Muscle 2 Flashcards
The neuromuscular junction
- The point of contact where your nervous system controls your muscles
how many neuromuscular junctions do each muscle fibre have
exactly 1
○ Controlled by firing of one neuron
Where do motor neurons come from
out of spinal cord
upper motor neurone
goes from brain to cord
lower motor nuerone
goes from cord to muscle
spinal reflexes
- Circuit bypasses higher centres - short circuits
polysynaptic
○ Can be polysynaptic
§ Involving extra modulatory neurons in the circuit
○ Causing relaxation of antagonist muscle
Muscle spindles
- Encapsulated intrafusal fibres within the muscle belly
- Monitor change in muscle length and rate of change in muscle length
muscle spindles are both
○ Static - sense constant tesion on muscle
○ Dynamic - sense when muscle is stretched
muscle spindle sensory and motor aspects
sensory in the middle and started contractile muscle parts toward the ends
contractile ends of muscle spindles
§ Shorten with muscle to maintain sensitivity in shortened muscles - activated by stretch tension
motor nuerones telling contractile ends to muscle spindles what to do
gamma-MNs
§ Slower
§ so they are not hyperactive when muscle is actively shortening
myotactic reflex also called
catch reflex
myotactic reflect mediated by
muscle spindle
muscle spindle sensory neurone synapses with
alpha motor neurone
Golgi tendon organs
- Encapsulated receptors
- In myotendinous junction
- Monitor tendon tension
- don’t have a motor aspect because they don’t have to stretch
golgi tendon organs monitor
tension that may be
○ Static - slow adapting and low intensity
○ Dynamic - rapid adapt, intense
inverse myotactic reflex also called
drop reflex
inverse myotactic reflex mediated by
Golgi tendon organs
- Inverse myotactic reflex
○ Sensory neuron synapses with an inhibitory interneuron
○ Inhibit aMN firing, relaxes muscle
○ Negative feedback prevents damage
○ A drop reflex
Contracting a flexor muscle, requires
relaxation of its associated extensor muscle
Excitatory neuron synapses with
synergist (agonist) muscle
Inhibitory interneuron synapse at
antagonist muscle
motor unit
§ Single motor neuron and the multiple muscle fibres that it innervates
More myofibres =
greater force
More motor units =
greater dexterity (fine coordination) § Take up more space in the brain
3 types of motor units
○ Type 1 - slow contracting, fatigue resistant
○ Type 2a - fast contracting, fatigue resistant
○ Type 2b - fast contracting, fast fatigue \
Type 1
slow contracting, fatigue resistant
Type 2a
fast contracting, fatigue resistant
Type 2b
fast contracting, fast fatigue \
- Slow motor units
○ Small forces, fatigue resistant
○ Continuous activity
- Fast motor units
○ Fatigable
○ High forces, fatigue quickly
○ Small bursts of explosive activity
which motor units recruited first
- Small slow Mus are recruited first
- Henneman’s size principle
Slow motor neurons have lower threshold for synaptic activation
