What you need
A prerequisite or corequisite for this lab (BIOL 347) is the lecture (BIOL
454, or equivalent), and the required text is Silverthorn, Human Physiology
(Fourth edition), San Francisco, Pearson - Benjamin Cummings, 2007
The lectures we give are not intended to be thorough. Prof. Russell will
cover these topics in Human Cellular Physiology I. Rather, this lecture
is to orient you to the neurophysiology you will be seeing in Interactive
Physiology. Also, I will use figures from your text.
Fig. 8-2 Model Neuron, dendrites, cell body, axon hillock, axon, myelin,
presynaptic terminal, postsynaptic dendrite
Connections, from other neurons, created graded electrical potentials at
synapses, on dendrites and cell bodies.
Cell body integrates the synaptic excitatory and inhibitory voltages.
If there is net excitation, axon propagates the all-or-none, non -decemental
action potential quickly over long distances.
Fig. 8-6b&c Myelin, multiple wrappings of membrane from Schwann cell
(1 to 1.5 mm), nodes of Ranvier (1-2 microns)
Membrane is wrapped around and cytoplasm is squeezed out, leaving only alternating
bands of electron density and lucency at high magnification.
Each layer of membrane has high resistance, and resistors in series block
current flow through membrane.
Each layer of membrae has high capacitance which would leak current, but
capacitors in series add reciprocally, decreasing capacitance and leakage.
Fig. 8.7 A graded potential (here shown through a Na+ channel in a postsynaptic
membrane) will get smaller with distance (spreads decrimentally)
Introduction. "Action" potential refers to the active voltage-gating
that opens the Na+ channel that allows nondecremental propagation. If that
did not happen, propagation would be decremental based on the passive spread
of current going down the axon and also leaking out the membrane.
Fig. 8-8a&b So a nice sized synaptic potential would not reach threshold
for the action potential at the axon hillock
Fig. 8-9 An action potential (voltage as a function of time) is mediated
by an increase then a decrease in Na+ permeability (early) and an increase
then decrease in K+ permeability late
1950's Sir Alan L. Hodgkin & Sir Andrew F. Huxley (Great Britain)
Nobel Prize in Physiology and medicine for "ionic mechanisms...excitation
inhibition...nerve cell membrane"
In general, They showed what was stated above:
For action potential, Na+ channels open then close, K+ channels open (then
Fig. 8-10 The Na+ channel activates then inactivates
Fig. 8-12 Refractory period. Another spike cannot be triggered during a
spile, and it is hard to trigger after a spike
Fig. 8-15c A spike depolarizes the axon to threshold ahead of it but cannot
behind it because of the refractory period.
Fig. 8-16 Since it is not decrimental, a spike is the same size (but slightly
later) as you go along the axon.
Fig. 8-17 Spikes are fast in giant axons of invertebrates and in myelinated
axons of vertebrates (because of saltatory conduction)
Myelinated axons have faster propagation.
Invertebrates do not have myelin, and that is why they have giant axons.
Here's why: action potential jumps from one node of Ranvier to next, "saltatory"
Fig. 8-19 Synaptic vesicles relaease neurotransmitters to receptors
Vesicles are interesting.
Transmitter is very concentrated, there are pumps to move transmitter "up
hill" (against gradient) into vesicle.
Sometimes part of transmitter synthesis is in vesicle.
Ca2+ in through voltage gated Ca2+ channel
Note that figure shows that Ca2+ activates calmodulin which activates protein
kinase and that "kinase phosphorylates synapsin proteins"
There are vesicle membrane proteins, target (presynaptic) membrane proteins,
and cytoplasmic proteins
Fig. 8-201 Voltage gated Ca2+ channels are necessary, and release is complicated
(here is shown one process, docking protein).
Fig. 8-23 Receptors are channels or G-protein coupled receptors
Fig. 8-27a If there is enough synaptic excitation, a spike will fire
Sir John C. Eccles 1963 Nobel
(with Hodgkin & Huxley) EPSP & IPSP
Postsynaptic potentials (Eccles, using spinal motor neurons)
EPSP - depolarize
increase sodium and potassium conductance
IPSP - hyperpolarize
increase potassium and chloride conductance
Excitatory and Inhibitory integrate before axon hillock "decides"
Fig. 8-27b But if there is enough inhibition, excitation will not generate
Fig. 11-4 There are 2 synapses in the autonomic nervous system, one in the
ganglion and one in the target (gland or smooth muscle)
Fig. 11-7 Nicotinic acetylcholine receptors (channels) are used in ganglia.
At the target, adrenergic receptors are used in the sympathetic system while
acetylcholine at muscarinic receptors is used in the parasympathetic system
Nicotinic Acetylcholine receptor [More on this later])
Acetylcholine is a ligand (neurotransmitter), nicotine is a pharmnacological
This receptor is a channel (for ions, giving the membrane electrical conductance
Channel is ligand gated.
Sodium (Na+) and potassium (K+) shown going through pore in membrane that
can be open or closed.
Sodium, higher outside the cell, is likely to go in.
Potassium, high inside the cell is likely to go out.
There is another kind of receptor, the G-protein-coupled receptor
For cholinergic transmission, the muscarinic receptor is an example
Fig. 11-11 This figure relates the autonomic nervous system to the somatic
motor system and to the hormonal system of adrenalin from the adrenal medulla.
Orientation for today's lab and demonstrations
Much of this laboratory will involve demonstrations, Excel, Web of Science,
EndNote, PhotoShop, etc. Also traditional (historical) physiology equipment
will be demonstrated to give you a greater appreciation for the shortcomings
that have veen overcome with newer equipment.
Students will work in groups on an exercise to become acquainted with the
use of modern computer with interface for physiology. The tutorial utilizes
the plethysmograph. This is perhaps the simplest devise to use and is most
commonly used to measure the pulse in the fingers. The plethysmograph has
many other creative uses in other labs.
The iWorx units are newly purchased and replace older PowerLab units that
fed into system 9 Macs via a SCSI cable. These iWorx interfaces come with
software and manuals and are much friendlier. However, all the future labs
will be difficult without first becoming acquainted with the use of this
Exam questions from the last few years related to this lab
What component of the Schwann cell actually insulates the myelinated axon?
Tightly wound cell membrane after the cytoplasm has been squeezed out
In what part of the neuron is the action potential generated?
What are the gaps between regions of myelination called?
Nodes of Ranvier
During the resting potential, what is the status of the voltage-gated sodium
When acetylcholine binds the nicotinic channel, which ions will move, and
in which direction will they move?
Sodium moves into the cell, and potassium moves out
Which direction does the sodium-potassium pump move potassium?
into the cell
What transmitter receptor is used in the ganglion of both sympathetic and
parasympathetic nervous systems?
An action potential depolarizes the membrane ahead of it to threshold, and
hence the action potential propagates. Why doesn't the action potential
cause an action potential to propagate behind it?
refractory period (sodium channel inactivation
Because of the high resistance and capacitance of a glass micropipette,
fast signals like action potentials can be missed or greatly distorted.
In other words, the micropipette acts like what kind of filter?
What does it mean to say that ion channels are "selective?"
for size, charge, etc
After the action potential arrives at the presynaptic membrane, what does
the voltage gated calcium channel in this membrane do?
calcium influx involved in vesicle release
Multiple layers of tightly wound membrane are a hallmark of what neural
myelin, Schwann cell
Ca+2 channels at the axon terminal open via which signal?
Which ion is most responsible for the resting potential of neurons?
This phenomena ensures the unidirectionality of action potentials.
Giant squid axons are larger due to the lack of _____________?
Will an IPSP usually fire an action potential?
All adrenergic receptors use which type of signaling pathway?
On a standard Cartesian coordinate graph, which axis is the independent
In making fine tipped microelectrodes, a very small capillary tube in heated
and pulled apart. What inside of the pulling apparatus is doing the pulling?
If fast noise is interfering with recordings on the physiograph, which type
of filter would you
High cut off (low pass) filter
Both the sympathetic and parasympathetic system use which receptor and neurotransmitter
at the first synapse?
Nicotinic receptor and Acetylcholine
Graded potentials decrease in size with increasing ______________.
The jump of action potentials from node to node is referred to as what?
The inside of the cell is __________ in respect to outside of the cell.
For most intents and purposes, Ramon y Cajal won out over Golgi, on the
basis of staining techniques concerning what issue?
whether cells were separate (and hence needed (what turned out to be synaptic)
Myelin is wrapped around the axon many times to prevent current leakage.
What happens to resistance due to these multiple wrappings?
When multiple layers of myelin are added in series, what happens to capacitance?
Sodium channels in the axon have activation and inactivation gates. Give
the activation and inactivation status when the neuron is at its resting
it is closed but not inactivated and, of course, it is not activated
Through axon membrane channels, which ion goes into the cell and which ion
leaves the cell?
Na+ enters, K+ leaves
Which ion(s) can pass through a cholinergic nicotinic receptor?
What causes Ca2+ channels to open in the axon terminal?
Do action potentials decrease in size as they move down the axon?
If graded potentials are summed and are above threshold at the axon hillock,
what will be generated?
an action potential
What type of gradient causes Na+ to rush into the cell when an action potential
chemical (electrochemical) gradient
What two gradients are responsible for the membrane's resting potential?
concentration and electrical
What type of system is the autonomic division of the nervous system?
Adrenergic receptors bind what hormone and what neurotransmitter?
epinephrine and norepinephrine
This page was last updated 1/23/08
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