b223 14 autonomic

central nervous system

brain and spinal cord

peripheral nervous system

peripheral nerves and ganglia

afferent sensory system

• general and special senses

efferent motor system

• somatic nervous system controlling skeletal muscles

• autonomic nervous system controlling smooth muscles, cardiac muscles, glands

afferent nervous system

general and special senses

efferent motor system

somatic nervous system controlling skeletal muscles

autonomic nervous system controlling smooth muscles, cardiac muscles, glands

somatic nervous system

controls skeletal muscles

autonomic nervous system

controls smooth muscles, cardiac muscles, glands

operates without conscious control via reflex centers in spinal cord and brainstem controlled by hypothalamus

regulated by higher brain centers that affect the hypothalamus

• limbic system, thalamus, cerebral cortex

coordinates processes that maintain homeostasis

• cardiovascular, respiratory, digestive, urinary, reproductive, etc.

divisions of the ANS

sympathetic division

• expenditure of energy

• dominant under conditions of physical or emotional stress (“fight or flight response”)

parasympathetic division

• conserve and restore body energy, rest and recovery

• dominant control during rest

sympathetic division

expenditure of energy

dominant under conditions of physical or emotional stress (“fight or flight”)

parasympathetic division

conserve and restore body energy, rest, and recovery

dominant control during rest

heart

sympathetic increases heart rate, parasympathetic decreases heart rate

pupils

sympathetic dilates pupils, parasympathetic constricts pupils

digestive tract

sympathetic decreases motility and secretions, parasympathetic increases

bronchioles

sympathetic dilates airways, parasympathetic constricts airways

effectors with sympathetic input only

sweat glands (increased secretion)

arrector pili muscles (contraction)

blood vessels of skeletal muscle, heart, lungs, brain (dilation)

blood vessels of digestive viscera and kidney (constriction)

effectors with parasympathetic input only

lacrimal glands (increased secretion)

structure of the ANS

efferent pathway is two neuron pathway

1. motor neurons in CNS send axons (preganglionic) to synapse on motor neurons in autonomic ganglia in PNS

2. motor neurons in autonomic ganglia (ganglionic cells) send axons (postganglionic axons) to synapse on effector

sympathetic structure

thoraco-lumbar division

• preganglionic cell body in lateral horn of spinal cord segments T1-L2

• preganglionic axon typically shorter

• ganglion typically closer to CNS

  • sympathetic chain ganglia

  • collateral ganglia

parasympathetic

cranio-sacral division

• preganglionic cell body in nuclei of CN III, VII, IX, X and lateral horn of spinal cord segments S2, S3, S4

• preganglionic axon typically longer

• ganglion typically near or in effector organ, so postganglionic axon is short

organization and anatomy of the sympathetic division

SC segments T1-L2 - ventral roots contain preganglionic axons

some axons synapse on cells of chain ganglia

some axons pass through going to collateral ganglia and adrenal medulla

sympathetic chain ganglia

sympathetic division thoraco-lumbar division of ANS

• 2 chains of ganglia - one on each side of the vertebral column

• innervate head, body wall, limbs, and viscera of thoracic cavity (heart, lungs)

collateral ganglia

sympathetic division thoraco-lumbar division of ANS

• located close to large abdominal arteries

• celiac, superior mesenteric, inferior mesenteric ganglia

• preganglionic pass through chain ganglia and form splanchnic nerves to reach collateral ganglia

• innervate abdominal and pelvic viscera

  • sympathetic activation decreases blood flow, decreased digestive activity, and releases stored energy molecules

adrenal medulla

sympathetic division thoraco-lumbar division of ANS

• central portion of the adrenal gland

• preganglionic fibers pass through chain ganglia and splanchnic nerve to celiac ganglia passes through to reach adrenal gland

• postganglionic cells in adrenal medulla are modified neurons that secrete into blood rather than onto effector

parasympathetic division cranio-sacral division of ANS

preganglionic neurons in the brainstem and sacral segments of spinal cord

ganglionic neurons in peripheral ganglia located near or within target organs

effects produced by the parasympathetic division include relaxation, food processing, energy absorption

SC segment S2, S3, S4

organization and anatomy of the parasympathetic division

• pelvic nerves carry preganglionic axons to parasympathetic intramural ganglia located in wall of viscera in inferior portion of abdominal pelvic cavity

• short postganglionic axon innervate effectors

cranial nerve III

organization and anatomy of the parasympathetic division

occulomotor

parasympathetic control of pupil and lens

cranial nerve VII

organization and anatomy of the parasympathetic division

facial

lacrimal and salivary glands

cranial nerve IX

organization and anatomy of the parasympathetic division

glossopharyngeal

salivary glands

cranial nerve X

organization and anatomy of the parasympathetic division

vagus

carries 75% of all parasympathetic output

parasympathetic control of heart, lungs, digestive tract and all other thoracic and abdominal viscera, except most inferior portions

autonomic activation

sympathetic and parasympathetic divisions are activated by different stimuli

sympathetic activation

has widespread effect on body due to:

sympathetic innervation is through out body and has systemic effects

each preganglionic axon branches to synapse onto 24 or more ganglionic cells

adrenal medulla releases mostly epinephrine, but some norepinephrine, into blood stream affecting tissues not innervated by ANS

parasympathetic activation

has localized effect

innervation limited to head and viscera, does not innervate body wall, skin

each preganglionic axon branches to synapse on to only 6-8 ganglionic cells

• less divergent than the sympathetic

postganglionic axons generally go to a single effector

neurotransmitter release and effects on target organs and tissues

synapse of preganglionic axon onto ganglionic cell in autonomic ganglion

• neurotransmitter is ACh in both sympathetic and parasympathetic ganglia

synapse of postganglionic axon to effector

• all parasympathetic postganglionic axons release ACh onto effectors

• sympathetic postganglionic axons to dual innervated viscera release NE onto effectors

neurotransmitters and postsynaptic effect

postsynaptic receptor properties determines effect of neurotransmitter on postsynaptic cell

many neurotransmitters have more than one type of post synaptic receptor

nicotinic cholinergic receptors

skeletal muscles, autonomic ganglia

excitatory

muscarinic cholinergic receptors

excitatory or inhibitory

visceral muscles, cardiac muscle, CNS

alpha adrenergic receptors

alpha 1: excitatory effect on smooth muscles of blood vessels of skin and viscera, causes constriction

alpha 2: inhibitory effects on digestion tract

beta adrenergic receptors

beta 1: excitatory on cardiac muscle

beta 2: inhibitory on smooth muscles of respiratory tract, causes relaxation

sympathetic postganglionic axons to

viscera that have dual innervation: release norepinephrine (NE) onto effectors (adrenergic synapses)

viscera that receive only sympathetic input: release NE or ACh or NO onto effectors

sympathetic postganglionic cells of adrenal medulla

release epinephrine (E) and norepinephrine (NE) into the blood stream

neurotransmitters and sympathetic function

sympathetic postganglionic NE axons end in branching network with multiple varicosities filled with neurotransmitter

removal of NE after release is slower

• reuptake and reuse

  • breakdown by monoamine oxidase (MAO) and catechol-O-methytransferase (COMT) in surrounding tissue and in liver

adrenergic synapses post synaptic receptors

NE stimulates alpha receptors more than beta receptors

E stimulates both alpha and beta receptors

localized sympathetic activity from NE release at varicosities

• primarily affects alpha receptors near the active varicosities

generalized sympathetic activity and release of E by adrenal medulla

• affect alpha and beta receptors through out body

alpha 1

alpha adrenergic receptors

activated by both NE and E

excitatory

• found through out body

• examples of effects

  • constriction of peripheral BV

  • closure of sphincters along digestive tract

alpha 2

alpha adrenergic receptors

activated by both NE and E

inhibitory

• directly counteracts parasympathetic innervation of digestive viscera

• examples of effects: IPSP’s by causing a reduction in cAMP

  • reduces motility and secretions in GI tract

beta 1

beta adrenergic receptors

activated by E more than NE

excitatory

• heart, kidney, adipose tissue

• examples of effects

  • increase heart rate and force of contraction

beta 2

beta adrenergic receptors

activated by E more than NE

inhibitory

• bronchioles, BV of heart and skeletal muscle

• examples of effects

  • increased blood flow in heart and skeletal muscle

  • dilation of airways for increased respiration

pharmacology and the ANS

propranolol (beta 1 and beta 2 blocker)

metroprolol (beta 1 specific blocker)

albuterol (beta 2 specific agonist)

nicotine (nicotinic cholinergic agonist)

atropine (muscarinic cholinergic blocker)

eyes (iris muscle) dual innervations

receptor type and sympathetic effect - alpha 1; contracts radial muscle (widens)

receptor type and parasympathetic effect - M.C.; contracts sphincter muscle (small)

heart (SA node) dual innervations

receptor type and sympathetic effect - beta 1; increases heart rate

receptor type and parasympathetic effect - M.C.; decreases heart rate

bronchiole muscles dual innervation

receptor type and sympathetic effect - beta 2; relax (dilate)

receptor type and parasympathetic effect - M.C.; constricts (contract)

kidneys sympathetic only

receptor type and sympathetic effect - beta 1; increase renin secretion

skin (arrector pili muscles) sympathetic only

receptor type and sympathetic effect - alpha 1; contracts

liver sympathetic only

receptor type and sympathetic effect - alpha 1 and beta 1; glycogenesis and glucogenesis

skin (arterioles) sympathetic only

receptor type and sympathetic effect - alpha 1; constricts

integration and control of autonomic functions

operates without conscious control via reflex centers in autonomic ganglia, spinal cord, and brainstem

reflex centers are controlled by hypothalamus

regulated by higher brain centers that affect the hypothalamus

• limbic system, thalamus, cerebral cortex

autonomic tone

• background level of activity

• activation of sympathetic and/or parasympathetic input can increase or decrease activity

• examples

  • heart rate - dual innervation

  • blood vessel diameter - sympathetic innervation only

visceral reflexes

• afferent input from sensory receptor/neuron

• processing center with one or more interneurons

• efferent pathways to effectors

reflex processing centers

• short reflexes (occur in autonomic ganglia)

• long reflexes (occur in CNS)

simple reflexes in SC provide relatively rapid and stereotypic responses to stimuli

processing centers in medulla and pons provide more complex sympathetic and parasympathetic reflexes

• cardiovascular, salivation, swallowing, digestive secretions, peristalsis, urinary function

autonomic tone

integration and control of autonomic functions

background level of activity

activation of sympathetic and/or parasympathetic input can increase or decrease activity

examples

• heart rate - dual innervation

• blood vessel diameter - sympathetic innervation only

visceral reflexes

integration and control of autonomic functions

afferent input from sensory receptor/neuron

processing center with one or more interneurons

efferent pathway to effectors

reflex processing centers

integration and control of autonomic functions

short reflexes (occur in autonomic ganglia)

long reflexes (occur in CNS)

short reflexes

bypass the CNS entirely

involve sensory neurons and interneurons with cell bodies located in the autonomic ganglia, control ganglionic motor neurons

typically control very simple motor responses with localized effects whereas long reflexes coordinate activity of an entire organ

short reflexes (enteric nervous system)

extensive network of intramural ganglia and nerve networks in walls of digestive tract

influenced by sympathetic and parasympathetic input but many complex visceral reflexes are initiated and coordinated locally without instructions from CNS

long reflexes

autonomic equivalent of polysynaptic reflexes in somatic system

sensory input

• visceral sensory neurons such as chemoreceptors, baroreceptors, etc.

• general senses such as pain, touch, temperature, etc.

• special senses (smell, taste, vision, etc.)

processing steps involve interneurons with in CNS

autonomic reflexes - parasympathetic

typically affect individual organs/systems reflecting the relatively specific, restricted pattern of parasympathetic innervation

• defecation reflex

• urination reflex

• direct light and consensual light reflex

• swallowing reflex

• coughing reflex

• baroreceptor blood pressure reflex

• sexual arousal

autonomic reflexes - sympathetic

some affect individual organs

• cardioacceleratory reflex

• vasomotor reflex

• pupil dilation reflex

• ejaculation of semen

sympathetic division typically activated as a whole

• release of NE and E as hormones produces widespread long lasting peripheral effects

higher levels of autonomic control

reflex centers are subject to regulation by hypothalamus

hypothalamus interacts with all other portions of the brain

• activity in the limbic system, thalamus, cerebral cortex effect autonomic function

• biofeedback

hypothalamus

controls autonomic function

regulates body temperature

coordinates circadian cycles of activity

produces emotions and behavioral drives

coordination of voluntary, emotional, and autonomic functions

coordinates activities of the endocrine and nervous systems

secretes hormones