6.5 Muscle and Innervation Flashcards
What is the main function of muscle cells?
Movement - the tissues are made up of elongated contractile cells
What are contractile elements and where can they be found?
- Myosin
- Actin
They are found in nearly all cells (used to move, change shape or allow the intracellular movement of organelles)
What makes muscle cells unique?
- Permanently orientated contractile machinery
- Allows directional movements/contractions that are appropriate for the tissue
- Able to stretch beyond their resting length
- Return to their resting state (elasticity)
- Increase in size (hypertrophy) or number (hyperplasia) or both
What are the three types of muscle?
- Skeletal
- Cardiac
- Smooth
Briefly summarise the three types of muscle.
Skeletal: - Attached to bones crossing joints, controls the eye - Striated appearance - Multinucleate, peripherally orientated - Somatic/voluntary innervation Cardiac: - Found only in the heart - Striated appearance - Usually only uninucleate, centrally located - Autonomic/involuntary innervation Smooth: - Found in visceral organs, incl blood vessels and glands - Non-striated - Uninucleate, centrally located - Autonomic/involuntary innervatioin
What is the sarcolemma?
Muscle cell membranes
- Bordered externally by a basal lamina and collagen + reticular fibres
What is the sarcoplasm?
Muscle cell cytoplasm
What is the sarcoplasmic reticulum?
Muscle cell smooth endoplasmic reticulum (SER)
What are the sarcosomes?
Muscle cell mitochondria (only occasionally used)
What is a sarcomere?
A contractile unit within a muscle cell
How do muscles develop and from where are they derived?
- From the myotomes (derived from dermomyotomes) of the somites, therefore mesodermal tissue
- Process is called myogenesis
- Somite cell differentiation is induced by Shh from the notochord
- Dermomyotome expresses Pax3+ and Pax7+ (positive) cells, which are myoblasts that can then divide and migrate (Pax3/Pax7 positive cells are able to release muscle precursor cells during development, e.g. myoblasts and satellite cells)
- Myoblasts withdraw from the cell cycle and express transcription factors MyoD and Myf5
- > these activate genes for muscle cells
How are multinucleate cells of skeletal muscle formed?
- Through the fusion of myoblasts (multinucleate fibres produced by fusion of myoblasts are called myotubes)
- Myotubes then develop into mature tubular cells (multinucleate syncytium)
- In skeletal myocytes, striated structure is seen
What are all of the different terms for muscle cells?
- Myocytes
- Muscle fibres
- Muscle cells
- Myofibrils
What stain is used to recognise striated muscle?
Paraffin stains
How can skeletal muscle be identified?
Aka striated or voluntary muscle
- Cells are cylindrical
- Multinucleate, nuclei are elliptical and located peripherally within the cell
- Cytoplasm shows alternating light and dark patterning using paraffin stains in longitudinal sections
- > striations are the result of overlapping contractile elements
Where are the satellite cells located in skeletal muscle?
On the periphery/outside of cells, allow small amount of regeneration
What sort of blood supply is available to striated muscle cells?
- Rich capillary network formed
- Blood vessels penetrate muscles
- Vessels run parallel and between various muscle fibres
What are the gross structures of skeletal muscle in increasing size?
- Sarcomere
- Microfilaments
- Myofibrils
- Muscle fibre
- Myocyte
- Muscle tissue
What is the epimysium?
- Sheath of connective tissue that surrounds individual muscles
- Extends inwards to form the septa (dividing walls) of the perimysium
What is the perimysium?
- Sheaths of connective tissue that surround fascicles of muscle
- Linked to the epimysium
What are fascicles?
Bundles of tissue surrounded by perimysium that contains hundred/thousands of muscle fibres
What is the endomysium?
- Sheath of connective tissue around individual muscle fibres
- Contained within the fascicles
What do the surrounding connective tissue layers allow for?
- Entry and exit of arteries, nerves, lymphatics and veins
- Freedom of movement is allowed between fascicles and muscle fibres (connective tissue reduces friction)
- Continuity of connective tissue allows for all forces generated to be transmitted to the tendons
Where do skeletal muscles attach to?
- Bone via tendons (strong structures of dense regular connective tissue, continuous with the various sheaths surrounding muscles)
- Tongue and pharynx muscle attach to investments of connective tissue instead of bone, allowing their movements
- Smaller fascicles within long muscles may also end in tapering points attaching to the connective tissue sheaths within the muscle tissues