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Central Nervous System (CNS) Part 3: Integration & Control Central Nervous System Central Nervous System (CNS): The portion of the nervous system made up of the brain and spinal cord. Acts as the Central Processing Unit (CPU) of the human nervous system. Incoming data is processed and coordinated Outgoing data is developed and sent out to the rest of the body Four C’s of the CNS: Communicate Command Control Coordinate The Brain 4 Major Parts of the Brain: Cerebrum: The largest part of the brain, controls complex activities, including complex motor control. Cerebellum: Controls muscle movements, regulates posture & balance, and plays a role in cognition. Diencephalon: Relays sensory information to the cerebrum & controls the Autonomic Nervous System (ANS). Brain Stem: Relays motor impulses, is involved in vital system control, & contributes to sensory organ control. Protecting The Brain Skull: Provides physical protection from traumatic injury. Blood-Brain Barrier: Prevents the passage of harmful substances from the blood stream into the brain. Created by a tight junction between the capillary cells & by astrocytes. Permeable to lipid-soluble substances (O2, CO2, alcohol, anesthetics). Protecting The Brain Meninges: 3 layers of protective coverings surrounding the brain & spinal cord. Dura Matter: Outermost layer Subdural Space: Separates the dura & arachnoid matter. Arachnoid Matter: Middle layer Subarachnoid space: Separate the arachnoid & pia matter. Pia Matter: Innermost layer Protecting the Brain Cerebrospinal Fluid (CSF): Clear liquid contained within the skull & spinal column to protect the CNS from chemical and physical injury. Contained within 4 ventricles: Lateral Ventricles: One on each side of the brain. Third & Fourth Ventricles: Connected through the cerebral aqueducts. Choroid Plexuses: Networks of capillaries in the walls of the ventricles where CSF is produced. Arachnoid Villi: Location where CSF is reabsorbed and dumped into the brain's sinus cavities for drainage. Hydrocephalus: Marked by a failure to drain CFS, resulting in increased intracranial pressure. Brain Blood Flow Blood flow to the brain requires 20% of the body’s oxygen & glucose. 4 minutes of oxygen deprivation is enough to cause irreversible brain damage. Embryonic Development Ectoderm: The tissue layer that develops into the neural plate. Neural Plate: Flat layer of nervous tissue that will then develop into the neural tube. Neural Tube: The neural plate rolls into the neural tube that develops into the brain & spinal cord. “Head” end develops into three primary areas/primary brain vesicles: Prosencephalon develops into the forebrain Mesencephalon develops into the midbrain Rhombencephalon develops into the hindbrain These three primary brain vesicles will develop into secondary vesicles that will in turn develop into all of the parts of the brain. The Brain Stem Brain Stem: The area of the brain which lies between the spinal cord and the diencephalon. Composed of 3 regions: Medulla Oblongata Pons Midbrain Retuicular Formation: A network of grey & white matter interspersed & extending throughout the brainstem. Functions to maintain muscle tone & arouse us from deep sleep! The Brain Stem Medulla Oblongata: Regulates vital body functions and nonvital functions. Located directly above the spinal cord. Vital functions: heartbeat and breathing. Nonvital functions: Reflexes, controlling sneezing, coughing, hiccuping, sweating, vomiting. Pyramids: Projections of white matter formed by the motor tracts passing into the spinal cord from the cerebrum. Most of these decussate (cross) to the opposite side. The Brain Stem Pons: Relays impulses between the medulla & midbrain. Contains origins of the Cranial Nerves 5-8. Contains pneumotaxic & apneustic areas which help to control breathing. The Brain Stem Midbrain (Mesencephalon): Relays…. Motor impulses from cerebral cortex to pons Sensory impulses from the spinal cord to the thalamus Superior collicili coordinates eye movements with incoming visual stimuli Inferior colliculi coordinates head and trunk movements with auditory stimuli Contains the origins of Cranial Nerves 3 & 4 The Cerebellum Cerebellum: The 2nd largest part of the brain that actually contains half of the CNS’s total neurons. Divides into… Considered part of the hindbrain Coordinates skilled movement May play a role in learning, cognition, & language processing. Right Cerebellar Hemisphere Left Cerebellar Hemisphere Vermis: Connects the right & left cerebellar hemispheres to the brainstem via 3 pairs of cerebellar peduncles. Folia: Ridges lining the outer gray matter of the cerebellum. Flocculonodular Lobe: Maintains posture & balance Diencephalon Diencephalon: The part of the forebrain extending from the brain stem to the cerebrum Plays a crucial role in the vital systems of the human body Primarily responsible for sensory relay & controlling the autonomic nervous system (ANS) Made up of 4 parts: Thalamus Hypothalamus Epithalamus Subthalamus Thalamus Comprises 80% of the diencephalons Considered the “Gateway to the Cerebral Cortex” Located in the very center of the brain. Nearly all incoming sensory information passes through the Thalamus. Primary relay station for sensory data Responsible for crude perception of touch, pressure, pain, & temperature, & helps regulate some autonomic activities. Contributes to motor function as well. Hypothalamus Located inferior to the thalamus Major control center for the autonomic nervous system & the endocrine system. Regulates many basic body functions & is crucial to maintaining homeostasis. Includes food & water intake, temperature, circadian rhythms, & emotional & behavioral patterns. Also produces hormones critical to homeostasis Control center of the Autonomic Nervous System Regulates the gastrointestinal tract, urinary tract, & cardiovascular system Epithalamus Superior & posterior to the thalamus. Consists of the… Pineal Gland: Endocrine gland that secretes hormones (including melatonin) Habenular Nuclei: Involved in olfaction (smell) and especially the emotional response to odors. Subthalamus Located directly below the thalamus Controls body movement Contains nuclei that work together with the basal ganglion cerebellum The Cerebrum Cerebrum: Largest part of the brain & the part we use the most for cognition. Divided into 2 hemispheres: Responsible for all the higher brain functions Gyri: Convolutions/folds that increase the surface area – the result of gray matter forming more rapidly than white matter during the embryonic stage. Right Cerebral Hemisphere Left Cerebral Hemisphere Longitudinal Fissure: Divides the two hemispheres of the cerebrum. Corpus Collosum: Broad band of white matter containing axons that connect the two halves of the brain & allow for communications between the hemispheres. The Cerebrum Each hemisphere is divided into 5 functional regions/lobes by… Fissures: Deep grooves Sulci: Shallow grooves 5 Lobes: Frontal Lobe Parietal Lobe Occipital Lobe Temporal Lobe Insula The Cerebrum Central Sulcus: Valley thatr runs from side to side across both central hemispheres. This is the area of separation between the motor and sensory cortex. Postcentral Gyrus: Primary somatosensory area located in the parietal lobe. Precentral Gyrus: Primary motor area contained in the frontal lobe. Contralateral: The left hemisphere coordinates the muscle movement of the right side of the body beginning below the neck and vice versa. The Cerebrum Cerebral Cortex: Outer portion of the brain comprised of gray matter. Gray Matter: Contains mainly nerve cell bodies and unmyelinated fibers. Cerebral cortex is made up of two kinds of neurons: Stellate Cells: Rceive sensory imput and project it for short distances. Pyramidal Cells: Acts as the output neurons of the cerebelum. The Cerebrum The cerebellum contains white matter underneath the cerebral cortex. White Matter: Contains mainly myelinated axons and appears to be white. Contains axons in 3 types of tracts: Association Tracts: Conduct impulses between gyri located in the same hemisphere. Commissural Tracts: Conduct nerve impulses from gyri in one hemisphere to corresponding gyri in the other hemisphere. Projection Tracts: Conduct nerve impulses from the cerebrum to the lower portions of the CNS. The Cerebrum Basal Nuclei or Basal Ganglia: Masses of gray matter buried deeply in the cerebral hemisphere. This is an exception to the rule that ganglia are located outside the CNS! These form the areas that contribute to motor control: Globus Pallidus Corpus Seriatum Putamen Caudate Nucleus Cerebral Cortex Areas Divided into 3 basic areas based on function: Sensory Areas: Receive & interpret sensory impulses. Association Areas: Handle the more complex integrative functions, e.g. emotion, memory, intellegence, reasoning, judgement, and personality traits. Motor Areas: Initiate movement. Functional Areas of the Cerebral Cortex Broca’s Area: Controls the planning and production of speech. Localized in the left frontal lobe. Wernicke’s Area: Interprets the meaning of speech by recognizing spoken words and turning them into thoughts & adding emotional content. Localized to the temporal and parietal lobes. Primary Visual Area #17: Recieves impulse messages for vision. Primary Auditory Areas #41 & #42: Interprets pitches, rhythm, and the basic characteristics of sound. Primary Gustatory Area #43: Receives impulses for taste. The Limbic System Limbic System: Composed of a ring of structures that encircle the upper part of the brainstem & the corpus collosum. Two primary nuclei: Amygdala: Important in the regulation of emotions. Hippocampus: Important in memory functions. Contains the olfactory bulbs. Limbic system considered the “emotional brain”. Hemispheric Lateralization The two hemispheres tend to be similar in structure and function. Each have specializes in certain functions. Right Hemisphere: Musical and artistic ability, space and pattern recognition, emotional content of language, odor discrimination. Left Hemisphere: Numeric & scientific processes, spoken and written language, logical reasoning. Lateralization is somewhat less pronounced in females than males. Brain Waves Brain Waves: Electrical signals from action potentials that occur rhythmically and can be detected by electrodes & recorded by electroencephalogram (EEG). 4 Categories of Brain Waves: Alpha: Produced when awake but resting with eyes closed, not present during sleep. Beta: Present when nervous system is active & person is engaged in awake mental activity. Delta: Present in awake infants and sleeping adults, indicative of brain damage in awake adults. Theta: Present in children & adults during emotional stress, may be a sign of brain disorder. Brain Death: A complete absence of brain waves. Higher Brain Functions Sleep: Hypothalamus controls the need for sleep while the brainstem controls sleep patterns. Rapid Eye Movements: Period of sleep in which the eyes track in a set pattern and dreaming occurs. Cognition: Association areas responsible for awareness, thinking, assimilating knowledge. Processed in the parietal, temporal and frontal lobes. Emotion: Prefrontal cortex helps control emotions, but hypothalamus and amygdala provide emotional source. Sensation: Postcentral gyrus is the primary somatosensory area, but cerebral cortex contains specific sense areas. Motor Control: Precentral gyrus is the primary motor area. Higher Brain Functions Memory: Hippocampus and limbic system responsible for consolidation and housing of the long-term memories. Amnesia: Anterograde Amnesia: Inability to store new information. Retrograde Amnesia: Inability to recall previously known information. Alzheimer’s Disease: Loss of the neurons secreting acetylcholine, beta-amyloid pllaques, and neurofibrillary tangles causes memory loss, confusion, developmental regression, and personality changes. Affects more than 10% of elderly over 65 years of age. Is the 4th leading cause of death among the elderly as the ANS systems degrade. Spinal Cord Spinal Cord: The outer portion of the CNS that functions in propagating impulses, integrating information, and processing reflexes. Spinal Nerves: Connect the sensory receptors to the CNS. Divisions: Divides into cervical, thoracic, lumbar, & sacral regions just like the vertebral column. Major Structures of the Spinal Cord Foramen Magnum: Opening at the base of the skull where the spinal cord begins & attaches to the medulla oblongata. Second Lumbar Vertebra (Superior Border): Where the spinal cord ends. Meninges: Layers of protective membrane surrounding the spinal cord. Dura Matter, Arachnoid Matter, & Pia Matter separated by the subdural & subarachnoid spaces. Cervical & Lumbar Enlargements: Points where the spinal cord connects to the nerves that lead out to the appendages. Major Spinal Cord Structures Conus Medullaris: The tapering ends of the spinal cord between the 1st & 2nd lumbar vertebrae. Cauda Equina: The “horse’s tail” comprised of a bundle of nerve roots extending downward from the end of the cord. Epidural Space: The space between the dura matter and the wall of the vertebral canal. Internal Anatomy of the Spinal Cord Under a cross section of the internal gray matter we can see… 2 Dorsal Horns (Posterior Horns): Contain somatic and autonomic sensory nuclei 2 Ventral Horns (Anterior Horns: Contain motor neurons. Gray Commisure: Connects the left & right halves of the spinal cord. Central Canal: A central canal filled with cerebrospinal fluid. Internal Anatomy of the Spinal Cord Under a cross section of the external white matter we can see.. Anterior Columns Posterior Columns Lateral Columns Each column contains tracts of axons.. Ascending Tracts: Carry sensory impulses toward the brain. Examples: Gracile fasciculus, cuneate fasciculus, dorsal & ventral spinocerebellar tracts, spinothalamic tract. Descending Tracts: Carry motor impulses from the brain. Examples: Corticospinal tracts, lateral & medial reticulospinal tracts, vestibulospinal tract, tectospinal tract. Spinal Nerves Technically part of the perepheral nervous system. 31 total pairs (62 nerves total): Each nerve provides a path for communication between the cord and the region of innervation,. Consists of two roots (bundles of axons). Posterior (Dorsal) Root: Contains sensory axons. Anterior (Ventral) Root: Contains motor neurons. Nerves correspond to the region and level of the vertebral column they extend from. E.g. thoracic nerves emerge through the intevertebral foramina between the thoracic vertebra. Protecting The Nerves Cranial & Thoracic Nerves have protective coverings. Endoneurium: Wraps around an individual axon. Perineurium: Wraps around fascicles (bundles of neurons). Epineurium: Wraps around the entire nerve fiber. Branches of the Spinal Nerves Rami: Divisions/branches of the spinal nerves. Two types: Anterior Rami & Posterior Rami Plexus: A joining of the anterior rami and the adjacent neurons, which then branch to serve a region of the body. Most important plexuses: Cervical Plexus: Serves the skin & muscles in the head, neck, shoulders & chest. Ex. Phrenic nerve. Brachial Plexus: Serves the shoulders & upper limbs. Ex. Axillary nerve. Lumbar Plexus: Serves the abdominal wall, genitals, & parts of the lower limbs. Ex. Femoral nerve. Sacral & Coccygeal Plexuses: Serve the buttocks, perineum, & lower limbs. Ex. Sciatic nerve (largest in the body). Intercostal Nerves: Spinal nerves T2-T12 do not form plexuses, and innervate the intercostal spaces. Reflexes Reflex: A fast, involuntary action that occurs in response to a stimuli. Inborn Reflexes: Ones we’re born with! Learned Reflexes: Ones we have to actively learn to integrate. Ex. Pulling away from heat Ex. Slamming on car breaks. Spinal Reflexes: Reflexes that are controlled by the spinal cord. Somatic Reflexes: Reflexes that involve skeletal muscles. Autonomic Reflexes: Reflexes that involve the viscera. Cranial Reflexes: Reflexes that are controlled by the brainstem. Reflexes Reflex Arc: The pathway the nerve impulses take to produce a reflex. Begins in the somatic receptors Travels across the afferent nerve fibers to interneurons Travels from the interneurons across the efferent nerve fibers to the appropriate skeletal muscle. Reflexes 5 Parts of a Reflex Arc: Sensory Receptor: Serves as a sensory receptor. Sensory Neuron: Nerve impulses travel along the axon terminal of the sensory neuron to the axon terminals Integrating Center: A single synapse between a sensory & motor neuron. Motor Neuron: Impulses from the integrating center travel along the motor neuron to the part of the body that needs to respond. Effector: The part of the body that responds to the motor nerve impulse, e.g. the muscle cell or the gland. Reflexes Most common reflexes: Stretch Reflex: Contraction of skeletal muscle in response to the stretching of the muscle. Golgi Tendon Reflex: Tension applied to a tendon will cause relaxation of the muscle. Prevents muscle & tendon damage when muscle force is too extreme. Flexor Reflex: Withdrawal of a limb in response to pain stimuli. E.g. knee joint flexing when tapped with a hammer E.g. rapidly removing hand from hot stove Crossed Extensor Reflex: Contraction of muscles in the limb opposite of the one experiencing a painful stimulus. Contralateral reflex allows the body weight to shift as the supporting limb is withdrawn. Poliomyelitis Poliomyelitis (Polio): Caused by a virus that destroyes motor neurons in the spinal cord & nuclei in the cranial nerves. Results: Paralysis & loss of reflexes