Neuroanatomy 2 Flashcards
What joins the bones of the base of the skull?
fibrous joints called sutures
What 3 distinct depressions can be found on the base of the skull when looking down from above?
3 cranial fossae
Anterior cranial fossa
Middle cranial fossa
Posterior cranial fossa
What are cranial foramina?
Small holes which allow nerves, arteries, veins to pass through the skull
In each cranial fossa
What bones make up the anterior cranial fossa?
Orbital part of the frontal bone
Cribriform plate and crista galli of the ethmoid bone
Lesser wings of the sphenoid bone
What foramen can be found in the anterior cranial fossa?
The cribriform plate - transmits olfactory fibres
What bones is the middle cranial fossa made up of?
Petrous and squamous parts of the temporal bone - inferior and medial part of the temporal bone, flat lateral part of the temporal bone respectively
Greater wing and body of the sphenoid bone - cont the pituitary fossa(sella turcica)
Where is the pituitary fossa? (sella turcica)
The body of the sphenoid bone in the middle cranial fossa in the base of the skull
What foramina are there on each side of the middle cranial fossa? [6]
optic canal - transmits optic nerve
superior orbital fissure - transmits several nerves to the orbital region
foramen rotundum - transmits maxillary branch of trigeminal nerve
foramen ovale - transmits mandibular branch of trigeminal nerve
foramen lacerum - internal carotid artery exits carotid canal here
foramen spinosum - transmits middle meningeal artery
Which nerves are transmitted by the superior orbital fissure to the orbital region?
Motor innervation
- oculomotor
- trochlear
- abducens
Sensory innervation
- ophthalmic branch of trigeminal nerve
Which foramen do the branches of the trigeminal nerve travel through?
Ophthalmic branch - superior orbital fissure
Maxillary branch - foramen rotundum
Mandibular branch - foramen ovale
What bones make up the posterior cranial fossa?
Which lobes rest in the anterior cranial fossa?
frontal lobes
Which lobes rest in the posterior cranial fossa?
What bones make up the posterior cranial fossa?
Occipital lobe
Cerebellum
Brainstem
Occipital bone
Petrous part of the temporal bone (most anterior border)
Which lobes rest in the middle cranial fossa?
Temporal lobes
What foramina are located in the posterior cranial fossa? [4]
Internal auditory meatus - transmits VIII and VII into inner ear cavity
Jugular foramen - transmits nerves IX,X,XI and internal jugular vein
Hypoglossal canal - transmits nerve XII
Foramen magnum - central singular foramen allows central nervous system fibres to become spinal cord
What passes through the cribriform plate?
Olfactory fibres
What is transmitted by the optic canal?
Optic nerve into the bony orbit
What is transmitted by the superior orbital fissure?
Oculomotor (III)
Trochlear (IV)
Abducens (VI)
Ophthalmic branch of the trigeminal (V)
What is transmitted by the foramen rotundum?
Maxillary branch of trigeminal nerve (V)
What is transmitted by the foramen ovale?
Mandibular branch of the trigeminal nerve (V)
What is transmitted by the foramen lacerum in the brain?
Internal carotid artery exits the carotid canal through this foramen to enter the skull
What is transmitted by the foramen spinosum in the skull?
Middle meningeal artery
What is transmitted by the internal auditory meatus in the skull?
Vestibulocochlear (VIII)
Facial (VII)
into the inner ear cavity
What is transmitted by the jugular foramen in the skull?
Glossopharyngeal (IX)
Vagus (X)
Acessory (XI)
Internal jugular vein
What is transmitted by the hypoglossal canal in the skull?
Hypoglossal nerve (IX)
What is transmitted by the foramen magnum in the skull?
Single central foramen - spinal cord
What are consequences of a traumatic head injury?
Brain damage
Damage structures passing through the foramina
Damage dura and meninges, CSF could leak out - clear liquid from nose or ears is suspicious
Significant bleeding
What is the pterion?
Area of the skull often referred to as the temple
Shallow depression where 4 bones meet:
Frontal, temporal, sphenoid, parietal
Weakest part of the skull and prone to fracture if struck
Middle meningeal artery lies behind it - can extradural haemorrhage if this happens
What is craniosyntosis?
When sutures of the skull fuse together too early
Skull becomes misshapen as brain continues to grow
What are burr holes?
What is a craniotomy?
Small holes (10-15mm diameter) drilled into the skull to relieve pressure quickly/immediately
Allows brain to expand or used to drain fluid
Craniotomy is a circular piece of the skull is removed to perform brain surgery, can be replaced later or have a prosthetic implant to close it
Describe the two bony orbits?
Shaped like cones
Broad opening at the front
Taper to a narrow part at the back
Formed from…
Frontal, sphenoid, zygomatic, maxillary bones
Also smaller ethmoid and lacrimal bones
What structures can be found within the orbits?
Eye - at front of the orbit
Extraocular muscles - 6 move the eye, 7th retracts upper eyelid
Nerves - II for vision, III,IV,VI control muscles, ophthalmic branch for sensation
Fat
Lacrimal gland - in the superior and lateral part of the orbit - produces tears to lubricate
Which 3 foramina are at the back of the orbit?
Optic canal
Superior orbital fissure
Inferior orbital fissure
What does the word extorsion mean?
rotate the eye so the top of the eye rotates laterally
What does the word intorsion mean?
rotate the eye so the top of the eye rotates medially
What is conjugate eye movements?
The fact that to look left, the eyes technically move differently - e.g. looking left your right eye adducts but left eye abducts
Which two eye muscles have a unique nerve supply?
What are the rest supplied by?
lateral rectus - CN 6
superior oblique - CN 4
Rest are CN 3
LR6SO4
What are the 7 muscles in the eye?
Levator palpebrae superioris
Superior rectus
Inferior rectus
Medial rectus
Lateral rectus
Superior oblique
Inferior oblique
Which eye muscle controls the upper eyelid?
What is a sign it is non-functional?
Levator palpebrae superioris
Drooping eyelid (ptosis)
Where do the 4 recti extraocular muscles all originate from?
Common tendinous ring
- fibrous ring
What are the…
nerve supply
action on the eye
findings if non-functional
… for the superior rectus?
- oculomotor nerve (CN III)
- elevate, intort, adduct
- unable to elevate
What are the…
nerve supply
action on the eye
findings if non-functional
… for the inferior rectus?
- oculomotor nerve (CN III)
- depress, extort, adduct
- unable to depress
What are the…
nerve supply
action on the eye
findings if non-functional
… for the medial rectus?
- oculomotor nerve (CN III)
- adduct
- unable to adduct
What are the…
nerve supply
action on the eye
findings if non-functional
… for the lateral rectus
- abducens nerve (CN VI)
- abduct
- unable to abduct
What are the…
nerve supply
action on the eye
findings if non-functional
… for the superior oblique?
- trochlear nerve (CN IV)
- intort, depress, abduct
- unable to depress if eye is adducted
What is a trochlea?
Anatomical structure that acts as a pulley
Why do the superior and inferior rectus muscles intort and extort the eye respectively?
Due to the angle at which they attach to the eye and therefore pull on the eye
When they pull on the eye they don’t only elevate/depress they also simultaneously intort/extort
Why are the oblique muscles there to intort /extort in the eyes?
To counter the intorsion/extorsion that secondarily occurs from the superior and inferior recti
How does the eye achieve ‘accommodation’ to adjust for how far away an object is?
The thickness of the lens is adjusted
Thicker lens for close objects, thin for far away
Controlled by parasympathetic ciliary muscles by CN III - so is an autonomic function
How is pupillary dilation/constriction controlled?
[2 muscles: their action, when they act, nerve supply]
Circular muscle - constrictor pupillae
constricts when too much light enters the retina (parasympathetic CNIII fibres)
Radial muscle - dilator pupillae
dilates the pupil when not enough light hits the retina
(sympathetic fibres - sympathetic chain)
both are autonomic functions we are unable to control
How may stimulation of the parasympathetic/ sympathetic system result in change of pupil size?
Constrictor pupillae - act when parasympathetic system is highly active - pupil constricts
Dilator pupillae - act when sympathetic system is highly active - pupil dilates
Pupillary response to light overrides both effects
What is the pupillary light reflex in the eye?
Automatically adjusts the amount of light entering the eye
Afferent (sensory) nerve - optic
Efferent (motor) nerve - oculomotor
They synapse with each other in the Edinger-Westphal nucleus
How does the pupillary light response work if light is shone into only one eye?
Both pupils will constrict
Pupil light is being shone into - direct pupillary response
Other - consensual pupillary response
Due to connection between the l/r nuclei (Edinger-Westphal nuclei)
Where is the lacrimal gland?
What does it do?
In the superior and lateral corner of the orbit
Produces tears to lubricate and moisten the eye surface
Tears drain by the nasolacrimal duct
What can a fracture to the walls of the orbit cause? (aka blow-out fracture)
Fracture of the inferior orbital wall is most common
Inferior rectus muscle can become trapped, holding the eye in position, patient unable to look up
What is cataracts?
Clouding of the lens
Develop slowly and painlessly
Can’t be prevented but are surgically treated by replacing the affected lens
What is oculomotor nerve palsy?
How does the affected eye present clinically?
Oculomotor nerve not functioning properly on one side
Affected eye rests in a ‘down and out’ position (depressed and abducted)
Lateral rectus and superior oblique muscles unopposed cause this
Drooping eyelid
Dilated pupil - loss of parasympathetic nerve supply
Affected side is unable to adduct
What is abducens nerve palsy?
Abducens nerve not functioning properly on one side
Affected eye unable to abduct as lateral rectus is no longer working
At rest, medial rectus may overpower and pull the eye medially at rest causing strabismus
How are eyes clinically examined?
Asks the patient to follow the doctor’s finger, drawing the shape of a letter ‘H’ in front of them
Observes the eyes to see if they are moving together and asks if the patient has any double vision
How are the superior oblique muscles of the eye examined?
Superior oblique - fine if patient can depress an abducted eye - tests function of the trochlear nerve
How can pupillary response represent head injuries?
Rise in intercranial pressure due to blood or etc
If oculomotor nerve gets compressed is can be unable to function, resulting in dilation of the ipsilateral pupil - good for examining unconscious patients - fixed and dilated pupil is a bad sign
What does the outer ear consist of?
Pinna - most outer part
Ear canal
Tympanic membrane
How does sound reach the tympanic membrane?
Pinna shape gathers sound waves and directs them into the ear canal
Ear canal directs the sounds towards the tympanic membrane, this vibrates
What is the middle ear cavity made up of?
3 ossicle bones - malleus, incus, stapes
Superior opening of the auditory tube
2 small muscles - tensor tympani, stapedius
Where is the malleus? What does it do?
In the middle ear cavity
It is a VERY small bone
Rests against the tympanic membrane
‘Hammer handle’ rests against tympanic membrane
‘Hammer head’ connects to the incus
Where is the incus?
What does it do?
In the middle ear cavity
It is a VERY small bone
As malleus ‘hammer’ hits incus ‘anvil’ sound waves are transmitted
Where is the stapes?
What does it do?
In the middle ear cavity
It is a VERY small bone
Receives sound wave vibrations from the incus and transmits them onto the oval window
What marks the boundary between the middle ear cavity and the inner eat cavity?
The oval window
What is the function of the auditory tube (Eustachian tube)?
Connects the middle ear cavity with nasal cavity
Allows air flow between external environment and middle ear
Maintains equal air pressure on either side of the tympanic membrane
What is the tensor tympani?
What is its nerve supply?
Small muscle in the middle ear cavity
Inserts on the malleus
Increases tension in the tympanic membrane when it contracts, reducing vibration
Nerve supply from mandibular branch of trigeminal nerve (CN V)
What is the stapedius?
What is its nerve supply?
A small muscle in the middle ear cavity
Inserts on the stapes, dampens vibrations of the stapes when it contracts
Supplied by the facial nerve (CN VII)
What does the inner ear cavity contain?
Bony labyrinth - cochlea and vestibular system
Vestibular system is the semicircular canals, utricle, saccule
What is the cohclea?
Part of the bony labyrinth in the inner ear cavity
Contains fluid, as sound waves travel through the fluid in the cochlea they are converted into electrical impulses in the cochlear nerve to travel to the auditory cortex
Where is the round window?
What does it do?
It is in the inner ear cavity
Bulges in and out to allow fluid in the cochlea to move
Where is the vestibular system?
What is it and what does it do?
In the inner ear cavity
Semicircular canals, utricle, saccule
Contains fluid that moves when we move our head
Detected by specialised cells that convert it to electrical impulses - vestibular nerve
3 semicircular canals - all perpendicular to each other perceive movement
Utricle and saccule perceive liner acceleration
What nerve carries signals from the inner ear?
What is the oculocephalic reflex?
Vestibulocochlear nerve (CN VIII)
Carries to the nuclei of the nerve in the pons - here connections to CN III, IV, VI help maintain fixed gaze even when moving our heads - the oculocephalic reflex
How do people get vertigo?
Perceiving movement when there is none, world still spinning or floor moving unevenly
e.g. spinning around many times then stopping
Disorder to the vestibular system - inflammation, infections, endo/perilymph disorders, cancer of vestibular system or nerves
What is vestibular schwannoma?
Benign tumor of Schwann cells surrounding the vestibulocochlear nerve
Leads to symptoms of unilateral hearing loss, tinnitus, vertigo, feeling of fullness in the ear
Can compress other cranial nerves if it gets big enough
What is otitis media?
