Biology 315. Anatomy and Physiology I. Chapter 14. The Brain and Cranial Nerves.
Tortora and Grabowski, 13th edition. 2012.
I. Brain Organization, Protection, and Nourishment.
A. Major Parts of the Brain: brain stem, cerebellum, diencephalon, and cerebrum
B. Blood Flow Through the Brain.: substantial; 20% cardiac output at rest;
Lack of blood flow > a couple of minutes = permanent damage.
Glucose supply must be constant (Sx of hyper/hypoglycemia)
1. Arterial supply
A. internal carotid arteries
B. Vertebral arteries. R. and L vertebral arteries join to become basilar artery inside the cranium
2. Venous drainage: venous sinuses into internal jugular veins
3. Blood Brain Barrier: protective
A) Tight jctns. seal endothelial cells of brain capillaries
B. Astrocytes processes press up against capillary walls
C. Lipid soluble substances pass easily; some other substances cross via AT, some slowly
C. Protective coverings of the brain
1. Cranial meninges like spinal meninges: dura, arachnoid, pia
2. Extensions of dura separate parts of the brain
*falx cerebri = separates the 2 hemispheres of cerebrum
*falx cerebelli = separates the 2 hemispheres of the CBLM
*tentorium cerebelli = separates the cerebrum from CBLM
D. Cerebrospinal Fluid;
1. Mechanical protection: shock absorber
2. Chemical protection: optimal chemical environment for accurate neuronal signaling.
3. Circulation/ medium for exchange of O2, nutrients, wastes, etc. 4. Produced in choroid plexuses = capillary networks and ependymal cells in ventricular walls;
1. Continuous circulation of CSF thru ventricles, spinal canal, and subarachnoid space.
Lateral ventricles (separated by septum pellucidum) ≡ through
3rd ventricle (in diencephalon) ≡ cerebral aqueduct of Sylvius in midbrain ≡ 4th ventricle in brain stem ≡Three openings in roof of 4th ventricle ≡Subarachnoid space, central canal of spinal cord
5. Reabsorption into blood via : arachnoid villi in superior sagittal sinus
6. Production must equal reabsorption ! About 125 ml total at any time, maintain constant pressure. Read about hydrocephalus.
II. The Brain Stem. = medulla, pons, midbrain.
A. Medulla: a continuation of the spinal cord to the pons
1. White matter: both sensory and motor tracts are present A. Motor: Pyramids bulges on the anterior side of medulla: the pyramidal tract/ direct pathways *pyramidal decussation. 90% of right crosses to L, and 90% L crosses to R
® side of brain controls most of L side of body.
*medial lemniscus: axons from gracile and cuneate nuclei through medulla, pons, midbrain.
2. Grey Matter: = nuclei
A. Cardiovascular center (h.r., force of contraction, b.v. diameter)
B. Rhythmicity center for resp. rate
C. Other: vomiting center; coughing center, etc.
D. Olivary nuclei : lateral swelings
E. Nuclei of posterior column system
*gracile and cuneate nuclei
F. Nuclei for cranial nerves VIII, IX, X, XI, XII.
B. Pons (= bridge) , between medulla and pons.
1. Nuclei/ Gray matter
*pneumotaxic center, apneustic center; help control breathing
*Nuclei for cranial nerves V, VI, VII, VIII.
2. White Matter : ascending sensory and descending motor tracts.
C. Midbrain = mesencephalon; from pons to diencephalon
1. Cerebral aqueduct passes through here
*cerebral peduncles = continuations of corticospinal, corticopontine, corticobulbar tracts + sensory tracts
3. Gray matter
*Tectum = posterior side of midbrain. 2 sets of paired bumps. –superior colliculi ( visual reflexes, tracking images, pupillary reflex, accommodation reflex, etc.)
– inferior colliculi (auditory reflexes, e.g., startle reflex ) *substantia nigra (lack of dopamine here associated with Parkinson’s Disease) *red nucleus (rubro); synapses from tracts in cerebrum/CBLM...
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