Kinesiology: The Myotomes

Image by Tamityville via Flickr

Today I will introduce a series of posts entitled "Kinesiology:" which will deal with the interesting facts and information that I've learned throughout my years in university. If you could, give me your opinions whether you liked this post, and whether you would like similar in the near future in the comments section.

   I have finished a Bachelor of Science in Kinesiology and Health Science program, and know a reasonable amount of background information on the subjects pertaining to health and physical activity. Today I will start  off with a brief introduction to Myotomes and their testing.

   Myotomes are defines as a groups of muscles supplied by a single nerve root. It also has to be noted that spinal nerves come in pairs, one from the left side and the other from the right side. So an injury to a single nerve root (either right or left) is associated with muscle weakness (a.k.a. incomplete paralysis) of the myotome (left side or right side muscles) supplied by that nerve root. When testing a myotome, key muscles are tested for weakness, not pain.

Image by EUSKALANATO via Flickr

   Myotomes are tested according to the principles of muscle testing and graded according to the findings. Usually muscles are graded according to percentage, or 0 - 5, when compared bilaterally to the unaffected side. Where 0 is "No response; total paralysis", and 5 is "100% - Normal response; segment is held against gravity with normal resistance being given to the part."

   Here is a list of upper extremity myotomes that correspond with spinal nerves C1 (Cervical 1) all through out to T1 (Thoracic 1)

C1 - None 
[None]
C2 -  Sternocaleiomastoid & Longus Colli 
[Neck Rotation]
C3 -  Trapezius & Splenius Capitis 
[Neck Flexion]
C4 - Levator Scapulae & Diaphragm 
[Shoulder Shrug & Diaphragmatic Push]
C5 - Supraspinatus, Infraspinatus & Middle Deltoid 
[Shoulder Abduction]
C6 - Biceps Brachii, Wrist Supinator & Wrist Extensor 
[Elbow Flexion & Wrist Extension]
C7 - Triceps & Wrist Flexor 
[Elbow Extension & Wrist Flexion]
C8 - Extensor Pollicis Longus, Extensor Pollicis Brevis & Abductor Pollicis Longus 
[Thumb Extension]
T1 - Hand Intrinsics, Flexor Digitorum Profundus, Flexor Pollicis & Opponens Pollicis 
[Finger Spread]

The section of T2 (Thoracic 2) to L1 (Lumbar 1) spinal nerves is mainly responsible for ribcage movement and therefore is mainly not listed in the testing of myotomes.

The lower extremity myotomes start at the level of L2 (Lumbar 2) spinal nerves down to S1&S2 (Sacral 1&2) nerves.

L2 - Illiopsoas & Hip Adductor 
[Hip Flexion]
L3 - Quadriceps Femoris 
[Knee Extension]
L4 - Tibialis Anterior & Extensor Hallucis 
[Ankle Dorsiflexion]
L5 - Extensor Hallucis, Peroneals & Gluteus Medius 
[Big Toe Extension]
S1-S2 - Hamstrings & Gastrocnemius 
[Knee Flexion]

Also as an added bonus here is a funny & educational video of all the myotomes in action

via: YouTube