Lecture 2 - Autonomic Nervous System, Membrane Potentials, Action Potentials PDF

Lecture 2: The Autonomic Nervous System Readings: Marieb and Hoehn Chapter 14 Sherwood and Ward Chapter 5 Objectives Knowledge Divisions of the ANS Differences between PNS and SNS General anatomical characteristics of the ANS Application Predict the neurotransmitter releas...

Lecture 2: The Autonomic Nervous System Readings: Marieb and Hoehn Chapter 14 Sherwood and Ward Chapter 5 Objectives Knowledge Divisions of the ANS Differences between PNS and SNS General anatomical characteristics of the ANS Application Predict the neurotransmitter released by different neurons of the ANS Describe how different organs respond differently to the same stimulus 2 Objectives Today’s focus Peripheral nervous system and types of receptors Neurons and resting membrane potential Graded potentials and action potentials 3 Peripheral Nervous System and Types of Receptors Somatic vs autonomic nervous system 5 Autonomic nervous system Involuntary, unconscious Motor neurons that innervate smooth muscle, cardiac muscle and glands. Regulates functions such as: – Heart rate – Blood pressure – Breathing – Pupil size – Bladder - Energy availability – Gut motility - Metabolism 6 Autonomic nervous system Activity regulated by CNS (spinal cord, brain stem, hypothalamus, cerebral cortex) Hypothalamus: – Integration center that receives inputs from the brain, sensory afferents and blood – Processes information and triggers both ANS (short term) and hormonal (long term) responses Brain stem Spinal cord – Reflexes integrated at the spinal cord level but are subject to conscious inhibition 7 Autonomic nervous system There are two divisions of the ANS: – Sympathetic Nervous System (SNS) – Parasympathetic Nervous System (PNS) They innervate (mostly) the same visceral organs, but have opposite effects. The SNS acts to mobilize the body’s energy stores. – Fight or flight The PNS acts to conserve the body’s energy stores. – Rest and digest They work together to maintain homeostasis. 8 SNS vs. PNS: Function 9 SNS vs. PNS: Anatomy The SNS and PNS differ in: Origin Fiber Length Location of Ganglia/Synapse Branching 10 Sympathetic nervous system Origin – Thoracolumbar (T1-L2) (lateral column of spinal cord) Fiber Length – Short preganglionic – Long postganglionic Ganglia / Synapse – Far from effector organ Branching – Extensive Neurotransmitter – Norepinephrine (sometimes Ach)* Ach = Sweat glands 11 Sympathetic Nervous System EpiPen Example of a drug that affects SNS Used in severe allergic reactions that cause anaphylactic shock – Blood pressure falls and airways close Epinephrine is injected, and results in SNS stimulation – Increases HR and contractility – Increases blood pressure – Vasoconstriction – Bronchodilation 12 Parasympathetic Nervous System Origin – Craniosacral (CNs, S2-S4) Fiber Length – Long preganglionic – Short postganglionic Ganglia / Synapse – Near or in effector organ Branching – Minimal Neurotransmitter – Acetylcholine 13 Parasympathetic Nervous System Cranial Outflow – Cell bodies in the brainstem – Supplies head, thorax, most of abdomen. Oculomotor nerve (CN III) – Constriction of eye pupil (miosis) Facial nerve (CN VII) – Lacrimal, nasal, salivary glands Glossopharyngeal nerve (CN IX) – Parotid gland 14 Parasympathetic Nervous System Cranial Outflow – Cell bodies in the brainstem – Supplies head, thorax, most of abdomen. Vagus nerve (CN X) – 90% of preganglionic parasympathetic fibers – Heart – Lung – Digestive tract (not large intestine) – Liver and gallbladder – Pancreas 15 Parasympathetic Nervous System Sacral Outflow – Cell bodies are in the ventral horn of S2-S4. – Supplies rest of abdomen, pelvis. S2-S4 – Large Intestine – Rectum – Bladder – Vagina & clitoris – Penis 16 Autonomic nervous system: Neural outflow Coles Notes Version Somatic: Skeletal muscle -Ach SNS: Smooth muscle, gland, heart -Ach, ganglion, norep -Ach, adrenal, ep/norep (blood) PNS: Smooth muscle, gland, heart -Ach, ganglion, Ach 17 Autonomic nervous system: Recap Parasympathetic Sympathetic “Rest and digest” “Fight-or-flight” system system Increased excitability Energy conservation Increased ability to “D” division perform physical work – Digestion Stress response – Defection “E” division – Diuresis – Exercise – Emergency – Excitement – Embarrassment 18 Cholinergic and Adrenergic Fibers Cholinergic Adrenergic Acetylcholine (Ach) Norepinephrine (NE) secreting secreting All preganglionic neurons Most postganglionic Most postganglionic neurons neurons of sympathetic NS of parasympathetic NS α1, α2, β1, β2 receptors Muscarinic and nicotinic receptors 19 Cholinergic Receptors Muscarinic Nicotinic G-protein coupled receptor Ligand gated cation channel Found in effector cells Found in synapses between stimulated by postganglionic pre- and postganglionic fibers synapses Ach binding always stimulatory, causing cell depolarization 20 Adrenergic Receptors α1 β1 - Vasoconstricti - Increase heart on rate & - Relax GI s.m. contractility - Glycogenolysi - Renin release s - Sweat gland secretion - Dilates pupils β2 α2 - Glycogenolysi - Vasoconstrictio s n - Gluconeogene - Decreased sis secretion from - Smooth salivary glands muscle relaxation - Increase 21  Conclusions: The ANS includes the sympathetic and parasympathetic nervous systems and is responsible for regulating non- voluntary systems of the body and body homeostasis The parasympathetic nervous system is energy saving and the sympathetic nervous system is energy consuming The parasympathetic nervous system has fibers that exit the brainstem and the sacrum The sympathetic nervous system has fibers that exit the spinal cord in the thoracic and lumbar regions Acetylcholine and norepinephrine are the neurotransmitters of the ANS, their actions are dependent on the receptors present on the target tissues The ANS regulates almost every organ in the body 22  Lecture 2 Pop Quiz 1) What are the two divisions of the autonomic nervous system? 2) List three changes to your body that occur when you get scared? 3) After a meal when you are relaxing, what cranial nerve is active in keeping your heart rate low? 4) What are the differences in nerve cell length and neurotransmitters between the two autonomic systems? 5) Why does stress kill people?