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DESCRIPTION
MusclesTRANSCRIPT
MUSCLES
What Functions Do Muscles Provide?
Basic Physiological Properties
1. Contractility 2. Excitability 3. Extensibility 4. Elasticity
These four properties are all involved in Movement
Muscle is a specialised tissue of mesodermal origin. About 40-50 percent of the body weight of a human adult is contributed by muscles. Based ontheir location, three types of muscles are identified : (i)Skeletal (ii) Visceral and (iii) Cardiac.
Each organised skeletal muscle in ourbody is made of a number of muscle bundles or fascicles held togetherby a common collagenous connective tissue layer called fascia. Eachmuscle bundle contains a number of muscle fibres
Each muscle fibre is lined by the plasma membrane called sarcolemmaenclosing the sarcoplasm. Muscle fibre is a syncitium as the sarcoplasmcontains many nuclei. The endoplasmic reticulum, i.e., sarcoplasmicreticulum of the muscle fibres is the store house of calcium ions. A characteristic feature of the muscle fibre is the presence of a large numberof parallelly arranged filaments in the sarcoplasm called myofilaments ormyofibrils.
Each myofibril has alternate dark and light bands on it. A detailed study of the myofibril has established that the striated appearance is due to the distribution pattern of two important proteins – Actin and Myosin.
The light bands contain actin and is called I-band or Isotropic band, whereas the dark band called ‘A’ or Anisotropic band contains myosin. Both the proteins are arranged as rod-like structures, parallel to each other and also to the longitudinal axis of the myofibrils.
Actin filaments are thinner as compared to the myosin filaments, hence are commonly called thin and thick filaments respectively. In the centre of each ‘I’ band is an elastic fibre called ‘Z’ line which bisects it. The thin filaments are firmly attached to the ‘Z’ line. The thick filaments in the ‘A’ band are also held together in the middle of this band by a thin fibrous membrane called ‘M’ line. The ‘A’ and ‘I’ bands are arranged alternately throughout the length of the myofibrils. The portion of the myofibril between two successive ‘Z’ lines is considered as the functional unit of contraction and is called a sarcomere. In a resting state, the edges of thin filaments on either side of the thick filaments partially overlap the free ends of the thick filaments leaving the central part of the thick filaments. This central part of thick filament, not overlapped by thin filaments is called the ‘H’ zone.
3. Smooth Muscle:
Involuntary peristaltic contractions of digestive tract
Vasoconstriction and vasodilation of blood vessels
Regulated By A.N.S
Smooth Muscle Characteristics
• Has no striations• Spindle-shaped cells• Single nucleus• Involuntary – no
conscious control• Found mainly in the
walls of hollow organs
Figure 6.2a
Skeletal Muscle Characteristics
• Most are attached by tendons to bones
• Cells are multinucleate
• Striated – have visible banding
• Voluntary – subject to conscious control
• Cells are surrounded and bundled by connective tissue
2. Cardiac Muscle:
Rhythmic "synchronized" beat Involuntary - regulatable by A.N.S.
Cardiac Muscle Characteristics
• Has striations• Usually has a single
nucleus• Joined to another
muscle cell at an intercalated disc
• Involuntary• Found only in the
heartFigure 6.2b
Characteristics of Muscles
• Muscle cells are elongated (muscle cell = muscle fiber)
• Contraction of muscles is due to the movement of microfilaments
• All muscles share some terminology– Prefix myo refers to muscle– Prefix mys refers to muscle– Prefix sarco refers to flesh
Skeletal Muscle Attachments
• Epimysium blends into a connective tissue attachment– Tendon – cord-like structure– Aponeuroses – sheet-like structure
• Sites of muscle attachment– Bones– Cartilages– Connective tissue coverings
Connective Tissue Wrappings of Skeletal Muscle (So as to keep Muscle
fibers together)• Endomysium – around
single muscle fiber
• Perimysium – around a fascicle (bundle) of fibers
• Epimysium- The outermost connective tissue
Figure 6.1
Characteristics of Muscles: AND….MYO, MYS and SARCO• Muscle cells are elongated
(muscle cell = muscle fiber)• Contraction of muscles is due to the
movement of microfilaments• All muscles share some terminology:
– Prefix myo refers to muscle
– Prefix mys refers to muscle– Prefix sarco refers to flesh
Muscle Cell =Muscle Fiber= Myocyte: But BEWARE…ALL Muscles cells are NOT ALIKE!!
• The myocyte is elongated
• Their characteristics depend on which type of muscle they are found: skeletal, muscle or cardiac.
• Which Type of Muscle are we referring to here??
The Cell: Called the Muscle Fiber The Muscle Fiber is VERY SPECIALIZED!!! 2. Sarcolemma: Muscle cell membrane 3. Sarcoplasm: Muscle cell cytoplasm it contains: a. Many small oval nuclei b. Many mitochondria c. Sarcoplasmic reticulum d. Transverse tubules
e. Myofibrils ( many of these)
Microscopic Anatomy of Skeletal Muscle Cell: A First Look
• Cells are multinucleate
• Nuclei are just beneath the sarcolemma
Figure 6.3a
Myofibril components… 1. Myofilaments
Actin: Thin threads Myosin: Thick threads
2. Sarcomere Contractile unit of myofibril
3. Sarcoplasmic reticulum Modified smooth E.R. Surrounds myofibril Contains calcium ions
4. Transverse tubules Cross channels of sarcoplasmic reticulum Open to extracellular fluid Function in muscle activation
We Will See The Role of Calcium
During ……Muscle Contraction
Smooth Endoplasmic Reticulum (SR) in Muscle Cells
• VERY SPECIALIZED
• It STORES and MOBILIZES Calcium ions
• What is the role of Ca++ in muscle contraction??
What Does the SER Look Like?
Function of Muscles
• Produce movement
• Maintain posture
• Stabilize joints
• Generate heat
Properties of Skeletal Muscle Activity
• Irritability – ability to receive and respond to a stimulus
• Contractility – ability to shorten when an adequate stimulus is received
Muscle Contraction Begins When..
• Stored Calcium is released into the sarcoplasm
• These ions are released into the sarcomeres
Relaxed and Contracted Sarcomeres
• Muscle cells shorten because their individual sarcomeres shorten – pulling Z discs closer together– pulls on sarcolemma
• Notice neither thick nor thin filaments change length during shortening
• Their overlap changes as sarcomeres shorten
Microscopic Anatomy of Skeletal Muscle
Sarcoplasmic reticulum – specialized endoplasmic reticulum
Figure 6.3a
Figure 6.3b
Microscopic Anatomy of Skeletal Muscle
• Myofibril– Bundles of myofilaments– Myofibrils are aligned to give distinct bands
• I band =
light band
• A band = dark band
Microscopic Anatomy of Skeletal Muscle
• Sarcomere– Contractile unit of a muscle
Figure 6.3b
Microscopic Anatomy of Skeletal Muscle
• Organization of the sarcomere– Thick filaments = myosin filaments
• Composed of the protein myosin
• Has ATPase enzymes
Figure 6.3c
Microscopic Anatomy of Skeletal Muscle
• Organization of the sarcomere– Thin filaments = actin filaments
• Composed of the protein actin
Figure 6.3c
Microscopic Anatomy of Skeletal Muscle
• Myosin filaments have heads (extensions, or cross bridges)
• Myosin and actin overlap somewhat
Figure 6.3d
Microscopic Anatomy of Skeletal Muscle
• At rest, there is a bare zone that lacks actin filaments
• Sarcoplasmic reticulum (SR) – for storage of calcium
Figure 6.3d
Neural Stimulus to Muscles• Skeletal muscles
must be stimulated by a nerve to contract
• Motor unit– One neuron– Muscle cells
stimulated by that neuron
Figure 6.4a
Those Myofiloments: How They Move: The Basis of Muscle Contraction
Plus: The Neuromuscular Junction: where it all happens: This IS Muscle
Physiology!
What Do You Think?
• Glycogen- Stored form of starch found in muscle
• What is the role of Glycogen in muscle physiology?
The Case of the Shrinking Sarcomere
• SEE THE I BAND DISAPPEAR during a contraction of the.. sarcomere? Yes. Which makes up myofilament.
• Will the I band reappear? When?
• What causes the I band to dissapear?
What is ACTUALLY happening when a Sacromere Shrinks?
• The thin filament ACTIN and the THICK filament MYOCIN form a CROSS-BRIDGE that cause a SLIDING motion.
• This shortens the sacromere or closes that GAP or I band and causes a CONTRACTION.
• Neither the ACTIN nor the Myocin filament actually shorten its the sacromere itself.
OBSERVE THE UNCOVERED ACTIN SITES…MYOCIN CAN NOW BIND…
Before Contraction Can Happen
• We must think about it …even if it is a reflex.
• We must involve the CNS…
Nerve Stimulus to Muscles
• Skeletal muscles must be stimulated by a nerve to contract
• Motor unit– One neuron– Muscle cells
stimulated by that neuron
Figure 6.4a
MOTOR END PLATE
• This is where the neuron and myofiber intercept.
• Muscle contraction is possible because of neural impulse at the motor end plate.
• It is the action potential that causes the release of Ca++ ions from the SR,
• The Ca++ can then bind to Troponin and change the configuration of Tropomyocin.
• ACTiN’s G binding sites are then exposed.
Nerve Stimulus to Muscles
• Synaptic cleft – gap between nerve and muscle– Nerve and
muscle do not make contact
– Area between nerve and muscle is filled with interstitial fluid
Figure 6.5b
Transmission of Nerve Impulse to Muscle
• Neurotransmitter – chemical released by nerve upon arrival of nerve impulse– The neurotransmitter for skeletal muscle is
acetylcholine
• Neurotransmitter attaches to receptors on the sarcolemma
• Sarcolemma becomes permeable to sodium (Na+)
Transmission of Nerve Impulse to Muscle
• Sodium rushes into the cell generates an action potential (AP)
• The action potential travels along the T-tubules to the SR to stimulate release of Calcium ions.
The SR Stores Ca ions and Release them When There is an AP!
Find the T-Tubules
Where do Ca ions go?
• The ions travels to the muscle tissue and bind to the ACTIN regulatory proteins ( TROPONIN) .
• This UNCOVERS Myosin Head BINDING Sites on ACTIN so as to allow CROSS BRIDGING ( once myosin is powered by ATP.
The Sliding Filament Theory of Muscle Contraction
• Activation by nerve causes myosin heads (crossbridges) to attach to binding sites on the thin filament
• Myosin heads then bind to the next site of the thin filament
Figure 6.7
The Sliding Filament Theory of Muscle Contraction
• This continued action causes a sliding of the myosin along the actin
• The result is that the muscle is shortened (contracted)
Figure 6.7
The Sliding Filament Theory
Figure 6.8
NOW the muscle Must RELAX
• Acetylcholine, the neurotransmitter is broken down by the enzyme acetylcholinesterase
• SO the stimulus to muscle ceases!• Calcium ions are actively transported back to
the SR• The actin and myocin cross bridges break• RELAXES------S T R E T C H of the
sarcomere. Get it??
WHERE DOES ALL OF THIS ENERGY for CONTRACTION
COME FROM?
Creatine Phosphate• This a high energy molecule found in muscle cells• 4 to 6 time more abundant in muscle fibers than
ATP!!• It CANNOT directly transfer a phosphate group to
a reaction• INSTEAD, when ATP is sufficient an enzyme in
mitochondrian, creatine phosphokinase promotes the synthesis of creatine phosphate.
• As ATP gets degraded, creatine phosphate can donate its phosphate bonds to ADP creating NEW ATP
Energy for Muscle Contraction• Direct phosphorylation
– Muscle cells contain creatine phosphate (CP)• CP is a high-energy
molecule– After ATP is depleted,
ADP is left– CP transfers energy to
ADP, to regenerate ATP– CP supplies are exhausted
in about 20 seconds
Figure 6.10a
Energy for Muscle Contraction
• Initially, muscles used stored ATP for energy– Bonds of ATP are broken to
release energy– Only 4-6 seconds worth of ATP is
stored by muscles• After this initial time, other
pathways must be utilized to produce ATP
Energy for Muscle Contraction
• Aerobic Respiration– Series of metabolic
pathways that occur in the mitochondria
– Glucose is broken down to carbon dioxide and water, releasing energy
– This is a slower reaction that requires continuous oxygen Figure 6.10b
Energy for Muscle Contraction
• Anaerobic glycolysis– Reaction that breaks down
glucose without oxygen– Glucose is broken down to
pyruvic acid to produce some ATP
– Pyruvic acid is converted to lactic acid
Figure 6.10c
Myoglobin• Myoglobin is oxygen carrier ( It is a
pigment)
• Synthesized in muscle
• Higher affinity for oxygen than hemoglobin
• One globin protein, rather than 4: therefore we say this protein has tertiary level structure as apposed to hemoglobin’s quartenary level structure.
• It can STORE oxygen as well as carry it.
Muscles and Body Movements
• Movement is attained due to a muscle moving an attached bone
Figure 6.12
Energy for Muscle Contraction
• Anaerobic glycolysis (continued)– This reaction is not as
efficient, but is fast• Huge amounts of glucose
are needed
• Lactic acid produces muscle fatigue
Figure 6.10c
Muscle Fatigue and Oxygen Debt
• When a muscle is fatigued, it is unable to contract
• The common reason for muscle fatigue is oxygen debt– Oxygen must be “repaid” to tissue to remove
oxygen debt– Oxygen is required to get rid of accumulated
lactic acid
• Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less
•SO YOU SAY one of the functions of muscles is to generate HEAT?
•HOW DO THEY DO THAT??
Muscles and Body Movements
• Muscles are attached to at least two points– Origin – attachment to a
immoveable bone– Insertion – attachment
to a movable bone– Action- What this
muscle and bone (together) accomplish
Figure 6.12
Example of how it works:
Name of Muscle: Biceps Brachii
Origin: Scapula of Shoulder girdle
Insertion: Proximal Radius
Action: Flexes elbow and supinates ( to turn backward = supinate ) forearm
Types of Ordinary Body Movements
• Flexion
• Extension
• Rotation
• Abduction
• Circumduction
Body Movements
Figure 6.13a–c
Body Movements
Figure 6.13d
:Prime mover: • major muscle of movement
Antagonist:
opposes movement;when primeMover is active, antagonist is stretched and relaxes
Synergists:• assist prime mover
• fixator--stabilizers
TYPES OF MUSCLES
All skeletal muscles have fascicles
Fascicle arrangement allows different functions of muscles
• parallel (fusiform)--strap• pennate (feather)
• convergent—fan, triangle
• circular (sphincter)—squeeze
Fascicle Arrangement
Determined by fascicular arrangement
Skeletal muscle shortens to 70% of resting length
• parallel--shorter, not powerful
• pennate--lots of fibers, powerful
Power and Range of Motion
Pennate Muscles
Figure 11–1c, d, e
• Unipennate:
– fibers on 1 side of tendon e.g., extensor digitorum
• Bipennate:
– fibers on both sides of tendon e.g., rectus femoris– tendon branches within muscle e.g., deltoid
• Multipennate:• Form angle with tendon
• Don’t move as far as parallel muscles
• Contain more myofibrils than parallel muscles
• Develop more tension than parallel muscles
Diseases of Muscles
Duchenne Muscular Dystrophy• Inherited muscle-destroying diseases
affects muscle (MALES only)• Muscles atrophy- wheelchairs at a
young age. Death from failure of respiratory muscles by young adulthood.
• Due to lack of protein called dystropin-associated glycoprotein (DAG) that helps maintain sarcolemma. NO CURE YET.
Myathenia Gravis
• The disease involves a SHORTAGE of
Acetylcholine receptors at the neuromuscular junction.
NT can’t bind and stimulate AP to muscle.
Myasthenia Gravis
Myasthenia Gravis
• Patients of Myasthenia Gravis usually have drooping eyelids
• Difficulty in swallowing and talking• Generalized muscle weakness and
fatigability• Antibodies to acetylcholine
receptors found in blood …suggests MG is autoimmune disease
• Respiratory Failure due to muscle failure here--Death
Botulism• Bacterium, Clostridium botulinum,
under anaerobic conditions, produces a toxin called botulinum.
• It prevents release of Acetylcholine from nerves at NM junction.
• Paralyzes muscles. Do you understand why?
1. Skeletal Muscle: Voluntary movement Maintenance of posture Heat production