L1- (Anatomy-1) Intro to neuroanatomy & Spinal cord .pdf

Lecture 1 INTRODUCTION TO NEUROANATOMY AND SPINAL CORD by: Dr. Ahmed Elnabawy Ahmed Learning Outcomes At the end of the lecture, the students should be able to: Identify the different parts of the nerv...

Lecture 1 INTRODUCTION TO NEUROANATOMY AND SPINAL CORD by: Dr. Ahmed Elnabawy Ahmed Learning Outcomes At the end of the lecture, the students should be able to: Identify the different parts of the nervous system anatomically and functionally Identify the external and internal features of the spinal cord text Mention the blood supply of the sipnal cord Correlate the meningeal covering of the spinal cord with a clinical application ❑ If the body is to maintain homeostasis and function effectively, its trillions of cells must work together in a coordinated fashion. ❑ If each cell behaved without regard to what others are doing, the result would be physiological chaos and death. ❑ We have two organ systems dedicated to maintaining internal coordination: ❑communicates by means of endocrine chemical messengers system (hormones) secreted into the blood ❑employs electrical and nervous chemical means to send messages very quickly from cell system to cell  What is Neuroanatomy ❑It is the study of the structural aspect of the nervous system. ❑ The nervous system is the "Master System" of the body, because it controls all the functions performed by other systems of the body.  Composition of the Nervous System The nervous system is composed of: 1. Neurons: (nerve cells). 2. Neuroglia: (non-excitable, supporting, protecting and nourishing cells). 1 2  Functions of the Nervous System 1. Through sense organs and simple sensory nerve endings, it receives information about changes in the body and external environment and it transmits coded messages to the spinal cord and brain. 2. The spinal cord and brain process this information, relate it to past experience, and determine what response is appropriate to the circumstances. 3. The spinal cord and brain issue commands primarily to muscle and gland cells to carry out such responses. 4. The brain stores the information to form memory.  Divisions of the Nervous System Anatomical Functional  The nervous system has two major anatomical subdivisions 1. central nervous system (CNS) ❑ consists of the brain & spinal cord ❑ enclosed and protected by the skull and vertebral column 2. peripheral nervous system (PNS) ❑ composed of nerves and ganglia. ❑ nerve: is a bundle of nerve fibers (axons) wrapped in fibrous connective tissue. ❑ ganglion: is a swelling in a nerve where the cell bodies of neurons are collected outside the CNS. N.B. A Nucleus is a collection of cell bodies of neurons inside the CNS.  nerves ❑ a bundle of nerve fibers (axons) wrapped in fibrous connective tissue. ❑ Include: 12 pairs of cranial nerves – 31 pairs of spinal nerves.  Cranial nerves ❖I : olfactory ❖II : optic ❖III : oculomotor ❖IV : troclear ❖V : trigeminal ❖VI : abducent ❖VII : facial ❖VIII: vestibulo-cochlear ❖IX : glossopharyngeal ❖X : vagus ❖XI : accessory ❖XII : hypoglossal  ❑ The peripheral nervous system is divided into sensory and motor divisions: The sensory (afferent) division : ❑ carries sensory signals from the receptors (sense organs and simple sensory nerve endings) to the CNS. ❑ This is the pathway that informs the CNS of stimuli within and around the body. 1. Somatic sensory division carries signals from receptors in the skin, muscles, bones, and joints. 2. visceral sensory division carries signals mainly from the viscera of the thoracic and abdominal cavities, such as the heart, lungs, stomach, and urinary bladder.  2) The motor (efferent) division: ❑ Carries signals from the CNS to gland and muscles. ❑ Cells and organs that respond to commands from the nervous system are called effectors. 1. somatic motor division carries signals to the skeletal muscles. This output produces muscular contractions that This output produces voluntary muscular contractions and somatic reflexes. Envolve one motor neuron 2. visceral motor division (autonomic nervous system) carries signals to glands, cardiac muscle, and smooth muscle. We usually have no voluntary control over these The responses of this system is involuntary control and its effectors are visceral reflexes. Envolve two motor neurons (preganglionic and postganglionic). It is either sympathetic or parasympathetic.  Anatomy of the Brain The brain is divided into three major portions 1) The cerebrum 2 cerebral hemispheres Cerebral Hemisphere Diencephalon Corpus Callosum 2) The cerebellum 3) The brainstem Midbrain cerebellum pons Medulla oblongata 1) The cerebrum ❖ consists of a pair of half-globes called the cerebral hemispheres and a medline area called the diencephalon. ❖ The 2 hemispheres are connected by a thick bundle of nerve fibers called the corpus callosum. 2) The cerebellum ❖ lies inferior to the cerebrum and occupies the posterior cranial fossa. 3) The brainstem ❖ Formed by (from above downwards): midbrain, pons, and medulla oblongata.  Gray and White Matter ❑ The brain is composed of gray and white matter. ❑ Gray matter is the site of the Cerebral cortex neuron cell bodies forms a surface layer called the cortex over the cerebrum and cerebellum, and White deeper masses called nuclei matter surrounded by white matter. ❑ The white matter thus lies deep to the cortical gray matter in most of the brain. Nuclei  f. magnum ANATOMY OF THE SPINAL CORD External Features Length ❑45 cm Location ❑In the upper two-thirds of the vertebral canal. Beginning ❑As the continuation of the conus medullaris medulla oblongata just L1 below the foramen magnum at the level C1 Termination ❑The lower end of the cord is called conus medullaris. ❑It ends at level of the lower border of L1 Enlargements ❑ Cervical enlargement: (C5-T1) in the cervical region where it gives rise to nerves of the upper limbs ❑ Lumbar enlargement: (L1-S2) in Cervical the lumbar region where it gives enlargment rise to nerves of the lower limbs ❑ 31 segments: 8 cervical, l2 SEGMENTS thoracic, 5 lumbar, 5 sacral and 1 coccygeal segment. ❑ Each segment has a pair of spinal nerves Lumbar ❑ Because the spinal cord is enlargment shorter than the vertebral column, each spinal cord segment at lower levels is located above the similarly numbered vertebral body cauda equina ❑ A bundle formed by The lumbar and sacral nerves which occupy the vertebral canal from L2 to S5. Conus Spinal 1. dura mater: is the outer layer and ends at the level S2. medullaris meninges 2. arachnoid mater: is the middle layer and ends at the level of S2. 3. pia mater: It is inner layer forms 2 ligaments to support the spinal cord: Cauda equina Filum terminale It extends from the Conus medullaris to the back of the coccyx. denticulate ligaments They extend from the pia mater between the dorsal and ventral nerve roots to anchor the spinal cord to the dura. The lateral edge is serrated and has 21 processes attached to the dura. Lumbar ❑ It is the lower part of the subarachnoid space. Cistern ❑ It extends from L2 to S2. ❑ It is used for lumbar puncture. ❑ Contains: 1. CSF 2. Cauda equine 3. filum terminale pia arachnoid dura  lumbar puncture (spinal tap) ❑ Several neurological diseases are diagnosed in part by examining cerebrospinal fluid for bacteria, blood, white blood cells, or abnormalities ofchemical composition. ❑ CSF is obtained by a procedure called a spinal tap, or lumbar puncture. ❑ Site: between the spines of L3 and L4 (sometimes L4 and L5). This is the safest place to obtain CSF because the spinal cord does not extend this far and is not exposed to injury by the needle. ❑ lumbar puncture is not performed if a patient has signs of high intracranial pressure, because the sudden release of pressure (causing CSF to jet from the puncture) can cause fatal herniation of the brainstem and cerebellum into the vertebral canal.  Fissures and Sulci of the spinal cord ❑ Anterior median fissure: deep fissure on the anterior surface. ❑ Posterior median sulcus: shallow midline groove on the posterior surface. ❑ Anterior lateral sulcus: one on each side. It marks the attachment of the Posterior median ventral root. sulcus. ❑ Posterior lateral sulcus: one on each side. It marks the attachment of the dorsal root. DRG Posterior lateral sulcus Dorsal root Spinal nerve ventral root Anterior lateral Anterior sulcus median fissure  Cross section (internal structure) of the spinal cord ❑ The spinal cord is divided into two halves by the anterior median fissure and posterior median septum. ❑ The two halves are connected by 3 commissures: 1. White commissure. 2. Anterior gray commissure: in front of the central canal. 3. Posterior gray commissure: behind the central canal. ❑ The spinal cord, like the brain, consists of two kinds of nervous tissue called gray and white matter. A. Gray matter has a relatively dull color because it contains little myelin. It contains the cell bodies and dendrites. B. White matter contains an abundance of myelinated axons, which give it a bright white appearance. 1. Gray Matter ❑ The spinal cord has a central core of gray matter around the central canal. It looks H-shaped in cross sections. It consists of: Two lateral horns two dorsal (posterior) horns two ventral (anterior) horns (sympathetic) receives the dorsal root of gives rise to the ventral present only in the spinal nerve root of spinal nerve thoracic & upper lumbar Contain 4 groups of contain motor cells segments )T1 to L2 or sensory cells: L3).It contains the preganglionic sympathetic nerve cells.  sensory cells of the dorsal horn 1. Posteromarginal nucleus: at the tip of the dorsal horn and mediates pain and temperature sensations. 2. Substantia gelatinosa of Rolandi: at the apex of the dorsal horn. It is associated with pain & temperature sensation. 3. Nucleus proprius in the center of the dorsal horn. It mediates pain, temperature, touch and pressure sensations. 4. Nucleus dorsalis (Clarke’s nucleus): at the base of the dorsal horn and extends from C8 to L2 segments. Associated with unconscious proprioception. 2. White Matter ❑ white matter of the spinal cord surrounds the gray matter. It consists of bundles of axons. ❑ These bundles are arranged in three pairs of columns (funiculi): a dorsal (posterior), lateral, and ventral (anterior) column on each side. ❑ Each column consists of subdivisions called tracts. ❑ Tracts may be ascending tracts (sensory) or descending tracts (motor).  Spinal nerves ❖ Each spinal nerve attached to spinal cord by 2 roots: 1. Dorsal root or sensory root: Sensory fibers and shows a dorsal root ganglion. 2. Ventral root or motor root: formed of motor fibers. ❖ N.B: Both dorsal & ventral roots unit just lateral to dorsal root ganglion forming spinal nerve (mixed nerve) ❖ Each spinal nerve exits vertebral canal through intervertebral foramen and immediately divides into two rami: 1. Dorsal ramus: Innervates skin and muscles of the back of the body wall. They do not form nerve plexuses at all. 2. Ventral ramus: Innervates skin and muscles of anterolateral body wall and limbs. They form nerve plexuses.  ARTERIAL SUPPLY OF THE SPINAL CORD 1. Single Anterior Spinal 2. Two Posterior Spinal Artery Arteries Two Posterior Spinal Arteries ❑branches of the vertebral artery ❑descends in the ❑descend along the anterior median fissure posterolateral fissure of the spinal cord. ❑supplies anterior 2/3 of ❑supply the posterior 1/3 the spinal cord. of the spinal cord. Anterior Spinal Radicular Artery Artery 3. Radicular Arteries ❑ They enter the vertebral canal through the intervertebral foramina and divide into anterior and posterior branches which join the anterior & posterior spinal arteries. ❑ The largest of these branches, the great ventral radicular artery, also known as the artery of Adamkiewicz, enters the spinal cord between segments T8 and L4. This artery usually arises on the left and, in most individuals, supplies most of the arterial blood supply for the lower half of the spinal cord