Structure And Function Of The Somatosensory System

Front 1

What type of receptor mediates cutaneous sensation?

Back 1

Exteroreceptors

Front 2

Primary cutaneous sensory experiences include:

Back 2

Touch, pressure, heat, cold and pain

Front 3

How are secondary cutaneous sensory experiences produced?

Back 3

They are a combination of several receptor types being stimulated simultaneously

Front 4

Are nociceptors free or encapsulated?

Back 4

Free nerve endings

Front 5

What do high-threshold mechanoreceptors respond to?

Back 5

Intense mechanical stimulation such as cutting, pinching and stretching

Front 6

What to polymodal nociceptors respond to?

Back 6

Intense mechanical stimuli, temperatures over 40 degrees Celsius and chemical substances that are present when tissue damage occurs

Front 7

What is hyperalgesia?

Back 7

When nociceptors become sensitized due to long-standing stimulation

Front 8

Does hyperalgesia raise or lower the threshold for evoking pain?

Back 8

Lowers the threshold

Front 9

Can the same thermoreceptor mediate both hot and cold sensations?

Back 9

Yes

Front 10

Where are low threshold mechanoreceptors located in the skin?

Back 10

Close to hair roots on hairy skin

Front 11

Are low threshold mechanoreceptors in the skin rapidly or slow adapting?

Back 11

Rapidly adapting

Front 12

What do low threshold mechanoreceptors mediate?

Back 12

A crude sense of touch

Front 13

Are low threshold mechanoreceptors in the skin free or encapsulated?

Back 13

Free

Front 14

Where are Meissner's corpuscles found in the skin?

Back 14

In the dermis of glabrous skin of the hand and foot, just below the epidermis

Front 15

Are Meissner's corpuscles free or encasulated?

Back 15

Encapsulated

Front 16

Are Meissner's corpuscles rapidly or slowly adapting?

Back 16

Rapidly adapting

Front 17

What constitutes adequate stimulus for Meissner's corpuscles?

Back 17

Low threshold stimuli-depression of the skin just a few microns

Front 18

Where are Ruffini corpuscles found in the skin?

Back 18

In the dermis of glabrous skin

Front 19

What are Ruffini corpscles made of?

Back 19

A bundle of collagen fibrils that are connected with collagen fibrils in the dermis

Front 20

What constitutes adequate stimulus for Ruffini corpuscles?

Back 20

Stretching of the skin

Front 21

Are Ruffini corpuscles rapidly or slowly adapting?

Back 21

Slowly adapting

Front 22

What type of information do Ruffini corpuscles provide?

Back 22

They provide information about the direction and magnitude of skin stretch

Front 23

Where are Merkel's discs found in the skin?

Back 23

At the junction of the dermis and epidermis in the distal extremities, external genitalia and lips. Found in hairy and glabrous skin.

Front 24

Are Merkel's discs rapidly or slowly adapting?

Back 24

Slowly adapting

Front 25

What constitutes adequate stimulus for Merkel's discs?

Back 25

Pressure

Front 26

Where are Pacinian corpuscles found in the skin?

Back 26

At the junction between dermis and subcutaneous tissue

Front 27

What constitutes adequate stimulus for Pacinian corpuscles?

Back 27

Very rapid indentation of the skin (100-400 Hz)

Front 28

What do Pacinian corpuscles consist of?

Back 28

Large ovoid bodies, axon surrounded by connective tissue and fluid-filled spaces

Front 29

Skin indentation of frequency below 100 Hz are signaled by what receptors?

Back 29

Meissner's corpuscles

Front 30

The size of a receptive field depends on what?

Back 30

The density of receptors and the number of receptors sending axons to one neuron

Front 31

What are three tests of cutaneous sensation?

Back 31

Light brushing, two-point discrimination and discriminative sensation (able to recognize letters/numbers drawn on body part)

Front 32

What are the four functions of cutaneous mechanoreceptors?

Back 32

Awareness of objects touching the skin, recognize objects without vision (stereognosis), judge the speed and direction of an object moving on the skin and to determine friction on the skin

Front 33

Sensory information from proprioceptors comes from what parts of the body?

Back 33

Muscles, tendons, joint capsules and ligaments

Front 34

Where are muscle spindles located?

Back 34

Within striated (extrafusal) muscle fibers

Front 35

How large are the connective tissue capsules that encase muscle spindles?

Back 35

About .2 mm in diameter and about 1-5 mm long.

Front 36

How many intrafusal muscle fibers are contained in each connective tissue capsule?

Back 36

2 to 12

Front 37

Are intrafusal or extrafusal fibers bigger?

Back 37

Extrafusal fibers

Front 38

Do intrafusal fibers generate force?

Back 38

No

Front 39

What are the two types of intrafusal fibers?

Back 39

Nuclear bag fibers and nuclear chain fibers

Front 40

Do muscles involved in fine, precise movements have a high or low density of muscle spindles?

Back 40

High density

Front 41

Ia afferent fibers spiral around the center of what fibers?

Back 41

Nuclear bag fibers and nuclear chain fibers

Front 42

II afferent fibers spiral around what fibers?

Back 42

The distal segment of nuclear chain fibers

Front 43

What constitutes adequate stimulus of a muscle spindle?

Back 43

Stretch of the intrafusal fibers and excitatory input to alpha motor neurons of the same muscle and synergistic muscles

Front 44

Muscle spindle density varies with what?

Back 44

Function of muscle

Front 45

How are muscle spindles arranged with extrafusal fibers?

Back 45

Parallel

Front 46

What happens to muscle spindles when extrafusal muscle is stretched?

Back 46

The muscle spindles are also stretched

Front 47

What happens to muscle spindles when extrafusal muscle contracts?

Back 47

The spindles are passively shortened

Front 48

Static sensitivity of muscle spindles is mediated by what type of fiber?

Back 48

Nuclear chain fibers

Front 49

Nuclear chain fibers gather what type of information for the CNS?

Back 49

Information about the length of muscle at any and all times

Front 50

What happens to nuclear chain fibers when extrafusal muscle is stretched?

Back 50

The nuclear chain fiber is stretched and generates increased frequency of action potentials in Ia and II afferents

Front 51

Are nuclear chain fibers rapidly or slowly adapting?

Back 51

Slowly adapting

Front 52

What happens to nuclear chain fibers when extrafusal muscle is shortened?

Back 52

Nuclear chain fibers are put on slack and the action potential firing rate will decrease

Front 53

Dynamic sensitivity of muscle spindles is mediated by what fibers?

Back 53

Nuclear bag fibers

Front 54

Are nuclear bag fibers rapidly or slowly adapting?

Back 54

Rapidly adapting

Front 55

Nuclear bag fibers provide what type of information to the CNS?

Back 55

Information about rate of muscle length change

Front 56

Nuclear bag fibers send information to the CNS via what fibers?

Back 56

Ia fibers only

Front 57

Nuclear chain fibers send information to the CNS via what fibers?

Back 57

Ia and II afferent fibers

Front 58

What neurons provide efferent innervation to muscle spindles?

Back 58

Gamma motor neurons

Front 59

Where are gamma motor neurons located in the spinal cord?

Back 59

In the ventral horn

Front 60

Where do gamma motor neurons terminate in the muscle spindle fiber?

Back 60

On the contractile portion of the fiber on either side of the centrally located sensory portion of the fiber

Front 61

What happens to intrafusal fibers when gamma motor neurons contract?

Back 61

The distal ends of the intrafusal fibers contract

Front 62

What is the function of gamma static motor neurons?

Back 62

They increase the sensitivity of nuclear chain fibers to muscle length (static sensitivity)

Front 63

What occurs when gamma static motor neurons are active?

Back 63

Ia and II afferent fibers discharge at a greater rate at all muscle lengths

Front 64

What is the function of gamma dynamic motor neurons?

Back 64

They increase sensitivity of the nuclear bag fiber to rate of change in muscle length (dynamic sensitivity)

Front 65

What occurs when gamma dynamic motor neurons are active?

Back 65

Ia afferent fibers discharge at a greater rate during change in length. Discharge rate returns to normal after new length is reached.

Front 66

Gamma dynamic motor neurons allow the nervous system to do what?

Back 66

React more quickly and forcefully to unexpected changes in muscle length

Front 67

Gamma static motor neurons allow the nervous system to do what?

Back 67

Have precise information about muscle length during movements requiring fine control

Front 68

Alpha-gamma co-activation allows the nervous system to do what?

Back 68

Maintain spindle sensitivity during shortening contractions

Front 69

Alpha-gamma co-activation prevents muscle spindles from doing what?

Back 69

Going on slack

Front 70

Where are golgi tendon organs (GTO's) located?

Back 70

Close to the musculotendinous junction, they follow collagen fibrils along a tendon

Front 71

How many GTO's are in a muscle compared to muscle spindles?

Back 71

About the same number of GTO's and muscle spindles

Front 72

Do GTO's have efferent innervation?

Back 72

No, only afferent innervation

Front 73

What afferent fibers come from GTO's?

Back 73

Ib afferent fibers

Front 74

What constitutes adequate stimulus of a GTO?

Back 74

Stretch of the part of the tendon in which the GTO lies

Front 75

Is a GTO rapidly or slowly adapting?

Back 75

Slowly adapting

Front 76

How many GTO's are in a muscle compared to muscle spindles?

Back 76

About the same number of GTO's and muscle spindles

Front 77

Do GTO's have efferent innervation?

Back 77

No, only afferent innervation

Front 78

What afferent fibers come from GTO's?

Back 78

Ib afferent fibers

Front 79

What constitutes adequate stimulus of a GTO?

Back 79

Stretch of the part of the tendon in which the GTO lies

Front 80

Is a GTO rapidly or slowly adapting?

Back 80

Slowly adapting

Front 81

Do golgi tendon organs have efferent innervation?

Back 81

No, the sensitivity cannot be controlled like a muscle spindle

Front 82

Are golgi tendon organs located in series or parallel to extrafusal muscle fibers?

Back 82

In series

Front 83

Why are golgi tendon organs located in series with extrafusal muscle fibers rather than parallel?

Back 83

They provide info to the CNS about muscle tension rather than muscle length

Front 84

Is a golgi tendon organ more sensitive to tension created by active contraction or by passive stretch?

Back 84

Active contraction

Front 85

What is the function of golgi tendon organs?

Back 85

They provide inhibitory feedback to alpha motor neurons that innervate extrafusal muscle, which allows for fine control of muscle activation

Front 86

Do golgi tendon organs play a protective role in muscle function?

Back 86

No

Front 87

What is kinesthesia?

Back 87

The perception of joint position and direction and velocity of joint movement

Front 88

What is the static component of kinesthesia?

Back 88

The ability to know where a joint is in space or in relation to the body when it's not moving

Front 89

What type of receptors detect the static component of kinesthesia?

Back 89

Slowly adapting receptors

Front 90

What type of receptors detect the dynamic component of kinesthesia?

Back 90

Rapidly adapting receptors

Front 91

What is the dynamic component of kinesthesia?

Back 91

Direction and velocity of movement