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Nervous system part 2 Central Nervous System (CNS) Cephalization Evolutionary development of the anterior portion of the CNS Increases the number of neurons in the head Highest level is reached in the human brain The brain Embryonic Neural development plate forms from ectoderm Neural plate invaginates to form a neural groove and neural folds Neural groove fuses dorsally to form the neural tube Anterior portion of the neural tube becomes three primary brain vesicles Prosencephalon-forebrain Gives rise to the telencephalon (cerebrum) and diencephalon (thalamus, hypothalamus, epithalamus, and retina) Mesencephalon- midbrain Rhombencephalon- Gives hindbrain rise to the metencephalon (pons and cerebellum) and myelencephalon (medulla oblongata) The brain Effect of space restriction on brain development Midbrain flexure and cervical flexure cause forebrain to move toward the brain stem Cerebral Cerebral hemispheres grow posteriorly and laterally hemisphere surfaces crease and fold into convolutions Regions and organization Adult brain regions Cerebral hemispheres Diencephalon Brain stem (midbrain, pons, and medulla) Cerebellum Regions and organization Spinal cord Central cavity surrounded by a gray matter core External white matter composed of myelinated fiber tracts Regions and organization Brain Similar pattern with additional areas of gray matter Nuclei in cerebellum and cerebrum Cortex of cerebellum and cerebrum Ventricles of the brain Contain cerebrospinal fluid Two C-shaped lateral ventricles in the cerebral hemispheres Third ventricle in the diencephalon Fourth ventricle in the hindbrain, dorsal to the pons Cerebral hemispheres Surface markings: ridges (gyri), shallow grooves (sulci), and deep grooves (fissures) Central sulcus- separates the precentral gyrus of the frontal lobe and the postcentral gyrus of the parietal lobe Longitudinal Transverse fissure- separates the two hemispheres cerebral fissure- separates the cerebrum and the cerebellum Cerebral hemispheres Lobes Frontal Parietal Temporal Occipital Insula Cerebral hemispheres Cerebral Thin 40% cortex superficial layer of gray matter of the mass of the brain Site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding Each hemisphere connects to the contralateral side of the body Left controls language, math, and logic Right controls insight, visual-spacial skills, intuition, and artistic skill Lateralization of cortical function in the hemispheres Cerebral hemispheres Functional areas Motor areas- control voluntary movement Primary motor cortex- conscious control of precise, skilled, voluntary movements Premotor cortex- controls learned, repetitious, or patterned motor skills Broca’s area- motor speech area the directs muscle of the tongue Frontal eye fold- controls voluntary eye movement Cerebral hemispheres Sensory areas- conscious awareness of sensation Primary somatosensory cortex- Capable of spatial discrimination: identification of body region being stimulated Somatosensory association cortex- Determines size, texture, and relationship of parts of objects being felt Visual areas- Receives visual information from the retinas Auditory areas- Interprets information from inner ear as pitch, loudness, and location, stores memories of sounds and permits perception of sounds Olfactory cortex- Region of conscious awareness of odors Gustatory cortex- Involved in the perception of taste Visceral sensory area- Conscious perception of visceral sensations, e.g., upset stomach or full bladder Vestibular cortex- Responsible for conscious awareness of balance (position of the head in space) Cerebral hemispheres Association areas- integrate diverse information Multimodal association area- receive input from multiple sensory areas, and sends output to multiple areas Anterior association area- Involved with intellect, cognition, recall, and personality, contains working memory needed for judgment, reasoning, persistence, and conscience, development depends on feedback from social environment Posterior association area- Plays a role in recognizing patterns and faces and localizing us in space, involved in understanding written and spoken language (Wernicke’s area) Limbic association area- Provides emotional impact that helps establish memories Diencephalon Encloses Three the third ventricle parts 1. Thalamus- 80% of the diencephalon, sorts, edits, and relays information 2. Hypothalamus- autonomic control center for many visceral functions: blood pressure, rate and force of heartbeat, digestive tract motility. Center of emotional response. Regulates body temperature, food intake, water balance, and thirst. Regulated sleep and sleep cycle, controls release of hormones from the pituitary gland 3. Epithalamus- secretes melatonin that regulates sleep cycle Brain stem Midbrain- control cranial nerves III (oculomotor) and IV (trochlear) Pons- Connect higher brain centers and the spinal cord, Relay impulses between the motor cortex and the cerebellum Medulla oblongata- Autonomic reflex centers, adjusts force and rate of heart contraction, adjusts blood vessel diameter for blood pressure regulation, generate respiratory rhythm, control rate and depth of breathing, regulate, vomiting, hiccupping, swallowing, coughing, sneezing Cerebellum Subconsciously provides precise timing and appropriate patterns of skeletal muscle contraction Receives impulses from the cerebral cortex of the intent to initiate voluntary muscle contraction Recognizes and predicts sequences of events during complex movements Plays a role in non-motor functions such as word association and puzzle solving Functional brain systems Limbic system Emotional or affective brain Amygdala—recognizes angry or fearful facial expressions, assesses danger, and elicits the fear response Cingulate gyrus—plays a role in expressing emotions via gestures, and resolves mental conflict Puts emotional responses to odors- Example: skunks smell bad The limbic system interacts with the prefrontal lobes, therefore: We can react emotionally to things we consciously understand to be happening We are consciously aware of emotional richness in our lives Hippocampus and amygdala—play a role in memory Functional brain systems RAS (reticular activating system) Sends impulses to the cerebral cortex to keep it conscious and alert Filters out repetitive and weak stimuli (~99% of all stimuli!) Severe injury results in permanent unconsciousness (coma) Motor function Helps control coarse limb movements Reticular autonomic centers regulate visceral motor functions: Vasomotor, Cardiac, Respiratory centers The 12 Pairs of Cranial Nerves Figure 14.8 I. Olfactory sense of smell II. Optic sight III. Occulomotor move eyelids IV. Trochlear move eyes V. Trigeminal face, jaw, chewing VI. Abducens eyes VII. Facial facial expressions VIII. Vestibulocochlear (Auditory) sense of equilibrium, hearing IX. Glossopharyngeal pharynx, tongue X. Vagus major organs, viscera XI. Accessory shoulders XII. Hypoglossal tongue Need to know all of the cranial nerves ? On Old October Third The Airplane Flew Above Ground Very Aggressively Home Higher mental functions Brian wave patterns and the EEG EEG- record electrical activity that accompanies brain function and measures electrical potential differences between cortical areas. Used to diagnose and localize brain lesions, tumors, infracts, infections, abscesses, and epileptic lesions Flat EEG is clinical evidence of death Higher mental functions Brain waves-patterns of neurological activity. Each persons’ brain waves are unique Alpha waves (8–13 Hz)—regular and rhythmic, low-amplitude, synchronous waves indicating an “idling” brain Beta waves (14–30 Hz)—rhythmic, less regular waves occurring when mentally alert Theta waves (4–7 Hz)—more irregular; common in children and uncommon in adults Delta waves (4 Hz or less)—high-amplitude waves seen in deep sleep and when reticular activating system is damped, or during anesthesia; may indicate brain damage Higher mental functions Brain waves change with age, sensory stimuli, brain disease, and the chemical state of the body Epilepsy A victim of epilepsy may lose consciousness, fall stiffly, and have uncontrollable jerking Not associated with intellectual impairments Occurs in 1% of the population Absence seizures, or petit mal- Mild seizures seen in young children where the expression goes blank Tonic-clonic (grand mal) seizures- Victim loses consciousness, bones are often broken due to intense contractions, may experience loss of bowel and bladder control, and severe biting of the tongue Higher mental functions Consciousness Conscious perception of sensation Voluntary initiation and control of movement Capabilities associated with higher mental processing (memory, logic, judgment, etc.) Loss of consciousness (e.g., fainting or syncopy) is a signal that brain function is impaired Clinically defined on a continuum that grades behavior in response to stimuli: Alertness, Drowsiness (lethargy), Stupor, Coma Higher mental functions Sleep and sleep-wake cycles State of partial unconsciousness from which a person can be aroused by stimulation Two major types of sleep (defined by EEG patterns) Nonrapid eye movement (NREM): State of partial unconsciousness from which a person can be aroused by stimulation Rapid eye movement (REM)- People deprived of REM sleep become moody and depressed, REM sleep may be a reverse learning process where superfluous information is purged from the brain Higher mental functions Sleep disorders Narcolepsy- Lapsing abruptly into sleep from the awake state Insomnia- Chronic inability to obtain the amount or quality of sleep needed Sleep apnea- Temporary cessation of breathing during sleep Higher mental functions Language Language implementation system Basal nuclei Broca’s area and Wernicke’s area (in the association cortex on the left side) Analyzes incoming word sounds Produces outgoing word sounds and grammatical structures Corresponding areas on the right side are involved with nonverbal language components Higher mental functions Memory Storage and retrieval of information Two stages of storage Short-term memory (STM, or working memory)—temporary holding of information; limited to seven or eight pieces of information Long-term memory (LTM) has limitless capacity Higher mental functions Factors that affect transfer from STM to LTM Emotional state—best if alert, motivated, surprised, and aroused Rehearsal—repetition and practice Association—tying new information with old memories Automatic memory—subconscious information stored in LTM Higher mental functions Declarative memory (factual knowledge) Explicit information Related to our conscious thoughts and our language ability Stored in LTM with context in which it was learned Higher mental functions Nondeclarative memory Less conscious or unconscious Acquired through experience and repetition Best remembered by doing; hard to unlearn Includes procedural (skills) memory, motor memory, and emotional memory Procedural memory Motor memory Emotional memory Protection of brain Bone (skull) Membranes (Meninges) Cover and protect the CNS Protect blood vessels and enclose venous sinuses Contain cerebrospinal fluid (CSF) Form partitions in the skull Three layers Dura mater, Arachnoid mater, Pia mater Protection of brain Watery cushion (Cerebrospinal fluid) Composition: Watery solution, less protein and different ion concentrations than plasma, constant volume Functions Gives buoyancy to the CNS organs Protects the CNS from blows and other trauma Nourishes the brain and carries chemical signals Protection of brain Blood-brain barrier Helps maintain a stable environment for the brain Separates neurons from some blood borne substances Absent in some areas, e.g., vomiting center and the hypothalamus, where it is necessary to monitor the chemical composition of the blood Homeostatic imbalances in the brain Traumatic brain injuries Concussion—temporary alteration in function Contusion—permanent damage Subdural or subarachnoid hemorrhage—may force brain stem through the foramen magnum, resulting in death Cerebral edema—swelling of the brain associated with traumatic head injury Homeostatic imbalances in the brain Cerebrovascular accidents (CVAs)(strokes) Blood circulation is blocked and brain tissue dies, e.g., blockage of a cerebral artery by a blood clot Typically leads to hemiplegia, or sensory and speed deficits Transient ischemic attacks (TIAs)—temporary episodes of reversible cerebral ischemia Tissue plasminogen activator (TPA) is the only approved treatment for stroke Homeostatic imbalances in the brain Degenerative brain disorders Alzheimer’s disease (AD): a progressive degenerative disease of the brain that results in dementia 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 and cerebral cortex Spinal cord Embryonic development By week 6, there are two clusters of neuroblasts Alar plate—will become interneurons; axons form white matter of cord Basal plate—will become motor neurons; axons will grow to effectors Neural crest cells form the dorsal root ganglia sensory neurons; axons grow into the dorsal aspect of the cord Spinal cord Gross anatomy and protection Location Begins at the foramen magnum Ends as conus medullaris at L1 vertebra Functions Provides two-way communication to and from the brain Contains spinal reflex centers Protections Bone, meninges, and CSF Cushion of fat and a network of veins in the epidural space between the vertebrae and spinal dura mater CSF in subarachnoid space Spinal cord Spinal nerves Cervical and lumbar enlargements 31 pairs The nerves serving the upper and lower limbs emerge here Cauda equina The collection of nerve roots at the inferior end of the vertebral canal Spinal cord Cross –sectional anatomy Two lengthwise grooves divide cord into right and left halves Ventral (anterior) median fissure Dorsal (posterior) median sulcus Spinal cord Pathway Generalizations Pathways decussate (cross over) Most consist of two or three neurons (a relay) Most exhibit somatotopy (precise spatial relationships) Pathways are paired symmetrically (one on each side of the spinal cord or brain) Spinal cord Ascending Pathways Consist of three neurons First-order neuron Second-order neuron Conducts impulses from cutaneous receptors and proprioceptors, Branches diffusely as it enters the spinal cord or medulla, Synapses with second-order neuron Interneuron, Cell body in dorsal horn of spinal cord or medullary nuclei, Axons extend to thalamus or cerebellum Third-order neuron Interneuron, Cell body in thalamus, Axon extends to somatosensory cortex Spinal cord Dorsal Column-Medial Lemniscal Pathways Anterolateral Pathways Transmit input to the somatosensory cortex for discriminative touch and vibrations Transmit pain, temperature, and coarse touch impulses within the lateral spinothalamic tract Spinocerebellar Tracts Convey information about muscle or tendon stretch to the cerebellum Spinal cord Descending Pathways and Tracts Deliver efferent impulses from the brain to the spinal cord Direct pathways—pyramidal tracts Indirect pathways—all others Involve two neurons: Upper motor neurons Pyramidal cells in primary motor cortex Lower motor neurons Ventral horn motor neurons Innervate skeletal muscles Spinal cord trauma and disorders Functional losses Parasthesias- Sensory loss Paralysis- Loss of motor function Flaccid paralysis—severe damage to the ventral root or ventral horn cells Impulses do not reach muscles; there is no voluntary or involuntary control of muscles. Muscles atrophy Spastic paralysis—damage to upper motor neurons of the primary motor cortex Spinal neurons remain intact; muscles are stimulated by reflex activity. No voluntary control of muscles Spinal cord trauma and disorders Transection Cross sectioning of the spinal cord at any level Results in total motor and sensory loss in regions inferior to the cut Paraplegia—transection between T1 and L1 Quadriplegia—transection in the cervical region Poliomyelitis Destruction of the ventral horn motor neurons by the poliovirus Muscles atrophy Death may occur due to paralysis of respiratory muscles or cardiac arrest Survivors often develop postpolio syndrome many years later, as neurons are lost Spinal cord trauma and disorders Amyotrophic Lateral Sclerosis (ALS) Also called Lou Gehrig’s disease Involves progressive destruction of ventral horn motor neurons and fibers of the pyramidal tract Symptoms—loss of the ability to speak, swallow, and breathe Death typically occurs within five years Linked to glutamate excitotoxicity, attack by the immune system, or both Developmental aspects of CNS CNS is established during the first month of development Gender-specific areas appear in both brain and spinal cord, depending on presence or absence of fetal testosterone Maternal exposure to radiation, drugs (e.g., alcohol and opiates), or infection can harm the developing CNS Smoking decreases oxygen in the blood, which can lead to neuron death and fetal brain damage Developmental aspects of CNS The hypothalamus is one of the last areas of the CNS to develop Visual cortex develops slowly over the first 11 weeks Neuromuscular coordination progresses in superior-to-inferior and proximalto-distal directions along with myelination Age brings some cognitive declines, but these are not significant in healthy individuals until they reach their 80s Shrinkage of brain accelerates in old age Excessive use of alcohol causes signs of senility unrelated to the aging process