Physiology of the Nerve

8/6/2019 Physiology of the Nerve

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Physiology of the NervePhysiology of the NerveNerve Function



IntroductionIntroduction

y All neurons or nerve cells consist of a cell

body, an axon, and one or more

dendrites.

y A nerve impulse is a wave of chemical and

electrical change that moves along the

membrane of the nerve cell.

y When the nerve is stimulated, channels inthat area of the membrane open and

sodium ions (Na+) flow in to the cell.



Materials & MethodsMaterials & Methods

y Frog

y Dissecting set

y

Glass rody Stimulating apparatus

y Femur clamp

y

NaCl crystalsy 10% HCl solution

y Boiling water



Materials & MethodsMaterials & Methods

y Muscle-nerve preparation.

y Mechanical: pinched.

y Thermal: nerve was cut and the free end was

touched with a hot glass rod.y Osmotic: dead end of the nerve was cut and

NaCl were applied

y Chemical: the free end of the nerve was

dipped in HCl.

y Electrical: mild electrical shock using thestimulator.



Results & DiscussionResults & DiscussionStimulus Observations

Mechanical Leg twitches

ThermalPanting: breathing heavily

Eyes closed

Osmotic

Nerve shrunk

Leg is twitching frantically and after a while, straightened;

Eyes opened; After a while the nerve does not respond

anymore.

ChemicalBreathing heavily

Movement of muscle (contraction)

ElectricalUpon application of electric shock, leg elevates and lifted.

When shock is removed it goes back to its original position.



Results & DiscussionResults & Discussion

y The stimuli applied caused changes in the

resting potential of the nerve.

y Sensory transduction is the process by

which these stimuli were converted to

neural signals which caused either action

or graded potentials in neurons. When a

response is strong, sensory receptors caninitiate electrical responses to stimuli.




y Sensory receptors are responsible for the

recognition of stimulus and initiates a

signal transduction.

Mechanoreceptors

Thermoreceptors

Nociceptors

Chemoreceptors Photoreceptors




y Membrane potentials generated depends onthe extracellular and intracellular ionconcentration of the nerve cell.

y

For example, applying electrical current foran electrical stimulus causes the voltagegated Na+ and K+ pumps to open and close.

Resting potential

Depolarization

Threshold Potential

Action potential

Hyperpolarization



Post Lab QuestionsPost Lab Questions

1) Why must the nerve be kept moist?

y So the nerve stays flexible. Thus, it will

be easy to maneuver.

y If it is dry, it will become brittle and will

break easily.




2) Nerves transmit signals due to electricalpotentials. How can stimuli, other thanelectrical produce impulses in the nerve?

y Sensory receptors (touch, pain, temperature,smell, taste, sound, and sight) are activated byenvironmental stimuli.

y The stimulus produces a receptor potential;the magnitude of the receptor potential is

proportional to the stimulus.y The receptor potential produces a train of

action potentials.




3) Does the impulse decrease with time? If

so, why?

y Impulse does decrease with time.

y The myelin sheath with time degrades, so

charges are not insulated as much and

thus not conducted as fast as it was

before.

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Physiology of the Nerve