olfactory and gustatory systems

Question 1

what do all sensory systems have?

Answer 1

a physical stimulus that is transformed into nerve impulses and action potentials using sensory receptor cells in the peripheral nervous system
the PNS must evoke a response to the signal in the form of perception of the sensation in the cortex of the CNS

Question 2

what are sensory receptor cells?

Answer 2

cells that detect a stimulus, take energy from the environment and change it into an electrochemical signal by sensory transduction
these electrochemical signals can be action or graded potentials

Question 3

what receptors can sensory receptor cells have?

Answer 3

ionotropic receptors (ligand gated ion channels)
G-protein coupled receptors
they can be specialised or more general

Question 4

what are sensory modalities?

Answer 4

different senses such as smell, vision, balance, hearing or pain
their specificity is achieved by the structure and position of their sensory receptor cells
they can be grouped by their structure and the morphology of their cells

Question 5

what is proprioception and where are the sensory receptor cells found?

Answer 5

the detection of how stretched muscle fibres are so we know if our muscles are contracted or relaxed
this allows us to tell where our limbs are in space
the sensory receptor cells are in muscles and ligands

Question 6

where are pain receptors found and what do they detect?

Answer 6

found in the skin and organs
detect mechanical pain (e.g. bruise), chemical pain (e.g. acid) and thermal pain (e.g. burning)

Question 7

what is the stimulus, receptor and location for hearing?

Answer 7

mechanical stimulus
mechanoreceptors found in the inner ear (cochlea)

Question 8

what is the stimulus, receptor and location for balance?

Answer 8

mechanical stimulus
mechanoreceptors found in the inner ear

Question 9

what is the stimulus, receptor and location for vision?

Answer 9

light stimulus
photoreceptors found in the retina

Question 10

what is the stimulus, receptor and location for touch?

Answer 10

mechanical stimulus
mechanoreceptors found in the skin

Question 11

what is the stimulus, receptor and location for temperature?

Answer 11

thermal stimulus
thermoreceptors found in the skin

Question 12

what is the stimulus, receptor and location for pain?

Answer 12

mechanical, thermal and chemical stimuli
nociceptors found in the skin and internal organs

Question 13

what is the stimulus, receptor and location for proprioception?

Answer 13

mechanical stimulus
mechanoreceptors found in the muscles, tendons and joints

Question 14

what is the stimulus, receptor and location for olfaction?

Answer 14

chemical stimulus
chemoreceptors found in the nasal cavity

Question 15

what is the stimulus, receptor and location for taste?

Answer 15

chemical stimulus
chemoreceptors found in the tough, pharynx, palate and epiglottis

Question 16

how are stimuli transformed by sensory transduction?

Answer 16

1. a stimulus activates a sensory receptor cell or protein which alters the cell’s membrane permeability
2. a receptor potential develops in the sensory cell because more or less ions can move into the cell changing the voltage
3. this causes neurotransmitter release onto afferent neuron terminals which binds to receptors and generates an EPSP
4. an action potential is generated in the afferent neuron and propagates along the axon to the CNS where the information is integrated

Question 17

how can some sensory receptor cells generate an action potential?

Answer 17

they have an axon so can act as an afferent neuron

Question 18

what is a receptor potential?

Answer 18

graded potentials generated in sensory receptor cells that increase as the stimulus increases

Question 19

how does a graded potential cause an action potential?

Answer 19

if it reaches the threshold it will generate an action potential in the axon initial segment

Question 20

what is an action potential?

Answer 20

potentials that are always the same size but the stimulus needs to meet a threshold to be generated

Question 21

how are action potentials generated in olfactory receptors?

Answer 21

these receptor cells have an axon segment and a dendritic segment
an ion influx causes membrane depolarisation and a graded receptor potential develops in the dendrites
if the graded potential is large enough to depolarise the soma an action potential is produced in the axon initial segment

Question 22

how are action potentials generated in taste receptors?

Answer 22

1. ion influx causes the membrane to depolarise and a graded receptor potential to develop
2. this opens calcium ion channels at the presynaptic terminal
3. this initiates synaptic vesicles to fuse with the membrane and release neurotransmitter
4. neurotransmitter diffuses across the cleft to the afferent neuron where it binds to receptors and generates an EPSP that can generate an action potential if it meets the threshold potential

Question 23

what information can sensory receptor cells convey?

Answer 23

the modality, location, intensity and timing of a stimulus

Question 24

what is the labelled line code of modality?

Answer 24

this is the principle that specific sensory information is conveyed to the brain through distinct neuronal pathways that are each labelled for a particular sensation

Question 25

what is the pathway of the labelled line code?

Answer 25

the sensory receptor cell is selective for one type of stimulus energy and axons of this cell only carry information from this cell the axons make connections to specific areas of the brain so information from one stimulus always travels down the same line to the brain

Question 26

how does the labelled line code allow us to associate sensations with a stimulus?

Answer 26

specific afferent neurons are electrically stimulated to create an action potential

Question 27

what is synaesthesia and what causes it?

Answer 27

a condition where stimuli are perceived as different sensations e.g. tasting words or hearing colours it is caused by sensory systems being mixed up and labelled line codes getting crossed

Question 28

how do receptors detect the location of a stimulus?

Answer 28

the spatial arrangement of activated receptors in a sense organ

Question 29

how do receptors detect the intensity of a stimulus?

Answer 29

it is determined by the size of the graded receptor potential and the frequency of action potentials which controls the amount of neurotransmitter released

Question 30

what is the intensity of a stimulus and what is the sensory threshold?

Answer 30

intensity is the total amount of stimulus energy delivered to the receptor the sensory threshold is the lowest stimulus strength that will generate an action potential

Question 31

how can receptors detect the timing of a stimulus?

Answer 31

rapidly adjusting receptors or phasic receptors respond to the beginning and end of a stimulus so we know when it starts and finishes slowly adapting receptors or tonic receptors respond to a prolonged stimulation and by decreasing the firing rate of action potentials (adaptation) as a stimuli is going on so we know it is still happening

Question 32

what is onset timing and how is it perceived?

Answer 32

the start of a stimulus when stimulus energy is received by the receptor so we know the stimulus has started

Question 33

why does the firing rate of action potentials in slowly adapting receptors decrease?

Answer 33

to avoid brain overload

Question 34

how does temperature decrease affect neural conduction velocity?

Answer 34

it decreases because rate of diffusion decreases so voltage-gated channels open slower action potential propagation speed decreases

Question 35

what is a compound action potential and how is it measured?

Answer 35

it is the sum of simultaneous action potentials from a bundle of axons measures the difference in membrane potential between two areas of the axon externally

Question 36

what do chemical senses allow us to do?

Answer 36

identify food sources avoid noxious substances find a mate or mark territories

Question 37

what are the two systems involved in chemical senses?

Answer 37

gustatory system detects taste olfactory system detects smell

Question 38

how do we sense taste and smell at the same time?

Answer 38

they are processed down different line codes in parallel and converge in the association cortex

Question 39

how do we distinguish between flavours?

Answer 39

detecting the temperature, smell and texture of foods also by activation of different proportions of taste receptors

Question 40

which organs contain taste receptors?

Answer 40

the tongue, inside of the cheeks, soft pallet, pharynx and epiglottis (cartilage over the trachea)

Question 41

what are lingual papillae?

Answer 41

ridges on the tongue covered with taste buds

Question 42

what are taste buds made up of?

Answer 42

many different chemoreceptive taste cells for different tastes taste cells project microvilli into taste pores

Question 43

what are the 5 flavours and which receptors do they use?

Answer 43

salty, sweet, sour, bitter and umami salty and sour taste cells use ion channels bitter, sweet and umami taste cells use G-protein coupled receptors

Question 44

what causes gustatory afferent neurons to be activated?

Answer 44

neurotransmitter has to be released from the presynaptic neuron and cause the postsynaptic neuron to be depolarised

Question 45

what is the basic structure of the olfactory system as a chemical enters it?

Answer 45

the chemical enters through the nasal cavity and is dissolved in mucus above the olfactory epithelium the epithelium contains olfactory receptors which are below the olfactory bulb that outputs to the olfactory cortex

Question 46

what is the structure of the olfactory bulbs and how many are there?

Answer 46

they contain small glomeruli cells where afferent cell bodies sit there are 3 olfactory bulbs

Question 47

what are olfactory receptor cells?

Answer 47

bipolar cells containing a dendrite and axon on opposite sides of the cell they are chemoreceptive so detect chemicals in small amounts

Question 48

why are olfactory receptor cells replaced often?

Answer 48

they can be damaged easily by bacteria

Question 49

what are odorant receptor cells?

Answer 49

receptor cells that can detect multiple odorants at one time they are all G-protein coupled receptors

Question 50

what is the transduction pathway of odorant receptor cells?

Answer 50

1. the odorant molecule binds to the receptor causing a conformational change 2. the G protein is activated and splits off into subunits, the alpha subunit binds to adenylyl cyclase activating it 3. adenylyl cyclase converts ATP to cAMP which binds to cAMP-gated ion channels opening them 4. this causes an influx of sodium and calcium ions that depolarise the cell 5. this forms a graded potential and calcium ions bind to chloride channels opening them depolarising the cell more

Question 51

how do olfactory receptor cells input to the olfactory bulb?

Answer 51

the olfactory bulb contains lots of glomerulus each glomerulus receives input from one type of olfactory receptor cell so all the cells that express one olfactory receptor protein converge in one glomerulus