In human autonomic nervous system physiology, which of the following types of nerves increases the rate of heartbeat?

Introduction / Context:
The human heart does not beat at a fixed rate throughout the day. Its activity is constantly adjusted according to physical activity, emotional state, stress, and rest. These changes are largely regulated by the autonomic nervous system, which has two major components: the sympathetic and parasympathetic divisions. This question tests whether you can identify which type of nerve fibres specifically increases the rate of heartbeat.

Given Data / Assumptions:

• Heartbeat is under involuntary control through the autonomic nervous system.
• Options mention sympathetic, parasympathetic, cranial, peripheral, and spinal nerves.
• Sympathetic and parasympathetic nerves usually have opposite effects on target organs.
• We assume a normal healthy adult heart without pacemaker implants or severe disease.

Concept / Approach:
The autonomic nervous system regulates internal organs without conscious effort. The sympathetic division prepares the body for activity, commonly described as the fight or flight response. It increases heart rate, increases the force of contraction, and redirects blood flow toward muscles. The parasympathetic division is associated with rest and digest functions and generally slows down heart rate. Cranial and spinal nerves are broader anatomical categories that may carry many different types of fibres but are not the specific functional division responsible for increasing heart rate.

Step-by-Step Solution:
Step 1: Recognise that heartbeat is influenced by autonomic nerves rather than voluntary motor nerves. Step 2: Recall that sympathetic nerves release noradrenaline at the heart, which increases rate and force of contraction. Step 3: Remember that parasympathetic fibres, mainly via the vagus nerve, release acetylcholine, which slows the heart. Step 4: Peripheral, cranial, and spinal nerves are general terms that include many sensory and motor fibres; they do not alone describe the functional effect on rate. Step 5: Since the question asks which type increases heart rate, the correct choice must be sympathetic nerves.

Verification / Alternative check:
Physiology textbooks describe experiments where stimulation of sympathetic cardiac nerves causes tachycardia increased heart rate, while stimulation of the vagus nerve causes bradycardia decreased heart rate. In stress, fear, or exercise, sympathetic activity rises, which everyone experiences as the heart beating faster. Beta blocker medicines that reduce sympathetic effects on the heart are clinically used to control high heart rate and blood pressure, confirming the direct link between sympathetic discharge and increased heart rate.

Why Other Options Are Wrong:
Peripheral nerves is a very broad term that includes both sensory and motor nerves and does not specifically describe the division that raises heart rate. Parasympathetic nerves mainly slow down the heartbeat, so they have an opposite effect. Cranial nerves include several sensory and motor nerves in the head and neck region and are not named as the main group that increases heart rate. Spinal nerves are mixed nerves emerging from the spinal cord and include many fibres, but the question focuses on functional divisions, not simple anatomical origin.

Common Pitfalls:
Learners sometimes confuse sympathetic with parasympathetic because both are parts of the autonomic system. A good way to remember is that sympathetic is linked with stress and emergency, so it speeds the heart, while parasympathetic is linked with relaxation and slows the heart. Also, avoid choosing overly general terms such as peripheral or cranial nerves when the question clearly points to a functional autonomic division.

Final Answer:
The nerves that increase the rate of heartbeat are Sympathetic nerves.