Muscle Flashcards
What are the 3 types of muscle?
Skeletal, smooth and cardiac
Outline the structure of skeletal muscle
Each muscle fibre (cell) is wrapped in endomysium. Many fibres and then wrapped together in perimysium to form a fascicle. Many fascicles are wrapped together in epimysium to form the muscle
What are the 2 different types of muscle fibres in skeletal muscle
Red (more mitochondria, so longer sustained contraction) and white (powerful, easily fatiguing contractions)
How are the nuclei located in skeletal muscle cells
The cells are multi-nucleated with the nuclei peripherally located
Why is skeletal muscle striated?
Due to the regular banding of the actin and myosin myofilaments in the muscle fibres
What is the M line
The line that holds the myosin fibres together
What is a sarcomere?
The area from one Z line to another (contractile unit)
What is the H zone
The section of myosin where there is no overlap with the actin
Describe the structure of cardiac muscle
The cells are striated with a central nucleus. There are no Z lines but intercalated discs (for simultaneous contraction) and no myofibrils instead the myofilaments form continuous masses
Why is ANP and BNP released by cardiac tissue?
They cause Na excretion by increasing the glomerular filtrate in the kidneys. Therefore, you lose more water, this lowers your blood pressure and blood volume so allows the heart to rest when it’s being over stretched
What are the Purkinje fibres?
Modified muscle cells that carry impulses from the AVN to the apex allowing simultaneous contraction of the ventricles. Lots of gap Junctions allow for fast conduction
Describe smooth muscle cells
Spindle shaped with central nucleus
What are the 2 different types of smooth muscle cells
Myoepithelial and myofibroblasts
What do myoepithelial cells do?
Contract to assist secretion of sweat, salvia and milk
What do myofibroblast cells do?
Produce collagen and contract to help in wound healing
What can occur from dysfunctional smooth muscle?
Asthma, irritable bowel syndrome and hypertension
What are neurotransmitters released from at smooth muscle?
Varicosities
Why are skeletal muscles surrounded by intermediate filaments?
To give the cells support
What is atrophy?
Where there is loss of muscle
What causes muscle atrophy?
Disuse, age, malnutrition, denervation
What is muscle hypertrophy?
And increase in muscle
What is hyperplasia?
Increase in the number of muscle cells
Which types of muscle can repair itself?
Smooth muscle. Skeletal muscle have satellite cells that can divide and differentiate. However, cardiac muscle can only lay down scar tissue using fibroblasts
What 3 diagnostic tests can be used to determine muscle damage?
Troponin, myoglobin and creatine kinase tests
What is fibrillation?
Contraction of individual muscle cells
What is fasiculation?
Contraction of whole muscle fascicles
What is the neurotransmitter released at neuromuscular junctions?
Acetyl Choline
How are CALCIUM ions released from storage in the SER for muscle contraction?
An impulse at the neuromuscular junction releases acetyl choline which depolarises the sarcolemma. The depolarisation spreads down t tubules where it is detected by voltage sensors, which then change their shape opening CALCIUM Gated Ion Channels in the SER
Why can’t myosin heads bind to actin without CALCIUM being present
Tropomyosin is blocking the binding site
Where do CALCIUM ions bind to on the actin filaments
TnC of the troponin complex
What does the binding of calcium to troponin cause?
A conformational change which moves the tropomyosin away from the myosin binding site on the actin filament
Outline the sliding filament model
- Ca binds to troponin, allowing the myosin heads to form cross bridges with the actin filaments
- ADP and Pi are released from myosin head allowing the head to bend and the sarcomere shortens (power stroke)
- ATP binds to the myosin head and cross bridges break
- ATP is then hydrolysed
