contents of the neurocranium, part ii the brain, its blood supply and the cranial nerves
TRANSCRIPT
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
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
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
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
V1 Superior orbital fissue
V2 Foramen rotundum
V3 Foramen ovale
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
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