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.