Alex McDonald, 27, of Hilly Park, Norton Fitzwarren, denies murdering Catherine McDonald, 57, in their home.
During the first day of the trial, the jury was told the accused had drunk at least four bottles of wine and had taken cocaine hours before the attack.
Exeter Crown Court heard she was killed in a "deliberate and determined way".
Prosecuting, Simon Laws QC, said: "He used a number of weapons and the attack was sexual as well as physical.
"This was not a case in which there was an argument that got out of hand, nor a man landing an unlucky blow."
A kitchen knife, knitting needle, a pair of scissors and power cord were used in the attack, he said.
The prosecution alleged Mr McDonald held a pair of scissors to his mother's throat as he sexually assaulted her.
When he had achieved that, he killed her, Mr Laws said.
The prosecution also suggested there were tensions between the two during the three months prior to her death.
He had moved back home having worked in bars along the Kent coastline since 2010.
The court also heard Mr McDonald was a recreational drug user and his drug taking and the effect on his mental health had worried his ex-girlfriend, who gave evidence.
On the night of the attack, the jury heard Mr McDonald had been exchanging texts of a sexual nature with a man he had been involved with in Kent.
The prosecution said it was fair to conclude by the end of these texts Mr McDonald was in "a state of sexual arousal".
So far, the accused has refused to give any account of what he did, the jury heard.
The prosecution also said people who knew the pair said they had a close and affectionate mother-son relationship and there was no evidence to show he had been violent to her before.
The accused has pleaded guilty to manslaughter.
The trial continues.
A man sexually assaulted, stabbed and strangled his mother with a power cord while she lay sleeping in her bed, a court has heard.