Nervous system

Goals of this presentation

(1) To orient you to learning with the Interactive Physiology 8 system suite
(2) To teach nerve cell function with Interactive Physiology
and
(3) To overview this material with a survey lecture based on figures from your textbook

What you need

A prerequisite or corequisite for this lab (BIOL 347) is the lecture (BIOL 454, formerly 346), and the required text is Silverthorn, Human Physiology (Fourth edition), San Francisco, Pearson - Benjamin Cummings, 2007

You can use the CD that comes with your book. Also, using the access code (inside the front cover), follow the instructions to log into www.physiologyplace.com - get (and remember) a name and password. Then you can log onto http://www.interactivephysiology.com by entering your name and password. When you click start, you come to the menu of 9 systems. Pick a system. For home work, you are required to go through Nervous system I and II to prepare for a quiz next week. When you click on a button within a topic (orientation, anatomy review, etc.), you will begin slides with animations and interactive pedagogy. You can turn the narration on or off. When you are finished with each slice, you can click "next" or pull down the next slide on the list on top. Mostly everything works, but it was my experience, and the experience of previous students, that your browser occasionally quits unexpectedly.

A previous TA, Nishant Kumar, now in Medical School at SLU, prepared a worksheet with questions and answers that will take you through Nervous system I step-by-step (as well as worksheets for most of the other systems).

Interactive Physiology is intended to reinforce your learning on the subject matter by presenting you with animations and by interactions where you answer the questions.

Comments

The lectures we give are not intended to be thorough. Prof. Bode 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.

Lecture

Fig. 8-2 Model Neuron, dendrites, cell body, axon hillock, axon, myelin, presynaptic terminal, postsynaptic dendrite

typical neuron
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)
1963 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 close)

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" (leaping) conduction

Fig. 8-21 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. 8-21 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" to fire.

Fig. 8-27b But if there is enough inhibition, excitation will not generate a spike

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 agonist.
This receptor is a channel (for ions, giving the membrane electrical conductance [g])
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. I have added a lab which appears to be for respiration, but "Exercise 1: Gravity on peripheral circulation" is simply a peripheral circulation exercise. 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 equipment.

End point: We will check each computer station to see that each group has created a journal page.

Quiz and midterm questions from 2005 relating to this lecture, the electrophysiology lab and Interactive Physiology

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?

Axon hillock

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 channels?

Closed

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?

Nicotinic

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?

low pass

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 structure?

myelin, Schwann cell

This page was last updated 8/8/06

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