Control and Coordination
Easy Overview
Your body is doing a million things right now — breathing, balancing, blinking — and you're not thinking about any of it. That's because your nervous system and endocrine system handle everything behind the scenes. This chapter is about the control room (brain) and the messaging systems (nerves and hormones) that keep you alive.
The neuron — your body's text message
Neurons are specialized cells that transmit electrical signals. A neuron has dendrites (receivers), a cell body (processor), an axon (wire), and axon terminals (output). The signal jumps from node to node (saltatory conduction) in myelinated neurons — way faster than unmyelinated ones. It's like a game of telephone, but biological.
Synaptic transmission — crossing the gap
Neurons don't actually touch each other. There's a tiny gap called the synapse. When an electrical signal reaches the end of a neuron, it triggers release of neurotransmitters (chemical messengers) that float across the gap and bind to receptors on the next neuron. Then the signal continues. Some drugs work by messing with this process.
The brain — the CEO
Your brain has three main parts. Cerebrum (biggest part): thinking, memory, voluntary movement. Cerebellum: balance and coordination (thank this when you catch a ball). Brainstem (medulla): automatic stuff — heartbeat, breathing, digestion — the stuff you never think about. The brain uses 20% of your body's oxygen despite being 2% of your weight. Energy hog.
Reflex arc — act first, think later
When you touch something hot, you pull your hand back before you even feel the pain. That's a reflex. The signal goes from sensory neuron → spinal cord → motor neuron — straight back, no brain involvement. The brain gets the message a split second later as pain. This delay saves your skin from burning.
Endocrine system — the slow messenger
While nerves act fast (milliseconds), hormones act slow (seconds to hours) but last longer. Glands like pituitary (master gland), thyroid, adrenal, pancreas, and gonads release hormones into the blood. These chemical messengers travel everywhere but only affect cells with the right receptors. Think of hormones as spam emails — only relevant if you subscribed.
Feedback mechanisms — keeping things steady
Your body loves balance (homeostasis). When blood sugar goes up after eating, insulin is released to bring it down (negative feedback). When you're cold, shivering generates heat. Positive feedback is rarer — like during childbirth, oxytocin makes contractions stronger, which triggers more oxytocin. A snowball effect that ends when the baby is born.
Key Points
- •Neuron: dendrites → cell body → axon → synaptic terminals; signal travels dendrite → axon
- •Myelinated neurons have faster saltatory conduction (signal jumps at nodes of Ranvier)
- •Synapse: neurotransmitters released from presynaptic neuron bind to receptors on postsynaptic
- •Brain: cerebrum (conscious), cerebellum (coordination), medulla (autonomous functions)
- •Reflex arc: sensory neuron → spinal interneuron → motor neuron (bypasses brain for speed)
- •Pituitary is the 'master gland' controlled by hypothalamus
- •Hormones: steroid (lipid-soluble, cross membrane) vs peptide (water-soluble, bind surface receptors)
- •Negative feedback maintains homeostasis; positive feedback amplifies change (childbirth, blood clotting)
Practice Questions
- Draw and label a neuron. Explain how an impulse travels along it.
- What happens at a synapse? How do neurotransmitters carry the signal across?
- Describe the structure and functions of the cerebrum, cerebellum, and medulla oblongata.
- What is a reflex arc? Give an example and explain why it bypasses the brain.
- Distinguish between hormonal and nervous coordination. How do they complement each other?