Seeing and hearing lecture 9

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What are we detecting with hearing?
Sound (Frequency and amplitude of vibrations travelling through the air)
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What are we detecting with vision?
Light (Intensity and weave length of light reflected from objects)
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Where does transduction take place in hearing?
The organ of corti in the ochlea
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Where does transduction take place in the vision?
The photo eceptors of the retina
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How does transduction take place with hearing?
Pressure -> Basilar membrane -> Hair cells -> Action potential
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How does transdution take place with vision?
Light -> Photoreceptors -> Photopigments -> Action potential
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What features are being represented with hearing?
Pitch, loudness, location, auditory scene analysis, grouping
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What features are being represented with vision?
Contrast, colour, edges, grouping, shapes, surfaces
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What is the vestibular system?
It provides informatino about the position and movement of the body relative to the external world, it tells us about balance and our orientation to the world.
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What does the vestibular system rely on?
Receptors in the inner ear (semicircular canals - semicircular structures which are angled in a certain away and contain fluid, and when you move your head that fluid moves and triggers hair cells to tell us about our bodies position in space).
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What connections does the vestibular system have?
A number of connections with other parts of the brain including the oculomotor system.
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What is the vestibulo-ocular reflext (VOR)?
The link between our eyes and our head movements.
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What does the show?
That we have really fast connections between the semi-circular canals and our eyes
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What causes motion sickness?
When there is a mismatch between our senses (i.e., vision and balance)
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What is the somatosensory system?
It provides information about the position and movement of the body and can be divided into proprioception/kinesthesia
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What is Proprioception?
Our perception of where our limbs and body is in space. The senses and position and movement of our limbs and trunk, the sense of effort, the sense of force and the sense of heaviness
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What is Kinesthesia?
It places emphaiss on the body's motions and incorporates routine or habitual behaviours to improve movements.
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What is the difference between kinesthesia and proprioception?
Kinesthesia = body's motions, proprioception = cogntive awareness
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What system is responsible for touch?
The somatosensory system
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What is touch?
Touch responds to changes at the surface of the body (the skin), it is responsible for our tactile sensation.
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Where is touch most sensitive?
Hands, lips, genitals
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What is the skin?
The organ of touch perception. Our skin protects us, while letting us perceive sensations of touch temperature and pain
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What does the skin consist of?
The epidermis, dermis and hypodermis
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What does the epidermis consist of?
Melanocyte, Stratum Corneum, Stratum lucidum, stratum granulosum, stratum spinosum, basal layer
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What does the skin protect us against?
Water, radiation
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What are mechanoreceptor?
A sensory receptor that responds to mechanical pressure or distortion, it responds to being moved
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What are the 5 tactile receptors?
The Meissner corpuscle, pacinian corpuscle, Ruffini organ, Merkel disks, Free nerve endings
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What can we categorise tactile receptors in terms of?
Sensitivity, adaptation rate, receptive field, location in the body
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What does it mean if a tactile receptor adapts quickly?
Means that there is no response to sustained pressure, only to changes in pressure (either an increase or decrease), so like if something is constantly poking that cell it will respond once when it starts being poked and maybe when it stops
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What does it mean if a tactile receptor has slow adaption?
IT means that the receptor continues to respond to pressure for as long as it is sustained within some reasonable time frame (it will constantly respond to being poked for a while)
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Where are the Meissner's corpuscles most commonly found?
In the hands
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What sort of information are Meissner corpuscles good at?
Rapidly adapting cell,transmitting information about low frequency vibrations, it responds the most to rough textures , detects large scale texture going over hands
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Where are the Pacinian Corpuscle found?
Deep in the skin
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What are the Pacinian Corpuscles?
More sensitive than the meissner corpuscles, rapidly adapting, most sensitive to high frequency textures (smooth things), as common as the meissners
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In what other animal are pacinian corpuscles found?
Birds. Ducks have them in beaks.
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What are Merkel disks?
Close to the skin , slowly adapting, account for 25% of receptors in the hand, clustered where we are particularly sensitive (lips, finger tips), responds to surface touch, light pressure, shapes, edges and rough textures
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What do merkel disks look like?
Star disks
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Where is the Ruffini organ found?
Dermis, (fat tissue)
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What do Meisner found?
Epidermis
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What do Meisner look like?
Long grains of wheat
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Tell me about Ruffini Corpuscles
Deep, slow responding, sensitive to large things or stretching of the skin, 20% of receptors in the hand, known for limb movement or finger position
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How can we test tactile sensations?
Electrical stimulation of receptors in the skin allows us to test the sensations produced. Meissner's give a tapping or "flutter", Pacinian = sense of vibration or tickle, Merkel's = sensation of light pressure, Ruffini's = no sensation??
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What do Pacinian look like?
Wide disks
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Where are Pacinian corpuscles found?
Fat tissue (dermis)
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What % of tactile receptors are found on the hand?
40% Meissner's corpuscles, 25% Merkel's disks, 10-15% Pacinian corpuscles, 20% Ruffini's corpuscles.
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What tactile receptor responds to texture?
Meissner's corpuscles
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What tactile receptor responds to light pressure, shapes, edges and rough textures / sustained touch and pressure.
Merkel's disk
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What tactile receptor responds to fine surface texture and rapid vibration?
Pacinian Corpuscles
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What tactile receptor has no tactile sensation and is related to movement and limb position?
Ruffini's Corpuscles
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What are the rapidly adapting tactile receptors?
Meissner and Pacinian Corpuscles
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What are the slowly adapting tactile receptors?
Merkel's disk and Ruffini's Corpuscles
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What are Cutaneous Mechanoreceptors?
Receptors in the skin
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What is a receptive field?
The receptive field of an individual sensory neuron is the particular region of the sensory space (the body surface or visual field) in which a stimulus will trigger the firing the firing of that neuron (where something is to make a neuron respond)
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The different corpsucles have different receptive fields which ones have which?
Mesiner and Merkels are small, Ruffins has medium, small and large and pacinian has large
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Why are we more sensitive in our fingers/hands/lips?
Because we have more sensitive tactile receptors which have a smaller receptive field (Meissner's and Merkels)
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What is the two-point threshold?
When you get two things and give someone a poke, after a certian distance they can detect that they are two separate things and not one thing.
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What is the two-point threshold of the tongue?
1.1mm
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What is the two-point threshold of the finger?
3 to 8 mm
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What is the two-point threshold of the back/shoulders?
36 to 75mm
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What is the aristotle illusion?
When you touch something with both fingers you feel it as one thing but if you cross your fingers it feels like two things
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Is touch active or passive?
It's active
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Are free nerve endings Mechanoreceptors
No
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What are free nerve endings?
The receptors which respond to pain stimuli, they are used by the brain to detect pain. They function as cutaneous receptors and are essentially used by the brain to detect pain. They are unencapsulated and have no complex sensory structures.
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What is the definition of pain?
A submodality (Group) of somatic sensation. The word pain is used to describe a wide range of unpleasant sensory and emotional experienced associated with actual or potential tissue damage. Nature has made sure that pain is a signal we cannot ignore
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What is pain also known as?
Nociception
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What are the different type of pain receptors?
Skin Nociceptors (high threshold pressure), Joint Nociceptors (moving pain) , Visceral Nociceptors (inside your body), Silent Nociceptors (have an injury already),
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What are the different types of pain?
Pricking, Burning, Aching pain
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What is pricking pain?
Sharp quick immediate response you get when you are hurt, you get an immediate signal, localised
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What is burning pain/soreness?
Slow and nagging pain, not localised
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What is aching pain?
Slow nagging pain inside not localised
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What explains the different types of pains?
The different fibres and pathways
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What are the different types of pain fibres?
A delta and C fibres
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What are A delta pain fibres?
They are myelinated meaning they are really fast and can transmit the signal very quickly, also smaller than C fibres. Carry information about fast quick pain.
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What are C pain fibres?
They are unmyelinated and slow so carry around information about slow burning pain
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What helps us with proprioception?
Muscle spindels, joint receptors, cutaneous afferents (mechanoreceptors), golgi tendon organ
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What is the golgi tendon organ?
Tendon attaches muscles to bones, when it is stretched it gives us information about where we are. Provides the brain with information about muscle tension
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What are muscle spindles?
Sensory receptors within the belly of a muscle that primarily detect changes in the length of this muscle
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What are joint receptors?
They are found in the synovial junctions between bones. The receptors detect mechanical deformation within the capsule and ligaments. They serve two main purposes, to protect the joint and serve as propriocepters
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How do pain receptors end up in the brain?
Through the medial lemniscal and spinothalamic pathway, all the nerves goes to the spinal cord and then up to the brain.
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What is the medial lemniscal pathway?
Contains large fibres and carries information about proproception and touch
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What is the spinothalamic pathway?
has small fibres and carries information about quick signals which are related to temperature and pain
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If you get touched on the left side of your body what side of your brain processes it?
The right
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What is the primary neuron?
Sensory receptor that detects sensory stimuli like touch or temperature (goes from skin to spine)
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What is the secondary neuron?
Acts as a relay and is located either in the spinal cord or the brain stem. (goes from spine to brain)
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What is the tertiary neuron relating to touch?
Has a cell body in the thalamus and projects to the parietal lobe of the brain (goes from spine to brain)
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What is the tertiary neuron relating to proprioception?
Has a cell body in the cerebellum and projects to the parietal lobe of the brain (goes from spine to brain)
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What stream are the motor areas of the brain located?
Dorsal stream
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What do you get to before you get to the motor areas of the brain?
The somatosensory areas in-front of the parietal lobe
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What is the somatoseonry homunculus / somatosensory cortex?
Has different areas for different parts of the body and relates to how sensory we are
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What do we have the most neurons dedicated to?
Hands and lips
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If you are blind and reading brain what part of your brain lights up?
Part of the brain for vision
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Can you change the organisation of the somatosensory cortex?
Yes, it often changes if a limb is removed
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Card 4

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Where does transduction take place in the vision?

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Card 5

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