THE GLOSSOPHARYNGEAL AND VAGUS NERVES (NINTH AND TENTH CRANIAL NERVES) Medical Assignment Help

The glossopharyngeal nerve

This mixed nerve arises in the medulla and leaves the skull through the jugular foramen with the vagus and accessory nerves. Its sensory fibres supply all sensation to the tonsillar fossa and pharynx (the afferent pathway of the gag reflex), and taste to the posterior third of the tongue. Motor fibres supply the stylopharyngeus muscle, autonomic  fibres supply the parotid gland, and a sensorybranch supplies the carotid sinus.

Isolated lesions are most unusual, since lesions at the jugular foramen also affect the vagus and sometimes the accessory nerves.

Glossopharyngeal neuralgia This is a rare, severe, paroxysmal neuralgia. Pain involves the pharynx and is triggered by swallowing.

The vagus nerve

This mixed nerve supplies the striated muscle of the pharynx (efferent pathway of the gag reflex), the larynx (including the vocal cords via the recurrent laryngeal nerves) and the upper oesophagus. There are some sensory fibres from the larynx. Parasympathetic fibres supply the heart and abdominal viscera

Ninth and tenth nerve lesions

A unilateral lesion of the ninth nerve causes diminished sensation on one side of the pharynx. A unilateral tenth nerve lesion causes unilateral failure of voluntary and reflex elevation of the soft palate, which is drawn to the side opposite the lesion. Individual lesions of these nerves are unusual.

Bilateral combined lesions of the ninth and tenth nerves cause weakness of elevation of the palate, depression of palatal sensation and loss of the gag reflex.

The cough is depressed and the vocal cords are paralysed. The patient complains of difficulty in swallowing, choking (particularly with fluids) and hoarseness. The causes of ninth and tenth nerve lesions are given.

Lesions of the recurrent laryngeal nerves

Unilateral paralysis of this important branch of each vagus causes hoarseness (dysphonia) and depression of the forceful, explosive part of the cough reflex. Bilateral acute lesions, e.g. postoperatively, are a serious emergency and cause respiratory obstruction. The left recurrent laryngeal nerve (which loops beneath the aorta) is more commonly affected than the right.

Causes of recurrent laryngeal nerve lesions include:

  1. Mediastinal tumours
  2. Aneurysm of the aorta
  3. Trauma or surgery to the neck

THE ACCESSORY NERVE (ELEVENTH CRANIAL NERVE)

This motor nerve to the trapezius and sternomastoid muscles arises in the medulla and leaves the skull through the jugular foramen with the ninth and tenth nerves. A lesion of the eleventh nerve causes weakness of the sternomastoid (rotation of the head and neck to the opposite side) and the trapezius (shoulder shrugging). The principal causes are shown.

THE HYPOGLOSSAL NERVE (TWELFTH CRANIAL NERVE)

The motor nerve to the tongue arises in the medulla and leaves the skull through the anterior condylar foramen.

Twelfth nerve lesions

A LMN lesion of the twelfth nerve leads to unilateral weakness, wasting and fasciculation of the tongue. When protruded the tongue deviates towards the weaker side.

Principal causes of lesions of the ninth, tenth and eleventh cranial nerves

Principal causes of lesions of the ninth, tenth and
eleventh cranial nerves

BULBAR AND PSEUDOBULBAR PALSY

Bulbar palsy

A bulbar palsy describes weakness of LMN type of the muscles supplied by the lower cranial nerves whose nuclei lie in the medulla (the ‘bulb’). The weakness is caused by lesions of the lower cranial nerve nuclei, the (ninth to twelfth) cranial nerves themselves or the muscles they supply.

The symptoms, signs and causes of a bulbar palsy are mentioned under the sections on the ninth to twelfth cranial nerves. Isolated lesions of these nerves are rare

Pseudobulbar palsy

In pseudobulbar palsy, bilateral supranuclear (UMN) lesions of the lower cranial nerves cause weakness and poverty of movement of the tongue and the pharyngeal musculature. Signs of a pseudobulbar palsy are a stiff, slow, spastic tongue (which is not wasted) and dysarthria with a ‘gravelly’ spastic voice that is slow and sounds ‘dry’. The gag reflex and palatal reflex are preserved. The jaw jerk is exaggerated. Emotional lability (inappropriate laughing or crying) often accompanies pseudobulbar palsy. The principal causes are:

MOTOR NEURONE DISEASE, in which there are often both upper UMN and LMN lesions

MULTIPLE SCLEROSIS, in which it occurs mainly as a late event

CEREBROVASCULAR DISEASE, in which it may occur with multi-infarct dementia Severe difficulty with swallowing, dysarthria and a slowmoving tongue also occur in the late stages of Parkinson’s disease and this should be distinguished from both pseudobulbar and bulbar palsy.

The crossed corticospinal ('pyramidal') tracts. The cortical representation of various parts of the body are shown.

The crossed corticospinal (‘pyramidal’) tracts. The
cortical representation of various parts of the body are shown.

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