The Central Nervous System

• Central nervous system – the brain and spinal cord

• Directional terms unique to the CNS• Rostral – toward the nose

• Caudal – toward the tail

Embryonic Development of the Brain

Figure 13.2a-e

Embryonic Development of the Brain

Figure 13.2a-e

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Embryonic Development of the Brain

Figure 13.2a-e

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are needed to see this picture.

Embryonic Development of the Brain

Figure 13.2a-e

Embryonic Development of the Brain

• Brain arises from the rostral part of the neural tube

• Three primary brain vesicles in 4-week embryo• Prosencephalon – the forebrain

• Mesencephalon – the midbrain

• Rhombencephalon – the hindbrain

Embryonic Development of the Brain

• Secondary brain vesicles• Prosencephalon

• Divides into telencephalon and diencephalon

• Mesencephalon – remains undivided

• Rhombencephalon • Divides into metencephalon and myelencephalon

Embryonic Development of the Brain

• Structures of the adult brain• Develop from secondary brain vesicles

• Telencephalon the cerebral hemispheres

• Diencephalon thalamus, hypothalamus, and epithalamus

• Metencephalon pons and cerebellum

• Myelencephalon medulla oblongata

Embryonic Development of the Brain

• Brain stem includes:• The midbrain, pons, and medulla oblongata

• Ventricles • Central cavity of the neural tube enlarges

Embryonic Development of the Brain

• Brain grows rapidly, and changes occur in the relative position of its parts• Cerebral hemispheres envelop the diencephalon

and midbrain

• Wrinkling of the cerebral hemispheres • More neurons fit within limited space

Brain Development from Week 5 to Birth

Figure 13.3a-d

Basic Parts and Organization of the Brain

• Divided into four regions• Cerebral hemispheres

• Diencephalon

• Brain stem: midbrain, pons, and medulla

• Cerebellum

Basic Parts and Organization of the Brain

Figure 13.4

Basic Parts and Organization of the Brain

• Organization • Centrally located gray matter• Externally located white matter• Additional layer of gray matter external to white

matter• Due to groups of neurons migrating externally

• Cortex – outer layer of gray matter• Formed from neuronal cell bodies• Located in cerebrum and cerebellum

Basic Parts and Organization of the Brain

Figure 13.5

Ventricles of the Brain

• Expansions of the brain’s central cavity

• Filled with cerebrospinal fluid

• Lined with ependymal cells

• Continuous with each other

• Continuous with the central canal of the spinal cord

Ventricles of the Brain

• Lateral ventricles – located in cerebral hemispheres• Horseshoe-shaped from bending of the cerebral

hemispheres

• Third ventricle – lies in diencephalon • Connected with lateral ventricles by

interventricular foramen

Ventricles of the Brain

• Cerebral aqueduct – connects 3rd and 4th ventricles

• Fourth ventricle – lies in hindbrain• Connects to the central canal of the spinal cord

Ventricles of the Brain

Figure 13.6a, b

Protection of the Brain – Cerebrospinal Fluid (CSF)

• Provides a liquid cushion for the brain and spinal cord

• The brain “floats” in CSF

• Formed in choroid plexuses in the brain ventricles

Protection of the Brain – Cerebrospinal Fluid (CSF)

Figure 13.27a

Protection of the Brain – Cerebrospinal Fluid (CSF)

Figure 13.27b

Protection of the Brain – Blood-Brain Barrier

• Prevents most blood-borne toxins from entering the brain• Impermeable capillaries

• Not an absolute barrier• Nutrients such as oxygen pass through

• Allows alcohol, nicotine, and anesthetics through