Lec 4 - Protection of the Central Nervous System and Major Parts of the Brain

What are the 3 outline topics of lecture 4?

Protection of the CNS; introduction of major parts of the brain; components of the ventricular system and the brain regions where each is located.

Three primary brain vesicles (3-4 week embryo)?

Prosencephalon (forebrain), mesencephalon (midbrain), rhombencephalon (hindbrain).

Prosencephalon divides into which secondary vesicles?

Telencephalon and diencephalon.

Mesencephalon becomes what in the secondary stage?

Mesencephalon (midbrain).

Rhombencephalon divides into which secondary vesicles?

Metencephalon and myelencephalon.

How many secondary brain vesicles are there (5-week embryo)?

Five.

Telencephalon adult structure and ventricle?

Cerebrum; lateral ventricles.

Diencephalon adult structure and ventricle?

Diencephalon (thalamus, hypothalamus, epithalamus; eye cup); third ventricle.

Mesencephalon adult structure and ventricle?

Midbrain; cerebral aqueduct.

Metencephalon adult structure and ventricle?

Pons and cerebellum; fourth ventricle.

Myelencephalon adult structure and ventricle?

Medulla (medulla oblongata); fourth ventricle.

Posterior neural tube adult structure and ventricle?

Spinal cord; central canal.

Which part of the neural tube forms prosencephalon, mesencephalon and rhombencephalon?

Anterior neural tube.

What does the CNS consist of?

The brain and the spinal cord.

Gray matter: location in CNS?

Cortex and nuclei.

Gray matter: composition?

Mostly neuron cell bodies, dendrites, and unmyelinated axons.

White matter: composition?

Mostly myelinated axons.

Axon bundles connecting CNS regions are called?

Tracts (nerves in the PNS).

Do tracts contain cell bodies?

Very few.

Fig 9.3c: labels in the posterior view of spinal cord and vertebra?

Central canal, gray matter, white matter, spinal nerve, spinal cord, pia mater, arachnoid membrane, dura mater, body of vertebra, autonomic ganglion.

Which 3 layers make up the meninges (Fig 9.3c)?

Pia mater, arachnoid membrane, dura mater.

Brain section color legend: cerebral cortex?

Yellow.

Brain section color legend: ventricle (cerebrospinal fluid)?

Red.

Brain section color legend: corpus callosum?

Green.

Brain section color legend: cerebellum?

Blue.

Brain section color legend: brain stem?

Orange.

Gyri (gyrus)?

Folds of the brain.

Sulci (sulcus)?

Gaps.

Fissure?

A large sulcus between gyri.

Which lobes are labeled in the lateral brain view?

Frontal, parietal, occipital, temporal.

Which sulci are labeled in the lateral brain view?

Central sulcus, parieto-occipital sulcus, lateral sulcus.

Which gyri are labeled in the lateral brain view?

Precentral gyrus and postcentral gyrus.

What are the 4 protections of the brain?

The skull, cranial meninges, cerebrospinal fluid, blood-brain barrier.

What encases the brain?

The bony skull, or cranium.

What does the spinal cord run through?

The vertebral column (bony vertebrae).

Where do meninges lie and what do they do?

Between bone and tissues; stabilize neural tissue and protect from bruising.

Name the 3 meninges.

Dura mater, arachnoid membrane, pia mater.

Fig 9.8e: bones of the skull labeled?

Frontal bone, parietal bone, temporal bone, occipital bone.

Fig 9.3b: what cushions the delicate brain tissue?

The meninges and extracellular fluid.

Fig 9.3b: layers from outside in?

Cranium, dura mater, subdural space, arachnoid membrane, subarachnoid space, pia mater, brain.

Fig 9.3b: which venous structure is labeled?

Venous sinus.

Define cerebrospinal fluid (CSF).

A salty solution similar to plasma; the brain floats in it.

Where is CSF produced?

By the choroid plexus in the ventricles.

How is CSF made at the choroid plexus?

Materials are selectively moved from plasma to ventricles; water follows due to osmotic gradient.

Where does CSF surround the brain?

It surrounds the entire brain, contained within the subarachnoid space (between arachnoid membrane and pia mater).

CSF flow path and return?

Flows from ventricles to subarachnoid space, then returns to plasma by villi.

CSF function?

Physical and chemical protection.

Fig 9.4a: lateral ventricles?

The first and second ventricles form the lateral ventricles; they connect to the third ventricle through narrow openings.

Fig 9.4a: cerebral aqueduct?

Leads from the third ventricle in the diencephalon to the fourth ventricle in the brainstem.

Fig 9.4a: fourth ventricle?

In the brainstem; narrows to become the central canal of the spinal cord.

Fig 9.4b: CSF secretion?

CSF is secreted into the ventricles and flows throughout the subarachnoid space, where it cushions the CNS.

Fig 9.4c: choroid plexus function?

Transports ions and nutrients from the blood into the CSF.

Fig 9.4c: what is transported across choroid plexus cells?

Water; ions, vitamins, nutrients (from capillary through ependymal cells).

Which choroid plexuses are labeled?

Choroid plexus of the third ventricle and of the fourth ventricle.

Fig 9.4d: CSF reabsorption?

CSF is reabsorbed into the blood at fingerlike projections of the arachnoid membrane called villi.

Fig 9.4d: where does CSF go from the arachnoid villus?

Into the blood in the venous sinus (separated by endothelial lining, dura mater).

Blood plasma to brain flow chart: transport from blood into brain?

Highly restricted by the blood-brain barrier.

Flow chart: transport from blood to CSF?

Selective transport across choroid plexuses.

Flow chart: CSF and brain interstitial fluid?

Free exchange.

Flow chart: exchanges between brain cells and interstitial fluid?

Regulated by plasma membrane properties (brain cells: neuroglia and neurons).

Flow chart: how CSF returns to blood?

Via the arachnoid villus to venous blood in the dural sinus.

Roles of CSF (3)?

Cushions and insulates delicate nervous tissue; gives buoyancy to the brain (it floats in CSF); exchange of gases (O2 and CO2), nutrients and wastes.

Blood-brain barrier basis?

Highly selective permeability of brain capillaries.

What promotes tight junctions in the BBB?

Astrocyte foot processes between endothelial cells.

What does the BBB protect against?

Toxic water-soluble compounds and pathogens.

What can cross the BBB?

Small lipid-soluble molecules.

Fig 9.5a: brain blood supply?

Extensive; about 400 miles of capillaries.

Fig 9.5a: arteries labeled?

Anterior cerebral, posterior cerebral, middle cerebral, circle of Willis, internal carotid artery.

Fig 9.5b: why are neurons protected from harmful substances in blood?

Brain capillaries are not leaky.

Fig 9.5b: astrocyte foot processes?

Secrete paracrines that promote tight junction formation.

Fig 9.5b: tight junctions?

Prevent solute movement between endothelial cells.

Other structures labeled at the BBB capillary?

Pericyte, capillary lumen, basal lamina (basement membrane), astrocyte endfoot.

Spinal cord segments are associated with?

Spinal nerves; each spinal nerve branches into two roots.

Dorsal root function?

Dorsal root neurons carry sensory information to the CNS.

Dorsal root ganglia contain?

Afferent (sensory) nuclei.

Afferent neurons connect with what, and where?

Interneurons in the dorsal horns.

Ventral root function?

Carries motor information from the CNS to muscles and glands.

Dorsal horns contain?

Visceral and somatic sensory nuclei.

Lateral horns contain?

Visceral motor nuclei.

Ventral horns contain?

Somatic motor nuclei.

Spinal cord white matter organization?

Divided into columns of tracts.

Ascending tracts?

Take sensory information to the brain.

Descending tracts?

Carry motor signals from the brain.

Propriospinal tracts?

Stay in the cord.

Where are spinal reflexes integrated?

In the spinal cord.

Fig 9.6: what does the spinal cord contain?

Nuclei with cell bodies of efferent neurons and tracts of axons going to and from the brain.

Fig 9.6a: dorsal root vs ventral root?

Dorsal root carries sensory (afferent) information to the CNS; ventral root carries motor (efferent) information to muscles and glands.

Fig 9.6b: gray matter nuclei labeled?

Visceral sensory nuclei, somatic sensory nuclei, autonomic efferent nuclei, somatic motor nuclei.

Fig 9.6c: white matter?

Tracts of axons carrying information to and from the brain.

Fig 9.6c: ascending tracts (green)?

Carry sensory information to the brain.

Fig 9.6c: descending tracts (blue)?

Carry commands to motor neurons.