Transcript 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) – 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. • 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. • 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. • 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: 1. 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. • 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. 2. 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. • 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. The End.