Chapter 8 Notes: The Autonomic Nervous System
Chapter 8 Notes: The Autonomic Nervous System BIOL 3160
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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.