Chapter 2 Neuron PDF

CELL OF THE NERVOUS SYSTEM THE NERVOUS SYSTEM: Neuron (nerve cell) is the information – processing and...

CELL OF THE NERVOUS SYSTEM THE NERVOUS SYSTEM: Neuron (nerve cell) is the information – processing and information – transmitting element of the nervous system. The Neuron THE NEURON Soma (cell body) contains the nucleus and much of the machinery that provides for the life processes of the cell process neural messages Dendrites (“dendron” means tree) receives the message from another neuron  Axon a long slender tube that carries information from the cell body to the terminal buttons Terminal Buttons little knobs at the end of the twigs branching out from the axon Transmit messages to another neuron SYNAPSE - the junction between a terminal button and a dendrite or soma during neural transmission THE CELL  Reflex Arc An impulse conduction route to and from the CNS (brain & spinal cord) Types of Neuron According to Structure Types of Neuron According to Structure Multipolar Neuron Bipolar Neuron (motor neuron) (inter neuron) the most common type found in give rise to one axon the CNS and one dendritic the somatic membrane gives rise tree at opposite ends to one axon but to the trunks of of the soma many dendritic  Types of Neuron According to Structure sensory neurons that receive pseudo-unipolar neurons with a sensory signals from sensory short extension that quickly organs and send them via short divides into two branches, one of axons to the central nervous which functions as a dendrite, the system other as an axon Unipolar Neuron (sensory neuron) motor neurons that conduct multipolar neurons that have motor commands from the short dendrites emanating from has only one stalk that leaves cortex to the spinal cord or from the cell body and one long axon the spinal cord to the muscles the some and divides into two branches a short distance away interneurons that interconnect bipolar neurons that have two various neurons within the brain main extensions of similar or the spinal cord lengths Functional Classification Afferent neurons (sensory) transmit nerve impulses to the spinal cord or brain Efferent neurons (motor) transmit impulses away from the brain or spinal cord Interneurons Conduct impulses from afferent neurons toward or to motor neurons Supporting Cells Astroglia (astrocytes or star cells) Glia / Neuroglia provide physical support to the neuron the most important cell in the CNS clean-up debris in the brain “the nerve glue”, glues the CNS together chemically buffers fluid from surrounding physically and chemically buffer the neurons from the rest of neurons the body supply neurons with nutrients and dispose their surrounded neurons and hold them in place waste products through the capillaries controls supply of chemicals needed Microglia insulate neurons so that messages will not scramble smaller type of glia, serves as phagocytes engulfing dead neurons act as housekeepers Oligodendroglia provide support to axons and produce myelin sheaths in the CNS Ependymal Cells are epithelial cells that monitor the composition of cerebrospinal fluid (CSF). Specialized ependymal cells also participate in the secretion of CSF. Schwann Cells supports axon and produce myelin sheaths in the PNS  Wallerian degeneration - when the axon of a typical neuron is injured by cutting, and severed the axonal connections from the cell body of the neuron. The detached section of the axon had no means of sustaining itself, and thus died. Retrograde degeneration – when part of the axon still attached to the cell body breaks down It has bee observed that the cell body deprived of life sustaining chemical substances normally provided by the two-way exchange with the axon, begins to breakdown as well. Hence, interrelated physiological events takes place at the same time  Chromatolysis - when the cell body loses Nissl substances and eventually the capacity to sustain itself Neuron in CNS or PNS are subject to degenerative stages in the face of serious “ injuries. However, all neurons do not respond the same way. The neuron in the PNS sometimes are able to reverse the effects of the degeneration, they repair their structural integrity and eventually give rise to new axon. The neuron in the CNS, however, unable to reverse the degenerative process. Transsynaptic degeneration – when a neuron form synapses with the dying neuron die too