Sensory System Flashcards
What are tonic receptors?
Tonic receptors are slow adapting receptors. They will respond to the stimulus as long as it persists, and produce a continuous high frequency of action potentials.
What are phasic receptors?
Phasic receptors are rapidly adapting receptors. They will respond quickly to stimuli but stop responding upon continual stimulation. Therefore action potential frequency decreases during prolonged stimulation. The receptor remains sensitive to a change in stimulus energy or removal of the stimulus.
What are nociceptors?
Nocioceptors are phasic receptors, which respond to noxious stimuli (stimuli that would cause tissue injury if they were to persist) and result in the sensation of pain.
What types of fibres carry pain?
type Aδ fibres and type C fibres that transmit the pain sensation.
How can receptors be categorised?
Mechanical – stimulated by the distension of skin (stretch) and pressure eg. in inflammation
Thermal – stimulated by extremities of temperature
Chemical – stimulated by exogenous and endogenous chemical agents, such as prostanoids, histamines etc
Polymodal – can respond to more than one stimuli
Where are mechanoreceptors found and what do they respond to?
These are located in joint capsules, ligaments, tendons, muscle and skin, and respond to deformation by the means of pressure, touch, vibration or stretch.
Give examples of mechnoreceptors?
Merkel's discs Meissner's corpuscle Pacinian corpuscle Ruffini end-organs Muscle spindles and Golgi tendon organs
Describe Merkel’s discs
These are tonic receptors present in skin, near the border of the dermis and epidermis. They respond to pressure and help to differentiate texture and shape of objects.
Small receptive field, slowly adapting. Sense gentle pressure.
Describe Meissner’s corpuscles
These are phasic present in the dermis of the skin skin, namely on the palms of the hands, soles of the feet, lips and tongue. Consisting of Aβ fibres, they enable two-point discrimination- fine touch.
Small receptive field, rapidly adapting. Sense slower vibration and light touch
Describe Pacinian corpuscles
These phasic receptors that also consist of Aβ fibres, and are the largest category of mechanoreceptors. They respond to pressure changes and vibration. They exist places such as: the dermis, hypodermis, ligaments and external genitalia
Large receptive field, rapidly adapting. Found deep in dermis. Sense fast vibration and gross pressure changes.
Describe Ruffini end organs
These are tonic receptors present in the dermis and respond to stretch
Large receptive field, slowly adapting. Sensitive to skin stretch, sustained pressure
Describe muscle spindles and golgi tendon organs.
These exist in skeletal muscle and detect sensory stimuli relating to stretch. Input is responsible for reflexes and motor control via the cerebellum. It is also transmitted to the DCML component of the spinal cord, reaching the cerebral cortex and provides information about posture, position and orientation
What do Krause end bulbs detect?
Thermoceptors - head and cold
Mucus membranes and joints
How is sensory acuity determined?
the size of the receptive field – acuity is higher with a smaller receptive field (and acuity is enhanced by lateral inhibition via inhibitory interneurons).
