Lec. 14 Notes
Neurophysiology III
Introduction:
Sensory neurons provide our bodies with information from our surrounding environment.
Specialized sensory neurons include:
1. Nerve cells-photoreceptors of the eye/hair cells-olfactory cells of the nose.
2. Nerve endings –naked endings and respond to pain or encapsulated in pacinian corpuscle. 3. Epithelial cells-taste cells on the tongue> these are non-neuronal!!
Somatic Senses vs. -involve receptors in the skin, muscles, tendons, joints, and visceral organs.

Special Senses
-The five senses (details about these later).

1. Exteroceptive senses=changes on the body surface from light, pressure etc. 2. Proprioceptive senses = have to do with the body’s position as well as it’s movement
Ex. muscle length/tension, equilibrium etc.
3. Visceroceptive/interoceptive senses=changes in the body’s internal environment. Ex. Blood pressure
Types of Stimulus:
*Photoreceptors> light
*Chemoreceptors>chemicals Ex. Changes in pH, metabolite concentrations etc.
*Mechanoreceptors>respond when deformed by mechanical forces. Receptors for sound and balance in the ear also involved with these.
*Thermoreceptors> warmth/cold
*Nociceptors>pain receptors. Specifically, tissue damage provides stimulus.
Definitions:
 Transduction= the receptor in a cell converts some of the stimulus energy into an electrical signal that provides information for the nervous system.
 Threshold=minimal level of excitement required for a nerve receptor to be excited.
 General Potential=weak stimulus that initiates a depolarization below threshold.
 Frequency code=the frequency of action potentials increases as the stimuli intensity increases. Objectives I-III are all pretty well covered in the intro. , so the bulk of the notes are started with
Objective IV.

Objective IV: Threshold
In order to excite a receptor it has to have its specific, corresponding stimulus as well as intense/strong enough to activate a threshold response for that receptor. The electrical change in the receptor is typically caused by open sodium channels.
*When general potentials are increased past the threshold point, they trigger a multitude of action potentials. Action potentials increase as the stimulus level increases.
Refer to pg. 286 in the lecture notes to see a clear diagram.
Objective V: Stimulus Quality/Type
The brain interprets the type of stimulus it is receiving (touch, sound, light) based on the receptor’s reaction. Eyes determine if we see light, touch determines pressure etc. *This concept is known as the labelled line code.
Objective VI: Receptor Adaptation
After repeated stimulation receptors eventually adapt. In other words, the frequency of action potentials gradually decreases. Pacinian corpuscles are examples of receptors that are very adept at rapidly adapting.
Diagram on pg. 288 in the Lec. Notes
Objective VII: Rate of Nerve Impulse Conduction