Chapter 8: Histology and Physiology of Muscles

CHAPTER 8:

HISTOLOGY AND PHYSIOLOGY OF MUSCLES

MUSCLES, MUSCLES, MUSCLES. We all know that this is very important and without these, we cannot move. But what is the physiology behind these muscles?

First, what are the function of the muscular movement:

1.    Body movement

2.    Maintenance of posture

3.    Respiration

4.    Production of body heat

5.    Communication

6.    Constriction of organs and vessels

7.    Heart beat

MUSCLE FIBERS:

1. Muscle fiber is a single skeletal muscle cell
2. Multinucleation
3. Large,elongated, and cylindrically shaped
4. Fibers usually extend entire length of muscle.

Myofibrils

Contractile elements of muscle fiber

Regular arrangement of thick and thin filaments

Thick filaments - myosin (protein)
Thin filaments - actin (protein)

Viewed microscopically myofibril displays alternating dark (the A bands) and light bands (the I bands) giving appearance of striations

Sarcomere

Functional unit of skeletal muscle

Found between two Z lines (connects thin filaments of two adjoining sarcomeres)

Regions of sarcomere
A band
Made up of thick filaments along with portions of thin filaments that overlap on both ends of thick filaments

H zone
Lighter area within middle of A band where thin filaments do not reach

M line
Extends vertically down middle of A band within center of H zone

I band
Consists of remaining portion of thin filaments that do not project into A band

NEUROMUSCULAR JUNCTION

Site where motor neuron meets the muscle fiber
Separated by gap called the neuromuscular cleft

Motor end plate
Pocket formed around motor neuron by sarcolemma

Acetylcholine is released from the motor neuron
Causes an end-plate potential (EPP)
Depolarization of muscle fiber

CHARACTERISTICS OF SKELETAL MUSCLE FIBER TYPES

MULTIPLE MOTOR UNIT SUMMATION IN A MUSCLE

MULTIPLE-WAVE SUMMATION

QUIZ1

QUIZ2