autonomic nervous system

what is the nervous system

one of the major control systems in the body

how is the nervous system divided

central and peripheral

what makes up the central nervous system (CNS)

brain and spinal cord

what is the function of the CNS

integrative and control center

what are the components of the peripheral nervous system (PNS)

sensory (afferent) neurons and somatic (motor) neurons

what type of neurons are part of the sensory system

sensory (afferent) neurons

what type of neurons are part of the motor system

somatic (motor) neurons

what is a neuron

a nerve cell; the structural unit of the nervous system

what is the neuron cell body

the major biosynthetic centre of the neuron

what is an axon

the conducting component of the neuron; each neuron has one axon

what are autonomic ganglia

structures that contain the cell bodies of motor neurons

what occurs at autonomic ganglia

preganglionic neurons synapse with ganglionic neurons

what response is associated with the sympathetic nervous system

fight or flight response

does the sympathetic nervous system tend to be excitatory or inhibitory

excitatory

where do sympathetic preganglionic neurons originate

spinal column between T1 ad L2 (thoracolumbar)

what is the legnth and path of sympathetic preganglionic axons

short; pass through spinal nerves to the autonomic ganglia

what is the length of the sympathetic postganglionic axon

very long; extends to the effector organ

how many ganglionic neurons are associated with one presynaptic neuron in the sympathetic nervous system

17 ganglionic nerons, resulting in divergence

what type of system is the parasympathetic nervous system

resting and digesting system

what is the main energy function of the parasympathetic nervous system

keeps energy use as low as possible

where do parasympathetic preganglioninc neurons originate

brain stem and sacral region of the spinal cord (cranio sacral outflow)

where are parasympathetic ganglia located

in the effector organ

what is the relative length of parasympathetic preganglionic neurons

very long

what is the relative length of parasympathetic postganglionic neurons

short and very specific

how do the SNS and PNS affect organs

they innervate the same organs but have opposite effects

what is the purpose of dual innervation by SNS and PNS

to create balance in organs and keep body systems running smoothly

what effect does the SNS have on heart rate

increased rate

what effect does the SNS have on force of heart contraction

increased force of contraction

what effect does the SNS have on cardiac automaticity

increased automaticity

what effect does the PNS have on heart rate

decreased rate

what effect does the PNS have on force of heart contraction

decreased force of contraction

what effect does the PNS have on cardiac conduction velocity

decreased conduction velocity

what effect does the SNS have on blood vessels

constricts most vessels and increases blood pressure

how does the SNS affect vessels of the abdominal viscera and skin

constricts them to divert blood to muscles, brain, and heart

how does the SNS affect skeletal muscle vessels during exercise

dilates them

what effect does the PNS have on blood vessels

little or no effect

what effect does the SNS have on the lungs

bronchial smooth muscle dilation

what effect does the PNS have on the lungs

bronchial smooth muscle contraction

what effect does the SNS have on the adrenal medulla

stimulates secretion of epinephrine and norepinephrine

what effect does the PNS have on the adrenal medulla

no effect

what neurotransmitters are used in the autonomic nervous system

acetylcholine (ACh), norepinephrine (NE), and epinephrine (EPI)

what role does acetylcholine (ACh) play in the SNS and PNS

it is the preganglionic neurotransmitter in both

what is acetylcholine’s role in the PNS postganglionic neuron

it is always the postganglionic neurotransmitter

is acetylcholine ever a postganglionic neurotransmitter in the SNS

sometimes

how is acetylcholine destroyed

by the enzyme cholinesterase

how is acetylcholine destroyed in the bloodstream

by pseudocholinesterase

what is the role of norepinephrine (NE) in the SNS

it is the postganglionic neurotransmitter in most of the SNS

what happens to most norepinephrine after release

it is subject to reuptake by presynaptic fibers

how is some norepinephrine destroyed

by monoamine oxidase (MAO) and catechol-o-methyl transferase (COMT)

what is epinephrine’s role in the SNS

it is another neurotransmitter of the SNS

where does the SNS preganglionic nerve fiber terminate for epinephrine release

in the adrenal gland

what does the adrenal gland do with epinephrine

releases it into circulation

where are ANS receptors found

on the cell membranes of ganglionic neurons and effector organs

what binds to ANS receptors

neurotransmitters

how does a neurotransmitter bind to a receptor

in a specific “lock and key” fashion based on shape

what are cholinergic receptors activated by

acetylcholine

how are cholinergic receptors divided

nicotinic receptors and muscarinic receptors

where are nicotinic receptors found

in the ANS (parasympathetic and sympathetic) and the skeletal muscle system

where are nicotinic receptors located within the ANS

on the postganglionic membrane

what binds to nicotinic receptors in the ANS

acetylcholine released from preganglionic cholinergic fibers

does ACh binding to nicotinic receptors directly affect the target organ

no, it generates another impulse sent to the target organ

where are muscarinic receptors found

at the parasympathetic end site on the target organ

which branch of the ANS uses muscarinic receptors

parasympathetic only

how many muscarinic receptor subtypes have been identified

five

what is another name for a muscarinic effect

parasympathetic effect or parasympathomimetic

what activates adrenergic receptors

norepinephrine and epinephrine

how are adrenergic receptors divided

alpha (1 and 2) and beta (1 and 2)

where are alpha adrenergic receptors generally found

in the walls of blood vessels, arteries, veins and skin

what effect does activation of alpha receptors have

vasoconstriction

where are beta-1 receptors found and what is their effect

in the heart; activation leads to cardiac stimulation

where are beta-2 receptors found and what is their effect

in bronchial smooth muscle; activation causes bronchodilation

which neurotransmitter do adrenergic receptors bind

norepinephrine

where are adrenergic receptors located

on cell membranes of target organs

what happens when norepinephrine (NE) binds to alpha-1 receptors

constriction of systemic blood vessels and dilation of pupils

what is the effect of NE binding to alpha-2 receptors

constriction of cardiac blood vessels

what is the effect of NE binding to beta-1 receptors

increased heart rate and increased force of contraction

what is the effect of NE binding to beta-2 receptors

bronchodilation

how is acetylcholine terminated in the synapse

it is quickly degraded by acetylcholinesterase, so its effects are short-lived

how is norepinephrine terminated

it is reabsorbed by postganglionic fibers (reuptake), prolonging its effects

what happens to norepinephrine after reuptake

it is either recycled and reused or degraded by MAO and COMT

what causes smooth muscle contraction

increased activity of myosin ATPase, which drives actin-myosin filament sliding

what is required to activate myosin ATPase in smooth muscle cells

significant increases in intracellular Ca²⁺ levels

why does Ca²⁺ influx into smooth muscle cells facilitate contraction

because extracellular Ca²⁺ concentration is normally higher, so influx raises intracellular levels needed for contraction

what happens when muscarinic receptors in bronchial smooth muscle are activated

the G protein changes configuration, which increases guanyl cyclase activity, leading to CTP converting to c’GMP, increasing cytoplasmic Ca²⁺ and causing bronchoconstriction

what happens when B2 adrenergic receptors in bronchial smooth muscle are stimulated

the G protein changes configuration, which increases adenyl cyclase activity, leading to ATP converting to c’AMP, decreasing cytoplasmic Ca²⁺ and causing bronchodilation

how much sympathetic innervation do post-synaptic fibers have in bronchial smooth muscle

there are very few post-synaptic sympathetic nerve fibers

what stimulates beta 2 receptors if sympathetic fibers are few

circulating norepinephrine and epinephrine from the adrenal gland

describe the SNS pathway to bronchial smooth muscle

sympathetic activation triggers the adrenal glands to release epinephrine and norepinephrine, which travel through the circulation to the bronchial smooth muscle and cause bronchodilation