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General Outcome: Explain how the Nervous System controls physiological processes The Nervous System A system of the body that coordinates & regulates the activities of the body Control System Maintains homeostasis homeo/stasis (same/changing) ◦ changes in order to keep a balance 5 major components Stimulus receptor -highly specific -receive stimuli Sensory Pathway modulator/regulator -Selects appropriate Response (spinal cord or brain) Motor Pathway effector -carries out the response (muscle or gland) Action The Nervous System & Homeostasis ◦ Organization of the Nervous System ◦ Structure of a neuron ◦ Action Potential ◦ Synaptic Transmission ◦ Structure of the Brain ◦ Senses: The Eye & Ear Nervous System Organizational Tree! Nervous System Central Nervous System (CNS) Decision maker Brain & Spinal Cord Peripheral Nervous System (PNS) Feeds into & out of CNS Sensory Pathway Somatic Pathway (Voluntary) under conscious control Examples? NS Overview Sympathetic (Stimulatory) Speeds you up! Excites you! Motor Pathway Autonomic Pathway (Involuntary) unconscious control Examples? Parasympathetic (Restores to normal) Restores balance! Restores Homeostasis! Sympathetic vs. Parasympathetic (to stimulate) (to restore) • Dilates Pupils Constricts pupils • Inhibits tears & salivation Stimulates the same • Increases heart rate Decreases heart rate • Increases respiration Decreases respiration • Inhibits digestion Stimulates digestion • Relaxes bladder & bowels Contracts them(#1&2’s) • Inhibits genitals Stimulates genitals • Initiates ejaculation • Adrenaline Response Anatomy of a Nerve Cell Two different types of cells are found in the nervous system: ◦ Glial Cells: non-conducting; important for support and metabolism of nerve cells ◦ Neurons: functional units of the nervous system (conduct nerve impulses) The Neuron: Wires within a nerve! See diagram on p.410 of text Types of Neurons – see your handout! Motor Neuron ◦ Connects the central nervous system to a muscle or a gland (also called efferent neurons) Sensory Neuron ◦ Connects a sensory receptor to the central nervous system (also called afferent neurons) Interneuron (or Association Neuron) ◦ Connect sensory neurons to motor neurons ◦ Connects two or more neurons ◦ Found in CNS The Neuron http://www.youtube.com/watch?v=36DSFSyxHw0 Dendrite – receives information from receptors or other neurons and conducts nerve impulses toward the cell body. Schwann Cells– special type of cell that produces the myelin sheath Cell Body – contains nucleus and organelles Nodes of Ranvier – gaps within the myelin sheath Impulses jump from node-to-node therefore speeding up the impulses Neurillemma – delicate membrane that promotes regeneration of damaged neurons Only found in myelinated neurons Myelin – a fatty protein that covers the axon Insulate the axon allowing nerve impulses to travel faster (Myelination is only found outside the brain and spinal cord) Axon – conducts nerve impulses away from the cell body To Do: Read p. 408-411 from text and Complete 66 word summary Complete Sections A thru C in your Notes Package Color and Label Neuron Diagram Structure of a Neuron From Nelson Biology The Job of Schwaan cells = Wrap Axons! Schwaan cells: Nourish the axon Provide insulation (myelin) Repair axon damage (neurilemma) Neurilemma = Found mainly in PNS •concentric rings around axon •created by the Schwaan cell • makes the impulse fast (insulated) Job of Myelin! Provide insulation like the covering on speaker wire Prevent loss of signal down axon! Damaged myelin results in a loss of signal down the axon! (Results in) Multiple Sclerosis (MS) Above is a map giving the geographical prevalence of Multiple Sclerosis (MS) world-wide. It has long been established that MS is more likely to occur in communities in the further Northern and Southern Lattitudes, possibly due to less sunlight, environmental factors or dietary reasons. http://www.msrc.co.uk/index.cfm?fuseaction=show&pageid=2325 A beauty of a neuron! Types of Neurons Sensory Neurons (Afferent Neurons) – conducts nerve impulse from sense organs to the brain and spinal cord (CNS) Interneuron (Association Neuron) – found within the CNS No myelination Intergrates and interprets sensory information and relays information to outgoing neurons Motor Neuron (Efferent Neurons) – conducts nerve impulses from CNS to muscle fiber or glands (effectors) To Do: Textbook Questions pg. 410 #1-4 Work on STS Assignment Remember: ◦ Purchase Key Booklet by next Friday ◦ Parent letter – if I don’t already have it Returning involuntary body functions to normal after a period of stress is the function of which division of the nervous system? A. B. C. D. Central Somatic Sympathetic Parasympathetic Syphilis is a STI that affects the central nervous system. The neurons damaged by syphilis are A. B. C. D. interneurons sensory neurons somatic motor neurons autonomic motor neuron Common Reflexes Babinski reflex: ◦ a tickle of a babies foot causes the toes to curl Pupillary reflex: ◦ iris diameter changes in response to light conditions Cross extensor reflex: ◦ in a standing position, fatigue of one leg causes withdrawal of weight onto the other leg Stretch reflex: ◦ -the body senses the muscles shortening so the tendency is to stretch them out in order to perform motor functions properly Knee jerk reflex (patellar): ◦ a tap on the patellar tendon causes top leg muscles to contract & lower leg muscles to relax simultaneously Withdrawal reflex: ◦ defensive strategy in response to a painful stimuli like heat & cold or a cut or pinch of some kind Others include: Vomiting, coughing, defecation, & milk release some of which are voluntary reflexes. Reflexes: Don’t need to write yet… are well established neural circuits that are preprogrammed to allow motor responses to certain stimuli some may be instinctual as in newborns some are learned as in repeated motor tasks involved in sport some are defensive to enhance survival and other reflexes help your eye to move as you read this page. Reflex Arc A reflex that does not require the brain Reflexes may be innate or acquired Reflex Arc Reflexes are autonomic responses to certain stimuli ◦ Involuntary/automatic They pathway that a nerve impulse takes is called a reflex arc Anatomy of a Reflex Arc How the Reflex Arc Functions: 1) Sensory organs (receptors) detect dangerous stimuli! 2) Impulse is passed from the sensory organ to a sensory neuron! 3) Sensory Neuron transfers the impulse to the Association neuron in the spinal cord! How the Reflex Arc Functions… 4) The INTERNEURON links the SENSORY to the MOTOR neuron! 5) The MOTOR neuron takes the impulse to the EFFECTOR! 6) The effector (usually a muscle) reacts. 7) Simultaneously, interneurons send the signal up to the BRAIN for interpretation! Reflex Arc Video Learner Outcome: Describe the composition and function of reflex arcs Design and perform an experiment to investigate the physiology of reflex arcs To Do: Reflex Lab Section E in your notes package ◦ P. 414 Questions # 2, 3, 5, 6 Action Potential how do nerves work??? In 1900 Bernstein hypothesized that nerve impulses where electrochemical in nature. ◦ Future experimentation proved this. Giant Squid Experiment: ◦ Cole and Curtis placed two tiny electrodes – one inside the large axon of a squid and the second across from the first outside the axon. Giant Squid Experiment Squid Axon •Cole and Curtis measured the electrical potential across the membrane. •The resting potential was found to be about – 70mV. When stimulated, the action potential jumped to about +40 mV. The action potential only lasted for a few milliseconds before the nerve cell returned to the resting potential. +40 threshold mV -70 1 2 ms 3 4 Definitions: Action Potential: ◦ the voltage difference across a nerve cell membrane when the nerve is excited (~40 mV) Resting Potential: ◦ Voltage difference across a nerve membrane when it is NOT transmitting a nerve impulse (almost always -70 mV) Maintaining Resting Potential Caused by an uneven distribution of positively charged ions across the membrane Set up and maintained by a Sodium-Potassium pump. 3 Na+ are pumped out of the cell, 2 K+ ions are pumped into the cell. sodium/potassium ion pump sodium/potassium pump 2 http://www.youtube.com/watch?v=9euDb4TN 3b0 http://www.youtube.com/watch?v=yQwQsEK21E These positive ions want to move with their concentration gradient by diffusion. More sodium moves out than potassium moves in leaving a “relative” negative charge inside the cell. The cell is polarized. resting potential clip Action Potential A Nerve impulse is an Action Potential When a neuron receives a stimulus it becomes more permeable to sodium than potassium ◦ When stimulated the ion gates for sodium open up. Positive ions flood into the cell making it positive. This rapid inflow is referred to as depolarization. After the impulse, the Na+ channels close and the K+ channels open. This is called repolarization. ◦ The flow of potassium ions out of the cell (with their concentration gradient) restores the resting potential. The potassium gates close relatively slowly which makes the inside of the neuron slightly more negative then resting potential (hyperpolarization) The Na+/K+ pump continues to pump the sodium and potassium across the membrane against the concentration gradient to restore the resting potential. Diagram from Textbook Summary of Impulse. 1. At rest – Na+/K+ pump moving 2. Stimulation – sodium gates open 3. The flood of sodium into the cytoplasm stimulates adjacent areas 4. Refractory – potassium gates open – sodium gates close 5. At rest – Na+/K+ pump moving ions Action potential overview Electropotential graph Movement of Action Potential Many action potentials are generated one after another along the cell membrane, causing a wave of depolarization (similar to falling dominos). When axons are myelinated, nerve impulses travel by saltatory conduction ◦ Gated ion channels are concentrated at the nodes of Ranvier ◦ Flow of ions across cell membrane can only happen at the nodes so action potentials “jump” from node to node ◦ This causes the signal to be transmitted down an axon much faster. myelinated vs. unmyelinated impuse Refractory Period: The time it takes (~0.001 s) for a depolarized neuron to repolarize ◦ return to resting potential During the refractory period another impulse can NOT be sent along the neuron. Threshold The amount of stimulus required to initiate an action potential (or, to cause depolarization to occur) Once threshold is reached the nerve impulse is passed along Draw diagram All-or-None Response A neuron will “fire” either 100%, or not at all. There is no difference in strength of a nerve impulse To Do: Read pages 415 – 419 in your textbook Complete Section D in your notes package Nerve impulse coloring diagram (pg. 7 notes package) Schwann Cell & Action Potential http://www.mcgrawhill.ca/school/applets/abbio/ch11/actionpotential_action.swf Synaptic Transmission Neurons are not directly connected to each other. The electrochemical action potential cannot jump the synaptic cleft (or synapse). Synaptic transmission is entirely chemical in nature. 1. http://www.youtube.com/watch?v=vGS7g uM1Gw0 Synapse movie clip Synapse At the end of axons, tiny synaptic vesicles contain neurotransmitters When an impulse reaches the end of an axon, these synaptic vesicles migrate toward the end of the axon They then release their neurotransmitter and it diffuses across the synaptic cleft Synapse Neurotransmitters attach to specific receptor sites and causes sodium channels to open resulting in a depolarization in the membrane. An action potential is created and the impulse travels down the neuron. Diffusion takes time, so the more synapses involved, the slower the response. Synapse Synaptic transmission can only occur in one direction. Since only presynaptic neurons contain synaptic vesicles, and only post synaptic neurons have receptor sites for them, the messages cant be sent in the other direction This explains why impulses can only travel from sensory neuron to interneuron to motor neuron and never in the other direction Figure 10(b), pg. 420 Synaptic vesicles in the end plate of the presynaptic neuron release neurotransmitters into the synaptic cleft. The neurotransmitters attach themselves to receptors on the postsynaptic membrane, causing it to depolarize. The action potential continues along the postsynaptic neuron. Synapse action at muscular juction Neurotransmitters Acetylcholine (Ach): (excitatory – passes message along) ◦ neurotransmitter produced in the presynaptic knob and stored in vesicles. ◦ when an action potential reaches the presynaptic knob the vesicles rupture releasing their contents (acetylcholine) into the synaptic cleft ◦ The acetylcholine diffuses across the synapse and binds to receptor sites on the postsynaptic knob Neurotransmitters How do we stop the message? ◦ Before another message can cross the cleft, it must be cleaned (remove the neurotransmitter) ◦ The enzyme acetyl cholinesterase removes acetylcholine from the receptor sites and breaks it into acetic acid & choline ◦ the acetic acid & choline are reabsorbed into the presynaptic knob to be reused Neurotransmitters • Not all neurons cause depolarization in the post synaptic membrane. Some neurons are inhibitory. Neurotransmitters can be: ◦ excitatory - passes along message to the next neuron, or ◦ Inhibitory – binds to the next neuron and inhibits the message from being passed on See figure 11 p. 422 Neurotransmitters Often it takes more than one neuron releasing its neurotransmitter into the synaptic cleft to elicit a response in the post synaptic neuron. ◦ This is referred to as SUMMATION Figure 11, pg. 422 Action potentials must occur simultaneously in A and B to reach the threshold in D. Other Types of Neurotransmitters: Serotonin Dopamine Norepinephrine GABA You will fill in some information regarding these in your notes package but do NOT have to memorize them. If used on a diploma you will be told what you need to know about them 13.2 Summary Electrochemical Impulse • Nerves conduct electrochemical impulses from the dendrites along the axon to the end plates of the neuron. • Active transport and diffusion of sodium and potassium ions establish a polarized membrane. • An action potential is caused by the inflow of sodium ions. • Nerve cells exhibit an all-or-none response. • Neurotransmitters allow the nerve message to move across synapses. To Do: Reflex/Synapse Worksheet Complete section F in your notes package Case Study “Drugs and the Synapse” p. 423-424 of text For Extra Practice: ◦ Pg. 418 # 1-4 ◦ Pg. 420 # 5-7 ◦ Pg. 425 #3-7