The Muscle System

This revision guide is meant to be used along side your lecture notes for SMBE1513/SQBS3273).

 

There aeer several functions of muscles, among others are:

  • for movement of skeleton
  • controls of opening e.g. eyelid, mouth, anus
  • stabilize joint (maintain posture)
  • produce heat through exercises, and
  • for showing emotion (facial expression)

 

Nomenclature and gross anatomy of muscles

First, you were introduced that muscles were named through several of their characters. Among these characters are:

  1. Shape e.g. deltoid muscle because it looks like the greek letter ‘delta’
  2. The number of heads e.g. biceps = 2 heads; triceps = 3 heads; quadriceps = 4 heads
  3. The location e.g. biceps brachii is so named because it is located in the arms (Lain: brachii, arm)
  4. Length – either short (brevis) or long (longus)
  5. Function – either for extension, adduction, abduction, etc.

For example, consider the muscle ‘extensor carpus radialus longus‘. You could have guessed by its name that the muscle lies between the wrist (carpus) and along the radius (radialus). It is considered long (longus) as it attaches at the distal end of the humerus (origin) to the metacarpal or palm of the hand (insertion). The name extensor indicates that the muscle’s function is to extends and abducts the wrist (continue below for explanation on muscle origin and insertion).

 

Muscles are needed for movement. For movement to happen, muscle must contract and often work in pairs. Thus, muscles are also categorized according to their functions when a movement is performed. Two examples of muscle categories are:

  1. Prime movers / agonist – which are the main muscle that carry out a function
  2. Antagonist – the opposite muscle that relaxes when prime movers contracts

 

Here is a video that explains the categories of muscles in details (LondonLeisureCollege)

 

Muscle attaches to bones through an extension of connective tissue called tendon. This structure is characteristically and functionally different from ligament. You are expected to understand how these two differs and examples where they can be located.

 

The attachment of muscle to bone/bones happens at two different sites called:

  1. Origin – part of the muscle which is stationary when movement is made, and
  2. Insertion – part of the muscle which is mobile when movement is made

Because of that, muscle can also be categorized according to the nature of their attachment. There are two categories of muscles with these features:

  1. Intrinsic
  2. Extrinsic

You are advised to understand what do these terms mean and the appropriate examples for each category.

 

Here is a good example of video explaining the origin and insertion as well as movement caused by the muscle pectoralis major (Latin: pectus, breast) (Interactive Biology)

 

Biomechanic of movement

 

The muscle exert force on the bone to cause movement. This resulted in a movement that functions just like the lever system. There are 3 classes of lever systems, each produces different level of mechanical advantage useful in the physiology of anatomy:

  1. First class lever
  2. Second class lever, and
  3. Third class lever

 

The video below give good explanation of the lever systems in anatomy (Dr. Akram Jaffar; Human Anatomy Education)

 

 

Microscopic anatomy of muscle

The muscle tissue is formed by an aggregation of muscle cells. Unlike most cells, muscle cells are long cells than extend to the length of protein fibres, called myofibrils (myo – muscle; fibril – fibre) inside the cells. These myofibrils also produces striation, unique to muscle tissue.

Myofibrils are made of three different filaments, the myofilaments, called thick, thin, and elastic filaments. Microscopically, the myofibres contain:

  • sarcomere – which is a functional unit of muscle
  • Z-disc
  • I band
  • A band
  • M line, and
  • H-zone

 

 

 

 

 

 

 

 

 

The contraction of muscle is made possible by the sliding of myofilaments in the myofibrils through mechanism called ‘the sliding filament’ theory. By now, you should be able to explain how the ‘sliding filament ‘ theory works and how the release of neurotransmitter, acetylcholine (ACH) causes muscle contraction.

 

The following is further explanation how muscle contracts (Biology/Medicine Animations)

 

 

Types of muscle tissues

There are only 3 types of muscle tissues in our body. Although they share similar microscopic anatomy (i.e. made of myofilaments, myofibres, etc), each is characteristically unique to fit their intended role. The 3 types of muscle tissues are:

  1. Skeletal muscle
  2. Cardiac muscle, and
  3. Smooth muscle

You should be able to identify how these muscle tissues are different from each other.

 

Special for the skeletal muscle, the fibres can be categorized into 2 types, which differ by their metabolic activity and their performance. The 2 categories of skeletal muscle fibres are:

  1. Slow oxidative / slow-twitch / type-I fibre – which is commonly known as dark meat
  2. Fast glycolytic / fast-twitch / type-II fibre – which is commonly known as white meat

By understanding the characters of each of the muscle fibre, you should be able to understand where they are located and how they function.

 

Introduction to Basic Anatomy & Physiology

This website meant to help students with their revision for the course Basic Anatomy and Physiology (SMBE1513) and Animal Physiology (SQBS3273). Revision is for topics covered by Saleha Shahar.

My main reference is Principles of Anatomy and Physiology, 12th Ed. by Gerard J. Tortora and Bryan H. Derrickson.

I also used online videos and websites for additional references. The links will be provided where needed (but remember, these are supportive sources to help you understand your main notes, which comes from Tortora and Derrickson).

 

In our first class, you were introduced to examples of common terminology used in Anatomy and Physiology:

  • Metabolism – which can be divided into two categories; catabolism and anabolism
  • Differentiation – which is different from growth or reproduction
  • Homeostatis – which is regulated by two different responses; positive feedback and negative feedback
  • Aging and death – which is inevitable

 

Next, you were introduced with the six level of organizations that made up a complete anatomy and physiology:

  • Chemical level – which is divided into inorganic component (water) and organic components (generally, complex structure that contains carbon and hydrogen)
  • Cellular level – which shows how numerous organelles in a cell contribute to the specific function of a cell (you have to know these organelles and their functions)

Cellular level of organization by Bozeman Science

  • Tissue level – which essentially compose of four types of tissues; epithelial tissue, muscle tissue, nervous tissue, and connective tissue (you have to know common examples for each types of tissue)

Tissue level of organization by Bozeman Science

  • Organ level
  • System level, and
  • Organismal level

 

In the next class, you will be introduced to the first system level of organization of the anatomy, the skeletal system.

The Skeletal System

In this class, you were introduced with the anatomy of skeletal system followed with the physiology of the system. Below are guides and videos links to help with your revisions. Remember, this guide must be used along side of your lecture notes.

 

First, you were introduced with terminology pertaining to the anatomical position. By now, you must be able to use terms:

  • medial – which is location closer to mid-line
  • lateral – which is location away from mid-line
  • proximal – location close to origin or joint
  • distal – location away from origin or joint
  • anterior – which is the opposite of posterior/dorsal
  • dorsal – which is opposite of ventral/anterior
  • superior – which is opposite of inferior

 

Here is an example use of anatomical terminology

 

Learning the skeletal system

The skeletal bones can be identified through four basic shapes. You have to know examples of bones that falls under each of these shapes:

  1. Long bones
  2. Short bones
  3. Irregular bones, and
  4. Flat bone

 

Bones carry certain characters that helps in their functions at providing support, for motion and protection. Again, you are recommended to understand the meaning of these terms and their appropriate examples. Among the characters of bone are:

  1. Fossa
  2. Sinus
  3. Foramen
  4. Meatus
  5. Condyles

 

The skeletal system can be systematically divided into two divisions. You have to know the example of bones for every components that make up this divisions.

  1. The axial skeleton – consists of the skull, hyaoid, sternum and ribs, and vertebral column
  2. The appendicular skeleton – consists of the upper extremities girdle (pectoral girdle) and lower extremities girdle (pelvic girdle)

 

The following is a summary of what we have covered so far

 

Relation of structure and function

From knowing the general features and functions of bones, you were introduced with examples of pathologies of the skeletal system.Through this, you should be able to appreciate how the structure of bones fit its functions. Among the skeletal pathologies that were introduced to you were:

  • Abnormalities of the vertebral column
  • Slipped disc/herniated disc
  • Osteoarthritis – which is different from rheumatoid arthritis
  • Damages to the calvarium (skullcap) and the face

 

The microscopic structure of the bones

Apart from gross anatomy of the skeletal system, you were also introduced to the microscopic structure of the bones. These microscopic details helps you understand how bones grow, heals from injury, or function as calcium storage and bone marrow production. Aspects that you must understand from microscopic anatomy of the bones are:

  1. The two types of bone tissues – spongy bone versus compact/dense  bone.
  2. Osteaon – as the functional unit of compact bone, and
  3. Types of bone cells – osteogenic cells, osteoblasts, osteocytes, and osteoclasts

 

Here is an excellent video on the microscopic structure of the bone

 

Here is an summary of how none repair and modelling occurs

 

Joint and movements

Finally, we end the topics with joints and movements. You are must be able to recall the four types of joints and where they are located:

  1. Bony joints / synostosis
  2. Fibrous joints
  3. Cartilaginous joints
  4. Synovial joints – which can be divided into ball and socket, condylar/ellipsoidal, saddle, plane/gliding, hinge, pivot.

 

The movement of the skeletal system happens at three different movement planes:-

  1. Frontal/coronal plane
  2. Sagittal plane, and
  3. Transverse plane

You should be able to recall and demonstrate movements on the above planes such as:

  • flexion and hyperflexion
  • extension and hyperextension
  • abduction and hyperabduction
  • adduction and hyperadduction
  • protraction versus retraction
  • circumduction versus rotation
  • supination versus pronation
  • dorsiflexion versus plantarflexion

 

Here is an example of movement on the three planes of movement

 

The next posting will touches on the muscle system.