Transcript Ch 15 ANS - Lake–Sumter State College

Chapter 15
Lecture Outline
15-1
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Autonomic Nervous System
and Visceral Reflexes
• Autonomic Nervous System (ANS)
– general properties
• Autonomic Effects on Target Organs
• Central Control of Autonomic
Function
15-2
Autonomic Nervous System
• portion of the nervous system that operates in
comparative secrecy
• it manages a multitude of unconscious processes
responsible for the body’s homeostasis
• homeostasis cannot be maintained without the
ANS
15-3
General Properties of ANS
• autonomic nervous system (ANS) – a motor nervous
system that controls glands, cardiac muscle, and smooth
muscle
– also called visceral motor system
– primary organs of the ANS
• viscera of thoracic and abdominal cavities
• some structures of the body wall
– cutaneous blood vessels
– sweat glands
– piloerector muscles
– carries out actions involuntarily
15-4
Visceral Reflexes
•
visceral reflexes - unconscious, automatic,
stereotyped responses to stimulation involving visceral
receptors and effectors
•
visceral reflex arc
–
–
–
–
–
•
receptors – nerve endings that detect stretch, tissue
damage, blood chemicals, body temperature, and other
internal stimuli
afferent neurons – leading to the CNS
interneurons – in the CNS
efferent neurons – carry motor signals away from the CNS
effectors – that make adjustments
ANS modifies effector activity
15-5
Visceral Reflex to High BP
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• high blood pressure
detected by arterial
stretch receptors (1),
afferent neuron (2)
carries signal to CNS,
efferent (3) signals
travel to the heart (4),
heart slows reducing
blood pressure
• homeostatic negative
feedback loop
2
Glossopharyngeal
nerve transmits signals
to medulla oblongata
Baroreceptors sense
1 increased blood pressure
3 Vagus nerve
transmits
inhibitory
signals
to cardiac
pacemaker
Common carotid
artery
Terminal
ganglion
4 Heart rate
decreases
Figure 15.1
15-6
Divisions of ANS
•
two divisions innervate same target organs
– may have cooperative or contrasting effects
sympathetic division
– prepares body for physical activity – exercise,
trauma, arousal, competition, anger, or fear
•
•
heart rate, BP, airflow, blood glucose levels, etc.
reduces blood flow to the skin and digestive tract
parasympathetic division
– calms many body functions reducing energy
expenditure and assists in bodily maintenance
•
•
digestion and waste elimination
“resting and digesting” state
15-7
Divisions of ANS
•
autonomic tone - normal background rate
of activity that represents the balance of the
two systems
–
parasympathetic tone
•
•
–
sympathetic tone
•
•
maintains smooth muscle tone in intestines
holds resting heart rate down to about 70 – 80 beats
per minute
keeps most blood vessels partially constricted and
maintains blood pressure
sympathetic division excites the heart but
inhibits digestive and urinary function, while
parasympathetic has the opposite effect
15-8
Neural Pathways
•
ANS components are in both the central and peripheral nervous
systems
–
control nucleus in hypothalamus and other brainstem areas
–
motor neurons in the spinal cord and peripheral ganglia
–
nerve fibers that travel through the cranial and spinal nerves
•
autonomic pathway
–
signal must travel across two neurons to get to the target
organ
–
must cross a synapse where these two neurons meet in an
autonomic ganglion
–
presynaptic neuron – first neuron (soma in the brainstem or
spinal cord)
–
postganglionic neuron – second neuron (axon extends the
rest of the way to the target cell)
15-9
Somatic versus Autonomic Pathways
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Somatic efferent innervation
ACh
Myelinated
fiber
Somatic effectors
(skeletal muscles)
Autonomic efferent innervation
ACh
Myelinated
preganglionic fiber
ACh or NE
Unmyelinated
postganglionic fiber
Autonomic
ganglion
Visceral effectors
(cardiac muscle,
smooth muscle,
glands)
Figure 15.2
ANS – two neurons from CNS to effectors
• presynaptic neuron whose cell body is in CNS
• postsynaptic neuron cell body in peripheral ganglion 15-10
Sympathetic
Division:
Efferent
Pathways
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Permission required for reproduction or display.
Eye
Pons
Salivary glands
Preganglionic neurons
Postganglionic neurons
Cardiac and
pulmonary plexuses
Regions of spinal cord
Cervical
Thoracic
Lumbar
Sacral
Celiac
ganglion
Superior
mesenteric
ganglion
Postganglionic fibers to
skin, blood vessels,
adipose tissue
Heart
Lung
Liver and
gallbladder
Stomach
Spleen
Pancreas
Inferior
mesenteric
ganglion
Small intestine
Large intestine
Sympathetic chain
ganglia
Rectum
Adrenal medulla
Kidney
Figure 15.4
Ovary
Uterus
Penis
Scrotum
Bladder
15-11
Preganglionic Pathways
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Soma of
preganglionic
neuron
To iris, salivary glands,
lungs, heart, thoracic
blood vessels, esophagus
Sympathetic nerve
2
Somatic
motor fiber
Spinal nerve
Preganglionic
sympathetic fiber
Postganglionic
sympathetic fiber
To somatic effector
(skeletal muscle)
1
Soma of
somatic motor
neuron
3
White ramus
Splanchnic nerve
Gray ramus
Preganglionic neuron
Postganglionic neuron
Somatic neuron
Figure 15.5
To sweat glands,
piloerector muscles,
and blood vessels
of skin and
skeletal muscles
Communicating
rami
Collateral ganglion
Soma of
postganglionic
neuron
Postganglionic
sympathetic fibers
Sympathetic
trunk
To liver, spleen, adrenal glands,
stomach, intestines, kidneys,
urinary bladder, reproductive organs
Sympathetic
ganglion
2
15-12
Adrenal Glands
• paired adrenal glands on superior poles of the kidneys
• each is two organs with different functions
– adrenal cortex (outer layer)
• secretes steroid hormones
– adrenal medulla (inner core)
• essentially a sympathetic ganglion
• secretes a mixture of hormones into bloodstream
– catecholamines - 85% epinephrine (adrenaline) and
15% norepinephrine (noradrenaline)
– also function as neurotransmitters
• sympathoadrenal system is the closely related functioning
adrenal medulla and sympathetic nervous system
15-13
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Parasympathetic
Division:
Efferent
Pathways
Preganglionic neur
Postganglionic neu
Pterygopalatine
ganglion
Oculomotor n. Ciliary ganglion
(CN III)
Facial n.Submandibular
(CN VII)
ganglion
Lacrimal gland
Eye
Submandibular
salivary gland
Otic ganglion
Parotid
salivary gland
Glossopharyngeal n.
(CN IX)
Vagus n.
(CN X)
Cardiac plexus
Regions of
spinal cord
Heart
Pulmonary
plexus
Esophageal
Cervical
plexus
Thoracic
Lumbar Celiac
ganglion
Sacral
Abdominal
aortic plexus
Lung
Stomach
Liver and
gallbladder
Spleen
Pancreas
Pelvic
splanchnic
nerves
Kidney and
ureter
Inferior
hypogastric
plexus
Descending
colon
Small intestin
Rectum
Figure 15.7
Pelvic
nerves
Penis
Ovary
Uterus
Scrotum
Bladder
15-14
Enteric Nervous System
• enteric nervous system – the nervous system of the
digestive tract
– does not arise from the brainstem or spinal cord
– innervates smooth muscle and glands
• 100 million neurons found in walls of the digestive tract
• no components in CNS
• has its own reflex arcs
• 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
15-15
Megacolon
• Hirschsprung disease – hereditary defect
causing absence of enteric nervous system
– no innervation in sigmoid colon and rectum
– constricts permanently and will not allow passage of
feces
– feces becomes impacted above constriction
– megacolon – massive dilation of bowel accompanied
by abdominal distension and chronic constipation
– maybe colonic gangrene, perforation of bowel, and
peritonitis
– usually evident in newborns who fail to have their first
bowel movement
15-16
Neurotransmitters and Receptors
• how can different autonomic neurons have different effects?
constricting some vessels but dilating others
• 2 fundamental reasons:
– sympathetic and parasympathetic fibers secrete different
neurotransmitters
– target cells respond to the same neurotransmitter
differently depending upon the type of receptor they have
• all autonomic fibers secrete either acetylcholine or
norepinephrine
• there are 2 classes of receptors for each of these
15-17
neurotransmitters
Acetylcholine (ACh)
• ACh is secreted by all preganglionic neurons in both
divisions and the postganglionic parasympathetic
neurons
– any receptor that binds it is called cholinergic receptor
• 2 types of cholinergic receptors
– muscarinic receptors
• Found in all cardiac muscle, smooth muscle, and gland cells
• excitatory or inhibitory due to subclasses of muscarinic receptors
– nicotinic receptors
• on all ANS postganglionic neurons, in the adrenal medulla, and at
neuromuscular junctions of skeletal muscle
• excitatory when ACh binding occurs
15-18
Norepinephrine (NE)
• NE is secreted by nearly all sympathetic
postganglionic neurons
– receptors for it called adrenergic receptors
• alpha-adrenergic receptors
– usually excitatory
– 2 subclasses (α1 & α2)
• beta-adrenergic receptors
– usually inhibitory
– 2 subclasses with different effects (β1 & β2)
15-19
(a) Parasympathetic fiber
Nicotinic
ACh receptor
Target
cell
Preganglionic
neuron
ACh
Postganglionic Muscarinic
neuron
receptor
Neurotransmitters
and Receptors
(b) Sympathetic adrenergic fiber
Nicotinic
ACh receptor
Target
cell
Preganglionic
neuron Postganglionic
NE
Adrenergic receptor
neuron
(c) Sympathetic cholinergic fiber
Nicotinic
ACh receptor
Target
cell
Preganglionic
neuron Postganglionic
neuron
ACh
Muscarinic receptor
Figure 15.8
15-20
Overview
• sympathetic effects tend to last longer than parasympathetic
effects
– ACh released by parasympathetics is broken down quickly at
synapse
– NE by sympathetics is reabsorbed by nerve, diffuses to
adjacent tissues, and much passes into bloodstream
• many substances released as neurotransmitters that modulate
ACh and NE function
– various hormones, neurotransmitters, and the gas, nitric oxide
15-21
Dual Innervation
• dual innervation - most viscera receive
nerve fibers from both parasympathetic
and sympathetic divisions
– antagonistic effect – oppose each other
– cooperative effects – two divisions act on
different effectors to produce a unified overall
effect
• both divisions do not normally innervate an
organ equally
15-22
Dual Innervation
• antagonistic effects - oppose each other
– exerted through dual innervation of same effector
cells
• heart rate decreases (parasympathetic)
• heart rate increases (sympathetic)
– exerted because each division innervates different
cells
• pupillary dilator muscle (sympathetic) dilates pupil
• constrictor pupillae (parasympathetic) constricts pupil
15-23
Dual Innervation of the Iris
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Brain
Parasympathetic fibers
of oculomotor nerve (III)
Superior
cervical
ganglion
Sympathetic
fibers
Ciliary
ganglion
Spinal cord
Adrenergic
stimulation of
pupillary dilator
Sympathetic
(adrenergic) effect
Cholinergic stimulation
of pupillary constrictor
Iris
Pupil
Parasympathetic
(cholinergic) effect
Figure 15.9
Pupil dilated
Pupil constricted
15-24
Dual Innervation
• cooperative effects - when two divisions
act on different effectors to produce a
unified effect
– parasympathetics increase salivary serous cell
secretion
– sympathetics increase salivary mucous cell
secretion
15-25
Without Dual Innervation
• some effectors receive only sympathetic fibers
– adrenal medulla, piloerector muscles, sweat glands and
many blood vessels
• sympathetic vasomotor tone - baseline firing frequency
• keeps vessels in state of partial constriction
• increase in firing frequency - vasoconstriction
• decrease in firing frequency - vasodilation
• shifts blood flow from one organ to another as needed
• sympathetic division acting alone can exert opposite effects on
the target organ through control of blood vessels
– during stress
• blood vessels to muscles and heart dilate
15-26
• blood vessels to skin constrict
Sympathetic and Vasomotor Tone
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Artery
sympathetic division
prioritizes blood vessels to
skeletal muscles and heart
in times of emergency
1
Sympathetic
nerve fiber
2
1 Strong sympathetic
tone
Smooth muscle
2 contraction
3
Vasomotor
tone
3 Vasoconstriction
(a) Vasoconstriction
blood vessels to skin
vasoconstrict to
minimize bleeding if
injury occurs during
stress or exercise
1
1 Weaker sympathetic
tone
2
3
2 Smooth muscle
relaxation
3 Vasodilation
(b) Vasodilation
Figure 15.10
15-27
Control of Autonomic Function
• ANS regulated by several levels of CNS
– cerebral cortex has an influence – anger, fear, anxiety
• powerful emotions influence the ANS because of the
connections between our limbic system and the
hypothalamus
– hypothalamus - major visceral motor control center
• nuclei for primitive functions – hunger, thirst, sex
15-28
Control of Autonomic Function
• ANS regulated by several levels of CNS
– midbrain, pons, and medulla oblongata contain:
• nuclei for cardiac and vasomotor control, salivation,
swallowing, sweating, bladder control, and pupillary
changes
– spinal cord reflexes
• defecation and urination reflexes are integrated in spinal
cord
• we control these functions because of our control over
skeletal muscle sphincters…but if the spinal cord is
damaged, the reflexes will remain
15-29
Drugs and the Nervous System
• neuropharmacology – study of effects of drugs on the
nervous system
• sympathomimetics enhance sympathetic activity
– stimulate receptors or increase norepinephrine release
• cold medicines that dilate the bronchioles or constrict nasal
blood vessels
• sympatholytics suppress sympathetic activity
– block receptors or inhibit norepinephrine release
• beta blockers reduce high BP by interfering with effects of
epinephrine/norepinephrine on heart and blood vessels
15-30
Drugs and the Nervous System
• parasympathomimetics enhance activity while
parasympatholytics suppress activity
• many drugs also act on neurotransmitters in CNS
– Prozac blocks reuptake of serotonin to prolong its moodelevating effect (SSRI: selective serotonin reuptake inhibitor)
– MAOI’s (monoamine oxidase inhibitors) prevent MAO from
breaking down neurotransmitters like NE
– caffeine competes with adenosine (the presence of which
causes sleepiness) by binding to its receptors
15-31
Adenosine and Caffeine
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NH2
N
N
O
H3C
N
N
N
CH3
N
OH O
O
N
N
CH3
OH
Figure 15.11
OH
Adenosine
Caffeine
15-32