Session 4 Flashcards
The structures of the head face and neck are innervated by
Cranial nerves (12 Pairs)
Majority of cranial nerves arise from the
Brainstem (unlike spinal nerves which arise from spina cord)
Similarity between cranial and spinal nerves
Both considered part of the peripheral nervous system
Which nerves are mixed
4 cranial nerves and all spinal nerves
What does a mixed nerve mean
Carry both motor and sensory
What are the other 8 cranial nerves that aren’t mixed
3 are purely sensory, 5 are purely motor
What is special about the 3 purely sensory cranial nerves
Carry special sensory function, such as hearing and balance, vision, and smell
Which nerve is for hearing and balance
CN VIII (8)
Which nerve is for vision
CN II (2)
Which nerve is for smell
CN I (1)
Examples of general sensation
Temperature, cold, proprioception
Special sense taste is carried where
within two of the mixed cranial nerves CN VII (7) and CN IX (9)
Cranial nerves have an important association with
Parasympathetic nervous system - account for the cranial outflow of this arm of the autonomic nervous system
Which cranial nerves carry parasympathetic function
Only 4- CN III, VII, IX and X
3,7,9,10
Explain numbering of cranial nerves
Generally follows the order in which they arise (or enter) the brainstem from rostral to caudal (cranial nerve I (olfactory) is most rostral)
Where does the cerebellum sit
Behind brain stem
Brain stem is made up of
Midbrain, pons, medulla
Frontal and parietal lobes separated by the
Central sulcus
What is corpus calosum
White matter that connects 2 hemispheres
What is septum pellucidum
Thin membrane covering cavity
Towards nostril is
Rostral (front of brain)
Medulla is continuous through
Foramen Magnum to become Spinal cord
Why does a problem in the brain stem have a large impact
Lots packed into small space
What nerve nuclei functions are found in midbrain
Eye movement, reflexes of pupils
What nerve nuclei functions are found in pons
Feeding, trigeminal (motor muscles for mastication), sleep
What nerve nuclei functions are found in medulla
Cardiovascular and respiratory
Pre central gyrus responsible for
Primary motor cortex
Post central gyrus responsible for
Primary somatosensory cortex
Frontal lobe controls
Voluntary motor control
Speech production
Social behaviour
Impulse control
Higher cognition (planning, thinking)
Temporal lobe controls
Language, emotion, long-term memory, sense of smell, hearing and taste
Parietal lobe controls
Somatosensory perception
Spatial awareness
Occipital lobe controls
Visual perception
Cerebellum controls
Co-ordination and motor learning
What is uncal herniation
Herniation of uncus of temporal lobe through the tentorium notch due to rise in pressure
Due to geographical proximity will push against 3rd cranial nerve III occulomotor
Describe homunculus
Legs dangle into central sulcus, face tongue and fingertips largest
Motor pathways cortex to peripheral nervous system cross where
Level of medulla on opposite side of brain
Spinal nerves decussate/cross to the opposite side at the level of the
Lower medulla
Cortical control of limb movement is from one primary motor cortex, which is
Contralateral
Where do pathways connecting the primary motor cortex with cranial nerves cross
Level of nuclei onto which they communicate
Cortical control of muscles is from one primary motor cortex which is
Contralateral
BUT
Most cranial nerves also have cortical input from the ipsilateral cortex ( a back- up)
What is sparing of forehead
Difference to tell if a problem with the cranial nerves or with stroke rather than Bell’s palsy or something different
Neurological signs of cranial nerve dysfunction can arise due to an injury or lesion involving
- The cranial nerve during its route outside of the CNS
- The brainstem where CN nuclei are located
- The neurones within forebrain/brainstem which connect other parts of brain to cranial nerves
Cranial nerves topography
2 CNs from forebrain - I olfactory and II optic
2 CNs from midbrain- III occulomotor and IV trochlear
4 CNs from pons- V trigeminal, VI abducens, VII , VIII
4 CNs from medulla- 9-12
2 CNs from forebrain
I olfactory II optic
CNs from midbrain
occulomotor III and trochlear IV
4 CNs from pons
V trigeminal, VI abducens and 7 and 8
Absence or reduced sense of smell
Anosmia/hyposmia
What can impact olfactory nerve
Head/facial impact: shearing olfactory neurones during passage through cribiform foramina
Anterior cranial fossa tumours: compression of olfactory bulb or olfactory tract
Associations with Parkinson’s disease, Alzheimer’s disease
Commonest cause for anosmia
Common cold / upper respiratory tract infection
Where is olfactory mucosa with olfactory receptors found
Within epithelium in superior part of nasal cavity either side of nasal septum
Route of olfactory nerve
- Olfactory mucosa
- Up through base of skull through cribiform foramina
- Olfactory bulb
- Olfactory tract
- temporal lobe
Importance of optic nerve being extension of forebrain
Carries extension of meninges, CN can be affected by raised ICP
How would you test optic nerve
Pupillary size and response to light (CN II forms sensory/afferent limb of pupillary light reflex)
Visual acuity (Shelley chart) and visual fields
Ophthalmoscopy (can directly visualise part of optic nerve)
What will patients with optic nerve lesions report
Blurred vision or complete absence of vision in eye supplied by affected CN
Clinical examination findings with optic nerve lesions
Poor visual acuity (Snellen chart)
Abnormalities in pupil size and response to light
Evidence of pathology involving the optic nerbe may be visible on opthalmoscopy
Optic nerve is part of the
Visual pathway - vision can be affected by diseases/lesions involving other parts of the visual pathway
What will you see in a vision problem caused by optic nerve due to raised ICP
Swollen optic disc= papilloedema
Example of diseases involving optic nerve
Optic neuritis- swelling damages optic nerve
Anterior ischeamic optic neuropathy (AION)- blood supply to front of optic nerve at back of eye affected by disease
What does pale optic disc mean
May have had an episode of optic neuritis
Optic nerve route
- Retinal ganglion cells axons
- Axons form optic nerve
- Exits back of orbit via optic canal
- Fibres from left and right optic nerve merge at optic chiasm (close to pituitary gland)
- Continue as right and left optic tracts
- Some fibres communicate from tract to brainstem, some continue visual pathway
What do fibres communicate from optic tract to brainstem
Information about light intensity- control pupil size
Pathology affecting a retina or an optic nerve on one side will cause
Blurring/visual symptoms in that one eye affected
Lesions involving visual pathway from optic chiasm or onwards will cause
Visual disturbance involving both eyes e.g. pituitary tumours compress optic chiasm causing bilateral symptoms (bitemporal hemianopia)
Lesions within different parts of the visual pathway give
Different patterns of visual loss e.g. retinal detachment, optic neuritis, pituitary tumour, strokes
Occulomotor, Trochlea and Abucens nerves all
Supply muscles within the orbital cavity responsible for moving the eye ball
Occulomotor, trochlea and Abducens nerves all have commonality in route after exiting brainstem at different levels, reach orbital cavity passing through
Cavernous sinus, superior orbital fissure, into orbital cavity
How do you test CN III, IV, VI
Observation of resting position of patient’s gaze
Asking patient to perform a series of eye movements
Oculomotor CN III target tissues
Somatic efferent fibres (motor to skeletal muscle)- all extra ocular muscles except 2, muscle in eyelid (levator palpebrae superioris)
Visceral efferent fibres (parasympathetic)- muscles inside eyeball (ciliary (thickness of lens), sphincter pupillae muscle). Not under voluntary control
Inspection of resting gaze
For CN III Oculomotor
Eyelid position (supplies LPS muscle that keeps eye lid retracted)
Eye movements
Pupils and pupillary light reflexes (via parasympathetic fibres, muscle controlling pupillary contraction)
Signs of oculomotor nerve lesion arise due to
Involvement of somatic fibres and or parasympathetic fibres
Classic signs of oculomotor nerve lesion
Double vision (Dipoplia)
Ptosis (eye drooping)
Abnormal eye position (down and out)
Pupil may or may not be dilated
Oculomotor nerve route has close relationship to
Tentorium cerebelli edge
2 causes for CN III lesion
Micro vascular ischeamia
Compressive
Features of micro vascular ischeamia causing CN III lesion
Risk factors over 50, diabetes or hypertension
Pupil sparing
Features of compressive occulomotor nerve lesion
Lesion compresses onto outside of CN III
Pupil involving
E.g. aneurysmal (PCA): associated with headache/retroorbital pain
Head injury
Tentorial (uncul) herniation e.g. secondary to increased ICP
Not all ptosis is due to
CN III lesion
What does the CN IV Trochlear do
Motor- supplies 1 muscle (superior oblique muscle)
Examination to investigate Trochlear CN IV
Inspection of resting gaze ,testing eye movements
Report double vision, abnormal eye position and difficulty moving eye downwards (Depression) when eye positioned inwards (adducted)
Trochlear nerve router
Arises from dorsal midbrain, runs via cavernous sinus, enters orbital cavity
Only cranial nerve to come off back of mid brain
Features of trochlear nerve lesions
Congenital or acquired
Acquired- micro vascular ischeamia, trauma (even minor), intracranial tumour
CN VI Abducens comes from
Pons
CN VI Abducens nerve supplies
Lateral rectus
Signs of Abducens CN VI problems
Report double vision- Dipoplia (worse in lateral gaze on side of lesion)
Abnormal eye position at rest
Difficulty/unable to move affected eye laterally
Abducens nerve lesions causes
Micro vascular ischeamia, head injury, tumour
Raised ICP (of any cause) —> false localising sign
Most likely nerve to be affected by raised ICP
Why is abducens nerve route susceptible to stretch
Due to vertical route and fixed at point of brainstem exit and entry to cavernous sinus
Raised ICP causing downward displacement of brain can stretch CN VI causing CN VI signs (false localising)
Trigeminal ganglion divisions
CN V Trigeminal nerve supplies
Skin and tissues of face, portion of scalp and deep facial structures
Anterior 2/3rds of tongue general sensation (not taste) via branch of Vc
Muscles of mastication (via branches of Vc)
Cranial nerve examination
Light touch Va,Vb and Vc dermatomes
Muscles of mastication action
Corneal reflex (lightly touch cornea with cotton wool and should see both eyes blink)
Potential clinical examination findings
Sensory deficits within dermatome regions (on affected side)
Weakness in muscles of mastication (on affected side if Vc involved)
Absent corneal reflex (CN Va is sensory part of this reflex)
Trigeminal nerve lesions cause
Trigeminal herpes zoster (shingles reactivation of VZ in trigeminal ganglion)
Trigeminal neuralgia (compression from an aberrant blood vessel)
Orbital and mandibular fractures (distal branches of CN V divisions)
Posterior cranial fossa tumours
What is this
Trigeminal herpes zoster
Sharp shooting pain in face suggestive of
trigeminal neuralgia
Ophthalmic division of trigeminal nerve pathway
Maxillary division of trigeminal nerve pathway
Mandibular division of trigeminal nerve pathway
