Lecture 3 - NM System

Question 1

What are the 3 types of muscle cell and their characteristics

Answer 1

Skeletal, striated multinucleated, both voluntary and involuntary

Smooth, hollow organs bv skin, single nuclei, not striated involuntary only

Cardiac, single nuclei striated, involuntary

Question 2

What are the layers of muscle tissue

Answer 2

Epimysium surrounds skeletal muscle
Endomysium is connective tissue that wraps each muscle fibre
Perimysium wraps bundles of muscle fibres
Fascicles bunch of muscle fibres surrounded by a perimysium

Question 3

What is the job of the motor neurone

Answer 3

Stimulate muscle contractions
Axons innervate each muscle fibre
Contacted through neuromuscular junction

Question 4

What is the chemical composition of muscles

Answer 4

75% water
20% protein myosin action tropomyosin
5% salts and other substances

Question 5

What is actin and what does it consist off

Answer 5

Actin is a thin myofilament that form a double helix attached to either end of the sarcomere

Contains tropomyosin - elongated protein winding along the groove of the F actin
Troponin has 3 units - one binds to actin one to tropomyosin and one to calcium ions

Question 6

What is myosin and the components

Answer 6

Golf shaped clubs that are two heavy chains wound together which then have heads that extend perpendicularly to the rod portion

They can bind to active sites on actin and form cross bridges

Are attached to the rod portion at the hinge region
Are ATPase which releases energy to bend the hinge region

Question 7

Describe the feature of a sarcomere and define them

Answer 7

Sarcomere is a basic functional unit of a muscle fibre

Z disk is an attachment for actin 
I band z disk to end of myosin 
A band is myosin only 
H zone is region of a band where there is no overlap between actin and myosin 
M line middle of the h zone 

Titan filaments are elastic chains of AA which make muscles extensible and elastic

Question 8

What is a NMJ and it’s function

Answer 8

Has a presynaptic terminal synaptic cleft and a post synaptic membrane.
Has synaptic vessels usually ACH
Acetylcholinesterase prevents accumulation of ACH

See notes for function

Question 9

See notes for Sliding filament theory and titin

Answer 9

Def

Question 10

Define a muscle twitch and the phases of a muscle twitch

Answer 10

Twitch = muscle response to a stimulus that causes APs in one or more muscle fibres

Phases lag contraction relaxation

Question 11

Define a motor unit and the all or nothing response

Answer 11

A single motor neurone with all the muscle fibres inner ages by it
Large muscles have many innervations
Small muscles = small innervations

All or nothing sub threshold stimulus : no stimulus no contraction
Threshold stimulus AP contraction

Question 12

Explain stimulus strength and motor u it response

Answer 12

Strength of contraction is graded,
Multiple motor unit summation depends on how many motor units are recruited

Submaximal stimulus
Maximal stimulus
Supramaximal stimulus

Question 13

Define and explain treppe and why it might occur

Answer 13

Treppe is a graded response of muscle contraction, it is a gradual increase in contraction strength until it levels out after a few contractions, it is believed that it occurs due to less CA2+ being uptaken into the sarcoplasmic reticulum

Question 14

What are the different types of muscle contraction frequencies

Answer 14

Incomplete tetanus - muscles partially relax between contractions

Complete tetanus - muscles don’t relax in between contractions

Multiwave summation - muscle tension increases as muscle contractions increase

Question 15

What are the types of muscle tension

Answer 15

Active tension - when a force applied to lift an object is by the muscles
Stretched muscles - not enough cross bridges
Crumpled muscles - myofibrils crushed so the cross bridges can’t contract

Passive tension - when there is tension within the muscle but no contraction
Total tension = active plus passive

Question 16

Types of muscle contractions and their subcategories

Answer 16

Isometric =No change in length but there is tension within the muscle e.g. postural muscles

Isotonic = change in length but tension is constant, split into two

Concentric = overcomes resistance and muscle shortens
Eccentric tension remains but muscle length increases

Question 17

Describe a type 1 fibre

Answer 17

Slow twitch 
Slow maximal shortening velocity 
Red and small 
Are fatigue resistant due to increased high oxidative capacity high capillary density 
Major fuel triacylglycerol

Question 18

Describe type 2a fibre

Answer 18

Fast twitch oxidative glycolytic 
Moderately fast contraction time 
Medium in size 
Fairly fatigue resistant 
Possess high levels of glycolytic enzymes and oxidative enzymes 
Are extremely adaptable to training

Question 19

Describe type 2x

Answer 19

Fast twitch glycolytic 
Large contraction forces 
Fast contractions 
Large and white in colour 
Low fatigue resistance high concentrations of PFK and lactate dehydrogenase enzymes

Question 20

Describe to 2b

Answer 20

Fast twitch glycolytic 
Very fast contractions
Very short time 
Very large and white 
Low resistance to fatigue 
High concentrations of pfk dehydrogenase

Question 21

What are the neurological adaptations to muscle train8ng

Answer 21

Neural control - increased motor unit recruitment efficiency
Improved coordination and primary mover activation
Hypertrophy in type 2 fibres
Hyperplasia after chronojc training

Question 22

What are the disadvantages of not training

Answer 22

Injury disuse

Strength loss is proportional to atrophy