Section 5 - Sensory receptors and somatic sensation Flashcards
Define sensation
Ability to feel something physically, especially by touching
Define perception
Conscious interpretation of those stimuli
Each of the principal types of sensation that we can experience (touch, pain, sight, sound) are called ______
Modality of sensation
T or F: nerve fibers transmit only impulses
True
Type of sensation felt when a nerve fiber is stimulated is determined by : _____
the termination point in the CNS, unique neurons in the CNS are capable of decoding specific modalities
Name the 3 types of sensory information
Mechanoreceptive sensation
Nociceptive sensation
Thermoreceptive sensation
Name the 2 branches from the mechanoreceptive sensation
- Tactile sensation (skin)
2. Proprioceptive sensation
Give examples of tactile sensation
Touch
Pressure
Vibration
Tickle and itch
Give examples of proprioceptive sensation
Muscle stretch sense
Joint position sense
T or F: thermoreceptive sensation detects pain
False, detects heat and cold
Nociceptive sensation detect pain
Name the 3 somatosensory receptors based on the type of sensation they detect
- Mechanoreceptors detect tissue deformation
- Thermoreceptors detect change in temperature
- Nociceptors detect pain
What are the two types of mechanoreceptors?
Skin tactile receptors
Muscle receptors
Name the 4 mechanisms of stimulation of the receptor
- Mechanical deformation
- Application of chemicals
- Change in temperature
- Tissue damage
Increasing the intensity of the stimulus will lead to a greater receptor potential and, eventually, to a greater AP _____
Frequency
*** same amplitude, more APs
When talking about adaptation of receptors, speed of adaptation varies with type of receptors, name them
Rapidly adapting receptors
Slowly adapting receptors
T or F: rapidly adapting receptors are best at detecting rapidly changing signals, while slowly adapting receptors are capable or detecting a long, continuous signal
True
Name the 6 receptors
- Free nerve endings
- Hair-end organ
- Pacinian corpuscle
- Meissner’s corpuscle
- Merkel’s discs
- Ruffini’s end-organ
T or F: Area of each receptor field varies directly with the density of receptors in the region
False, inversely (more density = small receptor field and vice-versa)
To get the best sensory discrimination (accuracy of sensation), is it better to have small or large receptive fields?
Small
Define the two-point discrimination
Method used to measure tactile acuity in rehab
Which provides more acuity?
When many primary sensory neurons converge onto a single secondary neuron OR when fewer neurons converge, secondary receptive fields are smaller so they are perceived as distinct stimuli
2nd part
Which tactile receptors are located in the epidermis vs dermis?
- Epidermis: Meissner corpuscule, Merkel discs and free nerve endings
- Dermis: Pacinian corpuscules and Ruffini organ
Name the 6 TACTILE receptors
- Free nerve endings
- Meissner’s corpuscules
- Merkel’s discs
- Hair end organ
- Ruffini’s end organ
- Pacinian corpuscules
Free nerve endings are found where and detecte what kind of touch?
- They are found everywhere on the skin
- Detect crude touch and pressure sensations
Meissner’s corpuscules are found where and detecte what kind of touch?
- They are located in the superficial layer of the skin (non-hairy part)
- Detect fine touch
Merkel’s discs are found where and detecte what kind of touch?
- They are located in the epidermis
- Detect touch and light pressure
Hair end - organ are found where and detecte what kind of touch?
- In contact with the root of the skin hair
- Detects hair movement
Ruffini’s end organ are found where and detecte what kind of touch?
- They are located in the deeper layer of the skin
- Detects heavy and prolonged touch and pressure signals
Pacinian corpuscules are found where and detecte what kind of touch?
- They are located in the deeper layer of the skin
- Detects tissue vibration or other rapid changes in the mechanical state of the tissue
Which receptors are rapidly adapting?
- Meissner’s corpuscules, Hair end organ and Pacinian corpuscules
True or false: Ruffini’s end organs are fast adapting receptors
FALSE
When does a pain sensation occur?
When the tissue is being damaged
Why is pain a protective mechanism?
Because it brings awareness of tissue damage and can prevent further damages to the body
What is the difference between fast and slow pain?
- Fast pain is a pricking sensation, sharp in character that is felt 0.1 sec after the stimulus
- Slow pain is an aching sensation that begins after a second or more
What kind of receptors are pain receptors?
Specialized free nerve endings
Where are the nociceptors located?
- Superficial layers of the skin
- Internal tissues
- Arterial walls
- Bones, joints and muscle surface
True or false: Nociceptors are stimulated by thermal, mechanical and chemical stimulus
True
Nociceptors are slow adapting receptors, true or false?
True
What are thermoreceptors
Free nerve endings that code changes in temperature
Thermoreceptors change within what range
the innocuous range
Temperatures that are likely to damage an organism are sensed by what receptors
nociceptors
True or False: nociceptors respond only to noxious heat
false they also respond to noxious cold
how do we determine sense of temperature
by comparison of the signals from each of the two types of thermoreceptors
Thermoreceptors respond to a temperature change with 2 phases (components), name them
with a phasic component followed by a tonic component
What is the difference between a phasic and tonic component
phasic is rapidly adapting and tonic is a slowly adapting component
Give a real-life example of the phasic and tonic components
when you get in a hot bath and it feels hot until your body adapts and then it’s only warm
Meissner’s corpuscles, merkel’s dics, hair receptors, Pacinian corpuscles and Ruffini’s end organs transmits their signals through what type of nerve fibers
type A-beta myelinated nerve fibers at 30-70 m/sec
Free nerve endings transmit their signals through what type of fibers
type A-delta nerve fibers at 6-30 m/sec (fast pain, cold sensation) or through type C unmyelinated fibers at 0.5-2 m/sec (slow pain, cold, warmth, crude touch & pressure sensations)
What is faster between high and low discrimation
high discrimination
where does the sensory information enter the spinal cord
through the dorsal roots of the spinal nerves
what are the 2 pathways for sensory information
the dorsal column (medial lemniscal system) and the antero-lateral system
what does decussate mean
crossing over on the other side
True or False sensory fibers only decussate on one pathway
false they decussate on both pathways
where is the sensory information from one side of the body transmitted
to the brain hemisphere on the opposite side of the body
what makes the relay to transmit sensory information from the receptor to the final point of the cerebral cortex
three order neurons
where is the dorsal column located
on the back of the spinal cord
which types of sensations does the dorsal column transmit
the tactile sensations (touch, vibration and fine pressure) and the proprioceptive sensations (i.e. limb position)
where do the dorsal column signals originate from
they originate from tactile receptors or proprioceptive receptors
What type nerve fibers are used in the dorsal column, for what reason and with what type of
degree
large myelinated nerve fibers for fast signal transmission with a high degree of spatial fidelity
Describe the 3 different order neurons for the dorsal column
the 1st order neurons synapse with the 2nd at the dorsal column nucleus
the 2nd order neurons decussate at the level of the medulla (brain stem)
The 2nd order neurons synapse with th 3rd in the thalamus
The 3rd order neurons transmit info to the primary somasensory cortex
what does the antero-lateral pathway transmit
a broad spectrum of modalities such as pain, thermal sensations, crude touch and pressure, tickle and itch, sexual sensations
where do the signals from the antero-lateral pathways originate
they originate from free nerve endings receptors (pain and thermal receptors)
what type of nerve fibers are used in the antero-lateral pathway for what use and with what type of degree
smaller myelinated and unmyelinated fibers for slow transmission and with a low degree of spatial orientation
Describe the 3 different order neurons for the antero-lateral pathway
The 1st order neurons synapse with the 2nd in the substantia gelatinosa
The 2nd order neurons decussate at the level of the spinal cord
The 2nd order neurons synapse with the 3rd in the thalamus
The 3rd order neurons transmit info to the primary somatosensory cortex
Where are fast pain fibers transmitted into
the neospinothalamic tract
Where are slow pain fibers transmitted into
the paleospinothalamic tract
what do neo and paleo mean
neo = new paleo = old
where do the fast pain fibers terminate
at the somatosensory cortex
where do the slow pain fibers terminate
at the thalamus level or below (even in the brain stem)
T or F slow pain fibers can be highly localized if it is simultaneously activated with tactile sensations
False the fast-sharp pain can
slow pain is ____ localized
poorly
Where is the primary somatosensory cortex located
in the post-central gyrus (in the parietal lobe)
How would you describe the primary somatosensory cortex
highly organized with distinct spatial orientation and each side of the cortex receives info from the opposite side of the body
T or F the somatosensory area II is much more extensive than the somatosensory area I
False
What is the name of the famous montrealer neurosurgeon who did the mapping of the somatosensory cortex
Dr Wilder Penfield
Penfield’s Homunculus gives an ____ representation of the body. Explain
unequal because the more a region of the body has receptors, the better it’s area of representation in the somatosensory cortex is
Classify these body regions in order of the ones with more receptors to the ones with the less receptors
lips
the somatosensory cortex is composed of how many cellular layers
6
within the cellular layers, the neurons are arranged in what direction
vertical columns
T or F the columns in the somatosensory cortex each have a specific modality and they interact between each other
True, the interaction allows the beginning of the analysis of the meaning of the sensory signals
T or F the degree of pain is the same for everyone
False it varies tremendously from person to person
How does the brain suppress inputs of pain signals
through the activation of the analgesia system
What are the three parts of the analgesia system
the periaqueductal gray of the mesencephalon and upper pons
the raphe magnus nucleus located in the lower pons
the pain inhibitory complex located in the dorsal horns of the spinal cord
what is the main neurotransmitter involved in the analgesia system
enkephalin (released at the 3 levels)
How do we call a pain in the internal organs that is often sensed on the surface of the body
reffered pain
How would you describe CIPA (congenital insensitivity to pain with anhidrosis)
inability to feel pain and temperature, inability to sweat
