Muscles and Muscle Tissue

In today's instalment on Anatomy and Physiology, we really get into the meat (pun intended) of the subject; the muscles. 

The human body has three types of muscle tissue, Cardiac, Smooth and Skeletal.  While all three types of muscle tissue are critical to our health and well-being, we are only going to concern ourselves with skeletal muscle.  After all, these are the muscles we tirelessly work at getting bigger and stronger!

Skeletal muscle is responsible for overall body mobility.  It can contract rapidly, but it tires easily and must rest after short periods of activity.  Nevertheless, it can exert tremendous power and are remarkably adaptable.  For example your forearm muscles can exert a force of a fraction of a gram to pick up a paper clip or, a force of several kilograms to pick up a kettlebell.

Muscle performs at least four important functions for the body.  It produces movement, maintains posture, stabilises joints and generates heat, amongst a range of other things.

Producing Movement

Almost all movements of the body result from muscle contraction.  Skeletal muscles are responsible for all movement and manipulation.  They enable you to respond quickly to changes in the external environment, e.g.  a boxer ducking under a high punch.

Maintaining Posture

We are rarely aware of the skeletal muscles that maintain body posture.  Yet these muscles function almost continuously, making tiny adjustments to counteract the never ending downward pull of gravity.

Stablising Joints

Even as muscles pull on bones to create movement, they are also continually stabilising and strengthening the joints.

Generating Heat

Muscles generate heat as they contract.  This heat is vitally important in maintaining normal body temperature.

Skeletal Muscles Names

Skeletal muscles are named according to a number of criteria.  To simplify the task of learning muscle names and actions, I’ve provided a number of cues.

• Muscle location.  Some muscle names indicate the bone or body region with which the muscle is associated.
• Muscle shape.  Some muscles are named for their distinctive shapes, e.g. the deltoid muscle is roughly triangular.
• Muscle size. Terms such as ‘maximus’ (largest), ‘minimus’ (smallest), ‘longus’ (long) and ‘brevis’ (short) are often used in muscle names, e.g. gluteus maximus.
• Direction of muscle fibres. The names of some muscles reveal the direction in which their fibres run in relation to some imaginary line, usually the midline of the body or the longitudinal axis of a limb bone.  In muscles that have the term ‘rectus’ (straight) in their names, the fibres run parallel to that imaginary line, e.g. rectus abdominus.  ‘Transversus indicates that the muscle fibres run at right angles to that line, and ‘oblique’ indicates that the fibres run obliquely to it, e.g. transverse abdominus.
• Number of origins. When ‘biceps’, ‘triceps’, or ‘quadriceps’ forms part of the muscle name, you can assume that the muscle has two, three or four origins respectively.
• Location of the attachments. Some muscles are named according to their points of origin and insertion.  The origin of a muscle is the point at which it attaches, or begins, on the anchoring bone.  The insertion is the point at which the muscle attaches to, or terminates, on the bone that the muscle moves.  The origin is always named first.  For example, the sternocleidomastoid muscle of the neck has a dual origin on the sternum (sterno) and clavicle (cleido), and it inserts on the mastoid process of the temporal bone.
• Muscle action. When muscles are named for the movement they produce, action words such as ‘flexor’, ‘extensor’, or ‘adductor’ appear in the name.  For example, the adductor longus, which is located on the inner thigh, brings about thigh adduction, i.e. it moves the thigh towards the centreline of the body.

Often, several criteria are combined in naming a muscle.  For instance, the name ‘extensor carpi radialis longus’ tells us the muscle’s action (extensor), what joint it acts on (carpi = wrist), and that it lies close to the radius of the forearm (radialis).  It also hints at the size (longus) relative to other wrist extensor muscles.  Unfortunately, not all muscle names are this descriptive.

The scope of the muscular system is all the more impressive because of the sheer number of skeletal muscles in the body; more than 600 of them!  Remembering all of the names, locations, and actions of these muscles is a monumental task.  Do not panic, we are only going to consider the principal muscles, a lot less than 600 but a daunting prospect nonetheless.

As you learn the names of the muscles, try to gain an understanding of what they actually do, functionally.  This will help enormously in developing your understanding of both Anatomy and Physiology.

Shoulder Muscles

Trapezius

Deltoid: Anterior, Lateral& Posterior

Front Torso Muscles

Pectoralis: Minor & Major

Serratus Anterior

Intercostals

Rectus Abdominis

Obliques: External & Internal

Transversus Abdominis

Back Torso Muscles

Intraspinatus

Teres Major

Rhomboid Major

Latissimus Dorsi

Pelvis / Hip Muscles

Iliopsoas

Gluteous : Maximus & Medius

Arm Muscles

Triceps Brachii

Biceps Brachii

Brachialis

Pronator Teres

Brachioradialis

Flexor Carpi Radialis

Palmaris Longus

Extensor Carpi Radialis Longus

Flexor Carpi Ulnaris

Extensor Carpi Ulnaris

Extensor Digitorum

Thigh Muscles

Pectineus

Tensor Fasciae Latae

Sartorius

Adductor Longus

Gracilis

Rectus Femoris

Vastus Lateralis & Medialis

Iliotibial tract

Adductor Magnus

Biceps Femoris

Semitendinosus

Semimembranosus

Lower Leg Muscles

Fibularis Longus

Extensor Digitorum Longus

Tibialis Anterior

Gastrocnemius

Soleus

Fibularis Longus

Calcaneal (Achilles) Tendon

 Next time, we look at the fascinating subject of muscle metabolism.  How do our muscles utilise the various energy sources within our bodies and, when do we begin 'burning' body fat.