Muscle Tissue Flashcards
General functions
Movement
Stabilizing Body Positions
Storing and Moving Substances
Heat Generation
Properties of Muscle Tissue
1) Excitable
A) Electrical signals
B) Chemical (neurotransmitters, hormones,
pH)
2) Contractility
3) Extensibility
4) Elasticity
Muscle Tissue
Muscle fibres use ATP to generate
force
1) Skeletal muscle
tissue
2) Cardiac muscle
tissue
3) Smooth muscle
tissue
Skeletal Muscle Tissue
- Attached to bones,
usually via tendons - Striated
- Largely voluntary
(somatic) and
neurogenic - Long parallel muscle
fibres - Multiple nuclei at
periphery - ~50% body weight
Role in locomotion,
breathing, protection,
heat generation, posture
stabilisation
Muscular system
* Each muscle consists of
thousands of muscle
fibres/cells
* Connective tissues
surround:
- Whole muscle
- Individual fibres
- Blood vessels
- Nerves
- Surrounds and protects
- SUPERFICIAL FASCIA
- Separates muscle and skin
- Adipose and areolar connective
tissue - DEEP FASCIA
- Holds muscles with similar
functions together - Dense irregular connective tissue
- 3 layers extend from deep fascia
to protect & strengthen skeletal
muscle tissue - EPIMYSIUM (encircles entire
muscle) - PERIMYSIUM (bundles 10-100
fibres into fascicles) - ENDOMYSIUM (separates
individual muscle fibres) - May extend to form a tendon
DENSE
IRREGULAR
AREOLAR
Muscle fibre, SEM
Muscle Fibre
surrounded
by Endomysium Perimysium
Epimysium
* EPIMYSIUM (encircles
entire muscle)
* PERIMYSIUM (bundles 10-
100 fibres into fasicles)
* ENDOMYSIUM (separates
individual muscle fibres)
* May extend to form a
tendon
Muscle structure
10x bicep curls, each arm (use
food can or water bottle!)
* 10-100μM
* Typical length ~10cm
* ~100 nuclei as
embryonic origin is
from fusion of ~100
myoblasts
* Peripheral nuclei lie
under the
sarcolemma (muscle
fibre plasma
membrane)
Cardiac Muscle Tissue
- Heart wall
- Striated
- Involuntary (autonomic)
- Branched fibres
- Mostly one nucleus
- Attach end to end by
intercalated discs (ID) - Desmosomes and gap
junctions in ID - Forms much of the heart
wall- PUMPS BLOOD - Striated
- Involuntary, myogenic
- Diameter 15μ
- Branched network of joined
fibres - Single (sometimes 2)
central nucleus - Same sarcomere structure as skeletal muscle
- Sarcolemma present
- Fibres connected end to end by thickenings of sarcolemma, the
intercalated discs - Intercalated discs contain
desmosomes (strength)
and gap junctions (rapid
conduction) - Endomysium &
perimysium but NO
EPIMYSIUM (pericardium
instead) - Regulated by the
troponin/tropomyosin - Pacemaker cells in
sinoatrial &
atrioventricular nodes
form the sites of
action potential
initiation - Not dependent on
neural activity - Myogenic
Smooth Muscle Tissue
- Walls of hollow structures
- Involuntary (Autonomic)
- Non-striated
- Small & thicker in centre
- Single centrally located
nucleus - Gap junctions (or lack of!)
effects strength - Roles in;
- Constricting bld
vessels/airways - Food movement and
breakdown - Bladder contraction
- Fluid movement
- Waste removal
- Small, spindle-shaped,
non-striated fibres - One centrally place
nucleus - Involuntary (autonomic
nervous system) - Neurogenic
- Length 0.02-0.5mm
- Diameter 10-40 mm
- Smooth are Smallest
- Two types of smooth
muscle
1) Multi-unit - Walls or large arteries,
airways, arrector pili, iris
and ciliary body
2) Single-unit (visceral) - Skin, walls of small
arteries/veins/hollow
organs (stomach,
intestines, uterus, bladder)
1) Multi-unit - No/few gap junctions
2) Single-unit muscle - Numerous gap junctions
allow simultaneous strong
peristaltic contractions - Thick/thin filaments & force generated via cross
bridge cycling - Filaments not arranged in sarcomeres
- Parallel thick/thin filaments run in multiple
directions= Contraction across several axes - No T-tubules
- Little SR
- Caveolae- pouch like
invaginations of
sarcolemma that
contain Ca2+ - Dense bodies- attach
thin filaments - Intermediate filaments-
attach dense bodies &
help transmit the force - Unlike skeletal muscle,
no troponin-
tropomyosin system - Smooth muscle contraction initiated by Ca2+ binding to calmodulin
- Sliding filament mechanism of muscle
contraction is initiated
Smooth Muscle Disorders
Asthma
Muscle Structure
- Sarcolemma- plasma
membrane of a muscle fibre - Transverse tubules (T-
tubules)- sarcolemma
invaginations that tunnel to
centre of muscle fibre - Sarcoplasm- glycogen and
myoglobin-rich cytoplasm
of a muscle fibre
Myofibrils
- Muscle fibres are packed
with myofibrils - Extend length of fibre
- Contain muscles
contractile machinery-
the myofilaments - Sarcoplasmic reticulum (SR)
surrounds each myofibril - Fluid-filled membranoussacs
- SR stores Ca2+
- Ca2+ release instigates
muscle contraction - Contain three kind of proteins in skeletal muscle;
1) Contractile proteins (generate force during
contraction)= Myosin and actin
2) Regulatory proteins (switch contraction on/off)=
Tropomyosin and Troponin
3) Structural proteins (maintain correct structural
properties)= Titin
Contractile Proteins
- Myofibrils contain
filaments/myofilaments - Bundles of overlapping
thick (myosin) and thin
(actin) filaments - Specific arrangement of
these filaments underlies
the striated appearance
of the muscle
Contractile Proteins- Myosin
- Thick filaments-
hundreds of myosin
molecules - Dimer containing 2
intertwined subunits - ‘Heads’ form
crossbridges, have actin
and ATP binding sites
Contractile Proteins- Actin
- Thin (actin) filaments- numerous G actin monomers
linked end to end to form two helically arranged
polymer strands - Each G actin monomer has a myosin binding site
Regulatory Proteins
- Associated with Actin
- Tropomyosin- a long fibrous molecule that blocks
myosin binding sites at rest - Troponin- a 3 protein complex. One attaches to actin,
another to tropomyosin and the third contains a Ca2+
binding site
Structural Proteins
- Myofilaments organised into sarcomeres
- Z lines- end borders, anchor actin (thin) filaments
- M lines- connect myosin (thick) filaments
- A band- darkest under microscope
- Spans thick filaments
- H zone- pale region within A band
- Thick filaments only
I band- thin filaments only, appears lightest under microscope
Titin - Links z-disc to M line
- Stabilises the position of the thick filament
- Helps sarcomere return to resting length
- Prevents overextension of sarcomeres
Sliding Filament Theory (Crossbridge Cycling)
- SR releases Ca2+ which binds to troponin
- Troponin moves tropomyosin away from the myosin-
binding site on actin - The sliding filament mechanism of muscle contraction is
initiated - A band- no change
- I band & H zone
shorten - Thick and thin
filaments slide past
each other pulling Z
lines closer
together - Sarcomere
shortens
Fascicles
Strength of a muscle and the direction of its pull are determined by orientation of its fascicles
