Anatomy of the Autonomic Nervous System PDF

Kubalak – 2022-2024 Anatomy of the Autonomic Nervous System Anatomy of the Autonomic Nervous System Steven W. Kubalak, PhD Professor, Department of Regenerative Medicine and Cell Biology BSB Room 615C Email: [email protected], Phone: 2-0624 OUTLINE 1. Introduction 2. Central Nervous System a. Brai...

Kubalak – 2022-2024 Anatomy of the Autonomic Nervous System Anatomy of the Autonomic Nervous System Steven W. Kubalak, PhD Professor, Department of Regenerative Medicine and Cell Biology BSB Room 615C Email: [email protected], Phone: 2-0624 OUTLINE 1. Introduction 2. Central Nervous System a. Brain and Spinal cord 3. Peripheral Nervous Systems a. Cranial nerves b. Spinal nerves 4. General histology of a nerve 5. Motor pathway 6. Sensory pathway 7. Spinal cord a. Rootlets, Roots, Spinal Nerve b. Dorsal primary rami c. Ventral primary rami 8. Somatic Plexuses a. Cervical, Brachial, Lumbar, Sacral 9. Parasympathetic System a. Preganglionic vs postganglionic neurons b. Function 10. Sympathetic System a. Preganglionic vs postganglionic neurons b. Rami Communicantes 11. ANS Function (in general) 12. Afferent System a. Referred pain b. Dermatomes c. Myotomes OBJECTIVES 1. Describe the structural organization of the central nervous system, the peripheral nervous system and the autonomic system 2. Name and describe the main function(s) of each of the 12 cranial nerves 3. Describe the similarities and differences of afferent and efferent neurons of the nervous system 4. Describe the structures forming the spinal cord as well as how these structures contribute to the formation of the different plexuses 5. Describe how the brachial plexus forms 6. Describe the specific features and function of the sympathetic and parasympathetic systems. READING REFERENCE Text: Gray’s Anatomy for Students, 4th edition, by Drake et al.: pages 29-48 1 Kubalak – 2022-2024 Anatomy of the Autonomic Nervous System INTRODUCTION Slides 1 and 2 In this lecture, we will describe the main features of the nervous system. We will discuss the essential components of the central and peripheral nervous systems as well as the autonomic system. We will also introduce (or in a few cases, revisit) some of the terminology needed throughout the curricula. CENTRAL AND PERIPHERAL NERVOUS SYSTEMS CNS • Brain • Spinal cord Slides 3, 4, and 5 The nervous system is classically divided in the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and the spinal cord whereas the PNS includes the 12 pairs of cranial nerves and the 31 pairs of spinal nerves and associated ganglia. Part of the PNS includes the autonomic nervous system (ANS). PNS • 12 pairs of cranial nerves • 31 pairs of spinal nerves • Sensory component o Afferent • Motor component o Efferent 1o Somatic 2o Visceral (Autonomic, ANS) o Sympathetic System o “Stressful” o Parasympathetic System o “Peaceful” o Enteric System [Figure 1.32 Gray’s Anatomy for Students 4e] The autonomic nervous system, also called visceral system, innervates parts of the body that are not normally under voluntary control. This includes smooth muscle, cardiac muscles and glands, for example. Functionally, the ANS consists of the sympathetic system (stressful part of the ANS), the parasympathetic system (peaceful part of the ANS), and the enteric system in the gastrointestinal tract. We will discuss in more details the ANS by the end of this lecture. [Purves Neuroscience 6e, Figure 1.12] 2 Kubalak – 2022-2024 Anatomy of the Autonomic Nervous System You will need to know both the number (Roman numerals) and the name of each cranial nerve: • • • • • • • • • • • • CN I CN II CN III CN IV CN V CN VI CN VII CN VIII CN IX CN X (CN XI) CN XII Olfactory Optic Oculomotor Trochlear Trigeminal Abducent Facial Vestibulocochlear Glossopharyngeal Vagus (Spinal Accessory) Hypoglossal Slide 6 and 7 [Netter 129 &170, respectively] This ventral view of the brain allows us to visualize of the 12 pairs of cranial nerves. The image at right (Slide 5) shows the 31 pairs of spinal nerves. We will have another lecture entirely dedicated to the vertebral column and spinal cord. We will discuss at that time the layers covering the spinal cord (dura matter, arachnoid, and pia matter). Otherwise, note that the spinal cord extends from the base of the skull to the level of the first or second lumbar vertebra (L1-L2) (see details later) and that 31 pairs of spinal nerves leave the spinal cord in a very organized manner. At this stage, know that the 31 spinal nerves are divided as follows: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. 31 pairs of spinal nerves • 8 cervical NN C1-C8 • 12 thoracic NN T1-T12 • 5 lumbar L1-L5 • 5 sacral NN S1-S5 • 1 coccygeal N Coc1 Connective tissue (CT) coverings, from the inside-out: Slide 8 A peripheral nerve is composed of many neurons that are organized, bound, and wrapped by connective tissue. The connective tissue has different names depending on what component of the nerve it is wrapping (see right margin). Endoneurium • CT wrapping around an individual nerve fiber. Perineurium • CT wrapping around a group or bundle of nerve fibers (also called fascicles). [Figure I.33 Moore, Clinically Oriented Anatomy 7e] Epineurium • CT wrapping found between the fascicles and binding all the fascicles together, resulting in an organized package of nerve fibers. The epineurium level is the gross anatomical structure that we recognize as a peripheral nerve in the dissection lab. 3 Kubalak – 2022-2024 Anatomy of the Autonomic Nervous System Slide 9 This is a summary diagram of a somatic motor pathway. When one decides to contract a muscle to do a movement, a cell initiates an impulse in the cortex of the brain. This impulse propagates itself through the upper motor neuron, reaches a specific level of the spinal cord (crossing or not the midline) and synapses via intermediate neurons on the lower motor neurons in the anterior horn of the spinal cord. The lower motor neurons then carry the impulses to the skeletal muscle for contraction (efferent neuron). 1 Don't need to know Fig names 2 [Figure 15.7 Tortora, Principles of Anatomy and Physiology 9e] Slide 10 Note how peripheral nerves usually have both efferent (motor) neurons and afferent (sensory) neurons. The first type (motor) sends impulses distally to target organs like muscles. The second type (sensory) sends impulses proximally to provide information on the state of distal structures (pain, temperature, tension, etc). This slide shows the cell body of the lower motor neuron in the anterior horn of the gray matter of the spinal cord (panel B). Observe how the axon passes distally through a structure called the ventral (anterior) root to reach the target organs. Also shown is the path of an afferent axon coming back to the CNS (panel A). Note how it passes through a structure called the dorsal (posterior) root. Observe also the presence of the dorsal root ganglion where one can see the cell body of this axon (a pseudo-unipolar cell). [Figure 1.25 Snell, Clinical Anatomy 7e] 4 Motor Pathway CUDCSL • Cerebral cortex • Upper motor neuron • Descending tract • Crosses (or not) • Synapses in spinal cord o intermediate neurons in anterior horn • Lower motor neuron o Efferent neuron o Cell body in anterior horn o Through ventral root o To skeletal muscle Sensory Pathway ACDS • Afferent neuron • Cell body in dorsal root ganglion • Through dorsal root • Synapses in spinal cord • Ascending tract to CNS Kubalak – 2022-2024 Anatomy of the Autonomic Nervous System Motor neurons from the ventral horn: → ventral rootlets → ventral root → spinal nerve → dorsal rami → ventral rami A similar pattern can be observed with dorsal rootlets and dorsal roots. Slide 11 This slide illustrates the concept of the spinal cord segment (two segments are shown here). One can see how each of the ventral roots and dorsal roots are in fact formed by numerous rootlets at each level of the spinal cord level (C1, C2, etc). Observe how the ventral and the dorsal roots meet laterally to form the spinal nerve at each level. Also observable on this figure (and in Slide 10) is the communication between the spinal nerve and the sympathetic chain ganglia (see later) called rami communicantes [Netter 174 7e] Dorsal and ventral roots are in very close proximity to each other. The spinal nerve is very short and divides into the dorsal and ventral primary rami almost immediately. Slide 12 This cross section of the spinal cord allows us to see again how the ventral and dorsal roots form the spinal nerve (in the intervertebral foramen). Note also how short the spinal nerve is and how it divides almost immediately into a ventral (anterior) primary ramus and a dorsal (posterior) primary ramus. Note how the dorsal primary ramus passes posteriorly between the transverse processes of adjacent vertebrae. [Netter 175 and 170 7e] 5 Kubalak – 2022-2024 Anatomy of the Autonomic Nervous System Slide 13 Dorsal primary rami pass posteriorly and provide motor innervation to the deep back muscles and sensory innervation to the skin adjacent to the vertebral column (on each side). Dorsal primary rami • Pass posteriorly • Motor innervation to back muscle • Sensory innervation to skin over back • Convey ANS sympathetic fibers The ventral primary rami provide motor innervation to the muscles of the trunk and abdomen at the thoracic level but also form plexuses at the cervical, lumbar and sacral levels. Note that at the thoracic level (image at right), the ventral primary rami become the intercostal nerves. They also convey the ANS. [Netter 197 7e] Slide 14 [Figure 1.49 Gray’s Anatomy 4e] Ventral primary rami • Pass anteriorly • Form thoracic nerves (intercostal, subcostal NN) • Form cervical, brachial, lumbar, sacral plexuses • Motor innervation to o Limb muscles o Trunk muscles • Sensory innervation to skin • Convey ANS sympathetic fibers Somatic Plexuses (The below refers to the somatic plexuses on the left side of the image to the right.) A plexus is a network of nerves. Plexuses are formed by the union, division and regrouping of nerve fibers from the ventral primary rami. We will examine the cervical plexus in Block 11, brachial plexus in Block 10, and the lumbar and sacral plexuses in Blocks 5 and 6. The thoracic nerves do not form a plexus; these will be discussed in Blocks 3, 4 and 5. Cervical plexus: C1 to C4 Brachial plexus: C5 to T1 Thoracic nerves Lumbar plexus: L1 to L4 Sacral plexus: L4 to S4 6 Kubalak – 2022-2024 Anatomy of the Autonomic Nervous System Ventral and dorsal primary rami have both sensory and motor nerve fibers. Slide 15 Make sure you understand that both the ventral and the dorsal primary rami have both sensory (in blue) and motor (in red) nerve fibers. [Figure 1.22, Snell, Clinical Anatomy 7e] AUTONOMIC NERVOUS SYSTEM (ANS) Slide 16, 17, and 18 Now, we will discuss the autonomic nervous system. [Netter 172 and 173 7e] Recall from the beginning of this lecture that the ANS consists of the sympathetic system (stressful part of the ANS) and the parasympathetic system (the peaceful part of the ANS). Both parasympathetic and sympathetic systems are two-neuron systems: each have preganglionic and postganglionic neurons. The ANS does not supply skeletal muscles like the voluntary motor system, but provides innervation to smooth muscle, cardiac muscle, certain glands and other structures (visceral organs) over which humans have no (or little) volitional control. The autonomic system has also been called in the past visceral nervous system, involuntary nervous system or vegetative nervous system. The parasympathetic system is shown here. The sympathetic system is on the following page. 7 Kubalak – 2022-2024 Anatomy of the Autonomic Nervous System Two neuron systems Both parasympathetic and sympathetic systems are twoneuron systems: each have preganglionic and postganglionic neurons ANS provides innervation to: • Smooth muscle • Cardiac muscle • Certain glands • Other visceral organs Parasympathetic System • “Peaceful” part of ANS • Origin o Cranial NN ▪ Brainstem o Caudal NN ▪ Lateral horn ▪ S2-S4 (pelvic splanchnics) Sympathetic System • “Stressful” part of ANS • Origin o Lateral horn ▪ T1-L2 Slide 19 [Netter 172 7e] In the autonomic system, the nerve fibers exit through the roots of spinal nerves and also through certain cranial nerves. A unique characteristic of the autonomic system is the fact that the nerve fibers leaving the central nervous system do not end in a structure like voluntary muscle fibers (i.e. spinal nerve into muscle of the extremities). Instead, they synapse in an autonomic ganglion with a second set of cells that give rise to fibers terminating in the end organ. So, two neurons are transmitting the impulse from the central nervous system to the end organ as opposed to a single neuron in the case of the skeletal muscle. The first neuron with the cell body in the central system is called the preganglionic neuron. The neuron with the cell body in the ganglion is termed the postganglionic neuron. Some sympathetic preganglionic fibers synapse in the sympathetic chain ganglia. Then, the post-ganglionic neurons leaving the ganglion of the sympathetic chain do so through spinal nerves to innervate the body walls and the limbs. Other preganglionic fibers pass through the sympathetic chain without synapsing and continue to internal organs of the thorax, abdomen and pelvis. In these cases, they synapse in a ganglion close to the organs they innervate. 8 • Preganglionic cell bodies • In spinal cord • Lateral horn • T1-L2 • Sympathetic chain • Paired structure • Lateral to spinal cord • Extends from cervical to sacral region • 3-4 cervical ganglia • 11 thoracic ganglia • 4-5 lumbar ganglia • 4-5 sacral ganglia • Unpaired ganglion impar Kubalak – 2022-2024 Anatomy of the Autonomic Nervous System On this diagram, observe that the sympathetic system consists of the preganglionic neurons sending fibers through the thoracic and upper lumbar splanchnic nerves, through the sympathetic trunk made of ganglia and of postganglionic fibers reaching the target organs. Recall that the cell bodies of the preganglionic neurons are located in the spinal cord, between the levels of T1 to L2 in a specific location of the lateral horn of the spinal cord, the intermediolateral column. The paired sympathetic trunks consist of a series of ganglia connected to each other by nerve fibers. Each trunk extends from the first cervical vertebra to the coccyx (ganglion impar). The ganglia are not evenly distributed along the chain. There are only 3 to 4 cervical ganglia, 11 thoracic ganglia, 4 or 5 lumbar ganglia and 4 sacral ganglia. Preganglionic fibers leave the spinal cord through the ventral root and enter the sympathetic chain through white rami communicantes but can then take different paths: 1. Can synapse in the ganglion at the level where it exited the spinal cord 2. Can ascend and synapse at a higher level ganglia 3. Can descend and synapse at a lower level ganglia 4. Can pass through the chain and synapse in a ganglion that is closer to the target organ (splanchnic nerves) Note that some postganglionic neurons leave the sympathetic trunk through a structure called the grey rami communicantes. This group of axons appears grey because these neurons are nonmyelinated. Postganglionic fibers (if they synapse in the chain) • Leave chain through grey rami and enter dorsal or ventral rami • Leave the chain ganglia directly Slide 20 [Netter, 232 7e] 9 Kubalak – 2022-2024 Anatomy of the Autonomic Nervous System Slide 21 Note how the white and gray rami communicantes connect the ventral primary rami to the sympathetic chain ganglia. White and grey rami connect the ventral primary rami to the sympathetic chain. [Figure 2.9, Gray’s Anatomy, 4e] Slide 22 [Netter, 173 7e] The parasympathetic system, like the sympathetic system, relies on a preganglionic and a postganglionic neuron. The preganglionic cell bodies lie in specific nuclei of 4 cranial nerves and in the sacral portion of the spinal cord. The parasympathetic system preganglionic fibers originate in the nuclei of the cranial nerves III, VII, IX and X and the 2 nd to 4th sacral nerves. The preganglionic fibers leave cranial or sacral locations to synapse in ganglia close to the organs that they innervate. The ganglia for the cranial nerves are: the ciliary ganglion (CN III), pterygopalatine ganglion and submandibular ganglion (CN VII) and the otic ganglion (CN IX). The ganglia for CN X and the pelvic splanchnics are located at or near the organ they innervate. Parasympathetic system • Preganglionic cell bodies • In brain stem • Nuclei of CN III, VII, IX, and X • In spinal cord • S2 – S4 • Preganglionic fibers • Leave as CN’s • Synapse in ganglia near organ • Leave spinal cord as pelvic splanchnics • Off ventral rami • Synapse in ganglia near organ • Postganglionic fibers • At or near organ 10 Kubalak – 2022-2024 Anatomy of the Autonomic Nervous System Slide 23 The sympathetic system is primarily an emergency system (fight or flight). It dilates the pupil of the eye, increases the heart rate and strength of the heartbeat, constricts the blood vessels in the skin and digestive tract, and slows down the peristalsis of the digestive tract. All of these changes are designed to facilitate high level of physical activities. The parasympathetic system constricts the pupil of the eye, adjusts the lens (accommodation), decreases the heart rate, increases secretions of digestive enzymes and peristalsis of the digestive system, and facilitates emptying of the bladder and rectum. Some organs of the body receive fibers from both the sympathetic and parasympathetic systems while some are believed to receive only one. It is thought that when both systems are present, the balance of the activity of the two systems regulates the organ. If only one system is present, the level of activity of that system regulates the organ. Slide 24 Sympathetic function • Dilates pupil • Increases heart rate • Increases cardiac contractility • Constricts blood vessels in skin and GI tract • Slows peristalsis of GI Tract • Relaxes bladder Parasympathetic function • Constricts pupil • Adjust lens • Decreases heart rate • Increase GI activity • Facilitates emptying of bladder This image is a summary of the somatic (left side of image) and ANS pathways (right side of image). You should be able to describe (i.e. redraw) this diagram from memory. Make sure you understand how the different pathways of the somatic and autonomic nervous systems are traveling through the anatomical structures described in this lecture namely ventral and dorsal roots, spinal nerve, rami communicantes, and ventral and dorsal primary rami. Be able to redraw this image from memory. [Figure 1.29, Snell, Clinical Anatomy 7e] Slide 25 Recall that the autonomic system also has afferent fibers, providing sensory information regarding the states of abdominal organs back to the central nervous system. To do so, these neurons travel back through the path taken by the sympathetic neurons (through the splanchnic nerves) but diverge from them at the spinal nerve. Visceral afferent neurons enter the dorsal root, have their cell bodies in the dorsal root ganglion and send their central processes into the spinal cord. At the level of the spinal cord, somatic and visceral sensory afferent neurons synapse with neurons from ascending sensory pathways [Figure 1.29 above]. When the information is interpreted by the central nervous system, the patient interprets the source of the pain as coming from the somatic region and not from the visceral region. When this happens, it is called “referred pain”. 11 Afferent (sensory) system • From abdominal viscera • travel along thoracic and lumbar splanchnic sympathetics (T5-L2) • From pelvic viscera • travel along pelvic splanchnics (S2-S4) • At spinal nerve, go through dorsal root • Synapse at spinal cord (both somatic and visceral synapse at same location) • Ascend to CNS • Interpreted as referred pain (see next slide) Kubalak – 2022-2024 Anatomy of the Autonomic Nervous System Slide 26 [Netter’s Clinical Anatomy 3e] Referred pain • Visceral pain perceived as somatic over a specific dermatome region Slide 27 Knowledge of the dermatome pattern is extremely useful to the clinician investigating the source of pain. For example, if a patient has compression of the sixth cervical nerve by a herniated intervertebral disc, he/she will have pain along the lateral side of the forearm and thumb. The dermatome pattern shown below differs slightly from the one shown in Drake (your textbook). For the upper and lower limbs, learn the dermatome pattern shown here, which is from Netter. [Netter 171 7e] 12 Dermatome • Segment of skin supplied by a single spinal nerve • We will use the dermatome pattern from Netter, plate 171, 7e. • Tested by touching center of dermatome (see image next page) Kubalak – 2022-2024 Anatomy of the Autonomic Nervous System Slide 30 Dermatome touch points for testing intactness of spinal nerve Myotome • Region of skeletal muscle innervated by a single nerve or spinal cord level • Note: individual muscles are usually innervated by more than one spinal cord level • Tested motor function by specific joint movements • Dermatomes are different than myotomes. Myotomes are the region of skeletal muscles innervated by a single nerve or spinal cord level. Note however, that individual muscles are usually innervated by nerves derived from more than one spinal cord level. Myotomes are tested by specific joint movements. In contrast, dermatomes are tested by touching relatively specific regions of the skin for sensation. Figure 7.15 from your text nicely demonstrates this using the upper limb. Panel A shows specific regions to test for dermatomes while Panel B gives examples of specific joint movements to test for myotomes. [Figure 7.15, Gray’s Anatomy 4e] 13