Upper motor neuron lesion spasticity hyperreflexia contralateral

If upper motor neurons to a muscle are severed, the ability to control and initiate movement in the muscle may be lost. However,

Table 3.1. Voluntary (somatic and branchiomotor) motor components of cranial nerves.

Nucleus

Type

Nerve

Muscles

Oculomotor Midbrain

Trochlear Midbrain

Somatic Preotic somites

Somatic Preotic somites

Trigeminal motor Branchiomotor Pons for chewing first arch

Abducens Pons

Somatic Preotic somites

III Oculomotor

IV Trochlear

Vc Mandibular

VI Abducens

Levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, inferior oblique

Superior oblique

Temporalis, masseter, digastric (anterior belly), mylohyoid, medial and lateral pterygoids, tensor palati, tensor tympani

Lateral rectus

Facial motor Branchiomotor VII Facial

Pons second arch

Nucleus ambiguus

Medulla for swallowing, phonation

Hypoglossal Medulla

Branchiomotor (see Section 16.3) third arch fourth arch sixth arch

Somatic Occipital somites

IX Glossopharyngeal

X Vagus, pharyngeal branches

X Vagus, recurrent laryngeal

XI Spinal accessory

XII Hypoglossal

Muscles of facial expression, buccinator, stapedius, occipitofrontalis, stylohyoid, digastric (posterior belly), platysma

Stylopharyngeus Muscles of pharynx Muscles of larynx Sternocleidomastoid, trapezius

Intrinsic tongue muscles, hyoglossus, genioglossus, styloglossus lower motor neurons are intact, and since some of the fibres to lower motor neurons from elsewhere are inhibitory, other centres which influence lower motor neurons, for example basal ganglia (Section 3.1), may cause an increase in muscle tone (hypertonic, spastic). Also, reflexes are disinhibited (hyperreflexic, exaggerated). The muscle will not become atrophied except through disuse. In this case, since upper motor neurons decussate before synapsing with cell bodies of lower motor neurons, the paralysis will be on the side opposite to the site of the lesion; they are contralateral with respect to each other. See Section 11.6 for consideration of facial nerve upper and lower motor neuron lesions (UMNL and LMNL, respectively).

These characteristics of UMNL and LMNL are important. Get them straight now! Study Table 3.1.

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Responses

  • alem temesgen
    Why are upper motor neuron lesions hyperreflexic?
    8 years ago
  • helen
    Why hypereflexia is upper motor neuron?
    8 years ago
  • Johanna
    Why upper motor neuron lesion cause hyperreflexia?
    8 years ago
  • mirren
    Is upper motor neoron trochler contralateral?
    7 years ago
  • gerda
    Why hypereflexia with upper motor nerve lesion?
    2 years ago

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