionic neurons in the sympathetic division of the ANS

25 Postganglionic Neurons
Parasympathetic Division: Because postganglionic neurons are short (parasym. ganglia are located near effectors), stimulation involves only one visceral effector (organ)

26 Autonomic Plexuses Axons form tangled networks – autonomic plexuses
Major ones are Cardiac plexus, which supplies the heart Pulmonary plexus, which supplies the bronchial tree There are also plexuses in the abdomen and pelvis

27 Sympathetic NS Structure
Pathway for thoracic and L1-3: Myelinated axon exits lateral gray horn via ventral root & spinal nerve Then passes through white ramus communicans and on to sympathetic trunk ganglion “white” refers to myelinated

28 Sympathetic NS Structure
Sympathetic trunk ganglia: lie anterior and lateral to vertebral column Typically 3 cervical, 11 or 12 thoracic, 4 or 5 lumbar, 4 or 5 sacral, and 1 coccygeal ganglion Although trunk extends to the neck, ganglion only receive preganglionic axons from the thoracic and lumbar segments

29 Sympathetic NS Structure
Cervical portion of trunk divided into: Superior ganglia: innervate head and heart Middle ganglia: innervate the heart Inferior ganglia: innervate the heart

30 Sympathetic NS Structure
The thoracic and lumbar portions innervate most other viscera, sweat glands, blood vessels and arrector pili muscles of hair follicles

31 Sympathetic NS Axons leave the sympathetic trunk in 4 possible ways:
They can enter spinal nerves They can form cephalic periarterial nerves They can form sympathetic nerves They can form splanchnic nerves They innervate different parts of the body (no need to know details)

32 Sympathetic NS Structure
Postganglionic axons leaving the sympathetic trunk ganglia enter the gray ramus communicans “gray” because unmyelinated

33 Parasympathetic NS Structure
Craniosacral outflow: Cell bodies found in 1) brain stem nuclei (axons emerge as part of a cranial nerve) and 2) lateral gray matter of sacral segments S2-S4 (axons emerge as sacral spinal nerves) All preganglionic axons of both cranial and sacral outflows end in terminal ganglia (the head terminal ganglia are named (see previous slide), the sacral terminal ganglia are not named and are found in the walls of the innervated viscera

34 Parasympathetic NS Structure
Cranial Outflow: (CNs III, VII, IX, & X) CN III innervates: Ciliary muscle (lens) pupillary sphincter (pupil) CN VII innervates: Lacrimal (tear film) Submandibular and sublingual (salivary) glands CN IX innervates: Parotid (salivary) gland CN X innervates: Heart, Larynx, Trachea, Bronchi, Lungs, Liver, Gallbladder, Stomach, Pancreas, Small intestine (and part of large intestine)


36 Parasympathetic NS Structure
Sacral Outflow: (S2, S3, S4) Form pelvic splanchnic nerves Innervate smooth muscle and glands in the walls of: Colon and rectum Urinary bladder External genitals Uterus

37 Structure of the Enteric Division
Please read half page section on page 593 of Tortora pdf This system is FYI only

38 Anatomy & Physiology: Patton & Thibodeau

39 Functions of Sympathetic NS
Primary role of the sympathetic NS is to maintain optimal blood supply in organs Normal activity of the sympathetic NS will stimulate smooth muscle in vessel walls (just at the right amount) Increase in sympathetic NS constricts vessels, decrease dilates vessels E.g., lying to standing: BP increased to prevent fainting

40 Functions of Sympathetic NS
Role of sympathetic NS described using fight or flight responses System prepares for vigorous muscle activity when under threat Vasoconstriction in skin and gut – all blood to muscles Blood glucose increases Bronchi/coronary vessel dilate BP/heart rate increase (Digestion reduces)

41 Regulation of Body Temperature
Sympathetic activity regulates temperature through effectors on skin Signals control Diameter of blood vessels Secretion of sweat glands Erection of hairs

42 Regulation of Blood Flow
Blood pools in skeletal muscle vessels when their walls are relaxed If pooling of blood in the lower limbs and abdomen is not prevented when a person assumes an upright position, the resulting drop in blood pressure can deprive the brain of adequate blood supply, causing syncope (fainting) Normally, the pooling of blood is prevented by vasoconstriction of the capacitance vessels, before the change in position

43 Sympathetic Control in Head
Sympathetic signals dilate the pupil of the eye and assist in elevating the upper eyelid. The levator palpebrae superioris muscle consists of both smooth and skeletal muscle fibers Only the smooth muscle fibers are innervated by the sympathetic nervous system (The skeletal muscle fibers are innervated by the oculomotor cranial nerve) Sympathetic fibers also innervate salivary glands; their activation causes secretion of thick saliva, which causes a sensation of dryness in the mouth

44 Working together Sym and parasym work together in normal conditions
E.g., para tends to slow/weaken heartbeat so sym functions to maintain normal beat/strength Sym dominates during times that require fight or flight Parasym dominates during inbetween times to “rest and repair”

45 Comparison of Sym & Parasym
Some organs have synergistic activity of the two systems (opposing actions are balanced to provide optimal organ function): Actions on thoracic & abdominal viscera Bladder and bowels Pupil of eye Some independent functions: Sym: e.g., elevation of upper eyelid Para: e.g., increasing convexity of lens

46 Comparison of Sym & Parasym
Parasympathetic cell bodies in brainstem and sacral spinal cord: craniosacral outflow Sympathetic cell bodies located T1-L2 levels: thoracolumbar outflow

47 Summary Parasympathetic activity decreases cardiac activity; facilitates digestion; increases secretions in the lungs, eyes, and mouth; controls convexity of the lens in the eye; constricts the pupil; controls voiding of the bowels and bladder; and controls the erection of sexual organs The sympathetic nervous system optimizes blood flow to the organs, regulates body temperature and metabolic rate, and regulates the activity of viscera

48 Clinical Correlations
Horner’s Syndrome Syncope Tests of Autonomic Function

49 Horner’s syndrome If a lesion affects the sympathetic pathway to the head, sympathetic activity on one side of the head is decreased This leads to ipsilateral drooping of the upper eyelid, constriction of the pupil, and skin vasodilation, with absence of sweating on the ipsilateral face and neck

50 Horner’s syndrome Interruption of blood supply, trauma, tumor, cluster headache, or stellate ganglion block may cause Horner's syndrome Cluster headache is a severe headache on one side of the head that lasts a few minutes to 3 hours and occurs as a series of headaches

51 CN III Tests (1)

52 Syncope (fainting) Loss of consciousness due to inadequate blood flow to the brain Blood flow to head restored when person is horizontal Vasovagal attack: Vagal stimulation to heart follow the intramuscular vasodilation Slows heart, further decreasing BP, nausea, salivation, increased perspiration Excessive activity of both sympathetic and parasympathetic systems Scary for bystanders!!

53 Tests of Autonomic Function
BP in supine position, then in standing position Sweat test (filter paper placed on skin and then weighed) Hand vasomotor test (skin temp recorded before and after hands in cold water – vasoconstriction) Valsalva test

54 Valsalva test

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