• Author / Uploaded
• Nicole

Citation preview

PhysioEx Exercise 3: Neurophysiology of Nerve Impulses Bernabe, Keith Jeronn C., Buen, Nicole Blanche Q., Candel, Camille Keith D., Co, Tricia Mae M. University of Santo Tomas College of Science Biology Department

Activity 1: The Resting Membrane Potential Overview There are three important signals in the nervous systems namely receptor potential, synaptic potential and action potentials. The main focus of this activity is the resting potential. Resting membrane potential is the potential difference between the intracellular and the extracellular through the membrane. The resting membrane potential depends on the resting permeability of the membrane because it follows the steady-state condition.

Objectives: 1.

To define the term resting membrane potential.

2.

To measure the resting membrane potential in different parts of neuron.

3.

To determine how the resting membrane potential depends on the concentrations of potassium and sodium.

4.

To understand the ion conductances/ion channels involved in the resting membrane potential

Methodology: Neurons Contro -

-

High Na+ 5 mMK+ - 25 mMK+ - 130 mMNa+ 150 mMNa+ - Recorded

Micromanipulator Controller -

-

Position 1 (recorded) Position 2 (recorded) Position 3 (recorded)

Low K+ -

5 mMK+ 30 mMNa+ 120 mMTmA+ Recorded Micromanipulator Controller -

-

Position 3 (recorded) Position 1 (recorded) Position 1 (recorded) Control

Micromanipulator Controller -

-

Position 1 (recorded) Position 3 (recorded) Position 4 (recorded)

Results:

Control Control Control Control High K+ High K+ High K+ High K+ Low Na+ Low Na+ Low Na+ Low Na+

Cell body extracellular Cell body intracellular Axon extracellular Axon intracellular Axon intracellular Axon extracellular Cell body extracellular Cell body intracellular Cell body intracellular Cell body extracellular Axon extracellular Axon intracellular

Voltage (mV) 0 -70 0 -70 -40 0 0 -40 -72 0 0 -72

Discussion: Na+ and K+ are one of the most important ions in neurons. The proteins called Na+/K+ pump transports Na+ and K+ ions. It moves from higher concentration to lower concentration. Increase in extracellular K+ changes the membrane potential to be less negative due to the K+ ions leaving behind a net negative charge by diffusion thus, making the resting membrane potential less negative. The Na+ channels are closed that is why the extracellular Na+ has not changed the membrane potential in the resting neuron because of the less leakage of Na+ channels than K+ channels. Na+ has low membrane permeability due to the short Na+ leakage channels. It diffuses down its concentration gradient inward. The cause of inward leakage would greatly destroy the membrane potential. The Na+ goes into the cell membrane and the K+ goes outside the cell membrane thus making the cell membrane more negative on the inside rather than on the outside. The resting period potential is the distinction between intracellular and extracellular across the membrane. It depends on intracellular and extracellular concentrations and on which the membrane is permeable to.

Activity 2: Receptor Potential Overview When the sensory neuron are stimulated by the stimulus it can generate an impulse called receptor potential by the help of sensory receptor that can be located at the end of the sensory neuron that contains receptor proteins. The energy of the stimulus conducted can be converted into electrical response that

includes the cooperation of the membrane ion channels. The process involves in this conversion is called sensory transduction that happens also at the end of the sensory neuron. Depolarization occurs when there is change from negative resting potential to a lesser negative level causing the membrane to be less polarized. Objectives 1.

To define the terms sensory receptor, receptor potential, sensory transduction, stimulus modality, and depolarization.

2.

To determine the adequate stimulus for different sensory receptors.

3.

To demonstrate the receptor potential amplitude increases with stimulus intensity.

Methodology:

Sensory Sensory Receptor Receptor

Modality Modality

Intensity Intensity

Amplitude Amplitude Response Response

Results:

Resting Potential Peak Value of Response Amplitude of Receptor

Pacinian corpuscle

Modality

---

Intensity

---

(mv)

(mv)

Response (mv)

-70

-70

0

Pacinian corpuscle

Pressure

Low

-70

-60

10

Pacinian corpuscle

Pressure

Moderate

-70

-45

25

Pacinian corpuscle

Pressure

High

-70

-30

40

Pacinian corpuscle

Chemical

Low

-70

-70

0

Pacinian corpuscle

Chemical

Moderate

-70

-70

0

Pacinian corpuscle

Chemical

High

-70

-70

0

Pacinian corpuscle

Heat

Low

-70

-70

0

Pacinian corpuscle

Heat

Moderate

-70

-70

0

Pacinian corpuscle

Heat

High

-70

-70

0

Pacinian corpuscle

Light

Low

-70

-70

0

Pacinian corpuscle

Light

Moderate

-70

-70

0

Pacinian corpuscle

Light

High

-70

-70

0

Olfactory receptor

---

---

-70

-70

0

Olfactory receptor

Pressure

Low

-70

-70

0

Olfactory receptor

Pressure

Moderate

-70

-70

0

Olfactory receptor

Pressure

High

-70

-70

0

Olfactory receptor

Chemical

Low

-70

-64

6

Olfactory receptor

Chemical

Moderate

-70

-58

12

Olfactory receptor

Chemical

High

-70

-45

25

Olfactory receptor

Heat

Low

-70

-70

0

Olfactory receptor

Heat

Moderate

-70

-70

0

Olfactory receptor

Heat

High

-70

-70

0

Olfactory receptor

Light

Low

-70

-70

0

Receptor

Modality

Intensity

Resting Potential Peak Value of (mv) Response (mv)

Amplitude of Response (mv)

Olfactory receptor

Light

Moderate

-70

-70

0

Olfactory receptor

Light

High

-70

-70

0

Free nerve ending

---

---

-70

-70

0

Free nerve ending

Pressure

Low

-70

-70

0

Free nerve ending

Pressure

Moderate

-70

-70

0

Free nerve ending

Pressure

High

-70

-65

5

Free nerve ending

Chemical

Low

-70

-70

0

Free nerve ending

Chemical

Moderate

-70

-70

0

Free nerve ending

Chemical

High

-70

-70

0

Free nerve ending

Heat

Low

-70

-60

10

Free nerve ending

Heat

Moderate

-70

-40

30

Free nerve ending

Heat

High

-70

-20

50

Free nerve ending

Light

Low

-70

-70

0

Free nerve ending

Light

Moderate

-70

-70

0

Free nerve ending

Light

High

-70

-70

0

Discussion: The sensory neurons used are Pacinian corpuscle, olfactory receptor and free nerve ending. These sensory neurons were stimulated to several stimulus modalities and paired with intensity. The modality, which consists of pressure, chemical, heat and light. The intensity of the stimulus were low, moderate and high. The sensory neurons were subject to different modality and intensity. As for the Pacinian corpuscle obtain the highest peak of value that is -30 and an amplitude response of 40 in pressure at intensity of high. In the olfactory receptor obtain its highest peak of value that is -45 and an amplitude response of -20 in chemical at intensity of high. The free nerve endings responded to different modalities as shown in the results due to the less specialized sensory end. All the sensory neuron is set to have the resting potential of -70.

Activity 3: The Action Potential: Threshold Overview: Nerve are consists of axons. The action potential conducts signal from axons, axons are thought to be long and thin. Axon hillock is the point where the cell body and the axon are connected. The junction between initial segment and axon hillock is where the action potential is first initiated it is also called the trigger zone. When the action potential is triggered it will then be conducted down to the axon. The stronger the action potential initiated the longer it will travel through the cell body to the axon.

Objectives 1.

To define the terms action potential, nerve, axon hillock, trigger zone, and threshold.

2.

To predict how an increase in extracellular K+ could trigger an action potential.

Methodology:

Neuron Neuron

stimulus of 10 10 stimulus of volts volts

stimulus stimulus of of 20 20 volts volts

stimulus 30 stimulus of of 30 volts volts

stimulus stimulus of of 40 40 volts volts

stimulus 50 stimulus of of 50 volts volts

Action Potential Action Potential

Results: Stimulus Voltage (mV) 10 20 30 40 50

Peak Value at R1 (μV) 0 100 100 100 100

Peak Value at R2 (μV) 0 100 100 100 100

Action Potential No Yes Yes Yes Yes

Discussion: Distinct membrane proteins provide basis for the threshold differences are found on each region of the neuron. The influx of sodium regenerates the action potential, which establishes local currents that depolarize difference adjacent sections of the membrane threshold. Adjacent sections of the membrane are where the action potential must be regenerated. The action potential is not graded rather it is an all-or-none. Therefore, the peak value of the action potential does not change.