Jaw jerk (masseter reflex)

Mô tả: Percussion of the chin causes contraction of the masseter muscles due to activation of a monosynaptic stretch reflex.6,57 The jaw jerk reflex may be present in a proportion of normal individuals without neurological disease. RELEVANT NEUROANATOMY AND TOPOGRAPHICAL ANATOMY6

Nguyên nhân: Common • Normal variant • Diffuse white matter disease (e.g. lacunar infarction) • Vascular dementia

Cơ chế: A brisk jaw jerk reflex is a sign of bilateral upper motor neuron disease. Loss of supranuclear innervation of the motor trigeminal nucleus causes hyperexcitability of alpha motor neurons innervating the masseter muscles (i.e., hyperreflexia, see ‘Hyperreflexia’ in this chapter).107

Ý nghĩa lâm sàng: A brisk jaw jerk reflex is a sign of bilateral upper motor neuron disease above the pons.