Sensory Receptors Flashcards
What are the 3 types of sensory receptors?
Mechanoreceptors
Proprioceptors
Nociceptors
What do mechanoreceptors respond to?
Mechanical stimuli such as pressure or stretch…can detect many stimuli
Transduction in ALL sensory receptors involves …
Opening or closing of ion channels
An adequate stimulus causes?
A graded membrane potential change called a receptor potential or a generator potential
The adequete stimulus in mechanoreceptiors -Membrane deformation activates?
Stretch-sensitive ion channels causing ion flow across the membrane.
The receptor potential is graded accounting to stimulus frequency. T or F
False - its graded according to stimulus intensity
What is the frequency coding of stimulus intensity?
The larger the stimulus, the larger the receptor potential and
the HIGHER THE FREQUENCY of APs in a sensory nerve
What happens in some mechanoreceptors if stimulus persists?
Aps persist
Not ALL the time - e.g we don’t feel our clothes on our backs until we move them or take them off…
What is adaptation in mechanoreceptors?
When they ADAPT to a maintained stimulus and only signal change
Why do nociceptors not show adaptaion?
Important they don’t as we shouldn’t ignore pain
What is the cutaneous Pacinian corpuscle?
The best understood mechanoreceptor
Its a myelinated nerve with a naked nerve ending which is enclosed in a connective tissue capsule of layered lamellae seperated by fluid inbetween
How does the Pacinian corpuscle respond to stimulus?
A mechanical stimulus deforms the capsule and nerve ending
Nerve ending stretches which opens ion channels
Na+ influx causes local depolarisation – a generator potential
APs are generated and fire at the myelinated nerve
How does the Pacinian corpuscle show adaptation?
After the initial response, the fluid in the capsule is redistributed which causes stimulus to dissipate, removing mechanical stretch of nerve ending stopping Aps firing.
When stimulus withdraws - capsule springs back and APs fire again
What happens if the capsule is removed in the Pacinian corpuscle?
Adaptation is lost
Somatic sensory neurons are activated by stimuli in a specific area..this is called?
The receptive field - e.g is touch only responds to area touched
Does convergence of neurons increase or decrease the sensitivity of an area?
Decrease it
So if you had convergence and a a large secondary receptive field..what do you have
An insensitive area
What is acuity?
The ability to locate a stimulus on the skin and differentiate it from another close-by…
High acuity means that two stimulus’s send how many signals to the brain?
Two
Low acuity means that two stimulus’s send how many signals to the brain?
One - perceived as just one stimulus
How can stimulus be so precise - for example with a pencil tip on the finger, how can we locate it so precisely?
Lateral inhibition - Information from afferent neurons with sensory receptors at edge of stimulus is strongly inhibited and
What is the structure of the muscle spindle?
Made of intrafusal fibres and specialised motor and sensory innervation
The ends of these fibres contain sarcomeres and are contractile which are controlled by gamma motoneurones
What is the function of the muscle spindle?
Monitor muscle length
As alpha motor neurones fire they cause contraction of extrafusal fibres causing muscle contraction -
Gamma motorneurons also fire on intrafusal fibres contracting the muscle spindels which restores tension and tells the brain to stop stretching in order to stop muscle ripping itself apart
What is the adequete stimulus for the muscle spindle stretch receptors?
Muscle stretch
As the muscle lengthens, ion channels open and so the length is monitored
How do we know what is happening regarding joint positioning?
Efferent control of spindle function
What is efferent control of spindle function?
Agonist muscle contracts and the spindle contracts so output is decreased.
This causes the antagonistic muscle to lengthen and those muscle spindles increase their outflow of action potentials.
What do the golgi tendon organs do?
Monitor muscle tension
Mechanism of the golgi tendon organs?
The nerve endings are intermingled with the tendons at the ends of muscles.
They act as stretch receptors and monitor the stretch in tendons.
Since tendons are inelastic, the muscles must develop tension to stretch them to stop them ripping off of bone
