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