Autonomic Nervous System - Western University - PDF

©  Autonomic Nervous System Dr. Sean McWatt, PhD [email protected] Functional Overview Central nervous system Peripheral nervous system Sensory Motor...

©  Autonomic Nervous System Dr. Sean McWatt, PhD [email protected] Functional Overview Central nervous system Peripheral nervous system Sensory Motor Autonomic Somatic Somatic Autonomic Viscera and enteroceptors Body Skeletal muscle Organs and glands Voluntary control Involuntary control This lecture primarily focuses on the autonomic nervous system, but we will compare it to the Parasympathetic Sympathetic Feed and breed Fight, flight, or fright structure and function of the Rest and digest somatic nervous system as well Adapted from Dr. Danielle Brewer-Deluce Learning Outcomes By the end of this lesson, you will be able to… Define homeostasis and explain its role and importance in bodily function Describe the role of the autonomic system in maintaining homeostasis and contrast it with the structure and function of the somatic system Differentiate between the functions of the sympathetic and parasympathetic nervous systems and describe their structural anatomy Consider the interface between somatic and autonomic systems. Can it be leveraged? Homeostasis Let’s try an experiment… These processes are automatic and happen unconsciously to Close your eyes and pay attention to your heart rate… maintain a stable state in our body How fast is it beating? Now, stand up as fast as you can! While standing, feel your pulse… Has you heart rate changed? Why? Homeostasis Greek: “Similar state” Homeostasis is a neutral state that is maintained in the body for stability despite changing internal and external environments Google Nest This happens unconsciously! Copyright © Dreamstime Stock Photos  Homeostasis Hypothalamus Receives sensory input from peripheral nervous system and reacts to maintain homeostasis Visceral pain Sends motor signals to Cerebrum Stretch receptors cardiac muscle, smooth Chemoreceptors muscle, and glands The hypothalamus is the main area of the brain responsible for receiving and integrating sensory information and generating a motor response to maintain homeostasis Diencephalon Pituitary gland Attached to hypothalamus by the infundibulum Ever been `hangry’? Brainstem Cerebellum The pituitary gland is an endocrine structure that is closely related to the hypothalamus Medial view (left hemisphere) Gilroy, Anatomy: An Essential Textbook, Copyright © 2013 by Thieme and plays a large role in regulating our mood Homeostasis Example Standing up… Here, we are Accordingly, we leveraging our somatic can use exercise to system (i.e., lower limb manipulate our muscles) to force our Carotid autonomic state in sinus autonomic system into a productive and a sympathetic state healthy way Aorta Arch Decreased firing rate Gravity causes Blood pressure Integrated in of visceral receptors blood to pool in drops in systemic brainstem and in carotid sinus and lower limbs arteries hypothalamus arch of aorta Balance restored! Increase in Increase in Efferent (motor) pathway heart rate and blood pressure ↑SNS activity and ↓PSNS activity contraction force Introduction to the ANS Autonomic Nervous System Component of the peripheral nervous system (PNS) Involuntary control of viscera (organs) Parasympathetic nervous system (PSNS) “Rest and digest” “Feed and breed” Sympathetic nervous system (SNS) “Fight, flight, or fright” Drake, Gray’s Anatomy for Students, 2nd Ed., Copyright © 2009 by Churchill Livingstone Somatic vs. Autonomic Autonomic: Visceral afferents Sensory input from organs Parasympathetic Visceral efferents (PSNS) Motor output to organs Smooth muscle Cardiac muscle Somatic: Glands General sensory Musculoskeletal All sympathetic movements and innervation travels through the reflexes (motor) sympathetic trunk, whereas the parasympathetic system is craniosacral, meaning it involves cranial nerves and sacral spinal nerves Anterolateral view Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins Somatic vs. Autonomic Neurons Somatic Motor The somatic motor system is a one- neuron system Visceral Motor The visceral motor systems involve two neurons: a presynaptic neuron extending from the CNS and a Presynaptic Ganglia Postsynaptic a.k.a. Preganglionic a.k.a. Postganglionic postsynaptic neuron in the PNS Drake, Gray’s Anatomy for Students, 2nd Ed., Copyright © 2009 by Churchill Livingstone Autonomic Nervous System Remember: myelinated The length of SNS Central Nervous System PSNS the presynaptic fibers appear white! neuron dictates Short where the Presynaptic neuron peripheral Sympathetic Begin in CNS ganglia will Long ganglion Acetylcholine Myelinated be found Parasympathetic Long Acetylcholine ganglion Postsynaptic neuron Short Synapse in (Nor)epinephrine periphery with Acetylcholine Target Organ neuron from CNS Target Organ a.k.a. Unmyelinated ADRENALINE Impacts of Autonomic System SNS: ↑ Heart rate and SNS: ↓ Saliva and tear contraction force production/excretion PSNS: ↓ Heart rate and PSNS: ↑ Saliva and tear contraction force production/excretion SNS: Bronchodilation, faster breath rate SNS: Pupillary dilation SNS only: Sweat gland PSNS: Bronchoconstriction, PSNS: Pupillary constriction excretion and slower breath rate hair erection SNS: Orgasm/ejaculation; ↓ Urinary function SNS: ↓ Digestive activity, blood diverted to periphery PSNS: Arousal/erection; ↑ Urinary function PSNS: ↑ Digestive activity https://www.mskcc.org/cancer-care/types/salivary-gland/salivary-glands-anatomy Drake, Gray’s Anatomy for Students, 2nd Ed., Copyright © 2009 by Churchill Livingstone Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins Sympathetic System  Sympathetic Trunk Cervical spinal cord Central canal CSF Gray Posterior horn matter Sensory input “H” Lateral horn Sympathetic output Anterior horn Motor output Sympathetic neurons Thoracic spinal cord White matter arise from the lateral horn of the spinal cord at levels T1 – L2 and join the sympathetic trunk Transverse view Drake, Gray’s Anatomy for Students, 2nd Ed., Copyright © 2009 by Churchill Livingstone Anterolateral view Sympathetic Trunk Signals can only leave sympathetic trunk – they can’t join Above T1 Neurons ascend or descend the All sympathetic sympathetic trunk to fibers enter the carry sympathetic sympathetic trunk between T1 and L2 (fight, flight, or fright) spinal levels signals throughout the periphery Below L2 Signals can only leave sympathetic trunk – they can’t join  Sympathetic Trunk Left sympathetic trunk/chain Paravertebral ganglia Right Left sympathetic sympathetic trunk/chain trunk/chain Sympathetic ganglia White rami Because they are communicantes myelinated, the Right Gray rami presynaptic neurons sympathetic communicantes create white rami trunk/chain communicantes Unmyelinated postsynaptic neurons where they enter the create gray rami comminicantes as sympathetic trunk they leave the sympathetic trunk Anterior view Anterolateral view Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins Drake, Gray’s Anatomy for Students, 2nd Ed., Copyright © 2009 by Churchill Livingstone Sympathetic Pathways Presynaptic neuron Postsynaptic neuron Target organ Gray ramus communicans Unmyelinated Target organ Sympathetic neurons can synapse and exit the same level that they originated Target organ at, OR they can ascend or descend to synapse and exit at different levels Anterior view Copyright © 2011 by Pearson Education Inc.  Sympathetic Pathways T1 L2 Because there is no input to the sympathetic trunk above T1 or below L2, there are no Anterior views white rami communicantes in those areas Drake, Gray’s Anatomy for Students, 2 nd Ed., Copyright © 2009 by Churchill Livingstone Sympathetic Pathways Presynaptic neuron Postsynaptic neuron Alternatively, presynaptic neurons can exit the sympathetic trunk without synapsing, forming splanchnic nerves that synapse at more distal Prevertebral ganglia in the Abdominal and pelvic organs ganglion abdomen Anterior view Copyright © 2011 by Pearson Education Inc. Sympathetic Pathways Presynaptic neuron The presynaptic neurons can even follow these splanchnic nerves all the way to the suprarenal (adrenal) glands and synapse directly within them Abdominal and pelvic organs Adrenal glands Anterior view Copyright © 2011 by Pearson Education Inc.  Referred Pain Brain can’t tell Sympathetic the difference! nervous system Interprets pain as coming from periphery Visceral afferent (sensory) neuron Following posterior pathway with somatosensory fibers C4 T5 The visceral sensory fibers of the sympathetic system follow the same pathway as the somatic sensory fibers, which confuses our brain Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins Referred Pain: Example Vagus n. PSNS In the case of the heart, this means that pain is referred back to the same level as Splanchnic nn. our upper limb PSNS and chest Visceral pain signal Anterior view Posterior view Anterior view confused by the brain… thinks it’s coming from the somatic system C4 brain… To the T5 Cardiac plexus Mixed SNS and PSNS Visceral afferent neuron Infarction Sensory ↓ Oxygen = pain Anterior view Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins Parasympathetic System  Autonomic Pathways Parasympathetic nervous system Cranial Sympathetic nervous system nerves The parasympathetic system is craniosacral, meaning its components arise from the brain and sacral region Pelvic nerves S2-S4 Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins Extra Info: Cranial Nerves Twelve pairs of nerves (bilateral) 1. Olfactory n. (CN I) 2. Optic n. (CN II) General somatic: 3. Oculomotor n. (CN III) Skeletal muscle, skin 4. Trochlear n. (CN IV) 5. Trigeminal n. (CN V) General visceral: 1. Ophthalmic n. (CN V1) Blood vessels, glands, 2. Maxillary n. (CN V2) intraocular muscles 3. Mandibular n. (CN V3) 6. Abducent n. (CN VI) 7. Facial n. (CN VII) Special somatic: 8. Vestibulocochlear n. (CN VIII) Vision, hearing 9. Glossopharyngeal n. (CN IX) 10. Vagus n. (CN X) Special visceral: 11. Spinal accessory n. (CN XI) Taste, smell 12. Hypoglossal n. (CN XII) Don’t memorize all of these While there are 12 cranial nerves in total, we will focus in on the four that have autonomic (parasympathetic) functions Gilroy, Anatomy: An Essential Textbook, Copyright © 2013 by Thieme Oculomotor n. (CN III) Oculomotor n. Dilation lets more light in, CN III Dim ight constriction lets less light in Bright l ligh t The oculomotor n. also has a large role in motor to the muscles that move the eye Inferior view Dilator pupillae m. Constriction Dilation of of pupil Postsynaptic pupil Postsynaptic neuron neuron Presynaptic neuron Sympathetic trunk (T1 – T4) Sphincter pupillae m. Sympathetic Oculomotor n. (CN III) Parasympathetic Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins Moore: Clinically Oriented Anatomy, 7th Ed. Copyright © 2014 by Lippincott Williams and Wilkins  Facial n. (CN VII) Parasympathetic fibres to lacrimal glands and mucosa of nose and palate Special sensory (taste) to anterior tongue Parasympathetic fibres to sublingual and submandibular glands Salivary glands Motor fibres to muscles of facial Facial n. expression CN VII The lacrimal glands produce and excrete tears in the eyes, while the sublingual and submandibular glands produce and excrete saliva in the mouth Mucosal glands produce mucus that lubricates the nasal and oral cavities, and helps to process Inferior view Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins air entering out respiratory system  Glossopharyngeal n. (CN IX) Sagittal view (right) Parasympathetic to parotid gland Visceral sensory from General and carotid sinus special sensory to Chemoreceptors posterior 1/3 of Motor to tongue Glossopharyngeal n. CN IX pharyngeal muscles The parotid gland produces and excretes saliva into the mouth to aid in digestion The carotid sinus contains chemoreceptors that Inferior view help to sense changes in our blood pressure Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins  Vagus n. (CN X) The vagus n. (CN X) is the most widespread cranial nerve, providing the vast majority of parasympathetic innervation to the body Its name literally means ‘wanderer’ Parasympathetic innervation to thoracic and upper abdominal organs Vagus n. CN X How can we leverage this dominance? Inferior view Agur and Dalley, Grant’s Atlas of Anatomy, 13th Ed. Copyright © 2013 by Lippincott Williams and Wilkins Let’s take a minute to breathe! Phrenic nn. Close your eyes and take five conscious breaths… Somatic (voluntary) What did you notice about your heart rate? Did you notice any changes or feelings in your digestive system? Is your breathing pattern any different from before you took that minute to pause? While I’m no meditation coach, there is strong evidence that mindful breathing can leverage the somatic system (phrenic n.) to activate the parasympathetic system (vagus n.) and reduce the harmful effects of chronic stress (sympathetic activity) Diaphragm Primary muscle of respiration Give it a try! Anterior view Netter, Atlas of Human Anatomy 6th Ed., Copyright © 2014 by Elsevier Summary Parasympathetic Summary Oculomotor n. (CN III) Pupillary constriction Facial n. (CN VII) Production of tears (lacrimal gland) Production of saliva (sublingual and submandibular glands) Production of mucus (nasal cavity and palate) Glossopharyngeal n. (CN IX) Production of saliva (parotid gland) Vagus n. (CN X) Bronchi and lungs Heart Esophagus, foregut, and midgut Gilroy, Anatomy: An Essential Textbook, Copyright © 2013 by Thieme Autonomic Sympathetic Summary Parasympathetic Cranial nerves T1 CN III (oculomotor n.) Lung CN VII (facial n.) CN IX (glossopharyngeal n.) CN X (vagus n.) L2 S2 Sympathetic S4 Gilroy, Anatomy: An Essential Textbook, trunk/chain Copyright © 2013 by Thieme Nervous System Comparison Learning Outcomes By now, you should better understand how to… Define homeostasis and explain its role and importance in bodily function Describe the role of the autonomic system in maintaining homeostasis and contrast it with the structure and function of the somatic system Differentiate between the functions of the sympathetic and parasympathetic nervous systems and describe their structural anatomy Consider the interface between somatic and autonomic systems. Can it be leveraged?  © [email protected]