Question | Answer |
Sensations begin with activation of what type of neuron? | The activation of primary receptors. |
Primary receptors vary in morphology and what else? | The cellular processes tht they use to detect stimuli |
Define: adequate stimulus | The stimulus to which a specific primary receptor is most responsive to. |
Receptors can be what two different things? | Simple nerve endings, or different cells |
What senses have their primary receptors located in the peripheral NS? | Taste, Mechanoreception, pain, temp, proprioception, hearing, Olfaction |
What senses have there primary receptors in the CNS? | Vision |
What is the conversion of stimulus energy into electrochemical energy? | transduction: the beginning of the sensation! |
Give the steps in the start and propogation of a typical sensation in a mechanoreceptor neuron. | Adequate stimulus: mechanical in the periph. target, such as muscle, skin, tendon. -> Stim produces local change in memb potential called receptor potential -> receptor potentials add up until they reach thresh -> AP starts and propagates down the nerve |
What causes receptor potentials (local changes in membrane potential)? | Opening and closing of ion channels. |
To start a receptor potential such as in taste, smell, what is the transducer mechanism in the receptor? | Chemoreceptors! recog. a ligand -> ligand binds -> channel opens -> local membr. depol |
To start a receptor potential such as in touch, pressure, vibr, muscle/joint position, distension of hollow organs, hearing and balance, what is the transducer mechanism in the receptor? | mechanoreceptors! movement occurs -> causes channel to open -> local depol of the primary recept mem |
To start a receptor potential such as in vision, what is the transducer mechanism in the receptor? | Photoreceptors! THESE ARE ALWAYS POLARIZED (CHANNELS OPEN) -> When light stimulus occurs, the channels close and the primary receptor mem is HYPERPOLARIZED!! |
What are the four attributes of a stimulus? | Timing, qualility, intensity, location |
What is a labeled line code? | The tuning of receptors to a narrow band of stimulus energy (stimulus quality!) |
What is another name for stimulus quality? | Modality |
What is meant by stimulus quality? | The type of stimulus that a receptor responds to. There are two parts to this: the receptor must be specific for the certain stimulus (labeled line code) and it must follow certain CNS pathways |
What is the important take home message about modality? | It isn't just the receptor specificity that is important. The pathway is just as important!!! |
What are the two ways that stimulus intensity can be encoded? | frequency, or population |
Stimulus Intensity: How does frequency code work? | receptor firing freq is proportional to the stimulus intensity. A receptor can function within a certain range. A certain intensity stimulus is needed to reach threshold, then it has a dynamic range (usable range) until it maxes out. |
Explain frequency code dynamic range | The range of stimulus intensity over which a change in receptor firing freq can be detected. Below this, intensity hasn't reached threshold, and above this, it is maxed out. All receptors have different dynamic ranges |
Explain what is meant by maxing out frequency code as it relates to stimulus intensity? | After a certain point, an increase in intensity will no longer produce a change in firing frequency. After this point, stimulus information will be lost. This point is called saturation. All receptors have different saturations. |
Stimulus Intensity: How does population code work? | Stimulus intensity is encoded by the of activated receptors. |
As the intensity of a stimulus increases, what also increases? | The number of active receptors (process called recruitment) and the firing frequency of the receptor (to a point of saturation!!!) |
Stimulus location: Explain what this is | The spacial distribution of sensory neurons that are activated by any one stimulus |
What is receptive field? | The area covered by a specific neuron that when a stimulus occurs in that area, it will cause the cell to fire AP's |
What determines the size and location of the receptive field? What is this called? | The location and distribution of the receptor endings. A place code |
If a person has a large receptive field in a certain area, they will have what kind of spacial resolution? | Very LOW. That area on the person's body would be unable to distinguish between two detectible stimuli if they were too close together. |
An area with a very high density of innervation would have what kind of receptive field? | A very small one. Examples: fingers, hands, face, upper lip. Lrg receptive field examples: back, belly, thigh |
What is two point discrimination? | A way to test the density of a receptive field. The more dense a receptive field, the smaller it will be size wise, and the more ability it will have to determine the distance between two identifiable stimuli |
What implecations does the density of a receptive field have on the CNS? | An increased receptive field density means an increased amt of information gathered there, so an increased amt of CNS tissue devoted to it! |
Stimulus timing: how are they encoded? | as changes in frequency of a sensory neuron's activity! |
All receptors do what in response to constant stimulation? What is this called? At what rate does this occur? | Decrease their firing freq. This is called adaptation. This can occur quickly or slowly, depending on the receptor. |
For slowly adapting receptors: explain how they show timing and how often they generate ap's | Signal timing/duration and intensity (magnitude!): They show timing by remaining persistantly depolarized until the stim ends and they generate aps during the entire time they are being stimulated |
For rapidly adapting receptors: explain what they show? | Signal Velocity (rate of change) and Duration: They only respond at the beginning and end of a stimulus, signalling the rate at which a stimulus is applied or removed. |
RA receptors DO NOT show what? They only respond when what? They encode the rate at which _______ ______ ________. | INTENSITY! Only respond when skin is moving. .....skin is indenting |
ALL sensory systems have what property? | Feature extraction! |
What is feature extraction? | putting together information sent by thousands of individual receptors into one complex sensory event. |
In feature extraction, what is involved? | All different types of neurons, that respond to different types of stimuli (modality), with different receptive fields (location), with varying intensities, over a certain period of time. |
Tap/flutter: give modality, receptive field size, intensity, timing (type) | Modality: Meissner's corpusles in the dermal pappilae, RecF: Very small, Intensity/Timing: RA |
Touch/Pressure: give modality, receptive field size, intensity, timing (type) | Merkel cells: RecF:small, Intensity/Timing: SA |
Vibration: give modality, receptive field size, intensity, timing (type) | Mod: Pacinian corpuscles, RecF: Large, Intensity/Timing: RA |
Stretch: give modality, receptive field size, intensity, timing (type) | Mod: Ruffini endings, RecF: Large, Intensity/Timing: SA |