Human Nervous System PDF

human nervous system Dr. Abdelraouf khatal  The Central Nervous System (CNS) Introduction Development of nervous System Protection of CNS ( Meninges) Ventricular system. - Cerebrospinal fluid. - Brain barriers. Anatomical view of CNS. Histological structure of CNS Cer...

human nervous system Dr. Abdelraouf khatal  The Central Nervous System (CNS) Introduction Development of nervous System Protection of CNS ( Meninges) Ventricular system. - Cerebrospinal fluid. - Brain barriers. Anatomical view of CNS. Histological structure of CNS Cerebrum. Cerebellum. Brainstem : 1. Midbrain. 2. Pons. 3. Medulla oblongata. Spinal cord  introduction The human body consists of numerous tissues and organs, which are diverse in structure and function, yet they function together and in harmony for the well-being of the body as a whole. It is obvious that there has to be some kind of influence that monitors and controls the working of different parts of the body. Although there are other mechanisms that help in such control (for example hormones), the overwhelming role in directing the activities of the body rests with the nervous system. Neuroanatomy is the study of the structural aspects of the nervous system. It cannot be emphasized too strongly that the study of structure is meaningless unless correlated with function. The nervous system and the endocrine system control the functions of the body. The nervous system is composed basically of specialized cells, whose function is to receive sensory stimuli and to transmit them to effector organs, whether muscular or glandular. The sensory stimuli that arise either outside or inside the body are correlated within the nervous system, and the efferent impulses are coordinated so that the effector organs work harmoniously together for the well-being of the individual. The human nervous system controls and integrates all body activities within limits that maintain life.  Three basic functions 1.Sensory input: - Transport sensory information from Sensory skin, muscles, joints, sense organs & input viscera to CNS via sensory receptors. 2. Integration (information processing): - Interpreting and remembering those changes. Integration - Connect sensory to motor neurons. - 90% of neurons in the body. 3. Motor output: -Reacting to those changes with effectors. - Muscular contractions. - Glandular secretions. Motor output Organization of the Nervous System to supply the three basic functions DIVISIONS OF NERVOUS SYSTEM The nervous system may be divided into the central nervous system (CNS), made up of the brain and spinal cord, the peripheral nervous system (PNS), consisting of the peripheral nerves and the ganglia associated with them. 1. Central nervous system (CNS): The central nervous system is a complex, hollow tube, whose rostral end, the brain, is enlarged and folded in an elaborate manner, whereas its caudal end, the spinal cord, is a long, tubular structure. The brain is housed in the cranial cavity and at the foramen magnum is continuous with the spinal cord, housed in the vertebral canal. Since the CNS, as well as most of the body, is bilaterally symmetric, the mid sagittal plane bisects it into right and left halves. The brain consists of the cerebrum, diencephalon, midbrain, pons, cerebellum and medulla oblongata. The midbrain, pons, and medulla oblongata together form the brainstem. The medulla oblongata is continuous below with the spinal cord. 2. Peripheral nervous system (PNS): The peripheral nervous system is a continuation of the CNS; it is composed of clusters of nerve cell bodies, known as ganglia, as well as of bundles of axons and central processes, known as nerves. It must be understood that the PNS is in physical continuity with the CNS, in fact cell bodies of many of the nerve fibers (axons) of the PNS are located in the CNS. Peripheral nervous system is part of nervous system (all the neural tissue) outside the CNS, includes:  Somatic (voluntary) nervous system (SNS)  Autonomic (involuntary) nervous system (ANS)  Enteric (involuntary) nervous systems (ENS) 1. The somatic nervous system: The somatic nervous system is composed of the 12 pairs of cranial nerves and their ganglia as well as of the 31 pairs of spinal nerves and their dorsal root ganglia. - All sensory neurons from cutaneous and special sensory receptors to the CNS. - All motor neurons to skeletal muscle tissue. 2. The autonomic nervous system: The autonomic nervous system innervates cardiac muscle cells, smooth muscle cells, and secretory cells of glands. - All sensory neurons from visceral organs to CNS. - All motor neurons to smooth & cardiac muscle and glands. Sympathetic division Parasympathetic division The somatic motoneuron directly innervates its skeletal muscle cell, whereas the autonomic nervous system the neuron whose cell body is located in the CNS (preganglionic or presynaptic neuron) synapses with a second neuron (postganglionic or postsynaptic neuron) located in a ganglion in the PNS. 3.Enteric nervous system: The enteric nervous system is situated completely within the wall of the digestive tract and controls the entire process of digestion. - All sensory & motor neurons control GI tract - All neurons function independently of ANS & CNS The human nervous system: Two Anatomical Divisions  Peripheral nervous system (PNS) includes: 1-Cranial nerves (12 pairs) 2-Spinal nerves (31 pairs): include 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal. 3- Their associated ganglia.  Embryonic Development of CNS The whole of the nervous system is derived from ectodermof the embryo, except its blood vessels and some neuroglial elements. Embryonic Development of Nervous system Neural plate Before the formation of the nervous system in the embryo, three main cell layers become differentiated. The innermost layer, the entoderm, gives rise to the gastro- intestinal tract, the lungs, and the liver. The mesoderm gives rise to the muscle, connective tissues, and the vascular system. The third and outermost layer, the ectoderm, formed of columnar epithelium, gives rise to the entire nervous system. During the third week of development, the ectoderm on the dorsal surface of the embryo becomes thickened to form the neural plate. With further development, invagination of the neural plate forming the neural groove. The neural folds on each edge of the neural groove fuse, converting the neural groove into a neural tube. Fusion starts at about the midpoint along the groove and extends cranially and caudally. The cells forming the lateral margin of the plate do not become incorporated in the neural tube but instead form a strip of ectodermal cells that lie between the neural tube and the covering ectoderm. This strip of ectoderm is called the neural crest The neural tube gives rise to the entire central nervous system, including neurons, glial cells, and ependymal cells. As the neural folds fuse and the neural tube separates from the overlying surface ectoderm that will form epidermis, a large population of neural cells separates and becomes a mass of mesenchymal cells called the neural crest. These neural crest cells undergo extensive migrations and contribute to the formation of the peripheral nervous system, as well as a number of other structures, include: (1) Chromaffin cells of the adrenal medulla. (2) Melanocytes of skin. (3) Odontoblasts of teeth. (4) Cells of the pia mater and the arachnoid. (5) Sensory neurons of cranial and spinal sensory ganglia. (6) Postganglionic neurons of sympathetic and para- sympathetic ganglia. (7) Schwann cells of peripheral axons. (8) Satellite cells of peripheral ganglia. Cephalization: Evolutionary development of the anterior portion of the CNS. Even before the complete closure of the neural tube, it is divisible into an enlarged cranial part and a caudal tubular part. The enlarged cranial part forms the brain. The caudal tubular part forms the spinal cord.  At about the end of fourth week, Anterior end of the neural tube gives rise to three primary brain vesicles: -Prosencephalon—forebrain Neural Primary brain vesicles -Mesencephalon—midbrain tube -Rhombencephalon—hindbrain  Primary vesicles give rise to Anterior five secondary brain vesicles: (cranial) Prosencephalon -Telencephalon and (forebrain) Diencephalon arise from the forebrain Mesencephalon (midbrain) -Mesencephalon remains undivided Rhombencephalon (hindbrain) -Metencephalon and myelencephalon arise from Posterior the hindbrain (caudal) Secondary brain Adult brain Adult vesicles structures neural canal regions Cerebrum: cerebral Lateral ventricles hemispheres (cortex, Telencephalon white matter, basal nuclei) Diencephalon (thalamus, hypothalamus, Diencephalon epithalamus), retina Third ventricle Brain stem: midbrain Cerebral aqueduct Mesencephalon Brain stem: pons Metencephalon Cerebellum Fourth ventricle Myelencephalon Brain stem: medulla oblongata Spinal cord Central canal Development of The Brain The prosencephalon, mesencephalon, and rhomben- cephalon are at first arranged craniocaudally. Their relative position is greatly altered by the appearance of a number of flexures. These are:  The cervical flexure, at the junction of the rhombencephalon and the spinal cord.  The mesencephalic (cephalic) flexure in the region of the midbrain.  The pontine flexure, at the middle of the rhombencephalon, dividing it into the metencephalon and myelencephalon.  The telencephalic flexure that occurs much later between the telencephalon and diencephalon. These flexures lead to the orientation of the various parts of the brain as in the adult. These flexures provide increased space for the folding and three-dimensional organization of the brain. Mesencephalon Cerebral hemisphere Metencephalon Outline of diencephalon Midbrain Diencephalon Myelencephalon Cerebellum Pons Medulla oblongata Telencephalon Spinal cord Spinal cord Week 5 Week 13 Cerebral hemisphere surfaces crease and fold into convolutions Cerebral hemisphere Cerebellum Pons Medulla oblongata Week 26 Spinal cord Development of human brain Embryonic (developmental) divisions of the Brain Primary vesicle Secondary vesicle Derivatives Cerebral cortex Telencephalon Cerebral white matter Basal ganglia Prosencephalon Thalamus Hypothalamus Diencephalon Subthalamus Epithalamus Mesencephalon Mesencephalon Midbrain Cerebellum Metencephalon Pons Rhombencephalon Myelencephalon Medulla oblongata  Forebrain Midbrain Hindbrain Development of the spinal cord A B D C E Protection of CNS The Central Nervous System (CNS) is covered and protected by: - Skin and Skull & vertebral column - Meninges (C.T. membranes) - CSF (cerebrospinal fluid ) - Brain barriers Meninges: The central nervous system is covered by three protective C.T. membranes called meninges: Dura mater, Archnoid mater & Pia mater. Cranial meninges are continuous with spinal meninges. 1.Dura mater : Outermost, fibrous membrane. The dura mater is toughest layer, which is derived from mesoderm, and is comprised of an outer endosteal layer and inner meningeal layer ( fibroelastic C.T.). These two layers are almost fused, except along certain lines, where they separate to form endothelium-lined large space filled with venous blood, dural venous sinuses which drain the blood & C.P.F from the brain. Dural venous sinuses are: Superior sagittal sinus: Lies along superior margin of falx cerebri & Inferior sagittal sinus: Lies along inferior margin of falx cerebri.  Falx cerebri Tentorium cerebelli 2.Arachnoid mater: The arachnoid mater is a delicate, impermeable membrane covering the brain and lying between the pia mater internally and the dura mater externally. It is separated from the dura by a potential space, the subdural space, filled by a film of fluid. It is separated from the pia by the subarachnoid space, which is filled with cerebrospinal fluid. The outer and inner surfaces of the arachnoid are covered with flattened mesothelial cells. The arachnoid is composed of connective tissue devoid of blood vessels. It has two components: a sheet of connective tissue in contact with the dura mater and a system of trabeculae connecting the layer with the pia mater. In certain areas, the arachnoid perforates the dura mater, forming protrusions that terminate in venous sinuses in the dura mater. These protrusions are called arachnoid villi. Arachnoid villi or (arachnoid granulation) which function as a site for absorption of CSF into the blood of the venous. 3.Pia mater: is a loose connective tissue containing many blood vessels. Between the pia mater and the neural elements is a thin layer of neuroglial processes, adhering firmly to the pia mater and forming a physical barrier at the periphery of the central nervous system. There are spaces between these membranes (Three potential spaces) -Epidural space or Extradural Space: between the dura mater and the surrounding bone of the vertebrae. - Subdural space : between dura & arachnoid. - Subarachnoid space : between the arachnoid and pia maters. It contains cerebrospinal fluid & large veins.  Ventricular System The ventricles are four fluid-filled cavities located within the brain; these are the two lateral ventricles, the third ventricle, and the fourth ventricle. The two lateral ventricles communicate through the interventricular foramina (of Monro) with the third ventricle. The third ventricle is connected to the fourth ventricle by the narrow cerebral aqueduct (aqueduct of Sylvius). The fourth ventricle, in turn, is continuous with the narrow central canal of the spinal cord. The ventricles are lined throughout with ependyma and are filled with cerebrospinal fluid. The ventricles are developmentally derived from the cavity of the neural tube.  Lateral ventricles are two vertical space found inside cerebral hemispheres. Third ventricle is single vertical space under corpus callosum (In diencephalon) Cerebral aqueduct runs through midbrain Fourth ventricle is small chamber between pons & cerebellum Central canal runs down through spinal cord The choroid plexus: The choroid plexus is invaginated folds of pia mater composed of a core of loose connective tissue rich in dilated fenestrated capillaries and covered by ependymal cells. The surface of the choroid plexus has numerous villous processes. Each process contains a plexus of capillaries. Because of the presence of these processes, the surface area of the choroid plexuses is considerable. It is further increased by the presence of microvilli that observed on the ependymal cells. Ependymal cells Capillary Section of choroid Connective plexus tissue of pia mater Wastes and CSF forms as a filtrate Cavity of unnecessary containing glucose, oxygen, solutes absorbed ventricle vitamins, and ions (Na+, Cl–, Mg2+, etc.) CSF formation by choroid plexuses The choroid plexus is found in the roofs of the third and fourth ventricles and in part in the walls of the lateral ventricles. The choroid plexus extends from the interventricular foramen, where it joins with the plexuses of the third ventricle and at the junction of the body of the lateral ventricle to the end of the inferior horn. There is neither choroid plexus in the anterior and posterior horns of the lateral ventricle nor in the aqueduct and central canal of spinal cord. The function of the choroid plexus: The choroid plexuses actively secrete cerebrospinal fluid, and this creates a small pressure gradient. At the same time, they actively transport nervous system metabolites from the cerebrospinal fluid into the blood explains the fact that the concentrations of potassium, calcium, magnesium, bicarbonate, and glucose are lower in the cerebrospinal fluid than in the blood plasma. Cerebrospinal Fluid : The cerebrospinal fluid is found in the ventricles of the brain and in the subarachnoid space around the brain and in the central canal of the spinal cord. It is produced by ependymal cells (these cells covering the choroid plexus)that filtrate the plasma from capillaries, and absorbed by arachnoid villi into dural venous sinus. Appearance: Clear and colorless fluid and possesses inorganic salts similar to those in the blood plasma. Volume: about 150 mL. Rate of production: 0.5 mL/minute. Pressure (spinal tap with patient in lateral recumbent position): 60–150 mm of water. This pressure may be raised by straining, coughing, or compressing the internal jugular veins in the neck. Composition: Protein: 15–45 mg/100 mL (only a trace of protein). Glucose: 50–85 mg/100 mL (about half that of blood). Chloride: 720–750 mg/100 mL. Number of cells: 0–3 lymphocytes/cubic mm. The Functions of the Cerebrospinal Fluid 1. Cushions and protects the central nervous system from trauma 2. Provides mechanical buoyancy and support for the brain 3. Serves as a reservoir and assists in the regulation of the contents of the skull 4. Nourishes the central nervous system 5. Removes metabolites from the central nervous system 6. Serves as a pathway for pineal secretions to reach the pituitary gland  Brain Barriers Three barriers can be recognized within brain: 1.The blood brain barrier 2.The blood CSF barrier 3.The brain CSF barrier  Brain Barriers 1.The blood brain barrier: It is the wall which separates the circulating blood present in capillaries from the surrounding brain nerve cells. It is formed of: a. The endothelium lining the capillaries (tightly adhering with tight junction). b.The continuous basement membrane of endothelium. c.The processes of the astrocytes. 2.The blood CSF barrier: It is the wall which separates the CSF from circulating blood present in capillaries, at choroid plexus. It is formed of: a. The endothelium lining the capillaries (tightly adhering with tight junction). b.The continuous basement membrane of endothelium. c.The basement membrane of the ependymal cells. d.The ependymal cells joined by tight junctions. 3.The brain CSF barrier: It is the wall which separates the CSF from surrounding brain tissues. It is formed of: a.The ependymal cells lining the ventricles. b.The basement membrane of the ependymal cells. c.The neuroglial processes. Spinal Cord  Spinal Cord The basic unit of the CNS is the spinal cord, which connects the CNS with the skin and muscles of the body. Simple and complex reflex circuits are located within the spinal cord. It receives sensory information ( afferents) from the skin and body wall, which are then transmitted to higher centers of the brain. The spinal cord receives movement instructions from the higher centers and sends motor commands (efferents) to the muscles. The spinal cord also has a motor output to the viscera and glands, part of the autonomic nervous system.  Spinal cord 45 cm in length in adult, extends from the medulla oblongata to L1 or L2. Thus, it occupies the upper two-thirds of the vertebral column. - Passes through the foramen magnum. Runs through the vertebral canal of the vertebral column. Spinal cord consists of: Five (regions) levels: 1 – Cervical 2 – Thoracic 3 – Lumbar 4 – Sacral 5 – Coccygeal Two enlargements: - Cervical enlargement , gives origin to the brachial plexus of upper limbs [from 3rd cervical to 2nd thoracic segments]. - Lumbar enlargement, gives origin to the lumber & sacral plexus of lower limbs [1st lumbar to 3rd sacral segments]. Spinal segment: is area of spinal cord that gives rise to a pair (right & left) of spinal nerves. There are 31 spinal segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral 1 coccygeal segments. Inferiorly, the spinal cord possesses: Medullary cone: (conus medullaris) is tapered tip of spinal cord at lumbar area. Cauda equinae is collection of nerve roots (dorsal & ventral roots of lowest spinal nerves) at L2 to S5 nerve roots resemble horse’s tail. Filum terminale is fibrous thread-like extension of pia mater - stabilizes spinal cord in canal. Spinal cord consists of:  Five Levels  Two Enlargements  31 Spinal Segments  31 Pairs of Spinal Nerves  In addition to a deep longitudinal fissure called the anterior median fissure in the midline anteriorly  and a shallow furrow called the posterior median sulcus on the posterior surface The Spinal Cord Spinal cord Anterior median fissure Pia mater Denticulate ligaments rootlets Dorsal root Ventral root Arachnoid mater Dura mater Spinal blood vessel Cross Section of Spinal Cord Cross-Section of the Spinal Cord (Histological structure): The spinal cord is formed of two symmetrical halves separates Posteriorly by a shallow furrow; the posterior median sulcus which is continuous with a delicate glial partition; the posterior median septum. Anteriorly by a deep longitudinal fissure; the anterior median fissure. The anterior median fissure and posterior median sulcus divide the surface of the cord into two symmetrical halves. Each half of the cord is further subdivided into posterior, lateral, and anterior columns by anterolateral and posterolateral sulci. Spinal Nerves The spinal cord gives attachment on either side to 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. Each spinal nerve arises by two roots, anterior motor root and posterior sensory root. Each root is formed by aggregation of a number of rootlets. These rootlets combine to form roots: i) Dorsal (posterior) or sensory root, has afferent nerves & a ganglion (spinal or sensory ganglion). The rootlets of the dorsal or sensory roots of spinal nerves enter the cord at the posterolateral sulcus on either side. ii) Ventral (anterior) or motor root, has efferent nerves. The rootlets of the ventral or motor roots of spinal nerves emerge through the anterolateral sulcus on either side. Two roots merge laterally and form the mixed spinal nerve After emerging from the intervertebral foramen, each spinal nerve is divided into a dorsal and a ventral rami. The dorsal ramus passes posteriorly to supply the muscles and skin of the back. The ventral ramus continues anteriorly to supply the muscles and skin over the anterolateral body wall and all the muscles and skin of the limbs. Internal structure of the spinal cord: On cross section, the spinal cord is oval or round in shape. It has gray matter as central H shaped with two anterior and two posterior horns connected by thin gray commissure containing small central canal. In thoracic and upper lumber segments two small lateral horns are seen. Central area of gray matter shaped like a butterfly, surrounded by white matter in three columns or funiculi (posterior, lateral & anterior) The gray matter of the spinal cord consists of a mixture of nerve cells and their processes, neuroglia, and blood vessels. The nerve cells are multipolar, and the neuroglia forms an intricate network around the nerve cell bodies. The relative amount of grey and white matter, and the shape and size of the grey columns, vary at different levels of the spinal cord. The amount of gray matter present at any given level of the spinal cord is related to the amount of muscle innervated at that level. Thus, its size is greatest within the cervical and lumbosacral enlargements of the cord, which innervate the muscles of the upper and lower limbs, respectively. The amount of white matter undergoes progressive increase from the lower part to the upper part of the spinal cord. This is a result of the fact that: Progressively more and more ascending fibres are added as the upper levels of the cord are reached. The number of descending fibres decreases as lower levels of the cord are reached as some of them terminate in each segment.  Variation in the Internal Structure of Spinal Cord at Different Levels Levels Cervical Thoracic Lumbar Shape Oval Round Oval Central canal More anterior Slight anterior Central Dorsal horns Thin &diverging Thin & parallel Thick & parallel Ventral horns Thick Thin & parallel Thick & parallel Lateral horns Absent Present Present only in L1,L2 &L3. White matter Abundant Abundant Little Cervical level Thoracic level Lumber level Comparison between different levels of spinal cord Cervical level Thoracic level Lumber level  Nuclei in Grey Matter Nuclei are collections of neurons occur in various horns of the spinal grey matter. Most nerve cells are large and multipolar, and their axons pass out in the anterior roots of the spinal nerves as alpha efferents, which innervate skeletal muscles (extrafusal muscle). The smaller nerve cells are also multipolar, and the axons of many of these pass out in the anterior roots of the spinal nerves as gamma efferents, which innervate the intrafusal muscle fibers of neuromuscular spindles.  Anterior horns contain motor nuclei. Posterior horns contain sensory nuclei. Lateral horns contain autonomic nuclei. Gray commissure contains anterior and posterior commissural nuclei. Sensory nuclei Autonomic nuclei Commissural nuclei. Motor nuclei  Nuclei of Gray horns Lateral horns nuclei Clark’s nucleus Lateral horns nuclei: The thoracic and upper two lumbar segments (T1-L2) contain sympathetic nuclei, while Parasympathatic nuclei present in S2, S3 & S4. A) Anterior horns nuclei (motor nuclei): Three groups of motor nuclei are present in the anterior horns: (1) Medial group: It includes: antero-medial group and postero-medial group It is present in all segments of spinal cord Function: innervate axial muscles (intercostal & abdominal). (2) Central group: Present in all the segments except thoracic segments. Function: unknown. (3) Lateral group: It includes antero-lateral and postero-lateral Present in all the segments except thoracic segments Function: innervate the skeletal muscles of upper and lower limbs. B. Posterior horns nuclei (sensory nuclei): They contain medium sized cells and are the 2nd order neurons of the sensory pathway (1) Posteromarginal nucleus: - It covers the tip of posterior horn - It is present in all levels of spinal segments - It mediates pain and temperature sensation. (2) Substantia Gelatinosa of Rolandi: - It is found at the apex of the posterior horns beneath the posteromarginal nucleus. - It is present in all levels of spinal segments. - Its cells forms the 2nd order neurons in the pathway of pain, temperature and sexual sensation (lateral spino– thalamic tract). (3) Main sensory nucleus (Nucleus proprious): - It is found in the center of the posterior horns. - It is present in all levels of spinal segments. - Its cells form the 2nd order neurons in the pathway of crude (light) touch (anterior spino–thalamic tract). (4) Clark’s nucleus (nucleus dorsalis): - It is found at the base of posterior horn. -It is present only in all thoracic segments of spinal cord to 3rd lumbar segment (T1–L3) -Its cells form the 2nd order neurons of anterior and posterior spinocerebellar tracts (unconscious proprioception). C) Lateral horns nuclei: Between the ventral and dorsal grey horns, an intermediate zone (lateral horn) contains: intermediolateral sympathetic nuclei and intermediomedial nuclei parasympathetic nuclei. Intermediolateral nucleus: -It extends from T1 to L2 segments of the cord. -It gives origin to preganglionic fibres of the sympathetic nervous system (thoracolumbar outflow). Intermediomedial nucleus: -It extends from S2 to S4 segments of the cord. -It gives origin to preganglionic fibres of parasympathetic nervous system (sacral outflow). anterior and posterior commissural D) Commissural nuclei: nuclei - They surround the central canal. - There are anterior and posterior commissural nuclei. - Present in all segments of spinal cord - They act as interneurons between sensory and motor nuclei  Type Nucleus Site Function MOTOR Antero-medial group All segments Innervate axial muscles Postero-medial group Ant. horn Central All segment Not known function Antero- lateral group Innervate the skeletal Postero-l ateral group except thoracic muscles of upper & lower limbs SENSORY Posteromarginal Tip of posterior horn of Mediates pain & all segments temperature Post. horn Substantia Gelatinosa of Apex of posterior horns 2nd order neurons of Rolandi below the lateral spino–thalamic posteromarginal nucleus. tract (pain & temperature) Main sensory nucleus Center of posterior horns 2nd order neurons of (Nucleus proprious) of all segments anterior spino–thalamic tract (position, movement and vibration) Clark’s nucleus (nucleus Base of posterior horn 2nd order neurons of dorsalis) from C8 to L4 segments spino–cerebellar tracts (unconscious proprioception) AUTONOMIC Intero-medio-lateral Lateral horn T1-L2 Sympathetic (thoracic & L1-L2 Lat. horn segments) Intero-medio-medial Lateral horn of sacral Parasympathetic segments (S.2,3 & 4) INTERNEUON Anterior commissural Around central canal of Interneurons between all segments sensory & motor nuclei Commissural Posterior commissural  White Matter  Consists of mixture of nerve fibers, neuroglia and blood vessels.  White color is due to high proportion of myelinated nerve fibers  The white matter of the spinal cord is arranged in columns/funiculi; anterior, posterior and lateral.  Posterior columns or funiculi, contains ascending tracts only. Posterior  Lateral & anterior columns or column funiculi contains ascending & descending tracts. Lateral column Anterior column  The tracts are formed by sensory nerve fibers ascending to the brain, motor nerve fibers descending from the brain and fibers of connector neurons.  Tracts are often named according to their points of origin and destination, e.g. spinothalamic, corticospinal. Types of spinal cord tracts: 1.Short associate tracts: There are 4 groups of short associate tracts in spinal cord: 1.Fasciculi proprii tract. 2.Septomarginal tract. 3.Comma-shaped tract 4.Lissauer tract. 2.Long tracts. There are 2 groups of long tracts in spinal cord: a. Long Ascending or Sensory tracts (8). b. Long Descending or Motor tracts (11). Long Ascending (Sensory) tracts: includes, - Gracil & Cuneate tracts- spinal cord to medulla oblongata. - Spinocerebellar (posterior & anterior)- spinal cord to cerebellum. - Spinothalmic (anterior & lateral)- spinal cord to thalamus. - Spino-olivary tract- spinal cord to cerebellum. - Spinotectal tract-spinal cord to midbrain. Long Descending (Motor) tracts: includes, - Crossed pyramidal tracts or lateral Corticospinal- cerebral cortex to spinal cord. - Rubrospinal tract- midbrain to spinal cord. - Olivospinal tract- cerebellum to spinal cord. - Recticulospinal tracts (lateral & anterior)- brain stem to spinal cord. - Vestibulospinal tract (lateral & anterior)- inner ear to spinal cord. - Tectospinal tract (lateral & anterior)- tectum to spinal cord. - Direct pyramidal or anterior Corticospinal- cerebral cortex to spinal cord. - Sulco marginal tract-brainstem to spinal cord. Positions of the main ascending and descending tracts present in a transverse section of the spinal cord Spinal cord –Cervical level: All tracts are present except, Septomarginal tract. All nuclei are present except Lateral horn nuclei & Clark’s nucelus found only in (C8-C12). Spinal cord –Upper Thoracic level: All tracts are present except, Septomarginal , Olivospinal & anteriorVestibulospinal. All nuclei are present except, Anteriolateral , Posteriolateral and Central nuclei. Lateral horn nuclei & Clark’s nuclei are appear. Spinal cord –Lower Thoracic level: All tracts are present except, Olivospinal , Direc pyramidal, AnteriorVestibulospinal, LateralTectospinal, Cuneat & Comma-shaped tracts. Appearance of Septomarginal short tract. All nuclei are present except, Anteriolateral ,Posteriolateral and Central nuclei. Lateral horn nuclei & Clark nuclei are appear. Spinal cord –Lumber level: The tracts disappear in Lumber level: Olivospinal , Direct pyramidal ,anteriorVestibulospinal, Cuneat & Comma-shaped tract Tectospinal, Rubrospinal & posterior Spinocerebellar tracts. All nuclei are present.  Type Nuclei Cervical Thoracic Lumber Sensory N. Posteromarginal Present Present Present SGR Present Present Present Nucleus propious Present Present Present Clark’s N. Presnt present L1,L2 & L3 only in C8 to C12 Motor N. Anteriomedial Present Present Present Anteriolateral Present Absent Present Posteriomedial Present Present Present Posteriolateral Present Absent Present Central N. Present Absent Present Autonomic N. Sympathatic N. Absent Present L1 , L2 & L3 Parasympathatic N. Absent Absent S2, S3 & S4 Commissural N. Anterior & Present Present Present Posterior N.  Tracts Cervical Upper Lower Lumbar thoracic thoracic A Short associate tracts 1.Fasciculi proprii tract. Present Present Present Present 2.Septomarginal tract. ------------- ------------- Present Present 3.Comma-shaped tract Present Present ----------- ---------- 4.Lissauer tract. Present Present Present Present Long Ascending (Sensory) B 1.Gracil. Present Present Present Present 2.Cuneate. Present Present ---------- ---------- 3.Posterior Spinocerebellar. Present Present Present ---------- 4.Anterior Spinocerebellar. Present Present Present Present 5.Spinothalmic (anterior & lateral). Present Present Present Present 6.Spino-olivary tract. Present Present Present Present 7.Spinotectal tract. Present Present Present Present Long Descending (Motor) C 1.Crossed pyramidal. Present Present Present Present 2.Rubrospinal. Present Present Present ---------- 3. Olivospinal. Present ---------- ---------- ---------- 4.Recticulospinal (lateral & anterior). Present Present Present Present 5. Lateral Vestibulospinal Present Present Present Present 6.AnteriorVestibulospinal. Present ----------- ---------- ---------- 7. Anterior Tectospinal Present Present Present ----------- 8. Lateral Tectospinal Present Present ------------- ----------- 9.Direct pyramidal. Present Present ------------ ----------- 10.Sulco marginal. Present Present Present Present