Chapter 13 Brain and Cranial Nerves PDF

Chapter 13 The Brain and Cranial Nerves The human brain is awesome! It functions 24 hours a day from the day we are born and only stops when we ARE TAKING AN EXAM  The Human Brain ❖The human body uses only ~3lbs of tissue to process all emotions, solve every equation, read every...

Chapter 13 The Brain and Cranial Nerves The human brain is awesome! It functions 24 hours a day from the day we are born and only stops when we ARE TAKING AN EXAM  The Human Brain ❖The human body uses only ~3lbs of tissue to process all emotions, solve every equation, read every book, and take every breath oAll of this occurs within 100 billion neurons and 10 trillion neuroglia that comprise the human brain  Brain Development ❖During the first 3 weeks of gestation, the human embryo's neural tube flexes as it grows, forming the three primary brain vesicles o Forebrain (Prosencephalon) Telencephalon→ cerebrum and lateral ventricles Diencephalon → Thalamus, hypothalamus, epithalamus, and third ventricle o Midbrain (Mesencephalon) Midbrain and cerebral aqueduct o Hindbrain (Rhomencephalon) Metencephalon→ Pons and cerebellum Myelencephalon→ Medulla oblongata  Brain Development ❖The brain grows at an amazing rate during development; at times, as many as 50,000 neurons are added each second! ❖At birth, the neonatal brain looks very much like that of an adult and almost all the neurons the brain will ever have are already present.  Major Parts of the Brain ❖The brain stem is the continuation of the spinal cord and consists of the medulla oblongata, pons, and midbrain ❖The cerebellum is the second largest part of the brain ❖The diencephalon gives rise to the thalamus & hypothalamus ❖The cerebrum is the newest (evolutionarily) and largest part of the brain as a whole. o It is in the cerebral cortex that perception, thought, imagination, judgment, and decision making occur. Brain Organization  Protective Coverings ❖The cranial meninges are protective and continuous with the spinal meninges: oExternal→internal Tough outer dura mater Spidery arachnoid mater Thin, delicate pia mater  Protective Coverings ❖Extensions of the dura mater form membranes that divide: Falx cerebri strong sickle-shaped fold which descends vertically in the longitudinal fissure R/L cerebrum Falx cerebelli small triangular process that separates R/L cerebellum Tentorium cerebelli hard structure Cerebrum/cerebellum  Protective Coverings ❖Clinically, the tentorium cerebelli is important because brain tumors are often characterized as o supratentorial (above the tentorium) o infratentorial (below the tentorium) o Most childhood tumors are infratentorial, while most adult tumors are supratentorial. o Hard structure. Brain swelling can cause the brain to be partly pushed down and herniate through the tentorium life-threatening Brain Blood Flow ❖Brain = 2% of total body weight ❖Brain uses 20% of the O2 and glucose (even when resting→ more during activity). ❖Internal carotid arteries o Anterior blood supply to the brain ❖Vertebral arteries o posterior blood supply to the brain ❖Circle of Willis ❖The internal jugular veins are the venous return  Brain Blood Flow ❖Blood brain barrier (BBB) o Protect brain from harmful substances Tight junctions of epithelial cells in capillaries Proteins, most antibiotics don’t pass Accessible only by active transport Infections? Water, fat soluble Encyclopedia of Life Sciences, © Wiley substances pass Including glucose, O2, Co2, alcohol  Production and Flow of CSF ❖Cerebral spinal fluid (~80-150ml) o Clear fluid O2, glucose, proteins, cations, anions, WBC o Circulates through the brain ventricles and subarachnoid space. Brain "floats" in it. ❖4 Ventricles o filled with CSF R and L lateral ventricles 3rd ventricle 4th ventricle → subarachnoid space  Cerebral Spinal Fluid ❖Basic Functions of CSF oMechanical protection oHomeostasis oCirculation Production and Flow of CSF ❖ Choroid plexuses Networks of blood capillaries that line the ventricles Produces most CSF Hydrocephaly o occurs with congenital abnormalities, head injury, meningitis, and episodes of bleeding into the brain.  Production and Flow of CSF ❖The choroid plexuses :  Production and Flow of CSF ❖CSF is gradually reabsorbed back into the blood through the arachnoid villi (finger-like projections that extend into the dural sinuses).  Production and Flow of CSF ❖Pathway of CSF olateral ventricles  interventricular foramina  third ventricle  cerebral aqueduct  fourth ventricle  median aperture (of Magendie ) and the lateral apertures (of Luschka )  Subarachnoid Space  arachnoid villi reabsorb CSF into bloodstream CSF is reabsorbed as quickly as it is made= constant pressure ~20mL/hr Parts of the Brain  Brain Organization ❖The brain stem is continuous with the spinal cord o medulla oblongata o Pons o Midbrain  Medulla oblongata ❖The medulla begins at the inferior border of the pons and extends to the foramen magnum ❖Contains all ascending and descending fibers (tracts) ❖Cardiovascular center oRate, force of heartbeat oBlood vessel diameter ❖Respiratory center oBreathing oReflexes for vomiting, coughing, sneezing ❖Nuclei for cranial nerves VIII-XII  The Medulla Oblongata ❖Has two external bulges called the pyramids formed by the largest motor tracts in the body. ❖Axons from the left pyramid cross over to the right and axons on the right cross over to the left (decussation of pyramids) o left hemisphere of the brain controls the right side muscles o right hemisphere controls the left side muscles  The Pons ❖Pons lies directly above the medulla and anterior to the cerebellum (2.5 cm). oacts as a bridge connecting Midbrain and medulla R and L cerebellar hemispheres oRelay center for ascending and descending tracts oRespiratory control inhalation and exhalation oNuclei for cranial nerves V-VIII  The Pons ❖Cranial nerves: V - VIII oCranial nerve V (trigeminal) emerges directly from the pons. oVI, VII, and VIII (abducens, facial, vestibulochochlear) emerge from the space between the pons and the medulla. CN V exits the pons, while 3 others come from the medullary pontine angle.  The Midbrain ❖Midbrain extends from the pons to the diencephalon. oThe cerebral aqueduct passes through the midbrain connecting the 3rd and 4th ventricles oSensory and motor tracts oNuclei for cranial nerves III, IV The Midbrain ❖On the anterior part of the midbrain are found the “little feet” of the cerebral peduncles. o Peduncles contain axons of the corticospinal, corticobulbar, and corticopontine tracts which conduct nerve impulses from motor areas in the cerebral cortex to the spinal cord, medulla, and pons, respectively. The Midbrain ❖Corpora quadrigemina osuperior colliculi Tracking moving objects with eyes, head and neck oinferior colliculi Reflex moving head and truck in response to sounds startle reflex.  The Midbrain ❖Substantia nigra- o control subconscious muscle activities o these neurons release dopamine--loss of these neurons is associated with Parkinson disease. ❖The red nucleus o control voluntary movements of the limbs. The Reticular Formation ❖Reticular formation - netlike arrangement of neuronal cell bodies and small bundles of myelinated axons oAscending portion is the reticular activating system (RAS), and consists of sensory axons that project to the cerebral cortex. The Reticular Formation ❖RAS functions oto maintain consciousness oa state of wakefulness in which an individual is fully alert, aware, and oriented. oInactivation of the RAS produces sleep oIt also prevents sensory overload by filtering out insignificant information DAMAGE TO RAS: coma  The Cerebellum ❖Cerebellum (“little brain”) - is the second largest part of the brain and lies inferior to the cerebrum and posterior to the medulla and pons. oTransverse fissure Separates cerebellum from cerebrum o2 hemispheres, central vermis oCoordinate complex movements oMaintain normal muscle tone oRegulate posture and balance The Cerebellum ❖Cross section o Gray matter o White matter (arbor vitae)  The Diencephalon ❖Located near the midline, above the midbrain. ❖Surrounds 3rd ventricle and contains the thalamic structures. o Thalamus o Epithalamus o Hypothalamus  The Diencephalon ❖The thalamus o functions as a relay station for all sensory impulses to the cerebral cortex (except smell) o Major role in cognition (awareness, knowledge acquisition) o Role in emotions, memory  The Diencephalon ❖Epithalamus is superior and posterior to the epithalamus thalamus thalamus. o Consists of Pineal gland (secretes melatonin) Biological clock Part of endocrine system (gland Habenular nuclei (emotional responses to odors).  The Diencephalon ❖The hypothalamus controls many homeostatic functions: o Controls the (ANS) thalamus o Pituitary gland o Coordinates between NS and endocrine systems. o Emotional and behavioral patterns o Body temperature hypothalamus measured by blood flowing through o Hunger/thirst o Circadian rhythms and sleep  The Cerebrum ❖The cerebral cortex is the “seat of our intelligence” oneurons in the cortex work so that we are able to read, write, speak, remember, and plan our life. oOuter gray matter develops faster than internal white matter Creates gyri, fissures and sulci Corpus callosum Separates R and L  The Cerebrum ❖The lobes of the cerebrum correspond to the bones of the braincase which bear the same names. parietal frontal parietal frontal temporal temporal occipital occipital parietal frontal occipital temporal  The Cerebrum ❖4 Lobes of the Cerebrum, separated by sulci oFrontal, parietal, temporal, and occipital ❖Central sulcus→ frontal from parietal ❖Lateral sulcus → frontal from temporal ❖Parieto-occipital → parietal from occipital  The Cerebrum ❖Precentral gyrus o primary motor area of cerebrum ❖Postcentral gyrus o primary somatosensory area of cerebrum MY BRAIN: 5% - names 3%- phone numbers 2%- stuff I should know for school 90% song lyrics  The Cerebrum ❖The cerebral white matter consists primarily of myelinated axons in three types of tracts. o Association tracts contain axons that conduct nerve impulses between gyri in the same hemisphere. o Commissural tracts conduct nerve impulses between corresponding gyri from one hemisphere to another. Corpus callosum- thick band of axons that connects corresponding areas of the two hemispheres. Through the corpus callosum, the left motor cortex (which controls the right body) is linked to the right motor cortex (which controls the left body). o Projection tracts convey impulses to lower parts of the CNS (thalamus, brain stem, or spinal cord) or visa versa. The Cerebrum  The Cerebrum ❖Basal nuclei – (gray matter) conspicuous centers of cell bodies deep in the cortex also control subconscious contractions of skeletal muscles. o 3 basal nuclei help initiate and terminate movements, suppress unwanted movements, regulate muscle tone o Ex: automatic arm swings while walking, laughter in response to a joke  The Cerebrum ❖Limbic system- Encircling the upper part of the brain stem and the corpus callosum o Ring of structures on the inner border of the cerebrum and floor of the diencephalon o “Emotional brain” because it plays a primary role in promoting emotions pleasure, pain, docility, affection, fear, and anger. o Functions in memory with the cerebrum Functional Organization of the Cerebrum ❖Brodmann’s areas -regions of cortex that have been “mapped” to specific cognitive functions o Sensory areas –perception and interpretation of sensory information ❖Motor areas controls voluntary contractions of specific muscles or groups of muscles ❖Association areas The Cerebrum Brodmann’s areas: Numbered Regions of Cortical tissue. Functional Organization of the Cerebrum ❖Sensory Areas o Primary sensory areas Receive input from peripheral sensory receptors o Secondary sensory areas and association areas Meaning, recognition  Functional Organization of the Cerebrum ❖Sensory Areas 1. Primary somatosensory areas (parietal lobe) (1,2,3) Touch, location, size, shape, texture Proprioception – position of limbs Pain Temperature Size of primary somatosensory cortical area relates to number of sensory receptors Sensory homunculus (“little man”) Functional Organization of the Cerebrum ❖Each sensory neuron carries only one type of sensation- modality ogeneral somatic tactile, temperature, pain, proprioception visceral internal organs ospecial taste, smell, vision, balance, hearing  Functional Organization of the Cerebrum ❖Sensory Areas 2. Primary visual area (occipital lobe)(17) Visual stimuli Shape Color movement  Functional Organization of the Cerebrum ❖Sensory Areas 3. Primary auditory area (temporal lobe)(41 & 42) Basic characteristics of sound Pitch Rhythm  Functional Organization of the Cerebrum ❖Sensory Areas 4. Primary gustatory area (43) Taste 5. Primary olfactory area (in temporal lobe)(28) Smell  Functional Organization of the Cerebrum ❖Motor areas oPrimary motor area Located in the precentral gyrus Electrical stimulation causes contraction of specific muscle fibers on opposite side of body Muscle groups unequally distributed Motor homunculus  Functional Organization of the Cerebrum ❖Motor areas oBroca’s speech area In left frontal lobe in 97% of people Planning and production of speech Controls muscles of the larynx, pharynx and mouth Impulses pass to primary motor area controls breathing muscles, allowing proper flow of air past vocal cords A cerebrovascular accident (CVA) or stroke in this area may allow clear thoughts, yet be unable to form words (nonfluent aphasia) Hemispheric Lateralization  The Twelve Cranial Nerves Cranial Nerves Cranial Nerves Spinal Cranial C1-8, T1-12, L1-5, S1-5, Roman Numerals Designation Co1 I – XII Number 31 pairs 12 pairs Origin Spinal cord Brain 2 - a dorsal and a ventral Number of roots Single root root Most mixed; some Contents Mixed sensory only All in the Head/Neck Target Limbs/Trunk (vagus n leaves) Spinal and cranial nerves are compared in this table.  Cranial Nerves ❖ Major functions of the 12 pairs of cranial nerves Cranial Nerves ❖Olfactory nerve (CN I) o Tract (not a true nerve) o Smell perception o Passes through cribriform plate  Cranial Nerves ❖Optic nerve (CN II) oTract (not a true nerve) oSpecial sense oFrom retina oPass through optic foramen Fuse to form optic chiasm  Cranial Nerves Oculomotor Trochlear Abducens (CN III) (CN IV) (CN VI) CN III, IV, and VI innervate the extraocular muscles that allow us to move our eyes.  Cranial Nerves ❖Oculomotor nerve (CN III) o Primarily motor nerve o Somatic motor 4 muscle of extrinsic eye muscle o Autononmic to smooth muscle Iris (pupil diameter) Ciliary body (lens shape o General sensory= proprioception  Cranial Nerves ❖Trochlear nerve (CN IV) oPrimarily motor nerve oSomatic motor: 1 extrinsic eye muscle oGeneral sensory= proprioception  Cranial Nerves ❖Trigeminal nerve (CN V) (the major sensory nerve of the face). o3 large branches V1= ophthalmic= general sensory Upper eyelid, forehead, scalp V2= maxillary= general sensory Skin of cheek, nose, upper dentition Mandibular= motor and general sensory Motor- muscles to mastication Sensory- mandibular area, lower dentition, proprioception  Cranial Nerves ❖Trigeminal nerve (CN V)  Cranial Nerves ❖Abducens nerve (CN VI) oPrimarily motor oSomatic motor 1 extrinsic eye muscle oGeneral sensory= proprioception  Cranial Nerves ❖Facial nerve (CN VII) oSpecial sense, general sensory, motor oMotor Somatic motor to muscles of facial expression Autonomic to salivary and lacrimal glands oSpecial sense Taste from anterior 2/3 of tongue oGeneral sense External ear Proprioception Cranial Nerves ❖Paralysis of CN VII is Bell’s Palsy and leads to loss of ability to close the eyes and impairment of taste and salivation.  Cranial Nerves ❖Vestibulocochlear (CN VIII) ❖Special sense – hearing and balance o Organ of corti = sound perception o Semicircular canals, saccule, utricle = equilibrium ❖2 branches o Vestibular and cochlear ❖Damage of CN VIII causes vertigo, ringing in the ears, and/or deafness.  Cranial Nerves ❖Glossopharyngeal nerve (CN IX) oSpecial sensory, general sensory, motor oMotor Somatic motor muscles of pharynx Autonomic to parotid gland oSpecial sensory Taste from posterior 1/3 of tongue oGeneral sensory Middle ear, carotid body (chemoreceptors), carotid sinus (baroreceptors)  Cranial Nerves ❖Vagus nerve (CN X) o“the wanderer” ocarries most of the parasympathetic motor efferents to the organs of the thorax and abdomen oSpecial sensory taste from base of tongue, epiglottis, pharynx  Cranial Nerves ❖Vagus nerve (CN X) o General sensory Proprioception from pharynx Sensory stretch and chemoreceptors (carotid arteries) Chemoreceptors – aorta Stretch – organs in thorax and abdomen  Cranial Nerves ❖Vagus nerve (CN X) oMotor Somatic motor to muscles of throat and neck Autonomic to smooth muscle Esophagus, stomach, small intestine, gallbladder, glands in GI tract Cardiac muscle  Cranial Nerves ❖Accessory nerve (CN XI) oPrimarily motor oSomatic motor Trapezius Sternocleidomastoid some muscles of pharynx oGeneral sensory = proprioception  Cranial Nerves ❖Hypoglossal nerve (CN XII) o very large nerve (a lot of resources) solely devoted to the tongue – it takes a lot of coordination to chew, talk, and swallow without injuring our tongue. o Primarily motor o Somatic motor Muscles of tongue o General sensory = proprioception ❖On Old Olympus Towering Tops, A Finn And German Viewed Some Hops oOlfatory, optic, oculomotor, trochlear, trigeminal, abducens, facial, acoustic (vestibulocochlear), glossopharyngeal, vagus, spinal (accessory), hypoglossal