Muscles 1 Flashcards
3 muscle types and briefly what they do:
Smooth muscles: mainly line hollow organs (gut, blood vessels) and are not under voluntary control
Cardiac muscles: located only in the heart, generates force to pup blood around the body and is not under voluntary control
Skeletal muscles: apply a force to the bones to control posture and body movements. Is under voluntary control. Striated/striped.
Primary Job of skeletal muscles
To develop tension or force
- muscles develop force in only one direction and they do this by shortening
(Skeletal muscle is important for movement and posture)
Secondary jobs of skeletal tissue
- support and protection for soft internal organs (e.g muscles of abdominal wall)
- provides voluntary control over major openings (allows the passage of substances into or out of our body)
- converts energy (in part) to heat which is used to maintain core temperature (eg shivering)
- provides major storage for energy and protein
SPCP
Structural features
-skeletal muscle fibres are huge and multinucleate cells containing large amounts of protein
- connective tissues ensheath the muscle, and connect fibres to the bones
- skeletal muscle is richly supplied with blood vessels and nerve fibres
Whole muscle structure
- muscle fibres are gathered into bundles called fascicles
- fasicles are gathered into bundles called muscles
- fibres, fascicles and muscles are each ensheathed in connective tissue
- connective tissue investments are gathered together to form tendons
- tendons connect muscles to bones
How various cells are arranged to form skeletal muscles
- muscles are attached to bone via tendon
- muscles are comprised of muscle tissue, nerves, blood vessels and connective tissue
- each muscle is made of multiple muscle fibres
- each muscle fibre is made of multiple myofibrils
Endomysium
Surround each muscle fibre
Perimysium
Surround each fascicle (bundle of muscle fibres)
Epimysium
Surround entire muscle
Surround each muscle fibre
Endomysium
Surround each facicle
Perimysium
Surround entire muscle
Epimysium
How many nuclei in a muscle fibre
Hundreds to thousands - on the outside
How big are muscle fibres
20-40 micrometers in diameter but may be centimetres long
Key structural composition of a muscle fibre
- comprised of bundles of myofibrils
- myofibrils are made of repeating units known as sarcomeres
- sarcomeres are made of contractile proteins or myofilaments (actin - thin filament, myosin - thick filament)
Two mayofilaments
- actin (thin filaments)
- myosin (thick filaments)
What gives muscle its striated (striped) appearance
The organisation of the myofilaments
Describe the purpose of the system of structures muscle fibres posses and some of these structures
- Muscle fibres possess a system of structures organised to regulate the activity of the force-producing elements
- Transverse tubules
SR
Two myofilaments are:
- actin (thin filaments)
- myosin (thick filaments)
Definition of transverse tubules (T-tubules) and their function
Tubular extention (invaginations) of the surface membrane
Function: to conduct electrical signals (action potentials) deep into the core of the fibre
Sacroplasmic reticulum (SR) definition
SR is an extensive membranous tubular network associated precisely with the T tubules at regular intervals.
How the membrane triplet (triad) is formed
The terminal chambers (terminal cisternae) of each SR structure associate with the T-tubules to form a membrane triplet called a triad
Function of the sacroplasmic Reticulum
- to take up and store calcium
- to release Ca2+ into the cytoplasm on the receipt of an action potential conducted along the associated T-tubules
The sacromeric structure of the myofilaments arise do to:
The arrangement if contractile proteins
- thick filaments (primarily myosin) interlace with thin filaments (primarily actin)
Actin definition
Actin is a globular protein
Structure of Thin filament
- Actin is a globular protein (G-actin)
- The globules assemble to form filamentous protien strands (F - actin)
- each thin filament is a twisted strand of 2 rows of F- actin terminating at one end of the Z-line
Structure of the myosin molecule
Long thin tail and globular head
Structure of the thick filament
(Myosin)
- the thick filament is formed from arrays of pairs of myosin molecules arranged with the tails pointing towards the M-line and forming a complex double headed structure
- the myosin heads are able to flex
Sacroplasmioc reticulum DEFINITION
Is a mesh network that is interconnected and wraps around each myofibril - functions as a Ca2+ store
Triad
Terminal cissternae of the SR and the t - tubes
The sacromere contains:
Thick and thin myofilaments - contractile proteins
The sliding filament theory
- Contractile proteins develop force
by triggered molecular interaction. - This allows association of the myosin head
with the nearby thin actin filament. - Due to this it allows the flexing of the myosin
head to allow it to “walk” along the thin
filament - in this process the interlaces thick and thin filaments slide past one another
- The arrangement of the myosin heads in a sarcomere means that when this process is activated, the ends of the sacromere are drawn closer together by the flexing of the myosin heads
- the sacromere Z- lines are drawn closer to the central M-line
Definition of Neuromuscular Junction
The myelinated axon of a motor neuron that terminates at a single point on the muscle fibre
- each muscle fibre receives contact from one motor neuron at one site
How electrical events in the brain initiate force production in the muscle:
- muscle contractions are triggered by electrical events (AP)
- AP’s arise in brain, are conducted down spinal cord to motor neurons in spinal cord
- APS in spinal cord motor neurons are conducted out of CNS along motor axons to muscle fibres
- arrival of AP at NMJ initiates SYNAPTIC TRANSMISSION which results in generation of AP in postscynaptic muscle fibre
- AP in muscle fibre triggers a process (excitation-contraction coupling) that results in development of force within the fibre
What does acetylcholine do
Acts at receptors on the muscle fibres membrane surface
- is a neurotransmitter
