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Description
Flashcards by Marissa Alvarez, updated more than 1 year ago
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Created by Marissa Alvarez
over 7 years ago
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| Question | Answer |
| Nervous system: Overview Anatomical Divisions CNS? PNS? | CNS: Brain & Spinal cord PNS: Peripheral nerves & Ganglia |
| Functional divisions: (4 of them) | -Afferent neurons (Arriving): info. from periphery to the CNS -Efferent neurons (Exit): info. from CNS out to the periphery Somatic (voluntary) & Autonomic (involuntary) |
| Two types of cells in the nervous system Neurons | conduct electrical impulses |
| Two types of cells in the nervous system Glial cells | support, nurture, and protect neurons. NEED SUPPORT CELLS |
| Types of neurons: Bipolar neurons | Single axon and single dendrite Located in sense organs *isolated to the eye |
| Types of neurons: Multipolar neurons | Single axon and multiple dendrites Most common type "work horse" |
| Types of neurons: Pseudounipolar neurons | Single process extends from cell body and branches into an axon and dendrite (cell body is b/w two stalks of an axon) First developed in the embryo as bipolar cells whose axon and dendrite later fuse into a single process Located in spinal and cranial ganglia |
| Dendrites | Receive stimuli from sensory cells, axons, or other neurons Convert these signals into small electrical impulses which are transmitted to soma (cell body) Often have arborized terminals which permit a neuron to receive very LARGE number of STIMULI |
| Neuronal Cell Body: (a.k.a. soma or perikaryon) Nucleus Nissl bodies Neurofilaments Microtubules Axon Hillock | Nucleus: Large, with dispersed chromatin and large nucleolus (centrally placed, "owl eye") Nissl bodies: Polyribosomes and rER (LOTS of rER & Golgi-protein being made) Abundant in larger neurons Neurofilaments: Intermediate filaments Part of cytoskeleton Microtubules: Move organelles within cell Direct axonal flow Axon hillock: LACKS rER and ribosomes (lacks staining: like a shadow) Contains many microtubules & neurofilaments |
| What type of neurons are shown in the image? What are the arrows pointing at? | **Note the BLUE Nissl substance in cell body, many have nice nucleolus |
| Axons Called what in cytoplasm? in plasma membrane? | Conduct impulses AWAY from the soma to the axon terminals (ONLY ONE DIRECTION) While dendrites taper, axons retain a CONSTANT diameter along their course. Diameter is PROPORTIONAL with SIZE of cell BODY. Length is highly variable. Axons may branch! Cytoplasm = axoplasm (devoid of rER) Plasma membrane = axolemma Terminate in axon terminals from which impulses are passed to another neuron or other type of cell (muscle or gland) |
| Lacks stain b/c lacks rER & ribosomes *like a SHADOW contains many microtubules & microfilaments | |
| From axon to nerve fiber Axon enveloped by? | If an Individual axon is enveloped by a MYELIN SHEATH, a nerve fiber *myelinated = FASTER impulse |
| Myelin sheath is produced by: what in the CNS? what in the PNS? | Oligodendrocytes in CNS Schwann cells in PNS **KEY POINT: ALL neurons have SUPPORT cells that protect it or serve some other function (none are their own entity) |
| Myelin sheath in the PNS | Lipoprotein sheath formed by several layers of plasma membrane of a SCHWANN cell wrapping around an axon Segments covered by ONE Schwann cell are separated by NODES OF RANVIER It is of constant thickness along the length of an axon (thicker axons have thicker myelin sheaths.) |
| Myelin sheath in the PNS | Nodes of Ranvier: represent a discontinuity between adjacent Schwann cells (NOT very long); lack myelin Schmidt-Lantermann clefts: cone-shaped, oblique discontinuities in the myelin sheath; formed by Schwann cell cytoplasm that is not displaced to the periphery during myelin formation S1 = Schmidt-Lantermann clefts |
| Myelin sheath in the CNS: | |
| Unmyelinated Nerve Fibers in the PNS: | In unmyelinated nerve fibers, the Schwann cells engulf ~8-10 axons (protects it) **EMBEDDED in Schwann-cell cytoplasm |
| The coverings of axons - SUMMARY CNS versus PNS Myelinated versus Unmyelinated | Axons are never completely “naked” They may be myelinated or unmyelinated In the CNS, myelin is formed by oligodendrocytes; In CNS, unmyelinated axons are insulated by astrocyte processes In the PNS, myelin is formed by Schwann cells, In PNS, unmyelinated axons (singly or in groups) are EMBEDDED in Schwann-cell cytoplasm |
| Disorders of Myelin: Multiple Sclerosis | MOST COMMON disease of myelin in CNS -damaged oligodendrocytes Most common demyelinating disease Unknown etiology; immune/viral factors suspected Multiple areas of demyelination in brain and spinal cord; progressive Weakness of lower extremities, visual problems, sensory disturbances |
| Disorders of Myelin: Guillain-Barre syndrome | -Schwann Cell degeneration -Usually viral infection -Pain in extremities Acute inflammatory demyelinating disease involving peripheral nerves Often preceded by viral infection, immunization, or allergic reactions Considered to be of autoimmune etiology Ascending muscle weakness and PARALYSIS (moving from lower extremity upward) Most patients recover but respiratory failure may lead to death |
| Peripheral nerves | |
| Connective Tissue Investments (in periphery): Epineurium Perineurium Endoneurium | Epineurium: Fibrous dense connective tissue that forms the external coat of nerves Perineurium: Layer of modified dense connective tissue that surrounds each bundle (fascicle) of nerve fibers **Inner surface consists of flattened EPITHELIOID cells joined by tight junctions (barrier function) Endoneurium: Thin layer of loose connective tissue surrounding individual nerve fibers (in b/w axons) -fibroblasts make endoneurium |
| Peripheral Nerve Fascicle/Bundle (toluidine blue stain) | Perineurium surrounds nerve bundles/fascicles Unmyelinated axons tend t be clustered into "donut shape" |
| Peripheral nerve (cross section, osmium stain) What is myelin made of? | Myelin = Lipids *can see the myelin because of stain (osmium + something else because osmium alone appears black) |
| Peripheral nerve fibers stained with osmium | |
| Dorsal root or sensory ganglion: pseudounipolar neurons | Black arrows (w/o stems) are pointing at Dorsal root or sensory ganglion (ROUND) -have a lot of myelin (fairly unique to DRG) *Support cells = Satellite cells *Pseudounipolar |
| Sympathetic Ganglion | Preganglionic fibers from spinal cord enter ganglion and terminate on dendrites (upper blue arrow) and cell bodies of postganglionic neurons *NOT as ROUND -More multipolar -less myelin |
| Parasympathetic Ganglion | Note: smooth muscle (peristalsis in intestine) involuntary! |
| CNS 2 components?? | |
| Spinal Cord | |
| White matter of Spinal Cord: Mostly myelinated or unmyelinated? | White Matter: Contains MOSTLY MYELINATED but also some unmyelinated nerve fibers |
| PYRAMIDAL cells from CEREBRAL cortex Golgi silver impregnation method | "no spikes" Function: Spatial recognition Long axons |
| PURKINJE cells in CEREBELLAR cortex Golgi silver impregnation method | VERY EXTENSIVE dendrites/dendritic tree Functions: Proper movement & Pain receptors in cerebellar cortex *Also found in the HEART |
| Specialized Receptors 2 Types: | 1. Meissener corpuscles 2. Pacinian corpuscles |
| Encapsulated receptor in dermis, joints, and mesenteries Multilayered capsule of fibroblasts, collagen, and fluid, surrounding a nerve terminal Pressure, touch, vibration DEEP CORE touch (Palm of your hands) | |
| Encapsulated receptors in dermis (skin) CT capsule enveloping nerve terminal and its Schwann cell Fine/LIGHT touch -how you get your finger prints -axon leading up to the nerve ending (bulge) | |
| Degeneration and Regeneration of Nerve Tissue | A. Normal nerve fiber B. Injured nerve fiber C. Muscle fiber atrophies; Scwann cells proliferate; axon penetrates into “track” laid down by Schwann cells; grows an average of 2.5 mm (1/10 of an inch)/day. D. Regeneration is complete. (regernation doesn't happen often) KEY POINT: Death to the CELL BODY is IRREVERSIBLE, but DAMAGED AXONS can REGENERATE. *Also, doesn't regenerate, just reattaches |
| Exam Question: The Axon Hillock of a Spinal Motor Neuron: A. Contains an abundance of rER B. Stains intensely histologicaly C. Is where the nucleus resides D. Contains microtubules and neurofilaments | D. Contains microtubules and neurofilaments |
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