Lesson 7: Ch.12: Microscopic Anatomy and Organization of Skeletal Muscle (2/3)

muscle cells

• composed of multi-nucleated cells (muscle fibers)

• consists of myofibrils (contractile units)

myofibrils (contractile units)

composed of myofilaments

myofilaments

composed of the contractile protein subunits:

1. actin

2. myosin

actin

forms the thin filaments, anchored by the Z disc

myosin

forms the thick filaments, anchored by the M line

sarcomere structures

1. sarcomere

2. transverse

3. sarcoplasmic reticulum

4. triad

sacromere

• smallest functional contractile unit of muscle

• from Z disc of an I band to next Z disc

transverse (T) tubule

indention of the sarcolemma (plasma membrane) forms a tubule at A/I band junction

A/I band junctoion

A band + I band

A band

region of sarcomere of containing thick filaments

I band

region of sarcomere containing only thin filaments

sarcoplamic reticulum

muscle cell’s smooth endoplasmic reticulum, used to store calcium (Ca²⁺) ions

triad

structure consisting of two terminal cisterns of the sarcoplasmic reticulum and a transverse tubule between them

endomysium

connective tissue where muscle fibers are ensheathed

perimysium

collagen membrane that ensheathed muscle fibers are bundled together in

fascicle

a fiber bundle resulting from ensheathed muscle fibers being bundled together in perimysium

epimysium

dense connective tissue that bundles fascicle bundles together

aponeuroses

falttened sheet of tendon

extension of the three connective tissues (endomysium, perimysium, & epimysium) from their bundles then combine to form

tendons or aponueroses

When does muscle contract

when it receives a signal from a neuron at the neuromuscular junction

meuromuscular/myoneural junction

area where a neuron’s (nerve cell) axon interacts with muscle cell

important structures of the neuromuscular junction

• moto unit

• synaptic cleft

motor unit

a motor neuron & muscle cells/fibers it targets

synaptic cleft

fluid filled gap between the nerve axon terminal and muscle fiber