CHAPTER 2 Neurophysiology AUTONOMIC NERVOUS SYSTEM What are the two structural divisions 1. Central nervous system of the human nervous system? 2. Peripheral nervous system What are the two f1111ctio11al divisions 1. Somatic nervous system of the human nervous system? 2. Autonomic nervous system (ANS) What is the function of the somatic Innervates skeletal muscle; largely nervous system? under voluntary control What is the function of the ANS? Maintenance of homeostasis through involuntary coordination of glandular, cardiac, and smooth muscle activity throughout the body What are the constituent parts of Enteric nervous system, sympathetic the ANS? nervous system (SNS), and parasympathetic nervous system (PNS) Generally speaking, what is the function of each part of the ANS? Enteric nervous system Coordination of various gut functions (motility, secretion, etc) (see Chap. 6) Sympathetic nervous system "Fight or flight" response. Coordinates the body's response to stressors. Parasympathetic nervous system "Rest and digest" response. Coordinates the process of energy conservation and replenishment. Where is the anatomic origin of SNS? lntermediolateral cell column of the spinal cord between segments. Tl to L3) (e.g., thoracolumbar) - ,\. · 11 Where is the anatomic origin Nuclei of cranial nerves (CN) III, VII, of the PNS? IX, and X aiici ~f>!nal cord segments S2 to S4 (e.g.,(sraniosacral spinal cord) 23 24 Deja Review: Physiology What type(s) of neurotransmitter(s) PNS and SNS preganglionic neurons and receptors are present in the use ACh as the neurotransmitter and pregn11glio11ic fibers of the PNS nicotinic receptors for transmission and SNS? Is the neurotransmitter/receptor No, while these receptors are nAChR combination used at the preganglionic (nicotinic Acetylcholine receptors) synapse the same as that used at the they differ from those at the NMJ. neuromuscular junction (NMJ)? The nicotinic subunits here have a different subunit makeup allowing for differences in pharmacologic influences Describe the axon length for the PNS and SNS in the following locations: PNS SNS Preganglionic nerve axon Long Short Postganglionic nerve axon Short Long Anatomically, where do most Either at the paravertebral chain preganglionic sympathetic fibers ganglion, or at collateral ganglia that synapse? follow large vessels in the abdomen (celiac, superior mesenteric, etc) Anatomically, where do most In microscopic ganglia associated with preganglionic parasympathetic the target organs fibers synapse? What receptor types are primarily used PNS: all receptors are muscarinic and at the effector organs of the PNS and ACh is the neurotransmitter SNS? What are their respective SNS: a 1, a2, /3 1, or /3 2; the primary neurotransmitters? neurotransmitter is norepinephrine (NE) There is an exception to the above Sweat glands have muscarinic receptors. rule regarding the SNS. What is it? The associated postganglionic SNS neurons release ACh. What is unique about the adrenal It is a specialized SNS ganglion where medulla? preganglionic fibers synapse directly with the effector organ (chromaffin cells) What does SNS stimulation of Secretion of epinephrine (Epi; 80'1\,) and chromaffin cells induce? NE (20%) into the circulation What is the purpose of releasing These substances activate organs that adrenal hormones into the circulation? receive little innervation (fat cells, hepatocytes etc) allowing them to assist in the stress response Neurophysiology 25 What are the SNS receptor types in the following locations and what are their effects? Heart SA node {3 1: increased pacemaker activity AV node {3 1: increased conduction velocity Myocardium {3 1: increased contractility Vascular smooth muscle Skin and splanchnic circuits Skeletal muscle and pulmonary circuits Peripheral veins c:x 1: constriction f32: dilation Eye Ciliary muscle fJ,y.relaxes muscle (for far vision) 2.. Radial muscle (Vt1i \\~\kl M\nffi'm) c:x 1: muscle contraction~ dilates pupil Bladder Detrusor muscle Bladder sphincter C:X 1: constricts Bronchioles Bronchial muscle {3 2: dilates smooth muscle Bronchial glands c:x 1: inhibits secretion {3 2: stimulates secretion Gastrointestinal tract Sphincters c:x 1: constricts Secretion c:x2: inhibition Motility c:x 1, c:x2, {32: decrease Kidney {3 1: increase renin secretion Male sex organs c:x 1: ejaculation Sweat glands Muscarinic: increase sweat production Adipose tissue {3 1, {33: increase lipolysis For which of the above SNS locations Vascular smooth muscle, kidney, sweat is there no corresponding PNS glands, fat cells, and liver innervation? 26 Deja Review: Physiology What is the mechanism of action for the following receptor types? Inositol 1,4,5-triphosphate (IP3) formation and increased intracellular [Ca2+] Adenylate cyclase inhibition and decreased cyclic adenosine monophosphate (cAMP) Adenylate cyclase activation and increased cAMP Adenylate cyclase activation and increased cAMP Nicotinic Ion channel for Na+ and K+ Muscarinic Heart (sinoatrial [SA] node): adenylate cyclase inhibition Smooth muscle and glands: IP3 formation and increased intracellular [Ca2+] What is the effect on the ANS of the following pharmacologic agents? A Ch Nicotinic and muscarinic agonist Albuterol /32 Agonist Atropine Muscarinic antagonist Butoxamine /32 Antagonist Carbachol Nicotinic and muscarinic agonist Cioni dine <Xz Agonist Curare Nicotinic antagonist Dobutamine /31 Agonist Hexamethonium Nicotinic antagonist (ganglion only) Isoproterenol /31 and /32 agonist Metoprolol (at therapeutic doses) /3 1 Antagonist Muscarine Muscarinic agonist Nicotine Nicotinic agonist NE a1 and /31 agonist Phenoxybenzamine a1, 2 Antagonist Phentolamine a 1, 2 Antagonist Phenylephrine a1 Agonist Prazosin a1 Antagonist Propranolol /31 and /32 antagonist Yohimbine <Xz Antagonist Neurophysiology 27 What autonomic centers are located in the following areas? Medulla Respiratory; swallowing, coughing, and vomiting; and vasomotor Pons Pneumotaxic Midbrain Micturition Hypothalamus Regulation of food and liquid intake and temperature regulation SENSORY SYSTEMS What four qualities of sensation must 1. Modality be encoded for effective transmission? 2. Location 3. Intensity 4. Duration What is a sensory receptor? A specialized cell that transduces physical environmental stimuli into neural signals What types of cells are usually Specialized epithelial and neuronal cells sensory receptors? What is meant by "receptive field"? Area on the body that changes the firing rate of its sensory neuron when stimulated What is the field called if it increases Excitatory the firing rate? What is the field called if it decreases Inhibitory the firing rate? A sensory receptor must transmit The receptors are simple transducers, its findings back to the CNS for each converting a different type of interpretation. How does the CNS energy into electrical impulses. These differentiate between an AP (action impulses follow defined pathways potential) from a retinal cell and an into the CNS and relay on specific AP from a somatosensory cell? nuclei. These pathways define how sensory perception is recognized. For an example of this, think about rubbing your eyes. That pressure is always perceived as flashes of light. How are afferent neurons of the By diameter (roman numerals I-IV) sensory systems classified? and conduction velocity (A and C) 28 Deja Review: Physiology Give the relative size of the following sensory neuron classifications: Largest II Medium III Small IV Smallest Give the relative conduction velocity of the following sensory neuron classifications: Aa Fastest A/J Medium Ao Medium c Slowest Describe the series of events that occur in sensory transduction. Sti111ulus acts on sensory receptor If an adcqm1tc stimulus intensity is achieved bAThre>h<>l<I D Receptor transduces this stimuli into Fails Succeeds a graded generator potential If graded potential Dexceeds threshold A train of action potentials is triggered. Low High Stimulus intensity is encoded by AP frequency and population coding. Figure 2.1 Sensory transduction sequence. What effect does intensity of the Larger stimuli create larger graded stimulus have on the receptor potentials (e.g., receptor potential) potential generated? What direction does the current Positive inward flow, depolarizing usually flow when sensory receptor the cell channels open? What is an exception to this flow Photoreceptors: stimulation decreases direction? inward current and hyperpolarizes the membrane Neurophysiology 29 As seen in Fig. 2.1, how does the Primarily with frequency coding; greater body encode intensity changes intensity leads to a higher frequency. in sensory stimuli? Also with population coding; a greater number of receptors will be triggered by a stimulus of increasing intensity. What is sensory adaptation? The dynamic change in the frequency of triggered AP's with a static stimuli; this occurs at the level of the receptor What types of adaptation do sensory Tonic (slowly adapting) and phasic receptors exhibit? (rapidly adapting) Which type of sensory adaptation detects Phasic the beginning of (onset) and the end of (offset) of a stimulus? What type of sensory adaptation responds Tonic consistently to prolonged stimuli? What type of sensory adaptation detects Tonic steady stimuli? What happens to action potential Decreases frequency in phasic receptors with constant stimulation? Label the three types of adaptation seen below: 2 Stimuli _J L Generator potential Action ---'11.1.1111 J.J.J.J..111111.J...J...LII I _,__I _--1.LLllI _._._II _,_I ----11-11--L-I__