Sensory Systems - Touch, Taste, and Smell Flashcards
What is sensation?
the detection of a stimulus
- stimuli are transmitted to the CNS
What is perception?
the point in which ew become aware of the info/stimuli
processes of awareness and assigning meaning to stimuli
- associated with cortical activity
What are the four processes in the sensory pathway?
- Transduction
- Encoding
- Transmission
- Processing/computation
What is transduction?
The conversion of an (external) stimulus into currency that our body can process (an electrical signal / depolarization / change in MP)
- Depolarization of receptor
What is encoding?
Occurs after transduction
When the graded potential is converted to an action potential
- Action potential generation
What is transmission?
The transfer of an action potential to the nervous system (propagation)
- Propagation over labelled line
What is processing/computation?
- CNS processing of the action potential
- finding meaning to the stimulus
- can either take a voluntary or involuntary pathway from here
a) immediate involuntary response
b) voluntary response
When the sensory system encodes info, what can it tell you about the stimulus? (4)
- What (characteristics)
- stimulus characteristics that are unique qualities for each sensory system - Where (location)
- where is the stimulus coming in from? - When (timing)
- how long is the stimulus turned on/off/duration - How much (intensity)
- is it a strong stimulus or a weak stimulus?
What encodes stimulus intensity?
The rate of frequency of action potentials
A larger stimulus will indicate a larger graded potential, but that does not imply a greater action potential
All action potentials have the same stereotyped shape, but you can change the FREQUENCY
Larger GP = More AP in the same amount of time
The maximum firing rate of action potentials is determined by what?
Absolute refractory period
What encodes the onset/offset of a stimuli’s duration?
The timing of action potentials
There are two types of receptors that encode stimulus onset/offset
What are the two types of receptors that encode stimulus onset/offset?
- Phasic (rapidly adapting RA) receptors
- Tonic (slow adapting SA) receptors
What are phasic receptors?
AKA rapidly adapting RA receptors
- tell you when a stimulus turns on or off
- produces quick, frequent APs and then rapidly adapts
- triggered by a change, then there is a firing of AP to indicate that the stimulus has gone on
- when the change goes away, we get another firing of AP to indicate that the stimulus has gone off
- in between the initial and final firing of APs, there are no APs being generated
What are tonic receptors?
AKA slowly adapting SA receptors
- tells us INFO about the duration
- continues to fire AP until the stimulus has gone away
Differentiate phasic from tonic receptors
Phasic = afferent neurons that can precisely encode when the stimulus onset / offset occur
Tonic = afferent neurons that encode for the entire stimulus duration
What is a receptive field?
The location in which a stimulus is detected because of cell or neuronal responses (can stimulate a corresponding neuron)
Each afferent neuron connected to a receptive field makes targeted synapses inside the CNS so that eventually the receptive fields are passed to interneurons
What is tactile acuity?
The ability to distinguish between two points of stimulation through a two-point discrimination test
Where in the body would have the highest tactile acuity?
Areas which have small receptive fields
Describe the relationship between receptive field size to sensory acuity
The smaller the receptive field, the greater the sensory acuity
Therefore,
The places in your body with the greatest sensory acuity are going to be places with a high density of receptors in a small receptive field
Describe the relationship between sensory acuity and receptor density
The greater the sensory acuity, the greater the receptor density
Therefore,
The places in your body with the greatest sensory acuity are going to be places with a high density of receptors in a small receptive field
If there is an overlap in receptor fields (A and B respectively) an action potential is generated in which receptive field?
If there is overlap, there will be action potentials generated in both regions
How do you interpret a homunculus? (The building of a person with bigger/smaller depictions)
Bigger depictions indicate a higher sensory acuity
WHAT encodes specific stimulus characteristics?
Receptor cells that have different sensitivities to stimuli are in charge of encoding specific stimulus characteristics
What are receptor cells?
Receptor cells can be neurons or special epithelial cells that make synapses on afferent neurons
Receptor cells transduce (convert) stimuli, using receptor proteins which create graded potentials
- they are channels that allow for changes in the membrane potential
Differentiate neurons from epithelial cells involved in the transduction of stimuli
Epithelial cells are metabotropic receptors, so they are involved in an indirect mechanism for membrane potential changes
- they cannot generate APs by themselves
- must communicate information to an afferent neuron
Only a neuron can fire an action potential
What is somatosensation?
What are the three main divisions of somatosensation?
- Nociceptors
- Thermoreceptors
- Mechanoreceptors
What are the two subdivisions of Nociceptors and Mechanoreceptors?
Nociceptors
1. Type A Fibers
2. Type C Fibers
Thermoreceptors
Mechanoreceptors
1. Proprioceptors
2. Tactile receptors
Nociceptors are associated with which sense: ____________________________
PAIN
Thermoreceptors are associated with which sense: ____________________________
TEMPERATURE
Proprioceptors and tactile receptors are associated with which sense: ____________________________
PROPRIOCEPTION AND TOUCH
What is proprioception?
Sense of self-movement
Awareness of orientation (where you are in the world)
What kind of channels are involved in touch and proprioception (mechanoreceptors)?
Mechanically gated ion channels
What are tactile receptors?
An epithelial sensory cell with a tactile disc
A tactile disc is made of a Merkel cell and a nerve terminal
- fine touch and pressure receptors
- crude touch and pressure receptors
What are proprioceptors?
Sensory neurons
A sensory receptor which receives stimuli from within the body, especially one that responds to position and movement
- found in joints and muscles
What are Merkel cells?
Merkel cells are connected to the nerve endings in the skin that are responsible for the sense of touch
Found in the base (stratum basale) of the epidermis in the integument
Match the receptor with its correct function:
- Nociceptors
- Thermoreceptors
- Proprioceptors
- Tactile receptors
a) Fine/crude touch and pressure receptors, vibrations
b) Pain sensations
c) Proprioception - self-movement
d) Temperature sensations
Nociceptors
b) Pain sensations
Thermoreceptors
d) Temperature sensations
Proprioceptors
c) Proprioception - self-movement
Tactile receptors
a) Fine/crude touch and pressure receptors, vibrations
Different mechanoreceptors cells are sensitive to different types of stimuli because of their __________________ and ________________________
Different mechanoreceptors cells are sensitive to different types of stimuli because of their LOCATION and CELL STRUCTURE
The different in sensitivity depends on where they are located
Where are thermo- and nociceptors located? What are they sensitive to?
Free nerve endings
- found close to the surface
- detect pain and temperature
Where are tactile receptors located? What are they sensitive to?
Contain tactile disc (Merkel cell and nerve terminal)
- close to the surface
- detects stimuli that is sustained and coarse
Mechanoreceptor cells sensitive to vibrations will be found where?
Vibrations = heavier stimulus
therefore, found deeper in the skin
Mechanoreceptor cells sensitive to fine texture will be found where?
light touches, light stimuli
therefore, found closer to the surface
Mechanoreceptor cells sensitive to skin stretch will be found where?
stronger, more intense stimuli
therefore, found deeper in the integument
Mechanoreceptor cells sensitive to sustained pressure/coarse texture will be found where?
closer to the surface
Why do sensory neurons involved in thermosensation and thermal nociception respond to different stimulus ranges?
They express different receptor proteins
(thermo-gated ion channels) that open at specific temperatures
Different receptor proteins allow for different responses to different stimulus ranges
What is the difference between thermoreceptors and nociceptors?
Thermoreceptors activate around normal temperatures
Nociceptor neurons do not detect stimuli until the stimulus is very strong/painful
What are the characteristics of proprioception/touch fibres (type of sensory axon, conduction velocity, diameter, myelination)?
Aa type Myelination ✅
AB type Myelination ✅
Increased diameter = increased conduction velocity
What are the characteristics of thermo & nociception fibres (type of sensory axon, conduction velocity, diameter, myelination)?
A-delta type Thin Myelination ✅
C type No Myelination ❌
Decreased diameter = decreased conduction velocity
Thermo/nociception and proprioception/touch receptors are differentiated via which two characteristics?
- Afferent fibres (types and characteristics)
- Spinal processing and ascending pathways
What is the spinal processing and ascending pathway of touch and proprioception receptors?
Fine touch, vibration, pressure, and proprioception sensations from the right side of the body get to the midbrain via the DORSAL COLUMN (decussation - left side)
What is the spinal processing and ascending pathway of thermo and nociception receptors?
Pain and temperature sensations from the right side of the body get to the midbrain via anterolateral system (decussation - left side)
What are chemosensory exteroreceptive senses?
Senses that evoke sensations in more than one sensory system
What are the two chemosensory exteroreceptive senses that humans have?
Olfaction and gustation
What is olfaction?
smell
What is gustation?
taste
What is flavour?
Flavour = integration of both olfaction and gustation
How does the olfaction sensory system detect odorants?
via the olfactory sensory neurons located in the nasal epithelium (roof of the nose)
Odorants = volatile chemicals
How are olfactory receptor proteins an example of metabotropic receptors?
They are ligand-gated channels that INDIRECTLY cause membrane potential changes / graded potentials
- Receptor activation
- odorant binds to the olfactory sensory receptors and causes some kind of metabolic reaction - Graded potential
- sodium ion channels open and depolarization can begin - Action potential
- if threshold membrane potential is reached then an AP will be generated and the info is relayed to the CNS
Each olfactory sensory neuron expresses just ______ type of olfactory receptor protein
ONE
Trace the path of olfactory information from the stimuli to cerebrum
Olfactory information enters the cerebrum directly, without passing through the brainstem or thalamus (hindbrain)
Cilantro contains high levels of chemicals often found in soaps of detergents
Why don’t some people like cilantro?
There are variations in the ORGA2 gene that affects how you react to the chemicals in cilantro
They will have olfactory sensory neurons that produce many action potentials for a low concentration of decanoic acid (since they are very sensitive to the chemical, it would not take much to get them to react)
What are the five basic qualities of gustation (taste)?
- Sour
- Sweet
- Bitter
- Umami
- Salty
Where are your taste buds located?
taste buds are located along the edge of the papillae
True or False:
Each taste bud only detects one basic quality of gustation (sweet, salty, sour, etc.)
FALSE!
Each taste bud detects multiple qualities
Each taste quality uses distinct transduction mechanisms and distinct primary afferent neurons
- can detect different stimuli because they have different receptors
Trace the path of gustatory information from the stimuli to cerebrum
Taste information must enter the CNS via the hindbrain (relayed to the cerebrum via the thalamus)
Compare the pathways of gustatory info to olfactory information
Olfactory info can bypass the hindbrain and enter directly to the cerebrum
Gustatory info must pass through the hindbrain to reach the cerebrum
