Hey Violetta, 
Thank you for your question! Based on some information found on the UMich Neuroscience Page, Biology 305 is a required core class for your intended major: https://lsa.umich.edu/lsa/academics/majors-minors/neuroscience-major.html. 
It is true that the course is not required for medical school, but is occasionally recommended for students as they prepare for the MCAT. If you plan on majoring in Neuroscience and taking the MCAT, it might be a great idea to consider taking Biology 305 before taking the MCAT just for a convenience sake. 
Now in terms of taking the class pass/fail, would that change the motivation and effort you would put into the course? The information obtained from the course is relevant to your potential major, so retaining that knowledge will be important for any career or professional choice you make in the future. This is something to keep in mind for taking any course as a pass/fail in the future!
Also, you can not take a course pass fail if it pertains to your major or minor : https://lsa.umich.edu/advising/policies-procedures/pass-fail.html
In that case, if you plan on majoring in Neuroscience, you would not be able to take the course pass/fail. If you have any other questions or concerns, please let us know or you can stop into our drop-in advising hours located on our website above!!
If you would like more advice about taking other courses pass/fail check out this past post: https://premedhubumich.com/question/taking-a-class-p-f-originally-asked-on-april-5th-2018/
Good Luck!
-Michael, PMH Advisor