The Peripheral Nervous System and Reflex Activity: Part C 13 The Peripheral Nervous System and Reflex Activity: Part C

Spinal Nerves 31 pairs of mixed nerves named according to their point of issue from the spinal cord Area Vertebrae Number Cervical C1 – C8 8 Thoracic T1 – T12 12 Lumbar L1 – L5 5 Sacral S1 – S5 Coccygeal C0 1

Exam Prep: Plexus Enlargements Cervical Cervical plexus Cervical Brachial (Intercostal) Lumbar Sacral Enlargements Cauda equina Cervical plexus Cervical nerves C1 – C8 Brachial plexus Cervical enlargement Thoracic nerves T1 – T12 Intercostal nerves Lumbar enlargement Lumbar nerves L1 – L5 Lumbar plexus Sacral plexus Sacral nerves S1 – S5 Cauda equina Coccygeal nerve Co1 Figure 13.6

What were the number for the nerves for the various plexuses? QUICK REVIEW What were the number for the nerves for the various plexuses? Area Vertebrae Number Cervical Thoracic Lumbar Sacral Coccygeal

What were the number for the nerves for the various plexuses? QUICK REVIEW What were the number for the nerves for the various plexuses? Area Vertebrae Number Cervical C1 – C8 8 Thoracic T1 – T12 12 Lumbar L1 – L5 5 Sacral S1 – S5 Coccygeal C0 1

What’s the difference between ventral and dorsal roots? Spinal Nerves: Roots What’s the difference between ventral and dorsal roots? Ventral roots Dorsal roots

What’s the difference between ventral and dorsal roots? Spinal Nerves: Roots What’s the difference between ventral and dorsal roots? Ventral roots motor (efferent) fibers innervate skeletal muscles Dorsal roots

What’s the difference between ventral and dorsal roots? Spinal Nerves: Roots What’s the difference between ventral and dorsal roots? Ventral roots motor (efferent) fibers innervate skeletal muscles Dorsal roots sensory (afferent) fibers conduct impulses from peripheral receptors

What do these two structures form? Spinal Nerves: Roots What do these two structures form? They form the spinal nerves These emerge from the vertebral column via the intervertebral foramina

Gray matter White matter Dorsal and Ventral root ventral rootlets of spinal nerve Ventral root Dorsal root Dorsal root ganglion Dorsal ramus of spinal nerve Ventral ramus of spinal nerve Spinal nerve Rami communicantes Sympathetic trunk ganglion Anterior view showing spinal cord, associated nerves, and vertebrae. The dorsal and ventral roots arise medially as rootlets and join laterally to form the spinal nerve. Figure 13.7 (a)

Spinal Nerves: Rami Most ventral rami form interlacing nerve networks called plexuses (cervical, brachial, lumbar, and sacral) Except T2–T12: Why is this?

Ventral rami of T2–T12 (intercostal nerves) Spinal Nerves: Rami Most ventral rami form interlacing nerve networks called plexuses (cervical, brachial, lumbar, and sacral) Except T2–T12: Why is this? Intercostals Ventral rami of T2–T12 (intercostal nerves) Rib muscles, anterolateral thorax, abdominal wall

Exam Prep: Plexus Enlargements Cervical Cervical plexus Cervical Brachial (Intercostal) Lumbar Sacral Enlargements Cauda equina Cervical plexus Cervical nerves C1 – C8 Brachial plexus Cervical enlargement Thoracic nerves T1 – T12 Intercostal nerves Lumbar enlargement Lumbar nerves L1 – L5 Lumbar plexus Sacral plexus Sacral nerves S1 – S5 Cauda equina Coccygeal nerve Co1 Figure 13.6

Branches of intercostal nerve Dorsal ramus Ventral ramus Spinal nerve Rami communicantes Intercostal nerve Sympathetic trunk ganglion Dorsal root ganglion Dorsal root Ventral root Branches of intercostal nerve • Lateral cutaneous • Anterior cutaneous Sternum (b) Cross section of thorax showing the main roots and branches of a spinal nerve. Figure 13.7 (b)

Cervical Plexus What does the ventral rami of the C1–C4 form?

What does the ventral rami of the C1–C4 form? Cervical Plexus What does the ventral rami of the C1–C4 form? Cervical plexus! (see the pattern?) General Innervations Skin/muscles of neck, ear, back of head and shoulders Phrenic nerve Innervates the diaphragm (receives fibers from C3–C5)

Segmental branches Hypoglossal Ventral nerve (XII) rami: Ventral rami Segmental branches Hypoglossal nerve (XII) Ventral rami: Lesser occipital nerve C1 Greater auricular nerve C2 Transverse cervical nerve C3 Ansa cervicalis C4 Accessory nerve (XI) Phrenic nerve C5 Supraclavicular nerves Figure 13.8

Table 13.3

Brachial Plexus What ventral rami forms the brachial plexus? C5–C8 and T1 often C4 and T2 What do these innervate?

Brachial Plexus What ventral rami forms the brachial plexus? C5–C8 and T1 often C4 and T2 What do these innervate? Upper limb

Brachial Plexus Major branches of this plexus: Roots five ventral rami (C5–T1) Trunks upper, middle, and lower Divisions anterior and posterior Cords lateral, medial, and posterior

(a) Roots (rami C5 – T1), trunks, divisions, and cords Roots (ventral rami): C4 C5 C6 Upper Posterior divisions C7 Middle Trunks Lateral C8 Lower Cords Posterior T1 Medial Axillary Musculo- cutaneous Radial Medial cutaneous nerves of the arm and forearm Median Ulnar (a) Roots (rami C5 – T1), trunks, divisions, and cords Anterior divisions Posterior divisions Trunks Roots Figure 13.9 (a)

Notice the flows of anterior to posterior! divisions Posterior divisions Trunks Roots Major terminal branches (peripheral nerves) Roots (ventral rami) Cords Divisions Trunks Anterior Musculocutaneous Upper C5 Lateral Posterior Median C6 Medial Anterior Ulnar Middle C7 Posterior Radial C8 Posterior Anterior Axillary Lower T1 Posterior (d) Flowchart summarizing relationships within the brachial plexus Figure 13.9 (d)

Brachial Plexus: Nerve Innervations Axillary Deltoid and teres minor Shoulder skin/joint capsule Musculocutaneous Biceps brachii and brachialis Skin of lateral forearm Median Most forearm flexors/pronators Some hand intrinsic muscles Ulnar Flexor carpi ulnaris Most hand intrinsic muscles Medial skin of hand Radial All extensor muscles Supinators Posterior skin of limb

Musculocutaneous nerve Axillary nerve Anterior divisions Posterior divisions Trunks Roots Radial nerve Musculocutaneous nerve Ulnar nerve Median nerve Muscular branch Median nerve Digital branch (c) The major nerves of the upper limb Figure 13.9 (c)

Table 13.4

What rami form the lumbar plexus? Ventral rami from L1–L4 Innervations Primarily anterior innervations thigh, abdominal wall, and psoas muscle

Lumbar Plexus Nerves to know Femoral nerve innervations Quadriceps skin of anterior thigh medial surface of leg Obturator nerve passes through obturator foramen innervate adductor muscles

Ventral rami: L1 L2 Iliohypogastric Ilioinguinal L3 Genitofemoral Lateral femoral cutaneous L4 Obturator Femoral L5 Lumbosacral trunk (a) Ventral rami and major branches of the lumbar plexus (b) Distribution of the major nerves from the lumbar plexus to the lower limb Figure 13.10

Iliohypogastric Ilioinguinal Femoral Lateral femoral cutaneous Ventral rami Iliohypogastric Ilioinguinal Femoral Lateral femoral cutaneous Obturator Anterior femoral cutaneous Saphenous (a) Ventral rami and major branches of the lumbar plexus (b) Distribution of the major nerves from the lumbar plexus to the lower limb Figure 13.10

Ventral rami: Iliohypogastric L1 Ilioinguinal Femoral L2 Lateral femoral cutaneous Iliohypogastric Ilioinguinal Obturator L3 Genitofemoral Anterior femoral cutaneous Lateral femoral cutaneous Saphenous L4 Obturator Femoral L5 Lumbosacral trunk (a) Ventral rami and major branches of the lumbar plexus (b) Distribution of the major nerves from the lumbar plexus to the lower limb Figure 13.10

Table 13.5

Sacral Plexus Arises from ventral rami of L4–S4 Sciatic nerve Sevres the buttock, lower limb, pelvic structures, and perineum Sciatic nerve Longest and thickest nerve of the body Composed of two nerves: tibial and common fibular Innervations hamstring muscles adductor magnus most muscles in the leg and foot

Ventral rami and major branches of the sacral plexus Superior gluteal L5 Lumbosacral trunk S1 Inferior gluteal Common fibular S2 Tibial S3 Posterior femoral cutaneous S4 Pudendal S5 Sciatic Co1 Ventral rami and major branches of the sacral plexus Figure 13.11 (a)

(b) Distribution of the major nerves from Superior gluteal Inferior gluteal Pudendal Sciatic Posterior femoral cutaneous Common fibular Tibial Sural (cut) Deep fibular Superficial fibular Plantar branches (b) Distribution of the major nerves from the sacral plexus to the lower limb Figure 13.11 (b)

Table 13.6

Innervation of Skin What is a dermatome?

All spinal nerves (except C1) participate in dermatomes Innervation of Skin What is a dermatome? Area of skin innervated by the cutaneous branches of a single spinal nerve All spinal nerves (except C1) participate in dermatomes Most dermatomes overlap

All spinal nerves (except C1) participate in dermatomes Innervation of Skin What is a dermatome? Area of skin innervated by the cutaneous branches of a single spinal nerve All spinal nerves (except C1) participate in dermatomes Most dermatomes overlap Why would this be important?

All spinal nerves (except C1) participate in dermatomes Innervation of Skin What is a dermatome? Area of skin innervated by the cutaneous branches of a single spinal nerve All spinal nerves (except C1) participate in dermatomes Most dermatomes overlap Why would this be important? Prevents complete numbness in the event that a single spinal nerve is destroyed

Anterior view (b) Posterior view Figure 13.12 C2 C3 C4 C5 T1 T2 T3 T2 L2 S1 L1 L3 C8 L4 S2 T12 S3 L5 C6 L1 L1 C6 S4 C7 S2 C7 S5 C8 S3 C8 L2 L2 S1 S2 S2 S1 L3 L3 L1 L5 L2 L5 L4 L4 L3 L5 L5 L4 S1 S1 Anterior view (b) Posterior view L4 L4 L5 L5 S1 Figure 13.12

Innervation of Joints Hilton’s law Any nerve serving a muscle that produces movement at a joint also innervates the joint and the skin over the joint We don’t need to know the law, but it is a helpful concept for exam questions