Sensory Physiology

Question 1

how are nerves classified

Answer 1

contribution to a compound action potential based on fiber diameter, myelin thickness, and conduction velocity

Question 2

Classification of afferent fibers, fiber diameter, conduction velocity, and receptor supplied of sensory fiber: Aalpha

Answer 2

Ia and Ib

large (13-30)

fast (80-20)

primary muscle spindles, golgi tendon organ (proprioception)

Question 3

Classification of afferent fibers, fiber diameter, conduction velocity, and receptor supplied of sensory fiber: Abeta

Answer 3

II

slightly slower and smaller than Aa

Secondary muscle spindles, skin mechanoreceptors

Question 4

Classification of afferent fibers, fiber diameter, conduction velocity, and receptor supplied of sensory fiber: Adelta

Answer 4

III

Slightly larger and faster than C fibers

Skin mechanoreceptors, thermal receptors, and nociceptors

Question 5

Classification of afferent fibers, fiber diameter, conduction velocity, and receptor supplied of sensory fiber: C fibers

Answer 5

IV

small (0.2-1.5)

very slow 0.5-2

skin mechanoreceptors, thermal receptors, and nociceptors

Question 6

Classification of afferent fibers, fiber diameter, conduction velocity, and receptor supplied of motor fiber: Aaplpha

Answer 6

12-20

72-120

the fastest and largest

Extrafusal skeletal muscles

Question 7

Classification of afferent fibers, fiber diameter, conduction velocity, and receptor supplied of motor fiber: Ay

Answer 7

slightly smaller and slower than the Aalpha fibers

Intrafusal muscle fibers

Question 8

Classification of afferent fibers, fiber diameter, conduction velocity, and receptor supplied of motor fiber: B

Answer 8

larger than C but smaller than Ay

preganglionic autonomic fibers

Question 9

Classification of afferent fibers, fiber diameter, conduction velocity, and receptor supplied of motor fiber: C

Answer 9

slowest and smallest of the muscle fibers

Postganglionic autonomic fibers

Question 10

Meissner corpuscle

Answer 10

low threshold, rapidly adapting, found in glaborus skin

Touch and vibration less than 100 Hz. flutter and tapping

Question 11

Pacinian Corpuscle

Answer 11

Low threshold, slowly adapting, found in both hairy and glaborus skin

Rapid indentation of the skin such as that during a high frequency vibration (100 to 400Hz) vibration

Question 12

Ruffini corpuscle

Answer 12

Low threshold, slowly adapting, found in glaborous skin
and in hairy skin

Magnitude and direction of stretch and pressure and proprioception

Question 13

Merkel cell

Answer 13

low threshold and slowly adapting, found in glaborus skin

Pressure

Question 14

Hair follicle receptor

Answer 14

rapidly and slowly adapting

motion across the skin and directional of that motion

Question 15

Tactile free nerve ending

Answer 15

high threshold, slowly adapting

Pain and temperature

Question 16

Muscle spindles

Answer 16

Limb proprioception

Question 17

Golgi tendon organ

Answer 17

limb proprioception

Question 18

Receptive fields

Answer 18

areas of innervation where an individual mechanoreceptor fiber conveys information from that limited area of skin

vary in size:
fingertips have small area but are very receptor dense (fine discriminative touch)

back skin has a large area but are dont have a dense receptor base (no fine discriminative touch)

Question 19

Two point discrimination

Answer 19

abillity to identify the site of stimulation and distingush between two stimuli that are at close distances

two point discrimination is better done by receptors with smaller receptive fields (fingertips) than large receptive fields (forearm)

Tactile acuity is important

allows for spacial resolution of detailed textures

Question 20

Somatosensory area 1 (SI)

Answer 20

involved in the integration of the information for position sense as well as size, shape and discrimination

somatic sensory area 1
primary sensory cortex
located in post-central gyrus
first stop for most cutaneous senses
crude identification of senses

Question 21

Somatosensory area II (S2)

Answer 21

responsible for comparisons between objects, different tactile sensations and determining whether something becomes a memory

an assosciation area
located in the wall of the lateral fissure
receives input from S1
somatotopic representation is less maintained
important to cognitive touch

Question 22

Parieto temporal occipital association area (PTO)

Answer 22

responsible for high level interpretation of sensory inputs

recieves input from multiple sensory areas
analyzes psatial coordinates of self in environment
identification of objects
many more functions
Large amount of association areas in our human brains is distinctive of being human compared to other mamals

Question 23

Phantom limb pain

Answer 23

pain in the body part that is no longer present due to the law of projection

-states thhat regardeless of the place along the afferent pathway that is stimulated, the sensation is perceived to come from the place that the innervation arises

Question 24

Pain

Answer 24

unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage

Question 25

Nociception

Answer 25

the neural process of encoding noxious stimuli (a stimulus that is damaging or threatens to damage consequences of encoding may be autonomic or behavioral . pain sensation doesnt necessarily have to be implied

Question 26

Hypersensitivity

Answer 26

increased responsiveness of nociceptive neurons to their input and or recruitment of a response to normally subthreshold inputs

Question 27

Hyperaesthesia

Answer 27

increased sensitivity to stimulus excluding the special senses

Question 28

Hyperalgesia

Answer 28

increased pain from a stimulus that normally provokes pain

Question 29

Allodynia

Answer 29

pain due to a stimulus that does not normally provoke pain classic example is the lay of sheets on skin that has been sunburned

Question 30

biphasic response to pain

Answer 30

initial Adelta fibers (much faster and larger but receptive fields much smaller) provide the precise localization of pain during phase two C fibers (slower smaller and respond to chemical and thermal stimuli and release substance P, glutamate, aspartate, calcitonin gene related peptide (CGRP) vasoactive intestinal polypeptide (VIP and nitric oxide) this generates a more dull and throbbing less localized pain

Question 31

what are the three modalities of nociceptors

Answer 31

Mechanical: response to mechanical forces ranging from moderate pressure with a blunt object to overtly tissue-damaging stimuli chemical: response to endogenous or exogenous chemical compounds such as pro inflammatory mediators, acids, or capsaicin THermal: response to noxious heat and cold will directly activate thermal receptors expressed by nociceptors

Question 32

TRPV1

Answer 32

ligand gated noselective cation channel in nociceptive neurons Found on many C-fibers and activated by vanilloid compounds (capsaicin) in addition to exogenous compounds, endogenous compounds (bradykinin) and heat greater than 43 degrees activation causes a release of an action potential and release of neuropeptide (CGRP) and substance P which leads to vasodilation and activation of immune cells, this leads to pro-inflammatory mediator release which acts as a positive feedback loop activating more of these TRPV1 channels found in, migraignes, dental pain, cancer pain, inflammatory pain, neuropathic pain, visceral pain, and osteoarthiritis

Question 33

TRPA1

Answer 33

nociceptors ligand gated that are activated by: allyl isothiocyanate in mustard oil, wasabi, and horseradish Anesthetics often have paradoxial pro-nociceptive effects acting through TRPA1 involved in inflammatory pain states: allergic contact dermatitis, chronic itch, painful bladder syndrome, migraine, irrritable bowel syndrome and pancreatitis

Question 34

TRPM8

Answer 34

can be activated by both innocuous cooling and noxious cold temperatures as well as a number of cooling agents such as menthol which are commonly used for their analgestic properties

Question 35

Rubbing the spot makes it feel better

Answer 35

No pain is sensed due to the inhibitory interneuron is blocking the nociceptive signal from continuing to move forward (closed gate) Strong stimuli of C fiber (opens gate) 1) activate an Abeta fiber buy normal stimuli. the central process of this fiber branches in the dorsal horn and synapses on an inhibitory interneuron and release EAA 2) activated interneuron will release glycine and inhibits the secondary sensory neuron of the nociceptive pathway 3) rubbing an area of affected skin activates the Abeta fiber and reduces the sensation of pain

Question 36

What is the descending inhibition of Pain receptors (specifically C fiber)

Answer 36

Periaqueductal grey are activated by EAA, opiates, and cannabinoids then descending pathway travels to Locus Coeruleus (NE) and Raphe nucleus (serotonin) serotonin and NE release into dorsal horns and activate inhibitory interneurons local inhibitory interneruons release opiates (enkephalin) these activate mu-receptors on presynaptic and post synaptic terminals of a C-fiber results in reduction of SP from the C-fiber and reduces nociception

Question 37

Central sensitization

Answer 37

Activity dependant synaptic plasticity in the spinal cord that generates post injury pain hypersensitivity together with cellular and molecular mechanisms responsible for this form of neuronal plasticity - Reduced threshold of dorsal horn neurons to noxious stimulation - commonly caused by chronic exposure to peripheral inflammation - alterations in transcription and translation of various receptors and ion channels. changes the level of synaptic input produced by the afferent fiber - receptive fields of the afferent expands - involves persistant stimulation of EAA receptors, intracellular Ca++ and activation of various intracellular signaling cascades

Question 38

Peripheral Sensitization

Answer 38

Neuroplastic changes relating to the function, chemical profile, or structure of the peripheral nervous system that encompasses changes in receptor, ion-channel, and neurotransmitter expression levels - Neuroimmune activation can increase intensity and duration of pain - at the site of inflammation, prostglandin E2 (PGE2) sensitizes the peripheral nociceptors via activation of receptors that are present on the peripheral terminals of nociceptors by reducing the firing threshold and increasing the responsiveness - PGE2 may come from nearby mast cells, neutrophils, macrophages, and T-Lymphocytes following a peripheral injury - adjacent non injured primary afferent nerve fibers can be come sensitized also

Question 39

Peptidergic nociceptors

Answer 39

Express neuropeptides -substance P -CGRP (calcitonin gene related peptide) Responsiveness to nerve growth factor Most visceral afferents are peptidergic -contributes to chronic visceral pain syndromes Half of cutaneous afferents are peptidergic Chronic inflammation upregulates neuropeptides

Question 40

Non-peptidergic nociceptors

Answer 40

- Do not express CGRP or SP neuropeptides - Responsive to GDNF (glial-derived neurotrophic factor) - Very few visceral afferents are non peptidergic - Half of cutaneous afferents are non-peptidergic - involved in somatic chronic pain states such as that of diabetic neuropathy

Question 41

Nociception distribution in the brain

Answer 41

S1 and S2: do recieve input from nocicieptors and play a role in localization of the pain Insular cortex: particularly important in interpretation of nociception - processes information about internal state if the body - Contributes to autonomic response to pain - integrates all signals related to pain - damage causes asymbolia - lesions in any single area alters the experience of pain but does not abolish it completely Amygdala: important in the emotional component to pain Hypothalamus and medula: integrating the physiological changes associated with visceral pain