Muscle Tissue Flashcards
What are the two categories of muscle?
Categorise the three types of muscle
Striated - cardiac and skeletal
Non-striated - smooth
What causes striations?
Repeating bands of the proteins actin and myosin
Present along the length of the myofibrils
For each type of muscle state:
- whether myoglobin is present
- type of control
- type of nerve-muscle communication
S - present, voluntary, direct
C - present, involuntary, indirect
M - absent, involuntary, indirect
What type of molecule is myoglobin?
What does it supply? To what?
Red protein
O2 to working striated muscles
What condition particularly does haemoglobin give O2 to myoglobin?
Low pH
When striated muscle dies or is damaged what happens?
What can this lead to?
Myoglobin is released into the bloodstream
Renal damage
What removes myoglobin from the blood?
What clinical observation does this lead to?
Kidneys
Tea-coloured urine
What is the outer membrane of a muscle cell called?
Sarcolemma
What is the cytoplasm of a muscle cell called?
Sarcoplasm
What is a sarcomere?
The contraction unit in a striated muscle
What are the thick and thin myofilaments?
Thin - actin
Thick - myosin
What is the epimysium?
Dense fibrous connective tissue surrounding muscle tissue
What are the sections of muscle tissue called?
Fascicles
What type of connective tissue surround fascicles?
Perimysium
What type of loose tissue surrounds muscle fibres?
Endomysium
What is underneath the endomysium?
Sarcolemma
What are the sections in a fascicle called?
Muscle fibres
What are the sections in a muscle fibre called?
Myofibril
What is the main function of skeletal muscle?
Contraction
What direction is movement?
Along the direction of a fascicle
What is created at the origin and insertion point?
Are they proximal or distal?
Give a rough example of each
Origin - tension, proximal
Shoulder
Insertion - movement, distal
Elbow
What do distal and proximal mean?
Distal - further away from the centre
(Proximal is the opposite)
What does the perimysium contain? (2)
Capillaries and nerves
What do skeletal muscle have a lot of - that you can look for in pictures
Mitochondria - dark
Why don’t Z lines line up in some pictures?
When the cell is activated
The middle section contracts first
What are the three types of muscle contraction speeds?
Slow
Fast
Intermediate
What are the two types of twitch fibres?
What colour are they?
Slow - red
Fast - white
What two things is continued muscle contraction dependent on?
Ca2+
ATP
What do cardiac muscles specifically have?
Intercalated discs
What types of granule do cardiac muscles have?
What are they released by?
When are they released?
ANP - atria
BNP - ventricles
Heart failure
How do you reduce arterial pressure? (2)
Decrease blood volume
Decrease systemic vascular resistance
What is hypertrophy?
Enlargement of individual cells
What is hyperplasia?
Multiplication of cells
What are three key features of purkinje fibres?
- abundant glycogen
- sparse myofibrils
- extensive gap junctions
Describe the function of purkinje fibres
- rapidly conduct action potentials
- enabling ventricles to contract in a synchronous manner
Where are nuclei in cardiac muscle?
Central
Where are nuclei in skeletal muscle
Peripheral
Describe the nucleus in smooth muscle cells
Single large central
What three things do smooth muscle cells not have?
Striations
Sarcomeres
T tubules
How does smooth muscle contraction compare with skeletal and cardiac? (3)
- slower
- more sustained
- requires less ATP
How do skeletal muscle repair?
- they cannot divide
- regenerate by mitotic activity of satellite cells (hyperplasia)
- satellite cells can fuse with existing muscle cells (hypertrophy)
What cells are responsible for repair in skeletal muscle?
Satellite
What type of muscle is incapable of repair?
What happens instead?
Cardiac
Fibroblasts invade and divide
Laying down scar tissue
How do smooth muscle repair?
- they retain their mitotic activity
What is the central line in a myofibril?
What does it not have?
M line
Myosin heads
What is the zigzagged line in a myofibril?
The z line
What does an A band include?
End to end of myosin
What is the light band in a myofibril?
I
What is the dark band in a myofibril?
A
What does the H band include?
The M line, not including the myosin
In white and red muscle compare:
Amount of myoglobin and mitochondria
Fibre diameter
Amount of cytochrome
White - lower
White - larger
White - lower
How do myocytes communicate in cardiac and smooth muscle?
Through ago junctions
Name two types of myofilaments
Actin and myosin
Describe the general structure of myosin
Two heads
Protrude at opposite ends
What are the two protein components of actin?
F actin fibres
G actin globules
What two molecules are associated with actin?
Describe them
Troponin - attach to each tropomyosin molecule
Tropomyosin - coil around the actin helix - reinforcing it
Describe how components of myofibrils change shape Erin contraction
- actin and myosin remain the same
- Sarcomeres shorten
- z lines come close together
What does the innveration of muscles mean?
A single motor neurone is able to innveration multiple muscle fibres
Causing fibres to contract at the same time
In neuromuscular junction transmission what is released into the synaptic cleft?
Ach
What does Ach bind to?
What does this cause?
What does this cause?
Ach receptors
Depolarisation of sarcolemma
Ca2+ released from gated Ca2+ ion release channels, into the sarcoplasm
What does Ca2+ bind to?
What does this lead to?
TnC subunit of troponin
Tropomyosin dissociates from troponin
Where do are Ca2+ returned to at the end?
Terminal cisternae of sarcoplasmic reticulum
What causes myasthenia gravis?
- Antibodies directed against Ach receptor
- Blocking the receptor
- Reduction in receptor number
- Reduced synaptic transmission
Symptoms of myasthenia gravis
Ptosis - drooping of one eyelid
Slurred speech
Difficulty holding head up
Choking on food
What are the five steps of the sliding filament theory?
- Myosin head forms a cross bridge with the actin filament
- The head pulls on the actin filament through a form of relaxation (passive)
- ATP attaches to the myosin head - breaking the bond with the actin filament
- ATP hydrolyses and cocks the myosin head back to the starting point (active)
- The myosin filaments slide along the actin - causing the band to shrink
Describe botulism toxin and Botox?
- clostridium botulinum produces botulism toxin
- it blocks neurotransmitter release at motor end plate
- skeletal muscles are in a non-contractile state
What is the botulism toxin used for?
- treat muscle spasms
- treat wrinkles
Describe organophosphate poisoning
- it inhibits function of Ach esterase
- Ach cavities at neuromuscular junction is increased
Name some symptoms of organophosphate poisoning
- Salivation
- muscle cramps
- urination
What type of mutation is duchenne muscular dystrophy?
C linked recessive of dystrophin gene
What causes duchenne muscular dystrophy?
- Absence of dystrophin
- Excess Ca2+ enters muscle cells
- Ca2+ taken up by mitochondria
- Water taken up into mitochondria
- Mitochondria and muscle cells burst
- Creatine kinase and myoglobin levels are high in the blood
- Muscle cells replaced by adipose tissue
What would show in a blood test for people with duchenne muscular dystrophy?
Creatine kinase
Myoglobin
What are some symptoms of duchenne muscular dystrophy?
- poor balance
- belly sticks out
- tight heel cord
- arms and shoulder back when moving
What is an agonist?
Primer movers (main muscle for a movement)
What is an antagonist?
Oppose agonists
What is a synergist?
The assist agonists
What is a neutraliser?
Prevent unwanted action that an agonist can perform
What is a fixator?
Act to hold a body part immobile whilst another part is moving
What is a first class lever?
Effort at one end
Load at the other
Fulcrum in middle
What is a second class lever?
Effort at one end
Fulcrum at other
Load in middle
What is a third class lever?
Load at one end
Fulcrum at other
Effort in middle
How are muscles organised?
Surrounded by what?
Grouped into compartments with similar actions
Thick dense fascia
What causes compartment syndrome?
- Trauma in one compartment
- Internal bleeding
- Exerts pressure on blood vessels and nerves
Name some symptoms of compartment syndrome
- deep poorly localised pain
- paresthesia (pins and needles)
- swollen shiny skin
How is compartment syndrome treated?
Fasciotomy
Covered by skin graft
Define muscle tone
The tension in a muscle at rest
Define muscle strength
The muscles ability to contract and create force in response to resistance
What is muscle tone regulated by?
- gravity
- use
- muscle elasticity
- motor neuron acitvity
Muscles retain tension and stiffness
What does this cause?
- muscles ready to react
- never fully relaxed
- improves with exercise
What causes atrophy?
Define it simply
The destruction is more than replacement:
- disuse
- surgery
- disease
Muscles wasting away
What is the opposite of atrophy?
What is the mechanism?
Hypertrophy
- New muscle fibrils produced
- New Sarcomeres added in the middle of existing ones
- New muscles fibres arise from mesenchymal cells
What is used to diagnose heart attacks?
What is used now?
Creatine kinase levels in blood
Troponin I assay
What leads to a rise in plasma creatine kinase levels?
- intramuscular injection
- vigorous physical exercise
- a fall
- acute kidney injury
How is troponin assay used as a marker for myocardial infarction?
What must you note?
- released from ischaemic cardiac muscle
(Not necessarily proportional to degree of muscle damage)
What causes malignant hyperthermia? (2)
- Severe reaction to certain drugs used for anaesthesia
- massive contractile fasciculation (involuntary movement)
