Spinal Nerves in Nervous System in Physiology

Spinal Nerves

1. Sreenu Thalla Assistant Professor Department of Pharmacology

2. Spinal Nerves

3. 31 pairs of nerves originate on the spinal cord, known as spinal nerves. All spinal nerves are mixed nerves, meaning that they carry both sensory and motor information. Spinal nerves are named by the region where they originate and a number: The   cervical  region has 8 pairs of spinal nerves called C 1  - C 8 The   thoracic  region has 12 pairs of spinal nerves called T 1  - T 12 The   lumbar  region has 5 pairs of spinal nerves called L 1  - L 5 The   sacral  region has 5 pairs of spinal nerves called S 1  - S 5 There is one pair of  coccygeal  nerves called C

4. Each spinal nerve originates on the spinal cord as  spinal nerve roots , called ventral and dorsal roots. These spinal nerve roots unite close to the spinal cord to form a spinal nerve. Perhaps surprisingly, spinal nerves are very short, only about 1-2 centimeters long before it divides into two branches known as  rami .

5. Function of Spinal Cord Forms a connecting link between the brain and the PNS Provides structural support and builds a body posture Facilitates flexible movements Myelin present in the white matter acts as an electrical insulation Communicates messages from the brain to different parts of the body Coordinates reflexes Receives sensory information from receptors and approaches towards the brain for processing.

6. The   brachial plexus  is divided into  roots ,  trunks ,  divisions ,  cords , and  branches roots :  ventral roots of spinal nerves C 5 , C 6 , C 7 , C 8 , and T 1 trunks :  superior, middle, and inferior trunks divisions :  each of the superior, middle, and inferior trunks have an anterior division and a posterior division (6 divisions total) Cords lateral cord:  the anterior divisions from the superior and middle trunks combine to form the lateral cord posterior cord:  the posterior divisions from the superior, middle, and inferior trunks combine to form the posterior cord medial cord:  comprised of the anterior division of the inferior trunk Branches - musculocutaneous nerve ,  axillary nerve ,  radial nerve ,  median nerve , and  ulnar nerve

7. 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).

8. The cervical nerves C 1 to C 5 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 C 5 to thoracic nerve T 1 . This plexus can branch into nerves that carry sensory messages to provide motor control to the muscles of the arms and upper back.

9. T 1 and T 2  thoracic spinal nerves supply the top of the chest, arms, and hands. T 3 , T 4 , and T 5  nerves supply into the chest wall as well as aid in breathing. T 6 , T 7 , and T 8   nerves supply into the chest and down into the abdomen. T 9 , T 10 , T 11 , and T 12   nerves supply into the abdomen and lower in the back.

10. L 1  lumbar spinal nerves provide sensations to the groin as well as the genitals. L 2 , L 3 , and L 4  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. L 5  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 L 1 to L 4 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.

11. Sacral Nerves S 1  sacral spinal nerves affect the hips and the groin area. S 2  nerves affect the back of the thighs. S 3  nerves affect the medial buttock area. S 4 and S 5  nerves affect the perineal area. The spinal nerves from lumbar L 4 to sacral nerves S 4 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 CO 1  spinal nerves innervate the skin around the coccygeal region, including around the tailbone.

12. Spinal Nerve Damage 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 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.

13. 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.

14. 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 lead to lower back pains.

15. 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.

16. Thank You

17. Clinical Application: Epidural (Childbirth) An  epidural  is a medical procedure commonly done to relieve pain during labor and delivery. In this procedure, a needle is inserted into the vertebral canal without puncturing the dura mater. With the tip of the needle/catheter  above  the  dura mater  ( epi   = above;  dural = of the dura mater), anesthetics are injected into the epidural space. The anesthetics then pass through the meninges and block neuronal impulses, thus inhibiting the transmission of sensation (in this case, pain) to the brain.

18. Just like in a lumbar puncture, the epidural needle can be inserted between L 3 /L 4  vertebrae, but because the pain impulses from the uterus reach the spinal cord at levels between T 10 -L 1 , epidurals are more commonly placed more superiorly. A common location for epidural placement is T 7 , which is easily identifiable at about the level of the inferior border of the scapula. When the drugs are injected, gravity can pull the drugs downward, blocking everything below the epidural location. Therefore, administering an epidural above the level of T 10  can relieve labor pain from uterine contractions as well as pain from the pelvic floor transmitted by the pudendal nerve (from S 2 , S 3 , and S 4  spinal nerves).

19. Nerve Name Nerves Involved Cutaneous Innervation Muscular Innervation axillary nerve ventral rami of C 5  and C 6  spinal nerves skin of the shoulder deltoid and teres minor muscles dorsal scapular nerve ventral rami of C 5  spinal nerve -- levator scapulae, rhomboid major, and rhomboid minor muscles long thoracic nerve ventral rami of C 5  through C 7  spinal nerve -- serratus anterior muscles median nerve ventral rami of C 5  through T 1  spinal nerves some skin of the hand anterior forearm flexor, palm, and digit muscles musculocutaneous nerve ventral rami of C 5  through C 7  spinal nerves some skin of the forearm biceps brachii, brachialis, and coracobrachialis muscles pectoral nerve ventral rami of C 5  through T 1  spinal nerves -- pectoralis major and pectoralis minor muscles radial nerve ventral rami of C 5  through T 1  spinal nerves posterolateral skin of the upper limb triceps brachii, brachioradialis, and posterior forearm muscles subscapular nerve ventral rami of C 5  and C 6  spinal nerves -- subscapularis and teres major muscles suprascapular nerve ventral rami of C 5  and C 6  spinal nerves -- supraspinatus and infraspinatus muscles ulnar nerve ventral rami of C 8  and T 1  spinal nerves some skin of the hand anterior forearm flexor and hand muscles

20. Nerve Name Nerves Involved Cutaneous Innervation Muscular Innervation common fibular nerve (superficial and deep branches) ventral rami of L 4  through S 2  spinal nerves skin of the anterolateral leg and foot tibialis anterior, extensor digitorum longus, fibularis longus and fibularis brevis muscles femoral nerve ventral rami of L 2  through L 4  spinal nerves skin of the medial lower limb and anterior thigh iliacus, sartorius, pectineus, rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius muscles genitofemoral nerve ventral rami of L 1  and L 2  spinal nerves skin of external genitalia cremasteric muscles (males only) iliohypogastric nerve ventral rami of L 1  spinal nerves skin of the hip and inferior abdomen internal oblique and transversus abdominis muscles ilioinguinal nerve ventral rami of L 1  spinal nerves skin of the medial thigh and external genitalia internal oblique and Transversus abdominis muscles inferior gluteal nerve ventral rami of L 5  through S 2  spinal nerves -- gluteus maximus muscles

21. lateral femoral cutaneous nerve ventral rami of L 2  and L 3  spinal nerves skin of the anterolateral thigh and knee -- obturator nerve ventral rami of L 2  through L 4  spinal nerves skin of thigh (medial) gracilis, adductor magnus, adductor longus, and adductor brevis muscles posterior femoral cutaneous nerve ventral rami of S 1  through S 3  spinal nerves skin of the posterior lower limb -- pudendal nerve ventral rami of S 2  through S 4  spinal nerves skin of external genitalia external anal sphincter, external urethral sphincter, and pelvic muscles sciatic nerve (branches into tibial and common fibular nerves) ventral rami of L 4  through S 3  spinal nerves skin of the leg and foot semitendinosus , semimembranosus , and biceps femoris muscles superior gluteal nerve ventral rami of L 4  through S 1  spinal nerves -- gluteus medius, gluteus minimus, and tensor fasciae latae muscles tibial nerve ventral rami of L 4  through S 3  spinal nerves skin of the sole of the foot and posterior leg flexor digitorum longus , gastrocnemius , and soleus muscles