Peripheral nerveAnatomy and Physiology

CNS

Sensory division Motor division

Autonomic nervous system

Sympathetic division

Parasympathetic division

PNS

Somatic nervous system

Hystology

Neuron

■ 4 regions

Neuron

■ Cell body Nucleus RNA Proteins

Neuron

■ Dendrites Input form other neurons

Neuron

■ Axon Only 1 per cell Action potentials Transport Long distance

Neuron

■ Presinactic terminals

Output information

Nervous Tissue: Support Cells (Neuroglia)■ Astrocytes

Abundant, star-shaped cells Brace neurons Form barrier between capillaries and neurons Control the chemical environment of the brain

Nervous Tissue: Support Cells

• Oligodendrocytes • Produce myelin

sheath around nerve fibers in the central nervous system

Nervous Tissue: Support Cells

• Satellite cells • Protect neuron cell bodies

• Myelin sheaths in jelly-roll like fashion

• One neuron

Schwann cell

• Up to 500 each neuron

• Nodes of Ranvier

Schwan cell

Myelin

■ 70 % lipid, cholesterol, and phospholipids ■ 30% protein ■ Faster conduction ■ Less energy used

Physiology

Axonal transport

■ Molecules synthesized in cell body

■ Return degradation products

Axonal transport

■ ATP energy source ■ Oxidative metabolism

Axonal transport

■ Ca calmodulin ■ Microtubules

Axonal transport anterograde

■ Kinesin ■ Fast – strong molecule attach ■ Slow – loose molecule attach ■ Impairment – terminal degeneration

Axonal transport retrograde

■ Fast, ■ 1/3 ½ from anterograde ■ Return molecules, vesicles ■ Nerve grow factor from target organ ■ HSV, Rabies, Polio and Tetanous toxin

Action potential - resting

■ Negative inside ■ Na, K, Cl ■ Passive transport ■ Channel

■ 3 mayor signals Voltage Chemical Pressure or stretch

Action potential

■ Increase memebrane resistence ■ Decreace memebrane capacitane ■ Ranvier nodes high channel concentration

Myelin

■ Current thought the membrane ■ Threshold reached ■ Self-propagation

External activation

anatomy

Peripheral nerve development

■ Ectomdermic origin ■ Motoneurons- neural

tube ■ Sensory neural crest

Neuronal navigation

■ Receptors ■ Signals ■ proteins

(a)

Fascicle

Perineurium Blood vessels

Endoneurium Nerve fibers

Anatomy

■ Fiber ■ Fascicle

Fiber types

■ Monofascicular ■ Oligofascicular ■ Polyfascicular

(b)

Axon

Endoneurium

Perineurium

Epineurium

Myelin sheath

Blood vessels

Fascicle

Connective tissue

■ Endoneurium Loose collagen Capillary network High resistance Barrier

(b)

Axon

Endoneurium

Perineurium

Epineurium

Myelin sheath

Blood vessels

Fascicle

Connective tissue

■ Perineurium Thin layer

(b)

Axon

Endoneurium

Perineurium

Epineurium

Myelin sheath

Blood vessels

Fascicle

Connective tissue

■ Epinerium Framework Vascular plexus Compression

Vascular supply

Dorsal ramus

Ventral ramus

Intercostal nerve

Lateral cutaneous

Anterior cutaneous

Spinal nerveRami communicantes

Dorsal root ganglion

Sympathetic trunk(chain) ganglion

Dorsal root

Ventral root

Sternum

Thoracic cavity

Branches of intercostal nerve

Classification of nerve fiber

Sensory receptors

• Free Nerve Endings !

• Encapsulated Nerve Endings !

• Expanded Tip Endings

- No end structure. - Most abundant. - Derived from unmyelinated nerve fibers.

Free nerve endings

-Vertical pattern. - Around the bodies of the sudoriferous glands. - Displacement of the Skin, Painful Stimuli and

Temperature.

Free nerve endings

- Great variety in size and shape. - Consist of a single myelinated nerve axon - Connective tissue sheath.

Encapsulated nerve endings

!Main types: !• Krause Bulbs • Pacinian Corpuscle • Meissner’s Corpuscle • Corpuscles of Ruffini

Encapsulated

•Glabrous skin of the palm and digits, lips, genitals •Rapidly adapting fibers. •Lower Frequency Stimulation less 50 hz

Meissner corpuscles

• Lamellar capsules • Abundant bellow the dermis of the digits. • Mechanoreceptor vibration pressure. 200 -300 HZ

Pacinian corpuscles

- Fluid-filled space traversed by collagen fibers. - Respond to Mechanical Stimuli and Tensional Forces on the

Surrounding Tissue. - Subcutaneous tissue finger.

Ruffini corpuscle

• Cylindrical or oval Bodies Semifluid core.

• Synovial membranes of certain joints, digits

• Epineurium of nerve trunks.

Krause bulb

•Epithelial cell specialized epithelial cell •Respond to Static Pressure. •Reading Braille !

Merkel disc

Spinal cord reflexes

■ Definition: Rapid, predictable and involuntary motor response to stimuli through pathways called reflex arcs.

Spinal cord reflexes

■ Two systems Autonomic reflexes (unconscious): digestion, sweating etc. Somatic reflexes: activate skeletal muscles.

Spinal cord reflexes

■ Characteristics: Structurally (number of neurons involved)

Monosynaptic arc: one synapse Polysynaptic arc: one or more association neurons.

The basic components of all human reflex arcs

Stimulus

ReceptorSkin

Sensory neuron

Spinal cord (in cross section)

Integration centerInterneuronMotor neuron

Effector

1

54

2 3

Stretch reflex

■ Monosynaptic ■ Alfa motoneurons ■ Stimulate muscle spindle

The stretch reflex

(a)(b)

Initial stimulus: muscle stretch

Afferent impulses from stretch receptor to spinal cord

Efferent impulses to alpha (α) motor neurons cause contraction of the stretched muscle that resists/reverses the stretch

Efferent impulses to antagonist muscles are damped (reciprocal inhibition)

Spinal cord (L2–L4)

Patella

Cell body of sensory neuron

Key: + Excitatory synapse – Inhibitory synapse

Motor neuron serving quadricepsMotor neuron serving antagonist muscle group (hamstrings)

Muscle spindleQuadriceps (extensors)

Hamstrings (flexors)

Muscle spindle

Patellar ligament

Interneuron

–

1

2

3

Muscle spindle

(a) (b) (d)(c)

Muscle spindleIntrafusal muscle fiber

Primary sensory (la) nerve fiber

Extrafusal muscle fiber

Time Time Time

Unstretched muscle; AP frequency constant

Stretched muscle; AP frequency increased

α − γ Neuron coactivation; AP frequency constant

α Motor neuron stimulation only; no APs, unable to signal length changes

Time

AP: Action Potential

The Golgi tendon reflex

■ Autogenic inhibition

++

+ –

Quadriceps (extensor)

Golgi tendon organ

Hamstrings (flexor)

Afferent fiber from Golgi tendon organEfferent fiber to muscle associated with stretched tendonEfferent fiber to antagonistic muscle

Spinal cord

Interneurons

Key: + Excitatory synapse – Inhibitory synapse

Golgi tendon organ

Tendon

γ Efferent motor fiber to spindle

Golgi tendon organ

CapsuleSensory fiber

Basics nerve injury

Response to trauma

■ Inflammatory response ■ Increase vascular permeability ■ Edema ■ Abnormal axonal transport ■ Vascular deficit

Nerve injury classification

■ Metabolic conduction block ■ Sunderland I – neuropraxia ■ Sunderland II – axonotmesis ■ Sunderland III ■ Sunderland IV ■ Sunderland V – neurotmesis

Metabolic conduction block

■ Local arrest of intraneural microcirculation ■ Immediately reversible when compression

removed

Sunderland I - Neuropraxia

■ Axon continuity preserved ■ Motor paralysis, some sensation spared ■ Spontaneously reversible within 3 months ■ Prolonged latency

Sunderland II - Axonotmesis

■ Axons ruptured ■ Endoneurial tube preserved ■ Fibrillations ■ Decreased amplitude

Sunderland III

■ Loss of continuity of endoneurial tube ■ Fibrillations ■ Decreased amplitude

Sunderland IV

■ Loss of continuity of perinerium ■ Completely blocked with scar tissue

Sunderland V - Neurotmesis

■ Complete nerve transection

Wallerian degeneration

■ Axonal degeneration ■ Proteolysis ■ calcium

Schuann cell response

■ Proliferation ■ Band of Bügner ■ Increase NGF receptors

Macrophage response

■ IL 1 stimulate Schuann cell ■ Increase NGF ■ Phagocytic

Cell body respose

■ Phases Reactive Recovery Degenerative