Sensory Flashcards
Is there a receptor for each type of stimuli
There is not a receptor for every specific stimulus meaning that some stimuli require multiple receptors. An example of this is the sensation of feeling wet using thermo, touch and pressure.
What is a sensory receptor
Specialised peripheral ending of afferent neurons
Each type responds to a specific stimulus
Receptor translate the energy from the stimulus into electrical signals through a process called signal transduction
What are the two receptor types
Specialised afferent ending - single cell receptor (free nerve endings)
Example is pain receptor
- Stimulus opens stimulus sensitive channels permitting Na entry causing local potential
- Local current flow between depolarised receptor and adjacent open voltage Na
Separate receptor cell (more common)
- Sensory receptors in sperate cell that once depolarised will open voltage gate Ca channel
- Ca will cause neurotransmitter release which will bind to chemically gated receptor channels allow Na entry
What are the four modes of information provided by sensory systems
Modality, location, intensity and timing (when and how often)
How does the brain recognise a specific modality if all receptors just produce AP’s
Modality is nerve specific not receptor specific meaning the brain knows what the stimulus is based on the afferent nerve.
What is a receptor field
Receptive field is the area of skin monitored by one sensory neuron.
Some receptors will share nerve fibers forming a receptive field between the two fibers.
Highly sensitive areas have very small receptive fields.
What is lateral inhibition
Lateral inhibition (local inhibition) increases accuracy
Receptor field direction under stimulus is stimulated more while the others are inhibited by interneurons.
Ability to localise touch is directly related to the density of tactile receptors _> higher density means higher ability to localise touch.
How can intensity of sensory system be interpreted if all nerves just produce AP’s of same amplitude
- More APs
- High frequency Aps
- Larger stimulus also leads to activity of more receptors
Tonic vs phasic receptors
Tonic receptors are very slow adapting and produce Aps as long as the stimulus is present (pain)
Phasic receptors are fast to adapt and stop firing AP just after stimulus is detected and dire again when it stops. (touch)
Nerve distribution in the homunculus
Highly sensitive areas have more nerves meaning they need more area
Types of cutaneous receptors (encapsulated and non encapsulated)
Encapsulated (cutaneous tissue and nerve ending encapsulated in thin sheath)
- Meissner corpuscles
- Pacinian corpuscles
- Ruffini corpuscles
Non encapsulated
- Hair follicle receptor
- Merkel’s disk
- Free nerve ending
Phasic and tonic with respect to light and deep touch
The light touch receptors are phasic meaning they will adapt over time but the deeper touch receptors are slow adapting.
Number of hot and cold receptors
There are separate receptors for hot and cold sensations and the receptors for cold are more abundant.
Thermal receptor adaptation
Note that thermoreceptors adapt quickly so hand in cold bath will adapt and not feel cold after some time.
Thermoreceptors adapt meaning that changes in temperature are sensed rather than the actual temperature itself. If you take the hand out of the cold bath and put it into room temp water it will feel hot.
Normally thermal stimulation is non noxious but extreme temperature can also trigger pain responses.
Three types of nociceptors
- Mechanical nociceptors
- Mechanical damage such as cutting or crushing
- Thermal nociceptors
- Temperature EXTREMES
- Polymodal nociceptors
- Respond equally to all kinds of damaging stimuli
- +/- Silent (sleep) nociceptors
- Mechanical stimulation during inflammation ONLY
Characteristics of fast pain
Fast pain (more tolerable):
- Occurs on stimulation of mechanical and thermal nociceptors
- Carried by small myelination A delta fibers
- Produces sharp, prickling sensation
- Easily localise
- Occurs first
Characteristics of slow pain
Slow pain:
- Occur on stimulation of polymodal nociceptors
- Carried by small myelination C fibers (slower conduction velocity)
- Produces dull, aching, burning sensation
- Poorly localised
- Occurs seconds and persists for longer time making it more unpleasant
How is the change from fast to slow pain mediated
The change between these two type of pain is mediated centrally. Nociceptors do not adapt meaning that the transition from fast to slow pain comes centrally.
How do local anaesthetics stop pain
Block Na channels on nociceptors
Ice will decrease speed of chemical reactions and therefore reduce pain
Pain neurotransmitters
- Substance P - Activates ascending pathways (sensory nerve fiber to synapse onto ascending) that transmit nociceptive signals to higher levels for further processing
- Glutamate - major excitatory neurotransmitter
In a state of hyper sensitivity glutamate will increase the excitability of dorsal horn neuron meaning even a little substance P will take it to threshold (faster)
What is the CNS analgesic system and how can it effect pain
- Suppresses transmission in pain pathways as they enter the spinal cored via opioid receptors
- Depends on presence of opiate receptors
- Endogenous opiates - endorphins, enkephalins, dynorphin
If pain persists for long time and individual can no longer avoid the pain (fight/flight) body will release endorphins that bind to opioid receptors that are inhibitory. May also bind to brain to help tolerate pain.
different section of ear anatomy
- External ear
- Pinna (funnels sound waves), external auditory meatus and tympanum
- Transmits airborne sound waves to fluid filled inner ear
- Amplifies sound energy
- Middle ear
- Transmits airborne sound waves to fluid filled inner ear
- Amplifies sound energy
- Inner ear
- Houses the cochlea and vestibular apparatus
