Autonomic Nervous System Flashcards
The ANS (Autonomic Nervous System) is
a visceral motor neuron system
that innervates
-Smooth muscle in organs and blood vessels
• Cardiac muscle
• Glands
Autonomic Motor Systems with
chain of two motor neurons
compared to single somatic motor axon
Autonomic motor system
• Preganglionic neuron: thinly myelinated
• Post-ganglionic neuron: unmyelinated
• Preganglionic and postganglionic neurons
synapse in a ganglion
Somatic motor system
• Axons are well myelinated and conduct
impulses more rapidly
• Have one axon that extends from CNS to the
muscle
Sympathetic and
parasympathetic divisions
- Innervate mostly the same structures
* Cause opposite effects
Sympathetic Nervous System
• Fight, flight, or fright response
• Increase heart rate and breathing rate
• Increases blood and oxygen to skeletal muscles
• Dilates pupils and airways
• Inhibits motility of the digestive tract and urinary
tracts
• Stimulates sweat glands
• Stimulates arrector pili muscles which causes
hairs to stand up vertically
Parasympathetic Nervous
System is active when person
is relaxed and body is at rest
-Conserves energy • Heart rate and breathing are at normal levels • Gastrointestinal tract digests food • Pupils are constricted
Anatomical Differences in Sympathetic and
Parasympathetic Divisions
Issue from different regions of the CNS – Sympathetic—also called the thoracolumbar division – Parasympathetic— also called the craniosacral division
Anatomical Differences in Sympathetic
and Parasympathetic Divisions
• Length of postganglionic axon fibers – Sympathetic—long because ganglia are typically close to CNS – Parasympathetic—short because ganglia are close to viscera • Branching of postganglionic axons – Sympathetic axons—may be highly branched – Parasympathetic axons—few branches
Anatomical Differences in Sympathetic
and Parasympathetic Divisions:
Neurotransmitter released by
postganglionic axons
Sympathetic: release norepinephrine
(adrenergic)
• Parasympathetic: release acetylcholine
(cholinergic)
The Parasympathetic Division
Cranial outflow
– Comes from cranial nerves in brainstem
– Innervates: organs of the head, neck,
thorax, and most of abdomen
• Sacral outflow
– Comes from visceral motor region of ventral
gray matter in spine
– Innervates: distal half of large intestine,
reproductive organs and erectile tissue in
external genitalia
Cranial Outflow (Parasympathetic)
• Preganglionic fibers run via – Oculomotor nerve (III) – Facial nerve (VII) – Glossopharyngeal nerve (IX) – Vagus nerve (X) • Cell bodies of cranial nerves located in cranial nerve nuclei in the brainstem • Ganglionic cell bodies located near viscera/organs/tissues being innervated 1
Path of Vagus Nerve (CN X)
sends branches through
parasympathetic autonomic
nerve plexuses:
- Nerve plexus = network of nerves
- Cardiac plexus
- Pulmonary plexus
- Esophageal plexus
- Celiac plexus
- Superior mesenteric plexus
Sacral Outflow
• Emerges from S2–S4
• Innervates organs of the pelvis and lower
abdomen and stimulates defecation,
urination, and erection
• Preganglionic cell bodies are located in
visceral motor region of spinal gray matter
• Axons run in ventral roots to ventral rami
and form pelvic nerves
• Run through the inferior hypogastric (or
pelvic) plexus
The Sympathetic Division
Issues from T1–L2 • Preganglionic fibers emerge from the LATERAL GRAY HORN in spinal cord • Supplies visceral organs and structures of superficial body regions • Contains more ganglia than the parasympathetic division
Sympathetic Trunk Ganglia
Located on both sides of the vertebral column • Linked by short nerves into sympathetic trunks • Sympathetic trunk ganglia are also called chain ganglia or paravertebral ganglia
Sympathetic neurons in the
thoracolumbar spinal cord send motor
axons through trunk ganglia
via the following sequence
Preganglionic axon (lightly myelinated) • Ventral root • Ventral ramus of spinal nerve • White ramus communicans • Associated sympathetic trunk ganglion Postganglionic axon (unmyelinated) • Gray ramus communicans • Ventral ramus of spinal nerve
White & gray rami communicans
• White rami communicans—contain lightly
myelinated preganglionic fibers traveling to
sympathetic trunk ganglia
• Gray rami communicans—contain
unmyelinated postganglionic fibers traveling
from ganglia to peripheral structures
Sympathetic preganglionic axons follow
one of three pathways
- Synapses with a postganglionic neuron at
the same level and exit on a spinal nerve at that
level
• # 2. Axon ascends or descends in the
sympathetic trunk to synapse in another ganglion
• # 3. Axon does not synapse in the sympathetic
trunk but instead passes through and exits in a
splanchnic nerve and synapses in a collateral
ganglion from which a postganglionic axon
extends to the visceral organ
Collateral (prevertebral) ganglia
(#3) differ from sympathetic trunk
ganglia in three ways
Unpaired, not segmentally arranged
• Occur only in abdomen and pelvis
• Lie anterior to the vertebral column
Splanchnic nerves
• Splanchnic nerves carry preganglionic
neurons to the collateral ganglia
Main sympathetic
collateral ganglia
- Celiac
- Superior mesenteric
- Inferior mesenteric
- Inferior hypogastric
Main sympathetic ganglia
Superior cervical • Middle cervical • Inferior cervical • Celiac • Superior mesentery • Inferior mesentery • Hypogastric
Sympathetic Pathways to the
Head
Preganglionic fibers originate in spinal cord at T1–T4 • Fibers ascend in the sympathetic trunk and synapse in superior cervical ganglion • Postganglionic fibers associate with eye, lacrimal gland, nasal mucosa, salivary glands
Sympathetic Pathways to
Thoracic Organs
Preganglionic fibers originate at spinal levels T1–T6
• Some fibers synapse in nearest sympathetic trunk
ganglion and the postganglionic fibers run to heart,
lungs and esophagus
• Functions
– Increase heart rate
– Dilate blood vessels to the heart wall
– Dilate bronchioles
– Inhibit muscles and glands in the esophagus and
digestive system
Sympathetic Pathways to
Abdominal Organs
• Preganglionic fibers originate in spinal cord
(T5–L2)
• Pass through adjacent sympathetic trunk
ganglia then travel in splanchnic nerves
• Synapse in collateral ganglia (celiac and
superior mesenteric ganglia) in abdomen
Sympathetic Pathways to the
Pelvic Organs
Preganglionic fibers originate in the spinal
cord from T10–L2
• Some preganglionic fibers pass directly to
autonomic plexuses and synapse in
collateral ganglia (inferior mesenteric or
inferior hypogastric ganglia)
• Postganglionic fibers go from these
plexuses to the bladder, reproductive
organs, and distal large intestine
Sympathetic Pathways to the
Pelvic Organs
Some preganglionic fibers descend in the
sympathetic trunk to lumbar and sacral
ganglia where they synapse
• Postganglionic fibers run in lumbar and sacral
nerves to inferior mesenteric, aortic and
hypogastric plexuses
The Role of the Adrenal Medulla in
the Sympathetic Division
• Adrenal medulla is major organ of the
sympathetic nervous system
• Constitutes largest sympathetic ganglia
• Secretes large quantities of norepinephrine
and epinephrine (=adrenaline) to produce
a widespread excitatory response, the
“surge of adrenaline”
• Stimulated to secrete by preganglionic
sympathetic fibers carried in thoracic
splanchnic nerve
Central Control of the ANS
– Reticular formation exerts most direct influence
• Medulla oblongata e.g., cardiac center, vasomotor
center, and digestive activities
• Periaqueductal gray matter in midbrain exerts
sympathetic fear response
– Control by the hypothalamus and amygdala
• Hypothalamus—the main integration center of the
ANS
• Amygdala—main limbic region for emotions
– Control by the cerebral cortex: for example calm
feelings achieved during meditation are associated with
cerebral cortex influence on the parasympathetic
centers of hypothalamus via various limbic structures
Central nervous system control of
autonomic nervous system
- Cerebral cortex
- Amygdala
- Hypothalamus
- Brainstem
- Spinal cord
Spinal cord control of autonomic
nervous system influences
visceral spinal reflexes
- Urination reflex
- Defecation reflex
- Erection reflex
- Ejaculation/orgasm reflex
Brainstem control of
autonomic nervous system
Reticular formation exerts most direct
influence over autonomic functions
• Medulla oblongata e.g., cardiac center,
vasomotor center, and digestive activities
• Periaqueductal gray matter in midbrain
exerts sympathetic fear response
Hypothalamus control of
autonomic nervous system
• Hypothalamus is main integration center of
the autonomic nervous system by influencing
preganglionic autonomic neurons in
brainstem and spinal cord through direct
connections and relays in reticular formation
and periaqueductal gray matter
• Medial and anterior parts direct
parasympathetic functions
• Lateral and posterior parts direct sympathetic
functions
Amygdala control of
autonomic nervous system
• Amygdala is main limbic region for emotions
• Amygdala communications with the
hypothalamus and the periaqueductal gray
matter can stimulate sympathetic activity,
especially previously learned fear-related
behavior
Cerebral frontal cortex control
of autonomic nervous system
People can exert some conscious control over some
autonomic functions by developing control over their
thoughts and emotions
• Feelings of calm achieved during meditation are
associated with cerebral cortex enhancing the
parasympathetic centers in the hypothalamus via
limbic structures
• Voluntary recall of a frightful experience can
activate the sympathetic system via the amygdala
Disorders of the Autonomic
Nervous System
• Raynaud’s disease—characterized by constriction of blood vessels – Provoked by exposure to cold or by emotional stress • Hypertension—high blood pressure – Can result from overactive sympathetic vasoconstriction
