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44 Cards in this Set
- Front
- Back
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two major components of nerve tissue
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neurons
neuroglial (support) cells |
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functional categories of neurons
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sensory: gather information from receptors
interneurons: form communicating network between neurons motor: convey impulses from nervous system to effector cells |
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structure of neurons
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euchromatic nucleus, with prominent nucleolus
perikaryon (cell body) size between 5-135 um Nissl bodies: well-developed rough endoplasmic reticulum, formed into dense structures well developed Golgi many mitochondria lysosomes present in cytoplasm lacking centrioles neurofilament/microfilament/*microtubule cytoskeleton |
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neuron cell processes
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axons
dendrites |
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axons
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one axon per cell
convey signal from perikaryon to target cell via axon terminal begin from elevated platform called axon hillock, lacking Nissl bodies some are insulated with myelin sheath enclosed by continuation of the plasma membrane called axolemma cytoplasm of the axon (axoplasm) does not contain Nissl bodies or ribosomes; ++ SER cytoskeleton formed by microtubules and neurofilaments |
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axonal transport
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high number of microtubules indicates intense transport activity
perikaryon => axon terminal is anterograde flow distal axon => perikaryon is retrograde flow |
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anterograde flow
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allows transport of actin filaments, proteins, organelles, and vesicles to distal portions of the axon
accomplished by kinesin (- => +) slow axonal transport (1-6 mm/day): used to move tubulin molecules, actin, and other cytoskeletal proteins fast axonal transport (10-40 mm/day): move membrane bound organelles, SER compartments, synaptic vesicles, and mitochondria |
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retrograde flow
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fast retrograde flow provides transport of materials taken up by axon terminal to perikaryon
*major pathway for neurotoxins/viruses transport motor is dynein (+ => -) |
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dendrites
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processes designed to deliver signal from cell periphery to perikaryon
typically thick, short, and tapered processes - profusely branching to form a dendritic tree surface covered with dendritic spines, where synapses are formed non-myelinated cytoplasmic composition similar to perikaryon, but lacking in Golgi |
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major types of neurons
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pseudounipolar
bipolar multipolar |
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pseudounipolar
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primarily sensory neurons
singular process from perikaryon the peripheral process (PP) reaches sensoryarea and transmits sensory information, delivering it via the central process (CP) both conduct like one axon, skipping perikaryon located in dorsal root ganglia and some cranial nerve ganglia |
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bipolar neurons
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sensory neurons with limited distribution, mainly within major sense organs
two processes extending from perikaryon, axon and dendrite dendrite branches in sensory area, acting as the receptor axon delivers impulses to the CNS |
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multipolar neurons
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most common type, both motor and interneurons
one axon, many dendrites depending on length, multiipolar neurons of the CNS can be classified in two ways: Golgi type I cells: long axon, serving as motor neurons of the motor nuclei of the CNS Golgi type II: short axon, smaller interneurons found in the CNS |
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electrophysiology
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plasma membrane acts as electric capacitor, giving the cell a negative membrane potential at rest
Na+ concentrations (10x) outside the cell maintained by active pumps action potentials briefly changes membrane potential, opening voltage sensitive channels and propagating a positive charge (120 m/sec). Na+ diffusion depolarizes the membrane hyperpolarized membranes (more negatively charged) become more difficult to depolarize |
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nerve cell communication
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two major types of synapses: electrical and chemical
electrical synapses in mammals use gap junctions, and allow passage of ions in a slow wave of depolarization chemical synapses are principal method of communication, where no protoplasmic continuity exists, but the signal is generated by neurotransmitters binding to a receptor site chemical synapses are either excitatory or inhibitory, where they depolarize or hyperpolarize the membrane respectively |
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chemical synapses regions
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presynaptic knob
synaptic cleft postsynaptic membrane |
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presynaptic knob
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contains synaptic vesicles (40-60 nm in diameter) which hold neurotransmitters
neurotransmitters: diverse chemicals capable of binding to receptors to generate waves of depolarization or hyperpolarization in postsynaptic cell |
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synaptic cleft
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narrow space between plasma membranes of synaptic cells
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postsynaptic membrane
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contains receptor sites for neurotransmitters
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action potential
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depolarization propogates along membrane towards the axon terminal
Ca++ channels briefly open, and cause the synaptic vesicles to fuse with presynaptic membrane neurotransmitter diffusion and receptor binding depolarize postsynaptic cell excess membrane is removed by endocytosis using clathrin-coated vesicles |
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neurotransmitter deactivation
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recapture and degradation
80% of neurotransmitters (acetylcholine) can be recaptured through high-affinity reputake: neurotransmitter is reincorporated by endocytosis into vesicles that are ready for repackaging enzymes breakdown remaining neurotransmitters in synaptic cleft *inhibition of deactivating factors for norepinephrine helps with depression |
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synapse morphotypes
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axodendritic: connection between axon and dendrite
axosomatic: connection between axon and perikaryon axoaxonic: connection between axon and another axon motor end-plate: connection between axon and neuromuscular junction -axon terminal contains presynaptic vesicles -synaptic cleft is space between -sarcolemma of muscle forms junctional folds, which are receptor locations |
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Curare toxin
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binds to acetylcholine receptors and acts as relaxant
South American dart frogs |
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botulinum neurotoxin
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brand named Botox, prevents release of acetylcholine from synaptic vesicles
produced by Clostridium botulinum |
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myasthenia gravis
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auto-antibodies to acetylcholine receptors is produced
auto-antibodies bind to the receptor sites, weakening muscle response |
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Rabies virus
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bites introduce virus to muscle tissue, where it starts replicating for 1-2 weeks
finds motor-end plate and gets into the cleft virus enters synaptic terminal and retrograde axonal transport carries it to the presynaptic cell. most of the CNS is quickly affected by severe inflammation, light intensity, or sounds - running water causes seizures (old name: hydrophobia) virus spreads to salivary glands, to be transmitted via bites after symptoms arise, there is no cure |
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support cells of the PNS
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Schwann cells: form the myelin sheath, surrounding axons of peripheral nerves, and envelope unmyelinated axons
satellite cells: found primarily in ganglia of peripheral nervous system. They insulate individual neuron bodies, but do not have myelin |
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nodes of Ranvier
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space between adjacent Schwann cells with high concentration of Na+ channels.
allows for saltatory conduction, significantly improving speed and voltage of action potential |
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support cells of CNS
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astrocytes
oligodendrocytes ependymal cells microglial cells |
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astrocytes
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largest neuroglial cells: support vascular structures and neurons, mostly bundles of intermediate filaments, composed of GFAP
large role in moving metabolic substances between blood and nerve cells, forming blood-brain barrier two types: protoplasmic astrocytes/fibrous astrocytes protoplasmic: found in gray matter, numerous short branching processes that form perivascular feet along capillaries fibrous: found in white matter, more prominent cytoskeleton, less branching and fewer processes *astrocytoma accounts for 20% of brain cancers, and 80% of all tumors that originate in the brain *local damage starts process of gliosis, which forms glial scars |
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astrocytoma
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accounts for 20% of brain tumors - including those that metastasized into the brain
give rise to 80% of all tumors that originate in the brain |
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oligodendrocytes
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most common neuroglial cells
tongue-like processes extend to wrap around axons forming segments of myelin sheath |
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multiple sclerosis
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disease caused by damage to myelin sheath of CNS axons by immune system
symptoms: loss of sensitivity, partial paralysis depending on area of damage |
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microglial cells
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phagocytic properties, smallest neuroglia
derived of blood monocytes cytoplasm contains many lysosomes, and the number of cells increase at sites of injury, so they may be responsible for removing debris *microglial cells are abundant in Alzheimer's and Parkinson's disease patients - could be responsible for plaque formation, demyelination, and nerve fiber destruction |
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ependymal cells
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line the lumen of brain ventricles and spinal cord cavities
responsible for production and absorption of CSF arranged as simple cuboidal epithelium, without basal lamina tightly bound by junctional complexes, possess microvilli, and occasionally cilia basal processes interdigitate with astrocyte processes, allowing exchange |
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peripheral nervous system (PNS)
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consists of
cranial, spinal, and peripheral nerves ganglia special nerve endings |
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nerves of the PNS
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sensory and motor nerve fibers composed of myelinated and non-myelinated axons
held by sheets of connective tissue endoneurium: surrounds individual fibers perineurium: surround nerve fascicles epineurium: surrounds individual nerves that extend into spaces between fascicles |
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ganglia of PNS
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clusters of neuron cell bodies outside CNS, encapsulated by connective tissue and satellite cells
sensory craniospinal ganglia: pseudounipolar neurons, with long peripheral process to receptor organ, and a short central process to spinal cord (dorsal root ganglia) or brain. Craniospinal ganglia surrounded by satellite cells motor ganglia: autonomic nervous system consisting of multipolar neurons and satellite cells |
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special endings
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either motor or sensory - sensory nerve endings have two major types
special senses nerve endings: specialized for smell, sight, hearing, and equilibrium somesthetic receptors: found throughout the body, epithelial tissues, connective tissues, muscles, and joints proprioceptors: collect information about angulations of joints and muscle tension |
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somesthetic receptors
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free nerve endings: branched sensory endings that mediate pain
encapsulated nerve endings: -Meissner's corpuscle - cylindrical structure formed of stacked lamellae, provide sense of touch, and are most common on skin of fingers and toes -Pacinian corpuscle: largest of encapsulated nerve endings, about 30 concentric sheets of connective tissue, separated with fluid; found in dermis and internal organs |
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proprioceptors
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muscle spindle
specialized receptor located in skeletal muscle stretch receptor covered with two capsules, internal and external, separated by fluid-filled space inside the spindle are intrafusal fibers surrounded by the nerve fibers of motor and sensory sensory fibers wrap around the intrafusal fibers and transmit information about the degree of stretching of the muscle motor nerve fibers regulate the sensitivity of the stretch receptor |
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Central Nervous System (CNS)
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consists of the spinal cord and brain
clusters of neurons in the CNS are called nuclei, which are supported by neuroglial cells nerve fibers organized into tracts organs of the CNS supported by meninges, choroid plexuses, ventricles, etc. white and gray matter |
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gray matter
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consists of neuron bodies, and unmyelinated fibers, with extensive vascular supply through capillaries
spinal gray matter: interior portion, organized into two horns (ventral: motor; dorsal: dorsal root ganglia) connected via gray commissure brain gray matter: external to white, thrown into gyri, in the cerebellum, these folds are called folia -cerebrum gray matter: 6 layers, three main types of neurons found are pyramidal, fusiform, and granule cells -cerebellum gray matter: 3 layers a. molecular layer: external layer with few cell bodies of neurons, called basket cells b. Purkinje layer: thin layer composed of large Purkinje cells c. ganular layer: adjacent to white matter, highly cellular, composed of small granule cells |
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white matter
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myelinated axons and glial cells
limited blood supply compared to gray matter rather dense with limited extracellular space, very few synaptic contacts within the white matter |
