Sensory Receptors Flashcards
What are sensory receptors?
- Nerve endings, often with specialised non-neural structures
- Transducers which convert different forms of energy into the frequency of action potentials
- They inform the CNS about the external and internal environment.
What is meant by sensory modality?
This is the type of stimulus that acts on a particular receptor
What is adequate stimulus?
This is the form of energy to which a receptor generally responds.
What are the 6 main types of sensory receptor?
- Mechanoreceptors
- Proprioceptors
- Nociceptors
- Thermoreceptors
- Chemoreceptors
- Photoreceptors
What are mechanoreceptors?
Receptors stimulated by mechanical stimuli (e.g. pressure, stretch or deformation)
What are proprioceptors?
Mechanoreceptors within joints and muscle which signal information about body and limb position.
What are nociceptors?
Receptors which respond to painful stimuli (e.g. heat and tissue damage)
What is meant by the receptor/ generator potential?
Graded potential formed by the opening of ion channels due to adequate stimulus.
If it reaches a threshold, it will cause the formation of an action potential.
What is adequate stimulus for cutaneous mechanoreceptors and proprioceptors?
Membrane deformation
What is meant by accessory structures on receptors?
Non-neural structures to which they are attached.
In cutaneous receptors, these structures play a large part in determining what sort of stimulus a receptor will respond to.
What are Pacinian Corpuscles?
Receptors attached to hair follicles. Sense Vibrations
What are Merkel’s receptors?
Receptors which sense steady pressure and texture.
What are Meissner’s Corpuscles?
Receptors which sense fluttering and stroking movements.
What are Ruffini Corpuscle’s?
Receptors which detect stretching of skin
Describe the process of adaptation for mechanoreceptors.
Initially, a mechanical stimulus is of large enough intensity to cause a generator potential above stimulus, generating an action potential.
Stimulus intensity remains constant but generator potential declines and, once it drops below threshold, action potentials stop firing.
What type of receptors do not adapt?
Nociceptors
Describe the structure of the Pacinian Corpuscle?
Myelinated axon with naked nerve ending, surrounded by a capsule of connective tissue, layered into lamella which are separated by fluid.
Describe the mechanism of action potential formation in the Pacinian Corpuscle.
Mechanical stimulus deforms the capsule of layer lamella and so deforms the nerve ending.
Stretching of the nerve ending opens ion channels.#
Sodium ions diffuse into the nerve ending, causing local depolarisation- generator potential.
This generator potential strength is proportional to stimulus intensity.
If generator potential reaches threshold, action potential fires in myelinated axon.
What is meant by neuronal convergence?
Multiple pre-synaptic neurons synapsing with a single post synaptic neuron.
What is meant by acuity?
The ability to differentiate one stimulus from another in close range.
What is the function of muscle spindle?
Monitor muscle length and rate of change of muscle length.
What is the function of Golgi tendon organs?
To measure tension on tendons
What produces tension on tendons?
Muscle contraction
What type of neurons innervate intrafusal muscle fibres?
Gamma motor neurons
What type of neurons innervate extrafusal muscle fibres?
Alpha motor neurons
Give one advantage of convergence of primary sensory neurons onto secondary neurons.
Allows summation of sub- threshold potentials, forming an action potential in the secondary neuron.
Give one disadvantage of convergence of primary sensory neurons onto secondary neurons.
Creates a larger sensory receptor field and so a relatively insensitive area. It makes it hard to distinguish one point of stimulus from another (low acuity)
What is the difference between how muscle spindle and golgi tendon organs operate in respect to muscle position?
Muscle spindle operates in parallel to the muscle fibre.
Golgi Tendon organ operates in series to the muscle fibre.
What re the two types of intrafusal fibres?
Nuclear bag fibres
Nuclear chain fibres
How does the spindle fibre contract?
Only the ends of intrafusal fibres contain contractile sarcomeres.
Gamma motor neurons innervate these ends of the intrafusal fibres
Muscle contraction causes gamma motor neurons to activate contraction of spindle fibres to match muscle length.
