Control and coordination in mammals

Overview of the Nervous System

The nervous system in mammals involves the brain, spinal cord and peripheral nerves. It is responsible for receiving information, processing it, and coordinating responses.
The central nervous system (CNS) refers to the brain and spinal cord, while the peripheral nervous system (PNS) includes all the nerves outside the CNS.
The nervous system is essential for homeostasis. It enables organisms to maintain a stable internal environment by coordinating responses to changes in the environment.

Cell Types in the Nervous System

There are two types of cells in the nervous system: neurons and neuroglia. Neurons transmit nerve impulses, while neuroglia support and protect neurons.
Anatomically, a neuron consists of a cell body, dendrites and an axon. The cell body contains the nucleus, the dendrites receive signals from other neurons, and the axon transmits these signals to other cells.
Neurons can generally be classified into motor neurons (carry signals from the CNS to effectors), sensory neurons (carry signals from receptors to the CNS), and interneurons (connect other neurons within the CNS).

Neurotransmission

Nerve impulses, or action potentials, are electrical signals that are generated and propagated along neurons due to changes in the voltage across the neuron membrane.
The propagation of action potentials involves an initial depolarization of the neuron (caused by an influx of Na+ ions), followed by a repolarization (caused by an efflux of K+ ions).
The change in voltage triggers the release of neurotransmitters at the neuron’s synaptic terminals, which can then bind to receptors on other cells and initiate a new action potential.

Hormonal Control

Hormonal control complements neural control, providing a slower but longer-lasting response to changes. This type of control is achieved by the endocrine system, which consists of glands that release hormones into the bloodstream.
Hormones are chemical messengers that bind to specific receptors on target cells, causing a change in the cell’s behaviour or function.
Examples of endocrine glands include the pituitary, thyroid, adrenal glands, and the pancreas. The hormones they release regulate a variety of processes, including growth, metabolism, stress response, and blood sugar levels.

Control of Heart Rate

Heart rate in mammals is controlled via both nervous and hormonal mechanisms. The sympathetic nervous system increases heart rate, while the parasympathetic nervous system decreases it.
Hormones such as adrenaline and noradrenaline can also influence heart rate, primarily during situations of stress or excitement.
The feedback control of heart rate involves baroreceptors (detect changes in blood pressure) and chemoreceptors (monitor oxygen and carbon dioxide levels in blood).

Homeostasis and Feedback Mechanisms

The body uses negative feedback mechanisms to maintain homeostasis. In these systems, a change in a variable triggers a response that reverses the change.
Examples of homeostatic control include the regulation of body temperature, water balance, and blood glucose levels.
Positive feedback mechanisms, on the other hand, amplify an initial change. They are less common but can be seen in processes such as childbirth and blood clotting.