The hypoglossal nerve is a purely motor nerve that originates in the medulla and innervates the muscles of the tongue. It emerges from the medulla between the pyramid and inferior olive, descends through the neck, and divides to supply branches to the extrinsic and intrinsic tongue muscles. Examination of the tongue evaluates strength, bulk, and dexterity to identify weaknesses or atrophies that may indicate supranuclear, nuclear, or infranuclear lesions along the nerve's path.

5.  Oldest
sensory modalities in the
phylogenetic history of mammals
 Olfactorysystem detects food and
influences social and sexual behavior

6. 3 cell types, basal, supporting, and olfactory
receptor cells
 Basalcells are stem cells that give rise to the
olfactory receptor cells
 continuous turnover unique to the olfactory
system
 receptorcells are actually bipolar neurons,
each possessing a thin dendritic rod that
contains specialized cilia extending from the
olfactory vesicle and a long central process
that forms the fila olfactoria

8. olfactory nerve (I)
Olfactory bulb
Olfactory tract
Optic nerve (II)
Optic chiasma
Optic tract
Oculomotor nerve (III)
Trochlear nerve (IV)
Trigeminal nerve (V)
Abducens nerve (VI)
Cerebellum
Medulla
Table 14.3 (1 of 12)

9.  small unmyelinated axons of the olfactory
receptor cells form the fine fibers of the first
cranial nerve
 travel centrally toward the ipsilateral olfactory
bulb to make contact with the second-order
neurons
 cribriform plate of the ethmoid bone,
separated at the midline by the crista galli,
contains multiple small foramina through which
the olfactory nerve fibers, or fila olfactoria,
traverse

10.  lies inferior to the basal frontal lobe
 The layers (from outside toward the
center of the bulb) are differentiated as
follows:
• Glomerular layer
• External plexiform layer
• Mitral cell layer
• Internal plexiform layer
• Granule cell layer

11.  Medial fibers of the tract contact the
anterior olfactory nucleus and the septal
area.
 Some fibers project to the contralateral
olfactory bulb via the anterior
commissure.
 Lateral fibers contact third-order
neurons in the primary olfactory cortex
(prepyriform and entorhinal areas)
directly

12.  Third-order neurons send projections to
the dorsomedial nucleus of the thalamus,
the basal forebrain, and the limbic
system

14.  Pyriform lobe includes the olfactory
tract, the uncus, and the anterior part of
the parahippocampal gyrus is known as
the entorhinal area the secondary
olfactory cortex
 The prepyriform and the periamygdaloid
areas of the temporal lobe represent the
primary olfactory cortex.

15.  Communications with superior and
inferior salivary nuclei are important in
reflex salivation .
 Patient with olfactory impairment c/o
loss of taste [every thing feels like mud.]

16.  Loss of smell sensation –patient miss
olfactory danger signals.
 olfactory deficits - two types
 1-conductive
 2-sensorineural
 1-interfernce of an odour in contact
 2-dysfunction of receptor/central
connections


17.  ensure nasal passages are open
 stimuli should be non irritant
 examine each nostril separately
occluding the other one with eyes closed
 ask the patient whether smells something
or not if yes identify the substance
 repeat the test in other nostril

18.  the side that might be abnormal should
be examined first
 perception of an odour –continuty of
olfactory pathway
 identification of an odour – intact cortical
functions

19.  Anosmia - Absence of smell sensation
 Hyposmia - Decreased sensation
 Dysosmia - Defect in sense of smell
 Cacosmia - Sensation of a bad or foul
smell
 Parosmia - Sensation of smell in the
absence of appropriate stimulus

20.  URTI
 Head trauma
 Nasal and sinus disease
 Idiopathic
• These Four are most Common Causes

21. Others- Olfactory groove meningioma
Frontal Lobe tumor
Sellar /Parasellar tumor
Vitamin deficiency (B6,B12,A)
Parkinsons Disease
Kallmans Synddrome
Psychiatric conditions
Cadmium Toxicity
Cocaine Abuse

22.  Kallmann syndrome (ie, hypogonadism
with anosmia)
 Foster Kennedy syndrome (ie,
papilledema, unilateral anosmia, and
optic atrophy usually associated with an
olfactory groove meningioma).
 Cranio cerebral Trauma – Results in
damage of olfactory nerve at the
cribriform plate of ethmoid

24.  Purely Motor Nerve
 Origin - Two nuclei from the medulla lies
beneath the floor of the fourth ventricle
under the medial aspect of the
hypoglossal trigone
 Axons emerge in the sulcus between the
pyramid and the inferior olive as many
rootlets

26.  Runsinferior to the tongue - innervates the
tongue muscles
Facial nerve (VII)
Vestibulocochlear
nerve (VIII)
Glossopharyngeal
nerve (IX)
Vagus nerve (X)
Accessory nerve (XI)
Hypoglossal nerve (XII)
Table 14.3 (12 of 12)

27.  rootletsof this nerve are collected into
two bundles, which perforate the dura
mater separately, opposite the
hypoglossal canal in the occipital bone
 The nerve descends almost vertically to a
point corresponding with the angle of the
mandible

28.  It descends through the neck at the level of
the angle of mandible, here it lies beneath
the carotid sheath
 It runs forward above the hyoid bone and
divides into number of fibers supplying the
tongue
 Branches of the hypoglossal nerve are
• Meningial
• Descending
• thyrohyoid
• Muscular

30. Its branches of communication are,
 Vagus.
 First and second cervical nerves.
 Sympathetic.
 Lingual

31.  Tounge has extrinsic – paired muscles
Genioglossus
Styloglossus
Hyoglossus
Chondroglossus
 Intrinsic muscles – Superior and inferior
longitudinales, transversus, verticalis
 Extrinsic mucles help in Protrusion and
retraction of the tounge, move the tounge up
and down
 Intrinsic muscles help in Change in Length,
width and curvature of the dorsal surface, and
turn the non protruded tip from side to side

32.  The centre that regulates the tounge
movements – lower portion of precentral
gyrus near and within the sylvian fissure
 The supranuclear fibres run in
corticobulbar tract through the genu of
the internal capsule and through the
cerebral peduncle
 The supranuclear pathway is crossed

33.  Examination consists of evaluating
1) Strength
2)Bulk
3)Dextirity of the tongue
 One has to look for
• Weakness
• Atrophy
• Abnormal movements
• Impairment of rapid movements

34.  Patient is asked to move tongue in and
out ,up and down , side to side
 Best by assessing the strength against
pressed cheek
 In unilateral weakness, the tounge is
deviated towards the same side
 In bilateral weakness, tounge movements
may be impaired

35.  Symptoms-
• Unilateral weakness- Speech and swallowing are
little affected
• Bilateral weakness – First stage of swallowing is
impaired
• Difficulty in articulation and respiratory difficulty
• Supranuclear, Nuclear, infranuclear lesions

36.  Supranulear Lesions
• Causes weakness but no atrophy
• Lesions are seen in cotrex, corticobulbar tract,
internal capsule, cerebral peduncle and pons
 Pseudobulbar Palsy
• Due to bilateral UMN disease causing bilateral
weakness
• Hemispheric lesion causes apraxia of tounge
movements
 Extrapyramidal
disorders causes slowing of
tounge movements

37.  Nuclear and Infra nuclear lesions –
causes weakness + Atrophy
 In addition to above, Fasciculations are
seen in Progressive nuclear disease
 The disorders include neoplasms,
vascular lesions, Motor neuron diseases,
Granulomas etc.

38.  Infra nuclear lesions
• Intracranial
• Extracranial
 Intracraniallesions same as nuclear
lesions and other causes includes
meningitis, SAH, Trauma
 Extracranial causes- penetrating wounds,
carotid aneurysms, infections