class ResponsesController < ApplicationController

  before_action :set_response, only: [:edit, :update, :destroy]

  def new
    @response = Response.new
  end

  def create
    question = Question.find(params[:question_id])
    response = Response.new(content: response_params[:content], user_id: session[:current_user])

    if response.save
      question.responses << response
      redirect_to response.question
    else
      render :new
    end
  end

  def edit
  end

  def update
    if @response.update(response_params)
      redirect_to @response.question
    else
      render :edit
    end
  end

  def destroy
    question = @response.question
    @response.destroy

    redirect_to question
  end

  def up_vote
    puts "=" * 50
    puts params
    puts "=" * 50

    @response = Response.find(params[:id])

    # @response.add_vote

    render text: @response.votes.count

  end

  private

  def set_response
    @response = Response.find(params[:id])
  end

  def response_params
    params.require(:response).permit(:content)
  end

end

class ResponsesController < ApplicationController

  before_action :set_response, only: [:edit, :update, :destroy]

  def new
    @response = Response.new
  end

  def create
    question = Question.find(params[:question_id])
    response = Response.new(content: response_params[:content], user_id: session[:current_user])

    if response.save
      question.responses << response
      redirect_to response.question
    else
      render :new
    end
  end

  def edit
  end

  def update
    if @response.update(response_params)
      redirect_to @response.question
    else
      render :edit
    end
  end

  def destroy
    question = @response.question
    @response.destroy

    redirect_to question
  end

  def up_vote
    response = Response.find(params[:id])

  end

  private

  def set_response
    @response = Response.find(params[:id])
  end

  def response_params
    params.require(:response).permit(:content)
  end

end

--- 
+++ 
@@ -37,7 +37,15 @@
   end
 
   def up_vote
-    response = Response.find(params[:id])
+    puts "=" * 50
+    puts params
+    puts "=" * 50
+
+    @response = Response.find(params[:id])
+
+    # @response.add_vote
+
+    render text: @response.votes.count
 
   end
 
Add render votes count which returns a string of the updated vote count for the corresponding response.
