Module 12- The Nervous System.pdf
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ODULE12.1:THENERVOUSSYSTEM-NERVOUS M THREE STAGES OF INFORMATION PROCESSING COMMUNICATION ensory Input: Sensors detect external...
ODULE12.1:THENERVOUSSYSTEM-NERVOUS M THREE STAGES OF INFORMATION PROCESSING COMMUNICATION ensory Input: Sensors detect external stimuli and S LINES OF COMMUNICATION internal conditions and transmit information along sensory neurons. eurons: These are nerve cells that transfer N information within the body. Integration: Sensory information is sent tothebrain or ganglia, where interneurons integrate the It uses two types of signals to communicate: information. Electrical signals(long-distance) Chemical signals(short-distance) otor Output: Motor output leaves the brain or M ganglia via motorneurons,whichtriggermuscleor anglia:Thesearesimpleclustersofneuronswhere G gland activity. the processing of information takes place. rain: It has a more complex organization of B neurons. NEURON STRUCTURE & FUNCTION ell Body: This is where most of a neuron’s C organelles are in. endrites: Highly branched extensionsthatreceive D signalsfrom other neurons. xon: It is a much longer extension that transmits A Inthisexample,thesiphonsurveystheenvironment signalsto other cells at synapses. through external stimuli. That information is then integratedandprocessed(concludingthatthereis xon Hillock: It is a cone-shaped base of an A prey). The motor output is then acteduponwhich axon. means catching the prey. ynapse: It is a junction betweenanaxonand S Ion pumps and Ion Channels establish the resting another cell → passing of neurotransmitters to potential of a neuron another cell. embrane Potential: Every cell has a voltage M (difference in electrical charge) across its plasma membrane. esting Potential: The membrane potential of a R neuron not sending signals(negatively charged). hanges in membrane potential act as signals, C transmitting and processing information. 26 RESTING POTENTIAL IN MAMMALIAN NEURON + concentration → highest INSIDE the cell K Na+ concentration → highest OUTSIDE the cell odium-potassium Pumps maintain thesegradients S across the plasma membrane. neuron at resting potential has many open K+ A channels; K+ diffuses out of the cell. T hebuildupofnegativechargewithintheneuronis themajor sourceof membrane potential. T he resting potential is always negative. It is only when a strong depolarizing stimulus causes the neuroncelltobeslightlylessnegativeandreaches a certain threshold will an action potential occur. efractory Period: After an action potential, a R second action potential cannot be initiated. It is a result of a temporary inactivationoftheNa+ channels. The nerve is unable to create anaction potential. CTION POTENTIAL A Summary It is amassivechangeinmembranevoltagewhen 1. Neurons are not sending signals;negatively themembrane potential passes a certain level. charged. 2. Allornone:Neuronswilleitherbestimulated It has aconstantmagnitude,all-or-none(triggered or not. or not at all), and can transmit signals over long 3. Iongatedchannelsopen:(1)Cellbecomes distances. more positive, and (2) Action potential 4. Period of no action potential and neurons Itoccurswhenneuronscontaingatedionchannels cannot be activated (5). open or closed in response to stimuli. epolarization: It is triggered by the opening ion D channels. It is a reduction in themagnitudeofthe membrane potential. n action potential occurs when the resting A potential is depolarized. 27 EVOLUTIONARY ADAPTATIONS OF THE AXON T he neurotransmitter diffuses across the synaptic STRUCTURE cleftand isreceivedby thepostsynaptic cell. Thespeedofanactionpotentialincreaseswiththe axon’s diameter(directly proportional). yelinSheaths:Itinsulatestheaxonsinvertebrates, M which causes an action potential’s speed to increase. It is made by glia (glial cells). The glial cells are called differently by location: Oligodendrocytes in the CNS (Central Nervous System) Schwann cells in the PNS (Peripheral Nervous System) EUROTRANSMITTERS N A single neurotransmitter may bind specifically to more than a dozen different receptors. eceptor activation and postsynaptic response R odesofRanvier:Itisthegapsbetweenthemyelin N endswhenneurotransmittersareremovedfromthe sheaths where voltage-gated Na+ channels are synaptic cleft. found. It is whereaction potentials are performed. cetylcholine: It is a common neurotransmitter in A altatory Conduction: It is a process where S vertebrates and invertebrates. It is involved in action potentials in myelinated axons jump muscle stimulation, memory formation, and between the nodes of Ranvier. learning. NEURON COMMUNICATION AT SYNAPSES T he presynaptic neuron synthesizes and packages theneurotransmittersinsynapticvesicleslocatedin the synaptic terminal. T he action potential causes the release of the neurotransmitter. 28 ODULE 12.2: THE DIVISIONS AND FUNCTIONS M GLIA / GLIAL CELLS OF THE VERTEBRATE NERVOUS SYSTEM Functions to nourish, support, and regulate neurons. ervous systems consist of circuits of neurons and N supporting cells y the timeoftheCambrianexplosion,specialized B systems of neurons had appeared that enabled animals to sense their environments and respond rapidly. nidarians: The simplest animals with nervous C systems that haveneurons arranged in nerve nets. These types of Glia are part of the CNS: Ependymal Cells ore complex animals have nerves, in which the M Astrocytes axons of multiple neurons are bundled together. Oligodendrocytes BILATERAL ANIMALS & CEPHALIZATION These types of Glia are part of the PNS: Schwann Cells ephalization: The clustering of sensory organs at C Microglia the front end of the body. ORGANIZATION OF THE VERTEBRATE NERVOUS entral NervousSystem(CNS):Itconsistsofabrain C SYSTEM and longitudinal nerve cords. Flatworms are the The CNS develops from the hollow nerve cord. simplest cephalized animals. T hecavityofthenervecordgivesrisetothenarrow eripheral Nervous System (PNS): It consists of P central canal of the spinal cordandtheventricles neurons carrying information into and out of the of the brain. CNS. T hecanalandventriclesfillwithcerebrospinalfluid, Nervous system organization correlates with Lifestyle whichsuppliestheCNSwithnutrientsandhormones andcarriesawaywastes.Thebrainandspinalcord S essilemolluscs(ex:clamsandchitons)havesimple contain: systems (they don’t really move). ray Matter: Consists of neuron cell bodies, G ore complex molluscs(ex:octopusesandsquids) M dendrites andunmyelinated axons. have more sophisticated systems. hite Matter: Consistsofbundlesofmyelinated W axons. 29 pinalCord:Itconveysinformationtoandfromthe S brain and generates basic patternsoflocomotion. It also produces reflexes independent of the brain. T HE PERIPHERAL NERVOUS SYSTEM IttransmitstheinformationtoandfromtheCNSand regulates movement and the internal environment. REGIONALLY SPECIALIZED VERTEBRATE BRAIN Afferent Neurons→ transmit information TO the CNS Efferent Neurons→ transmit information AWAY The vertebrate brain has three major regions. FROM the CNS F orebrain: Activities include processing of olfactory input, regulation of sleep, and any complex processing. Midbrain:Coordinates routing of sensory input. indbrain: Controls involuntary activities and H coordinates motor activities. The PNS has 2 Efferent Components otor System: It carries signals to skeletal muscles M and is voluntary. utonomicNervousSystem:Itregulatesthesmooth A omparison of vertebratesshowsthatrelativesizes C and cardiac muscles and is generally involuntary. of particular brain regions vary. ympathetic Division: Regulates arousal and S energy generation (fight-or-flight response) arasympathetic Division: It has antagonistic P effectsontargetorgansandpromotescalming and a return to “rest and digest” functions. 30 T hese size differences reflect the relative importance of the particular brain function. T he Cerebral Cortex controls voluntary movement and cognitive functions. Frontal Lobe:It has the following functions Control of skeletal muscles (motor cortex) Decision making & planning (prefrontal cortex) Forming speech (Broca’s area) Temporal Lobe:It has the following functions Hearing (auditory cortex) Comprehending language (Wernicke’s area) Parietal Lobe:It has the following functions Sense of touch (somatosensory cortex) Integration of sensory information (Sensory association cortex) Occipital Lobe:It has the following functions Combining images and object recognition (visual association cortex) 31
