Voluntary Movement Flashcards
what are skeletal muscles innervated by?
alpha motor neurons
what is muscle contraction innervated by?
alpha motor neurons
describe the activation of skeletal muscles?
- axons branch and innervated thousands of muscle fibres
- axon exits the spinal cord via the ventral route
- then innovates muscles
how do you get finer control of muscles?
- the smaller number of alpha-motor neurons the finer control you have
- typically a muscle fibre will receive innervation from one alpha motor neuron
how does the alpha-motor neuron control reflexes?
action potential - sensory - synapse - alpha-motor neurons - muscle - contraction
- at the same will innovate an inhibitory interneuon in the spinal cord
- triggers the alpha-motor neuron that controls the antagonist muscle
what did Fritsch and Hitzig find?
- found that if you stimulate different parts of the brain it causes movement in the contralateral side of the animals body
what is meant by contralateral?
opposite side of the body
what are the parts of the gyrated brain?
gyprus - top part of the fold
- sulcus - invagination
what is the PMC?
- the primary motor cortex, involved with voluntary movement
- it is anterior to the primary sulcus
- contains an orderly map of the contalateral body parts
- there is dispropportionate mapping
when do action potentials fire from cortical motor neurons?
fire before and during movement
what can we see from graphs of action potentials of the cortical motor neurons?
- can see theres action potential that happen much earlier than their initation of movement
- silent during flexion
- fire action potentials for movement
how many layers are there in the PMC?
6
which layer contains neurons that control movement?
5
what are pyrimidal neurons?
- cell body like a pyramid
- dendritic branching and spines
what neurons do you find in layer 5?
- giant pyramidal neurons called Betz cells
- they control movement
where do Betz cells project ot?
- send axons from the PMC to the brain
- go down the white matter tract through mid-brains and then medulla
- once at the medulla-spinal cord junction it transverses to the other side of the spinal cord
- synapses with an alpha-motor neuron
how is flexion and extension coordinated?
- neurons terminate to coordinate flexion and extension
- coritcal motor neuron: synapse at the spinal cord, generally controls agonist muscle and the antagonist muscle
what do interneurons do?
indirectly suppress antagonist muscles
what do you need to initiate/control movement?
- activation of the PMC isnt enough
- need other sensory information
- cerebellum and basal ganglia are needed
what is primary lateral sclerosis?
- progressive weakness in voluntary muscle movement
- loss of corticospinal motor neurons
- generally effects legs first
- not fatal but patients will be in a wheelchair
what is amyotrophic lateral sclerosis (ALS) caused by?
- loss of corticospinal motor and alpha-motor neurons
- some motor neurons are spared
what are the features of ALS?
- begins with trouble in executing fine movements of the hands
- wont be able to stand, walk, use their arms or hands
- retain cognitive abilities
- ultimately affects muscles of respiration
how can you asses motor functions in rodents?
open filed and rotarod
how does open field assessment work?
- measure how much they move in the field
- see profound changes when theres a disease model
- can measure anxiety like behaviours
how does rotarod assessment work?
- central beam that spins mice try to cling on - may eventually fall off
- if your studying disease, they wont hold on for as long
what is the basal ganglia?
- collection of different brain areas that receive input from the cortex, thalamus and brainstem
- essential for controlling and regulating movement
what is the striatum?
contains the candate nucelus and putamen
- between the CN and P there are gaps, here the internal capsule is loacted
- axons of white matter tract
what is the globus pallidus?
- internal segment (GPi)
- external segment (GPe)
what is the STN?
subthalamic nucleus
what is the susbtantia nigra?
- pars compacta (SNpc)
- pars reticula (SNpr)
where is the input from the basal ganglia from?
the cortex, from glutamatergic neurons
where does the input initially go in the basal ganglia?
the striatum, make synapses with medium spiny neurons (MSNs)
what are glutamatergic neurons?
release glutamate
how can you record action potential firing in MSNs?
- brain slice
- microscope
- see the cells
- put a recording electrode for a whole cell recording
- put a stimulatory electrode to activate the cortex and record action potientials
what affect do cortical neurons have on MSNs?
- depolarise MSNs as they release glutamate
- causes EPSPs - increases the probability of action potentials firing in the MSNs
how can you record action potential in vivo?
- have a mice brain - insert a recording electrode into the striatum - connect a computer and measure the extracellular action potential
what happens if you activate the cortex?
- get high activity in the striatum
what are the 2 output nuclei of the basal ganglia?
- GPi
- SNpr
- they serve different functions
what are the 2 pathways from the striatum to the output nuclei?
- direct
2. indirect
what does the direct pathway do?
facilitate of movement
what does the indirect pathway do?
suppression of movement
what neurotransmitters do MSNs release?
GABA
how do MSNs affect the output nuclei in the direct pathway?
- hyper-polarise their target cells
- release GABA
- IPSPs which decrease the probability of an action potential firing the target nuclei
- the striatum inhibits the GPi and the SNpr
how would you record the action of the direct pathway?
- place the recording electrode in the GPi or record the SNpr
- before stimulating the cortical neurons (AP firing in the GPi)
- but as soom as they’re stimulated theres no AP fired
- profound inhibitory effect on output nuclei
where do the output nuclei send information?
to the thalamus
what neurotransmitters do GPi and SNpr release?
GABA
how is the thalamus effected in the direct pathway?
- normally GPi and SNpr would inhibit the thalamus as they produce GABA
- but theyve been inhibited
- so there is increased firing in the thalamus (disinhibition of the thalamus)
how is the cortex effected in the direct pathway?
- thalamus has glutamatergic projections
- sends it cortex back to the cortex
- leads to further activation of the cortex
- facilitates the thalamus
what are the steps of the indirect pathway (draw an image)?
- MSNs send their axons to the GPe
- GPe release GABA and projects to the GPi/SNpr
- leads to disinhibition of the GPi and SNpr
- inhibition of the thalamus
- decreased activation in the cortex
- suppresses movment
what are the 2 routes of the indirect pathway?
- GPe also sends projections to the STN
- decreased activity of GPe
- less inhibition of the STN
- STN action potentials will increase (they are glutamatergic actions that project to the output nuclei)
what is the function of SNpc?
- release dopamine
- send their axons to the striatum
- they activate the neurons and regulate the function of the striatum
what is dopamine?
- intermediate in the synthesis of noradrenaline
- also a neurotransmitter itself
what is reserpine?
- lead to movement problemsin animals
- blocked the uptake of neurotransmitters into synaptic vesicles
- movement problems could be rescued by dopamine but not noraadrenaline
what is the process of making dopamine?
tyrosine
L-Dopa
Dopamine
what do neurons in the SNpc release dopamine onto?
- release it onto MSNs
- binds to postsynaptic receptors (GPCRs)
what are the dopamine receptors?
D1-like in the direct pathway
D2-like in the indirect pathway
