u3 ch14 study guide THE AUTONOMIC NERVOUS SYSTEM

SNS

somatic nervous system

ANS

autonomic nervous system

autonomic nervous system (ANS): overview

consists of motor neurons that innervate: smooth muscle, cardiac muscle and glands

general visceral motor system: responsible for regulating involuntary body activities like heart rate, digestion and breathing

SNS and ANS: similarities

both are composed of motor neurons

SNS and ANS: differences

effectors, efferent pathways and ganglia, neurotransmitters, response to the neurotransmitters

SNS effector

skeletal muscle (voluntary)

ANS effector

Cardiac muscle, smooth muscle, glands (involuntary)

efferent pathways: SNS

uses single neuron

extends from CNS to skeletal muscle

cell body → in the CNS

axon → heavily myelinated fiber (thick)

efferent pathways: ANS

uses two neuron chain

preganglionic neuron and postganglionic neuron

ANS efferent pathways two neuron chain: Preganglionic neurons

extends from CNS to the ganglion

cell body → in CNS

axon → lightly myelinated fiber (thin)

ANS efferent pathways two neuron chain: Postganglionic neuron

extends from ganglion to the effector organ

cell body → outside CNS

axon → nonmyelinated fibers (thinnest)

Neurotransmitters and effects: SNS

all somatic motor neurons release acetylcholine (ACh)

effects are always stimulatory

Neurotransmitters and effects: ANS

preganglionic fibers release ACh

postganglionic sympathetic fibers release norepinephrine

postganglionic parasympathetic fibers release ACh

effect is either stimulatory or inhibitory, depending on type of receptors

ANS preganglionic fibers release

ACh

Postganglionic sympathetic fibers release

norepinephrine

postganglionic parasympathetic fibers release

ACh

divisions of ANS: sympathetic division

‘fight or flight’ system

mobilizes the body during activity, promotes adjustments during exercise/threat

diverts blood from abdominal viscera and skin to skeletal and cardiac muscles and brain when necessary

originates in thoracolumbar region

divisions of ANS: parasympathetic division

‘rest and digest’ system

promotes maintenance activities, conserves body energy

promotes adjustments when a person is relaxing or reading after a meal

90% of all parasympathetic fibers are derived from → cranial nerve X (vagus)

originates in craniosacral region

ANS fibers/neurot: CHOLINEREGIC FIBERS

releases acetylcholine (Ach)

all preganglionic axons (sympathetic and parasympathetic)

all parasympathetic postganglionic axons

ANS fibers/neurot: ADRENERGIC FIBERS

releases norepinephrine (NE)

most sympathetic postganglionic axons (sweat glands exception)

how is action of neurotransmitter decided?

on the receptor it binds to

receptors of neurotransm: general

action of neurot depends on receptors

each neurotransm binds to 2(+) types of receptors

allows neurotransmitter to exert DIFFERENCE effects at different targets

receptors for neurotransmit: CHOLINERGIC RECEPTORS

binds to ACH

two types:

Nicotinic receptors

Muscarinic receptors

receptors for neurotransmit: ADRENERGIC RECEPTORS

binds to NE

two types:

alpha adrenergic

beta adrenergic

Cholinergic receptors: Nicotinic receptors

found on:

• cell bodies and dendrites of all postganglionic neurons of sympathetic and parasympathetic fibers

• sarcolemma of skeletal muscle cells at neuromuscular junction

effect on ACh on nicotinic receptors is always stimulatory

Cholinergic receptors: Muscarinic receptors

found on: effector cells stimulated by parasympathetic fibers

subclasses: M1, M2, M3, M4, M5

effect depends on subclass of receptors on target organ

• stimulatory (mostly)→ M1, M3, M5 (ex: smooth muscles and GI tract glands)

• inhibitory (some) → M4 (ex: cardiac)

Cholinergic receptors: muscarinic receptors STIMULATORY ONES

M1, M3, M5

cholinergic receptors: muscarinic receptors INHIBITORY

some

M4 (heart)

what is M4 for

cardiac

Adrenergic receptors: general

responds to NE or epinephrine

found on effector cell stimulated by sympathetic fibers

effects depend on subclass of receptor predominating the target one

2 classes: alpha (a1, a2) and beta (B1, B2, B3)

Adrenergic receptors: Stimulatory

a1, B1, B3

Adrenergic receptors: Inhibitory

a2, B2

what does NE binding to cardiac muscle B1 receptors cause

increase in heart rates

epinephrine binding to B2 receptors cause…

bronchial relaxation

interactions of autonomic divisions: DUAL INNERVATION

most visceral organs have both SYMPATHETIC and PARASYMPATHETIC innervation

interactions of autonomic divisions: ANTAGONISTIC INTERACTIONS

works in opposite to each other, allows for precise control of vsiceral activity

Antagonistic interaction example: Sympathetic division

increases heart and respiratory rates

inhibits digestion and elimination

dilation of pupils for far vision

Antagonistic interaction example: Parasympathetic division

decrease heart and respiratory rates

allows for digestion and discarding of waste

constriction of pupils

important

SNS vs ANS

What division of the ANS uses NE as the neurotransmitter?

sympathetic division

ANS Sympathetic

two neuron chain preganglionic neuron and postganglionic

effectors: cardiac muscle, smooth muscle, glands

postganglionic fibers release norepinephrine NE

adrenergic fibers

ANS Parasympathetic

two neuron chain preganglionic neuron and postganglionic

effectors: cardiac muscle, smooth muscle, glands

postganglionic fibers release ACh

cholinergic fibers

The ACh effect on what receptors is always stimulatory?

cholinergic: NICTOTINIC receptors

What ACh receptor is always stimulatory EXCEPT for the cardiac muscle?

cholinergic: MUSCARINIC receptors

inhibitory for → M4 (cardiac muscle)

what receptor responds to NE or epinephrine and what division does it belong to?

ADRENERGIC receptors and sympathetic division

drug table

note: asthma, hypertension, myasthenia gravis

What drug class and process dilates the bronchioles by binding to B2 receptors for asthma?

drug class: sympathetic activators

receptor bound: adrenergic receptors

effects: enhance sympathetic activity by binding to adrenergic receptors or increasing NE release

ex: albuterol

what drug class and process use beta-blockers and decrease the blood pressure during hypertension?

drug class: sympathetic inhibitors

receptor bound: adrenergic receptors

effects: decrease sympathetic activity by blocking adrenergic receptors

ex: propranolol

what drug class and receptor bound increases availability of ACh for myasthenia gravis?

drug class: acetylcholinesterase inhibitors

receptor bound: NONE, binds to enzyme (ACh R) that degrades ACh

effects: indirect effect at all ACh receptors; prolong effects of ACh

ex neostigmine

effects of ans (local vs diffused): PARASYMPATHETIC division

short lived, highly localized control over effectors because 

• ACh is quickly destroyed by acetylcholinesterase

effects of ans (local vs diffused): SYMPATHETIC division

long lasting, body-wide effects because:

• NE and epinephrine are secreted into the blood as part of sympathetic response

control of ANS functioning: CNS , hypothalamus

main integrative center of ANS activity

cerebral input → may modify ANS but foes so subconsciously

other controls → brain stem, spinal cord, cerebral cortex

how does the brain stem influence ANS activity?

regulates pupil size, heart, blood pressure, airflow, salivation

how does the spinal cord influence ANS activity?

reflexes for urination, defecation, erection and ejaculation

Series of events in sympathetic pathway

thoracolumbar origin, short preganglionic fiber, ACh release at ganglion, long postganglionic fiber, NE release at effector

What is an effect of norepinephrine binding to beta 2 adrenergic receptors?

vasodilation

does the somatic or autonomic NS have ganglia in motor pathways?

autonomic only

what receptor would you target to get an inhibitory effect on the heart (reduce heart rate)

muscarinic receptors

Sympathetic responses generally are widespread because

NE and epinephrine are secreted into the blood as part of the sympathetic response

Drugs called beta-blockers

decrease heart rate and blood pressure

Sympathetic division excitation causes

increased blood glucose, decreased GI peristalsis, and increased heart rate and blood pressure

Which of the following drug classes would be useful for smoking cessation

products?

nicotinic agents