The skeleton and the muscles Flashcards
Structure of skeletal muscle cells (6)
- Long multinucleated cells, myocytes.
- Nuclei are on the peripheral of the cells.
- Myocytes contain myofibrils: actin and myosin.
- Sarcolemma is the membrane that surrounds the myocyte. T-tubules runs through this and allows simultaneous contraction.
- Sarcoplasmic reticulum is the endoplasmic reticulum that releases Ca2+ in muscle contraction.
Gross structure of skeletal muscle cells
- Myocytes are joined to other myocytes via connective tissue: endomysium.
- Myocytes are grouped in fascicles bundles which are held together by perimysium.
- Group of fascicles are grouped to form a muscle organ. This is held together by the epimysium.
Name the different arrangement of muscle fibres, and give examples of each arrangement (6)
- Flat: Latissimus dorsi
- Fusiform, muscle with a ‘belly’: biceps brachii
- Circular, usually surrounds an opening: Obicularis Oris and Obicularis Oculi surround the eye.
- Pennate, feathered muscle: Deltoid
- Quadrate, stabilisers and performs another function: Quadratus femoris in the pelvis.
- Multihead: Triceps brachii
- Convergent, muscle fibres broad at origin but narrower at insertion: Pectoralis major.
Muscle fibre arrangement in pectoralis major and minor
Convergent
Function of skeletal muscles
- Locomotion: voluntary movement of limbs and other structures/ structures, like the eyes and mouth.
- Maintains posture.
Micro-arrangement of skeletal muscle cells.
One contractile unit= sarcomere.
Sarcomere is composed of the interaction of myofibrils, actin and myosin.
Z line: Composed of actin filaments. The unit between 2 Z lines is a sarcomere.
H- zone: composed only of myosin filaments.
M-line: Contains no filaments, right in the middle. Disappears during contraction.
A band: Dark band composed of the overlapping of actin and myosin filaments.
I band- Light band composed of only actin filaments.
Describe what occurs in skeletal muscle during contraction.
The sarcomere shortens —> The distance between the origin and insertion of the muscle also shortens.
Acetylcholine is released at the end motor plate into the sarcolemma, which triggers contraction—> Communication between nerve and muscle.
T-tubules within the sarcolemmma branch out across the muscle fibre, this causes simultaneous contraction across the fibre.
Release of AcH triggers the release of calcium ions in from the sarcoplasmic reticulum.
Regeneration of skeletal muscle cells.
Limited: Not all myocytes can regenerate. Satellite cells are the only ones capable of multiplying.
Structure of cardiac muscle cells
Myocardium: cardiac muscle.
Contraction is involuntary.
- Cells are branched and connected by intercalated discs: fascia adhesions connect intercalated discs. -
- Desmosomes allow contraction co-ordination
- Gap junctions between discs allow action potential conduction.
Faintly striated and uninucleated cells.
Describe the contraction in cardiac muscle
Contraction is involuntary and not initiated by the NS—> BUT the ANS controls heart rate.
Contraction is intrinsically generated by nodes controlled by the ANS.
The vagus nerve is the parasympathetic nerve that slows down heart rate.
The accelerator nerve increases heart rate from the sympathetic system.
Structure of smooth muscle
Spindle shaped cells that have one central nucleus.
Contractile patterns are not arranged as sarcomeres: protein filaments criss-cross in an ‘X’ pattern to form a focal density.
Cells are surrounded by a network of connective tissue.
Function of smooth muscle
Allows slow sustained contractions of structures to move contents in the viscera.
Contraction in smooth muscle.
Contraction is of low force but sustained longer than cardiac and skeletal muscle.
Contractions are rhythmic and cells run parallel to the contraction.
Contract occurs towards the focal density, which is usually at the lumen.
Contraction is involuntary —> stimulated by hormones and the ANS.
Muscle dystrophy
A genetic disease that causes progressive weakness in muscles.
Cardiomyopathy
Deterioration in heart muscle function.
