Chapter 13 The Spinal Cord Spinal Nerves and

Chapter 13 The Spinal Cord, Spinal Nerves, and Spinal Reflexes Lecture Presentation by Lee Ann Frederick University of Texas at Arlington © 2012 Pearson Education, Inc.

13 -2 Spinal Cord Functions: • Link between brain and rest of the body • Conduction: has tracts of nerve fibers for upward and downward travel of sensory and motor information • Can work independently of brain • Reflexes – quick responses to stimuli © 2012 Pearson Education, Inc.

Location and Gross Anatomy of the Spinal Cord • Located in vertebral canal • Arises from the brainstem at the foramen magnum of the skull to between L 1 and L 2 vertebrae • ~ 18 inches (45 cm) long • 1/2 inch (14 mm) wide © 2012 Pearson Education, Inc.

Enlargements of the Spinal Cord are caused by greater amounts of gray matter in those regions • Cervical enlargement • Nerves of shoulders and upper limbs • Lumbar enlargement • Nerves of pelvis and lower limbs © 2012 Pearson Education, Inc.

Figure 13 -2 Gross Anatomy of the Adult Spinal Cord. Posterior median sulcus Dorsal root Conus medullaris The tapered terminal end of the spinal cord. Located below the lumbar enlargement (between L 1 -L 2) Cauda equina: Nerve roots extending inferiorly below conus medullaris (L 2 -S 5) that innervates the pelvic organs and lower limbs Dorsal root ganglion Cervical spinal nerves C 1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 White matter Central canal Spinal nerve Cervical enlargement Gray matter Ventral root Anterior median fissure C 3 T 1 T 2 T 3 T 4 T 5 T 6 T 7 KEY Spinal cord regions Thoracic spinal nerves T 8 T 9 = Cervical T 10 = Thoracic T 11 = Lumbar = Sacral T 12 L 1 Posterior median sulcus T 3 Lumbar enlargement Conus medullaris L 2 Filum terminale: Thin thread of fibrous tissue (pia mater) at end of conus medullaris that helps anchor the conus medullaris to the coccyx Lumbar spinal nerves L 3 Inferior tip of spinal cord L 4 Cauda equina L 5 L 1 Sacral spinal nerves S 1 S 2 S 3 S 4 S 5 Coccygeal nerve (Co 1) a The adult spinal cord extends from the brain only to the level of vertebrae L 1–L 2; © 2012 Pearson Education, Inc. S 2 Filum terminale b (in coccygeal ligament)

Cross Section of Spinal Cord • Spinal Cord has a small central canal lined with ependymal cells which help circulate the CSF • Spinal cord has bilateral symmetry: Grooves divide the spinal cord into left and right side • Posterior median sulcus – shallow depression on posterior side • Anterior median fissure – deeper groove on anterior side © 2012 Pearson Education, Inc.

• Spinal Tissue divided into: Inside Gray matter (shaped like H) - Location of mostly cell bodies and unmyelinated axons - Greater amount in spinal cord segments serving limbs Outside White Matter - Location of mostly myelinated axons © 2012 Pearson Education, Inc.

Figure 13 -2 Gross Anatomy of the Adult Spinal Cord Posterior median sulcus Dorsal root White matter Dorsal root ganglion Cervical spinal nerves C 1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 T 1 T 2 T 3 T 4 T 5 T 6 Gray matter Central canal Spinal Ventral nerve root Cervical enlargement Anterior median fissure C 3 T 7 Thoracic spinal nerves T 8 T 9 Posterior median sulcus T 10 T 11 T 12 L 1 L 2 Lumbar spinal nerves L 3 L 4 L 5 Lumbar enlargement Conus medullaris T 3 Inferior tip of spinal cord Cauda equina L 1 Sacral spinal nerves S 1 S 2 S 3 S 4 S 5 Coccygeal nerve (Co 1) © 2012 Pearson Education, Inc. S 2 Filum terminale (in coccygeal ligament)

Spinal cord gives rise to 31 pairs of Spinal Nerves • Spinal nerves are part of PNS • C 1 -C 8, T 1 -T 12, L 1 -L 5, S 1 -S 5, Co 1 • Spinal cord segment: refers to the part supplied by each pair of spinal nerves - First pair of spinal nerves pass between the skull and C 1 - Rest pass through the intervertebral foramina • Spinal nerves are mixed nerves: contain sensory and motor nerve fibers © 2012 Pearson Education, Inc.

The Spinal cord is protected by the vertebrae and the spinal meninges Spinal Meninges are specialized membranes that isolate spinal cord from surroundings • Protecting spinal cord • Carry blood supply • Continuous with cranial meninges • Meningitis: Viral or bacterial infection of meninges © 2012 Pearson Education, Inc.

The Three Meningeal Layers of the spinal cord 1. Dura mater • Outer layer, Dense irregular CT 2. Arachnoid mater • Middle avascular layer 3. Pia mater • Delicate Inner vascularized layer • Downward extensions of the pia mater anchor the spinal cord at the coccyx- filum terminale © 2012 Pearson Education, Inc.

Figure 13 -3 b The Spinal Cord and Spinal Meninges ANTERIOR Subarachnoid space Vertebral body Dura mater Arachnoid mater Pia mater Rami communicantes Spinal cord Adipose tissue in epidural space A sectional view through the spinal cord and meninges, showing the peripheral distribution of spinal nerves © 2012 Pearson Education, Inc. Autonomic (sympathetic) ganglion Ventral root of spinal nerve Ventral ramus Dorsal ramus Denticulate Dorsal root ligament ganglion POSTERIOR

Epidural Space • Between spinal dura mater and walls of vertebral canal • Contains blood vessels, loose connective and adipose tissue • Anesthetic injection site; Epidural shot Subdural Space • Between dura mater and arachnoid mater • Little or no space Subarachnoid space • Between arachnoid mater and pia mater • Filled with cerebrospinal fluid (CSF) that carries dissolved gases, nutrients, and wastes • Site of lumbar puncture or spinal tap to withdraw CSF for diagnostic purposes • L 3 & L 4 • L 4 and L 5 © 2012 Pearson Education, Inc.

Figure 13 -4 The Spinal Cord and Associated Structures Spinal cord Anterior median fiss § Paired denticulate ligaments are found along length of spinal cord § Extend from pia mater to dura mater § Help suspend anchor the spinal cord laterally Pia mater Denticulate ligaments Dorsal root Ventral root, formed several “rootlets” fr one cervical segmen Arachnoid mater (reflected) Dura mater (reflecte Spinal blood vessel © 2012 Pearson Education, Inc.

13 -3 Gray Matter and White Matter Gray matter: § Centrally located; H-shaped, surrounds central canal § Contains neuron cell bodies (organized in nuclei), neuroglia, unmyelinated axons Nuclei are masses of gray matter within the CNS § Sensory nuclei receive and relay sensory information from peripheral receptors; Located on posterior (dorsal) side § Motor nuclei issue commands to peripheral effectors; Located on anterior (ventral) side © 2012 Pearson Education, Inc.

Gray Horns • Projections of gray matter towards the outward surface of the spinal cord Posterior gray horns contain somatic and visceral sensory nuclei Anterior gray horns contain somatic motor nuclei Lateral gray horns-only found in thoracic and upper lumbar segments-; contain visceral motor nuclei § Sensory or motor nucleus location within the gray matter determines which body part it controls © 2012 Pearson Education, Inc.

Gray commissures (bridge of “H”) • Found posterior and anterior to central canal • Contain axons that laterally cross spinal cord © 2012 Pearson Education, Inc.

Figure 13 -5 a The Sectional Organization of the Spinal Cord Posterior white column Posterior median sulcus Posterior gray commissure Posterior gray horn Dorsal root ganglion Lateral white column Lateral gray horn Anterior gray horn Somatic Visceral Somatic Functional Organization of Gray Matter The cell bodies of neurons in the gray matter of the spinal cord are organized into functional groups called nuclei. Sensory nuclei Motor nuclei Ventral root Anterior white column Anterior gray commissure Anterior white commissure Anterior median fissure The left half of this sectional view shows important anatomical landmarks, including the three columns of white matter. The right half indicates the functional organization of the nuclei in the anterior, lateral, and posterior gray horns. © 2012 Pearson Education, Inc.

Figure 13 -5 b The Sectional Organization of the Spinal Cord POSTERIOR Posterior median sulcus Posterior gray commissure Structural Organization of Gray Matter The projections of gray matter toward the outer surface of the spinal cord are called horns. Posterior gray horn Dura mater Lateral gray horn Arachnoid mater (broken) Dorsal root Central canal Anterior gray horn Anterior gray commissure Anterior median fissure Pia mater ANTERIOR A micrograph of a section through the spinal cord, showing major landmarks in and surrounding the cord. © 2012 Pearson Education, Inc. Dorsal root ganglion Ventral root

Organization of White Matter into three columns • Posterior white columns lie between posterior gray horns and posterior median sulcus • Anterior white columns lie between anterior gray horns and anterior median fissure • Lateral white columns located on each side of spinal cord between anterior and posterior columns © 2012 Pearson Education, Inc.

Organization of White Matter • Each column contains tracts or fasciculi whose axons share functional and structural characteristics Tract: Bundles of axons with common origin or destination • Relay same information in same direction Ascending tracts • Carry sensory information to brain Descending tracts • Carry motor commands away from brain © 2012 Pearson Education, Inc.

Figure 13 -5 a The Sectional Organization of the Spinal Cord Posterior white column Dorsal root ganglion Lateral white column Posterior gray horn Lateral gray horn Anterior white column The left half of this sectional view shows important anatomical landmarks, including the three columns of white matter. The right half indicates the functional organization of the nuclei in the anterior, lateral, and posterior gray horns. © 2012 Pearson Education, Inc.

13 -4 Spinal Nerves and Plexuses Anatomy of Spinal Nerves • Every spinal cord segment is connected to a pair of spinal nerves (31 pairs total) • Every spinal nerve • Is surrounded by three connective tissue layers • That support structures and contain blood vessels © 2012 Pearson Education, Inc.

Three Connective Tissue Layers of Spinal Nerves 1. Epineurium • Outer layer • Dense network of collagen fibers 2. Perineurium • Middle layer • Divides nerve into fascicles (axon bundles) 3. Endoneurium • Inner layer • Surrounds individual axons © 2012 Pearson Education, Inc.

Figure 13 -6 A Peripheral Nerve Blood vessels Connective Tissue Layers Epineurium covering spinal nerve Perineurium (around one fascicle) Endoneurium Myelinated axon Fascicle © 2012 Pearson Education, Inc. Schwann cell

Figure 13 -6 b A Peripheral Nerve. Blood vessels Connective Tissue Layers Perineurium (around one fascicle) Endoneurium Power. Point® Lecture Presentations prepared by Jason La. Pres Lone Star College—North Harris b © 2012 Pearson Education, Inc.

§ The 31 pairs of spinal nerves extend from spinal cord into the periphery and innervate muscles, skin and internal organs • Most enter through the intervertebral foramen • Spinal Nerves are Mixed Nerves: Carry both afferent (sensory) and efferent (motor) fibers © 2012 Pearson Education, Inc.

Within the vertebral canal-near its attachment to the spinal cord- each spinal nerve forms two branches, a ventral and a dorsal root Ventral (Anterior) root • Carries axons of motor neurons which have received motor commands from the anterior horn of spinal cord away from the spinal cord to the periphery to control somatic and visceral effectors Dorsal (Posterior) root • Carries axons of sensory neurons which bring sensory information to the posterior horn of spinal cord • Dorsal (posterior) root ganglia: Swelling on dorsal root containing cell bodies of sensory neurons The ventral root and the dorsal root come together to form a spinal nerve © 2012 Pearson Education, Inc.

Figure 13 -3 a The Spinal Cord and Spinal Meninges White matter Ventral root Gray matter Dorsal root ganglion Spinal nerve Dorsal root Meninges Pia mater Arachnoid mater Dura mater A posterior view of the spinal cord, showing the meningeal layers, superficial landmarks, and distribution of gray matter and white matter © 2012 Pearson Education, Inc.

• Each spinal nerve has branches that collect sensory information and distributes motor commands © 2012 Pearson Education, Inc.

Spinal Nerves - Branches Distal to the vertebral canal – after it passes through the intervertebral foramina, each spinal nerve forms branches: • Posterior (dorsal) ramus - supplies to the skin & muscles of the back • Anterior (ventral) ramus – supplies to the extremities and anterior wall of the trunk • Meningeal ramus – supplies to the meninges and vertebrae • Rami communicantes (autonomic nerves) – supplies to the internal organs © 2012 Pearson Education, Inc.

Figure 13 -8 Dermatomes Figure 13 -7 Dermatomes. NV C 2–C 3 C 2 C 3 Dermatomes: Specific bilateral region of the skin that is monitored by a pair of spinal nerves C 3 C 4 T 2 • Each spinal nerve (except C 1) services its own dermatome (though there is overlap) C 6 L 1 L 2 C 8 • Clinically important to determine damage or infection of spinal nerve or dorsal root ganglion T 1 C 7 L 3 L 4 KEY • Results in loss of sensation or signs on skin in dermatome Spinal cord regions L 5 C 5 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 T 11 T 12 S 2 C 4 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 T 11 T 12 L 1 L 2 C 5 T 2 C 6 L 4 L 3 L 5 T 1 C 7 S 4 S 3 L 1 S 5 C 8 S 1 L 5 L 2 S 2 L 3 = Cervical = Thoracic = Lumbar S 1 = Sacral L 4 ANTERIOR © 2012 Pearson Education, Inc. ANTERIOR POSTERIOR

Figure 13 -9 Shingles § Viral infection of dorsal root ganglia § Caused by varicella-zoster virus § Same herpes virus as chickenpox § Produces painful rash and blisters on dermatome served by infected nerves § Those who have had chickenpox are more at risk § Virus can remain dormant within anterior gray horns § Unknown trigger for reactivation © 2012 Pearson Education, Inc.

13 -4 Spinal Nerves and Plexuses • The ventral ramus branch of each thoracic nerve (T 1 -T 12) goes directly to the intercostal muscles. • The ventral ramus of all other spinal nerves form a network by joining with other anterior rami branches…. plexus before going to their respective regions • The plexus will then give rise to individual nerves that control specific skeletal muscles of the neck, arms and legs. © 2012 Pearson Education, Inc.

13 -4 Spinal Nerves and Plexuses The Four Major Plexuses of Ventral Rami 1. Cervical plexus 2. Brachial plexus 3. Lumbar plexus 4. Sacral plexus © 2012 Pearson Education, Inc.

The Cervical Plexus • Includes ventral rami of spinal nerves C 1–C 5 • Innervates skin and muscles of neck, thoracic cavity, diaphragmatic muscles • Major nerve: Phrenic nerve (controls diaphragm): Damage to spinal cord above C 3 causes breathing difficulties © 2012 Pearson Education, Inc.

Figure 13 -10 Peripheral Nerves and Nerve Plexuses Cervical plexus Brachial plexus C 1 C 2 C 3 C 4 C 5 C 6 C 7 C 8 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 T 11 © 2012 Pearson Education, Inc. Lesser occipital nerve Great auricular nerve Transverse cervical nerve Supraclavicular nerve Phrenic nerve Axillary nerve Musculocutaneous nerve Thoracic nerves

The Brachial Plexus • Includes ventral rami of spinal nerves C 5–C 8, & part of T 1 • Innervates skin and muscles of pectoral girdle and upper limbs • Major nerve: Radial, ulnar and Median nerve: • Median Nerve Passes through the wrist. • Carpal Tunnel Syndrome: Inflammation of the carpal tendons can put pressure on this nerve causing numbness and pain in the fingers © 2012 Pearson Education, Inc.

Figure 13 -12 a The Brachial Plexus Trunks of Brachial Plexus Spinal Nerves Forming Brachial Plexus Dorsal scapular nerve Suprascapular nerve C 4 C 5 C 6 C 7 C 8 T 1 Superior Middle Inferior Musculocutaneous nerve Median nerve Ulnar nerve Radial nerve Lateral antebrachial cutaneous nerve Superficial branch of radial nerve Deep radial nerve Ulnar nerve Median nerve Palmar digital nerves Major nerves originating at the right brachial plexus, anterior view © 2012 Pearson Education, Inc.

No thoracic plexus! • Ventral rami of thoracic nerves do not interconnect • Become intercostal nerves to innervate intercostal muscles © 2012 Pearson Education, Inc.

The Lumbar Plexus • Includes ventral rami of spinal nerves T 12–L 4 • Supplies genitals, lateral and ventral abdominal wall and anterior/medial thigh • Major nerves • Femoral nerve: Extension of leg • Obturator nerve: Adduction of hip © 2012 Pearson Education, Inc.

Figure 13 -10 Peripheral Nerves and Nerve Plexuses T 12 L 1 Lumbar plexus Sacral plexus Radial nerve L 2 L 3 L 4 L 5 S 1 S 2 S 3 S 4 S 5 Co 1 Ulnar nerve Median nerve Iliohypogastric nerve Ilioinguinal nerve Lateral femoral cutaneous nerve Genitofemoral nerve Femoral nerve Obturator nerve Superior Inferior Gluteal nerves Pudendal nerve Saphenous nerve Sciatic nerve © 2012 Pearson Education, Inc.

The Sacral Plexus • Includes ventral rami of spinal nerves L 4–S 4 • Supplies to the buttocks and lower extremities • Major nerve: Sciatic nerve, longest & largest nerve in body: Flexion of leg • Two branches of the sciatic nerve 1. Tibial nerve 2. Common Fibular nerve Sciatica: Compression of nerve against ishium results in numbness of lower extremity or pain radiating from lower back to leg © 2012 Pearson Education, Inc.

Figure 13 -13 b The Lumbar and Sacral Plexuses Spinal Nerves Forming the Sacral Plexus Lumbosacral trunk L 4 nerve L 5 nerve Nerves of the Sacral Plexus S 1 nerve Superior gluteal S 2 nerve Inferior gluteal S 3 nerve Sciatic Posterior femoral cutaneous S 5 S 4 nerve Co 1 Pudendal Sacral plexus, anterior view © 2012 Pearson Education, Inc.

Figure 13 -13 e The Lumbar and Sacral Plexuses Superior gluteal nerve Inferior gluteal nerve Pudendal nerve Posterior femoral cutaneous nerve Sciatic nerve Tibial nerve Common fibular nerve Sural nerve © 2012 Pearson Education, Inc. Nerves of the sacral plexus, posterior view

13 -5 Neuronal Pools • Five Patterns of Neural Circuits in Neuronal Pools 1. Divergence • Spreads stimulation to many neurons or neuronal pools in CNS 2. Convergence • Brings input from many sources to single neuron 3. Serial processing • Moves information in single line 4. Parallel processing • Moves same information along several paths simultaneously 5. Reverberation • Positive feedback mechanism • Functions until inhibited © 2012 Pearson Education, Inc.

a Divergence A mechanism for spreading stimulation to multiple neurons or neuronal pools in the CNS © 2012 Pearson Education, Inc.

b Convergence A mechanism for providing input to a single neuron from multiple sources © 2012 Pearson Education, Inc.

c Serial processing A mechanism in which neurons or pools work sequentially © 2012 Pearson Education, Inc.

d Parallel processing A mechanism in which neurons or pools process the same information simultaneously © 2012 Pearson Education, Inc.

e Reverberation A positive feedback mechanism © 2012 Pearson Education, Inc.

13 -6 Reflexes are rapid, automatic responses to specific stimuli • Show little variability • Preserve homeostasis by making rapid adjustments in functions of organs or organ systems-negative feedback Spinal reflexes • Occur in spinal cord • Typically fast reflexes (ex: flexor reflex) Cranial reflexes • Occur in brain • Involving special sense organs © 2012 Pearson Education, Inc.

Figure 13 -15 Events in a Neural Reflex arc: Specific pathway followed by a nerve impulse in a reflex Activation of a sensory neuron Arrival of stimulus and activation of receptor Dorsal root Sensation relayed to the brain by axon collaterals Information processing in the CNS REFLEX ARC Receptor Stimulus Response by effector Effector Ventral root Activation of a motor neuron KEY Sensory neuron (stimulated) Excitatory interneuron Motor neuron (stimulated) © 2012 Pearson Education, Inc.

Figure 13 -16 The Classification of Reflexes can be classified by development response complexity of circuit processing site Innate Reflexes Somatic Reflexes Monosynaptic Spinal Reflexes • Genetically determined • Control skeletal muscle contractions • Include superficial and stretch reflexes Acquired Reflexes Visceral (Autonomic) Reflexes • Learned • Control actions of smooth and cardiac muscles, glands, and adipose tissue • One synapse Polysynaptic • Multiple synapse (two to several hundred) • Processing in the spinal cord Cranial Reflexes • Processing in the brain Somatic Reflexes are often used to diagnose neurological Impairment © 2012 Pearson Education, Inc.

Ipsilateral reflex arc • Stimulus and response occur on same side of body Contralateral reflex arc • Stimulus and response occur on opposite sides of body © 2012 Pearson Education, Inc.

Stretch reflex are Monosynaptic reflexes involving muscle spindles that regulate muscle length: Example: Patellar Reflex Receptor (muscle spindle) Spinal cord Stretch REFLEX ARC Stimulus Effector Contraction Response © 2012 Pearson Education, Inc. KEY Sensory neuron (stimulated) Motor neuron (stimulated)

Withdrawal Reflexes are Polysynaptic Reflexes that move body part away from stimulus (pain or pressure). Example: Flexor reflex Distribution within gray horns to other segments of the spinal cord Painful stimulus Flexors stimulated Extensors inhibited KEY Sensory neuron (stimulated) Motor neuron (inhibited) Excitatory interneuron Inhibitory interneuron Motor neuron (stimulated) © 2012 Pearson Education, Inc.

Crossed extensor reflexes: Polysynaptic reflexes • Example: stepping on a tack Flexor reflex pulls injured foot away • Flexor muscles stimulated • Extensor muscles inhibited Crossed extensor reflex straightens uninjured leg and supports shifting weight • Extensor muscles stimulated • Flexor muscles inhibited © 2012 Pearson Education, Inc.

The crossed extensor reflex, which involves a contralateral reflex arc To motor neurons in other segments of the spinal cord Extensors inhibited Flexors stimulated Extensors stimulated Flexors inhibited Sensory neuron (stimulated) Excitatory interneuron Motor neuron (stimulated) Painful stimulus © 2012 Pearson Education, Inc. Motor neuron (inhibited) Inhibitory interneuron Figure 12. 11 2

Figure 13 -21 The Babinski Reflexes The plantar reflex (negative Babinski reflex), a curling of the toes, is seen in healthy adults. © 2012 Pearson Education, Inc. The Babinski sign (positive Babinski reflex) occurs in the absence of descending inhibition. It is normal in infants, but pathological in adults.

Spinal cord injury • Can be due to accidents, fall, violence • Can result in abnormal reflexes and/or paralysis • Extent of paralysis dependent on location of injury Monoplegia: paralysis of one limb Paraplegia: paralysis of both lower limbs Quadriplegia: paralysis of all four limbs © 2012 Pearson Education, Inc.