Chapter 47

Question 1

What signals the “touch” sensation?

Answer 1

results from stimulation of tactile receptors in the skin or in tissues immediately beneath the skin

Question 2

What are free nerve endings responsible for?

Answer 2

touch and pressure (also tickle and itch); found all over the skin (ex: cornea)

Question 3

What are Meissner’s corpuscles responsible for?

Answer 3

Touch (great sensitivity); encapsulated nerve ending of a large myelinated sensory nerve fiber

Question 4

What are Merkel’s discs responsible for?

Answer 4

Extremely sensitive protruding/dome shaped receptor and aid in localizing touch sensations to specific surface areas and texture

Question 5

What are Hair end organs responsible for?

Answer 5

detects mainly movement of objects on the surface of the body or initial contact with the body (touch receptors); found at the base of the hair (basal nerve fiber)

Question 6

What are Ruffini endings responsible for?

Answer 6

multibranched encapsulated endings that adapt slowly, detect continuous states of deformation of the tissues (ex: heavy prolonged touch and pressure signals)
Found in joint capsules (signal the degree of joint rotation)

Question 7

What are Pacinian corpuscles responsible for?

Answer 7

stimulated only by rapid local compression of the tissues (adapt very very quickly) and vibrations; found just beneath the skin and deep in the fascial tissues.

Question 8

Meissner’s corpuscles, Iggo dome, hair, pacinian corpuscles, and Ruffini’s endings utilize what types of neurons?

Answer 8

Type Aβ nerve fibers

Question 9

Tactile free nerve endings utilize what types of neruons?

Answer 9

C fibers

Question 10

What is the nerve topography in the Dorsal Column-Medial Lemniscal System?

Answer 10

Carries signals upward to the medulla of the brain mainly in the dorsal columns of the cord
Signals synapse and cross to the opposite side in the medulla
Cont. upward through the brain stem to the thalamus by way of the medial lemniscus

Question 11

What types of sensations are felt in the dorsal columns?

Answer 11

Touch sensations requiring high degree of localization of the stimulus
Touch sensations requiring transmission of fine gradations of intensity
Phasic sensations, such as vibratory sensations
Sensations that signal movement against the skin
Position sensations from the joints
Pressure sensations related to fine degrees of judgment of pressure intensity

Question 12

Where are the 1st, 2nd, and 3rd-order synapses for the dorsal column neurons?

Answer 12

First-order: dorsal column nuclei (cuneate and gracile nuclei)
Second-order: Ventrobasal complex (in the thalamus; where the medial lemniscus fibers end)
Third-order: Somatic Sensory Area I of the Postcentral gyrus in the Cerebral Cortex

Question 13

What types of fibers are in the dorsal column, with respect to size and myelination and CV?

Answer 13

Composed of large myelinated nerve fibers that transmit signals to the brain at velocities of 30 to 110 m/sec

Question 14

What is the nerve topography in the ALS?

Answer 14

Dorsal nerve roots  spinal cord  synapse in dorsal horns  cross to the opposite side of the cord and ascend via the anterior and lateral white columns of the cord  terminate at all levels of the lower brainstem and thalamus

Question 15

What types of fibers are in the ALS with respect to size and myelination and CV?

Answer 15

Smaller myelinated fibers that transmit signals @ velocities ranging from a few meters-40m/sec

Question 16

What types of sensations are felt in the ALS?

Answer 16

Pain
Thermal sensations, including both warmth and cold sensations
Crude touch and pressure sensations capable only of crude localizing ability on the surface of the body
Tickle and itch sensations
Sexual sensations

Question 17

Where are the 1st, 2nd, and 3rd-order synapses for the ALS?

Answer 17

First-Order: dorsal horn in Lamina I, V (Aδ fibers) and Lamina II (C fibers)
Second-Order: Ventero-Posterior Lateral nucleus of the thalamus
Third-Order: Somatic Sensory Area I of the Postcentral gyrus in the Cerebral Cortex

Question 18

Where is the somatosensory cortex (area I)?

Answer 18

Somatosensory area I lies right behind the central fissure and is located in the postcentral gyrus; it displays high degree of localization of different parts of the body

Question 19

Size of the different parts of the bodoy on the homunculus is directly proportional to what?

Answer 19

The # of sensory fibers in each area.

Question 20

If there is a lesion in the somatosensory area I, what will be the response to different sensations?

Answer 20

Person is unable to localize discretely the different sensations in the different parts of the body
However they can localize these sensations crudely, such as to a particular hand, to a major level of the body trunk, or to one of the legs

Question 21

If there is a lesion in the somatosensory area I, what will be the response to sensing pressure?

Answer 21

Person is unable to judge critical degrees of pressure against the body

Question 22

If there is a lesion in the somatosensory area I, what will be the response to weight of objects?

Answer 22

Person is unable to judge the weights of objects

Question 23

What is the function of the somatosensory association area?

Answer 23

Aids in deciphering deeper meanings of the sensory information in the somatosensory areas

Question 24

Where does the somatosensory association areas get info from?

Answer 24

Receives info from: somatosensory area I, ventrobasal nuclei of thalamus, other areas of thalamus, visual cortex, and auditory cortex

Question 25

What are the Sx of lesions to the somatosensory area I?

Answer 25

The sensory modalities are still preserved both in quality and intensity however the sensations are poorly localized

Question 26

What are the Sx of lesions to the somatosensory association area?

Answer 26

The person loses the ability to recognize complex objects and complex forms felt on the opposite side of the body.

Loses most of the sense of form of his or her own body or body parts on the opposite side; forgets its even there (amorphosynthesis)

Question 27

Which area of the somatic sensory Cx is excited first?

Answer 27

IV

Question 28

What do layers I and II receive? Their Fxn?

Answer 28

Layers I and II receive diffuse, nonspecific input signals from brain centers that facilitate specific regions of the cortex; controlling overall excitability of the respective regions stimulated

Question 29

Where do layers II and III send axons?

Answer 29

Neurons in layers II and III send axons to related portions of the cerebral cortex on the opposite side of the brain through the corpus callosum

Question 30

Where does layer V send axons?

Answer 30

Axons in layer V project to more distant areas (basal ganglia, brain stem, and spinal cord) where they control signal transmission

Question 31

What is the fxn of layer VI?

Answer 31

Layer VI (axons extend to thalamus) provides signals from the cerebral cortex that interact w/ and help to control the excitatory levels of incoming sensory signals entering the thalamus

Question 32

What is 2-point discrimination?

Answer 32

Tests tactile discrimination by using two needles pressed lightly against the skin at the same time, and the person determines whether two points of stimulus are felt or one point; different parts of body display different distances of the needles due to the different concentrations of tactile receptors present in the tissue
Ex: Finger tip: 1-2 mm Back: 30-70mm

Question 33

What is the role of surround inhibition in enhancinh sensory contrast?

Answer 33

When a sensory pathway is excited it gives rise simultaneously to lateral inhibitory signals; these spread to the sides of the excitatory signal and inhibit adjacent neurons via inhibitory transmitters.
This blocks the lateral spread of the excitatory signals and therefore increases the degree of contrast in the sensory pattern perceived in the cerebral cortex

Question 34

What is the Weber-Fechner Principle?

Answer 34

Interpreted Signal Strength= Log (stimulus) + Constant

Greater the background sensory intensity = Greater the additional change must be for the mind to detect the change

Question 35

What is the power law?

Answer 35

Interpreted Signal Strength= K x (Stimulus-k)y
K,k, and y are different for each type of sensation

This equation shows a linear relation can be attained btwn interpreted stimulus strength and actual stimulus strength over a large range for almost any type of sensory perception

Question 36

What is proprioception?

Answer 36

unconscious perception of movement and spatial orientation arising from stimuli within the body itself

Question 37

What is Static Position Sense?

Answer 37

conscious perception of the orientation of the different parts of the body with respect to one another

Question 38

Knowledge of position, both static and dynamic, depends on knowing what 2 factors?

Answer 38

degrees of angulation of all joints in all planes and their rates of change

Question 39

What types of information does the ALS pathway signal?

Answer 39

Pain, heat, cold, crude, tactile, tickle, itch, and sexual sensations

Question 40

Where is the first-order synapse for the ALS pathway?

Answer 40

dorsal root sensory nerve fibers synapse in the Dorsal horn laminae I, IV, V, and VI

Question 41

Where is the ALS decussation?

Answer 41

ALS fibers cross in the anterior commissure of the cord to the opposite anterior and lateral white columns (anterior and lateral spinothalamic tracts)

Question 42

Where is the 2nd-order synapse for the ALS pathway?

Answer 42

upper terminus of the 2 spinothalamic tracts is mainly twofold
Reticular nuclei of the brain stem (pain signals)
Two different nuclear complexes of the thalamus: ventrobasal complex (tactile signals) and intralaminar nuclei (pain signals)

Question 43

Where is the 3rd-order synapse for the ALS pathway?

Answer 43

Somatic Sensory Area I of the Postcentral gyrus in the Cerebral Cortex

Question 44

What is the role of the thalamus in somatic sensing?

Answer 44

If the somatosensory cortex is destroyed that person loses most critical tactile sensibilities but a slight degree of tactile sensibility does return.

Therefore, the thalamus has a slight ability to discriminate tactile sensation even though its job is mainly just to relay this info to the cortex