Subdivisions of Nervous System
Autonomic Nervous System
(Chapter 9)
Central nervous system
• Autonomic Nervous System (ANS)
– general properties
– anatomy
• Autonomic Effects on Target Organs
Brain
Spinal
cord
Visceral
sensory
division
• Who Controls Autonomic Function
• Somatic Nervous System
Peripheral nervous system
Sensory
division
Somatic
sensory
division
Motor
division
Visceral
motor
division
Somatic
motor
division
Skin, bones,
Muscles, Joints,
Senses
Sympathetic
division
15-1
12-2
Parasympathetic
division
Role of the Autonomic Division in
General Properties of ANS
Homeostasis
• autonomic nervous system (ANS) – a motor nervous
system that controls glands, cardiac muscle, and
smooth muscle
• Maintains homeostasis
•
Primary effectors of the ANS
• viscera of thoracic and abdominal cavities
– cutaneous blood vessels
– some exocrine glands
– piloerector muscles
– eyes
– some endocrine glands
• carries out actions involuntarily – no intent/awareness
• visceral effectors do not depend on the ANS to function
15-3
Figure 11-1
Divisions of ANS
•
Divisions of ANS
•
2 Divisions dualing innervate most organs
–
–
sympathetic division (Fight or Flight)
prepares body for physical activity: exercise, trauma, arousal,
competition, anger, or fear
• increases heart rate, BP, airflow
• reduces blood flow to skin and digestive tract
• increases blood to skeletal muscle
• Glycogen to glucose (blood glucose)
• Fat breakdown
• Pupil dilation
• Salivation increased
2 Divisions dualing innervate most organs
–
parasympathetic division (Rest and digest)
calms many body functions reducing energy expenditure and
assists in bodily maintenance
– Constricts pupils and bronchioles
– Slows heart
– Stimulates
• Digestion
• Insulin release
• Urination
parasympathetic division (Rest and digest)
calms many body functions reducing energy expenditure and
assists in bodily maintenance
• digestion and waste elimination
15-5
15-6
1
Autonomic tone
•
Neural Pathways
autonomic tone - represents the balance of the two
systems according to the body’s changing needs
•
–
parasympathetic tone
• maintains smooth muscle tone in intestines
• holds resting heart rate down to about 70 – 80 beats
per minute
–
sympathetic tone
• keeps most blood vessels partially constricted and
maintains blood pressure
ANS has components in
both the central and
peripheral nervous systems
– nuclei in the
hypothalamus and
other brainstem regions
– motor neurons in the
spinal cord and
peripheral ganglia
– nerve fibers that travel
through the cranial and
spinal nerves
15-7
15-8
Somatic versus Autonomic Pathways
Autonomic Control Centers in the Brain
(the 2 major pathways of motor neurons)
• Hypothalamus
– Water balance,
temperature, and
hunger
Temperature control
Water balance
• Medulla oblongata
–
–
–
–
Respiration
Cardiac
Vomiting
Swallowing
ACh
Hypothalamus
Eating
behavior
• Pons
– Respiration
Somatic efferent innervation
Pons
Urinary bladder
control
Secondary
respiratory center
Blood pressure
control
Respiratory center
Myelinated
fiber
Somatic effectors
(skeletal muscles)
Autonomic efferent innervation
Medulla
ACh
Myelinated
preganglionic fiber
ACh or NE
Unmyelinated
postganglionic fiber
Visceral effectors
(cardiac muscle,
smooth muscle,
glands)
Autonomic
ganglion
Preganglionic cell bodies in grey matter
15-10
Figure 11-3
Sympathetic Nervous System
•
Aka thoracolumbar division (T1 – L2)
•
relatively short preganglionic and long postganglionic
fibers
•
Sympathetic Nervous System
–
each paravertebral ganglion is connected to a spinal nerve by
two branches – communicating rami (rami communicants)
–
preganglionic fibers are small myelinated fibers that travel
from spinal nerve to the ganglion via white communicating
ramus (myelinated)
–
postganglionic fibers leave the ganglion via gray
communicating ramus (unmyelinated)
• forms a bridge back to the spinal nerve
–
postganglionic fibers extend to the target organ
preganglionic cell bodies in lateral horns & gray matter of
spinal cord
– lead to
1.
2.
sympathetic chain of ganglia (paravertebral ganglia)
collateral (prevertebral) ganglia
15-11
15-12
2
Other ganglia of Sympathetic Nervous System
Sympathetic Chain Ganglia
•
•
collateral ganglia (prevertebral ganglia)
Some preganglionic fibers pass thru sympathetic chain
- splancic nerves
- synapse in collateral (prevertebral ganglia)
contribute to network called the abdominal aortic plexus
–
3 major collateral ganglia in this plexus
•
•
–
celiac, superior mesenteric, and inferior mesenteric
postganglionic fibers accompany these arteries and their branches to
their target organs
solar plexus – collective name for the celiac and superior
mesenteric ganglia
•
nerves radiate from ganglia like rays of the sun
15-14
Preganglionic Pathways
Efferent Pathways of
sympathetic division
3 pathways of preganglionic neurons
entering sympathetic chain
Soma of
preganglionic
neuron
Salivary glands
To iris, salivary glands,
lungs, heart, thoracic
blood vessels, esophagus
Preganglionic neurons
Postganglionic neurons
Cervical
Spinal nerve
Somatic
motor fiber
Thoracic
Preganglionic
sympathetic fiber
Lumbar
Sacral
Postganglionic
sympathetic fiber
To somatic effector
(skeletal muscle)
1
White ramus
Gray ramus
Preganglionic neuron
3 pathways of leaving
sympathetic chain
Liver and
gallbladder
Stomach
Superior
mesenteric
ganglion
Spleen
Pancreas
3
Splanchnic nerve
Somatic neuron
Lung
Celiac
ganglion
To sweat glands,
piloerector muscles,
and blood vessels
of skin and
skeletal muscles
Soma of
somatic motor
neuron
Heart
Cardiac and
pulmonary plexuses
Regions of spinal cord
Sympathetic nerve
2
Postganglionic neuron
Eye
Pons
Communicating
rami
Collateral ganglion
Soma of
postganglionic
neuron
Postganglionic
sympathetic fibers
Sympathetic
trunk
Postganglionic fibers to
skin, blood vessels,
adipose tissue
Inferior
mesenteric
ganglion
Small intestine
Large intestine
Rectum
Sympathetic chain
ganglia
Adrenal medulla
Kidney
To liver, spleen, adrenal glands,
stomach, intestines, kidneys,
urinary bladder, reproductive organs
Sympathetic
ganglion
2
15-15
Ovary
Penis
Scrotum
Uterus
Bladder
Adrenal Glands
Summary of Sympathetic Innervation
• essentially a sympathetic ganglion
secretes catecholamines:
- 85% epinephrine (adrenaline)
- 15% norepinephrine (noradrenaline)
• effectors in body wall are innervated by sympathetic
fibers in spinal nerves
• effectors in head and thoracic cavity are innervated by
fibers in sympathetic nerves
• sympathoadrenal system is adrenal medulla and
sympathetic nervous system
• effectors in abdominal cavity are innervated by
sympathetic fibers in splanchnic nerves
15-17
15-18
3
The Adrenal Medulla
Parasympathetic Division
Adrenal cortex:
endocrine gland
(steroid hormones)
• parasympathetic division (aka craniosacral division)
Adrenal medulla:
modified sympathetic
ganglion.
• origin preganglionic neurons
– midbrain, pons, and medulla (III, VII, IX, X)
– sacral spinal cord segments S2-S4
Adrenal gland
Kidney
(b)
(a)
ACh
Preganglionic
sympathetic
neuron
Chromaffin
Cell: modified
postganglionic
sympathetic
neuron.
(c)
Adrenal medulla
• terminal ganglia in or near target organs
– long preganglionic, short postganglionic fibers
Blood vessel
Epinephrine is a
neurohormone that
enters the blood.
To target
tissues
15-20
Parasympathetic Sacral Nerves
Parasympathetic Cranial Nerves
•
Facial n.
(CN VII)
Postganglionic neurons
Ciliary ganglion
Submandibular
ganglion
Submandibular
salivary gland
Thoracic
Lumbar
Sacral
Facial nerve (VII)
– tear, nasal and salivary glands
•
Heart
Pulmonary
plexus
Esophageal
plexus
Liver and
gallbladder
Spleen
Pancreas
Pelvic
splanchnic
nerves
Kidney and
ureter
Transverse
colon
Descending
colon
Inferior
hypogastric
plexus
Small intestine
Rectum
Pelvic
nerves
Penis
Uterus
•
Postganglionic neurons
Ciliary ganglion
Lacrimal gland
Eye
Submandibular
ganglion
Submandibular
salivary gland
Otic ganglion
Parotid
salivary gland
Glossopharyngeal n.
(CN IX)
form pelvic splanchnic
nerves that lead to the
inferior hypogastric
plexus
Vagus n.
(CN X)
Heart
Cardiac plexus
Regions of
spinal cord
Cervical
Pulmonary
plexus
Esophageal
plexus
Lung
Thoracic
•
Stomach
Abdominal
aortic
plexus
Ovary
•
Glossopharyngeal nerve (IX)
– parotid salivary gland
Lung
Celiac
ganglion
Facial n.
(CN VII)
Arise from levels S2 to S4 of
the spinal cord
Parotid
salivary gland
Glossopharynge
al n.
(CN IX)
Cardiac plexus
Regions of
spinal cord
Cervical
•
Lacrimal gland
Eye
Otic ganglion
Vagus n.
(CN X)
Oculomotor n.
(CN III)
Preganglionic neurons
Pterygopalatine
ganglion
Oculomotor n.
(CN III)
Preganglionic neurons
Pterygopalatine
ganglion
Oculomotor nerve (III)
– pupil constriction/lens focus
Vagus nerve (X)
– viscera as far as proximal half of
colon
– cardiac, pulmonary, and
esophageal plexus
– 75% of all Parasympathetic fibers
most form pelvic nerves to
their terminal ganglion on
the target organs
Lumbar
Sacral
Celiac
ganglion
Stomach
Liver and
gallbladder
Abdominal
aortic
plexus
Spleen
Pancreas
– distal half of colon, rectum,
urinary bladder, and
reproductive organs
Kidney and
ureter
Transverse
colon
Descending
colon
Small intestine
Rectum
Pelvic
nerves
Bladder
Scrotum
Penis
Ovary
15-21
Uterus
Neurotransmitters and Receptors
Enteric Nervous System
• What determines if an autonomic neuron is excitatory or
inhibitory
• enteric nervous system – nervous system in wall of
digestive tract
– does not arise from the brainstem or spinal cord
– innervates smooth muscle and glands
• Effects determined by
1. type of neurotransmitter released
2. type of receptors found on target cells
• semiautonomous
• 2 things to remember:
• has its own reflex arcs
– sympathetic (NE) and parasympathetic fibers (Ach) secrete different
neurotransmitters
• regulates motility of esophagus, stomach, and
intestines and secretion of digestive enzymes and acid
• normal digestive function also requires regulation by
sympathetic and parasympathetic systems
Bladder
Scrotum
– target cells respond to the same neurotransmitter differently
depending upon the type of receptor they have for it
15-23
• all autonomic fibers secrete either Ach or NE
• there are 2 classes of receptors for each of these neurotransmitters
15-24
4
ANS Neurotransmitters
Neurotransmitters and Receptors
• Both Symp and
Parasymp
preganglionics release
ACh
• Parasymp
postganglionics also
release ACh
– Called cholinergic
synapses
• Most Sympathetic
postganglionics release
Norepinephrine
– Called adrenergic
synapses
– A small number
release ACh
(a) Parasympathetic fiber
Nicotinic
receptor
ACh
Target
cell
ACh
Preganglionic
neuron
Postganglionic
neuron
Muscarinic
receptor
(b) Sympathetic adrenergic fiber
Nicotinic
receptor
ACh
Target
cell
Preganglionic
neuron
Postganglionic
neuron
NE
MOST
Adrenergic receptor
(c) Sympathetic cholinergic fiber
Nicotinic
receptor
ACh
Target
cell
Preganglionic
neuron
Postganglionic
neuron
ACh
Muscarinic receptor
15-26
9-23
Comparison of nicotinic and muscarinic ACh receptors
Acetylcholine (ACh)
•
ACh is secreted by all preganglionic neurons in both divisions and
the postganglionic parasympathetic neurons
– called cholinergic fibers
– any receptor that binds it is called cholinergic receptor
•
2 types of cholinergic receptors
– muscarinic receptors
• all cardiac muscle, smooth muscle, and gland cells have
muscarinic receptors
• excitatory or inhibitory due to subclasses of muscarinic
receptors
– nicotinic receptors
• on all ANS postganglionic neurons, adrenal medulla, and
neuromuscular junctions of skeletal muscle
• excitatory when ACh binding occurs
5 types of muscarinic receptors!!
15-27
9-28
Monoamine NTs (Catecholamines)
Norepinephrine (NE)
•
•
NE is secreted by nearly all sympathetic postganglionic
neurons
– called adrenergic fibers
– receptors for it called adrenergic receptors
Use G-proteins and Second Messengers
• alpha-adrenergic receptors
– usually excitatory
– 2 subclasses use different second messengers (α1 &
α2)
• beta-adrenergic receptors
– usually inhibitory
– 2 subclasses with different effects, but both act
through cAMP as a second messenger (β1 & β2)
15-29
7-65
5
ANS
•
Many drugs have been
developed to affect ANS
receptors
– Drugs that promote
actions of a NT are
agonists
– Drugs that inhibit
actions of a NT are
antagonists
•
Postganglionics have
unusual synapses called
varicosities
– release NTs along a
length of axon
– Target cell doesn’t
have clusters of
receptors at specific
sites
– Neuroatransmitters
diffuses to receptors
9-26
Dual Innervation
Dual Innervation
• dual innervation - most viscera receive fibers from both
parasympathetic and sympathetic divisions
• antagonistic effects - oppose each other
cooperative effects – two divisions act on different
effectors to produce a unified overall effect
– parasympathetics increase salivary serous cell
secretion
– sympathetics increase salivary mucous cell secretion
– exerted through dual innervation of same effector cells
• heart rate decreases (parasympathetic)
• heart rate increases (sympathetic)
– exerted because each division innervates different cells
15-33
Dual Innervation of the Iris
15-34
Sympathetic and Vasomotor Tone
Brain
Parasympathetic fibers
of oculomotor nerve (III)
Superior
cervical
ganglion
sympathetic division
prioritizes blood vessels to
skeletal muscles and heart
in times of emergency
Sympathetic
fibers
Ciliary
ganglion
blood vessels to skin
vasoconstrict to
minimize bleeding if
injury occurs during
stress or exercise
Cholinergic stimulation
of pupillary constrictor
Iris
Pupil
Sympathetic
(adrenergic) effect
Sympathetic
nerve fiber
1 Strong
sympathetic
tone
2
2 Smooth muscle
contraction
3
Vasomotor
tone
Spinal cord
Adrenergic
stimulation of
pupillary dilator
Artery
1
Parasympathetic
(cholinergic) effect
3 Vasoconstriction
(a) Vasoconstriction
1
1 Weaker
sympathetic
tone
2
3
2 Smooth muscle
relaxation
3 Vasodilation
Figure 15.9
(b) Vasodilation
Pupil dilated
Pupil constricted
15-35
Figure 15.10
15-36
6
Somatic Motor Division
Somatic Motor Division
• Single neuron
– CNS origin
– Myelinated
• Terminus
– Branches
– Neuromuscular junction
Figure 11-11 (1 of 5)
Anatomy of the Neuromuscular
Junction
Anatomy of the Neuromuscular
Junction
Schwann cell sheath
Somatic motor neuron
The neuromuscular junction
Axon terminal
Mitochondria
Muscle fiber
Terminal bouton
Motor end plate
Figure 11-12 (1 of 3)
Anatomy of the Neuromuscular
Junction
Synaptic
vesicle (ACh)
Figure 11-12 (2 of 3)
Events at the Neuromuscular
Junction
Somatic motor
neuron
Axon terminal
Presynaptic
membrane
Ca2+
Synaptic cleft
Nicotinic ACh
receptors
Postsynaptic
membrane
ACh
Voltage-gated
Ca2+ channel
Skeletal
muscle
fiber
(a)
Figure 11-12 (3 of 3)
Ca2+
Action potential
Acetyl + choline
AChE
Nicotinic
receptor
Motor end
plate
Figure 11-13a
7
Events at the Neuromuscular
Junction
Open channel
Closed channel
ACh
K+
Na+
K+
Na+
(b)
Figure 11-13b
8