Cranial Nerves
12 pairs of cranial nerves are peripheral nerves.
There are 12 pairs of cranial nerves originating from nuclei in inferior surface of brain, some sensory, some motor and some mixed.
They are called cranial as they arise from brain inside cranial cavity.
12 pairs cranial nerve are-
I- Olfactory nerves, sensory
II- Optic nerves, sensory
III- Oculomotor nerves, motor
IV- Trochlear nerves, motor
V- Trigeminal nerves, mixed
VI- Abducens nerves, motor
VII- Facial nerves, mixed
VIII- Vestibulocochlear nerves, sensory
IX- Glossopharyngeal nerves, mixed
X- Vagus nerves, mixed
XI- Accessory nerve, motor
XII- Hypoglossal nerves, motor
I - Olfactory Nerve; Sensory
These are nerves of sense of smell, carry afferent impulses for sense of smell. The nerve's olfactory (hair) receptors are located within mucosa of nasal cavity, pass upwards through cribriform plate of ethmoid bone and then pass olfactory bulb. Area for perception of smell in temporal lobe of cerebrum.
Central connection- Olfactory bulb
Function- smell
Peripheral connection- Olfactory mucosa
Nerve type- sensory
II - Optic Nerve; Sensory
These are nerves of sense of sight, carry afferent impulse for vision.
The fibre originate in ratina of eye and they combine to form optic nerve, which passes through optic canal of orbit. They then pass through optic foramina of sphenoid into cranial cavity and join at optic chiasma.
Optic chiasma provide site for crossing over or desiccation of optic nerve fibers, terminating in opposite side of brain. The nerve proceed as optic track to lateral geniculate bodies of thalmus.
Impulse pass from visual area in occipital lobe sight is perceived. In cerebellum impulse from eyes contribute to maintenance of balance posture and orientation of head in space.
III- Oculomotor nerve; motor
These nerves arise from nuclei near cerebral aqueduct they supply-
Four of six extrinsic muscles, which move eyeball.
Ciliary muscles, which alter shape of lens.
Circular muscles of iris, which constrict the pupil.
Levator palpebrae muscle, which raise movement of upper eyelids.
IV- Trochlear nerve; motor
These nerve arise from nuclei near cerebral aqueduct. They supply superior oblique muscles of eyes, which movement of eyeball.
V- Trigeminal nerve; mixed
Largest pair of cranial nerve, supplying the front part of head and dividing into-
Ophthalmic nerve; Supply lacrimal gland, conjunctiva of eyes, forehead, eyelids (sensory anterior aspect of scalp and mucous membrane of nose.)
Maxillary nerve; Supply cheeks, upper gums, upper teeth, lower eyelids (sensory).
Mandibular nerve; both sensory and motor fibers; mixed
Supply teeth and gums of lower jaw, pinnae of ear, lower lip and tongue.
They are chief sensory nerves for face and head (including oral and nasal cavities and teeth), receiving impulse of pain, temperature and touch.
VI- Abducens nerve (motor)
These nerve arise from nuclei lying underfloor of 4th ventricles.
They supply lateral rectus muscle of eyeballs causing abduction (movement of eyeball).
VII- Facial nerves; mixed
These nerves composed of both motor and sensory nerve fibres, arising from nuclei in lower part of pons.
Motor fibre supply muscles of facial expression.
Sensory fibres convey impulse from taste buds in anterior 2/3rd of tongue to taste perception area in cerebral cortex.
VIII- Vestibulocochlear; auditory nerve; sensory
These nerve composed of-
Vestibular nerves
Cochlear nerves
Vestibular nerves
Arise from semicircular canals of inner ear and convey impulses to cerebellum. They are associated with maintenance of posture and balance.
Cochlear nerves
Originate in organ of corti in inner ear and convey impulse to hearing areas in cerebral cortex where sound is perceived.
IX- Glossopharyngeal nerve; mixed
Motor fibres arises from nuclei in medulla oblongata and stimulate muscle of tongue and pharynx and sensory cells of parotid (salivary glands).
Sensory fibres convey impulses to cerebral cortex from pharynx and posterior tongue and from taste in tongue and pharynx.
These nerve are essential for swallowing.
Monitoring of blood pressure , O2 and CO2 in blood.
X- Vagus nerve (mixed)
The only cranial nerves to extend beyond head and neck region.
They pass down through neck into thorax and abdomen.
Fibres emerge from medulla.
These nerve form imprtant part of parasympathetic nervous system.
Sensory portion
Taste bud in epiglottis and pharynx.
Proprioceptors in muscles of throat and neck.
Baroreceptrors in arc of aorta and chemoreceptors in aortic bodies (for respiration) near arc of aorta.
Motor portion
Skeletal muscles in throat and neck.
Smooth muscles in esophagus, stomach, small intestine, large intestine, gallbladder.
Cardiac muscle in heart
Function
Swallowing and voice production
Parasympathetic; smooth muscle contraction and relaxation in organ of gastrointestinal track, slowing heart rate
Secretion of digestive fluid
XI- Accessory nerve; motor
These nerves arise from nuclei in medulla oblongata and in spinal cord.
The fibres supply sternocleidomastoid and trapezius muscles.
Branches join vagus nerves and supply pharyngeal and laryngeal muscles.
Function-
Movement of head and pectoral girdle, head rotating.
XII- Hypoglossal nerves ; motor
These nerves arise from nuclei in medulla oblongata.
They supply the muscles of tongue and muscles surrounding hyoid bone and contribute to swallowing and speech.
0 Comments