Gross Anatomy of the Brain

Anatomy

Central nervous system

brain and spinal cord

Peripheral nervous system

ganglia and nerves

Subdivisions of CNS

• Cerebral Hemispheres x2

• Basal Ganglia

• Diencephalon (thalamus and hypothalamus)

• Brainstem

• Cerebellum

• Spinal cord

Fissures or sulci

depressions

in the cortex

Lobes of cerebral hemisphere

• Frontal

• Parietal

• Temporal

• Occipital

• Limbic

• Insula

Limbic lobe

• On the medial surface the parahippocampal gyrus is separated from the temporal lobe by the collateral sulcus.

• The cingulate gyrus from the frontal and parietal lobes by the cingulate sulcus

Insula Lobe

• Lobe covered by frontal, parietal and temporal lobe (covering parts termed the operculum)

• Strongly involved in sensory processing

Central sulcus

• Central sulcus separates frontal from parietal lobes

• Precentral and Post central gyri are adjacent to the central sulcus

• Precentral sulcus is anterior to the Precentral gyrus and likewise the sulcus posterior to the postcentral gyrus will be the post central sulcus

Lateral Sulcus (Sylvian Fissure)

• The Lateral Sulcus (or fissure) separates superior temporal gyrus from the frontal and parietal lobes

• Superior temporal sulcus is found centrally on the temporal lobe

Parieto-occipital sulcus

• Parieto-occipital sulcus Separates parietal and occipital lobe

• Calcarine fissure important for visual fields

• The Cuneus is above and the Lingual gyrus below

Primary sensory (somatosensory)

• Parietal lobe

• Post central gyrus

• Organized somatotopically (homunculus)

Where is the primary sensory (gustatory) located?

Insula (and operculum)

Where is the primary sensory (olfactory) located?

Olfactory Bulb

Where is the primary sensory (auditory) located?

Superior temporal gyrus and transverse temporal (Heschl’s gyrus)

Where is the primary sensory (visual) located?

cortex around the calcarine fissure (lingual gyrus and cuneus

Where is the primary motor lcoated?

• Precentral gyrus

• Layer V of cortex are the upper motor neurons

Where is the secondary motor located?

Posterior portions of middle and superior frontal gyri

Where is the supplemental motor located?

Medial portion of superior frontal gyrus

What is the Association cortex?

• Have no primary motor component

• Have only higher order sensory processing

  • Integration of signals

  • Multimodal neurons (respond to more than one sensory cues)

• Motor planning

• Learning and memory

• Social awareness

• Abstract thought

Broca’s (motor) speech area

• Opercular and triangular parts of the inferior frontal gyrus

• Important for the speech production

Wernicke’s (motor) speech area

• Posterior part of superior temporal gyrus (Brodmanns area 22 temporal lobe)

• Important for speech and language comprehension

• Supramarginal gyrus (area 40 and angular gyrus 39) are also important for language

Importance of prefrontal area

• Social awareness, working memory and decision making

• Has been implicated in restraining “animal instincts”

• Involved in motivation and has high level of dopamine input from Brainstem ventral tegmental area (VTA)

• Orbitalfrontal cortex is one area involved in higher sensory processing integrating all senses to from a sensory perception

What can lesions in prefrontal area result in?

• Absence of “willpower” (abulia)

• Confabulation

• Depression

• Mania

• Utilization Behavior

Importance of parietal area

• Visual association area (parietal eye fields)

• Spatial association (non-dominate side)

• Lesions in this association area are also associated with neglect

• Higher visual processing

  • The “where” of an object

What is hemineglect?

• Can result from damage the association cortex

• Patient will ignore or “neglect” to notice one side of sensory space

• Usually contralateral

Importance of temporal area

• Auditory association

• Area is bilaterally connected to hippocampus

• Higher visual and auditory processing

  • The what of an object including recognizing features and object naming (or object recognition through sounds)

  • Face recognition has been linked to temporal lobe association cortex.

  • Prosopagnosia: inability to recognize and identify faces

Importance of occipital area

• Involved in visual processing

• Occipital association cortex is continuous with the parietal and temporal association areas

• Dorsal processing stream integrates with motion sensitive areas (the “where” of an object

• Ventral stream integrates object recognition areas (the ”what”) of an object

What is subcortical white matter?

• Commissural fibers

• Projection fibers

  • Internal capsule (mostly up down)

  • Fasciculi (mostly longitudinal)

What are commissures

connect the left and right hemispheres to each other

Corpus collosum

What are Anterior Commissures?

Interconnects olfactory bulbs and amygdala

What are Posterior Commissures?

Important for pupillary light reflex

What is an internal capsule?

• Are projection fibers that physically encapsulate the thalamus.

• These are projections to and from cortical and subcortical structures

What is Diencephalon

• Connects the forebrain with the rest of the CNS.

• It is located caudal to the forebrain and rostral to the Midbrain

• Consists of thalamus, hypothalamus, epithalamus and pretectum.

What is the thalamus

• Bulk of Diencephalon

• Relay between sensory to cortex and motor and cortex

• Primary Function: conscious sensation and conscious movement

What is the hypothalamus?

• Primary function: autonomic and instinctual functions

  • Hormonal

  • Autonomic

  • Behavioral

• Receives input from many areas including circulation

What is the primary basal ganglia?

Primary function: is to initiate wanted movement and inhibit unwanted movement

What are the Three Main Nuclei of Basal Ganglia

• Caudate

• Putamen

• Globus pallidus

Anatomical parts of cerebellum

• Floccular nodular lobe

• Anterior Lobe

• Posterior Lobe

Functional parts of cerebellum

• Floccular nodular lobe: balance

• Vermis: Correcting movements of trunk

• Paravermis: correcting movements of extremities

• Hemispheres: timing movements

Functions of the brainstem

• Conduit for ascending and descending tracts

• Nuclei for second order sensory neurons (Cranial and spinal nerves)

• Nuclei for lower motor neurons of the cranial nerves

• Nuclei for critical neuroransmitter and neurohormones

• Nuclei for life supporting autonomic functions

Parts of the brainstem

• Midbrain

• Pons

• Medulla

Longitudinal Divisions of the Brainstem (Tectum)

• dorsal (roof) of the brainstem

• mostly midbrain tectum (superior and inferior colliculi)

• includes meduallary velum

• (dorsal columns and nuclei in the medulla are tectum but are usually always referred to by their names)

Longitudinal Divisions of the Brainstem (Tegmentum)

• intermediate longitudinal zone

• contains most ascending fibers, cranial nerve nuclei and reticular formation

Longitudinal Divisions of the Brainstem (Base)

• ventral brainstem

• contains descending fibers and related nuclei

• dominated by the cerebral peducles (midbrain), Base of pons and pyramids (medulla)

What are the Rostral Caudal Divisions of the brainstem

1. spinal cord-medulla transition

2. caudal (closed) medulla

3. middle and rostral (open) medulla

4. caudal pons

5. caudal midbrain

6. rostral midbrain

What are the 3 meninges?

• Dura

• Arachnoid

• Pia

What are meninges?

• Thick dural layer

• Thin arachnoid layer

• CSF filled space

• Thin pia layer

What is the the dura layer?

Two dural layers

• Periostial

• Meningeal

What are Spinal Meninges

One Layer of dura

• Meningeal

• Periostial becomes vertebrate perostium

(Note: Unlike in the cranium the vertebral column has a true epidural space)

Epidural puncture

Epidural injection is possible because of the true space between vertebrae and dura mater

Lumbar puncture

Lumber punctures go deeper. Through the dura and arachnoid and into the subaracnoid space

What are Infoldings?

• At important fissures of the brain the menigeal layer of dura folds in on itself.

• (Falx Cerebri and tentorium cerebelli can be seen here)

• Where the meningeal layer pulls away from the periostial layer, and folds in sinuses are created

• These sinuses drain venous blood and CSF into the jugular vein

Importance of sinuses and infoldings

Dural venous sinuses interconnect and drain through the jugular foramen into the internal jugular vein

Importance of the lateral ventricle

where most CSF is made

Where is CSF formed?

• the ventricles by the choroid plexus

• about 350-500ml a day

• 25 ml in ventricles rest in subarachnoid region

• turns over 2-3 times a day

What is CSF?

• clear liquid

  • colorless

  • cell free (5 cells per ul)

• ionic makeup different from blood

  • lower in protein and glucose

  • lower in K+ and CA++

  • higher in MG++ and CL-

Importance of choroid plexus

• in every ventricle

  • not in cerebral aqueduct or central canal

  • largest amount in atrium of lateral ventricle (glomus)

Whats actively makes CSF?

• a blood filtrate, actively made by choroid epithelium in the choroid plexus

What is the function of CSF?

• adds buoyancy to brain

• provides stable ionic environment

• gylmphatic system: acts as lymphatic system form CNS

Importance of buoyancy

• top a brain in isotonic saline (equivalence of being surrounded in CSF)

• brain affected by gravity

Importance of ventricular circulation

• CSF enters the subarachnoid space from the fourth ventricle

• CSF circulates around in the subarachnoid space until it can be cleared

What is a spinal tap done?

Lumbar cistern

• largest pocked of CSF

• where the spinal cord ends (conus medullaris) but the arachnoid and dura continue and house spinal route (cauda equina)

What are the 2 reasons a spinal tap is done in the lumbar cistern?

1. Where most CSF is pooled

2. Low risk of hitting and thus damaging spinal cord

Where is a large portion of CSF drained?

Through the arachnoid granulations in the superior sagittal sinus

Where are arachnoid granulations?

in spinal nerve roots

Where else can CSF leak out of?

• cranial and spinal nerves

• CSF exiting where large blood vessels enter an exit meninges might be regulated by glia cells

Where does some CSF drain into?

the nasal cavity

What is rhinorrhea?

• runny nose caused by excessive CSF leakage

• often due to trauma

• can be due to space occupying lesions or congenital malformations

What is hydrocephalus?

• “water on the brain”

• symptom of excess CSF in the ventricular system

• can be congenital or acquired

What is noncommunicating hydrocephalus?

• Caused by a blockage of CSF flow out of the ventricular system

• Caused by a blockage or or stenosis of with in the ventricular system

  • most commonly at the cerebral aqueduct

• Excess CSF in the ventricular system

• Some ventricles are enlarged, some are normal

• Key is that the CSF can not get out of the ventricular system

What is communicating CSF

• CSF NOT cleared fast enough through the subarachnoid space

• Excess CSF in CNS

• All ventricles are enlarged

• Caused by a decrease or impaired filtration of CSF through arachnoid granulations

• Choroid tumors causing an increase in CSF production

• Key is that the CSF has freedom to flow out ventricular system and into subarachnoid space

• Since in some cases CSF pressure, as measured by spinal tap, is “normal” this can be called Normal Pressure Hydrocephalus

  • Ex Vacuo: excess CSF in the ventricular system as a result of decreased brain mass

What would cause an enlarged third ventricle?

• Stenosis or blockage at the cerebral aqueduct —> enlarged lateral and third ventricle

• Normal size fourth ventricle

What is hydrocephalus ex-vacuo?

• ventricular enlargement due to decrease in brain tissue

  • particularly basal ganglia

• Seen in degenerative diseases:

  • Parkinson’s

  • Alzheimer’s

  • Huntington’s

• Normal pressure

How does spina bifida cause hydrocephalus?

• Arnold-Chiari malformation

• Herniation of the cerebellum blocking the flow of CSF out of the fourth ventricle

  • compress the foramen

• Rated type I, II and III on level of severity

• Chiari II usually accompanies a myelomeningocele

What arteries supply the CNS?

• Internal carotid

• Vertebral arteries

Importance of internal carotid artery

• branch of common carotid

• supplies most of cerebellum

Importance of vertebral arteries

• Branch of subclavian

• Supply brainstem, cerebellum, posterior cortex

In arterial plexi, where are arteries more dense?

more dense in gray matter, than white matter

What are the branches of the internal carotid?

• Anterior cerebral artery (ACA)

• Middle cerebral artery (MCA)

Importance of posterior communicating artery

• branched off internal carotid first

• vertebral supply

Arteries to know in the circle of Willis

• Anterior cerebral (ACA) x2

• Anterior communicating x1

• Middle cerebral (MCA) x2

• Lenticulostriate x many both sides

• Anterior Choroidal x2 (first of lenticulostriate

• Posterior communicating x2

• Posterior cerebral (PCA) x2

• Superior cerebellar x2

• Basilar x1

• Anterior inferior cerebellar (ACIA) x2

• Posterior Inferior cerebellar (PICA) x2

• Anterior spinal artery x1

Importance of anterior cerebral artery

Medial surfaces of the frontal and parietal lobes and the cingulate gyrus

Importance of lenticulstriate arteries

• branches off the MCA that supply Deep structures

  • Basal ganglia

  • Internal capsule

Importance of middle cerebral arteries

• Cover most of the lateral surface of the brain

  • Superior branches (pink) cover frontal and parietal lobes

  • Inferior (yellow) cover temporal and occipital lobes

Importance of posterior cerebral artery

• covers the inferior and medial temporal and occipital lobes

• Perforating arteries supply thalamus and parts of internal capsule

• lesion: visual defect

What supplies blood to the inferior surface of the brain?

Covered by parts of most main arteries

• ACA (red)

• MCA (yellow)

• PCA (blue)

What is barrel syndrome?

brachial diplegia and sometimes bilateral paresthesia due to watershed infarcts in the anterior and middle cerebral artery watershed territory

What causes barrel syndrome?

• Blockage in internal carotid

• Areas of the cortex that have overlaped coverage (ACA and MCA)

• If there is a decrease in blood flow to two adjacent arteries these areas are the first to become ischemic

Why are arteries relationship to cranial nerves important?

• Neuroanatomically (being able to locate CNS structures)

• Clinically aneurysms at key locations may compress cranial nerves causing dysfunction

  • Ballooning of arteries

  • Bulging of arteries become space occupied

• neurological deficits

Important arteries for spinal cord blood supply

• Radicular arteries: arise from the aorta along the vertebral column and help supply the cord and anastomose with the spinal arteries

• Segmental medullary arteries: similar but doesn’t anastomose

• Artery of adamkiewicz: described as the largest radicular artery

  • is variable from person to person but general originates from a posterior intercostal artery in the lower thorax

  • widely assumed now that in most people it is in fact a segmental artery and is mostly responsible for the anterior lumbar and sacral cord

  • Major anastomotic artery of spinal cord

• stroke in anterior spinal cord, paralysis in top ½ of body

Arterial supply of CNS

lateral: upper body

medial: lower body

Importance of superficial cerebral veins

Superficial veins are on the surface of the cerebrum and mainly drain into the superior sagital sinus (SSS)

Importance of Superficial Middle cerebral vein

• Can be found traveling along the lateral fissure

• Interconnects multiple sinuses

• Can drain down, or up to SSS

Importance of Superior and Inferior Anastomotic veins

• Interconnect superficial intermediate vein to the superior sagittal sinus or transverse sinus respectively

• Can drain to transverse sinus or up SSS

Importance of Dural Venous sinuses

• Channels that form between two dural layers

• Valveless veins that drain most venous blood and CSF from the brain

Know unpaired (midline) sinuses

• Superior sagittal (SSS)

• Inferior sagittal (ISS)

• Straight Sinus

• Confluence

• Occipital

  • (sometimes paired)

Know paired sinuses (have right and lefr)

• Cavernous

• Transverse

• Superior Petrosal

• Inferior Petrosal

• Sigmoid

What is the main drain for the brain?

interior jugular vein

Importance of deep cerebral veins

Drain deep structures and primarily drain into the great vein of galen then the straight sinus