1. Chapter 16 Anatomy & Physiology Seeley/Stephens/Tate Fifth Edition
(c) The McGraw-Hill Companies, Inc. 1

2. The Autonomic System ---simplified
The peripheral nervous system consist of:
Afferent neurons: from the periphery to CNS, Reflex loop (sensory - ascending)
Efferent neurons: from the CNS to periphery, Somatic motors – skeletal muscles
ANS – smooth muscles, cardiac muscle and glands
(motor – descending)
Innervation of these two systems differ:
Afferent neurons connect directly to CNS through synapses.

3. Efferent neurons of somatic division connect directly from the CNS to the skeletal muscles.
Efferent neurons of ANS, which have come out from the spinal cord goes through autonomic ganglions.
Preganglionic neuron (myelinated)--- autonomic ganglion --- postganglionic neuron (unmyelinated)
There are two types of ANS; sympathetic division and parasympathetic division.
The sympathetic division: preganglionic fibers from the T and L regions of the spinal cord make ganglia at the synaptic chain ganglia. They usually stimulate tissue metabolism, increases alertness, get ready for emergencies.
The parasympathetic division: they originate from the brainstem and the S region of the spinal cord. Conserve energies and sedentary. Also digestion.

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7. The neuro transmitters of ANS
Recall, the neurotransmitters for the afferent neurons and somatic efferent neurons is Ach.
In ANS both Ach and norepinephrine (NE), are used.
Cholinergic neurons use Ach..
Adrenergic neurons use NE.
In the sympathetic division:
Preganglionic neurons are cholinergic
Most of the post ganglionic neurons are adrenergic
While the postganglionic sweat glands, thermoregulaters are cholinergic.

8. In the parasympathetic division
Both preganglionic and postganglionic neurons are cholingeric (nicotinic or muscarinic), they generally excitatory (sm. muscles), but can be inhibitory (heart).
There are other neurotransmitters of ANS, such as, fatty acids like prostaglandins and peptides such as, gastrin, somatostatin, dopamine, etc…
Receptors of ANS
There are two types:
Cholinergic receptors: ( two subtypes)
Nicotinic receptors for nicotine (alkaloid from tobacco).
Found in postganglionic neurons in the autonomic neurons and skeletal muscles.
Muscrininc receptors for muscarine ( from mushrooms)
Found in the effector cell responding to Ach.

9. Ach on the nicotinic receptor opens Na+ channels ( excitatory)
Ach on the muscarinic receptors modulate G-proteins and the response could be either excitatory or inhibitory. Examples,
Ach + muscarine receptor of cardiac muscle is inhibitory.
Ach + muscarine receptor of smooth muscle is excitatory.

10. The action of NE on the adrenergic receptors; modulates G-proteins.
NE is released from the adrenergic postganglionic neurons of the sympathetic division ---- to adrenergic receptors of the effector cells.
Two types of adrenergic receptors could be found in the same cell, alpha receptors and beta receptors.
The action of NE on the adrenergic receptors;
modulates G-proteins.
The response could be either excitatory or inhibitory depending on the tissues. For example:
NE + beta receptor of cardiac muscles is excitatory.
NE + beta receptor of the stomach smooth muscle is inhibitory.
Both epinephrine and NE can bind to alpha and beta receptors.
Epinephrine binds to alpha or beta receptors equally.
NE binds to alpha more strongly than beta.

14. Dual innervations of organs with sympathetic and parasympathetic divisions with opposing or cooperative effects.
The sympathetic division has a more general effect than the parasympathetic division, because epinephrine and norepinephrine are released from the adrenal medulla and circulates through the circulatory system.
Review clinical focus.

16. The End. 8