Chapter 12 Flashcards
What is included in the peripheral nervous system?
cranial nerves
peripheral nerves
Cranial nerves:
arising from the brain and brainstem
Peripheral nerves:
including all neural structures (axons of sensory, motor, and autonomic neurons) distal to the spinal nerves e.g., the median and tibial nerves
What are the three connective tissue sheaths of peripheral nerves?
endoneurium
perineurium
epineurium
Endoneurium:
Separates individual axons
Perineurium:
Surrounds bundles of axon (fascicles)
Epineurium:
Encloses the entire nerve trunk.
Function of peripheral nerves:
Supply both the viscera (autonomic) and somatic structures
What kind of axons are somatic peripheral nerves?
sensory
autonomic
motor
What do cutaneous branches supply?
the skin and subcutaneous tissues, including sensory and autonomic related information
What do muscular branches supply?
the muscles, tendons, and joints
How are peripheral axons classified?
according to diameter and speed of conduction
What are some examples of peripheral nerves?
Ia, Ib, II, Aα, and C
From where does the cervical plexus arise?
arising from ant. rami of C1-C4
What forms the brachial plexus?
formed by ant. rami of C5-T1
What forms the lumbar plexus?
from ant. rami of L1-L4
What forms the sacral plexus?
from (part of L4) – S4
Function of cervical plexus:
Provides cutaneous sensory information from the posterior scalp to the clavicle
What does cervical plexus innervate?
Innervates the anterior neck muscles and diaphragm.
What is innervated by the brachial plexus?
Entire upper limb is innervated by the brachial plexus branches.
What does the lumbar plexus unnervate?
the skin and muscles of the anterior and medial thigh
What does the sacral plexus innervate?
Innervates the posterior thigh and most of the leg and foot; contains parasympathetic axons
What does movement of promote?
blood flow
flow of axoplasm through the axons
What does blood flow throughout the nerves do?
supply nutrition and oxygen and to remove waste from neural tissues
What does flow of axoplasm through the axon do?
facilitates transport of chemicals from the axons and surrounding structures to the cell body & vice versa
Where do motor axons synapse with muscle fiber?
at neuromuscular junctions
What are signs of peripheral nerve damage?
sensory
autonomic
motor
What does sensory changes include?
decreased or lost sensation
What is included in abnormal sensation?
Hyperalgesia
Dysesthesia
Paresthesia
Allodynia
What do autonomic changes depend on?
the pattern of axonal dysfunction
Autonomic changes in a single nerve:
Signs are usually observed only if the nerve is completely severed
Autonomic changes in many nerves:
Problems may include difficulty regulating blood pressure, heart rate, sweating, bowel and bladder functions, and impotence.
Signs of motor changes in peripheral nerves
paresis or paralysis
Mononeuropathy:
Involves a single nerve and is considered a focal dysfunction
Multiple mononeuropathy
Involves several nerves and is multifocal
Polyneuropathy
Involves many nerves and is a generalized disorder that typically has a distal and symmetrical presentation.
Classification of traumatic injuries to peripheral nerves:
Traumatic myelinopathy
Traumatic axonopathy
Traumatic severance
What is traumatic myelinopathy?
loss of myelin limited to the site of injury.
What is affected by myelinopathy?
function of large diameter axons
What causes traumatic myelinopathy?
focal compression
What does traumatic axonopathy disrupt?
Wallerian degeneration; occurs distal to the lesion.
What does axonopathies affect?
all sizes of axons; reflexes, somatosensation, and motor functions are significantly reduced or absent
Why are regenerating axons able to reinnervate appropriate targets?
because myelin and connective tissues remain intact
When does traumatic severance occur?
when nerves are physically divided by excessive stretching or a laceration.
What is affected in traumatic severance?
Axons and connective tissue
What happens when axons and connective tissue are completely interrupted?
immediate loss of sensation and/or muscle paralysis in the area supplied.
In traumatic severance, when does Wallerian degeneration begin?
distal to the lesion 3 to 5 days later. Then axons in the proximal stumps begin to sprout
What does multiple mononeuropathy involve?
Involves two or more nerves in different parts of the body
-asymmetrical presentation
When does multiple mononeuropathy occur?
when diabetes or vasculitis (inflammation of blood vessels) cause ischemia of the nerves
What are the hallmark signs of polyneuropathy?
symmetrical involve-ment of sensory, motor, and autonomic fibers, often progressing from distal to proximal
Where doe symptoms typically being in polyneuropathy?
begin in the feet and then appear in the hands and areas of the body supplied by the longest axons
What are the causes of polyneuropathy?
not trauma or ischemia; can be toxic, metabolic or autoimmune
common causes: diabetes, nutritional deficiencies secondary to alcoholism and autoimmune diseases
What is Charcot-Marie-Tooth diease?
common inherited for of polyneuropathy
What does Charcot-Marie-Tooth diease cause?
paresis of muscles distal to the knee with resulting foot drop, step-page gait, frequent tripping, and muscle atrophy ;in progression, muscle atrophy and paresis affect the hands.
What does therapy for Charcot-Marie-Tooth diease involve?
strengthening, stretching, conditioning, muscle, joint and skin protection
Myasthenia gravis:
an autoimmune disease that damages ACh receptors at the neuromuscular junction
What is myopathy?
intrinsic to muscles
What is intact in myopathy?
Sensation and autonomic function remain intact because the nervous system is not affected by myopathy.
What can nerve conduction study (NCS) differentiate between?
processes between primarily demyelinating (myelinopathy) and damaging axon (axonopathy)
UMN and LMN paresis
mononeuropathy and polyneuropathy
Local conduction block and Wallerian degeneration
What signs correlate highly with electrodiagnostic evidence of peripheral neuropathy?
Absence of ankle jerk reflex despite facilitation
Impaired vibration
Impaired position sense of the great toe
