Sensory receptors Flashcards
What are sensory receptors?
Nerve endings often with specialised non-neural structures.
Transducers that convert forms of energy into APs.
Inform CNS about internal and external environment.
What are Mechanoreceptors?
Stimulated by mechanical stimuli - pressure, stretch, or deformation.
Detect many stimuli - hearing, balance, blood pressure and skin sensations of touch and pressure
What are Proprioreceptors?
Mechanoreceptors in joints and muscles that signal information related to body or limb position.
What are Nocireceptors?
Respond to painful stimuli - tissue damage and heat
What are thermorecpetors?
Detect warmth and cold.
What are chemoreceptors?
Detect chemical changes eg pH, pO2 and pCO2.
What are photoreceptors?
Respond to particular wavelengths of light.
What are the functions of cutaneous mechanoreceptors and proprioreceptors?
Process peripheral signals.
All transduction involves opening or closing of ion channels.
What is the frequency of 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 is adaptation?
Some mechanoreceptors ADAPT to a maintained stimulus and only signal change. It responds only to a change or a novel event. E.g onset of a stimulus.
What receptors do not adapt?
Nocireceptors because its important not to ignore a painful stimuli.
What is a Pacinian corpuscle?
Mechanoreceptor.
Myelinated nerve with a naked nerve ending, enclosed by a connective tissue capsule of layered membrane lamellae separated by fluid (onion).
Describe how the Pacinian corpuscle responds?
- A mechanical stimulus deforms the capsule and nerve ending.
- This stretches the nerve ending and 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 rapid adaptation?
Fluid redistribution in the capsule – rapidly dissipates stimulus - removes mechanical stretch of nerve ending – APs stop firing.
Withdrawal of the stimulus - capsule springs back - AP fire again.
What is a receptive field?
A specific area in which a somatic sensory neuron is activated by a stimuli.
What 2 factors determine our ability to tell 2 different ares of skin apart?
Receptor field size.
Neuronal Convergence.
What is convergence?
Multiple presynaptic neurons input on a smaller number of post-synaptic neurones.
What is the 2 point discrimination test?
Distance between points adjusted until you just perceive 2 points rather than one.
What is acuity?
The ability to locate a stimulus on the skin and differentiate it from another closeby.
What allows us to locate a stimulus precisely?
Lateral inhibition of surrounding sensory neurones increases the contrast between relevant and irrelevant information.
What are some examples of proprioreceptors?
Muscle spindles – which monitor muscle length and rate of change of muscle length and so they control reflexes and voluntary movements.
Golgi tendon organs - monitor tension on tendons,
tension is produced by muscle contraction, so monitoring muscle tension.
Joint receptors - monitor joint angle, rate of angular movement and tension on the joint.
What are the 3 main functions of Proprioreceptors?
Control voluntary movement.
Drive spinal cord reflexes.
Perceive limb and body position/movement in space.
What are muscle spindles?
Capsulated intramural fibres with specialised sensory and motor innervation. They lie parallel to muscle fibres.
What is then relevance of gamma innervation of muscle spindles?
If not present, then when muscle contracts, muscle spindle would be floppy and spindle discharges could stop.
The brain would not be informed about muscle length.
A lack of information flow to the brain about muscle length could prevent use of that muscle.
