A lower motor neuron lesion is a lesion which affects nerve fibers traveling from the lower motor neuron(s) in the anterior horn/anterior grey column of the spinal cord, or in the motor nuclei of the cranial nerves, to the relevant muscle(s).One major characteristic used to identify a lower motor neuron lesion is flaccid paralysis – paralysis accompanied by loss of muscle tone. This is in contrast to an upper motor neuron lesion, which often presents with spastic paralysis – paralysis accompanied by severe hypertonia. Signs and symptoms
Muscle paresis or paralysis
Fibrillations
Fasciculations – caused by increased receptor concentration on muscles to compensate for lack of innervation. Hypotonia or atonia – Tone is not velocity dependent. Hyporeflexia - Along with deep reflexes even cutaneous reflexes are also decreased or absent. Strength – weakness is limited to segmental or focal pattern, Root innervated patternThe extensor plantar reflex is usually absent. Muscle paresis/paralysis, hypotonia/atonia, and hyporeflexia/areflexia are usually seen immediately following an insult. Muscle wasting, fasciculations and fibrillations are typically signs of end-stage muscle denervation and are seen over a longer time period. Another feature is the segmentation of symptoms – only muscles innervated by the damaged nerves will be symptomatic. Causes
The most common causes of lower motor neuron injuries are trauma to peripheral nerves that serve the axons, and viruses that selectively attack ventral horn cells.
Aphagia is the inability or refusal to swallow. The word is derived from the Ancient Greek prefix α, meaning "not" or "without," and the suffix φαγία, derived from the verb φαγεῖν, meaning "to eat." It is related to dysphagia which is difficulty swallowing (Greek prefix δυσ, dys, meaning difficult, or defective), and odynophagia, painful swallowing (from ὀδύνη, odyn(o), meaning "pain"). Aphagia may be temporary or long term, depending on the affected organ. It is an extreme, life-threatening case of dysphagia. Depending on the cause, untreated dysphagia may develop into aphagia. Behavioural classification
The following behavioural classifications result from studies performed on rats, in which lesions were made on the lateral hypothalamus region in the brain. Passive aphagia: An animal with passive aphagia will not respond to food if it is presented. However, if food is inserted into the mouth, the animal will chew. Active aphagia: Active aphagia is a complete rejection of food. The animal will physically push food away or move its head from it. One might first sample the food by smelling or tasting, then spit out anything in the mouth. Afterwards the animal will show a complete repulsion to the food. The animal reacts to food as if it is bitter or foul. Mixed aphagia: When presented with food, the animal initially does not react positively or negatively. However, when food is placed in the mouth, the animal demonstrates active aphagia, spitting out the food and refusing to eat thereafter.These studies point to the function of the hypothalamus in regulating food intake.