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THE NERVOUS SYSTEM *THE NERVOUS SYSTEM: OVERVIEW Swift, brief response to stimuli Monitors internal & external environment Integrates sensory information Coordinates voluntary & involuntary responses of other systems ORGANIZATION Central Nervous System (CNS) Processes data and transmits commands Intelligence, memory, emotion Consists of: Brain Spinal cord Peripheral Nervous System (PNS) All neural tissue outside of the CNS “the highway” of communication ORGANIZATION, CTD. PNS Afferent division Carries info from receptors to CNS Efferent division Carries commands from CNS to muscles, glands, adipose tissue in body Divided into: Somatic Nervous System (SNS) – skel musc. contraxns Autonomic Nervous System (ANS) – automatic stuff like smooth & cardiac muscle, glandular secretion, and adipose tissue…divided into: Sympathetic Nervous System Parasympathetic Nervous System Peripheral nervous system (PNS) Central nervous system (CNS) Cranial nerves and spinal nerves Communication lines between the CNS and the rest of the body Brain and spinal cord Integrative and control centers Sensory (afferent) division Somatic and visceral sensory nerve fibers Conducts impulses from receptors to the CNS Somatic sensory fiber Motor (efferent) division Motor nerve fibers Conducts impulses from the CNS to effectors (muscles and glands) Somatic nervous system Somatic motor (voluntary) Conducts impulses from the CNS to skeletal muscles Skin Visceral sensory fiber Stomach Skeletal muscle Motor fiber of somatic nervous system Sympathetic division Mobilizes body systems during activity Sympathetic motor fiber of ANS Structure Function Sensory (afferent) division of PNS Motor (efferent) division of PNS Parasympathetic motor fiber of ANS Autonomic nervous system (ANS) Visceral motor (involuntary) Conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands Parasympathetic division Conserves energy Promotes housekeeping functions during rest Heart Bladder Figure 11.2 FIGURE 8.2 Dendrites (receptive regions) Cell body (biosynthetic center and receptive region) Nucleolus Axon (impulse generating and conducting region) Nucleus Nissl bodies Axon hillock (b) Impulse direction Node of Ranvier Schwann cell Neurilemma (one interTerminal node) branches Axon terminals (secretory region) Figure 11.4b FIGURE 8.3 *CELLULAR ORGANIZATION Neurons (carry electrical impulses) Cannot divide (lack centrioles) Neuroglia (supportive cells) Regulate environment Provide framework Phagocytic Smaller but more numerous Can divide *CLASSIFICATION OF NEURONS Structural Pyrimidal Cell found in brain Multipolar Motor neurons Unipolar Most sensory neurons Bipolar Some special sensory organs – sight, smell, hearing Functional Sensory neurons ~10 mil. Motor neurons ~500,000 Interneurons ~20 billion! *SENSORY NEURONS Form afferent division of PNS Receive info from sensory receptors Monitor external and internal envts, then relay to CNS Somatic sensory receptors External receptors: touch, temp, pressure, sight, etc. Proprioceptors: monitor position and movement Visceral (internal) receptors Monitor digestion, respiration, CV, etc. and taste, deep pressure, and pain *MOTOR NEURONS Form efferent division of PNS Send messages to effectors (which DO something) Somatic motor neurons (SNS) Visceral motor neurons (ANS) *INTERNEURONS Located in CNS only Connect other neurons Distribute info and coordinate activity Also play a role in planning, memory, and learning FIGURE 8.4 NEUROGLIA -- CNS CELL TYPES: Astrocytes lg., numerous, maintain blood-brain barrier, repairs Oligodendrocytes Insulate axons (white matter/gray matter) Microglia small, rare phagocytes Ependymal line CNS cavities NEUROGLIA PNS Cell types: Satellite cells Surround and support cell bodies Schwann cells Myelinate axons outside of CNS Demyelination neural Schwann cell plasma membrane Schwann cell cytoplasm Axon 1 A Schwann cell envelopes an axon. Schwann cell nucleus 2 The Schwann cell then rotates around the axon, wrapping its plasma membrane loosely around it in successive layers. Neurilemma Myelin sheath (a) Myelination of a nerve fiber (axon) 3 The Schwann cell cytoplasm is forced from between the membranes. The tight membrane wrappings surrounding the axon form the myelin sheath. Figure 11.5a ANATOMICAL ORGANIZATION PNS Cell bodies (gray matter) located in ganglia Axons (white matter) bundled together into nerves CNS Collection of cell bodies with common function = center Center with discrete boundary = nucleus Neural Cortex: thick layer of gray matter Columns made of tracts (bundles of axons of CNS) Pathways link centers to rest of body *MEMBRANE POTENTIAL All undisturbed cells are polarized Outside of cell has + charge, inside has – This is a potential difference, called membrane potential Unit = Volt (V) [cell membrane potential usu. measured in millivolts, or mV “Normal,” or undisturbed cell’s membrane potential = resting potential In neurons, resting potential is approximately -70mV Why is there a potential in resting cells? * https://www.youtube.com/watch?v=_bPFKDdWlCg Sodium Potassium Pump https://www.youtube.com/watch?v=OZG8M_ldA1M Crash Course Action Potential https://www.youtube.com/watch?v=HYLyhXRp298 Action Potential Bozeman FIGURE 8.7 The sodium-potassium pump ACTIVE TRANSPORT Is one type of active transport system 1Cytoplasmic Na+ binds to the sodium-potassium pump. Na+ binding stimulates phosphorylation by ATP. EXTRACELLULAR FLUID [Na+] high [K+] low 2 Na+ Na+ Na+ Na+ Na+ [Na+] low [K+] high Na+ CYTOPLASM ATP P ADP Na+ Na+ Na+ K+ is released and Na+ 3 sites are receptive again; the cycle repeats. K+ P K+ Phosphorylation causes the 4 protein to change its conformation, expelling Na+ to the outside. K+ K+ Loss of the phosphate 5 restores the protein’s original conformation. P K+ K+ P i 6 Extracellular K+ binds to the protein, triggering release of 23the Phosphate group. *WHAT HAPPENS WHEN IT CHANGES? Any substance that alters permeability of membrane or alters the activity of pumps in the membrane Exposure to chemicals Mechanical changes Temperature changes Change in extracellular fluid Change in resting potential can have an immediate effect VOCAB Depolarization Polarization Graded potential Ex: goblet/gland cell Action potential Skeletal muscles Axons of neurons Threshold Trigger analogy All – or – none principle *NEURAL COMMUNICATION Info travels thru action potentials (=electrical or nerve impulses) At end of axon, info (neurotransmitters) is passed to another neuron or to an effector https://www.youtube.com/watch?v=VitFvNvRIIY The Synapse Bozeman *NEUROTRANSMITTERS A single neurotransmitter may bind specifically to more than a dozen different receptors Receptor activation and postsynaptic response cease when neurotransmitters are cleared from the synaptic cleft Neurotransmitters are removed by simple diffusion, inactivation by enzymes, or recapture (reabsorption) into the presynaptic neuron PRESYNAPTIC NEURON Neurotransmitter FIGURE 48.18 Neurotransmitter receptor Inactivating enzyme POSTSYNAPTIC NEURON (a) Enzymatic breakdown of neurotransmitter in the synaptic cleft Neurotransmitter Neurotransmitter receptor Neurotransmitter transport channel (b) Reuptake of neurotransmitter by presynaptic neuron *THE SYNAPSE Presynaptic neuron—conducts impulses toward the synapse Postsynaptic neuron—transmits impulses away from the synapse PRESYNAPTIC NEURON FIGURE 48.18A Neurotransmitter Neurotransmitter receptor Inactivating enzyme POSTSYNAPTIC NEURON (a) Enzymatic breakdown of neurotransmitter in the synaptic cleft FIGURE 48.18B Neurotransmitter Neurotransmitter receptor Neurotransmitter transport channel (b) Reuptake of neurotransmitter by presynaptic neuron ACETYLCHOLINE Acetylcholine is a common neurotransmitter in vertebrates and invertebrates It is involved in muscle stimulation, memory formation, and learning Vertebrates have two major classes of acetylcholine receptor, one that is ligand gated and one that is metabotropic A number of toxins disrupt acetylcholine neurotransmission These include the nerve gas, sarin, and the botulism toxin produced by certain bacteria Acetylcholine is just one of more than 100 known neurotransmitters The remainder fall into four classes: amino acids, biogenic amines, neuropeptides, and gases TABLE 48.2 TABLE 48.2A TABLE 48.2B TABLE 48.2C AMINO ACIDS Amino acid neurotransmitters are active in the CNS and PNS Known to function in the CNS are Glutamate Gamma-aminobutyric acid (GABA) Glycine BIOGENIC AMINES Biogenic amines include Epinephrine Norepinephrine Dopamine Serotonin They are active in the CNS and PNS NEUROPEPTIDES Several neuropeptides, relatively short chains of amino acids, also function as neurotransmitters Neuropeptides include substance P and endorphins, which both affect our perception of pain Opiates bind to the same receptors as endorphins and can be used as painkillers GASES Gases such as nitric oxide (NO) and carbon monoxide (CO) are local regulators in the PNS Unlike most neurotransmitters, NO is not stored in cytoplasmic vesicles, but is synthesized on demand It is broken down within a few seconds of production Although inhaling CO can be deadly, the vertebrate body synthesizes small amounts of it, some of which is used as a neurotransmitter NEUROTRANSMITTER OVERVIEW https://www.youtube.com/watch?v=Ths T8HOeOtQ FIGURE 8.15 PNS: ANATOMY Peripheral Nerves, ctd Spinal Nerves Connect to the spinal cord 31 pairs, ea monitors a dermatome *REFLEXES Reflex arc Wiring of a single reflex Is this an example of positive or negative feedback? Types of reflexes Monosynaptic – sensory neuron synapses directly on motor neuron Ex: stretch reflex used by docs to test general condition of spinal cord, peripheral nerves, and muscles. Polysynaptic reflexes – contain interneurons, so longer delay between stimulus and response Withdrawal reflex Flexor reflex *REFLEX ARC* Components of a reflex arc (neural path) 1. Receptor—site of stimulus action 2. Sensory neuron—transmits afferent impulses to the CNS 3. Integration center—either monosynaptic or polysynaptic region within the CNS 4. Motor neuron—conducts efferent impulses from the integration center to an effector organ 5. Effector—muscle fiber or gland cell that responds to the efferent impulses by contracting or secreting FIGURE 8.28 Stimulus Skin 1 Receptor Interneuron 2 Sensory neuron 3 Integration center 4 Motor neuron 5 Effector Spinal cord (in cross section) Figure 13.14 The patellar (knee-jerk) reflex—a specific example of a stretch reflex 2 Quadriceps (extensors) 1 3a 3b 3b Patella Muscle spindle Spinal cord (L2–L4) Hamstrings (flexors) Patellar ligament 1 Tapping the patellar ligament excites muscle spindles in the quadriceps. 2 Afferent impulses (blue) travel to the spinal cord, where synapses occur with motor neurons and interneurons. 3a The motor neurons (red) send + – Excitatory synapse Inhibitory synapse activating impulses to the quadriceps causing it to contract, extending the knee. 3b The interneurons (green) make inhibitory synapses with ventral horn neurons (purple) that prevent the antagonist muscles (hamstrings) from resisting the contraction of the quadriceps. Figure 13.17 (2 of 2) SENSORY RECEPTORS Specialized to respond to changes in their environment (stimuli) Activation results in graded potentials that trigger nerve impulses Sensation (awareness of stimulus) and perception (interpretation of the meaning of the stimulus) occur in the brain *CLASSIFICATION OF RECEPTORS Based on: Stimulus type Location Structural complexity *CLASSIFICATION BY STIMULUS TYPE Mechanoreceptors—respond to touch, pressure, vibration, stretch, and itch Thermoreceptors—sensitive to changes in temperature Photoreceptors—respond to light energy (e.g., retina) Chemoreceptors—respond to chemicals (e.g., smell, taste, changes in blood chemistry) Nociceptors—sensitive to pain-causing stimuli (e.g. extreme heat or cold, excessive pressure, inflammatory chemicals) UNENCAPSULATED DENDRITIC ENDINGS Thermoreceptors Cold receptors (10–40ºC); in superficial dermis Heat receptors (32–48ºC); in deeper dermis UNENCAPSULATED DENDRITIC ENDINGS Nociceptors Respond to: Pinching Chemicals from damaged tissue Temperatures outside the range of thermoreceptors Capsaicin UNENCAPSULATED DENDRITIC ENDINGS Light touch receptors Tactile (Merkel) discs Hair follicle receptors Table 13.1 ENCAPSULATED DENDRITIC ENDINGS All are mechanoreceptors Meissner’s (tactile) corpuscles—discriminative touch Pacinian (lamellated) corpuscles—deep pressure and vibration Ruffini endings—deep continuous pressure Muscle spindles—muscle stretch Golgi tendon organs—stretch in tendons Joint kinesthetic receptors—stretch in articular capsules Table 13.1 *CLASSIFICATION OF NERVES Most nerves are mixtures of afferent and efferent fibers and somatic and autonomic (visceral) fibers Pure sensory (afferent) or motor (efferent) nerves are rare Types of fibers in mixed nerves: Somatic afferent and somatic efferent Visceral afferent and visceral efferent Peripheral nerves classified as cranial or spinal nerves *GANGLIA Contain neuron cell bodies associated with nerves Dorsal root ganglia (sensory, somatic) Autonomic ganglia (motor, visceral) CRANIAL NERVES Twelve pairs of nerves associated with the brain Most are mixed in function; two pairs are purely sensory Each nerve is identified by a number (I through XII) and a name “On occasion, our trusty truck acts funny—very good vehicle anyhow” The cranial nerves are: I - Olfactory nerve Old II - Optic nerve Opie III - Occulomotor nerve Occassionally IV - Trochlear nerve Tries V - Trigeminal nerve/dentist nerve Trigonometry VI - Abducens nerve And VII - Facial nerve Feels VIII - Vestibulocochlear nerve/Auditory nerve Very IX - Glossopharyngeal nerve Gloomy X - Vagus nerve Vague XI - Accessory nerve/Spinal accessory nerve And XII - Hypoglossal nerve hypoactive KNOW THE FIRST FOUR AND ONE OF THE SENTENCES. (You pick whichever one you like best.) Odor Of Orangutan Terrified Tarzan After Forty Voracious Gorillas Viciously Attacked Him Old Opie Occasionally Tries Trigonometry And Feels Very Gloomy, Vague And Hypoactive Frontal lobe Temporal lobe Infundibulum Facial nerve (VII) Vestibulocochlear nerve (VIII) Glossopharyngeal nerve (IX) Vagus nerve (X) Accessory nerve (XI) Hypoglossal nerve (XII) Filaments of olfactory nerve (I) Olfactory bulb Olfactory tract Optic nerve (II) Optic chiasma Optic tract Oculomotor nerve (III) Trochlear nerve (IV) Trigeminal nerve (V) Abducens nerve (VI) Cerebellum Medulla oblongata (a) Figure 13.5 (a) A PERSON ATTEMPTING TO SHOW HIS TEETH AND RAISE HIS EYEBROWS WITH BELL'S PALSY ON HIS RIGHT SIDE BELL'S PALSY IS THE MOST COMMON ACUTE MONONEUROPATHY CRANIAL NERVE VII CAUSED BY A HERPES VIRUS Cranial nerves I – VI I II III IV V Olfactory Optic Oculomotor Trochlear Trigeminal VI Abducens Cranial nerves VII – XII VII Facial VIII Vestibulocochlear IX X XI XII (b) Glossopharyngeal Vagus Accessory Hypoglossal Sensory function Motor function PS* fibers Yes (smell) Yes (vision) No No Yes (general sensation) No No Yes Yes Yes No No Yes No No No Yes No Sensory function Motor function PS* fibers Yes (taste) Yes (hearing and balance) Yes Some Yes No Yes (taste) Yes (taste) No No Yes Yes Yes Yes Yes Yes No No *PS = parasympathetic Figure 13.5 (b) *SPINAL NERVES 31 pairs of mixed nerves named according to their point of issue from the spinal cord 8 cervical (C1–C8) 12 thoracic (T1–T12) 5 Lumbar (L1–L5) 5 Sacral (S1–S5) 1 Coccygeal (C0) Cervical plexus Brachial plexus Cervical enlargement Intercostal nerves Cervical nerves C1 – C8 Thoracic nerves T1 – T12 Lumbar enlargement Lumbar plexus Sacral plexus Cauda equina Lumbar nerves L1 – L5 Sacral nerves S1 – S5 Coccygeal nerve Co1 Figure 13.6 *SPINAL NERVES: ROOTS Each spinal nerve connects to the spinal cord via two roots Ventral roots Contain motor (efferent) fibers from the ventral horn motor neurons Fibers innervate skeletal muscles) *SPINAL NERVES: ROOTS Dorsal roots Contain sensory (afferent) fibers from sensory neurons in the dorsal root ganglia Conduct impulses from peripheral receptors Dorsal and ventral roots unite to form spinal nerves, which then emerge from the vertebral column via the intervertebral foramina Gray matter White matter Ventral root Dorsal root Dorsal root ganglion Dorsal ramus of spinal nerve Ventral ramus of spinal nerve Spinal nerve Dorsal and ventral rootlets of spinal nerve Rami communicantes Sympathetic trunk ganglion Anterior view showing spinal cord, associated nerves, and vertebrae. The dorsal and ventral roots arise medially as rootlets and join laterally to form the spinal nerve. Figure 13.7 (a) *INNERVATION OF SKIN Dermatome: the area of skin innervated by the cutaneous branches of a single spinal nerve All spinal nerves except C1 participate in dermatomes Most dermatomes overlap, so destruction of a single spinal nerve will not cause complete numbness C2 C3 C4 C5 C6 C7 C8 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 C2 C3 C4 C5 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T2 C5 C6 C6 C7 L1 C8 L2 T12 S2 S3 T2 C5 C6 L1 C8 L2 S1 L4 S2 S3 S4 S5 C6 C7 C6 C7 C8 C8 L2 S2 S1 L1 L3 L5 L4 T11 T12 L1 L3 L5 C7 C6 S1 S2 L3 C5 L2 L5 L4 L3 L5 L5 L4 S1 Anterior view S1 (b) Posterior view L4 L5 L4 L5 S1 Figure 13.12 THE AUTONOMIC NERVOUS SYSTEM “In practical terms, conscious activities have little to do with our immediate or long term survival…” Sympathetic Fight or flight Parasympathetic Rest and digest Central nervous system (CNS) Peripheral nervous system (PNS) Sensory (afferent) division Motor (efferent) division Somatic nervous system Autonomic nervous system (ANS) Sympathetic division Parasympathetic division Figure 13.1 FIGURE 8.33 *AUTONOMIC NERVOUS SYSTEM (SUMMARY) The Sympathetic Nervous System Stimulates tissue metabolism Increases alertness Prepares for emergency (sudden, intense activity) Stimulates sweat glands and arrector pili muscles Reduces circ. to skin and body wall Accelerates blood flow to muscles Releases stored lipids from fat tissue Dilates pupils Increases heart rate Reduces blood flow by visceral organs not important to short term survival (digestion) AUTONOMIC NERVOUS SYSTEM The Parasympathetic Nervous System Constricts pupils Increases secretions by digestive glands Increases smooth muscle activity of digestive tract Constricts respiratory pathways Reduces heart rate Relaxation, food processing, and energy absorption FIGURE 8.34 *AGING AND THE NERVOUS SYSTEM Reduction in brain size/weight Reduction in number of neurons Decreased blood flow to brain Fewer dendritic branchings and interconnections, neurotransmitter production goes down Intracellular and extracellular changes in neurons * Memory consolidation more difficult Senses less acute Reaction times and reflexes slower Precision of motor control decreases * Sciatica -- A common condition arising from compression of, or damage to, a nerve or nerve root. Restless legs syndrome (RLS) is a disorder of the part of the nervous system that affects the legs and causes an urge to move them. Because it usually interferes with sleep, it also is considered a sleep disorder * Guillain-Barré syndrome -- causes muscle weakness, loss of reflexes, and numbness or tingling in your arms, legs, face, and other parts of your body. In GBS, the immune system attacks the myelin sheath of certain nerves. This causes nerve damage. May be triggered by a viral or bacterial infection *MULTIPLE SCLEROSIS (MS) An autoimmune disease that mainly affects young adults Symptoms: visual disturbances, weakness, loss of muscular control, speech disturbances, and urinary incontinence Myelin sheaths in the CNS become nonfunctional scleroses Shunting and short-circuiting of nerve impulses occurs Impulse conduction slows and eventually ceases *MULTIPLE SCLEROSIS: TREATMENT Some immune system–modifying drugs, including interferons and Copazone: Hold symptoms at bay Reduce complications Reduce disability