LS4004 Muscle 1 Essays

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Human Physiology I
Basic Skeletal Muscle
Structure
Dr Jan Lauritzen,
Room MB1006,
Email: j.lauritzen@kingston.ac.uk
J S Lauritzen
Muscle Physiology

Learning Objectives
• At the end of this lecture you should be able to:– Describe the ultrastructure of skeletal muscle fibres and the function of these components. • Directed Reading
Human Physiology:An Integrated Approach (2013) Pearson
New International Edition / Interactive Physiology 10System Suite CD-ROM by Dee Unglaub Silverthorn.
J S Lauritzen
Muscle Physiology

Properties of muscle tissue
• Specialized for contraction.
• Has distinct properties from those of other cells.
• Cytoplasm is referred to as sarcoplasm.
• Cell membrane is referred to as sarcolemma. J S Lauritzen
Muscle Physiology

Muscle tissue Location

Functions

Skeletal

Combined with connective and nervous tissue in skeletal muscles
In organs such as skeletal muscles of limbs

Moves or stabilizes skeleton
Guards entrances and exits of digestive, respiratory and urinary tracts
Generates heat
Protects internal organs

Cardiac

Heart

Circulates blood
Maintains blood (hydrostatic) pressure

Smooth

Encircles blood vessels
In walls of digestive, urinary and reproductive organs Moves food, urine and reproductive tract secretions
Controls diameter of respiratory passages Alters tissue blood flow by regulating diameter of blood vessels

J S Lauritzen
Muscle Physiology

Types of Muscle

Striated
Voluntary

Striated
Involuntary
J S Lauritzen
Muscle Physiology

Non-striated
Involuntary

Functional components of a skeletal muscle
Motor neurons





Nerve cells whose axons innervate skeletal muscle fibres.
Cell bodies located in brainstem or spinal cord.
Axons are myelinated.
Large diameter and hence propagate action potentials at high velocities.

Neuromuscular junction





Site where nerve fibre and muscle fibre meet.
Region of single muscle fibre membrane lying directly under terminal portion of axon specialized to form a motor end plate.
Membranes of nerve fibre and muscle fibre are separated by synaptic cleft.
Transmission across cleft is mainly via acetylcholine (ACh).

Motor unit





Comprises a motor neuron and muscle fibres it controls.
Number of muscle fibres in motor unit varies considerably.
The fewer muscle fibres in motor unit, the finer the movement.
Coarse movements are associated with larger numbers of muscle fibres per motor unit.
J S Lauritzen
Muscle Physiology

Structural components of a skeletal muscle
Sarcomere





Elementary motor of skeletal muscle.
Bounded by Z lines (disks).
Mainly contains contractile proteins: actin, myosin and tropomyosin-troponin.
Also contains myoglobin (for O2 storage and transport).

Myofibrils

• Chains of sarcomeres lined up end to end.
• Many bundled in parallel within muscle cell.

Muscle fibre

• Bundle of myofibrils lying in parallel.
• Syncytium of many myoblasts having formed a single continuous cell with multiple nuclei

Muscle

• Bundle of muscle fibres sheathed in connective tissue.
J S Lauritzen
Muscle Physiology

Review
• Muscle tissue is specialised for:
– Contraction

• A motor unit consists of:
– A motor neuron and the muscle fibres it controls

• The neurotransmitter at the neuromuscular junction is:
– Acetylcholine (ACh)

J S Lauritzen
Muscle Physiology

Muscle cells formed from myoblasts. If muscle damaged form from satellite cells

J S Lauritzen
Muscle Physiology

Source of calcium

Propagation of action potentials J S Lauritzen
Muscle Physiology

J S Lauritzen
Muscle Physiology

High powered magnification of a sarcomere

Cross-sectional arrangement of the thick and thin filaments
J S Lauritzen
Muscle Physiology

Contractile Filaments
• Myosin: Resembles a golf club (shaft and a head).
– ‘Heads’ stick out at an angle of 120o to each other.

• Head has affinity for actin.
Tails have affinity for myosin.
– i.e. Tails stick together whilst heads stick to actin. J S Lauritzen
Muscle Physiology

Light chains

Heavy…