L6 - Mechanoreceptors Flashcards
What is sensory transduction?
External or internal stimulus converted to electrical signals in neurons
What nerves are found at the epidermis?
Free nerve endings which have pain, cool & warn receptors
4 main nerve endings in skin, from deepest to most superficial
- Pacinian corpuscle - highly sensitive (lowest mechanical stimulation threshold) encapsulated ending surrounded by connective tissue that forms a sponge around the outside. These are known as vibration detectors (rapidly adapting) that have large receptive fields & stop firing after first activation, staying silent until stimulus is removed.
- Ruffini endings - slowly adapting receptors
- Merkel cell complexes - slowly adapting receptors (sit on base of skin, less sensitive, higher resolution, small receptive fields). Fires continuously throughout the stimulus as their axons have many branches
- Meissner corpuscles - rapidly adapting (but less rapidly and less sensitive than Pacinian corpuscles). Fires AP at the start& ends of the stimulus
Which nerve ending encode the Braille pattern?
The slowly adapting Merkel’s discs. Their axons give rise to discrete stimuli as a result of each embossment. These give a high signal to noise ration. Other types of afferent encode different aspects of the stimulus but does not allow understanding of the message.
3 Types of Mechanoreceptor axon in skeletal muscle
- Muscle spindles (1A) encode length/stretch, via generator potentials like those of cutaneous afferents (in parallel sensory system). STATIC response e.g. knee-jerk reflex
- Golgi tendon organs (1B) encode tension, via generator potentials like those of cutaneous afferents (in series sensory system). DYNAMIC response. It is involved with reflex inhibition.
- Muscle spindles can be turned on by activity in gamma motor neurons (change rate of adaptation)
Which are the most rapidly conducting axons of the body?
Golgi tendon organ axons
Two different sensations in the ear are? What do they detect? What do the other structures involved do?
Hearing & Balance where vibrations will reach the tympanic membrane which lead to the detection of movement via hair cells in cochlea or semicircular canals.
All other structures are involved in the amplification of vibrations in the air into the fluid filled chamber of the cochlea with minimal energy loss.
When the Malleus, Incus and Stapes are vibrated by the tympanic membrane, this moves fluid around inside the cochlea and the semi – circular canals.
• The cochlea is for hearing.
• The semicircular canals are for balance.
Are detectors in the ear neurons?
No they are hair cells
Kinocillium?
Tallest tip of hair cell (cilium)
Tip link?
How the tip of one cilium connects with the tip of another
How do we get the mechanosensory transduction process?
If tip link is stretched
Within the cochlea is a structure centred around the tectorial membrane, which slides back and forth in accordance with the vibration which is connected to the kinocilium. There is an inner hair cell and three outer hair cells.
o Only the inner hair cell transduces information & the axons that end on it
o Changes in membrane potential in the outer hair cells tune the system so that they change the way that the inner cell responds.
o Depolarisation of the outer hair cells alters the physical deformation of the inner hair cells.
o The outer hair cells use efferent innervation axons from the brain, which change the properties of the outer hair cells and hence the inner hair cells.
o A reason for this is so that when we vocalise, we do not deafen ourselves to the sound of our own voice, by reducing our ear’s sensitivity to sound.
o Could be why our recorded voice sounds different to our voice
Within the cochlea is a structure centred around the tectorial membrane, which slides back and forth in accordance with the vibration which is connected to the kinocilium. There is an inner hair cell and three outer hair cells.
o Only the inner hair cell transduces information & the axons that end on it
o Changes in membrane potential in the outer hair cells tune the system so that they change the way that the inner cell responds.
o Depolarisation of the outer hair cells alters the physical deformation of the inner hair cells.
o The outer hair cells use efferent innervation axons from the brain, which change the properties of the outer hair cells and hence the inner hair cells.
o A reason for this is so that when we vocalise, we do not deafen ourselves to the sound of our own voice, by reducing our ear’s sensitivity to sound.
o Could be why our recorded voice sounds different to our voice
If you lose the tip link, if they are damaged, can they grow back?
No, hence loud sounds damage one’s ability to hear.
Where are the ion channels located?
At the tip link
Extracellular space in the region around the techtorial membrane is high in _ and low in _?
High in K+ and low in Na+ (opposite of how it “usually” is).
