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Topic: Axon hillock

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	Action Potentials (Site not responding. Last check: 2007-11-05)
		As one area of axon is being depolarized and letting in sodium rapidly (because it has just reached threshold) the preceding area of membrane is still in the depolarizing phase of its action potential, thus that area of membrane may not be immediately stimulated to produce another action potential anyway.
		Axons that serve internal organs are generally slower, but such a reduction in speed is hardly a handicap for such systems.
		As the axon increases in diameter (and thus cross sectional area) the resistance to ion flow decreases, allowing the ions (and consequently the current) to flow faster.
	www.alsa-or.org /research/actionpot.htm (2140 words)

	Axon hillock - Wikipedia, the free encyclopedia
		The axon hillock is the anotomical part of a neuron that connects the cell body to the axon.
		It is attributed as the place where EPSPs from numerous synaptic inputs on the dendrites or cell body accumulate.
		If the accumulated potential reaches the threashold, an action potential propagates through the rest of the axon (or "backwards" towards the dendrites as seen in backpropagation).
	en.wikipedia.org /wiki/Axon_hillock (89 words)

	Axon (from nervous system) -- Encyclopædia Britannica
		The axon arises from the soma at a region called the axon hillock, or initial segment.
		Large axons acquire an insulating myelin sheath and are known as myelinated, or medullated, fibres.
		The axon of a motor neuron may be quite long, reaching, for example, from the spinal cord down to a toe.
	www.britannica.com /eb/article?tocId=75823 (950 words)

	Redistribution of Syntaxin mRNA in Neuronal Cell Bodies Regulates Protein Expression and Transport during Synapse ...
		by 5-HT; syntaxin mRNA was retargeted to the axon hillock of the
		to accumulate at the axon hillock as the synapse matures.
		The exclusion of syntaxin mRNA from the axon hillock of SNs with stable synapses is reversed in a protein synthesis-dependent
	www.jneurosci.org /cgi/content/full/23/5/1804 (8731 words)

	ION 526 COURSE » CHAPTER 1 » SECTION 1.1 Biological Neuron
		The speed of propagation down the axon depends on the thickness of the myelin sheath that provides for the insulation of the axon from the extracellular fluid and prevents the transmission of ions across the membrane.
		Since the axons themselves are poor conductors, the action potential is transmitted as depolarizations occur at the nodes of Ranvier.
		The nerve pulses passing along the axon of a particular neuron are of approximately constant amplitude but the number generated pulses and their time spacing is controlled by the statistics associated with the arrival at the neuron's many synaptic junctions of sufficient excitatory inputs [Müller and Reinhardt 90].
	www.ii.metu.edu.tr /~ion526/demo/chapter1/section1.1 (1381 words)

	Case History (Site not responding. Last check: 2007-11-05)
		Axon - The axon is just one of the many processes in a multipolar cell.
		Myelinated axons can be identified by the osmium positive (electron dense or fl) staining of their myelin sheath.
		These are approximately 24 nm diameter and can be identified in the myelinated axons coursing longitudinally through the center of EM print C and in the dendrite in EM print B. The walls of microtubules are composed of the globular protein tubulin.
	cats.med.uvm.edu /cats_teachingmod/neurobiology/histology_lab/neuronal_processes/history.html (909 words)

	Axonal Action-Potential Initiation and Na+ Channel Densities in the Soma and Axon Initial Segment of Subicular ...
		Thus, the results suggested that action potentials initiate in the axon at some distance from the soma and that the local density of Na channels in the axon hillock/initial segment, which is not high, does not determine the lowest threshold of the neuron for action-potential initiation.
		Axons beyond the initial segment in sections processed with detergent, on the other hand, were more darkly stained and could often be followed to the alveus.
		Although this method is not unequivocal because of limitations on identifying axons, possible variations in thickness of the myelin, et cetera, the results suggest that the axons of the subicular pyramidal neurons are myelinated beyond an initial segment of ~20 µm.
	www.jneurosci.org /cgi/content/full/16/21/6676 (9442 words)

	Expert About hi:Hillock
		Hillock wants to change those feeling, he knows that the patient that has a good experience will return for his continued care appointments, which make for healthy teeth and gums.
		Hillock has given numerous presentations on Dean Witter's successful recovery from the 1993 World Trade Center bombing and Morgan Stanley's response to the 9/11 WTC terrorist attack.
		diam(1) diam(0:1) = daxon:dsoma // linear taper of //diameter of hillock between that of soma and axon } // myelininated and nodal sections are handled in pairs for i=0, nmyelin-1 { myelin i.
	expertsite.biz /dir/hi/hillock.htm (999 words)

	ANATOMY & PHYSIOLOGY I
		Theinitial segment of the axon is adjacent to the axon hillock.
		Depolarization of the axon hillock to threshold produces a conducted change, or action potential, in the membrane.
		Axons may be categorized as Type A, B, or C on the basis of diameter, myelin content, and conduction velocity.
	rmoskowitz.tripod.com /neural.html (1491 words)

	Structure of the Neuron - Axon Hillock (Site not responding. Last check: 2007-11-05)
		Larger neurons have a markedly expanded region at the initial end of the axon.
		This axon hillock is the site of summation for incoming information.
		At any given moment, the collective influence of all neurons that conduct impulses to a given neuron will determine whether or not an action potential will be initiated at the axon hillock and propagated along the axon.
	psych.athabascau.ca /html/Psych289/Biotutorials/1/hillock.shtml (62 words)

	ANSWER 2 (Site not responding. Last check: 2007-11-05)
		That is, a stimulus applied at one point may not be adequate to produce an action potential, but the same stimulus applied further along the axon hillock may be large enough to generate an action potential.
		Therefore, as the graded potential spreads along the length of the axon hillock, (and is decreasing in size), it may actually reach a more sensitive part of the axon where the graded potential provides a stimulus that is large enough to produce an action potential.
		The area of the axon hillock that activates an action potential may have been partially depolarised from previous stimuli or it may be in its refractive period where the membrane has not yet repolarised fully, therefore requiring a smaller stimulus (ie.
	www.life.sci.qut.edu.au /trezise/SAQ2.htm (171 words)

	THE ACTION POTENTIAL PAGE
		is reached, there is a sudden opening of all of the voltage-gated Na channels in the region of ap generation (the axon hillock), increasing the permeability of the membrane for Na This causes a rapid rise in the tmp in the direction of the equilibrium potential for Na (ie.
		This electrically excitable region of the axon is referred to as the axon hillock.
		In a sensory neuron, the axon hillock is the point where the dendrites attach to the axons.
	faculty.etsu.edu /currie/action.htm (1148 words)

	[No title]
		If the membrane depolarization is great enough, the signal will be transmitted down the axon proper (between axon hillock and axon terminal) to the axon terminal (sends information to effector cells via neurotransmitter release).
		It is important to note that because protein synthesis does not happen in the axon, these must be made in the cell body and then must be transported down the axon to the terminal.
		Because there are no ribosomes in the axon terminal, synaptic vesicles originate in the cell body where their proteins are sorted into the trans-Golgi network and then they are shuttled down the axon by an axonal transport mechanism.
	www-personal.umich.edu /~spark/notes/M1/mcb501/20020206-mcb.doc (4416 words)

	THE NERVE IMPULSE AND SYNAPTIC TRANSMISSION
		The axon attaches to the cell body at a wide place called the axon hillock.
		The cell membrane in the axon hillock and the axon have a very special membrane mechanism called voltage dependent ion channels.
		When the voltage dependent channels in the axon hillock open up and allow sodium ions in, a chain reaction is started.
	people.eku.edu /falkenbergs/psy311/synaessa.htm (561 words)

	Excitation of Central Nervous System Neurons by Nonuniform Electric Fields -- McIntyre and Grill 76 (2): 878 -- ...
		The model consisted of a myelinated axon with 20 nodes separated by 20 myelin internodes with an internodal spacing of 1000 µm.
		The electrode was positioned radially from the central axis of the neuron, and the threshold needed to generate a propagating action potential was calculated (±1%) at 50-µm intervals along the longitudinal axis of the neural structure.
		Axons, but not cell bodies, are activated by electrical stimulation in cortical gray matter.
	www.biophysj.org /cgi/content/full/76/2/878 (6258 words)

	HyperBook X5000 (Site not responding. Last check: 2007-11-05)
		Note that the place where the axon leaves the soma is called the axon hillock.
		When Professor Mindstein refers to activity in the nerve cells, what he usually means is the nerve impulse, or action potential, which typically begins at the axon hillock.
		You will also note that the axon of the neuron has a covering on it that may remind you of a series of hot dog buns around a long wiener.
	epsych.msstate.edu /biological/eye/neuron/neuron5.html (213 words)

	Modeling Action Potential Initiation and Back-Propagation in Dendrites of Cultured Rat Motoneurons -- Lüscher and ...
		by the unfavorable geometry at the transition from the axon to
		Full-size action potential recorded in the axon is shown becoming progressively smaller at the initial segment (thick stippled line), at the soma (thin solid line), and at the dendritic locations D1 and D2 (thick solid line and thin stippled line, respectively).
		High Na -channel density at initial segment and axon hillock ensures success of the retrograde axonal action potential to invade the soma.
	jn.physiology.org /cgi/content/full/80/2/715 (7687 words)

	quiz2.99a (Site not responding. Last check: 2007-11-05)
		Depolarization of the cell dendrites and body leading to a passive current flow that depolarizes the axon hillock area.
		A significant change (that is, about 10%) of the total positive ions inside the nerve cell near (that is within 1 mm) of the axon hillock.
		meters) the lipid bilayer membrane of the axon hillock.
	socrates.berkeley.edu /~alanburr/physiol/examquiz/quiz2.htm (426 words)

	Neuroscience at a Glance
		It is initiated at the initial segment of the axon hillock of the neuron and is propagated down the axon to the presynaptic terminals.
		Axon is the neuronal process that originates at the axon hillock and conducts information away from the neuronal cell body to the nerve terminal and synapses.
		Axon hillock is the site at which the axon originates from the neuronal cell body, and is in continuity with the initial segment of the axon.
	www.medicalneuroscience.com /ngloss.htm (6828 words)

	Computational Analysis of Action Potential Initiation in Mitral Cell Soma and Dendrites Based on Dual Patch Recordings ...
		from the soma, and the axon emerging from the soma and axon hillock.
		Axon consisted of nodes and myelinated segments, plus the portion (x to 1) of the initial segment with high sodium channel density.
		Conradi, S. Observations on the ultrastructure of the axon hillock and initial axon segment of lumbosacral motoneurons in the cat.
	jn.physiology.org /cgi/content/full/82/6/3006 (9341 words)

	Week 3
		If incoming messages (information) received are sufficient in magnitude, the dendrites and cell bodies communicate the messages received to the axon hillock, which in turn activates the axon.
		Axons are specialized projection fibers designed to allow neurons to transmit electrical signals (action potentials, or ap's) to distant synaptic terminals and effector organs (target organs).
		If the axon hillock receives enough stimulatory information from the dendritic region, the axon hillock may reach a special value of membrane potential known as "the threshold membrane potential." If the axon hillock reaches threshold, it will trigger a full-blown action potential.
	faculty.etsu.edu /currie/week4new.htm (1069 words)

	CellTissueBody6explore (Site not responding. Last check: 2007-11-05)
		axon serves as a cable transmitting the nerve impulses.
		Axon hillock is the place og origin of the actively transmitted nerve impulses
		Nerve impulses arise on the special part of the cell - axon hillock and are actively transmitted on the axon even more than a meter far away.
	www.bioanim.com /celltissuehumanbody6/Htmlwd/neuReflLok3wd.html (189 words)

	Coincidence Detection Guide (Site not responding. Last check: 2007-11-05)
		As in the previous two conductances, we extend the somatic conductance to the Dendrites, the Axon Hillock and the Node, supposing uniformity.
		From [Petersetal] and [Carr&Boudreau], the length of the Axon Hillock is estimated to be 30 um.
		The exception is made for the Axon Myelinated, which has a lower capacitance so as to increase the velocity of propagation of action potentials through the fiber.
	www.glue.umd.edu /~vgrau/CD/guide.html (3136 words)

	Development of a Silicone Retinal Implant: Epiretinal Stimulation of Retinal Ganglion Cells in the Rabbit
		To determine axon thresholds the recording electrode was lowered to the retina at various points along a line perpendicular to the line connecting the receptive field center and the recording electrode, 1.5 mm to 2 mm from the cell body (Figures 2-3).
		Cathodal stimulation near the axon hillock may produce electric fields penetrating the cell body as shown in red at the left.
		But cathodal stimulation far from the axon hillock could create fields entering the cell at the hillock as shown in the center figure, leading to hyperpolarization there and elevated thresholds for cell bodies.
	www.ai.mit.edu /projects/implant/poster2.html (1983 words)

	Saltatory Conduction of APs (Site not responding. Last check: 2007-11-05)
		Since an axon can be unmyelinated or myelinated, the action potential has two methods to travel down the axon.
		Basically, after the action potential is initiated at the axon hillock (and you still don't know exactly why), the electrical activity of the first action potential spreads (the positiveness of the AP spreads) and that triggers the nearby voltage-gated channels.
		Every little bit of axon has to be involved in the AP, since every little bit of the axon is affected by the current spread.
	distance.stcc.edu /AandP/AP/AP1pages/nervssys/unit11/saltator.htm (587 words)

	When a localised graded potential reaches threshold levels of excitation/stimulation, the axon hillock converts the ... (Site not responding. Last check: 2007-11-05)
		When a localised graded potential reaches threshold levels of excitation/stimulation, the axon hillock converts the graded potential to an action potential which travels down the axon.
		The axon and the axon are able to generate an action potential.
		The temporal or spatial summation of the graded potentials stimulates the axon hillock by chemical change.
	www.life.sci.qut.edu.au /trezise/SAQ1.htm (142 words)

	Search Results for axon - Encyclopædia Britannica
		This is the region where the plasma membrane generates nerve impulses; the axon conducts these impulses away...
		Besides the axon, neurons have other branches called dendrites that are usually shorter than axons and are unmyelinated.
		Once an action potential has been generated at the axon hillock, it is conducted along the length of the axon until it reaches the terminals, the fingerlike extensions of the neuron that are next to...
	www.britannica.com /search?query=axon&submit=Find&source=MWTEXT (489 words)

	Biology 250 Experimental Human Physiology Laboratory Fall Semester 1998
		The Strength-Duration Curve: Certain combinations of stimulus strength and duration of stimulation evoke no response in the axon; such combinations are said to be subthreshold.
		The initial segment of the axon, the axon hillock, has properties somewhat different than the distal axon.
		Ordinarily, both axon hillock and distal axon respond only to electrical stimuli.
	www.public.coe.edu /~kredborg/physlabs2000/00LAB3.htm (927 words)

	[No title]
		Next, a theoretical silicon axon and the axon that was designed for this project will be discussed.
		A signal is initiated by the hillock when the sum of action potentials received by the cell reach a threshold value.
		So we see that the axon- hillock is like an integrator with a comparator, firing when the summed input exceeds a predetermined value.
	www.ent.ohiou.edu /~southard/ee715final.html (1886 words)

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