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Stack #215106

Neuro Unit II Lecture 3

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
Created by: StudyBuddies