Neuro Unit II Lecture 3
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| Sensations begin with activation of what type of neuron? | The activation of primary receptors.
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| Primary receptors vary in morphology and what else? | The cellular processes tht they use to detect stimuli
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| Define: adequate stimulus | The stimulus to which a specific primary receptor is most responsive to.
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| Receptors can be what two different things? | Simple nerve endings, or different cells
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| What senses have their primary receptors located in the peripheral NS? | Taste, Mechanoreception, pain, temp, proprioception, hearing, Olfaction
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| What senses have there primary receptors in the CNS? | Vision
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| What is the conversion of stimulus energy into electrochemical energy? | transduction: the beginning of the sensation!
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| 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
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| What causes receptor potentials (local changes in membrane potential)? | Opening and closing of ion channels.
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| 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
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| 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
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| 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!!
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| What are the four attributes of a stimulus? | Timing, qualility, intensity, location
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| What is a labeled line code? | The tuning of receptors to a narrow band of stimulus energy (stimulus quality!)
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| What is another name for stimulus quality? | Modality
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| 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
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| 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!!!
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| What are the two ways that stimulus intensity can be encoded? | frequency, or population
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| 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.
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| 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
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| 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.
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| Stimulus Intensity: How does population code work? | Stimulus intensity is encoded by the of activated receptors.
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| 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!!!)
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| Stimulus location: Explain what this is | The spacial distribution of sensory neurons that are activated by any one stimulus
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| 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
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| 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
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| 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.
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| 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
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| 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
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| 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!
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| Stimulus timing: how are they encoded? | as changes in frequency of a sensory neuron's activity!
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| 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.
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| 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
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| 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.
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| 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
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| ALL sensory systems have what property? | Feature extraction!
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| What is feature extraction? | putting together information sent by thousands of individual receptors into one complex sensory event.
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| 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.
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| Tap/flutter: give modality, receptive field size, intensity, timing (type) | Modality: Meissner's corpusles in the dermal pappilae, RecF: Very small, Intensity/Timing: RA
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| Touch/Pressure: give modality, receptive field size, intensity, timing (type) | Merkel cells: RecF:small, Intensity/Timing: SA
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| Vibration: give modality, receptive field size, intensity, timing (type) | Mod: Pacinian corpuscles, RecF: Large, Intensity/Timing: RA
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| Stretch: give modality, receptive field size, intensity, timing (type) | Mod: Ruffini endings, RecF: Large, Intensity/Timing: SA
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