BMS2-2 Introduction to the Central Nervous System Classification PDF

NEUROANATOMY - INTRODUCTION • THE STUDY OF NERVOUS SYSTEM STRUCTURES AND HOW THEY RELATE TO FUNCTION FUNCTIONS OF THE NERVOUS SYSTEM • 3 specific functions: • Sensory Input - Sensory receptors present in skin & organs respond to external & internal stimuli by generating nerve impulses that travel...

NEUROANATOMY - INTRODUCTION • THE STUDY OF NERVOUS SYSTEM STRUCTURES AND HOW THEY RELATE TO FUNCTION FUNCTIONS OF THE NERVOUS SYSTEM • 3 specific functions: • Sensory Input - Sensory receptors present in skin & organs respond to external & internal stimuli by generating nerve impulses that travel to central nervous system (CNS) • Integration - The brain & spinal cord combine & sum up all the data received from body & send out nerve impulses. • Motor Output - Nerve impulses from the CNS go to the effectors (muscles & glands). Muscle contractions & gland secretions are responses to stimuli received by sensory receptors. DIVISIONS OF THE NERVOUS SYSTEM DIVISIONS OF THE NERVOUS SYSTEM Functional Division: Somatic & Visceral • Somatic: Nerves carrying conscious sensation from periphery back to CNS, nerves innervating voluntary muscles • Visceral: Motor component Sensory component Involuntary structures (internal organs, blood vessels, glands - (autonomic: sympathetic & parasympathetic) DIVISIONS OF THE NERVOUS SYSTEM Structural Division: Central Nervous System (CNS) & Peripheral Nervous System (PNS) • CNS: Brain & spinal cord (Brain: Cerebrum, diencephalon, midbrain, pons, cerebellum, medulla oblongata) • PNS: All nervous structures outside CNS • Carries info to & from CNS • Sensory receptors, motor endings, nerves, ganglia Cranial & spinal nerves; Peripheral part of autonomic nervous system (ANS) via sympathetic trunk & ganglia, & enteric nervous system • Peripheral nerves: Incl. those supplying skin, muscles, joints, & supplying viscera • Cranial nerves: Peripheral nerves attached to brain • Spinal nerves: Peripheral nerves attached to spinal cord AXES & PLANES İN CNS • 2 AXES DESCRIBİNG ORGANISATION OF CNS • ROSTRAL – CAUDAL AND DORSAL – VENTRAL • THESE ARE MOST EASILY UNDERSTOOD IN ANIMALS W/ SPINAL CORD RUNNING HORIZONTALLY RATHER THAN VERTICALLY ➔ ROSTRAL-CAUDAL AXIS RUNS FROM NOSE TO TAIL DORSAL-VENTRAL AXIS RUNS PERPENDICULARLY TO THIS AXES & PLANES İN CNS • USING THIS SYSTEM IN HUMAN SPINAL CORD, 'TOP TO BOTTOM' IS 'ROSTRAL TO CAUDAL‘ • ‘BACK TO FRONT' IS 'DORSAL TO VENTRAL‘ • HOWEVER, İN THE HUMAN BRAIN THESE AXES TURN THRU 90 DEGREES ➔ FRONT OF BRAIN IS ROSTRAL TOP IS DORSAL BASE IS VENTRAL ORGANISATION OF SPINAL NERVES ORGANISATION OF SPINAL NERVES ORGANISATION OF SPINAL NERVES • Grey Matter: In many parts of the CNS, neuronal cell bodies are grouped together and are, more or less, segregated from axons. Such collections of cell bodies is make up the grey matter. • Nuclei : Small aggregations of neuronal cell bodies, which usually share a common functional role, are termed nuclei • Axons tend to be grouped together to form white matter, so called because axons are often ensheathed in myelin which gives a lighter colour. CELLULAR ARCHITECTURE • Nervous tissue is made up of nerve cells: Neurons • Neuroglial cells: The supporting (connective) tissue of the CNS STRUCTURE OF A TYPICAL NEURON Each neuron made up of: • Cell body/soma/perikayon • Cell processes called neurites • Axons that pass between similar origins or destinations within the CNS tend to run together in defined pathways, or tracts. • Tracts often cross the midline (decussate), which means that one half of the body is, in many respects, controlled by, and sends information to, the opposite side of the brain. • The neurons are intricately connected with each other, and it is through these connections that the body perceives changes in the internal and external environment and then produces appropriate responses to these changes. CLASSIFICATION OF NEURONS BASED ON NUMBER OF PROCESSES • Unipolar: Has a single process. Found in cells of spinal ganglia, mesencephalic nucleus of trigeminal nerve & also found during fetal life. • Bipolar: has 1 axon & 1 dendrite. Is found in the 1st neuron of the retina, ganglia of CN III & olfactory mucosa • Pseudounipolar: Start out as bipolar neurons in the embryo, but their processes fuse into one as the neuron matures. Found in dorsal root ganglia & sensory ganglia of cranial nerves. • Multipolar: Have an axon and multiple dendrites. The commonest type found in brain and spinal cord NEURITES • Processes arising from the cell body of a neuron are called neuritis. There are 2 types: 1- Several short branching processes: dendrites 2- One longer process: axon • Dendrites terminate near the cell body and the Nissl substance extends into them • The axon extends away from the cell body & is devoid of Nissl substance • On one side of the soma is a mound called the axon hillock, from which the axon (nerve fibre) originates • The part of the axon just beyond the axon hillock is called the initial segment • Anaxonic: have no axon and are found in the brain and retina. ACCORDING TO THE LENGTH OF AXON • Golgi type I: have long axons • Golgi type II: have short axons near the cell body. ACCORDING TO THE SHAPE OF THE NERVE CELLS • Pyramidal cells: have a base and 3 angles with the dendrites originating from the angles while the axons originate from the base. • Purkinje cells: have a dendrite that branches into a dendritic tree. • Fusiform cells • Stellate (star-shaped) cells. Oligodendrocytes: NEUROGLIAL CELLS • Myelinate tracts • Are counterparts of Schwann cells of peripheral nerves Astrocytes: • Nutrition of the nervous system Microglia: • Act like macrophages of the CNS Ependymal cells: • Columnar cells lining cavities of the CNS • Neurons communicate with each other through synapses • Axo-dendritic synapse the commonest • Axo-somatic synapse • Axo-axonal synapse (less common) • Dendro-axonic synapse • Dendro-dendritic synapse • Somato-somatic synapse • Somato-dendritic synapse SYNAPSES THE REFLEX ARC • A reflex arc is the functional unit of the nervous system • A monosynaptic reflex consists of: • A receptor e.g. skin • A sensory neuron • A motor neuron • An effector e.g. muscle