Skeletal muscle Flashcards
Define motor unit Explain the principle fibre types in human skeletal muscle Explain how the force of contraction is controlled by a-MNs Explain how muscle spindles and Golgi tendon organs regulate muscle contraction Explain the operation of the y-loop
What are the 2 regions in the spinal cord?
Anterior and posterior
Where are cell bodies located in the spinal cord?
Anterior horn
What forms synapses with skeletal muscle?
a - MNs
What is a muscle?
Lots of muscle fibres bundled in big groups
How many synapses does a muscle fibre have?
A single one - focal innervation
Define motor unit:
A motor unit is made up of a motor neurone and the skeletal muscle fibers
These are innervated by that motor neurone’s axonal terminals
What can be used in surgery to stop muscles contracting?
Nicotinic antagonist neurotoxins
What happens when a muscle fibre is innervated by the same a-MN?
Spreads throughout the muscle - smooth contraction (asynchronously)
What is type 1 muscle fibre?
Slow twitch (0.1s)
What is type 2 muscle fibre?
Fast twitch (0.01s)
What are type 1 muscle fibres properties? (4)
Energy source: Oxidative
Colour: red
Function: posture
Examples: Abs
What are type 2 muscle fibre properties? (4)
Energy source: Glycolytic
Colour: White
Function: Rapid movements
Examples: Eye muscles
What happens if we want to lift something heavy? (3)
More a-MNs are recruited
Increased AP firing rate of a-MNs (summation)
Slow twitch recruited first but also fast twitch
What happens when a-MNs send ACh to nicotinic receptors in skeletal muscle? (2)
Renshaw cells inhibit a-MN (glycine) - literal inhibition
y-MNs attach to muscle spindles
What are muscle spindles and what do they do? (4)
Mechanoreceptors
Sensitive to stretch
Attached to muscle fibres
Innervated by y-MNs
Explain the y(gamma) loop: (5)
Initial motor output excites a and y MNS Dorsal root ganglia, glutamate released excites a-MNs a-MN: AP for muscle fibre contraction y-MN: AP for muscle spindle contraction Type 1a afferent to excite again
What are Golgi tendon organs? (4)
Mechanoreceptors sensitive to stretch
Located between muscles and tendons
When a muscle is stretched, this distorts afferent terminal endings in GTO
Generates APs in the type 1b afferents
What are the 2 distinct functions of a Golgi tendon organs?
Protect tendons from being overloaded (inverse stretch reflex)
Controlling isotonic contractions
What are the 2 types of contraction?
Isometric (same length)
Isotonic (same tension)
