This is New Testament terminology. Please see I Cor. 10:16-17; Eph. 5:29-32.
This is MISAPPLIED Biblical terminology. I Corinthians 10:16-17 refers to the Lord's Supper where Paul teaches about the Lord's Supper in ABSTRACT generic terms or terms applicable to all baptized believers in local church relationship when observing the Supper (because it cannot be observed by all christians at once) and then makes the concrete application to the church at Corinthin in I Cor. 10:20-21.
Notice the teaching is about SANCTIFICATION not salvation as the context introduces "submission" to authority and continues this primary point all the way into Ephesians 6. Notice also that it begans with a GENERIC man and wife in Ephesians 5:23-25 and then proceeds to PLURAL men and wives in Ephesians 5:28 and finalizes in a LOCALIZED concrete application to a man and wife in Ephesians 5:29-32. Paul is simply instructing the church at Ephesus what the submissive roles of the wife to the husband, and thus men and their wives are, as he does children to parents and servants to masters. The church at Ephesus and all churches have a submissive role to Christ as their head in regard to SANCTIFICATION. The issue here is submission and authority in a practical working relationship between Christ and the New Testament Church in regard to progressive sanctification as with the wife to her husband.
The wife has a physical head SEPARATE from her husbands physical head. The term "head" simply means position of authority not some spiritual union where a head is attached to a headless body. Likewise the New Testament assembly has a SEPARATE METAPHORICAL HEAD OTHER THAN CHRIST:
I Cor. 12:21
And the eye cannot say unto the hand, I have no need of thee: nor again the head to the feet, I have no need of you.
Hence, Christ as our "head" simply means final authority in regard to WORKING RELATIONSHIPS with each other (members of one another) under Christ.
This has nothing to do with spiritual union (although that is a Biblical doctrine obtained by regeneration and justification) but with practical daily working relationships between members of the same local church under the final authority of Christ. The church at Corinth was "the body of Christ" just as the church at Ephesus was "the body of Christ" and each one contained their own "members in particular."