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Anatomy and Physiology Unit 4: Nervous and endocrine systems

The nervous system sends fast electrical signals; the endocrine system sends slower chemical messages through the blood.

Covers: Neurons, action potentials, brain regions, reflexes, hormones, endocrine glands

Study guide

The nervous system controls the body with fast electrical signals. The central nervous system (CNS) is the brain and spinal cord; the peripheral nervous system (PNS) is the nerves that connect it to the body. The PNS includes the somatic system (voluntary control of skeletal muscle) and the autonomic system, which has a sympathetic "fight or flight" branch and a parasympathetic "rest and digest" branch.

Neurons are the signaling cells. Dendrites receive signals, the cell body processes them, and the axon carries the signal away to the axon terminals. A myelin sheath speeds conduction. Sensory neurons carry information to the CNS, motor neurons carry commands to muscles and glands, and interneurons connect them.

An action potential is a rapid electrical impulse. At rest, the inside of the neuron is negative (about −70 mV). A stimulus that reaches threshold opens sodium channels, and Na⁺ rushes in (depolarization); then potassium channels open and K⁺ flows out (repolarization). The sodium-potassium pump restores the resting state. At the synapse, the signal triggers the release of neurotransmitters that cross the gap and bind to receptors on the next cell.

Brain regions have specialized jobs. The cerebrum handles thinking, memory, language and voluntary movement, divided into frontal, parietal, temporal and occipital lobes. The cerebellum coordinates balance and movement. The brainstem (medulla, pons, midbrain) controls breathing and heart rate, and the hypothalamus regulates temperature, hunger and hormones. A reflex arc routes a signal through the spinal cord for a fast automatic response, like pulling your hand from a hot stove.

The endocrine system uses hormones carried in the blood for slower, longer-lasting control. The pituitary gland (the "master gland," controlled by the hypothalamus) regulates other glands. The thyroid controls metabolism, the adrenal glands release adrenaline and cortisol, the pancreas releases insulin (lowers blood sugar) and glucagon (raises it), and the gonads release sex hormones. Most hormones are regulated by negative feedback.

Glial cells support neurons. Oligodendrocytes form myelin in the CNS, and Schwann cells form it in the PNS. Astrocytes help form the blood-brain barrier, microglia clear debris and pathogens, and ependymal cells line the ventricles and help make cerebrospinal fluid. When an action potential reaches the axon terminal, calcium enters and triggers the release of neurotransmitter by exocytosis. Acetylcholine acts at neuromuscular junctions and parasympathetic synapses, and norepinephrine at most sympathetic targets. Dopamine affects movement and reward, GABA is the main inhibitory neurotransmitter, and serotonin affects mood and sleep. Right after firing, a neuron goes through a brief refractory period when it can't fire again.

The thalamus relays sensory signals to the cortex, and the corpus callosum connects the two cerebral hemispheres. Broca's area in the frontal lobe controls speech production, and the limbic system (including the hippocampus and amygdala) handles memory and emotion. The brain and spinal cord are wrapped in three meninges (dura, arachnoid and pia mater) and cushioned by cerebrospinal fluid. Sympathetic stimulation raises heart rate and blood pressure, dilates the pupils and bronchioles, releases glucose, and slows digestion. Parasympathetic stimulation, carried largely by the vagus nerve, slows the heart, constricts the pupils and stimulates digestion.

The anterior pituitary releases growth hormone, TSH, ACTH, FSH, LH and prolactin. The posterior pituitary releases ADH and oxytocin, which drives labor contractions and milk letdown. Parathyroid hormone raises blood calcium, and calcitonin from the thyroid lowers it. The pineal gland makes melatonin, and in the pancreas beta cells make insulin while alpha cells make glucagon.

Key ideas

• Neurons: dendrites receive, axons send, synapses pass signals with neurotransmitters.
• Action potentials are all-or-none electrical impulses.
• CNS = brain and spinal cord; PNS = all other nerves.
• Cerebrum (thinking), cerebellum (balance and coordination), brainstem (breathing, heart rate).
• Hormones travel in blood: insulin lowers blood sugar; glucagon raises it.

Formulas and rules

Common mistakes

• Mixing up the cerebrum and cerebellum.
• Thinking hormones act instantly like nerves. They're slower but last longer.

Words to know

Dendrite

The part of a neuron that receives signals.

Central nervous system

Brain and spinal cord.

Cerebellum

The brain region for balance and coordination.

Insulin

The hormone that lowers blood sugar.

Neurotransmitter

A chemical that carries a signal across a synapse.

Neuron signal path

Dendrite → cell body → axon → synapse.

Peripheral nervous system

Nerves connecting the CNS to the body.

Sympathetic division

"Fight or flight."

Parasympathetic division

"Rest and digest."

Axon

Carries signals away from the cell body.

Myelin sheath

Insulation that speeds conduction.

Action potential

A rapid electrical impulse: Na⁺ in, then K⁺ out.

Resting potential

About −70 mV inside a neuron.

Synapse

The junction between neurons where neurotransmitters cross.

Cerebrum

Thinking, memory, language and voluntary movement.

Brainstem

Controls breathing and heart rate.

Hypothalamus

Regulates temperature, hunger and hormones.

Reflex arc

A fast automatic response routed through the spinal cord.

Pituitary gland

The "master gland," controlled by the hypothalamus.

Glucagon

Raises blood sugar.

Sample practice questions

5 more questions like these, from level 1 to 5, are in the practice set.