Transcript The Muscular System

Sport Sciences
Human Anatomy
Week 2: The Muscular System
Types and functions
Learning Outcomes
By the end of this session you should be able to:
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Describe 3 types of muscle
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List the three functions
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Identify the major muscles of the body.
Did you know?
•Muscle constitutes about 50% of
total body weight
•Muscle tissue weighs more than fat
tissue
•Muscle is made up of approx 30%
protein and 70% salt solution
Student Task
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Use the sticky labels provided to identify
the major muscles on a partner
3 Types of Muscle
1 Involuntary muscle (smooth muscle)
2 Cardiac muscle
3 Skeletal muscle (voluntary muscle)
Involuntary Muscle
Muscles which we cannot control
 Found in the body’s internal organs (e.g.
walls of the intestine and in the blood
vessels)
 Work automatically without conscious
control to keep us alive
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Cardiac Muscle
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Involuntary muscle
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Found only in the walls of the heart
Skeletal Muscle
Sometimes called STRIATED or STRIPED
(because of their striped appearance
under a microscope)
 Make up majority of muscles in the body
 Under conscious control
 Used primarily for movement
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Skeletal Muscle
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Can be stimulated (by the nervous system)
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Can contract (contractility) after stimulation
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Can lengthen (extensibility)
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Can return to normal length (elasticity)
3 Important Functions
1 Movement
2 Support and posture
3 Heat production
Week 2: Structure of Muscle
Learning Outcomes
By the end of this session you should be
able to:
1.
Explain the structure of skeletal muscle
2.
Explain the sliding filament theory
Group Task

Work in groups of 2 or 3 to find out
some information about one of the
following:
1. The structure of muscle
2. Sliding filament theory
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You have only 20 minutes to complete
this task
Macroscopic Structure
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Made up of parallel fibres
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Fibres are specialised muscle cells
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Long, narrow and cylindrical (about as
thick as a human hair)
Fibres
Each fibre is surrounded by a layer of
connective tissue (collagen) called
ENDOMYSIUM
 The fibres are bound together in bundles
called FASCICULI
 Each fasciculus is surrounded by a layer of
connective tissue called PERIMYSIUM
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Muscle Structure
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The fasciculi are then bound together as one
muscle, and are surrounded by a layer of
connective tissue called EPIMYSIUM
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At the end of the muscle, the layers of
connective tissue combine to form a tendon
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The tendon inserts into the periosteum of the
bone to move the lever
Microscopic Structure
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Each individual muscle fibre is
composed of MYOFIBRILS
Myofibrils
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Lie in parallel and give the fibre a striped
(striated) appearance
A single muscle fibre is composed of several
hundred to several thousand myofibrils
Myofibrils contain the contractile units of the
muscle
These units are protein filaments called ACTIN
(thin) and MYOSIN (thick)
These face each other like two combs with their
teeth interlocked at the ends
Sliding filament theory
Under the microscope the myofibrils appear
as extremely thin lines
• The myofibril is composed of numerous
longitudinal filaments of two types: thick and
thin
• The thick filaments are composed of myosin
and the thin filaments of actin
• Contraction of a muscle occurs by the thick
myosin and thin actin filaments sliding
between each other
•
•
But what propels the filaments to slide
between each other?
Sliding filament theory
A bridge is formed between the actin and
myosin filaments during muscle contraction –
CROSS BRIDGE
• The bridge then swings through an ‘arc’ pulling
the actin filaments past the myosin ones –
POWER STROKE
• Each bridge then detaches itself from the thin
filament and re-attaches itself at another site
further along
• This is called the ratchet mechanism
•
Sliding filament theory
The thin actin filaments also contain two other
proteins - tropomyosin and troponin
• When the muscles are relaxed, the tropomyosin
molecules cover the attachment site and prevent
the myosin bridges from binding with the actin
filaments
• Troponin displaces the tropomyosin and enables
binding to occur
• Calcium ions activate the troponin allowing it to
displace tropomyosin
•
Sliding filament theory
The whole ratchet mechanism occurs 50-100
times per second to bring about a contraction
• Muscle contraction needs ATP as well as Calcium
• ATP = Adenosine Tri-phosphate = High energy
compound
• 1 cross bridge requires 1 x ATP molecule to
move
•
Sliding Filament Theory
Myofibrils have dark and light bands (or
striations)
 These bands make up a SARCOMERE
 Sarcomeres are the contractile units of the
muscle
 Each sarcomere consists of 2 protein
filaments (actin and myosin)
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The sarcomere lies between the 2 Z lines
 The I band contains only actin filaments
 The H zone contains only myosin filaments
 The A band contains both actin and
myosin filaments
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When a muscle contracts….
The I band shortens
 The A band remains the same length
 The H zone disappears
 The myosin pulls the actin across so that
the 2 filaments slide closer together, but
the filaments themselves do not shorten in
length
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Learning Outcomes
By the end of this session you should be able to:

Explain the structure of skeletal muscle

Explain the sliding filament theory
Week 2: Muscle Fibre Types
Jack Walton
Learning Outcomes
By the end of this session you should be
able to:
1. Identify 3 different types of fibres
2.
Describe the characteristics of each type
3.
Identify which sports use each type
Muscle Fibre Types
Muscles are composed of thousands and
thousands of individual muscle fibres
 Not all fibres are alike in structure and function
 Can be classified into 3 types:
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– Type I
– Type IIA
– Type IIB
Type I Fibres
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Slow twitch or slow oxidative fibres:
Red in colour
Large amounts of mitochondria, myoglobin and
capillary network
Work slowly (split ATP at a slow rate)
Able to repeatedly contract or maintain
contraction for a long duration
High resistance to fatigue
Fibres work mainly aerobically
Type IIA Fibres
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Fast twitch or fast oxidative glycolytic fibres
(FOG)
Similar to Type I Fibres
Red in colour
Large amounts of myoglobin, many
mitochondria and capillaries
Resistant to fatigue
Work rapidly to split ATP, fast contraction
speed
Work aerobically or anaerobically
Used in high intensity, short duration activities
such as 200m swim or 800m
Type IIB Fibres
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Fast twitch or fast twitch glycolytic (FTG) fibres
White in colour
Low number of myoglobin, few mitochondria,
few capillaries
Fatigue easily
Fast contraction speed, split ATP quickly
Much stronger force of muscle contraction
These are used for activities of a very high
intensity (anaerobic)
– e.g. powerlifting or 100m sprint
Type IIC ?
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Recent research has suggested that there may
be a third muscle fibre type
– Type IIc fast twitch glycolytic fibres
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There is little known on these fibres at this point
Muscles tend to be composed of both fast twitch
and slow twitch muscle fibre types
 The amounts vary from muscle to muscle and
from person to person
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Fibre Mix
Most skeletal muscle is a mixture of all 3
types
 Proportion of types varies in relation to
usual action of the muscle
 For example – the postural muscles of the
neck and back and leg have a higher
proportion of Type I Fibres
 Why do you think this is?
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Fibre type and athletic success
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Some outstanding
athletes have a much
higher percentage of
whatever fibre type is
most advantageous to
their event
Elite distance runners calf muscles composed of
90% slow twitch (Type I)
fibres
Fibre type and athletic success
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Sprinters - 92% fast twitch (Type II)
fibres
What role does genetics play in
determining this?
The slow and fast twitch characteristics of
muscle fibres appear to be determined
early in life, perhaps within the first few
years
Fibre type and athletic success
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Studies have revealed that identical twins have
nearly identical fibre compositions
Little evidence showing change of fibre type
from a few weeks training
More recent evidence suggests the possibility of
fibre type change with high volume of training
However, the percentage of change is too small
to make a difference in sports that require a
high percentage of one fibre type to another
Fibre type and athletic success
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Unlikely that a sprinters fibre type can be
changed to a long distance runners
Therefore genetics do play a fairly important
role in certain types of athletic events
This does not mean that people with a high
percentage of slow twitch fibres cannot compete
in sprinting events, it just reduces their capacity
to compete at a high level
Russia - have attempted to fibre type young
athletes to select their best sport –
Effects of Exercise on Fibre
Type
Can change the characteristics of some fibre
types
 Some Type IIB fibres can transform into Type
IIA fibres with long distance endurance training
 Prolonged endurance training has been shown
to increase the diameter of Type IIB fibres,
increase the no. of mitochondria within the
fibres, and increase the capillaries surrounding
the fibres
 The fibres can then use the aerobic energy
system more efficiently
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Effects of Exercise (cont)
Strength training can
increase the size of
Type IIB fibres
(greater muscle mass
- hypertrophy)
 No increase in the
number of fibres
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Learning Outcomes
By the end of this session you should be
able to:
1. Identify 3 different types of fibres
2.
Describe the characteristics of each type
3.
Identify which sports use each type