Structure and Function of the MSK System – Muscles Flashcards
Characteristics of skeletal muscles
Primarily involved in locomotion
Also involved in maintaining posture
Under voluntary control
Composed of muscle cells (muscle fibres)
Often known as striated muscle due to the appearance of the contractile proteins
Characteristics of smooth muscle
Lines structures including the stomach, intestines, and blood vessels
Primary function is to influence movement of material into, out of, and within the body
Involuntary muscle type
Non-striated – different arrangement of muscle cells compared to skeletal muscle
Characteristics of cardia muscle
Only found in the heart
Involuntary muscle type – moves blood through the circulatory system
Contraction of cardiac muscle regulated by the sinoatrial node
Striated structure – similar to skeletal muscle
Where is the origin of skeltal muscle found
Origin of a muscle is the end of the muscle that is attached closest to the trunk or to the more stationary bone
Composition of skeletal muscles
Skeletal muscle is a collection of muscle cells/muscle fibres
Each fibre is a long, cylindrical cell with up to several hundred nuclei near the surface
Skeletal muscle fibres are the largest cells in the body, formed by fusion of many individual embryonic muscle cells
Fibres lie in parallel arrangement, sheathed in connective tissue
Adjacent muscle fibres bundled together into units known as fascicles
How does growth and repair of skeletal muscle occur
Satellite (stem) cells activate & differentiate into muscle when needed for growth & repair
What do myofibrils consist of
several types of proteins organised into repeating contractile structures known as sarcomeres
Composed of thin and thick filaments
Proteins include:
Actin (thin filaments)
Myosin (thick filaments)
Tropomyosin & troponin (regulatory proteins)
What is actin
Actin makes up thin filaments of the muscle fibre
One actin molecule is a globular protein – usually multiple G-actin molecules polymerise to form long chains/filaments known as F-actin
In skeletal muscle, two F-actin polymers twist together like DNA creating thin filaments
Each G-actin molecule has a single myosin binding site and vice versa
Allows for cross-bridging of actin and myosin
What is myosin
Myosin makes up thick filaments of the muscle fibre
One myosin molecule is composed of two identical protein chains, each containing one large heavy chain and two smaller light chains
Phosphorylation of the light chains in skeletal muscle enhances contractile force
Heavy chains of myosin form the motor domain that uses ATP to create movement
What does a sarcomere consist of
Consists of thin & thick filaments in a repeating pattern of alternating light & dark bands
Z disks – zigzag protein structures, act as attachment sites for thin filaments
I bands – region occupied by thin filaments
A band – runs along the entire length of a thick filament, outer edges thick/thin overlap
H zone – region occupied by thick filaments
M line – proteins that act as attachment sites for thick filaments
What is muscle tension, load, contraction and relaxation
Muscle tension – force created by a contracting muscle
Load – weight or force that opposes muscle contraction
Contraction – creation of tension in a muscle, requires ATP
Relaxation – release of tension created by a contraction
How does muscle contraction occur at neuromuscular junction
Conversion of ACh signal from a somatic motor neuron into an electrical signal in MF
Explain excitation-contraction coupling
Muscle action potentials are translated into calcium signals
Calcium signals in turn initiate a contraction-relaxation cycle
Contraction-relaxation cycle
Sliding filament theory of contraction
One cycle is called a muscle twitch
4 major events in EC coupling
Ach is released from somatic motor neuron
Ach initiates action potential in muscle fibre
Triggers calcium release from sarcoplasmic reticulum
Calcium combines with troponin to initiate contraction
