Flashcards in Control of Movement One Deck (31):
What are the three causes of movement under normal physiological conditions?
- Reflexes (somatic not autonomic, i.e stretch reflex)
- Rhythmic motor pattern i.e breathing, chewing, locomotion (walking)
Where ins the CNS do motor neurons extend from?
Brainstem (cranial nerves -9/12)
Spinal Cord (spinal nerves 30)
What major CNS landmarks are involved in motor skills
Motor regions of cerebral cortex
What is another name for motor neurons?
Lower Motor Neurons (LMNs)
Where are the nuclie located for the LMNs?
- Brain stem (III, IV, V, VI, VII, IX, X, XI and XII cranial nerves)
- Spinal cord (Ventral Horn)
What are the types of motor neurons?
Alpha motor neurons
Gaba Motor neurons
Whats the function of Alpha motor neurons ?
- Innervate Extrafusal muscle fibers
- Directly responsible for the generation of force by muscles
What is the function of Gaba motor neurons ?
- Innervate intrafusal muscle fibres
- Responsible for controlling the excitability of stretch receptors in muscle spindles
What is the function of forebrain input in motor control?
Voluntary movements and muscle tone
What is the role of the spinal cord and brainstem in motor control?
Reflex movements and rhythmic motor patterns
What is crucial for the regulation of motor control?
Sensory feedback i.e propioreceptors
What are Alpha motor neurons considered to be?
The final common pathway
What is the final common pathway?
Alpha motor neurons
Why are A-LMNs considered to be the final common pathway?
The final decision to move is made by alpha motor neurons. Excitatory and inhibitory synpatic inputs all converge here.
What are the sources of synaptic inputs for alpha motor neurons?
1) Descending tracts i.e corticospinal and reticulo spinal
2) Spinal interneurons 1a, 1b
3) Propriospinal neurons (regulate function between limbs)
4) Afferent fibres (muscle receptors) i.e 1a afferents from the muscle spindles
What is the motor unit?
The functional and anatomical elements of the motor system
What are the components of an individual muscle unit?
1) Cell body of a-MN
2) Axon with all its branches
3) All neuromuscular junctions (end plates) formed by the motor neuron
4) All muscle fibers (extrafusal) innervated by this motor neuron
How many neuromuscular junctions does a mature muscle fibre have?
How many neuromuscular junctions does a immature muscle fibre have?
Can have multiple but these become pruned with growth
How many muscle fibers can a single A-MN innervate?
5-2000 muscle fibers (innervation ratio)
How are A-MNs classified?
based on their anatomical (size), Physiological and Biochemical properties.
What are two major classes of A-MNs?
S-type (type 1) = Slow Twitch
FF-type (type 2B) = Fast Twitch, fatigable
What are some properties of the s-type AMNs?
Number of units in a muscle = Many
Size of AMN cell body = Small
Fatigue = Little or none
Metabolism = Aerobic
Mitochondria = high density
Twitch time = Long (>50ms)
Power = Weak
Colour = Red as capillary and myoglobin rich
Are FF and S type fibres recruited simultaneously?
No. S type always first before ff type
Whats the size principle?
The fact that the S type is always recruited before the FF type regardless of task
What are FF types useful for then?
They are useful for large powerful contractions (high levels of muscle force)
What are some physiological consequences of the size principle?
- Some s type units fire almost always (except during REM)
- S-type units are best for carrying sustained light loads (non-fatigable)
- weak contractions can be graded with greater precision than strong contractions
- It is necessary to exercise with heavy loads to prevent f type atrophy
When are S-type fibres not recruited?
During REM sleep
What controls the force of muscle contraction?
Frequency coding - High Hz firing = Increased force
Recruitment - Increased MN = increased recruitment
Whats the twitch and contraction theory?
An AP from a A-MN causes a twitch (single contraction of all muscle fibres it innervates)
- Multiple AP's (frequency) leads to sustained contraction through summation of twitches (no time for Ca to exit)