Sensory Receptors 1-2 Flashcards
Define sensory receptors
They are nerve endings with specialized non-neural structures. They convert different forms of energy into action potentials
Name three types of sensory receptors and their function
1: Mechanoreceptors - React to mechanical stimuli i.e pressure, stretch etc…
2: Proprioceptors - Orientate the limbs and the rest of the body (found in muscles and joints)
3: Nociceptors - Pain receptors
An adequate stimulus on one of these receptors causes what ?
A graded potential (Receptor potential/Generator potential)
Activates stretch sensitive ion channels causing ion flow across the membrane.
The larger the stimulus the larger the ____ and the higher the ____of ____.
What is this known as ?
Receptor potential
Frequency of APs
Frequency coding
What is adaption ?
When mechanoreceptors adapt to a maintained stimulus and only signal change
What shows rapid adaption ?
Mechanoreceptors
What receptor does not show adaption ?
Nociceptors
What are the 2 rapid adapting receptors ?
Pancinian corpuscle
Meissner’s corpuscle
What are the 2 slow adapting receptors ?
include Merkel’s discs and Ruffini endings
What is a pancinian corpuscle ?
a myelinated nerve with a naked nerve ending, enclosed by a connective tissue capsule of layered membrane lamellae separated by fluid (like an onion)
If the capsule was removed from the pancinian corpuscle what would happen to the adaption properties ?
bare nerve ending loses much of adaptation
continues to produce a receptor/generator potential
Our ability to tell 2 points on the skin apart depends on two things, what are they ?
1: Neuronal convergence
2: Large receptive field
Define neuronal convergence
Simultaneous sub-threshold stimuli to sum at the secondary neuron, forming a large secondary receptive field and initiating APs.
What indicates a sensitive area ?
Convergence and a large secondary receptive field
Define acuity
The ability to locate a stimulus on the skin and differentiate it from another close by
What is high and low acuity ?
high acuity: 2 signals go to the brain
low acuity: 1 signal goes to the brain
What is lateral inhibition ?
Where does this occur ?
Information from neurons with sensory receptors at the edge of a stimulus is strongly inhibited, compared with information from the centre of the stimulus.
In the spinal cord for cutaneous information
What does lateral inhibition allow for ?
Allows precise localisation to a single skin hair movement.
Name three types of proprioceptors
Golgi tendon organ
Muscle spindle
Joint receptors
What do these main three forms of proprioceptor do ?
1: They send information to the brain to control voluntary movement.
2: The muscle spindle and GTO send information to the brain to control spinal cord reflexes.
3: They provide sensory information to perceive limb and body position and movement in space.
Muscle spindles lie in ____ to muscle fibres
Parallel
What does a muscle spindle comprise of ?
Extrafusal fibres and intrafusal fibres
What are the two types of intrafusal fibre ?
1: Nuclear bag fibres (Bag chaped and nuclei collected together)
2: Nuclear chain fibres (nuclei lined up in chain)
What do the 1a sensory afferent neurons do to the intrafusal fibre ?
Wrap around the center of the intrafusal fibre thus creating annulospiral endings
The type II sensory afferents do what ?
create flower spray endings by attaching to the non-contractile ends of the muscle fibre
What t=do the gamma motor neurons attach to ?
The contractile ends of the intrafusal fibre
What kind of fibre innervates the GTO ?
1b afferent MN
GTO are in ____ to muscle spindle
series
What happens to the muscle spindle if alpha MNs fire without gamma ?
The extrafusal fibres will contract and the muscle spindle will stay the same length and therefore become slack
What happens when both alpha and gamma fire in conjunction ?
Both the extrafusal fibre and the muscle spindle shorten
DRGs regenerate, true or false ?
False
