Physiology 31 Lecture Outline Chapter 8 – Neurons: Cellular and Network Properties I. Overview A. Nervous System Organization B. Cells of the Nervous System C. Electrical Signals in Neurons D. Cell-to-Cell Communication E. Integration of Neural Information Transfer II. Nervous System Organization A. The _________ System works closely with the endocrine system to maintain bodily homeostasis. 1. The nervous system reacts rapidly via nerve __________, and has 3 major functions: a. __________ (afferent) input - sensory receptors within and near the body’s surface respond to _________ and send nerve impulses to the CNS b. __________ - the CNS receives, processes, and interprets the sensory input, then decides what to do about it c. _________ (efferent) output – the CNS sends nerve impulses to _________ organs (muscles and glands) in response to the sensory input 3. The endocrine system reacts more slowly via ____________. 4. _____________ is the study of nervous system function and disorders. B. Divisions of the Nervous System 1. Central Nervous System (_____) - consists of ________ & ______cord. Most impulses that stimulate muscles to contract and glands to secrete originate in the CNS. 2. Peripheral Nervous System (____) – outside the CNS; consists primarily of cranial nerves and spinal nerves a. __________ nerves – carry signals to & from the brain b. __________ nerves – carry signals to & from the spinal cord c. Cranial & spinal nerves are composed of sensory and motor neurons 1) Sensory (__________) neurons, whose cell bodies end near the CNS, conduct nerve impulses from the ______ to the CNS. 2) Motor (_________) neurons, whose cell bodies originate in the _____, conduct impulses from the CNS to muscles & glands. 3. _____ Subdivisions include the somatic and autonomic nervous systems a. _________ (voluntary) Nervous System (SNS) - consists of 1) Somatic _______ neurons convey impulses from the ___, muscles, bones, and joints to the CNS 2) Somatic ______ neurons conduct impulses from the CNS to _______________ tissue. 2 b. __________ (involuntary) Nervous System (ANS) functions 1) Visceral Sensory neurons from ____________ in internal organs and blood vessels convey signals to CNS 2) Visceral _______ neurons convey impulses from the CNS to ______ muscle, ______ muscle, and ______. The ANS is further subdivided into: a) ___________ NS – controls “flight or fight” functions b) ________________ NS – controls “rest and digest” (vegetative) functions III. Cells of the Nervous System A. __________ tissue is composed of two cell types 1. _________ (nerve cells) that are the electrical signaling units 2. __________ (glial cells) that support, nourish and protect neurons B. Neurons are ________ cells that generate and carry electrical signals. 1. Types of ________ include a. Pseudo__________ - has ___ process extending from cell body. Dendrites located at distal tip of axon; monitors ___________ (afferent) stimuli (touch or pain). b. _________ – have ___ main dendrite and ___ axon; rare - found in retina, inner ear, and olfactory area of brain; have mostly _________ functions. c. ____________ - usually have ________ dendrites and one axon; includes _______ (efferent) neurons found in brain & spinal cord d. ____________ (association neurons) – multipolar neurons found only in the _____; not purely sensory or motor; conduct impulses to other neurons; 90% of all neurons in the CNS. 2. _________ are composed of dendrites, a cell body, and an axon a. __________ – treelike extensions from the cell body that _____ incoming signals from neighboring cells and conduct them to the b. Cell body (______) – control center of the neuron that contains the nucleus and other organelles; ___________ incoming signals and sends out a response via the c. ______ - single process extending from cell body that ________ the nerve impulse from the neuron to another neuron, or to an __________ (muscle or gland). Axonal regions: 1) Axon _________ (trigger zone) - cone-shaped structure where the axon joins cell body. 2) Axon ____________ – infrequent branches off the axon 3) Axon ___________ - specialized processes at end of axons, which contain synaptic _______ containing neuron________, which influence other neuron, muscle, or gland activities. 3. Axons __________ materials both ways a. _________grade transport is the movement of substances (e.g., peptides) from the _____ down the axon b. ________grade transport moves materials from the axon __________ to the soma for disposal or recycling 3 C. _______ cells are the support cells of the nervous system 1. ______ Neuroglia a. ___________ - star-shaped cells with many processes; most abundant glial cell in the CNS; functions: 1) Form structural _________ between capillaries and neurons of the CNS; help to form the blood-brain barrier 2) Take up & release _____ (e.g., K+) to control the neuronal environment c. __________ - small, phagocytic cells that destroy pathogens in the CNS d. ___________ cells – epithelial cells that line brain ventricles and the spinal cord central canal. Functions: 1) Produce and help circulate cerebrospinal fluid (____) 2) Source of neural ______ cells to replace neurons e. Oligo___________ - similar to astrocytes but with shorter & fewer processes. Functions: 1) Produce ________ _______ (lipid & protein) around CNS neuron axons, which insulates axons, increasing _______ of nerve impulse conduction. 2) Multiple sclerosis (___) involves an autoimmune destruction of this myelin sheath. 2. _____ Neuroglia a. __________ cells - flattened cells arranged in series around axons or dendrites; produce the _______ sheath around PNS neuron axons 1) ______________ is the outer nucleated cytoplasmic layer of a Schwann cell; helps to _________ damaged myelinated PNS neuron axons or dendrites 2) Nodes of _________ are gaps between myelin sheath segments on the neuron axon that play a role in nerve transmission b. ___________ cells - support neurons in _________ (bundles of neuron cell bodies in PNS). IV. Electrical Signals in Neurons A. Neurons are ___________ (responsive to stimuli) cells, able to generate electrical signals as ___ move across their cell membranes. B. Membrane ________ (voltage) results from the uneven distribution of _____ across the cell membrane, and is influenced by 1. Ion _____________ gradients in a resting neuron a. A higher concentration of ___, Cl-, and Ca2+ in the ____ results in a more __________ charge outside the neuron b. A higher concentration of _______ and K+ in the _____ results in a more ___________ charge inside the neuron c. The difference in charge is the membrane’s _________ (voltage) 2. Membrane ____________ to the ions a. A resting neuron’s membrane is more permeable to ___ than to Na+ or Ca2+ (K+ leaks slowly out of K+ ion channels) b. ___ is the major ion that contributes to the ________ membrane potential 4 c. In an average neuron, the _________ membrane __________ (difference in charge across the membrane) is about ____ mV C. Ion movement across cell membranes creates _________ signals 1. Electrical currents in the body are created by the flow of _____ (esp. sodium [___] and potassium [___]) through openings (ion channels) in the plasma membrane a. A cell with a difference in charge across it membrane is said to be ____________ b. If the neuron membrane increases its permeablilty to Na+, ___ moves _____ the cell, which ____________ the membrane (the potential becomes more __________) c. If the membrane becomes more permeable to K+, ____ moves _____ of the cell, which ______________ the membrane (the potential becomes more ___________) D. Three types of gated _________ control neuronal ion permeability 1. _____________ gated ion channels in sensory neurons open due to pressure or __________ 2. ___________ (ligand) gated ion channels in most neurons open in response to _________ (e.g., neurotransmitter) binding 3. __________-gated ion channels open or close in response to changes in membrane __________ E. Electrical ________ may be graded potentials or action potentials 1. _________ (local) potentials are variable strength signals that travel ______ distances and gradually lose strength 2. ______ potentials are strong, uniform depolarizations that travel from the cell body to the axon ________ without losing strength F. Graded Potentials reflect the strength of the ___________ that initiates them 1. _______ potentials are __polarizations or ______polarizations that usually occur in __________ or the cell body 2. Neurons can be stimulated by __________, light, heat, voltage, or mechanical distortion of the plasma membrane 3. When stimulated, neuronal ion ________ open or close, causing _____ to enter or leave the neuron 4. The resulting change in membrane ____________ is directly proportional to the strength of the initial stimulus a. A weak stimulus will initiate a weak _________ potential that will not travel far b. A strong stimulus will stimulate a strong graded potential that may be converted to an _________ potential 5. Example of a depolarizing ________ potential: a. A chemical binds to _______ in the neuron plasma membrane (usually in the dendrites or cell body) b. The receptors are _______-gated sodium channels that open and allow ____ to diffuse into the neuron c. Na+ _______ causes the neuron’s internal negative charge to become more positive (__________), thus the voltage moves from –70 mV toward ______ d. Incoming Na+ ions produce a _________ that travels to the cell body, then to the cell’s trigger zone (axon _________) e. This limited short range change in voltage in the neuron is called a ________ potential 5 f. If the graded potential depolarizes the membrane to the ____________ voltage (about ____ mV), voltage-gated Na+ channels are opened, and an ______ potential is initiated 6. Two types of ________ potentials are inhibitory & excitatory post synaptic potentials a. ___________ post synaptic potentials (_____s) result from _______polarization of the post synaptic neuron’s membrane; IPSPs make the neuron_____ likely to fire an action potential b. ____________ post synaptic potentials (_____s) result from ___polarization of the post synaptic neuron’s membrane, which makes the neuron _____ likely to fire an action potential 1) If the depolarization is not strong enough to reach _______, the graded potential will ____ out 2) If the depolarization does reach __________, an ________ potential will be generated G. Action Potentials travel ______ distances without losing strength 1. Action potential _______ from graded potentials in that a. All action potentials have the same _________ b. Action potentials do not diminish in _________ as they travel c. Action potentials are “____ or ______” – they will only be generated if _________ is reached in the neuron’s trigger zone H. Action Potentials result from the movement of ____ and ____ through voltage-gated ion channels in the membrane 1. ___________-gated ion channels are found in the highest concentration in the ________ zone (axon hillock) of a neuron 2. If an ___________ graded potential is strong enough when it reaches the trigger zone, it can open these ion channels and generate an _______ potential down the axon 3. The __________ of events that cause an action potential include: a. Prior to the action potential, the neuron has a resting potential of about ____mV, and voltage-gated ion channels are _______ b. A stimulus in the neuron initiates a ________ potential, which travels toward the axon ________, and may generate an action potential, depending on the _________ of the local potential c. If enough ____ ions enter the axon hillock to reach _________ voltage (about ___ mV), _________-gated Na+ channels open, and more Na+ ions rush into the neuron d. An ______ potential is generated down the axon as more voltage-gated ____ channels are opened (like a row of dominos falling), as the ___polarization wave rises to about ____ mV e. Voltage-gated Na+ channels ____ as voltage-gated ___ channels open, causing K+ to move ___ of the neuron, and __polarization occurs (voltage moves back towards the ________ potential) f. ______polarization, a decrease in membrane voltage slightly below the resting potential (___ mV), often occurs because voltage-gated K+ channels are _____ to close 4. The ___/___ pump restores the ion balance of the neuron by pumping Na+ ions ___ and K+ ions ____ the neuron 6 I. Action potentials will ____ fire during the Absolute Refractory Period 1. The ___________ period is a period of neuronal insensitivity to restimulation during and after the action potential 2. ___________ refractory period – occurs from start to end of the action potential, when the ____ channels are still open a. During this time (about 1msec) the neuron cannot be further __________, regardless of the stimulus strength b. Ensures ____ ___ transmission of the action potential 3. ________ refractory period – lasts until _____polarization ends, when ____ channels are still open, but Na+ channels are closed a. During this time an exceptionally _______ stimulus can trigger another action potential J. Stimulus _________ is coded by the frequency of action potentials 1. A stronger stimulus will generate a greater __________ of action potentials (no. of APs fired per second) in a neuron than a weaker stimulus K. _________ neurons and those with myelinated axons conduct action potentials faster 1. Neurons with larger diameters have decreased ___________ to electrical current flow, thus ________ action potentials 2. ______________ axons have voltage-gated Na+ channels along their whole ______, thus depolarization of one part of the neuron membrane propagates the action potential from axon hillock to axon __________ like a row of dominos falling over 3. ___________ axons have the majority of their voltage-gated Na+ channels in the nodes of _________ between the myelin sheaths a. Na+ ions ________ inside the membrane between the nodes, then open the voltagegated ____ channels at the nodes to propagate the action potentials (__________ conduction) b. The result is ________ nerve conduction than in unmyelinated axons L. Electrical activity can be altered by _________ 1. Some chemicals ______ action potential conduction by binding to Na+, K+, or Ca2+ _________ in the neuron membrane a. ____________ (e.g., tetrodotoxin from puffer fish) and local ___________ bind to and block ____ channels b. If Na+ channels are blocked, ____ cannot enter the axon. How would this affect nerve conduction? 2. Changes in ECF concentrations of ____ and Ca2+ alter the electrical activity of the nervous system a. _____kalemia (high blood [___]) shifts the resting membrane potential toward _________, causing neurons to fire ______ potentials in response to smaller graded potentials, which can cause heart failure b. _____kalemia (low blood [___] ______polarizes neurons, making them ____ likely to fire action potentials, which results in muscle weakness V. Cell-to-Cell Communication A. The _____________ of neural communication depends on: 1. ________ molecules secreted by neurons 2. Target cell ___________ for the chemicals 7 3. _________ – the connections between neurons and their effectors B. ___________ passes from cell to cell at the synapse 1. A __________ is the place where a neuron meets its _________ (another neuron, muscle or gland cell). Each synapse has 3 parts: a. ____synaptic neuron axon terminal b. Synaptic ______ – minute gap between presynaptic axon and c. _____synaptic cell membrane 2. _________ synapses are those in which adjacent cells are joined by ___ junctions, which allow ___ to diffuse directly from cell to cell. These synapses are found in glia, _______ & smooth muscle 3. ___________ synapses are those in which neurons communicate with effectors via neuron_________. These synapses are the most common in the nervous system C. _______ is the signal for neurotransmitter release at the synapse 1. Axon _________ contain many mitochondria and synaptic _______ that house neurotransmitter chemicals 2. Neuro_____________ are released from the ____synaptic axon terminal to the ______synaptic cell membrane as follows a. An action potential __________ the axon terminal b. Depolarization opens voltage gated ____ channels, and Ca2+ enters the axon _________ c. Calcium binds to intracellular regulatory _________ and initiate ___________ d. Neuro___________ released from the vesicles diffuse across the synaptic ______ and bind to ligand-gated __________ on the postsynaptic cell membrane e. A response (e.g., ____ potential) is initiated in the postsynaptic cell 3. Neuro________ (e.g., tetanus and botulinum) can inhibit certain proteins (e.g., voltagegated Ca2+ __________) in the neuron’s exocytotic apparatus, thus ___________ nerve transmission D. Neuro________ convey information from neurons to other cells 1. __________ molecules released from neurons may function as neurotransmitters, neuromodulators, or neurohormones 2. Neurotransmitters and neuromodulators act as _________ and/or ___________, with target cells near by a. Neurotransmitters act at a _______ and elicit _____ responses b. Neuromodulators act at synaptic and _________ sites, and are ___________ acting 3. Neurohormones are secreted into the _____ where they travel to distant target cells E. Neurotransmitters are grouped into several _______, according to their structures. The classes are: ACh, amino acids and amines, polypeptides, purines, gases, and lipids 1. Acetylcholine (____) – synthesized from acetylCoA and ______, and used in the PNS a. Neurons that secrete ACh, and ACh receptors are called _________ b. ACh is _________ in skeletal muscle and neurons, but __________ in cardiac muscle c. ACh may be excitatory or inhibitory in _______ muscles and glands, depending on their types of __________ 2. ______ _____, such as glutamate, aspartate, glycine, and gamma-aminobutyric acid (GABA) a. _____________ AAs in the CNS are glutamate and aspartate b. _____________ AAs in the CNS include glycine and GABA 8 3. Amino acid derived ______ are mostly made from ________, such as epinephrine (__________) and norepinephrine (catecholamines), and dopamine, which also function as neurohormones a. Neurons that secrete ___epinephrine, and the NE receptors are called __________. NE is the main neurotransmitter of the __________ NS. b. Catechol______ are used in the _____; they are excitatory in _______ muscle and excitatory or inhibitory in ______ muscle and glands c. __________ inhibits involuntary skeletal _______ movements; lack of dopamine leads to ___________ disease d. Indol_______ include 1) ___________, made from tryptophan in the ____ is involved in sleep, alertness, thermoregulation and _______ 2) __________ is a vasodilator 4. Poly_________ include a. Substance __ involved in some ______ pathways b. ________ peptides (endorphins & enkaphalins) are _________ (suppress pain) F. Multiple _________ types amplify the effects of neurotransmitters 1. Neurotransmitter receptors are either ______-gated ion channels or ___ _________linked receptors that stimulate 2nd messengers 2. ___________ receptors, to which ____ binds, have two subtypes a. ___________ receptors (nicotine is an agonist) are _____-gated ion channels found on skeletal ________, in the sympathetic NS and in the CNS 1) ACh binds to and opens ____ channels in the postsynaptic neuron, allowing Na+ to enter and K+ to leave the neuron 2) Na+ influx ________ the neuron, causing a ______ potential. If the depolarization is strong enough, an _______ potential is triggered in the postsynaptic cell. 3) Ligand-gated ion channels are _________ – they open ion channels b. _________ receptors (fungal muscarine is an agonist) are found in the ____sympathetic NS and CNS; they are linked to __ _______ with 2nd messengers 1) ACh binds to the G protein-linked receptor, which activates a ___ _______, which activates a ____ messenger 2) __________ vary according to the receptor subtype 3. __________ receptors include alpha (__) and beta (__), which are also ___ ________linked receptors and initiate 2nd messenger cascades 4. ________ and neuropeptides have ____________ effects that use a second messenger, such as _____, to change the metabolism of the postsynaptic cell. a. When the ligand binds to the _______, it activates the production of a ____ messenger, which causes the following effects in the postsynaptic cell b. Metabolic _________ can be turned on and off c. Other internal messengers can enter the _________ and trigger the synthesis of new ________ d. Intracellular messengers can bind to another ____ ___________ and open it G. Neurotransmitter activity is quickly __________ in several ways 1. ACh is broken down by acetylcholinesterase (______), then ________ is actively _________ back into the presynaptic axon to make more ACh 9 2. Norepinephrine (____) is actively ___________ back into the presynaptic axon, to be used again or broken down by monoamine oxidase (_____) 3. _______, polypeptides, and amino acid neurotransmitters in the CNS move into the _____ or are actively _________ back into the presynaptic axon to be metabolized or used again VI. ____________ of Neural Information Transfer A. Neural pathways may involve ______ neurons simultaneously 1. Neuronal ______ are the pathways among neurons, like a circuit board of an electrical appliance. Types of neuronal circuits are a. __________ circuit – one nerve fiber branches and synapses with _________ postsynaptic cells; allows one neuron to control _____ other cells (e.g., 1 motor neuron controls many skeletal muscle cells) b. __________ circuit – several neurons synapse with ___ neuron or a neuronal pool; allows input from several body regions (e.g., eyes, inner ear) to another area (e.g., brain area for equilibrium) 2. Summation and inhibition – a neuron may receive input from ___________ of presynaptic neurons at one time, causing the following effects a. ____________ – the process of “_________ up” postsynaptic potentials (+____s and –_____s) and responding to their ____ effect; if the EPSPs override the IPSPs, a nerve impulse may be generated. Two types of summation are: 1) ___________ (time) summation – occurs when one presynaptic neuron generates EPSPs so _________ that each is generated before the other decays; which can add up to __________ and cause an action potential 2) __________ (space) summation – occurs when EPSPs from _______ presynaptic neurons add up to ___________ at the axon hillock of one postsynaptic neuron 3. Postsynaptic __________ occurs when one neuron suppresses the effect of a another neuron (e.g., a neuron that generates ____s prevents neurotransmitter release by another neuron) B. Synaptic activity can be _________ 1. ___________ modulation allows selective modulation of axon __________ and their target cells a. Presynaptic ___________ occurs when a presynaptic neuron __________ neurotransmitter release by a postsynaptic cell b. Presynaptic __________ occurs when the presynaptic neuron ___________ neurotransmitter release by the postsynaptic cell 2. ______synaptic modulation occurs when a modulatory neuron, usually _________, synapses with the _________ or cell body of a postsynaptic cell C. Disorders of _________ transmission are responsible for many diseases 1. Synaptic ________ are exposed to the ______cellular fluid, thus are more accessible to _______ than intracellular receptors 2. Common drugs that act on synaptic activity include ________ and nicotine (stimulants), and _________ (a depressant) 3. Nervous system disorders related to faulty synaptic transmission include _____________, schizophrenia, and depression a. Drugs used to treat schizophrenia, anxiety, and ________ act by influencing activity at the synapse