CONTROL OF HUMAN MOVEMENT Flashcards
How many neurones are present in the brain
100 billion
How much % of total energy does the brain consume
20% of total energy
Why doesn’t the brain feel pain
It has no nerves
Therefore feels no pain
What type of relationship do curvature and velocity have
positive relationship
what is space
a set of points with some added structures
What does Fitts Law state
If you need accuracy you become slower
What are coordinates
A set of numbers that uniquely determine a point in space
Can one space have multiple coordinate systems
Yes
What can a coordinate frame also be called
A reference frame
Define egocentric
coordinate system attached to our body
Define allocentric
coordinate system attached to external world/ object
If you are trying to find kinetics is it inverse of forward dynamics
Inverse
you are trying to find kinetics so you go from
kinematics –> kinetics which is inverse
If you are trying to find kinematics it inverse of forward dynamics
Forward
you are trying to find kinematics so you go from
kinetics –> kinematics which is forward
What does kinetics refer to
forces & torques
What does kinematics refer to
distances & angles
What is newtons 2nd law
F=ma
What is feedforward control
You plan in advance
Pre determined actions
What type of loop is feedforward control
open loop
what are the pros of feedforward control/ open loop
Movement can be controlled without gathering/ processing any external info
good for fast movement
what are the cons of feedforward control/ open loop
Error made by controller accumulates over time
No flexibility to environmental changes
High cost of planning, no generalisation
what is feedback control
You have policies (rule/ strategy), controller is gathering/ processing sensory feedback
eg- tube tourist example: ask around then go there, then ask again
what type of loop is feedback control
closed
what are the pros of feedback control/ closed loop
Flexible- can deal with unexpected events
Robust- control error does not accumulate over time
General- control is invariant to starting or goal opposition
what are the cons of feedback control/ closed loop
Processing sensory feedbacks is time consuming- not good for fast movement
Controller can become unstable when sensory feedbacks are noisy and the feedback gain is high (how seriously one takes the answer)
Can also become unstable when feedbacks are delayed
What is variability
When the same movement is repeated, controller behaviours under uncertainties result in different movement patterns
What 2 problems does the brain solve
Localisation
Planning
What is localisation
representation of the location of the object
What is planning
plan of reaching based on the representation
What sensory info is needed for localisation & planning
Destination (target)
extrinsic info, spatial location of the target through visual info & auditory info
Where am I/ what am I doing?
intrinsic info, kinetic & kinematic info of the body
-Muscle spindle: length and velocity of each muscle
-Golgi tendon organs: force produced by each muscle
-Mechanoreceptors: force exerted/ received on skin
What level of cortical control do voluntary movements need
a higher level of cortical control
How do you grab the apple in a reaching movement
general plan –> motor commands
Multi-stage sensorimotor transformations are required
What is an intrinsic coordinate system
joint angle coordinate
Muscle lengths
Proprioreceptive info
What is an extrinsic coordinate system
Allocentric/ egocentric coordinates
Exteroceptive (sensory info); visual & auditory
What is the PRR
Parietal reach region
What is the PPC
Posterior Parietal cortex
What are the sources of variability
- input- estimation of location & target
- intrinsic- Sensors and motor neurons, fluctuations in membrane potentials , this limits the accuracy and precision of the control
- output- caused by motor neurons and muscles (increased excitability + more motor neurons) this is called signal dependent noise
What are the internal models split into
Inverse- used to plan movement for a given task goal
Forward- predict consequence of the movement without sensory feedback
What does the inverse model do
determines the motor commands that will produce a behavioural goal
what does the forward model do
stimulates the interaction of the motor system and the world
can therefore predict behaviours
What is the efference copy
Within the forward model a copy of motor commands is sent to the muscles
this is the efferenence copy
What is directional tuning
Neurons in the primary motor cortex have their own preferred directions
What is a saccade
A very quick movement
What section of the body are feedforward controls usually used for
eye movement
What is intermittency
pause until sensory feedback arrives and then resumes
What can prediction do?
Compensate for sensorimotor delays
What is the observer model
How to mix what we predicted and what was sensed
What is the forward dynamic model
What is my current status (position, velocity, joint angle etc)
What is the forward sensory model
in that status what sensory info am I supposed to sense
tactile, gravity etc
What are the 2 types of memory
explicit (declarative) and Implicit (procedural)
What is explicit (declarative) memory
eg- name/ address
able to explain what you’ve learnt
easily forgotten
what is Implicit (procedural) memory
eg- learning to ride a bike/ play piano
- takes place without consciously thinking about it
- unable to explain what you’ve learnt
- can be retained for extended periods of time without practice
What type of memories are motor skills
implicit
How are internal models maintained
generalisation
retrieval
what is generalisation
when a skill is learned the brain needs to utilise it in a different scenario
what is retrieval
among the skills already learned the brain needs to select the appropriate skill to use depending on the scenario
what cues work well for retrieving internal models
state-related cues
- visual feedbacks of movement
- proprioreceptive feedbacks (hand position etc)
what cues DONT work well for retrieving internal models
State-unrelated cues
- static cues (background colours etc)
- visual motions not related to the movement
When getting sensory feedback what is the most important thing
PROPRIORECEPTION! More so than vision
patients who have lost proprioreception have particular difficulty controlling the dynamic properties of their limbs
What does the stretch reflex do
keep the muscle at desired length
What do alpha motor neurone do
cause contraction of muscle
what do gamma moto neurons do
adjust the sensitivity of the reflex and allow muscles to contact until they reach desired lengths
What was sherringtons reflex hypothesis
movement is generated by stretch reflexes - which is a sensory afferent
What was merlons servo reflex hypothesis
gamma motor neuron drive precedes the movement (alpha motor neurone drive)
how can muscle spindle discharges be recorded
microneurography
what does EPH stand for
Equilibrium point hypothesis
What is EPH
EPH assumes the brain controls a virtual equilibrium point to control the reaching movement
what is coriolos force
rotation force- think spinning room get pinned against wall trying to move arms
what is the optical control model of movement
assumes that the controller tries to minimise or maximise a certain benefit produced by resultant action
what is jerk
the rate of change of acceleration
related to smoothness of the movement
what are properties the brain optimises
smoothness
torque
uncertainty
signal dependant noise
what is the function of dendrites
receives information
what is the function of the cell body
processes and integrates the information received in the dendrite
what is the function of the axon
carries the information along long distances from one part of the neuron to the other
what is the function of the axon terminal
Transmits the information to next cell in the chain
what is a bundle of axons together called
a nerve
what is the value for resting membrane potential
-70mV
What is threshold for membrane potential
-55mV or higher
what happens when threshold is reached
an action potential is triggered
what is depolarisation
ions go into the cell membrane making it become more positive
makes action potential more likely
what is repolarization
due to the electrochemical gradient, ions flow back through the cell causing it to become more negative
what is hyper polarisation
if membrane potential becomes lower than -70mV
makes action potential less likely
what are the passive electrical properties of neurone
wires conduct current by electron flow in metal
neurons conduct current by ion flow in fluid
what is RL
longitudinal resistance
want this low
What is RM
medial resistance
want this high
what is space constant
how FAR voltage travels
what is time constant
how FAST voltage travels
what are the 2 factors decay is defined by
space constant
time constant
anything that increases medial resistance does what to space constant
increases space constant
anything that reduces longitudinal resistance does what to space constant
increases space constant
anything that increases space constant does what to conduction velocity
increase conduction velocity
anything that reduces time constant does what to conduction velocity
increase conduction velocity
what does RMP stand for
resting membrane potential
describe how an action potential is initiated
- Cell membrane becomes depolarized
- Once depolarization reaches threshold, Na+ channels open
- Resulting in an influx of Na+ leads to further depolarization
- Adjacent Na+ channels are opened, causing a chain reaction
- Meanwhile, K+ channels open more slowly causing an outflow of K+
- Resulting in outflow of K+, repolarizes membrane potential
- Na+ channels become closed, and temporarily deactivated
what are the 3 states of and Na channel
open/ closed/ deactivated
what are the 2 states of a K channel
open/closed
how fast do Na and K channels open and why
Na channels open quickly
K channels open more slowly
This is crucial for ensuring action potential only travels in one direction
What increases conduction velocity
increased neuron diameter
myelination
temperature
how does increases neurone diameter increase conduction velocity
diameter affects RL more than RM
therefore larger space constant
therefore faster conduction
why does myelination increase conduction velocity
myelin insulation increases space constant
space constant increases conduction velocity
action potential jumps at nodes of ranvier in salutary conduction
give 2 examples of diseases that are effects of demyelination
MS
Guillian-Barre syndrome
how to measure conduction velocity
stimulate motor neuron at 2 sites
measure latency of evoked responses
calculate velocity by speed = distance/ time
what is a reflex
An action that is performed without conscious thought as a response to a stimulus
what do all reflexes require
sensorimotor integration
- Sensory receptor
- Afferent pathway
- Synapse onto alpha motor neuron
- Neuromuscular junction
what does it mean that the stretch reflex is autogenic
Autogenic means same muscle that detects the stretch is the same muscle that will contract
what’s afferent
towards CNS
what’s efferent
away from CNS
how does a stretch reflex cause contraction
- stretch of muscle spindles
- afferent info from muscle spindle to spinal cord
- sensory neuron syntheses with motor neuron in cord
- efferent info from motor neuron to muscle
- muscle contracts
what does EMG stand for
electromyography
what does EMG measure
measures muscles response or electrical activity in response to a nerves simulation of the muscle
what is the purpose of stretch reflex
acts as a negative feedback control system to maintain desired limb position
why does loss of supra spinal input cause hyper reflexia/ spasticity
Descending input from the brain, normally acts to regulate (inhibit) reflex gain in the spinal cord
Spinal cord injury, stroke, and other conditions that effect upper motor neurons can abolish this tonic inhibitory input
This causes reflex gain to increase – ‘hyper-reflexia’
Can result in severely increased muscle tone and spasticity
what type of reflex is a stretch reflex
monosynaptic & dysnaptic
flexion withdrawal reflex is what type of reflex
polysnaptic
describe how Hand is moved away from painful stimulus
- painful stimulus
- pain receptors in free nerve endings stimulated
- afferent info to spinal cord via type 3 sensory neurons
- sensory neurons synapse with spinal cord interneurons
- interneurons synapse with spinal cord motor neurons
- flexor muscles in affected limb contract
- injured area removed from stimulus
what is crossed extension reflex
contralateral limb to stimulus
what type of reflex is crossed extension reflex
polysnaptic
too little movement in a reflex could be caused by
sensory nerve damage
to much movement in a reflex could be caused by
cereal palsy
stroke
brain injury
upper spinal cord injury
what is a motor unit
one alpha neuron and all of the muscle fibres it activated
describe the chain of events in a muscle contraction
- Action potential (AP) stimulates the release of a neurotransmitter across the neuromuscular junction
- AP spreads across the sarcolemma/ muscle membrane and into fiber along the T tubules (extensions of the membrane)
- Causes the release of calcium from the sarcoplasmic reticulum
- Calcium binds to muscle and causes cross bridge cycling
what does one action potential create
a single twitch
what do multiple action potentials create
generates continuous force
tetanic contraction
how do muscles generate extra force
increasing frequency of firing of motor units
recruiting more motor units
what is an innervation number
number of fibres per motor neuron
what does an innervation number mean
lower innervation number = more control
what does NMJ stand for
neuromuscular junction
How do u perform EMG
electrical signal can be recorded by inserting a needle electrode into the muscle
OR a surface electrode at skin level
What is a neuromuscular junction
a chemical synapse between a motor unit and a muscle
what is the relationship between muscle force and the EMG signal
the amplitude of EMG signal is proportional to force produced by muscle
how do we see the action potential on the EMG
action potentials from numerous motor units summate to produce EMG signal
factors that affects the relationship between force and muscle activity
type of muscle contraction
type of muscle fibres
joint angle
how does type of muscle contraction affect the relationship between force and muscle activity
concentric v eccentric
how does type of muscle fibres affect the relationship between force and muscle activity
- Slow v fast
- Fast = higher resting membrane potential (RMP), greater density sodium channels, faster action potentials
how does joint angle affect the relationship between force and muscle activity
- Maximum force at particular length
- When optimal cross bridge overlap
what does muscle fatigue due to the with duration
causes prolonged twitch duration meaning an increased relaxation time due to biochemical changes in muscle
frequency of motor units firing decreases therefore less force
how does the nervous system know when to reduce firing rate
Peripheral detection (build up of metabolites like lactate) spinal suppression of motor neuron firing rates changes in voluntary activation
why does the nervous system reduce firing rate
reduce the likelihood of neuronal fatigue
more likely to maintain fine motor control
what is low frequency fatigue
caused by intense exercise
wobbly legs following day
takes hours/ days to recover
doesn’t change EMG signal
what is high frequency fatigue
caused by continuous high frequency stimulation
recovers immediately when stimulation stopped
caused by failure of transmission of action potential along muscle membrane
reduces EMG signal
what is the function of the basal ganglia
Initiating movements
what is the function of the cerebellum
Sensory motor coordination of ongoing movement
what is the function of the motor cortex
planning, initiating and directing voluntary movements
what is the function of the brainstem centres
basic movements and postural control
what is the hierarchy of motor control in the brain
- Spinal cord
- Motor neurons are final motor output of nervous system - Muscles
- Combined action of motor units produces smooth tetanic muscle contraction - Peripheral sensation
- Feedback from proprioception etc used to guide ongoing movement, both in spinal and supraspinal loops
what does grey matter contain
cell bodies of neurons
sensory, motor & interneurons
what does white matter contain
axonal tracts
what are the parts of the spinal cord top to bottom
cervical
thoracic
lumbar
sacral
what root does sensory info enter via in spine
dorsal root
what root do motor neurons exit via in spine
ventral root
what are the 4 main tracts of spine
corticospinal
rubrospinal
vestibulospinal
reticulospinal
what are the 2 lateral tracts of the spine
corticospinal
rubrospinal
what are the 2 medial tracts of the spine
vestibulospinal
reticulospinal
minimal concious control
where is corticospinal tracts and what is its function
From motor cortex to spinal cord. Major pathway for voluntary movements precise control of limbs especially individual finger movements 90% crosses over (contralateral)
where is rubrospinal tracts and what is its function
from red nucleus (in midbrain) to spinal cord. Upper limb control (small pathway in humans)
cross over straight after exiting red nucleus
compensate for damage to corticospinal tract
where is vestibulospinal tracts and what is its function
from vestibular nuclei (in medulla) to spinal cord. Automatic balance reflexes
sensory system
spatial orientation for coordinating movement with balance
output mainly to eyes
where is reticulospinal tracts and what is its function
from reticular formation (in the brainstem) to spinal cord.
Postural control and balance
how to measure integrity of corticospinal tract
TMS of motor cortex Babinski reflex (extension of big toe)
where do the motor neurons lie that allow flexion
more centrally
where do the motor neurons lie that allow extension
on outside
what does gray matter look like
H shape
white matter ascending tracts contain what
sensory neurons
white matter descending tracts contain what
axons of upper motor neurones
what is the primary motor cortex also known as
M1 or Brodmanns area
what is a motor homunculus
Shows what a persons body would look like if it grew in proportion to the area of the cortex concerned with its movement
what is the function of the primary motor cortex
generates the nerve impulses initiating movements
where is brocas area located
a circular dot in the premotor cortex
what is the function of brocas area
involved in language expression
What does kinematics relate to
direction
amplitude
speed
path
what does kinetics relate to
force & muscle activity
how do you extract movement info directly from cortical neurons in reaching movements
put a micro electrode array into motor cortex
single unit recordings made during reaching movements in multiple directions
What is TMS
Non invasive brain stimulation technique
Uses electromagnetic induction to activate neurons
Stimulates M1 and records MEPs using EMG
Also records excitability of CS tract
How does TMS stimulate cortical interneurons
Stimulate at sub threshold intensities
This targets inhibitory interneurons
Gets a decrease in CS tract activity leading to decreased MEP and decreased voluntary EMG
Does MEP latency vary between people
yes
does m1 excitability increase immediately before movement
yes
what happens to MEPs if you have an injury along the corticomotor pathway
you may show abnormal MEPS
what does a decrease in MEP from the same TMS intensity show
decreased corticomotor excitability
What is the function of the basal ganglia
control the strategic aspects of movement
does the basal ganglia connect to the spinal cord
no direct connection
what does damage to the basal ganglia result in
problems initiating/ terminating movements
what are the 5 nuclei in the basal ganglia
caudate putamen globus pallidas subthalamatic nucleus substantia nigra
how do you identify the caudate
looks like a C (and called caudate)
which basal ganglia nuclei form the striatum
caudate
putamen
What are the 2 parts to the globus pallidus nuclei
internal
external
What are the input nuclei in basal ganglia
STRIATUM (caudate & putamen)
Receives connections from cortex
What are the output nuclei in basal ganglia
globus pallidus internal (GPi)
Substantia nigra
provide tonic inhibitory output to thalamus
no output directly to spinal cord
what does the direct pathway motor loop of basal ganglia do to movement
facilitates movement
what does the indirect pathway motor loop of basal ganglia do to movement
inhibits movement
what is the route of the direct pathway motor loop of basal ganglia
motor cortex striatum GPi thalamus back to motor cortex
what is the route of the indirect pathway motor loop of basal ganglia
motor cortex striatum GPe STN Gpi Thalamus back to motor cortex
what does the direct pathway motor loop of basal ganglia do to drive
increases drive/ movement initiation
what does the indirect pathway motor loop of basal ganglia do to drive
decreases drive
movement termination
What is Parkinson’s disease
degeneration of dopamine neurons
more indirect pathway,
less direct pathway
therefore movement suppressed
what is Huntington’s disease
Movement facilitated-
rapid jerky motions
Caused by mutation of Huntingtin gene
Down regulation of indirect pathway, more direct pathway therefore movement facilitated
what is hyperkinetic
increased/ too much movement
What is hypokinetic
reduced movement
medical treatment of basal ganglia pathology is aimed at what
restoring balance between indirect and direct pathway
what is the function of cerebellum
modulates movement accuracy
receives afferent info from spinal cord
what does damage to cerebellum cause
inaccurate/ poorly timed movement
what are the 3 anatomical parts of the cerebellum
anterior lobe
posterior lobe
flocculonodular lobe
what are the 5 cell types in the cerebellum
purkinje cell Golgi cell granule cell stellate cell basket cell
what are the 3 layers in the cerebellum
molecular layer
purkinje layer
granular layer
what are the 2 inputs to the cerebellum (fibres)
climbing fibres
mossy fibres
what is the output of the cerebellum
purkinje cells
what are the 3 functional regions to the cerebellum
vestibulocerebellum
spinocerebellum
cerebrocerebellum
describe vestibulocerebellum
regulates balance & eye movement
coordinates movements of head & eyes
the flocculondular lobe (bottom part)
what are the inputs to vestibulocerebellum
vestibular system
visual system
somatosensory system (neck)
what are the outputs of vestibulocerebellum
vestibular nuclei in the brainstem
damage to vestibulocerebellum results in what
damage results in deficits in smooth eye movements and balance
what are the inputs to spinocerebellum
- Motor and sensory cortex
- Somatosensory receptors (trunk & limbs) via spinal cord. Conveying info about touch pressure & limb position
- Auditory and visual systems
what are the outputs to spinocerebellum
Vestibular & retricular nuceli (movements of neck, proximal parts of arm), posture & balance
- Red nucleus, direct control to distal parts of arm
- Motor cortices (Via VL thalamus), control via corticospinal tract
describe the spinocerebellum
- Controls posture and locomotion as well as eye movements
- Inactivation of spinocerebellum causes movements to become slower and more
- consists of vermis and intermediate hemispheres (middle part)
describe cerebrocerebellum
consists of lateral hemispheres (side parts)
- Part of high-level internal feedback circuit that plans movement and regulates cortical motor programmes
- Controls mental rehearsal of complex motor actions and measures movement
what are the inputs to cerebrocerebellum
-Cerebral cortex (Sensorimotor & secondary visual regions)
what are the outputs to cerebrocerebellum
- Motor, pre motor, pre frontal & parietal cortices (via VL thalamus)
- Inferior olive (via red nucleus)
what does damage of cerebrocerebellum result in
-Damage results in irregularities in the timing of movement components
Ataxic gait
Impaired balance
Slurred speech
what is ataxia
abnormal execution of multi jointed voluntary movements, characterised by lack of coordination
ataxic gait is weird retarded walk
what is dysmetria
inaccuracy in range and direction of movement
what is dysdiadochokinesia (ddk)
Impaired ability to perform rapid alternating movements
what are compressions of sound waves
compressions are regions of high pressure due to particles being close together
what are rarefactions of sound waves
rarefactions are regions of low pressure due to particles being spread further apart.
what is amplitude
a measure of loudness
what is frequency
how many sound waves there are each second
what is frequency measured in
Hertz
what is the range of human hearing
20-20,000 Hz
what is the range of human hearing
20-20,000 Hz
0-140decibels
what happens to hearing with age
it deteriorates
what are the 3 sections to the ear
outer ear (air) middle ear (air) inner ear (fluid)
what does the cochlea look like
spiral
what’s the function of the middle ear
converts high amplitude at ear drum into low amplitude at oval window
what is the function of strapedius reflex
protects ear against loud sound
how does the strapedius reflex work
contraction of ‘tensor tympani’ and ‘stapedius’ pulls stapes away from oval window
decreases transmission of vibrational energy to cochlea
strapedius reflex occurs in response to very loud sound
what happens to tympanic membrane & Eustachian tubes when flying at TAKE OFF
Pressure in middle ear is larger than ear canal
Therefore tympanic membrane moves outwards
If you swallow you open up the Eustachian tubes and equalise pressure allowing tympanic membrane to return to normal position
what happens to tympanic membrane & Eustachian tubes when flying at LANDING
Pressure in middle ear is smaller than ear canal
Therefore tympanic membrane moves inwards
If you swallow you open up the Eustachian tubes and equalise pressure allowing tympanic membrane to return to normal position
what are the 3 scale in cochlea
vestibuli
media
tympani
what part of the ear is the cochlea in
inner ear
where is the organ of corti found
embedded into basilar membrane
how are hair cells in organ of corti activated
when hair cells moved in one direction = depolarisation
when hair cells moved in another direction = hyperpolarisation
what are large hairs called
kinocillium
what are small hairs called
stereocilia
what happens when sound moves away from kinocillium
movement = inhibited
what happens when sound moves towards kinocillium
movement = excited
what is Fourier analysis of sound
any waveform can be decomposed into sine waves of various frequencies
decomposes time based sound signals into their frequency components
what are otoacoustic emissions
echoes in response to clicks delivered to the ear
what happens to outer hair cells in response to sound
they contract and relax in response to activation from sound. can be known as active undamping
what is wernickes area of brain linked to
speech
what type of frequency is human hearing most sensitive at
speech frequencies
what is sound localisation split into
judging distance
judging direction
what is inter aural time delay (ITD)
a click from the left will arrive at the left ear first, then right ear soon after
the bigger the animals head the bigger the ITD
what size head is better for detecting HIGH frequency sounds
a smaller head is better for detecting high frequency sounds
are sounds with a narrow band of frequencies hard or easy to localise
narrow band of frequency = hard to localise
are there any photoreceptors in the optic nerve
NO
where is the sclera
white jelly over eyeball
where are zonular fibres
next to lens
where are cilary muscles
after the zonular fibres
lens, zonular, ciliary
how do you determine lens strength
difference in refractie index, combined with lens curvature
what do relaxed ciliary muscles do to the lens
oval - long/ stretched
what do contracted ciliary muscles do to the lens
circular/ round
what is myopia
short sighted
what is hypermetropia
long sighted
how do you compensate for myopia
biconcave lens
what lens compensates for hypermetropia
biconvex lens
what is presbyopia
when the lens seizes up
the lens no longer bulges when ciliary muscles contract
happens with age - why older people need reading glasses
what are the 2 muscles that control pupil diameter
sphincter pupillae (around pupil) dilator (on top of iris)
why does the pupil change size
adapts to light levels
what is an ophthalmoscope
shines light directly onto subjects retina
adjustable lens used to bring retina into focus
optician can work out what strength glasses to give based on the ophthalmoscope lens required to bring retina into focus
what colour is the longest wavelength
red
what colour is the shortest wavelength
purple
what do ciliary muscles look like when they are contracted
thick
what do ciliary muscles look like when they are relaxed
thin
do rods, cones, horizontals and bipolars have action potentials
NO
What part of eye contains highest % of photoreceptors
fovea
in bright light can cone cells be used
YES
in bright light can rod cells be used
NO
Which one out of rods and cones is responsible for colour
cones
remember c for cones c for colour
what protein in the eye needs to be constantly regenerated as it is bleached by light
rhodopsin
what are the 3 stages of phototransduction
- photopigment bleaching
- cell membrane hyperpolarized via G protein
- Neural output of ganglion cell is modified
describe stage 1 of phototransduction (photopigment bleaching)
Two molecules (retinal & opsin) combine to form photopigment called rhodopsin (unbleached state)
Light photon interacts with rhodopsin causing configurational change
Retinal & opsin part company (bleached)
describe stage 2 of phototransduction (cell membrane hyperpolarized via G protein)
Released opsin activates enzyme phosphodiesterase (PDE) via transducing G protein
PDE converts cGMP to GMP (cGMP normally opens Na+ channels)
Closure of Na+ channels causes hyperpolarization of cell because K+ continues to leak out
describe stage 3 of phototransduction (Neural output of ganglion cell is modified)
Rod/ cone hyperpolarization results in LESS neurotransmitter release (glutamate)
Modulates membrane potential of bipolar cell
Changes firing rate of ganglion cell (bipolar can be excitatory or inhibitory)
what is scotopic vision
low light vision
rods ONLY
High sensitivity
what is photopic vision
high luminance
cones ONLY
Low sensitivity
what is mesopic vision
medium light
rods and cones
medium sensitivity
what is 0 visual acuity
a blind spot
what is lateral inhibition of the eye
centre surrounded receptive field, edge detection, contrast illusions
what are the 3 colours of cones
red
green
blue
what is a monochromat
someone who is completely colour blind
what is a dichromat
someone who can only see 2 colours
what are the 3 main contributors to orientation
vision (visual space) vestibular system (inertial space) proprioreception (internal space)
what type of movement/ velocity do canals control
angular velocity/ rotation
what type of movement/ velocity do otoliths (utricle & saccule) control
linear acceleration/ tilt
what does movement towards stereocillium cause
depolarises receptor and increases firing rate of afferent
what are otoconias in the ear
calcium carbonate deposits
why do canals detect movement in any direction
the canals are perpendicular to each other
what is positional alcohol nystagmus
caused by the cupola no longer being neutrally buoyant and therefore room feels like its spinning when you lie down after alcohol
what is the vestibular ocular reflex (VOR)
stabilises gaze during head motion
rotates eyes to compensate for head movement
what is caloric vestibular stimulation
method of modulating firing rate of the primary vestibular afferents of ear canal with warm or cold water
what is GVS
galvanic vestibular stimulation
activates the nerves from all canals, causing a head roll sensation
causes locomotor and balance responses
what is higher the utricle or saccule
utricle is on top of saccule
define proprioreception
the sense of the relative position of neighbouring parts of the body
what does gamma motor neuron do to muscle spindle
gamma motor neurons contract muscle spindle
what are the 2 roles of the muscle spindle
detect static length of muscle (position)
detect rate of change of muscle stretch (velocity)
what is alpha gamma coactivation
maintains sensitivity of spindle in the face of changing muscle length
what do the primary endings in a muscle spindle react to
velocity and position
what do the secondary endings in a muscle spindle react to
position ONLY
what is GTO and what does it signal
Golgi tendon organ
signals force and heaviness
what happens to ankle proprioception with age
ankle proprioception declines with age
Define balance
maintaining centre of mass (COM) within the base of support (BOS)
When swaying forwards what stops us from falling
constantly activating calf muscles
what is motion parallax
objects appear to move relative to each other depending on focus point
eg- you may think your train is moving when actually the other train is moving
describe beginning of walking stance
eccentric contraction of extensors provides braking action
describe end of walking stance
concentric action of extensors provides push off power
what happens when humans run around curves
we have to slow down due to anti gravity function
however dogs don’t have this and can therefore keep running at same speed
when walking what % is swing and what % is stance
40% swing
60% stance
what is locomotor CPG
A complex spinal neural network capable of producing functional locomotor muscle activation patterns without any contribution from afferent feedback
why do we move our eyes
to bring points of interest over the fovea (foveating)
to prevent blurring of visual scene
what are the 2 types of eye movement
fast
slow
describe fast eye movement
saccades
describe slow eye movement
vestibular ocular reflex
optokinetic reflex
These maintain stable image on retina
Smooth pursuit- tracks moving objects
Vergence- points eyes in same direction
what are the 2 types of saccade
reflex (stimulus driven)
voluntary
what are hypermetric saccades
eyes going too far and then having to readjust
what are hypometric saccades
eyes severely undershoots, has to do lots of little adjustments to get eyes to look where he wants to look
what part of brain is important for tuning saccadic eye movements
cerebellum
when does the Vestibular ocular reflex (VOR) go wrong
vestibular loss
-viral infection, head injury (loss of balance/ disorientation
ageing
-vestibular hair cells lost with age
alcohol
-alcohol nystagmus causes changes in gravity of fluid in canals
what is optokinetic reflex (OKR)
performs similar function to VOR
better for low frequency movements
what is smooth pursuit
ability to track a moving object
must involve some prediction as visual feedback is too slow
what is vergence
ability to direct eyes towards the same point
what are the 4 methods of eye tracking
scleral coil
infrared reflectance
electrooculography (EOG)
Video-oculography
what is scleral coil method of eye tracking
contact lens with embedded wire coils
very uncomfortable & invasive
can measure eye position very accurately in all 3 axes
what is infrared reflectance method of eye tracking
Beam of infrared reflected from cornea onto sclera
As eye rotates the beam is reflected in a different direction
This change in position is detected by the IR detector
Can be used in dark
what is electrooculography method of eye tracking
Retina produces measurable electric charge
Permenant electrical dipole between cornea and retina
As eye rotates, voltage between electrodes changes
Works with eyes closed
Can measure both horizontal & vertical movement
Cheap & easy
what is video oculography method of eye tracking
use software to track pupil
describe divergence
picture 2 eyeballs looking parallel
describe convergence
picture 2 eyeballs with their gaze meeting in the distance
What is the “after-effect” in force-field adaptation?
Error in opposite direction in early post-exposure
what is a contextual cue
a piece of information that is related to a specific motor skill
what is equifinality in EPH
Movement is independent of initial position, and only depends upon final position
Why would you sometimes want to SUPPRESS reciprocal inhibition?
To simultaneously activate agonist and antagonist muscles surrounding a joint
What is the evidence for prediction in smooth pursuit eye movement?
The eye movement continues briefly after the target disappears
