Exam 2 Sensory Flashcards
Describe the function of the sensory system
To interface between internal and external environments and the nervous system. This provides an “abstraction not a replication of the real world
What senses particular features of our environment What encodes these features What transmits this information to the CNS for decoding and use? It allows CNS to communicate with the outside world It answers questions about What? Where? When? How much?
Function of sensory system
Describe organization of the Sensory sytem
Most important is the transducer because it converts signal into membrane potential
and then the encoder converts mV into AP
Component of Sensory sytem:
What is the first functional element of the sensory receptor, usually non-neural tissue
It allows only a portion of the stimulus to be conveyed to the transducer
Filter
This component of the sensory system conditions the stimulus making the receptor function with relative specificity for one modality
This has two roles:
1) Limits access
2) changes stimulus parameters
For example, the lens of the eye ____ out UV light (limits access) and focuses image on the retina (changes paramters)
Filter
What component of the sensory system converts stimulus into a change in voltage across the membrane of the sensory receptor with a minimal loss in information
Transducer
What component of the sensory system creates the receptor potential? (generator potential, local potential)
The mechanism of the change in the membrane potential is a simultaneous change in the membrane permeability of Na+ and K+ ions
Transducer
Do receptor membranes respond to electrical stimulation?
No because they have no APs, no refactory periods
Receptor potentials are graded: they increase in magnitude as a stimulus gets stronger
-the receptor potential does not propagate (it travels only very short distances)
The receptor potential is a graded potential meaning:
that the ____ the stimulus on the transducer, the _____ the receptor potential
The stronger the stimulus on the transducer, the larger the receptor potential
-but with too much light or sound it starts to level off
This component of the sensory receptor converts the magnitutde of a receptor potential into a frequency code that is carried by action potentials along the axon
-it is the location (trigger zone) of the voltage-gated Na+ and K+ channels capable of producing APs
Encoder
What component of the sensory sytem:
If the receptor potential entering the trigger zone is above the threshold, an AP is generated
- As long as the receptor potential stays above threshold, the cell will continue to fire APs
- The larger the receptor potential, the higher the frequency of APs
Encoder
An example of a sensory receptor is a Pacinian corpuscle ( a skin receptor senstivie to vibration and touch)
What components make up the:
Filter:
Transducer:
Encoder:
Filter: connective tissue capsule
Transducer: the unmylelinated free nerve ending
-it produces a receptor potential when deformed
Encoder: the trigger zone (the first Node of Ranvier)
Explain this image about Paracinian corpuscle
- A. Forces 1, 2 and 3 generate receptor potentials by the transducer. Force 3 is strong enough to cause the encoder to generate action potentials.
- B. As long as a force is applied to the free nerve ending (transducer), receptor potentials are generated with or without a filter.
- C. If a force is applied other than at the free nerve ending, no receptor potential is generated.
-because to convert stimulus energy you need a transducer
What are six types of sensory receptors?
Mechanoreceptors
Thermoreceptors
Chemoreceptors
Osmoreceptors (pressure)
Photoreceptors
Nociceptors (Pain)
What does poly-modal receptor mean?
Responds to 2 or more forms of stimulus such as mechanical and thermal
What are the three divisions that poly-modal receptors can be divided into?
Specialized receptor cells
Specialized endings on nerve fibers
Free nerbe endings
These are the most senstive receptor types
An example is the photoreceptor
Specialized receptor cell
An example of this receptor is the pacinian corpuscle
Specialized endings on nerve fibers
These receptors have no anatomical specialization at the receptor site
They encompass the full range of sensory modalitlies and are the most common receptor type
An example is the pain receptor
Free nerve endings
Sensory receptors are connected to ____?
All the terminals of any one _____ have the same kind of ______
Sensory Units
Receptor
Sensory receptors all have a ______?
- it is that fraction of the total energy of a particular modality that initiates a response in a sensory receptor or sensory unit
- The sensory unit with the greatest number of sensory receptors has the largest _______
Receptive Field
What are the five attributes of sensory coding?
Modality
Location
Intensity
Temporal
Affect
What attribute of sensory coding tell the body “What is present?” (Quality)
Modality and Sub-modality
How is modality coding done by?
This is an anatomical grouping of receptors and pathways devoted to the particualr modality (Place Theory)
Labeled Lines
-Example: specific receptors, pathways and relays carry stimulus modality X information and nothing else
Stimulating (e.g. by chemical currents) anywhere along this chain will give sensation of modality X
Remember that electrical currents applied to the transducer itself will not stimulate it
What is submodality coding done by?
•“pattern codes”
-the pattern of activity within the system of labeled lines
–Example: Color vision uses 3 cone types, Red (R), Green (G) and Blue (B). In various combinations of stimulation, different colors are perceived.
-Different colors that combine togethe r
What type of coding is accomplished by an anatomical sorting or organization of the pathways and their central projections (the labeled line idea applied to a location)
–This type of coding is especially well developed where the receptors lie in “sheets” as in the skin.
–An example is the somatotopic organization of the skin on the cortex. Pathway terminations for different parts of the body in the somatosensory cortex are located on a map called a homunculus.
Location (Spatial) coding
What type of coding is done by the total number of impulses per second coming from the receptor population?
Intensity
What are the basic mechanisms of intensity coding?
–rate
–recruitment
–adaptation
–threshold
–saturation
What is the frequency (number per second) of action potentials in individual sensory units. The stronger the stimulus, the more action potentials are sent up the afferent fibers of the sensory unit.
Rate
What is the number of units that get activated by the stimulus increases with intensity of the stimulus?
Recruitment
Explain this image
A patch of skin innervated by 4 similar sensory units, each having a different threshold. The stronger the stimulus, the greater the recruitment.
-Depending on stimulus sensory units are recruited and depending on strength different units are activated
What is a measure of how well a sensory receptor maintains its response to a constant stimulus?
Adaptaion
–Slowly adapting sensory receptors keep producing membrane potentials as long as the stimulus is applied.
–Rapidly adapting sensory receptors stop producing membrane potentials even when the stimulus is still present.
What is the minimum value of intensity?
Just barely perceivable is the ______ stimulus
Threshold
What is this definition: As intensity increases, eventually the nerve fiber reaches its upper limit for carrying impulses. Further increases in stimulus do not produce a corresponding increase in the response.
Saturation
What type of coding is:
•Different patterns of firing may provide information about submodality.
A response is dependent on the rate of change of stimulus application within a particular frequency range. Most receptors do not respond to constant stimuli but are more sensitive to stimulus change
Temporal coding
What type of coding is:
•This is the least measurable criterion. This attribute takes into account emotional content (such as pain) and learning and memory which depends on prior input.
Affect coding
