BBB Revision exercise, Book 3, Chapters 1-3 - Answers
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1. Transduction is the conversion of energy of sensory stimulus into
electrical change (receptor potential, graded), which can give rise to
action potentials (all-or-none). Thus, information about the stimulus is
transmitted to the nervous system. (Section 1.2.1)
2. In three types of sensory receptors, the receptor potential arises
because of the following (Section 1.2.2):-
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Mechanoreceptors - touch, hearing; mechanical deformation of cell membrane;
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Electromagnetic receptors - vision; absorption of light by photosensitive
molecules in cell membrane;
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Chemoreceptors - smell, taste; absorption of chemical by receptor molecules
on cell membrane of receptor cell.
3. "Proximal stimulus" refers to the energy impinging on the sensory surface,
e.g. the light hitting the photoreceptor membrane in the eye, or the changes
in air pressure resulting in changes in the hair cells in the cochlea of
the inner ear. This is the physiological process of "sensation". "Distal
object" is the feature, in the environment, which has caused the energy
involved in the proximal stimulus, e.g. the surface reflecting light which
enters the eye. Processing in the nervous system which results in interpretation
of the proximal stimulus, and so recognition of the distal object, is the
psychological process of "perception". It can include comparison of the
external information with internal information (cognition), i.e. recognition.
(Section 1.3)
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4. Communication needs (Section 1.4):
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Emitter - the individual animal which sends out the signal,
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Message - the information which is carried via the channel (medium, e.g.
air carrying sound waves),
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Receiver - the individual animal which receives the signal; the signal
can influence its behaviour (at least potentially).
5. Their ears are anatomically and physiologically adapted to be attuned
to the particular frequencies, both higher and lower (see Section 2.2.4).
This is an example of peripheral filtering , which contrasts with
which occurs further into the central nervous system.
6. The male's advertisement call may attract a female (good) and so
enable mating - but it could also inform a predator of the frog's position
and result in a good meal for the predator (definitely not so good for
the frog).
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7. See Figure 3.2. The outer ear (pinna) and middle
ear serve for effective transfer of the energy of sound waves into the
inner ear. The sound passing (through air) down the external auditory canal
is transferred to the middle ear through the tympanum (ear drum). In the
middle ear, the sound passes through solid elements as ear ossicles (malleus,
incus, stapes - Fig. 3.4) transfer the energy through the middle ear to
the oval window and into the cochlea of the inner ear. In the inner ear,
the fluid medium in the cochlea carries the sound wave on past the actual
receptor cells.
8. Pitch equates to the frequency of sound (Figure 3.1). The physical
properties of the basilar membrane in the cochlea make detection of pitch
possible (Sections 3.2.5, 3.2.6). Hair cells at different positions are
maximally sensitive to different frequencies. Perception of pitch - in
the auditory cortex?
9. Four synapses, from the spiral ganglion cells (see Fig. 3.5) on up
to the cortex (see Fig. 3.10).
10. Voiceless sound (e.g. 'ss') does not involve the vocal cords for
its production, but voiced sound (e.g. vowels) does. See Section 3.4.1
for more details of the generation of voiced sounds.
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