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The Brain and Cranial Nerves • Largest organ in the body at almost 3 lb. • Brain functions in sensations, memory, emotions, decision making, behavior Principal Parts of the Brain • Cerebrum • Diencephalon – thalamus & hypothalamus • Cerebellum • Brainstem – medulla, pons & midbrain Protective Coverings of the Brain • Bone, meninges & fluid • Meninges same as around the spinal cord – dura mater – arachnoid mater – pia mater Blood Supply to Brain • Uses 20% of our bodies oxygen & glucose needs – blood flow to an area increases with activity in that area – deprivation of O2 for 4 min does permanent injury • at that time, lysosome release enzymes • Blood-brain barrier (BBB) – protects cells from some toxins and pathogens • proteins & antibiotics can not pass but alcohol & anesthetics do – tight junctions seal together epithelial cells, continuous basement membrane, astrocyte processes covering capillaries Cerebrospinal Fluid (CSF) • 80-150 ml (3-5oz) • Clear liquid containing glucose, proteins, & ions • Functions – mechanical protection • floats brain & softens impact with bony walls – chemical protection • optimal ionic concentrations for action potentials – circulation • nutrients and waste products to and from bloodstream Origin of CSF • Choroid plexus = capillaries covered by ependymal cells – 2 lateral ventricles, one within each cerebral hemisphere – 3rd ventricle – 4th ventricle Brain Stem Medulla Oblongata Pons Midbrain Medulla Oblongata • Nuclei of 5 cranial nerves • Cardiovascular center – force & rate of heart beat – diameter of blood vessels • Respiratory center – medullary rhythmicity area sets basic rhythm of breathing • Reflex centers for coughing, sneezing, swallowing Ventral Surface of Medulla Oblongata • Ventral surface bulge – pyramids – large motor tract – decussation of most fibers • left cortex controls right muscles Dorsal Surface of Medulla Oblongata • 5 cranial nerves arise from medulla -- 8 thru 12 XII = Hypoglossal Nerve • Controls muscles of tongue during speech and swallowing XI = Accessory Nerve • Proprioception X = Vagus Nerve • Receives sensations from viscera • Controls cardiac muscle and smooth muscle of the viscera • Controls secretion of digestive fluids IX = Glossopharyngeal Nerve • Stylopharyngeus m. (lifts throat during swallowing) • Somatic sensations & taste on posterior 1/3 of tongue VIII = Vestibulocochlear Nerve • hearing • if damaged deafness or tinnitus (ringing) is produced • sense of balance • vertigo (feeling of rotation) • ataxia (lack of coordination) Pons • One inch long • help control breathing • Cranial nerves 5 thru 7 VII = Facial Nerve • facial muscles • salivary & nasal and oral mucous glands & tears VI = Abducens Nerve • Movement of eye V = Trigeminal Nerve • muscles of mastication • touch, pain, & temperature receptors of the face Midbrain • One inch in length • Extends from pons to diencephalon IV = Trochlear Nerve • Movement of eye III = Oculomotor Nerve • Movement of eye Cerebellum • 2 cerebellar hemispheres • Function – correct voluntary muscle contraction and posture based on sensory data from body about actual movements – sense of equilibrium Cerebellum • Cerebellar cortex = grey matter • Arbor vitae = tree of life = white matter Diencephalon Surrounds 3rd Ventricle • Surrounds 3rd ventricle • Superior part of walls is thalamus • Inferior part of walls & floor is hypothalamus Thalamus • 1 inch long mass of gray mater in each half of brain • Relay station for sensory information on way to cortex • Crude perception of some sensations Hypothalamus • Mammillary bodies are relay station for olfactory reflexes; infundibulum suspends the pituitary gland • Major regulator of homeostasis – receives somatic and visceral input, taste, smell & hearing information; monitors osmotic pressure, temperature of blood Functions of Hypothalamus • Controls and integrates activities of the ANS which regulates smooth, cardiac muscle and glands • Synthesizes regulatory hormones that control the anterior pituitary • Contains cell bodies of axons that end in posterior pituitary where they secrete hormones • Regulates rage, aggression, pain, pleasure & arousal • Feeding, thirst & satiety centers • Controls body temperature • Regulates daily patterns of sleep Epithalamus • Pineal gland – endocrine gland the size of small pea – secretes melatonin during darkness – promotes sleepiness & sets biological clock • Habenular nuclei – emotional responses to odors Cerebrum (Cerebral Hemispheres) • Cerebral cortex is gray matter overlying white matter – 2-4 mm thick containing billions of cells – grew so quickly formed folds (gyri) and grooves (sulci or fissures) • Longitudinal fissure separates left & right cerebral hemispheres • Corpus callosum is band of white matter connecting left and right cerebral hemispheres • Each hemisphere is subdivided into 4 lobes Lobes and Fissures • • • • • • Longitudinal fissure (green) Frontal lobe Central sulcus (yellow) Parietal lobe Occipital lobe Temporal lobe Limbic System • Emotional brain--intense pleasure & intense pain • Strong emotions increase efficiency of memory II -- Optic Nerve • Connects to retina supplying vision I -- Olfactory Nerve • Extends from olfactory mucosa of nasal cavity to olfactory bulb • Sense of smell