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98 Cards in this Set

  • Front
  • Back
4 components of Somatosensation:
1. Touch
2. Temp
3. Proprioception
4. Pain
How somatosensation is different from other sensation:
Receptors distributed throughout body vs concentrated in small specialized areas.
6 STEPS in somatosensation pathway:
1. Stimulus
2. Sensory receptor
3. Spinal cord
4. Medulla/brainstem
5. Thalamus
6. Cortex
What is the Dorsal root ganglion?
Cell bodies of sensory neurons for neck and down
What is the Trigeminal ganglion?
Cell bodies for neurons of sensation of face/head
Type of neurons in DRG and CN V ganglion:
How many DRGs are there?
2 at every spinal cord level (one on each side of it)
How many cell bodies are in a DRG?
How many Trigeminal ganglia are there?
2 - one on each side of the head
3 general categories of sensory receptors:
1. Exteroreceptive
2. Proprioceptive
3. Interoceptive
Exteroreceptive codes what type of info?
Codes information from external world, primarily in skin.
3 Types of exteroreceptive receptors:
1. Mechanoreceptors (touch)
2. Thermoreceptors (warm/cool)
3. Nociceptors (sharp/burning pain)
Proprioceptive codes what type of info?
Codes information about muscle length, tension, and joint angles
2 types of Proprioceptive receptors:
1. Muscle afferent
2. Joint/tendon afferents
Interoceptive codes what type of info?
Codes info about changes inside the body
Interoceptive receptors are also called:
Visceral afferents
4 Functions of the Sensory Neuron:
Encode stimulus
Receptive field
The area in the periphery where an application of an adequete stimulus will cause a receptor to respond
2 Types of potentials that occur during stimulus transduction:
-Receptor potential
-Action potential
2 Factors that determine Stimulus Intensity:
1. Rate code
2. Spatial summation code
What is the Rate Code?
The frequency of AP firing
What is the Spatial summation code?
# of neurons firing
2 factors that determine speed of AP transmission down an axon:
-Axon diameter
-Myelin thickness
Rate conduction velocity in 4 different axons:
Fastest = large myelinated alpha
Fast = large myelinated beta
Moderately fast = thin myelinatd
Slow = unmyelinated
Large myelinated axons
A-alpha fibers ~100 m/s

A-beta fibers ~50 m/s
Thin myelinated axons
A-delta fibers
~15 m/s
Unmyelinated axons
C fibers
~1 m/s
What is the clinical diagnostic tool for measuring conductino velocity for whole peripheral nerves?
Compound Action Potential
What is Compound Action Potential?
Electrical stimulation of peripheral nerves to measure conduction velocities
3 Things that can be determined by Compound Action Potential measurement:
-If a Fiber Type is Missing
-If a Fiber Type is Damaged
-If Receptors are malfunctioning
6 Conditions diagnosed via CAP (compound AP)
1. Diabetes
2. Shingles
3. Nerve entrapment
4. Multiple sclerosis
5. Complications of drug tx
6. Nutritional deficiencies
5 Environments for Receptive Terminals:
1. Skin
2. Muscle
3. Joint
4. Bladder
5. Intestine
What allows sensory neurons to be specific for certain stimuli?
Specialized sensory endings
3 Characteristics that set the Sensitivity and Function of different receptors:
1. Location (superfic vs deep)
2. Type (capsulated or not)
3. Slowly or rapidly adapting
What are Slowly Adapting nerve endings for?
Responding to Sustained, Unchanging stimuli - like pressure and shape of objects.
What are Rapidly Adapting nerve endings for?
Responding to CHANGING stimuli; like impact and motion of objects on the skin.
2 Factors that determine Spatial Resolution for a Stimulus:
1. Receptive Field Size
2. Innervation density
What type of receptors have small vs. large receptive fields?
Superficial rec = Small field
Deep receptors = Large field
Where would innervation density be high? Low?
High = very sensitive areas like fingers and mouth
Low = insensitive areas like back and calves
What do Mechanoreceptors mediate?
3 Characteristics of how Mechanoreceptors behave:
1. Very sensitive to FORCE
2. Silent if no stimuli
3. Myelinated axons so stimulus reaches spinal cord VERY FAST.
Where are Mechanoreceptors located?
Superficial (Merkel/Meissner's)
Deep (Ruffini/Pacinian)
How many types of mechanoreceptors? What are they?
1. Merkel disks
2. Meissner's corpuscles
3. Ruffini Endings
4. Pacinian Corpuscles
5. Hair follicle
What do Merkel Disks detect?
-Fine touch
-2point discrimination
Why are Merkel Disks especially important?
They are the best at detecting TEXTURE of objects - give the sharpest resolution
What is the Receptive Field like for Merkel's Disks?
Multiple small spots are innervated by a single A-beta axon
What type of response do Merkel's disks exhibit? How does this affect their operation?
Slowly adapting - so APs fired are proportional to the force of indentation
What other receptors detect 2pt discrimination and fine touch?
Meissner's corpuscles
How are Meissner's corpuscles different from Merkel's discs in terms of function?
They sense abrupt changes in edges, bumps, and corners - help adjust grip and release when lifting objects.
What is the receptive field like for meissner's corpuscles?
one single spot
What is a Meissner's Corpuscle structure like?
A stack of flattened epithelial cells with sensory terminals entwined between layers.
What is the response of Meissner's corpuscles?
Rapidly adapting - so it senses when skin indentation is on and off, not intermediate degrees.
What are the Deep mechanoreceptors and where are they located?
deep in the dermis:
1. Ruffini endings
2. Pacinian corpuscles
3. Hair follicles
Ruffini endings detect:
-Stretch of skin
-Application of vertical force of Gravity applied to skin
-Shape of grasped objects
What is the receptive field like for Ruffini endings?
Large and diffuse
What is special about Ruffini endings?
They are encapsulated
Type of Response in Ruffini endings:
Slowly adapting - responds to skin stretch in 1 direction
What do Pacinian corpuscles detect?
High frequency vibration
Why are Pacinian corpuscles special?
They are the most sensitive mechanoreceptors.
What is the receptive field like for Pacinian corpuscles?
Large and diffuse
What is the nerve ending of a Pacinian corpuscle like? Why?
Encapsulated - to filter out all sustained stimuli.
What type of response do Pacinian corpuscles have?
Rapidly adapting - so there is one AP per indentation.
What do hair follicles detect?
Movement of hairs
Where is the receptive field of hair follicles?
Around the base of a hair follicle.
How does the nerve ending interact with the hair follicle?
The bare axon is wrapped around the base of it
What type of response do hair follicles have?
Rapidly adapting
What nerve endings detect texture of objects?
Meissner's and Merkel's
Why don't Pacinian corpuscles detect texture of Braille patterns?
Because their receptive fields are larger than the dot spacings.
What are 2 types of Mechanoreceptors that have FREE nerve endings?
What mechanoreceptors are best at detecting texture?
What are the 2 types of free nerve ending receptors?
what do thermoreceptors encode?
Skin temperature
What is the normal resting state of thermoreceptors at normal skin temp?
Always discharging continously
What do thermoreceptors respond to?
Changes in temp
What happens to thermoreceptors when they are at a constant abnormal skin temp?
They stop firing because they adapt to the new temperature.
What receptors will increase their firing when the skin is cooled?
Cool receptors
How do cool receptors respond when the skin is warmed?
They stop firing.
How do cool receptors respond when the skin is normal?
Discharge continuously
What type of axons do cool receptors have?
what is the range of cool receptors?
8-38 (outside of this range they don't work)
What is the receptive field of cooling thermoreceptors like?
Very small and infrequently distributed in skin.
What is the range of Warming receptors?
What type of axons do warming receptors have?
Unmyelinated - C
How do warming receptors respond to cooling of the skin?
They stop firing.
what do Nociceptors respond to?
Stimuli that damage or threaten to damage tissue
What percent of sensory neurons in the DRG are nociceptors?
What do nociceptors provide almost all innervation to?
Tooth pulp
What are the 2 general types of nociceptors?
-C-polymodal nociceptors
What do A-mechanonociceptors respond to? (2 stimuli types)
1. Intense Mechanical Force
2.Very intense noxious heat >52
Where do the free nerve endings of A-mechanonociceptors terminate?
At the epidermal-dermal junction.
What type of response do A-mechanonociceptors show?
What type of axons do they have?
Response: slowly adapting
Axons: Adelta
What type of injury would be detected by A-mechanonociceptors?
-Hitting your thumb with a hammer
-Sharp pricking pain
-Quicker b/c of myelinated fiber
What types of stimuli excite C-Polymodal nociceptors?
MANY -> thus the poly
-Hot chili peppers, high thermal heat, force, etc.
What sets C-Polymodal nociceptors apart from A-mechanonociceptors?
-Unmyelinated C fibers
-Can detect chemicals released from inflammation
What type of response is shown by C-nociceptors?
Slowly adapting.
So the two receptors with C-fiber axons are:
-Warming receptors
-C-polymodal nociceptors
The 3 receptors with Adelta fibers are:
-Hair follicles (some)
All other mechanoreceptors in the skin have: