Peripheral Nerve Diseases; Anatomy, Physiology and Pathophysiological Process

1. Peripheral Nerve Diseases; Anatomy, Physiology and Pathophysiological Process Berrin Aktekin Yeditepe University Department of Neurology

2. Functional Organization of the PNS Figure 14.1

4. Basic Anatomical Scheme of the PNS in the Region of a Spinal Nerve A nerve is composed of numerous nerve fibers Figure 14.2

6. Spinal Nerves • 31 pairs – contain thousands of nerve fibers • Connect to the spinal cord • Named for point of issue from the spinal cord - 8 pairs of cervical nerves (C1 – C8) - 12 pairs of thoracic nerves (T1 – T12) - 5 pairs of lumbar nerves (L1 – L5) - 1 pair of coccygeal nerves (Co1)

7. Spinal Nerves Posterior View

8. Spinal Nerves • Connect to the spinal cord by the dorsal root and ventral root • Dorsal root – contains sensory fibers - cell bodies located in the dorsal root ganglion • Ventral root– contains motor fibers arising from anterior gray column

9. Spinal Nerves • Branch into dorsal ramus and ventral ramus - dorsal and ventral rami contain sensory and motor fibers • Rami communicantes – connect to the base of the ventral ramus - lead to the sympathetic chain ganglia

10. Spinal Nerves

11. Innervation of the Back • Dorsal rami – innervate back muscles - follow a neat, segmented pattern - innervate a horizontal strip of muscle and skin (in line with emergence point from the vertebral column)

12. Innervation of the Back Figure 14.7b

13. Innervation of the Anterior Thoracic and Abdominal Wall • Thoracic region – ventral rami arranged in simple, segmented pattern • Intercostal nerves supply intercostal muscles, skin, and abdominal wall - each gives off lateral and anterior cutaneous branches

14. Introduction to Nerve Plexuses • A network of nerves • Ventral rami (except T2 – T12) - branch and join with one another - form nerve plexuses in the cervical, brachial, lumbar, and sacral regions - primarily serve the limbs - fibers from ventral rami crisscross

15. Motor Unit=Myotom

18. The Cervical Plexus • Buried deep in the neck under the sternocleidomastoid muscle • Formed by ventral rami of first 4 cervical nerves (C1 – C4) • Most are cutaneous nerves • Some innervate muscles of the anterior neck • Phrenic nerve – major nerve

19. The Brachial Plexus and Innervation of the Upper Limb • Brachial plexus lies in the neck and axilla • Formed by ventral rami of C5 – C8 • Cords give rise to main nerves of the upper limb

20. Fig 14.9a The Brachial Plexus

21. Lumbar Plexus and Innervation of the Lower Limb • Arises from L1 – L4 • Smaller branches innervate the posterior abdominal wall and psoas muscle • Main branches innervate the anterior thigh - femoral nerve innervates anterior thigh muscles - obturator nerve innervates adductor muscles

22. The Lumbar Plexus

23. Sacral Plexus • Arises from spinal nerves L4 – S4 • Caudal to the lumbar plexus • Often considered with the lumbar – lumbosacral plexus • Sciatic nerve – largest nerve - 2 nerves in one sheath: Tibial nerve – innervates most of the posterior lower limb; Common fibular (peroneal) nerve – innervates muscles of the anterolateral leb

24. The Sacral Plexus

25. Autonomic Nervous System • General visceral motor part of the PNS • Has 2 divisions (with opposite effects): - Parasympathetic: ‘housekeeping’ activities (rest and digest) - Sympathetic: extreme situations (fight or flight)

31. Sensory System • Five sense !!! • Peripheral Sensory System • Spinothalamic • Dorsal Column • Cortical-integrative Sensory System • Visceral Sensory System

32. Innervation of the Skin: Dermatomes • Dermatome – an area of skin • Innervated by cutaneous branches of a single spinal nerve • Upper limb – skin is supplied by nerves of the brachial plexus • Lower limb: Lumbar nerves – anterior surface Sacral nerves – posterior surface

34. Peripheral Sensory System • Spinothalamicsystem-Cutaneous • Pain- • Temperature • Light touch/pressure • Dorsal Column-Medial Lemniscal System-Proprioception • Vibration • Position

36. Spinothalamic system

37. Dorsal Column-Medial Lemniscal System-

38. Peripheral Sensory Receptors • Most fit into 2 main categories: 1. free nerve endings of sensory neurons - monitor general sensory information such as touch, pain, pressure, temperature, and proprioception 2. complete receptor cells – specialized epithelial cells or small neurons that transfer sensory information to sensory neurons - monitor most special sensory information such as taste, vision, hearing, and equilibrium

39. Sensory Receptors of the PNS • Also classified according to: a) Location – based on body location or location of stimuli to which they respond b) Type of stimulus detected – kinds of stimuli that most readily activate them c) Structure – divided into 2 broad categories free or encapsulated nerve endings

40. Classification by Location • Exteroceptors – sensitive to stimuli arising from outside the body - located at or near body surfaces - include receptors for touch, pressure, pain, temperature, and most receptors of the special sense organs • Proprioceptors – monitors degree of stretch and sends input on body movements to the CNS - located in musculoskeletal organs such as skeletal muscles, tendons, joints, and ligaments • Interoceptors(visceroceptors) – receive stimuli from internal viscera (digestive tube, bladder, lungs) - monitor a variety of stimuli such as changes in chemical concentration, taste stimuli, stretching of tissues, and temperature - activation causes visceral pain, nausea, hunger, or satiety

41. Classification by Stimulus Detected • Mechanoreceptors – respond to mechanical forces - such as touch, pressure, stretch, vibrations, and itch • Thermoreceptors – respond to temperature changes • Chemoreceptors – respond to chemicals in solution (molecules tasted or smelled) and to change in blood chemistry • Photoreceptors in the eye – respond to light • Nociceptors – respond to harmful stimuli that result in pain (noci = harm)

49. Peripheral Neuropathy • Weakness or sensory loss or both based on nerve injury • Generally distal symptoms, legs before arms, but there are exceptions • Mostly symmetrical but can be asymmetric or focal • Small fiber - diminished pain/temperature, preserved strength, reflexes • Large fiber - loss position, vibration touch/pressure, areflexia

50. Symptoms of Peripheral Neuropathies • Symptoms are related to the type of affected nerve and may be seen over a period of days, weeks, or years • Muscle weakness is the most common symptom of motor nerve damage • Sensory nerve damage causes a more complex range of symptoms because sensory nerves have a wider, more highly specialized range of functions