Contents of the Neurocranium, Part II The Brain, its Blood Supply and the Cranial Nerves.

Contents of the Neurocranium, Part II

The Brain, its Blood Supplyand the Cranial Nerves

Embryology

• Central nervous system begins as neural tube

• Anterior portion of neural tube differentiates into three primary divisions:– Hindbrain

– Midbrain

– Forebrain

Embryology

• Lateral walls of the forebrain expand and protrude from both sides of the neural tube

• Median portion of forebrain is the diencephalon

• Lateral projections form the telencephalon

Embryology Two primary axes

of growth in the developing brain

1. Longitudinal flexion of anterior neural tube

2. Inferior spiral rotation of the telencephalon

Ventricles

• Lumen of neural tube becomes the CNS ventricular system

• Shape of ventricular system reflects developmental deformation of neural tube

Ventricles

• Lateral ventricles– Anterior horn

– Body

– Posterior horn

– Inferior horn

• Third ventricle– Interventricular foramen (of

Monro)

– Cerebral aqueduct

• Fourth ventricle

HindbrainCerebellum

• Motor coordination

• Cognitive functions– temporal coordination– planning

HindbrainMedulla Oblongata

• Anatomical and physiological junction of brain and spinal cord

• Initiates respiration

• Regulates heart rate

• Origin of cranial nerves IX, X, XI, and XII

HindbrainPons

• Bridge between cerebellum and the rest of the brain

• Origin of cranial nerves V, VI, VII, and VIII

Midbrain• Least differentiated

primary brain division

• Contains cerebral aqueduct

• Origin of cranial nerves III and IV (from dorsal surface)

MidbrainCorpora Quadrigemina

Superior Colliculi• Visual tracking

• Coordination of head turning & eye movements

• Inferior Colliculi• Sound location

• Focusing attention to auditory stimuli

MidbrainSubstantia Nigra

• Darkly pigmented (neuro-melanin) nucleus

• Produces dopamine

• Parkinson’s disease—destruction of the cells of the substantia nigra

MidbrainSubstantia Nigra

• In 1982, 6 drug addicts in Santa Clara, CA manifested with Parkinson’s disease (oldest patient was 41 yrs. old)

• Each had injected synthetic heroin—MPPP (1-methyl-4-phenyl-4-propionpiperidine), an analog of meperidine (Demerol)

• The poorly synthesized designer drug contained a contaminant—MPTP (1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine), which kills the cells of the substantia nigra

MidbrainCerebral Peduncles

• Major fiber bundles connecting forebrain to hindbrain

• Contain descending axons of upper motor neurons from cortex

DiencephalonThalamus

• Potato-shaped structure

• Sensory relay for all afferents except olfaction

DiencephalonThalamus

• Thalami form walls of 3rd ventricle

DiencephalonHypothalamus

– Body temperature

– Hunger– Thirst– Sexual activity

– Goal-seeking behavior

– Endocrine functions– Affective behavior– Visceral motor

system

• 4 g neural structure

• Connected to pituitary gland

• Regulates:

TelencephalonBasal Ganglia

• Caudate nucleus• Globus pallidus• Putamen• Modulate and integrate components

of motor activity (and cognitive functions)

• System depends on dopamine— affected by Parkinson’s disease

TelencephalonAmygdala

• Lies at tail of caudate nucleus but is not functionally part of the basal ganglia

• Involved in the control of rage, aggression and sexuality

TelencephalonHippocampus

• Composed of three-layered cortex (archicortex)

• Fornix—major output pathway• Involved in the formation of

new episodic memories

TelencephalonCerebrum

• Composed of six-layered neocortex and deep white matter• Center of sensory input, motor output, and higher

cognitive functions

Cerebrum

Primary Fissures

• Longitudinal cerebral fissure

Cerebrum

Primary Fissures

• Lateral fissure

• Central sulcus

CerebrumLobes

• Frontal

• Parietal

• Occipital

• Temporal

CerebrumLobes

• Insula

CerebrumWhite Matter

• Corpus callosum—primary connection between left and right cerebral hemispheres

CerebrumWhite Matter

• Internal capsule—primary pathway of fibers ascending to cortex from thalamus and descending from cortex to cerebral peduncles

Motor Cortex

• Primary motor cortex lies along the precentral gyrus in the frontal lobe

• Motor output projects to contralateral side

Motor Output Pathways

• Voluntary movement—conducted to lower motor neurons via the pyramidal pathway

Motor Output Pathways

• Balance, posture, limb coordination information conducted by numerous extrapyramidal pathways

Somatosensory Cortex

• Primary somatosensory cortex lies along the postcentral gyrus in the parietal lobe

• Representation of body is from contralateral side

Somatosensory Cortex

Somatosensory cortex (like motor cortex) is mapped somatotopically and proportionate to sensitivity, not size

Other Sensory Cortices

• Visual cortex—occipital lobe

• Auditory cortex—superior portion of temporal lobe

• Rhinal (olfactory) cortex—anterior medial temporal lobe

• Gustatory (taste) cortex—inferior aspect of postcentral gyrus

Language Areas

• Occur only in the left hemisphere of most people (96 % of right-handed individuals, 72% of left-handed individuals)

• Broca’s area—motor speech center, in frontal lobe

• Wernicke’s area—language interpretation center, in temporal & parietal lobes

Cranial NervesI. OlfactoryII. OpticIII. OcculomotorIV. TrochlearV. TrigeminalVI. AbucensVII. FacialVIII. VestibulocochlearIX. GlossopharyngealX. VagusXI. Spinal AccessoryXII. Hypoglossal

Cranial NervesExit from Neurocranium

I Cribriformplate


II Optic canal


III, IV, VI Superior orbital fissure


V1 Superior orbital fissue

V2 Foramen rotundum

V3 Foramen ovale


VII, VIII Internal auditory meatus


IX, X, XI Jugular foramen


XII Hypoglossal Canal


Blood Supply

• Vertebral arteries– Provide ~30% of blood

supply to brain

• Internal carotid arteries – Provide ~70% of blood

supply to brain

Circle of WillisVertebral aa. basilar a. posterior

cerebral aa.

Internal carotid a. middle cerebral aa. anterior cerebral aa.

Posterior communicating arteries connect posterior cerebral aa. and internal carotid aa.

Anterior communicating ARTERY (sing.) connect anterior cerebral arteries

Blood Supply

Blood Supply

Venous Drainage

• Blood from the cortex drains to surface veins that drain into the dural venous sinuses

Venous Drainage• Blood from the deep

brain (thalamus, basal ganglia) drains into great cerebral vein (of Galen) before entering the straight sinus

• Blood from the lower brainstem drains through the foramen magnum into the vertebral venous plexus

Cerebrovascular Accident (CVA)

• Ruptured aneurysm—failure of a localized defect in the elasticity of a vessel

• Arterial thrombus—blockage of an artery• Embolism—clot from elsewhere in the

body that lodges in a cerebral artery• Hypertensive apoplexy—sudden effusion of

blood into cerebral tissue due to rise in blood pressure

Contents of the Neurocranium, Part II The Brain, its Blood Supply and the Cranial Nerves.

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