FOCA 2023 Introduction to the Nervous System PDF

FOCA 2023 Introduction to the Nervous System Dr. Mark Hankin Professor & Senior Anatomist Director, Anatomical Sciences Education Center [email protected] Jul 12, 2023 Disclosures & Conflicts of Interest Authorship Anatomy & Physiology Revealed v4 2019, McGraw-Hill Clinical Anatomy: A Case Study Appro...

FOCA 2023 Introduction to the Nervous System Dr. Mark Hankin Professor & Senior Anatomist Director, Anatomical Sciences Education Center [email protected] Jul 12, 2023 Disclosures & Conflicts of Interest Authorship Anatomy & Physiology Revealed v4 2019, McGraw-Hill Clinical Anatomy: A Case Study Approach 2013, McGraw-Hill Test Prep for the USMLE® – Clinical Anatomy Q&A 2019, Thieme Medical Publishers If you have used any of these resources, I hope you found them helpful. 2 Session Objectives The nervous system is distributed across all body regions and in all organ systems. 1. Describe the organization of the nervous system, including its anatomical and functional divisions. 2. Describe the spinal cord, including the general organization of its gray and white matter components, and its relationship to the vertebral column. 3. Describe a typical spinal nerve, including its origin from dorsal and ventral spinal roots, its main motor and cutaneous (sensory) branches and distribution, and any autonomic component. 4. Describe the meninges of the spinal cord. 5. Describe the basic organization of the autonomic nervous system, including its components, pathways, and distribution. By the end of FOCA, you should understand the anatomy involved in signs and symptoms associated with the nervous system – e.g., pain, sensory changes, weakness, and other changes in bodily function. 3 Signs & Symptoms Related to the Nervous System Carpal Tunnel Syndrome Symptoms Median nerve compressed in carpal tunnel Sensory deficits: tingling, numbness, pain Thenar muscle wasting Flexor digitorum Sensory: Paresthesia (tingling), anesthesia or hypesthesia, pain Motor: Weakness of some hand muscles Signs Long-term: atrophy of some hand muscles Thenar muscle 4 Nervous System Organization Create Concept example write and a then word create a flow chart to see How things conect Anatomical Divisions of the Nervous System CNS: Central Nervous System Brain – In cranial cavity (skull) Spinal cord – In vertebral canal PNS: Peripheral Nervous System somatic autonomic All tissue outside the CNS Spinal nerves – 31 pairs that arise from spinal cord Cranial nerves – 12 pairs that emerge from cranial foramina (holes in skull) 6 Drake GAS 2e 1.33 Thieme, Atlas of Anatomy Spinal Nerves Peripheral Nervous System Cranial Nerves Functional Divisions of the Nervous System SOMATIC functions: Conscious sensation, voluntary movement via skeletal muscles Skin, joints, skeletal muscle So ma tic PNS Output G. Soma = body ic at m So t en r e eff othinkoftouchingsomethingandtnetsignalgoestoons outsidetoons sensoryinformationfrom Afferent t en r e aff omic… ry l o n era Auto t sens c s s Vi NOT re ju PNS Internal organs ’ ey th i CNS Efferent of muscles contraction skeletal movement through nervoussystem somatic muscles contraction smooth muscle activity internet of motorinformatiinonfroitnoistingteripner Visc era = A l effe Sym utonom ren t ic: Pa path ras Visceral motor Skeletal muscles Somatic aff ere nt is always ymp etic or ath etic L. Viscus = internal organ Organs, glands, smooth & cardiac muscle VISCERAL functions: Homeostasis, autonomous regulation of organ function 8 The Neuron is the Structural Unit of the Nervous System Neuronal Processes body cen madeof en es organ b odies carsnucleus in group ofcenbodie o utside asGanglion ocf en group Dendrites recievesignalsfromotherneurons Many per neuron Carry afferent impulses (i.e., toward cell body) Axonsendsignalsalongtootherneurons One per neuron Carries efferent impulses (i.e., away from cell body) Form nerves Theb weisa fattyprotective gained sheet Motor neuron Sensory neuron D COA8e 1.28 9 Primary Sensory Neurons are Pseudounipolar means Except for olfaction & vision, all sensory neurons in the PNS are pseudo-unipolar Cell bodies in sensory ganglia (e.g., DRG) general IEEE go Dorsal Root Ganglion (DRG) k NO SYNAPSES IN THESE GANGLIA Whentwoneuronscometogetheritscalled a synapse Sensory ganglion (DRG) CNS (e.g., spinal cord) Skin Axon Peripheral process Central process afferent sensory 10 O gus e CNS & PNS Have Gray & White Matter Gray Cell body CNS crosssectionofthe matteraceregrumiscalled Cell bodies (somata) Appears pinkish-gray Cortex & nuclei White matter CNS: Pathways Ganglia GM Spinal cord Think of axons Myelinated axons as highways q Appears white because myelin reflects light information Axon with myelin Gray matter Nerve cell bodies WM CNS: Cortex & nuclei PNS: Ganglia PNS Tracks Pathways Horns White matter Myelinated axons Nerves sending to differentspots PNS: Nerves Schuenke Thieme, Atlas of Anatomy vol3 3e 8.2D 11 Spinal Cord and Spinal Nerves The spinal cord occupies the vertebral canal and gives rise to 31 pairs of spinal nerves. Spinal Cord soppy upper extermity Spinal cord has two expanded regions that innervate the limbs spinalcord stops between Cervical enlargement: Formed by C4-T1 spinal cord segments L1 L2 gym Lumbar/lumbosacral enlargement Formed by L1-S3 spinal cord segments cumberp uncture B LEE 13 Spinal Cord Ends at the L1/L2 Intervertebral Disc Conus medullaris (medullary cone) is the inferior tapered end of the spinal cord Adult: conus usually opposite L1/L2 intervertebral (IV) disc is ⎻ May be as high as T12, or as low as L3 Filum terminale anchors conus inferiorly to the coccyx I 7 Cauda Equina and Cauda equina (L. horse’s tail) are spinal nerve roots from lumbosacral enlargement Cauda equina located in the lumbar cistern, which is the enlarged, subarachnoid space inferior to conus medullaris Dural sac & lumbar cistern end at S2 vertebral level Subarachnoid space contains cerebrospinal fluid (CSF) anchnoid Lumbar Cistern T12 L1 L2 L3 est Duramata g LP Epidural conakso O LLP treatchronic durgle pain Madog's've Lumbar punctures (LPs) performed at L3-L4 or L4-L5 because this is inferior to the spinal cord & nerve roots in cauda equina ”move out of the way” unmyliontedatons Spinal Cord Gray Matter has Three Areas nueroncell body later ventral In 3D…across spinal levels 1 Somatic afferent (sensory) informationcominginto Cns In 2D…at one spinal level Visceral efferent endsout (autonomic) cell bodies symlpaasympothiclnotsittf.ee sweat glands Somatic efferent (motor) Pointer motor exitsthe Thinkot spinalcord vagusgqtqtgef.tn patellerbone Thieme, Atlas of Anatomy Spinal Cord Segment É Formed by the set of dorsal & ventral rootlets that arise from the cord and form a single spinal nerve On each side motfferent o Dorsal rootlets form a single dorsal root (motor) Sensory unipolar neuron Dorsal root ganglion (DRG) Ventral rootlets form form a single ventral root (sensory) motor b ceilbointogte O Dorsal & ventral roots converge to form a single short spinal nerve (mixed motor and sensory) Dorsal root anons that THIEF Ventral root Hollinshead, Anatomy for Surgeons Tnetwnyitsamix Spinal Cord and the Spinal Nerve What kind of cell is this? Dorsal horn Posterior (Dorsal) Sensory (Afferent) Dorsal root Dorsal root psuedounipolar ganglion (DRG) neuron Dorsal horns & roots Spinal nerve Dorsal ramus Ventral horn whole Posterior The backsia Mixed Motor (Efferent) Ventral horns and roots mixed sensory motor Rami & peripheral nerves Anterior (Ventral) f Ventral root motorcifer'd volventer PNS somatic and viseral motor out coming O Ventral ramus mixedset anteior abdomen resard O autonomic gonaglia Test your Understanding Which of the following structures convey only sensory fibers (axons)? A. Dorsal ramus B. O Dorsal root sensory C. Intermediolateral cell column of spinal cord A. Spinal nerve is both B. Ventral root motor columninstead of segment 19 What Happens to 31 Spinal Nerves? Spinal Cord Region Ventral Rami Cervical (8) ** C1-C8 Thoracic (12) T1-T12 Lumbar (5) L1-L5 Sacral (5) S1-S5 Coccygeal (1) Co1 Givesthe no swallowing some facial T1 C7 speech coughingreflex nonsinaximinary region I arm shoulder forearm hand T1-11 ventral rami form intercostal nerves L1 T12 S1 T12 ribs soppinchestcarity L1 S3 L1 won L5 Cervical plexus: C1-C4 ventral rami Brachial plexus: C5-T1 ventral rami Lumbar plexus: L1-L4 ventral rami Sacral plexus: S1-S4 ventral rami Thoracic ventral rami do not form a plexus: rather, they are intercostal nerves (T1-T11) C8 T1 T1 **8 cervical nerves – only 7 cervical vertebrae Most ventral rami form somatic plexuses C1 C1 cowerextermity comingjustaborethe sacrum L5 S1 L5 S1 S5 Thieme, Atlas of Anatomy S5 Co sciatic longest thicknerve ECA 6e Spinal cord Spinal nerve Dorsal ramus amixednerve Ventral ramus Dorsal root ganglion (DRG) Dorsal rootlets Dorsal root Ventral root Exemplar: Brachial Plexus Starts at C5-T1 intervertebral foramina…and ends in the axilla (“armpit”) Formed by ventral rami of C5-T1 spinal nerves Branches supply the upper limb What fiber types (functional modalities) are present in this plexus and its branches? Sensory and motor mixed Nielsen & Miller, Atlas of Human Anatomy 22 Dermatomes Area of skin innervated by sensory fibers from a single spinal segment & nerve Trigeminal n. (CN V) Sensory fibers in ventral & dorsal rami supply areas of skin…dermatomes Dermatomes on the trunk are relatively orderly, narrow regions (bands) Dermatomes on the neck, posterior head & limbs, are more irregular in shape General sensation: pain, temperature, touch, pressure, vibration, proprioception Dorsal rami supply dermatomes on the back, and back of neck & head Ventral rami supply dermatomes almost everywhere else, except the face & anterior scalp (innervated by trigeminal nerve (CN V) 23 Sensation from the Head Face & anterior scalp Vertex Trigeminal nerve (CN V) CN V1 Ophthalmic n. Neck & posterolateral scalp around tffes Spinal nerves C2-C3 - Ventral & dorsal rami have different distributions th Thisisallafferent CN V2 Maxillary n. upperjaw.up.to CN V3 Dorsal rami (C2-C3) É Mandibular n. Ventral rami Cervical plexus (also C2-C3) as ECA 6e 8.16 24 Key Dermatomes for the Limbs Upper Limb C5: Over deltoid C6: Thumb C7: Middle finger C8: Little finger T1: Medial forearm T2: Axilla (tickle n.) motororsensory information Tryto draw this Blankline drawing findarmsand legsonline Lower Limb L4: Great (big) toe L5: Middle toe S1: Little toe 25 Test your Understanding A 45-year-old man with numbness and tingling over his right lateral palm comes to the Family Medicine clinic. You diagnose carpal tunnel syndrome. In which of the following is the injury most likely localized? branchfor the A. Branch of a dorsal ramus The 0 B. C. D. E. Branch of a ventral ramus Dorsal horn of spinal cord Dorsal root Ventral root been Median nerve Sensory deficits Tingling, numbness, pain Muscle wasting Thenar muscles compressed in carpal tunnel sensoryandmotorinformation 26 Spinal Meninges The spinal cord is surrounded by three connective tissues layers called meninges. protective layerof Meninges the brain Middle circuitingfluid Spinal Cord Three connective tissue layers surround the brain and spinal cord Outer Subarachnoid space, with CSF 1. Dura mater is tough, dense CT.Toughest coversdonerootsleeve 2. Arachnoid mater is delicate, avascular, and semitransparent. Subarachnoid space, between the arachnoid and pia mater, contains cerebrospinal fluid (CSF) Inner 3. Pia mater follows the surfaces of the brain, spinal cord & nerve roots. Think of it as “shrink wrap” covering thespinalcordandbrain mooddelicate contain spacetyigh COA8e 1.31 28 What do the meninges really look like? Important points: Dura mater is thick, whereas arachnoid & pia mater very thin (basically, transparent) Arachnoid trabeculae Arachnoid trabeculae (L. beam) connect arachnoid & pia Arachnoid mater held against dura mater by pressure of CSF in subarachnoid space g 29 Two Structures Stabilize the Spinal Cord Filum terminale ospinescoraena Piffurgenrvescoming into goes ec.no Anchors inferior end of spinal cord (conus medullaris) to the coccyx Et Posterior view ventrif the Denticulate ligament under doramater Anchors lateral sides of spinal cord to the dura mater and wall of vertebral canal anchors Separates dorsal and ventral rootlets Lumbar cistern of subarachnoid space ECA 5e 4.18 Contains cerebrospinal fluid & cauda equina Common location for lumbar puncture (LP; spinal tap) Grays 41e 45.1E 30 Rohen, Color Atlas of Anatomy Lumbar enlargement 061 53 Conus medullaris Cauda equina Denticulate lig. Oinsidethe donemater É'd orentrdrooites y Filum terminale DRG Dorsal rootlets Posterior views 31 Cranial Nerves Bestway to learn I match roman numeral to name 2 Whatthey do sensory motor or both Cranial Nerves 12 Cranial nerves (CN osensory tobrain seiggeren osensor motor I-XII) efferent O Oy emerge from foramina (holes) or fissures (cracks) in skull Most connect to the brainstem O Except: CN I (cell bodies in olfactory epithelium of nasal cavity) CN XI (motor neurons with cell bodies in cervical spinal cord) Fiber types (neural modalities) in each Sensory Motor Sensory & motor Otarproduction odigestivetract Some also carry parasympathetic fibers CNT 10 9,3 I Moore, COA8e 10.4 33 i i Autonomic Nervous System (ANS) Involuntary nervous system Only two types: sympathetic or parasympathetic; both are classified as “visceral efferent” If you don’t understand the ANS after these slides, then you are in good company. The ANS is complicated, and developing a working knowledge takes practice and careful study. Today is the first step, and we will return to the ANS many times as we discuss its distribution in each body region. The faculty is here to help you, so please ask us! Functional Divisions of the Nervous System SOMATIC functions: Conscious sensation, voluntary movement via skeletal muscles Skin, joints, skeletal muscle So ma tic Somatic G. Soma = body aff ere nt Afferent t en r e aff omic…ry) l n o era Autot sens c s Vi (NOTre jus ’ ey th Internal organs Skeletal muscles ic at m So CNS Efferent Visc era (= A l eff Sym utono eren mic t pat Pa : h Q ras Visceral L. Viscus = internal organ t en r e eff motorfunction somatic skeletal muscles ymp etic o ath r etic ) involuntary VISCERAL functions: Homeostasis, autonomous regulation of organ function Organs, glands, smooth & cardiac muscle tort Hormoneproduction 35 Autonomic Nervous System = Visceral Efferent Autonomic pathways involve two-neurons arranged in series: comesbefore ganglion 1. Preganglionic (presynaptic) 2. Postganglionic (postsynaptic) Cell bodies located in a ganglion (sympathetic or parasympathetic – but not a DRG!) Axons innervate targets organ Pretgonglonicneuron Cell bodies located in CNS Axons synapse in a ganglion man (sympathetic or parasympathetic, ardofgrey thatsoutsideof but not a DRG!) Si a closerto Target Distance fromtargetorgan Preganglionic neuron ycenbodiegtngongig.ua Iiiingfisers neuron Acetylcholine post ganglionic ganglionic Norepinephrine neron t argeorge inside postgagiani fiber Postganglionic neuron DO Short preganglionic axons Long preganglionic axons Long postganglionic axons Short postganglionic axons Sympatheticnervous system parasympatheticnervoussyst Schuenke, Thieme Atlas of Anatomy vol3 3e 10.2A 36 Sympathetic Division (Thoracolumbar Outflow) omoresimpothicmotorspherfen Sympathetic: Fight or flight blue Soild lineare Preganglionic cells in lateral horn (intermediolateral cell column) of T1L2/L3 spinal cord Postganglionic cell in sympathetic ganglia - Paravertebral ganglia in sympathetic trunk; postganglionic axons in rami communicantes pass to all spinal nerves & supply sweat glands, arrector pili muscles, vascular smooth muscle (constriction) - Preganglionic axons in splanchnic nerves synapse in prevertebral (pre-aortic) ganglia (e.g., celiac, mesenteric, aorticorenal); postganglionic axons follow arteries (periarterial plexuses) to visceral targets: smooth & cardiac muscle & glands postganglic fibers o o o o g o o I J T Nearaorta 37 Parasympathetic Division (Craniosacral Outflow) Terminal omg piles contrasteers arena gratiaside conto pagans Parasympathetic: Rest & digest Preganglionic cells in brainstem or S2-S4 spinal cord Preganglionic axons (outflow) in in vagus nerve (CN X) and pelvic splanchnic intermund gang c cintaget organ Postganglionic cells in ganglia in/on wall of organ (intramural), or in one of 4 discrete ganglia in head - Intramural ganglia & (very short) postganglionic axons innervate mucous & salivary glands, and smooth & cardiac muscle No parasympathetics in the body wall or limbs. 38 Visceral Afferents & Referred Pain Pain from internal organs (visceral) and skin (somatic) are both transmitted via DRG neurons, both of which terminate spinal ganglion on the same neurons in the dorsal horn. Because of this convergence, the brain perceives pain from an internal organ as diffuse pain from the dermatome at the same spinal cord level(s) associated with somatic afferents. This phenomenon is called referred pain. canbeDro Pseudo-unipolar (sensory) neuron Example: since visceral afferents from the heart synapse in T1-T4 spinal cord, the pain associated with a myocardial infarction is perceived in the T1-T4 dermatomes. Schuenke, Thieme Atlas of Anatomy vol3 3e 10.4Ba 39 The Real Sympathetic Chain 1. 2. 3. 4. 5. 6. Sympathetic chain Sympathetic ganglion Gray ramus communicans pathic sym connection White ramus communicans Greater splanchnic nerve b etween Lesser splanchnic nerve connection ventralramona sympatricsystem t sortsoutsympatric information 40 Test your Understanding A physician assistant student and her preceptor in a gastroenterology rotation discuss the autonomic nervous system. Which of the following is correct regarding the ANS? A. Innervation of the GI tract includes only sympathetic and parasympathetic divisions B. It includes only sympathetic, parasympathetic neurons and their processes C. Preganglionic cell bodies are located only in the thoracolumbar regions of spinal cord D. Postganglionic sympathetic fibers synapse in ganglia in/near target organs E. Somatic nerves convey parasympathetic fibers to the limbs Test your Understanding A physician assistant student and her preceptor in a gastroenterology rotation discuss the autonomic nervous system. Which of the following is correct regarding the ANS? A. Innervation of the GI tract includes only sympathetic and parasympathetic divisions B. It includes only sympathetic, parasympathetic neurons and their processes C. Preganglionic cell bodies are located only in the thoracolumbar regions of spinal cord D. Postganglionic sympathetic fibers synapse in ganglia in/near target organs E. Somatic nerves convey parasympathetic fibers to the limbs 42 END 43