Transcript Muscle control

Muscle control
Muscles and how they work: a review
The more you read/see something explained in a
different way, the more sense it makes. Here are some
more You Tube finds, which explain how muscles work.
• First, an overview:
• http://www.youtube.com/watch?v=hzXVe4RS8-A
• Next, the detail of the sliding filament theory:
• http://www.youtube.com/watch?v=ELyoJZom5N0
• Finally, a good explanation of how muscle spindle and
Golgi tendon organs work. We will refer to these when
we look at REFLEXES next week.
• http://www.youtube.com/watch?v=7T4NI_2qDEM
Acetylcholine
• A key neurotransmitter in the PNS and also
found in the CNS
• Drugs to treat a number of the conditions
which we are interested in as SLT have their
action on Ach
• If they reduce the action of Ach they are
called anticholinergics (PD, CPOD)
• If they prevent the breakdown of Ach they are
called cholinesterase inhibitors (MG, AD)
• Each muscle fibre is innervated by one neuron…
• But one neuron can innervate a large number of
muscle fibres
• The greater the number of motor neurons that are
activated, the greater the number of muscle fibres that
will contract
• Each muscle fibre contracts in an all-or-nothing
fashion (just like nerve fibres fire in an all-or-nothing
fashion) to their fullest extent
• Factors that affect the force of contraction include the
number of muscle fibres contracting (ie the number of
motor units, and the size of these units)
Facial muscles, tongue, muscles of
mastication and larynx
• Have a low ratio of nerve fibre: muscle fibres
• Enables high degree of precision in movement
• Contrast this with larger limb muscles, or muscles to control posture
• Larynx 1:6-12
v
Hip 1:2000
• ie one neuron innervates 6 to 12 muscle fibres in the larynx,; in the eye
muscles, this ratio can be as low as 1:5; for some of the larger, postural
muscles, the ratio is much higher
• In addition, the type of muscle fibre determines the speed and
sustainability of muscle contractions
• Video of the vocal cords in action:
•
https://www.youtube.com/watch?v=v9Wdf-RwLcs
Types of skeletal muscle fibre
• Muscle fibres vary in colour…depending on the amount of
myoglobin they contain
• Myoglobin= a red-coloured protein, binds oxygen, found in
muscles (like haemoglobin, found in red blood cells)
a. Slow-twitch, fatigue resistant fibres: found in the postural
muscles of neck, back and legs
b. Fast-twitch, fatigue resistant fibres: found in leg muscles
c. Fast-twitch, B fibres: fatigable. White as opposed to a & b
which are red in colour. Produce strong, rapid contractions;
for eg, in the muscles of the shoulders and arms
MUSCLES have a mixture of all 3 fibres; proportion depends
on the particular function of the muscle, and its use
Exercise can induce change in muscle
fibres
• Think of a marathon runner v a weighlifter
• What type of fibres predominate in the key
muscles in these athletes?