Download The autonomic nervous system

Comparison Of Autonomic
& Somatic Nervous Systems
2 Neuron Chain
Preganglionic Neurons

1st neuron in spinal
cord: thoracic and
lumbar spinal nerves
Sympathetic

1st neuron in 4
cranial nerves in the
brain stem (III, VII,
IX, X) or in S2 –S4 of
spinal cord
Parasympatheitc
Postganglionic Neurons

2nd neuron in
sympathetic trunk
ganglion, a chain of
ganglion that is found
on either side lateral
to spine
Sympathetic

2nd neuron in
individual ganglion
closer to organ it
serves

both sympathetic &
parasympathetic
neurons lie outside CNS
Parasympathetic
Axons of Autonomic
Nerves

Preganglionic:
 in cranial or spinal n. (from CNS 
ganglion)
 myelinated

Postganglionic:
 from ganglion  visceral effector
 unmyelinated
ANS Neurotransmitters
based on the neurotransmitter
they produce & release autonomic
neurons are classified as either:
1. Cholinergic
 release acetylcholine (ACh)
1. Adrenergic
 release norepinephrine (NE) aka
noradrenalin

Cholinergic Neurons &
Receptors
Cholinergic neurons include:
1. all Sympathetic & Parasympathetic
preganglionic neurons
2. Sympathetic postganglionic neurons
that innervate most sweat glands
3. all Parasympathetic postganglionic
neurons

Receptors
that bind ACh called cholinergic
receptors
 2 types:
1. Nicotinic receptors


in plasma membranes & dendrites of
symp. & parasymp postganglionic neurons
& in NMJ
1.
Muscarinic receptors

in plasma membrane of all effectors
(smooth muscle, cardiac muscle, glands)
Muscarine: mushroom poisonmimics
actions of ACh

ACh
when activates nicotinic receptors
 depolarization (excitation)
 when activates muscarinic
receptors  sometimes
depolarization, sometimes
hyperpolarization (inhibition)
depending on the cell

NE
most sympathetic postganglionic
neurons are adrenergic
 Adrenergic receptors bind both NE
& Epinephrine (Epi)
 2 types receptors:
1. Alpha receptors (α)


subtypes: α1, α2
Beta receptors (β)
2.

subtypes: β1, β2, β3
αlpha & βeta Receptors
α1 & β1 produce excitation when
activated
 α2 & β2 receptors cause inhibition
of effector tissues
 β3 found only on cells of brown
adipose where activation causes
thermogenesis (heat production)

αlpha & βeta Receptors
cells of most effectors have either
α or β receptors
 some visceral effectors contain
both
 NE stimulates α more strongly
than β
 Epi is potent stimulator of both

MAO
MonoAmine Oxidase: inactivates
NE in synaptic cleft
 group of pharmaceuticals that are
MAO inhibitors so prolong effect
of NE

Agonists
substance that binds to & activates a
receptor
 in the process mimicking the effect of
a natural neurotransmitter or
hormone
 example: phenylephrine is an
adrenergic agonist @ α1 receptors;
used in cold remedies

 constricts blood vessels in nasal mucosa
 reduces production of mucus
Antagonists
substance that blocks receptors so
prevents the natural neurotransmitter
or hormone from exerting its effect
 example: propanolol a β1 blocker,
used to treat HTN  decreases heart
rate & force of contraction  lowers
BP

 side effects: hypoglycemia, mild
bronchoconstriction, decreases frequency
& severity of migraines
Autonomic Tone
balance between sympathetic &
parasympathetic activity
 regulated by hypothalamus

 if turns up sympathetic tone, turns
down parasympathetic tone @ same
time
Sympathetic Responses
dominate during physical or
emotional stress
 occur during “E situations”

 Exercise
 Emotions
 Emergency
 Excitement
Sympathetic Responses

Fight or Flight Response
 pupils dilate
 HR, force of contraction, & BP increase
 airways dilate
 vessels to kidneys & GI tract constrict
slowing down digestion & urine production
 vessels  muscles (skeletal & cardiac),
liver, & adipose tissue  dilate
 hepatocytes increase glycogenolysis &
adipose increase lipolysis  blood glucose
increases
 anything nonessential slowed down
Sympathetic Stimulation
effects longer lasting than
parasympathetic responses (NE
lasts longer in synaptic cleft than
ACh)
 effects more widespread (more
tissues activated)

Parasympathetic Responses
enhance “rest & digest” activities
 remeber SLUDD:

 Salivation
 Lacrimation
 Urination
 Digestion
 Defecation