T5 (Fys) Känselbesvär

Question 0

What is a typical difference in synthesis of a receptor/generator potential in an afferent nerve ending with a receptor cell and a free nerve ending?

Answer 0

The former typically has a lower threshold for action potential generation.

Question 1

What is sensory transduction?

Answer 1

The process of converting šensory stimulus into electrical signals.

Question 2

Name the different types of afferents and the sensation they pervey. What factor separates the afferents from each other?

Answer 2

Ia: sensory receptors of muscles, largest diameter
Aβ: sense of touch, intermediate diameter
Aδ/C: sense of pain and temperature, smallest diameter

Question 3

How do receptive fields correlate with two-point discriminating?

Answer 3

For a certain type of afferent, the smaller the receptive Field, the smaller the two-point discrimination.

Question 4

What is the difference of the Aβ classification and Ia classification as pertsining to the type of axon concerned?

Answer 4

The former is a general system for axon conduction velocity whilst the latter system is used for classification of motor axons.

Question 5

What is gained from having both rapidly and slowly adapting afferents? What may determine the type of adaptation shown by an afferent?

Answer 5

The two types gives sense of both ongoing stimulation (dynamic stimuli, rapidly adapting afferents) as well as spatial attributes such as size and shape (static stimuli, slowly adapting afferents). For at least some classes the receptor cells are responsible for the type of adaptation, e.g. Palinin corpuscles make the afferent adapt faster.

Question 6

Give examples of the extreme differences in two-point discrimation in different areas of the body.

Answer 6

Finger: 4 mm
Call: 45 mm

Question 7

What is the value of parallell pathways in somatic sensing?

Answer 7

They will conduct differently (speed, intensity) in different areas (vertebral, cerebral) to define the stimulus.

Question 8

What is stereognosis?

Answer 8

The ability to identy objects based on what they feel like when manipulation with the hand.

Question 9

List the four main mechanoreceptors specialized for receiving taktiken information. How common are they in the human hand and what stimuli do they react to?

Answer 9

Merkel: small receptor field, 25% of mechanosensory, edges/points/cornea/curves
Meissner: small receptor field, 40% of mechanosensory, skin motion (texture)

Pacinian: large receptorfield, 10-15% of mechanosensory, vibration
Ruffini: large receptor field, 20% of mechanosensory, skin stretch

Question 10

Explain how Merkel cells serve somatic sensory afferents. Where are they found anatomically?

Answer 10

Rather than producing EPSP they apparently modulate the response of the afferent through release of signal molecules and use of voltage-dependent ion channels (that is, the action potential is produced in the afferent, not the sensory cell). They are found in the epidermal ridges.

Question 11

How is dynamic muscle tensing monitored compared with static?

Answer 11

Muscle spindles sense both.

Dynamic: primary endinga, group Ia afferents (fast adapting) are coiled around the intrafusal muscle fibers of the muscle spindle.

Static: seconday endinga, group II afferents are coiled around the intrafusal muscle fibers of the muscle spindle

Question 12

What relationship generally exists for muscle spindle occurence and muscle size? Do muscle spindles lack from some muscles alltogether?

Answer 12

The smaller the muscle, the higher the amount of proprioceptic muscle spindles. The muscles of the inner ear (m. tensor tympani, m. stapedius) lack muscle spindles.

Question 13

What is the difference in the task of muscle spindles and Golgi tendon organs?

Answer 13

Muscle tendons communicate muscle length to the CNS, whilst the Golgi tendon organs communicate muscle contraction force.

Question 14

What afferent communicates with the Golgi tendon organ?

Answer 14

Group Ib.

Question 15

What is the function of joint receptors?

Answer 15

They have little effect on the monitoring of large skeltal joined but apparently function in monitoring and signaling the natural ranges of movement possible for the finger joints.

Question 16

Outline the dorsal column-medial lemniscal systems first-order neurons pathway.

Answer 16

Lower limbs: medially in dorsal column (fasciculus gracilis)-dorsal column nuclei (nucleus gracilis)

Upper limbs, trunk and cervical region: laterally in dorsal column (fasciculus cuneatus, wedge-shaped bundle)-nucleus cuneatus

Question 17

Outline the route of the second-order neurons of the dorsal column-medial lemniscal system.

Answer 17

Now called internal accurate fibers, they cross sides (decussation, X) and form the dorso-ventral elongated medial lemniscus (upper body afferents now medially, lower body laterally), which synapses with thalamic neurons in the ventral posterior lateral nucleus (VPL).

Question 18

Outline the route of the third-order neurons of the dorsal column-medial lemniscal pathway.

Answer 18

FROM VPL neurons travel via internal capsule and terminate in the postcentral gyrus of the cerebral cortex (primary somatosensory cortex) and partially also to secondary somatosendory cortex. (capsula interna)

Question 19

Outline the passage of the trigeminothalsmic system (tactile information from the face).

Answer 19

First order neurons: skin-trigeminal ganglion principle nucleus of trigeminal brainstem complex
Second order: trigeminal ganglion principle nucleus of trigeminal brainstem complex-(crossmidline, trigeminal lemniscus)-ventral posterior medial nucleus (VPM)(-SI and SII)

Question 20

Describe the route of proprioceptic stimuli from the body through afferent neurons.

Answer 20

First order: sensory cell-Clarke’s nucleus
Second order: Clarke’s nucleus-ipsilateral posterior lateral column-medulla-cerebellum/proprioceptive neurons
Third order: proprioceptive neurons-medial lemniscus-accompany mechanoreceptive fibers to VPL

Question 21

How does the route of the proprioceptic afferents of the face differ from that of the mechanoreceptor afferents?

Answer 21

The ganglia is found in the mesencephalic trigeminal nucleus instead If the trigeminal ganglia.

Question 22

How is sensory information organized in the thalamus? What is the vain of this organization!

Answer 22

Sensory information from the body is received in the VPL whilst sensory information from the face is received in the VPM. In this way sensory information remains segregated for different parts of the body.

Question 23

How are Brodmann’s areas organized in the postcentral sulcus?

Answer 23

Sinister ventral view of the gyrus: 1 is middle superior, 2 is the posterior wall, 3b is the anterior wall and 3a lies under 3b

Question 24

What types of stimuli does each Brodmann’s area respond to?

Answer 24

3b & 1: primarily cutaneous stimuli

3a: stimulation of proprioceptors
2: both tactile and proprioceptic stimuli

Question 25

What are the main interconnections between Brodmann’s areas?

Answer 25

3b receives the most of the ventral posterior complex input, distinguish it out in particular to areas 1 and 2. This makes area 3b the first location of processing of somatosensory information.

Question 26

What connections are there from SI to other areas of the brain?

Answer 26

SII (tactile learning and memory), 5a and 7b. In addition descending projections travel to the thalamus, brainstem and spinal chord, modulating ascending signals.

Question 27

Give examples of plasticity in the adult cerebral cortex.

Answer 27

Amputation: the loss of sensory input to a certain somatosensory area of the SI remains the area to serve nearby areas instead.

Anesthesia: the experience of a locally anesthetized area feeling larger than normal may be attributes to the affected cortical area being temporarily remppas to serve adjacent areas

Question 28

What fiber types conduct pain? What are their subcategories and signifying stimuli?

Answer 28

Aδ (fast, myelinated, type I perveys mechanical/chemical and type II perveys thermic stimuli) and C type (slow, non-myelinated) fibers.

Question 29

What is the role of TRP channels in pain sensation?

Answer 29

The receptor (transient receptor potential receptor) containing TRP allows Na ion and Ca ion influx when reacting to heat or tissue damage chemicals.

Question 30

What receptor families and channels are central for pain sensation!

Answer 30

TRP-family: TRPV1 reacting to capsaicin, TRPA1 reacting to chemical irritants (acid-sensing)

ADIC3: charmikas pain resulting from low pH during ischemia

NAV1.7: sodium channel central for the action potential of pain

Question 31

Describe the route of pain stimuli to the brain (anterolateral system).

Answer 31

First order: site of stimuli-dorsolateral tract of Lissauer-a few vertebrates up/down-synapsing at Rexed’s laminae (1&2 for C fibers, 1&5 for Aδ fibers)
Second order: from laminae 1&5-ascending through anterolateral quandrant of contralateral half of spinal chord

Question 32

Explain the phenomenon of referred pain.

Answer 32

Since visceral pain receptors share pain-relating axons with cutaneous nociceptors, pain can be localized apart from the organ to cutaneous sites, corresponding with the developmental dermatomes.

Question 33

Why is dissociated sensory loss signature of a spinal chord lesion?

Answer 33

Because of the different levels at which the medial lemniscal pathway (mechanosensing) and anterolateral pathway (pain pathway) cross sides.

Question 34

What of the brain concist the pain matrix?

Answer 34

Somatosensory cortex
Insulates cortex
Amygdala
Anterior cingulate cortex

Question 35

What components are there to the experience of pain? How do their afferent routes differ?

Answer 35

Sensory-discriminative: From anterolateral system to ventral posterior nucleus to SI/II

Affective-motivational: anterolateral system-midline thalamic nuclei-anterior cingulate cortex/insulin cortex

Question 36

Outline the pain AMD temperature pathway of the face.

Answer 36

First order: sensory cell-(trigeminal ganglion)-middle/caudal(spinal nucleus of trigeminal complex)-VPM nucleus of thalamus-SI

Question 37

What other modalities is the anterolateral system responsible for, in addition to pain noxious temperature sensation?

Answer 37

Innocuous forms of touch and thermoception (-17C-43C).

Question 38

Why is lamina 1 of the spinal chord and anterolateral pathway interesting compared tuntohermojen laminae?

Answer 38

It contains the pathways of not only noci- and thermoception but also those of non-discriminative touch and innoxious thermoception, in addition to histamine (itch) and the burn of lactic acid (the latter forming interoception) which modulate homeostasis.

Question 39

What substances produce peripheral sensitization and hyperalgesia in tissue damage?

Answer 39

Released by nociceptors: substance P, calcitonin gene-related peptide (CGRP) and ATP. These further increase the inflammatory response.

Other cells (mast, platelets, basophilic etc.): extracellular protons, arachidonic acid and other lipid metabolites,mbradykininem histamine, serotonin, prostaglandins etc. Cytokines also impact receptors but mainly increase production of other inflammatory factors.

Question 40

Define allodynia.

Answer 40

The “induction of pain by normally innocuous stimuli” in central sensitization.

Question 41

Explain the central sensitization achieved through ‘windup’.

Answer 41

The perceived pain increases despite the repeated noxious stimulus remaining the same. This makes for short-term potentiation events in the afferents, with activation of L-type calcium channels and removal of Mg block of NMDA receptors.

Question 42

Where does sensitization occur as pertaining to allodynia?

Answer 42

Centrally. An LTP-response ensues in post-synaptic potentials, increasing intracellular Ca ion levels. Also reduction in GABAergic and glutamergic receptors along with increased prostaglandin synthesis by COX-enzymes contribute.

Question 43

What is neuropathic pain?

Answer 43

Pain induced due to damaged afferents. Hard to treat with conventional methods.

Question 44

What endogenous mechanisms of pain modulation have been proposed?

Answer 44

1) descending neural pathways (midbrain periaqueductal gray)
2) gate theory
3) endogenous opioid receptors (interneuron synapsing with first order and second order afferent synapse)