Please enable JavaScript.
Coggle requires JavaScript to display documents.
Case 2: Skeletal Muscle 1 and 2, image - Coggle Diagram
Case 2: Skeletal Muscle 1 and 2
List the Types of Muscles
Cardiac Striated Muscles
Striated Skeletal Muscles
Smooth Muscle
NOTE:
Striated Cardiac Muscle and Smooth Muscles are Involuntary Muscles
Striated Skeletal Muscles are Voluntary Muscles
Skeletal Muscle Disorders
List the types of areas of Primary Causes of Skeletal Muscle Disorders
Muscle
Neuromuscular Junction
Nervous System
Although the primary cause may be found else where, the disease itself will eventually manifest in the Skeletal Muscles.
List Neuromuscular Disorders/Diseases (Rare):
Muscular Dystrophies: Group of Genetic Disorders eg: Duchenne
Metabolic Myopathies eg: McArdle Disease
Inflammatory Myopathies eg: Dermatomyositis
Toxic Myopathies eg: Steroid Myopathy
Disease of Neuromuscular Junction eg: Myasthenia gravis
Neurogenic Atrophy (Primary nerve - Secondary Muscle)
Rhabdomyosarcoma (Cancer)
List Neuromuscular Disorders/Disease (Common):
Sarcopenia
Sarcopenia is a loss of skeletal muscle mass thus decreasing the Quality, Strength and Function of the Muscle.
Skeletal Muscle
Describe the characteristics of Skeletal Muscle
There are 660 Skeletal Muscles in the body
Skeletal Muscles make up approximately 45% of Body weight
Skeletal Muscles vary in shape and size
Example:
A Stapedius Muscle of the Inner Ear is a few mm
Sartorius Muscle in the Lower Limb is over 45cm
Percentage of Skeletal Muscles in the body is Lower in individuals with Anorexia
Percentage of Skeletal Muscles in the body is Higher in Body Builders
List the Functions of Skeletal Muscles
Movement and Locomotion: Converts chemical energy into mechanical work and force
Maintain posture and body position
Supports soft tissue (Abdominal wall , floor of the Pelvic Cavity)
Encircle openings of the Digestive Tract and Urinary Tract
Heat production
Energy Production: Acts as a reservoir for Protein Storage
Skeletal Muscle Naming and Shapes
Outline the criteria for the Naming of Skeletal Muscle
Skeletal Muscles are named according to the following characteristics:
Direction: Orientation of the Muscle Fascicles relative to the body's midline eg: Convergent, Circular
Size: Relative Size of the muscle eg: Gluteus maximus (minimus), Abductor brevis (longus)
Shape: Shape of the muscle eg: Deltoid, Trapezium, Rhomboid
Action: Principle action of the muscles eg: Extensors, Flexors
Number of Origins: Number of Tendons at the origin eg: Triceps or Biceps Brachii
Location: Structure near which a muscle is found eg: Supraspinatus
Origin and Insertion: Sites where muscles originates and inserts
Musculotendinous Unit
What is the Musculotendinous Unit (MTU) ?
Musculotendinous Unit is when Muscles and Tendons Work together to move Bone in order to generate movement.
Most Muscles cross at least one joint and are attached at the articulating bones via a tendon.
When the muscle contracts, tension is placed on the Tendon and Bone, resulting in movement.
The Musculotendinous Unit draws one articulating bone to another bone
The Origin is the attachment to the bone that moves the least or stationary bone.
The Insertion is the attachment to the bone that moves the most or moveable bone.
Skeletal Muscle Actions
Outline the types of Actions and give an example
Extensor
Increases the angle at a joint
Knee: Quadriceps
Flexor
Decreases the angle at a joint
Knee: Hamstrings
Abductor
Moves the limbs away from the midline of the body
Hip: Gluteal
Adductor
Moves limbs towards the midline of the body
Hip: Adductor group, Groin
Levator
Moves insertion upwards
Depressor
Moves insertion downwards
Rotator
Rotates muscles around an axis
Sphincter
Constricts an opening
NOTE:
What is an Agonist and an Antagonist ?
Agonist is the Primer mover of any skeletal movement
Antagonist acts on the same joint to produce opposite movement
Eg: When you Extend your knee joint
Agonist are the Quadriceps of the knee
Antagonist are the Hamstrings of the Knee
Muscle Architecture
Describe the Muscle Architecture
Muscle
Muscle is the main structure we can see
Muscle Fascicles
The muscle is then made up of a bundles of Muscle Fascicles
Muscle Fibres (Cell) or Myofibre
Muscle Fascicles are then made up of 10-100 Muscle Fibres (Cell)
Muscle cell is a thin, elongated cell.
Even though the muscle fibre has a unique appearance it is STILL a living cell.
With Multi-Nuclei, Mitochondria and other organelles
Myofibril
The Muscle Fibre(Cell) is then made up of Myofibril.
Myofibrils are long, thin-like structures which run from one end of muscle cell to another end of muscle cell.
Sarcomere
Each Myofibril is made up of Sarcomere
Sarcomere is the smallest functional unit for Muscle contraction in the Skeletal Muscle
Myofilaments
Sarcomere are made up of Filaments responsible for muscle contraction
Collectively these filaments are known as Myofilaments
List the 2 major Filaments which are responsible for muscle contraction
Actin - Thinner Filament
Myosin - Thicker Filament
Muscle Fibre (Cell) Arrangements
The Red Middle Line represents the Axis of Force Production of the whole muscle
The Axis of Muscle Tendon shortening
Two Blue Lines represent the Direction of Force Production by the individual muscle fibres (Cell)
The Axis of Muscle Fibre shortening
List the Types of Muscle Arrangements
Parallel Fibres
Pennate Fibres
Describe Parallel Fibre arrangement
Muscle Fibres are arranged parallel to the force-generating axis of the muscle.
Describe Pennate Fibre arrangement
Pennate muscle fibres are arranged at an angle to force-generating axis
Usually insert into a central tendon
Because of the structure and arrangement, fewer sarcomeres can be found in series, resulting in a shorter fibre length.
Eg: Unipennate, Bipennate, Multipennate.
However, more muscle cells (fibre) can be packed in parallel in these muscles.
NOTE:
When comparing two Muscles with Parallel and Pennate Arrangement of similar sizes are compared:
Muscles with pennate muscles fibres contract slower, BUT with a greater force.
The Layers of Connective Tissue in the Skeletal Muscle
List the Connective Tissue Found in the Skeletal Muscle
From the Surface to the Core:
Epimysium
Perimysium
Endomysium
Epimysium
Epimysium is a sheath of dense irregular connective tissue, that covers each muscle
This allows for the muscle to contract and move, whilst maintaining structural integrity.
It separates the individual muscles from each other, and other structures.
Allows for independent movement
Perimysium
Perimysium covers the individual Muscle Fascicles which are made up of 10-100 Muscle fibres (Cells)
Endomysium
Endomysium covers each Muscle Fibre (Cell) forming the Basement Membrane
The connective tissue of the epimysium, perimysium, endomysium and tendons is continuous.
Skeletal Muscle Fibre/ Cell
Outline the structure of the Skeletal Muscle Fibre
Skeletal Muscle Fibre are:
Highly differentiated
Elongated
Multinucleated
The Membrane of Skeletal Muscle Fibre is known as the Sarcolemma
The Cytoplasm of Skeletal Muscle Fibre is known as the Sarcoplasm
The Muscle Fibre (Cells) are post-mitotic therefore, muscles fibres can NOT divide and repair muscle tissue
The diameter of Fast Twitch Fibre is BIGGER than the diameter of Slow Twitch Fibre
Muscle Fibre Types
How do we separate Muscle Fibre types ?
There are 2 ways to separate Muscle Fibre:
Colour: Red and White Fibres
Red Fibres
1 (Slow Oxidative)
2A (FOG)
White Fibres:
2X (FG)
2B
Speed of Contraction: Slow and Fast Twitch Fibres
Slow Twitch Fibres:
1 (SO)
Fast Twitch Fibres:
2A (Fast Oxidative Glycolytic)
2X (Fast Glycolytic)
2B
Slow Contraction (Twitch) Fibres are Type 1 Fibres
Fast Contraction (Twitch) Fibres are Type 2 Fibres
What is a Twitch ?
A twitch is the simplest muscle contraction in response to a single stimulus.
Describe the Types of Muscle Fibres based on Colour
Red Fibres are known as Slow Oxidative or Fast Oxidative as they predominantly use Oxidative Metabolic Pathways to produce ATP.
They totally Oxidize fats, carbohydrates in the presence of Oxygen to produce ATP, Carbon Dioxide and Water in the Mitochondria
Therefore, they Have a High Myoglobin (RED COLOUR) and Mitochondria Content
Thus, giving them a Red Colour.
White Fibres are known as Glycolytic fibres, because they predominantly use the breakdown of Muscle Glycogen into Lactate to produce ATP.
This takes place in the Cytosol and Oxygen is NOT required
Therefore, Muscle Fibres have a Lower Oxygen (Myoglobin) and Mitochondrial Content
Thus, giving them a non-red colour - white.
2A Fibres are a Hybrid between the 1 and 2X fibres and are referred to as the Fast Oxidative Glycolytic (FOG) Fibres.
Myofibrils
Outline the structure of the Myofibrils
Each Muscle Fibre (Cell) is densely packed with Myofibrils
Myofibrils run in parallel rows from one end of the Muscle Fibre (Cell) to the other end.
Other organelles are restricted to the narrow cytoplasmic spaces that remain between adjacent myofibrils.
Describe the structure found in Myofibrils
Each myofibril contains Myofilaments:
Actin: Thin Filament
Myosin: Thick Filament
The Thick and Thin Myofilament overlap in the myofibril causing a striated appearance
There are repeating I (Light) and A (Dark) bands along the Myofibril
In the middle of the I (Light) Band is the Z Disc (Line)
What is the Functional Unit of the Muscle ?
The functional unit of muscle contraction is the Sarcomere
Sarcomere is located between two Z Discs
Sarcomere consists of Thick and Thin Filaments
Muscle Fibre/ Muscle Cell Structure and Arrangements of of the Filaments in the Sarcomere
What is a Sarcomere ?
Sarcomere:
Sarcomere is a repeating functional unit within the myofibril of the skeletal muscle cell.
Sarcomere runs from one Z Line to the opposite Z Line
Sarcomere is divided into the two halves of I band, A Band, H-Zone, M Line and Z Line
What is a I (Light) Band ?
I (Light) Band
Light / I Band is a lighter and less dense area of the Sarcomere
Light Band is a part of the myofibril which consists of ONLY Thin Filaments (Actin)
A Z Disc (Line) passes through the centre of each I/Light Band
What is a A (Dark) Band ?
A (Dark) Band
Dark/ A Band is a darker, and more dense and middle-most area of the Sarcomere
Dark Band contains BOTH Thin and Thick Filaments
Thick and thin Filaments overlap in the Peripheral Regions of the A Band
Middle most region of the A band contains ONLY Thick Filaments this is known as the H Zone
The Band remains the SAME size during muscle contraction
What is the H Zone ?
H zone is the narrow region in the centre of each A Band
H zone consist of ONLY Thick Filaments (Myosin)
H Zone shortens during contraction due to increasing overlap of Actin and Myosin Filaments
H Zone is no longer visible when the muscle is fully contracted.
What is the M Line ?
M Line is a region in the centre of the H Zone
M Line contain proteins that hold Thick Filaments together in the centre of the Sarcomere
What is the Z Discs ?
Z Discs are narrow, plate-shaped regions of dense material that sperate one sarcomere from the next.
Sarcoplasmic Reticulum
Each Myofibril is surrounded by a structure known as the Sarcoplasmic Reticulum
What is the Sarcoplasmic Reticulum ?
Sarcoplasmic Reticulum us a modified Smooth ER
Sarcoplasmic Reticulum consists of interconnected sacs and tubes that surround each myofibril.
At the end of each SR there is an expanded portion known as Terminal Cisternae
Each SR has 2 Terminal Cisternae
What are Terminal Cisternae ?
Terminal Cisternae are the expanded portions at the end of each Sarcoplasmic Reticulum.
Terminal Cisternae store Ca2+, that is used for muscle contraction (regulation)
Most of the Ca2+ is stored in the Terminal Cisternae in the relaxed muscles
The concentration of Ca2+ is higher in the Sarcoplasmic Reticulum than in the Cytoplasm
SR Membrane contains Ca2+ Calcium Release Channels called Ryanodine Receptors
Transverse Tubules (T-Tubules)
T-Tubules separate Terminal Cisternae of adjacent SR
What are Transverse Tubules ?
Terminal Cisternae of adjacent SR are separated by ONLY a very narrow gap
The Narrow Gap contains Transverse Tubules (T-Tubules)
T-Tubules are extensions of the Sarcolemma that enter the cell.
T-Tubules contain extra-cellular fluid
The internal membranes of the T-Tubules are extensions of the Sarcolemma
They contain voltage-gated Ca2+ channels known Dihydropyridine (DHP) Receptors
What is the function of T-Tubules ?
T-Tubules allow action potentials to move into the interior of the muscle cell.
What is a Triad ?
Triad is the structure where the Terminal Cisternae and the T-Tubules meet.
Mitochondria
What are Mitochondria ?
Mitochondria are found just beneath the Plasma Membrane between the Myofibrils
Oxidative Enzymes are found in the mitochondria
More mitochondria are found in the Slow Twitch Fibres
Endurance training may double the Mitochondrial content
NOTE:
Slow Twitch fibres have a HIGH Mitochondrial and Myoglobin Content
AND a HIGH Oxidative Enzyme Capacity
As they use the Oxidative Metabolic Pathway to produce ATP in the presence of Oxygen
Fast Twitch Fibres have a LOW Mitochondrial and Myoglobin Content
AND a LOW Oxidative Enzyme capacity
As they produce ATP in the absence of Oxygen
Muscle Innervation and Blood Supply
Describe the Muscle blood Supply
Each Muscle surrounded by a Capillary Network made of Veins, Arteries, and Capillaries which enter the muscle through its various layers
This capillary network enables Nutrients and Oxygen to be delivered to the muscle and for waste products and Carbon Dioxide to be taken away from the muscles.
Describe the Muscle Innervation
Muscle is also surrounded by branches of the Motor Neuron and Nerves
These Nerves and Neurons enter the muscle in its various layers
Describe the Capillary Supply and Density in the Types of Muscle Fibres
Slow Twitch Fibres have a Rich Capillary Supply
Slow Twitch Fibres have a High-intermediate Capillary Density
Fast twitch Fibres have a Poor Capillary Supply
Fast Twitch Fibres have a Low Capillary Density
Sliding Filament Theory
Sliding Filament Theory is used to explain the mechanisms of muscle contraction
Describe the Sliding Filament theory
Mechanism of Muscle Contraction is explained using the Sliding Filament Theory
The Thin Filaments slide over the Thick Filament resulting in the shortening of the sarcomere and muscle
How Does this Happen ?
The Head of the Thick Filament (Myosin) is able to bind to the Thin Filament (Actin)
After the attachment, the Head of the Thick Filament will bend 45 degrees towards the centre of the Sarcomere
Thus pulling the Thin Filament towards the M Line
The heads then detach from the thin filaments and then repeat the cycle
This is known as the Cross Bridge Cycle
BOTH ATP Hydrolysis and Ca2+ are required for the Cross Bridge Cycle
The Z Discs move towards each other
The length of the Myofilaments does NOT change, they merely slide over each other
Width of Band A will remains Constant
Width of the I Band and the H Zone will change (narrows)
Each Sarcomere shortens
Shortening of ALL sarcomeres results in Muscle Contraction
Thin Filament (Actin) Structure
Describe the structure of the Thin Filament
Actin Filaments consist of 3 proteins:
Structural protein:
Actin
Regulatory Proteins:
Tropomyosin
Troponin Complex
Actin Monomers form a double stranded filament
Actin (Protein) has a Myosin-Binding Site
Troponin is able to bind to Ca2+
In relaxed muscles, Tropomyosin physically covers the Myosin-Binding Site on the Actin - these binding sites have a low Ca2+ Concentration
In contracted muscles, Tropomyosin does NOT cover the Myosin-Binding Site on the Actin - these binding sites have a high Ca2+ Concentration
Troponin and Tropomyosin work together to regulate the binding to Actin to Myosin
The binding of Ca2+ to Troponin plays a role in the regulation of muscle contraction
Thick (Myosin) Filament Structure
What are Thick Filaments made of ?
Thick Filaments are made up of the large protein called Myosin.
Describe the Structure of the Myosin Molecule
Myosin is a Hexamer consisting of:
A Long, Thin Fibrous Rigid Coiled Tail
Two Heads
Hinge Region
Tail:
Tail is made of 2 Identical Myosin Heavy Chain (MHC), forming a Fibrous Rigid Coil
2 Heads:
Each Head is an extension of the myosin Heavy Chains (MHC)
Each Head has an Action-Binding Domain and an ATPase Site
An ATPase is an enzyme which is able to hydrolyze ATP into ADP and a separate inorganic Phosphate Molecule
During the ATP Hydrolysis, energy is released which is used to play a role in biological work such as muscle contraction
In each of the Actin Binding Domain an Actin Molecule is needed to bind for muscle Contraction to take place.
Each different Muscle Fibre Type (Slow or Fast Twitch Fibres) will contain a different Isoform of Myosin heavy Chain
Type 1 Fibres: MHC1
2A Fibres: MHC2A
2X Fibres: MHC2X
Hinge Region:
Has 2 Pairs of Non-Identical Myosin Light Chains (MLC)
Assembled Thick Filament
Describe the Structure of an assembled thick filament
Approximately 300 molecules of myosin on one thick filament
Thin Rod-Tails overlap to form the thick filament with the heads protruding out of the filament.
Half of the heads are aligned at one end of the filament, and the other half at the opposite end.
The 3-D Structure gives a "bottle-brush" appearance
Cross Bridge between the Thick Filament and Thin Filaments
Each Actin Molecule of the thin filament has a myosin binding site
Each Head of the thick filament has an actin binding domain
Describe what happens when Muscles are Relaxed according to the Cross Bridge
When the muscle is relaxed the Calcium (Ca2+) concentration in the Sarcoplasm is low.
The myosin and actin binding domains are unable to interact
This is because the Tropomyosin is covering the Myosin Binding Sites in the Actin molecule
Preventing the binding of the Head of the thick filament to the thin filament
Describe what must happen for the Muscles to Contract
For muscles to contract the Calcium (Ca2+) concentration in the Sarcoplasm must increase
Calcium will then bind to Troponin
Resulting in a conformational change in Troponin Molecules, which in turn moves Tropomyosin off Myosin Binding Sites
This exposes the Myosin Binding Sites in each of the Actin Molecules
The heads of the thick filament are then able to bind to the thin filament, thus forming a Cross Bridge between the 2 filaments
The Regulation of the Calcium (Ca2+) Concentration in the Sarcoplasm
Calcium Concentration increase is essential for Muscle contraction
How is the Ca2+ Concentration increased in the Sarcoplasm ?
Muscle Fibre depolarization begins at the motor end plate
The Action Potential is then transmitted along the Sarcolemma
Once the Action Potential arrives at the Transvers Tubules, the AP will descend in to the Fibre via the T-Tubules.
Resulting in the depolarization of the T-Tubule Membrane
Voltage-Gated Ca2+ Channels will then open in the Sarcoplasmic Reticulum Cisternae
Resulting in a rapid release in Ca2+ from the SR cisternae to Sarcoplasm
Cross Bridge Motion
Describe the Cross Bridge Motion after Ca2+ release into Sarcoplasm
The released Calcium (Ca2+) binds to Troponin C (TnC)
Resulting in the rotation of the Troponin-Tropomyosin Complexes
Thus, uncovering the Myosin Binding Site on Actin Molecule
As a result, the Myosin Head then binds to Actin to form the Cross-Bridge
The Myosin Head then moves 45 degrees inwards, towards the M Line
Because the Myosin head is attached to the thin Filament, it will cause the Actin Filament to moves towards the M Line.
Cross Bridge Cycle
Describe the cross Bridge Cycle
When the muscle is relaxed: Fibres are resting and the Cross bridge is not attached to Actin.
ADP and Pi are found on the Myosin Head
Tropomyosin prevents the Myosin Head from binding to Actin
When the Ca2+ Molecules are released from the SR Cisternae, they bind to the Troponin C (TnC)
Troponin-Tropomyosin Complex rotates
Allowing the Myosin head to bind to the Actin in a Strained 90 Degree Position
The inorganic Phosphate (Pi) is released from the Myosin Head.
This release is known as a Power Stroke, that releases energy causing the Filaments to slide inwards towards the M Line
And the Myosin head to bend 45 degrees inwards into a Relaxed Position
The ADP is also released allowing for the new ATP Molecule to bind to Myosin Head allowing the Myosin Head to be released from Actin.
The ATP is then Hydrolyzed into ADP and inorganic Phosphate, releasing energy that causes the Myosin Head (Without the Actin Filament) to return to its original Position
Resulting in the shortening of the Sarcomere
NOTE: As long as there is a supply of ATP and Ca2+ the Cross Bridge Cycle will continue.
Cross bridges Form where thick and thin filaments overlap
Sarcomere Length-Tension Relationship
Describe the Sarcomere Length-Tension Relationship
Cross bridge formation is responsible for force generation
There is a direct relationships between Force Developed by a Muscle and the Number of Overlapping Cross-Bridges/ Length of the Sarcomere
At resting length of the Sarcomere a maximum number of overlapping cross-bridges are formed
What is the optimal Sarcomere operating Length ?
Sarcomere length to produce a maximum number of overlapping cross bridges is 80%-120% of the resting length.
When the Sarcomere is Overly Shortened there is a high degree of overlapping cross bridges formed (Less than 80% of resting Sarcomere length)
BUT further muscular contraction is stopped by the budding of Myosin Filaments against Z Disc
Tension decreases due to this halt
When the Sarcomere is Overly Lengthened, there is little interaction between the 2 Filaments (More than 120% of Resting Sarcomere Length)
Less Tension is produced
When Sarcomere are so over stretched there is NO Cross-Bridge formation
NO Tension is produced
Muscle Relaxation
Describe the sequence of events involved in Muscle Relaxation
For muscles to Relax:
Ca2+ is pumped back into the Sarcoplasmic Reticulum from the Sarcoplasm
Ca2+ is released from Troponin C
Resulting in the cessation of interaction between Actin and Myosin
This is an ATP dependent process
What are the effects of Inhibiting the Active Transport of Ca2+ ?
Relaxation does NOT occur
Even if there are no more action potentials
What is the Function of ATP in Muscles ?
ATP provides energy for BOTH:
Muscle Contraction: Formation of Cross Bridges
Muscle Relaxation: Active transport of ca2+ from Sarcoplasm back to Sarcoplasmic Reticulum
Force Production and Shortening Velocity
What are the effects of muscle Architecture on Force Production and Shortening Velocity ?
An increase in the number of sarcomeres in series within myofibril, causes an increase in the overall velocity of shortening of the fibre (Less force)
An increase in the number of sarcomeres arranged in parallel to each other, the greater the capacity for maximum force production (Less Shortening Velocity)
