Muscle Tissue
Geoffrey T. Meyer
Muscle - Prefixes
Myo (Greek) = muscle
eg. Myology = the study of muscle
Myositis = inflammation of muscle
Sarco (Greek) = “flesh”
eg. Sarcoplasm = the cytoplasm of muscle
Sarcomere = basic contractile unit of
muscle
Contractile mechanisms
This is fundamental to many cell types -not
just “muscle”
eg. Macrophages
Contractile mechanisms
Macrophages = phagocytes which move freely to
engulf (phagocytose) cell debris & microorganisms
Macro = big
Phage = swallow
Cyte = cell
Muscle
Packaging of contractile proteins is related to the
functions required
Thus there are different such arrangements
These are classified into different “types” of
MUSCLE
Specialised contractile proteins
Muscle is a concentration of such proteins
Myosin
Actin
Troponin
Tropomysin
& many structural
proteins
Packaging of muscle proteins
Depends on the force required
eg. Slow steady contraction of tubes in the body to maintain “tonus” or steady contractions
Use individual cells with orientated packages of
contractile proteins
Slow contracting packages of
muscle proteins
Common in tubes of the body
Arteries & veins
Intestine
Lungs
Urinary system
Reproductive tubes
Slow contracting packages of
muscle proteins
PROPERTIES
Cells contract slowly
Often rhythmically – eg. peristalsis in gut tube
Have tonic and slowly changing tensions
Under nervous control of the
Autonomic Nervous System (involuntary)
Called then INVOLUNTARY muscle
Slow contracting packages of
muscle proteins
Contractile proteins arranged in a dispersed
pattern - not in regular parallel arrays as
in muscle which moves the skeleton
ie. Skeletal muscle is “striped” in
appearance
INVOLUNTARY muscle is not striped
& is thus then called
Smooth muscle
Skeletal muscle
Muscles which move the skeleton need
1. Much more power
2. Tougher connective tissue support
3. Much faster contraction
Skeletal muscle - mass
Much more power = mass – many Kg
Geoff in
his early
athletic
career
Skeletal muscle – anatomical forms
Skeletal muscle – Connective tissue
Tougher connective tissue support - fascial layers & tendons
Epimysium
-Perimysium
Endomysium
Skeletal muscle – Connective tissue
Aponeurosis
A fibrous or
Membranous
sheet-like tendon
Fascia
Fibrous sheet
binding skin to
underlying muscles
or supporting/
separating muscles
Tendon
Band of connective
tissue that attaches
muscle to bone
Skeletal muscle - contraction
Much faster contraction, highly ordered contractile
filaments and a very rapid nerve supply
Cross
striations
Skeletal muscle
Design characteristics
Large cells = syncytium of
fused myoblasts to form
long multinuclear muscle
fibres
Highly organised contractile
protein myofilaments
Why multi-nucleation?
From a physical perspective?
Contractile force can be efficiently generated by the shortening of a long
tube
From a regulatory view?
It takes fewer neurons to synchronise contraction of a few large cells
versus many individual smaller cells
But there are problems with having such a large cell
When cells become very large, signals from the cell membrane would not
be able to efficiently reach a single nucleus.
Also a single nucleus cannot efficiently regulate a very large cell
So large cells become multinucleated with each nucleus controlling a given
volume of cytoplasm = DNA unit.
Skeletal muscle
Design characteristics
Large cells = syncytium of
fused myoblasts to form
long multinuclear muscle
fibres
Highly organised contractile
protein myofilaments
Skeletal muscle – cell = fibre
Packaging
Myofilaments
(contractile
proteins)
into
small bundles
myofibrils
Myofibrils
Myofilaments
Sarcomere
Z
Z
Sliding myofilaments
Much faster
contraction
Skeletal muscle - LS
Skeletal muscle - tubules
Transport problem because of huge cells
1. To transport wave of depolarisation into
contractile filaments –
T Tubes, which are extensions of the
sarcolemma
2. Internal tubules to hold calcium Sarcoplasmic reticulum
Skeletal muscle – tubules
Complex system of tubes within fibres (cells) for internal
transport
Transport
Problem
1. External
2. Internal
Skeletal muscle - TS
Large fibres
&
peripheral
nuclei
Skeletal muscle – large cells
Comparison of Smooth & Skeletal muscle
Skeletal muscle – Nerve supply
Skeletal muscle – Nerve supply
Skeletal muscle – Nerve supply
Muscle
Spindle
Skeletal muscle – Capillaries
Skeletal muscle – Blood supply
Large muscle fibres & metabolically active
& need a large amount of blood = oxygen
But some muscles can work without oxygen
for short times
Skeletal muscle – Blood supply
These are
Fast twitch muscles as in sprinters
Most muscles use oxygen & can work for a
long time – with an adequate blood supply
These are Slow Twitch muscles
Skeletal muscle - Types
Cardiac Muscle
Heart
Left
Ventricle
muscle
Cardiac muscle
A variant of skeletal muscle Striated or striped
Very fast contraction – but critical relaxation
Internal tubular system
Differences:
Individual cells joined very tightly at
Intercalated discs
Branched individual fibres
Central nuclei – like smooth muscle
Cardiac Muscle - size
Smooth – Cardiac
Skeletal
Peripheral nuclei
5 µm
15-25 µm
Central nuclei
50 µm
Cardiac Muscle - TS
Cardiac Muscle - LS
Cardiac muscle
A variant of skeletal muscle Striated or striped
Very fast contraction – but critical relaxation
Internal tubular system
Differences:
Individual cells joined very tightly at
Intercalated discs
Branched individual fibres
Central nuclei – like smooth muscle
Cardiac Muscle - LS
Intercalated
disc