Musles 2 Flashcards
Muscle fibres are ____ self activated, contraction of Skeletal muscles is under _______________ of the CNS
Not
Voluntary control
The nerve cells that activate skeletal muscle fibres that are located in the spinal cord
Motor neuron
Motor neuron purpose in this process
The nerve cells that activate skeletal muscle fibres that are located in the spinal cord
Motor neurons are activated by
Cells called the motor cortex
Where are the cell bodies of the motor neurons found and where fos the axon span to
The cell bodies of motor neurons are found in the spinal cord
- They grow a very long axon out to the periphery where it makes synaptic contact with muscle fibres at a single point on each of its partner muscle fibres, the NMJ
Definitiontion of Neuromuscular junction
The site where an action potential from the brain is delivered to a muscle fibre to initiate contraction
The myelinated axon of a motor neuron terminates at…
… a single point on the sarcolemma of the muscle fibre (NMJ)
How to form an excitory synapse
Eacj muscle fibre receives contact from ONE motor neuron at ONE site, to form an excitory synapse
(There are no inhibitory synapses on skeletal muscle fibres)
How many muscle fibres are contacted by a single motor neuron
Each motor neuron axon branches into the muscle to make contact with many muscle fibres (dozens to hundreds)
A motor unit consists of:
A motor neuron and all the muscle fibres it controls
What part of the spinal cord are motor neuron cell bodies found in
Ventral
Where do motor axons project out of and and what do they form
Motor axons project out of the spinal cord to form ventral nerve roots and eventually to form spinal nerves
How axons get to target muscle and what they’re up to inside the muscle
Axons project together to the target muscle, in the muscle they branch so that each axon innervates many fibres, though each fibre is connected to only one axon
A whole muscle is
A collection of motor units
What motor neurons tend to be located close together in the spinal cord
The motor neurons whose axons project to the same muscle tend to be located close together in the spinal cord.
Big motor units development of force and control over small increments of force
Very big motor units (ie hundreds of fibres) develop a lot of force, but do not provide much control over small increments in force (e.g big muscles of leg)
Small motor neurons and development of force and fine control over force
Small motor units (less then 20 fibres) do not develop much force, but provide fine control over force because activation of each unit in turn adds only a small amount to the total muscle force (small muscles of hand)
What is recruitment
The number of motor units activated at any one time can be varied to change the amount of force produced
Where is the NMJ normally found and what does this mean
- in the middle third of the fibres length
- so the wave of depolarisation (AP) spreads over the sarcolemenna away from the NMJ in both directions
What is actin and what does it assemble to form
Actin is a globular protien (G-actin)
The globules assemble to form a filamentous protein strand (F-actin)
Each thin filament is a twisted strand of two rows of F-actin, it terminated at one end of the Z-line
Associated with each thin filament is
a pair of strands of tropomysosin that attaches to the actin at regular sites via the binding at regular intervals of the globular protein, troponin.
Troponin binds…
Tropomyosin and actin
Excitation-Contraction Coupling
- a term used to describe the steps from plasma membrane excitation to calcium release to muscle contraction
Muscle tension / force is dependent on:
- the rate at which the muscle is stimulated
- the number of muscle fibres recruited
what is a twitch
When a single action potential results in a pulse of Ca2+ release into the cytoplasm, and a short period of tension development
Tetanus
Many action potentials fired in rapid sequence results in a sustained release of Ca2+ from the SR, a sustained period of actin-myosin interaction, and a sustained period of contraction.
Determinant of the number of the number of cross bridges
The Sarcomeres length
Length - tension relationship
Each muscle has an optimal length where it will be the strongest, and when either longer or shorter then that length, it will be weaker.
- When over stretched the thin and tick filaments don’t interact - limiting the count of force.
- When slack - doesn’t have anywhere to go - already over lapse on itself.
Motor neuron
The nerve cells that activate skeletal muscle fibres that are located in the spinal cord
What is ATP hydrolysed by
Myosin ATPase
Stabiliser vs neutraliser
Stabiliser acts isometrically
Neautraliser: eliminates unwanted movement caused by another muscle eg pronator
What determines the force delivered when a muscle is activated
- amount of force provided by each fibre
- number of fibres activated
