Lower Motor Neurons Flashcards
How are LMN connected and what is their function?
1 MN is connected to a group of muscle fibers, making a motor unit.
They are the link between UMN and muscles.
They are responsible for voluntary movements
What happens if LMN are damaged? What are the clinical signs?
muscle weakness flaccidity hypotonia loss of tendon reflexes loss of sensation
Classification of motor neurons
Alpha MN: most abundant and for contraction, innervate extrafusal muscle fibers
Beta MN: for slow twitch muscles, innervate intrafusal muscle fibers and collateral extrafusal fibers
Gamma MN: for propioception, innervate intrafusal fibers and sensory afferent fibers
Where are LMN located?
At the anterior horn of the spinal cord and motor nuclei of cranial nerves
Causes of LMN lesion
- Trauma
- irradiation
- neoplasticism invasion
- viral (Parsonage Turner syndrome)
- allergic
- electrical injury
- narrow thoracic outlet
Median nerve lesion
Origin C5 - T1
No pronation of forearm
No flexion of index finger and terminal phalanx of thumb
Weakened flexion of fingers
Sensory impairment over radical 2/3 of Palm
Carpal tunnel syndrome
Compression of the nerve at wrist
Dysesthesia and pain on fingers
Paresthesia, worsened at night
Sensory loss of thumb, index and middle finger
Ulnar nerve lesion
Origin C8 - T1
Claw hand deformity
Wasting of hand muscles
Deficit in wrist flexors
No adduction and abduction of fingers
Radial nerve lesion
Origin C6 - C8 (mainly C7)
Paralysis of:
- Elbow extension and flexion (when hand perpendicular to floor)
- supination of forearm
- extension of wrist and fingers
- extension and abduction of thumb
- sensory impairment on radial part of dorsal hand
Lumbosacral plexus lesion
Weakness and paralysis of all leg muscles
Amyotrophy
Areflexia
Anesthesia from toe to perianal region
No sphincterian involvement
Femoral nerve
Origin L2,3,4 roots
Weakness of extension of lower leg
Wasting of quadriceps muscle
Failure in fixation of knee
No knee tendon reflex
Sciatic nerve lesion
No knee flexion
Weakness of gluteal muscles
Paralysis of all muscles below knee
Common peroneal nerve
Weakness in dorsoflexion of foot
Weakness in eversion (outside rotation)
Numb dorsum of foot
Tibial nerve lesion
Calcaneovalgus deformity of foot
Weakness in plantar flexion and inversion
No sensation at plantar aspect of foot
No Achilles’ tendon reflex
what can cause muscle fasciculations?
LMN lesions, pericaronial and axonal membrane instabilites
