The Spinal Cord • the Brain • Brain Function

Home , Choroid plexus, Pia mater, Subdural space

About This Chapter

• Emergent properties of neural networks • Evolution of nervous system • Anatomy of the central nervous system • The spinal cord • The brain • Brain function

© 2016 Pearson Education, Inc. Emergent Properties of Neural Networks • Plasticity is the restructure of the brain networks in response to sensory input and experience. • Affective behaviors are related to feeling and emotion • Cognitive behaviors link to thinking

• The CNS consists of the brain and the spinal cord. • Gray matter – Unmyelinated nerve cell bodies – Clusters of cell bodies in the CNS are nuclei – Dendrites – Axon terminals • White matter – Myelinated axons – Axon bundles connecting CNS regions are tracts • Contain very few cell bodies

Posterior View of Spinal Cord and Vertebra

Central canal Gray matter White matter

Spinal nerve Pia mater Spinal Arachnoid Meninges cord membrane Dura mater

Body of Autonomic vertebra ganglion

Spinal nerve

• Brain is encased in bony skull, or cranium • Spinal cord runs through vertebral column • Meninges lie between bone and tissues to stabilize neural tissue and protect from bruising – Dura mater – Arachnoid membrane – Subarachnoid space contains cerebrospinal fluid secreted by choroid plexus – Pia mater • The brain floats in cerebrospinal fluid (CSF) secreted by the choroid plexus in the ventricles.

Posterior View of the CNS

Cranium

Cerebral hemispheres

Cerebellum

Cervical spinal nerves

Thoracic spinal nerves

Sectioned vertebrae

Lumbar spinal nerves

Sacral spinal nerves

Coccygeal nerve

Sectional View of the Meninges

The meninges and extracellular fluid cushion the delicate brain tissue.

Venous sinus

Cranium

Dura mater

Subdural space Arachnoid membrane Pia mater Brain

Ventricles of the Brain

Lateral ventricles The lateral ventricles consist of the first and second ventricles. The third and fourth ventricles Third ventricle extend through the brain stem and connect to the central canal that runs through the spinal cord. Compare the frontal view to the Fourth ventricle cross section in Fig. 9.10a. Cerebellum

Central canal Spinal cord Lateral view Frontal view

Cerebrospinal Fluid Secretion

Cerebrospinal fluid is secreted into the ventricles and flows throughout the subarachnoid space, where it cushions the central nervous system. Arachnoid villi

Choroid plexus of third ventricle

Pia mater

Arachnoid membrane

Sinus

Choroid plexus of fourth ventricle Spinal cord

Central canal

Subarachnoid space

Arachnoid membrane

Dura mater

Choroid Plexus

The choroid plexus transports ions and nutrients from the blood into the cerebrospinal fluid.

Capillary

Ependymal cells

Water Ions, vitamins, nutrients

Cerebrospinal Fluid Reabsorption

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

Cerebrospinal fluid Bone of skull Dura mater Endothelial lining Blood in venous sinus Fluid movement Arachnoid Cerebral cortex villus Dura mater (inner layer) Pia Subarachnoid Arachnoid Subdural mater space membrane space © 2016 Pearson Education, Inc. The Blood-Brain Barrier

• Highly selective permeability of brain capillaries • Astrocytes foot processes promote tight junctions between endothelial cells • Protects brain from toxic water soluble compounds and pathogens • Small lipid-soluble molecules cross the blood-brain barrier

This cerebral angiogram shows the extensive blood supply Neurons are to the brain, which has about 400 miles of capillaries. protected from harmful substances in the blood because brain capillaries are not leaky.

Astrocyte

Anterior cerebral artery

Astrocyte foot Posterior Tight junctions secrete cerebral processes prevent solute paracrines that artery movement between promote tight endothelial cells. Middle junction formation. cerebral artery

Circle of Willis

Internal Capillary carotid lumen artery

Basal lamina

• Oxygen – Passes freely across blood–brain barrier – Brain receives 15% of blood pumped by heart • Glucose – Membrane transporters move glucose from plasma into the brain interstitial fluid – Brain responsible for about half of body’s glucose consumption – Progressive hypoglycemia leads to confusion, unconsciousness, and death.

• Segments associated with spinal nerves • Dorsal root neurons carry sensory information. • The cell bodies of afferent neurons are located in the dorsal root ganglia. • Ventral roots carry information from the CNS to muscles and glands. • Afferent neurons connect with interneurons in the dorsal horns.

• Ventral horns contain cell bodies of afferent neurons. • Ascending tracts take sensory information to the brain and descending tracts carry signals from the brain. • Propriospinal tracts stay in the cord • Spinal reflexes are integrated in the spinal cord.

• Oldest region of the brain • 11 of 12 cranial nerves originate from the brain stem • Cranial nerves can include sensory fibers, efferent fibers, or both (mixed nerves). – Many nuclei are associated with reticular formation • Controls wakefulness, sleep, muscle tone, pain modulation

• Medulla – Somatosensory and corticospinal tracts – Pyramids – Controls involuntary functions: blood pressure, breathing, swallowing, vomiting

• Pons – Relay station, coordinates control of breathing • Midbrain – Eye movement, relay signals for hearing and seeing reflexes

Lateral View of Brain Stem

Thalamus

Cut edge of ascending Optic tract tracts to cerebrum Midbrain

Pons Cut edges of tracts leading to Cranial cerebellum nerves

Medulla oblongata Functions of the Brain Stem

Midbrain Spinal cord • Eye movement

Pons

• Relay station between cerebrum and cerebellum • Coordination of breathing [Fig. 18.14]

Medulla oblongata • Control of involuntary functions [Fig. 11.3]