Sensory systems Flashcards
What are the different types of sensory receptor?
Mechanoreceptors - touch
Chemoreceptors - chemical shit
Thermoreceptors - heat
Nociceptors - pain (dont call them pain receptors though)
Proprioceptors - joint movement and all that stuff
Probably some others but i cba
What are the different types of sensory receptors that are found?
identify them on the photo below
A - Meissner’s corpuscle - Light touch
B - Merkle’s corpuscle - Touch
C - Free nerve ending - Pain
D - Pacinian corpuscle - Deep pressure
E - Ruffini corpuscle - Heat
How do different types of sensory receptors differ in terms of their complexity of structure?
Some are simple (free nerve endings) such as nociceptors, cold receptors
Some have much more complex structures that you need to know - eg Pacinian corpuscles (Deep pressure) & Meissner’s corpuscles (light touch)
What is meant by the term ‘transduction’ when talking about sensory receptors
Adequate stimulus will cause sensory receptors to transduce it into a depolarisation
This depolarization is called the Receptor (or Generator) potential
The size of the receptor potential encodes the intensity of the stimulus
How do receptor potentials travel through the body?
Adequate stimulus = receptor potential produced
The receptor potential then evokes the firing of action potentials which travel in the body
The frequency of these APs encodes the intensity of the stimulus
What is the receptive field?
Receptive field is a portion of sensory space that can elicit neuronal response when stimulated
Ie its the area corresponding to a specific nerve - this allows us to pinpoint the location that a stimulus acts on us
Shown below are membrane potential readings from different parts of a neuron when stimulated in 2 different ways
What is the difference between the 2 stimuli and how?
The top stimulus - Shorter & weaker:
- Smaller receptor potential indicates lower stimulus intensity
- Lower frequency of action potentials = low stimulus intensity
- Lower duration of AP series = shorter duration
Bottom stimulus - Longer & more intense:
- Receptor potential longer with more depolarisation
- Action potentials have higher frequency and the series of APs lasts longer
Some areas of the skin have lots of sensory receptors with small receptive fields
Some have few receptors with large visual fields
How is this relevant to acuity?
Lots of receptors with small areas they cover = high acuity. You can distinguish between 2 stimuli at a pretty short distance from each other
In order to distinguish 2 points from each other - each point must stimulate a different receptive field
What are the 3 types of primary afferent fibres that transmit cutaneous signals?
Aβ
- 2nd Largest myelinated fibres
- 30-70 m/s
- Touch, pressure, vibration
Aδ
- Smallest myelinated fibres
- 5-30 m/s
- Cold, “fast” pain, pressure
C
- Unmyelinated
- 0.5-2 m/s
- Warmth, “slow” pain
What types of primary afferent fibres mediate proprioceptive sensation?
Aα
Aβ
eg muscle spindles, golgi tendon organs etc
Where do primary afferent fibres enter the CNS?
Either enter through dorsal root ganglia or cranial nerve nuclei
What types of fibres correspond to mechanoreceptive information and how do these travel through the CNS?
Aα & Aβ - mechanoreceptive fibres
Project straight up through ipsilateral dorsal columns
Synapse in cuneate & gracile nuclei
2nd order fibres cross over midline (decussate) in the brain stem & project to reticular formation, thalamus and cortex
How do nociceptive and thermoreceptive fibres travel through the CNS?
Aδ & C
synapse in the dorsal horn
the 2nd order fibres cross over the midline in the spinal cord
project up through the contralateral spinothalamic (anterolateral) tract to reticular formation, thalamus and cortex
In the diagram below, identify the sensory modalities and fibre types that correspond to that diagram
Left:
- Mechanoreceptors - Aα & Aβ
Right:
- Nociceptors & thermoreceptors - Aδ & C
What would be the effect on sensation of damage to the:
A) Dorsal columns
B) Anterolateral quadrant
A) causes loss of touch, vibration, proprioception below lesion on ipsilateral side
B) causes loss of nociceptive & temperature sensation below lesion on contralateral side
What is meant by ‘adaptation’
When a stimulus is applied - sensory receptors will transduce it and action potentials are produced
If a stimulus is applied over a long period of time - certain receptors will adapt to the stimulus and will stop firing action potentials until the stimulus is removed or changes
This is why you cant feel your clothes touching you unless you move - as the mechanoreceptors adapt
What spicy thing can happen here involving nociceptive and mechanoreceptive transmissions?
This synapse acts as a gate for Nociceptive (pain) information
Transmission of Mechanoreceptive information up the A(beta) will inhibit the Nociceptor fibre at its synapse in the dorsal horn (stopping the pain transmission)
This is through a small branch that goes off the Mechano fibre at the site of the Nocic. synapse
That’s why rubbing/holding an injured area can make it feel better
What is meant (for all this pain stuff) by descending control?
As well as Mechanorecptive inhibition - Descending controls come from the periaqueductal grey matter (PAG) which sends impulses to the Nucleus Raphe Magnus (NRM)
Neurones from the NRM travel down the spinal cord to near the Nociceptor synapse in the dorsal horn and activate the inhibitory neuron - thus stopping the pain transmission
