The Spinal Cord and Spinal Nerves PDF

Principles of Anatomy and Physiology Gerard Tortora and Bryan Derrickson Sixteenth Edition Chapter 13 The Spinal Cord and Spinal Nerves This slide deck contains animations. Please disable animations if they...

Principles of Anatomy and Physiology Gerard Tortora and Bryan Derrickson Sixteenth Edition Chapter 13 The Spinal Cord and Spinal Nerves This slide deck contains animations. Please disable animations if they cause issues with your device. Copyright ©2021 John Wiley & Sons, Inc. Introduction The purpose of this chapter is to: 1. Identify and describe the anatomical features of the spinal cord and spinal nerves 2. Discuss the functions of the spinal cord and spinal nerves, and understand how they help maintain homeostasis in the body 3. Understand spinal reflex arcs Copyright ©2021 John Wiley & Sons, 2 Inc. Functions of the Spinal Cord 1. Processes reflexes 2. Integrates EPSPs and IPSPs 3. Conducts sensory impulses to the brain and motor impulses to effectors Copyright ©2021 John Wiley & Sons, 3 Inc. Spinal Cord Anatomy Copyright ©2021 John Wiley & Sons, 4 Inc. Protection of the Spinal Cord The spinal cord is protected by: Bone (vertebrae) Connective tissue (meninges) Fluid (cerebrospinal fluid) Copyright ©2021 John Wiley & Sons, 5 Inc. Meninges The meninges are composed of three layers: 1. Dura mater 2. Arachnoid mater 3. Pia mater Copyright ©2021 John Wiley & Sons, 6 Inc. Copyright © 2017 John Wiley & Sons, Inc. All rights reserved. External Anatomy of the Spinal Cord The spinal cord begins as an extension of the medulla oblongata at the level of the foramen magnum and terminates at the level of L2 Copyright ©2021 John Wiley & Sons, 8 Inc. External Cord Anatomy Arising from the conus medullaris is the filum terminale, an extension of the pia mater that extends inferiorly and blends with the arachnoid and dura to anchor the spinal cord to the coccyx. The cauda equina or “horses tail” are the roots of the lower spinal nerves that angle down alongside the filum terminale. External Cord Anatomy The spinal cord has two enlargements, one in the cervical area from C4–T1, and another in the lumbar area between T9–T12. The cervical enlargement correlates with the sensory input and motor output to the upper extremities. The lumbar enlargement handles motor output and sensory input to and from the legs.  Internal Cord Anatomy In the spinal cord, the white matter is on the outside, and the gray matter is on the inside. In the brain the white matter is on the inside, and the gray matter is on the outside. Internal Anatomy of the Spinal Cord (1 of 2) Copyright ©2021 John Wiley & Sons, 12 Inc. Internal Anatomy of the Spinal Cord (2 of 2) - Filled with CSF Copyright ©2021 John Wiley & Sons, 13 Inc. Sensory and Motor Processing The internal anatomy of the spinal cord allows sensory and motor information to be processed in an organized way Copyright ©2021 John Wiley & Sons, 14 Inc. Comparison of Various Spinal Cord Segments (1 of 2) Table 13.1 Comparison of Various Spinal Cord Segments Copyright ©2021 John Wiley & Sons, 15 Inc. Comparison of Various Spinal Cord Segments (2 of 2) Table 13.1 Comparison of Various Spinal Cord Segments Copyright ©2021 John Wiley & Sons, 16 Inc.  External Cord Anatomy Two bundles of axons, called roots, connect each spinal nerve to a segment of the cord by even smaller bundles of axons called rootlets. The posterior (dorsal) root and rootlets contain only sensory axons, which conduct nerve impulses from sensory receptors in the skin, muscles, and internal organs into the central nervous system. External Cord Anatomy Each posterior root has a swelling, the posterior (dorsal) root ganglion, which contains the cell bodies of sensory neurons. The anterior (ventral) root and rootlets contain axons of motor neurons, which conduct nerve impulses from the CNS to effectors (muscles and glands).  Epidural Anesthesia Epidural anesthesia is commonly administered to women about to go into labor. In this procedure, a needle is placed between the bones of the posterior spine until it just penetrates the ligamentum flavum yet remains superficial to the dura mater. Local anesthetic is used to provide pain relief – even complete anesthesia if a cesarean section is required.  Lumbar Puncture A needle inserted into the subarachnoid space for the purpose of withdrawing CSF (for diagnosis or to reduce pressure) or to introduce a drug or contrast agent is called a lumbar puncture. CSF is often collected to diagnose meningitis or some other disease of the CNS. Agents injected into the SAS include drugs such as antibiotics, chemotherapeutic agents, or analgesics, or contrast media for radiographic procedures. The pressure of CSF in the SAS can also be measured during a lumbar puncture.  Lumbar Puncture The site used for most lumbar punctures is between the 3 rd and 4th (or 4th and 5th) lumbar vertebrae - below the termination of the actual cord in the region of the cauda equina. With the needle in the SAS, CSF can be sampled. Anesthetics can also be given in this way, but using 1/10 the dose required for epidural anesthesia. Spinal Nerves Copyright ©2021 John Wiley & Sons, 22 Inc. Spinal Nerves (1 of 2) Spinal nerves connect the CNS to sensory receptors, muscles, and glands and are part of the peripheral nervous system 31 pairs of spinal nerves Anterior and posterior roots attach a spinal nerve to a segment of the spinal cord Copyright ©2021 John Wiley & Sons, 23 Inc. Spinal Nerves (2 of 2) Spinal nerves Copyright ©2021 John Wiley & Sons, 24 Inc. Connective Tissue Covering of Spinal Nerves Copyright ©2021 John Wiley & Sons, 25 Inc.  Peripheral Nerves Spinal nerves are the paths of communication between the spinal cord and specific regions of the body. Nerves are arranged in fascicles surrounded by a perineurium, with the entire nerve sheathed by a CT epineurium. Peripheral Nerves 31 left-right pairs of spinal nerves emerge from the cord at regular intervals (called segments). Except for the first cervical pair the spinal nerves leave the vertebral column from the intervertebral foramen between adjoining vertebrae – the first pair leaves between the skull and the first cervical vertebrae. Cervical – 8 pairs, C1-C8 Thoracic – 12 pairs, T1-T12 Lumbar – 5 pairs, L1-L5 Sacral - 5 pairs, S1-S5 Coccygeal – 1 nerve pair Peripheral Nerves Piercing the dura, the segmental (spinal) nerves exit the central nervous system into the peripheral nervous system and almost immediately split into 3 major branches: An anterior ramus, posterior ramus, and rami communicantes (connections to sympathetic ganglia).  Peripheral Nerves The anterior rami of the segmental nerves may travel alone (such as the intercostal nerves which run underneath each of the 12 ribs), or they can join together to form large “braided ropes” – a plexus of nerves. There are a number of major nerve plexuses, all formed from anterior rami of spinal nerves, and all located anterior to the spine: The cervical plexus, brachial plexus, celiac (solar) plexus, lumbar plexus, sacral plexus, and coccygeal plexus Branches of a Spinal Nerve Shortly after passing through its intervertebral foramen a spinal nerve divides into several branches known as rami Copyright ©2021 John Wiley & Sons, 30 Inc. Dermatomes Certain segments of the skin are supplied by spinal nerves that carry somatic sensory nerve impulses to the brain Copyright ©2021 John Wiley & Sons, 31 Inc. Cervical Plexus Copyright ©2021 John Wiley & Sons, 32 Inc. Cervical Plexus (1 of 3) Supplies the skin and muscles of the head, neck, superior portion of the shoulders and chest, and diaphragm Copyright ©2021 John Wiley & Sons, 33 Inc. Cervical Plexus (3 of 3) Deep (Largely Motor) Branches –have to know only the phrenic nerve Nerve Origi Description n Phrenic (FREN-­- C3– Diaphragm. ik) C5 Copyright ©2021 John Wiley & Sons, 34 Inc. Brachial Plexus Copyright ©2021 John Wiley & Sons, 35 Inc. Brachial Plexus (1 of 6) Provides almost the entire nerve supply to the shoulders and upper limbs. Lesion of the median nerve results in carpal tunnel syndrome. Copyright ©2021 John Wiley & Sons, 36 Inc. Brachial Plexus (2 of 6) Copyright ©2021 John Wiley & Sons, 37 Inc. Brachial Plexus (3 of 6) Copyright ©2021 John Wiley & Sons, 38 Inc.  Nerve Plexuses The long thoracic nerve emerges from the cords of the brachial plexus to supply the serratus anterior muscle. Because of its long, relatively superficial course, it is susceptible to injury either through direct trauma or stretch of the plexus. Injury (resulting in a “winged scapula” in which the arm cannot be abducted beyond the horizontal position) has been reported in almost all sports.  Nerve Plexuses Injuries to the brachial plexus are not uncommon: Erb’s palsy is a paralysis of the arm that most often occurs as an infant's head and neck are pulled toward the side at the same time as the shoulders pass through the birth canal. A similar injury may be observed at any age, including adults, following a traumatic fall or other trauma whereby the nerves of the plexus are violently stretched.  Nerve Plexuses The ulnar nerve is the largest unprotected (by muscle or bone) nerve in the human body. It emerges from the medial and lateral cords of the brachial plexus to supply the medial half of the hand. Striking the medial epicondyle of the humerus where the nerve is exposed is referred to as bumping one’s “funny bone”. Damage to the nerve leads to abnormal sensations in the 4–5th fingers and an inability to abduct or adduct the little and ring fingers.  Nerve Plexuses Injuries to the brachial plexus or peripheral nerves: Median nerve injury, either at the plexus or occurring more distally, results in numbness, tingling and pain in the palm and fingers. Carpal tunnel syndrome is a common type of median nerve injury that is seen in people who perform repetitive motions of the hand and wrist like typing on a computer keyboard. Lumbar Plexus Copyright ©2021 John Wiley & Sons, 43 Inc. Lumbar Plexus (1 of 4) Copyright ©2021 John Wiley & Sons, 44 Inc. Lumbar Plexus (2 of 4) Copyright ©2021 John Wiley & Sons, 45 Inc. Lumbar Plexus (4 of 4) Nerve Origi Distribution n Femoral L2–L4 Largest nerve arising from lumbar plexus; distributed to flexor muscles of hip joint and extensor muscles of knee joint, skin over anterior and medial aspect of thigh and medial side of leg and foot. Obturator (OB-­- L2–L4 Adductor muscles of hip joint; skin over too-­rā′-tor) medial aspect of thigh. Copyright ©2021 John Wiley & Sons, 46 Inc.  Sacral Plexus Know only sciatic nerve. Copyright ©2021 John Wiley & Sons, 47 Inc.  Sacral Plexus & Coccygeal plexus (form by the S4/S5 & coccygeal nerve) Copyright ©2021 John Wiley & Sons, 48 Inc. Sacral Plexus (2 of 6) Copyright ©2021 John Wiley & Sons, 49 Inc.  Sacral Plexus (5 of 6) Nerve Origin Distribution Sciatic (sī-­AT-­ik) L4–S3 Actually two nerves—­tibial and common fibular—­- bound together by common sheath of connective tissue; splits into its two divisions, usually at the knee. (See below for distributions.) As sciatic nerve descends through thigh, it sends branches to hamstring muscles and adductor magnus. Copyright ©2021 John Wiley & Sons, 50 Inc. Spinal Cord Physiology Copyright ©2021 John Wiley & Sons, 51 Inc. Spinal Cord Physiology In order to maintain homeostasis, the spinal cord must propagate nerve impulses and integrate information How does information travel in the spinal cord? White matter tracts conduct nerve impulses to and from the brain Gray matter receives and integrates incoming and outgoing information to perform spinal reflexes Copyright ©2021 John Wiley & Sons, 52 Inc. Sensory and Motor Tracts Copyright ©2021 John Wiley & Sons, 53 Inc. Reflexes and Reflex Arcs A reflex is a fast, involuntary, unplanned response to a particular stimulus Reflexes help maintain homeostasis The gray matter of the spinal cord serves as the integrating center for spinal reflexes Copyright ©2021 John Wiley & Sons, 54 Inc. Reflexes Interactions Animation: Reflexes Copyright ©2021 John Wiley & Sons, 55 Inc. General Components of a Reflex Arc Interactions General Components of Animation: a Reflex Arc Copyright ©2021 John Wiley & Sons, 56 Inc. Reflex Arcs: Vocabulary Terms Ipsilateral = same side Contralateral = opposite side Monosynaptic = one Polysynaptic = more than one Reciprocal innervation = neural circuit simultaneously contracts one muscle and relaxes its antagonists Copyright ©2021 John Wiley & Sons, 57 Inc. Stretch Reflex Causes contraction of a muscle that has been stretched Copyright ©2021 John Wiley & Sons, 58 Inc. Tendon Reflex Causes relaxation of the muscle attached to the stimulated tendon Copyright ©2021 John Wiley & Sons, 59 Inc. Flexor (Withdrawal) Reflex Causes withdrawal of a limb to avoid injury or pain Copyright ©2021 John Wiley & Sons, 60 Inc. Crossed-Extensor Reflex Maintains balance during a withdrawal reflex Copyright ©2021 John Wiley & Sons, 61 Inc.  Reflexes Some important spinal reflexes include: The patellar reflex in which the leg extends in response to stretch of the patellar tendon. This reflex can be blocked by damage in the corticospinal tracts from diabetes, neurosyphilis, or damage to the lumbar region of the spinal cord. The Achilles reflex causes contraction of the calf when a force is applied to the Achilles tendon. It is absent after damage to the lower cord or lumbosacral plexus.  Reflexes Some important spinal reflexes include: The Babinski, or plantar flexion reflex is considered normal in adults if they flex (curl) the big toe when the sole of the foot is stimulated. If the sole of the foot is stimulated and the patient extends the big toe, it would indicate damage in the corticospinal tract. Infants normally extend their toes when stimulated in this way; so an “abnormal Babinski” does not Disorders (1 of 4) Traumatic Injuries – monoplegia, paraplegia, hemiplegia, quadriplegia Damage that results from traumatic injuries depends on: o Degree of spinal cord section or o Degree of compression of the segments involved Copyright ©2021 John Wiley & Sons, 64 Inc. Disorders (2 of 4) Extent of paralysis from traumatic injury depends on location A – no function from neck down B – some arm and chest muscle control C – most thigh muscles D – most leg muscles Copyright ©2021 John Wiley & Sons, 65 Inc.  Damage to the Cord “Transection” of the spinal cord means that ascending and descending tracts are partially or completely severed. If transection occurs, say in a motor vehicle or diving accident, paralysis will occur depending on the level of the injury. Transection: at the base of skull results in death by asphyxiation in the upper cervical area results in quadriplegia between the cord enlargements results in some form of paraplegia Disorders Spinal cord compression Degenerative diseases Shingles Poliomyelitis Copyright © 2017 John Wiley & Sons, Inc. All rights reserved. Spinal cord compression - The spinal cord may be compressed by bone, blood (hematomas), pus (abscesses), tumors (cancerous or not), or a ruptured or herniated disk. © John Wiley & Sons, Inc. All rights reserved.  Degenerative diseases Multiple Sclerosis Demyelination of Oligodendroglia. Amyotropic Lateral Sclerosis (ALS – Lou Gehrig) A progressive nervous system disease that affects nerve cells in the brain and spinal cord, causing loss of muscle control. Stephen Hawking © John Wiley & Sons, Inc. All rights reserved. Disorders (3 of 4) Shingles Acute infection of the PNS caused by herpes zoster virus (also causes chickenpox) Causes pain, discoloration of the skin and line of skin blisters Copyright ©2021 John Wiley & Sons, 70 Inc. © John Wiley & Sons, Inc. All rights reserved. Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.  Poliomyelitis (Polio) Caused by the poliovirus. The virus spreads from person to person and can infect a person’s spinal cord, causing paralysis. Copyright ©2021 John Wiley & Sons, 73 Inc. Copyright © 2017 John Wiley & Sons, Inc. All rights reserved.