TEAS Science: The Nervous and Endocrine Systems — Complete Review

Your body has two master control systems that coordinate everything you do: the nervous system, which sends fast electrical signals, and the endocrine system, which sends slower chemical messengers called hormones. Together they keep your body in balance—a state called homeostasis—and together they are a dependable source of questions on the TEAS Science section's Human Anatomy and Physiology category.

This complete review covers neuron structure, the divisions of the nervous system, the major endocrine glands and their hormones, and—most importantly—how these two systems work together. Understanding the big picture will help you answer both the memorization questions and the trickier 'how does this work' questions.

Part 1: The Nervous System

The nervous system is the body's rapid communication network. It detects changes (stimuli), processes information, and triggers responses—all in fractions of a second using electrical and chemical signals.

The Neuron: The Basic Unit

Neurons are the specialized cells that carry nerve signals. You must know the main parts and what each does:

• Dendrites: Branch-like extensions that RECEIVE signals from other neurons.
• Cell body (soma): Contains the nucleus and organelles; integrates incoming signals.
• Axon: The long fiber that CARRIES the electrical impulse away from the cell body.
• Myelin sheath: A fatty insulating layer that speeds up signal transmission along the axon.
• Axon terminals: The endings that release neurotransmitters to pass the signal to the next cell.
• Synapse: The tiny gap between two neurons where neurotransmitters carry the message across.

Divisions of the Nervous System

The nervous system is organized into a clear hierarchy. The TEAS frequently asks you to identify which division a structure or function belongs to.

• Central Nervous System (CNS): The brain and spinal cord. This is the control center that processes and interprets information.
• Peripheral Nervous System (PNS): All the nerves outside the CNS that connect it to the rest of the body.
• Within the PNS — Somatic nervous system: Controls VOLUNTARY movements of skeletal muscle.
• Within the PNS — Autonomic nervous system: Controls INVOLUNTARY functions like heartbeat, digestion, and breathing.
• Autonomic split — Sympathetic: The 'fight-or-flight' response (speeds heart rate, dilates pupils).
• Autonomic split — Parasympathetic: The 'rest-and-digest' response (slows heart rate, stimulates digestion).

Major Brain Regions

• Cerebrum: The largest part; controls thinking, voluntary movement, and the senses.
• Cerebellum: Coordinates balance, posture, and fine motor movement.
• Brainstem (medulla, pons, midbrain): Controls vital automatic functions like breathing, heart rate, and blood pressure.
• Hypothalamus: Links the nervous and endocrine systems; regulates temperature, hunger, thirst, and controls the pituitary gland.

Part 2: The Endocrine System

The endocrine system is a collection of glands that release hormones directly into the bloodstream. Hormones travel to target organs and tissues, where they regulate processes like growth, metabolism, reproduction, and the stress response. Compared with the nervous system, endocrine signals are slower to start but longer lasting.

Major Glands and Their Hormones

• Pituitary gland: The 'master gland.' Releases growth hormone and controls other glands. Directed by the hypothalamus.
• Thyroid gland: Releases thyroid hormone (T3/T4) to regulate metabolism; also releases calcitonin to lower blood calcium.
• Parathyroid glands: Release parathyroid hormone (PTH) to RAISE blood calcium—the opposite of calcitonin.
• Adrenal glands: Release adrenaline (epinephrine) for fight-or-flight and cortisol, the long-term stress hormone.
• Pancreas: Releases insulin (lowers blood sugar) and glucagon (raises blood sugar).
• Ovaries (female): Release estrogen and progesterone.
• Testes (male): Release testosterone.

Part 3: How the Two Systems Work Together

The nervous and endocrine systems are not separate—they are partners. The hypothalamus in the brain is the key link: it receives nervous-system information and responds by controlling the pituitary gland, which then controls much of the endocrine system. This is why the hypothalamus is often called the bridge between the two systems.

• Speed: The nervous system acts in milliseconds; the endocrine system acts over seconds, minutes, or longer.
• Duration: Nervous responses are brief; hormonal responses last longer.
• Messengers: The nervous system uses neurotransmitters across synapses; the endocrine system uses hormones in the blood.
• Shared goal: Both maintain homeostasis—keeping internal conditions stable despite a changing environment.

Homeostasis and Negative Feedback

Most hormone systems are regulated by negative feedback: when a hormone reaches the right level, it signals the gland to stop releasing more—like a thermostat shutting off the heat once the room is warm enough. Understanding negative feedback helps you reason through endocrine questions instead of memorizing every detail.

• Example: When blood sugar rises after a meal, the pancreas releases insulin. As blood sugar drops back to normal, insulin release slows—negative feedback.
• Example: When body temperature rises, the hypothalamus triggers sweating and vasodilation to cool you down, then stops once temperature normalizes.

High-Yield Facts to Memorize

• CNS = brain + spinal cord; PNS = everything else.
• Sympathetic = fight or flight; parasympathetic = rest and digest.
• The pituitary is the 'master gland,' controlled by the hypothalamus.
• Insulin lowers blood sugar; glucagon raises it.
• Calcitonin lowers blood calcium; PTH raises it.
• The hypothalamus links the nervous and endocrine systems.
• Negative feedback keeps hormone levels in balance.

Study Strategy

Focus on understanding relationships rather than rote memorization. If you know that the systems are opposites (sympathetic vs. parasympathetic, insulin vs. glucagon, calcitonin vs. PTH) and that the hypothalamus connects everything, you can reason through most questions even when you do not recall a specific fact.

Pair this review with practice questions to lock in the details, and you will be ready to earn every point these two systems offer on test day.