Lec 17 Flashcards
What are the three levels of processing sensory information?
- The receptor level
- The circuit level
- The perceptual level
What are the 4 criteria to create a signal at the receptor level?
- The stimulus energy must match the receptor specificity
- The stimulus must be applied within the receptive field
- Transduction needs to occur
- Graded potentials need to reach the threshold
What is the difference between a generator potential and a receptor potential?
The receptor potential is found in special senses and has a separate cell that releases a chemical messenger to the neuron fiber, and generator potentials for free or encapsulated dendrites are all one cell.
What is adaptation of reception?
It is the reduction in sensitivity to a constant stimulus that is not painful.
What are the two types of reception adaptation?
- Peripheral adaptation happens at the level of the receptor and reduces the amount of information sent to the CNS
- Central adaptation happens at the level of the neural pathway and involves brain nuclei
What are the two types of receptors that differ in adaptation? Give some examples of each.
Phasic receptors are fast acting eg. lamellar and tactile corpuscles and gives information on rate of change, and Tonic receptors are sustained responses with little to no adaptation eg. nociceptors and proprioceptors.
What happens in first order neurons?
Information is sent to the CNS, and branches, some of it goes to second order neurons and some may lead to motor reflexes
Where do second order neurons lead?
The brain (thalamus/cerebellum)
What do third order neurons do?
They take info from the thalamus and send it to the appropriate brain area.
What are the three main pathways for information to ascend the spinal cord?
- Dorsal column-medial lemniscal pathways
- Spinothalamic pathways
- Spinocerebellar pathways
What kind of information is sent up the dorsal column-medial lemniscal pathways?
Mostly single type of receptor specific information such as discriminative touch, proprioception, or vibrations
What kind of information is sent up the spinothalamic pathways?
Less precise things such as pain, temperature, coarse touch and pressure.
What kind of information is sent up the spinocerebellar pathways?
information about muscle/tendon stretch
Where do the different ascending pathways dessicate?
The dorsal column-medial lemniscal pathways desiccate at the medulla, the spinothalamic pathways desiccate in the spinal cord, and the spinocerebellar pathways do not desiccate.
What is the difference between sensation and perception?
Sensation is the noticing in changes in the environment, and perception is the interpretation of that information. Perception drives response.
What are the six properties of sensory perception, and what do they mean?
- Perceptual detection is the awareness of an input or sum of inputs.
- Magnitude estimation is the determination of the intensity of the stimulus based on action potential rate
- Spatial discrimination is the localization of the stimulus
- Feature abstraction is the coming together of multiple features to come together for the sensory experience.
- Quality discrimination is the ability to distinguish sub modalities of a sensation like taste.
- Pattern recognition is the recognition of familiar things.
What chemicals can cause pain or the transmission of pain?
histamine, K, ATP, acids, bradykinin
What is sharp pain?
Pain carried by the smallest of myelinated sensory fibers, A delta fibers
What is burning pain?
It is carried more slowly by non myelinated fibers called C fibers and are indicative of an inflammatory reaction.
What are the pain neurotransmitters? What tract does pain take up the spinal cord?
Neurotransmitters are glutamate and substance P. Pain takes the spinothalamic tract up the 2nd order neuron.
What are the endogenous opioids (painkillers)?
Endorphins and enkephalins
What part of the midbrain is involved in pain supression?
The periaqueductal grey matter
What is the difference between pain threshold and pain tolerance?
The same amount of stimulus is needed to generate the sensation of pain (threshold), but the ability to withstand high levels of pain varies on a lot of factors (tolerance)
What is somatic/musculoskeletal pain?
It is aching/throbbing/cramping that is associated with innervated bones and muscles.
What is visceral pain?
Pain associated with the organs of the thorax or abdomen, it can be aching or burning and is associated with problems such as muscle spasms or irritating chemicals.
What is referred pain?
Pain from one area of the body that comes from somewhere else.`
What is hyperalgesia?
Pain amplification
What is phantom pain?
A type of hyperalgesia that involve a learned pain.
What are the three types of tongue papillae?
- Fungiform papillae
- Vallate Papillae
- Foliate Papillae
Describe fungiform papillae
They are mushroom shaped and cover the whole tongue. They have 1-5 tastebuds per papilla.
Describe vallate papillae
They are the largest papillae, and there are 8-12 that make a V at the back of the tongue.
Describe foliate papillae
They are lateral on the tongue, and there are a lot in childhood but they dwindle in number over time.
Where are a small number of tastebuds scattered?
The soft palate, cheeks, and pharynx
What cells are tastebuds?
gustatory epithelial cells
What are gustatory epithelial cell microvilli called?
Gustatory hairs
What opening do gustatory hairs go through to get to the tongue?
the taste pore
What are food chemicals called?
Tastants
What neurotransmitters are associated with taste?
Serotonin and ATP
What are gustatory stem cell populations called? What is the turnover rate of the cells?
Basal epithelial cells turn over every 7-10 days
How many modalities of taste can a taste bud sense?
All 5, but each taste cell only has 1 kind of receptor
What are the 5 modalities of taste?
- Sweet
- Salty
- Sour
- Bitter
- Umami
What taste receptor has the lowest threshold? Why?
Taste receptors are most sensitive to bitter tastes to avoid poison.
What can be said about the adaptation of taste receptors?
They adapt rapidly
What three things do we know about taste mechanisms?
- Saltiness is the influx of Na+, which depolarizes gustatory epithelial cells.
- Sourness is the influx of H+, which blocks the leaky K+ channels leading to depolarization.
- Sweet, bitter, and umami all bind to their receptors and couple to the G protein gustducin, and open channels leading to depolarization and the release of ATP.
What are the four types of receptors in the mouth?
All except photoreceptors.
What does the general sensation of taste come from?
80% from smell
What three cranial nerves are vital to taste? What part of the body do they innervate?
The facial nerve (7) carries impulses from the first 2/3 of the tongue, the glossopharyngeal nerves (9) carries impulses from the back 1/3 of the tongue, and the pharynx, and the vagus nerves (10) carry impulses from the epiglottis and lower pharynx.
What kind of receptors are involved with smell?
chemoreceptors
What tissue is located in the roof of the nasal cavity?
olfactory epithelium (pseudostratified columnar)
What structure is covered by the olfactory epithelium?
The superior nasal conchae
How can we generally describe olfactory sensory neurons?
They are bipolar with olfactory cilia that are surrounded by columnar supporting cells.
What is the purpose of the long olfactory cilia?
They increase the surface area
How can we describe olfactory cilia motility and the role mucus plays?
They are not motile, and are covered in mucus that odorant chemicals dissolve in.
What is formed from olfactory axon groups?
They form filaments of the olfactory nerves.
Which way do the olfactory cilia synapse? Through which structure? Into what structure?
Superiorly through the cribriform plate into the olfactory bulbs.
What are mitral cells? What do they make up?
They are output cells in the olfactory bulb. They make up the olfactory tract.
How long is an olfactory neuron lifespan?
30-60 days
How many odorants can be in each smell?
Up to hundreds!
How many odorant receptors do humans have?
roughly 350
What is the relationship between receptors, odorants, and receptor types?
Each receptor responds to one or more odorant type, which binds to multiple receptor types
How many odorants can one receptor CELL respond to?
Only 1
How can we say it only takes a few odorant molecules to activate the receptor cells?
Olfactory senses are very sensitive
What other types of receptors are in the nasal cavities?
Pain/Temperature
What are the two qualities of an odorant that allow it to be smelled (access the receptors)?
They must be volatile (readily vaporized) and able to dissolve in the mucus.
What protein is activated when the odorant binds to the receptor? What secondary binding process happens?
G proteins. GTP binds to adenylate cyclase
What does adenylate cyclase do in the olfactory system?
It releases cAMP that opens a specialized channel in the cell to allow Na and Ca to go into the cell.
What do an influx of Na and Ca do to an olfactory nerve cell?
The Na leads to depolarization, and the Ca causes adaptation in the process.
Where do the olfactory nerves transmit signals?
Straight to the olfactory cortex or to the limbic system.
