Somatosensory System

Question 1

Intrafusal fibers

Answer 1

Non-force producing muscle fibers (lengthen and stretch with changes in muscle length)

Question 2

Afferent axons

Answer 2

SENSORY INFO- innervate endings of muscle spindle and send feedback to the spinal cord

Question 3

Muscle spindles

Answer 3

Specialized sensory receptors (provide feedback on muscle stretching to CNS)

Question 4

Efferent axons

Answer 4

MOTOR COMMANDS- yMN’s innervate polar (contractile) ends of intrafusal fibers and send excitatory inputs from spinal cord

Question 5

Gamma motor neuron

Answer 5

stimulates intrafusal muscle fibers

Question 6

Sensory endings

Answer 6

sense length of intrafusal muscle fibers (part of afferent axons)

Question 7

Center of muscle spindle

Answer 7

Non-contractile region

Question 8

Capsule

Answer 8

connective tissue surrounding intrafusal fibers and sensory receptors that compose spindle

Question 9

Extrafusal (skeletal muscle) fibers

Answer 9

Fibers that cause muscle contraction (parallel with intrafusal fibers)

Question 10

Nuclear bag fibres

Answer 10

instrafusal fibres w/ nuclei arranged in a central ‘bag’ region

Question 11

Nuclear chain fibres

Answer 11

intrafusal fibres w/ nuclei arranged along a straight chain

Question 12

primary afferents (group 1a)

Answer 12

wrap around all types (bag/chain) types of intrafusal fibres

Question 13

secondary afferents (group 2)

Answer 13

‘flower spray endings’ onto ONLY nuclear chain type intrafusal fibers

Question 14

Secondary muscle spindle ending

Answer 14

Combination of a secondary afferent and the intrafusal fibres it contacts

Question 15

Primary muscle spindle ending

Answer 15

Combination of a primary afferent and the intrafusal fibres it wraps around

Question 16

Larger stretches of the muscle lead to…

Answer 16

Larger receptor potentials

Question 17

Dynamic phase

Answer 17

when the muscle is being stretched

Question 18

The difference in the firing rate of muscle spindles

Answer 18

provides the CNS with sensory input proportional to the velocity

Question 19

Primary endings are more sensitive to…

Answer 19

the dynamic phase of movement (velocity)

Question 20

Secondary endings are more sensitive to…

Answer 20

muscle length

Question 21

Human microneurography

Answer 21

method of inserting an electrode directly into a peripheral nerve to record action potentials from sensory and motor neurons

Question 22

Do secondary and primary endings respond equally as much to the dynamic phase?

Answer 22

No, primary endings are more responsive to velocity

Question 23

Gamma motor neurons (yMN’s)

Answer 23

stimulated at the same time as the alpha-MN, the intrafusal fibers contract along with the extrafusal (skeletal) muscle fibers WHICH ALLOWSTHE MUSCLE SPINDLE TO KEEP RESPONDING DURING CONTRACTIONS

Question 24

Without yMN

Answer 24

the spindle would stop providing feedback where your limbs are (floppy/slack fibers)

Question 25

Co-activation

Answer 25

when alpha (extrafusal) and gamma (intrafusal) motor neurons respond together (same message from CNS)

Question 26

Proprioception

Answer 26

our bodies understanding of where it is in space (position)

Question 27

Kinesthesia

Answer 27

our brains understanding of movement (basically proprioception of movement)

Question 28

Mechanotransduction

Answer 28

mechanical stimulus (energy) is converted to electrical info (voltage change) in sensory afferent neurons

Question 29

cutaneous receptive field

Answer 29

region of the skin capable of evoking action potentials in a given cutaneous afferent

Question 30

non-hairy skin

Answer 30

glabrous

Question 31

Type 1 cutaneous receptors are...

Answer 31

superficial

Question 32

Type 2 cutaneous receptors are...

Answer 32

deep

Question 33

Which receptors are slow adapting?

Answer 33

Merkel cells and Ruffini endings

Question 34

Which receptors are fast adapting?

Answer 34

Meissner's corpuscles and pacinian corpuscles

Question 35

Place the receptors in order from most sensitive to indentation to least

Answer 35

1) Pacinian corpuscles (FA2) 2) Meissner's corpuscles (FA1) 3) Merkel cells (SA1) 4) Ruffini endings (SA2)

Question 36

If a receptor has a low mechanical threshold what does this imply?

Answer 36

It is easily activated and sensitive to indentation (force)

Question 37

Which receptor is known for irregular discharge when stimulated?

Answer 37

Merkel cells (SA1)

Question 38

Qualities of Merkel cells (SA1)

Answer 38

-irregular discharge when stimulated -highly sensitive to edges/curvature -30um threshold

Question 39

Qualities of Ruffini endings (SA2)

Answer 39

-regular discharge -very sensitive to skin stretch -high (300um) threshold -NOT IN NON-HUMAN PRIMATES

Question 40

Slow adapting receptors will...

Answer 40

continue to fire until stimulus is removed

Question 41

Fast adapting receptors will...

Answer 41

adapt to changes in indentation (held stimulus will stop firing)

Question 42

Qualities of Meissner's corpuscle (FA1)

Answer 42

-codes for velocity of skin indentation (motion) -40% of innervation in hand -sensitive to low frequency vibration (30-50Hz) -6um threshold

Question 43

Qualities of Pacinian corpuscle (FA2)

Answer 43

-codes for ACCELERATION (change in indentation rate/velocity) -picks up high frequencies (50-500Hz) -extremely low threshold (0.08um)... most sensitive to indentation

Question 44

Type 1 receptors have _______ mechanoreceptor(s)/hotspots per axon

Answer 44

multiple

Question 45

Type 2 receptors have _______ mechanoreceptor(s)/hotspots per axon

Answer 45

one

Question 46

Which type of receptor has larger receptive fields?

Answer 46

Deep (Type 2)

Question 47

Which type of receptor has a higher innervation ratio?

Answer 47

Superficial (Type 1)

Question 48

Which receptors are highest in density on the tips of fingers?

Answer 48

SA1 and FA1

Question 49

Which receptors are equally distributed?

Answer 49

SA2 and FA2

Question 50

What do merkel cells (SA1) respond most to?

Answer 50

Edges, curvature, and texture

Question 51

What do Meissner's corpuscles (FA1) respond most to?

Answer 51

slip/motion detection, grip control

Question 52

What do Ruffini endings (SA2) respond most to?

Answer 52

skin stretch

Question 53

What do Pacinian corpuscles (FA2) respond most to?

Answer 53

feeling vibration through objects, perception of fine texture

Question 54

Vibration sensitivity

Answer 54

-receptors are very sensitive to alternating inputs -sensitive to acceleration of skin indentation

Question 55

Spatial code

Answer 55

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

Question 56

How do thermally-gated receptors work?

Answer 56

Heat deforms the protein channel allowing ions to flow in

Question 57

When will nociceptors turn on in relation to thermoreceptors?

Answer 57

When thermoreceptors peak/asymptote

Question 58

When do nociceptors turn on?

Answer 58

become active once the heat becomes tissue damaging

Question 59

Why are spicy foods hot?

Answer 59

Capsaicin artificially creates a sensation of heat (chemical signal)

Question 60

Capsaicin

Answer 60

lipid based so it diffuses easily across cell membrane and binds inside cell (chemically igniting feeling of heat)

Question 61

What are Golgi tendon organ's (GTO's) attached to?

Answer 61

Tendon on one side, muscle fibres on the other

Question 62

What is one property of collagen receptors in GTO's

Answer 62

They remain taut when stretched (crush 1b afferents)

Question 63

Is it a 1:1 ratio of muscle fibre to GTO

Answer 63

No! multiple muscle fibres attach to each GTO

Question 64

What are GTO's helpful for detecting?

Answer 64

Active force production, not passive stretch

Question 65

On a graph, what are GTO's similar to?

Answer 65

GTO firing closely follows EMG reading

Question 66

What are joint receptors good at detecting?

Answer 66

Extreme stretch and pressure (know ends of ROM)

Question 67

What is one fault of joint receptors?

Answer 67

Don't give distinguishable signals (flexion/extension), not much info about angles, not great for proprioception