Midterm 3 Flashcards
What is sensory modulation of locomotion important for?
- initating walking
- controlling phase transitions
- regulating level of muscle activity
what occurs with stimulation of afferent type 1 (group 1) in decerebrates?
flexion is inhibited! The stimulation interrupts the flexor AP firing rate
In the experiment with the decerebrated cat, what happened when they dropped one of the stepping plates by 4cm?
The cat’s extensors had a big reaction (i think), and we see an EMG burst. The cat can react accordingly to the dropped plate despite having their nerves cut.
What is tonic descending input?
Tonic: always on
- constant descending input can modulate muscle activity
- these inputs can be IPSP or EPSP, and descending neurons will make synaptic connections with neurons in the reflex arc
- we can modulate how much of IPSP or EPSP is dropped, so that we can get enough input for a reaction
- Allows a previous reflex input that didn’t have enough bang, to get to the threshold
where does input descend onto to balance EPSP and IPSP?
1a inhibitory interneuron
what needs to be done before we initiate a movement?
reciprocal/1b inhibition needs to be removed. (we have to set the table before moving)
What is the theory behind the recovery of walking in patients who have lost the ability?
the theory is that we can kick start the CPG by repetitive practice. If we provide appropriate sensory feedback through specific movements, people can regain the ability to walk
In decerbrate subjects, how can we explain the avoidance of obstacles?
with walking, we visually plan the next step to prevent stumbling. We talk input from a lot of higher centres, like motor cortex, visual input and brainstem. When people are decerebrated, we lose this input. HOWEVER, we also get feedback from moving limbs that contribute to the CPG. this is why we can still avoid obstacles even after losing all descending input from higher centres.
______ allows for better control of reflexes
tonic input
what can happen when someone has a really bad stroke?
they can lose inhibition of the 1a afferent, which results in uncontrolled reflexes (you forget how to set the table for a movement).
What do tonic signals do from the brainstem?
Initiate signals (constantly)
What does supraspinal control from motor cortex and brain stem do for movement?
- balance
- task selection
- navigation
- obstacle avoidance
What is the organization from top to bottom of inputs for CPG?
- visual cortex
- motor cortex and cerebellum
- basal ganglia and brainstem
- feedback from limbs
- spinal cord with CPG
- muscles
What happened with Baby Hugo when he was hooked up to a treadmill?
He can walk backwards, and when he gets turned around, he starts adducting and then he starts to braid. its a super complex movement and he cant even walk yet, but it is because afferent information is driving his CPG
What is the vestibular sense?
It is a system within your ear that is important for proprioception?
how many peripheral apparati are there? where are they located?
2, one per ear
why is it important for the vestibular sense to have two ear inputs?
because it allows for the system to work well. A stimulus on one side results in an opposite reaction on the other side. Allows perception of position to be much more accurate.
what happens if we lose vestibular sense, or it starts malfunctioning?
we get nauseous or dizzy
what are the major roles of the vestibular system?
- Roll
- Pitch - anterior posterior
- Yaw - rotational around the z axis
where is the vestibular system?
inner ear
Is the vestibular system separate from the ear/cochlea?
No, it is continuous with the ear system, like a balloon animal, the three hoops and big swelling all flow into the cochlea.
what nerve is important for the vestibular system
8th cranial nerve
what nerve innervates the semicircular canal
8th cranial nerve, vestibular branch
what nerve innervates the cochlea?
8th cranial nerve, cochlear branch
Describe the morphology of the semircular canal
The bone is hollowed out with caverns in it. (like an aero bar)
draw the vestibular system, including the tunnel and membranous labyrinth
what is the fluid within the bone and membranous labyrinth? What does it do?
Bone = perilymph. suspends the labyrinth
Membranous labyrinth = endolymph
what is the ampulla?
The “swelling” of the vestibular system
Describe the position of the semicircular canals
anterior and posterior go 45 degrees off centre, and between them is 90 degrees.
Lateral lay horizontal, 90 degrees out from the face
What happens to the vestibular system when we drink wine?
Wine is high in nitrates. These increase the blood pressure within the canals, which causes activations of the hair cells
Describe the morphology of the hair receptor
- kinocillium (1 per receptor, the longest cillia)
- stereocillia (40-70 per cell)
- hair cell
what is the hair bundle?
the portion of the hair receptor that contains kinocilium and stereocillia
what are the types of hair receptors
Type 1
- very straight
Type 2
- bulbous
what nerve innervates hair receptors?
8th cranial nerve afferent
What is special about the hair receptors?
they are always on, since they are super leaky. they fire at 100Hz pretty much all the time, so there is always background discharge. They are also pushable! That makes them special too
what does it mean for a hair cell to have a morphological axis of polarity?
it means that they have a specific direction of force that yields polarization. It is dependant on the position of their kinocillium
What direction promotes depolarization in hair cells
towards the kinocillium
what direction promotes hyperpolarization in hair cells
away from the kinocillium
what direction increases the firing rate of hair cells (excitation)?
towards kinocillium
what direction decreases the firing rate of hair cells (inhibition)?
away from kinocillium
draw out the crista
where are crista found in the vestibular system?
In the swellings at the end of each duct
Where do hair cells reside?
in the crista
How many crista are there?
3 - one for each duct
what is special about the crista?
it actually stops fluid, none goes through it. the cupula spans across the tube and acts like a sail
where else is the design of the cupula found?
nowhere!
describe the morphology of the macula
hair cells reside in otolithic membrane (fluid) which is covered by a layer of hard calcium rocks
what is the direction of the hairs in the macula?
opposite. utricle = hairs oriented towards each other. sacula = hairs oriented away from each other
As you go around the shape of the maculas, what happens to the hair orientation?
It changes! This is so that it can get a fine reaction for every single body position/acceleration
which plane is the utricle in?
horizontal
which plane is the sacule in?
vertical
what is the line in the utricle?
striola
what promotes a larger reaction in the macula hair sensors?
more gravitational pull. the weight in the membrane pulls the hairs down, so the more you tilt, the more pull and reaction there is
what do the hard calcium rocks do in the macula?
they help pull the otolith membrane down
(I think this is right) what happens with head tilts backward and forward, acceleration and deceleration?
backward/acceleration = depolarization
forward/deceleration = hyperpolarization
What occurs in the saccule when we consume alcohol?
The orientation changes so that there are two armies that are kinda ignoring each other
describe what happens in the vestibular system during spinning
the acceleration pulls against the hair. the fluid lags behind until it eventually catches up, so if we spin at a constant velocity for long enough, the hair stops spinning.
increased speed = increased discharge frequency
describe what happens to the vestibular system when we roll our head
the otholympic system picks up basically any movement. turning to the left = increase in firing, upwards direction of fluid. turning to the right (ampulla?)= decrease in firing, downwards fluid direction
why is it important for the ducts to work in pairs?
because they each provide an opposite response to the other.
How important is the vestibular system
important, but we still really need other receptors, like skin/vision/proprioceptors.
What is GVS
galvanic vestibular stimulation
How do we set up GVS?
- place two rubber things on the mastoid
- stimulate cathodal and anodal side
What occurs with stimulation of GVS when standing?
you end up leaning. it causes the head to roll on the trunk, and the trunk to roll on the pelvis
what is the GVS used to detect?
vestibular deficiency. also used to artificially activate it
what does stimulation do to cathodal and anodal side?
cathodal = increased firing rate
anodal = decreased firing rate (where we sway)
do we sway towards the side with increased or decreased firing rate?
decreased, aka anodal side
What is the sway a compensation for?
An error message
what happens if we stimulated someone GVS while they walk?
clear veering towards anodal side. shows that vestibular system has a big role in proprioception
When do we see more of an effect when testing GVS? running or walking?
walking
what happens when we use GVS for people when walking with their head down?
they end up turning really sharp - in a C. instead of veering, they turn
