Spinal Cord and Nerves Review Sheet PDF

Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. SPINAL CORD AND SPINAL NERVES Spinal Cord Protection System – 4 Ways to protect the cord 1. Bone – each vertebra provides a wall of protection surround the spinal cord 2. Meninges (pl.) - Are connective tissue coverings that run...

Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. SPINAL CORD AND SPINAL NERVES Spinal Cord Protection System – 4 Ways to protect the cord 1. Bone – each vertebra provides a wall of protection surround the spinal cord 2. Meninges (pl.) - Are connective tissue coverings that run continuously around both the spinal cord and the brain. - 3 Sections of the Meninges (from outer to inner) and a space between each: 1. Outer spinal mining = AKAS "Dura Mater" - The dura merges with the periosteum of the skull and the vertebral canal. - A tough white fibrous connective tissue (inelastic). - The dura mater contains channels, called dural sinuses which collect venous blood to return to the cardiovascular system. * Epidural Space (L4) – space between the dura mater and the vertebrae - Filled with fat, CT, and blood vessels - It serves as padding around the cord. NOT FOUND IN THE BRAIN!!! - This is the site for the injection of anesthetics, such as a saddleblock for childbirth. * Subdural Space – space between the dura mater and arachnoid 2. Middle Spinal Meninx = AKAS “Arachnoid” - Termed Arachnoid because of spiderweb-like appearance from the loose connective tissue strands that extends downward into the subarachnoid space * Subarachnoid Space - contains circulating cerebrospinal fluid - Located between the arachnoid and the pia mater - Lumbar Puncture – a procedure by which withdrawal of CSF is made in the subarachnoid space at approximately L4. 1 Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. 3. Inner Spinal Meninx = AKAS "Pia Mater" - Layer that adheres to the surface of the spinal cord and brain. - Blood vessels exit the pia mater to enter the nerve tissue of the brain and spinal cord. 3. Denticulate Ligaments - They are what hold the spinal cord suspended in the middle of its Dural Sheath. - Are membranous extensions of the pia mater. - They protect the spinal cord against shock and sudden displacement. 4. Cerebrospinal Fluid - Found in the subarachnoid space and central canal of the gray commissure. Spinal Cord General Features - Spinal Cord Length - 17 or 18 inches - It begins as a continuation of the Medulla Oblongata, passes through the Foramen Magnum of the occipital bone and terminates at the conus medullaris (L2). - 4 Major Parts to the Spinal Cord: 1. 2 Enlargements can be seen: * Cervical Enlargement (Superior Enlargement) - Extends from C4 to T1 - Nerves that supply the upper extremities arise from the cervical enlargement. * Lumbar Enlargement (Inferior Enlargement) - Extends from T9 to T12 - Nerves that supply the lower extremities arise from the lumbar enlargements. 2. Conus Medullaris * Located inferior to the lumbar enlargement, the spinal cord tapers to a conical portion known as the Conus Medullaris. 2 Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. * Ends at the 1st and 2nd lumbar vertebrae 3. Cauda Equina: AKA "Horse's Tail" * Some nerves that arise from the lower portion of the cord and do not leave but instead flow away and wisp out. 4. Filum Terminale * The meninges extend beyond the end of the spinal cord down to the sacrum. From the sacrum, a non nervous fibrous tissue cord of the pia mater (filum terminale) extends down to the coccyx where it is anchored. Spinal Cord Cross-Section - The spinal cord is divided into right and left sides by 2 grooves: 1) Anterior (Ventral) Median Fissure - deeper 2) Posterior (Dorsal) Median Sulcus - shallow - The spinal cord consists of both Gray and White matter. - Gray Matter: * Lacks myelin which gives it a gray color * Forms the H-shaped area within the white matter. - Parts of the H- shaped area: 1. Horns = sides of the H a. Dorsal Horn b. Lateral Horn c. Ventral Horn 2. Gray Commissure = cross bar of the H 3. Central Canal = located in the gray commissure - Contains CSF – Both subarachnoid space and central canal have CSF in it) * Gray Matter Consists of: 1. Nerve cell bodies and several nuclei - that serve as relay stations for nerve impulses and origins for certain nerves. - Collections of nerve cell bodies in the gray matter of the CNS are known as nuclei. 3 Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. - Collections of nerve cell bodies located outside of the CNS are known as ganglia (sing.= ganglion). 2. Unmyelinated (unlike white matter) Axons 3. Dendrites of Association 4. Motor Neurons Only - white matter has both sensory and motor neurons White Matter: * White matter gets its name because it contains myelin, a phospholipid with a whitish color. * White matter is organized into three regions (Columns) on each side: 1. dorsal columns 2. lateral columns 3. ventral columns * White matter consists of “bundles” of myelinated axons * It forms the sensory and motor tracts of the spinal cord. Remember, gray matter only has motor neurons. * 2 Spinal Tracts located within the Columns: 1. Ascending Tract – to be discussed in further detail 2. Descending Tract - to be discussed in further detail 2 Major Spinal Cord Functions: Impulse conduction and Reflex Integration 1. Impulse Conduction- 2 Major Conduction Pathways 1. Ascending tracts – conduction pathways that carry sensory impulses from body parts to the brain. 2. Descending tracts – pathways that carry motor impulses from the brain to muscles and glands. - The names of the tract usually indicate: * Which white column the tract travels * Where the cell bodies of the tract originates * Where the axons of the tract terminates - Example #1: Anterior Spinothalamic Tract = located in the anterior white column = originates in the spinal cord 4 Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. = terminates in the thalamus (region of the brain) - Crossing over of the spinal tracts: Impulses reaching the spinal cord from the left side of the body eventually pass over to tracts running up to the right side of the brain and vise versa. In some cases this crossing over occurs as soon as the impulses enter the cord, or it doesn’t take place until the tracts enter the brain itself. 2. Reflex Integration “AKA Reflex Arc” - The reflex arc is the functional unit of the nervous system. The neuron is the structural unit of the nervous system. - Reflexes are responses to stimuli that do not require conscious thought and they occur more quickly than reactions that require thought processes. - Many reflexes are mediated in the spinal cord without going to the higher brain centers. - In the withdrawal reflex the reflex action withdraws the affected part before you are aware of the pain. (Like picking up a hot tea kettle ) Location of Spinal Nerves: - The spinal cord consists of 31 "Spinal Segments", named and numbered according to the region and level of the spinal cord which they emerge. Cervical –contains 8 spinal nerves, the 8th cervical nerve runs between C7 and T1. Thoracic –contains 12 spinal nerves Lumbar - contains 5 spinal nerves Sacral–contains 5 spinal nerves Coccyx - contains 1 spinal nerve - The first pair emerges between the occipital bone and the atlas. - The other pairs of spinal nerves emerge from the intervertebral foramina between adjacent vertebrae. They are named from the vertebra above which they emerge. - Since the spinal cord ends at about L2, nerves below this point continue as the Cauda Equina before emerging from the spine. Structure of Spinal Nerves: 5 Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. - A nerve is a bundle of fibers – just like a muscle is a bundle of fibers. Fasciculus - a bundle of individual nerve fibers - Each nerve and its subunits have connective tissue coverings: 1. Endoneurium – covering over each individual fiber in the spinal nerve 2. Perineurium – covering around each Fasciculus 3. Epineurium - the outer covering around the entire nerve; continuous with the meninges - Each spinal nerve is connected to the spinal cord via Roots (AKA Rami) (pl), Ramus (singular): *2 Roots: 1. Dorsal Ramus – Possesses only sensory fibers - can be recognized by the dorsal root ganglia (group of nerve cell bodies) 2. Ventral Ramus –posses on motor fibers *Note: The 2 rami join to form the spinal nerve just before they exit the spinal column. Having both sensory and motor fibers makes each spinal nerve a mixed nerve. * Most of the spinal nerves will divide into branches (networks) to innervate all the effectors of the body. The networks are referred to as Plexuses. - Plexuses * A plexus is a network of nerves. The network begins from the first projection (rami) off the spinal cord and continues to divide extensively. * The thoracic region is the only region of the body that does not form a plexus. * Names and Locations of the (4) Plexus: 1. Cervical Plexus = C1 - C4 and contributes to C5 - Supplies the skin and muscles of the head, neck, upper shoulders, & diaphragm. - Names of the nerves emerging off the cervical plexus: 1. Lesser Occipital 2. Ansa Cervicalis 3. Transverse Cervical 4. Supraclavicular 5. Phrenic 2. Brachial Plexus = C5 - C8 and T1 - Supplies the upper extremities, neck, and shoulder regions. 6 Anatomy and Physiology 2 Review Sheet Kimberly Denise Vigee’, N.D. - Names of the nerves emerging off the brachial plexus: 1. Axillary 4. Ulnar 2. Musculocutaneous 5. Radial 3. Median 3. Lumbar Plexus = L1 - L4 - Supplies some of the lower extremity, external genitals, and abdominal wall. - Names of the nerves emerging off the lumbar plexus: 1. Iliohypogastric 2. Ilioinguinal 3. Genitofemoral 4. Lateral femoral Cutaneous 5. Obturator 6. Femoral 4) Sacral Plexus = L4 - L5 and S1 - S4 - Supplies the lower extremities and buttocks. - Names of the nerves emerging off the sacral plexus: 1. Superior gluteal 2. Inferior gluteal 3. Sciatic 4. Posterior femoral cutaneous 5. Pudendal * Distributions of the Plexuses: Mneumonic: R eal Truckers D rink C old B eer? Rami: Dorsal Ramus - innervate deep muscles and skin of dorsal surface of trunk. Ventral Ramus - innervates muscles & structures of the extremities & the lateral & ventral trunk. Trunks: superior, middle, and inferior Divisions: anterior and posterior Cords: medial, lateral, posterior Branches: what we know as individual nerves: radial nerve, median nerve, etc. 7