**Core Concept:**
Horizontal acceleration is a measure of the rate at which an object changes its direction of motion. In mammals, detection of horizontal acceleration is crucial for maintaining balance and posture, particularly during movements such as walking, running, or jumping. This process involves the vestibular system, which is located within the inner ear and consists of three semicircular canals and two otolith organs.

**Why the Correct Answer is Right:**
The correct answer, **Option C: Vestibular System**, is responsible for detecting changes in the head's rotational movement, including horizontal acceleration. The vestibular system consists of two otolith organs (ocular and utricle) and three semicircular canals (anterior, posterior, and lateral). The utricle and saccule are responsible for detecting linear acceleration (gravity), while the semicircular canals are responsible for detecting angular acceleration, including changes in direction.

**Why Each Wrong Option is Incorrect:**
Option A (Visual System) is responsible for detecting changes in light intensity and position, which is essential for vision but not related to detecting acceleration. Option B (Spinal Cord) is involved in reflexes and motor control but not directly responsible for detecting acceleration. Option D (Neurons) is a general term for cells that transmit information within the nervous system but does not represent a specific system or organ responsible for detecting acceleration.

**Why the Correct Answer is Right:**
The vestibular system plays a crucial role in maintaining balance and posture by detecting changes in acceleration, particularly horizontal acceleration. This information is then transmitted to the brain for appropriate reactions, such as adjusting muscle tone, eye movements, and balance reactions. For example, during walking or running, the vestibular system helps detect changes in the head's rotational movement and adjusts the body's muscles to maintain balance and posture.

**Why Each Wrong Option is Incorrect:**
Option A (Visual System) primarily detects visual information, while Option B (Spinal Cord) is involved in reflexes and motor control but not specifically detecting acceleration. Option D (Neurons) are essential components of the nervous system, but they do not represent a specific system or organ responsible for detecting acceleration. The vestibular system, on the other hand, specifically detects acceleration and helps maintain balance and posture in mammals.