University:
Glendale Community College
Course:
BIO160 | Introduction to Human Anatomy and Physiology
Academic year:

2020
Views:

425

Pages:

19
Author:

saamstrysv

Types of Neurons • Sensory Neurons (afferent neurons) – receptors that detect changes in the external environment and within the body (temperature, pressure, vibrations, light, chemicals) – this information is transmitted into brain or spinal cord • Interneurons (association neurons) – positioned between sensory neurons and motor neurons in the CNS – 90% of human neurons are interneurons – interneurons process, store and retrieve information • Motor Neurons (efferent neurons) – send signals out to muscles and glands Types of Neurons Characteristics of Neurons • Excitation (irritability) – cells respond to changes in the body and external environment (the cells respond to stimuli) • Conduction – cells produce signals that travel from cell to cell • Secretion – when a signal reaches the end of an axon, a chemical neurotransmitter is released Structure of a Neuron Dendrites Cell Body (Soma) Axon Hillock Initial Segment Axon Nissl (clumps of RER) Schwann Cells Nodes of Ranvier Terminal Arborization Terminal Bouttons Dr. Franz Nissl (1860-1919) was born in Germany, he gravitated to medicine and as a student in Munich he wrote on pathology of cortical cells in which he used a stain he created which opened up a new era in neurocytology and neuropathology. Nissl Granules brought out by basic aniline stains perpetuate his name."But he also did outstanding work in psychiatry and demonstrated the correlation of nerves and mental disease by relating them to changes in glial cells, blood elements, blood vessels, and brain tissue in general. He worked with Alzheimer on general paresis. In the last 10 years of his life he did studies in which he established connections between the cortex and certain thalamic nuclei. Axon Hillock Neurons and Glia – immunofluorescent preparation Neuron Morphologies • Multipolar Neuron – many dendrites – one axon that may brach – most common type of neuron • Bipolar Neuron – one dendrite – one axon – olfactory, retina, inner ear • Unipolar Neuron – only one process comes off soma – also called pseudounipolar neurons – sensory from skin and organs to spinal cord Neuroglia • Neuroglia are cells other than neurons in the nervous system (90% of cells in the CNS are glia, but they only account for 50% of the volume of the CNS). • Many Schwann Cells cover each axon in the PNS. • Each Oligodendrocyte covers parts of multiple axons in the CNS. • Astrocytes – most abundant glial cells - form framework of CNS – form an important part of the “blood-brain barrier” by separating neurons from capillaries – help regulate the composition of brain tissue intercellular fluid – can produce action potentials like neurons • Ependymal Cells form a ciliated simple columnar epithelium that lines cavities in the CNS and circulate cerebrospinal fluid (CSF). • Microglia are bone marrow derived macrophages that move into the CNS and concentrate in areas of infection, trauma or stroke. Neuroglia of the Central Nervous System Ventricles of the Human Brain Myelin Sheath • Myelin is formed by multiple wrappings of a glial cell membrane around an axon. – Myelin is formed by oligodendrocytes in the CNS and by Schwann cells in the PNS. – Myelination takes place during development of the nervous system. – Wrappings of glial cell plasma membrane are about 20% protein and 80% lipid and make the axons look shiny white. – Not all axons are myelinated, but all axons are covered by glial cells. – Schwann cells hold short unmyelinated axons in grooves with only one membrane wrapping. • Gaps between myelin segments are called Nodes of Ranvier – these “gaps” are extremely small spaces where two myelin segments meet. Myelin Sheath Formation Unmyelinated Axon Myelinated Axons Myelin Sheath Node of Ranvier Axons Schwann Cell Node of Ranvier