Nervous Supply Quiz Review

Nervous Supply

Spinal Nerves

  • Overview: The human body has a total of 31 pairs of spinal nerves originating from the spinal cord. These spinal nerves participate in mixed communication, enabling both sensory and motor functions between the spinal cord and peripheral body parts, including the upper and lower limbs, neck, and trunk.

  • Structure:

    • All spinal nerves except the first pair are categorized as mixed nerves.

    • They facilitate two-way communication through specific pathways.

  • Naming Convention: Most spinal nerves are named according to the vertebra above which they exit through the neural foramen. An important exception occurs with the cervical spinal nerves where the first cervical nerve (C1) exits above the atlas (the first cervical vertebra), leading to the unique count of 8 cervical spinal nerves.

  • Distribution: The breakdown of spinal nerve pairs includes:

    • 8 cervical (C1-C8)

    • 12 thoracic (T1-T12)

    • 5 lumbar (L1-L5)

    • 5 sacral (S1-S5)

    • 1 coccygeal (Co1)

  • Roots of Spinal Nerves:

    • Each spinal nerve consists of a dorsal root, which carries sensory information into the spinal cord and is identifiable by the presence of a dorsal root ganglion, and a ventral root that carries motor information away from the spinal cord.

    • The merging of the dorsal and ventral roots results in the formation of the spinal nerve.

  • Branches of Spinal Nerves: Upon exiting the neural foramen, each spinal nerve splits into three main branches:

    1. Meningeal Branch: Supplies the meninges, blood vessels of the spinal cord, intervertebral ligaments, and vertebrae.

    2. Dorsal Branch (Ramus): Extends posteriorly to supply muscles and skin located in the back.

    3. Ventral Branch (Ramus): Extends anteriorly to supply muscles of the limbs and trunk located on the body's anterior side.

  • Visceral Branch: In the thoracic and lumbar regions, additional branches referred to as visceral branches provide inputs from the autonomic nervous system.

  • Nerve Plexuses: In both the cervical and lumbar regions, the ventral branches of the spinal nerves intertwine to create networks known as nerve plexuses.

Nerve Structure and Function

  • Spinal Nerve Composition: The structure of spinal nerves includes white matter and grey matter. The terminology used to describe nerve root structures includes:

    • Anterior Rootlets

    • White Matter (anterior, lateral, posterior funiculus)

    • Grey Matter (anterior hom, posterior hom)

    • Posterior Rootlets: Which comprise the sensory input portion of the nerve.

    • Posterior Root Ganglion: Contains the cell bodies of sensory neurons.

    • Branches include Anterior ramus and Posterior ramus, which serve distinct function.

Brachial Plexus

  • Formation: The brachial plexus is created from the anterior rami (branches) of spinal nerves C5-T1. This plexus is vitally significant for sensation and motor control in the arms and shoulders.

  • Major Branches of Brachial Plexus:

    1. Musculocutaneous Nerve: Supplies muscles of the anterior arm and skin of the forearm.

    2. Ulnar Nerve: Supplies muscles in the forearm and hand, as well as skin on the medial side of the hands.

    3. Median Nerve: Supplies flexor muscles in the forearm and skin of the hands.

    4. Radial Nerve: Supplies the muscles of the posterior arm (including extensor muscles in the forearm) and sensory input from the skin of the back of the hand.

    5. Axillary Nerve: Supplies the deltoid muscle and teres minor (part of the rotator cuff), as well as sensation from the skin of the shoulder.

Branches of the Brachial Plexus

  • Additional branches play crucial roles in muscle and sensory functions:

    • Lateral and Medial Pectoral nerves: Supply pectoralis major and minor muscles located in the chest.

    • Dorsal Scapular Nerve: Provides innervation to the rhomboid major and levator scapulae muscles.

    • Lower Subscapular Nerve: Supplies subscapularis and teres major muscles.

    • Thoracodorsal Nerve (Middle Subscapular): Supplies the latissimus dorsi muscle.

    • Suprascapular Nerve: Innervates the supraspinatus and infraspinatus muscles which assist in shoulder movement.

Lumbosacral Plexus

  • Overview: The lumbosacral plexus encompasses the spinal nerves T12-S5 and is essential for supplying the pelvic cavity, lower abdominal wall, external genitalia, buttocks, thighs, legs, and feet.

  • Major Branches of the Lumbosacral Plexus:

    1. Obturator Nerve: Supplies adductor muscles of the thigh.

    2. Femoral Nerve: Supplies muscles in the anterior thigh and provides sensory input from the skin of the thighs and legs.

    3. Sciatic Nerve: The largest and longest nerve in the body, comprising tibial and common peroneal contributions that innervate the hamstrings, legs, and feet.

    4. Pudendal Nerve: Supplies muscles of the perineum.

    5. Superior and Inferior Gluteal Nerves: Innervate the gluteal muscles and tensor fasciae latae.

Nerve Distribution in Lumbar Region

  • Spinal Nerves T12 to L5: Include the following nerves:

    • Subcostal Nerve

    • Iliohypogastric Nerve

    • Ilioinguinal Nerve

    • Lateral Cutaneous Nerve of Thigh

    • Femoral Nerve

    • Genitofemoral Nerve

    • Accessory Obturator Nerve

    • Obturator Nerve

Nerve Distribution in Sacral Region

  • Spinal Nerves L4 to S5: Include important nerves such as:

    • Lumbosacral Trunk

    • Superior Gluteal Nerve

    • Nerve to Piriformis

    • Inferior Gluteal Nerve

    • Nerve to Quadratus Femoris and Inferior Gemellus

    • Nerve to Obturator Internus and Superior Gemellus

    • Perforating Cutaneous Nerve

    • Common Fibular Nerve

    • Sciatic Nerve

    • Tibial Nerve

    • Nerve to Levator Ani and Coccygeus

    • Pudendal Nerve

    • Posterior Femoral Cutaneous Nerve

Nerves of the Thoracic Region

  • Ventral Branches: Unlike the nerves in the cervical and lumbosacral regions, the ventral branches of the thoracic nerves do not converge to form a plexus.

  • Function of Thoracic Nerves: These branches develop into intercostal nerves, which are responsible for innervating the intercostal muscles and upper abdominal muscles, in addition to receiving sensory input from the skin of the thorax and abdomen.