Post on 04-Jul-2020
To review the different types of neurons associated with the ANS.
To clearly identify the position and role of the sympathetic trunk & collateral ganglia.
To address the two different types of receptors for neurotransmitters of the sympathetic ANS:
- Cholinergic Receptors
- Adrenergic Receptors
To relate how drugs interact (influence) the receptors seen in the sympathetic ANS.
Types of Neurons of ANSGanglion – Collection of nerve cell bodies
outside of the CNS.
Preganglionic Neurons – CB in CNS which
projects its axon to a peripheral ganglion
Postganglionic Neurons – CB in peripheral
ganglion its axon projects to an effector.
Figure 14.5a
Spinal cord
Dorsal root
Ventral root
Sympathetictrunk ganglion
Sympathetictrunk
Rib
Ventral ramus
of spinal nerve
Gray ramus
communicans
White ramuscommunicans
Thoracicsplanchnic nerves
(a) Location of the sympathetic trunk
3 cervical
11
thoracic
4 lumbar
4 sacral
1
coccygeal
Paravertebral
ganglia
Sympathetic Trunk
Pathways with Synapses in
Collateral Ganglia� Most fibers from T5 – L2 synapse in collateral ganglia
� They form thoracic, lumbar, and sacral splanchnic nerves
� Their ganglia include the celiac and the superior and inferior mesenteric
Neurotransmitter Effects� Somatic nervous system
� All somatic motor neurons release acetylcholine (ACh)
� Effects are always stimulatory
� ANS� Preganglionic fibers release ACh
� Postganglionic fibers release norepinephrine or ACh at effectors
� Effect is either stimulatory or inhibitory, depending on type of receptors
Figure 14.2
+
AChSmooth muscle
(e.g., in gut),
glands, cardiac
muscle
Ganglion
Adrenal medulla Blood vessel
ACh
ACh
ACh
NE
Epinephrine andnorepinephrine
Acetylcholine (ACh) Norepinephrine (NE)
Ganglion
Lightly myelinated
preganglionic axon
Lightly myelinated
preganglionic axons
Unmyelinated
postganglionic
axon
Unmyelinatedpostganglionic axon
Stimulatory
or inhibitory,
depending
on neuro-
transmitter
and
receptors
on effector
organs
Two-neuron chain from CNS to effector organs
AUTONOMIC NERVOUS SYSTEM
PARASYMPATHETIC
SYMPATHETIC
Neurotransmitters I. Cholinergic fibers release the neurotransmitter
ACh� All ANS preganglionic axons
� All parasympathetic postganglionic axons
II. Adrenergic fibers release the neurotransmitter NE� Most sympathetic postganglionic axons
� Exceptions: sympathetic postganglionic fibers secrete ACh at sweat glands and some blood vessels in skeletal muscles
Cholinergic Receptors�Two types of receptors bind ACh
1. Nicotinic (stimulatory)Found on:All ganglionic neurons both (sympath & para) Motor end plates of skeletal muscle cells Hormone-producing cells of the adrenal medulla
2. Muscarinic (inhibitory or excitatory)* Found on:All effector cells stimulated by postganglionic cholinergic fibers
* depends on target organ
Table 14.2
Adrenergic Receptors� Two types
� Alpha (α) (subtypes α1, α2) - Excitatory
� Beta (β) (subtypes β1, β2 , β3)
� Effects of NE depend on which subclass of receptor predominates on the target organ.
β1 – increases heart activity
β2 – relaxes smooth muscle of bronchioles
Table 14.2
Effects of Drugs� Over-the-counter drugs for colds, allergies, and nasal
congestion
� Stimulate α-adrenergic receptors
� Beta-blockers
� Drugs that attach to β2 receptors to dilate lung bronchioles in asthmatics; other uses
Visceral Reflexes� Visceral reflex arcs have the same components as
somatic reflexes
� Main difference: visceral reflex arc has two neurons in the motor pathway
� Visceral pain afferents travel along the same pathways as somatic pain fibers, contributing to the phenomenon of referred pain
Figure 14.7
Spinal cord
Dorsal root ganglion
Autonomic ganglion
Stimulus
Response
Visceral sensoryneuron
Integration center• May be preganglionic
neuron (as shown)• May be a dorsal horn
interneuron• May be within walls
of gastrointestinal tract
Sensory receptor
in viscera
2
3
1
5 Visceral effector
Efferent pathway(two-neuron chain)• Preganglionic neuron• Ganglionic neuron
4
HW for Week 4Due in lab:
Diseases & Disorders of the nervous system W.S.
Labeling:
pg 337 (spinal cord)
pg. 378 (eye)
Study Guide will be provided for in lab (Tuesday)
Preview dissection of eye and eye related reflexes.