HSS2011 Human Anatomy: Nervous System II: Brain and Cranial Nerve PDF

HSS2011 Human Anatomy: 1 Nervous system II: Brain and cranial nerve Dr. Benson Lau Associate Professor, Department of Rehabilitation Sciences Updates/clarification of the ppts at 1st Nov 24:...

HSS2011 Human Anatomy: 1 Nervous system II: Brain and cranial nerve Dr. Benson Lau Associate Professor, Department of Rehabilitation Sciences Updates/clarification of the ppts at 1st Nov 24: 2 P. 18 Diencephalon is not regarded as part of the brainstem. Though some refences stats that diencephalon is part of the brainstem, more sources states it is not. P. 52 Cranial Nerve VIII is a pure sensory nerve. Some reference, including the textbook, indicates there is a motor function of CN VIII. However we can’t find compelling evidence from other sources. P. 59 CN IX is involved in gagging reflex by sending sensation (e.g. touching roof of mouth) to medulla, and the motor command is sent via CN X to the pharyngeal muscles. Lecture II: Neuroanatomy of the brain and Cranial Nerve 3 II.1: Overview of the Brain II.2: Brainstem and cerebellum II.3: Forebrain II.4: Cranial Nerves II.1: Overview 4 of the Brain  II.1.1: Overview of the Brain 5 About 1.45 – 1.6 kg for humans Divided into 3 major portions: Cerebrum Cerebellum and Brainstem II.1.1: Overview of the Brain 6 Cerebrum: 83% of brain volume Has pair of half globes called hemispheres Separated by longitudinal fissure Connected by Corpus callosum (bundle of nerve fibers) Gyrus: thick folds/elevations on cerebrum Sulcus: deep groove/depression  II.1.1: Overview of the Brain 7 Cerebellum (Blue area): inferior, posterior to cerebrum Separated from cerebrum by transverse cerebral fissure 10% of brain volume  II.1.1: Overview of the Brain 8 Brainstem (Green area): Essential for survival; vital functions Consists sub-regions Continues as spinal cord inferiorly II.1.1: Overview of the Brain 9 Cortex Gray matter in the brain: At outer surface of cerebrum (cortex) Nuclei: deeper masses, collection of neuronal soma Nucleus White matter in the brain: Bundle of axons Connecting brain to spinal cord, or within the cerebrums  II.1.2 Meninges 10 Three membranes protect and provide structures for the brain Dura matter, arachnoid mater and pia mater  II.1.2 Meninges 11 Dura mater: Dense fibrous connective tissue Has two layers: periosteal & meningeal Periosteal layer: attached to cranial bones Meningeal layer: inner layer Dural sinuses: space between the two dural layers (e.g. superior sagittal sinus) Collect blood and empties into veins II.1.2 Meninges 12 In some areas, dura mater fold inward to separate major parts of brain E.g. Falx cerebri, Falx cerebrelli Arachnoid & pia mater: Similar to spinal cord Arachnoid mater: Transparent Over subarachnoid space, filled with CSF Pia mater: Delicate Cover cerebrum II.1.3 Ventricles and cerebrospinal fluid 13 Hollow space in the brain, filled with cerebrospinal fluid (CSF)  II.1.3 Ventricles and cerebrospinal fluid 14 Ventricular system: 4 chambers (ventricles) Lateral ventricles X 2: in each cerebral hemisphere Third ventricle: connect to lat. Ventricles via interventricular foramen Fourth ventricle: connect to third ventricle via cerebral aqueduct Fourth ventricle continues as central canal in spinal cord On floor of ventricles, spongy mass of blood capillaries form choroid plexus, produces CSF II.1.3 Ventricles and cerebrospinal fluid 15 Functions of CSF: 1. Provide buoyancy: prevent brain from collapse due to own weight 2. Protection: prevent brain from striking the cranium 3. Chemical stability: remove metabolic wastes, maintain chemical environment II.1.4 Brain Barrier system (BBS) 16 Gives protection to the brain by regulating substances from blood stream into the brain 1. Blood-Brain barrier (BBB): Astrocytes contact blood capillaries, stimulates tight junctions between endothelial cells 2. Blood-CSF barrier: Formed at choroid plexuse, by ependymal cells II.2: Brainstem and cerebellum 17 II.2.1 Brainstem 18 Consists of Diencephalon Midbrain Pons Medulla oblongata II.2.2 The Medulla Oblongata 19 Contains all nerve fibers travel between brain and spinal cord Four pairs of cranial nerves (nerves directly arise from the brain to peripheries) Several nuclei with basic physiological functions: Cardiac center: regulate rate and force of heartbeat Vasomotor center: regulate blood pressure and vasoconstriction; Respiratory centers: regulate rate and depth of breathing Others: speech, cough, sneezing, swallowing, etc II.2.2 The Medulla Oblongata 20 On the surface: Pyramids: clublike ridges Anterior median fissure: separates pyramids Internal structures: Ascending and descending tracts: e.g. tectospinal and corticospinal tracts Nucleus E.g. inf. olivary nucleus Fourth ventricle II.2.3 The Pons 21 Rostral to the medulla Has pair of cerebellar peduncles, connecting to the cerebellum 4 pairs of cranial nerves begin/end here Internal structures: Continuation of ascending/descending tracts e.g. tectospinal tract Part of fourth ventricles  II.2.4 The midbrain 22 Cerebral aqueduct passes through Colliculus: Superior: visual reflex (e.g. blinking) and visual attention (tracking moving objects) Inferior: transduce auditory info to the brain; auditory reflexes (e.g. startle reflex)  II.2.4 The midbrain 23 Internal structures: Central /periaqueductal gray: awareness of pain Substantia nigra: motor center, improves motor performance by suppressing unwanted movements II.2.5 Cerebellum 24 Motor coordination center Consists two hemispheres, connected by vermis (narrow wormlike bridge) Folia: = gyri on cerebrum Connect to: Medulla via inferior peduncles Pons via middle peduncles Midbrain via superior peduncles Internal structures: Arbor vitae: white matter Specific types of neurons: granule cells and Purkinje cells II.2.5 Cerebellum 25 Highly important in motor coordination Involved in: Learning motor skills Maintain muscle tone and posture Coordinates eye and body movement Coordinate complex actions Received info from cerebrum and joints; compare planned and actual movement, send feedback to cerebrum  II.2.6 Reticular formation 26 Loosely organized gray matter, runs vertically through brainstem Functions: Somatic motor control: adjust muscle tone, balance, posture via reticulospinal tract Work with cerebellum for motor coordination Cardiovascular control Pain modulation: regulate/block pain signal to the brain Sleep and consciousness: control state of consciousness Habituation: ignore repetitive, inconsequential stimuli II.3: Forebrain 27 II.3.1 Diencephalon 28 Diencephalon: most rostral part of brainstem; part of forebrain Consists: Thalamus, hypothalamus and epithalamus II.3.1 Thalamus 29 Oval shape, separate into right and left parts Consists of 23 nuclei Gateway to the cerebral cortex: almost all sensory input passes by E.g. vision, hearing, somatosensory function Relays signals from cerebellum to cerebrum Also involved in memory and emotion as limbic system II.3.1 The Hypothalamus 30 Walls and floor of the third ventricle Connected to the thalamus via infundibulum Very important in regulation of endocrine system and autonomic nervous system Functions: Produce and secret hormones: Regulate growth, metabolism, reproduction, etc. Autonomic effects: Influence brainstem functions e.g. heart rate, blood pressure, digestive function, etc Thermoregulation Regulate appetite Emotion, reproductive response, memory, etc. II.3.1 the epithalamus 31 Epithalamus: Pineal gland + habenula Pineal gland: secrets melatonin, regulate sleep and consciousness II.3.2 Gross anatomy of cerebrum 32 Extensive folding (gyri) to greatly increase surface area to house neurons Surface of cerebrum divided into 5 lobes: Frontal: anterior, superior part of the brain. Parietal: separate from frontal by central sulcus. Occipital: caudal part. Separated from parietal lobe by parieto-occipital sulcus. Temporal: lateral, separated from parietal lobe by lateral sulcus. Insula: deep to the lateral sulcus II.3.2 Gross anatomy of cerebrum 33 Functions of the 5 lobes: Frontal: For higher cognitive functions Parietal: For sensation Occipital: For vision Temporal: For hearing, smell, etc Insula: for taste, visceral sensation.  II.3.2 White matter in the cerebrum 34 Projection tracts: Extend vertically, between brain and spinal cord centers Examples: Corticospinal tract: carry motor commands to spinal cord Commissural tracts: Cross from one hemisphere to the other E.g. Corpus callosum: largest tract Anterior and posterior commissures Association tracts: Connect different regions in same hemisphere  II.3.3 Sub-systems in the cerebrum 35 Limbic system: Center of emotion and learning Consists: Hippocampus Amygdala Cingulate gyrus Amygdala: Receives input from vision, taste, smell, etc Important for association of sensation to emotion Sense of fear: no amygdala, no fear  II.3.3 Sub-systems in the cerebrum 36 Basal nuclei: Later to thalamus, a.k.a. basal ganglia Consists: Caudate nucleus Putamen Globus pallidus Involved in motor control Planning and execution of movement Sends feedback of action to motor cortex II.3.4 Higher functions and structures of the cerebrum 37 Primary cortex: Cerebrum regions connect directly with sensory or motor neurons i.e. with third order neurons or upper motor neurons Association cortex: Regions involved in integrative functions E.g. interpretation of sensory input Planning motor output Cognitive processes, etc May receive input from multiple seses and integrate these E.g. prefrontal cortex II.3.4 Higher functions and structures of the cerebrum 38 II.3.4 Higher functions and structures of the cerebrum 39 Special senses: Include taste, smell, hearing, equilibrium and vision Signals from sense organs/receptors are firstly sent to primary sensory cortex Then signals are relayed to nearby association area, where sensation is integrated with memory and interpreted  II.3.4 General/somatosensory senses 40 General senses include touch, pressure, stretch, temperature, pain, which are received by skin receptors Sensory signals sent via ascending tracts to contralateral side of thalamus, then to postcentral gyrus, a.k.a. primary somatosensory cortex Signals relayed to association area, for interpretation II.3.4 General/somatosensory senses 41 Sensory homunculus: A diagram showing which cortex receive general sensation from particular body areas The more cortex area for a body part, the much innervated and sensitive i.e. hand and face are much sensitive than trunk and lower limbs II.3.4 Motor control 42 Intention to move begins in motor association area Neurons compile a program for the muscle movement for an action Then the program transmitted to precentral gyrus /primary motor area Motor commands then being sent to brainstem and spinal cord for carrying out II.3.4 Motor control 43 Motor homunculus shows amount and region of cortex for motor action of body parts Amount of cortex in proportion to number of muscles/motor units; more innervation, more complex movement can be made I.e. action of hand is much complex than the trunk and feet II.3.4 Language 44 Integration of sensory and motor functions Broca area Wernicke area: Sensory association area; receive auditory, visual and other sense information recognition of spoken and written language Formulate phrases; send to Broca area Broca area: Motor association area: generate motor program for muscles of larynx, tongue, cheeks and lips Transduce signal to primary motor cortex for execution Wernicke Area  II.4: Cranial Nerves 45 Key information for each Cranial nerve: 1. Name 2. Function (Sensory/motor/mixed) 3. Connection to the brain/brainstem (origin/termination) II.4 Cranial Nerves 46 The brain mainly communicates with other body parts via spinal cord and spinal nerves Cranial nerves: Directly arise from the brain and brainstem 12 pairs in total II.4 Cranial Nerves 47 II.4 Cranial nerves 48 To remember the order and name of cranial nerves, a useful mnemonic: Take initial letter from the nerve ‘’Oh, once one takes the anatomy final, very good vacation ahead’’ Olfactory, optic, oculomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, hypoglossal II.4 Cranial nerve 49 To remember function of Cranial nerves, better classify first Cranial nerves classified as Predominantly Sensory (I, II, VIII), Motor (III, IV, VI, Xi, XII) or Mixed (V, VII, IX, X) II.4 Cranial nerves: Sensory nerves I, II, VIII 50 Name: Olfactory nerve (I): Function: sense of smell Nerve with olfactory receptors Origin/termination: Olfactory mucosa to olfactory bulbs II.4 Cranial nerves: Sensory nerves I, II, VIII 51 Name: Optic Nerve (II) Function: Vision Origin/termination: Retina Thalamus/midbrain  II.4 Cranial nerves: Sensory nerves I, II, VIII 52 Name: Vestibulocochlear Nerve (VIII) Function: (sensory): hearing & equilibrium; (motor): stabilize hair cells of cochlea Origins: cochlea, vestibule and semicircular ducts of inner ear Termination: medulla and pons (sensory); outer hair cells (motor) II.4 Cranial nerves: Motor III, IV, VI 53 CN III, IV and VI are for eye movements Origin: III: Midbrain IV: midbrain VI: pons Termination (extra orbital muscles): III: extra orbital muscles (superior, midal and inferior rectus, inferior oblique) IV: superior oblique VI: lateral rectus II.4 Cranial nerves: Motor III, IV, VI 54  II.4 Cranial nerves: Motor XI, XII 55 Name: Accessory Nerve (XI); Hypoglossal Nerve (XII) Functions: XI: Swallowing; head/neck/shoulder movements XII: Tongue movement for speech, food manipulation and swallowing Origins: Medulla Oblongata (XI: also with spinal nerves C1 – C6) Terminations: XI: Palate; pharynx; trapezius and sternocleidomastoid muscles (head and neck muscles) XII: muscles of tongues  II.4 Cranial Nerves: Mixed (V, VII, IX, X) 56 Name: Trigeminal Nerve (V) Divisions: V1, V2, V3 Functions: V1: General sensation from upper face V2: General sensation from lower face V3: Same as V1 and V2, lower on face; mastication Origins; V1: Superior region of face; nasal mucosa, etc V2: middle region of face; nasal mucosa etc V3: Inferior region of face; tongue (sensory); Pons(motor) Terminations: V1 and V2: Pons V3: Pons (sensory); muscles for mastication, etc II.4 Cranial Nerves: Mixed (V, VII, IX, X) 57 Name: Facial Nerve (VII) Functions: Sensory: taste Motor: facial expression; secret tears saliva, nasal/oral mucus Origins: Sensory: taste buds, anterior two-thirds of tongue Motor: pons Termination: Sensory: thalamus Motor: muscles for mastication, facial expression, glands for saliva/tear/mucus secretion II.4 CN VII 58 II.4 Cranial Nerves: Mixed (V, VII, IX, X) 59 Name: Glossopharyngeal Nerve (IX) Functions: Sensory: general senses of tongue and outer ear, gagging (afferent fiber) Motor: salivation, swallowing, gagging Origins: Sensory: pharynx, ear, tongue Motor: medulla Termination: Sensory: medulla Motor: salivary gland; muscle dilates pharynx II.4 Cranial Nerves: Mixed (V, VII, IX, X) 60 Name: Vagus Nerve (X) Function: Sensory: taste, sense of hunger, gastrointestinal discomfort Motor: swallowing, speech, heart rate regulation, broncho constriction Origins: Sensory: internal organs; tongue; pharynx, etc Motor: medulla Termination: Sensory: medulla Motor: tongue, pharynx and larynx, internal organs like lungs and heart Reference: 61 Textbook: Saladin, K. S., Sullivan, S. J., & Gan, C. A. (2020). Human anatomy(Sixth edition or newer edition). McGraw-Hill Education. Chapter 15