- Long (up to 130mm) multinucleate cells / syncitia
- nuclei lie peripherally, immediately below sarcolemma
- contractile elements (myofibrils) extend throughout length of fibre
- Structure
- interface between muscle and connective tissue includes epimysium, perimysium and
endomysium sheaths
- myofibrils organised into repeating contractile units - sarcomeres, this gives striated
appearece
- sarcomeres contain overlapping arrays of myofilaments organised into A (myosin) bands and I (actin) bands which are
attached by Z discs at the end of the sarcomere by associated protein.
- a-actinin, titin and nebulin involved in maintianing
structure
- Muscle contraction initiated by rise in cytosolic Ca++
- depolarising signal carried by transverse or T-tubules to sarcoplasmic reticulum
- arranged at regular intervals along actin filament are regulatory proteins troponin and tropomyosin
-
- innervation of skeletal muscle is by fibres of somatic motor system and takes place at
motor end plate (NMJ)
- diseases of NMJ (myasthenia gravis) lead to muscle weakness
- Sub-classification of fibres into
- fast twitch (white muscle)
- Slow twitch
- fast contracting fatigue-resistant
- fast contracting fatigue-susceptible
- slow contracting fatigue-resistant
- hypertrophy or atrophy are response of muscle to inflammation opr injury
- some myoblasts persist as quiescent stem cell (satellite cells) in adult
6.8.1 Skeletal Muscle [Phys]
| Action potential in muscle. Trigger for contraction.
Ultrastructure of muscle (myofibrils; actin and myosin; cross-bridges). Banding
(striations) of muscle. Mechanism of contraction (sliding-filament theory). Theory of
cross-bridge cycling (and force development). Mechanism of excitation-contraction coupling
(t-tubules; link between t-tubules and sarcoplasmic reticulum Ca2+-release;
disinhibition by Ca2+i of actin-sites for Ca2+i-binding,
giving contraction). Mechanism of relaxation (sarcoplasmic reticulum, Ca2+
ATPase). Motor units and frequency of firing (for gradation of force; tetanic tension). |
Length–tension curve of muscle. Electron microscopy
of muscle. 3-D arrangement of myofilaments. Relation of sliding-filament theory to
length-tension relationship. |
|