Nervous System PDF

Nervous System  Nervous System Two Major Divisions: A.Central nervous system – consisting of brain and spinal cord B.Peripheral nervous system- nerves emerging from the CNS and the ganglia Neuroglia – cells that occupy space between neurons. Th...

Nervous System  Nervous System Two Major Divisions: A.Central nervous system – consisting of brain and spinal cord B.Peripheral nervous system- nerves emerging from the CNS and the ganglia Neuroglia – cells that occupy space between neurons. They are the supporting cells of the neurons  Neurons (Nerve Cells) Structural units of the nervous system Highly specialized cells that conduct Loading… messages in the form of nerve impulses Special characteristics: Extreme longevity Amitotic Exceptionally high metabolic rate  Neuron Cell body (perikaryon, soma) + one or more cell processes enclosed by neurolemma Nissl bodies- rough endoplasmic reticulum in the Perikaryon  Nerve Cell Processes Dendrites Main receptive input regions Provide a surface area for receiving signals from other neurons Loading… Convey incoming messages toward the cell body Axon Conducting region of the neuron Generates nerve impulses and transmits them away from the cell body  Axon Axon hillock: cone-shaped area of the cell body where the axon arises from Axon terminals (synaptic knobs, boutons): knoblick distal endings of the terminal endings of axons  Movement of impulses in axon Anterograde movement: Movement toward the axon terminal Retrograde movement: Movement away from the axon terminal  Myelin Sheath Whitish, fatty, segmented covering Protects and electrically insulates fibers Increases speed of transmission of nerve impulses Associated only with axons (dendrites are unmyelinated)  Saltatory Conduction Myelin sheath influences the axon to conduct impulses Node of Ranvier –short gaps created by the myelin sheath along the axon Saltatory conduction- a conduction that is created by the nodes of Ranvier. It is faster than the conduction in unmyelinated axons  Nerve impulse Their ability to receive, conduct and transmit signals depends upon the opening and closing of specific ion channel proteins in their membrane Resting potential- Na+ ions is only 1/10th pf extracellular fluids, internal K+ ion is about 10x greater than the outside of the cell, difference of about -90mV the inside negative to the outside  Nerve impulse Their ability to receive, conduct and transmit signals depends upon the opening and closing of specific ion Loading… channel proteins in their membrane Na+ ions is only 1/10th pf extracellular fluids, internal K+ ion is about 10x greater than the outside of the cell, difference of about -90mV the inside negative to the outside referred to as the  Resting potential Nerve Impulse Depolarization- sudden influx of extracellular Na+ions that lowers the membrane potential (makes the inside less negative) Followed by an outflow of K+ ions that restores the resting potential these changes create an Action potential Nerve Impulse Thus, action potential initiated in the initial segment of the axon is propagated along its entire length Upon arriving at the axon ending, it initiates discharge of stored neurotransmitter that stimulates another neuron or a non- neural effector cell  Synapse The specialized region of contact where neurotransmitter is released from an axon to stimulate another cell is called a synapse Junction that mediates information transfer from one neuron to the next or from a neuron to an effector cell  Synapse Maybe excitatory or inhibitory depending on whether the transmitter depolarizes or hyperpolarizes the presynaptic membrane Types: Axodendritic, axosomatic, axoaxonic, dendrodendritic, dendrosomatic synapses Electrical, chemical synapses Synapses  Classification of Neuron according to geometry processes Description Location Unipolar Single short process Ganglia (Pseudounipolar) (Originate as bipolar neurons) Bipolar 2 processes (an Rare axon and a Found in some dendrite) special sense organs (olfactory epithelium, retina) Multipolar 3 or more processes Most common (neurons of cerebrum and cerebellum) According to function Classification of Neurons Functional Description Structural Sensory (Afferent) Transmit impulses Almost all are from sensory unipolar neurons receptors in the skin or internal organs towards the cNS Motor Carry impulses away Multipolar neurons (Efferent) from the CNS to effector organs (muscles, glands) Interneurons Lie between motor Almost all are and sensory neurons multipolar Shuttle signals through CNS pathways (integration) According to Function  Distribution of Neurons Gray matter- contains cell bodies of neurons, dendrites and the terminations of axon arriving at the region White matter-consist mainly of myelinated axons  Cerebral Cortex The cerebral cortex has its gray matter at the outer zone of the hemisphere of the brain. It receives and analyzes sensory information from the body and responds by voluntary initiation of motor activity. Involved in learning and memory The cells are arranged in six major layers  Cerebral Cortex Major cell type A. Pyramidal cell- soma is roughly triangular in section with a large vesicular nucleus and abundant Nissl bodies B.Stellate or granule cell-relatively small 6-10um in diameter with numerous highly branched dendrites and single short axon  Cerebral cortex Horizontal cells- largely confined to one layer of the cortex, are fusiform with radiating dendrites and short axon radiating in opposite directions  Cerebellar Cortex Receives information from eyes, ear and stretch receptor of the muscles Has important role in coordination and maintenance of balance and normal posture  Cerebellar Cortex 3 Layers A. Molecular layer- contains few small neurons and many unmyelinated nerve fibers B.Middle layer- consist of a single layer of large Purkinje cells. C.Granule cell layer-consist of closely packed,small cells with short dendrites and an axon Cerebellar Cortex  Spinal Cord Receives motor commands from the brain and relay them via spinal nerves that emerge from each segment of the vertebral column to innervate muscles and other effectors in the periphery Sensory fiber enter cord through dorsal root Motor fiber leave through roots  Spinal Cord A short distance from the cord the dorsal and ventral roots join to form spinal nerve Loading… In cross section the H-shaped area of gray matter nerve cell bodies and their dendrites Around gray matter are dorsal,lateral, and ventral columns of white matter Spinal Cord Neuroglial Cell Origin Location Function Type Astrocytes Neural CNS Structural support, tube repair processes Blood–brain barrier, metabolic exchanges Oligodendrocy Neural CNS Myelin production, tes tube electric insulation Schwann cells Neural PNS Myelin production, tube electric insulation Ependymal Neural CNS Lining cavities of cells tube central nervous system Microglia Bone CNS Macrophagic marrow activity Neuroglial cells Nervous System: Levels of Organization  Autonomic Nervous System Thoracolumbar division – involve in symphatetic division of ANS. Principal neurotransmitter: Epinephrine and norepinephrine Craniosacral division- involve in parasymphatetic division of ANS Principal neurotransmitter: Acetylcholine  Meninges Meninges- three layers of connective tissue covering the brain and spinal cord 3 layers: A.Dura mater-outermost covering B.Arachnoid- intermediate layer C.Pia mater-innermost layer  Dura mater- dense connective tissue adhering loosely to inner aspect of skull Arachnoid-consist of closely apposed cells in contact with the dura and inner long arachnoid trabecular cells that traverse subarachnoid space to connect to pia mater. It is devoid of blood vessels Pia mater-very loose connective tissue, on the side towards the arachnoid , by a thin single layer of squamous cell Meninges Thank you for listening!