Review of Terminology(the “sarco-” words)

• Sarcolemma – the cell membrane of a muscle fiber.

• Sarcoplasm – the cytoplasm of a muscle fiber.

• Sarcoplasmic reticulum – the endoplasmic reticulum of a muscle fiber.

• Sarcomere – the smallest unit of contraction within a myofibril.

Sarcomere

Sarcolemma

Sarcoplasmic Reticulum

A similar picturecan be found on page 169 of the reading packet,figure 8.4.

* Note that the sarcoplasmic reticulum “surrounds” each myofibril.

* Also note that the sarcoplasmic reticulum seems to form repeating units that “surround” individual sarcomeres.

Z-line Z-line

Review of Terminology(the “myo-” words)

• Myocytes – a muscle fiber or cell.• Myofibrils – units of alternating

filamentous proteins contained within the sarcoplasm of a muscle fiber and which extend from end to end within the fiber.

• Myofilaments – filamentous proteins called actin (thin) filaments and myosin (thick) filaments.

sarcomere

Myofibril

* Note that a sarcomere is a repeating unit of contraction within the myofibril.

* The myofibril can be seen to be made up of repeating units of overlapping myofilaments.

Myofilaments

• Thick myofilament– Myosin

• Thin myofilament– Actin

• Arrangement is so orderly that the muscle looks striped or “striated” microscopically

sarcomere

sarcomere lengthened

shortened

New Terminology

• T-tubules – extensions of the sarcolemma which carry “electrical” impulses deep within a muscle fiber.

• This allows the impulse to be brought very close to the sarcoplasmic reticulum throughout the fiber, and thus to get very close to each and every sarcomere.

Skeletal Muscle Fiber(Myocyte)

sarcoplasmic reticulum (the “blue” tubes)

T-tubules (the “purple” tubes)

Myofibril

A similar picturecan be found on page 169 of the reading packet,figure 8.4.

Sarcolemma

Motor Unit(page 170; figure 8.6)

• Defined as a motor neuron and all the muscle fibers it innervates

• By using more motor units, the muscle contracts with more force.

• A small number are used in muscles with fine control

• A large number are used in muscles with crude control

Neuromuscular Junction(page 170; figure 8.5)

• This is defined as the place where the motor neuron axon “connects” to the muscle fiber.

• It is also the site where the motor neuron stimulates the muscle fiber to begin the sequence known as Action Potential and eventually contraction.

Signal from brain

Motor end plate

Axon branch of motor neuron

Motor End Plate

Neuromuscular Junction

Our Goals !!

• 1. To define and track the sequence of “electrical” events which happen in a phenomenon called “Action Potential”.

• 2. To define and track the sequence of interactions between myofilaments that occur during contraction and relaxation of muscle tissue.

• 3. To determine the connections between numbers one and two above.