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79 Cards in this Set
- Front
- Back
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neurons
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convey electrical impulses, synthesize and secrete neurotransmitters, membrane potentials and can carry electric charge
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glia (neuroglia)
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support and maintain neuronal envirnment
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Nerve Cell Body (NCB)
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= periaryon, soma
nissl bodies neurofilaments and neurotubules residual bodies |
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nissle bodies
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granular ER, ribsomes, clumps in stains
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neurofilaments
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intermediate filaments, fcn in cell meovement) and neurotubules, for neurotransmitters to travell
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residual bodies
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old lysosomes that have some debris - brown pigment
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Neuronal Processes
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dendrites and axons
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dendrites
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dendritic spines (protrusions of PM) - shorter and branching
carry impulses towards hte cell body |
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Axons
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usually one per neruon, usually carry electrical impulses away from the cell body
axon hillock initial segment: site of generation of action potential axon collaterals terminal boutons - when it synapses on another neuron motor end plate - when it synapes on muscles |
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Axonal Transport - bidirectional
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transport mediated by neurotubules
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Axonal Transport - anterograde
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kinesin - mediated, down the axon, away from the cell body, neurotransmitter travels
transport of a vesicle along a microtubule |
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Axonal Transport - retrograde
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dynein - mediated, things are taken up at the synapse, transport of a vesicle along a microtubule, towards the cell body
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synapse
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= point of contact between 2 neurons
axodendritic, axosomatic, axoaxonic, dendrodendritic main types: electrical synapse-gap jcn, chemical synapse membrane ion pumps maintain baseline electrical gradient between inside and outside of neuron ion channel proteins electrical synapse chemical synapse |
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Ion channel proteins
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form pores or "gates" that can alter membrane permeability to ions in response to specific signals
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ligand-gated channels
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open and close in response to neurotransoutter binding, located mainly at synapse
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voltage-gated channels
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widely distributed on cell membrane and involved in rapid depolarization
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simplified chemical axosomatic synapse
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terminal boutons are synapsing on a NCB of another neuron
1. presynaptic neuron: nerve impulse causes depolarization of PM, synaptic vesicles migrate to presynaptic membrane and fuse with it and exocytose neurotransmitters into the synaptic cleft, and then the nt's pass through the synaptic cleft 2. 2nd neuron is considered the post-synaptic neuron 3. nt binds to receptors on the postsynaptic membrane and alters postsynaptic membrane potential depolarization and progration of impulse = excitatory synapse hyperpolarization = inhibitory synpase blocks transmission of impulse |
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Neuron classification: based on structure on structure or function, structure (number of processes)
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multipolar
bipolar pseudounipolar |
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pseudopolar neuron
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during development, the dendrite and axon fuse. An initial short segment extends from the NCB and then splits into a peripheral pricess and a central process, both have the structure of axons so both are refered to as axons
sensory neurons |
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multipolar neuron
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possess a single axon and many dendrites
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multipolar
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motor neurons
interneurons (only CNS) |
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bipolar neurons
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has two extensions, specialized sensory neurons
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neuron classification by function
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motor neurons
sensory neurons receptors |
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motor neurons function
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axons = efferent fibers: carry impulses away from CNS, synapse on other motor neurons or effector organs (tissues): muscle (skeletal, smooth, cardiac), glands (salivary)
motor endplate: specialized termination of a motor neuron which synapses on muscle interneurons: found in between two neurons |
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sensory neurons function
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bipolar: special sensory (eye and ear)
pseudounipolar: peripheral process (axon) = afferent fibers: carry impulses towards CNS, originate in tissues as receptor endings. Central process (axon) enters the CNS only located in sensory ganglia in PNS multipolar |
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receptors
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specialized structures which act as transducers or converters that convert sensory stimulation into electrical impulse. Sensor stim includes mech stim (tactile, pressure, shearing on skin), pain, thermal, chemical, stretch, receptors are classified according to their structure or the stim that they convery
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Receptor Structural Classification
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specialized cells or modified neurons that synpase on pseudounipolar neurons (olfactory epithelium, taste buds)
specialized endsing of peripheral processes of sensory neurons |
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specialized endsing of peripheral processes of sensory neurons
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free nerve endings
encapsulated nerve ending stretch receptors |
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free nerve endings
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located in or below epithelium (skin, mucosa), convey pain, touch, themral
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encapsulated nerve endings
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touch, pressure, found deeper in skin, sometimes in connective tissue
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stretch receptors
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proprioception or muscle position sense, detect stretch on a muscle or tendon
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classification of receptors based on stimulus conveyed:
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mechanoreceptors: tactile, pressure
nociceptors: pain chemoreceptors: olfaction, taste, blood pH proprioceptors: muscle spindle, golgi tendon organ detect stretch on muscle and tendons, can be bone photoreceptors (eye) barorecptors (blood vessel stretch or BP) |
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Basic architecture of the NS
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neuron NCBs are located in specific locations of the CNS and PNS
axons extend from the NCBs and travel together forming nerves in the PNS and white matter tracts in the CNS |
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NCBs and Axons in the CNS
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NCBs - gray matter: nuclei, cell colums, layers
axons - white matter: tracts, fibers |
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NCBs and Axons in the PNS
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NCBs - ganglia
Axons - nerves: spinal, cranial, other |
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components of PNS
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ganglia
peripheral nerves |
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gangia
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collections of neuron NCBs
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autonomic motor ganglia
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contain NCBs of motor (multipolar) nuerons
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autonomic motor ganglia: sympathetic
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sympathetic chain ganglia - runs outside the vertebral column, connects with the soinal nerve (where motor neruons are located)
prevertebral (preaortic) ganglia |
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autonomic motor ganglia:
parasympatheitc |
cranial nerve motor ganglia
intramural ganglia: in walls of organs, tiny ganglia, between layers of smooth muscle |
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sensory ganglia
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contain NCBs of pseudounipolar neurons
dorsal root ganglia cranial nerve sensory ganglia - in the head (5th CN) |
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Peripheral Nerves
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collections of axons referred to as "components" of the nerve
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spinal nerves
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31 pairs, innervate body wall, come up and branch into dorsal and ventral
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cranial nerves
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12 pairs, innervate head and neck structures, exfcept for vagus nerve that innervates the viscera
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other peripheral nerves
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roots, rami, plexus, visceral nerves
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CT sheaths
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endoneurium
perineurium erpineurium |
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endoneurium
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around each individual axon
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perineurium
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around a bunch of axons
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epineurium
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around the whole nerve
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nerve
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collection of axons, nerves can carry axons of motor neurons or sensory neurons, two different traffic patterns
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peripheral nerve distribution
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a nerve to a particular tissue is made up of many axons of sensory and/or motor neurons. these axons are referred to as motor efferent fibers or sensory afferent fibers
the axons can be traced back to the neuron NCB located either in gray matter of the spinal cord or a peripheral ganglion |
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tissue that receive innervation
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somatic
visceral |
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somatic
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"outer" body = skin (cutaneous), skeletal muscle (motor and sensory_, tendons, ligaments, bone (outside the body cavities
somatic motor to skeletal muscle somatic sensory to skin, and all others |
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visceral
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"inner" body = cardiac muscle, smooth muscle, glands receive autonomic innervation
visceral motor to cardiac and smooth muscle as wall as glands visceral sensory - organ distension, blood vessel distension |
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NS support cells
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PNS: schwann cell, satellite cell
CNS: oligodendrocyte, astrocte, microglia, ependymal cell |
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Schwann Cells
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enclosed in their own basal lamina and located adjacent axons
synthesize and maintain myelin sheath a single axon will have man segments of myelin along its length with the schwann cell nucleus visible outside the myelin segment |
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Myelin Formation
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schwann cells cup around axon
schwann cell "feeds out" elongating cytoplasmic process which wraps around the axon in a spiraling fashion as the process wraps around the schwann cell, most of the schwann cell's cytoplasm is extruded. The resulting myelin sheath is compact concentric layers of schwanna plasma membrane |
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internode
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1 segment of myelin
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nodes of Ranvier
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between internodes, axon surrounded by schwann cell basil lamina
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EM Level characteristics of Myelin
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Major dense line:electron-dense line represents fusion of cytoplasmic surfaces of schwann cells plasma membrane
intraperiod line: lighter line represents the fusion of outer plasma membrane surfaces Schmidt-Lanterman's Cleft: areas of retained cytoplasm Alternating dark and light dense lines: represent the different surfaces of the PM |
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unmyelinated axons
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in the PNS they sit in clefts or indentations in the schwann cells, one schwann cell may surround many unmyelinated axons
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CNS Oligodendrocytes
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synthesize and maintain the myelin sheath
one may provide more than 1 segment of myelin along the axon one may provide myelin to more than 1 axon they do not have a basal lamina; axon is bare at the nodes of ranvier unmyelination axons in the CNS are not associated with them |
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Myelin
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made of lipids and proteins
insulated, increases the speed of propogation of impulses down an axon and prevents dissipation of current thickness varies per axon |
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Myelin Proteins
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serve as anchoring attachments between myelin membranes and mediate myelin compaction
are strong antigenic targets for immune attack myelin basic proteins (CNS and PNS) proteolipid protein (CNS) myelin protein zero (PNS) other proteins different kinds of proteins depending on CNS or PNS responsible for intracellular communication, |
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demyelinating diseases and factors affecting myelin formation
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myelin sheath may be directly affected or demyelination may result from pathology of myelinating cells
nutritional deficieny, Vit B12 deficieny = hypomyelination toxins: heavy metals |
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Genetic Demyelinating Diseases
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Adrenoleukodystrophy: peroxisomal disorder affects myelin lipid
pelizaeus-Merzbacher: mutation of proteolipd protein gene results in degerneration of CNS myelin in chidlren or hypomelination |
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Multiple Sclerosis
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Autoimmune: autoantibodies target olgiodendrocytes and myeline, acute or replasing remitting, mutliple focal demyelinationg lesions in brain, SC, optic nerve
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progressive multifocal leukoencephalopathy (PML)
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causes by human polyoma virus (JC virus), occurs in immunoisuppressed individuals
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CNS Astrocytes
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provide structural support and maintain neuronal extracellular environment
during development, provide scaffolding support for migrating neurons component of the BBB: astrocytic process wrap around blood vessels and nerves astrocytic reaction to insult or injury: proliferation and/or hypertrophy reactive astrocytosis glial scarring - encapsulates walls off the area of infection, protective mechanism |
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fibrous astrocyte
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ehite matter
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protoplasmic astrocyte
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gray matter
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CNS microglia
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derived from monocytes, are phagocytic, have immune fucntion
express MHC II and are antigen-presenting cells become activated during disease and produce chemoattractants that recruit WBCs across the BBB HIV type I infects microglial cells which produce cytokines toxic to neurons |
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CNS ependymal cells
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line cavities of the CNS (ventricles and central canal)
may be squamous to columnar, microvilli and cilia may be present desmosome attachment between cells in certain areas of the ventricles, the ependymal cells are specialized |
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choroid plexus epithelium
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secrete CSF
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Glial Tumors (Gliomas)
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astrocytomas: most common
Ependymomas Oligodendrogliomas Primitive neuroectodermal tumors: derived from undifferentiated cells (more harmful the more undifferntiated), medulloblastomas (childhood tumprs) schwannoma |
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Neural tissue repair and regeneration
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mature neurons do not divide
regeneration of peripheral nerves is possible but limited (stem cells) |
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Wallerian or Anterograde degeneration
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axon distal to cut loses support from NCB and degenerates
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Retrograde degeneration
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chromatolysis = swelling of NCB, proximal axon initially degenerates but since still attached to NCB it can regenerate when NCB recovers
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regeneration
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distal axon: schwann cell proliferate forming "tube" can form another channel of myelin, ner axonal sprouts
proximal axon: grows towards schwann cell tube. If it can find correct path, and grow through and reach the effector organ, it can potentially function again |
