Download Chapter 15 Autonomic NS

Autonomic Nervous
System
Chapter 15
Autonomic Nervous System
Autonomic Nervous System
- Regulate activity of smooth muscle, cardiac
muscle & certain glands
- Structures involved
General visceral afferent neurons
General visceral efferent neurons
Integration center within the brain
- Receives input from limbic system and other
regions of the cerebrum
Basic Anatomy of ANS
• Preganglionic neuron
– cell body in brain or spinal cord
– axon is myelinated type B fiber that extends to autonomic
ganglion
• Postganglionic neuron
– cell body lies outside the CNS in an autonomic ganglion
– axon is unmyelinated type C fiber that terminates in a visceral
effector
Autonomic vs Somatic NS
Somatic nervous system
consciously perceived sensations
excitation of skeletal muscle
one neuron connects CNS to organ
Autonomic nervous system
unconsciously perceived visceral sensations
involuntary inhibition or excitation of smooth
muscle, cardiac muscle or glandular secretion
two neurons needed to connect CNS to organ
preganglionic and postganglionic neurons
Somatic/Autonomic Nervous System
Sympathetic
Division of
the ANS
Sympathetic Ganglia
Trunk(chain) ganglianear vertebral
column on either
side
Prevertebral(collateral)
gangliaanterior to vertebral
column close to
large abdominal
arteries.
Sympathetic Division Structure
•
Sympathetic preganglionic neurons pass to the
sympathetic trunk. They may connect to postganglionic
neurons in the following ways:
1.
2.
3.
4.
May synapse with postganglionic neurons in the ganglion it
first reaches.
May ascend or descend to a higher of lower ganglion before
synapsing with postganglionic neurons.
May continue, without synapsing, through the sympathetic
trunk ganglion to a prevertebral ganglion and synapse with
postganglionic neurons.
May pass through sympathetic trunk ganglion and a
prevertebral ganglion and then extend to chromaffin cell of
adrenal medulla.
Pathways of
Sympathetic
Fibers
Parasympathetic
Division of the
ANS
Parasympathetic
Ganglia
terminal ganglia close to
or in the wall of organs
Parasympathetic Division Structure
•Parasympathetic preganglionic neurons synapse with postganglionic
neurons in terminal ganglia.
• The cranial outflow consists of preganglionic axons that
extend from the brain stem in four cranial nerves.
– The cranial outflow consists of four pairs of ganglia and the
plexuses associated with the vagus nerve (X).
•
•
•
•
Ciliary ganglia
Pterygopalatine ganglia
Submandidibular ganglia
Otic ganglia
• The sacral parasympathetic outflow consists of
preganglionic axons in the anterior roots of the 2nd
through 4th sacral nerves and they form the pelvic
splanchnic nerve.
Autonomic Plexuses
Cardiac plexus
Pulmonary plexus
Celiac (solar) plexus
Superior mesenteric
Inferior mesenteric
Hypogastric
Renal plexus
Pathway from Spinal Cord to
Sympathetic Trunk Ganglia:
• Preganglionic axons → anterior root of a spinal
nerve → white ramus → sympathetic trunk
ganglion.
• White rami communicantes: structures
containing sympathetic preganglionic axons
that connect the anterior ramus of the spinal
nerve with the ganglia of the sympathetic
trunk.
Organization of Sympathetic
Trunk Ganglia
• Sympathetic trunk ganglia: 3 cervical, 11 or 12
thoracic, 4 or 5 lumbar, 4 or 5 sacral and 1
coccygeal.
• Postganglionic neurons from the
- superior cervical region: head and heart.
- middle cervical ganglion and the inferior
cervical ganglion: heart.
• Thoracic sympathetic trunk- heart, lungs, and
bronchi.
Pathways from Sympathetic Trunk
Ganglia to Visceral Effectors
• Axons leave the sympathetic trunk in 4
possible ways:
- spinal nerves
- cephalic periarterial nerves
- sympathetic nerves
- splanchnic nerves
Spinal nerves
• Gray ramus: Axons of some postganglionic
neurons leave the sympathetic trunk by
entering a short pathway called a gray ramus
and merge with the anterior ramus of a spinal
nerve.
• Gray rami communicantes: structures
containing sympathetic postganglionic axons
that connect the ganglia of the sympathetic
trunk to spinal nerves.
Cephalic Periarterial Nerves
• Some sympathetic preganglionic neurons that
enter the sympathetic trunk ascend to the
superior cervical ganglion where they synapse
with postganglionic neurons. Some of these
leave the sympathetic trunk by forming
cephalic periarterial nerves.
• Serve visceral effectors in the skin of the face
and head.
Sympathetic Nerves
• Some axons of the postganglionic neurons
leave the trunk by forming sympathetic nerves.
• Innervate the heart and lungs.
Splanchnic Nerves
• Some sympathetic preganglionic axons pass
through the sympathetic trunk without
terminating in it. Beyond the trunk they form
nerves called splanchnic nerves which extend
to prevertebral ganglia.
• T5-T9 or T10- Greater splanchnic nerve.
• T10-T11- Lesser splanchnic nerve.
• L1-L4- Lumbar splanchnic nerve.
Cranial Parasympathetic Outflow
• The cranial outflow has four pairs of ganglia
and are associated with the vagus nerve.
1.
2.
3.
4.
Ciliary gangliaPterygopalatine gangliaSubmandibular gangliaOtic ganglia-
• Vagus nerve carries nearly 80% of the total
craniosacral flow.
Sacral Parasympathetic Outflow
• Consists of S2-S4.
• Pelvic splanchnic
nerves
Neurotransmitters
and Receptors
Adrenergic and Cholinergic
Receptors
Sympathetic vs. Parasympathetic
Physiological Effects of the ANS
• Most body organs receive dual innervation
– innervation by both sympathetic & parasympathetic
• Hypothalamus regulates balance (tone) between
sympathetic and parasympathetic activity levels
• Some organs have only sympathetic innervation
– sweat glands, adrenal medulla, arrector pili mm &
many blood vessels
– controlled by regulation of the “tone” of the
sympathetic system
Sympathetic Responses
• Dominance by the sympathetic system is caused by
physical or emotional stress -- “E situations”
– emergency, embarrassment, excitement, exercise
• Alarm reaction = flight or fight response
–
–
–
–
–
–
dilation of pupils
increase of heart rate, force of contraction & BP
decrease in blood flow to nonessential organs
increase in blood flow to skeletal & cardiac muscle
airways dilate & respiratory rate increases
blood glucose level increase
• Longer lasting than parasympathetic due to lingering of
NE in synaptic gap and release of norepinephrine by the
adrenal gland
Parasympathetic Responses
• Enhance “rest-and-digest” activities
• Mechanisms that help conserve and restore body energy
during times of rest
• Normally dominate over sympathetic impulses
• SLUDD type responses = salivation, lacrimation,
urination, digestion & defecation and 3 “decreases”--decreased HR, diameter of airways and diameter of pupil
• Paradoxical fear when there is no escape route or no way
to win
– causes massive activation of parasympathetic division
– loss of control over urination and defecation
Sympathetic vs. Parasympathetic
Autonomic Reflexes
• Autonomic reflexes occur over autonomic reflex
arcs. Components of reflex arc:
–
–
–
–
–
sensory receptor
sensory neuron
integrating center
motor neurons (pre & postganglionic)
visceral effectors
• Unconscious sensations and responses
– changes in blood pressure, digestive functions etc
– filling & emptying of bladder or defecation
Control of Autonomic Functioning
Hypothalamus is major control center
– input: emotions and visceral sensory information
• smell, taste, temperature, osmolarity of blood, etc
– output: to nuclei in brainstem and spinal cord
– posterior & lateral portions control sympathetic NS
• increase heart rate, inhibition GI tract, increase temperature
– anterior & medial portions control parasympathetic
NS
• decrease in heart rate, lower blood pressure, increased GI
tract secretion and mobility
Autonomic vs Somatic NS - Review
• Somatic nervous system
– consciously perceived
sensations
– excitation of skeletal
muscle
– one neuron connects
CNS to organ
•Autonomic nervous system
–unconsciously perceived
visceral sensations
–involuntary inhibition or
excitation of smooth muscle,
cardiac muscle or glandular
secretion
–two neurons needed to
connect CNS to organ
•preganglionic and
postganglionic neurons
Autonomic vs Somatic NS - Review
Autonomic Dysreflexia
• Exaggerated response of sympathetic NS in cases of
spinal cord injury above T6
• Certain sensory impulses trigger mass stimulation of
sympathetic nerves below the injury
• Result
– vasoconstriction which elevates blood pressure
– parasympathetic NS tries to compensate by slowing heart rate
& dilating blood vessels above the injury
– pounding headaches, sweating warm skin above the injury and
cool dry skin below
– can cause seizures, strokes & heart attacks