Fichas
Sensory Systems
Fichas del conjunto (82)
- 1What is the purpose of the senses?- a sense is information from the world
- the senses can evaluate what, where, when, how much/how strong the information is - 2What is sensory reception?the detection of stimuli by sensory receptors
- 3What do sensory receptors do?detect stimuli outside & inside the body
- 4What is sensory detection specificity?- sensory detectors are specialised to respond to specific types of change
- very sensitive to a very specific stimuli due to the physical limit - 5What are some examples of sensory detectors?1. mechanoreceptors
2. photoreceptors
3. chemoreceptors
4. electroreceptors
5. magnetoreceptors - 6What are some examples of mechanoreceptors?- hair cells in the ears
- touch receptors - 7What do photoreceptors detect?light (vision)
- 8What do chemoreceptors detect?taste & smell
- 9What do electroreceptors detect?electrical fields
- 10What do magnetoreceptors detect?magnetic fields
- 11How do sensory detectors broadly transmit sensory information?send information to the CNS via electrical signals
- 12What is a receptive field?a part of sensory space in which a stimulus can drive an electrical response in a sensory neuron
- 13What quality does the stimulus have to have to drive a response?stimulus has to be appropriate to the type of sensory receptor (modality)
- 14What can the receptive field be?Can be straight-forward: skin surface
Or more abstract: volume, space and timing of a sound - 15Are receptive fields distinct?No - receptive fields can overlap
- 16How is the receptive field represented in the nervous system?A central neuron (in the brain or spinal cord) responds to the receptive field indirectly
- 17What is an on centre-off surround receptive field?- stimulation of one part of the RF = excitation (centre)
- stimulation of another part of the RF = inhibition (surround)
- this can also be reversed - 18What is an example of a retinal receptive field?- light from a specific area in space hits a photoreceptor
- photoreceptors output to bipolar cells (ON/OFF)
- many bipolar cells output to ganglion cells and then to the CNS - 19How does the stimulus affect a response in an on centre-off surround neuron?- excitation is highest when stimulus occurs in the ON part of the receptive field (centre)
- can be inhibitory when stimulus occurs in the OFF part of the receptive field (edge) - 20What are the roles of the sensory areas in the cortex?Primary areas: relay information to certain association areas
Association areas: integrate information both within and across modalities - 21How does sensory information transmit to the CNS?- sensory information from the periphery first enters the thalamic nuclei
- the thalamus sends projections to the cortex - 22What is the role of the thalamus?major site for initial processing of sensory information
- 23How many layers are there in the sensory areas of the cortex?6 layers
- 24What are the physical properties of layer 1?- the "molecular layer"
- almost no neuron cell bodies (connections)
- lots of dendrites from pyramidal cells from lower layers and axons synapsing on those dendrites - 25What are the physical properties of layer 2?- many small densely packed pyramidal neurons with a granular appearance
- inputs from other layers mostly - 26What are the physical properties of layer 3?- pyramidal neurons
- outputs: cortical areas - 27What are the physical properties of layer 4?- inner granular layer
- thickest in sensory cortex
- receives input from thalamus - 28What are the physical properties of layer 5?- largest pyramidal neurons
- outputs: brain stem and spinal cord - 29What are the physical properties of layer 6?- inner granular layer
- many spiny stellate (excitatory) interneurons
- outputs: thalamus - 30What is a property of layer 4 in the primary visual cortex?so thick and specialised that it is subdivided into 4A, 4B and 4C
- 31Summary of inputs of layers:1: connections
2: layer 4
3: layer 4
4: thalamus
5: layers 2 & 3
6: layers 2 & 3 - 32Summary of outputs of layers:1. connections
2. layers 5 & 6
3. layers 5 & 6; opposite hemisphere
4. layers 2 & 3
5. brain stem & spinal cord
6. thalamus - 33What is sensory transduction?conversion of stimulus energy into a change in the membrane potential of a sensory receptor
- 34How does sensory transmission occur?- occurs to the CNS via APs
- larger receptor potentials generate higher frequency APs - 35Why do action potentials have a threshold?- there is spontaneous activity even when there is no stimulus
- must be able to distinguish signal from noise - 36How does the sensitivity of a sensory receptor vary?- threshold stimulus of sensory detector response:
- bloodhound sensitivity to odours 10-100 million times higher than humans - 37Why can the amplitude of APs not encode information about the stimulus?APs are the same amplitude every time
- 38How do APs encode stimuli information?through the rate of firing
- 39Why must the rate of firing of APs be variable?- the strength of stimuli and motor response can vary
- light can vary from barely detectable to very intense
- muscular contractions can vary from very weak to very forceful - 40What must action potentials be able to do?- control the strength of muscular contractions
- represent the intensity of a physical stimulus - 41How does the firing rate of a motor neuron control the motor response?high rate --> strong muscular contraction
lower rates --> weaker contraction - 42How does the size of the stimulus and rate of firing increase a response?- the size of a stimulus is encoded in the frequency of firing of APs in an axon
- a high frequency cause the neuron to release more NT which activates more receptors etc. - 43How does the maximum capacity of a sensory receptor vary depending on the stimuli qualities?Loudness of a tone: frequency coding of neuron
Pitch: range fractionation (ranges) of sensitivity --> certain cells respond to different frequencies - 44How does range fractionation occur in the ear?- vibrations of the air cause the liquid inside the ear to move
- different vibrations cause different parts of the liquid to move
- liquid moves hair fibres in one area which are connected to specific receptors - 45What are the 3 main types of somatosenses?1. Cutaneous senses
2. Proprioception & kinesthesia
3. Organic Senses - 46What are the cutaneous senses?skin senses commonly referred to as touch
- 47What types of stimuli do the cutaneous senses respond to?Pressure: caused by mechanical deformation of the skin vibration
Vibration: occurs when we move our skin across a surface
Heating & cooling: sensations produced by objects that raise/lower skin temperature
Pain: events which cause tissue damage - 48What is proprioception and kinesthesia?provides information about body position and movement
- 49What are the organic senses?arise from receptors in and around the internal organs
- 50What is the purpose of the skin?- protect the cells from the environment
- participates in thermoregulation by producing sweat (cooling) or restricting the circulation of blood (warming) - 51What is the appearance of the skin?varies widely across the body from mucous membrane to hairy skin
- 52What is glabrous skin?smooth, hairless skin found on the palms & soles of feet
- 53What is the composition of the skin?contains subcutaneous tissue (fat), dermis layer and epidermis layer with various receptors scattered throughout the layers
- 54What are the types of receptor in the skin?- Merkel's disks
- Ruffini corpuscles
- Meissner's corpuscles
- Pacinian corpuscles
- Hair follicle endings
- Free nerve endings - 55What are the characteristics of Merkel's disks?- small, sharp bordered receptive field
- located in hair and glabrous skin
- detection of form & roughness especially in the fingertips - 56What are the characteristics of Ruffini corpuscles?- large, diffuse bordered receptive field
- located in hairy & glabrous skin
- detection of static force against skin; skin stretching; proprioception - 57What are the characteristics of Meissner's corpuscles?- small, sharp bordered receptive fields
- located in glabrous skin
- detection of edge contours; braille-like stimuli especially by fingertips - 58What are the characteristics of Pacinian corpuscles?- large, diffuse bordered receptive fields
- located in hairy & glabrous skin
- detection of vibration; information from end of elongated object being held eg. tool - 59What are the characteristics of hair follicle endings?- located at the base of the hair follicle
- detection of movement of hair - 60What are the characteristics of free nerve endings?Hairy & glabrous skin: detection of thermal stimuli; painful stimuli; tickle
Hair skin: detection of pleasurable touch from gentle stroking with soft object - 61What are the two main types of mechanoreceptor in the skin?Fast adapting: respond initially but ignore steady pressure
Slow adapting: respond during both - 62What are some types of fast adapting receptor?- Pacinian corpuscles
- Meissner's corpuscles
- hair follicle displacement - 63What shape and length are Pacinian corpuscles?- oval
- 0.5-2mm long - 64Where are Pacinian corpuscles located?situated in deeper layers of skin
- 65What are the physical properties of Pacinian corpuscles?unmyelinated end of axon which multiple layers of connective tissue
- 66How do Pacinian corpuscles respond?- adapts in 1-2 seconds upon initial pressure
- stops responding to prolonged pressure - 67What are the physical properties of hair follicle receptors?complex mesh of sensory endings around the hair follicle
- 68How do hair follicle receptors vary across species?in some species these hair follicles around the nose and mouth are elongated into whiskers and tactile hairs which provide these animals with crucial information
- in whiskers the sensory detectors involved include both fast and slow adapting types - 69How does the size of mechanoreceptor RFs vary depending on body location?- size of RF varies with differing sensitivities
- eg. hand more sensitive to pain & touch than thigh --> smaller Rf with higher resolution
- this means more sensory neurons are packed into these areas which higher granularity - 70How does sensory information enter the spinal cord?via the dorsal root ganglia
- 71What is a dermatome?- area of skin sending input into each DRG
- adjacent dermatomes overlap - 72What are the different routes into the cerebral cortex?- not necessarily anatomically distinct
- some go ipsilateral util medulla then cross over
- other cross over within the entry level segment of the spinal cord (contralateral)
- all go via the thalamus - 73What specifies how information passes through the thalamus?the area of the thalamus depends on the modality of the stimuli
- 74What area of the thalamus does touch information go through?ventero-posterior lateral/medial (VPM/L) nuclei
- 75How does touch information travel from the thalamus to the cortex?- axons from the thalamus project to the primary somatosensory cortex
- this in turns sends axons to the secondary somatosensory cortex - 76How is the somatotopic map of the cerebral cortex represented?Not isomorphic the the sensory surfaces
- 77Why is the somatotopic map not isomorphic?- partly due to smaller, refined RFs of most biologically important areas
- partly due to the increased complexity of neuronal connectivity in these areas of the cortex
- the higher levels of analysis in the cortex have less topographically precise maps - 78What is a homunculus?a visual representation of the amount of processing dedicated to each part of the body
- 79How are visual maps of the cerebral cortex arranged?- several maps in parallel: both hierarchical and parallel projections of sensory information processing in the brain
- difference aspects of the stimuli can be processed in parallel as well as hierarchical processing with increasing complexity - 80How does processing occur within a cortical column?- cells respond to stimuli from the same modality
- cells respond to inputs originating from the same type of sensory receptor
- cells respond to stimuli from the same area --> RFs - 81What evidence is there for sensory cortical columns?- micro-recordings show that the cortical neurons in the sensory areas appear to be roughly organised into columns
- oriented perpendicular to the cortical surface - 82What is the summary of sensory cortical column activity?- layer 4 receives input from thalamus
- most cortical outputs to thalamus originate in layer 6
- most outputs to other sub-cortical nuclei originate in layer 5 (pyramidal tract - motor pathways)
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- (The brain) Neuroscience and Behaviour Fichas sobre Sensory Systems, creado por Amy Walker el 27/01/2020.
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- Amy Walker
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