1(a). MOTOR CONTROL
Created Dec 5, 2019 111 PM
Tags
Updated Jan 21, 2020 1019 PM
What is...?
Motor control - the generation of signals to coordinate contraction of the
musculature of the body and the head, to maintain posture or make a
movement
Movement - the transition between two postures
Motor Neurons
There are two types of motor neurons:
alpha-motor neurons
large neurons (equal to or more than 70 micrometers in diameter)
stretches from the spinal cord to the extrafusal muscle fibers of skeletal
muscle
extrafusal muscle fibers are the skeletal standard muscle fibers that
are innervated by alpha motor neurons
generates tension by contracting the muscle
the number of fibers that the single neuron stimulates determines how
fine or gross our control is
in the bicep, only one neuron stimulates many muscle fibers due to
the lack in need for fine control (gross control)
in the hands, there are many neurons which stimulate the muscle
fibers due to the need for fine control
gamma-motor neurons
smaller neurons (about 35 micrometers in diameter)
stretches from the spinal cord to the intrafusal muscle fibers of skeletal
muscle
1(a). MOTOR CONTROL 1
, intrafusal muscle fibers are buried in the muscle (not the outer
layer) and serve as specialised sensory organs (proprioceptors)
that detect the amount and rate of change in length of muscle
(contraction)
gives the general tone of the muscle (if not, they'd be flabby)
it is in a continuous state of slight contraction which gives the
tone
controls the general tone of the muscle
not particularly involved with actual contraction
Neurotransmitters
There are two main neurotransmitters involved in motor control:
glutamate GLU
the primary excitatory neurotransmitter
released by a glutamatergic neuron (uses Glu as a neurotransmitter)
it causes the influx of positive ions
when Glu is released and binds to an NMDA receptor, the sodium or
calcium ion channels are opened
NMDA is N-methyl-D-aspartic acid and is a receptor for Glu
this causes the influx of sodium or calcium ions which are positive
this increases the chance of causing an action potential to be
generated
gamma aminobutyric acid GABA
the primary inhibitory neurotransmitter
released by GABAergic neurons (uses GABA as a neurotransmitter)
it causes the influx of negative ions
when GABA is releases and binds to a GABAA receptor, the
chlorine channels are opened
this causes an influx of chloride ions which are negative
this causes hyperpolarisation
where the resting membrane potential is lower than 70 mV
1(a). MOTOR CONTROL 2
, this makes it more challenging to reach the threshold potential for
an action potential to be generated
essentially inactivates the neuron (but not really)
this lowered membrane potential is resetted if an action potential is
generated
Due to several neurons competing with their own neurotransmitters at the
synapse, it becomes a competition of which neurotransmitter would win
Reflex Arc
The reflex arc is highlighted in the knee-jerk reaction, though there are many
other examples which won't be discussed
it is an autonomic response
this is the reaction when the hammer hits the patellar tendon
due to the sudden stretch caused by the hammer hitting the tendon, a
series of action potentials are generated
the afferent neuron sends the signals to the spinal cord from the
muscle
the action potentials split in the spinal cord and:
synapses to an alpha motor neuron
Glu binds to NMDA receptors and excites the cholinergic motor
neuron
this causes the extensor muscle to contract
synapses to an interneuron (which are almost always inhibitory)
Glu binds to NMDA receptors and excites the GABAergic
interneurons
this causes the hyperpolarisation of alpha motor neurons to the
flexor muscle
this ensures that the flexor muscle is relaxed
acetylcholine is prevented from being released at the
neuromuscular junction
The Brain and Movement
1(a). MOTOR CONTROL 3
, Stages of Movement
There are multiple stages involved with moving:
Identifying the target
Placing the target in a 3-dimensional space
Calculating the trajectory of the intercepting limb
Calculating the force needed to exert
The Lobes of the Brain
There are four main lobes of the brain, of which some are discussed in more
detail
frontal lobe
parietal lobe
temporal lobe
occipital lobe
However, there are two more lobes of interest:
insula lobe
limbic lobe (consists of parts of the frontal, parietal and temporal lobe)
Frontal Lobe
The frontal lobe is the part of the brain that controls important cognitive skills
in humans
it is composed of several cortices which are (but not limited to; this
concerns the motor function of the frontal lobe):
primary motor cortex M1
the primary eliciter of movement (initiates action)
it requires the least amount of electrical stimulation compared to
the other areas
it has a functional somatotopic motor map
it is the projection of the body surface onto a brain area that is
responsible for that specific area of body
premotor area PMA
1(a). MOTOR CONTROL 4
Created Dec 5, 2019 111 PM
Tags
Updated Jan 21, 2020 1019 PM
What is...?
Motor control - the generation of signals to coordinate contraction of the
musculature of the body and the head, to maintain posture or make a
movement
Movement - the transition between two postures
Motor Neurons
There are two types of motor neurons:
alpha-motor neurons
large neurons (equal to or more than 70 micrometers in diameter)
stretches from the spinal cord to the extrafusal muscle fibers of skeletal
muscle
extrafusal muscle fibers are the skeletal standard muscle fibers that
are innervated by alpha motor neurons
generates tension by contracting the muscle
the number of fibers that the single neuron stimulates determines how
fine or gross our control is
in the bicep, only one neuron stimulates many muscle fibers due to
the lack in need for fine control (gross control)
in the hands, there are many neurons which stimulate the muscle
fibers due to the need for fine control
gamma-motor neurons
smaller neurons (about 35 micrometers in diameter)
stretches from the spinal cord to the intrafusal muscle fibers of skeletal
muscle
1(a). MOTOR CONTROL 1
, intrafusal muscle fibers are buried in the muscle (not the outer
layer) and serve as specialised sensory organs (proprioceptors)
that detect the amount and rate of change in length of muscle
(contraction)
gives the general tone of the muscle (if not, they'd be flabby)
it is in a continuous state of slight contraction which gives the
tone
controls the general tone of the muscle
not particularly involved with actual contraction
Neurotransmitters
There are two main neurotransmitters involved in motor control:
glutamate GLU
the primary excitatory neurotransmitter
released by a glutamatergic neuron (uses Glu as a neurotransmitter)
it causes the influx of positive ions
when Glu is released and binds to an NMDA receptor, the sodium or
calcium ion channels are opened
NMDA is N-methyl-D-aspartic acid and is a receptor for Glu
this causes the influx of sodium or calcium ions which are positive
this increases the chance of causing an action potential to be
generated
gamma aminobutyric acid GABA
the primary inhibitory neurotransmitter
released by GABAergic neurons (uses GABA as a neurotransmitter)
it causes the influx of negative ions
when GABA is releases and binds to a GABAA receptor, the
chlorine channels are opened
this causes an influx of chloride ions which are negative
this causes hyperpolarisation
where the resting membrane potential is lower than 70 mV
1(a). MOTOR CONTROL 2
, this makes it more challenging to reach the threshold potential for
an action potential to be generated
essentially inactivates the neuron (but not really)
this lowered membrane potential is resetted if an action potential is
generated
Due to several neurons competing with their own neurotransmitters at the
synapse, it becomes a competition of which neurotransmitter would win
Reflex Arc
The reflex arc is highlighted in the knee-jerk reaction, though there are many
other examples which won't be discussed
it is an autonomic response
this is the reaction when the hammer hits the patellar tendon
due to the sudden stretch caused by the hammer hitting the tendon, a
series of action potentials are generated
the afferent neuron sends the signals to the spinal cord from the
muscle
the action potentials split in the spinal cord and:
synapses to an alpha motor neuron
Glu binds to NMDA receptors and excites the cholinergic motor
neuron
this causes the extensor muscle to contract
synapses to an interneuron (which are almost always inhibitory)
Glu binds to NMDA receptors and excites the GABAergic
interneurons
this causes the hyperpolarisation of alpha motor neurons to the
flexor muscle
this ensures that the flexor muscle is relaxed
acetylcholine is prevented from being released at the
neuromuscular junction
The Brain and Movement
1(a). MOTOR CONTROL 3
, Stages of Movement
There are multiple stages involved with moving:
Identifying the target
Placing the target in a 3-dimensional space
Calculating the trajectory of the intercepting limb
Calculating the force needed to exert
The Lobes of the Brain
There are four main lobes of the brain, of which some are discussed in more
detail
frontal lobe
parietal lobe
temporal lobe
occipital lobe
However, there are two more lobes of interest:
insula lobe
limbic lobe (consists of parts of the frontal, parietal and temporal lobe)
Frontal Lobe
The frontal lobe is the part of the brain that controls important cognitive skills
in humans
it is composed of several cortices which are (but not limited to; this
concerns the motor function of the frontal lobe):
primary motor cortex M1
the primary eliciter of movement (initiates action)
it requires the least amount of electrical stimulation compared to
the other areas
it has a functional somatotopic motor map
it is the projection of the body surface onto a brain area that is
responsible for that specific area of body
premotor area PMA
1(a). MOTOR CONTROL 4
