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<!-- DFIN ActiveDisclosure(SM) XBRL Schema Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2020-08-10T15:16:40.4501015+00:00 -->
<!-- Version            : 5.0.1.476 -->
<!-- Package ID         : bd928dd0fd4e445ab8ac8a72fd41f3b2 -->
<!-- Copyright (c) 2020 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
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  <xsd:element id="slno_AssetAcquisitionContingentConsiderationChangeInFairValue" name="AssetAcquisitionContingentConsiderationChangeInFairValue" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="debit" />
  <xsd:element id="slno_IncomeLossFromMinorityInterestInvestments" name="IncomeLossFromMinorityInterestInvestments" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="slno_IssuanceOfCommonStockSharesUnderEquityIncentivePlans" name="IssuanceOfCommonStockSharesUnderEquityIncentivePlans" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="slno_IssuanceOfCommonStockValueUnderEquityIncentivePlans" name="IssuanceOfCommonStockValueUnderEquityIncentivePlans" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
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  <xsd:element id="slno_EarnoutPaymentsMember" name="EarnoutPaymentsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="slno_ExpirationOfWarrants" name="ExpirationOfWarrants" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="slno_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityExpiration" name="FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityExpiration" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" xbrli:balance="credit" />
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  <xsd:element id="slno_IncentiveStockOptionsMember" name="IncentiveStockOptionsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
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  <xsd:element id="slno_WarrantsToPurchaseCommonStockMember" name="WarrantsToPurchaseCommonStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
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  <xsd:element id="slno_TwoThousandAndTenAndTwoThousandAndTwelveConvertiblePromissoryNotesMember" name="TwoThousandAndTenAndTwoThousandAndTwelveConvertiblePromissoryNotesMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="slno_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" name="SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="slno_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedinPeriodWeightedAverageRemainingContractualTerm" name="SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsVestedinPeriodWeightedAverageRemainingContractualTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
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  <xsd:element id="slno_ClassOfWarrantOrRightWarrantsExpirationDate" name="ClassOfWarrantOrRightWarrantsExpirationDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="slno_ClassofWarrantOrRightLiquidatedDamagesAmountPercentofVolumeWeightedAveragePrice" name="ClassofWarrantOrRightLiquidatedDamagesAmountPercentofVolumeWeightedAveragePrice" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="slno_ClassOfWarrantOrRightWarrantsExpirationMonthAndYear" name="ClassOfWarrantOrRightWarrantsExpirationMonthAndYear" type="xbrli:gYearMonthItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="slno_SeriesAWarrantsToPurchaseCommonStockMember" name="SeriesAWarrantsToPurchaseCommonStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
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  <xsd:element id="slno_SeriesDWarrantsToPurchaseCommonStockMember" name="SeriesDWarrantsToPurchaseCommonStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
</xsd:schema>
