Mcdb 1b Exam Sensory System

Transduce physical/chemical stimuli into signals that are transmittable and interpretable as action potentials
most are modified neurons
specialized for different stimuli
most have membrane receptor proteins to detect stimulus and respond by altering glow of ions

Receptor protein itself is part of ion channel and by changing its conformation, it opens/closes channel pore
ex: pressure sensitive Na+ channel

Receptor protein is linked to a G protein that activates a cascade of intracellular events that open/close ion channels
ex: taste/smell molec.s with NA+ or K+ channel
cGMP gated Na+ channel and light

Generate Action potentials directly

Cant generate action potentials
generate AP by inducing release of neurotransmitters

Some cells respond less when stimulation is repeated
ability of animals to ignore continuous stimuli can be due to this

Receptors that respond to chemical stimuli
ex. smell/taste molecules

Neurons embedded in epithelial cells at top of nasal cavity
molecs from environment diffuse thru nasal mucous to reach surface of olfactory hairs(on ends of dendrites)
bind to odorant molecule, activates G protein

1.G protein is activated
2. enzyme is activated that increases level of 2nd messenger cAMP which opens a cation channel
3. depolarization of membrane
4. AP fired

1000 genes
only ~380 receptors
414 pseudogenes
each odorant may bind to one or more specific receptor proteins

NOBEL PRize 2004
odorant receptors

By combo of bound receptor proteins
each olfactory receptor recognizes a # of similar structures that are part of odorants
allows characterization of new molecules

Sense of taste

Small bumps on human tongue
house taste buds
taste buds replaced every few days

Sweet, bitter, umami= G protein coupled receptors
salty and sour= ion channels