chemical sensations

Sensory receptors transduce...

environmental energy into electrochemical signaling

sensation

the detection of external stimuli by receptors

perception

conscious awareness of our sensations (what the brain perceives)

receptor

a protein specialized to detect a particulat stimulus

examples of receptors

rods (light), taste cells (taste)

sense organs

receptors that are associated with groups of other tissues

transduction

receptor proteins convert environmental stimuli to nervous system (electrical) activity

example of transduction

heat stimulates thermoreceptors on sensory neurons

2 types of transduction

long-axon receptors and ganglion cells

long-axon receptor transduction

sensory receptors (ion channels) on neuron depolarize neuron and create a CNS reaction

example of long-axon transduction

olfaction

ganglion cells transduction

sensory receptors on a cell cause the release of neurotransmitters
-neurotransmitters activate neurons to create CNS response

example of ganglion cells tranduction

taste

modality of information transmitted

type of stimulus (sight, sound, etc)

What is the modality determined by?

CNS region targeted

Why can you see colors when you rub your eyes?

the pressure is opening ion channels associated with sight

What is the location of information transmitted determined by?

receptive field: area that stimulates sensory neurons

In the center of the retina what is the relationship between the number of receptors to neurons

1:1

In the periphery of the retina what is the relationship between the number of receptors to neurons

2:1

during high intensity (bright conditions) which location of the retina shows the best image?

center

during low intensity (dark conditions) which location of the retina shows the best image?

periphery

What is perceived when you are pricked with 2 needles close to each other in an area with a large receptive field?

perceive one point/prick

What is perceived when you are pricked with 2 needles close to each other in an area with a small receptive field?

perceive 2 points/pricks

Lateral Inhibition

receptor with the largest stimulus tells neighbors to shut up rather than spreading the stimuli out

intensity

amplitude of stimulus

3 steps to encode intensity

1) firing rate
2) number of neurons
3) types of neurotransmitters released

duration

how long the stimulus lasts

adaptation

decrease response to stimulus over time

phasic receptors

rapidly adapting sensors
-sense changes

tonic receptors

slowly adapting sensors
-proprioception

What receptors sense light

photoreceptors

What receptors sense temperature

thermoreceptors

What receptors sense pain

nociceptors

What receptors sense odors, taste, and body fluid composition

chemoreceptors

What receptors sense pressure and stretch

mechanoreceptors

What receptors sense internal organs

interoreceptors

What receptors sense position and movement

proprioceptors

What cranial nerves stimulate taste and where

7 (front), 9 (back), and 10 (epiglottis)

filiform papillae

abundant, small spikes
-no taste buds

foliate papillae

parallel ridges of tongue
-taste buds degenerate by age 2-3

fungiform papillae

mushroom shaped, concentrated at tip and sides
-each bump contains about 3 taste buds

vallate papillae

massive bumps on back of tongue
-each bump contains 7-12 taste buds

What is the percentages between fungiform and vallate papillae

50-50

taste buds

contain all 5 taste cells
-carry out gustation

gustation

chemical sensation of taste

structure of taste buds

taste hairs in taste pores contain taste receptors
-contain basal cells to replace lost taste cells

What do taste receptors release to the CNS nerves

ATP

each taste cell expresses ____ type of taste receptor

only one

Mechanism for tasting sour

H sensing channels (acids)

Mechanism for tasting salty

Na channel

Mechanism for tasting sweet

GPCRs (Gq); saccharides

Mechanism for tasting umami

GPCRs (Gq); gluramate

Mechanism for tasting bitter

GPCRs (Gq); alkaloids

T/F: there is a taste map for the tongue

F

Primary afferent taste pathway

CN7, 9, and 10

secondary afferent taste pathway

solitary tract nucleus connected with limbic system and thalamus

tertiary afferent taste pathway

ventral posterior medial thalamus
-project to primary gustatory cortex for taste perception

What part of brain senses whether or not you like something?

insular taste cortex

What part of brain determines what something is?

frontal cortex

T/F: there is a taste map for the brain

T: different tastes stimulate different regions of the primary gustatory cortex

What makes up flavor

taste + smell

What cranial nerve senses odors

1

nasal cavity

lined with respiratory and olfactory epithelium

olfactory epilthelium

contains sensory neurons

olfactory nerve

formed by olfactory sensory neurons

primary afferent passage of olfactory system

olfactory nerve

olfactory bulb

connects olfactory nerve to olfactory tracts

secondary afferent passage of olfactory system

olfactory bulb

olfactory sensory neurons (OSN)

project olfactory cilia into nasal cavity

olfactory cilia

increase surface area
-each expresses one type of odorant receptor

How do OSNs form CN1

axons pierce cribriform plate and synapse in olfactory bulb

how often are OSNs replaced

1-12 months by basal cells

Why do OSNs need to be replaced

air damages plasmalemma

How many odorants bind to Gs (G-proteins/GPCRs)

one or a few

What is the process of odorant receptors

-odorant molecule binds to receptor
-G-protein activated
-ion channels activated
-cAMP channels depolarize OSNs

What cells make up olfactory bulbs

mitral cells, glomeruli, periglomerular cells, granule cells

glomeruli

collections of OSN axons and mitral cell dendrites
-correspond with a specific odorant receptor

periglomerular cells

lateral inhibitory cells stimulated by OSNs

granule cells

lateral inhibitory cells stimulated by mitral cells and feedback from piriform cortex

limbic system

amygdala, entorhinal cortex

Amygdala limbic function

emotion

entorhinal cortex limbic function

memory

tertiary afferent olfactory pathway

orbitofrontal cortex, hippocampus, hypothalamus, olfactory bulbs

orbitofrontal cortex role

conscious perception

hippocampus role

memory

hypothalamus role

autonomic response

olfactory bulb role

modify sensitivity via granule cells