A-Level Biology - Control and Coordination in Mammals

Objective: Compare the features of the nervous system and the endocrine system

This section details a comparison of the nervous and endocrine systems in mammals, highlighting their structures, mechanisms of communication, speed of response, duration of effects, and examples of their functions.

The Nervous System

The nervous system is responsible for rapid communication and control within the body. It utilizes electrical and chemical signals to transmit information.

Structure

• Central Nervous System (CNS): Consists of the brain and spinal cord.
• Peripheral Nervous System (PNS): Consists of all the nerves that branch out from the CNS.
• Neurons: The basic functional units of the nervous system. They consist of:
  • Dendrites: Receive signals from other neurons.
  • Cell body: Contains the nucleus.
  • Axon: Transmits signals to other neurons, muscles, or glands.
  • Myelin sheath: A fatty layer that insulates the axon and speeds up signal transmission.
• Synapses: The junctions between neurons where signals are transmitted.

Mechanism of Communication

Neurons communicate via electrical impulses (action potentials) and chemical signals (neurotransmitters).

1. An electrical impulse travels down the axon to the synapse.
2. The impulse triggers the release of neurotransmitters into the synaptic cleft.
3. Neurotransmitters bind to receptors on the postsynaptic neuron, causing a change in its electrical potential.

Speed of Response

Very fast (milliseconds).

Duration of Effects

Short (milliseconds to seconds).

Examples of Functions

• Rapid responses to stimuli (e.g., withdrawing from a hot surface).
• Sensory perception (e.g., sight, smell, touch).
• Muscle movement.
• Thought, memory, and learning.

The Endocrine System

The endocrine system uses hormones to regulate a wide range of bodily functions. It communicates via chemical signals released into the bloodstream.

Structure

• Glands: Organisms that secrete hormones. Examples include:
  • Pituitary gland: Often called the "master gland" as it controls other endocrine glands.
  • Thyroid gland: Regulates metabolism.
  • Adrenal glands: Produce hormones involved in stress response and blood pressure.
  • Pancreas: Produces insulin and glucagon to regulate blood sugar levels.
  • Ovaries (in females): Produce oestrogen and progesterone.
  • Testis (in males): Produce testosterone.

Mechanism of Communication

Hormones are released from endocrine glands into the bloodstream and travel to target cells throughout the body. Only cells with specific receptors for a particular hormone will respond.

Speed of Response

Slow (seconds to hours).

Duration of Effects

Long (minutes to days).

Examples of Functions

• Growth and development.
• Metabolism regulation.
• Reproduction.
• Mood and sleep.
• Blood sugar regulation.

Comparison Table

Feature	Nervous System	Endocrine System
Communication Method	Electrical and chemical signals (neurotransmitters)	Chemical signals (hormones)
Speed of Response	Fast (milliseconds)	Slow (seconds to hours)
Duration of Effects	Short (milliseconds to seconds)	Long (minutes to days)
Target Cells	Specific neurons or muscle/gland cells	Cells with specific hormone receptors
Distance of Signal Travel	Short distances (synaptic cleft)	Long distances (through the bloodstream)
Examples of Functions	Rapid responses, sensory perception, muscle movement	Growth, metabolism, reproduction, mood regulation

In summary, the nervous system provides rapid, short-lived responses, while the endocrine system provides slower, longer-lasting responses. Both systems work together to maintain homeostasis and coordinate bodily functions.