The peripheral nervous system and reflex activity (part c) provides knowledge of spinal nerves. The goal is for you to learn: Describe the formation of a spinal nerve and the general distribution of its rami; define plexus, name the major plexuses and describe the distribution and function of the peripheral nerves arising from each plexus. | 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 8 cervical (C1–C8) 12 thoracic (T1–T12) 5 Lumbar (L1–L5) 5 Sacral (S1–S5) 1 Coccygeal (C0) Figure Cervical nerves C1 – C8 Thoracic nerves T1 – T12 Lumbar nerves L1 – L5 Sacral nerves S1 – S5 Coccygeal nerve Co1 Cervical plexus Intercostal nerves Cervical enlargement Lumbar enlargement Cauda equina Brachial plexus Lumbar plexus Sacral plexus Spinal Nerves: Roots Each spinal nerve connects to the spinal cord via two roots Ventral roots Contain motor (efferent) fibers from the ventral horn motor neurons Fibers innervate skeletal muscles) Spinal Nerves: Roots Dorsal roots Contain sensory (afferent) fibers from sensory neurons in the dorsal root ganglia Conduct impulses from peripheral receptors Dorsal and ventral roots unite to form spinal nerves, which then emerge from the vertebral column via the intervertebral foramina Figure (a) Dorsal root ganglion Gray matter White matter Ventral root Dorsal root Dorsal and ventral rootlets of spinal nerve Dorsal ramus of spinal nerve Ventral ramus of spinal nerve Sympathetic trunk ganglion Spinal nerve Rami communicantes 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. Spinal Nerves: Rami Each spinal nerve branches into mixed rami Dorsal ramus Larger ventral ramus Meningeal branch Rami communicantes (autonomic pathways) join to the ventral rami in the thoracic region Spinal Nerves: Rami All ventral rami except T2–T12 form interlacing nerve networks called plexuses (cervical, brachial, lumbar, and sacral) The back is innervated by dorsal rami via several branches Ventral rami of T2–T12 as intercostal nerves supply muscles of the ribs, anterolateral thorax, and abdominal wall Figure (b) Dorsal ramus Ventral ramus Intercostal nerve Spinal . | 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 8 cervical (C1–C8) 12 thoracic (T1–T12) 5 Lumbar (L1–L5) 5 Sacral (S1–S5) 1 Coccygeal (C0) Figure Cervical nerves C1 – C8 Thoracic nerves T1 – T12 Lumbar nerves L1 – L5 Sacral nerves S1 – S5 Coccygeal nerve Co1 Cervical plexus Intercostal nerves Cervical enlargement Lumbar enlargement Cauda equina Brachial plexus Lumbar plexus Sacral plexus Spinal Nerves: Roots Each spinal nerve connects to the spinal cord via two roots Ventral roots Contain motor (efferent) fibers from the ventral horn motor neurons Fibers innervate skeletal muscles) Spinal Nerves: Roots Dorsal roots Contain sensory (afferent) fibers from sensory neurons in the dorsal root ganglia Conduct impulses from peripheral receptors Dorsal and ventral roots unite to form spinal nerves, which then emerge from the vertebral column via the intervertebral foramina .
