Lecture 13 Flashcards
Motor Control in the Peripheral Nervous System
how are motor neurons slightly different to other neurons
they have a long axon at one end which allows transport of electrochemical signals
what is an electrical signal
action potential
what are the two types of synapses
between neuron and neuron
between neuron and muscle fibre
how does a neuron to neuron synapse work
electrical > chemical > electrical
how does a neuron to muscle fibre synapse work
electrical > chemical
what is acetylcholine
a neurotransmitter
when do muscles contract
when acetylcholine is released by motor nerves
what does a muscle fibre contain that are very important to allow muscle contraction
filaments such as actin and myosin
1 muscle fibres is innervated by how many motor neurons
1 muscle fibre is innervated by ONLY 1 motor neuron
how many muscle fibres can a motor neuron innervate
many muscle fibres
what do Alpha (a) motor neurons innervate and what does this cause
skeletal muscle, cause muscle contractions
what is a motor unit
a motor neuron and all the muscle fibres it innervates
how many muscle fibres would be in a motor unit found in the hand or the eye (why is this important)
< 100 muscle fibres = key for precise movements
how many muscle fibres would be found in a motor unit in something like the lower leg
> 1000 muscle fibres
what is a characteristic of all fibres within a motor unit
they are all similar
- produce the same type of movement (fast twitch and slow twitch are grouped together)
on a nueral signal what all happen to the motor unit
the whole motor unit is activated
what is the corticospinal tract
connection between cortex and spine
what is the medulla known as
the switch board
what % of neurons cross the midline at the medulla
75%
what do the neurons that cross the midline at the medulla control
peripheral movement
- distal movements on the contralateral (opposite) side
what % of neurons stay on the ipsilateral (same) side of the body
25%
what do the neurons that stay on the same side of the body control (also example)
control axial muscles on both sides of the body
- example = core etc
what do motor neurons form in the spinal tract
form “pools” or “bundle’s” in the spinal tract
how are motor neurons organised into bundles in spinal cord
somatotopically = according to function (similar to motor cortex organisation)
what is afferent information
carrying information to the brain
what is efferent information
carrying information leaving the brain
what type of afferent fibres do muscle spindles have
1a afferent
what carries neural impulse from CNS to muscle spindles
gamma motor neurons
what fibres do golgi tendon organs have
type 1b afferent fibres
how do golgi tendon organs cause muscles relax
when a muscle contracts the golgi tendon is fired
what is proprioceptive neuromuscular facilitation stretching
completely maximal contraction before the stretch
how does proprioceptive neuromuscular facilitation stretching allow for a deeper stretch
the maximal contraction prior to the stretch causes more intense relaxation of the muscle in the stretch phase which allows for a deeper stretch
where do afferent neurons from GTO and muscle spindles project
project to the spinal cord
where are short reflex loops in the spinal cord
same spinal level
what are examples of short reflex loops
stretch reflex
golgi tendon reflex
gamma reflex
where are long reflex loops in the spinal cord and what type of movements are they
across spinal levels
- more complex movements
what are examples of long reflex loops
flexion reflex (standing on a pin)
postural control
what are the 5 steps to the short reflex loop (stretch reflex with patella tendon hammer)
- muscle is stretched, muscle spindle fibres activate
- impulse passed on to afferent neuron (type Ia) to spinal column
- this synapses onto alpha motor neuron for agonist, also onto inhibitory internueron to antagonist
- alpha motor neuron of agonist is stimulated so the muscle will contract
- this relieves the stretch on the muscle so the spindle organ stops firing
what are the 4 steps to the short reflex loop (golgi tendon reflex)
- muscle contracts = tendon is stretched > golgi organ fires
- afferent (type 1b) neuron synapses onto an inhibitory interneuron (in the spine)
- inhibitory interneuron synapses onto motor neuron which inhibits the agonist. antagonist is activated by alpha neuron that causes the muscle to contract
- agonist relaxes = tendon stretch is reduced so golgi stops firing
what is the goal of long reflex loops
adjustments in limb and body position
what level do long reflex loops act on
subconscious level
what does longer reflex loops have influence on
posture and stability
in the tuning of spinal reflexes, how does the spinal cord and brain operate
spinal cord works with the brain not independently
what does the gamma motor neuron do
prepare the muscle spindle for action
in terms of muscle, what can be increased in preparation for movement
muscle tone can be increased in preparation for movement
