Midterm 2 Flashcards
Describe the typical behaviour of a joint receptor, how does it fire according to different stimulus?
Joint receptors fire in an ambiguous fashion, a particular firing rate could mean one of two very different joint angles. They mostly fire at the end of movements and very few are able to code for the middle of the movement.
What is an important role of joint receptors?
Joint receptors play a reflexive role for limiting extreme joint movement, indirectly influencing position/movement sense. They become activated by a muscle contraction and can prevent overextension injuries
What are the five major receptors in glabrous or non-Harry skin
- Merkell cell
- Meissner‘s corpuscles
- Ruffini endings
- Pacinian corpuscles
What receptors are slow adapting?
Merkel cell and Ruffini endings
What receptors are fast adapting
Meissner’s corpuscle’s and Pacinian corpuscles
Which receptors are type one
Meissner’s corpuscles and Merkel cells
What receptors are type two
Ruffini endings and Pacinian corpuscles
Describe the Merkel cell, what are its functions and characteristics
- Slow adapting type one
- highly sensitive to edges and curvature
- Moderately low threshold of 30 XM
- Two types of code one for velocity of push on skin second I don’t know
- Extremely reliable, has an irregular discharge when stimulated and drops neural transmitters to discharge action potential
Draw the discharge frequency of each skin receptor
Describe the Meissner’s corpuscle school, its characteristics and function
- Fast adapting type one
- Important for motion detection and grip control
- codes for velocity of skin indentation and movement across skin
- Sensitive to low frequency vibration around 40 to 50 hz, with a very low threshold of 6XM
-  Axon connects to multiple cells
Describe Ruffini endings, its characteristics and function
- slow adapting type two
- responsible for sensing skin stretch
- Hi threshold of indentation of 300 XM
- One axon per Rafini ending, it is way deep in the dermis and spirals out into different branches - Regular discharge when stimulated, not in nonhuman primates, 30% in a hand have a background discharge but none do in the feet
How do you Ruffini endings sense skin stretch
They are very sensitive to lateral skin stretch, instead of pushing down and stretching the skin that way, the stretch polls on collagen near the receptors therefore pulling on the receptor and sending a discharge
Describe the Pacinian corpuscles, their functions and characteristics
- Fast adapting type two
- important for sensing fine texture
- Picks up high frequencies of 300 to 400 Hz with an extremely low threshold of 0.08 XM
- It is located way down in the dermis, and is very similar to the joint receptors
- Codes for indentation
Define Mecano transduction
Mecano transduction is the process by which mechanical energy gets converted into a voltage change in sensory afferent neurons
Describe how the body senses vibration
Pacinian corpuscles are surrounded by concentrically arranged fluid filled Lamela around the nerve terminal. These receptors are very sensitive to alternating inputs, such as those enduring mechanical vibration, seem to follow vibrations up to approximately 400 Hz. They are found in the skin, joint capsules, during stimulus every time the neuron fires an action potential for every single oscillation of the stimulus.
What happens to our vibration sensitivity as we age?
The fluid filled Lamela around Pacinian corpuscles dries out and we lose the layers, so it does not perform nearly as well and we cannot sense vibration as easily
Define cutaneous receptive field
Cutaneous receptive field is the region of skin that is capable of driving a response in a particular neuron
How does the diversity of glabrous skin receptors change across the hand? What areas of a hand have higher density of what receptors
Tip of the finger: SA1 and FA1
SA1 to and FA2 are more equally distributed
How does the cutaneous receptive field size change across receptors?
Type one receptor fields are very small, type two are very large. Ruffini endings receptive fields line up with the muscle and the shape of the skin
How does probe size affect receptor behavior?
With smaller probe areas we can get higher discharge rates and fewer receptors. With larger probes, individual receptors fire less, but Moer afferent will be active
Describe the spatial code
The spatial code states that curvature of the physical stimulus changes how the receptors respond. The formation of the skin under the receptor changes how it responds. Receptors fire more for a smaller probe head but will utilize less receptors, while large probes will have lower discharge but more receptors activated
How can we classify the different receptors
Receptive field size, adaptation rates, spike train regularity
Write out the image of receptors and the receptive fields, agitation, innervation density, discharge frequency
How do the receptors respond to micro slips
Slips of objects are detected by accelerometers, type two units responded to transient micro slips. Fast adopting type one responds differently to different services, and slippery stuff gets more activity. Seems like primarily meissner
Define kinesthesis versus proprioception
The main difference is that proprioception encompasses the broader sense of position and movement without conscious thought.
Kinesthesis is the ability to perceive the position and movement of one’s own body parts
Proprioception is the unconscious perception of movement and spatial orientation arising from stimuli within the body
What is Tim’s definition of kinesthesis
Involves consciousness and correcting for yourself
What are the four major contributors to kinesthesis
Sense of position/ movement of limbs, tension/force, effort/heaviness and sensations of body image and posture
What are the sources of proprioception/kinesthesis
Muscle spindle = velocity and length of muscle. Two pipelines and has efferent plus afferent
skin = legs and velocity of skin stretch, onset of movement, acceleration
GTO = tension and force
joint. = pressure, contraction sensitivity, reflexes
Describe the early evidence of somato sensory role in proprioception.
Subjects were partially deaffarrenated, and they found that familiar tasks remained. In one experiment, the subject knew how to drive stick before and after the procedure but once he got a new car he couldn’t learn how to drive it.
Guillian Barr syndrome
The disembodied lady
What occurred in the animal model when testing the somatosensory role in proprioception
Animals incurred vitamin B6 toxicity which led to large fibre neuropathy, or the loss of all large proprioceptive units
Describe the relationship between muscle spindles and vibration
The sensation of vibration increases Spindle discharge, which is interpreted as lengthening muscle. This discovery is seen as the first strong piece of evidence to support that muscle spindles play a conscious role in position/movement
Describe the selective removal of skin and joint inputs
If you cut off all the blood flow to the hand, and move the fingers around, we initially thought the proprioceptor’s will be out of whack. But this is not true. The spindles in the forearm able to detect the position of the hand
If you isolate the fingers by either ice chemic block which is a blood pressure cuff around the rest, or by anaesthetic injection into the digital nerves, early experiments demonstrating no major deficit in finger proprioception.
What occurs to joint position sense after total joint replacement
Not much. anaesthetic causes decrease in sensitivity while dextran increases sensitivity. Shows that joint receptors may have some role in proprioception
What receptor codes for finger position and lateral skin stretch
Slow adapting type two
What receptor codes for which joint is moving
Fast adapting type one
How can we imitate movement with stretching skin
If we stretch skin in a similar way that occurs during a movement, it can imitate the movement even when it doesn’t happen
Define reflex
Reflex is an automatic motor response to a sensory stimulus. It is evoked from stimulation of peripheral nerves and it’s circuitry is entirely within the spinal cord, involving sensory neurons, inter neuron and motor neurons
