Download Physio Lab 5 PhysioEx 3

PhysioEx 2 and 3
You will need to compare and contrast skeletal and cardiac muscle this month.
PhysioEx2: Skeletal Muscle Physiology
Complete activities 1-7 and the worksheet questions that apply to these sections.
There are three types of muscle in the body: skeletal muscle, smooth muscle and cardiac muscle. The three
types share common characteristics as well as exhibit unique qualities. For instance, all three are excitable cells (which
means they can reverse their resting membrane potential), all three use calcium for muscle contraction (make sure you
understand this process), and all three utilize contractile proteins. They differ in the source of calcium (intracellular vs.
extra-cellular), the appearance of the contractile proteins (striated vs. non-striated), the number of nuclei present in
each fiber (a fiber is an individual muscle cell), the size of their fibers, the shape and orientation of the fibers (spindle,
rod, or branching), and whether the muscle is voluntary or involuntary.
PhysioEx 3 – Neurophysiology of Nerve Impulses
Complete all activities (1-8) and be sure to complete the worksheets in the back.
All cells have a resting membrane potential (RMP). Intracellular fluid is rich in negatively charged proteins that
are balanced mainly by positively charge potassium ions. As the cell membrane is permeable or “leaky” to potassium
but not to protein, the excess unbalanced negative charge leads to the voltage difference across the membrane. Thus
the RMP is a “diffusion potential” since it is due to the diffusion of potassium. There is also a small contribution to the
RMP by the electrogenic sodium-potassium ATPase pump (which transports 3 sodium ions out of the cell and two
potassium ions into the cell while using ATP). This difference in electrical charge across the plasma membrane is a
voltage difference- with the inside of the cell being more negative than the outside. The RMP of the body cells can
range from -40mV to -90mV.
Of the four tissue types in the body, epithelium, connective tissue, muscle and nervous, the latter two are
capable of altering their membrane potential. Muscle and nervous tissue have a RMP of -70 to -90 mV. Frogs/ squid
neurons have a RMP of -65mV. These tissues have the ability to decrease their voltage difference (that is, to become
more positive inside) and this is called depolarization. When a threshold stimulus arises, muscle and nerve cells can
reverse their membrane potential (this is called an action potential). An action potential (reversal of the cell’s
membrane potential) means the inside of the cell is now positive with respect to the outside of the cell. This is an all-ornone event that occurs at the trigger zone found at the axon hillock. The opening of both voltage operated (gated)
sodium and potassium channels is what marks the beginning of the action potential (although they open at different
speeds) and, at its peak, +40mV, the sodium channels close while voltage operated (gated) potassium channels
continue to remain open a bit longer. The efflux of potassium ions returns the membrane potential to resting, so that
the cell returns to being more negative inside. This is called “repolarization.” The higher than normal rate of potassium
efflux actually lasts a while, and this causes the membrane potential to “over-shoot” its RMP so that the cell is actually
hyperpolarized (-75mV).
In this exercise, you will be experimenting with a portion of a nerve. Your instructor should have explained how
ions are transported across a cell membrane and how action potentials are generated. Make sure you understand that
a nerve is a collection of axons outside of the nervous system. In other words, it is NOT an intact neuron. NO CELL
BODIES ARE PRESENT.
So, ask yourself, before you begin this exercise: if neuron cell bodies are not present, would I expect neurotransmitters to
have any effect on the nerve? Why or why not?
Would I expect drugs that block neurotransmitter receptors to have any effect on my experimental nerve? Why?
Exercise 3, activity 1
What happens when you get to the threshold? Na VGC open.
Were you playing with an intact neuron? No, it was a nerve, which is a collection of axons, disconnected from their cell
bodies.
If you bang your ulnar nerve, your pinky and ring finger will tingle. But if you take that segment out, it is just axons.
That’s a question on p2. Would a neurotransmitter work on a bunch of axons? No. Would you find Ligand Gated
Channels? No. if dealing with a drug that blocks , it won’t work. Curare does not work for that reason.
Activity 2 mechanical stimulation
If you bang your funny bone (ulnar nerve), the mechanical stimulation stimulates an action potential.
Thermal stimulation is when you made the glass warmer: did you get a larger curve? Yes, it produced a higher peak.
Axons fire all the time, don’t they? So how can you get an increase in size of action potential? If you just touch
superficial area of the nerve, it will only stimulate the neurons that are superficial within the nerve bundle. Heat will
stimulate more neurons in a nerve. If you stimulate all the axons, you would get a maximum curve. Thereafter, if you
increase stimulation, you will not get a higher peak. It is at its max.
Activity 4 chemical stimulation
In this activity, you apply ether. The first field medics were during the civil war. That produced a greater survival rate,
but to save them, they needed to amputate limbs in the field. They used ether for anesthesia. You can’t just hold a cloth
with ether over the face; it will suppress the respiratory system, and the person will stop breathing. One person has to
hold the cloth, then take it off when the patient falls asleep, and put it back on when they wake up. This is because ether
only temperately blocks VGCs. Within 6 minutes, the action potential returns.
Question (#6) is about curare, an anesthesia from tree sap. It is used by South American Indians on arrow tips to shoot
monkeys, which they then eat. Curare blocks nicotinic Ach receptors; monkey gets flaccid paralysis, falls down, and
can’t move but is still alive. People can eat the meat and not get poisoned. The receptors for curare are found on
neuronal cell bodies or skeletal muscles only. If enough curare gets to a skeletal muscle, the diaphragm will be so
relaxed, one cannot breathe.
Know what receptors are blocked by each substance, where the receptors are located, and whether it causes excitation,
or inhibition, and does it cause flaccid or spastic paralysis.
Activity 7
Lidocaine in is a sodium VGC blocker. When used in this experiment, it produced a flat line, stops the AP.
Activity 8
The bigger the nerve, the less the resistance, and myelinated nerves also have less resistance.
Look at Q17 in review sheet:
Answer: There would be no differences in conduction velocity because the experiment uses just an axon which can be
stimulated from either end to elicit an action potential.