Lecture 7 - Motor System

Question 1

Anatomy of muscle fibres

Answer 1

Made up of myofibril, the sources of muscle fibre striations

The myofibril is made up of a thick (myosin) and thin (actin) filament which overlapping proteins (in sarcomere)

Myofilaments are composed of myofibril, sarcomeres are the repeating functional units of myofilaments

Muscle cells are made up of muscle fibers (cells)

Question 2

Z and M lines

Answer 2

Z lines are where the sarcomere ends and where the filaments attach

M is the middle line

Question 3

Sliding filament model

Answer 3

Sacromere can not shorten for muscle contraction so they must slide

Thin filaments will be pulled by thick ones toward the centre (m line) , z lines move in/closer together

Myosin head (thick) is bounded to ATP but then is ADP with an additional phosphate

Myosin head binds so the actin and performs a power stroke pulling actin, releasing the ATP

The myosin releases from the actin because a new atp binds to the head of molecule

Question 4

Muscle is not always contracting

Answer 4

Tropomysin the protein, blocks myosin from binding to actin. Tropomysin is a regulator

Calcium binds to troponin, moving tropomyosin aside exposing a binding site triggering power strokes (muscle contraction)

Calcium=trigger ion

Question 5

Excitation Contraction Coupling

Answer 5

ACh is released into the synaptic cleft. ACh binds to receptors and opens sodium ion channels which leads to an AP in the sacrolemma

AP in the sacrolemme travels along T tubules to the triads where it triggers release of calcium ions from the sarcoplasmic reticulum. This happens because reads positive charge from sodium potassium channels leading to voltage gated calcium channels opening

Contraction begins an will continue as long as ATP is availible and AP are produced

Sliding theory

Question 6

Different types of muscle fibers

Answer 6

Muscle fibers differ in how they produce ATP, some use oxidative metabolism others use glycolic

Type I : Slow and oxidative (SO)
walking, standing

Type IIA: Fast and oxidative (FO) Fast, Fatigue Resistant (FR)
fast walking

Type IIAB: Fast Oxidative and Glycolytic (FOG) Fast intermediate fatigue (FI)
jogging

Type IIB: Fast and Glycolytic (FG) Fast and Fatigable (FF)
sprinting, no oxygen fast twitch

lower energy and force, fast recovery to high energy and force, long recovery

Question 7

Myoglobin

Answer 7

responsible for making ATP

Question 8

Motor units vs Pools

Answer 8

Motor unit: single motor neurone and all the muscle fibres it innervates
-1 neuron + muscle fiber

Motor pool: all the motor units innervating a given muscle
-distributed incase of injury doesn’t wipe out entire function
-not just one spinal segment

Question 9

Twitch contraction

Answer 9

Multiple Twitches in a row result in a build up of force

rating of AP firing, calcium enters