NEUSCI | MOD 6 | PERIPHERAL NERVOUS SYSTEM

PERIPHERAL NERVOUS SYSTEM

• Includes all neural structures distal to the spinal nerves (LOWER MOTOR NEURONS)

• Axons of sensory, motor, and autonomic neurons, along with specialized sensory endings and entire postganglionic autonomic neurons

Peripheral Nerves

• is a collective term for the cranial and spinal nerves

  • Cranial nerve injuries are considered peripheral nerve injuries

  • Some textbooks consider spinal nerves as the only component of peripheral nervous system, and cranial nerves are a separate entity

Three Connective Tissue

• Each peripheral nerve consists of parallel bundles of nerve fibers and are surrounded by ________?

Epineurium

• Outermost; encloses the entire nerve trunk. The connective tissue of the epineurium is continuous with the dura mater (meninges) surrounding the CNS

Perineurium

• Middle; Surrounds bundles of axons called Fascicles

Endoneurium

• Innermost; separates individual axons

• Within the nerve, AXONS are electrically insulated from each other by _____ and by a ____?

Type A

• Typical large and medium sized, myelinated fibers - High velocity
  

Type B

• Intermediate, myelinated fibers

Type C

• Small, unmyelinated fibers

• Conduct impulses at a low velocitY

• 1⁄2 of sensory fibers in MOST PERIPHERAL NERVES

Axons of Anterior (Ventral) Rami

• Innervates the skeletal, muscular, and cutaneous areas of the limbs (UE and LE), and the Anterior and Lateral Trunk (Chest, abdomen, shoulder, hips) (Mostly muscles for movement and power)

Axons of Posterior (Dorsal) Rami

• Innervates the paravertebral muscles, posterior parts of the vertebrae, and overlying cutaneous areas (Posterior trunk) (Postural, endurance muscles)

○ Cutaneous distribution

Intervertebral Foramina

• All of the 31 pairs of spinal nerves, except the first pair and those in the sacrum (C2 - L5) exit the vertebral column through ___________ located between the adjacent vertebrae

C1

• Which spinal nerve Exits between the skull and the first cervical vertebrae?

S1-S5

• Which spinal nerves Exit from the single bone of the sacrum through the sacral foramina?

31

• How many spinal nerves do we have?

33

• How many spinal vertebra do we have?

26

• How many spinal bones do we have?

Cervical Plexus (C1-C4)

•  Innervates the superficial neck structures, including several of the muscles attached to the hyoid bone

• Also innervates the skin of the neck and posterior portion of the head (Motor/Sensory)

Brachial Plexus (C5-T1)

• The five major nerves emerging from the brachial plexus to supply the upper limb are the: Axillary, Radial, Musculocutaneous, Ulnar, and Median (MARMU)

Lumbosacral Plexus (L1-S4)

• Due to overlapping relationship, they are considered as the LUMBOSACRAL PLEXUS

• Four major nerves exit the lumbosacral plexus and enter the lower limb are: Obturator, Femoral, Tibial, and Common Fibular (Peroneal) nerve

Coccygeal Plexus (S5-C0)

• Innervation to the pelvic floor muscles and sensory cutaneous innervation to the skin over the coccyx

Movement

• Promotes the flow of blood throughout the nerves and the flow of axoplasm

Stationary

• Axoplasm thickens and becomes more resistant to flow

Movement

• Axoplasm to thin and flow more easily, facilitating retrograde and anterograde transport

Anterograde Transport

• Delivers new structural and signaling components to their proper locations in the neurons

Retrograde Transport

• Moves chemicals from the axons and surrounding structures to the cell body

Endoneurium

• Connective tissues support the changes in length that nerves undergo during movements

• Increase in nerve length without injury is made possible by axons wrinkling within the _______ when the nerve is not stretched

Tensile Stress

• As a nerve is stretched → Axons unfold → Fascicles glide to each other → Stretch exceeds capacity → ________ (Stretching of nerves – Tingling sensation)

Neuromuscular Juntion

• Also known as MYONEURAL JUNCTION, MOTOR END-PLATE, SYNAPSE

•  It is a chemical synapse formed when motor axons synapse with muscle fibers causing muscle contraction

Acetylcholine (ACh)

• This nerve-muscle synapse requires only depolarization of the motor axon, releasing ______, which diffuses across the synaptic cleft and binds with receptors to elicit depolarization of the muscle membrane

• Actions of neurotransmitters is always EXCITATORY

• ______ released into the synaptic cleft is rapidly broken down to acetic acid and choline by the enzyme

Acetylcholinesterase

• Keeps ACh from accumulating within the synaptic cleft

Choline

• Reabsorbed by the presynaptic terminal → Forms ACh

Acetic Acid

• Used for glucose metabolism

Sensory Changes

• Decreased or lost sensation and/or abnormal

sensations

• Hyperalgesia, Dysesthesia, Paresthesia, Allodynia

• Damages in the PN are not uniform, it may manifest in different degrees/intensities

Autonomic Changes

• Lack of sweating and loss of sympathetic control of smooth muscle fibers in arterial walls, impotence and difficulty regulating blood pressure, heart rate, sweating, and bowel and bladder functions

Motor Changes

• Paresis (weakness) or paralysis, muscle atrophy, fibrillation, and fasciculation

Trophic Changes

• Skin becomes shiny, nails become brittle, and subcutaneous tissues thicken, poor healing of wounds and infections, and neurogenic joint damage

Wallerian Degeneration

A. CHANGES IN DISTAL SEGMENT OF THE AXON

1. The changes spread distally from the site of the lesion and include its terminations

2. On the first day, the axon becomes swollen and irregular; by the third or fourth day, the axon is broken into fragments

3. Entire axon is destroyed within a week

Proximally

B. CHANGES IN PROXIMAL SEGMENT OF THE AXON

• Similar to those that take place in the distal segment but extend only _______ above the lesion as far as the first node of Ranvier (Only affected by degeneration)

Retrograde Degeneration

C. CHANGES IN THE NERVE CELL BODY IN WHICH THE AXON RISES

• The changes that take place in the proximal segment of the axon

• Chromatolysis and synaptic stripping occurs

• The dendrites of the healthy neuron that are connected to the damaged neuron will disconnect to prevent damage to the healthy one. The unhealthy neuron will degenerate and become Schwann cells

• Basically in retrograde degeneration → whole neuron is damaged

Chromatolysis

• The Nissl material becomes fine, granular and dispersed throughout the cytoplasm

Synaptic Stripping

• Synaptic terminals withdraw from the surface of the injured nerve cell body and its dendrites and are replaced by Schwann cells

Compression

• Sustained pressure applied externally, such as tourniquet, or internally, such as from bone, tumor, or soft tissue impingement resulting in mechanical or ischemic injury. Most common

Laceration

Mechanism of Nerve Injury 

• Knife, gunshot, surgical complication, injection injury (usual in buttocks)
  

Neuropaxia

• Mild degree of neural insult that results in blockage of impulse conduction across the affected segment

Axonotmesis

• Only the axon is physically disrupted, with preservation of the enveloping endoneurial and other supporting connective tissue structures (perineurium and epineurium)

Neurotmesis

• severe; complete disruption of the axon and all supporting connective tissue structures, whereby the endoneurium, perineurium, and epineurium are no longer in continuity

SUNDERLAND’S CLASSIFICATION

Type 1

SUNDERLAND’S CLASSIFICATION

• Injury corresponds to Seddon’s designation of neurapraxia

Type 2

SUNDERLAND’S CLASSIFICATION

• Involves loss of axonal continuity with preservation of all supporting neural structures, including the endoneurium

Type 3 & 4

SUNDERLAND’S CLASSIFICATION

• result in progressively more neural disruption

• (Under axonotmesis, but not enough for neurotmesis classification)
  

Type 5

SUNDERLAND’S CLASSIFICATION

• corresponds to Seddon’s neurotmesis (complete neural disruption)

Mononeuropathy

• is focal dysfunction, and multiple mononeuropathy is multifocal

• Carpal Tunnel Syndrome is the most common _______

Multiple Mononeuropathy

• presents as asymmetric involvement of individual nerves

  ○ Ex. (L) foot, thigh, hand

Polyneuropathy

• is a generalized disorder that typically presents distally and symmetrically

○ Ex. Both (L) and (R) segments, distal to proximal

Mononeuropathies

•  Various types of trauma, including repetitive stimuli, prolonged compression, or wounds, may injure peripheral nerves

• Depending on the severity of damage, traumatic injuries to peripheral nerves are classified into three categories:

• Traumatic Myelinopathy

• Traumatic Axonopathy

• Severance

Multiple Mononeuropathies

• Involvement of two or more nerves in different parts of the body occurs most commonly when diabetes or vasculitis cause ischemia (loss of blood supply) of the nerves

Vasculitis

• ______ the inflammation of blood vessels, may cause multiple mononeuropathy by restricting blood flow or by weakening vessel walls, resulting in rupture

Polyneuropathies

• HALLMARK: Symmetric involvement of sensory, motor, and autonomic fibers, often progressing from distal to proximal

• Polyneuropathies are not due to trauma or ischemia. The cause can be TOXIC (lead, arsenic, nickel), metabolic, or AUTOIMMUNE (GBS)

• The most common causes of polyneuropathies are diabetes, nutritional deficiencies secondary to alcoholism, and autoimmune diseases

Stocking/Glove Distribution

• Distal pattern of symptoms typically begin in the feet and then appear in the hands

Guillain-Barre Syndrome

• Most common polyneuropathy (Caused by raw meat)

Lambert-Eaton Myasthenic Syndrome (LEMS)

• is a unique condition characterized by weakness and  fatigability of proximal limb muscles with sparing of  ocular muscles. Weakness peaks after rest or  immediately upon awakening in the morning

• There is reduced release of acetylcholine quanta  from the presynaptic nerve terminal.

• Weakness and fatigability primarily affect the lower  limbs

BOTULISM

• Wound infection or ingestion of the botulinum toxin  from improperly stored foods causes interference  with the release of ACh from the motor axon

• Botulinum toxin (Botox) is used therapeutically in  people with spasticity or dystonia, to weaken  overactive muscles

Myasthenia Gravis

• "grave muscle weakness”

• an autoimmune disease that damages ACh receptors at the neuromuscular junction, repeated use of a  muscle leads to increasing weakness

• The hallmark of MG is muscle weakness that  increases during periods of activity and improves  after periods of rest

• Most common involved: eye and eyelid movement, facial expression, chewing, talking, and swallowing

Spinal Cord

• Aka known as medulla spinalis

• The spinal cord is roughly cylindrical in shape

• The spinal cord is continuous with the medulla and ends at  the L1-L2 intervertebral space in adults

• Young child: upper border of L3

• 42-45cm in length, with a diameter of 10mm

• It occupies the upper two-thirds of the vertebral canal of the vertebral column and is surrounded by the three meninges: Dura mater, Arachnoid mater, Pia mater

Cerebrospinal Fluid

• Surrounds the spinal cord in the subarachnoid space, acts as cushion to prevent damage/trauma to the SC

Cervical Enlargement

• Which enlargement si associated with Brachial Plexus, C5-T1?

Lumbar Enlargement

• Which enlargement is associated with Lumbosacral Plexus, L4-S1?

Conus Medullaris

• Spinal cord tapers inferiorly at the cone-like region called ________?

Filum Terminale

• Prolongation of the pia mater, a bundle of connective tissue and glia that descends to attach to the posterior surface of the coccyx

Cauda Equina

• horse’s tail, roots that extend inferiorly from lumbosacral enlargement and conus medullaris

L2-S5 Nerve Roots

• The _______ travel downward below the end of the spinal cord before exiting the vertebral canal

Meninges

• The spinal cord and brain are surrounded by connective tissue membranes called ____?

Dura Mater

• “tough mother”; The most superficial and thickest membrane, also known as PACHYMENINX

Arachnoid Mater

• “spider layer”; middle layer

• Damaged = Bleeding due to deep connections with blood vessels
  

Pia Mater

• “delicate mother”; deepest, tightly bound to the surface of the spinal cord

Epidural Space

• Between the walls of the vertebral canal and the dura mater of the spinal cord that contains spinal nerve roots, blood vessels, etc.

  ○ Area where anesthesia is administered (Epidural or spinal anesthesia)

  ○ Epidural anesthesia (For widespread anesthesia effects that is given usually for childbirth process)

Spinal Tap/Lumbar Puncture

• L4-L5 - Ligaments are thin enough that syringes can puncture

  ■ For CSF samples

Subdural Space

• Between Dura and arachnoid mater

Subarachnoid Space

• Between the pia mater and arachnoid mater

Contains CSF

○ MEDIAL: Proprioceptive and touch

○ LATERAL: Pain and temperature

• DORSAL ROOT GANGLION: contains the cell bodies of sensory neurons

  ○ _______: Proprioceptive and touch

  ○ _______: Pain and temperature

Anterior Cord

• The ________ also has two anterolateral sulcus, where nerve rootlets emerge from the cord

Posterior Cord

• The ________ has two posterolateral sulcus, where nerve rootlets enter the cord

Funiculi

• White matter in each half of the spinal cord is organized into three columns, or _______; myelinated

  ○ Ventral

  ○ Dorsal

  ○ Lateral

Dorsal Horn

• Thin, sensory. Containing endings and collaterals of first-order sensory neurons, interneurons, and dendrites and somas of tract cells

Ventral Horn

• Larger, motor. Contains the cell bodies of

  lower motor neurons (Alpha)

Lateral Horn

• Autonomic function. contains the cell bodies of preganglionic sympathetic (T1-L2) and preganglionic parasympathetic (S2-S4)

Medial Group

• Innervating the skeletal muscles of the neck and trunk, including the intercostal and abdominal musculature (postural, breathing, etc)

  ■ Responsible for axial muscles

Central Group

• Innervate diaphragm (PHRENIC NUCLEUS) → (C3-C5)

  ○ Innervate the sternocleidomastoid and trapezius muscles (ACCESSORY NUCLEUS) → CN XI (Spinal Accessory Nerve)

  ○ second lumbar down to the first sacral segment of the cord (LUMBOSACRAL NUCLEUS)→ (L2-S1)

  ■ Onuf’s Nucleus/Onufruwickz Nucleus →

  S2-S4 - Responsible for Sphincter (Bowel/Bladder) Erection/Ejaculation

Lateral Group

• Innervating the skeletal muscles of the limbs

• Responsible for appendicular muscles

  (C5-T1, L2-S2-S4)

Substantia Gelatinosa

NERVE CELL GROUPS OF POSTERIOR GRAY COLUMN

• Pain, Temperature, and Touch

Nucleus Proprius

NERVE CELL GROUPS OF POSTERIOR GRAY COLUMN

• Senses of position and movement

  (proprioception), two-point discrimination, and vibration

Nucleus Dorsalis

NERVE CELL GROUPS OF POSTERIOR GRAY COLUMN

• Proprioceptive endings (neuromuscular

  spindles and tendon spindles)

Visceral Afferent Nucleus

NERVE CELL GROUPS OF POSTERIOR COLUMN

Lamina I-VI

• Through which lamina is dorsal horn located?

Lamina VII

• Through which lamina is intermediolateral horn?

Lamina VII-IX

• Through which lamina is ventral horn located?

Lamina X

• Through which lamina is central region located?

Anterior Spinal Artery

• Travels along the anterior surface of the spinal cord to supply the anterior two thirds of

  the spinal cord

• Damaged ASA – total motor loss, impaired

  sensory/auton