CNS PDF - General Human Anatomy

GENERAL HUMAN ANATOMY The Nervous System The nervous system receives, transmits, and integrates information throughout the body through the conduction of nerve impulses. made of nervous tissue (neurons and glia) Structural anatomical classification: The nervous sys...

GENERAL HUMAN ANATOMY The Nervous System The nervous system receives, transmits, and integrates information throughout the body through the conduction of nerve impulses. made of nervous tissue (neurons and glia) Structural anatomical classification: The nervous system has two major divisions. 1. A central nervous system (CNS), which consists of the brain and spinal cord (both of which develop from the neural tube in the embryo), where information about the body's internal and external environment is processed. 2? A peripheral nervous system (PNS), which consists of 12 pairs of cranial nerves, and 31 pairs of spinal nerves. Elements of this system develop from neural crest cells and as outgrowths of the CNS. Peripheral nerves transmit information between the CNS and target organs and tissues in the rest of the body. II- Functional classification: Both the CNS and PNS contain components of each functional division. 1- The somatic nervous system controls voluntary functions such as contraction of skeletal muscles. 2- The autonomic (visceral) nervous system controls involuntary functions such Yura - Dr / Abeer Madkour Mahmoud ???? Axon Dendrite Nerve cell body Synapse (soma, perikaryon) A The nerve cell (neuron) is the basic structural unit of the nervous system The Central Nervous System Both the brain and spinal cord are covered with membranes (meninges) and are suspended in cerebrospinal fluid (CS). Meninges are further protected by the bones of the skull and the vertebral column. The brain and spinal cord of the central nervous system consist of: 1- Gray matter, which contains the cell bodies, dendrites, and unmyelinated axons of neurons. 2- White matter, which contains the myelinated axons of neurons; and 3- Neuroglial cells, which are abundant in both white and gray matter. The Brain Resides in the cranial cavity of the skull. The parts of the brain are: 1- The cerebrum: it is the largest part of the brain, consists of two cerebral hemispheres, which are connected by a mass of white matter called the corpus callosum. integretion Each cerebral hemisphere consists of an outer cerebral cortex of gray matter (containing cell bodies), an inner core of white matter (made up of axons forming masses tracts or pathways), and islands of gray matter deep within the brain known as (basal ganglia The ventricles are spaces within the cerebral hemisphere and brain stem filled with cerebrospinal fluid (CSF). The cerebral cortex is thrown into folds (elevations, gyri) separated by fissures (depressions, sulci), This arrangement greatly increases the surface area of the cortex. A number of the large sulci are conveniently used to subdivide the surface of each hemisphere into lobes, which are named from the bones of the cranium they lie under (frontal, parietal, temporal and occipital lobes). i- Frontal lobe: located anteriorly and contains the motor area of the brain. behavior memories  GENERAL HUMAN ANATOMY 65 ji-Parietal lobe: located posterior to frontal lobe and contains the sensory area of the brain. i Occipital lobe: located posteriorly and contains the visual area. iv- Temporal lobe: located inferiorly and contains the auditory area (hearing) 2. Diencephalon: thalamus, hypothalamus, epithalamus and metathalamus. 3. The cerebellum has two lateral lobes and a midline portion (the vermis). 4- The brainstem: its components are the midbrain, pons, and medulla oblongata. Diencephalon Hypothalamus Thalamus Parts of the brain Cerebellum (metencephalon) sidhrain Modulla oblongata 66 The spinal cord: The spinal cord is the part of the CNS in the upper two-thirds of the vertebral can is roughly cylindrical in shape and is circular to oval in cross-section. The spinal cord extends from the medulla oblongata to approximately the leve the disc between vertebrae L1 - L2 in adults. In neonates, the spinal cord ente approximately to the lower border of the 3rd lumbar vertebra (L3). ~ The distal end of the cord (the conus medullaris) is cone shaped. A fine filamen. connective tissue (the filum terminale) continues inferiorly from the apex of: conus medullaris. The spinal cord is segmentally organized into 31 segments:) 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal spinal cord segment.  GENERAL HUMAN ANATOMY 67 The gray matter in the spinal cord is located centrally and is surrounded by white matter tracts. The gray matter forms an H-shaped area that bilaterally consists of - Anterior horns (which contain motor neurons), - Posterior horns (which contain sensory neurons), and - Lateral horns contain cell bodies for preganglionic autonomic (visceromotor) motor neurons and is only seen in the spinal cord segments from T1- L2 for the Preganglionic sympathetic neurons and from 52 -54 for the Preganglionic parasympathetic neurons. The white matter surrounds the gray matter and is rich in nerve cell processes, which form large bundles or tracts that ascend and descend in the cord to other spinal cora levels or carry information to and from the brain. Cerebral White cortex matter Posterior' Basal hom ganglia Anterior hom Gray White matter matter Gray and white matter in the central nervous system. Meninges The meninges are three connective tissue coverings that surround, protect, and suspend the brain and spinal cord within the cranial cavity and vertebral canal. They consist of: ? The dura mater, which is the thickest and most external layer; ? The arachnoid mater, which is the fine, weblike avascular membrane directly beneath the dura. ? The pia mater, which is the delicate membrane of connective tissue that intimately envelops the brain and spinal cord. Peripheral nervous system includes the 12 pairs of cranial nerves arising from the brain or brainstem and the 31 pairs of spinal nerves arising from the spinal cord. Spinal nerves: Each spinal cord segment gives rise to bilateral dorsal and ventral rootlets, which exit the spinal cord laterally. The rootlets from each segment unite to  Dr / Abeer Madkour Mahmoud form the dorsal or posterior (conveys sensory neurons) abral ventral or antero, (conveys motor neurons) roots. At the respective intervertebratoramen, the roge unite to form left and right spinal nerve trunks, which further divide into a ventra (anterior) ramus (supplying the limbs and anterolateral boay wall) and dorsat (posterior) ramus (supplying the deep back muscles and skin of the back). Somatic motor nerve fiber Intrins ic back muscles Somatic sensory nerve ending in ski Posterior root Spmal ganglon Spmalnerve Basic organization of a Posterior spinal nerve Posterior rootlets ramus Antenor root Anterior ramus Anterior rootlets All muscles except intrinsic back muscles Somatic motor Somatic sensory nerve fiber nerve ending in skm N.B.: - The vertebral canal is longer than the spinal cord in adults due to unequal growth during fetal development. Consequently. nerve roots in the upper vertebral canal course horizontally, in the middle obliquely and in the bottom vertically. - The Cl- C7 spinal nerves exit the vertebral canal superior to their respective cervical vertebrae. The C8 spinal nerve exits inferior to the C7 vertebra. All of the remaining spinal nerves segmentally exit the vertebral canal inferior to their respective vertebra.