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Chapter 16

Chapter 16. Anatomy & Physiology Fifth Edition Seeley/Stephens/Tate (c) The McGraw-Hill Companies, Inc. The Autonomic System --- simplified. The peripheral nervous system consist of : Afferent neurons : from the periphery to CNS, Reflex loop (sensory - ascending)

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Chapter 16

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

  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.

  4. 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.

  5. 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.

  6. Ach on the nicotinic receptoropens Na+ channels ( excitatory) • Ach on the muscarinic receptorsmodulate 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.

  7. Adrenergic receptors • 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.

  8. 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 theadrenal medulla and circulates through the circulatory system. • Review clinical focus.

  9. The End.

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