Transcript 30. Autonomic NS. Sympathetic nervous system

Autonomic
Nervous
System.
Sympathetic
NS
Introduction to ANS
• Regulates activity of smooth muscle,
cardiac muscle and glands
• Operates without conscious control
• Named autonomic because was thought
to be AUTONOMUS (working without
CNS)
Autonomic
Nervous
System
• But to operate it
depends on
continuous flow
of sensory input
from:
– Visceral organs
and
– Blood vessels(not
consciously perceived)
into
– INTEGRATING
CENTERS IN
THE CNS.
Autonomic Nervous System
• Structurally then ANS includes:
– Autonomic sensory neurons
– Integrating centers in the CNS
– Autonomic motor neurons to smooth muscle,
cardiac muscle and glands
Where in the CNS? Hypothalamus and brain stem
Comparing the ANS and
Somatic NS
• Structurally then SNS includes:
– Somatic sensory neurons
– Integrating centers in the CNS (Cortex)
– Somatic motor neuron to skeletal muscles
only
Comparing the ANS and
Somatic NS
• Somatic- the effect of a motor neuron is
always excitation
• Autonomic- the effect of a motor neuron is
either excitatory or inhibitory
Autonomic Nervous System
• Makes all routine adjustments in
physiological systems.
• The ANS pathway from the CNS to the
effector always involves 2 neurons
synapsing in an autonomic ganglion
ANS
– Preganglionic (neuron #1) – cell body is in
the CNS, axon extends to the ganglion
outside the CNS
– Postganglionic (neuron #2) – cell body is in
the ganglion, axon extends to the visceral
effector
Nerve Fibers of the ANS
• Preganglionic (neuron #1)
– Always myelinated
– Neurotransmitter is always ACh
• Postganglionic (neuron #2)
– Always nonmyelinated
– Neurotransmitter is Ach or norepinephrine
Subdivisions of the ANS
• Sympathetic Division
– Fight-or-flight
• Parasympathetic Division
– Rest-and-digest
• These divisions are anatomically distinct
Sympathetic
• Sympathetic division (thoracolumbar)
– Cell bodies for all the neurons #1 reside in the
thoracic and lumbar portions of the spinal
cord.
• T1 – L2
Sympathetic
– Stimulates
•
•
•
•
heart beat
tissue metabolism,
increases alertness,
prepares the body to deal
with emergencies
• (“fight or flight” division)
T1-L2
Parasympathetic
•Parasympathetic division (craniosacral)
–Cell bodies reside in the brain stem (cranial
nerves) or in the sacral portion of the spinal
cord.
Cranial & Sacral
Parasympathetic
– Slows the heart rate,
– inhibits senses,
– prepares the body for rest and relaxation;
(“rest and digest” division).
The Sympathetic Division
Sympathetic Chain Ganglia
– Synapses of neurons #1 and #2 are in a chain
of ganglia that run alongside the spinal cord
– Extends on both sides of the vertebral column
– Carries preganglionic fibers and cell bodies of
postganglionic neurons
Ganglia
Anatomy of the chain
• Rami communicantes from the spinal
nerves connect to the chain
A closer look at spinal nerves
Routes of Preganglionic Axons
• Cell bodies of neurons #1 lie in the lateral
gray horns of the spinal cord
• The axons of neurons #1 leave the spinal
cord via the ventral root
• These axons pass to the spinal nerve
• Axons leave the spinal nerve via the white
branches (rami communicantes)
• Connect with the sympathetic chain
ganglia
Routes of Preganglionic Axons
• There are 3 possible routes that
sympathetic neurons may follow
• Possibility #1: synapses within the
ganglion at that level and
– Second neuron leaves at that level via the
gray ramus communicans, exits to the
visceral effector
Routes of Preganglionic Axons
• Possibility #2: neuron #1 goes up or down
the chain and synapses at some other
level.
– Second neuron: leaves at that other level via
the gray ramus communicantes, and exits to
the visceral effector.
Routes of Preganglionic Axons
• Possibility #3: neuron #1 does not
synapse in the chain (exception!!) but exits
and synapses in a collateral ganglion
near a major blood vessel.
– Neuron #2 travels from that ganglion to the
visceral effector.
Where are the Collateral
Ganglia ?
• Location –Near a major blood vessel
– Celiac ganglion
• Innervates upper abdominal viscera
– Superior mesenteric
• Innervates middle abdominal viscera
– Inferior mesenteric
• Innervates lower abdominal & pelvic organs
The Adrenal Medulla
• Yet another type of innervation:
– Going to the adrenal medulla
– No synapse in ganglia
– No synapse in collateral ganglia
– YES synapse in the adrenal medulla
Adrenal Medulla
• Only preganglionic neurons are in this
pathway
• Neuron #1 stimulates the medulla,
• The medulla releases norepinephrine and
epinephrine (adrenaline) to blood
Adrenal Medulla
Figure 17-06
Effects of Sympathetic
Stimulation
• Widespread
– The sympathetic chain allows one
preganglionic fiber to synapse with many
postganglionic neurons
• Enhanced & prolonged by the adrenal
medulla
Convergence
• See heart
Neurotransmitters of
Sympathetic Division
• Preganglionic fibers release acetylcholine
(Ach) Therefore they are called:
– Cholinergic
• Postganglionic fibers (most) release
norepinephrine (NE) (=noradrenaline)
– Adrenergic
• Adrenal medulla releases norepinephrine
and epinephrine (adrenalin)
Functions of the
Sympathetic Division
•
•
•
•
•
•
Heart: increases rate
Lung bronchioles: dilates bronchioles
Salivary glands: produce viscous fluid
Stomach: decreases motility
Pupil: dilates
Sweat glands: produce secretions
Summary of Sympathetic
Division
• Cell bodies are found in the thoracic and
lumbar portions of the spinal cord
• Preganglionic fibers are short, connect to
the sympathetic chain, and synapse with
long postganglionic fibers
• Preganglionic fibers produce ACh,
postganglionic fibers produce NE or Ach
• “Fight or flight” division
ANS either increases excitation
or inhibits the activity
– Ex. Sympathetic fibers increase heart rate,
parasympathetic fibers decrease heart rate.
– Homeostasis comes from the balance of the
two.