muscle tissues Flashcards
what is muscle tissue specialised for
contraction
what the three types of muscle tissue?
- skeletal
- cardiac
- smooth
describe somatic muscle tissue
- voluntary control (conscious)
- striated structure
- skeletal muscle tissue
describe autonomic muscle tissue
- involuntary control (unconscious)
- striated or non-striated
- cardiac muscle tissue (striated- only found in walls of heart to pump blood)
- smooth muscle tissue (non-striated- lines hollow organs to propel its contents through the organ)
- heartrate, breathing etc.
what is striated muscle tissue?
features repeating functional units called sarcomeres which make up myofibrils
what are the roles of skeletal muscle roles?
- voluntary (conscious) movement of skeleton
- involuntary (subconscious) control of balace/posture
describe the cells in skeletal muscle tissue?
- often called fibres as they resemble fibres
- very long (up to 30cm), elongated, cylindrical cells
- they contain multiple periphically located nuclei which lie around the outside of the cell as the cells are packed with protein units (myofibrils) which are important for producing contractions
what is each individual skeletal muscle made up of?
(classed as an organ)
- skeletal muscle tissue
- nervous tissue
- connective tissue
- blood vessels
what is a fasicle?
a bundle of muscle fibres bound together via the endomysium tissue wrapped by perimysium
what is the name for muscle fibres?
myocytes
what is perimysium?
connective tissue
what is the epimysium?
dense connective tissue which externally surrounds entire muscles
what is the endomysium?
the innermost connective tissue which surrounds individual muscle fibres
what are sarcomeres?
contractile units of skeletal muscle
how do sarcomeres contract?
the sliding filament mechanism
- a conformational change causes the filaments to slide over each other causing the sarcomere to contract
describe the electron-microscopic cell structure of skeletal muscle
- myofibrils composed of repeating protein units called myofilaments
- dark thicker bands (mysoin)
- light thinner bands (actin)
- z lines bisect light bands, dividing each myofibril into contractile units called sarcomeres
what do somatic motor neurons do?
innervate (supply with nerves) skeletal muscle
(1 neuron innervates several muscle fibres)
what makes up a motor unit?
a single motor neuron together with all the muscle fibres it innervates
what is excitation-contraction coupling?
- the neuronal action potential is converted to a chemical messenger called acetylcholine at the neurotransmitter junction
- this is detected by receptors on the plasma membrane of muscle cells/fibres
- stimulates an action potential in muscle fibres which contract
what happens at the neurotransmitter junction?
the synapse of a motor neuron interacts with a muscle fibre
what is the sarcolemma and its role?
- the sarcolemma is the modified plasma membrane of skeletal muscle cells
- it ivagenates into sarcoplasm to form membranous T tubules
- T tubules propagate action potentials into the interior of the cell
- it is continuous with the extracellular space
what does ivagenates mean?
pores into
what is the sarcoplasmic reticulum?
- modified smooth endoplasmic reticulum
- Ca2+ is concentrated within in the sarcoplasmic reticulum when muscle cells are relaxed and is required for actin to interact with myosin to give contraction
- therefore, when muscle contraction isn’t wanted, the Ca2+ is kept away from the myofibrils
what two things support synchronous contraction of sarcomeres?
sarcolemma and sarcoplasmic reticulum
what is the function of cardiac muscle?
- specialised for continuous autonomous contractions
- pumps blood through the cardiovascular system
where is cardiac muscle found?
ONLY in the heart
what is the structure of cardiac muscle?
- elongated, some branched, cylindrical cells
- striated
what are the three layers of the heart wall?
- pericardium- outer supporting tissue
- myocardium- cardiac muscle tissue
- endocardium- single layer of epithelial cells
describe the histological structure of cardiac muscle
- branched structure of individual cardiac muscle cells
- regular connective tissue supports its rich capillary network
- intercalated discs anchor cardiac cells together
what is the name for cardiac muscle cells?
cardiomyocytes
what are intercalated discs?
- allow cardiomyocytes to function as syncytium (a single unit)
- specialised intercellular junctions
- contain desmosomes
- contain gap junctions
- found at adjoining edge of cariomyocytes
what is the function of a gap junction?
allow ions and signals to pass from cell to cell
what are the similarities between cardiac and skeletal muscle?
- identical arrangement of sarcomeres
- striated
- contain T tubules and sarcoplasmic reticulum
- contain numerous mitochondria
- contain glycogen and lipid granules
- contraction occurs by sliding-filament mechanism
what are the differences between cardiac and skeletal muscle?
- cardiac is autonomous contraction
- SR of cardiac muscle slowly leaks Ca2+
- there are specialised cardiac muscle cells (the conducting system)
- cardiac muscle cells have intercalated discs
what do pacemaker cells do?
undergo spontaneous depolarisation which sets the basic heart rhythm
describe the conducting system of the heart
- autonomous contraction
- initiated at the sinoatrial node (pacemaker cells are found here)
- left and right atria contract
- atrioventricular node
- atrioventricular bundle
- purkinje fibres
- ventricles contract pushing blood into aorta
- cardiac muscle fibres
what is the function of smooth muscle?
-specialised for continuous contractions
- typically typically to propel lumen contents (peristalsis- wave of contraction and relaxation in gastrointestinal tract)
where is smooth muscle found?
lining hollow organs
describe the structure of smooth muscle cells
- elongated, spindle-shaped with tapered ends
- single centrally located nuclei
- no sarcomeres therefore non-striated muscle
what is peristalsis?
involuntary constriction and relaxation of the muscles of the intestine or another canal, creating wave-like movements that push the contents of the canal forward
what is the gastrointestinal tract?
Muscular tube lined by a mucous membrane
Two muscle layers at right angles
Peristalsis is how food moves through the GI tract
describe peristalsis in the GI
- Lined internally by epithelium called the mucosa/mucous membrane- the mucosa is made up of three components: the epithelium, a supporting lamina propria and a thin smooth muscle layer, the muscularis mucosae, which produces local movement and folding of the mucosa.
- Submucosa is directly beneath the mucosa
- The muscularis propria is directly beneath the submucosa. The muscular wall proper consists of smooth muscle that is usually arranged as an inner circular layer and an outer longitudinal layer. In the stomach only, there is an inner oblique layer of muscle. The action of the two layers, at right angles to one another, is the basis of peristaltic contraction.
- The adventitia is directly below the muscularis propria. his outer layer of loose supporting tissue conducts the major vessels, nerves and contains variable adipose tissue. Where the gut lies within the abdominal cavity (peritoneal cavity), the adventitia is referred to as the serosa (visceral peritoneum) and is lined by a simple squamous epithelium known as mesothelium.
- Muscular tube lined by a mucous membrane
- Two smooth muscle layers at right angles- muscularis propria
describe smooth muscle contraction
- No myofibils or sarcomeres
- Actin and myosin arranged in a criss-cross lattice
- Anchored to cytoplasm and cell membrane via dense bodies
- In a relaxed state the cell is elongated (a)
- Muscle cell becomes shortened and globular
what is the parasympathetic ganglia?
layer between two different layers of muscle- it modulates the intensity of peristalsis
what is desmin?
third type of filament which anchors actin and allows the myosin to slide over it, as this happens the cells shorten and twist (contract)- these contractions happen more slowly and use less energy
