Coordination and Control in Humans

Coordination and control are essential for maintaining homeostasis in the human body. This involves the nervous system and endocrine system working together to detect changes, process information, and initiate appropriate responses.

The Nervous System

Structure of the Nervous System

The human nervous system is divided into two main parts:

Human Nervous System Central Nervous System Peripheral Nervous System Brain Spinal Cord Somatic Autonomic

Neurons: The Building Blocks

Neurons are specialized cells that transmit electrical impulses. There are three main types:

Dendrites Cell Body Cell Body Axon Terminal Myelin Sheath Node of Ranvier

Structure of a typical motor neuron

The Reflex Arc

A reflex action is a rapid, automatic response to a stimulus that doesn't involve conscious thought. The pathway is called a reflex arc:

  1. Stimulus detected by receptor
  2. Sensory neuron transmits impulse to CNS
  3. Relay neuron in spinal cord processes information
  4. Motor neuron carries impulse to effector
  5. Effector (muscle or gland) produces response
Receptor Sensory Neuron Relay Neuron Motor Neuron Effector Spinal Cord

The reflex arc pathway

The Endocrine System

The endocrine system is a complex network of glands and organs that uses hormones as chemical messengers to regulate nearly every physiological process in the body. Unlike the nervous system's rapid electrical signals, the endocrine system provides slower but more sustained regulation through hormonal communication.

Feature Endocrine System Nervous System
Signal Type Chemical (Hormones) Electrical (Action Potentials)
Transmission Through bloodstream Through neurons
Response Time Seconds to days Milliseconds
Duration Long-lasting Brief

Key Characteristics

How Hormones Work

  1. Hormone synthesis and release from endocrine gland
  2. Transport through bloodstream
  3. Binding to specific receptors on target cells
  4. Cellular response (e.g., gene activation, enzyme modification)
  5. Feedback regulation of hormone levels

Endocrine Disorders

Diabetes Mellitus

Caused by insulin deficiency or resistance, leading to high blood glucose levels.

Hyperthyroidism

Overactive thyroid gland producing excessive thyroxine.

Gland Hormone(s) Produced Function
Pituitary Growth hormone (GH), ADH, TSH, FSH, LH Master gland, regulates other glands, growth, water balance
Thyroid Thyroxine Regulates metabolic rate
Pancreas Insulin, Glucagon Regulates blood glucose levels
Adrenal Adrenaline, Cortisol Prepares body for 'fight or flight', stress response
Ovaries Estrogen, Progesterone Female sexual characteristics, menstrual cycle
Testes Testosterone Male sexual characteristics, sperm production

Negative Feedback Mechanisms

Most hormonal regulation uses negative feedback to maintain homeostasis:

  1. Stimulus disrupts balance
  2. Receptor detects change
  3. Control center (often pituitary) processes information
  4. Effector (endocrine gland) produces response
  5. Response counteracts original stimulus
Stimulus Receptor Control Center Negative Feedback

Negative feedback mechanism in hormonal control

Comparison of Nervous and Endocrine Systems

Feature Nervous System Endocrine System
Communication method Electrical impulses and neurotransmitters Chemical hormones in bloodstream
Speed of response Very fast (milliseconds) Slower (seconds to hours)
Duration of effect Short-lived (milliseconds to seconds) Long-lasting (minutes to days)
Target Specific muscles or glands Any cell with appropriate receptors
Control type Voluntary and involuntary Involuntary only

Disorders of Coordination and Control

Nervous System Disorders

Endocrine System Disorders

Glossary of Terms

Axon: Long fiber that carries impulses away from the cell body of a neuron.

Dendrite: Short branched extension of a nerve cell that receives impulses.

Effector: Muscle or gland that carries out a response to a stimulus.

Homeostasis: Maintenance of stable internal conditions despite external changes.

Hormone: Chemical messenger secreted by endocrine glands into bloodstream.

Myelin sheath: Fatty layer that insulates axons and speeds up impulse transmission.

Negative feedback: Mechanism where the output inhibits the original stimulus.

Neurotransmitter: Chemical that transmits impulses across synapses.

Receptor: Cell or organ that detects stimuli and converts them to impulses.

Reflex arc: Neural pathway that mediates a reflex action.

Synapse: Junction between two neurons where impulses are transmitted chemically.

Target organ: Organ or tissue that responds to a specific hormone.

Self-Assessment Questions

1. Name the two main divisions of the human nervous system.
The two main divisions are the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).
2. What is the function of myelin sheath in a neuron?
The myelin sheath insulates the axon, speeding up the transmission of nerve impulses.
3. List the sequence of components in a reflex arc.
Receptor → Sensory neuron → Relay neuron (in CNS) → Motor neuron → Effector
4. How does the endocrine system differ from the nervous system in terms of speed of response?
The endocrine system is slower (seconds to hours) compared to the nervous system which responds in milliseconds.
5. Name two hormones produced by the pancreas and state their functions.
Insulin (lowers blood glucose) and Glucagon (raises blood glucose).
6. What is the role of the pituitary gland in the endocrine system?
The pituitary gland is the 'master gland' that controls other endocrine glands by secreting various regulatory hormones.
7. Explain how negative feedback helps to control thyroxine levels in the blood.
High thyroxine levels inhibit TSH secretion from the pituitary, which then reduces thyroxine production by the thyroid gland, maintaining homeostasis.
8. What would happen if a person's adrenal glands failed to produce adrenaline?
The person might have difficulty responding to stress or emergency situations (reduced 'fight or flight' response), potentially with low blood pressure and reduced energy mobilization.
9. Describe two differences between sensory and motor neurons.
1) Sensory neurons carry impulses from receptors to CNS, while motor neurons carry impulses from CNS to effectors. 2) Sensory neurons have their cell bodies in ganglia outside the CNS, while motor neurons have their cell bodies within the CNS.
10. Why is the reflex arc important for survival?
Reflex arcs allow for rapid, automatic responses to potentially harmful stimuli without waiting for brain processing, providing immediate protection from danger.