motor units, muscle spindles, golgi tendon organs and joint receptors Flashcards
What motor neurons make up LMN and what do they do?
Alpha motor neurones
Innervate bulk of fibres within a muscl that generate force
What is the function of gamma motor neurones
Innervate a sensory organ called the muscle spindle
Triceps brachii and anconeus msucle work together to produce a force, what name is given to these muscles?
Synergistic muscle
Biceps brachii and brachialis oppose triceps and anconeus, what name is given to these muscles?
Antagonistic muscles
How many spinal nerves are there?
31 pairs
What is a motor unit?
An alpha motor neuron and all the muscle fibres it innervates
What is a motor neuron pool?
All the alpha motor neurones that innervate a single muscle
How is force of muscle contraction graded?
Frequency of action potential discharge of alpha MN
Recruitment of synergistic motor units
How is a muscle twitch sustained into a contraction?
Summation of twitches causes a sustained contraction
Benefit of a smaller motor unit?
Allows for finer movements e.g. extraocular eye muscles
How do fast and slow fibres differ?
How fast myosin ATPase splits ATP to make energy for cross bridge cycling
Features of slow fibres
Type 1 ATP from oxidative phosphorylation Red (High myoglobin) Slow contract and relax Fatigue resistant
Features of fast (IIa) fibres?
fast contract and relax
Oxidative phosphorylation
Fatigue resistant
Features of fast (IIb) fibres?
ATP from glycolysis
Fast contraction
not fatigue resistant
White
What are the 3 types of motor units?
Slow
Fast fatiguing
Fatigue resistant
Relationship between speed of twitch and size of alpha MN?
Fast- large or intermediate
Slow- Small
What is the Henneman size principle?
Smaller alpha MNs have a lower threshold than larger ones hence slow are more easily activated
What is the myotatic reflex?
When a skeletal muscle is pulled, it pulls back
What does the muscle spindle consist of?
Capsule
Intrafusal fibres
Sensory afferents
Gamma MN efferents
Describe the myotatic reflex arc
Stretch spindle Activate 1a Afferent Excitatory synaptic transmission in spinal cord Activation of alpha MN Contraction
Three types of intrafusal fibres?
Bag 1 (dynamic)- sensitive to rate of change of muscle length Dynamic MN
Bag 2 (Static)- more sensitive to absolute length Static MN
Chain fibres- absolute length
Static MN
Two types of afferent fibres?
1a
II, more slowly conducting
What are golgi tendon organs?
Located at tendon muscle junction
Monitor changes in muscle tension
What is the function of golgi tendon organs?
Act to regulate muscle tension to protect muscle from overload and regulate at an optimal range
What type of fibres innervate golgi tendon organs?
1b
What are paciniform endings?
Found in periosteum near articular attachments and fibrous part of joing capsule
Acceleration detectors
What are Ruffini endings?
Found mainly in joint capsule
Static postion and speed of movement
