Lecture 10-12 - Somatosensory System

Question 1

What are muscle spindles?

Answer 1

Specialized sensory receptors found in skeletal muscle that provide feedback on muscle stretching to the CNS

Question 2

What is another name for skeletal muscle fibres?

Answer 2

Extrafusal muscle fibres

Question 3

How are intrafusal and extrafusal muscle fibres organized?

Answer 3

they run in parallel

Question 4

What are intrafusal fibres?

Answer 4

non-force producing muscle fibres that lengthen and stretch with changes in muscle length

Question 5

What are afferent axons?

Answer 5

innervate sensory endings of muscle spindle and send feedback to spinal cord

Question 6

What are efferent axons?

Answer 6

gamma MNs innervate polar ends (contractile) of intrafusal fibers and send excitatory inputs from the spinal cord

Question 7

What do sensory endings do in a muscle spindle do?

Answer 7

sense length of intrafusal muscle fibres

Question 8

Does the middle (central) part of a muscle spindle contract?

Answer 8

No

Question 9

What is the capsule of a muscle spindle?

Answer 9

connective tissue surrounding intrafusal fibers and receptors that compose the spindle

Question 10

What are extrafusal fibres?

Answer 10

fibres that cause muscle contraction

Question 11

What do gamma motor neuron endings do in a muscle spindle?

Answer 11

stimulate intrafusal muscle fibres

Question 12

What afferents wrap around all types of intrafusal endings?

Answer 12

primary afferents ( group Ia)

Question 13

What is a primary afferent and the intrafusal fibres it wraps around called?

Answer 13

muscle spindle primary ending

Question 14

What afferents make ‘flower spray endings’?

Answer 14

Secondary (group II)

Question 15

What is the secondary afferent and the intrafusal fibres it contacts called?

Answer 15

muscle spindle secondary ending

Question 16

What are the two major categories of intrafusal muscle fibres?

Answer 16

Bag and chain

Question 17

How are bag intrafusal fibres arranged?

Answer 17

nuclei arranged In a central ‘bag’ region

Question 18

How are chain intrafusal fibres arranged?

Answer 18

nuclei arranged along a straight ‘chain’

Question 19

How do mechanically gated ion channels in muscle spindles work?

Answer 19

Cytoskeletal strands bind ion channels together so as muscles stretches the strands becomes stiff and pull on the ion channels so they open allowing more Na+ to enter the cell. Larger stretches lead to larger receptor potentials

Question 20

What does the firing rate of muscle spindles correspond to?

Answer 20

Changes in muscle length

Question 21

What provides the CNS with a sensory input proportional to the length of the muscle?

Answer 21

Difference in the firing rate between the initial and final length of the muscle

Question 22

What provides the CNS with a sensory input proportional to the velocity of muscle stretch?

Answer 22

Difference in firing rate of muscle spindles during the dynamic phase (when the muscle is being stretched) of muscle stretch

Question 23

What do chain type intrafusal muscle fibres do?

Answer 23

Measure muscle length

Question 24

What do bag type muscle fibres do?

Answer 24

Measure the dynamic phase of muscle stretch “velocity of stretch”

Question 25

What nerve endings are more sensitive to the dynamic phase of movement (velocity of stretch)?

Answer 25

Primary endings

Question 26

What does the firing rate of primary endings during the dynamic phase closely correspond to?

Answer 26

the velocity of muscle stretching

Question 27

What do higher velocities result in?

Answer 27

Larger dynamic responses

Question 28

What are secondary endings sensitive to?

Answer 28

Muscle length

Question 29

What type of nerve endings are useful for proprioception?

Answer 29

secondary endings

Question 30

what type of nerve endings are useful for kinesthesia?

Answer 30

primary endings

Question 31

What would happen without Gamma MNs?

Answer 31

if the muscle were to contract to a shorter length, the intrafusal fibres would become slack and the spindle would stop providing feedback about where the limbs are

Question 32

Why do we have gamma MNs?

Answer 32

To make sure that the length of the muscle spindle is the same as the length of the muscle and allows the muscle spindle to keep responding during contractions

Question 33

What is alpha-gamma co-activation?

Answer 33

Alpha MNs and Gamma MNs are activated together, they receive the same input so muscles stay the same length. Thought to occur because the same motor commands coming from the cerebral cortex connect both the alpha and gamma MN in the spinal cord.

Question 34

What do muscle spindles play an integral role in?

Answer 34

Proprioception and kinesthesia

Question 35

What is prorioception?

Answer 35

Our bodies understanding of where it is in space

Question 36

What is kinesthesia

Answer 36

our brains understanding of movement

Question 37

What is mechanotransduction?

Answer 37

Mechanical energy gets converted into a voltage change in sensory afferent neurons

Question 38

What is another name for EPSP?

Answer 38

receptor potential

Question 39

What is a cutaneous receptive feild?

Answer 39

region of the skin that is capable of evoking action potentials in a given cutaneous afferent (all cells and part of skin that are innervated by one axon)

Question 40

What is non hairy skin?

Answer 40

"glabrous" skin

Question 41

How many types of receptors are located in glabrous skin?

Answer 41

4

Question 42

Where are type 1 cutaneous receptors found?

Answer 42

Close to surface of skin (superficial)

Question 43

What are the 2 type 1 cutaneous receptors?

Answer 43

Meissner and Merkel cell

Question 44

Are merkel cells slow or fast adapting?

Answer 44

slow

Question 45

What is the fast adapting type 1 cutaneous receptor?

Answer 45

Meissner's corpuscle

Question 46

What type of cutaneous receptors are Ruffinin endings and pacinian corpuscles?

Answer 46

Type 2s (deep)

Question 47

What is the slowly adapting type 2 cutaneous receptor?

Answer 47

Ruffini endings

Question 48

Are pacinian corpuscle fast or slow adapting?

Answer 48

fast adapting

Question 49

What is the ranking of most (lowest threshold) --> least (highest threshold) sensitive to indentation?

Answer 49

1. Pacinian 2. Meisner 3. Merkel 4. Rufinni

Question 50

Which cutaneous receptor has irregular discharge (uneven spacing between AP's) when stimulated?

Answer 50

Merkel Cells (SA1)

Question 51

Which cutaneous receptors are highly sensitive to edges and curvature?

Answer 51

Merkel cells

Question 52

What are ruffini endings very sensitive to?

Answer 52

Skin stretch

Question 53

Are ruffini endings found in non-human primates?

Answer 53

No

Question 54

Which cutaneous receptor codes for velocity of skin indentation and motion across skin?

Answer 54

Meissner corpuscles

Question 55

What is the main cutaneous receptor found in the hand?

Answer 55

Meissner corpuscles

Question 56

Are meissner corpuscles sensitive to low or high frequency vibration?

Answer 56

Low

Question 57

Do fast adapting cutaneous receptors constantly fire APs?

Answer 57

No, they only fire when there is a change in stimulus

Question 58

What do Pacinian corpuscles code for?

Answer 58

acceleration (change in indentation rate)

Question 59

What type of frequencies do pacinian receptors pick up?

Answer 59

high frequencies

Question 60

Do deep (type 2) receptors have smaller or larger receptive fields?

Answer 60

Larger

Question 61

Why do type 1 receptors have smaller receptive fields?

Answer 61

they have more than 1 cell attached to a axon

Question 62

Where in the hand are Merkel and Meissner recepetors highly dense?

Answer 62

The tip of the finger

Question 63

What type of cutaneous receptors are more evenly distributed in the hand?

Answer 63

Pacinian and ruffini

Question 64

What are the functional roles of merkel cells?

Answer 64

Edges, curvature and texture

Question 65

What are the functional roles of Meissner corpuscles?

Answer 65

slip/motion detection and grip control

Question 66

What is cutaneous receptor is responsible for detecting skin stretch?

Answer 66

Ruffini endings

Question 67

What cutaneous receptor is responsible for feeling vibration through objects and perception of fine texture?

Answer 67

Pacinian corpuscles

Question 68

What is spatial code?

Answer 68

The CNS can determine the location of stimuli based on which afferents specifically are active

Question 69

Which type or cutaneous receptors code for spatial details (size and shape of objects)?

Answer 69

SA1's

Question 70

What happens when you are probed with a small probe?

Answer 70

High discharge rate in few afferents

Question 71

What happens when you are probed with larger probe?

Answer 71

Individual receptors fire less, but more afferents will be active

Question 72

What is a nociceptor?

Answer 72

Pain receptor (is a chemoreceptor)

Question 73

What do nociceptors signal for?

Answer 73

Tissue damage

Question 74

If you were to put your hand on hot stove when would the nociceptors become active?

Answer 74

Once the heat becomes tissue damaging

Question 75

How do thermally gated receptors work?

Answer 75

Heat deforms protein channels allowing it to open

Question 76

T/F: Thermoreceptors are active at lower temperatures than pain receptors

Answer 76

true

Question 77

Why are spicy food hot?

Answer 77

Capsaicin which is found in spicy food is lipid-based and passes right through the cell membrane. It attaches to VR-1 receptor and opens channel thus artificially creates the sensation of heat

Question 78

Where do GTO's attach?

Answer 78

Attache to muscle fibres and tendon

Question 79

Is there 1 or multiple muscle fibres per GTO?

Answer 79

multiple

Question 80

What are GTOs innervated by?

Answer 80

type 1b afferent

Question 81

What are GTOs very sensitive to?

Answer 81

active force production

Question 82

What is the relationship between GTO firing rate and force output?

Answer 82

linear relationship

Question 83

What are the 4 types of joint receptors?

Answer 83

1. Ruffini endings 2. Pacinian corpuscles 3. Golgi Endings 4. Free nerve endings

Question 84

What do ruffini endings in the join code for?

Answer 84

joint position and intra-articular pressure

Question 85

What joint receptor codes for high frequency joint acceleration?

Answer 85

pacinian corpuscles

Question 86

What do golgi endings code for?

Answer 86

tension in ligaments, mainly at ends of ROM

Question 87

What joint receptors code for tissue damaging stimuli?

Answer 87

Free nerve endings

Question 88

Can joint receptors tell the difference between pressure, flexion/extension and intorsion/extorsion?

Answer 88

No

Question 89

Are joint receptors activated in all directions?

Answer 89

Yes

Question 90

What are joint receptors most useful for?

Answer 90

Knowing where we are at ends of ROM (joint position)

Question 91

Do joint angles give us info on joint angle?

Answer 91

No

Question 92

What amount of joint receptors increase their discharge with on direction of joint rotation?

Answer 92

1/4

Question 93

Are joint receptors useful for proprioception?

Answer 93

No