14 The Brain and Cranial Nerves

Figure 14-12a The Brain in Lateral View Central sulcus FRONTAL LOBE PARIETAL LOBE OCCIPITAL LOBE Lateral sulcus TEMPORAL LOBE Cerebellum Pons Medulla oblongata Lateral view, cadaver brain 2

Figure 14-12b The Brain in Lateral View Precentral gyrus Central sulcus Postcentral gyrus FRONTAL LOBE PARIETAL LOBE OCCIPITAL LOBE TEMPORAL LOBE Lateral sulcus Cerebellum Pons Medulla oblongata Lateral view 3

Figure 14-12c The Brain in Lateral View Insula Retractors along the lateral sulcus showing the insula 4

Figure 14-12d The Brain in Lateral View Precentral gyrus Central sulcus Postcentral gyrus Cingulate gyrus PARIETAL LOBE FRONTAL LOBE Parieto- occipital sulcus OCCIPITAL LOBE Pons TEMPORAL LOBE Cerebellum Medulla oblongata Midsagittal section 5

14-9 The Cerebrum Three Functional Principles of the Cerebrum Each cerebral hemisphere receives sensory information from, and sends motor commands to, the opposite side of the body The two hemispheres have different functions, although their structures are alike Correspondence between a specific function and a specific region of cerebral cortex is not precise

14-9 The Cerebrum White Matter of the Cerebrum Association fibers Connections within one hemisphere Commissural fibers Bands of fibers connecting two hemispheres Projection fibers Connect cerebrum with lower areas

14-9 The Cerebrum Association Fibers Arcuate fibers Are short fibers Connect one gyrus to another Longitudinal fasciculi Are longer bundles Connect frontal lobe to other lobes in same hemisphere

14-9 The Cerebrum Commissural Fibers Corpus callosum Anterior commissure

14-9 The Cerebrum Projection Fibers Pass through diencephalon Link cerebral cortex with: Diencephalon, brain stem, cerebellum, and spinal cord Internal capsule All ascending and descending projection fibers

Figure 14-13a Fibers of the White Matter of the Cerebrum Arcuate fibers Longitudinal fasciculi Lateral view 11

Figure 14-13b Fibers of the White Matter of the Cerebrum Longitudinal fissure Corpus callosum Projection fibers of internal capsule Anterior commissure Anterior view 12

14-9 The Cerebrum The Basal Nuclei Are masses of gray matter Are embedded in white matter of cerebrum Direct subconscious activities

14-9 The Cerebrum Anatomy of Basal Nuclei Caudate nucleus Curving, slender tail Lentiform nucleus Globus pallidus Putamen

Figure 14-14a The Basal Nuclei Head of caudate nucleus Lentiform nucleus Tail of caudate nucleus Amygdaloid body Thalamus The relative positions of the basal nuclei in the intact brain, lateral view 15

Figure 14-14b The Basal Nuclei Corpus callosum Head of caudate nucleus Lateral ventricle (anterior horn) Internal capsule Septum pellucidum Putamen Fornix (cut edge) Thalamus Third ventricle Choroid plexus Pineal gland Fornix Lateral ventricle (posterior horn) A horizontal section as seen in a dissection 16

Figure 14-14c The Basal Nuclei Lateral ventricle Corpus callosum Head of caudate nucleus Septum pellucidum Internal capsule Claustrum Lateral sulcus Insula Anterior commissure Putamen Lentiform nucleus Globus pallidus Tip of lateral ventricle Amygdaloid body Frontal section 17

14-9 The Cerebrum Functions of Basal Nuclei Involved with: The subconscious control of skeletal muscle tone The coordination of learned movement patterns (walking, lifting)

14-9 The Cerebrum Motor and Sensory Areas of the Cortex Central sulcus separates motor and sensory areas Motor areas Precentral gyrus of frontal lobe Directs voluntary movements Primary motor cortex Is the surface of precentral gyrus Pyramidal cells Are neurons of primary motor cortex

14-9 The Cerebrum Motor and Sensory Areas of the Cortex Sensory areas Postcentral gyrus of parietal lobe Receives somatic sensory information (touch, pressure, pain, vibration, taste, and temperature) Primary sensory cortex Surface of postcentral gyrus

14-9 The Cerebrum Special Sensory Cortexes Visual cortex Information from sight receptors Auditory cortex Information from sound receptors Olfactory cortex Information from odor receptors Gustatory cortex Information from taste receptors

Figure 14-15a Motor and Sensory Regions of the Cerebral Cortex Primary motor cortex (precentral gyrus) Central sulcus Primary sensory cortex (postcentral gyrus) Somatic motor association area (premotor cortex) PARIETAL LOBE Somatic sensory association area FRONTAL LOBE Visual association area Prefrontal cortex OCCIPITAL LOBE Gustatory cortex Visual cortex Insula Auditory association area Lateral sulcus Auditory cortex TEMPORAL LOBE Olfactory cortex Major anatomical landmarks on the surface of the left cerebral hemisphere. The lateral sulcus has been pulled apart to expose the insula. 22

14-9 The Cerebrum Association Areas Sensory association areas Monitor and interpret arriving information at sensory areas of cortex Somatic sensory association area Interprets input to primary sensory cortex (e.g., recognizes and responds to touch)

14-9 The Cerebrum Sensory Association Areas Visual association area Interprets activity in visual cortex Auditory association area Monitors auditory cortex Somatic motor association area (premotor cortex) Coordinates motor responses (learned movements)

14-9 The Cerebrum Integrative Centers Are located in lobes and cortical areas of both cerebral hemispheres Receive information from association areas Direct complex motor or analytical activities

14-9 The Cerebrum General Interpretive Area Also called Wernicke’s area Present in only one hemisphere Receives information from all sensory association areas Coordinates access to complex visual and auditory memories

14-9 The Cerebrum Other Integrative Areas Speech center Is associated with general interpretive area Coordinates all vocalization functions Prefrontal cortex of frontal lobe Integrates information from sensory association areas Performs abstract intellectual activities (e.g., predicting consequences of actions)

Figure 14-15b Motor and Sensory Regions of the Cerebral Cortex Frontal eye field Speech center Prefrontal cortex General interpretive area The left hemisphere generally contains the general interpretive area and the speech center. The prefrontal cortex of each hemisphere is involved with conscious intellectual functions. 28

14-9 The Cerebrum Interpretive Areas of Cortex Brodmann areas Patterns of cellular organization in cerebral cortex

Figure 14-15c Motor and Sensory Regions of the Cerebral Cortex Regions of the cerebral cortex as determined by histological analysis. Several of the 47 Brodmann areas are shown for comparison with the results of functional mapping. 30

Table 14-8 The Cerebral Cortex 31

14-9 The Cerebrum Hemispheric Lateralization Functional differences between left and right hemispheres Each cerebral hemisphere performs certain functions that are not ordinarily performed by the opposite hemisphere

14-9 The Cerebrum The Left Hemisphere The Right Hemisphere In most people, left brain (dominant hemisphere) controls: Reading, writing, and math Decision making Speech and language The Right Hemisphere Right cerebral hemisphere relates to: Senses (touch, smell, sight, taste, feel) Recognition (faces, voice inflections)

Figure 14-16 Hemispheric Lateralization Left Cerebral Hemisphere LEFT HAND Prefrontal cortex Speech center C O R P U S Writing C A Auditory cortex L L O S U M General interpretive center (language and mathematical calculation) Visual cortex (right visual field) 34

Figure 14-16 Hemispheric Lateralization Right Cerebral Hemisphere RIGHT HAND Prefrontal cortex Anterior commissure C O R P U S Analysis by touch C A Auditory cortex L L O S U M Spatial visualization and analysis Visual cortex (left visual field) 35

14-9 The Cerebrum Monitoring Brain Activity Brain activity is assessed by an electroencephalogram (EEG) Electrodes are placed on the skull Patterns of electrical activity (brain waves) are printed out

14-9 The Cerebrum Four Categories of Brain Waves Alpha waves Beta waves Theta waves Delta waves

14-9 The Cerebrum Alpha Waves Beta Waves Found in healthy, awake adults at rest with eyes closed Beta Waves Higher frequency Found in adults concentrating or mentally stressed

Alpha waves are characteristic of normal resting adults Figure 14-17a Brain Waves Alpha waves are characteristic of normal resting adults 0 Seconds 1 2 3 4 39

Beta waves typically accompany intense concentration Figure 14-17b Brain Waves Beta waves typically accompany intense concentration 0 Seconds 1 2 3 4 40

14-9 The Cerebrum Theta Waves Delta Waves Found in children Found in intensely frustrated adults May indicate brain disorder in adults Delta Waves During sleep Found in awake adults with brain damage

Theta waves are seen in children and in frustrated adults Figure 14-17c Brain Waves Theta waves are seen in children and in frustrated adults 0 Seconds 1 2 3 4 42

Delta waves occur in deep sleep and in certain pathological conditions Figure 14-17d Brain Waves Delta waves occur in deep sleep and in certain pathological conditions 0 Seconds 1 2 3 4 43

14-9 The Cerebrum Synchronization Seizure A pacemaker mechanism Synchronizes electrical activity between hemispheres Brain damage can cause desynchronization Seizure Is a temporary cerebral disorder Changes the electroencephalogram Symptoms depend on regions affected

14-10 Cranial Nerves Cranial Nerves 12 pairs connected to brain Four Classifications of Cranial Nerves Sensory nerves carry somatic sensory information, including touch, pressure, vibration, temperature, and pain Special sensory nerves carry sensations such as smell, sight, hearing, balance Motor nerves: axons of somatic motor neurons Mixed nerves: mixture of motor and sensory fibers

14-10 Cranial Nerves Cranial Nerves Are classified by primary functions May also have important secondary functions Distributing autonomic fibers to peripheral ganglia The 12 cranial nerve groups are identified by: Primary function Origin Pathway Destination

Figure 14-18 Origins of the Cranial Nerves Olfactory bulb: termination of olfactory nerve (I) Olfactory tract Optic nerve (II) Infundibulum Oculomotor nerve (III) Pons Basilar artery Vertebral artery Cerebellum Medulla oblongata Spinal cord 47

Figure 14-18 Origins of the Cranial Nerves Optic chiasm Optic tract Mamillary body Trochlear nerve (IV) Trigeminal nerve (V) Abducens nerve (VI) Facial nerve (VII) Vestibulocochlear nerve (VIII) Glossopharyngeal nerve (IX) Vagus nerve (X) Hypoglossal nerve (XII) Accessory nerve (XI) 48

14-10 Cranial Nerves Olfactory Nerves (I) Primary function: Origin: Special sensory (smell) Origin: Receptors of olfactory epithelium Pathway: Olfactory foramina in cribriform plate of ethmoid Destination: Olfactory bulbs

14-10 Cranial Nerves Olfactory Nerve Structures Olfactory bulbs Located on either side of crista galli Olfactory tracts Axons of postsynaptic neurons Leading to cerebrum

Figure 14-19 The Olfactory Nerve Olfactory tract (to olfactory cortex of cerebrum) Left olfactory bulb (termination of olfactory nerve) OLFACTORY NERVE (N I) Olfactory nerve fibers Cribriform plate of ethmoid Olfactory epithelium 51

14-10 Cranial Nerves Optic Nerves (II) Primary function: Origin: Special sensory (vision) Origin: Retina of eye Pathway: Optic canals of sphenoid Destination: Diencephalon via optic chiasm

14-10 Cranial Nerves Optic Nerve Structures Optic chiasm Optic tracts Where sensory fibers converge And cross to opposite side of brain Optic tracts Reorganized axons Leading to lateral geniculate nuclei

Figure 14-20 The Optic Nerve Eye Olfactory bulb Pituitary gland Olfactory tract OPTIC NERVE (N II) Optic chiasm Optic tract Lateral geniculate nucleus (in thalamus) Optic projection fibers Midbrain (cut) Visual cortex (in occipital lobes) 54

14-10 Cranial Nerves Oculomotor Nerves (III) Primary function: Motor (eye movements) Origin: Midbrain Pathway: Superior orbital fissures of sphenoid

14-10 Cranial Nerves Oculomotor Nerves (III) Destination: Somatic motor Superior, inferior, and medial rectus muscles Inferior oblique muscle Levator palpebrae superioris muscle Visceral motor Intrinsic eye muscles

14-10 Cranial Nerves Oculomotor Nerve Structures Oculomotor nerve Controls four of six eye-movement muscles Delivers autonomic fibers to ciliary ganglion Ciliary ganglion controls intrinsic muscles of iris and lens

14-10 Cranial Nerves The Trochlear Nerves (IV) Primary function: Motor (eye movements) Origin: Midbrain Pathway: Superior orbital fissure of sphenoid Destination: Superior oblique muscle

14-10 Cranial Nerves The Abducens Nerves (VI) Primary function: Motor (eye movements) Origin: Pons Pathway: Superior orbital fissures of sphenoid Destination: Lateral rectus muscle

Figure 14-21 Cranial Nerves Controlling the Extra-Ocular Muscles Superior rectus muscle OPTIC NERVE (N II) Optic chiasm OCULOMOTOR NERVE (N III) TROCHLEAR NERVE (N IV) Superior oblique muscle Trochlea Levator palpebrae superioris muscle Trigeminal nerve (N V), cut Inferior oblique muscle Vestibulocochlear nerve (N VIII), cut Facial nerve (N VII), cut Inferior rectus muscle Medial rectus muscle Ciliary ganglion Lateral rectus muscle (cut) ABDUCENS NERVE (N VI) 60

14-10 Cranial Nerves The Trigeminal Nerves (V) Primary function: Mixed (sensory and motor) to face Origin: Ophthalmic branch (sensory) Orbital structures Nasal cavity Skin of forehead, upper eyelid, and eyebrow Part of nose

14-10 Cranial Nerves The Trigeminal Nerves (V) Origin: Maxillary branch (sensory) Lower eyelid Upper lip, gums, and teeth Cheek and nose Palate and part of pharynx

14-10 Cranial Nerves The Trigeminal Nerves (V) Origin: Mandibular branch (sensory) Lower gums, teeth, and lips Palate and part of tongue Mandibular branch (motor) Motor nuclei of pons

14-10 Cranial Nerves The Trigeminal Nerves (V) Pathway: Ophthalmic branch Superior orbital fissure Maxillary branch Foramen rotundum Mandibular branch Foramen ovale

14-10 Cranial Nerves The Trigeminal Nerves (V) Destination: Sensory nerves Sensory nuclei in pons Motor nerves of mandibular branch Muscles of mastication

14-10 Cranial Nerves Trigeminal Nerve Structures Trigeminal nerves Largest cranial nerves With three major branches Semilunar ganglion Contains cell bodies of sensory neurons

Figure 14-22 The Trigeminal Nerve Superior orbital fissure Supra-orbital nerves Ophthalmic branch Semilunar ganglion Ciliary ganglion Pons TRIGEMINAL NERVE (N V) Foramen rotundum Maxillary branch Infra-orbital nerve Foramen ovale Lingual nerve Otic ganglion Submandibular ganglion Mandibular branch Pterygopalatine ganglion Mental nerve 67

14-10 Cranial Nerves The Facial Nerves (VII) Primary function: Origin: Mixed (sensory and motor) to face Origin: Sensory Taste receptors on anterior 2/3 of tongue Motor Motor nuclei of pons Pathway: Internal acoustic meatus to facial canals (stylomastoid foramina)

14-10 Cranial Nerves The Facial Nerves (VII) Destination: Sensory Sensory nuclei of pons Somatic motor Muscles of facial expression Visceral motor Tear and nasal mucous glands Submandibular and sublingual salivary glands

14-10 Cranial Nerves Facial Nerve Structures Facial nerve branches Temporal Zygomatic Buccal Mandibular Cervical branches

14-10 Cranial Nerves Facial Nerve Structures Geniculate ganglia Hold cell bodies of sensory neurons Pterygopalatine ganglia Postganglionic fibers innervate glands (lacrimal, nasal cavity, and pharynx) Submandibular ganglia Innervate salivary glands

Figure 14-23a The Facial Nerve Pterygopalatine ganglion Greater petrosal nerve Geniculate ganglion FACIAL NERVE (N VII) Temporal branch Pons Zygomatic branches Posterior auricular branch Buccal branch Stylomastoid foramen Chorda tympani nerve (with mandibular branch of N V) Mandibular branch Lingual branch (with lingual nerve of N V) Cervical branch Submandibular ganglion The origin and branches of the facial nerve 72

Figure 14-23b The Facial Nerve Temporal branch Zygomatic branch Buccal branch Mandibular branch Cervical branch The superficial distribution of the five major branches of the facial nerve 73

14-10 Cranial Nerves The Vestibulocochlear Nerves (VIII) Primary function: Special sensory Vestibular branch Balance and equilibrium Cochlear branch Hearing

14-10 Cranial Nerves The Vestibulocochlear Nerves (VIII) Origin: Receptors of inner ear Pathway: Internal acoustic meatus of temporal bones Destination: Vestibular and cochlear nuclei of pons and medulla oblongata

14-10 Cranial Nerves Vestibulocochlear Nerve Structures Vestibular branch Originates at receptors of vestibule (balance) Connects to vestibular nuclei of pons and medulla oblongata Cochlear branch Originates at sensors of cochlea (hearing) Connects with cochlear nuclei of pons and medulla oblongata

Figure 14-24 The Vestibulocochlear Nerve Tympanic cavity (middle ear) Semicircular canals Vestibular branch (N VIII) Facial nerve (N VII), cut Internal acoustic meatus VESTIBULOCOCHLEAR NERVE (N VIII) N V Pons N VI N VII N IX N XII N X Medulla oblongata N XI Tympanic membrane Auditory tube Cochlea Cochlear branch (N VIII) 77

14-10 Cranial Nerves The Glossopharyngeal Nerves (IX) Primary function: Mixed (sensory and motor) to head and neck

14-10 Cranial Nerves The Glossopharyngeal Nerves (IX) Origins: Sensory Posterior 1/3 of tongue Part of pharynx and palate Carotid arteries Motor Motor nuclei of medulla oblongata

14-10 Cranial Nerves The Glossopharyngeal Nerves (IX) Pathway: Jugular foramina between occipital and temporal bones Destination: Sensory Sensory nuclei of medulla oblongata Somatic motor Nerves involved in swallowing Visceral motor Parotid salivary gland

14-10 Cranial Nerves Glossopharyngeal Nerve Structures Superior and inferior ganglion Sensory neurons of tongue and pharynx Otic ganglion Synapse visceral motor fibers

Figure 14-25 The Glossopharyngeal Nerve Pons N V N VIII N VII N VI GLOSSOPHARYNGEAL NERVE (N IX) Otic ganglion Medulla oblongata Inferior (petrosal) ganglion Superior (jugular) ganglion Parotid salivary gland Lingual branch Pharyngeal branches Carotid sinus branch Carotid body Carotid sinus Common carotid artery 82

14-10 Cranial Nerves The Vagus Nerves (X) Primary function: Mixed (sensory and motor) Widely distributed in thorax and abdomen

14-10 Cranial Nerves The Vagus Nerves (X) Origins: Sensory Part of pharynx Auricle and external acoustic meatus Diaphragm Visceral organs of thoracic and abdominopelvic cavities Motor Motor nuclei in medulla oblongata

14-10 Cranial Nerves The Vagus Nerves (X) Pathway: Jugular foramina Between occipital and temporal bones

14-10 Cranial Nerves The Vagus Nerves (X) Destination: Sensory Sensory nuclei and autonomic centers of medulla oblongata Visceral motor Muscles of the palate and pharynx Muscles of the digestive, respiratory, and cardiovascular systems in thoracic and abdominal cavities

14-10 Cranial Nerves Vagus Nerve Structures Vagus nerves Branch and radiate extensively Superior (jugular) ganglion and inferior (nodose) ganglion Hold sensory neurons

Figure 14-26 The Vagus Nerve Superior pharyngeal branch VAGUS NERVE (N X) Pons Medulla oblongata Auricular branch to external ear Superior ganglion of vagus nerve Inferior ganglion of vagus nerve Pharyngeal branch Superior laryngeal nerve Internal branch Superior laryngeal nerve External branch 88

Figure 14-26 The Vagus Nerve Recurrent laryngeal nerve Cardiac branches Cardiac plexus Right lung Left lung Liver Anterior vagal trunk Spleen Stomach Celiac plexus Pancreas Colon Small intestine Hypogastric plexus 89

14-10 Cranial Nerves The Accessory Nerves (XI) Primary function: Motor to muscles of neck and upper back Origin: Motor nuclei of spinal cord and medulla oblongata

14-10 Cranial Nerves The Accessory Nerves (XI) Pathway: Jugular foramina between occipital and temporal bones Destination: Internal branch Voluntary muscles of palate, pharynx, and larynx External branch Sternocleidomastoid and trapezius muscles

14-10 Cranial Nerves Accessory Nerve Structures Spinal root Motor fibers that originate in anterior gray horns of first five cervical segments of spinal cord Cranial root Motor fibers that originate in medulla oblongata

14-10 Cranial Nerves Accessory Nerve Structures Internal branch Joins the vagus nerve External branch Controls muscles of neck and back

14-10 Cranial Nerves The Hypoglossal Nerves (XII) Primary function: Motor (tongue movements) Origin: Motor nuclei of medulla oblongata Pathway: Hypoglossal canals of occipital bone Destination: Muscles of tongue

Figure 14-27 The Accessory and Hypoglossal Nerves HYPOGLOSSAL NERVE (N XII) Trigeminal nerve (N V) ACCESSORY NERVE (N XI) Internal branch: to palatal, pharyngeal, and laryngeal muscles with vagus nerve Medulla oblongata Cranial root of N XI Intrinsic muscles of tongue Spinal root of N XI Styloglossus muscle External branch of N XI Genioglossus muscle Geniohyoid muscle Spinal cord Hyoglossus muscle Trapezius muscle Hyoid bone Thyrohyoid muscle Sternocleidomastoid muscle Sternohyoid muscle Ansa cervicalis (cervical plexus) Sternothyroid muscle Omohyoid muscle 95

Table 14-9 Cranial Nerve Branches and Functions 96

Table 14-9 Cranial Nerve Branches and Functions 97

14-10 Cranial Reflexes Cranial Reflexes Monosynaptic and polysynaptic reflex arcs Involve sensory and motor fibers of cranial nerves Clinically useful to check cranial nerve for brain damage

Table 14-10 Cranial Reflexes 99