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Lecture Outline – Ch. 44: Nervous System I. Neurons II. Action Potentials III. Relationship between Stimuli Input IV. Nervous System Organization The Nervous System Includes all nerve cells (neurons) and support cells Neurons Specialized “excitable” cells: receive input, integrate, send output 1 Synaptic terminals: Bring signals from other neurons. 2 Dendrites: Receive signals from other neurons. 3 Cell body: Integrates signals; Coordinates. synaptic terminal 4 Action potential starts here. 5 Axon: Conducts the action potential. dendrite synapse 6 Synaptic terminals: Transmit signals to other neurons. 7 Dendrites (of other neurons). 5 Neurons Synapse: Region connecting two neurons or neuron and muscle • Electrical signal converted to chemical cue (neurotransmitter); then back to electrical impulse • Neurotransmitter may excite or inhibit the next neuron Neurons synaptic terminal synaptic vesicle Signal reaches end of axon. Synaptic vesicles release neurotransmitter. gap neurotransmitter Receptor binds neurotransmitter. dendrite of postsynaptic neuron Neurotransmitter signals next neuron. Neurons Neurons are electrical: • At rest, neurons maintain an electrical difference across their membrane • (-) inside cell; (+) outside cell • charge = about -70 mV Neurons Neurons Neurons Chemically-gated or ligand-gated channels Ligands: hormones or neurotransmitters Open channels & cause changes in cell membrane permeability Neurons Common Neurotransmitters: 1) Acetylcholine: Activates skeletal muscle (muscle) • Curare blocks Ach receptor 2) Dopamine: Controls movement (brain) • Parkinson’s Disease 3) Epinephrine: Activates fight-or-flight response (body) • a.k.a. Adrenaline 4) Serotonin: Influences mood (brain) • Anti-anxiety / anti-depressants 5) Endorphins: Influences mood; reduces pain sensation • Runner’s high Neurons Neurons Transmit Signals via Action Potentials: Action Potential (AP): The electrical signal passed along the length of a neuron (+) inside cell; (-) outside cell • During action potential, charges flip Na+ action potential (axon) (extracellular fluid) • Action potential propagated down axon Na+ action potential (axon) K+ (extracellular fluid) Action Potentials Action Potentials are fast: axon • Long axons are wrapped with myelin node axon • Speeds up signal myelin nucleus myelin-forming cell myelin sheath Action Potentials Action potentials can be measured electrically: • Stimulation from a neighbor neuron excites the cell (brief increase in voltage = EPSP) potential (millivolts) • Inhibition from another neuron causes a brief decrease in voltage (IPSP) threshold resting potential EPSP IPSP time (milliseconds) Action Potentials synaptic vesicle Pre-synaptic terminal IPSP = inhibitory postsynaptic potential Neurotransmitter potential (millivolts) neurotransmitter dendrite of Post-synaptic neuron EPSP = excitatory post-synaptic potential Neurotransmitter + Individual EPSP & IPSP weak EPSP IPSP time (milliseconds) Action Potentials Action Potentials Action potentials can be measured electrically: potential (millivolts) • Sum of all excitatory & inhibitory ‘blips’ = summation • If threshold voltage is reached, an action potential occurs (highly + voltage, briefly) action potential resting potential threshold Less (-) More (-) time (milliseconds) Stimuli Input Information Coding in the Nervous System: 1) Determine stimulus type (e.g. light / sound / touch) • All APs are similar in structure • Wiring pattern in brain distinguishes stimuli 2) Signal intensity of stimulus • All APs are similar in size (all-or-none response) • Intensity coded by: 1) Frequency of action potentials 2) # of neurons responding Stimuli Input Information Coding in the Nervous System: 1 fires slowly 1 fires rapidly 2 silent 2 fires slowly 1 fires moderately 2 silent Stimuli Input Information Coding in the Nervous System: 3) Integrate/coordinate signals 4) Determine Output Neural Pathways Direct Behavior: • Reflex: Involuntary movement in response to stimulus • Simplest behavior: 1) Receptor: Detects stimulus 2) Sensory neuron: Sends stimulus message 3) Association neuron: Integrates stimuli 4) Motor neuron: Activates effector 5) Effectors: Performs function (muscle / gland) 1 A painful stimulus activates a pain receptor. 2 Signal transmitted by a pain sensory neuron. stimulus receptor dorsal root sensation relayed to the brain REFLEX ARC 5 Effector muscle causes withdrawal effector response. ventral root 4 Motor neuron stimulates the effector muscle. 3 Signal transmitted to a motor neuron by an interneuron within the spinal cord. Stimuli Input Increased Complexity in Nervous System = Increased centralization Nerve Net: Nervous tissue woven throughout body (no head) Cephalization: Nervous tissue centralized in “head” region ring of ganglia brain nerve cords diffuse network of neurons (a) Hydra Nerve Net (b) Flatworm cerebral ganglia (brain) (c) Octopus Cephalization Nervous System Organization Brain and spinal cord 1) Bone (Skull; Spinal Cord = vertebrae) 2) Meninges (Triple-layer of connective tissue) • Contains cerebrospinal fluid (cushioning / nourishment) 3) Blood-brain Barrier • Selective barrier in blood vessels Spinal Cord: Nervous System Organization Myelin = Insulation around axons • Increases AP conduction rate Nervous System Organization Spinal Cord: CNS Nervous System Organization Brain and Spinal Cord Motor Pathways PNS Sensory Pathways Sensory neurons registering external stimuli Sensory neurons registering external stimuli Somatic nervous system (voluntary) Sympathetic nervous system "fight or flight" Autonomic nervous system (involuntary) Parasympathetic nervous system "rest and repose" Nervous System Organization Thought Question: How far can you safely drive behind the car in front if you are travelling at 60 mph? Think about: Your reaction time (what has to happen for you to stop if the car in front of you stops?) How far you go per second (at what speed are you traveling?) Lecture Outline – Ch. 45 Sensory Input I. Brains II. Sensory Input A. Sound B. Sight C. Odor/Taste D. Pain E. “Spidey Senses” The Brain: (a) Vertebrate Brains (c) optic lobe thalamus cerebrum cerebellum cerebrum midbrain cerebellum medulla forebrain midbrain hindbrain EMBRYONIC VERTEBRATE BRAIN cerebrum midbrain cerebellum (b) GOOSE BRAIN (d) cerebrum SHARK BRAIN midbrain (inside) cerebellum HUMAN BRAIN Brains: What are the major differences? The Brain: Human Brain meninges skull 1) Hindbrain: Automatic Behaviors A) Medulla: Controls breathing, heart rate, blood pressure B) Pons: Controls wake/sleep transitions; sleep stages C) Cerebellum: Coordinates movement hindbrain cerebellum pons medulla spinal cord Human Brain The Brain: (Figure 38.12) pituitary gland pineal gland midbrain - Reticular Formation 2) Midbrain: Relay / “Screening” Center A) Reticular Formation: Controls arousal of brain • Filters sensory input from body B) Visual / Auditory Reflex Centers The Brain: Human Brain (Figure 38.12) cerebral cortex 3) Forebrain (Cerebrum): “Seat of Consciousness” A) Cerebral Cortex • Two hemispheres (Connection = Corpus Callosum) • Left hemisphere controls right side of body (and vise versa) corpus callosum The Brain: Human Brain Parietal Lobe Frontal Lobe Occipital Lobe Temporal Lobe 3) Forebrain (Cerebrum) A) Cerebral Cortex Four regions: 1) Frontal: Primary motor area; complex reasoning 2) Parietal: Primary sensory area 3) Temporal: Primary auditory and olfactory areas 4) Occipital: Primary visual area Human Brain primary sensory area Frontal Lobe primary motor area premotor area higher intellectual functions leg trunk arm hand Parietal Lobe sensory association area face speech motor area tongue primary auditory auditory association area area: language comprehension memory Temporal Lobe visual association area primary visual area Occipital Lobe Human Brain Motor and Sensory areas Human Brain Cortical Regions Involved in Different Tasks: Hearing Words Seeing Words Reading Words Generating Verbs 0 max The Brain: Human Brain hypothalamus thalamus 3) Forebrain (Cerebrum) B) Limbic System • Produce emotions; form memories C) Thalamus • Relays information from body to limbic system / cerebral cortex The Brain: Human Brain limbic region of cortex B) Limbic System • Hypothalamus: Homeostatic control center • Amygdala: Produces sensations of pleasure, fear, or sexual arousal • Hippocampus: Formation of long-term memory C) Thalamus • Relays to limbic system / cerebral cortex cerebral cortex corpus callosum thalamus hypothalamus hippocampus amygdala Sensory Input What is a Sensory Receptor? Specialized cells that signals when stimulated Receptors named after stimuli they respond to: 1) Thermoreceptors: Heat / Cold 2) Mechanoreceptors: Motion; pressure; gravity 3) Photoreceptors: Light (photons) 4) Chemoreceptors: airborne/waterborne molecules 5) Nociceptors: Pain (chemical release) Sensory Input Pressure: Skin: Pressure Electrical Signal free nerve endings (touch, pain, or temperature) Merkel’s disc (steady touch) hair endorgan (hair movement) Pacinian corpuscle (rapid movement) Ruffini’s endorgan (pressure) Meissner’s corpuscle (light touch, rapid movement) Sound: Sensory Input Sound waves are vibrations in fluid (air, water) Sound: Sensory Input Ear: Sound Electrical Signal 1) Sound wave enters ear (auditory canal) Outer ear Middle ear bones of middle ear 2) Tympanic membrane vibrates Inner ear vestibular system (detects head movement and gravity) auditory nerve to brain 3) Vibration passes to inner ear bones 4) Inner ear (cochlea) converts vibrations to electrical signal cochlea auditory canal tympanic membrane auditory tube (Eustachian tube) to pharynx Sensory Input Vision: Eye: Light Electrical Signal Some animals only sense light/dark Many arthropods have a compound eye, where many images are pieced together into a visual mosaic Compound eyes Vision: Sensory Input Eye placement changes vision: • Forward-facing: many carnivores that need depth perception • Widely spaced: herbivores - allows better predator detection Vision: Sensory Input Eye: Light Electrical Signal Mammals: collects & focuses light waves; transmits signal to brain 1) Light enters via cornea (transparent covering), through the pupil (opening in center of iris) 2) The iris is a pigmented ring of muscle that controls light entry 3) Light is focused on the retina (sheet of photoreceptors) by the lens (transparent surface) Vision: Sensory Input 4) Muscles attached to lens contract to change the lens shape and focus image on the fovea for any visual distance retina Distant object, lens thins to focus on retina. Close object, lens fattens to focus on retina. Vision: Sensory Input Abnormally long eyeball: the image is focused in front of the retina: nearsightedness Abnormally short eyeball: the image is focused behind the retina: farsightedness Vision: Sensory Input Eye: Light Electrical Signal 5) Light on the retina triggers receptors; optic nerve excited Rods: Dim-light vision (many but scattered) Cones: Color vision (Red/green/blue) The blind spot is where the optic nerve connects to eyeball No photoreceptors, so images disappear blind spot fovea Sensory Input Odor/Taste: Nose / Tongue: Chemical Electrical Signal olfactory epithelium olfactory structure of brain nasal cavity bone air with odor molecules nasal cavity 1) Chemicals enter nasal cavity; bind to receptors (olfactory epithelium) olfactory receptors mucus layer olfactory dendrites 2) Olfactory bulb (in brain) excited Sensory Input Odor/Taste: Nose / Tongue: Chemical Electrical Signal The human tongue 1) Dissolved chemicals enter taste buds on tongue (via taste pore) 2) Chemicals bind with receptors; papillae stimulate nerves • Five primary tastes: • Sweet / Salt / Bitter / Sour / Umami • Olfaction enhances taste Taste bud taste pore microvilli taste receptor cells nerve fibers to brain Sensory Input Pain is a specialized Chemical Sense: 1) Damaged cells spill chemicals 2) Nociceptors detect tissue damage Self-Check Sensation Type(s) of receptor; Description of sense Touch Sound Sight Taste Smell Pain 54 Some senses are unfamiliar to humans Other Senses: Sensory Input Electrolocation: Animal produces electrical field; interpret distortion in field Magnetic Field Detection: Echolocation: Animal emits pulse interprets returning signal Animals detect and orient based on earth’s magnetic field Lecture 10 Summary 1. Neurons (Ch. 44) Structure Types 2. Action Potentials (Ch. 44) How electrical charge is set up AP stimulus, propagation, transfer to next cell 3. Stimuli (Ch. 44) Coding of stimuli Route in NS Nervous System Organization 4. Brain Regions and Function (Ch. 44,45) 5. Sensations (Ch. 45) Types of receptors Touch, sound, vision, taste, smell, pain Other senses