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7/08/12 The Brain (& CNS)! Lecture 12a BIOL241 Final Exam (Exam 4)! • • • • • Chapters 11 – 15* 100 points Multiple choice, T/F, matching, fill in Short answer, essays (2)* Labeling (brain [including functions], cranial nerves, spinal cord) 1 7/08/12 Outline • Overview of the human brain • Tour through the brain – structures and functions • Cerebral hemispheres and higher mental functions • Meninges • Ventricles and CSF • Brain disorders The Human Brain • Composed of wrinkled, pinkish gray tissue • Surface anatomy includes cerebral hemispheres, cerebellum, and brain stem • Ranges from 750 cc to 2100 cc • Contains almost 98% of the body’s neural tissue • Average weight, adult: 1300 – 1400 gm (~3 lb) • 1010 to 1011 neurons • Trillions of connections • men = larger • Women = better connected 2 7/08/12 Major Regions and Landmarks Figure 14–1 Embryology of the Brain Table 14-1 3 7/08/12 Regions of the Adult Brain • Telencephalon (cerebrum) – cortex, white matter, and basal nuclei • Diencephalon – thalamus, hypothalamus, and epithalamus • Mesencephalon –midbrain (brain stem) • Metencephalon – pons (brain stem), cerebellum • Myelencephalon – medulla oblongata (brain stem) Basic Pattern of the Central Nervous System • Spinal Cord – Central cavity surrounded by a gray matter core – External to which is white matter composed of myelinated fiber tracts • Brain – Similar to spinal cord but with additional areas of gray matter – Cerebellum has gray matter in nuclei – Cerebrum has nuclei and additional gray matter in the cortex Figure 12.4 4 7/08/12 Some terms • nucleus: collection of neuron cell bodies in the CNS • tract: collection of axons in the CNS • ganglia: collection of neuron cell bodies in the PNS • nerve: collection of axons in the PNS – Cranial nerves – Spinal nerves Tour of the brain • From caudal/inferior to rostral/superior 5 7/08/12 The Brain Stem • Processes information between spinal cord and cerebrum or cerebellum • Controls automatic behaviors necessary for survival • Associated with 10 of the 12 pairs of cranial nerves (covered later) • Includes: – mesencephalon (midbrain) – pons – medulla oblongata – Note: some consider the diencephalon part of the brain stem as well Brain Stem Figure 12.15a 6 7/08/12 Anatomy: Brain stem Most cranial nerves are located in the brain stem Brain Stem Figure 12.15b 7 7/08/12 Posterior view Medulla Oblongata • Most inferior part of brain, connects brain to spinal cord • Relays information • Pyramids – two longitudinal ridges formed by corticospinal tracts • Regulates autonomic functions: – regulates arousal, heart rate, blood pressure, pace for respiration and digestion • Cranial nerves IX, X, XI, XII come off or enter 8 7/08/12 Medulla Oblongata Figure 12.16c Medulla Oblongata 9 7/08/12 Medulla Nuclei • Cardiovascular control center – adjusts force and rate of heart contraction • Respiratory centers – control rate and depth of breathing • Additional centers – regulate vomiting, hiccupping, swallowing, coughing, and sneezing Pons 10 7/08/12 Pons • Involved in somatic and visceral motor control • Contain the nuclei for cranial nerves V, VI, VII, VIII • Contains nuclei of the reticular formation • Control of respiration that modifies the info from the medulla • Nuclei and tracts passing through to the cerebellum (motor and somatosensory info) • Nuclei and tracts to other portions of the CNS (just passing through) Cerebellum 11 7/08/12 Cerebellum • “little brain” • Second largest part of brain (~10% mass) • Provides precise timing and appropriate patterns of skeletal muscle contraction to coordinate repetitive body movements and help learning complex motor behaviors • Adjusts the postural muscles of the body, controls balance and equilibrium • Has 2 hemispheres, covered with cerebellar cortex • Recognizes and predicts sequences of events • Cerebellar activity occurs subconsciously (as does all processing that occurs outside the cerebral cortex) Cerebellum – side (or) view 12 7/08/12 Cerebellum • Cerebellum receives impulses of the intent to initiate voluntary muscle contraction • Monitors all proprioceptive info and visual info about body position • Cerebellar cortex calculates the best way to perform a movement • Programs and fine tunes movements by detecting mismatches in intended and actual movements -- when learning to ride a bike, throw a curve ball or tie your shoe, cerebellum activity is high. When they become automatic, cerebellum is no longer involved Mesencephalon 13 7/08/12 Mesencephalon • Also called midbrain • Processes sight, sound, and associated reflexes • Maintains consciousness • Cranial nerve nuclei III and IV • 2 basic divisions – tectum (roof) – tegmentum Mesencephalon • Process of visual and auditory sensations – corpora quadrigemina (in tectum) = superior colliculi (visual reflex) and inferior colliculi (auditory reflex) • Substantia nigra (in tegmentum) – Neurons inhibit activity of cerebral nuclei by releasing dopamine – If damaged, results in less dopamine released and muscle tone increases: muscle rigidity, difficulty initiating movement = Parkinson’s Disease • Reticular formation: maintain consciousness 14 7/08/12 Midbrain Nuclei Figure 12.16a Mesencephalon 15 7/08/12 Diencephalon Figure 12.12 Diencephalon • Located under cerebrum and cerebellum • Links cerebrum with brain stem • Integrates sensory information and motor commands • Cranial nerve II 16 7/08/12 Diencephalon • Pineal Gland – Secretes hormone melatonin • Thalamus: – relays and processes sensory information • Hypothalamus: – hormone production – emotion – autonomic function Diencephalon: Thalamus • Paired, egg-shaped masses connected at the midline by the intermediate mass • Nuclei project to and receive fibers from the cerebral cortex Figure 14–9 17 7/08/12 Thalamus • Sensory Relay station • All sensory that is projected to the cerebral cortex stops here first except smell • Filters ascending sensory information for primary sensory cortex • Relays information between basal nuclei and cerebral cortex • Mediates sensation, some motor activities, cortical arousal (thus learning, and memory) Diencephalon: Hypothalamus • Lies below thalamus Figure 14–10a 18 7/08/12 Hypothalamus • Captain of the Autonomic nervous system, master overseer of homeostasis – Emotions and behavior: mediates perception of pleasure, fear, and rage – Regulation of body temperature, blood pressure, digestive tract motility, rate and depth of breathing, and many other visceral activities – Food intake (drives) – Water balance/thirst – Day/night rhythms – Endocrine functions- ADH and oxytocin Structures of the Hypothalamus • Mamillary bodies: – Relay station for olfactory information – control reflex eating movements 19 7/08/12 Pituitary Gland • Major endocrine gland, controls all others • Connected to hypothalamus via infundibulum (stalk) • Interfaces nervous and endocrine systems because it is controlled by the hypothalamus Telencephalon • Basal nuclei • Cerebrum 20 7/08/12 The Basal Nuclei (Ganglia) Figure 14–14b, c Basal Nuclei • Also called basal ganglia • Masses of gray matter found deep within the cortical white matter • The corpus striatum is composed of three parts – Caudate nucleus – Lentiform nucleus = putamen and the globus pallidus – Fibers of internal capsule running between and through caudate and lentiform nuclei • Direct subconscious activities 21 7/08/12 Functions of Basal Nuclei • Are involved with: – Subconscious control of skeletal muscle tone – Regulate attention and cognition – Regulate intensity of slow or stereotyped movements (walking, lifting) – Inhibit antagonistic and unnecessary movement – Subconscious habit learning – May store simple movement patterns Basal Nuclei Figure 12.11b 22 7/08/12 Cerebrum • Largest part of brain (make up 83% of its mass) • Controls higher mental functions including all conscious thoughts and experience including all intellectual functions (more about this later) • Processes somatic sensory and motor information • Divided into left and right cerebral hemispheres • Surface layer of gray matter (cerebral cortex) (Cerebral) Cortex • Gray matter covering cerebral hemispheres • Accounts for 40% of the mass of the brain • Folded surface increases surface area • Elevated ridges = gyri (gyrus) • Shallow depressions = sulci (sulcus) • Deep grooves = fissures 23 7/08/12 Cerebral Gray and White Matter • Gray matter: – Cell bodies – Found in cerebral cortex and basal nuclei • White matter: – Fiber tracts (axons) – Deep to cerebral cortex – Surrounding basal nuclei White Matter of the Cerebrum • Myelinated fibers (axons) – Association fibers: • arcuate: local • longitudinal: within one hemisphere – Commissural: between hemispheres – Projection: link cerebral cortex with rest of CNS Figure 14–13 24 7/08/12 Examples • Projection Fibers: Internal capsule – all ascending and descending projection fibers to and from cerebral cortex, passes though basal nuclei • Commissural fibers: corpus callosum – Connect the two cerebral hemispheres Fiber Tracts in White Matter Figure 12.10b 25 7/08/12 Limbic System Figure 12.18 The Limbic System • One of two networks of neurons working together and spanning wide areas of the brain – the other is the consciousness regulating reticular formation (where?) • A of the medial functional grouping of the medial cerebral hemispheres and diencephalon that: – establishes emotional states and drives – links conscious functions of cerebral cortex with autonomic functions of brain stem – Allows us to react emotionally to conscious understanding and to be aware of emotions – facilitates memory storage and retrieval 26 7/08/12 The Limbic System Figure 14–11a Components of the Limbic System • Amygdala – deals with anger, danger, and fear responses, along with emotional smell memories • Limbic lobe of cerebral hemisphere: – Cingulate gyrus: plays a role in expressing emotions via gestures, and resolves mental conflict (emotion) – Hippocampus: convert new information into long-term memories (patient H.M.?) 27 7/08/12 Components of the Limbic System Continued • Fornix: – tract of white matter that connects hippocampus with hypothalamus • Diencepalic structures: – Portions of thalamus, hypothalamus Reticular Formation Sends impulses to the cerebral cortex to keep it conscious and alert Figure 12.19 28 7/08/12 Higher Level Functions of Cerebral Hemispheres The Cerebral Cortex 4 Lobes: Frontal Parietal Temporal Occipital Figure 14–12b 29 7/08/12 Cerebral cortex • It enables sensation, communication, memory, understanding, and voluntary movements • Temporal lobe: memory, hearing • Frontal lobe: executive function, language • Parietal lobe: sense of self • Occipital lobe: vision Cerebral Cortex landmarks • • • • • • Lateral sulcus Longitudinal fissure Central sulcus Precentral gyrus (primary motor) Postcentral gyrus (primary sensory) Association areas are for integrating information 30 7/08/12 Motor and Sensory Areas of the Cortex • Central sulcus separates motor and sensory areas Figure 14–15a Functional Areas of the Cerebral Cortex • The three types of functional areas are: – Motor areas – control voluntary movement – Sensory areas – conscious awareness of sensation – Association areas – integrate diverse information 31 7/08/12 Functional Areas of the Cerebral Cortex Figure 12.8a Functional Areas of the Cerebral Cortex Figure 12.8b 32 7/08/12 Motor Areas • Precentral gyrus of frontal lobe: – directs voluntary movements • Primary motor cortex: – is the surface of precentral gyrus 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 33 7/08/12 Association Areas • Any brain region that receives input from more than one sensory modality • aka “integrative areas” or higher level association areas • Relative abundance determines intellectual capacity • Include: – Prefrontal cortex – Language areas – General (common) interpretation area – Visceral association area Functional Principles of the Cerebral hemispheres 1. Each cerebral hemisphere receives sensory information from, and sends motor commands to, the opposite side of body 2. The 2 hemispheres have somewhat different functions although their structures are alike 3. Correspondence between a specific function and a specific region of cerebral cortex is not precise 4. No functional area acts alone; conscious behavior involves the entire cortex 34 7/08/12 Higher level: Prefrontal Cortex • Most complicated region, coordinates info from all other association areas • Important in intellect, planning, reasoning, mood, abstract ideas, judgement, conscience, and accuratley predicting consequences • Phineas Gage? Phineas Gage 35 7/08/12 Phineas Gage • In 1848 in Vermont, had a 3.5-foot-long, 13 lb. metal rod blown into his skull, through his brain, and out of the top of his head. Gage survived. In fact, he never even lost consciousness. • Friends reported a complete change in his personality after the incident. He lost all impulse control. “Right Brain – Left Brain” 36 7/08/12 Hemispheric Lateralization • Functional differences between left and right hemispheres • In most people, left hemisphere (dominant hemisphere) controls: – reading, writing, and math, decisionmaking, logic, speech and language (usually) • Right cerebral hemisphere relates to: – recognition (faces, voice inflections), affect, visual/spatial reasoning, emotion, artistic skills Brain Waves • Alpha waves – regular and rhythmic, lowamplitude, slow, synchronous waves indicating an “idling” brain (drifting off) • Beta waves – rhythmic, more irregular waves occurring during the awake and mentally alert state • Theta waves – more irregular than alpha waves; common in children but abnormal in adults • Delta waves – high-amplitude waves seen in deep sleep and when reticular activating system is damped 37 7/08/12 Types of Brain Waves Figure 12.20b Ventricles of the brain 38 7/08/12 Ventricles • Lined by ependymal cells which help to form the choroid plexus • There are two lateral ventricles in the cerebral hemispheres • Third ventricle is located in the diencephalon • Fourth ventricle is located between the pons and the cerebellum Cranial meninges 39 7/08/12 Cranial meninges • Dura mater consists of an outer (endosteal layer) and an inner (meningeal layer) – In between the layers find the dural sinus • Arachnoid membrane covers the surface of the brain, have a subarachnoid space • Pia mater is anchored to the brain by astrocytes, wraps brain tightly like saran wrap Inter-Layer Spaces – just like in the brain • Subdural space: – between arachnoid mater and dura mater • Subarachnoid space: – between arachnoid mater and pia mater – contains collagen/elastin fiber network that’s “spiderweb-like” (arachnoid trabeculae) – filled with cerebrospinal fluid (CSF) àSubdural, subarachanoid spaces are frequent sites of intracranial bleeding 40 7/08/12 Cerebrospinal Fluid (CSF) • • • • Surrounds all exposed surfaces of CNS Cushions, supports, and transports Interchanges with interstitial fluid of brain Like plasma or interstitial fluid elsewhere except much more pure • Arachnoid villi protrude superiorly into dural sinus and permit CSF to be absorbed into venous blood Choroid Plexuses • Clusters of capillaries lined by ependymal cells that form tissue fluid filters, which hang from the roof of each ventricle • Have ion pumps that allow them to alter ion concentrations of the CSF • Help cleanse CSF by removing wastes 41 7/08/12 CSF flow: through ventricles, to arachnoid space, to dural sinuses (back to circulation) Blood Supply to the Brain • Supplies nutrients and oxygen to brain • Delivered by internal carotid arteries and vertebral arteries • Removed from dural sinuses by internal jugular veins 42 7/08/12 Blood–Brain Barrier • Isolates CNS neural tissue from general circulation • Formed by network of tight junctions between endothelial cells of CNS capillaries and by feet of astrocyte processes • Astrocytes control blood–brain barrier by releasing chemicals that control permeability of endothelium Blood–Brain Barrier • Lipid–soluble compounds (O2, CO2), steroids, and prostaglandins diffuse into interstitial fluid of brain and spinal cord • Other things have to be transported in 43 7/08/12 Cerebrovascular Disease • Disorders interfere with blood circulation to brain • Stroke or cerebrovascular accident (CVA): – shuts off blood to portion of brain – neurons die • Tissue plasminogen activator (TPA) is the only approved treatment for stroke (except aspirin) • Transient Ischemic Attach (TIA) Degenerative Brain Disorders • Alzheimer’s disease – a progressive degenerative disease of the brain that results in dementia (usually frontotemporal) • Parkinson’s disease – degeneration of the dopamine-releasing neurons of the substantia nigra • Huntington’s disease – a fatal hereditary disorder caused by accumulation of the protein huntingtin that leads to degeneration of the basal nuclei 44