motor Flashcards
how is the motor system arranged and what does this include
hierarchically.
the highest level of control is in the primary motor cortex, this projects directly to the spinal cord via the corticospinal tract, it also regulates the motor tracts that originate in the brainstem.
the next level of control is the brainstem, it is a lateral descending system that controls the distal part of the limbs. it is important for goal directed movements of the hand and arm.
the lowest level of control is from the spinal cord, it contains neuronal circuits that mediate reflexes such as walking and chewing. they control simple monosynaptic reflexes and polysynaptic reflexes with interneurons. it is a direct pathway to the muscles.
what happens if you artificially stimulate the motor cortex and what must this mean
you dont get any complex movements you only get twitches and this means there must be something else contributing to complex movements.
what does the basal ganglia and cerebellum do for motor signalling
they receive information from many different areas of the cortex and they project it to the motor cortex via the thalamus.
they are aware of the situation the person is in, as they are getting info from the senses and other areas.
so they monitor the commands going down to the muscles to make sure they are appropriate for the situation.
what happens if the commands sent to the muscles are not appropriate for the situation
the basal ganglia and cerebellum step in and calculate correction signals which they send back up to the motor cortex for approval before it is sent back to the muscles.
the basal ganglia loop only feeds back to the motor cortex (subcortical loop)
the cerebellum mainly feeds back to the motor cortex but can send its signals down the brainstem, spinal cord and onto the muscles so it can bypass asking the motor cortex for approval.
the history of motor cortex discovery
1870- it was discovered and electric stimuli to different areas of the frontal lobe produced movements on the opposite side of the body.
mid 20th century- electric stimulation used to identify specific motor effects of discrete sites in the frontal lobe in different species.
why is the stimulation of the brain okay
because it has no nociceptors and so it feels no pain
what is brodmanns area 4 and where is it located
it was found to be the area in which the lowest intensity stimulation elicited movement, now known as the primary motor cortex.
it is located just before the central sulcus (fissure of rolando) and is sometimes called the precentral gyrus to highlight its position.
how is brodmanns area arranged
what if you lesion part of this
it is arranged in a very orderly fashion along the gyrus of the control area for the leg, trunk, hand etc.
the motor homonculus shows a person but the size of their body parts shows the amount of the cortex that is used to control that area. the hands and mouth are the biggest.
the tracts connecting to it that lead all the way to the muscle will also die, this is called valarian degeneration.
what are upper and lower motor neurons
upper motor neurons carry the motor commands from the motor cortex and down to the spinal cord.
they cross the midline in the brainstem.
they then synapse with an interneuron which will synapse to a lower motor neuron which carries the info to the muscles.
the cranial nerves are also upper motor neurons but they dont come from the motor cortex.
what are the upper motor neurons involved in
where do other upper motor neurons come from and what are they for
planning, initiating, directing movements.
if they dont come from the motor cortex they come from phylogenetically ancient motor centres of the brain stem such as the red and vestibular nuclei, superior colliculus and the reticular formation.
they are for regulating muscle tone and postural muscles, maintaining balance and orientation of the head and body.
what is the overall pathway of how motor info reaches the muscles
what is the final common pathway
the main way is for the primary motor cortex to send info down the UMN to the spinal cord and then to the LMN and to the muscles.
but the UMN can be bypassed by the cerebellum, so there is an indirect path that goes from the brainstem centres and straight to the spinal cord.
reaching the LMN is called the final common pathway that leads to movement.
what is the basal ganglia made up of and what does it do for motor signalling
how does this link to tourettes
caudate, putamen, substantia nigra, and subthalamic nucleus.
they provide input to the UMNs and connects with the motor cortex.
they help to initiate and terminate movements, suppress unwanted movements and establishes a normal level of tone.
tourettes is when you cannot stop the unwanted movements.
what is the circuitry of the cerebellum like and what is one of its main functions
it monitors movements for differences in intended and actual movements
if there are any discrepancies it will send an error signal
it has a very simple circuitry and works very quickly.
what is proprioception and how does it work in one sentence.
knowing the orientation of your body without having to look at it.
this is done by muscle spindles informing the brain about how long the muscles are/how stretched.
what is the structure of the muscle spindle like
the muscle spindle is made of muscle fibres within a capsule, there are nerves going in and out of it.
the muscle fibres in the spindle are known as intrafusal fibres.
the muscle fibres not inside a spindle are called extrafusal fibres.
there are two types of intrafusal fibres-
bag fibres have all their nuclei gathered in one place and so they have a bulge in the middle.
chain fibres have their nuclei spread out down the fibre.
what sensory fibres reach the muscle spindles
when does each type relay info
the sensory fibres are the Ia and II afferents, they send info up to the brain.
the Ia afferents wrap around the muscle fibre, so when the muscle stretches the Ia fibres will be stretched apart, this will fire APs and tell the brain that the bodys orientation is changing.
Ia afferents relay info on the dynamic phase of the muscle stretch as the stretch is occuring.
II afferents relay info onto the static phase of muscle stretch when it has reached its final length.
static=long
what is the structure and speed of the Ia afferent
II afferent
it is the largest axon in the body and it is the fastest conducting. their terminal ending is annulospiral and wrapped around the equator of both bag and chain fibres.
they have a flower spray terminal ending embedded in the equator regions of the bag fibres and they have annulospiral endings on the chain fibres.
what do the gamma motor neruons do to the muscle fibres
they make the muscle fibres contract.
the intrafusal and extrafusal fibres have to contract together.
they are the efferent innervation of the spindles
what happens if you add 5HT onto a gamma motor neuron
what about noradrenaline
it will fire more rapidly
it will fire less rapidly
5HT will make the intrafusal fibres stiffer and so it will be able to transmit stretches better.
NA will make the fibres more floppy so they are less able to transmit sensory info.
so when we are writing the hand will have 5HT to be able to do fine muscle movements and the rest of the body will have NA.
where are the primary and secondary somatosensory cortices found
anterior parietal lobe and posterior parietal cortex.
where are seratonergic and noradrenergic fibres present in high amounts
in the ventral horn of the spinal cord.
what is sound localisation important for
what is binaural vs monaural
catching prey, communication, perception of auditory space, know where a sound is.
hearing using sound from both ears or hearing using sound from on ear.
what is a monaural cue
to detect it only requires sound input from one ear.
for example detecting sound elevation in the vertical plane.
there are also head related transfer functions which is how the position of the head and ear affect how a sound is heard and localized.
what is a binaural cue
two main
these require input from both ears.
for example detecting a sounds position on the horizontal plane (azimuth)
you can also detect interaural timing differences (the difference in the arrival time of sound to each ear), this is normally for low frequencies of sound.
or you can detect the interaural level differences (difference in intensity of sound reaching each ear) and this is mainly for high frequency sounds.
which strategy do animals use for hearing and why
most species use both strategies for localising sound, but most of the time one dominates.
this depends on the animals hearing range and head size or evolutionary history.
where does the output from the hair cells go to
where are the timing and intensity difference calculations done
aVCN- anterior ventral cochlea nucleus
in the lateral and medial superior olive and the medial nucleus of the trapezoid body.
what happens in the interaural level differences circuit
input from the left ear goes to the aVCN.
and then has excitatory input on the lateral superior olive.
input from the right ear goes to the medial nucleus of the trapezoid body and then has an inhibitory input on the lateral superior olive.
the LSO detects the difference between the excitatory and inhibitory inputs.
so if sound goes directly into the left ear then the excitatory input will be a lot bigger than the inhibitory from the right ear so the LSO will be very active.
if the sound is coming from the front then there will be fairly equal excitatory and inhibitory outputs.
the closer the sound is to the left ear the higher the activity of the LSO as it will receive more excitatory input.
this happens vice versa in the other ear, so if one LSO is activated on one hemisphere then the other will be inhibited.
describe interaural level differences using the words ipsilateral and contralateral
how has it been conserved
they are encoded by cells in the LSO that compare the coincidence of excitatory ipsilateral and inhibitory contralateral inputs.
it evolved over 200 million years ago and is highly conserved among mammals.
what is the jeffress model and who is it for
it only applys to birds.
interaural timing differences are encoded by cells that compare the coincidence of excitatory ipsilateral and contralateral inputs.
it is mainly for low frequency hearing.
the overall position of a sound is encoded by the particular channel activated.
this is created by neuronal delay lines (labelled lines model).
it happens in the nucleus laminaris.
mammals interaural timing differences HELPPPPPPP
there are two excitatory inputs to the medial superior olive, one from the ipsilateral ear and one from the contralateral.
the overall position of a sound is encoded by the balance between the average population response of the two MSO channels.
Knudson and Knudson experiment
showed that vision is the dominant sense for space perception.
glasses were glues to the owls face that were prisms, so it made it seem like they were looking 20 degrees to the left.
when a sound and light was flashed in front of the owl it would think that the light was 20 degrees left but the sound would still seem to come from dead ahead.
over time the owl will think that the sound is also 20 degrees to the left, the auditory response shifts to match that of the visual response.
when the prisms are removed the visual response immediately returns to normal, the auditory response will follow but it takes longer.
In mammals vs birds how are both ITDs and ILDs represented
In mammals both ITDs and ILDs are represented by two hemispherically tuned channels with the balance of output accurately encoding a sounds position.
In birds ITDs are encoded by cells tuned to a narrow range of ITDs. This produces a precise hardwired topographic map of ITDs, whereas that of mammals is more dynamic and adaptable.
how is the auditory and visual map connected
the auditory map in the exterior inferior colliculus is aligned with the visual map in the optic tectum.
when the prisms are added the instruction from the optic tectum realigns the exterior inferior colliculus to match.
the visual input is dominant.
McGurk affect
what you see (someones mouth forming a word) is what you will hear.
someone mouths duck but the word uck is played over it, you will hear duck because the visual input takes over.
perception is very context dependant.
how do we selectively focus our attention
we can focus on one sound because we can focus our vision on the person speaking.
resetting rhythmic brain oscillations allows us to focus our attention.
you use active sensing to scan the scene using motor and visual systems
when we select our attention on the speaker the oscillations synchronise to the temporal pattern of the relevant speech stream
how can we predict auditory information
visual cues (stimulus driven entrainment)
Supertaskers
2.5% of the world are good at multitasking, the wiring in their brain is more efficient so their brain activity is lower and the reduced burden on the brain gives an improved focus ability.
what dominates over other modalities
the most statistically relaible input
