Sensation/Perception Flashcards
What are the four types of sensation?
- superficial
- deep
- visceral
- special
What are the superficial sensations?
touch, pain, temperature, two point discrimination
What are the deep sensations?
proprioception, deep muscle pain, vibration
What is psychophysics?
- a field that deals with physical stimuli and the mental phenomena related to their perception
- it relates stimulus intensity to perception in what are known as “power curves”
Sensation is proportional to the ___ of the stimulus.
power/intensity
What is a generator potential?
- the transmembrane potential difference produced by activation of a sensory receptor
- generator potentials sum to reach the threshold for action potential generation
What is the “neural code”?
the firing pattern of populations of neurons used to represent sensory input
Stimulus intensity is usually encoded by what characteristic of the neural code?
the number or rate of action potentials as well as the number of neurons activated
What is “contrast enhancement” with regards to coding of sensory inputs?
parallel processing of cells of different thresholds refines acuity
How are temporal aspects of a stimulus encoded in firing patterns of sensory receptors?
adaptation to persistent stimuli varies across different receptor subtypes, so slowly and rapidly adapting mechanoreceptors will have different firing patterns
What is adaptation?
a decrease in neural response to a maintained stimulus
How is spatial information about a stimulus encoded?
through the function of receptive fields and the location of the sensory receptors currently firing
What is a receptive field?
- usually defined as the area of skin where stimulation produces activation of a neuron
- but can be defined at different levels like the thalamus and cortex
Which sorts of receptive fields have higher acuity?
smaller ones
What is the “labelled lines” theory of sensory coding?
essentially that somatotopy is retained and there is a specific pathway for conduction of info about a somatopic location or for a specific modality
How does “pattern theory” differ from the “labelled lines theory”?
- pattern theory is related to certain sensory systems like color perception in which information is integrated across multiple primary afferents, so it is the pattern of activation of whole neuronal populations that form the basis of perception
- e.g. three color receptors combine to respond to the spectrum of visible light
Convergence of primary afferents is an important processing step in what way?
- individual inputs may have different strength in stimulating the subsequent neuron
- interneurons may modify the interactions between receptors (surround inhibition)
What is surround inhibition?
central signals are facilitated and eccentric signals are inhibited (by interneurons or that central signal) in order to sharpen the contrast between them
What are two possible reasons a secondary receptive field may be rather large?
- the primary receptive field was larger
- many neurons converge on the same secondary neuron
Convergence can have what effect on receptive field size?
the more neurons that converge on a single secondary neuron, the larger the secondary receptive field, and the lower the acuity
Convergence is an important concept with regards to ___ pain.
- referred pain
How is convergence an important concept with regards to referred pain?
referred pain is the result of visceral input onto secondary neurons that also receive sensory info from cutaneous nerves
What is the first step in percept construction from sensory information?
convergence
Our construction of a percept from the same sensory input varies from individual to individual based on what?
experience, knowledge, and previous associations
What is template matching?
a method of percept construction whereby every object, event, or other stimulus that we encounter and want to derive meaning from is compared to some previously stored pattern or template
What is stereognosis?
the mental perception of depth or three-dimensionality by the senses, usually in reference to the ability to perceive the form of solid objects by touch
Name the seven primary cutaneous tactile receptors.
- free nerve endings
- hair follicle
- pacinian corpuscle
- krause endbulb
- meissner’s corpuscle
- ruffini endings
- merkel cells
Cutaneous tactile receptors are all innervated by what type of peripheral nerve fibers?
A-beta fibers
Hair follicle endings are innervated by ___ fibers, function to sense ___, and are located ____.
- A-beta fibers
- hair displacement
- thin skin
Ruffini endings are innervated by ___ fibers, function to sense ___ due to their ____ receptive fields, and are located ____.
- A-beta fibers
- pressure on skin in a specific direction
- elongated receptive fields
- dermis of thin skin
Krause corpuscles are innervated by ___ fibers, function to sense ___, and are located ____.
- A-beta fibers
- light touch
- lips, tongue, genitals
Pacinian corpuscles are innervated by ___ fibers, function to sense ___, and are located ____.
- A-beta fibers
- deep pressure and vibration
- deep dermis of thin skin
Meissner corpuscles are innervated by ___ fibers, function to sense ___, and are located ____.
- A-beta fibers
- vibration
- dermis of glabrous skin (high density in fingers/face)
Merkel cells are innervated by ___ fibers, function to sense ___, and are located ____.
- A-beta fibers
- pressure on the skin
- epidermis of glabrous skin
Which cutaneous tactile receptor is highly concentrated in the skin of the hands and face?
meissner corpuscles
Which cutaneous tactile receptor has elongated receptor fields to sense touch in a specific direction?
ruffini’s corpuscles
Free nerve endings are innervated by ___ fibers, function to sense ___, and are located ____.
- A-delta and C fibers
- respond to mechanical, thermal, or noxious skin stimulation
- everywhere
Pain and temperature are picked up by what cutaneous receptor?
free nerve endings
Damage to a free nerve ending will result in a pain signal, but most pain is actually caused by what sort of stimulus picked up by free nerve endings?
substances released by damaged tissues like histamine, prostaglandins, and substance P
What is the function of muscle spindles?
detect stretch within muscles and the rate of change in length
What is the purpose of muscle spindles having a rapidly- and slowly-adapting component?
this helps encode stimulus about the stretch of muscle as well ast the rate of change in length of muscle
What are the two types of intrafusal muscle fibers?
bag and chain
Name the two types of afferent innervation to muscle spindles.
- primary (aka annulospiral)
- secondary
Annulospiral afferents innervate what portion of the muscle spindle?
the equatorial region of all bag and chain intrafusal muscle fibers
Secondary afferent fibers innervate what specific part of the muscle spindle anatomy?
the juxtaequatorial region of chain fibers
What are the two types of efferent innervations to the muscle spindle?
dynamic gamma and static gamma
What is the difference between dynamic and static gamma efferent innervations to the muscle spindle?
- dynamic innervate the polar regions of bag fibers
- static innervate the polar regions of chain fibers
Describe the events that cause muscle spindle afferent firing.
- muscle stretch stretches the muscle spindle in parallel
- this deforms the annulospiral and secondary afferent nerve endings
- sodium channels open
- the afferent nerves are depolarized
- this causes an increase in afferent nerve firing
Muscle spindle afferents project to where?
- alpha motor neurons in the ventral horn
- spinocerebellar neurons in Clarke’s column
How do gamma motorneurons boost muscle spindle output?
they increase firing the firing rate of afferents innervating chain fibers at a constant length to increase their sensitivity and prevent a pause in firing when the muscle shortens
Golgi tendon organs transmit information about what?
the amount of tension exerted at the myotendinous junction
Do muscle spindles or golgi tendons contribute more to sensation of joint position?
golgi tendons
Golgi tendon organs are innervated by what sort of afferent fibers?
Ib afferents
Describe the structure of how Ib afferents innervate golgi tendon organs.
Ib afferent nerve endings are woven between the collagen fibers of the golgi tendon and are compressed/pinched when the collagen fibers are stretched due to increased tension
Name the four primary afferent axons?
- Aalpha
- Abeta
- Adelta
- C
Which of the four primary afferent axons has the fastest conduction velocity?
A(alpha)
Conduction velocity depends on what two features of an axon?
diameter and degree of myelination
Pain and temperature sensation is carried via what sorts of afferent axons?
A(delta) and C fibers
What are the three major sensory modalities?
- discriminative touch (touch, pressure, vibration)
- pain and temperature
- unconscious proprioception
