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
What is the stretch reflex
Stretch reflex is a contraction of a muscle evoked by stretch. Mediated by 1A input from spindles, and involves a single synapse contracting the agonist muscle
What is the response time of a stretch reflex?
Response latency 20-40ms, biceps 22ms but legs have a lot longer of a pathway
Describe 1A afferent divergence
1A afferent nerve separates and synapses onto other motor neurons, either homonymous or heteronymous
Define homonymous and heteronymous
Homonymous= muscle being stretched
Heteronymous = antagonist muscle that is relaxing
Describe Reciprocal inhibition
Reciprocal inhibition is the switching of the sign to inhibit antagonist muscles instead of excite them.
Describe 1b inhibition (convergence)
Inhibits the agonist muscle to prevent injury of the agonist muscle, and involves at least two synapses. Receives information from joint afferents, cutaneous afferent, descending inputs.
What is the pathway of 1b inhibition?
Agonist afferent EPSP —> 1b inhibitory neuron —> IPSP agonist motoneuron
What is GTO facilitation
Facilitation via inhibition of an inhibition, which results in a decreased EPSP signal that isn’t too strong for an antagonist muscle
What is the pathway for GTO facilitation?
Agonist 1b afferent EPSP—> 1b inhibitory neuron IPSP —>
A. —> agonist motoneuron
B. —> interneuron —> antagonist motoneuron
How do we keep motoneurons on when they are getting blasted by inhibition?
There are so many things to talk to, that they are always stimulated. They get information from joint afferent, cutaneous afferents, descending inputs like convergence
What kinds of inputs modulate reflex responses?
Peripheral and descending inputs
Define renshaw cell
Renshaw cell is an interneuron in the spinal cord that connects right back to the cell body that turned it on. It drops IPSP onto a motoneuron
- activated by collateral from motoneurons
Why are renshaw cells important?
Because of the refractory periods for neurons, it allows them to have a break before it is turned on again
The renshaw cell connection is ________
Strong
Describe the pathway of the renshaw cell
Renshaw cells hit both the agonist and antagonist, relieving the activity of both through inhibition (agonist) and inhibition of inhibitory neuron (antagonist)
What cells are both inhibitory and excitatory?
Renshaw cell, idk about anything els
Describe the flexor and crossed extension reflex
Flexor reflex - activates flexors, inhibits extensors. Acts as a protective reflex and coordinates activation of flexor muscles
Crossed extension reflex - activates extensors, inhibits flexors
Describe presynaptic inhibition
Presynaptic inhibition is selective inhibition of the presynaptic neuron. It drops the amount of neurotransmitters that are spit out, changes the membrane potential. It’s a way to dial back the monosynaptic Drive/reflex. Look up a picture, it acts on the terminal of the pre synaptic neuron but does not have the charge directly go to the inhibitory neurons
When you move it is not because you’re turning stuff on, but rather that you’re turning off ______
Inhibition
Describe a longer latency response
Longer latency response is a rapid motor response that occurs between a short latency response and a voluntary response. it is longer than the monosynaptic response, and shorter than voluntary reaction time. It involves parallel spinal and supraspinal pathways.
Which glabrous skin receptors are reliable or unreliable
Merkel cells are very reliable. Meissner’s corpuscles are reliable. Ruffini endings are kind of reliable. Pacinian corpuscles is reliable
Which glabrous skin receptors connected to multiple cells, along with a one to one connection
Meissner’s corpuscles axons connect to multiple cells. Ruffini endings have one axon per ending.
What percentage of Ruffini endings have a background discharge. Where in the body do none of them have background discharge?
30%, the foot
Which receptor is not found in nonhuman primates
Ruffini endings
What receptor codes for acceleration of indentation
Pacinian corpuscle
What receptor can follow vibrations up to ___ Hz
Pacinian, 400 Hz
Describe the firing rate of Pacinian corpuscles during oscillation
Pacinian corpuscles fire for every single oscillation of the stimulus
What does pulling on tendons do?
Activate muscle spindles. The subject feels like a body part has moved in such a way as to match the increase in muscle spindle discharge
What do pressure on undergarments do?
Pressure undergarments and functional need racing hopes to increase proprioceptive awareness, accuracy around a joint, and kinaesthetic awareness during the task
What occurs with more effort
Bigger error in position matching
What occurs in sense of effort? What is the pathway of information
When you move, a copy of the motor command or corollary discharge is sent to sensory centers. Afferent feedback from the movement is then sent to this part of the brain for comparison and error detection. The error is dependent on the effort and not on the position of the limb.
What can explain why movements are not matched when individuals are blindfolded?
It has to do with sense of effort. The motor code is compared with sensory information from muscles. The mismatch between the two results in error.
What is the Hoffman reflex?
The Hoffman reflex is a test to measure the integrity of the spinal cord and peripheral nerves. It also tests the strength of the monosynaptic reflex and is used as a way to measure the level of the motor neuron pool.
What kind of fibres or motor neurons are involved in the Hoffman reflux?
1A and Alpha motor neurons
What does the H wave an M wave represent in the Hoffman reflects?
The M wave is first, and it appears with increased stimulation. It is a direct motor response and represents activation of motor neurons and contraction. Uses only afferent fibres
The H wave is second, and it disappears with increased stimulation. It is the end direct response representing the monosynaptic reflex through the spinal cord. Use afferent and efferent fibres.
Why is it that the M wave grows but the H away decreases with continued stimulation?
It occurs due to anti and orthodramic activation in nerves. (The direction of the impulse)
What causes changes in the Mwave, and what causes changes in the H reflects
The M wave will change with the stimulus. Any changes in the H reflex amplitude could be due to changes in the motoneuron pool or to changes in the level of stimulation
What is important to look at to know that stimulation is it a constant level
The MH ratio
What is the amplitude of the tendon reflex dependent on?
Tap size. The bigger the tap the bigger the volley of spikes from the spindles. Tapping a tendon causes the muscle to stretch slightly. if the tendon is flexed it is not typically activated.
What happens to the reflexes when presented with height threat and anxiety
Often reflexes stay relatively constant, while T reflexes increase. It shows that T reflexes have a bit more of a role in proprioception, and links the response to sympathetic stimulation.
What is autogenic excitation
It enhances the activity of the neuron or circuit itself, and plays a role in amplifying neural responses. It is linked to homonymous muscles
What does the 1A inhibitory interneuron do
Is inhibits antagonist muscles, while exciting agonist muscles
What is autogenic inhibition
A process that inhibits the muscle to relax it, preventing it from muscle damage or excessive force
What is recurrent inhibition
Mechanism wear a neuron sends a signal that inhibits its own activity through a feedback loop. Typically involves Renshaw cells.
What do Renshaw sells cause
Inhibition to the motor neuron pool
What are Renshaw sells Aktivated by?
They are activated by collateral from Alpha motor neurons
What is the connection of presynaptic inhibition
It is an axo-axonal synapse. Resulting in selective inhibition of only the presynaptic neuron.
What occurs in presynaptic inhibition?
A neuron acts on the pre-synaptic neuron of an axle axonal synapse. It reduces the release of neurotransmitters from the presynaptic neuron and does not change the sign of a signal
What do the M1 M2 and M3 waves represent in Reflex responses
The M1 wave represents the short latency response involving only circuitry in the spinal cord
The M2 wave represents the long latency response
The M3 wave represents the cognitive processing?
Of the M1, M2 and M3 waves which are “squashable”
M2 and M3. It shows that are reaction can be altered and tuned. If we ask someone to respond to a force as quick as possible and then ask them to not respond M1 does not change by M2 and M3 go way down
Why were cats used as a model of choice to test spinal control of Loco motion?
Because there’s a huge variance in dog sizes/breeds
What was found after testing spinal control of locomotion by cutting the spinal cord?
They found that many rhythmic movements were still possible in a variety of animals. The circuitry for many of these movements resides in the spinal cord. I found the cats were able to walk with absolutely no efferent information, with no change in AP
What is the half centre model? (CPG)
CPG stands for central pattern generator, which are neural circuits that produce rhythmic outputs without sensory feedback. It consists of two groups of neurons that reciprocally inhibit each other, create an alternative actively patterns. When the first one fires, it inhibits the second one, resulting in the first discharging action potentials while the second does not. Then, when the second is firing, the first is not. It results in this isolation between the two neurons and allows for smooth contractions
What sensory information helps us to control phase transitions
Joint receptors = as you put the joint into extension, the joint receptors start a fire. All of the flexors start to scream, so that might be the queue for flexors to start contracting. Joint receptors are compressed when standing, but when walking, the right leg joint receptor gets compressed while the left has nothing.
Pressure = pressure on the foot can tell how much force is being generated by your muscles, and can cue our bodies to what phase we are in
What is the breakdown of what happens when transitioning from standing to walking
Stretch of hip flexors, unloading of GTO, loading through joint receptors, pressure on foot
What is meant by phase dependent reflex reversal
If you stimulate the foot while it is in the air, you get flexion. If you stimulate the foot while it’s on the ground, you get extension. It’s a totally different response but is entirely functional. It is important to keep in mind that this is not a simple flexion extension reflex, stimulation during different states provides different responses
