Flashcards
Neuroscience Modules 7-11
Cards in this deck (47)
- 1What is the optic disk?Where nerve fibres exist retina and retinal blood vessels originate
- 2What is the Macula?Region in middle of retina critical for central; yellowish hue and no large blood vessels
- 3What is the Fovea?Dark spot about 2mm in diameter where the retina is its thinnest; anatomical reference point in centre of retina
- 4What is the anterior segment of the eye?Outer 1/6 of the eye
- Includes cornea, iris, ciliary body and lens
- Filled with aqueous humour - 5What is the posterior segment of the eye?Inner 5/6 of the eye
- Includes retina, choroid and optic nerve
- Filled with vitreous humour - 6What accounts for 80% of focusing and what accounts for 20% of focusing?The cornea, which is fixed accounts for 80% and the lens, which adjusts shape accounts for 20%
- 7Explain accommodationAccommodation is the process in which the eye is able to maintain a clear focus on an object when the distance varies through the change in shape of the lens.
This occurs through the ciliary muscles which thicken the lens. - 8Explain what the term 'near point' isNear point is where lens cannot adjust further due to hardening of lens. Near point increases as age increases due to the ciliary muscles weakening.
- 9Explain what the pupillary light reflexThe pupillary light reflex regulates the amount of light reaching the retina. It does this through the connections in the eye and neurone in the brain stem which contract the pupil
- 10Explain the components of the retinaThe organisation of the retina contain the following 3 vertical components (from both upwards)
- Photoreceptor
- Cell bodies of bipolar, amacrine and horizontal cells
- Cell bodies of ganglion cells - 11What are the two sub-components of photoreceptorsRods & Cones
Rods: Long, cylindrical outer segment
- 1000x more sensitive
- 120 million
- Dark vision
Cones: Shorter, tapering outer segment
- 5 million1
- Light vision - 12Describe the structure of photoreceptorsContain light-sensitive photopigments in stacks of discs in outer segment
- 13State the 3 different spectral sensitivities of conesCones: 3 different pigments, so 3 different sensitivities
- Short wavelength (S) = (blue)
- Medium wavelength (M) = (green)
- Long wavelength (L) = (red) - 14Give three differences between rods and conesRods:
1. Highest concentration in the periphery (peripheral vision)
2. High sensitivity
3. Very numerous
Cones
1. Highest concentration in fovea (centre of retina)
2. Low sensitivity
3. Less numerous - 15Explain the process of transduction of lightWhen retinal absorbs one photon of light, it changes shape
This shape change increases binding of a regulatory protein called transducing
Binding of transducing sets off a cascade that leads to activation of the enzyme phosphodiesterase (PDE)
PDE activation causes Na+ channels to close, inhibiting the photoreceptor
This removes the inhibition of bipolar cells, allowing ganglion cells to fire action potentials - 16Explain the perception of colour: Young-Helmholtz Trichromatic Theory- Cones are sensitive to red (long-wavelength), green (medium-wavelength) and blue (short-wavelength)
- Brain assigns colours based on ratio of activity of three cone types
- Equal mixing of red, green and blue light is perceived as white
- All other colours are combinations of these three wavelengths - 17Explain the perception of colour: Opponent process theory- The opponent process theory suggests that we perceive colour in terms of paired opposites
- Activation of one member of pair inhibits the other member - 18Explain lateral inhibitionLight shown to a single receptor leads to rapid firing rate of nerve fibre
Adding light into neighbouring receptors leads to reduced firing rate of initial nerve fibre - 19What range of wavelength can the human eye perceive400-700nm
- 20When an object is closer than 9m what happens to the lens of the eye?Ciliary muscles tighten, causing lens to thicken
- 21What is the receptive field?- Area of retina where light changes neuron’s firing rate
- Light anywhere outside of this has no effect on firing rate - 22What are the two different classes of bipolar cells?ON and OFF bipolar cells
- 23Describe the difference in pathways for the ON and OFF bipolar cellsOFF bipolar cells: hyperpolarise in response to light (light turns them off)
OFF bipolar cells depolarise in response to glutamate
AND
ON bipolar cells: depolarise in response to light (light turns them ON)
ON bipolar cells hyperpolarise in response to glutamate - 24Describe the bipolar receptive fields in regard to surroundsIN A NUTSHELL
The response of the bipolar cell to light in the centre of its receptive field is opposite to its response to light in the surround of its receptive field - 25Describe the function of ganglion cell receptor fieldsON centre and Off-centre ganglion cells receive input from the corresponding type of bipolar cell
Fire action potentials regardless of light exposure
ON-centre cell fires many action potentials when light is shone on centre of receptive field
Off-centre cell fires many action potentials if dark spot covers centre of receptive field - 26What are the main differences between M and P type ganglion cellsM type is 5% of ganglion cells, larger receptive fields and more rapid conduction of action potentials
P type is 90% of ganglion cells, and has a sustained discharge as long as stimulus is present - 27What is the optic nerveThe optic nerve is:
formed from axons of ganglion cells
- About 1 million fibres
- Exits retina at optic disc (head of nerve)
- Joins with opposite optic nerve at the optic chiasm - 28What is the optic chiasmOptic chiasm (X shape structure in the centre of brain)
- Partial crossing of the optic nerve fibres
- Medial (nasal) retinal fibres, responsible for the lateral (temporal) portion of the visual field, cross
- Lateral (temporal) retinal fibres, respondible for the medial (nasal) portion of the visual field do not cross - 29What is the optic tractOptic tract
- Extends from the optic chiasm
- 3 sites of termination
- Lateral geniculate nucleus (LGN) of thalamus (most)
- Superior colliculus
- Protected area - 30Describe the Extrageniculate pathways- Important for directing visual attention and eye movemetns toward visual stimuli
- Terminate in the mid brain
- Projections to pretectal area are important for pupillary light reflex (constriction of pupil w light) and accommodation reflex (change in lens shape with nearby object)
- Projections to superior colliculus are important for orienting the eyes in response to new stimuli - 31Which fibres cross at the optic chiasm?---
- 32Compare and contrast M and P type ganglion cells- M type: large; 5% ganglion cells; larger receptive fields, more rapid conduction of action potentials, more sensitive to low-contrast stimuli
- Transient burst of action potentials when stimulated
- P-type: small; 90% of ganglion cells
- Sustained discharge as long as stimulus is present - 33Which layers of the LGN contain information from ipsilateral eye?Layers 2, 3 and 5
- 34Describe the components of a hyper columnA single location column, left and right dominance columns and a complete set of orientation columns
- 35Which aspect of the sound wave corresponds to loudness?Amplitude
- 36Name the cavity which carries sound wave from the oval window to the apex of cochleaScala vestibuli
- 37Where in the cochlea is the high frequency sound (5000Hz) represented?Base of the cochlea, near to the oval window
- 38Describe the process that occurs when the stereocillia bendK+ channels open, endlymph has high K+ so K+ rushes into the hair
- 39What are the 5 basic tastes- Sweet: sugars (fructose and sucrose), certain proteins (e.g monellin) and artificial sweatnesses
- Sour: acids
- Salty: salts
- Bitter; ions like K+ and Mg2+ to organic molecules like quinine and caffeine
- Unami: savoury taste of amino acid glutamate - 40What are the 3 types of papillae- Fungiform papillae
- Folitate papillae
- Circumvallate papillae - 41What did scientists used to think about the way the tongue tastes different flavours?That there are different sections of the tongue that taste different flavours
- 42What do we now know about the way the tongue tastes different flavours?- Most of the tongue is sensitive to all basic tastes
- 43What are the 3 sub-types of taste cellsType I: Most abundant; support cells mediating intense taste sensation; also involved in the taste of salt
Type II: Most extensively studied; specific receptor proteins that allow for the detection of sweet, bitter or umami
Type III: Involved in the sensation of sour taste - 44Explain transduction in taste cellsTransduction in Taste cells
- When tastant enters mouth, its molecules combine w saliva and bind to taste receptors
- Salty and sour tastes: sensed via ionotropic receptors, directly depolarizing the taste cell by opening ion channels
- Bitter, sweet and umami: sensed via G-protein coupled receptors; activate secondary messenger cascades to depolarize the taste cell
This depolarisation (voltage-shift) – receptor potential
- Causes opening of voltage-gated calcium channels, allowing calcium to flow in
- Calcium influx triggers release of transmitter molecules
- Salty and sour: serotonin release
- Bitter, sweet, umami; ATP release
Transmitter excites post-synaptic axon to fire action potential - 45What occurs when there is a low-concentration of salt= Salt sensitive taste cells - Low concentrations: salt-sensitive taste cells
- Use special Na+ selective channel (insensitive to to voltage and generally open)
- When you eat something salty, (Na+) rises outside cell
- Na+ diffuses down concentration gradient and flows into cell, causing membrane to depolarise
- Depolarisation causes voltage-gated Na+ and calcium channels to open, triggering release of serotonin onto gustory afferent - 46What occurs when sourness is tasted?- Sourness – high acidity – low pH
- Acids dissolve in water producing Hydrogen ions (H+) or protons
- Protons may affect taste receptors in several ways, but processes are poorly understood
- Likely that H+ binds to and blocks K+ channels, leading to depolarisation
- May also be due to other effects
- Depolarisation causes voltage-gated Na+ and calcium channels to open, triggering release of serotonin onto gustory afferent - 47—
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- Flashcards on Neuroscience Modules 7-11 , created by Hattie Ellis on 14/09/2022.
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