Muscle Flashcards
How is force produced
The movement of actin fibres over myosin fibres, with the aid of a number of accessory proteins
4 types of contractile cells
Muscle cells, myoepithelial cells, myofibroblasts, and pericytes
Types of muscle cells
Skeletal, cardiac or smooth muscle cells
Myoepithelial cells
Found with secretory units of some exocrine glands. They have flattened cells and a contractile protien arrangement similar to smooth muscle
Myofibroblasts
Characteristics of both fibroblasts and smooth muscle cells. Enlarge in injury and secrete collagen to provide scaffold for repair and then contract the wound
Pericytes
Found around capillaries and venules. Can can act as stem cells but also have contractile properties
How are myotubules formed
Within the mesenchyme of the mesoderm, cells will align and eventually lose their separating cell membranes
Names given to skeletal muscle
Skeletal, voluntary and striated
Muscle tissue is formed from
Muscle cells and associated connective tissue
Muscles are formed from
Muscle fibres, blood vessels, nerves, lymphatics, connective tissue and specialised sense organs
Characteristics of skeletal muscle fibres
- Striated
- Multinucleated
- Unbranched
- Nuceli are at the periphery of the fibre, just under te cell membrane
What is the cell membrane in muscle fibres called
The sarcolemma
A bundle of muscle fibres
Fascicle
Connective tissue around the muscle as a whole
Epimysium
Connective tissue around the fascicle
Perimysuim
Connective tissue around a single muscle fibre
Endomysium
What is a sarcomere
The smallest contractile unit of a muscle cell
What forms a myofibril
Hundreds or thousands of sarcomeres placed end to end
Where do sarcomeres extend from/to
From one Z line to the next
What is a motor unit
The motor neurone and all of the muscle fibres it innervated
Fewer number of muscle fibres in a motor unit =
Finer movement of control
Synapse at the end of the motor neurone
Motor end plate
Muscle fibres in a motor unit are all
Of the same class
What type of junction to almost all muscle fibres have
Neuromuscular junction
Neuromuscular junction
- Nearly all mucle fibres have one
- Motor axons terminate at a motor end plate
- Action potential cause the release of acetylcholine
- Initiates an action potential in sarcolemma
Tubules within the muscle cell
T-tubules
T-tubules
- Extend from sarcolemma into the cell
- Ramify and surrounding each myofibril at the A-I junction of each sarcomere
Specialised smooth ER
Sarcoplasmic reticulum
Sarcoplasmic reticulum
- Very high concentrations of Ca2+
- LIes on either sides of the T-tubules
T-tubule and sarcoplasmic reticulum =
Triad
What does an action potential at the neuromuscular jucntion cause
The release of acetylecholine which causes an action potential in the muscle cell
An action potential in the muscle cell travels along what
The sarcoplasmic reticulum and invades the T-tubules
What does the action potential in the sarcoplasmic reticulum cause
The release of Ca2+
The release of Ca2+ causes
The myosin fibrils to ratchet across the actin fibrils, shortening the sarcomere
Three types of skeletal muscle fibres
Type I, type IIa, type IIb
Type I muscle fibres
- Slow contracting fibres
- Depend on oxidative metabolism
- Have abundant mitochondira and myoglobin
- Resistant to fatigue and produce less force
Type IIA muscle fibres
- Intermediate between the other two types
- Relatively uncommon
- Fast twitch but fatigue resistant
Type IIB muscle fibres
- Relatively fast contracting fibres
- Depend on anaerobic metabolism
- Fewer mitochondia and myoblogin than type I
- Fatigue relatively easy and produce greater force
The myotendinous junctions
Where the collagen of the tendons attaches to the end of the muscle fibres
How is the muscle attached to collagen
Through complex interdigitations
Why are tendons slow to hear
They have a poor blood supply
Specialised sense organs within muscles
Muscle spindles
What do muscle spindles provide
Information of the amount of stretch and tension in the muscle
Special fibres within the muscle spindle
Intrafusal fibres
Normal contracile fibres
Extrafusual muscle fibres
Cardiac muscle
- Forms major part of walls of heart chambers and origins of great vessels
- Has striations
- Shorter than skeletal muscle fibres
- Branch to form a complex network
Nuclei in cardiac muscle
Have a single nucleus located at the centre of the fibre
Dark irregular lines in cardiac muscle
Intercalated discs
Function of intercalated discs
Site of end-to-end attachment, maintain mechanical integrity and allow the transmission of electrical impulses
Dyad in cardiac muscle
T-tubule and only one branch of sarcoplasmic reticulum
Skeletal muscle regenerative capacity
- Has a population of myoblasts called satellite cells at the outer surface of sarcolemma
- Following damage they become activated to proliferate and form new muscle fibres
What competes with the regeneration of tissue
Scar tissue
Cardiac muscle regenerative capacity
- Small population of stem cells but they play little roles in effective repair
- After muscle is killed, new muscle is not regenerated
Smooth muscle
- No visible striations
- Not under conscious control
- Predominantly found in organs
Smooth muscle cells
Elongated, spinde-shaped cells with a single cigar shaped nucleus
Actin and myosin in smooth muscle
- Not as well organised as skeletal or cardiac muscle
- Converge on dense bodies in cytoplasm
- Converge on focal densities at periphery of the cell
Where is smooth muscle found
The gut, respiratory tract, blood vessels, uterus and iris of the eye
Contraction of smooth muscle
- Typically recieves signals for both contraction and relaxation
- Smooth muscle either contracts continuously or rhythmically in absence of stimuli
- Appropriate stimuli can modulate contraction either positively or negatively
Where does stimuli for smooth muscle originate
Nerve fibres of autonomic nervous system or a hormone
