Brachial Plexus

The brachial plexus is a network of nerve fibres that supplies the skin and musculature of the upper limb. It begins in the root of the neck, passes through the axilla, and enters the upper arm.

The anterior rami of cervical spinal nerves C5, C6, C7 and C8 along with the first thoracic spinal nerve T1 forms this plexus.

The Brachial plexus is divided into Roots, Trunks, Divisions, Cords and Branches for easier understanding. This division is of no functional and practical significance. Roots and trunks lie in the neck in relation with the subclavian artery, divisions lie behind the clavicle, and cords and branches lie in the axilla around the axillary artery.

Roots of the Brachial Plexus are the spinal nerve rami from where it originates. As we already saw the roots are C5, C6, C7, C8 and T1. At each vertebral level, a pair of spinal nerves arise on either side through intervertebral foramina and divides into anterior and posterior nerve fibres. The posterior rami innervate the skin and muscles of the body. The anterior rami form the plexus.

At the base of the neck, the roots join together to form the trunks. They are Superior, Middle and Inferior trunks. While C5 and C6 forms the superior trunk and C8 and T1 forms the inferior trunk, the middle trunk is a continuation of C7. These trunks move laterally and cross the posterior triangle of the neck.

In the posterior triangle of the neck, the trunks divide into two branches one of which moves anteriorly and the other moves posteriorly, thus forming anterior and posterior divisions. The three anterior and three posterior nerve fibres thus formed moves to the axilla.

These divisions join together to form cords in the axilla. The cords are named based on its relative position to the axillary artery. Anterior divisions of superior and middle trunks merge together to form lateral cord and all the posterior divisions merge together to form posterior cord. The anterior division of inferior trunk continues as the medial cord.

The cords give out five major branches in and around axilla which are the main innervations of the upper limb. They are as follows.

Musculocutaneous Nerve arising from Roots C5, C6 and C7. Its motor Functions is to Innervate the brachialis, biceps brachii and coracobrachialis muscles. It gives off the lateral cutaneous branch of the forearm, which innervates the lateral half of the anterior forearm, and a small lateral portion of the posterior forearm.

Branches of the Brachial Plexus
Branches from the roots
• Nerve to serratus anterior (C5, C6, C7)
• Dorsal scapular nerve (C5)
• Muscular branches to the 3 scalene muscles
Branches from the trunks
• Suprascapular nerve (C5, C6)
• Subclavius nerve (C5, C6)
Branches from the cords
o Medial cord
• Medial head of median nerve (C8, T1)
• Medial pectoral (C8, T1)
• Ulnar nerve (C8, T1)
• Median cutaneous nerve of forearm (C8, T1)
• Medial cutaneous nerve of arm (T1)
o Lateral cord
• Lateral pectoral (C5, C6, C7)
• Lateral head of median (C5, C6, C7)
• Musculocutaneous (C5, C6, C7)
o Posterior cord
• Radial (C5,C6,C7,C8,T1)
• Axillary (C5, C6)
• Nerve to latissimus dorsi (C6, C7, C8)
• Subscapular (C5, C6)

Axillary Nerve originates from C5 and C6and innervates the teres minor and deltoid muscles. It gives off the superior lateral cutaneous nerve of the arm, which innervates the inferior region of the deltoid (“regimental badge area”). Median Nerve originates from C6 – T1. (Also contains fibres from C5 in some individuals) and innervates most of the flexor muscles in the forearm, the thenar muscles, and the two lateral lumbricals that move the index and middle fingers. It gives off the palmar cutaneous branch, which innervates the lateral part of the palm, and the digital cutaneous branch, which innervates the lateral three and a half fingers on the anterior (palmar) surface of the hand. Radial Nerve arises from C5-C8 and T1 and innervates the triceps brachii and the extensor muscles in the posterior compartment of the forearm. It also innervates the posterior aspect of the arm and forearm and the posterior, lateral aspect of the hand.Ulnar Nerve is formed from C8 and T1. It innervates the muscles of the hand (apart from the thenar muscles and two lateral lumbricals), flexor carpi ulnaris and medial half of flexor digitorum profundus. It senses the anterior and posterior surfaces of the medial one and half fingers and associated palm area.

Clinical Significance:

There are two major types of injuries that can affect the brachial plexus. An upper brachial plexus injury(Erb’s Palsy) affects the superior roots, and a lower brachial plexus injury(Klumpke Palsy) affects the inferior roots.

Erbs Palsy results in abduction at the shoulder, lateral rotation of the arm, supination of the forearm, and flexion at the shoulder. Loss of sensation down the lateral side of the arm, which covers the sensory innervation of the axillary and musculocutaneous nerves.

The affected limb hangs limply, medially rotated by the unopposed action of pectoralis major. The forearm is pronated due to the loss of biceps brachii. This is position is known as ‘waiter’s tip’, and is characteristic of Erb’s palsy.

Nerves originating from the roots C5 and C6 are affected, including Musculocutaneous and Axillary.

In Klumpke Palsy, Ulnar and median nerves originating from T1 are affected. All the small muscles of the hand (the flexors muscles in the forearm are supplied by the ulnar and median nerves, but are innervated by different roots).  Loss of sensation along the medial side of the arm. The metacarpophalangeal joints are hyperextended, and the interphalangeal joints are flexed. This gives the hand a clawed appearance.

Innervation to remember

Terminal Branch Sensory Innervation Muscular Innervation
musculocutaneous nerve Skin of the anterolateral forearm Brachialis, biceps brachii, coracobrachialis
axillary nerve Skin of lateral portion of the shoulder and upper arm Deltoid and teres minor
radial nerve Posterior aspect of the lateral forearm and wrist; posterior arm Triceps brachii, brachioradialis, anconeus, extensor muscles of the posterior arm and forearm
median nerve Skin of lateral 2/3rd of hand and the tips of digits 1-4 Forearm flexors, thenar eminence, lumbricals of the hand 1-2
ulnar nerve Skin of palm and medial side of hand and digits 3-5 Hypothenar eminence, some forearm flexors, thumb adductor, lumbricals 3-4, interosseous muscles

Cranial Nerves

CN I – Olfactory
CN II – Optic
CN III – Oculomotor
CN IV – Trochlear
CN V – Trigeminal
CN VI – Abducens
CN VII – Facial
CN VIII – Auditory
CN IX – Glossopharyngeal
CN X – Vagus
CN XI – Accessory
CN XII – Hypoglossal

Most of the nerves originate from the spinal cord. The remaining nerves which originate directly from the Brain are called Cranial Nerves. 10 of 12 of the cranial nerves originate in the brainstem. Cranial nerves relay information between the brain and parts of the body, primarily to and from regions of the head and neck.

The cranial nerves are considered components of the peripheral nervous system (PNS), although on a structural level the olfactory, optic and terminal nerves are more accurately considered part of the central nervous system (CNS).

All the cranial nerves are paired and are present on both sides.
There are twelve cranial nerves pairs, which are assigned Roman numerals I–XII. Some experts argue that there are 13 cranial nerves including nerve ‘zero’. The numbering of the cranial nerves is based on the rostral-caudal (front to back) position in which they emerge from the brain.
The Cranial Nerve Zero is a very small terminal nerve (nerve N or O) existing in humans but may not be functional. In other animals, it appears to be important to sexual receptivity based on perceptions of pheromones.

Some Important Points to Remember

1. The only cranial nerve which arises on dorsal aspect – Trochlear nerve

2. The cranial nerve with longest intracranial course – Trochlear nerve

3. The cranial nerve with the longest course – Vagus ( Vagabond Nerve / Wandering Nerve )

4. The cranial nerve most commonly involved in raised intracranial tension – Abducens

5. The cranial nerve most commonly involved in basal skull fractures – Facial Nerve

6. Commonest cranial nerve affected in spinal anaesthesia – Abducens

7. Cranial nerves carrying parasympathetic fibres – 3, 7, 9, 10

8. Thinnest cranial nerve – Trochlear Nerve

9. Thickest cranial nerve – Trigeminal Nerve

10. Cranial nerve palsies in which deviation occurs to the healthy side (opposite side ) – VII and X

11. Cranial nerve palsies in which deviation occurs to same side (diseased side ) – V and XII

12. Cranial nerve involved in Bell’s palsy – VII

13. Cranial nerve involved in herpes zoster ophthalmicus – V

14. Cranial nerve involved in Ramsay hunt syndrome – VII

15. TIC Douloureux – Neuralgia of V nerve ( Trigeminal Neuralgia )

16. Neuralgic pain in the tongue, soft palate, pharynx – Neuralgia of glossopharyngeal nerve

Joints of the Body

A joint is defined as the point at which two or more bones articulate. Joints can be easily classified by the type of tissue present. Using this method, we can split the joints of the body into fibrous, cartilaginous and synovial joints.

Fibrous joints can be further subclassified into sutures, gomphoses and syndesmoses.

Sutures are immovable joints (called a synarthrosis), only found between the flat, plate-like bones of the skull.

Gomphoses are also immovable joints and can be found where the teeth articulate with their sockets, with periodontal ligaments.

Syndesmoses are slightly movable joints (called an amphiarthrosis) comprised of bones held together by an interosseous membrane. Eg: The middle radio-ulnar and middle tibiofibular joint

Cartilaginous joints have bones attached with fibrocartilage or hyaline cartilage.

Synchondroses or primary cartilaginous joints involve only hyaline cartilage. The joints can be immovable (synarthroses) or slightly movable (amphiarthroses). Eg: The joint between the diaphysis and epiphysis of a growing long bone

Symphyses or secondary cartilaginous joint can involve fibrocartilage or hyaline cartilage and are slightly movable (amphiarthroses), an example of a which is the pubic symphysis.

A synovial joint is a joint filled with synovial fluid which tends to be fully moveable (diarthroses), and are the main type of joint found in the body. They allow a huge range of movements are classified by their movement.

Hinge Permits flexion and extension. Elbow joint is a notable example.
Pivot Allows rotation; a, round bony process fits into a bony ligamentous socket. Examples include the atlantoaxial joint & proximal radio-ulnar joint (top of the neck and elbow)
Ball & Socket Permits movement in several axes; a rounded head fits into a concavity. An example is the glenohumeral joint (shoulder).
Saddle Concave and convex joint surfaces unite at saddle joints, e.g. Metatarsophalangeal joint (toes)
Plane Permit gliding or sliding movements, e.g. Acromioclavicular joint (collarbone to shoulder blade)
Condyloid Permits flexion, extension, adduction, abduction and circumduction e.g. Metacarpophalangeal joint (in the middle of your hand).

Anatomical Terms for Movements

Flexion refers to a movement that decreases the angle between two body parts.

Extension refers to a movement that increases the angle between two body parts.

Abduction is a movement away from the midline – just as abducting someone is to take them away.

Adduction is a movement towards the midline.

Medial rotation is a rotational movement towards the midline. It is sometimes referred to as internal rotation.

Lateral rotation is a rotating movement away from the midline.

Elevation refers to movement in a superior direction (e.g. shoulder shrug), depression refers to movement in an inferior direction.

Pronation at the forearm is a rotational movement where the hand and upper arm are turned inwards. Pronation of the foot refers to turning of the sole outwards so that weight is borne on the medial part of the foot.

Supination of the forearm occurs when the forearm or palm are rotated outwards. Supination of the foot refers to turning of the sole of the foot inwards, shifting weight to the lateral edge.

Inversion and eversion refer to movements that tilt the sole of the foot away from (eversion) or towards (inversion) the midline of the body.

Dorsiflexion refers to flexion at the ankle so that the foot points more superiorly. Dorsiflexion of the hand is a confusing term, and so is rarely used. The dorsum of the hand is the posterior surface, and so movement in that direction is the extension. Therefore we can say that dorsiflexion of the wrist is the same as the extension.

Plantar Flexion refers extension at the ankle so that the foot points inferiorly. Similarly, there is a term for the hand, which is palmar flexion.

Trios from Homeopathic Materia Medica

Trio of Condylomata – Thuja, Staphysagria, Nitric Acid – (Nash)
Trio of Cholera – Camphor, Veratrum Alb, Cuprum Metallicum
Trio of Climacteric Remedies – Lachesis, Sepia, Sulphur
Trio of Offensive Urine – Nitric Acid, Kreosotum, Sepia
Trio of Offensiveness – Mercurius Solubilis, Kreosotum, Baptisia Tinctoria – (Nash)
Trio of Pain – Coffea, Chamomilla, Aconitum Napellus
Trio of Pleurisy – Aconitum Napellus, Bryonia Alba, Sulphur – (Nash)
Trio of Ptosis – Sepia, Causticum, Gelsemium – (Nash)
Trio of Restlessness – Aconitum Napellus, Arsenic Alb, Rhus Toxicodendron
Trio of Spasmodic Cough – Drosera, Ipecacuanha, Cuprum Metallicum – (Nash)
Trio of Weakness – Arsenic Alb, Muriatic Acid, Carbo Vegetabilis – (Nash)
Three Remedies for the Treatment of Chronic Rheumatism And Paralysis – Causticum, Rhus Toxicodendron, Sulphur – (Nash)