Week 3 Flashcards
What does syncytium mean
A multinucleate mass of cytoplasm resulting from fusion of cells
In skeletal muscles
What are intercalated discs
Join adjacent cardiac muscle cells together
What shape are smooth muscle nuclei
Spindle shaped
What is the sarcolemma
The plasma membrane of the muscle cell
What’s a myofibril
A chain of sarcomeres
What’s a myofilament
Contain the actin and myosin myofilaments
What is a sarcomere
The contractile unit
What is a triad
A special internal membrane system that controls muscle contraction by regulating calcium release
How does the skeletal muscle triad work
The sarcoplasmic reticulum Ca2+ channel protein lines up with the Ca2+ channel protein in the t-tubular system
Depolarisation of the t-tubular system causes opening of the SR calcium channels
Calcium which is held in the SR lumen by calsequestrin (calcium binding protein) can then be released into the muscle cytoplasm (cytosol/sarcoplasm)
What are the 3 major types of skeletal muscle fibres
Red fibres
Intermediate red
White
What are red fibres
Contract slowly, do not fatigue quickly, low glucose metabolism
Red colour from high levels of myoglobin
Maintenance of posture e.g. back muscles
What are intermediate red fibres
A combination of red and white fibre characteristics
Contract quickly intermediate rate of fatigue and glucose metabolism
Seen in big leg muscles
What are white fibres
Responsible for rapid contraction
Contract quickly and fatigue quickly, high glucose metabolism (including anaerobic)
Little myoglobin content
Seen in muscles that move the eye
Why is the motor system of the body important
Set muscle (or motor) tone of the body
Bring about voluntary movements
What is a motor unit
Defined as a somatic efferent plus all the muscle fibres it supplies
The combination of an individual motor neuron and all off the muscle fibres it innervates
What does a motor unit comprise of
1 a-motoneurone
All extrafusal muscle fibres it supplies
Extra-ocular muscles and quadriceps
What are structural components of the motor system
Motoneurones
Skeletal muscles
The neuromuscular junction
From what part of the nervous system do motoneurones originate
Efferent systems
Somatic motor efferent (or upper motoneurones)
A-motoneurone (or lower neurones)
Why are skeletal muscles important
Movement
Posture
Heat generation
Stability of joints
What is a myocyte
The single cell of muscle
What is a fascicle
A group of myocytes
Fasciculi collect to form a muscle
What is the endomysium
The connective tissue sheath enveloping a myocyte
What is the perimysium
The tissue sheath enveloping a fascicle
What is the epimysium
The tissue sheath enveloping all fascicles of a muscle and its neurovascular bundle
What is a tendon
An organised tough band of fibrous connective tissue mass that forms a point of confluence of contraction by single myocytes of a muscle
Brings together single contractions of myofibrils hence myocytes to produce combined actions at a single point
How are skeletal muscles classified
According to architecture of their fascicles
What are common assemblies of fascicles
Convergent muscle
Strap muscle
Circular muscle (also known as sphincteric muscle)
Fusiform muscles
Pennated muscles - unipennate, bipennate, multipennate
What are the two types of motoneurone
Upper motoneurone
Lower motoneurone
What is the lower motoneurone responsible for
Transmitting the signal from the upper motor neurone to the effector muscle to perform a movement
Three main types- somatic motor neurons, special visceral efferent (branchial) motor neurons, general visceral motor neurons
What are upper motor neurones responsible for
They’re first order neurons which are responsible for carrying the electrical impulses that initiate and modulate movement
Characteristics of muscle fibres of motor unit
Have the same physiological profile- contraction speeds, susceptibility to fatigue
Have the same histochemical profile- myosin fibre typing, enzyme expression profile, metabolic profile
The characteristics of the motor unit allow for
Uniform development of force throughout muscle
The nervous system to regulate the rate and speed of contraction of movements it may choose
Muscle contraction to be distributed throughout the muscle
Muscle fibres can be classified into 3 categories according to
How quickly they develop force
How long they take to relax
What are the 3 broad types of muscle fibres
Fast twitch type FF
Intermediate twitch type FR
Slow twitch type S
What is a neuromuscular junction
A specialised synapse
Between a motor neuron and a muscle cell
Tuned for rapid reliable neurotransmission
Role of Ca2+ in excitation-contraction coupling
Calcium conc. higher inside than out
Action potential in presynaptic terminal
Depolarisation opens voltage-gated Ca2+ channels
Ca2+ enters presynaptic terminal
Fusion of vesicles with presynaptic membrane
Acetylcholine ACh released (exocytosis)
Ca2+ induced vesicle fusion
Calcium entry into presynaptic terminal triggers vesicle fusion
Ca2+ sensor in synaptotagmin
Change in conformation on Ca2+ binding triggers vesicle fusion
Exact mechanism is unclear
How are skeletal muscles classified
By the architecture of their fascicles
Motor unit characteristics
The motoneuron determines the characteristics of the muscle it innervates
Same muscle type as neurone connected
