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Chapter 14 The Brain and Cranial Nerves Lecture Outline Principles of Human Anatomy and Physiology, 11e 1 INTRODUCTION • The brain receives sensory input, integrates it, makes decisions, and regulates movement. • It is also the center for intellect, emotions, behavior, and memory. Principles of Human Anatomy and Physiology, 11e 2 Chapter 14 The Brain and Cranial Nerves • One of the largest organs in the body at almost 3 lb. • Brain functions in sensations, memory, emotions, decision making, behavior 3 Blood Flow in the Brain • An interruption of blood flow for 1 or 2 minutes impairs neuronal function. – A total deprivation of oxygen for 4 minutes causes permanent injury. • Because carbohydrate storage in the brain is limited, the supply of glucose to the brain must be continuous. – Glucose deficiency may produce mental confusion, dizziness, convulsions, and unconsciousness. 4 BBB • A blood-brain barrier (BBB) protects brain cells from harmful substances and pathogens by serving as a selective barrier to prevent passage of many substances from the blood to the brain. • An injury to the brain due to trauma, inflammation, or toxins causes a breakdown of the BBB, permitting the passage of normally restricted substances into brain tissue. • The BBB may also prevent entry of drugs that could be used as therapy for brain cancer or other CNS disorders, so research is exploring ways to transport drugs past the BBB. Principles of Human Anatomy and Physiology, 11e 5 Protective Covering of the Brain • The brain is protected by the cranial bones and the cranial meninges. Principles of Human Anatomy and Physiology, 11e 6 CEREBROSPINAL FLUID • Cerebrospinal fluid (CSF) is a clear, colorless liquid that protects the brain and spinal cord against chemical and physical injuries. Principles of Human Anatomy and Physiology, 11e 7 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 Principles of Human Anatomy and Physiology, 11e 8 Origin of CSF • Choroid plexus = capillaries covered by ependymal cells – 2 lateral ventricles, one within each cerebral hemisphere – roof of 3rd ventricle – fourth ventricle 9 Hydrocephalus • Blockage of drainage of CSF (tumor, inflammation, developmental malformation, meningitis, hemorrhage or injury) – Continued production cause an increase in pressure --hydrocephalus – In newborn or fetus, the fontanels allow this internal pressure to cause expansion of the skull and damage to the brain tissue • Neurosurgeon implants a drain shunting the CSF to the veins of the neck or the abdomen 10 XII = Hypoglossal Nerve • Controls muscles of tongue during speech and swallowing • Injury deviates tongue to injured side when protruded • Mixed, primarily motor Principles of Human Anatomy and Physiology, 11e 11 XI = Spinal Accessory Nerve • Cranial portion – arises medulla – skeletal mm of throat & soft palate • Spinal portion – arises cervical spinal cord – sternocleidomastoid and trapezius mm. Principles of Human Anatomy and Physiology, 11e 12 X = Vagus Nerve • Receives sensations from viscera • Controls cardiac muscle and smooth muscle of the viscera • Controls secretion of digestive fluids Principles of Human Anatomy and Physiology, 11e 13 IX = Glossopharyngeal Nerve • Stylopharyngeus m. (lifts throat during swallowing) • Secretions of parotid gland • Somatic sensations & taste on posterior 1/3 of tongue Principles of Human Anatomy and Physiology, 11e 14 VIII = Vestibulocochlear Nerve • Cochlear branch begins in medulla – receptors in cochlea – hearing – if damaged deafness or tinnitus (ringing) is produced • Vestibular branch begins in pons – receptors in vestibular apparatus – sense of balance – vertigo (feeling of rotation) – ataxia (lack of coordination) Principles of Human Anatomy and Physiology, 11e 15 VII = Facial Nerve • Motor portion – facial muscles – salivary & nasal and oral mucous glands & tears • Sensory portion – taste buds on anterior 2/3’s of tongue Principles of Human Anatomy and Physiology, 11e 16 VI = Abducens Nerve • Lateral rectus eye muscle Principles of Human Anatomy and Physiology, 11e 17 V = Trigeminal Nerve • Motor portion – muscles of mastication • Sensory portion – touch, pain, & temperature receptors of the face • ophthalmic branch • maxillary branch • mandibular branch Principles of Human Anatomy and Physiology, 11e 18 IV = Trochlear Nerve • Superior oblique eye muscle Principles of Human Anatomy and Physiology, 11e 19 III = Oculomotor Nerve • Levator palpebrae raises eyelid (ptosis) • 4 extrinsic eye muscles • 2 intrinsic eye muscles – accomodation for near vision (changing shape of lens during reading) – constriction of pupil Principles of Human Anatomy and Physiology, 11e 20 II = Optic Nerve • Completely sensory • Contains axons that conduct nerve impulses for vision Principles of Human Anatomy and Physiology, 11e 21 I = Olfactory Nerve • Completely sensory • Contains axons that conduct nerve impulses for olfaction, which is the sense of smell Principles of Human Anatomy and Physiology, 11e 22 The Brain – The 3 Main Parts Cerebrum: The thinking center of the brain. (memory, planning, calculating, consciousness) Cerebellum: The coordination center for muscles. (Balance, Sports) Medulla: The autonomic (automatic) control center. (Breathing, heart beat, digestion) Medulla Oblongata • • • • • Continuation of spinal cord Ascending sensory tracts Descending motor tracts 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 • Information in & out of cerebellum • Reflex centers for coughing, sneezing, swallowing etc. Principles of Human Anatomy and Physiology, 11e 24 Pons • The pons is located superior to the medulla. It connects the spinal cord with the brain and links parts of the brain with one another by way of tracts – relays nerve impulses related to voluntary skeletal movements from the cerebral cortex to the cerebellum. – contains areas, which help control respiration along with the respiratory center in the medulla Principles of Human Anatomy and Physiology, 11e 25 Cerebellum • 2 hemispheres • Function – correct voluntary muscle contraction and posture based on sensory data from body about actual movements – sense of equilibrium and balance 26 Cerebellum Structure • Cerebellar cortex (outside) & central nuclei are grey matter • Arbor vitae = tree of life = white matter (inside) 27 THE CEREBRUM • The cerebrum is the largest part of the brain . – The surface layer, the cerebral cortex, is 2-4 mm thick and is composed of gray matter. The cortex contains billions of neurons. – The cortex contains gyri (convolutions), deep grooves called fissures, and shallower sulci. Beneath the cortex lies the cerebral white matter, tracts that connect parts of the brain with itself and other parts of the nervous system. • The cerebrum is nearly separated into right and left halves, called hemispheres, by the longitudinal fissure. – Internally it remains connected by the corpus callosum, a bundle of transverse white fibers. Principles of Human Anatomy and Physiology, 11e 28 Hemispheric Lateralization • Segments the brain into 2 parts. • Lateralization literally means that certain functions are located on one side of the brain. – Left Brain: known for rational and logical thinking – Right Brain: known for creative and intuitive thinking – Left side controls right side of body and right side controls left side of body. 29 Brain Waves • Rapid fluctuations of voltage between parts of the cerebral cortex that are detectable with an electroencephalograph • Can often tell the mental state of a person • Frequency measured in Hz, when activity is slower there is slower brain activity • 4 Types of Waves: – Delta Waves: below 4 Hz occur during sleep – Theta Waves: (4-7 Hz) are associated with sleep, deep relaxation, and visualization – Alpha Waves: (8-13 Hz) occur when we are relaxed and calm – Beta Waves: (13-38 Hz) when we are actively thinking and problem solving Principles of Human Anatomy and Physiology, 11e 30 Brain Waves Principles of Human Anatomy and Physiology, 11e 31 Memory • The brain is an enormously complex network of billions of neurons connected by more than 90,000 miles of fibers • With memory, your brain needs to form association between a complex visual image and a name, which are encoded by different groups of neurons in various parts of your brain Learning • Learning mainly takes place at synapses: the junctions between neurons where information is relayed. • A synapse’s performance changes when we learn something new • Plasticity is the capability for change associated with learning. Wakefulness and Sleep • We sleep and wake up in a 24-hour cycle called a Circadian Rhythm • To wake up, the reticular activating system (RAS) must be stimulated. – Either by: Touch, Light, Noise, Movement • The cerebral cortex responds to the RAS and causes you to wake up. • Sleep is a state of altered consciousness which you can be awakened from. When we are sleeping we are in REM. • Sleep occurs when the RAS activity is low. Aging and the Nervous System • The older we get, the more the Nervous System gets weaker – # of synaptic contacts declines – Decrease in brain mass and nerve cells – Decreased capacity for sending nerve impulses • Processing of info decreases • Conduction velocity decreases • Voluntary motor movement decreases • Reflex times increase 35 35 Cerebral Palsy • Neuromuscular disability • Infants and toddlers affected and diagnosed • Voluntary muscles are poorly controlled or paralyzed • Caused by brain damage either genetics or accidental • 2 out of every 1000 newborn affected 36 Alzheimer’ Disease • Most common form of dementia (weakening of mind due to age) • Mind literally deteriorates alongside the brain • Causes not well understood • Old people mainly affected • 1 in 8 older Americans affected by AD • • • • • Symptoms usually reveal during or after age 65: Confusion Mood Swings Trouble with language Long term memory loss 37