Musles 2

Question 1

Muscle fibres are ____ self activated, contraction of Skeletal muscles is under _______________ of the CNS

Answer 1

Not
Voluntary control

Question 2

The nerve cells that activate skeletal muscle fibres that are located in the spinal cord

Answer 2

Motor neuron

Question 3

Motor neuron purpose in this process

Answer 3

The nerve cells that activate skeletal muscle fibres that are located in the spinal cord

Question 4

Motor neurons are activated by

Answer 4

Cells called the motor cortex

Question 5

Where are the cell bodies of the motor neurons found and where fos the axon span to

Answer 5

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

Question 6

Definitiontion of Neuromuscular junction

Answer 6

The site where an action potential from the brain is delivered to a muscle fibre to initiate contraction

Question 7

The myelinated axon of a motor neuron terminates at…

Answer 7

… a single point on the sarcolemma of the muscle fibre (NMJ)

Question 8

How to form an excitory synapse

Answer 8

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)

Question 9

How many muscle fibres are contacted by a single motor neuron

Answer 9

Each motor neuron axon branches into the muscle to make contact with many muscle fibres (dozens to hundreds)

Question 10

A motor unit consists of:

Answer 10

A motor neuron and all the muscle fibres it controls

Question 11

What part of the spinal cord are motor neuron cell bodies found in

Answer 11

Ventral

Question 12

Where do motor axons project out of and and what do they form

Answer 12

Motor axons project out of the spinal cord to form ventral nerve roots and eventually to form spinal nerves

Question 13

How axons get to target muscle and what they’re up to inside the muscle

Answer 13

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

Question 14

A whole muscle is

Answer 14

A collection of motor units

Question 15

What motor neurons tend to be located close together in the spinal cord

Answer 15

The motor neurons whose axons project to the same muscle tend to be located close together in the spinal cord.

Question 16

Big motor units development of force and control over small increments of force

Answer 16

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)

Question 17

Small motor neurons and development of force and fine control over force

Answer 17

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)

Question 18

What is recruitment

Answer 18

The number of motor units activated at any one time can be varied to change the amount of force produced

Question 19

Where is the NMJ normally found and what does this mean

Answer 19

• 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

Question 20

What is actin and what does it assemble to form

Answer 20

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

Question 21

Associated with each thin filament is

Answer 21

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.

Question 22

Troponin binds…

Answer 22

Tropomyosin and actin

Question 23

Excitation-Contraction Coupling

Answer 23

• a term used to describe the steps from plasma membrane excitation to calcium release to muscle contraction

Question 24

Muscle tension / force is dependent on:

Answer 24

• the rate at which the muscle is stimulated
• the number of muscle fibres recruited

Question 25

what is a twitch

Answer 25

When a single action potential results in a pulse of Ca2+ release into the cytoplasm, and a short period of tension development

Question 26

Tetanus

Answer 26

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.

Question 27

Determinant of the number of the number of cross bridges

Answer 27

The Sarcomeres length

Question 28

Length - tension relationship

Answer 28

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.

Question 29

Motor neuron

Answer 29

The nerve cells that activate skeletal muscle fibres that are located in the spinal cord

Question 30

What is ATP hydrolysed by

Answer 30

Myosin ATPase

Question 31

Stabiliser vs neutraliser

Answer 31

Stabiliser acts isometrically
Neautraliser: eliminates unwanted movement caused by another muscle eg pronator

Question 32

What determines the force delivered when a muscle is activated

Answer 32

• amount of force provided by each fibre
• number of fibres activated