Sensory Physiology and Pain Flashcards
what do extero-receptors detect?
- vision
- hearing
- taste
- smell
- receptors on skin: physical change temperature or pain
what do intero-receptors detect?
information from internal organs and processes
proprioception helps to detect what?
position and load
what is adequate stimulus?
the least amount of energy in a stimulus needed to generate a receptor potential to form an action potential downstream
what is the adequate stimulus for vision?
light
what happens when light is received by cells within the retina?
cGMP gated sodium channels CLOSE causing hyperpolarization
- retinal in rhodopsin undergoes a conformational change to activate the G protein transducin which activates posphodiesterase to catabolize cGMP
what happens when darkness is received by cells within the retina?
cGMP gated sodium channels are OPEN causing depolarization
how are ON center bipolar cells activated?
ON center bipolar cells have metabotropic glutamate receptors that are inhibited by glutamate, so they are activated when light is present
how are OFF center bipolar cells activated?
OFF center bipolar cells have ionotropic glutamate receptors that are excited by glutamate, so in the dark they are active
what is the role of horizontal cells and lateral Inhibition of the retina?
horizontal cells receive input from photoreceptors and inhibit neighboring bipolar cells through inhibitory interneurons, sharpening contrast through lateral inhibition
*only effects the surrounding cells
structure and function of the external ear
air filled with pinna andexternal auditory canal
- function is to funnel sound waves into the middle ear
structure and function of the middle ear
air filled with a tympanic membrane, malleus, incus and stapes
- function is to transmit signal from tympanic membrane to oval window
structure and function of the inner ear
fluid filled with semicircular canals and a cochlea (scala vestibuli, scala tympani, and scale media) that contains the organ of corti
what is impedance matching?
process by which sound waves from the air filled middle ear are efficiently transferred to the fluid-filled cochlea in the inner ear
*without this you would have hearing loss
what do the scala vestibuli,
scala tympani, and scale media contain?
- scala vestibuli and scala tympani contain perilymph (low K+)
- scale media contains endolymph (high K+)
what is the adequate stimulus for hearing?
sound waves
what happens when a sound wave strikes the tympanic membrane?
vibration of ossicles vibrates the oval window then the organ of corti induces cilia to bend and OPEN mechanical sensitive K+ channels causing influx of K+ from endolymph into the hair cell which releases glutamate
what is the adequate stimulus for vestibular balance?
head movement
what are the structures included in the vestibular system?
3 perpendicular semicircular canals with ampulla and two otolith organs (utricle and saccule) that are also filled with endolymph
what is stimulated when you move your head counterclockwise?
stimulates left horizontal canal hair cells to
bend towards the kinocilium and inhibits right horizontal canal.
nystagmus is the result of
vestibulo-ocular reflex
what are the two components of nystagmus and which one is it defined by
- Slow Component: the eyes move opposite to the direction of the head spin to maintain visual stability
- Fast Component: once the eyes reach their movement limit, they rapidly snap back in the same direction as the head movement.
*defined by the fast
what is vertigo and what induces it?
inappropriate sense of motion can be induced by:
- low blood pressure
- infections
- anesthesia
- certain drugs (loop diuretics, erythromycin, nitrous oxide, chemotherapy)
- temperature
- displaced otoconia
- tumors
- visual clues
what drugs can be used for treatment of vertigo or motion sickness?
Anti-histamines
* Meclizine (Bonine®, Antivert®)
* Dimenhydrinate (Dramamine®)
* Promethazine (Phenergan®)
* Diphenhydramine (Benadryl®)
Parasympatholytics
* Scopolamine (Transderm-Scop®)
what is anosmia?
absence of smell
what is hyposmia?
impaired sense of smell
what is hyperosmia?
enhanced smell sensitivity
what is dysosmia?
distorted sense of smell
what are granule and periglomerular cells?
inhibitory interneurons of the glomerulus that make dendrodendritic synapses with neighboring mitral cells providing lateral inhibition
what happens once an odorant molecule binds to a chemoreceptor of the cilia?
the Gαs of trimeric G-protein (Golf) is released and activates adenylyl cyclase to generate cAMP that binds to gated sodium channels to open them and cause depolarization
what is ageusia?
absence of taste
what is hypogeusia?
decreased taste sensitivity
what is hypergeusia?
increased taste sensitivity
what is dysgeusia?
distortion of taste, including taste sensation in the absence of taste stimuli
*oxybutynin can cause it
taste buds contain what three main cell types?
- Taste receptor cells (gustatory cells): detect taste stimuli using chemoreceptors
- Supporting cells → provide structural support but do not detect taste
- Basal stem cells → continuously regenerate new taste receptor cells
what is the mechanism of taste transduction for bitter, sweet and umami?
binds GPCRs to increase IP3 and calcium to open transient receptor potential channels resulting in depolarization and neurotransmitter release
what other receptor may umami taste activate?
truncated metabotropic glutamate receptor (mGlu4).
what is the mechanism of taste transduction for sour?
hydrogen ions (H⁺) from acids enter the cell through epithelial sodium channels (ENaCs) or block potassium (K⁺) channels which leads to depolarization, triggering neurotransmitter release
what is the mechanism of taste transduction for salty?
sodium ions (Na⁺) enter directly through ENaCs, causing depolarization and signal transmission to the brain.
what is taste adaptation?
a rapid effect of continuous exposure to a taste that reduces sensitivity over time
- 50% is through receptors
- 50% through CNS
what is taste blindness?
the inability to taste phenylthiocarbamide (PTC)
- 15–30% of people cannot taste PTC, a bitter compound, due to genetic differences in T2R38 receptors.
what are the thresholds for stimulation for the 4 taste sensations?
Sour taste, HCl 9 X 10-4 M
Salty taste, NaCl 1 X 10-2 M
Sweet taste, sucrose 1 X 10-2 M
Bitter taste, quinine 8 X 10-6 M (very low)
what are the 4 types of pain?
- Acute Pain → Short-term pain that results from injury or illness
- Nociceptive Pain → Pain caused by damage to tissues, such as from cuts, burns, or inflammation.
- Chronic Pain → Long-lasting pain that persists beyond normal healing time
- Neuropathic Pain → Pain caused by nerve damage or malfunction
what is long-term potentiation (LTP)?
a process where pain pathways become hyperactive, increasing sensitivity and potentially contributing to chronic pain conditions.
what are the differences that separate somatosensory and pain afferent nerves?
- nociceptors have a higher threshold for activation
* meaning they require more stimulus energy to trigger an action potential. - nociceptors do not readily fatigue
* in response to continuous stimulation - nociceptors can be considered tonic receptors
* meaning they respond consistently to ongoing stimuli within the normal physiological range. - nociceptors do not rapidly plateau as stimulus intensity increases
* the stimulus becomes stronger, the nociceptor continues to increase its firing rate - plateau response of nociceptors approaches the absolute refractory period
* which is when a nerve can’t fire another action potential, regardless of the strength of the stimulus.
what stimuli can induce nociception?
mechanical (fast, slow), thermal (fast, slow) and chemical (slow) through TRP channels
what is Capsaicin?
is a lipophilic molecule that upon chronic exposure can desensitize the C-fibers to pain and is used to treat trigeminal neuralgia
what is calcitonin gene related peptide?
a potent vasodilator which can promote edema and also promote pain pathways in the CNS (e.g., migraines)
what is substance P?
molecule that acts on mast cells to cause degranulation and release histamine and can also induce slow pain, by sensitizing nociceptive terminals
what is histamine?
molecule that can promote pruritus (itch) which can cause us to scratch to relieve the pain and itch
what is sensitization?
process by which nociceptors become more responsive and trigger pain more easily in response to weaker stimuli due to repeated prolonged inflammation and injury in both the peripheral nervous system (PNS) and the central nervous system (CNS)
what are the inflammatory mediators that contribute to sensitization?
bradykinin, prostaglandins, and
leukotrienes
what are some effects of sensitization?
allodynia (non-painful stimuli become painful)
hyperalgesia (normal pain becomes more intense)
increased tenderness or soreness.
what is the Neospinothalamic Tract in terms of pain pathways ?
- carries signals for sharp, acute, well-localized pain that travel quickly because of myelinated Aδ fibers
- Glutamate is the main neurotransmitter involved in this pathway
- somatosensory cortex helps to localize the pain
what is the Paleospinothalamic tract in terms of pain pathways ?
- carries dull, aching, or chronic pain that travels slowly because of unmyelinated C fibers
- substance P is the main neurotransmitter, though glutamate is also released in some cases
- pain is less localized and felt as a continuous, dull ache
There are two main types of second-order neurons
- nociceptive-specific neurons: these only respond to painful (noxious) stimuli
- wide dynamic range (WDR) neurons: these respond to both painful (noxious) and non-painful (non-noxious) stimuli from Aβ, Aδ, and C fibers
which neurons are the most prevalent cell type in the dorsal horn and what laminae are they most abundant?
WDR neurons, laminae V
what is “wind up”?
refers to the process where these WDR neurons gradually increase their firing rate in response to repeated stimulation
what is laminae II/III called?
substantia gelatinosa
what is long term potentiation (LTP)?
a process where repeated stimulation of neurons leads to an increase in the strength of the connection between those neurons which can make the nerves more sensitive and cause chronic pain
what happens during the initial phase of LTP?
- AMPA receptors are activated by glutamate allowing sodium ions to enter the neuron, causing a depolarization (activation) of the neuron.
- NMDA receptors become active and release Ca2+
what happens if there is continuous stimulation in the late phase of LTP?
alteration of the neuron’s transcriptional program, meaning the neuron starts to produce new proteins
increase in the production of certain voltage-gated channels (like sodium and calcium channels)
what are the three thermoreceptors and where are they located?
cold (C and Aδ fibers)
warm (C fibers)
pain
