Final answer:
Tonic neck reflex or Fencer position usually refers to a newborn reflex fading by 6 months, but the question seems to address conditions like opisthotonos and spasmodic torticollis (cervical dystonia), which are unconventional neural or muscular responses leading to abnormal postures. Opisthotonos is linked to tetanus and muscle spasms due to neurotransmitter disruption, whereas spasmodic torticollis involves involuntary neck muscle contractions. Assessing these conditions involves testing the accessory nerve's function via muscle strength exercises.
Step-by-step explanation:
The term tonic neck reflex, also referred to as the Fencer position, relates to a primitive reflex found in newborns that simulates a fencer's stance and typically fades by 6 months of age. However, the question seems to describe conditions such as opisthotonos and spasmodic torticollis (cervical dystonia), which are associated with abnormal neck and head postures in adults. Opisthotonos is a severe condition characterized by uncontrolled muscular spasms and backward arching of the neck and spine, often seen in patients with tetanus. This posture results from the action of specific pathogen-produced toxins that block neurotransmitters responsible for muscle relaxation, such as GABA, causing extreme muscle spasms.
Spasmodic torticollis, on the other hand, involves involuntary contractions of the neck muscles, leading to abnormal postures like the head being tilted to one side or forward or backward. In identifying and assessing neuropathies or muscular issues related to these conditions, the function of the accessory nerve can be examined through the strength and movement tests of the sternocleidomastoid and trapezius muscles.
Muscle strength testing, including flexing and extending the neck or shoulder shrugging against resistance, helps determine the integrity of muscles and nerves. A clasp-knife response, which may indicate upper motor neuron disease, is one example of a reflex that is tested during such a neurological exam. Any asymmetry in strength or movement may suggest damage or dysfunction of the accessory nerve or associated muscles.