Module 12 - The Nervous System PDF
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This document provides an overview of the nervous system, covering topics such as neuron structure and function, lines of communication, and the three stages of information processing. It also delves into the resting and action potentials in neurons.
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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
