Is the hash of the previous block included in the block header?
The block header is 80 bytes:


Version number: 4 bytes
Previous block header hash: 32 bytes
Merkle root: 32 bytes
Timestamp: 4 bytes
Bits: 4 bytes
Nonce: 4 bytes


The merkle tree hashes all the transactions in the block, the bits field is used to compute the target hash for the header, finally, the nonce is used as a counter to generate new block headers from a given merkle tree.