BIO 012 Lecture Notes - Lecture 14: Salivary Gland, Basilar Membrane, Spasticity
19 Jun 2018
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Chapter 46
p. 947 What is the function of a sensory receptor cell? What is sensory transduction? What is a
receptor potential? What is the difference between ionotropic and metabotropic receptors?
(Also refer to pages 938-939 for the above question). If all sensations from various mediums
are transduced to action potentials, how are these sensations perceived as different by the
nervous system?
The sensory receptor cells are called sensors or receptors and they transduce physical and
chemical stimuli such as light and sound waves, pressure, and odorant and taste molecules into
neural signals. These signals are then transmitted to the central nervous system for processing
and interpretation. The first steps of this process of sensory transduction is a change in the
membrane potential of the receptor cell in response to a specific type of stimulus. Ionotropic
receptors are where stimuli directly affect ion channels. Neurotransmitter binding to an
ionotropic receptor causes a direct change in ion movement across the plasma membrane of
the postsynaptic cell. These proteins enable fast, short lived responses. Responds to stimuli is
quick. Ex: pressure, temperature, voltage. Metabotropic receptors is where stimuli indirectly
affect the ion channels. They induce signaling cascades in the postsynaptic cell that secondarily
lead to changes in ion channels. Responds to stimuli slowly. Different cells pick up the
sensations which causes how they are perceived to be seen differently.
p. 948 How is intensity of a sensation coded by the nervous system? What is meant by “adaptation”
with regard to the nervous system? Why would this be beneficial for organisms? Also, do ALL
sensory systems and sensory organs undergo the same degree of adaptation? Why or why
not?
Sensation is coded by the nervous system through phasic and tonic receptors because that
shows how fast the sensory receptors adapt to different types of stimuli. Adaption is a gradually
diminishing activity in response to a maintained, repeated, or sustained stimuli. This would
benefit organisms because they would be able to ignore background or unchanging conditions
while remaining sensitive to changes and new info. No the sensory systems and sensory organs
do not undergo the same degree of adaption because some sensory cells adapt very little or
very slowly while others adapt quickly. Tonic receptors adapt slowly. Ex: throbbing pain. While
phasic receptors adapt quickly. Ex: slight touch from a high five or slight temp change in the
shower. The sensations we perceive differ because the messages from different kinds of
sensory cells arrive at different places in the CNS.
(Section 46.3)
p. 952 What is a mechanoreceptor? (when you are done with this chapter, think about what types of
mediums effect these receptors)
Mechanoreceptors are sensory receptors that respond to mechanical forces. Physical distortion
of a mechanoreceptors plasma membrane cause ion channels to open, altering the membrane
potential of the cell to create a graded receptor potential, which in turn leads to either the
release of neurotransmitter or the generation of action potentials.
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p. 953 Why are hair cells considered mechanoreceptors? What is the difference (in terms of function)
of the vertebrate auditory system and the vestibular system? What are hair cells and
stereocilia?
Hair cells are considered mechanoreceptors (because they are responsible for touch and they
are very sensitive. They are receptors that transduce sound for the brain) which are the sensory
systems for the vertebrate auditory system and vestibular (equilibrium-maintaining) systems.
Both systems are housed in the complex structures of the vertebrate ear. The vertebrate
auditory system does acoustic feature discrimination, sound source localization, frequency
analysis, and auditory scene analysis. Vestibular system detects sensory info about motion,
equilibrium, and spatial orientation. Hair cells are sensory receptors. Stereocilia are the
mechanosensing organelles of hair cells which respond to fluid motion in numerous types of
animals for various functions, including hearing and balance. Stereocilia are on top of the hair
cells.
p. 955 How are sound waves collected and transferred to mechanical pressure in the fluid of the
cochlea? What is the Organ of Corti and what are the primary functional cells that respond to
the pressure waves in the fluid of the cochlea? Trace the path of both high frequency and low
frequency sounds through the cochlea across the basilar membrane, and out the round
window.
When the sound waves go through the ossicles and leave the stapes to enter the oval window,
the vibrations that form become pressure waves. The organ of corti sits on top of the basilar
membrane in the cochlea and it transduces pressure waves into action potential through the
hair cells. The stereocilia responses are graded membrane potentials which add up to action
potentials and release neurotransmitters. High frequency sounds reach the base, medium
sounds reach further down the basilar membrane and low frequency sounds reach the apex.
Leftover energy from the waves is then sent into the tympanic canal and out through the round
window.
p. 956 What are the various forms of deafness discussed on p 956 and what is the physiological
reason for each?
One form is conduction deafness which is the loss of function of the tympanic membrane and/or
the ossicles of the middle ear. Repeated ear infections in the middle ear, or loud noises can
cause this. The consequence is less efficient conduction of sound wave from the tympanic
membrane to the oval window. Hearing aids amplify the signal.
Another form is sensorineural where the nerve of the hair cells is damaged usually by a loud
noise. Mutations in ion channels (proteins) can affect this too. If the protein is not put together
properly then they won’t open and close properly. You won’t get a depolarization when the
tectoral membrane hits the hair cell and then you won’t be able to hear and may need cochlear
implants. Therefore sensorineural damage is something people are born with.
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P. 956 What are semicircular canals and what is their function? What are the utricle and saccule and
what is the function of each? What are the ampulla? What are the ossicles? How are hair cells
utilized for the functions listed above for the semicircular canals, utricle, and saccule?
Semicircular canals sense angular acceleration. They are 1. Anterior: somersaults; 2. Posterior:
cartwheel; 3. Lateral: spinning. The utricle and saccule sense linear acceleration. The utricle
senses horizontal acceleration while the saccule senses vertical acceleration. The ampulla is
where the hair cells are located. They are bulges at the base of the semicircular canals and two
of these bulges have the utricle and saccule in them. The ossicles are the malleus, incus, and the
stapes. The tympanic membrane hits the ossicles which then vibrate and (the stapes) hit the
oval window and enter and become pressure waves. Then they go in the vestibular canal and
then the cochlear canal where the meet the organ of corti. Then the tectoral membrane hits
the stereocilia which causes the action potential to travel down the cochlear nerve.
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Document Summary
What is the difference between ionotropic and metabotropic receptors? (also refer to pages 938-939 for the above question). The sensory receptor cells are called sensors or receptors and they transduce physical and chemical stimuli such as light and sound waves, pressure, and odorant and taste molecules into neural signals. These signals are then transmitted to the central nervous system for processing and interpretation. The first steps of this process of sensory transduction is a change in the membrane potential of the receptor cell in response to a specific type of stimulus. Ionotropic receptors are where stimuli directly affect ion channels. Neurotransmitter binding to an ionotropic receptor causes a direct change in ion movement across the plasma membrane of the postsynaptic cell. Metabotropic receptors is where stimuli indirectly affect the ion channels. They induce signaling cascades in the postsynaptic cell that secondarily lead to changes in ion channels.
