Advanced Human Physiology - The Central Nervous System PDF

Advanced Human Physiology Chapters 8 The Central Nervous System Lectures by Glorimar Aponte-Kline M.D. Utah Tech University  Spinal Cord The CNS consists of the brain and the spinal c...

Advanced Human Physiology Chapters 8 The Central Nervous System Lectures by Glorimar Aponte-Kline M.D. Utah Tech University  Spinal Cord The CNS consists of the brain and the spinal cord. Spinal cord is protected by: 1) Vertebrae –spinal cord located within the vertebral canal. 2) Meninges- surround spinal cord. Consists of dura mater, arachnoid mater, pia mater. Spinal Cord consists of : 1) Spinal nerves - 31 pairs - part of PNS - at each vertebra, two spinal nerves come off; one to left side and one to right side. - Each spinal nerve carries sensory afferent axons and motor efferent axons. - contain a dorsal root and ventral root. - connect spinal cord to sensory receptors and effectors (muscles & glands) 2) 4 Regions are cervical, thoracic, lumbar and sacral Copyright © 2019 by John Wiley & Sons, Inc. All rights reserved. Organization of Spinal Cord Tissues of CNS are divided into: a. Gray matter consists of: Unmyelinated axons mostly cell bodies and dendrites of neurons - Nuclei are clusters of neuron cell bodies (similar in function) in the CNS - Ganglion is a cluster of neuron cell bodies (similar in function) in periphery (PNS) neuroglia Central canal filled with cerebral spinal fluid Function is mostly integrative b. White matter consists of: Myelinated axons Tracts groups of axons bundled together that are sending AP’s to other groups of neurons. They run from a given area to another area within the brain or spinal cord (CNS). - contain very few cell bodies Corpus Callosum: axons that cross between the hemispheres of cerebrum Function is mostly to conduct either sensory or motor information to another part of the nervous system, or body.  Organization of Spinal Cord Gray matter- subdivided into horns. 1) Dorsal gray horn – contain axons of sensory neurons & axons & cell bodies of interneurons 2) Lateral gray horn- contain cell bodies of autonomic motor neurons 3) Ventral gray horn- contain cell bodies of somatic motor neurons White matter –divided into columns which contain tracts ( bundles of axons) 1) Dorsal white column 2) Ventral white column 3) Lateral white column 4) Sensory tracts 5) Motor tracts Processing of Sensory Input and Motor Output  Sensory and Motor Tracts Sensory Tracts: 1) Doral Columns- touch, pressure, vibration, and proprioception. 2) Spinothalamic Tract- pain, temperature, itch, and tickle. 3) Dorsal & Ventral Spinocerebellar Tract- proprioception. Motor Tracts: 1) Direct Motor (Pyramidal)Pathway –cause voluntary movement of skeletal muscle. (a) lateral corticospinal tract (b) ventral corticospinal tract (c) corticobulbar tract 2) Indirect Motor (Extrapyramidal)Pathway- cause involuntary movements that regulate posture, balance, and muscle tone (a) tectospinal tract (b) vestibulospinal tract (c) rubrospinal tract (d) lateral and medial reticulospinal tract Reflexes Reflex – a fast, predictable Sensory information may be sent to brain Reflex sequence of involuntary Arc actions that occurs in stimulu response to a particular s sequence. In a spinal reflex, sensory information entering the spinal cord is acted on without input from the brain. However, sensory information about a stimulus may be sent to the brain. Brain Each Cerebral hemisphere is divided into four lobes: Frontal, Parietal, temporal, occipital Parietal Lobe Frontal Lobe Occipital Lobe Temporal Lobe  Protective coverings of the Brain Cranium- serves as protective armor for the brain. Meninges: Dura, Arachnoid, Pia mater –surround the brain and act as shock absorber. Blood Brain Barrier –formed by capillary endothelial cells that are extensively interconnected by tight junctions. - Only lipid soluble substances and water can diffuse across endothelial cell membrane and into ISF of brain and spinal cord. - Passive or active transport mechanisms are required for water-soluble compounds to Cerebrospinal fluid (CSF) Cerebrospinal fluid (CSF): CSF secreted by choroid plexus, regions composed of capillaries and ependymal glia cells in wall of lateral ventricles, third ventricle and fourth ventricle 80-150 ml volume and volume replenished 3X a day Contains glucose, proteins lactic acid, some leukocytes, urea, Na+, K+, Ca+2, Mg+2, Cl-, HCO3- It provides mechanical protection – shock absorber It provides chemical protection -optimal chemical environment for accurate neuronal signaling. It provides circulation- allows exchange of nutrient and waste between blood and neural tissue Once formed, CSF flows into four interconnected ventricles, and also through spinal cord central canal and into subarachnoid space over the entire surface of brain and spinal cord. CSF is reabsorbed back into circulatory system at venous sinuses. Abnormality in CSF drainage Hydrocephalus is a condition where normal drainage of CSF is blocked so that fluid volume and pressure rises, and damages the brain. Correction of Hydrocephalus Shunt takes excess CSF from ventricle to central canal in spinal cord where it will eventually drain back to venous sinus and back into circulatory system ….and then excess fluid eventually eliminated from body as urine. Parts of the Brain Corpus Callosum  The Brain: The Brain Stem Brain Stem (medulla, pons midbrain) 2. Pons portion of brainstem is transition from spinal cord to higher bulbous protrusion above medulla brain centers. Relay station from each side of 1. Medulla Oblongata is transition cerebellum to and from cerebral from spinal cord to brain proper cortex. crossover of tracts between spinal Nuclei influence respiration cord and cerebral cortex = Pyramids 3. Midbrain(mesencephalon) small area Nuclei control involuntary functions: between lower brain stem and diencephalon. Includes superior and 1) heart rate and blood Inferior colliculus. pressure Eye movements 2) respiration Some auditory reflexes 3) swallowing Some visual reflexes 4) vomiting Parts of the Brain Cerebellum Movement coordination- execute voluntary movements by modifying skeletal muscle activity. Regulates posture and balance. Equilibrium and balance- from inner ear receptors Cerebellar dysfunction: patients experience problems in walking, balance and accurate hand and arm movement. Diencephalon Thalamus: relay station and integration of sensory input allows crude sensations of pain, temperature and pressure Hypothalamus: control of homeostasis, hunger, thirst, endocrine function. Pituitary- production and secretion of hormones Pineal gland-”circadian rhythms”, secretes melatonin Circadian rhythm: 24 hour light-dark cycle Suprachiasmatic nucleus (SCN) of the hypothalamus- has intrinsic activity that is synchronized with the sensory information (light cycles) received thru the eyes. Melatonin (pineal gland) linked to circadian rhythms disrupted by shift work and jet lag Shift of light-dark cycles causes sleep disturbances, depression, seasonal affective disorder, diabetes, obesity. Parts of the Brain Corpus callosum connects the two hemispheres: axons passing from one side of cerebral hemisphere to the other. Gray matter is divided into 3 major regions: 1. Cerebral cortex- outer layer of cerebrum 2. Basal ganglia (basal nuclei):control of movement, suppress unwanted movement, and regulate muscle tone: Parkinson’s disease 3. Limbic system: link between higher cognitive functions(reasoning) and emotions(pleasure, pain, aggression, affection, fear and anger). Major areas are: Amygdala & cingulate gyrus: emotion and memory Hippocampus: learning and memory Components of the Limbic System Parkinson’s disease: Destruction of basal nuclei neurons that produce neurotransmitter called dopamine. Dopamine levels are low. Patients show increased muscle tone and rigidity. Patients are slow to initiate a movement and slow or stop a movement. Oral or injectable dopamine is ineffective because it is unable to cross BBB. Treatment: Giving Dopamine precursor called” L-dopa” can cross BBB because it is carried across the BBB on an amino acid transporter into ISF and neurons metabolize it to dopamine, thus restoring blood levels of dopamine. Most recent treatments involves implantation of fetal stem cells which can establish and grow and start producing dopamine.  The Brain: The Brain Stem Oldest region of the brain Consists of the medulla, pons and midbrain 11 of 12 cranial nerves originate from the brain stem (CN II - XII), CN I enters forebrain. Cranial nerves can include sensory nerves (contain only axons of sensory neurons), motor nerves (contain only axons of motor nerves), or mixed nerves for the head, neck, and many organs in the thoracic and abdominal cavities. Many nuclei are associated with reticular formation (Reticular Activating System) it is a web of interconnected neurons, starting in the brain stem and running throughout the brain. “keeps conscious brain awake” Controls wakefulness, sleep, muscle tone, pain modulation Other nuclei in brain stem control stretch reflexes, breathing and blood pressure. Integrative Functions: Reticular Activating System (RAS) RAS (Reticular Activating System) Neurons here originate in the reticular formation of the brainstem and project their axons to large areas of the brain. Arousal or awakening from sleep involves increased RAS activity. Arousal- sensory stimuli activate RAS which activates cerebral cortex resulting in consciousness (wakefulness).  Brain Function: Cerebrum (cerebral cortex) Cerebrum is the largest part of the brain. It provides us with intelligence. From a functional viewpoint, it can be divided into three specializations Sensory areas Sensory input translated into perception (awareness) Motor areas Direct skeletal muscle movement Association areas Integrate information from sensory and motor areas Can direct voluntary behaviors (see next slide) Functional differences between the two cerebral Hemispheres. Called a Hemispheric lateralization ( cerebral dominance)-left brain- right brain dominance Functional areas of the cerebral cortex  Brain Function: Sensory Information Special senses have devoted regions of the brain: Primary visual cortex- Occipital lobe -receives information from the eyes(vision) Primary auditory cortex- Temporal lobe- receives information from the ears (sound) Olfactory cortex- Temporal lobe – receives information from chemoreceptors in nose(smell) Gustatory cortex- in insula - receives information from the taste buds Neural pathways extend from sensory areas to association areas, which integrate stimuli into perception  Brain Function: Sensory Information Integration of spinal reflexes- information entering spinal cord is acted without input from the brain, but sensory information about stimulus can be sent to the brain creating perception of the stimulus. Primary somatic sensory cortex (AKA somatosensory cortex, sensory strip, post-central gyrus) located in parietal lobe. Termination point of pathways from skin, musculoskeletal system, and viscera Somatosensory pathways carry information about: Touch Temperature Pain Itch Vibration Body position (proprioception) Cross over of ascending axons: left hemisphere receives somatic sensations from right side and vice versa. Damage to somatosensory cortex : reduced sensitivity of skin on opposite side of body Functional areas of the cerebral cortex Brain Function: Motor System Three major types of motor output: Skeletal muscle movement Somatic motor division Neuroendocrine signals- neurohormones secreted into blood by neurons in: Hypothalamus and adrenal medulla Visceral responses Autonomic division-smooth, cardiac muscles, or glands Brain Function: Motor System Voluntary movement originate in: Primary motor cortex (aka: motor strip, pre-central gyrus, motor association area) located in the frontal lobe. Premotor cortex ( Motor association area) -Receives input from primary motor cortex and executes specific sequences of muscle contractions and remembers such movements. Cross over of descending axons (somatic motor tracts): left hemisphere controls skeletal muscles in right side of body and vice versa. Damage to primary motor cortex : affects motor function on opposite side of body Brian Function: Homunculus Hemispheric lateralization ( cerebral dominance)-left brain-right brain dominance  Brain Function: Language Wernicke’ s Broca ’s Integration of spoken language involves two regions: Wernicke’s area : at junction of parietal and temporal lobes. Translates words into thoughts. Broca’s area: in posterior part of frontal lobe, close to motor cortex. Translates thoughts into speech. Damage to Wernicke’s area causes receptive aphasia = unable to understand spoken or written communication-nonsense speech because unable to retrieve words. Damage to Broca’s area causes expressive aphasia = are able to understand spoken or written communication but are unable to respond appropriately – speech is words strung together in random order. Language Processing Neural Pathway for Language Production. 1. Information about a word is conveyed to Wernicke’s area. If the word is written, Wernicke’s area receives input about the word from the primary visual cortex. If the word is spoken, Wernicke’s area receives input about the word from the primary auditory cortex. 2. Once Wernicke’s area receives this information, it translates the written or spoken word into the appropriate thought. 3. For a person to say this word, Wernicke’s area transmits information about the word to Broca’s area. 4. Broca’s area receives this input and then develops a motor pattern for activation of the muscles needed to say the word 5. The motor pattern is conveyed from Broca’s area to the primary motor cortex, which subsequently activates Integrative Function: Sleep Sleep is defined as easily reversible state of inactivity without external environment interaction. See (next slide) Four stages with two major phases Non-Rapid eye movement (NREM) sleep - high amplitude, low frequency waves Adjusts body positions without conscious commands from brain Rapid eye movement (REM) sleep - low amplitude , high frequency waves Brain activity inhibits motor neurons to skeletal muscle, paralyzing them- vision and respiratory not affected. Dreaming takes place Integrative Function: Sleep NREM Sleep Stages progresses from stage 1 to stage 4. Stage 1: is a transition stage between wakefulness and sleep. The person is relaxed with both eyes closed and has fleeting thoughts. People awakened during this stage often say that they have not been asleep. Stage 2 or light sleep: is the first stage of true sleep. It is easy to awaken a person. Stage 3: is a period of moderately deep sleep. It is a little more difficult to awaken a person. Stage 4 or slow-wave sleep: is the deepest level of sleep. It is very difficult to awaken a person. Intervals of NREM and REM alternate through the night. Person falls asleep by sequentially going through all four stages of NREM sleep in about 45 min. Then NREM in reverse order before entering REM sleep. During an 8 hour sleep period, there are 4 -5 NREM-REM cycles Brain Function: Sleep Sleep disorders Insomnia: inability to sleep Sleep apnea: stopping normal breathing during sleep Somnambulism: sleepwalking, most common in children