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Chapter 8 Notes: The Autonomic Nervous System

by: Olivia Addis

Chapter 8 Notes: The Autonomic Nervous System BIOL 3160

Marketplace > Clemson University > Biological Sciences > BIOL 3160 > Chapter 8 Notes The Autonomic Nervous System
Olivia Addis

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Notes from lecture and the textbook.
Human Physiology
Dr. Tamara McNutt-Scott
Class Notes
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This 4 page Class Notes was uploaded by Olivia Addis on Tuesday February 23, 2016. The Class Notes belongs to BIOL 3160 at Clemson University taught by Dr. Tamara McNutt-Scott in Fall 2015. Since its upload, it has received 35 views. For similar materials see Human Physiology in Biological Sciences at Clemson University.


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Date Created: 02/23/16
Chapter 9: The Autonomic Nervous System  Autonomic Nervous System Neurons  The neurons of the ANS innervate organs who are not under voluntary control,  but function involuntarily including: cardiac muscle, smooth muscle, and glands.  o Unlike somatic pathways for voluntary control that is just 1 neuron that  originates in the CNS and goes directly to the effector organ, ANS  neurons have a 2­neuron pathway.  The ganglion of the first neuron is located in the gray matter of the  CNS, and the first neuron is called the preganglionic neuron  because it synapses with a ganglion of the PNS, and the axon of  that neuron is called the postganglionic neuron. The postganglionic neuron will synapse at the effector organ (CM, SM, or glands).   Autonomic control is important for organ systems.   There are multiple features that the autonomic neurons possess: o Resting tone (tension) in the absence of nerve stimulation, which is  maintaining a baseline­firing rate that can be either increased or decreased. o Denervation hypersensitivity – autonomic nerve damage will lead to an  increase in target tissue sensitivity to stimulating agents.  in order to compensate for the nerve; to allow for balance for  homeostatic purposes  o Autonomic innervation – target tissues display autorhythmicity, which is  the ability of organs to be stimulated independent of their innervation, but  this occurs through depolarization in the tissues.   the innervation will work to increase or decrease tissue activity  Divisions of the ANS – Sympathetic and Parasympathetic Systems Work Together  Sympathetic: also called the thoracolumbar division because it originates from  the thoracic and lumbar regions of the spine.   gas; “fight or flight” responses o Form component of the spinal nerve; therefore the preganglionic neuron is myelinated and the postganglionic neuron is unmyelinated. o Sympathetic chain ganglion parallels – collateral ganglia – the spinal  cord on each lateral side so ganglia are close to the CNS.  o Observes divergence (1 branches to synapse with many) and convergence (many synapse with 1).  o Mass activation is allows the sympathetic division to be constantly active  to a certain degree and to increase its activity in response to “fight or  flight” situations.   Due to working together in mass activation, sympathetic division  and adrenal medulla make up the sympathoadrenal system.  Parasympathetic: also called the craniosacral division because it originates from  the brain (midbrain, pons, and medulla) and the sacral region of the spine.   brake; rest and digest responses o Synapse in ganglia that are next to or in the target organ – ganglia called  terminal ganglia o Supply the postganglionic fibers that synapse with the effector cells. o Not associated with spinal nerves, but some cranial nerves; sacral region  associated with parts of the large intestine, rectum, and urinary and  reproductive systems.  Neurotransmitters  The two divisions have different effects because they release different  neurotransmitters.   Acetylcholine (ACh) is the NT of all preganglionic axons, meaning that this  occurs in both divisions of the ANS.  o Ach is released by postganglionic axons in the PNS, making the  transmission at those synapses cholinergic. o Norepinephrine (NE) is released by postganglionic axons in the SNS,  making the transmission at those synapses adrenergic.   Few SNS that innervate blood vessels in SkM and sweat glands are cholinergic (release ACh).   Variscosities (diffuse synapse) are swellings that contain NT so that NT could be  released along an axon rather than just at a terminal.  synapse in passing with  their target cells.   Parasympathetic and Sympathetic divisions can innervate the same target cells  with antagonistic effects.  o The axon of the parasympathetic neuron will release ACh and inhibit. o The axon of the sympathetic neuron will release NE and enhance the cell.  Sympathetic and Adrenal medulla are related so the medulla  releases epinephrine and norepinephrine. These NT plus dopamine  (released in CNS) make up amino derivatives known as  catecholamines.  Adrenergic Stimulation – norepinephrine and epinephrine are released as NT  Epinephrine in the blood and norepinephrine released from sympathetic nerve  endings.  heart and smooth muscle are stimulated to contract.  o “fight or flight” boost the ability of the CV system to respond to physical  emergencies.   Response of target tissue dependent on receptor due to the presence of different  receptor proteins. o Alpha and beta adrenergic receptors with different subtypes.  Different subtypes cause vasoconstriction in viscera and skin,  increased HR and contractility, and bronchoconstriction.  o Act via G­proteins  causes the opening or closing of ion channels in the  PM or the activation of an enzyme in the membrane  Begins the sequence that culminates the effects on the target cells.  Clinical Application: drugs can be agonists (stimulate) or antagonists (block  action).  o The use of drugs that specifically stimulate/block various receptors can be  used to clinically treat diseases.   Ex: propranolol, which is used for hypertension by use of non­ selective beta­blockers  lowers cardiac rate an BP due to  hypertension Cholinergic Stimulation – ACh is NT   Preganglionic release is always excitatory, postganglionic release can be either  excitatory or inhibitory.  o Response is receptor type­dependent, with subtypes.  o Types of receptors include: nicotinic or muscarinic.  Nicotinic – direct process that causes depolarization because ACh  opens cation channels in the receptor  excitatory  Muscarinic – indirect process because of the G­protein mechanism; can either cause hyperpolarization by opening K channels, causing  inhibition and decreasing HR or cause depolarization by closing K  channels, causing excitation like causing the smooth muscles in the digest tract to contract  o Other auntonomic NTs referred to as nonadrenergic, noncholinergic fibers  – Ex: ATP, BIP, Nitric Oxide  Organs With Dual Innervation – Innervated by Both PNS and SNS  Three different possible actions in dual innervation: o Antagonistic: two systems cause opposite effects; Ex: HR because PNS  lowers HR and SNS raises HR. o Complimentary: Either division will cause similar effects; Ex: Saliva  production occurs with stimulation of the PNS or the SNS; PNS causes  normal saliva production and SNS causes thicker saliva.  o Cooperative: Different effects by PNS and SNS, but they work together to  complete a single action; Ex: “Point and shoot” for the penis, requiring  stimulation of both to occur – Parasympathetic “points” causing erection  and sympathetic “shoots” causing ejaculation.  Organs without Dual Innervation – Only Sympathetic  Includes: adrenal gland, arrector pili muscle, sweat glands and most blood vessels. o Sweat glands secrete a chemical called bradykinin in response to  sympathetic stimulation, which then stimulates the dilations of the blood  vessels near the sweat glands.  Increase blood flow helps to eliminate heat.   Regulation achieved by increasing or decreasing in tone (firing rate) of SNS  fibers. Control of ANS by Higher Brain Centers  Autonomic reflexes, involving sensory information to brain centers and then  responses by modifying preganglionic neuron activity, will regulate visceral  functions.  The medulla houses neural centers that control ANS activity, but is ultimately  responsive to the hypothalamus, which is a higher brain center and as the  “homeostatic control center” regulates the ANS.   Limbic system – visceral response to emotional states.  Cerebellum – impulses from the cerebellum to the medulla influence the activity  of the ANS. o Motion sickness is the  cerebellum responding to the change in motion. 


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