Neurons and Nervous Systems

1. Neurons & Nervous
Chapter 39

2. 2
Neurons & Nervous SyNeurons & Nervous Sy
OutlineOutline
EVOLUTION OF THE NERVOUS SYSTEMEVOLUTION OF THE NERVOUS SYSTEM
 Gradual increase in the complexity of the nervous systemGradual increase in the complexity of the nervous system
 All vertebrates have a well-developed brainAll vertebrates have a well-developed brain
NERVOUS TISSUENERVOUS TISSUE
 NeuronsNeurons
 Nerve impulseNerve impulse
BRAIN AND SPINAL CORDBRAIN AND SPINAL CORD
 Spinal cordSpinal cord
 CerebrumCerebrum
­ Sensory inputSensory input
­ Motor controlMotor control
 HomeostasisHomeostasis
 Limbic systemLimbic system
PERIPHERAL NERVOUS SYSTEMPERIPHERAL NERVOUS SYSTEM
 NervesNerves
 Somatic systemSomatic system
 Autonomic systemAutonomic system

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Neurons & Nervous SyNeurons & Nervous Sy
Invertebrate Nervous OrganizationInvertebrate Nervous Organization
HydrasHydras
Nerve net composed of neurons in contactNerve net composed of neurons in contact
with one anotherwith one another
Also in contact with contractileAlso in contact with contractile
epitheliomuscular cellsepitheliomuscular cells
PlanariansPlanarians
Ladderlike nervous systemLadderlike nervous system
Cephalization - a concentration of gangliaCephalization - a concentration of ganglia
and sensory receptors in the headand sensory receptors in the head
Annelids, Arthropods and MolluscsAnnelids, Arthropods and Molluscs
Complex animalsComplex animals
True nervous systemsTrue nervous systems

4. 4Evolution of the Nervous
System

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Neurons & Nervous SyNeurons & Nervous Sy
Vertebrate Nervous OrganizationVertebrate Nervous Organization
Central nervous systemCentral nervous system
Develops from an embryonic dorsalDevelops from an embryonic dorsal
tubular nerve cordtubular nerve cord
Cephalization and bilateral symmetryCephalization and bilateral symmetry
result in several paired sensory receptorsresult in several paired sensory receptors
Vertebrate brain is organized into threeVertebrate brain is organized into three
areasareas
HindbrainHindbrain
MidbrainMidbrain
Forebrain

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Neurons & Nervous SyNeurons & Nervous Sy
Human Nervous SystemHuman Nervous System
Nervous system has three specificNervous system has three specific
functionsfunctions
Receiving sensory inputReceiving sensory input
Performing integrationPerforming integration
Generating motor outputGenerating motor output

7. 7Organization of the
Human Nervous
System

8. 8
Neurons & Nervous SyNeurons & Nervous Sy
Human Nervous SystemHuman Nervous System
Central nervous system (CNS)Central nervous system (CNS)
Includes the brain and spinal cordIncludes the brain and spinal cord
Lies in the midline of the bodyLies in the midline of the body
The peripheral nervous system (PNS)The peripheral nervous system (PNS)
Contains cranial nerves and spinal nervesContains cranial nerves and spinal nerves
thatthat
Gather info from sensors and conductGather info from sensors and conduct
decisions to effectorsdecisions to effectors
Lies outside the CNSLies outside the CNS

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Neurons & Nervous SyNeurons & Nervous Sy
Nervous TissueNervous Tissue
NeuronsNeurons
Cell body contains nucleusCell body contains nucleus
Dendrites receive signals from sensoryDendrites receive signals from sensory
receptorsreceptors
Axon conducts nerve impulsesAxon conducts nerve impulses
­ Covered by myelin sheathCovered by myelin sheath
­ Any long axon is also called a nerve fiberAny long axon is also called a nerve fiber

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Neurons & Nervous SyNeurons & Nervous Sy
Types of NeuronsTypes of Neurons
Motor NeuronsMotor Neurons
Accept nerve impulses from the CNSAccept nerve impulses from the CNS
Transmit them to muscles or glandsTransmit them to muscles or glands
Sensory NeuronsSensory Neurons
Accept impulses from sensory receptorsAccept impulses from sensory receptors
Transmit them to the CNSTransmit them to the CNS
InterneuronsInterneurons
Convey nerve impulses between variousConvey nerve impulses between various
parts of the CNSparts of the CNS

11. 11Neuron
Anatomy

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Neurons & Nervous SyNeurons & Nervous Sy
Nerve Impulses:Nerve Impulses:
Resting PotentialResting Potential
Resting PotentialResting Potential
The membrane potential (voltage) whenThe membrane potential (voltage) when
the axon is not conducting an impulsethe axon is not conducting an impulse
­ The inside of a neuron is more negativeThe inside of a neuron is more negative
than the outside -65 mVthan the outside -65 mV
­ Due in part to the action of the sodium-Due in part to the action of the sodium-
potassium pumppotassium pump

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Neurons & Nervous SyNeurons & Nervous Sy
Action PotentialAction Potential
An action potential is generated only afterAn action potential is generated only after
a stimulus larger than the thresholda stimulus larger than the threshold
Gated channel proteinsGated channel proteins
Suddenly allows sodium to pass throughSuddenly allows sodium to pass through
the membranethe membrane
Another allows potassium to pass throughAnother allows potassium to pass through
other directionother direction

14. 14Resting and Action Potential
of the
Axonal Membrane

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Neurons & Nervous SyNeurons & Nervous Sy
Propagation of Action PotentialsPropagation of Action Potentials
In myelinated fibers, an action potentialIn myelinated fibers, an action potential
at one node causes an action potentialat one node causes an action potential
at the next nodeat the next node
Saltatory (jumping) ConductionSaltatory (jumping) Conduction
Conduction of a nerve impulse is an all-Conduction of a nerve impulse is an all-
or-nothing eventor-nothing event
Intensity of signal is determined by howIntensity of signal is determined by how
many impulses are generated within amany impulses are generated within a
given time spangiven time span

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Neurons & Nervous SyNeurons & Nervous Sy
Transmission Across a SynapseTransmission Across a Synapse
A synapse is a region where neuronsA synapse is a region where neurons
nearly touchnearly touch
Small gap between neurons is theSmall gap between neurons is the
synaptic cleftsynaptic cleft
Transmission across a synapse is carriedTransmission across a synapse is carried
out by neurotransmittersout by neurotransmitters
Sudden rise in calcium at end of oneSudden rise in calcium at end of one
neuronneuron
Stimulates synaptic vesicles to mergeStimulates synaptic vesicles to merge
with the presynaptic membranewith the presynaptic membrane
Neurotransmitter molecules are releasedNeurotransmitter molecules are released

17. 17Synapse Structure and
Function

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Neurons & Nervous SyNeurons & Nervous Sy
Synaptic IntegrationSynaptic Integration
A single neuron is on the receiving end ofA single neuron is on the receiving end of
Many excitatory signals, andMany excitatory signals, and
Many inhibitory signalsMany inhibitory signals
IntegrationIntegration
The summing of signals fromThe summing of signals from
Excitatory signals, andExcitatory signals, and
Inhibitory signalsInhibitory signals

19. 19Synapse
Integration

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Neurons & Nervous SyNeurons & Nervous Sy
CNS: Brain and Spinal CordCNS: Brain and Spinal Cord
Spinal cord and brain are wrapped inSpinal cord and brain are wrapped in
three protective membranes, meningesthree protective membranes, meninges
Spaces between meninges are filled withSpaces between meninges are filled with
cerebrospinal fluidcerebrospinal fluid
Fluid is continuous with that of centralFluid is continuous with that of central
canal of spinal cord and the ventricles ofcanal of spinal cord and the ventricles of
the brainthe brain

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Neurons & Nervous SyNeurons & Nervous Sy
Spinal CordSpinal Cord
The spinal cord has two main functionsThe spinal cord has two main functions
Center for many reflex actionsCenter for many reflex actions
Means of communication between theMeans of communication between the
brain and spinal nervesbrain and spinal nerves
The spinal cord is composed of grayThe spinal cord is composed of gray
matter and white mattermatter and white matter
Cell bodies and short unmyelinated fibersCell bodies and short unmyelinated fibers
give the gray matter its colorgive the gray matter its color
Myelinated long fibers of interneuronsMyelinated long fibers of interneurons
running in tracts give white matter itsrunning in tracts give white matter its
colorcolor

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Neurons & Nervous SyNeurons & Nervous Sy
The BrainThe Brain
Cerebrum is the largest portion of theCerebrum is the largest portion of the
brain in humansbrain in humans
Communicates with, and coordinates theCommunicates with, and coordinates the
activities of, the other parts of the brainactivities of, the other parts of the brain
Longitudinal fissure divides into left andLongitudinal fissure divides into left and
right cerebral hemispheresright cerebral hemispheres

23. 23The Human
Brain

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Neurons & Nervous SyNeurons & Nervous Sy
Cerebral CortexCerebral Cortex
A thin but highly convoluted outer layer ofA thin but highly convoluted outer layer of
gray mattergray matter
Covers the cerebral hemispheresCovers the cerebral hemispheres
Contains motor areas and sensory areasContains motor areas and sensory areas
as well as association areasas well as association areas
Primary motor area is in the frontal lobePrimary motor area is in the frontal lobe
just ventral to central sulcusjust ventral to central sulcus
Primary somatosensory area is just dorsalPrimary somatosensory area is just dorsal
to central sulcusto central sulcus

25. 25The Lobes of a Cerebral
Hemisphere

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Neurons & Nervous SyNeurons & Nervous Sy
CerebrumCerebrum
Rest of cerebrum is composed of whiteRest of cerebrum is composed of white
mattermatter
Descending tracts communicate withDescending tracts communicate with
lower brain centerslower brain centers
Ascending tracts send sensoryAscending tracts send sensory
information to primary somatosensoryinformation to primary somatosensory
areaarea
Basal nucleiBasal nuclei
­ Integrate motor commandsIntegrate motor commands
­ Ensure that the proper muscle groups areEnsure that the proper muscle groups are

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Neurons & Nervous SyNeurons & Nervous Sy
DiencephalonDiencephalon
A region encircling the third ventricleA region encircling the third ventricle
Consists of hypothalamus and thalamusConsists of hypothalamus and thalamus
Hypothalamus forms floor of the thirdHypothalamus forms floor of the third
ventricleventricle
Thalamus consists of two masses of grayThalamus consists of two masses of gray
matter located in the sides and roof of thematter located in the sides and roof of the
third ventriclethird ventricle
Pineal glandPineal gland
Also located in the diencephalonAlso located in the diencephalon


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Neurons & Nervous SyNeurons & Nervous Sy
CerebellumCerebellum
Separated from the brain stem by theSeparated from the brain stem by the
fourth ventriclefourth ventricle
Receives sensory input from the eyes,Receives sensory input from the eyes,
ears, joints, and musclesears, joints, and muscles
Sends motor impulses out the brain stemSends motor impulses out the brain stem
to the skeletal musclesto the skeletal muscles

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Neurons & Nervous SyNeurons & Nervous Sy
Brain StemBrain StemContains the midbrain, the pons, and theContains the midbrain, the pons, and the
medulla oblangatamedulla oblangata
MidbrainMidbrain
­ Acts as a relay station for tracts passingActs as a relay station for tracts passing
betweenbetween
 The cerebrum, andThe cerebrum, and
 The spinal cord or cerebellumThe spinal cord or cerebellum
PonsPons
­ Helps regulate breathing and headHelps regulate breathing and head
movementsmovements
Medulla oblongataMedulla oblongata
­ Contains reflex centers for vomiting,Contains reflex centers for vomiting,
coughing, sneezing, hiccuping, andcoughing, sneezing, hiccuping, and

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Neurons & Nervous SyNeurons & Nervous Sy
Limbic SystemLimbic System
Complex network of tracts and “nuclei”Complex network of tracts and “nuclei”
Incorporates medial portions ofIncorporates medial portions of
The cerebral lobes,The cerebral lobes,
The subcortical basal nuclei, andThe subcortical basal nuclei, and
The dicenephalonThe dicenephalon
Integrates higher mental functions andIntegrates higher mental functions and
primitive emotionsprimitive emotions
HippocampusHippocampus
AmygdalaAmygdala

31. 31The Limbic
System

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Neurons & Nervous SyNeurons & Nervous Sy
Peripheral Nervous SystemPeripheral Nervous System
Somatic systemSomatic system
 Contains cranial nerves and spinal nervesContains cranial nerves and spinal nerves
­ Gather info from sensors and conduct decisions to effectorsGather info from sensors and conduct decisions to effectors
­ Controls the skeletal musclesControls the skeletal muscles
 Conscious of its activityConscious of its activity
Autonomic systemAutonomic system
 Controls the smooth muscles, cardiac muscles, and glandsControls the smooth muscles, cardiac muscles, and glands
 Usually unaware of its actionsUsually unaware of its actions
 Divided into two divisionsDivided into two divisions
­ Sympathetic divisionSympathetic division
­ Parasympathetic divisionParasympathetic division

33. 33Cranial and Spinal
Nerves

34. 34A Reflex Arc Showing
the
Path of a Spinal
Reflex

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Neurons & Nervous SyNeurons & Nervous Sy
Autonomic SystemAutonomic System
Regulates activity of cardiac and smoothRegulates activity of cardiac and smooth
muscle, and glandsmuscle, and glands
Divided into sympathetic andDivided into sympathetic and
parasympathetic divisionsparasympathetic divisions
Function automatically and usually in anFunction automatically and usually in an
involuntary mannerinvoluntary manner
Innervate all internal organsInnervate all internal organs
Utilize two neurons and one ganglion forUtilize two neurons and one ganglion for
each impulseeach impulse

36. 36Autonomic System
Structure and
Function

37. 37
Neurons & Nervous SyNeurons & Nervous Sy
Sympathetic andSympathetic and
Parasympathetic DivisionsParasympathetic Divisions
Sympathetic divisionSympathetic division
Especially important during fight or flightEspecially important during fight or flight
responsesresponses
Accelerates heartbeat and dilates bronchiAccelerates heartbeat and dilates bronchi
Parasympathetic divisionParasympathetic division
Promotes all internal responsesPromotes all internal responses
associated with a relaxed stateassociated with a relaxed state
Promotes digestion and retards heartbeatPromotes digestion and retards heartbeat

38. 38
Neurons & Nervous SyNeurons & Nervous Sy
ReviewReview
EVOLUTION OF THE NERVOUS SYSTEMEVOLUTION OF THE NERVOUS SYSTEM
 Gradual increase in the complexity of the nervous systemGradual increase in the complexity of the nervous system
 All vertebrates have a well-developed brainAll vertebrates have a well-developed brain
NERVOUS TISSUENERVOUS TISSUE
 NeuronsNeurons
 Nerve impulseNerve impulse
BRAIN AND SPINAL CORDBRAIN AND SPINAL CORD
 Spinal cordSpinal cord
 CerebrumCerebrum
­ Sensory inputSensory input
­ Motor controlMotor control
 HomeostasisHomeostasis
 Limbic systemLimbic system
PERIPHERAL NERVOUS SYSTEMPERIPHERAL NERVOUS SYSTEM
 NervesNerves
 Somatic systemSomatic system
 Autonomic systemAutonomic system

39. Neurons & Nervous
Ending Slide Chapter 39