Lecture 13 - Sensory Systems: Touch, Taste, and Smell Flashcards
Sensation
Detection of a stimulus
Perception
Processes of awareness and assigning meaning to it
What do sensory (afferent) pathways do?
They transduce information about stimuli and transmit them to the CNS
What is perception associated with?
Cortical activity
How is stimulus intensity encoded?
This is encoded by the rate (frequency) of action potentials (AP)
What do larger graded potentials generate?
They generate more action potentials in the same amount of time
What does the absolute refractory period set?
It sets the maximum firing rate (APs/s)
Phasic and rapidly adapting (RA) afferents
Can precisely encode stimulus onset (and sometimes offset)
Tonic and slowly adapting (SA) afferents
Can encode stimulus duration
Receptor field
The location where appropriate stimuli can generate neuronal responses - can infer location of stimulus
What do afferents do?
They make targeted synapses inside the CNS so receptive fields are “inherited” by interneurons at later processing stages
Sensory acuity proportion to receptive field and receptor density
Sensory acuity is inversely proportional to receptive field size and directly proportional to receptor density
What do receptor cells do and name 2 types
Transduce stimuli using receptor proteins, which create graded potentials
Receptor cells can be:
1. Neurons
2. Special epithelial cells that make synapses on afferent neurons
Divisions of somatosensation
- Nociceptors (pain)
- Thermoreceptors (temperature)
- Mechanoreceptors
Touch and proprioception sensing mechanism
Both rely on mechanoreceptors, which express mechanically-gated ion channels
True or False: Mechanoreceptor cells can detect multiple different types of stimuli
True - they are sensitive to different types of stimuli because of their location and cell structure
Name 5 types of stimuli mechanoreceptor cells can detect
- Sustained pressure
- Coarse pressure
- Fine texture
- Vibrations (ex. during gripping an object)
- Skin stretch (ex. during movement)
True or False: Sensory neurons involved in thermosensation and thermal nociception cannot respond to different stimulus
False - sensory neurons involved in thermosensation and thermal nociception respond to different stimulus ranges because they express different receptor proteins
Where is the distinction of pain/temperature and tactile sensation maintained?
Afferent fibres
Transduction
Conversion of a stimulus to a change in membrane potential
How are distinctions in afferent fibres maintained?
Through spinal processing and ascending pathways
True or False: Nociceptive pathways can be modulated?
True - tactile sensation and descending inhibition can both modulate the activity of nociceptive pathways
ie. somatosensory pathways can interact
Name 2 chemosensory exteroreceptive sense and which perceptions do they produce?
- Olfaction - smell
- Gustation - taste
The integration of these 2 senses is called flavour!
Olfaction
Detects odorants via olfactory sensory neurons located in the nasal epithelium
Transduction mechanism and encoding principle of olfaction
Mech: olfactory receptor proteins are examples of metabotropic receptors which indirectly cause graded potentials by activating an enzyme that converts ATP to cAMP, causing Na+ channels to open –> AP occurs
Olfactory info enters the cerebrum directly, without passing through the brainstem or thalamus
Transduction mechanism and encoding principle of gustation
Mech: the 5 basic qualities of taste (sour, sweet, bitter, umami, and salty) is transduced by taste receptor cells located in taste buds. Each of these taste qualities is transduced with distinct mechanisms and primary afferent neurons
Taste info enters the CNS at the hindbrain and is relayed to the cerebrum via the thalamus
