Section 6 Flashcards
What is proprioception?
Refers to our capacity to know the position of the different parts of our bodies
What do somatosensory receptors detect?
Cutaneous or muscular changes produced by mechanical, thermal, or sometimes chemical stimuli, and to convey this information to the CNS
Where are cell bodies of somatosensory receptors located?
In the dorsal root ganglion
What do we call the region of the skin that is innervated by a specific nerve?
Dermatoma
Cutaneous or subcutaneous receptors have receptive fields that are defined by ____________
The area of the skin where a stimulation can elicit a response in that receptor
How do you achieve a greater capacity to identify the precise location of an object touching the skin?
By having a high concentration of receptors in that area which have small receptive fields
How does the size of a somatosensory neurons receptive field vary based on where the receptor is?
Receptors located deeper in the skin will tend to have larger receptive fields than the ones located on the surface
Explain why several somatosensory receptors can be simultaneously activated even if the stimulus is very small?
The receptive fields of somatosensory receptors overlap
What is tactile acuity?
The capacity to detect the most delicate features of a stimulus
What technique would you use to assess tactile acuity?
Two-points threshold technique
Describe the two-points threshold technique
Typically assessed by applying two points of a drawing compass on the skin and asking participants if they perceive one of two points
The smaller the distance required to discriminate two points, the _______ (smaller/greater) the tactile acuity
greater
Regions such as the face and hands have much _______ (smaller/greater) tactile acuity compared to other regions such as the back and legs
greater
What are the two general types of somatosensory receptors?
Fast-adapting (FA) and slow-adapting (SA)
Describe fast-adapting somatosensory receptors
Respond strongly to the onset of a mechanical stimulus, but then quickly decrease their firing rate even if the stimulus is maintained
List three characteristics of FA type I receptors
- attached to Meissner corpuscles
- have smaller receptive fields
- mostly found in the fingertips and are extremely sensitive to movement and low frequency vibration, which is important for perceiving slip and maintaining grip when manipulating objects
List three characteristics of FA type II receptors
- Attached to Pacinian corpuscles that absorb much of the mechanical energy applied on the skin
- Located deeper in the skin and therefore have large receptive fields
- Most sensitive to high frequency vibration on the skin, which is important for perceiving fine textures or manipulating tools
Describe slow-adapting somatosensory receptors
Their response is sustained throughout the application of the mechanical stimulus
List three characteristics of SA type I receptors
- attached to Merkel cells
- located closer to the surface of the skin and therefore have small receptive fields
- play an important role in perceiving pattern, texture, and shape
List three characteristics of SA type II receptors
- attached to Ruffini endings
- have large receptive fields
- responsive to stretching of the skin, which can be useful for perceiving hand conformation
What are proprioceptors?
Convey information on the mechanical forces originating from body movements and posture in order to inform on the position of limbs and other body parts
Where are proprioceptors located?
muscle spindles, Golgi tendon organ, and ligaments
What are nociceptors?
They respond to pain and temperature throughout the body, and have never endings that are free from any specialized endings
Why do nociceptors have a high response threshold?
Because there is no reason for them to be activated by stimulus intensities that are too low to cause injury
List all the nerve cell types that would be thickly myelinated
tactile and proprioceptive A-beta and A-alpha fibers
List all the nerve cell types that would be thinly myelinated
nociceptors (A-delta fibers)
What myelination do C-fibers have?
None at all
What causes congenital insensitivity to pain?
A genetic mutation that causes impairments in the development of small-diameter fibers such as A-delta and C fibers
How is it possible that we have first and second pain?
We have two different types of pain fibers
Describe first and second pain
First: the initial feeling of pain that causes you to move that body part away from the source
Second: The more diffuse pain you feel a few seconds after removing yourself from the source
What happens to the different somatosensory fibers when your limb goes numb?
Myelinated fibers get impaired pretty quickly, but C fibers stay in tact
The axons of the peripheral somatosensory receptors enter the CNS through the _______ (dorsal/ventral) part of the spinal cord
dorsal
Describe the spinothalamic pathway
Temperature and pain fibers will enter the dorsal horn of the spinal cord and make a synapse onto projection neurons. Then, the axon of the projection neuron will cross to the anterolateral quadrant on the opposite side of the spinal cord and ascend vertically towards the brain
Describe the dorsal column-medial lemniscal (DCML) pathway
Instead of synapsing in the spinal cord, the axons of tactile and proprioceptive nerve fibers will directly ascend vertically upwards towards the brain through the dorsal columns on the ipsilateral part of the brain
Dorsal columns are bundles of _____ (white/gray) matter
white
At what point do axons of tactile and proprioceptive nerve fibers cross over to the other side of the brain?
When the axons reach the medulla
Describe the Brown-Sequard syndrome
Because tactile and thermoalgesic axons have different pathways, spinal cord lesions will result in having a tactile deficit on the same side of the body as the lesion, but a thermoalgesic deficit on the contralateral side of the body relative to the lesion
Which location is one of the few where nociceptive and tactile information interact?
dorsal horn
Describe the gate control theory of pain
It was hypothesized that a large-diameter tactile afferent could stimulate an inhibitory neuron (interneuron) in the spinal cord, which would then go on to inhibit the spinal projection neurons that would have conveyed nociceptive information to the brain, thereby blocking the transmission of nociceptive signals coming from the small-diameter nociceptors
What is the intensity theory of pain?
Proposed that pain resulted from excessive activation in any kind of nerve fiber
What is the specificity theory of pain?
Proposed that pain was a specific sense distinct from touch
What is the only type of somatosensory neuron that does not make a synapse in the thalamus?
Proprioceptive fibers
Although proprioceptors do not project to the thalamus, what other brain region do they project to?
Cerebellum
Describe the pathway tactile information takes once at the thalamus
Will first project to the ventral posterior nucleus of the thalamus, and from there will reach the post-central gyrus which houses the primary somatosensory cortex
Describe the asymmetry in the primary somatosensory cortex
It is asymmetric in the way the different body parts are represented, with the size of the cortical area dedicated to the face and hands being the largest relative to the rest of the body
What three areas of the thalamus do nociceptive neurons send information to?
Ventral posterior nucleus, superior-suprageniculate complex, and medio-dorsal nucleus
Describe the ventral posterior nucleus pathway for nociceptors
Projects to the somatosensory cortex, contributing to the sensory-discriminative dimension of pain (where is the pain and how intense is it?)
Describe the superior-suprageniculate complex pathway for nociceptors
Projects to a brain area called the insula, which is responsible for monitoring the internal state of the body
Describe the medio-dorsal nucleus pathway for nociceptors
Projects to the anterior cingulate cortex, which serves the affective dimension of pain (what makes pain unpleasant)
Lesions to the ACC or to the white matter tract that leads to it leads to what condition?
asymbolia (feel pain but do not care about it)
What do patients experience when there is a lesion in their primary somatosensory cortex?
They do not perceive pain on the contralateral side of the body, but will report a vague unpleasant sensation in a broad area surrounding the site of stimulation
What are the functions of smell?
- warning
- nutrition
- social communication
Microbial threats are associated with the basic emotion of _______
disgust
Non-microbial threats are associated with the basic emotion of _____
fear
We perceive our environment with our sensory organs via what two types of interactions?
Physical and chemical senses
What is the main difference between physical and chemical stimuli?
In the physical senses, the stimulus source interacts physically with our sensory cells but never the sensory organs, whereas in chemical senses the stimulus source needs to enter the body before it can reach receptor cells
What are odorants?
Substances that can evoke smell perceptions
What structure divides the nasal cavity into two separate asymmetrical spaces?
The nasal septum
What are the names of the three bone structures that line the lateral walls of the nasal cavity?
Upper, middle, and lower turbinates
What is the role of the turbinates?
Increases the surface area of the mucosa, which is needed for additional tasks of the nose such as warming cleaning, and humidifying the air going to the lungs
Most of the nasal cavity is covered with respiratory epithelium. Which part is instead covered with olfactory epithelium?
The uppermost portion stretching from the olfactory cleft to the middle turbinate
What are the two ways that odorants can enter the nasal cavity and get in contact with the olfactory epthilium?
Orthonasal olfaction and retronasal olfaction
Describe orthonasal olfaction
Most of the air we breathe reaches our lungs, but some molecules are transported to the upper portion of the nasal cavity, get in contact with olfactory receptor cells, and evoke an odor perception
Describe retronasal olfaction
Volatile molecules are released from the mouth’s content, and reach the nasal cavity via the pharynx
Which type of olfaction is the most important contributor to flavor perception?
retronasal olfaction
When an appropriate odorant reaches the olfactory receptor, a cascade of intracellular events leads to a depolarization - where does the nerve impulse get sent to?
The glomeruli
Where are glomeruli located?
in the olfactory bulb
How are olfactory receptors organized in relation to what odors they respond to?
Olfactory cells each only carry one type of olfactory receptor, meaning they respond to specific types of physiochemical properties of odorants, such as functional groups
How is olfactory information coded?
Axons of all olfactory neurons carrying the same receptor converges onto the same glomerulus
Where are mitral cells located?
olfactory bulb
The axons of mitral cells make up what structure?
The olfactory tract
Where do mitral cells terminate?
via the olfactory triangle and lateral olfactory stria, which together form the primary olfactory cortex
List the 6 structures that comprise the primary olfactory cortex
- anterior olfactory nucleus
- olfactory tubercle
- piriform cortex
- entorhinal cortex
- amygdala
- hippocampus
List two structures that are part of the secondary olfactory area
insular cortex and orbitofrontal cortex
Describe three characteristics that makes the olfactory pathway distinct from other sensory systems
- information processing in the olfactory system takes place mainly ipsilaterally
- there is no obligatory thalamic relay in the olfactory pathway
- The primary and secondary olfactory cortex is not exclusively processing olfactory information
What is the Proust effect?
the effect whereby certain smells can evoke intense and direct emotional memories
True/false
olfactory disturbances are relatively common
true
Which is more common, congenital or acquired olfactory disturbances?
acquired
List 4 causes of acquired olfactory dysfunction
- chronic rhinosinusitis
- viral infections
- traumatic brain injury
- neurodegenerative diseases
What is quantitative olfactory dysfunction?
Describes conditions in which patients perceive odors as less strong or do not perceive them at all
List two types of quantitative olfactory dysfunction
- anosmia
2. hyposmia
What is qualitative olfactory dysfunction?
Describes conditions in which patients perceive odors which are nevertheless quantitatively altered
List two types of qualitative olfactory dysfunction
- parosmia
2. phantosmia
What are the three functions of taste?
- warning
- nutrition
- electrolyte balance
What are supertasters?
Subgroup of the population that are particularly sensitive to taste
What is an important chemical requirement of taste stimuli for humans to be able to perceive it?
Needs to be somewhat hydrophilic
TRUE/FALSE
if saliva production is impaired, gustatory sensitivity is also impaired
true
Sour taste is evoked by ______
acids
salty taste is evoked by _______
salts of the alkali metal group
Umami taste is evoked by ______
salts of glutamic acid
Sweet taste is evoked by ______
carbohydrates
Bitter taste is evoked by ______
alkaloids
What are the bumps on our tongue called?
Papillae
List the four types of papillae found on the tongue. Which one is not involved in gustation?
- fungiform papillae
- foliate papillae
- circumvallate papillae
- filiform papillae (not involved in gustation)
Where are fungiform papillae most densely located?
tip of the tongue
Where are foliate papillae most prominently found?
on the sides of the tongue in more posterior regions
Where are circumvallate papillae located?
very back of the tongue
what are filiform papillae involved in?
Somatosensation
Where are taste buds located?
in the epithelium of the papillae
How do tastants reach the taste buds?
There is a small opening on the taste buds where the tastant can enter and get in contact with taste receptor cells
How does sensory transduction work?
Tastants dock to GPCRs which triggers an intracellular cascade resulting in the depolarization of the nerve cell
In addition to the tongue, where else are taste buds located?
palate and in the larnyx
Taste buds of the two anterior thirds of the tongue send their axons via the ______, a branch of cranial nerve _____
chorda tympani, VII
Taste buds on the posterior third of the tongue and palate send their axons along the _______, cranial nerve ____
glossopharyngeal nerve, IX
The taste buds located on the larynx have their axons travel with the _______, cranial nerve _____
vagus nerve, X
Where do all the taste bud fibers terminate?
At the solitary tract in the medulla
TRUE/FALSE
there is a mandatory relay station for taste in the thalamus
true
Where is the primary gustatory cortex located?
in the anterior portion o the insular cortex and the portion of the frontal lobe covering the insula
What structure makes up the secondary gustatory cortex?
The orbitofrontal cortex
What do we call taste dysfunctions?
Dysgeusia
List two types of quantitative gustatory dysfunction
- ageusia
2. hypogeusia
List one type of qualitative gustatory dysfunction
parageusia
Why are quantitative gustatory dysfunctions so rare?
It would require all 3 bilateral cranial nerves to be damaged
