Neurons & Nervous Systems 1 Human Nervous System Nervous system has three specific functions Receiving sensory input Performing integration Generating

1Neurons & NerNeurons & Nervous Systemsvous Systems

Human Nervous SystemHuman Nervous System

Nervous system has three specific Nervous system has three specific functionsfunctions

Receiving sensory inputReceiving sensory input

Performing integrationPerforming integration

Generating motor outputGenerating motor output

Regulating autonomous functionsRegulating autonomous functions


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 Contains cranial nerves and spinal nerves that nerves that

Gather info from sensors and conduct Gather info from sensors and conduct decisions to effectorsdecisions to effectors

Lies outside the CNSLies outside the CNS


Nervous TissueNervous TissueNeuronsNeurons

Cell body contains nucleusCell body contains nucleus

Dendrites receive signals from sensory Dendrites 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


Types of NeuronsTypes of Neurons

Motor NeuronsMotor NeuronsAccept nerve impulses from the CNSAccept nerve impulses from the CNSTransmit them to muscles or glandsTransmit them to muscles or glands

Sensory Neurons Sensory Neurons Accept impulses from sensory Accept impulses from sensory receptorsreceptors

Transmit them to the CNSTransmit them to the CNS

InterneuronsInterneuronsConvey nerve impulses between Convey nerve impulses between various parts of the CNSvarious parts of the CNS

5Neurons & NerNeurons & Nervous Systemsvous SystemsNerve Impulses:Nerve Impulses:

Resting PotentialResting Potential

Resting PotentialResting Potential

The membrane potential (voltage) The membrane potential (voltage) when the axon is not conducting an when the axon is not conducting an impulseimpulse

The inside of a neuron is more negative The 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


Action PotentialAction Potential

An action potential is generated only An action potential is generated only after a stimulus larger than the after a stimulus larger than the thresholdthreshold

Gated channel proteinsGated channel proteins

Suddenly allows sodium to pass Suddenly allows sodium to pass through the membranethrough the membrane

Another allows potassium to pass Another allows potassium to pass through other directionthrough other direction


Propagation of Action PotentialsPropagation of Action Potentials

In myelinated fibers, an action In myelinated fibers, an action potential at one node causes an potential at one node causes an action potential at the next nodeaction potential at the next node

Saltatory (jumping) ConductionSaltatory (jumping) Conduction

Conduction of a nerve impulse is an Conduction of a nerve impulse is an all-or-nothing eventall-or-nothing event

Intensity of signal is determined by Intensity of signal is determined by how many impulses are generated how many impulses are generated within a given time spanwithin a given time span


Transmission Across a SynapseTransmission Across a SynapseA synapse is a region where neurons A synapse is a region where neurons nearly touchnearly touch

Small gap between neurons is the Small gap between neurons is the synaptic cleftsynaptic cleft

Transmission across a synapse is carried Transmission across a synapse is carried out by neurotransmittersout by neurotransmitters

Sudden rise in calcium at end of one Sudden rise in calcium at end of one neuronneuron

Stimulates synaptic vesicles to merge with Stimulates synaptic vesicles to merge with the presynaptic membranethe presynaptic membrane

Neurotransmitter molecules are released Neurotransmitter molecules are released into the synaptic cleftinto the synaptic cleft


Synaptic IntegrationSynaptic Integration

A single neuron is on the receiving A single neuron is on the receiving end ofend 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 signals Inhibitory signals


CNS: Brain and Spinal CordCNS: Brain and Spinal Cord

Spinal cord and brain are wrapped in Spinal cord and brain are wrapped in three protective membranes, three protective membranes, meningesmeninges

Spaces between meninges are filled Spaces between meninges are filled with cerebrospinal fluid (CSF)with cerebrospinal fluid (CSF)

Fluid is continuous with that of central Fluid is continuous with that of central canal of spinal cord and the ventricles canal of spinal cord and the ventricles of the brainof the brain

Blood Brain Barrier (BBB): Functional Blood Brain Barrier (BBB): Functional barrier between blood and CSFbarrier between blood and CSF


Spinal CordSpinal CordThe 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 the Means of communication between the brain and spinal nervesbrain and spinal nerves

The spinal cord is composed of gray The spinal cord is composed of gray matter and white mattermatter and white matter

Cell bodies and short unmyelinated Cell bodies and short unmyelinated fibers give the gray matter its colorfibers give the gray matter its color

Myelinated long fibers of interneurons Myelinated long fibers of interneurons running in tracts give white matter its running in tracts give white matter its colorcolor


The BrainThe Brain

Cerebrum is the largest portion of the Cerebrum is the largest portion of the brain in humansbrain in humans

Communicates with, and coordinates Communicates with, and coordinates the activities of, the other parts of the the activities of, the other parts of the brainbrain

Longitudinal fissure divides into left Longitudinal fissure divides into left and right cerebral hemispheresand right cerebral hemispheres


Cerebral CortexCerebral Cortex

A thin but highly convoluted outer A thin but highly convoluted outer layer of gray matterlayer of gray matter

Covers the cerebral hemispheresCovers the cerebral hemispheres

Contains motor areas and sensory Contains motor areas and sensory areas as well as association areasareas as well as association areas

Primary motor area is in the frontal Primary motor area is in the frontal lobe just ventral to central sulcuslobe just ventral to central sulcus

Primary somatosensory area is just Primary somatosensory area is just dorsal to central sulcusdorsal to central sulcus


CerebrumCerebrumRest of cerebrum is composed of white Rest of cerebrum is composed of white mattermatter

Descending tracts communicate with Descending tracts communicate with lower brain centerslower brain centers

Ascending tracts send sensory Ascending tracts send sensory information to primary somatosensory information to primary somatosensory areaarea

Basal nucleiBasal nuclei

Integrate motor commandsIntegrate motor commands

Ensure that the proper muscle groups are Ensure that the proper muscle groups are either activated or inhibitedeither activated or inhibited


DiencephalonDiencephalonA region encircling the third ventricleA region encircling the third ventricle

Consists of hypothalamus and thalamus Consists of hypothalamus and thalamus

Hypothalamus forms floor of the third Hypothalamus forms floor of the third ventricleventricle

Thalamus consists of two masses of gray Thalamus consists of two masses of gray matter located in the sides and roof of matter located in the sides and roof of the third ventriclethe third ventricle

Pineal glandPineal gland

Also located in the diencephalonAlso located in the diencephalon

Secretes melatoninSecretes melatonin


CerebellumCerebellum

Separated from the brain stem by the Separated 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 Sends motor impulses out the brain stem to the skeletal musclesstem to the skeletal muscles


Brain StemBrain Stem

Contains the midbrain, the pons, and the medulla Contains the midbrain, the pons, and the medulla oblangataoblangata MidbrainMidbrain Acts as a relay station for tracts passing Acts 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 head movementsHelps regulate breathing and head movements

Medulla oblongataMedulla oblongata Contains reflex centers for vomiting, coughing, Contains reflex centers for vomiting, coughing, sneezing, hiccuping, and swallowingsneezing, hiccuping, and swallowing


Limbic SystemLimbic System

Complex network of tracts and Complex network of tracts and “nuclei”“nuclei”

Incorporates medial portions ofIncorporates medial portions ofThe cerebral lobes,The cerebral lobes,

The subcortical basal nuclei, andThe subcortical basal nuclei, and

The dicenephalonThe dicenephalon

Integrates higher mental functions Integrates higher mental functions and primitive emotionsand primitive emotionsHippocampusHippocampus

AmygdalaAmygdala


Peripheral Nervous SystemPeripheral Nervous SystemSomatic systemSomatic system

Contains cranial nerves and spinal nervesContains cranial nerves and spinal nerves

Gather info from sensors and conduct decisions to Gather info from sensors and conduct decisions to effectorseffectors

Controls the skeletal musclesControls the skeletal muscles

Conscious of its activityConscious of its activity

Autonomic systemAutonomic system Controls the smooth muscles, cardiac muscles, and Controls the smooth muscles, cardiac muscles, and glandsglands

Usually unaware of its actionsUsually unaware of its actions

Divided into two divisionsDivided into two divisions

Sympathetic divisionSympathetic division

Parasympathetic divisionParasympathetic division


Autonomic SystemAutonomic System

Regulates activity of cardiac and Regulates activity of cardiac and smooth muscle, and glandssmooth muscle, and glands

Divided into sympathetic and Divided into sympathetic and parasympathetic divisionsparasympathetic divisions

Function automatically and usually in Function automatically and usually in an involuntary manneran involuntary manner

Innervate all internal organsInnervate all internal organs

Utilize two neurons and one ganglion Utilize two neurons and one ganglion for each impulsefor each impulse

21Neurons & NerNeurons & Nervous Systemsvous SystemsSympathetic andSympathetic and

Parasympathetic DivisionsParasympathetic DivisionsSympathetic divisionSympathetic division

Especially important during fight or Especially important during fight or flight responsesflight responses

Accelerates heartbeat and dilates Accelerates heartbeat and dilates bronchibronchi

Parasympathetic divisionParasympathetic division

Promotes all internal responses Promotes all internal responses associated with a relaxed stateassociated with a relaxed state

Promotes digestion and retards Promotes digestion and retards heartbeatheartbeat


SomaticAutonomous

Motor Sensory

SympatheticParasympathetic

AfferentEfferent

ExcitatoryInhibitory

AgonistAntagonist

Define the following pairs of terms:

PresynapticPostsynaptic

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Neurons & Nervous Systems 1 Human Nervous System Nervous system has three specific functions Receiving sensory input Performing integration Generating