The Autonomic Nervous System (ANS) Comparison of somatic nervous system (SNS) & ANS

Transcription

1 The Autonomic Nervous System (ANS) Comparison of somatic nervous system (SNS) & ANS Effectors Pathways Neurons Ganglia 1

2 ANS: visceral motor pathways Effectors. Smooth muscle, examples... arrector pili muscles airways blood vessels stomach, intestines, uterus, urinary bladder, other hollow organs Cardiac muscle Glands (exocrine glands) sweat glands, salivary glands, intestinal glands, etc Adipose tissue ANS has 2 divisions Sympathetic and Parasympathetic Sympathetic division: energy consuming increases metabolism required for alarm reactions (fight-or-flight response) times of increased alertness exercise energy consuming Parasympathetic division: energy conserving maintains resting metabolism 2

3 Many effectors are dually innervated innervated by both divisions dual innervation allows fine control Sympathetic increases heart rate (HR) Parasympathetic decreases HR exceptions to dual innervation Only one division innervates Sweat glands, adipose tissue, lacrimal glands, blood vessels Cooperation of divisions required for Reproductive system function Compare ANS divisions sympathetic division parasympathetic division 3

4 important vocabulary autonomic nuclei preganglionic neuron preganglionic fiber autonomic ganglia ganglionic neurons postganglionic fibers Sympathetic Division overview thoracolumbar origin from CNS increases somatic activity energy expending supports exertion alarm reaction (fight-or-flight response) activated by mental stress physical stress physical activity (exercise) 4

5 Parasympathetic Division overview craniosacral origin from CNS resting conditions energy conserving decreased somatic activity increased visceral activity SLUDD Salivation Lacrimation Urination Digestion Defecation Side note: Enteric Nervous System (ENS) located in walls of GI tract regulates GI activity (enteric refers to intestine) up to100 million neurons more about the ENS in BIOL 242 5

6 Sympathetic (thoracolumbar) division Recall: autonomic pathways have 2 neurons... Preganglionic neuron soma in CNS Ganglionic neuron soma in a ganglion 6

7 Sympathetic division Preganglionic neuron somas (visceral motor neuron somas) lateral horns of thoracolumbar region of cord Synapse in sympathetic ganglia sympathetic ganglia: 3 categories Sympathetic chain ganglia Collateral ganglia Suprarenal medullae 7

8 sympathetic chain ganglia contain ganglionic neuron cell bodies Ganglionic neuron fibers enter gray ramus then spinal nerves which innervate effectors in body wall and limbs OR sympathetic nerves which innervate effectors in thoracic cavity heart, airways collateral ganglia contain ganglionic neuron cell bodies Preganglionic fibers enter splanchnic nerves and pass through to collateral ganglia Ganglionic fibers innervate effectors in abdominopelvic cavity: stomach, intestines, urinary bladder, uterus, etc. 8

9 suprarenal (adrenal) glands inner core: suprarenal medulla or adrenal medulla suprarenal medullae Contain unusual neurons Preganglionic fibers extend all the way to the suprarenal medullae Ganglionic neurons are in the medullae These neurons are endocrine cells Release neurotransmitters into blood ~80% epinephrine (E) (adrenalin) ~20% norepinephrine (NE) (noradrenalin) 9

10 Rami communicantes White ramus Myelinated preganglionic fibers Gray ramus Unmyelinated postganglionic fibers Rami communicantes white rami: located along spinal segments of thoracolumbar region gray rami: Located along each spinal segment of entire spinal cord 10

11 Sympathetic outflow sympathetic chain effectors in head sympathetic nerves effectors in thoracic cavity viscera splanchnic nerves effectors: abdominal cavity viscera spinal nerves effectors in body wall and limbs note: 8% of the fibers in spinal nerves are sympathetic fibers The other 92% are Sympathetic pathway divergence Extremely divergent 1 preganglionic fiber may synapse on up to 25 ganglionic neurons 11

12 Effects of sympathetic activation Increased respiratory activity cardiovascular activity (BP & HR) mental alertness dilation of airways sweat gland activity muscle tone Increased metabolism adipose tissue: lipolysis skeletal muscle and liver: glycogenolysis Decreased GI tract & urinary tract activity Neurotransmitters & Sympathetic function sympathetic preganglionic neurons are cholinergic Acetylcholine excitatory synapse between preganglionic and ganglionic neurons 12

13 Neurotransmitters & Sympathetic function sympathetic preganglionic neurons are cholinergic excitatory synapse sympathetic ganglionic neurons are of several varieties adrenergic, most cholinergic, rare nitroxidergic, rare sympathetic ganglionic neurons have no axon terminals; they have varicosities Most sympathetic ganglionic neurons are adrenergic Release norepinephrine (NE) 13

14 Fates of norepinephrine binds to receptors on effector cells reabsorbed into ganglionic fibers reused or broken down by MAO (monamine oxidase) diffuses out of synapse inactivated by COMT (catechol-o-methyltransferase) sympathetic stimulation duration postsynaptic effects last for several seconds duration (not 20 msec as in cholinergic synapses, recall AchE breaks down Ach) NE is not subject to rapid enzymatic degradation Most tissues contain little of either COMT or MAO Neither COMT or MAO are in blood to breakdown NE & E from adrenal medullae circulating NE and E may remain elevated for 30 seconds or more effects on effectors last several minutes 14

15 Effects on effectors of sympathetic stimulation Diverse 2 classes of receptors: alpha (α) & beta (β) both are adrenergic second messengers are activated with various functions alpha (α) receptors, 2 types activate intracellular enzymes α 1 receptors activation cause Ca ++ ion release from the endoplasmic reticulum Usually excitatory on smooth muscle: constricts peripheral blood vessels constricts sphincters of GI tract & urinary bladder α 2 receptors activation lower camp: activation or inhibition of key enzymes Usually inhibitory at neuromuscular and neuroglandular junctions 15

16 beta (β) receptors, 3 types Activation increases camp, causes a change in metabolic activity of effector β 1 receptor activation increase metabolism of skeletal muscle increases heart rate and force of contraction β 2 receptor activation causes relaxation of smooth muscle in: airways, blood vessels of heart and skeletal muscle β 3 lipolysis in adipose tissue fatty acids are released into blood for tissue use sympathetic cholinergic ganglionic fibers Few in number Secrete Ach Locations Sweat glands Increase activity Blood vessels to skeletal muscle Dilation which increases blood flow 16

17 nitroxidergic ganglionic fibers Secrete nitric oxide (NO) Effect Relaxes smooth muscle in blood vessel walls Dilation of blood vessels in various tissues Parasympathetic (craniosacral) division 17

18 Parasympathetic division Preganglionic neuron somas brainstem FYI CN nuclei III, VII, IX, & X lateral horns of S2 S4 Ganglia are near or in effectors Ganglia categories Terminal (near) Intramural (in wall) Parasympathetic cranial outflow innervates structures in head ventral cavity 18

19 Parasympathetic cranial outflow: effectors smooth muscles of eye: ciliaris sphincter pupillae glands: nasal, lacrimal, salivary ventral cavity viscera CN X: Vagus nerve Accounts for ~75% of all parasympathetic outflow vagal preganglionic fibers extend directly to terminal/intramural ganglia in thorax and abdomen Innervates ventral cavity viscera except pelvic organs Intramural ganglia in walls of organs 19

20 FYI slide: a look at intramural ganglia Parasympathetic sacral outflow pelvic nerves 20

21 Model of parasympathetic sacral outflow Pelvic nerves From S2- S4 Source of pelvic nerves Pelvic viscera Parasympathetic sacral outflow Smooth muscle and glands of pelvic organs Distal colon, rectum, anus/kidney/urinary bladder/ reproductive organs Preganglionic fibers form the pelvic nerves which project to intramural ganglia 21

22 Parasympathetic activation: major effects Pupil constriction Increased GI tract secretions motility Reduced HR Reduced force of heart contractions Airway constriction Sexual arousal: change in blood flow glandular secretions Defecation Urination Neurotransmitters and Parasympathetic function All* PS fibers release Ach *Really, most *chapter 28 Effects are short lived AChE present at synapse tissue cholinesterase is in surrounding tissues Less divergent than sympathetic pathways 1 preganglionic to 6-8 ganglionic fibers 22

23 Acetylcholine receptors on effectors 2 categories Nicotinic receptors Muscarinic receptors Acetylcholine receptors Nicotinic receptors SNS NMJ and in all ANS synapses between preganglionic and ganglionic neurons Always excitatory: opening of chemically gated Na + channels Muscarinic receptors All parasympathetic effectors Neuromuscular or neuroglandular junctions G proteins are activated with longer lasting effects than activated nicotinic receptors Excitatory or inhibitory depending on effector 23

24 Autonomic Tone Result of continuous level of spontaneous activity of ANS neurons Balance of both divisions determine minute to minute effects ANS neurons increase or decrease activity to modify effectors to small degree For example: subtle changes in HR are result of small adjustments Crises result in parasympathetic inhibition and sympathetic stimulation Visceral Reflexes 24

25 Read and enjoy but not for 252- FYI only Higher order functions page Memory States of consciousness Sleep levels Non-rapid eye movement (NREM) Rapid eye movement (REM) 25

26 Falling asleep: first comes NREM sleep stages, followed by REM sleep, then we cycle NREM stages Stage 1: 1-7 minutes, eyes closed, fleeting thoughts, easily aroused dozing Stage 2: next 15 minutes, more difficult to arouse Stage 3: occurs at about 20 minutes in, deep sleep Stage 4: deepest levels of sleep, variable time but usually by an hour NREM sleep is followed by REM sleep 26

27 REM sleep high levels of cortical activity exceeding that of active awake brain function eye movement increases when dreams occur, skeletal muscles are inhibited ANS activity increases Increased HR, increased BP, changes in blood flow penile erections (due to ANS activity, not sexual dreams) this allows a determination of erectile dysfunction source (psychological vs. physiological) REM sleep 3-5 episodes for 7 8 hrs of sleep episodes get progressively longer 1 st period ~10-20 minutes, ~50 minutes for last one totaling minutes of REM sleep necessary for being well rested making good decisions 27

28 FYI May be of interest to you Arousal and RAS What accounts for getting tired/sleepy... Neurotransmitters and behavior Effects of aging on the nervous system Pages