Physiology of the Nerve

Physiology Ph ysiology of the Nerv Ner ve Nerve Function

Introduction y

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All neurons or nerve cells consist of a cell body, an axon, and one or more dendrites. A nerve impulse is a wave of chemical and electrical change that moves along the membrane of the nerve cell. When the nerve is stimulated, channels in that area of the membrane open and sodium ions (Na+) flow in to the cell.

Materials y

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Methods

Frog Dissecting set Glass rod Stimulating apparatus Femur clamp NaCl crystals 10% HCl solution Boiling water

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Muscle-nerve

Methods

preparation. Mechanical: pinched. Thermal: nerve was cut and the free end was touched with a hot glass rod. Osmotic: dead end of the nerve was cut and NaCl were applied Chemical: the free end of the nerve was dipped in HCl. Electrical: mild electrical shock using the stimulator.

Results

& Discussion

Stimulus Mechanical

Thermal

Observations Leg twitches Panting: breathing heavily Eyes closed Nerve shrunk 

Osmotic

Leg is twitching frantically and after a while, straightened; Eyes opened; After a while the nerve does not respond anymore.

Chemical

Electrical

Breathing heavily Movement of

muscle (contraction)

Upon application of electric shock, leg elevates and lifted. When shock is removed it goes back to its original position.

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& Discussion

The stimuli applied caused changes in the resting potential of the nerve. 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 can initiate electrical responses to stimuli.

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Sensory receptors are responsible for the recognition of stimulus and initiates a signal transduction. 

Mechanoreceptors

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Thermoreceptors

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Nociceptors

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Chemoreceptors

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Photoreceptors

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& Discussion

Membrane

potentials generated depends on the extracellular and intracellular ion concentration of the nerve cell. For example, applying electrical current for an electrical stimulus causes the voltage gated Na+ and K+ pumps to open and close. 

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Resting

potential Depolarization Threshold Potential Action potential Hyperpolarization

Post Lab Questions 1) Why must the nerve be kept moist? So the nerve stays flexible. Thus, it will be easy to maneuver. If it is dry, it will become brittle and will break easily. y

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Post Lab Questions 2) Nerves transmit signals due to electrical potentials. How can stimuli, other than electrical produce impulses in the nerve? Sensory receptors (touch, pain, temperature, smell, taste, sound, and sight) are activated by environmental stimuli. The stimulus produces a receptor potential; the magnitude of the receptor potential is proportional to the stimulus. The receptor potential produces a train of  action potentials. y

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Post Lab Questions 3) Does the impulse decrease with time? If  so, why? y

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Impulse

does decrease with time. The myelin sheath with time degrades, so charges are not insulated as much and thus not conducted as fast as it was before.