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Function of the Nervous System  Spinal nerves: carry impulses to and from the spinal cord  Cranial nerves: carry impulses to and from Functions of Nervous System Figure 11.3 Organization of the nervous system. Nervous Tissue Types A. Ganglion: Cluster of cell bodies in...

Function of the Nervous System  Spinal nerves: carry impulses to and from the spinal cord  Cranial nerves: carry impulses to and from Functions of Nervous System Figure 11.3 Organization of the nervous system. Nervous Tissue Types A. Ganglion: Cluster of cell bodies in a PNS (Green in picture) B. Nucleus: Cluster of cell bodies in the b CNS (Green in picture) C. Nerve: Bundle of axons in PNS c D. Tract: Bundle of axons in CNS (examples are colored in picture) d E. Gray matter: unmyelinated axons, cell bodies, dendrites, axon e terminals, blood vessels (Green in picture) F. White matter: myelinated axons and blood vessels (Green in picture) f Structures of the Nervous System Axons convey messages away from the cell body, One directional information Axon’s Functional Characteristics Generates nerve impulses and transmits them along axolemma Junction of Axon axon hillock Down axon terminals & axon When it arrives at the axon terminal, neurotransmitters (a signaling chemical) are released into the extracellular space Neurotransmitters then sends signal (either to excite or inhibit) a nearby neuron  Astrocytes: Most abundant; Many functions including anchor neurons to capillaries (for nutrients) Control chemical environment around neurons Microglial cells: Important in immunity; when invading microorganisms near neurons they help destroy them Monitor health of neurons Most are multipolar Neuroglia in the CNS Ependymal cells: Cilia circulate cerebrospinal fluid that cushions the brain and spinal cord Oligodendrocytes: Wrap around nerve fibers, producing an insulating cover called a myelin sheath  Satellite cells: Surround cell bodies in PNS; similar function to astrocytes of the CNS Schwann cells: Surround all nerve fibers and form myelin sheath; similar function to oligodendrocytes in this way Vital to regeneration of damaged peripheral nerves The gaps in Schwann cells Neuroglia in the are called Nodes of Ranvier  Efferent vs Afferent Division of the PNS Efferent Afferent MOTOR SENSORY Signals FROM the CNS to effector organs Signals TO the CNS from sensory organs Somatic (Voluntary) nervous system: carry Somatic sensory fibers convey impulses impulses from the CNS to the skeletal from the skin, muscles, and joints muscles Visceral sensory fibers transmit impulses Autonomic (Involuntary) nervous system: from visceral organs visceral motor nerve fibers regulate the activity of smooth muscles, cardiac muscles, and glands. Why is the myelin sheath important? Whitish, fatty (protein-lipoid), segmented cover on many nerve fibers Protects and electrically insulates fibers Increases speed of nerve impulses (aka action potentials) Non-myelinated fibers conduct impulses more slowly So, myelinated fibers conduct nerve impulses rapidly….. Nonmyelinated fibers conduct impulses more slowly **Note that myelin sheaths are associated ONLY with axons ---- dendrites are always nonmyelinated Clinical application: Multiple Sclerosis Autoimmune disorder: Demyelinating of the CNS Immune system attacks the myelin surrounding nerve fibers Causes hardened patches (sclerosis) in the brain and spinal cord Results in disruption of communication between CNS and rest of body Membrane Potentials Neurons communicate with one another through electrochemical signals. Cell membrane causes the resistance to current flow Action potentials (aka nerve impulses) are electrochemical signals which occur over longer distances Formation of action potentials is dependent upon the existence of a resting membrane potential Action Potentials Stimuli occurring at dendritic nerve endings trigger the opening of gated ion channels, which enables a local flow of ions across the plasma membrane. If the inside of the plasma membrane becomes more positive than resting membrane potential (reaches about - 55mV) an Action Potential will be triggered (depolarization) If the inside of the plasma membrane does not reach threshold potential (-55mV), an AP will not be triggered (as it follows an ‘all or nothing’ principle) The AP continues along the axon When the AP hits the axon terminal, it crosses to neighboring neurons via a synapse Stages of an AP crossing a chemical synapse AP arrives at axon terminal Opening of calcium channels – releasing calcium into terminal Release of neurotransmitters (ex. Acetylcholine) Formation of a postsynaptic potential Action potential at the postsynaptic neuron (Remember what was discussed in Chapter 9)  A synapse is a Chemical specialized junction synapse That mediates the transfer of information transmits a between neurons signal from one neuron to another using neurotransmitte rs. This is how that happens! Focus Figure 11.3 Chemical Synapse © 2019 Pearson Education, Inc. What's the difference between a NERVE and a Tract? A nerve is a bundle of axons in the Peripheral nervous system A tract is a bundle of axons in the Central Nervous system This is what happens to demyelinated axons  White Matter vs Gray Matter White Matter Gray Matter Cerebral cortex Myelinated neuronal axons, some are Nonmyelinated neurons nonmyelinated he first 25 weeks of fetal development have relatively smooth brains. Rapid growth of the brain results in t nd folds called convolutions which increase surface area allowing more neurons to develop.  Neuroplasticity is how your brain compensates for damage or disease. This allows nerve cells to form new connections Why do we care about Meninges? Function of meninges: Cover and protect CNS Protect blood vessels and enclose venous sinuses Contain cerebrospinal fluid (CSF) Form partitions in skull Consists of three layers Dura mater (superficial; strongest) Arachnoid mater (middle; subarachnoid space contains blood vessels; CSF) Pia mater (deep; clings tightly to brain; lots of BV) Figure 12.22 Meninges: dura mater, arachnoid mater, and pia mater. Cerebrospinal Fluid (CSF) Cerebrospinal fluid (CSF) forms a liquid cushion of constant volume around brain Functions Gives buoyancy to CNS structures Reduces weight of brain by 97% by floating it so it is not crushed under its own weight Protects CNS from blows and other trauma Nourishes brain and carries chemical signals Composed of watery solution formed from blood plasma  Blood Brain Barrier (1 of 3) Helps maintain stable environment for brain Substances from blood must first past through continuous endothelium of capillary walls before gaining entry into neurons Tight junctions ensure substances pass through, not around, endothelial cells; also supported by astrocytes Simple diffusion – allows lipid-soluble substances, as well as blood gases to pass freely through cell membrane (drugs that affect are lipid soluble) Specific transport mechanisms – facilitated diffusion moves substances important to the brain such as glucose, amino acids and specific ion Denies metabolic wastes, proteins, toxins, and most drugs Basement membrane of endothelial cells – enzymes destroy chemicals that would activate brain neurons  The Blood Brain Barrier FIGURE 12.26 Absent in some areas: THE BLOOD Vomiting center (monitor blood for poisonous BRAIN BARRIER. substances) Hypothalamus (samples composition of blood – water balance, other metabolic activities) Blood Supply  Deep artery that supplies brain, eyes, nose, Brain supplied by forehead 2 Internal carotid Vertebral  Branches: Ophthalmic, Anterior Internal Carotid Arteriescerebral, arteries Artery Middle cerebral (noted in green) 2 vertebral arteries (noted in green) Ascends through the neck into the brain via transverse foramen of cervical vertebrae and enters skull via foramen magnum Supplies brainstem, cerebellum, SC Branches: spinal, posterior inferior Blood: Circle of Willis Branches of Internal Carotids and Vertebral arteries form the Circle of Willis A circle shape at the base of the brain **Important because if an artery supplying the brain with blood becomes damaged, blood flow from other vessels can often replace it  Clinical Application: Cerebrovascular Clinical Accidents (CVAs) Application: Traumatic Brain Injuries Also referred to as “strokes” Brain injuries include: 3rd leading cause of death in Concussion: temporary North America alteration in function Ischemia: tissue deprived of Contusion: permanent damage blood supply, leading to death of Subdural or subarachnoid brain tissue hemorrhage: pressure from blood may force brain stem Can be caused by blockage of through foramen magnum, cerebral artery by blood clot resulting in death Cerebral edema: swelling of Glutamate acts as excitotoxin, brain associated with worsening condition traumatic head injury Hemiplegia (paralysis on one side) or sensory and speech deficits may result Name the 4 main areas of the BRAIN Cerebrum: Initiates and coordinates movement and regulates temperature. Enables speech, judgement, thinking, reasoning, problem-solving, also function in vision, hearing, touch, and other senses Diencephalon: includes the thalamus, hypothalamus, and epithalamus. The endocrine system coordinator for the release of hormones, relaying sensory and motor signals to the cerebral cortex, and regulates circadian rhythm. Cerebellum: Analysis of sensory input, memory, learning, cognitive thought. Coordinates muscle control, maintains balance and equilibrium, fine tunes movements. Received information from the body and sends feedback via the thalamus. Brainstem: vital functions; breathing, consciousness, blood pressure, heart rate, sleep. Includes the Pons, Midbrain, and Medulla Oblongata(contains 4 of 12 cranial nerves). Which arteries supply the brain with blood? What is the Circle of Willis Major Landmarks: Fissures Longitudinal fissure: Runs from posterior to Source: anterior along sagittal https://upload.wiki media.org/wikiped plane ia/commons/0/04/ Human_brain_lon Divides cerebrum into gitudinal_fissure.p ng left and right cerebral hemispheres Transverse cerebral fissure: separates cerebrum from cerebellum Figure 12.5c Lobes, sulci, and fissures of the cerebral hemispheres. CEREBRUM  Largest part of the brain  Left and right Figure 12.5a Lobes, sulci, and hemispheres divided fissures of the cerebral by longitudinal fissure hemispheres.  Communicate through and are connected by the corpus collosum – a bundle of myelinated nerves  Three basic regions: Gray Matter; White Matter; Basal Nuclei (ganglia) Figure 12.7b Functional and structural areas of the cerebral cortex.  Cerebral Cortex Cerebral White Matter Responsible for communication between 3 functional areas: Sensory, motor, and cerebral areas, and association areas between cortex and lower Each hemisphere associated with CNS contralateral side of body Consists of myelinated Outer layer composed of gray matter All neurons in cortex are interneurons fibers bundled into large “Executive suite” – Our conscious mind tracts Responsible for the analysis of Classified according to sensory input, memory, learning, cognitive thought, and voluntary direction they run: movements Association, commissural, Higher level functions like memory and projection fibers and language in overlapping domains  Premotor Cortex Motor areas Located in frontal lobe, motor areas act to control voluntary movement Primary motor cortex in precentral gyrus Premotor cortex anterior to precentral gyrus Broca’s area anterior to inferior premotor area Frontal eye field within and anterior to premotor cortex; superior to Broca’s area Helps plan movements Staging area for skilled motor activities Controls learned, repetitious, or patterned motor skills Coordinates simultaneous or sequential actions Controls voluntary actions that depend on sensory feedback What if premotor cortex was injured??? Muscle strength or ability to perform discrete individual movements is not impaired; only control over movements is lost Example: damage to premotor area controlling movement of fingers would still allow fingers to move, but voluntary control needed to type would be lost Difficulty with using sensory feedback  Basal Nuclei Basal Ganglia: Cognition and emotion, regulates intensity of slow movement, filters out incorrect response, inhibits unnecessary movement. Closely associated with subthalamic nuclei (diencephalon) and substantia nigra (midbrain) Functions of basal nuclei are thought to: Influence muscle movements Play role in cognition and emotion Regulate intensity of slow or stereotyped movements Filter out incorrect/inappropriate responses Inhibit antagonistic/unnecessary movements Parkinson’s disease and Huntington’s disease are disorders of the basal nuclei  Cerebrum: Lobes Each cerebral hemisphere is divided by sulci into lobes Frontal Temporal: Parietal Occipital Insula Figure 12.5c Lobes, sulci, and fissures of the cerebral hemisphere  Frontal Lobe Largest lobe Location: Anterior portion of brain Protected by: Frontal bone Separated from parietal lobe (via central sulcus) and temporal lobe (via lateral sulcus) Areas Primary motor area (movement) Motor association area (movement) Important role in learned complex movements Primary olfactory cortex (smell) Broca’s area (motor speech production) Function Cognitive thought & memory Control of voluntary movements  Temporal Lobe Primary auditory area (hearing) Auditory association area (hearing) Processes/gives meaning to what we hear Wernicke’s area (speech comprehension) Function Special senses (hearing, smelling) Learning and memory retrieval Emotions Stores memories of sounds and permits perception of sound stimulus Interprets information from inner ear as pitch, loudness, and location Primary olfactory (smell) cortex Medial aspect of temporal lobes Involved in conscious awareness of odors Location: Superior and toward posterior part of brain Parietal Protected by: Parietal bone Anteriorly, contains postcentral Lobe gyrus Separated from frontal lobe (via central sulcus) and occipital lobe (via parietal-occipital sulcus) Areas Primary somatosensory area (cortex) Sensory association area (general senses) Processes/gives meaning to what we sense *Received general sensory information from skin, proprioceptors of skeletal muscles, joints and tendons. And responsible for spatial discrimination (identifying the region of the body being  Occipital Lobe Location: Posterior portion of brain Protected by: Occipital bone Separated from parietal lobe (via parietal- occipital sulcus) Areas Primary visual area (cortex) Visual association area (vision) Processes/gives meaning to what we see “visual memory” Function Insula Smallest lobe of brain Location: Deep in cerebrum, deep to frontal, parietal, and temporal lobes Function Special senses (taste, hearing) Vestibular Visceral sensation Vestibular cortex Posterior part of insula and adjacent parietal cortex Responsible for conscious awareness of balance (position of head in space) Sensory Homunculu s Motor Homunculu s The Diencephalon Between brainstem and cerebrum Consists of three paired gray-matter structures Thalamus Hypothalamus Epithalamus Diencephalon Thalamus Pair of oval masses of gray matter Makes up 80% of diencephalon Functions: Processes and relays information between cerebral cortex and PNS, spinal cord, or brain stem Part of limbic system (regulate emotion) Helps with somatic sensory receptors, visual, and auditory centers Receive motor input from cerebellum and relays to cerebral cortex Relays input from one area of cerebral cortex to another Hypothalamus The hypothalamus is the main visceral control and regulating center that is vital to homeostasis Damage to this part Regulates body temperature: sweating or shivering of the brain causes Regulates hunger and satiety in response to nutrient blood levels or hormones disorders such as Severe body Regulates water balance and thirst wasting Obesity Regulates sleep-wake cycles Sleep disturbances Dehydration Controls endocrine system functions such as: Emotional Secretions of anterior pituitary gland Production of posterior pituitary hormones (ADH, oxytocin) imbalances Chief homeostasis controls: Controls autonomic nervous system Examples: blood pressure, rate and force of heartbeat, digestive tract motility, pupil size Initiates physical responses to emotions Part of limbic system: perceives pleasure, fear, rage, biological rhythms, and drives (sex drive) Epithalamus Most dorsal portion of diencephalon Emotional response to olfaction Contains pineal gland (body) Extends from posterior border Secretes melatonin that helps regulate sleep-wake cycle Brain Stem Consists of three regions: midbrain, pons, medulla oblongata Controls automatic behaviors necessary for survival Contains fiber tracts connecting higher and lower neural centers Nuclei are associated with 10 of the 12 pairs of cranial nerves  Midbrain Smallest part of brainstem (1.5cm) Located between Pons and Diencephalon Cerebral peduncles: two ventral bulges that contain motor tracts Form pillars that hold up cerebrum Contains the substantia nigra Contains neurotransmitter – dopamine Parkinson’s Disease Function: visual response, coordination of movement, control “flight or fight” response  Pons Located between midbrain and medulla oblongata Composed of conduction tracts: Longitudinal fibers connect higher brain centers and spinal cord Transversal/dorsal fibers relay impulses between motor cortex and cerebellum Origin of cranial nerves V (trigeminal), VI (abducens), and VII (facial) Function: Helps medulla with breathing; acts as a bridge between higher areas and SC, higher areas and cerebellum  Medulla Oblongata (aka Medulla) Inferior portion of brainstem Blends into spinal cord at foramen magnum Contains: Cranial nerves vestibulocochlear (VIII), glossopharyngeal (IX), vagus (X), and hypoglossal (XII) Vestibular and cochlear nuclei: mediate responses that maintain equilibrium Nucleus cuneatus and nucleus gracilis: relay ascending somatic and proprioceptive sensory information from spinal cord Function: Autonomic reflex center: Cardiac: regulates heart rate and force of contraction Respiratory: regulates respiration Vasomotor: regulates blood vessel diameter Various other centers: regulates Vomiting Note: Works in Hiccupping conjunction with Swallowing hypothalamus Coughing/Sneezing  Cerebellum Function: The cerebellum is in the posterior part of the cranium and consists of two hemispheres. It controls muscle co-ordination, skilled movement maintains balance and equilibrium fine tunes movements at the conscious and subconscious levels. 11% of brain mass Located posterior to pons and medulla Purkinje cells originate in cortex, synapse Receives info from cerebral cortex, eye, ear, and the with cerebellum muscles of the body Monitors the intentions for movement and the actual Flocculonodular lobes: receive info from equilibrium apparatus of inner movements that occur ears, adjusts posture to maintain Combines this info to evaluate how the body is performing balance Cerebellum Then sends feedback to the cortex to initiate any Processing: necessary adjustments via the thalamus **This process helps to smooth and coordinate complex movements, maintain posture, and regulates balance. It  The Reticular Formation Reticular activating system (RAS) Sends impulses to cerebral cortex to keep it conscious and alert Filters out repetitive, familiar, or weak stimuli (~99% of all stimuli is not relayed to consciousness) Inhibited by sleep centers, alcohol, drugs Severe injury that twists the brain stem can result in permanent unconsciousness (coma) Motor function of reticular formation helps control coarse limb movements Language Language implementation system involves association cortex of left hemisphere Main areas include: Broca’s area: involved in speech production Patients with lesions in Broca’s understand words, but cannot speak Wernicke’s area: involved in understanding spoken and written words Patients with lesions in Wernicke’s can speak, but words are nonsensible Corresponding areas on right side are involved with nonverbal language components – ex. Tone of voice and “body language” Memory Processing Figure 12.19 Memory processing. Memory: storage and retrieval of information Different kinds of memory Declarative: memory of facts (names, Two stages of declarative memory storage: faces, words, dates) Short-term memory (STM, or working Procedural: memory of skills (playing memory): temporary holding of piano) information Motor: memory of motor skills (riding a Limited to seven or eight pieces of information bike) Long-term memory (LTM) – limitless Emotional: memory of experiences capacity (BUT can be forgotten; ability linked to an emotion (heart pounding declines with age) when you hear rattlesnake) Factors affecting transfer from STM to LTM Emotional state: best if alert, motivated, surprised, or aroused Rehearsal: repetition and practice Association: tying new information with  Sleep and Sleep-Wake Cycles Sleep: state of partial unconsciousness from which person can be aroused by stimulation Cortical activity is depressed, but brain stem activity doesn’t change Types major types of sleep (defined by EEG patterns): Non–rapid eye movement (NREM) sleep Broken into four stages (move into deeper sleep as go from 1 to 4) Decreased BP and HR Rapid eye movement (REM) sleep Dreams typically occur Increased HR, RR, BP; great oxygen use; rapid eye movement but most skeletal muscles actively inhibited How is sleep regulated? Alternating cycles of sleep and wakefulness reflect natural circadian (24-hour) rhythm Hypothalamus plays large role in sleep Contains biological clock and regulates sleep-inducing center Releases orexins that help cortex to wake up Typical sleep pattern alternates between REM and NREM sleep PD: Pathophysiology So what happens when the neurons degenerate? There is a decrease in dopamine – a neurotransmitter – which sends signals from the substantia nigra to corpus striatum and works with other neurotransmitters to coordinate movement What does a decrease in dopamine cause? A decrease in signals sent from the substantia nigra to corpus striatum. What’s so important about the corpus striatum? Produces smooth, purposeful movements What does this mean for people withis disrupted. Balance of neurotransmitters PD? Results in tremors in hands, legs, jaw; rigidity; slowness of movement; impaired balance NIH: National Institute of Neurological Disorders and Stroke. Parkinson’s Disease: Hope Through Research. Accessed on 11/9/2017. Available at: https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Hope-Through-Research/Parkinsons-Disease-Hope-Through-Research Memory Declarative Motor Short term memories become long term memories dependent up on; emotions, rehearsal, automatic memory, and linking new information with old memories. Thalamus: Acts as a relay center and manages emotions Hypothalamus: Controls autonomic nervous system, vital in maintaining overall body homeostasis, and synthesizes major hormones. Limbic System RETICULAR ACTIVATING SYSTEM: prevents sensory overload Sleep cycles, orexins are chemicals that are released during sleep that cause reticular neurons to fire and arouse the brain, which stimulate us to wake. Amygdaloid body Flocculonodular lobe: receives infor. From equilibrium apparatus of inner ears, adjusts posture to maintain balance. Ascending Pathway Sensory Information from the peripheral nerves are transmitted to the cerebral cortex Also called the somatosensory pathway Ascending Sensory Pathways The spinal cord, basically a highway for nerves, streamlines sensory and motor signals to the brain and the body. Information detected by sensory receptors in the periphery is transmitted along ascending neural tracts in the spinal cord. Located in the white matter of the spinal cord, the ascending sensory tracts arise from either the the cells of the spinal ganglia or the intrinsic neurons within the grey matter that receive primary sensory input. There are many sensory tracts and pathways carrying different types of sensory information from the periphery to the cerebral cortex. In humans the major sensory pathways include: The spinothalamic tracts: The spinothalamic tract, one of the most important pathways of the nervous system, lies anteriolaterally to the ventral horn of the spinal grey matter. This pathway comprises of three neutron sets and forms part of the somatosensory system. The lateral spinothalamic tract carries information about pain and temperature, and the anterior spinothalamic tract carries information about crude touch. Descending tracts Carry Motor information from the brain down the spinal cord to the appropriate body part. Includes corticospinal tracts, vestibulospinal, rubrospinal, reticulospinal tracts Functions of different areas of the brain Plans movement: Premotor Cortex Plans speech, directs muscles of speech production: Broca’s Area Controls eye movement: Frontal eye field Understanding spoken language: Wernicke’s area Basal Ganglia: Cognition and emotion, regulates intensity of slow movement, filters out incorrect response, inhibits unnecessary movement. Closely associated with subthalamic nuclei (diencephalon) and substantia nigra (midbrain)