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44 Cards in this Set
- Front
- Back
What is the modality
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A type of physical phenomenon that can be sensed
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Types of modalities
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– Photonic
– Chemical – Temperature - Pressure > auditory >somatic |
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Somatic pressure sensations can be divided into
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- externoceptors
- internoceptors - proprioceptors |
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Types of externoceptors
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- Meissners corpuscle
- Pacinian corpuscle - Ruffini's corpuscle - Merkel's disk - Free nerve endings |
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Meissners corpuscle
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– Light touch
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Pacinian corpuscle
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– deep pressure
– vibration |
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Ruffini's corpuscle
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– skin stretch,
– sense of position – movement |
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Merkel's disk
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– vibrations at low frequencies
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Free nerve endings
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– touch,
– pressure, – stretch, – temperature – pain |
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Internoceptors and proprioceptors
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Provide information concerning position of the body
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How we sense a particular modality depends on
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– The type of receptor
– Where the fibers terminate in the brain |
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Synesthesia
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A neurological phenomenon in which simulation of one sensory pathway leads to autonomic, involuntary experiences in a second sensory pathway
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Grapheme
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Color synesthesia: individual letters and numbers (collectively referred to as graphemes) are shaded or tinged with color
- See a color think of the number, see the number and think of the number in a specific color |
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Possible neural basis for grapheme color synesthesia
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– Crosstalk between different regions specialized for different functions
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Receptor/generator potential
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Depolarization of the receptive portion of the sensory axon caused by application of the sensory stimulus
– The exception is rods and cones which hyperpolarize |
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What are the special senses and which nerves they carried by
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- olfatory nerve <-- smell
- optic nerve <-- vision - facial nerve (chorda tympani)<-- taste - glossopharyngeal nerve <-- taste - vestibulocochlear nerve <-- hearing and balance |
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What are the general senses and which nerves are they carried by
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The general senses [somatosensory] are those that are detected from all parts of the body and transmitted to the CNS via
- Trigeminal nerve <-- sensation to the face - All spinal nerves [except C1] |
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Type of receptors that can be excited to generate an impulse
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– Mechanical receptors [deformation]
– Chemical – Temperature – Electromagnetic [i.e. light] |
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Mechanical receptors
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By mechanical deformation of the receptor which stretches the membrane and opens ion channels
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Pacinian corpuscle characteristics
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– Activated via mechanical D formation
– 20 – 60 concentric lamellae composed of fibrous connective tissue supported by gelatinous material – Nerve ending located centrally within inner bulb in a fluid filled cavity - a single afferent unmyelinated nerve ending is activated the stretch |
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Chemical activation of ion channels
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Chemical binds --> single transduced in cell --> opening of Na channel --> depolarization --> activation of afferent nerve --> Ca influx and release of NT
– Example: taste buds |
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Electromagnetic radiation affect on receptor [Dark]
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– In the dark, cGMP levels are high and cGMP gates [sodium channels] are open. Positively charged sodium enters the photoreceptor and depolarizes it.
– resting potential is – 40 MV [high compared to most cells] – Result is tonic release of neurotransmitter in the absence of light |
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Electromagnetic radiation affect on receptor [Light]
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– In the light, rhodopsin in the outer segment of the rod is stimulated by a photon of light
– Activation of signaling cascade culminating with DECRASED cGMP levels – CLOSING of cGMP gated sodium channels – Potassium channels are unaffected and get net HYPERPOLARIZATION of cell to – 70mV – Reduced neurotransmitter release |
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Modality: intensity
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Intensity or amount of a sensation depends on the strength of a stimulus
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Sensory threshold
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The lowest stimulus intensity a person can detect [Anything about this well elicit an action potential]
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How can different levels of intensity be transmitted
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– By sending more impulses along the single fiber [Frequency coding or Temporel summation]
– By increasing the number of Perlow fibers transmit information [Population coding or spatial summation] |
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Modality: duration
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The relationship between the stimulus intensity and the perceived intensity
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Adaptation
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If the stimulus persists for a long time the intensity diminishes
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Differences in adaptation between cell types
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– Carotid and aortic baroreceptors may take up to two days to completely adapt
– Pacinian corpuscles adapt to extinction within a few hundreds of the second because of their morphology |
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Modality: location
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– Ability to locate the site of stimulus
– Ability to distinguish two closely spaced stimuli |
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What is necessary for two point discrimination
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– Receptor density
– Size of receptive fields |
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Contrast
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– You need to have at least one receptor between two points to perceive two touches
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Differences and size of receptive fields and affect on point discrimination
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– Fingertips have SMALLER receptive fields than the back, so the chance of two touches hitting targets that are at least one receptor way from each other is greater
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Lateral inhibition
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– Allows sensory cortex to detect two touches versus one
– lateral inhibition blocks the lateral spread of expiratory signals and therefore increases the degree of contrast in the sensory patterns perceived by the cortex |
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Merkels disc: stimulus, sensation, adaptation?
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Stimulus: steady indentation
Sensation: pressure Meditation: slow |
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Meissner's corpuscle: stimulus, sensation, adaptation?
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Stimulus: low-frequency vibration
Sensation: gentle fluttering Adaptation: rapid |
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Ruffini's corpuscle: stimulus, sensation, adaptation?
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Stimulus: rapid indentation
Sensation: stretch Adaptation: slow |
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Pacinian corpuscle: stimulus, sensation, adaptation?
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Stimulus: vibration
Sensation: vibration Adaptation: rapid |
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Hair receptor: stimulus, sensation, adaptation?
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Stimulus: hair deflection
Sensation: brushing Adaptation: rapid or slow |
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A(alpha) [Ia] fiber functions
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– Proprioception
– Stretch – Primary muscle spindle afferents – Motor befriend to muscle [extrafusal] |
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A(alpha) [Ib] fiber functions
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– Contractile fibers: golgi tendon organ efferents
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A(beta) [II] fiber functions
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Mechanoreception:
– Discriminative touch – Pressure – Joint rotation – Secondary muscle spindle efferents |
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A(gamma) [II] fiber functions
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– Muscle spindle intrafusal efferents
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Relative size + conduction velocities of sensory fibers
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Ia=Ib > II (Ab) > II (Ay) > III > C
** larger size correlates with faster conduction velocity ** C fibers nonmyelinated |