Bio 201 Chapter 14 Lecture

Chapter 14: Part 1 The Brain and Cranial

Development of the Brain  Three

to four-week embryo: prosencephalon, mesencephalon and rhombencephalon.  Five-week embryo: telencephalon (cerebrum), diencephalon (thalamus, hypothalamus and epithalamus), mesencephalon (midbrain), metencephalon (pons and cerebellum) and myelencephalon (medulla oblongata).

Development of the Brain

Major Parts of the Brain  Brain

stem- continuation of the spinal cord; consists of the medulla oblongata, pons and midbrain.  Cerebellum- second largest part of the brain.  Diencephalon- gives rise to thalamus, hypothalamus and epithalamus.  Cerebrum- largest part of the brain.

The Brain

Protective Coverings of the Brain n The cranium n The cranial meninges: dura mater, arachnoid mater and pia mater.

Protective Coverings of the Brain  Three

extensions of the dura mater separate parts of the brain: b.Falx cerebri separate the two cerebral hemispheres. c.Falx cerebelli separate the two cerebellar hemispheres. d.Tentorium cerebelli separate the cerebrum from the cerebellum.

Extensions of the Dura Mater

Extensions of the Dura Mater

Brain Blood Flow and the Blood-Brain Barrier  Brain

receives approximately 20% of the total blood supply.  Internal carotid and vertebral arteries carry blood to the brain.  Internal jugular veins return blood from the brain.  Blood-brain barrier (BBB) protects brain from harmful substances.

Cerebrospinal Fluid (CSF)  Clear fluid.  Circulates through

cavities in the brain (ventricles) and the spinal cord (central canal) and also in the subarachnoid space.  Absorbs shock and protects the brain and the spinal cord.  Helps transport nutrients and wastes from the blood and the nervous tissue.

Ventricles     

CSF-filled cavities within the brain. Lateral ventricles: cerebral hemispheres. Third ventricle: diencephalon. Cerebral aqueduct: midbrain. Fourth ventricle: brain stem and the cerebellum.

Formation and Circulation of CSF in the Ventricles   

Choroid plexuses- networks of capillaries in the walls of the ventricles. Ventricles are lined by ependymalcells. Plasma is drawn from the choroid plexuses through ependymal cells into the ventricles to produce CSF.

Formation and Circulation of CSF in the Ventricles

Circulation of CSF CSF from the lateral ventricles → interventricular foramina → third ventricle → cerebral aqueduct → fourth ventricle → subarachnoid space or central canal.  CSF is reabsorbed into the blood by arachnoid villi. 

Medulla Oblongata PyramidsBulges on the anterior aspect of the medulla. Formed by the large corticospinal tracts that pass from the cerebrum to the spinal cord.  A common site for decussation of ascending and 

Centers of the Medulla Oblongata  Vital

centers: Cardiovascular centerRespiratory center Also includes centers for vomiting, swallowing, sneezing, coughing and hiccupping.  Houses five pairs of cranial nerves, VIII-XII.  Portion of the ventricle found here is the fourth ventricle.

Midbrain or Mesencephalon Extends from the pons to the diencephalon.  Part of the ventricle found here- cerebral aqueduct.  Cerebral peduncles: axons of the corticospinal, corticopontine and corticobulbar tracts.  Tectum- situated posteriorly and contains four rounded elevations: two superior ones called superior colliculi and two inferior ones called inferior colliculi. 

Midbrain or Mesencephalon

Midbrain  Substantia

nigra: large area with dark pigments. Help control subconscious muscle activities. Loss of neurons here is associated with Parkinson disease.

 Red

nucleus: Help control voluntary movements of the limbs.

 Contains

cranial nerves III-IV.

Midbrain

Reticular formation  Extends

from the upper part of the spinal cord, throughout the brain stem, and into the lower part of the diencephalon.

 Part

of the reticular formation called the reticular activating system (RAS) consists of sensory axons that project to the cerebral cortex.

 The

RAS helps maintain consciousness.

The Cerebellum  Second

largest part of the brain.

 The

central constricted area is the vermis.

 The

anterior and posterior lobes control subconscious aspects of skeletal movement.

 The

flocculonodular lobe on the inferior side contributes to the

The Cerebellum

The Cerebellum

The Cerebellum  Cerebellar

cortex- gray matter in the form of parallel folds called folia.  Arbor vitae- tracts of white matter.  Cerebellar peduncles- three pairs: superior, middle and inferior. Attach cerebellum to the brain stem.  Functions- coordinate movements, regulate posture and balance.

Thalamus   

Intermediate mass Several nuclei: Major relay station for most sensory impulses.

Hypothalamus  

Inferior to the thalamus. Consists of mammillary body, median eminence, infundibulum, and a number of nuclei.

Functions of the Hypothalamus  Control

of the ANS.

 Production  Regulation

of hormones

of emotional and behavioral patterns, eating and drinking, body temperature, and circadian rhythms.

Epithalamus  Small

region superior to the thalamus.

 Consists

of pineal gland which secretes a hormone called melatonin.

 Melatonin

induces sleep.

End of Chapter 14, Part 1