Download autonomic nervous system

Biology 141
The Autonomic Nervous System
Chapter 15
Overview


The CNS


spinal cord
brain
The peripheral nervous
system

sensory-somatic nervous
system

Responds to the external
environment



12 pairs of cranial nerves
and
31 pairs of spinal nerves.
autonomic nervous system

Responds to the internal
environment


Parasympathetic nervous
system
Sympathetic nervous system
Divisions of the Nervous System
ANS

Function:


operates without conscious control.
Regulation:

Control:
hypothalamus and brain stem.
 receives input from limbic system and other
regions of the cerebrum


Regulate activity of

smooth muscle, cardiac muscle & certain glands
ANS

Sensory receptors associated with
interoceptors (receptors that monitor
internal environments)
Located in blood vessels, viscera, smooth muscle
 Chemoreceptors


Baroreceptors monitor BP
Internal pain - angina
 Mechanoreceptors


Monitor vessel stretch
Comparison
SOMATIC vs. ANS

Somatic



contains both sensory
and motor neurons.
input from the special
and somatic senses.
sensations are
consciously perceived.


innervate skeletal
muscle to produce
conscious, voluntary
movements.
effect of a motor
neuron is always
excitation.
Comparison
SOMATIC vs. ANS

ANS




contains both sensory
and motor neurons.
Input from
interoceptors.
input not consciously
perceived.
may receive input
from somatic senses
and special sensory
neurons.


regulate visceral
activities
Effect: exciting or
inhibiting activities of
cardiac muscle,
smooth muscle, and
glands.
Comparison
SOMATIC vs. ANS

Somatic motor
pathways
consist of a
single motor
neuron

Autonomic motor
pathways consists
of two motor
neurons in series
Motor Neurons in Series

first autonomic
cell body in the CNS
 myelinated axon extends to an autonomic ganglion
or adrenal medullae


second autonomic
cell body in an autonomic ganglion
 nonmyelinated axon extends to an effector.

Somatic has 1 motor neuron
ANS has 2 motor neurons in series
First motor neuron: preganglionic

Preganglionic neuron



cell body in brain or spinal cord
axon is myelinated
extends to autonomic ganglion
Second motor neuron: postganglionic

Postganglionic neuron


cell body lies outside the CNS in an autonomic
ganglion
axon is unmyelinated fiber that terminates in a
visceral effector
First Neuron terminates in a ganglion or
adrenal medulla

Can use either NE or ACh as the neurotransmitter
ANS Efferent Branches

The output (efferent) part of the ANS is
divided into two principal parts:



the sympathetic division
the parasympathetic division
Organs that receive impulses from both
sympathetic and parasympathetic fibers are
said to have dual innervation.
Parasympathetic and Sympathetic

Parasympathetic

Sympathetic
Dual innervation

Dual innervation




one speeds up
organ
one slows down
organ
Sympathetic NS
increases heart
rate
Parasympathetic
NS decreases
heart rate
Anatomy of Autonomic Motor
Pathways

Components

Preganglionic neuron





Sympathetic
Parasympathetic
Autonomic ganglia
Postganglionic neuron
Autonomic Plexus
Preganglionic Neurons
Sympathetic
 Also called thoracolumbar
division


Cell bodies in the lateral
horns of the gray matter in
segments T1-T12 and L1L2
Axons are called the
thoracolumbar outflow
Parasympathetic
 Also called craniosacral
division

Cell bodies in the brain
stem



cranial nerve nuclei III,
VII, IX, and X
Cell bodies in the lateral
gray horns of segments S2S4
Axons are called
craniosacral outflow
Autonomic Ganglia
Sympathetic
 2 groups

Sympathetic trunk ganglia
(Vertebral chain ganglia)



lie in a vertical row on either
side of the vertebral column
Innervate above the diaphragm
Prevertebral ganglia (collateral)


Anterior to vertebral column
close to large arteries
Innervate below the diaphragm
Autonomic Ganglia
Parasympathetic
 1 group: terminal ganglia

Located near or in viscera
Postganglionic Neurons

postganglionic
neuron can be
branched to receive
signals from
multiple ganglionic
locations.
Autonomic Plexuses:
Tangled neural networks that lie along major arteries.

Major autonomic
plexuses



Cardiac: supplies the
heart,
Pulmonary: supplies the
lung,
Celiac (solar): liver,
gallbladder, stomach,
pancreas, spleen, kidney,
reproductive organs

Major autonomic
plexuses




superior mesenteric: small
and large intestines
inferior mesenteric: large
intestines
Renal: kidneys and ureters
Hypogastric: pelvic viscera
Structure of the Sympathetic
Division





Preganglionic – leave
spinal cord through
ventral root
Enter the ganglion via
the white ramus
Synapse with
postganglionic
Leave via gray ramus
Terminates on visceral
effectors
3 Pathways of Sympathetic Fibers

Spinal nerve route


Sympathetic chain
route


out same level
up chain & out spinal
nerve
Collateral ganglion
route

out splanchnic nerve
to collateral ganglion
Divergence of Sympathetic Neurons

Divergence:


Mass activation due to
divergence



1 preganglionic cell synapses on many
postganglionic cells
multiple target organs
fight or flight response explained
Adrenal gland

modified cluster of postganglionic cell
bodies that release epinephrine &
norepinephrine into blood
Horner’s Syndrome

Sympathetic innervation to one side of the
face is lost (mutation, injury, or disease).

Affects outflow
Drooping of eyelid
 Constricted pupil
 Lack of sweating

Structure of the parasympathetic
division

Preganglionic

Cranial


Sacral


From ventral root of spinal
nerve
Terminal ganglia


As part of a cranial nerve
In the walls of viscera
Postganglionic

Innervate smooth
muscle and glands of the
visceral walls
Parasympathetic Cranial Nerves

Oculomotor nerve



Facial nerve



pterygopalatine and submandibular ganglions
supply tears, salivary & nasal secretions
Glossopharyngeal


ciliary ganglion in orbit
iris
otic ganglion supplies parotid salivary gland
Vagus nerve

supply heart, pulmonary and GI tract as far as
the midpoint of the colon
Parasympathetic Sacral Nerve

Form pelvic
splanchnic
nerves
ANS Neurotransmitters

Classified as either cholinergic or adrenergic
neurons based upon the neurotransmitter
released

Adrenergic

Cholinergic
ANS NEUROTRANSMITTERS

Cholinergic

Produce and release acetylcholine (ACh)
All sympathetic and parasympathetic preganglionic
 All parasympathetic postganglionic
 Only sweat gland sympathetic postganglionic


Adrenergic

Produce and release norepinephrin (NE)

Most sympathetic postganglionic
neurons(noradrenalin)
Cholinergic Neurons

Excitation or inhibition depending upon
receptor subtype and organ involved.
Cholinergic Receptors

Cholinergic receptors


integral membrane proteins in the postsynaptic plasma
membrane. 2 types: Nicotinic and muscarinic
Activation of nicotinic
receptors


excitation
Nicotinic receptors are
found on postsynaptic
cells of ANS cells and at
NMJ

Activation of muscarinic
receptors



excitation or inhibition
Muscarinic receptors are
found on plasma
membranes of all
parasympathetic effectors
(viscera, smooth muscle)
Adrenergic Neurons

Adrenergic neurons release norepinephrine (NE) )




from postganglionic
sympathetic neurons only
Excites or inhibits organs
NE lingers at the synapse until enzymatically inactivated
Effects triggered by adrenergic neurons typically are longer lasting
than those triggered by cholinergic neurons.
Physiological Effects of the ANS

Autonomic Tone



Sympathetic Response



balance between sympathetic and parasympathetic
activity
regulated by the hypothalamus
Supports rigorous functions and rapid ATP production
Fight or flight response
Parasympathetic Response

Enhances rest and digestive functions, storage of ATP
Fight or Flight

Alarm reaction


dilation of pupils
Increase
heart rate
 respirations
 BP
 Blood flow to skeletal muscles
 Blood sugar



decrease in blood flow to nonessential organs
Long lasting

lingering NE in synaptic gap
Pathway

Autonomic Reflexes

Receptor



Sensory neuron


Responds to stimuli
Transduce stimuli to action potential
Action potential travels to CNS
Integrating center (CNS)

Interneurons relay sensory info to motor neurons




2 Motor neurons (pre and post ganglionic)


Hypothalamus
Brain stem
Spinal cord
Carries action potential from the CNS to an effector
Effector

Smooth or cardiac muscle, glands
Autonomic Control by Higher Centers


Major control and integration center: hypothalamus
Receives input from







Viscera
Olfaction
Gustation
Changes in temp
Osmolarity
Blood chemistry levels
Limbic system

Output to

Brain stem





Heart
Blood vessels
Salivary glands
swallowing
Spinal cord


Intestines
bladder
DISORDERS

Raynaud’s phenomenon




excessive sympathetic stimulation of smooth
muscle in the arterioles of the digits
Result - vasoconstriction
the digits (fingers and toes) become ischemic
(lack blood) after exposure to cold or with
emotional stress.
Digits may become necrotic
Autonomic Dysreflexia

Exaggerated response of sympathetic NS in
cases of spinal cord injury above T6



Sensory impulses from below the injury are unable to
ascend to the brain
Causes mass stimulation of sympathetic nerves below the
injury
Result

vasoconstriction which elevates blood pressure

parasympathetic NS tries to compensate



slows heart rate, dilates blood vessels above the injury
Produces a pounding headache, hypertension, flushed skin,
profuse sweating above the injury and cool dry skin below
can lead to seizure, stroke or heart attack