Spinal Nerve Yuniarti Anatomy Department Faculty of Medicine UNISBA
Nervous system • Structurally : • - CNS (Central Nervous System) • * Brain • * Spinal cord • - PNS (Peripheral Nervous System) • The PNS consists of nerves and ganglia. • * Cranial nerve • * Spinal nerve • * A collection of neuron cell bodies outside the CNS is a ganglionmotoric and sensory ganglia. • Functionally : • - SNS ( Somatic Nervous System ) • - ANS ( Autonomic Nervous System)
Peripheral nerve system • Peripheral nerve consist : • - a bundle peripheral nerve fibers • - the connective tissue • - the blood vessels • Peripheral nerve fibers consist : • - Axon • - Neurolemma • - Endoneurium • Peripheral nerve covering : • - Endoneurium • - Perineurium • - Epineurium
Type peripheral nerve fibers : 1. Somatic fibers - General sensory fibers / General somatic afferent (GSA) fibers transmit sensations from the body to the CNS - Somatic motor fibers / General somatic efferent (GSE) fibers transmit impulses to skeletal (voluntary) muscle 2. Visceral fibers - Visceral sensory fibers / General visceral afferent (GVA) fibers transmit pain or subconscious visceral reflex sensations ( ex: blood gas & blood pressure levels) - Visceral motor fibers / General visceral efferent (GVE) fibers transmit impulses to smooth (involuntary) muscle & glandular tissue
Two varieties of visceral motor fibers : • - Presynaptic /preganglionic fibers • emerge from the synapse outside the CNS in • a parasymphatetic ganglion • - Postsynaptic / postganglionic fibers • continue to innervate muscles & glands **Work together to conduct impluses from CNS to smooth muscle or glands
Spinal nerves initially arise from the spinal cord as rootlets. • The rootlets converge to form two nerve roots : • An anterior (ventral) nerve root, consisting of motor (efferent) fibers passing from nerve cell bodies in the anterior horn of spinal cord gray matter to effector organs located peripherally. • A posterior (dorsal) nerve root, consisting of sensory (afferent) fibers from cell bodies in the spinal sensory or posterior (dorsal) root ganglion (“DRG”) that extend peripherally to sensory endings and centrally to the posterior horn of spinal cord gray matter.
The posterior and anterior nerve roots unite, within or just proximal to the intervertebral foramen, to form a mixed (both motor and sensory) spinal nerve, which immediately divides into two rami): • a posterior (dorsal) ramus • an anterior (ventral) ramus
In addition to posterior & anterior rami, • spinal nerves also give off : • Meningeal branch • Supplies the vertebrae, vertebra ligament, blood vessels • of spinal cord & meninges • Rami communicantes • component of the autonomic nervous system
Posterior rami, supplying nerve fibers to : -The synovial joint of the vertebral column -Deep muscle of the back -The overlying skin in a segmental pattern Anterior rami, supplying nerve fibers to : -Anterior region of the trunk -Lateral region of the trunk -Upper limb -Lower limb Anterior rami merge with all or portions of one or more adjacent anterior rami, forming nerve plexuses
Posterior rami and the anterior rami of spinal nerves T2-T12 generally do not merge with the rami of adjacent spinal nerves to form plexuses.
INTERCOSTAL or THORACIC NERVE Anterior rami Nerve T2 innervates the intercostal muscle, axilla & posteromedial aspect of the arm Nerve T3-T6 innervates the intercostal muscle & abdominal muscle & the overlying skin Posterior rami Innervates the deep back muscle & skin of the posterior aspect of thorax
The unilateral area of skin innervated by the sensory fibers of a single spinal nerve is called a dermatome • The unilateral muscle mass receiving innervation from the fibers conveyed by a single spinal nerve is a myotome
Important to distinguish between the distribution of the fibers carried by spinal nerves (segmental innervation or distribution—i.e., dermatomes and myotomes labeled with a letter and a number, such as “T4”) and of the fibers carried by branches of a plexus (peripheral nerve innervation or distribution, labeled with the names of peripheral nerves, such as “the median nerve”)