Upper vs. Lower Motor Neuron Lesions
Whee are Upper Motor Neurons Located?
-Brain -90% of spinal cord
Effect of Upper Motor Neuron lesions on reflexes
-Hyperreflexia -Loss of inhibition from the CNS -Cerebellum and midbrain typically "dampen" reflex response
Effect of Lower Motor Neuron lesions on reflexes
-Hyporeflexia -Disruption of reflex arc -Sensory in is disrupted -Motor out is disrupted
Causes of spinal cord compression
-Instability -Osteophytes -Tumor -Infection
Signs/symptoms of spinal nerve compression
-Myotomal weakness in mm served by that nerve -Dermatomal sensory changes in skin served by that nerve -Hyporeflexia
Where are Lower Motor Neurons located?
-Peripheral nerves -Proximal end of peripheral nerve in the spinal cord
Process of a typical reflex
-Quick stretch to golgi tendon organ -Sensory input travels along myelinated afferent fiber -Mono-synaptic activation of efferent quad motor nerve -Poly-synaptic inhibition of efferent hamstring motor nerve -Descending inhibition from CNS tracts
Reverse Supinator sign
-Results from Upper Motor Neuron lesion -Involuntary, rapid finger flexion in response to repeated tapping of the brachioradialis tendon
Babinski sign
-Results from Upper Motor Neuron lesion -Ext/ABD of toes in response to J-stroke on sole of foot
Clonus sign
-Results from Upper Motor Neuron lesion -Involuntary, rapid, rhythmic muscle contractions in response to quick stretch with end range hold
Cauda equina signs
-Saddle anesthesia -Bowel/bladder changes -Multi-segmental weakness -Multi-segmental sensory loss
2 Major descending tracts
1. Lateral -Corticospinal -Rubrospinal 2. Ventromedial - Vestibulospinal -Reticulospinal
Spinal cord starts at ___________________ and ends at _________
Base of brain; L2 Below L2 = peripheral nerves
Hoffman's sign
-Results from Upper Motor Neuron lesion -Involuntary, rapid flexion and adduction of the thumb in response to a downward flick of the ipsilateral middle finger
SIgns/symptoms of spinal cord compression
-Variable depending on spinal segmental level and degree of compression -Non-segmental weakness at and below level of lesion -Non-dermatomal sensory changes at and below level of lesion -Hyperreflexia below level of lesion -Upper motor lesion signs present below level of lesion
Organization of the Spinal Cord
1. Contains 30% of total CNS neurons 2. Ascending sensory tracts to the brain stem and thalamus 3. Descending motor tracts from the cerebral cortex and cerebellum 4. Complete circuitry for the involuntary reflexes 5. Ascending and descending tracts for intersegmental communication 6. Cell bodies for somatic motor neurons 7. Cell bodies of preganglionic autonomic neurons
2 major ascending pathways
1. Dorsal column/medial lemniscus - vibration, proprioception, and pressure 2. Spinothalamic - diffuse pain, localized pain, tempreature -crosses in spinal cord These pathways are disrupted if there is a problem with the spinal cord
What is a commissure?
Bundle of neurons passing from one side of the brain or spinal cord to the other
Where does the PNS begin?
Cell bodies on motor nerves within spinal nerves in the spinal cord
Upper Motor Neuron Lesions cause damage to the ________ nervous system
Central Nervous System
What is a group of tracts called?
Columns or funiculi
What damage do nerve lesions cause?
Depending on whether the nerve is purely motor, purely sensory, or mixed, the lesion could cause loss of motor, sensation, or both at that nerve level
What re spinal cord tracts?
Parallel axons sharing common destination, origin, and function
Lower Motor Neuron Lesions cause damage to the ________ nervous system
Peripheral Nervous System
Which portion of the disc is most prone to herniation?
The lateral portion because it does not have the ALL or the PLL
Where is the spinal nerve?
Where the dorsal and ventral nerves meet
Where are the nerves pure?
Where the nerve is purely sensory or purely motor rather than mixed
Ascending spinal cord tracts = ______________; Descending spinal cord tracts = ____________________
afferent information; efferent information
Dorsal = _____________; ventral = __________________
sensory and afferent; motor and efferent