Changes

3. Cardiac

3. Cardiac

==Skeletal Muscle==

==1. Skeletal Muscle==

[[Image:Striated Muscle 1.jpg|thumb|right|150px|Striated muscle - Copyright RVC 2008]]

[[Image:Striated Muscle 1.jpg|thumb|right|250px|Striated muscle - Copyright RVC 2008]]

[[Image:muscle.jpg|thumb|right|150px|Triad Junction - Copyright RVC 2008]]

[[Image:muscle.jpg|thumb|right|250px|Triad Junction - Copyright RVC 2008]]

*Each muscle '''belly''' is composed of multiple '''fascicles''', each of which consists of a bundle of muscle '''fibers'''

 

*Muscle "fiber" means a single cell, which is multi-nucleate, and known as '''syncitia'''

Each muscle '''belly''' is composed of multiple '''fascicles''', each of which consists of a bundle of muscle '''fibers'''. Muscle "fiber" means a single cell, which is multi-nucleate, and known as '''syncitia'''.

**'''Parallel''' fibers: running from origin to insertion)

 

***Long fibers allow for a faster contraction and a greater range of motion

'''Parallel''' fibers: Run from origin to insertion, long fibers allow for a faster contraction and a greater range of motion.

**'''Pennate''' fibers: at an angle to line of pull of an internal tendon or aponeurosis

 

***Short fibers allow for a greater force capacity

'''Pennate''' fibers: Run at an angle to the line of pull of an internal tendon or aponeurosis. Short fibers allow for a greater force capacity.

*Within each fiber are groups of parallel, longitudinal myofibrils

 

**Myofibrils are arranged as '''sarcomeres''', bound by Z-discs, which are the functional unit of muscle contraction

Within each fiber are groups of parallel, longitudinal myofibrils. Myofibrils are arranged as '''sarcomeres''', bound by Z-discs, which are the functional unit of muscle contraction. Each sarcomere contains 2 separate groups of myofilaments:

**Each sarcomere contains 2 separate groups of myofilaments:

 

***Thin filament, containing '''Actin''', located centrally

1. Thin filament, containing '''Actin''', located centrally.

***Thick filament, containing '''Myosin''', originating from either side of each Z-disc

 

*Two basic types of skeletal myofibre:

2. Thick filament, containing '''Myosin''', originating from either side of each Z-disc.

**<u>'''Primary: Oxidative'''</u>

 

***Grossly '''red'''

There are two basic types of skeletal myofibre:

***'''High''' myoglobin level

 

***'''Slow''' rate of contraction

1. '''Primary: Oxidative'''

***High '''oxidative''' activity

 

***Function - postural, sustained activity

Grossly red, with high myoglobin level, slow rate of contraction and a high oxidative activity. The function is for postural, sustained activity.

**<u>'''Secondary: Glycolytic'''</u>

 

***Grossly '''white'''

2. '''Secondary: Glycolytic'''

***'''Low''' myoglobin level

 

***'''Fast''' rate of contraction

Grossly white, with low myoglobin level, fast rate of contraction and a high glycolytic activity. The function is for exercise and bursts of activity.

***High '''glycolytic''' activity

 

***Function - exercise, bursts of activity

===Neurogenic Contraction===

*'''Neurogenic Contraction''': Muscle activation is initiated by a nervous impulse crossing the Neuromuscular Junction  

 

**Each muscle fiber is controlled by a single motor neuron

Muscle activation is initiated by a nervous impulse crossing the Neuromuscular Junction. Each muscle fiber is controlled by a single motor neuron. The neurotransmitter, '''Acetylcholine (Ach)''', binds receptors in the muscle fiber to open Na+ channels. This causes a wave of depolarization along the sarcoplasmic membrane, further opening voltage-gated Na+ channels, which propagates the signal along the sarcolemma. Depolarization of the sarcoplasmic reticulum causes Calcium to be released, which activates muscle contraction.

**The neurotransmitter, '''Acetylcholine (Ach)''', binds receptors in the muscle fiber to open Na+ channels

 

**This causes a wave of depolarization along the sarcoplasmic membrane, further opening voltage-gated Na+ channels, which propagates the signal along the sarcolemma

Muscle contraction occurs when (thin) Actin filaments slide past (thick) Myosin filaments. The myosin heads bind actin subunits, forming cross-bridges, hydrolyzing ATP and providing energy for contraction. Myosin heads undergo power stroke, displacing Actin and releasing ADP and Pi. In the off state, tropomyosin coiled-coils block the helical grooves of the actin filament. Tropomyosin movement relieves the steric block, allowing access to myosin binding sites. Calcium regulates muscle contraction by binding troponin-C, which is attached to the thin filament. This causes inhibition of the steric block keeping Actin and Myosin from interacting. Increased Calcium causes a negative feedback inhibition of Ca release, and it is pumped back into the sarcoplasmic reticulum by the Ca/ATPase pump.

**Depolarization of the sarcoplasmic reticulum causes Calcium to be released, which activates muscle contraction

 

***Muscle contraction occurs when (thin) Actin filaments slide past (thick) Myosin filaments

Types of Muscle Contraction:

***Myosin heads bind Actin subunits, forming cross-bridges, hydrolyzing ATP and providing energy for contraction

 

***Myosin heads undergo power stroke, displacing Actin and releasing ADP and Pi

'''Concentric''': muscle shortens and bones are brought closer together.

**In the off state, tropomyosin coiled-coils block the helical grooves of the actin filament

'''Isometric''': muscle is active but does not change in length (force without motion).

**Tropomyosin movement relieves the steric block, allowing access to myosin binding sites

 

***Calcium regulates muscle contraction by binding troponin-C, which is attached to the thin filament

'''Eccentric''': muscle is active while lengthening.

***This causes inhibition of the steric block keeping Actin and Myosin from interacting

*Increased Calcium causes a negative feedback inhibition of Ca release, and it is pumped back into the sarcoplasmic reticulum by the Ca/ATPase pump

*Types of Muscle Contraction:

**'''Concentric''': muscle shortens and bones are brought closer together  

**'''Isometric''': muscle is active but does not change in length (force without motion)

**'''Eccentric''': muscle is active while lengthening

==Smooth Muscle==

==Smooth Muscle==