M1 Anatomy Flashcards
Cranial Nerve Names
CN 0: Terminal
CN I: Olfactory
CN II: Optic
CN III: Oculomotor
CN IV: Trochlear
CN V: Trigeminal
CN VI: Abducens
CN VII: Facial
CN VIII: Vestibulocochlear
CN IX: Glossopharyngeal
CN X: Vagus
CN XI: Accessory
CN XII: Hypoglossal
Cranial Nerves of the Midbrain (mesencephalon)
Source of:
CN III: Oculomotor
CN IV: Trochlear
Cranial Nerves of the Pons
Source of:
CN V: Trigeminal
CN VI: Abducens
CN VII: Facial
CN VIII: Vestibulocochlear
Cranial Nerves
of
Medulla Oblongata
Source of:
CN IX: Glossopharyngeal
CN X: Vagus
CN XI: Accessory
CN XII: Hypoglossal
Cranial Nerve Origins
- Brain: (3)
- 0 I II
- Midbrain: (2)
- III IV
- Pons: (4)
- V VI VII VIII
- Medulla Oblongata: (4)
- IX X XI XII
Olfactory Nerve
- Cranial Nerve I
- Sensory nerve fibers of olfaction
- Capable of some regeneration if damaged
- Technically part of CNS
Olfactory Nerve Pathway
- Olfactory Mucosa
- Cribriform plate of ethmoidal bone
- Synapse on Olfactory bulbs
- Olfactory Tract
- Brain
Optic Nerve
- Cranial Nerve II
- Sensory nerve transmitting visual information
- Technically part of CNS
Optic Nerve Pathway
- Optic disc of retina
- Optic nerve
- Optic canal
- Optic chiasm
- Optic tract
- Visual cortex
Oculomotor Nerve
- Cranial Nerve III
- Innervates
- Extrinsic eye muscles enabling most movements of the eye including rising eyelid
- Intrinsic eye muscles enabling pupillary constriction and accommodation.
Oculomotor Nerve Pathway
- Midbrain of brainstem
- Red Nucleus
- Substancia Nigra
- Cavernous Sinus
- Superior Orbital Fissure
Trochlear Nerve
- Cranial Nerve IV
- Motor nerve to the superior oblique muscle of the eye (contralateral).
- The smallest cranial nerve.
- The only cranial nerve to exit the rear aspect of the brainstem.
Trochlear Nerve Pathway
- Dorsal aspect of midbrain
- Cavernous sinus
- Superior orbital fissure
- Orbit
- Superior oblique muscle
Trigeminal Nerve
- Fifth Cranial Nerve (V)
- Sensation in face
- Motor of biting and chewing
- Largest cranial nerve
- Three sensory branches
- Ophthalmic (V1)
- Maxillary (V2)
- Mandibular (V3)
Trigeminal Nerve Pathway
- Trigeminal Ganglion in Meckel’s Cave
- Pons
Trigeminal Ganglion
- Synapse of sensory nerves of Trigeminal Nerve
- Located in Meckel’s Cave
- Formed by three branches
- Ophthalmic nerve (afferent)
- Maxillary nerve (afferent)
- Mandibular nerve (mixed - joined by efferent component outside skull).
Ophthalmic Nerve
- First division of Trigeminal Nerve (CN V)
- Sensation for
- eyeball
- skin of upper face
- anterior scalp
- Smallest of trigeminal branches
- Three branches
- lacrimal
- frontal
- nasociliary
Ophthalmic Nerve Pathway
- Orbit
- Superior Orbital Fissure
- Lateral Cavernous Sinus
- Trigeminal Ganglion
Maxillary Nerve
- Second division of Trigeminal Nerve (CN V)
- Sensation of:
- Maxilla
- Nasal cavity
- Sinuses
- Palate
- Mid face
Maxillary Nerve Pathway
- Infraorbital foramen
- Inferior orbital fissure
- Pterygopalatine fossa
- Foramen rotundum
- Lateral Cavernous sinus
- Trigeminal Ganglion
Mandibular Nerve
- Third division of Trigeminal Nerve (CN V)
- Largest of Trigeminal branches
- Sensation of
- Inside of cheek
- Anterior 2/3 of tongue (not taste)
- Teeth of mandible
- Chin
- Lower lip
- Scalp
- Anterior ear
- Motor to muscles of mastication
Mandibular Nerve Pathway
- Afferent
- Foramen Ovale
- Trigeminal Ganglion
- Efferent
- Pons
- Under Trigeminal Ganglion
- Foramen Ovale
- Joins afferent nerves outside skull.
Abducens Nerve
- 6th Cranial Nerve (VI)
- Motor neuron to lateral rectus muscle responsible for outward gaze.
- Nucleus in floor of 4th Ventricle in Pons, medial to Facial nerve.
Abducens Nerve Pathway
- Pons
- Junction of Pons and Medulla Oblongata
- Cavernous Sinus
- Superior Orbital Fissure
- Lateral Rectus muscle
Facial Nerve
- 7th Cranial Nerve (VII)
- Emerges from Pons
- Afferent: taste for anterior 2/3rd of tongue
- Efferent: muscles of facial expression
Facial Nerve Pathway
- Pons
- Internal Auditory Meatus
- Facial Canal in Temporal bone
- Stylomastoid Foramen
Vestibulocochlear Nerve
- 8th Cranial Nerve (VIII)
- Afferent: sound and equilibrium
- Pons
Vestibulocochlear Nerve Pathway
- Internal Acoustic Meatus
- Pontomedullary junction
- Pons
Glossopharyngeal Nerve
- 9th Cranial Nerve (IX)
- Joins brainstem from sides of upper medulla oblongata
- Exits skull via jugular foramen
- Efferent:
- Stylopharyngeal muscle
- Parasympathetics to Parotid
- Afferent:
- Carotid sinus and body
- tympanic membrane
- Upper pharynx
- Posterior 1/3 tongue: taste and sensation
Vagus Nerve
- 10th Cranial Nerve (X)
- Longest autonomic nerve in the body
- Leave medulla between pyramid and cerebellar peduncle
- Leaves skull via jugular foramen
- Motor and sensory of viscera to colon
Accessory Nerve
- 11th Cranial Nerve (XI)
- Motor neuron to SCM and Trapezius
- Neuron body in spinal cord
- Enters skull via foramen magnum
- Exits skull via jugular foramen
Hypoglossal Nerve
- 12th Cranial Nerve (XII)
- Motor neuron to all extrinsic and intrinsic muscles of tongue
- except palatoglossus
- Arises from small rootlets anterior medulla oblongata
- Exits skull via hypoglossal canal
Optic Canal
- Canal between orbit and middle cavity of skull in Sphenoid bone
- Optic foramen is opening
- Contains Optic Nerve (CN II) and Ophthalmic artery
Superior Orbital Fissure
- Cleft between lesser and greater wings of sphenoid.
- Contains:
- Oculomotor Nerve (CN III)
- Trochlear Nerve (CN IV)
- 3 branches of Ophthalmic Nerve (CN V1)
- lacrimal
- frontal
- nasociliary
- Abducens Nerve (CN VI)
- Ophthalmic Vein
Foramen Rotundem
- Sphenoid bone
- Connects middle cranial fossa with pterygopalatine fossa
- Contains Maxillary Nerve (CN V2)
Foramen Ovale
- posterior part of the sphenoid bone, posterolateral to the foramen rotundum in Greater Wing.
- Middle cranial fossa
- Contents
- O: otic ganglion (inferior)
- V: V3 cranial nerve (mandibular division of the trigeminal nerve)
- A: accessory meningeal artery
- L: lesser petrosal nerve
- E: emissary veins
Stylomastoid Foramen
- Temporal bone
- Termination of Facial Canal
- Transmits
- Facial Nerve (CN VII)
- Stylomastoid artery
Internal Auditory Canal / Meatus
- Petrous portion of Temporal bone
- Connects Posterior Cranial Fossa with inner ear
- Contents
- Facial Nerve (CN VII)
- Vestibulocochlear Nerve (CN VIII)
- Labyrinthine artery
- Vestibular ganglion
Jugular Foramen
- Petrous portion of temporal bone and occipital bone
- Contents
- Interior petrossal sinus
- Sigmod sinus
- Glossopharyngeal Nerve (CN IX)
- Vagus Nerve (CN X)
- Accessory Nerve (CN XI)
Hypoglossal Canal
- Occipital bone
- Medial and superior to occipital condyles
- Transmits Hypoglossal Nerve (CN XII)
Foramen Magnum
- Occipital Bone
- Contents:
- Anterior and Posterior spinal arteries
- Vertebral arteries
- Medulla Oblongata
- Ascending fibers of Accessory Nerve (CN XI)
Cranial Nerves controlling eye movement
- Oculomotor (CN III)
- Trochlear (CN IV)
- Abducens (CN VI)
Sections of the Brainstem
- Midbrain or mesencephalon
- Pons
- Medulla Oblongata
Midbrain Functions
- vision
- hearing
- motor control
- sleep/wake, arousal (alertness)
- temperature regulation
Midbrain Regions
- tectum (posterior)
- cerebral aqueduct
- tegmentum
- cerebral peduncles.
Midbrain Location
- Superior aspect of brainstem
- Rostral: diencephalon
- Caudal: Pons and Cerebellum
Occipital Ossification
- Timeline
- Begins at 6-12 weeks in utero
- Begins unifying at 4 years old
- Finishes unifying by 6 years old
- Joins with sphenoid between 18 - 25 years old
- 6 centers, all primary
Axis Primary Ossification Centers
5 Total
1 - centrum for body
2 - each half of neural arch
2 - dens
Axis Secondary Ossification Centers
2 Total
1 - tip of dens
1 - lower surface of body
Primary Ossification Centers for C3-L5
3 total
start at 9 weeks in utero
finish by one year
1 - centrum for body
2 - each half of neural ring
Secondary Ossification Centers of Vertebral Column
5 Total
Appear at puberty and finish by 25-30 years old
1 - tip of SP
2 - tip of TPs
2 - ring epiphyses at upper and lower body surfaces
Atlas Ossification
3 primary centers
No secondary centers
1 - Anterior arch (fuses by age 7)
2 - each side of posterior arch (fuses by age 3)
Axis Fusion Timeline
- Dens Primary centers fuse by 7th month in utero
- 2-3 yo: Neural arch fuses posteriorly
- 3-6 yo: Neural arch fuses to body and dens
- 3-6 yo: Dens fuses with body
- 3-6 yo: tip of dens appears
- 12 yo: tip of dens fuses with dens
Human skull has how many bones?
- 8 Cranial bones
- 14 Facial bones
Total 22 bones
What are the 8 cranial bones?
- Occipital bone
- 2 Temporal bones
- 2 Parietal bones
- Frontal bone
- Sphenoid bone
- Ethmoid bone
What are the 14 facial bones?
- 2 inferior nasal conchae
- 2 lacrimal bones
- 2 maxilla bones
- 2 nasal bones
- 2 palatine bones
- 2 zygomatic bones
- mandible
- vomer
Carotid Canal
- Passageway in temporal bone from neck to middle cranial fossa.
- Contains:
- Internal Carotid Artery
- Carotid Plexus of nerves
- Sympathetics to head from Superior Cervical Ganglion
Foramen Spinosum
- Greater wing of sphenoid connecting middle cranial fossa and neck.
- Contains:
- Middle meningeal artery
- Middle meningeal vein
- Meningeal branch of Mandibular Nerve (CN V3)
Spinomedullary Junction
Where the brainstem and spinal cord meet in the Foramen Magnum
What three muscles arise from the styloid process?
Stylohyoid
Stylopharyngeus
Styloglossus
What cranial nerves innervate the three muscles of the styloid process?
Stylohyoid - CN VII Facial
Stylopharyngeus - CN IX Glossopharyngeal
Styloglossus - CN XII Hypoglossal
Lambda
Convergence of
lambdoid and saggital
sutures
Bregma
Convergence of
coronal and sagittal
sutures
What ligament attaches to the basion?
Apical ligament
McRae’s Line
between basion and opisthion
Chamberlain’s Line
between hard palate and opisthion
McGregor’s Line
between hard palate and inferior most portion of occiput
Nasion
most anterior portion of frontonasal suture
Clinical significance of McRae’s Line
Normal position of the tip of the dens is 5mm below. Above this line it is a sign of basilar invagination.
Clinical significance of Chamberlain’s line
If tip of dens is greater than 3mm above it indicates basilar invagination
Clivoaxial Angle
Angle between posterior aspect of Clivus and posterior border of axial peg.
Clinical significance of Clivoaxial angle
Angle should be 150-180 degrees.
Less than 150 indicates possible compression of the contents of the foramen magnum.
Less than 130 associated with delay or failure to recover after foramen magnum decompression.
Normal neuroaxis behavior on CCJ flexion
The neuraxis stretches by about 10% of its total length on CCJ flexion.
Powers Ratio
Ratio of distance of two lines
Basion to C1 spinolaminar line (BC)
divided by
C1 anterior arch to Opistion (AO)
Clinical significance of Powers Ratio
If BC/AO is >1
indicates possible anterior atlanto-occipital dissociation
BaSN Angle
Cranial Base Angle
represents skull base curvature
- normal: 125°-143°
- platybasia: >143°
- basilar kyphosis: <125°
The more obtuse this angle the more
retrognathic the mandible becomes.
Koenigsberg Modification
of
Cranial Base Angle
Line at base of anterior cranial fossa to tip of dorsum sellae
with clivus angle
Normal is 114 - 134
Grabb - Oaks Measurement
Line drawn from basion to posterior inferior C2 body
A perpendicular line drawn to dura
A value of 9mm or more indicates ventral brainstem compression.
Harris Lines
Basion Axial distance
and
Basion Dental interval
should both be less than 12mm
(Rule of 12s)
Significance of Harris Lines
distances of greater than 12mm is an indication of craniocervical instability.
Rule of 12s
Does dural venous drainage follow the arteries of the brain?
No, dural venous drainage does NOT follow the arteries of the brain.
To where to the veins of the brain drain?
The veins of the brain do not follow the arteries, but instead, drain into the dural sinuses, which subsequently drain into the internal jugular vein.
What are the dural sinuses made of?
Visceral periosteum and dural reflection lined with endothelium.
Which two dural sinuses are made differently than the others.
The Inferior Sagittal and Straight Sinuses both lack bony components as part of their wall.
What is “ag”
“ag” is arachnoid granulations
What is “s”
”s” is a sagittal sinus pocket
What is “SL”
“SL” is the sagittal sinus (superior)
What is “VC”
“VC” is a draining cortical vein
Deep Venous Sinuses
Drain into the Straight Sinus
- Inferior Sagittal Sinus
- Thalamostriate Veins
- Internal Cerebral Veins
Basilar Plexus
Connects the Inferior Petrosal Sinuses
Lies on the Clivus
Occipital Sinus Drainage
Drains from the
The confluence of Sinuses
to
Marginal Sinus
Posterior Condylar Vein
Drains from the Sigmoid Sinus to the Suboccipital Cavernous Sinus via posterior condyloid canal
Occipital Venous Drainage Diagram
Veins of the Craniocervical Junction
- Sub-occipital Cavernous Sinus
- Marginal Sinus
- Internal Vertebral Venous Plexus
What are the suboccipital muscles?
Circle of Willis Inferior Lateral
The cerebellar tonsil is part of the posterior lobe of the cerebellum, also known as the neocerebellum, which is responsible for coordinating the voluntary movement of the distal parts of limbs
The flocculonodular lobe has important connections to the vestibular nuclei and uses information about head movement to influence eye movement. Lesions to this area can result in multiple deficits in visual tracking and oculomotor control (such as nystagmus and vertigo), integration of vestibular information for eye and head control, as well as control of axial muscles for balance. This lobe is also involved in the maintenance of balance equilibrium and muscle tone.
the vermis is associated with bodily posture and locomotion. The vermis is included within the spinocerebellum and receives somatic sensory input from the head and proximal body parts via ascending spinal pathways
The thalamus has several functions, such as the relaying of sensory signals, including motor signals to the cerebral cortex and the regulation of consciousness, sleep, and alertness.
The fornix is a C-shaped bundle of nerve fibers in the brain that acts as the major output tract of the hippocampus. The fornix also carries some afferent fibers to the hippocampus from structures in the diencephalon and basal forebrain. The fornix is part of the limbic system.
The corpos callosum spans part of the longitudinal fissure, connecting the left and right cerebral hemispheres, enabling communication between them. It is the largest white matter structure in the human brain
the cingulate gyrus is highly influential in linking motivational outcomes to behavior (e.g. a certain action induced a positive emotional response, which results in learning). Part of the limbic system
The telencephalon, commonly called the cerebral hemispheres, is the largest portion of the central nervous system (CNS) and consists of the cerebral cortex, subcortical white matter (commissural, association, and projection fibers), and basal nuclei.
Atlanto-Axial Rotary Fixation
Atlanto-Axial Rotary Fixation
Atlanto-Axial Rotary Fixation
Atlanto-Axial Rotary Fixation
How many muscles typically attach to the Atlas?
How many muscles typically attach to the axis?
Superficial Neck Muscles
Clinical considerations
Larger lever arm
Greater capacity to exert torque
Local segmental instability if used in absence of deep muscle activation (Winters etal).
Deep Neck Muscles (4th Layer)
Clinical Consideration
Contribute to fine control of head movement
Segmentally arranged
Shorter, stiffer (Toursel etal 2002)
Higher spindle density
More involved in postural support (due low-threshold, slow twitch characteristics) Boyd etal (2002)
Relationship of V2 section of vertebral artery to cervical nerves.
Alar Ligaments
attach the axis to the base of the skull and originate from the posterior surface of the upper third of the dens and typically travel caudocranially (in 50 % of cadeveric dissections) or horizontally (in 50 % of subjects).
Each ligament is narrowest at its origin and comparatively wider at its insertion giving it a “V-shaped” configuration
The alar ligaments limit axial rotation and lateral flexion on the contralateral side and, apart from the transverse ligament, are the strongest stabilisers of the atlas preventing anterior displacement in the event of rupture of the transverse ligament.
Tectorial membrane
an upward extension of the posterior longitudinal ligament
Anterior atlanto-occipital membrane
anterior aspect of the atlas to the anterior rim of the foramen magnum and is located immediately posterior to the prevertebral muscles
It serves to limit atlanto-occipital extension at the craniocervical junction.
Posterior atlanto-ocipital membrane
believed to play very little part in stability of the atlantooccipital articulation
This broad ligament attaches the posterior arch of the atlas to the posterior margin of the foramen magnum and is continuous with the posterior atlantoaxial membrane and, subsequently, the ligamentum flavum
Interdigitations with both the dura mater and the related rectus capitis posterior minor muscle parenchyma may be present in this ligament; additionally, a connective tissue bridge (exhibiting increased vascularity) joining the rectus capitis posterior minor muscle to the spinal dura is frequently present, particularly in the midline. This myoligamentous complex (comprising the posterior atlanto-occipital membrane, interspinous ligament, ligamentum nuchae, rectus posterior major and minor muscles and obliquus capitis supripr and inferior muscles) adds further stability to the craniocervical junction
Os odontoideum
a separate ossicle with a smooth cortical border lying superior to a small hypoplastic dens and body of the axis in the location of the odontoid process
The anterior arch of the atlas may be rounded and hypertrophic in contrast to the normal anterior arch morphology. While the (type II) odontoid fracture is typically associated with a flattened uncorticated sharp margin to the adjacent body of the axis and normal morphology to the anterior arch of the atlas, the os odontoideum exhibits a well-corticated convex upper margin and rounded hypertrophic anterior atlas arch
Calcification in the alar ligament
Rarely, nodular calcification/ossification can be seen in the alar ligament which can mimic type III fracture of the occipital condyle or type I fracture of the odontoid process
Dentate Ligaments
1) each DL is composed of a single narrow fibrous strip that extends from the craniovertebral junction to T12, and each also features 18-20 triangular extensions that attach to the dura at their apices;
(2) the triangular extensions are smaller and more numerous at the cervical levels, and are larger and less numerous at the thoracic levels;
(3) the apices of the extensions attach to the dura via fibrous bands at cervical levels (each band 3-5 mm long) and lower thoracic levels (21-26 mm long), whereas they attach directly to the dura at upper thoracic levels;
(4) the narrow fibrous strip of the DL features longitudinally oriented collagen fibers, whereas the triangular extensions are composed of transverse and obliquely oriented collagen fibers. The collagen fibers are thicker and more abundant at the cervical than at the thoracic levels.
(5) The first (superiormost) pair inserts into the lateral borders of the foramen magnum, with the vertebral artery anterior to them and the hypoglossal nerve (CN XII) posterior. The inferiormost pair is at the level of the conus medullaris, namely, between the T12 and L1 segmental nerve roots, and its pia mater fuses with the filum terminale.
(6) Each triangular ligament has a vertically oriented base that emanates from the spinal cord between the exit point of the ventral root and entry point of the dorsal root, and an apex which points laterally and attaches to the dura mater just posterosuperior to the neural foramen
https://pubmed.ncbi.nlm.nih.gov/22555553/
https://radiopaedia.org/articles/denticulate-ligaments?lang=us
Dorsal Meningovertebral Ligaments
The dorsal meningovertebral ligaments in the cervical region anchored the posterior dural sac to the ligamentum flavum or laminae.
the occurrence rate of dorsal meningovertebral ligaments was 100% at C1-C2 and C4–C5.
The thickest ligaments were observed at the C1 and C2 vertebrae.
the orientation of the ligaments mostly was craniocaudal.
At C1 & C2 the Dorsal Meningovertebral Ligaments become thicker and become known as Myodural bridges”
Case courtesy of Dr Matt Skalski, Radiopaedia.org, rID: 65838
Myodural Bridges
Anatomical soft tissue bridges which cross the cervical epidural space, connecting suboccipital muscle fascia and dura have passive and active functions to anchor the spinal cord.
These myodural bridges may be involved in a dural tension monitoring system to prevent dural infolding and maintain patency of the spinal cord.
Failure of this system could result in altered cerebral spinal fluid flow, changes in sensorimotor function, cervicocephalic headaches, and dural related pathologies.
the Superior Myodural bridge connects the RCPMi fascia to the dura via the Occipito-atlantal interspace.
The Inferior Myodural bridge connects the fascia of the RCPMa and OCI to the dura via the Atlanto-axial interspace.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4025088/pdf/jcca_v58_2j_p184-enix.pdf
