Lab Activity 21 The Brain Portland Community College

Lab Activity 21 The Brain Portland Community College BI 232

Brain Meninges: Dura Mater • Continuous with the spinal meninges • Dura mater: An outer and inner fibrous connective tissue • Outer later is fused to the periosteum of the cranial bones (no epidural space) • Between the layers are tissue fluids, blood vessels and venous sinuses. • Venous sinuses are large collecting veins. • Venous sinuses drain into the internal jugular veins 2

Dural Folds • The inner layer of dura mater that extends into the cranial cavity. • Provide additional stabilization and support for the brain • Contain the dural sinuses 3

Dural Folds • Falx cerebri projects between the cerebral hemispheres in the longitudinal fissure • Superior sagittal sinus & inferior sagittal sinus • Tentorium cerebelli separates the cerebellar hemisphere from the cerebrum • Transverse sinus • Falx cerebelli divides the cerebellar hemispheres 4

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Brain Meninges: Arachnoid & Pia Mater • Arachnoid mater consists of the arachnoid membrane and fibers of the arachnoid trabeculae that attach to the pia mater • Pia mater: attached to the surface of the brain, anchored by processes of astrocytes • Contains branches of cerebral blood vessels that penetrate the surface of the brain. • CSF is between these two membranes in the subarachnoid space 6

Ventricles 7

CSF Circulation • CSF is made from tufts of blood capillaries called choroid plexuses • CSF cushions and provides buoyancy to the brain. 8

CSF circulation • CSF flows through the arachnoid granulations under the dura mater and returns to venous sinuses returning the fluid to the cardiovascular system. 9

Blood Supply to the brain • Blood vessels supply the brain with nutrients and oxygen. • The two main arteries are the vertebral arteries and internal carotid arteries 10

Blood Supply to the Brain • The vertebral arteries join to form the basilar artery before branching into the arterial circle (circle of Willis) that forms a loop around the pituitary gland. • Joins with the internal carotid arteries anteriorly 11

Brain Regions • Forebrain • Cerebrum • Diencephalon • Midbrain • Corpora Quadrigemina • Hindbrain • Pons • Medulla oblongata • cerebellum 12

Cerebrum • Frontal lobe (many higher functions) • Intellect, abstract reasoning, creativity, social awareness and language • Precentral gyrus = primary motor cortex • Broca’s area is the motor speech area • Parietal lobe • Sensation (except smell), language • Postcentral gyrus=primary somatic sensory cortex • Wernicke's area involved in the formation of language 13

Cerebrum • Occipital lobe • Primary vision cortex • Shape, color and distance of an object are perceived here • Temporal lobe • Primary auditory cortex, interprets impulses sent from the inner ear • Translates words into thought 14

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Precentral Gyrus: (frontal lobe) contains the primary motor area Central Sulcus Postcentral Gyrus: (parietal lobe) contains the primary somatosensory area. 16

Cerebral Hemispheres • Left hemisphere involved with language and reasoning (Broca area usually on left) • Right hemisphere involved in space and pattern perceptions, artistic awareness, imagination 17

Sulci & Gyri Sulci • Sulci: Shallow depressions of the cerebral cortex • Central sulcus is between the frontal and parietal lobes • Lateral sulcus is between the parietal lobes and temporal lobes. • Fissures: Deep grooves • Longitudinal: separates cerebral hemispheres • Transverse: separates cerebrum form the cerebellum • Gyri: The elevated ridges of the cerebral cortex • Serve to increase the surface area 18

Longitudinal Fissure Transverse fissure Transverse Fissure 19

Central Sulcus Lateral Sulcus 20

Diencephalon Structures • Thalamus • Hypothalamus • Epithalamus 21

Diencephalon: Hypothalamus • Pituitary gland: Attaches to the hypothalamus via the infundibulum • Mamillary bodies: Process olfactory sensations. (smell to memory) Pituitary gland (not in this picture) would be hanging here Mamillary body 22

Diencephalon: Hypothalamus • Major Functions: 1. Controls somatic motor activities at the subconscious level 2. Controls autonomic function 3. Coordinates activities of the nervous and endocrine systems 4. Secretes hormones 5. Produces emotions and behavioral drives 6. Coordinates voluntary and autonomic functions 7. Regulates body temperature 8. Coordinates circadian cycles of activity 23

Diencephalon: Thalamus • Relay station for sensory input 24

Diencephalon: Epithalamus • Superior to the third ventricle, contains the pineal gland Pineal gland 25

Brainstem 3 Structures: • Midbrain (mesencephalon) • Pons • Medulla oblongata Corpora quadrigemina 26

Midbrain Pons Medulla Corpora 27 quadrigemina

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Midbrain • Functions: • Connects pons to cerebellum • Superior colliculi: visual reflex centers • Inferior colliculi: auditory reflex centers 30

Brainstem: Pons • Functions: • Sensory and motor nuclei of Cranial nerves V, VI, VII, and VIII • Respiratory control: • Apneustic center and pneumotaxic center to modify the activity of the respiratory rhythmicity center in the medulla • Nuclei and tracts that process and relay information to and from the cerebellum 31

Medulla Oblongata • Functions: • Center for the coordination of complex autonomic reflexes (heart rate, respiratory rhythm, blood pressure) • Control of visceral functions (vomiting, swallowing) • Decussation of pyramids: a crossover point for the major motor tracts 32

Cerebellum • Functions: • Coordination of movements • Adjustment of postural muscles Arbor Vita (white matter that looks like a leaf) Vermis 33

Cerebrum Vs Cerebellum cells Cerebrum Slide Cerebellum Slide 34

Cerebral Cortex • The superficial layer/rim of gray matter in the cerebral hemispheres • Gray matter consists of cell bodies, dendrites, and unmyelinated axons. 35

White Matter & Basal Nuclei • White matter consists primarily of myelinated axons • Is beneath the gray matter cortex • Notice how it is the opposite arrangement from the spinal cord (Spinal cord: white matter is on the outside and gray matter is on the inside. ) • Corpus callosum: Connects the right and left hemispheres • Basal nuclei: Islands of gray matter within the white matter. • Function: Involved in the subconscious control of skeletal muscle tone and the coordination of learned movement patterns 36

White Matter & Basal Nuclei White Matter Basal Nuclei Corpus Callosum 37

Sheep Brain Dissection • Follow instructions in book for the sheep brain dissection. • When finished discard brain in the container provided. Wash utensils and put back so other classes can use the materials. • ID structures on the brain models for next week’s quiz. 38

Cranial Nerves • Nerves that originate from the brain rather than the spinal cord • Part of the peripheral nervous system (not the central nervous system) • CNs (except for XII) are in sequence from anterior to posterior • May contain one or more of the following: • Sensory: receives neural input • Somatic Motor: predominantly innervates muscles • Mixed: have significant sensory and motor functions 39

CN I: Olfactory Nerve • Function: • Sensory for smell • Exiting foramen=cribriform plate • Origin forebrain • Test: Have patient identify aromatic substances like vanilla or coffee • Symptoms of nerve damage: Anosmia: diminished or absent sense of smell 40

CN II: Optic Nerve • • Function: • Sensory for vision • Exiting foramen= optic canal • Origin=forebrain Tests: 1. Eye chart 2. Check peripheral vision 3. Funduscopic exam 41

CN II: Optic Nerve • Optic chiasm: Fibers from the nasal half of each retina cross over to the opposite side of the brain. • Symptoms of nerve damage: • Loss of vision (peripheral or central) • Abnormal funduscopic appearance 42

CN II: Optic Nerve Pathology Papilledema. Note swelling of the disc, hemorrhages, and exudates, with preservation of the physiologic cup. Proliferative Diabetic Retinopathy. Note the multiple hemorrhages throughout the retina. 43

Cranial Nerves III, IV & VI (Control Eye Movements) 44

CN III: Oculomotor nerve • Function: • Somatic Motor to extraocular muscles (voluntarily move the eye) • Parasympathetic (motor) to iris and lens (pupillary constriction) • Exiting Foramen= superior orbital fissure • Origin= midbrain • Tests: 1. Check pupils for size, shape and equality 2. Shine light in each eye and check for pupil constriction 3. Have patient follow an object in all directions to check for symmetric eye movements 45

CN III: Oculomotor Nerve Injury • Symptoms of nerve damage: • Double vision (diplopia): The affected eye turns outward when the unaffected eye looks straight ahead • The affected eye can move only to the middle when looking inward and cannot look upward and downward. • Ptosis: eyelid droop • Pupil may be dilated and sometimes fixed 46

Oculomotor Nerve Injury Right Eye Injured side Normal 47 side

Pupillary Reflex Efferent Afferent Consensual reflex: Both pupils should constrict at the same time 48

Originates in the midbrain CN IV: Trochlear Nerve • Function: • Somatic motor to superior oblique muscle of the eye. • Exiting foramen= superior orbital fissure • Origin= midbrain • Test: Check eye movements • Symptoms of nerve damage: • Outward rotation of the affected eye • Vertical diplopia Normal side Injured side 49

Originates in the pons CN VI: Abducens Nerve • Function: • Somatic Motor to lateral rectus muscle of the eye. Exiting foramen=superior orbital fissure Origin= pons • Test: Check eye movements • Symptoms of nerve damage: • The affected eye will tend to be deviated inward because of the unopposed action of the medial rectus muscle. • Cannot move eyeball laterally beyond the midpoint Injured side Normal 50 side

CN V: Trigeminal Nerve 3 Branches 1. Ophthalmic 2. Maxillary 3. Mandibular 51

Originates in the pons CN V: Trigeminal Nerve • Function: • Somatic Motor (mandibular branch) to muscles of mastication (chewing) • Sensory (all branches)to face and cornea. • Exiting foramen= Ophthalmic branch=superior orbital fissure • Maxillary branch= foramen rotundum • Mandibular branch = foramen oval • Origin= pons 52

CN V: Trigeminal Nerve Test: Have patient bite down while you palpate the masseter muscle Test: Touch patient with an open paperclip and ask “sharp or dull” Test: Touch cornea with a wisp of cotton. Patient should blink 53

CN V: Trigeminal Nerve • Symptoms of nerve damage: • Inability to firmly bite down (mandibular branch only) • Loss of sensation (each branch can be affected independently) • Loss of corneal reflex (may indicate brain stem injury) • Trigeminal Neuralgia (Tic Douloureux): debilitating intermittent pain on one side of the face 54

Originates in the pons CN VII: Facial Nerve 5 Branches 1. Temporal 2. Zygomatic 3. Buccal 4. Mandibular 5. Cervical • Function: • Somatic Motor to muscles of facial expression • Parasympathetic (motor) to lacrimal and salivary glands 55 • Sensory taste to anterior 2/3 tongue

CN VII: Facial Nerve 56

CN VII: Facial Nerve Testing • • • Exiting foramen= enters internal acoustic meatus exits via stylomastoid foramen Origin= Pons Tests: 1. Check taste on anterior 2/3 of tongue by having patient taste sugar, salt, sour and bitter 2. Check symmetry of facial muscles: • Close eyes, smile, whistle, puff out cheeks (make funny faces) 3. Check tearing with ammonia fumes 57

CN VII: Facial Nerve • Symptoms of nerve damage: • Mild weakness to total paralysis of facial muscles (may include twitching), • Drooping eyelid • Drooping corner of the mouth • Drooling or dry mouth • Impairment of taste • Excessive tearing in the eye or dry eye 58

CN VII: Facial Nerve Injury (Bell’s Palsy) Normal side Injured side Paralyzed facial muscles Patients can still feel their face because sensory is supplied by the 59 trigeminal nerve

Originates in the medulla CN VIII: Vestibulocochlear • Function: Sensory • Vestibular system for balance & equilibrium • Cochlea for hearing • Exiting foramen= internal acoustic meatus • Origin= Pons-medulla border • Tests: • Auditory component of the nerve: • Hearing test • Vestibular control of balance and movement: • Romberg test (tests equilibrium) 60

CN VIII: Vestibulocochlear Tests • Simple hearing test: • Rub fingers together near the ear and ask “right or left” If there is lateralization (hearing louder on one side) there is a problem • Other hearing tests: • Performed by an audiologist with special equipment to determine tones, frequencies and degree of hearing loss 61

CN VIII: Vestibulocochlear Tests Romberg Test • Have patient stand with arms at side and feet together • Have patient stand with their eyes closed • Stand close to prevent falls • Normally, they should maintain position for 20 seconds with only minimal swaying • If they loose their balance, they have failed 62 the equilibrium test.

CN IX: Glossopharyngeal • Function: • Somatic Motor to muscles of pharynx • Parasympathetic (motor) to salivary glands • Sensory to pharynx and taste to posterior tongue • Exiting foramen= Jugular foramen • Origin= medulla oblongata 63

CN IX: Glossopharyngeal • Tests: • Gag reflex: Touch each side of the throat with the tongue depressor • Evaluate swallowing movements • Say AHH, and watch the palate and uvula elevate. • Evaluate taste on posterior 1/3 of tongue • Symptoms of nerve damage: • Loss of gag reflex • Difficulty swallowing • Loss of taste 64

Originates in the medulla CN X: Vagus Nerve • Function: • Somatic Motor to muscles of pharynx and larynx • Parasympathetic (motor) fibers of the heart and other viscera • Sensory to pharynx and larynx 65

CN X: Vagus Nerve • Test: • Inspect palate • Test gag reflex • Symptoms of nerve damage: • Loss of gag reflex • Difficulty swallowing • Hoarse voice • Exiting foramen = Jugular foramen • Origin = Medulla oblongata 66

Originates in the medulla CN XI: Accessory Nerve • Function: Somatic Motor to sternocleidomastoid and trapezius muscles 67

CN XI: Accessory Nerve • Exiting foramen = jugular foramen • Origin = medulla oblongata • and spinal cord • Test: • Shrug shoulders against resistance • Turn head against resistance. 68

CN XI: Accessory Nerve • Symptoms of nerve damage: • Weakness • Uneven shoulders • Winged scapula 69

Originates in the medulla CN XII: Hypoglossal Nerve • Function: Somatic Motor to tongue 70

Hypoglossal Nerve Injury • Exiting foramen = hypoglossal canal • Origin = medulla oblongata • Test: • Ask patient to stick out tongue • Symptoms of nerve damage: • When paralyzed, the tongue will point to the damaged side Normal side Injured side 71

Lab Activities • Identify cranial nerves on models • You will be responsible for testing cranial nerves in the upcoming weeks. 72

The End 73