Copyright ©Mark Nelson, 2002. All rights reserved.
Chapter 9: Properties of Sensory Systems
What you need to know

(exam questions will be a drawn from this subset of material)

What is the "law of specific nerve energies"?   (p. 210-211)
    The idea that each sensory nerve carries information about one particular subjective sensation.

Does the "law of specific nerve energies" arise because each sensory nerve only responsds to one type of stimulus energy?  (p. 211)
     No. Sensory nerves usually respond best to one particular form of stimulus energy, but other stimuli can also evoke a response.
    For example, "seeing stars" after being hit in the eye.

What does sensory nerve activity give rise to one particular subjective sensation?   (p. 211)
    The subjective sensation is related to the specific part of the brain that processes the sensory activity..
    Different sense organs send their messages to different parts of the brain, which determines how the message is interpretted.

What is synesthesia?  (p. 211)
     A neurological condition in which specific stimuli give rise to more than one type of subjective sensation
    (tasting shapes, seeing sounds, hearing colors, etc.)

What names are used to categorize sensory receptors based on the type of energy to which they are most sensitive?   (p. 212-213)
    chemo-, electro-, hygro-, magneto-, mechano-, noci-, photo-, thermo- RECEPTORS (See Table 9-1)

What's the difference between a sense organ and a sensory receptor?  (p. 212-213)
    A sense organ refers the the entire sensory apparatus (eye, ear, etc.),
    whereas a sensory receptor refers to an individual cell.
    A sense organ typically contains multiple sensory receptors as well as a variety of accessory structures.

What is sensory filtering?    (p. 213)
     the term used to describe the role of sense organs in limiting and shaping physical stimuli

What is sensory transduction?  (p. 213-214)
     the process by which an external physical stimulus is converted into a change in membrane potential of a sensory receptor

What is a receptor potential?   (p. 213-214)
    the change in membrane potential of a sensory receptor in response to a physical stimulus

Do sensory receptors generate action potentials ? (p. 213-214)
    some classes of receptor can generate APs (e.g. certain mechanoreceptors), whereas other do not (e.g. photoreceptors)

What is a generator potential?  (p. 214)
     it is sometimes used to refer to the receptor potential that arises in those classes of receptors that are capable of generating APs

What is sensory coding?   (p. 215-217)
    the mapping of attributes of a physical stimulus (intensity, duration, frequency, etc.) into neural activity

What is a common way that sensory receptors are thought to encode stimulus strength?  (p. 217)
     in the amplitude of the receptor potential (non-spiking receptors) or the frequency of action potentials (spiking receptors)

What is sensory adaptation?   (p. 218-220)
    the decline in response of a receptor over time to a constant stimulus

What do the terms tonic, phasic, and phasi-tonic refer to?  (p. 218-220)
    -tonic receptors show little or no adaptation to a constant stimulus; they encode information about stimulus level (e.g. position)
    -phasic receptors adapt rapidly to a constant stimulus; they encode information about changes in a stimulus (e.g. velocity, acceleration)
   - phasi-tonic receptors show characteristics of both phasic and tonic receptors.

Sketch a representative (receptor potential / generator potential / spike train) for a (phasic / tonic / phasi-tonic) receptor
in response to constant-amplitude step stimulus?   (p. 219)
    -see Fig. 9-9; note that 9-9A is labelled as "tonic" in the figure caption, but it is actually "phasi-tonic"

What is the receptive field of a sensory neuron?  (p. 221)
     the region(s) of the sensory receptor surface that, when stimuluated, cause a change in (membrane potential / spike activity) of that neuron

What is contrast enhancement?   (p. 222)
    an increased responsiveness of sensory neurons to changes in intensity across a receptor surface,

What is lateral inhibition?  (p. 223)
     a mechanism for contrast enhancement, based on inhibition of neighboring neurons in a sensory array

What is the relationship between sensory adaptation and lateral inhibition?   (p. XX)
   -sensory adaptation is a mechanism for enhancing the coding of changes in stimulus intensity across time
    -lateral inhibition is a mechanism for enhancing the coding of changes in stimulus intensity across

What is range fractionation?  (p. 226-227)
     the use of multiple receptor cells to cover a broad range of stimuli,
    in which each cell is sensitive to only a small fraction of the total range

What are the functional advantages of range fractionation?   (p. 227)
    it increases the resolution and sensitivity of the sense organ and in some cases reduces ambiguity;
    these benefits come at the cost of needing more sensory receptors to cover the range

What is topographic organization?  (p. 227-228)
     the point-to-point mapping of a sensory surface onto a particular region of the CNS;
     points maintain their neighbor relationships in a topographic mapping; but the distances may be distorted

What are the specific terms used for topographic organization in the (visual / auditory / somatosensory) systems?   (p. 228)
    retinotopic (visual), tonotopic (auditory), somatotopic (somatosensory)

What is columnar organization?  (p. 229-230)
    a pattern of  functional organization often found in association with topographic maps in the vertebrate cerebral cortex,
    in which columns of neurons perpendicular to the coritcal surface process information about the same stimulus attribute