Chapter 1 - Gross Anatomy Flashcards
Isthmus
Connects the sinuous middle frontal gyrus to the pre-central gyrus
“subcentral gyrus”
Present in 98% of patients
Between central sulcus and sylvan fissure (lateral sulcus)
Inferior parietal lobule components
Angular gyrus
Supramarginal gyrus
Termination of the Sylvian fissure
Supramarginal gyrus
Termination of the superior temporal sulcus
Angular gyrus
Brodmann’s area 3, 1, 2
Primary somatosensory cortex
Brodmann’s area 41 & 42
Primary auditory areas (transverse gyri of Heschl)
Brodmann’s area 4
Precentral gyrus, primary motor cortex (aka “motor strip”)
Large concentration of giant pyramidal cells of Betz
Brodmann’s area 6
Premotor area or supplemental motor area.
Immediately anterior to motor strip, it plays a role in contralateral motor programming.
Brodmann’s area 44
Dominant hemisphere: Broca’s area (classically “motor speech area”)
Parts of the Pars triangularis & pars opercularis of the inferior frontal gyrus
Brodmann’s area 17
Primary visual cortex
Brodmann’s area 40 & part of 39
Wernicke’s area (dominant hemisphere)
May also include approximate posterior third of superior temporal gyrus
Inferior portion of Brodmann’s area 8
Frontal eye field
Initiates voluntary eye movement to the opposite direction
Pars marginales pleural
partes marginales
The cingulate sulcus terminates posteriorly in the _________
pars Marginales
- seen on the medial surface of the brain
- visible on 95% of CTs and 91% of MRIs
- extend a greater distance into the hemispheres
- posterior to the widest biparietal diameter on axial CT
AC-PC line
- Connects the anterior commissure and the posterior commissure on a mid-line saggital image
- Used in functional neurosurgery
- Used as the baseline for axial MRI & recent CT scanners
- Talairach definition: superior edge of AC & inferior edge of PC
- Schaltenbrand definition: middle of AC & PC
- Talairach vs Schaltenbrand definition: difference of 5.81 deg +/-1.07 deg
Anterior commissure
Horizontally positioned white matter tract that crosses in front of the fornix
Posterior commissure
The white-matter band at the level of the pineal that crosses at the posterior third ventricle
Orbitomeatal line vs. Talairach AC-PC
Orbitomeatal line (used in old CTs) is ~9 deg steeper
Somatotopic organization of the primary sensory cortex: Medial surface of the brain
Genitals (inferior)
Toes
Foot
Leg (corner)
Somatotopic organization of the primary sensory cortex:
Convexity of brain
Hip Trunk Neck Head Shoulder Arm Elbow Forearm Wrist Hand Fingers Thumb Eye Nose Face Upper lip Lips Lower lip Teeth, gums Intraabdominal
Somatotopic organization of the primary motor cortex:
Medial surface of the brain
Toes
ankle
knee
Somatotopic organization of the primary motor cortex:
Convexity of the brain
Hip Trunk Shoulder Arm Elbow Wrist Hand Fingers Thumb Neck Brow Eye Face Lips Jaw Tongue Swallowing
Central sulcus on axial imaging
- visible on 93% of CTs and 100% of MRIs
- curves posteriorly as it approaches the intrahemispheric fissure
- often terminates in the paracentral lobule, just anterior to the pars marginalis
Parieto-occipital sulcus (or fissure) on axial imaging
- more prominent over the medial surface
- on axial imaging is longer, more complex, and more posterior than the pars marginalis
Post-central sulcus on axial imaging
- usually bifurcates and forms an arc or parenthesis (“lazy-Y”) cupping the pars Marginalis
- the anterior limb does not enter the pars Marginalis bracket and the posterior limb curves behind the pars Marginalis to enter the interhemispheric fissure
Hand “knob”
- knob-like protrusion (shaped like an inverted omega) on axial imaging
- has a posteriorly projecting hook-like appearance with the posterior limit of the Sylvian fissure on sagittal imaging
- superior aspect of the precentral gyrus
- contains alpha motor neurons for hand function
Pterion
Estimated location
2 finger-breadths above the zygomatic arch
1 thumbs breadth behind the frontal process of the zygomatic bone
Asterion
Junction of the lambdoid, occipitomastoid and parietomastoid sutures
Asterion location relative to internal structures
Usually lies within a few millimeters of the posterior-inferior edge of the junction of the transverse and sigmoid sinuses (not always reliable)
Lambda
Junction of the lambdoid and sagittal sutures
Junction of the coronal suture and superior temporal line.
Stephanion
Posterior margin of the foramen magnum in the midline
Opisthion
Junction of the coronal and saggital sutures
Bregma
Taylor Haughton lines
- Can be constructed on an angiogram, CT/MRI scout film, or skull Xray
- Can be used to approximate the Sylvian fissure and the motor cortex
- Frankfurt plane
- Nasion-inion across calvaria and divided into 4ths
- Posterior ear line
- Condylar line
Reid’s baseline
From inferior margin of the orbit through the center of the external auditory meatus
Inion
Marks external occipital protuberance
Condylar line
Perpendicular to the baseline (Frankfort) through the mandibular condyle
Posterior ear line
Perpendicular to the baseline through the mandibular condyle
Rolandic fissure
central sulcus
Approximating the motor cortex
- Superior aspect is almost straight up from the external acoustic meatus near the midline
- Approximate by connecting a point 2 cm posterior to the arc extending from the nation to the inion to a point 5 cm straight up from the external acoustic meatus
- Connect T-H lines
- a line drawn 45 deg to Reid’s base line starting at the pterion points in the direction of the motor strip
Connecting T-H lines to approximate the central sulcus
Connect the point where the posterior ear line intersects the circumference of the skull (~1 cm behind the vertex, 3-4 cm behind the coronal suture) to the point where the condylar line intersects the line representing the Sylvian fissure
Sylvian fissure (lateral fissure) approximation - with skin
Line connecting the lateral canthus to the point 3/4 of the way posterior along the arc running over convexity from nasion to inion
squamosal suture
Between the temporal and parietal bones
sphenosquamous suture
Between the sphenoid and temporal bones
Sylvian fissure approximation on skull
Sylvian fissure follows the squamosal suture and then deviates superiorly to terminate at Chater’s point
Chater’s point
6 cm above the external acoustic meatus on a line perpendicular to the OML
Lateral ventricles location in the non-hydrocephalic adult
- 4-5 cm below the outer skull surface
- Center of body of ventricles sit in the mid pupillary line
- Frontal horn is intersected by a line passing perpendicular to the calvaria along the mid pupillary line
- anterior horns extend 1-2 cm anterior to the coronal suture
Average length of the third ventricle
~2.8 cm
Scapular line - vertebral landmark
T2-T3
Inferior scapular pole - vertebral landmark
~T6 posteriorly
Intercristal line
Line drawn between the highest point of the iliac crest across the back
Crosses the midline either at the interspace between L4 and L5 spinous processes or at the L4 spinous process itself
Porus acusticus
Internal auditory canal
- filaments of the acoustic portion of VIII penetrate tiny openings of the lamina cribrosa of the cochlear area
Transverse crest
Separates the superior vestibular area and facial canal (above) from the inferior vestibular area and cochlear area
Vertical crest
“Bill’s bar” - named after Dr. William House
- separates the meatus to the facial canal anteriorly (containing VII and nervus intermedius) from the vestibular area posteriorly (containing the superior division of the vestibular nerve)
5 nerves of the internal auditory canal
- Facial nerve (VII) (superior position)
- Nervus intermedius
- Acoustic portion of the VIII
- Superior branch of the vestibular nerve
- Inferior branch of the vestibular nerve
Nervus intermedius - in the IAC
- Somatic sensory branch of the facial nerve
- Primarily innervating mechanoreceptors of the hair follicles of the inner surface of the pinna and deep mechanoreceptors of nasal and buccal cavities and chemoreceptors in the taste buds on the anterior 2/3 of the tongue
Superior branch of the vestibular nerve - in the IAC
- Passes through the superior vestibular area to terminate in the utricle and in the ampullae of the superior and lateral semicircular canals
Inferior branch of the vestibular nerve - in the IAC
- Passes through inferior vestibular area to terminate in the saccule
Average length of frontal horn anterior to foramen of Monro
25 mm
Average distance from cloves to floor of 4th ventricle at level of fastigium
36.1 mm (33.3-40.0 mm)
Fastigium
apex of the 4th ventricle within the cerebellum
Average length of the 4th ventricle at the level of the fastigium
14.6 mm (10.0-19.0 mm)
Average distance from fastigium to opisthion
32.6 mm (30.0-40.0 mm)
Angle of the mandible - vertebral landmark
C1-C2
1 cm above the thyroid cartilage (=hyoid bone) - vertebral landmark
C3-C4
Level of thyroid cartilage - vertebral landmark
C4-C5
Crico-thyroid membrane - vertebral landmark
C5-C6
Carotid tubercle - vertebral landmark
C6
Cricoid cartilage - vertebral landmark
C6-C7
Nasal slits contents
Anterior ethmoidal n, a, v
Superior orbital fissure contents
- CN III, IV, VI, ophthalmic, division of V (includes nasocilliary, frontal and lacrimal nerves)
- Superior ophthalmic v
- Recurrent meningeal branch from lacrimal a
- Orbital branch of the middle meningeal a
- Sympathetic filaments from ICA plexus
Inferior orbital fissure contents
- CN V2
- Zygomatic n
- Filaments from pterygopalatine branch of maxillary n
- Infraorbital a & v
- Vein between inferior ophthalmic v & pterygoid venous plexus
Foramen lacerum
- Usually nothing
- Vidian artery in 30%
- ICA traverses upper portion
Carotic canal
- Internal carotid a
- Ascending sympathetic nerves
Incisive foramen
- Descending septal artery
- Nasopalatine n
Greater palatine foramen
Greater palatine n, a, v
Lesser palatine foramen
Lesser palatine n
Internal acoustic meatus
CN VII CN VIII (state-acoustic)
Hypoglossal canal
- CN XII
- Meningeal branch of the ascending pharyngeal a.
Foramen magnum
- Spinal cord (medulla oblongata)
- CN XI (spinal accessory) entering the skull
- Vertebral a
- Anterior & posterior spinal arteries
Foramen cecum
Occasional small vein
Cribriform plate
Olfactory nerves
Optic canal
- CN II (optic)
- ophthalmic a
Foramen rotundum
- CN V2 (maxillary division)
- Artery of the foramen rotundum
Foramen ovale
- CN V3 (mandibular div)
- Portio minor (motor for CN V)
Foramen spinosum
- Middle meningeal artery & vein
Jugular foramen
- Internal jugular vein
- CN IX, X, XI
Stylomastoid foramen
- CN VII
- Stylomastoid artery
Codyloid foramen
Vein from transverse sinus
Mastoid foramen
- Vein to mastoid sinus
- Branch of occipital artery to dura mater
Vascular supply of the internal capsule
- Anterior choroidal
- Lateral striate branches (aka capsular branches) of MCA (most of anterior and posterior limbs)
- Direct branches of the internal carotid a (genu)
Anterior choroidal artery areas of supply
All of retrolenticular part (including optic radiation) and ventral part of posterior limb of IC
Anterior thalamic subradiation
Connects medial and anterior thalamic nucleus to frontal lobe
Superior thalamic subradiation
- Connects rolandic areas to ventral thalamic nuclei
- General sensory fibers from body & head to terminate in post central gyrus
Posterior thalamic subradiation
- Connects occipital & posterior parietal to caudal thalamus
Inferior thalamic subradiation
- Connects transverse temporal gyrus of Heschl to MGB
Ligaments connecting the atlas to the occiput
- Anterior atlantooccipital membrane (anterior margin of foramen magnum to anterior arch of C1)
- Posterior atlantooccipital membrane (posterior margin of foramen magnum to posterior arch of C1)
Ligaments connecting the axis (odontoid) to the occiput
- Tectorial membrane
- Alar ligaments
- Apical odontoid ligament: tip of dens to foramen magnum
Alar ligaments - connection from odontoid to occiput
- Occipital-alar portion: side of dens to occipital condyle
- Atlanta-Alar portion: side of the dens to the lateral mass of C1
Ligaments connecting the axis to the atlas
- transverse atlantal ligament (horizontal component of the cruciate ligament)
- Atlanta-alar portion of the alar ligaments
- descending band of the cruciate ligament
Strongest ligament of the spine
transverse atlantal ligament (or transverse ligament)
Separation of dorsal and ventral nerve roots in the spinal nerves
Dentate ligament
Interomediolateral gray nucleus
Only present from T1 to ~L1 or L2 where there are sympathetic (thoracolumbar outflow) nuclei
Laminae according to the scheme of Rexed
Lamina II - substantia gelatinosa
Laminae III & IV - nucleus proprius
Lamina VI - in the base of the posterior horn
Pain and temp 1st order neurons
- Small, finely myelinated afferent
- Soma in the DRG
- Enter cord at dorsolateral tract (zone of Lissauer)
- Synapse in the substantia gelatinosa
Pain and temp 2nd order neurons
- Axons cross obliquely in the anterior white commissure ascending ~ 1-3 segments while crossing to enter the lateral spinothalamic tract
- Synapse in the VPL of the thalamus
Pain and temp 3rd order neurons
- Pass through the internal capsule to post central gyrus (Brodman 3,1,2)
Fine touch receptors
- Meissner’s
- Pancinian corpuscles
- Merkel’s disks
- Free nerve endings
Fine touch 1st order neurons
- Heavily myelinated afferents
- Soma in dorsal root ganglion (no synapse)
- Short branches synapse in nucleus proprius of posterior gray
- Long fibers enter the ipsilateral posterior columns without synapsing (below T6: fasciculus gracilis; above T6 fascicles cuneatus)
- Synapse: nucleus gracilis/cuneatus, just above pyramidal decussation
Fine touch 2nd order neurons
- Axons form internal arcuate fibers, decussate in lower medulla as medial lemniscus
- Synapse in VPL of thalamus
Fine touch 3rd order neurons
Pass through internal capsule primarily to the post central gyrus
Light (crude) touch receptors
- Meissner’s
- Pancinian corpuscles
- Merkel’s disks
- Free nerve endings
- Peritrichial arborizations
Light (crude) touch - first order neuron
- Large, heavily myelinated afferents (Type II)
- Soma on dorsal root ganglion (no synapse)
- Some ascend uncrossed in posterior columns (with fine touch);
- most synapse in Rexed VI & VII
Light (crude) touch - second order neuron
- Axons cross in the anterior white commissure (a few don’t cross)
- Enter anterior spinothalamic tract
- Synapse in VPL of thalamus
Light (crude) touch - third order neuron
Pass through internal capsule primarily to postcentral gyrus
