final Flashcards
explain the net effect of photo transduction in dark conditions
- depolarising inward currentt (influx of Na+ and Ca2+)
- hyperpolarising outward current (efflux of k+)
net effect = depolarisation of photoreceptors in dark
explain the net effect of phototransduction in light condiiotns
- depolarising inward current blocked (Na+ and Ca2+ channels are closed)
- hyperpolarising outward current (efflux of k+ ions)
net effect = hyperpolarisaiotn of photoreceptors in light
what makes up the right visual field
temporal portion of the right eye
nasal poriton of left eye
what makes up the left visual field
temporal portion of left eye
nasal portion of right eye
what does a lesion in the right optic nerve result in
loss of vision to the eye of origin (right eye)
- as the info has not crossed over yet so only in the eye effected - the nerve only carries info from one eye
what does a lesion in the right optic chiasm result in
affects nasal retina acosn from each that cross to the contralateral side leaving uncrossed from the temporal iin tract - (nasal sees temporal)
bitemporal heminopsia
what does a lesion in the right optic tract result in
as lesion is on riight side, lose left visual field
left homologous heminospia
what does a lesion in the right myers luc result in
lose info from the left superior visual field on both eyes
what does a lesion in the visual cortex result in
loss it left hand side of both eyes - however fovea is spared
left homoymous heminsopsia with macula sparing
what is the main featture of lower motor neurons
innervate muscles
where does the corticobulbar tract originate and terminate
originate in M1 and terminate in brainstem
what muscles is the corticobulbar tract control?
muscles of face and enck, mastication, swallowiing…
where does the corticospinal tract originate and terminate
originate in M1 and terminate in spinal cord
what muscles is the corticopsinal tract control?
proximal and distal limb muscles
what happens with 90% of corticospinal axons
they cross the body midline (decussate) in medulla and fronm lateral corticospinal tract
what happens with 10% of corticospinal axons
terminate ipsiillaterally or bilaterally and from the ventral corticospinal tract
what does the VOR compensate for?
VOR compensates nealry perfectly for rapid head movments at 1hz>
what does VOR gain refer to
ratio of eye to head movemtn
what does OKR compensate for?
OKR compensates for nealry perfeclty for low frequency around 0.1hz
what is OKR gain
ration of eye movement to retinal image motion
what is the superior colliculus and frontal eye fields important for?
they play an important role in planning an initiating saccades to visual targets
what is myopia
= near sighted, image falls In front of the retina
what is the cornea
- cornea: transparent tissue that permits light rays to enter the eye
what is hyperopia
- hyperopia (far sighted) = light rays are focused beyond the retina
what does damage to the retina cause
- damage to this region results in loss in acuity and distortion of central vision – progressing to blind spots and later complete loss of vision
what is the msot common cause of vision loss in people over 55
macular degeneration
what causes macular degeneration
by degeneration of photoreceptors
what do bipolar cells do
give a graded response not action potential
what do ganglion cells do
go out of optic disc, via optic nerve to brain
what do horizontal cells do
modulate the reaction between photoreceptor and bipolar cells
what do amacrine cells fo
modulate the reaction between bipolar cells and ganglion cells
what is the biochemical process when light hits
biochemical process when light hits:
- photon absorbed by retinal changes the configuration
- this change causes changes to opsin which:
- activates transducin ( intracellular messenger)
- activates phophodiesterase (PDE)
- hydrolyses cGMP less cGMP
what does rods and cones differ in?
- shape – rod-like vs cone-like
- photopigment – and therefore their response characteristics
- pattern of synaptic connections – which determines spatial acuity
- rods – convergence from rods to rod bipolar cells: pools the signal (hence, low light vision)
- rod bipolar cells synapse on amacrine cells
- these amacrine cells synapse on cone bipolar cells and in turn the ganglion cells - distribution across retina – rods in the periphery, cones in the fovea
- cones: through at low density, packed into fovea, high special activity
- rods: throughout periphery, none in the centre, low spatial acuity
how many pigments does rods contain
- rods contain a single photopigment (rhodopsin)
how many pigments does cones contain
3 differnet types of photopogment
- Describe two differences between photoreceptors and other sensory cells.
Just like other sensory cells (e.g. bipolar cells or ganglion cells), photoreceptors are a class of neuron that is found in the retina. What makes photoreceptors unique is that they are found on the deepest layer of the retina. Another difference is that photoreceptors exhibit a graded change in membrane potential in response to light instead of action potential and hyperpolarise in the presence of light.
- What is light adaptation in the retina and why is it so important?
Light adaptation is a phenomena and is the process of the compensating for an increase illumination. This compensation is important as due to the illumination increasing, sensitivity decreases (as photoreceptors are most sensitive to light at lower levels of illumination), preventing the receptors from saturating and thereby extending the range of light sensitivities they operate at.
- What are the advantages of animals having both rods and cones, rather than just one type of photoreceptor.
There are a variety of significant advantages of animals having 2 types of photoreceptors. The most significant benefit is that rods and cones are used for different purposes. Rods are found in periphery and they respond well under low light vision or night vision. Cones are found in central vision region and are 3 types which each detect light at different wave lengths. Therefore, by having both rods and cones animals are able to see and process visual stimuli across a broad range of light conditions.
- Explain the concept of feedforward postural control and provide one example. In your answer, explain what is predictive or anticipatory about the feedforward postural control.
Feedforward postural control is a “preprogramed” response that involves activation of leg and trunk muscles prior to an expected body perturbation. Feedforward postural control is typically anticipatory, meaning the response predicts instability hence prepares for that instability before it occurs. Both the vestibular nuclei and reticular formation play a role in providing information to the spinal cord to maintain posture however in the feedforward control reticular formation has the greatest contribution. The relevant neurons in the reticular formation initiate feedforward adjustments that stabilise posture during ongoing movements. For example, if an individual was to pull a handle with his arm to trigger an auditory tone, activity in the biceps begin 200ms after the tone, but a proximal leg muscle, the gastrocnemius muscle activity actually began prior to the bicep highlighting how we can anticipate instability in our posture and compensate for that instability.
- How do neurons in the abducens nuclei control the amplitude and direction of an eye movement.
In order for the eyes to fixate on a new target in space two tasks must be achieved by the neurons in the abducens nuclei: controlling the amplitude of the movement and controlling the direction of the movement. Amplitude of the saccadic eye movement is encoded by the duration of neuron activity in the lower motor neurons. Neurons in the abducens nucleus fire a burst of action potentials just prior to abducting the eye and are silent when the eye is adducted. The amplitude of the movement will then be correlated with the duration of the burst of action potentials in the abducens neurons. Direction of movement is controlled by two gaze centres in reticular formation which determine which eye muscles are activated. The Paramedian pontine reticular formation (PPRF) is a collection of local circuit neurons in the midline of the pons and these are the neurons responsible for generating horizontal eye movements. In the PPRF, neurons innervate the cells in the abducens nucleus which contains 2 types of cells. One type of the cells is composed by lower motor neurons that innervate the lateral rectus muscle on the same side and the other type called internuclear neurons send their axons across their midline leading to the medial rectus muscle being innervated. Therefore the neurons in the abducens nuclei are responsible for controlling the amplitude and direction of eye movements.
- First, identify each of the association cortices. Second, describe the main function of each associative areas and some of primary symptoms that patients with damage in this area might show.
The association cortex (including the frontal, parietal and temporal lobes) brings together sensory and much other information to produce useful behaviour whatever the circumstance may be. Each lobe within the association cortices plays a different role and deficits in those areas result in different symptoms. The parietal lobe is primarily responsible for mediating attention as well as a sense of where things are. Damage to this area would cause contralateral neglect syndrome, which is classified as an inability to attend to objects or even one’s own body, in a portion of space, however an individual’s visual acuity, somatic sensation and motor ability remain intact. If the left parietal lobe is damage it is more severe and the individual can only see the right side as only the left lobe is being used, however, if the left lobe is damaged the right will take over the whole field. The main function of the temporal lobe is that is especially important for recognising objects and conditions therefore damage to this region will result in agnosia, the difficulty in recognising, identifying and naming objects – individuals acknowledge the presence of something but cannot identify it. The most studied agnosia is prosopagnosia which is the inability to recognise faces. The frontal association cortex is especially important for electing and planning appropriate behavioural responses. Damage to the frontal lobe can cause a variety of symptoms however the greatest would be that individuals lose their “personality”. The first case of this was Phineas Gage who had suffered a rod going through his left eye socket destroying his frontal lobe. Even after recovery those who knew Phineas said his personality completely changed and was not the same personality.
in what wat are ion channels simnilar to active transporters
both miantian ion concentration gradietns
which property is chaacteristic of NA+ channels but not K+ channels
ability to inactivate
which substacne binds only to the extracellular domain of ligand gated ion channels?
neurotransmitters
what is scoptic vsiion
low ligth
if you have a lesion in hte right optic tract your vision loss will afect
the left side of space
where do ganglion cells cross at
optic chiasm
what neurons innervate striated
alpha motor neurons
what neurosn innervate specilsied fibresa
gamma motor neurons
which motor units are resistant to fatigue
slow and fast fatigue resistant
according to the size principle, in which order are motor units recruited in response to increasing synaptic input
slow, fast fatigue-resistant, fast-fatiguable
motor neuorns with cell bodies in the cerebral cortex and brainstem are parrt of which motor system
upper motor neurons
what layer of the primary motor cortex are located in which cortical layer
5
the peripheral msucle group that an upper motor neuron projects to is the
muscle field
what structure can be found exclusively at an electrical synapse
connexon
what is a connexon
assembly of proteins that form the pore for a gap junction between the cytoplasm of two adjacent cells
what is the action fo the neurotransmitter at a chemical synapse
it transfers an action potential sform the presynaptic neuron to the postsynaptic neuron
what is the main excitatory neurotransmitter in the adult brain
glutamate
on the way to the retina, light passes through tissues and fluids in which order
cornea, aqueous humor, lens, vitreous humour, retina
during accomodation, the shape of the _____ is change dby the ______ in order to see objects are varying distances
lens, ciliary muscle
what does convergence allow?
rods to pool signals generating larger reposnes in bipolar cells
where does ganglion cells cross
optic chiasm
- loss of colour vision
- retina is still functioning
- sees shades of grey
He most likely systained damage to what area?
v4
damage to the striate cortex below the calcarine sulcus would result in diffculty processing information from whcih visual field
superior
object in the superior temporal quadrant of hte visual field would be mapped on what quadrant of the retina
inferior nasal
what system is responsible for the processing info regarding self motion, head positon, and spatial orientation
vestibular
what type of movement does the saccule respond to?
vertical
what type of movement does the utricle respond to
horizontal
as motor unit size increases, which property of the alpha motor neuron decreases
excitability
what technique is helpful in mapping primary motor cortex
cortical stimulation
what percentage of pyramidal tract fibres decussate to form the lateral corticospinal tract
90%
what is the muscle field
the group of muscles whose activity is directly facilitated by a giver upper motor neuron
how are the upper motor neurons in the superior colliculus organised
as a topographical map of eye movement vectors
- What are the distinct characteristics (both function and structure) of magnocellular versus parvocellular streams?
There are many differences between magnocellular and parvocellular pathways. Magnocellular layers are made of 2 layers composed of large neurons whereas the parvocellular layers is made of 4 layers with much smaller neurons. M ganglion cells terminate in the Magnocellular pathways and have larger receptive fields, faster conduction and are insensitive to different wave lengths of light. P ganglion cells terminate in the parvocellular pathways – they have smaller receptive fields, closer conduction, sustained responses, sensitive to differences in wave lengths and are involved in colour not motion. The magnocellular pathway conveys information that is critical for the detection of rapidly changing stimuli whilst the parvocellular pathway mediates high acuit
