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Central Nervous System - Spinal Cord, Spinal Nerves & Spinal Reflexes

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Central Nervous System - Spinal Cord, Spinal Nerves & Spinal Reflexes Central Nervous System - Spinal Cord, Spinal Nerves & Spinal Reflexes Chapter 13A Central Nervous System Central nervous system (CNS) is responsible for: Receiving impulses from receptors Integrating information Sending impulses to the effectors It is composed of: Brain Spinal cord Spinal Cord - Functions Spinal cord has the following functions: 1. Receive and send impulses: receives impulses from receptors and sends impulses to the effectors. 2. Communication with the brain: has bundles/cables of nerve fibers (tracts) that take sensory impulses up to the brain or motor impulses down from the brain. 3. Movement: muscle contraction for basic movement is controlled by the spinal cord…although the initiation, the speed and the direction of movement is controlled by the brain. 4. Reflexes: simple reflexes are controlled by the spinal cord….pulling your finger back when you touch a hot plate. Complex reflexes are controlled by the brain… remembering not to touch a hot plate again! Spinal Cord - Protection Meninges Spinal cord Meninges Pia mater Arachnoid mater Dura mater Vertebra Vertebral foramen Spinal cord is protected by bones and 3 connective tissue membranes called meninges. From outside inside: 1. Boney protection: vertebrae vertebral foramina align form vertebral canal houses spinal cord. 2. Dura mater: outermost tougher meninx. 3. Arachnoid mater: middle avascular meninx. 4. Pia mater: innermost meninx that sticks to the spinal cord. Spinal Cord –Spaces There are spaces between the protective bones and the 3 meninges. 1. Epidural space – space between vertebrae and the dura mater- filled with adipose tissue. 2. Subdural space –space between dura mater and arachnoid-filled with interstitial fluid (no such space in healthy person; space appears when there is trauma or underlying pathological conditions). 3. Subarachnoid space – space between arachnoid and pia mater- filled with cerebrospinal fluid (CSF). Spinal Cord Lumbar puncture/spinal tap Lumbar puncture/Spinal tap: a sample of CSF is removed from subarachnoid space chemical analysis for diagnosis of certain diseases and disorders- like Meningitis, Multiple Sclerosis, CNS tumors etc.. Epidural anesthesia: an anesthetic shot given in the epidural space of lumbar region numbs specific spinal nerves in the immediate area of injection…usually used for child birth, surgery in the pelvic region and legs. Meningitis: inflammation of meninges…bacterial or viral. If left untreated infection spreads to brain death. Spina bifida: incomplete closure of the pedicles of the vertebrae spinal cord and nerves not well protected paralysis of lower extremities and pelvic organs….May be due to lack of vitamin B/folic acid during pregnancy. Spinal Cord – External Structure During early childhood development, vertebral column and spinal cord grow. Around age 4 or 5 years, spinal cord growth slows down while vertebral column continues to grow. Therefore in an adult, spinal cord extends from the base of the brain ends at L1 or L2. Termination ee pinalS Cord The level of the spinal cord segments do not relate exactly to the level of the vertebral bodies i.e. damage to the bone at a particular level e.g. L5 vertebrae does not necessarily mean damage to the spinal cord at the same spinal nerve level. Spinal Cord – External Structure Spinal cord is not uniform along its length. The amount of gray matter is greatest in segments of spinal cord dedicated to the sensory & motor control of the limbs. Two regions of the spinal cord are wider: Cervical enlargement: located in the cervical and upper shoulder region supplies nerves to the shoulder and upper limbs. Lumbar enlargement: located in the thoracic region innervates pelvis and lower limbs. Conus medularis: tapered, cone shaped ending of the Termination spinal cord. ee pinalS Cord Located in L1-L2 region. Cauda equina: A group of nerves that originate from the conus medullaris includes lumbar (2nd-5th), L1 sacral (1st to 5th) and coccygeal (1) spinal nerves. L2 - Resemble horse’s tail. L3 L4 - Function:- send and receive messages between the L5 lower limbs and the pelvic organs, which consist of the bladder, the rectum, and the internal genital organs. Spinal Cord – Anchoring Pia mater Arachnoid Dura mater Spinal cord is located inside the vertebral canal. It needs to be anchored to prevent it from moving around: Filum terminale: extension of pia mater from conus medullaris to anchor spinal cord down to the coccyx. Denticulate ligament: extensions of pia mater-attaches laterally to arachnoid and dura mater-stabilizes side-to-side movement of spinal cord within vertebral column. Spinal Cord – Internal Structure Anterior or Posterior?? Posterior/dorsal Anterior/ Posterior/ Ventral dorsal Anterior or Posterior?? Anterior/ventral To understand the internal structure of the spinal cord…..you have to get the directions right!!!! Here you see spinal cord inside a vertebra. Which side is anterior and which is posterior?? Spinal Cord – Internal Structure Posterior/dorsal side Posterior median sulcus White matter Gray matter Anterior median fissure Anterior/ventral side Superior view Anterior median fissure: a deep groove that runs along the anterior surface of the spinal cord. Posterior median sulcus: a depression that runs along the posterior surface of the spinal cord. The tissue can be divided into gray matter and white matter. Gray matter: in the shape of letter H….towards the center. White matter: around the gray matter….along the periphery. Spinal Cord – Internal Structure- Gray matter Central canal Gray commissure Gray matter:- dominated by the cell bodies of neurons, neuroglia, and unmyelinated axons, surrounds the narrow central canal and forms a butterfly shape or letter H shape. Horns:- the projections of gray matter toward the outer surface of the spinal cord 2 arms of the letter H. Gray commissure- the cross bar that connects the gray horns/middle portion of the gray matter. Central canal: located in the center of the gray commissure has CSF lined by ciliated ependymal cells to circulate CSF. Spinal Cord – Internal Structure- Gray matter Posterior/Dorsal Posterior side gray horn Posterior/Dorsal gray horn: posterior part of gray matter Function: contains sensory nuclei- somatic and visceral - receives information from skeletal muscles and skin (somatic) and visceral organs (visceral) and relays it to CNS. Anterior side Dorsal root ganglion Posterior side Dorsal root ganglion: contains the cell bodies of sensory neurons whose axons carry information to the spinal cord. Anterior side Dorsal root Posterior side Dorsal root: contains the axons of the sensory neurons whose cell bodies are in the dorsal root ganglion. Anterior side What structure is within the dorsal root ganglion? Cell bodies of sensory neurons Spinal Cord – Internal Structure- Gray matter Posterior side Anterior/Ventral gray horn: anterior part of gray matter Function: contains motor nuclei (somatic) –sends commands to skeletal muscles. Anterior/Ventral Anterior side gray horn Posterior side Ventral root: connected to ventral horns of spinal cord Contains axons of motor neurons send message out to effectors Anterior side Ventral root Posterior side Lateral gray horn: lateral side of gray matter Function: contains visceral motor nuclei –sends commands to smooth muscle, cardiac muscle and glands. Anterior side Lateral gray horn What types of neurons travel through the dorsal root? Sensory neurons What types of neurons travel through the ventral root? Motor neurons A single spinal nerve contains the axons of BOTH sensory and motor neurons. The sensory fibers enter the CNS through the dorsal root. The motor fibers emerge from the CNS via the ventral root. Spinal Cord – Internal Structure- White matter Posterior median sulcus Posterior white column Lateral white column Posterior/ dorsal horn Anterior white column The superficial white matter contains large numbers of myelinated and unmyelinated axons. The structural components of white mater are divided into columns. 1. The posterior white column- lies between the posterior gray horns and posterior median sulcus -has ascending tracts only- carry sensory information from the spinal cord to the brain. * tracts-bundles of myelinated axons in CNS (brain and spinal cord) 2. The lateral white column- includes the white matter on either side of the spinal cord between the anterior and posterior columns- has both ascending (carry sensory information from spinal cord to brain) & descending tracts (convey motor information from brain to the spinal cord). 3. The anterior white column- lies between the anterior gray horns and the anterior median fissure- has both ascending & descending tracts. Spinal Nerves Nerves are part of peripheral nervous system (PNS). Functions of the nerves: Bring sensory impulses to the spinal cord. Take motor impulses to the muscles and glands (effectors). Spinal Nerves - Structure Nerve Muscle Nerve organization is strikingly similar to muscle organization! Remember: A muscle is made of fascicles each fascicle is made of many muscle fibers. Endomysium is connective tissue inside the fascicle. Perimysium is connective tissue around each fascicle. Epimysium is connective tissue that wraps around the entire muscle! Spinal Nerves - Structure A nerve is the primary structure of the peripheral nervous system (PNS) that encloses the axons of peripheral neurons…made of fascicles each fascicle is made of a group of nerve fibers (axons). Endoneurium: is connective tissue around nerve fibers (axons) inside
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