Transcript Chapter 10
Lecture Exam 2 Material represented from chapters corresponding to ALL Nervous System Physiology Nervous System Physiology: – – – – – Intro., Resting Membrane Potential Ch. 5 (156-162) Nerve Impulse Conduction Ch. 8 Central Nervous Sys. (Functional Regions) Ch. 9 Sensory Physiology Ch. 10 Peripheral Nervous Sys. (ANS & SNS) Ch. 11 Stop at Muscle Physiology. Chapter 10 Sensory Physiology Perception and Sensation Figure 10-4: Sensory pathways Perception = interpretation of sensation, utilizing regions of the brain Sensation = conscience awareness of a stimulus event detected by sensory receptors Sensory Receptor Types Chemoreceptors – Respond to chemical ligands Mechanoreceptors – Respond to various forms of mechanical NRG Photoreceptors – Respond to light Thermoreceptors – Respond to temperature Nociceptors – Respond to pain Figure 10-1: Sensory receptors Sensory Transduction Converts Stimuli into Graded Potentials Transduction = conversion of stimulus NRG into info..that can be processed by the nervous system Adequate stimulus = NRG form to which receptors respond – i.e. light, temp., pain, mechanical NRG, ect.) Threshold stimulus = the minimum stimulus required to activate a receptor Generator potential – = graded potentials whose amplitude is proportional to the strength of the stimulus I.E. stronger stimulus, stronger generator potential If generator potential reaches threshold, it initiates an action potential that travels along the sensory neuron to the CNS Sensory Adaptation = reduction in sensitivity in the presence of a constant stimulus caused by a decreased generator potential thus causing a decreased number of action potentials per second sent over the sensory neuron decreased perception of sensation Phasic receptors rapidly adapting Tonic receptors slow adapting or do not adapt Pain, vision, & proprioception DO NOT adapt Receptive Fields of Neurons Fig. 10-2 Receptor fields of sensory neurons Convergence of primary sensory neurons allows Convergence of primary sensory neurons allows simultaneous, subthreshold stimuli to sum at the secondary simultaneous subthreshold stimuli to sum at the sensory neuronsensory & initiate an action potential. secondary neuron and initiate an action potential. Two-Point Discrimination Figure 10-3: Two-point discrimination Somatic Pathways Figure 10-9: Sensory pathways cross the body’s midline Somatic Senses Figure 10-10: The somatosensory cortex Temperature Free nerve endings Cold receptors – detect loss of heat (stimuli below body temp.) Warm receptors – detect gain of heat (stimuli above body temp.) Pain receptors Pain Nociceptors Fast pain – sharp, & localized – transmitted via alpha-delta (myelinated) fibers Slow pain – Duller, more diffuse – Transmitted via C (unmyelinated) fibers Referred Pain Figure 10-13: Referred pain Chapter 11 Efferent Division : Autonomic (ANS) and Somatic Motor Control (SNS) (Control of Body Systems) Autonomic Division: Homeostatic balancing Controls – Smooth & cardiac muscle – Glands & adipose Antagonistic branches – Parasympathetic "Rest & digest" Restore body – Sympathetic “Fright, fight, or flight" Energetic action Figure 11-1: Homeostasis and the autonomic division Autonomic Pathways: Communicate to Body Coordinates homeostatic responses – Autonomic – Endocrine – Behavioral Blood pressure Osmolarity Tonic regulation Antagonistic control Receptor directed response Figure 11-2: The hypothalamus and brain stem initiate autonomic, endocrine, and behavioral responses Autonomic Control Centers Hypothalamus – Water balance – Temperature – Hunger Pons – Respiration – Cardiac – Vasoconstriction Medulla – Respiration Figure 11-3: Autonomic control centers in the brain Comparison of Sympathetic Pathways Preganglionic neuron – Short – Origin: spinal cord – NT: cholinergic (ACh) Ganglia – Sympathetic chain – Near spinal cord – Nicotinic Receptor Postganglionic neuron – Long – NT: adrenergic (NE) Figure 11-7: Sympathetic and parasympathetic pathways Comparison of Parasympathetic Pathways Preganglionic neurons – Originate in Brain stem Lower cord – NT: cholinergic (ACh) Ganglion – Near target – Nicotinic receptors Postganglionic neuron – NT: cholinergic (ACh) Figure 11-7: Sympathetic and parasympathetic pathways Figure 11-5: Autonomic sympathetic and parasympathetic pathways Synapses in Autonomic Nerves Varicosities NT released to ECF No cleft Impact – Large area – Slow acting – Long duration Figure 11-8: Varicosities of autonomic neurons Acetylcholine synthesis & recycling Figure 8-21: Synthesis and recycling of acetylcholine at the synapse Norepinephrine Release and Recycling Figure 11-9: Norepinephrine release at a varicosity of a sympathetic neuron Autonomic Neurotransmitters Sympathetic Division Parasympathetic Division Neurotransmitter Norepinephrine Acetylcholine Synthesized (made) from Tyrosine Acetyl CoA + choline Inactivated by (ENZ) Monoamine oxidase (MAO) Acetylcholinesterase AChE ENZ location in Mitochondria of varicosity Synaptic cleft Varicosity of reuptake Norepinephrine Choline *Varicosity = swollen regions along autonomic axons that store and release neurotransmitters. Table 8-4-1: Major Neurocrines Adrenal Medulla: A Modified Sympathetic Ganglion Sympathetic stimulation – Catecholamine release to blood Epinephrine Norepinephrine – Travel to: Multiple targets Distant targets Figure 11-10: The adrenal medulla SENSITIVITY OF PERIPHERAL ADRENERGIC RECEPTORS TO CATECHOLAMINES Receptor Found In Sensitivity Second Messenger 1 Most sympathetic target tissue NE > E Activates phospolipase C 2 Gastrointestinal tract & pancreas NE > E Inhibits cAMP 1 Heart muscle, kidney NE = E Activates cAMP 2 Certain blood vessels and smooth muscle of some organs E > NE Activates cAMP NE = Norepinephrine (neurotransmitter) E = Epinephrine (hormone from adrenal medulla) Alpha Receptor Stimulation Norepinephrine 1 receptor 2 receptor Activates Phospholipase Reduces/Inhibits cAMP levels Release of Ca+2 Smooth muscle relaxation & decrease in gland secretion Smooth muscle contraction & gland secretion Beta Receptor Stimulation Epinephrine Activation of adenylate cyclase cAMP 1 Receptor 2 Receptor Stimulation of metabolism, cardiac muscle stimulation Inhibition and relaxation of smooth muscle in respiratory passageways and in blood vessels of skeletal muscles Receptor Agonists (mimics) Cholinergic Antagonists (blockers) Acetylcholine Indirect Agonists/Antagonists AChE* inhibitors: neostigmine; parathion Inhibits ACh release: botulinus toxin Muscarine Atropine; scopolamine Nicotine -bungarotoxin (muscle only), tetraethylammonium (TEA) (ganglia only), curare Muscarinic Nicotinic Adrenergic Norepinerphrine; Epinephrine Stimulates NE release: ephedrine, amphedimines Prevents NE uptake: cocaine Pheylephrine “alpha-blockers” Isopreterenol “beta-blockers”; propranolol (1 & 2); metoprolol (1 only) *AChE = acetylcholinesterae Review of Efferent Pathways: Motor & Autonomic Figure 11-11: Summary of efferent pathways COMPARISION OF SNS & ANS SOMATIC AUTONOMIC 1 2 Number of neurons in efferent pathway Neurotransmitter/receptor at neuron-target synapse ACh (nicotinic) ACh (muscarinic) or NE ( or ) Target tissue Skeletal Muscle Smooth and cardiac muscle; some endocrine and exocrine glands; some adipose tissue Structure of axon terminal regions Boutons Boutons and varicosities Effects on target tissue Excitatory only: muscle contracts Excitatory or Inhibitory Peripheral components found outside the CNS Axons only Preganglionic axons, ganglia, postganglionic neurons Summary of function Posture and movement Visceral function, including movement in internal organs & secretion; control of metabolism Somatic Motor Division: Controls Skeletal Muscles Body movement Appendages Locomotion Single neuron – CNS origin – Myelinated Terminus – Branches – Neuromuscular junction Figure 11-11: Summary of efferent pathways Neuromuscular Junction: Overview Terminal boutons Synaptic cleft – Matrix – AChE – Hold together End motor plate – On muscle – Nicotinic receptors Figure 11-12: Anatomy of the neuromuscular junction Neuromuscular Junction: Mechanism of Signal Conduction Axon terminal – AP signals – ACh release Motor end plate – 2 ACh bind – opens cation channel – Na+ influx – Membrane depolarized Stimulates fiber contraction Figure 11-13: Events at the neuromuscular junction Summary Autonomic branches: sympathetic and parasympathetic – Regulate glands, smooth & cardiac muscles – Team with endocrine to regulate homeostasis – Are regulated by hypothalamus, pons & medulla – Have pathways with 2 neurons and a ganglion – Use varicosities to release NTs – Have diverse receptors: tonic & antagonistic regulation Summary Somatic Control Efferent motor neurons control skeletal muscles – Single long myelinated neuron from CNS – Neuromuscular junction structure & mechanism