BIOLOGY 1A Lecture Notes - Lecture 38: Somatosensory System, Sensory System, Sensory Neuron
SENSORY SYSTEMS
Nervous system organization- afferent from sensory systems
I.
Sensation beings with sensory neurons
Sensory neurons are cells that have specializations that convert stimulus
energy to changes in membrane potential:
Stimulus energy
Sensory system
Photons
Vision/sleep wake cycle
1.
Vibration
Audition (hearing)
2.
Chemical odorants
Olfaction (smell)
3.
Gustation (taste)
4.
Mechanical pressure, temperature,
pain
Somatosensation
(touch)
5.
i.
Proprioception: a sense of relative positions of the body
ii.
Vestibular sense: sense of orientation and balance
iii.
a.
Classifications of sensory receptors: convert stimulus energy into change
of membrane potential
Photoreceptors: photons (vision)
i.
Chemoreceptors: taste and smell
ii.
Mechanoreceptors: vibration (hearing and somatosensation)
iii.
Thermoreceptors: temperature (somatosensation)
iv.
Nociceptors: pain (somatosensation)
v.
Other fish, platypus, insects have electromagnetic receptors
vi.
b.
II.
From sensation to perception
The stimulus triggers either hyperpolarization or depolarization.
This leads to action potential in afferent neuron which the CNS is
able to understand.
i.
a.
Properties of sensory systems
The greater the stimulus, the greater the depolarization, the higher
the frequency of action potential
1)
Only FREQUENCY of action potential varies2)
i.
Concept of a labeled line
Depolarizing sensory neuron in any way will activate same
circuits in the brain leading to same perception
1)
No sensation
Change the membrane potential of the neuron to
activate same perception
a)
2)
ii.
b.
Photoreceptors: modified GPCRs
Rods and cones have a clel body w a nucleus and an axon which
releases signaling molecule
Outer segments is filled with disks (like coins stacked up) 1)
Disks have modified GPCRs which are called RHODOPSIN2)
Signaling moleucle is already bound- retinal
Sits there bound to its receptor all the time. Sits at cis
conformation
a)
Qhen retinal absorbs photon it transforms to trans
conformation
b)
GPCR is activated and starts transductionc)
3)
i.
Photoreceptor= GPCR= rhodopsinii.
Signaling molecule= retinaliii.
Light changes confirmation of retinal to activate the GPCRiv.
c.
Phototransduction: from activation of GPCR to closing of an ion channel
Light activates rhodopsini.
The G-protein called transducin is activated and binds to
phosphodiesterase
ii.
cGMP is hydrolyzed after phosphodiesterase is activated iii.
cGMP is attached to an Na+ channel which is gatediv.
Hyperpolarization!!!v.
vi.
In the dark, lot of Na+ openvii.
Light--> Close Na+--> hyperpolarization!!!!!!viii.
Cones allow us to see color
3 different kinds of opsins (red, green, blue)1)
ix.
d.
III.
Ex. 1: Color blindness
Human primates and trichromats- we have 3 opsins (3 different GPCRs,
which absorb either red, green or blue light)
a.
Both red and green opsins are on X chromosome, and so color blindness is
more common in males than females
b.
Treating color blindness with gene therapy
Squirrel monkeys have blue cones but either green OR red and so
they are color blind
i.
Transfecting genes encoding the missing opsin into primate retinas
which gives them color vision even though they never had it before
ii.
c.
IV.
Ex. 2: Thermoreceptors
Transient receptor potential (TRP) channels are large family of ion
channels that allow the passage of Na+ or Ca2+ into the cell
a.
Some are gated by temperatureb.
Leads to depolarization of membrane potentialc.
Different TRP channels are gated by different temperaturesd.
Mice lacking TRPM8 are insensitive to cold touch
Does not have ion channeli.
e.
TRP channels are gated by temperature and chemicals
Ex. minti.
f.
V.
Labeled line
Capsacin feels hoti.
Not changing temperature but depolarizing sensory neuron in the
same way leading to perception of heat
ii.
The Capsacin causes a sensory cell to depolarize when it binds to
thermoreceptor
iii.
a.
VI.
Lecture 38- Sensory Systems
Friday, April 27, 2018
9:03 PM
Document Summary
Sensory neurons are cells that have specializations that convert stimulus energy to changes in membrane potential: Proprioception: a sense of relative positions of the body. Vestibular sense: sense of orientation and balance b. Classifications of sensory receptors: convert stimulus energy into change of membrane potential i. ii. iii. iv. v. vi. This leads to action potential in afferent neuron which the cns is able to understand. b. The greater the stimulus, the greater the depolarization, the higher the frequency of action potential. Depolarizing sensory neuron in any way will activate same circuits in the brain leading to same perception. Change the membrane potential of the neuron to activate same perception c. Rods and cones have a clel body w a nucleus and an axon which releases signaling molecule. Outer segments is filled with disks (like coins stacked up) Disks have modified gpcrs which are called rhodopsin. Signaling moleucle is already bound- retinal a) b) c)
