Peripheral Nerves PDF

Meninges Protective layers of the spinal cord as well as its structures The meninges are connective tissue coverings that extend around the spinal cord and the brain Collagen and elastin fibers Consist of 3 layers which are: ○ 1. Dura mater - outermost covering ○ 2....

Meninges Protective layers of the spinal cord as well as its structures The meninges are connective tissue coverings that extend around the spinal cord and the brain Collagen and elastin fibers Consist of 3 layers which are: ○ 1. Dura mater - outermost covering ○ 2. Arachnoid mater - middle layer ○ 3. Pia mater - innermost layer (fused to the spinal cord) Subarachnoid space between Pia and Arachnoid, filled with CSF Meningitis Inflammation of the meninges secondary to an infection Bacterial, viral, fungi infection Signs and symptoms ○ High fever ○ Severe Headache ○ Stiff neck ○ Other – vomiting, nausea, seizures, photophobia, phonophobia, confusion, petechiae Tx: – IV antibiotic, antiviral or antifungal Kernig’s Sign: ○ Patient lies supine and the examiner flexes one of the patient’s leg at the knee and hip ○ Resistance when trying to extend the leg at the knee while the hip is flexed At a full 90 degrees, if there is resistance, then it is a + Kernig’s sign ○  Brudzinski’s Sign: ○ Neck flexion induces involuntary flexion of the hip and knees ○ Spinal Nerve Is a mixed nerve: ○ Posterior root: contains sensory axons conducting nerve impulses (sensory receptors) ○ Anterior root: contains motor axons conducting nerve impulses from the CNS to effector organs and cells ○ ○ Dorsal root: afferent and ventral is efferent 31 total spinal nerves ○ Cervical nerves (8 pairs): C1-C8 ○ Thoracic nerves (12 pairs): T1-T12 ○ Lumbar nerves (5 pairs): L1-L5 ○ Sacral nerves (5 pairs): S1-S5 ○ Coccygeal nerve (1 pair) ○ Communication pathways between the spinal cord and the rest of the body  Arise: from the spinal cord and are formed by the merging of two roots ○ Dorsal (Posterior) Root - contains sensory (afferent) fibers that transmit sensory information from the body Each dorsal root also has a sensory ganglion (cell bodies of these sensory neurons reside ○ Ventral (Anterior) Root: Contains motor (efferent) fibers that transmit motor commands from the spinal cord to muscles and glands Function ○ Carry sensory information from peripheral receptors (skin, muscles, joints) to the central nervous system ○ Convey motor signals from the central nervous system to skeletal muscles ○ Through their rami communicates autonomic fibers innervate smooth muscles and glands Spinal nerves Rami ○ Branches that emerge from the spinal nerves after they exit the spinal column ○ Two primary branches or rami Dorsal (Posterior) Ramus: innervates the intrinsic muscles of the back and overlying skin Contain both sensory and motor fibers Ventral (Anterior) Ramus: Innervates the muscles and skin of the anterior and lateral aspects of the trunk and the limbs Larger than the dorsal rami ○ Rami communicates ○ Small nerve fibers connect spinal nerves to the sympathetic trunk, which is part of the autonomic nervous system. They play a role in ○ Relay autonomic signals between the spinal cord and various target organs ○ Components White Rami Communicantes: Carry pre-ganglionic sympathetic fibers from the spinal nerves to the sympathetic trunk Present only in the lower cervical, thoracic, and upper lumbar regions (C7 to L2) Gray Rami Communicantes: Carry post-ganglionic sympathetic fibers from the sympathetic trunk back to the spinal nerves which control the tone of smooth muscles, glands, and cardiac tissue They distribute fibers to various effector organs and tissues Present at every spinal nerve level, extending throughout the entire vertebral column  1st cervical nerve emerges between the atlas and occipital bone All other spinal nerves emerge from the vertebral column through the intervertebral foramina between adjoining vertebrae Approx. 42-45 cm (16 - 18 inches) long and originates at the medulla oblongata and terminates at conus medularis (L2) Spinal cord ends near the level of the superior border of the second lumbar vertebra Cauda equina ○ Arrangement of nerves with roots of the lumbar, sacral and coccygeal nerves ○ Responsible for innervating the lower body, including the legs, pelvic organs, and bladder. CSF Produced in choroid plexus of ventricles Cerebrospinal fluid circulates in the subarachnoid space CSF enter the cerebral venous sinuses (superior sagittal sinus) through arachnoid villi (small, finger-like projections of the arachnoid membrane) Plexuses Ventral rami of T2-T12 go directly to body structures Other spinal nerves form plexuses ○ networks of intersecting nerves that primarily serve to distribute nerve fibers to specific regions of the body ○ Allow for more complex innervation of muscles and organs (networks) ○ May also branch 4 major nerve plexuses, found together with their peripheral nerves ○ Cervical Plexus ○ Brachial Plexus ○ Lumbar Plexus ○ Sacral Plexus Cervical plexus ○ Formed from C1-C4 and part C5 ○ Innervates the skin and muscles of Head Neck Superior shoulders Chest ○ Important nerve of this plexus is phrenic nerve: Innervate the diaphragm ○ The primary danger of a cervical fracture or trauma is that the phrenic nerve may have been severe damaged leading to diaphragm paralysis Injury to the phrenic nerve Complete severing of the spinal cord above the origin of the phrenic nerve (C3, C4,C5) causes respiratory arrest Breathing stops because the nerve no longer send impulses to the diaphragm Brachial plexus Network of nerves that originates from the spinal cord in the neck (C5 to T1) and extends into the arm Responsible for the motor and sensory innervation of the shoulder, arm, and hand Innervates: Shoulders & Upper limbs Formed by the ventral rami of the spinal nerves and divides into roots, trunks, divisions, cords, and branches ○ Roots: C5, C6, C7, C8, T1 ○ Trunks: Upper (superior), Middle, and Lower (inferior) ○ Divisions: Each trunk divides into an anterior and posterior division  ○ Cords: Lateral, Medial, and Posterior cords are formed by the divisions Interject and cause innervation ○ Branches: Major branches include the musculocutaneous, axillary, radial, median, and ulnar nerves Motor Function: Controls muscles of the shoulder, arm, and hand Sensory Function: Provides sensation to the skin of the shoulder, arm, and hand Lumbar Plexus Formed from L1-L4, nearer to the abdominal area and partially in lower limbs Supplies ○ Anterolateral abdominal wall ○ External genitals ○ Part of the lower limbs Important nerves ○ Femoral nerve* (the largest nerve of this plexus) ○ Obturator nerve* (has some abdominal function as well) Femoral nerve Innervates the anterior thigh muscles, lower abdomen, buttocks, and the skin of the anteromedial leg and thigh Damage causes ○ Inability to extend the leg and flex the hip ○ Loss of sensation in the skin over the anteromedial aspect of the thigh Obturator Nerve Innervates the adductor muscles of the medial thigh and small hip muscles Serves the skin of the medial thigh and hip joint Damage leads to the inability to adduct the thigh and loss of sensation over the medial aspect of the tight Sacral plexus Formed from L4-L5 and S1-S4 Supplies ○ Buttocks ○ Perineum ○ Lower limbs Important nerves: ○ Sciatic nerve (innervates most of the lower limb) ○ Pudendal nerve (innervates the perineum)  Sciatic nerve The major nerve of this plexus Largest nerve of the human body Travels through the greater sciatic notch of the hip bone down to the posterior thigh Innervates the lower trunk and the posterior surface of thigh and leg Divides in the popliteal region into the: ○ Common fibular nerve innervates the lateral aspect of the leg and foot damage leads to inability to dorsiflex the foot or "footdrop“ ○ Tibial nerve innervates the posterior aspect of the leg and foot damage leads to inability to plantar flex and invert the foot or "shuffling gait" Sciatica Compression or irritation of the sciatic nerve Damage leads to inability to extend hip and to flex the knee -"sciatica“ Causes  ○ herniated disc ○ dislocated hip ○ osteoarthritis of the lumbosacral spine ○ pressure form uterus in pregnancy ○ Inflammation ○ Irritation ○ improperly administered gluteal IM injections T2-12 Rami Do not form plexus Are intercostal nerves Innervate ○ Intercostal muscles ○ Muscles and skin of the chest wall and back ○ Abdominal muscles Cutaneous Innervation and Dermatomes Each spinal nerve except C1 receives sensory input from a specific area of the skin called a dermatome A dermatome map is a diagram of the cutaneous regions innervated by the branches of each spinal nerve CN V (trigeminal nerve) innervates most of the skin of the face and scalp Knowing which spinal cord segment supplies each dermatome makes it possible to locate damaged regions of the spinal cord If the skin in a particular region is stimulated but the sensation is not perceived, the nerves supplying that dermatome are probably damaged Shingles Acute infection of the peripheral nervous system caused by HZ After chickenpox infection, the virus retreats to a posterior root ganglion Reactivation (weak immune system) leaves the ganglion and travels down sensory neurons of the skin by fast axonal transport Result in pain, discoloration of the skin, and characteristic line of skin blisters (mark the distribution dermatome)