Block 8 (Neuro) - Sensory 1-4 Flashcards
What are the three common steps to coding and processing of all sensory information?
- A physical stimulus is present
- That stimulus is transduced into a message of electrical signals
- There is typically a response to that message by the CNS.
True or false - all colors, tones, smells, sounds, and tastes are not real outside the CNS.
True
What is the accurate organization of the essential properties of an object/stimulus that allows us to interpret and manage/manipulate it successfully?
Perception
What are the three main functions of receptors?
- Sensation
- Control and coordination of movements
- Arousal
What are the 4 elementary attributes of a stimulus?
- Modality (one of the 5 senses)
- Intensity (strength of stimulus)
- Duration (perceived time a stimulus is present)
- Location (homunculus)
Every stimulus has a sensory threshold - how is this threshold defined?
Lowest detectable intensity which can be perceived at least 50% of the time
True or false - threshold is due to changes in the receptor of changes in the receptor’s threshold.
False - it is not due to the receptor; changes occur in the CNS.
What is the capacity to process a certain type of signal that must be present for that stimulus to be perceived?
Detectability
What is an attitude or bias towards certain sensations that allows us to tolerate certain stimuli and prevent false alarms?
Criterion
The perceived duration of a stimulus is a function of the ___ and NOT of the ___.
CNS; receptor
Duration is the relationship between the ___ intensity and the ___ intensity.
Stimulus; perceived
___ occurs in most stimulus pathways, resulting in a decrease of the perceived intensity of a stimulus during long-term stimulation.
Adaptation
Where is perception of stimuli greatest/sharpest?
At regions of greatest contrast
What is the basic outline for all sensory modalities, beginning with receptors?
- Receptors (transduction)
- 2nd order neurons (transmission)
- 3rd order neurons (thalamus - modulation)
- Cortex
Where does perception occur?
Cortex
What is the conversion of a particular form of energy into an electrochemical signal by a receptor?
Signal transducton
What is the process of relaying a signal to the next neuron in the pathway via a series of APs?
Neural encoding
True or false - signal transduction is always excitatory.
True
What are the two ways of encoding intensity?
- Frequency coding - stronger stimuli evoke a greater number of AP’s from a single receptor (frequency increases)
- Population coding - stronger stimuli excite a greater number of receptors (population increases)
What is the area innervated by a single receptor?
Receptive field
What are the two types of receptors related to duration?
- Rapidly adapting (fire AP’s only at on/off of stimulus)
2. Slowly adapting (AP’s throughout stimulus duration)
What determines the modality of a receptor?
Labeled line code - the specific type of receptor and its transducing abilities
Most sensory inputs to the CNS follow a pattern of extensive ___ or ___.
Convergence; divergence
What are the three types of inhibition?
- Feed-forward: allows the primary incoming input to inhibit the input of surrounding neurons, resulting in one response over all others
- Feed-back: allows the most active output cell from a nucleus to inhibit or suppress the less active cells of that nucleus (less robust than feed-forward)
- Distal: allows for resetting of the gain of selected synapses by the cortex directly
What does it mean to increase contrast?
Inhibition of surrounding areas enhances the perception of the stimulus
Where does adaptation occur in the pathway?
In the spinal cord, NOT in the receptor or its afferent fibers
At the most sensitive areas, the number of receptors per unit area of skin is ___, while the size of the receptive field of each receptor is proportionally ___.
Large; small
As the size of the receptor field gets larger, what happens to the number of receptors?
Decreases
Receptor output is greatest when a stimulus is applied at the ___ of the receptive field.
Center
The cortex is arranged in ___.
Columns
What is the primary receptor on hairy skin?
Hair follicle receptor (also has deep receptors and Merkel’s)
What are the receptors on glaborous (hairless) skin?
Superficial: Merkel’s (slowly adapting), Meissner’s (rapidly adapting) - small receptive fields, very sensitive
Deep: Pacinian’s (rapidly adapting), Ruffini (slowly adapting) - large receptive fields
What are the three types of nociceptors?
- Mechanical
- Thermal (hot >45 C, cold <15 C)
- Polymodal (chemical and mechanical)
What size/type of fibers are the fastest and what type of information do they carry?
Large, myelinated fibers; proprioceptive information
What types of information do small, thinly myelinated fibers carry?
Sensory information
What type of information do the smallest myelinated and unmyelinated fibers carry?
Pain and temperature
What are the three types of proprioceptors involved in proprioception?
- Muscle spindle receptors within the muscle tissue (primary position sensor)
- Mechanoreceptors in joint capsules and tendons
- Mechanoreceptors in the skin
What are the two types of muscle receptors?
- Muscle spindle
2. Golgi tendon organ (GTO)
Force and change in length of muscles are dependent on what three factors?
- Initial length
- Velocity of length change
- External loads (tension) opposing movement
Where are muscle spindles found?
Within the extrafusal muscle fibers in parallel with the muscle
What innervates muscle spindles?
Group 1a and 2 axons (large and medium myelinated axons)
What are muscle spindles composed of?
Intrafusal muscle fibers (contractile), sensory axons (afferents), and motor axons (efferents which regulate sensitivity)
Each muscle spindle has three types of intrafusal fibers - what are they?
- Nuclear chain fibers
- Nuclear bag fibers
a. Dynamic
b. Static
What are nuclear chain fibers?
Thin fibers with nuclei arranged in a single file; afferents include groups 1a and 2
What are nuclear bag fibers?
Thicker fibers with nuclei grouped in the central region
What are the two subtypes of nuclear bag fibers and how do they differ?
- Dynamic: sensitive to rate of change (rapidly adapting); afferents include group 1a only
- Static: slowly adapting stretch receptors; afferents include both group 1a and2
What happens when a muscle is loaded (stretched)?
Intrafusal fibers are stretched, leading to an increase in the number of AP’s sent to the CNS
Motor axons are called ___ motor neurons and innervate only the ___ regions of the intrafusal muscle fibers. This is known as the ___ system.
Gamma; polar; fusimotor
Where are GTOs found?
At the junction of the muscle fibers and the tendon (in series with muscle)
What innervates GTOs?
Group 1b axons (large, myelinated)
What are GTOs composed of?
A weave of collagen fibers (from tendon) and unmyelinated nerve branchesm within the GTO
What happens in a GTO when tension on a tendon is increased?
Intertwined fibers are compressed, resulting in increased number of APs to the CNS
Spindles sense changes in the ___ of the muscle. GTOs sense changes in ___ of the muscle.
Length; tension
What are the primary differences between dynamic and static muscle spindle fibers?
Dynamic: length is actively changing; sensitive to velocity; rapidly adapting
Static: steady-state phase; slowly adapting
How do spindles reset their sensitivity?
Gamma motor neurons
Activation of static gamma motor neurons reflects information about the ___ of the muscle. What fibers does it reset?
Actual length; static bag and nuclear chain fibers
Activation of dynamic gamma motor neurons reflects information about the ___ of the muscle. What fibers does it reset?
Phasic fluctuations in length; dynamic bag fibers only
What is intrafusal creep?
Dynamic bag fibers respond to stretch with a viscous resistance; static fibers react uniformly to stretch (no creep). Central regions of the dynamic fibers respond to stretch like a spring. Polar regions react more like a shock absorber.
When stretch is slow, the entire spindle act like a ___. When stretch is fast, what happens?
Spring (polar region keeps pace)
When stretch is fast, the central region acts like a spring but the polar region lags, resulting in a slight recoil to the stretch - this is intrafusal creep
Intrafusal creep allows dynamic fibers to code for ___.
Velocity
Contraction of the polar regions of the intrafusal fibers allows for restting of the spindles during tension, primarily via ___.
Alpha-gamma coactivation
What is fusimotor set?
The setting of motor system gain before and during motor activation in order to fine tune the motor system to various types of activity.
How is muscle tone regulated?
Through a negative feedback system
What are the two crucial components of a negative feedback system?
- Gain of the system
2. Loop delay
What is the gain of a system?
Strength and effectiveness; the larger the gain, the greater the muscle force to a given stimulus
What are the three ways in which the CNS can modify gain?
- Adjusting the level of fusimotor activity
- Presynaptic modulation of the inputs to the alpha-motor neurons
- Direct input to the alpha-motor neurons by the CNS
What is loop delay?
Inherent delays built into the motor system which can affect the time it takes to produce or adjust a motor response
What are the 5 submodalities of taste?
Sweet, salty, sour, bitter, umami
Most foods have a distinctive ___ as a result of the interaction of taste and smell occurring simultaneously.
Flavor
Scattered about the surface of the tongue are small projections called ___. They have three shapes - what are they?
Papillae
- Ridges (foliate)
- Pimples (valate or circumvallate)
- Mushrooms (fungiform)
Each papilla has from one to several hundred ___. Each of these has 50-150 ___.
Taste buds; receptor cells
Where on the tongue are the 4 primary taste submodalities distributed?
Sweet - anterior
Salty and sour - lateral
Bitter - posterior
Taste cells are not true neurons - what are they?
Specialized epithelial cells with the morphological characteristics of chemical synapses
When a taste cell is activated by an appropriate ___, the membrane depolarizes, resulting in a receptor potential and possibly an AP. Depolarization results in the opening of ___ and release of ___ (specifically). These depolarize the sensory axons and produce AP.
Chemical; voltage-gated Ca2+ channels; NT (ATP)
How do salt-sensitive taste cells respond to changes in salt concentration?
A specialized Na+ channel is open all the time; increases in salt increase the gradient, resulting in a depolarization of the taste cell. This activates the voltage-gated Na+ and Ca2+ channels, triggering release of NT (ATP)
The larger the anion in a salt molecule, the more it ___ depolarization.
Inhibits
The higher the ___, the more sour a food tastes.
Acidity
How is sourness perceived?
Acids dissolve and generate protons. These do two things:
- Diffuse through non-gated Na+ channels, resulting in depolarziation
- Blocking K+ channels, resulting in depolarization
How is bitterness perceived?
Stimulus: quinine
Receptors: T2R (poison detectors)
Second messenger system (IP3/DAG)
How is sweetness perceived?
Stimulus: various
Receptors: T1R2 and T1R3 (both components must be present to activate the receptor)
Second messenger system
How is umami perceived?
Stimulus: amino acids, especially glutamate
Receptors: T1R1 and T1R3 (both must be present)
Second messenger system
What is the primary gustatory cortex (area ___)?
Area 43 (in the ventral parietal lobe)
Where are the olfactory receptors?
Within the nasal cavity (confined to a specialized patch of epithelium)
What are olfactory receptor cells?
Bipolar neurons with short peripheral processes and long central processes
What are olfactory knobs?
Projection of short arm of olfactory process
What are olfactory cilia?
Project from olfactory knob, forming a dense mat
What is the central process?
Unmyelinated axon, forms bundle with 10-100 other axons, surrounded by Schwann cells and projecting to olfactory bulb
What are basal cells?
Precursors to new olfactory receptors
What happens when an odorant binds to a specific recognition site?
G-protein mediated activation of AC -> cAMP -> interacts DIRECTLY with cation channels conducting Na/Ca, resulting in depolarization. Ca also opens Cl channels, which results in further depolarization
Olfactory receptors synapse onto second-order neurons in the ___.
Glomerulus
Within the glomerulus are either tufted or mitral second order neurons. Where do these project?
Mitral - all higher levels of olfactory perception
Tufted - only to the anterior olfactory nucleus and the olfactory tubercle
