Muscle Tissue

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Muscle is specialised for contraction and transmission of impulses that aid contraction

Characterised by ability to contract

3 types based on:

Organisation/appearance of cells

Nervous control

Location in the body

Muscles have very specific and limited functions - highly specialised

Associated with CT and nervous tissue

Contraction due to interaction of actin and myosin as microfilaments in the sarcoplasm

Transmission of force goes through connective tissue of collagen fibres

Outermost covering (fascia) is connected to origin/insertion/tendons/ligaments

No connective tissue means no force transmitted

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Types:

Striated Muscle:

Characteristic banding pattern visible on light microscope

Skeletal muscle: voluntary muscle

Cardiac muscle: involuntary muscle

Smooth muscle:

Visceral or "involuntary" muscle

Found in internal organs and other locations

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CT forms basework:

Endomysium surrounds individual cells

Perimysium surrounds muscle bundles

Epimysium surrounds entire muscle

Specialisation has caused loss of other capabilities such as ability to divide. Repair is by scarring.

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Muscle repair:

Highly differentiated muscle cells cannot divide

Injury will cause a loss of material. Scarring will fill in the space with collagen, but collagen is not contactible, which causes loss of function

Skeletal muscle has a reserve of myoblasts, meaning they may regenerate but not much.

No regeneration in cardiac and smooth muscles.

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Neural relationship in muscle:

Varies with the muscle type:

Skeletal muscle most elaborate

Smooth muscle simple but direct

Cardiac muscle controlled by non neuronal network and internally

Control is monitored closely by the central nervous system (brain & spinal cord)

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Skeletal Muscle

Appearance:

Striation

Long fibres

Multinucleated (peripheral ie. sits on the side of cells.)

Very large cells 100-150 microns diameter and several centimeters to a meter of length

Blood vessels between

Invested by intercellular collagen

Nervous control:

Somatic (voluntary)

Location:

Usually attached to bones of skeleton

Definitions:

Muscles are bundles of individual cells, MYOFIBERS

MYOFIBERS contain contractile MYOFIBRILS (1000)

MYOFIBRILS are composed of MYOFILAMENTS (1000)

MYOFILAMENTS are organized in SARCOMERES (1000)

SARCOMERE is the basic unit of contraction and contains Actin and Myosin

Myosin: Multiple heads at each end of a long molecule - filament. Heads change angle.

Actin: Receptor sites for heads in long filament

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Bands:

I-band: Only Actin

A-band: Actin and myosin

H-Band: Only myosin

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Cardiac Musles

Cells:

Striation (not easy to see under Light Miscroscope)

Branched

Mononucleated

Nervous Control:

Visceral (involuntary)

Contraction not an inherent property

No direct neuronal stimulation needed

Location:

Heart

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Myocytes of cardiac muscle are individual cells that are much smaller that myofiber of skeletal muscle. MONONUCLEATED with the nucleus in the center

Myocytes butted end-to-end to form anastomosing network (cross connection)

Extremely well vascularised

Capillaries lies among and between cells

Cardiac muscle can not sustain any oxygen deficit (need O2 )

unique intercalated disk - Diagnostic feature of cardiac muscle

Contain myofibrils and sarcomeres

Cardiac fibres surrounded by loose connective tissue

No perimysium

Connective tissue surrounding heart is called epicardium

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Smooth Muscle

Cells:

Fusiform cells

No striations

Each cell only has one oval nucleus in the centre

Not branched

No sarcomeres but have actin and myosin so can still contract. But float inside muscle cell rather than align.

Nervous cells:

Involuntary

Location:

Walls of GIT, airways and urogenital tracts