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Lumbar nerves

The lumbar nerves are the five pairs of spinal nerves emerging from the lumbar vertebrae. They are divided into posterior and anterior divisions.

Structure [ edit ]

Main article: Spinal nerves

The lumbar nerves are five spinal nerves which arise from either side of the spinal cord below the thoracic spinal cord and above the sacral spinal cord. They arise from the spinal cord between each pair of lumbar spinal vertebrae and travel through the intervertebral foramina. The nerves then split into an anterior branch, which travels forward, and a posterior branch, which travels backwards and supplies the area of the back.

Posterior divisions [ edit ]

The middle divisions of the posterior branches run close to the articular processes of the vertebrae and end in the multifidus muscle. The outer branches supply the erector spinae muscles.

The nerves give off branches to the skin. These pierce the aponeurosis of the greater trochanter.

Anterior divisions [ edit ]

The anterior divisions of the lumbar nerves (Latin: rami anteriores) increase in size from above downward.

The anterior divisions communicate with the sympathetic trunk. Near the origin of the divisions, they are joined by gray rami communicantes from the lumbar ganglia of the sympathetic trunk. These rami consist of long, slender branches which accompany the lumbar arteries around the sides of the vertebral bodies, beneath the Psoas major. Their arrangement is somewhat irregular: one ganglion may give rami to two lumbar nerves, or one lumbar nerve may receive rami (branches) from two ganglia. The first and second, and sometimes the third and fourth lumbar nerves are each connected with the lumbar part of the sympathetic trunk by a white ramus communicans.

The nerves pass obliquely outward behind the Psoas major, or between its fasciculi, distributing filaments to it and the Quadratus lumborum.

As the nerves travel forward, they create nervous plexuses. The first three lumbar nerves, and the greater part of the fourth together form the lumbar plexus. The smaller part of the fourth joins with the fifth to form the lumbosacral trunk, which assists in the formation of the sacral plexus.

The fourth nerve is named the furcal nerve, from the fact that it is subdivided between the two plexuses.

Divisions [ edit ]

First lumbar nerve [ edit ]

The first lumbar spinal nerve (L1) [1] originates from the spinal column from below the lumbar vertebra 1 (L1). The three terminal branches of this nerve are the iliohypogastric, ilioinguinal, and the genitofemoral nerves.

L1 supplies many muscles, either directly or through nerves originating from L1. They may be innervated with L1 as single origin, or be innervated partly by L1 and partly by other spinal nerves. The muscles are:

quadratus lumborum (partly)
iliopsoas muscle (partly)

Second lumbar nerve [ edit ]

The second lumbar spinal nerve (L2) [2] originates from the spinal column from below the lumbar vertebra 2 (L2).

L2 supplies many muscles, either directly or through nerves originating from L2. They may be innervated with L2 as single origin, or be innervated partly by L2 and partly by other spinal nerves. The muscles are:

quadratus lumborum (partly)
iliopsoas (partly)

Third lumbar nerve [ edit ]

The third lumbar spinal nerve (L3) [3] originates from the spinal column from below the lumbar vertebra 3 (L3).

L3 supplies many muscles, either directly or through nerves originating from L3. They may be innervated with L3 as single origin, or be innervated partly by L3 and partly by other spinal nerves. The muscles are:

quadratus lumborum (partly)
iliopsoas (partly)
obturator externus (partly)

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Fourth lumbar nerve [ edit ]

The fourth lumbar spinal nerve (L4) [4] originates from the spinal column from below the lumbar vertebra 4 (L4).

L4 supplies many muscles, either directly or through nerves originating from L4. They are not innervated with L4 as single origin, but partly by L4 and partly by other spinal nerves. The muscles are:

quadratus lumborum
gluteus medius muscle
gluteus minimus muscle
tensor fasciae latae
obturator externus
inferior gemellus
quadratus femoris
tibialis anterior

Fifth lumbar nerve [ edit ]

The fifth lumbar spinal nerve 5 (L5) [5] originates from the spinal column from below the lumbar vertebra 5 (L5).

L5 supplies many muscles, either directly or through nerves originating from L5. They are not innervated with L5 as single origin, but partly by L5 and partly by other spinal nerves. The muscles are:

gluteus maximus muscle mainly S1
gluteus medius muscle
gluteus minimus muscle
tensor fasciae latae
tibialis anterior
tibialis posterior
extensor digitorum brevis
extensor hallucis longus

Lumbar spinal nerve 3
Lumbar spinal nerve 4
Lumbar spinal nerve 5
The spinal cord with spinal nerves
The plan of the lumbosacral plexus

Function [ edit ]

Areas of distribution of the cutaneous branches of the posterior divisions of the spinal nerves. The areas of the medial branches are in black, those of the lateral in red.

Additional images [ edit ]

The lumbar plexus and its branches.
Lumbar spinal nerves.Deep dissection. Posterior view.

References [ edit ]

This article incorporates text in the public domain from page 924 of the 20th edition of Gray’s Anatomy (1918)

^American Medical Association Nervous System — Groups of Nerves
^American Medical Association Nervous System — Groups of Nerves
^American Medical Association Nervous System — Groups of Nerves
^American Medical Association Nervous System — Groups of Nerves
^American Medical Association Nervous System — Groups of Nerves

Myotomes

Myotome

A myotome is a group of muscles innervated by the ventral root a single spinal nerve. This term is based on the combination of two Ancient Greek roots; “myo-” meaning “muscle”, and “tome”, a “cutting” or “thin segment”.

Like spinal nerves, myotomes are organised into segments because they share a common origin. However, myotome testing can be difficult since individual muscles can be innervated by more than one nerve and by nerves that originate from different spinal cord levels. It is generally done by checking a patient’s ability to perform specific actions and checking for muscle weakness.

Key facts about myotomes

Development	Develop from somites
Myotome testing	Through precise movements (resisted isometric contraction) and tendon reflexes
Clinical notes	Intervertebral disc herniation

This article will discuss the development, testing, and function of myotomes.

Contents

Development
What is a myotome?

Myotome testing

Cervical and thoracic myotomes
Lumbar and sacral myotomes

Herniated disc

+ Show all

Development

The rostrocaudal organisation of the spinal cord happens early in intrauterine development. During the third week of gestation, the notochord has developed and the mesoderm lateral to it has differentiated into three columns. The column running directly next to the notochord is the paraxial mesoderm. The paraxial mesoderm will then start to divide into cube-shaped, bilaterally paired segments called somites. Each of these segments corresponds to a division of the vertebral column and spinal cord in an adult. By the end of the fifth week of gestation, all pairs of somites are present as 38-40 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 8-10 coccygeal segments. Each somite will differentiate into three different regions. The ventral portion will form the sclerotome while the dorsal portion forms the dermomyotome which later splits into the dermatome and myotome.

sclerotome – forms the ribs and vertebrae
dermatome – forms connective tissue and dermis of the skin
myotome – forms the skeletal muscle of the neck, trunk, and limbs

What is a myotome?

Spinal nerve
Nervus spinalis
Synonyms: Nerve trunk of the motor neuron, Nerve trunk , show more.

A myotome is a group of muscles which are innervated by a single spinal nerve which has derived from the same embryological segment. In this way, it is described as the motor equivalent of a dermatome, which is an area of skin innervated by a single spinal nerve. Individual muscles can be innervated by more than one nerve or by a nerve which originates from multiple spinal nerves. Therefore, muscles can be made up of more than one myotome.

For example, the quadriceps femoris muscle is innervated by the femoral nerve. The femoral nerve arises from the lumbar plexus and has its origins from L2-L4. Therefore the quadriceps femoris muscle is a part of the L2, L3, and L4 myotomes. The main function of the quadriceps femoris muscle is to extend the leg at the knee joint so this movement can be used to test L2-L4 myotomes. The femoral nerve also innervates the iliacus, pectineus, and sartorius muscles. Therefore all of these muscles, including the quadriceps femoris muscle, are part of the L2-L4 myotomes.

Check out our learning materials to learn more about the spinal nerves anatomy.

Myotome testing

Myotomes are tested by asking patients to perform different movements which are associated with different spinal nerves because individual muscles can be a part of multiple myotomes where myotomes are made up of multiple muscles which can perform different actions. Specifically, the clinician performs the tests with resisted isometric contractions, and the joint being tested should be at the resting position, or near it. Muscle contractions should be held for at least 5 seconds. This will help pinpoint if specific spinal nerves are lesioned, diseased, or injured if the patient is unable to perform these movements fully.

Looking for a way to improve your learning process? Check out our 8 steps to create your own anatomy flashcards.

Like dermatomes, myotomes can overlap. So even though myotomes have been mapped to certain areas of the body, the mapping is not precise because of natural variation in where muscles receive their innervation. For example, the musculocutaneous nerve (C5-C7) innervates the muscles in the anterior compartment of the arm – coracobrachialis, biceps brachii, and brachialis muscles. If it is absent, these muscles can instead be innervated by branches from the median nerve (C5-T1).

Round up your knowledge with our materials about the body movements.

Cervical and thoracic myotomes

The cervical and thoracic myotomes (C1-T12) are tested with the patient in a seated position. These are tested with movements of the neck and upper limb through the shoulder, elbow, wrist, metacarpophalangeal, and interphalangeal joints. Because the accessory nerve (CN XI) also innervates muscles of the neck, these can also be tested with some of the same movements.

Movements for cervical and thoracic myotome testing

C1-C2	Flexion of the neck
C3 and CN XI	Lateral flexion of the neck
C4 and CN XI	Elevation of the shoulder
C5	Abduction, lateral rotation, and flexion of the arm at the shoulder joint
C5-C6	Flexion of the arm at the shoulder joint
C6	Supination at the shoulder joint
C6-C7	Extension of the forearm at the elbow joint Flexion and extension of the hand at the wrist joint
C6-C8	Medial rotation, adduction, and extension of the arm at the shoulder joint
C7-C8	Pronation at the shoulder joint Flexion and extension of the digits of the hand at the metacarpophalangeal and interphalangeal joints
C8	Extension of the thumb at the metacarpophalangeal joint Ulnar flexion at the wrist joint
T1	Abduction of finger III metacarpophalangeal joints Adduction of finger II, III, IV at the metacarpophalangeal joints
T2-T12	Generally not tested. These nerves innervate the muscles of the thoracic and abdominal wall.

This type of testing relies on the patient being conscious and able. If the patient is unconscious, myotomes can be tested with tendon reflexes instead:

C6 – tendon of the biceps brachii muscle in the cubital fossa
C7 – tendon of the triceps brachii muscle posterior to the elbow

Spinal Nerves: Definition, Function, Diagram, Number, & Facts

Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.

Reviewed by

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul Mcleod, Ph.D., is a qualified psychology teacher with over 18 years experience of working in further and higher education.

The spinal nerves are the body’s major nerves within the peripheral nervous system (PNS). These nerves are integral to the PNS because they control motor, sensory, and autonomic functions between the spinal cord and the body.

There are 31 pairs of spinal nerves located at the cervical, thoracic, lumbar, sacral, and coccygeal levels:

8 pairs of cervical nerves (C1-C8).
12 pairs of thoracic nerves (T1-T12).
5 pairs of lumbar nerves (L1-L5).
5 pairs of sacral nerves (S1-S5).
1 pair of coccygeal nerves (CO1).

Each of these nerves branches out from the spinal cord, dividing and subdividing to form a network connecting the spinal cord to every part of the body.

Spinal nerves are structures that receive sensory information from receptors of the periphery body, and then transmit this information to the CNS.

Similarly, the spinal nerves transmit motor commands from the CNS to the muscles and glands of the periphery, so the brain’s instructions can be carried out quickly.

Table of Contents

Anatomy of Spinal Nerves

Spinal nerves are relatively large nerves that are distributed evenly along the spinal cord and the spine. The spine is a column of vertebrae bones that protects the spinal cord.

These spinal nerves are large as they are formed by both sensory and motor nerve roots merging together. These nerve roots emerge from the spinal cord, the sensory roots from the back of the spinal cord, whereas the motor roots emerge from the front.

Each nerve root comprises of approximately 8 nerve rootlets and as they join together, they form the spinal nerves which project off the spinal cord.

The spinal nerves are formed within a few centimetres of the spine on each side. Some groups of nerves merge to form a large plexus of nerves, whereas some divide into smaller branches without forming a plexus.

Spinal nerves emerge from the spinal column through an opening between adjacent vertebrae (known as intervertebral foramen).

This is the case for all spinal nerves except the first pair, which emerge between the occipital bone and the uppermost vertebrae.

Types and Functions

As spinal nerves contain both sensory and motor fibers, they therefore have both sensory and motor functions. For sensory functions, the spinal nerves receive sensory messages from the skin, internal organs, and the bones.

These spinal nerves will then send this sensory information to the sensory roots before reaching the sensory fibres at the back of the spinal cord.

For motor functions, the motor roots receive nerve messages via the front of the spinal cord and then transmits these messages to the spinal nerves.

Eventually, this information will be sent to small nerve branches which will activate the muscles of the limbs and other body parts.

Cervical Nerves

There are 8 cervical nerves on each side of the spine (C1 to C8), located at the top of the spine, of the cervical vertebrae.

C1, C2, and C3 cervical spinal nerves help to control the head and neck, including forward, backward, and sideward movements.
C4 help to control the upper shoulder movements, as well as helping to power the diaphragm.
C5 help to control the deltoids and biceps, the areas of the upper arm, down to the elbows.
C6 help to control the wrist extensions, with some supply given to the biceps.
C7 help to control the triceps as well as the wrist extensor muscles.
C8 help to control the hands, as well as finger flexion (hand grip).

The cervical nerves C1 to C5 can form a cervical plexus through the merging of these nerves. These can divide into smaller nerves which can carry sensory messages and provide motor control to the muscles of the neck and shoulders.

Likewise, a brachial plexus can be formed by the combining of the nerves from C5 to thoracic nerve T1.

This plexus can branch into nerves which carry sensory messages to provide motor control to the muscles of the arms and upper back.

Thoracic Nerves

Next, below the cervical nerves, are 12 pairs of thoracic nerves on each side of the spine (T1 to T12), located at the thoracic vertebrae of the spine.

T1 and T2 thoracic spinal nerves supply the top of the chest, arms, and hands.
T3, T4, and T5 nerves supply into the chest wall as well as aid in breathing.
T6, T7, and T8 nerves supply into the chest and down into the abdomen.
T9, T10, T11, and T12 nerves supply into the abdomen and lower in the back.

Lumbar Nerves

Below the thoracic nerves are 5 pairs of lumbar nerves on each side of the spine (L1 to L5), located at the lumbar vertebrae of the spine.

L1 lumbar spinal nerves provide sensations to the groin as well as the genitals.
L2, L3, and L4 nerves provide sensations to the front of the thighs and the inner side of the lower legs. They also help to control movements of the hip and knee muscles.
L5 nerves provide sensations to the outer side of the lower legs and the upper foot. These also help to control the hips, knees, feet, and toe movements.

The lumbar nerves L1 to L4 can combine to form the lumbar plexus, dividing into nerves that carry sensory messages and provide motor control to the muscles of the abdomen and legs.

Sacral Nerves

Further down the spine are 5 pairs of sacral nerves on each side of the spine (S1 to S5), located at the sacrum.

S1 sacral spinal nerves affect the hips and the groin area.
S2 nerves affect the back of the thighs.
S3 nerves affect the medial buttock area.
S4 and S5 nerves affect the perineal area.

The spinal nerves from lumbar L4 to sacral nerves S4 can form the sacral plexus through the merging of these nerves. This plexus can divide into nerves that carry sensory messages and provide motor control to the muscles of the legs.

Coccygeal Nerves

Finally, at the base of the spine are 1 pair of coccygeal nerves on each side of the spine (CO1), located at the coccyx.

CO1 spinal nerves innervate the skin around the coccygeal region, including around the tailbone.

Spinal Nerve Damage

Below are some of the symptoms that can be experienced if damage were to occur to the spinal nerves:

Pain – from mild to severe
Changes in sensory sensations
Weakness of muscles
Diminished or weakened reflexes
Feelings of numbness
Lower back problems
Tingling sensations in the limbs

Conditions which can affect the spinal nerves include the following:

Compressive neuropathy

This condition can occur when the spinal nerves are compressed. This can happen when the nerves that exit the spinal cord become trapped or swollen and it can be extremely painful.

This condition typically affects older people, and the effects can be temporary or long-lasting, permanently destroying the spinal nerves.

Herniated disc

Also known as a slipped disc, this can occur when the vertebrae of the spine, including the cartilage, ligaments, and muscles, are disrupted. This disruption can cause the vertebrae to slip out of place.

A herniated disc can also cause nerve compression and usually causes neck pain as a first symptom, accompanied by sensations of tingling, numbness, and weakness in other parts of the body.

A Herniated disc can cause permanent damage to the spinal cord.

Trauma

Spinal nerves can become damaged either mildly or severely after traumatic accidents. Trauma to the neck can come as a result of falling or blunt force to the neck for instance.

This trauma can result in swelling, stretching, or tears of the cervical spinal nerves, or the cervical plexus.

Lifting heavy objects or blunt force to the lower back can result in the lumbar spinal nerves or lumbar plexus being damaged and leads to lower back pains.

Spinal infections

types of spinal infections can include disc infections and spinal bone infections and typically cause inflammation and pain which may travel into other parts of the body.

A spinal infection may begin near spinal nerve roots and thus will take effect on the spinal nerves which branch from it.

Guillan Barre Syndrome (GBS)

This is a condition which attacks the myelin sheath (protective insulating layer) of the neurons.

As this is a demyelinating condition, it can weaken the spinal nerves over time and cause weakness and tingling sensations all over the body. Eventually, it may even impair the muscles which control breathing.

Treatments of spinal nerve damage depend on the issue at hand. If there is an infection or inflammatory problem, anti-inflammatory medication can usually manage the milder symptoms.

Similarly, mild nerve pain may be managed with over-the-counter pain medication.

Otherwise, specific exercises and physical therapy may be recommended by a doctor to help alleviate the pressure caused by more severe spinal nerve damage and help reduce the overall pain.