Sacral Plexus

The sacral plexus is a nerve plexus which provides motor and sensory nerves for the posterior thigh, most of the lower leg and foot, and part of the pelvis.This is a continuation of Lumbar Plexus and sometimes is together referred to as Lumbosacral plexus. It is situated in the posterior pelvic wall in front of the piriformis muscle.
The lumbosacral trunk connects the lumbar plexus with the sacral plexus. The lumbosacral trunk comprises the anterior division of L5 and a part of anterior rami of the L4 and it appears at the medial margin of the psoas major and runs downward over the pelvic brim to join the first sacral nerve.
Anterior rami of S1, S2, S3 and S4 forms this plexus with contributions from L4 and L5. The nerves converge towards the inferior part of Grater Sciatic Foramen and form a flattened band and continue downwards as sciatic nerve. Some branches also arise from the flattened band in this course.
On the back of the thigh, Sciatic Nerve splits into the tibial nerve and common fibular nerve.
Posteriorly the plexus is related to piriformis muscle and anteriorly to the pelvic fascia. The internal iliac artery, internal iliac vein, the ureter, and the sigmoid colon also are anterior to this plexus. The superior gluteal artery and vein are between the lumbosacral trunk and the S1, and the inferior gluteal artery and vein are between the S2 and S3.
Superior Gluteal Nerve, Inferior Gluteal Nerve, Sciatic Nerve, Posterior Femoral Cutaneous Nerve, and the Pudendal Nerve, are the major branches of this plexus.
In addition to the five major nerves of the sacral plexus, Nerve to piriformis, Nerve to obturator internus, Nerve to quadratus femoris also arise from this plexus. These tend to be nerves that directly supplying muscles, except the perforating cutaneous nerve, which supplies the skin over the inferior gluteal region and the pelvic splanchnic nerves, which innervate the abdominal viscera.

Nerves of the sacral plexus
Nerve Segment Innervated muscles Cutaneous branches
Superior gluteal nerve L4-S1 Gluteus medius muscle
Gluteus minimus
Tensor fasciae latae
Inferior gluteal L5-S2 Gluteus maximus
Posterior femoral cutaneous S1-S3 Posterior cutaneous femoral

Inferior cluneal nerves
Perineal branches
Direct branches from plexus
S1-2 Piriformis
Obturator internus
L5, S1-2 Obturator internus & Superior gemellus
Quadratus femoris
L4-5, S1 Quadratus femoris & Inferior gemellus
Sciatic L4-S3 Semitendinosus (Tib)
Semimembranosus (Tib)
Biceps femoris

• Long head (Tib)
• Short head (Fib)

Adductor magnus (medial part, Tib)

Common fibular L4-S2 Lateral sural cutaneous
Communicating fibular
• Superficial fibular
Peroneus longus
Peroneus brevis
Medial dorsal cutaneous
Intermediate dorsal cutaneous
• Deep fibular
Tibialis anterior
Extensor digitorum longus
Extensor digitorum brevis
Extensor hallucis longus
Extensor hallucis brevis
Peroneus tertius
Lateral cutaneous nerve of big toe
Intermediate dorsal cutaneous
Tibial nerve L4-S3 Triceps surae
Tibialis posterior
Flexor digitorum longus
Flexor hallucis longus
Medial sural cutaneous
Lateral calcaneal
Medial calcaneal
Lateral dorsal cutaneous
• Medial plantar
Abductor hallucis
Flexor digitorum brevis
Flexor hallucis brevis (medial head)
Lumbrical (first and second)
Proper digital plantar
• Lateral plantar
Flexor hallucis brevis (lateral head)
Quadratus plantae
Abductor digiti minimi
Flexor digiti minimi
Lumbrical (third and fourth)
Plantar interossei (first to third)
Dorsal interossei (first to fifth)
Adductor hallucis
Proper plantar digital
Pudendal and coccygeal
Pudendal S2-S4 Muscles of the pelvic floor:
Levator ani
Superficial transverse perineal
Deep transverse perineal
Sphincter anus externus
Urethral sphincter
Inferior rectal

Posterior scrotal/labial
Dorsal penis/clitoris
Coccygeal S5-Co1 Coccygeus Anococcygeal
Dorsal branches
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Lumbar Plexus

The network of nerve fibres in the lumbar region, supplying musculature and skin of lower limb is called lumbar plexus. It lies in the substance of psoas major muscle, anterior to the transverse processes of lumbar vertebrae.

It is formed by the anterior rami of the first four lumbar nerves (L1-L4) and from contributions of the last thoracic nerve also known as subcostal nerve (T12). Additionally, the ventral rami of the fourth lumbar nerve also pass communicating branches, the lumbosacral trunk, to the sacral plexus.

The roots of lumbar plexus divide into several cords and the cords combine together to form major nerves of lumbar plexus. These nerves travel through the posterior abdominal wall and reach the lower limb passing in front of the hip joint. With the exception of the obturator nerve which exits the pelvis through the obturator foramen, the larger branches of plexus leave the psoas major at various sites to run obliquely down through the pelvis to leave under the inguinal ligament

The major branches of lumbar plexus are Iliohypogastric Nerve, Ilioinguinal Nerve, Genitofemoral Nerve, Lateral Cutaneous Nerve of the Thigh, Obturator Nerve and Femoral Nerve.

Nerves of the lumbar plexus

Nerve Segment Motor Function Sensory Function
Iliohypogastric T12-L1 • Transversus abdominis
• Abdominal internal oblique
The posterolateral gluteal skin in the pubic region
Ilioinguinal L1 The skin on the upper middle thigh. In males, also the skin over the root of the penis and anterior scrotum

In females, the skin over mons pubis and labia majora

Genitofemoral L1, L2 • Cremaster in males The genital branch – the skin of the anterior scrotum (in males) or the skin over mons pubis and labia majora (in females).

The femoral branch – the skin on the upper anterior thigh.

Lateral femoral cutaneous L2, L3 The anterior and lateral thigh down to the level of the knee.
Obturator L2-L4 • Obturator externus
• Adductor longus
• Adductor brevis
• Gracilis
• Pectineus
• Adductor magnus
The skin over the medial thigh
Femoral L2-L4 • Iliopsoas
• Pectineus
• Sartorius
• Quadriceps femoris
the skin on the anterior thigh and the medial leg
The saphenous nerve is the largest cutaneous branch of the femoral nerve.
Short, direct muscular branches T12-L4 • Psoas major
• Quadratus lumborum
• Lumbar intertransverse



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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

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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

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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).
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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.

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