Central Nervous System (CNS)
•CNS – composed of the brain and spinal cord
•Cephalization
–Elaboration of the anterior portion of the CNS
–Increase in number of neurons in the head
–Highest level is reached in the human brain
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The Brain
•Composed of wrinkled, pinkish gray tissue
•Surface anatomy includes cerebral hemispheres, cerebellum, and brain stem
Embryonic Development
•During the first 26 days of development:
–Ectoderm thickens along dorsal midline to form the neural plate
–The neural plate invaginates, forming a groove flanked by neural folds
–The neural groove fuses dorsally and forms the neural tube
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Surface ectoderm

(a) 19 days

(b) 20 days

(c) 22 days

(d) 26 days
Neural folds
Neural crest
Surface ectoderm

Neural groove

Neural tube

Anterior (rostral) end
Embryonic Development
Figure 12.1
Level of section

Neural plate

Primary Brain Vesicles
•The anterior end of the neural tube expands and constricts to form the three primary brain vesicles
–Prosencephalon – the forebrain
–Mesencephalon – the midbrain
–Rhombencephalon – hindbrain
Neural Tube and Primary Brain Vesicles
Figure 12.2a, b

Secondary Brain Vesicles
•In week 5 of embryonic development, secondary brain vesicles form
–Telencephalon and diencephalon arise from the forebrain
–Mesencephalon remains undivided
–Metencephalon and myelencephalon arise from the hindbrain
Secondary Brain Vesicles
Figure 12.2c

Adult Brain Structures
•Fates of the secondary brain vesicles:
–Telencephalon – cerebrum: cortex, white matter, and basal nuclei
–Diencephalon – thalamus, hypothalamus, and epithalamus
–Mesencephalon – brain stem: midbrain
–Metencephalon – brain stem: pons
–Myelencephalon – brain stem: medulla oblongata
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Adult Neural Canal Regions
Figure 12.2c, d

Adult Neural Canal Regions
•Adult structures derived from the neural canal
–Telencephalon – lateral ventricles
–Diencephalon – third ventricle
–Mesencephalon – cerebral aqueduct
–Metencephalon and myelencephalon – fourth ventricle
Adult Neural Canal Regions
Figure 12.2c, e

Space Restriction and Brain Development
Figure 12.3

Basic Pattern of the
Central Nervous System
•Spinal Cord
–Central cavity surrounded by a gray matter core
–External to which is white matter composed of myelinated fiber tracts
•Brain
–Similar to spinal cord but with additional areas of gray matter
–Cerebellum has gray matter in nuclei
–Cerebrum has nuclei and additional gray matter in the cortex
Basic Pattern of the Central Nervous System
Figure 12.4

Ventricles of the Brain
•Arise from expansion of the lumen of the neural tube
•The ventricles are:
–The paired C-shaped lateral ventricles
–The third ventricle found in the diencephalon
–The fourth ventricle found in the hindbrain dorsal to the pons
Ventricles of the Brain
Figure 12.5

Cerebral Hemispheres
•Form the superior part of the brain and make up 83% of its mass
•Contain ridges (gyri) and shallow grooves (sulci)
•Contain deep grooves called fissures
•Are separated by the longitudinal fissure
•Have three basic regions: cortex, white matter, and basal nuclei
•Deep sulci divide the hemispheres into five lobes:
–Frontal, parietal, temporal, occipital, and insula
•Central sulcus – separates the frontal and parietal lobes

Major Lobes, Gyri, and Sulci of the Cerebral Hemisphere
•Parieto-occipital sulcus – separates the parietal and occipital lobes
•Lateral sulcus – separates the parietal and temporal lobes
•The precentral and postcentral gyri border the central sulcus

Major Lobes, Gyri, and Sulci of the Cerebral Hemisphere
Cerebral Cortex
•The cortex – superficial gray matter; accounts for 40% of the mass of the brain
•It enables sensation, communication, memory, understanding, and voluntary movements
•Each hemisphere acts contralaterally (controls the opposite side of the body)
•Hemispheres are not equal in function
•No functional area