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83 Cards in this Set
- Front
- Back
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endocrine system
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communicates by means of chemical messengers (hormones) secreted into to the blood
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Nervous System
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employs electrical and chemical means to send messages from cell to cell
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3 Steps of Nervous System
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-sense organs recieve info about changes in the body and the external environment, & transmits coded messages to the spinal cord & brain
- brain& spinal cord processed this info, relates it to past experiences, & determines what response is appropriate to the circumstances -brain & spinal cord issue commands to muscles & gland cells to carry out such a response |
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Subdivisions of Nervous System
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Central Nervous System(CNS) & Peripheral Nervous System(PNS)
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Central Nervous Systems
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brain & spinal cord enclosed in bony coverings
-enclosed by cranium & vertebral column |
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Peripheral Nervous System
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all the nervous system except the brain & spinal cord
-composed of nerves & ganglia |
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Nerve
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a bundle of nerve fibers (axons) wrapped in fibrous connective tissue
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Ganglion
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a knot-like swelling in a nerve where neuron cell bodies are concentrated
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Divisions of PNS
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Sensory & Motor
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Sensory (afferent) division
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carries sensory signals from various receptors to the CNS
-informs the CNS of stimuli within or around the body |
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Somatic Sensory Division
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carries signals from receptors in the skin, muscles, bones, and joints
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Visceral Sensory Division
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carries signals from the viscera of the thoracic and abdominal cavities
-heart, lungs, stomach, and urinary bladder |
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Motor (efferent) Division
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carries signals from the CNS to gland and muscle cells that carry out the body's response
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effectors
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cells and organs that respond to commands from the CNS
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Somatic/ Visceral Motor Division
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Somatic- carries signals to skeletal muscles
Visceral- carries signals to glands, cardiac muscle, and smooth muscle |
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Sympathetic Division
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-tends to arouse body for action
-accelerating heart beat and respiration, while inhibiting digestive and urinary systems |
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Parasympathetic Division
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-tends to have calming effect
-slows heart rate and breathing -stimulates digestive and urinary systems |
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excitability (irritability)
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respond to environmental changes called stimuli
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Conductivity
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neurons respond to stimuli by producing electrical signals that are quickly conducted to other cells at distant locations
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Secretion
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when electrical signals reaches end of nerve fiber, a chemical neurotransmitter is secreted that crosses the gap and stimulates the next cell
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Function of Sensory (afferent) Neurons
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-specialized to detect stimuli
-transmit info about them to the CNS ~begin in almost every organ in the body & end in CNS ~afferent- conducting signals toward CNS |
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Function of Interneurons (association) Neurons
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-lie entirely within the CNS
-receive signals from many neurons & carry out the integrative function -90% of all neurons are interneurons -lie btwn, & interconnect the incoming sensory pathways, & the outgoing motor pathways of the CNS |
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Function of Motor (efferent) Neurons
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-send signals out to muscles and glad cells (the effectors)
~motor b/c most of them lead to muscles ~ efferent neurons conduct signals away from the CNS |
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STRUCTURE OF A NEURON
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GKHGHBH
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Soma
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the control center of the neuron
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Dendrites
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vast number of branches coming from a few thick branches from the soma
-primary site for receiving signals from other neurons -provide precise pathway for the reception and processing of neural info |
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Axon (nerve fiber)
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originates from a mound on one side of the soma called the axon hillock
-axon collaterals- branches of axon -specialized for rapid conduction of nerve signals to points remote of the soma -axoplasm-cytoplasm of axon -axolemma-plasma membrane of axon -schwann cells and myelin sheath enclose axon |
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Synaptic Knob (terminal button)
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little swelling that forms a junction (synapse) with the next cell
-contains synaptic vesicles full of neurotransmitter |
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VARIATION IN NEURON STRUCTURE
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klsfjks
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Multipolar Neuron
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one axon and multiple dendrites
-most common -most neurons in the brain & spinal cord |
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Bipolar Neuron
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one axon & one dendrite
-olfactory cells, retina, inner ear |
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Unipolar Neuron
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single process leading away from the soma
-sensory from skin and organs to spinal cord |
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Anaxonic Neuron
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many dendrites but no axon
-help in visual processes |
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Axonal Transport
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two way passage of proteins, organelles, and other material along an axon
-microtubules guide materials along axon ~motor proteins (kinesin & dynein) carry materials "on their backs" while they "crawl" along microtubules |
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Anterograde / Retrograde Transport
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anterograde- movement down the axon away from the soma
(kinesin-motor protein in anterograde transport) retrograde- movement up the axon toward the soma (dynein- motor proteins in retrograde transport) |
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Fast Axonal Transport
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occurs at a rate of 20-400 mm/day
-fast anterograde: organelles, enzymes, synaptic vesicles, & small molecules -fast retrograde: for recycled materials & pathogens- rabies, herpes simplex, tetanus, polio viruses |
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Slow Axonal Transport or Axoplasmic Flow
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0.5-10 mm/day
-always anterograde -moves enzymes, cytoskeletal components, and new axoplasm down the axon during repair & regeneration of damaged axons |
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Neuroglial Cells
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-support & protect neurons
-bing neurons together & form framework for nervous tissue -in fetus, guide migrating neurons to their destination neuroglia outnumber the neurons by as much as 50-1 |
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SIX TYPES OF NEUROGLIAL CELLS
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oligodendrocytes (CNS)
ependymal cells (CNS) microglia (CNS) astrocytes (CNS) schwann cells (PNS) satellite cells (PNS) |
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Oligodendrocytes (CNS)
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form myelin sheaths in CNS
-each arm-like process wraps around a nerve fiber forming an insulating layer that speeds up signal conduction |
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Ependymal Cells (CNS)
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-line internal cavities of the brain
-cuboidal epithelium with cillia on apical surface -secretes and circulates cerebrospinal fluid (CSF) |
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Microglia (CNS)
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-small wandering macrophages formed white blood cell called monocytes
-though to perform a complete checkup on the brain tissue several times a day -wander in search of cellular debris to phagocytize |
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Astrocytes (CNS)
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-most abundant glial cell in CNS
-cover entire brain surface & most nonsynaptic regions of the neurons in the gray matter of the CNS |
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Functions of the Astrocytes
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form a supportive framework of nervous tissue
-have extensions that contact blood capillaries that stimulate them to form a tight seal called blood brain barrier -convert blood glucose to lactate & supply this to the neurons for nourishment -nerve growth factors secreted by astrocytes promote neuron growth and synapse formation astrocytosis or sclerosis- when neuron is damaged, astrocytes form hardened scar tissue & fill space formerly occupied by the neuron |
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Schwann Cells (PNS)
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-envelope nerve fibers in PNS
-wind repeatedly around a nerve fiber -produces myelin sheath similar to ones produced by oligodendrocytes in CNS -assist in the regeneration of damaged fibers |
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Satellite Cells (PNS)
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-surround the neurosomas in ganglia of the PNS
-provide electrical insulation around the soma -regulate the chemical environment of the neurons |
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Tumors
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masses of rapidly dividing cells
-mature neurons have little or no capacity for mitosis and seldom form tumors |
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Brain Tumors arise from...
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-meninges(protective membranes of CNS)
-by metastasis from non-neuronal tumors in other organs -most come from glial cells that are mitotically active throughout life |
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Gliomas
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grow rapidly and are highly malignant
-blood-brain barrier decreases effectiveness of chemotherapy -treatment consists of radiation or surgery |
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Myelin Sheath
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insulating layer around a nerve fiber
-formed by oligodendrocytes in CNS and Schwann cells in PNS |
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Myelination
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production of the myelin sheath
-begins 14th week of fetal development -proceeds rapidly during infancy -completed in late adolescence -dietary fat is important to nervous system development |
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Creating Myelin (in PNS)
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Schwann cells spiral repeatedly around a single nerve fiber
-no cytoplasm btwn the membranes -neurilemma-thick outermost coil of myelin sheath ~contains nucleus and most of its cytoplasm ~external to neurilemma is basal lamina and a thin layer of fibrous connective tissue (endoneurium) |
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Creating Myelin (in CNS)
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oligodendrocytes reach out to myelinate several nerve fibers in its immediate vicinity
-anchored to multiple nerve fibers -cannot migrate around any one of them like Schwann Cells -must push newer layers of myelin under the older ones -nerve fibers in the CNS have no neurilemma or endoneurium |
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Nodes of Ranvier
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gaps between segments
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Internodes
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myelin covered segments from one gap to the next
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Initial Segment
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short section of nerve fiber btwn the axon hillock and the first glial cell
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Trigger Zone
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the axon hillock and the initial segment
-plays an important role in initiating a nerve segment |
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Diseases of Myelin Sheath
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Multiple Sclerosis
Tay-Sachs Disease |
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Multiple Sclerosis
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-oligodendroctes and myelin sheaths in the CNS deteriorate
-myelin replaced by hardened scar tissue -nerve conduction disrupted (double vision, tremors, numbness, speech defects) -onset btwn 20-40 and fatal from 25-30 yrs after diagnosis |
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Tay-Sachs Disease
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a hereditary disorder of infants of Eastern European Jewish Ancestry
-abnormal accumulation of glycolipid called GM2 in the myelin sheath ~normally decomposed by lysosmal enzyme -blindness, loss of coordination, and dementia fatal before age 4 |
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Mesaxon
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neurilemma wrapping of unmyelinated nerve fibers
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Conduction Speed of Nerve Fibers
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speed at which nerve signal travels along a nerve fibers depends on two factors
-diameter of fiber -presence of absence of myelin |
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Conduction Speed
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small unmyelinated fibers- 0.5-2.0 m/sec
Small myelinated fibers- 3-15.0 m/sec Large myelinated fibers- up to 120 m/sec -slow signals supply the stomach and dilate pupil where speed is less of an issue -fast signals supply skeletal muscles and transport sensory signals for vision and balance |
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Regeneration of Peripheral nerves
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this can occur if its soma is intact and at least some of its neurilemma remains
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Regeneration Tube
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formed by Schwann cells, basal lamina, and the neurilemma near the injury
-regeneration tube guides the growing sprout back to the original target cells and reestablishes synaptic contact |
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Regeneration of damaged nerve fibers in the CNS
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CANNOT OCCUR AT ALL
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Nerve Growth Factor
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a protein secreted by a gland, muscle, and glial cells and picked up by the axon terminals of the neurons
-prevents apoptosis (programmed cell death) in growing neurons -enables growing neurons to make contact with their target cells |
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Electrophysiology
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cellular mechanisms for producing electrical potentials and currents
-basis for neural communication and muscle contraction |
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Electrical Potential
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a difference in the concentration of charged particles btwn one point and another
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Electrical Current
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a flow of charged particles from one point to another
-in the body, currents are movements of ions such as Na+ or K+ through gated channels in the plasma membrane |
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Resting Membrane Potential (RMP)
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charge difference across the plasma membrane
-70 mV in a resting, unstimulated neuron -negative value means there are more negatively charged particles on the inside of the membrane than on the outside exists because of unequal electrolyte distribution btwn extracellular fluid and intracellular fluid |
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Resting Membrane Potential results from the combined effect of three factors...
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-ions diffuse down their concentration gradient through the membrane
-plasma membrane is selectively permeable & allows some ions to pass easier than others -electrical attractions of cations and anions to each other |
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Creation of Resting Membrane Potential
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potassium ions have the greatest influence on RMP
-plasma membrane is more permeable to K+ than any other ion -leaks out until electrical charge of cytoplasmic anion attracts it back in and equilibrium is reached and net diffusion of K+ stops |
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Local Potentials
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disturbances in membrane potential when a neuron is stimulated
-neuron response begins at the dendrite, spreads through the soma, travels down the axon, and ends at the synaptic knobs When neuron is stimulated by chemicals, light, heat , or mechanical disturbance -opens Na+ gates and allows Na+ to rush in to the cell -Na+ inflow neutralizes some of the internal negative charge -voltage measured across the membrane drifts toward zero depolarization- case in which membrane voltage shifts to a less negative value |
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Characteristics of Local Potentials
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differences of local potentials from action potentials
-are graded- vary in magnitude with stimulus strength -are decremental- get weaker the farther they spread from the point of stimulation (voltage shift caused by Na+ inflow diminishes rapidly w/ distance) -are reversible- when stimulation ceases, K+ diffusion out of cell returns the cell to its normal resting potential |
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Action Potentials
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more dramatic change produced by voltage-regulated ion gates in the plasma membrane
-only occur where there is a high enough density of voltage-regulated gates -soma (50-75 gates) -cannot generate an action potential -Trigger Zone(300-500 gates)- where action potential is generated |
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Action Potential is a rapid up and down shift in the membrane voltage ...
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-sodium ions arrive at the axon hillock
-depolarize the membrane at that point -threshold- critical voltage to which local potentials must rise to open the voltage-regulated gates (55mV) |
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Refractory Period
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the period of resistance to stimulation
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Two Phases of Refractory Period
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Absolute Refractory Period-
-no stimulus of any strength will trigger AP -as long as Na+ gates are open -from action potential to RMP Relative Refractory Period- -only especially strong stimulus will trigger new AP |
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Neuromodulators
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hormones, neuropeptides, and other messengers that modify synaptic transmission
-may stimulate a neuron to install more receptors in the postsynaptic membrane adjusting its sensitivity to the neurotransmitter -may alter the rate of neurotransmitter synthesis, release, reuptake, or breakdown |
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Enkephalins
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a neuromodulator family
-small peptides that inhibit spinal interneurons from transmitting pain signals to the brain |
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Nitric Oxide (NO)
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simpler neuromodulator
-a lightweight gas release by the postsynaptic neurons in some areas of the brain concerned with learning & memory -diffuses into the presynaptic neuron -stimulates it to release more neurotransmitter -one neuron's way of telling the other to "give more back" -some chemcial communication that goes backward across the synapse |
