3.6 Neuronal Coordination

Human neuronal coordination involves the complex interaction between the nervous system and various parts of the body to maintain homeostasis and respond to external stimuli.

The neural system of all animals is composed of neurons . These neurons  detect, receive and transmit different types of stimuli. 

Components of the Nervous System

1. Central Nervous System (CNS): Comprising the brain and spinal cord, the CNS processes information and coordinates activities.
2. Peripheral Nervous System (PNS): Consists of nerves that connect the CNS to the rest of the body. It includes:
   • Somatic Nervous System: Controls voluntary movements.
   • Autonomic Nervous System: Regulates involuntary functions and is further divided into:
     • Sympathetic Nervous System: Prepares the body for ‘fight or flight’ responses. The sympathetic nervous system prepares the body in response to stress by activating the organs and glands in the endocrine system.
     • Parasympathetic Nervous System : This functions opposite to the sympathetic system and allows the body to recover , for example clams the body by slowing the heart and breathing.

“Overview of Nervous System” by OpenStax via Wikimedia Commons is licensed under CC BY 4.0

Neuronal Communication

• Neurons: The basic units of the nervous system. The nervous system comprises about 100 billions of neurons. The function of neurons is to receive and transmit signals .Neurons transmit signals through electrochemical impulses.
• The structure of neurons include three majorts namely
  • a cell body or soma  : contains nucleus of the cell and keeps the cell alive.
  • Dendrite : This has a branching tree like structure . It collects information from other cells and sends it to soma. Some neurons have hundreds or even thousands of dendrite
  • axon: This is a long, segmented fibre . This tranmits information away from soma to other neurons or to muscles and glands.
    • Myelin sheath :  is a layer of fatty tissue surrounding the axon of a neuron that both acts as an insulator and allows faster transmission of the electrical signal.
    • terminal button : Axons branch out toward their ends, and at the tip of each branch is a terminal button.

• Synapses : These are junctions where neurons communicate with other neurons, muscles or glands through neurotransmitters.A synaptic connection between a neuron and a muscle cell is called a neuromuscular junction. Also called: neuronal junction. Synapses can be  chemical i.e. these synapses communicate using chemical messengers.
• Or can be electrical; in these synapses, ions flow directly between cells.
• At a chemical synapse, an action potential triggers the presynaptic neuron to release neurotransmitters. These molecules bind to receptors on the postsynaptic cell and make it more or less likely to fire an action potential.
• Upon binding with its receptor on a receiving cell, a neurotransmitter opens or closes ion channels. As a result the voltage across the membrane, or membrane potential, of the receiving cell may alter locally .
• Neurotransmitter molecules attach to receptor proteins on postsynaptic cells after diffusing across the synaptic cleft. Ion channels in the cell membrane open or close in response to postsynaptic receptor activation. Depending on the ions involved, this might be either hyperpolarizing, making the inside of the cell more negative, or depolarizing, making the inside of the cell more positive.
• The alteration may increase the target cell’s propensity to fire its own action potential in specific situations. Here, the membrane potential change is referred to as an excitatory postsynaptic potential, or EPSP.
  In other situations, the alteration is known as an inhibitory post-synaptic potential, or IPSP, and it reduces the likelihood that the target cell will fire an action potential.
  An EPSP depolarizes a cell by increasing its internal potential and moving the membrane potential closer to the point at which an action potential would be fired. Occasionally, a single EPSP isn’t very big , but it can sum together with other EPSPs to trigger an action potential.

Coordination Mechanism

1. Sensory Input: Sensory neurons detect changes in the environment and send signals to the CNS.
2. Integration: The CNS processes these signals and determines the appropriate response.
3. Motor output : Motor neurons carry signals from the CNS to effectors to excute the response.

Reflex Actions

Reflexes are rapid, involuntary responses to stimuli, involving a simple pathway called the reflex arc.Reflex actions, which minimize bodily harm from potentially hazardous situations like touching something hot, are instinctive (involuntary) and quick responses to stimuli. For many organisms, therefore, reflex behaviors are vital to survival.

Reflex action bypasses the conscious brain. This explains why the reaction is so quick.

Skin receptors pick up on a stimulation, such as a temperature shift.
Relay neurons are found in the spinal cord of the central nervous system (CNS) and receive electrical signals from sensory neurons. Motor neurons and sensory neurons are linked by relay neurons.
An effector receives electrical signals from a motor neuron.
Effector triggers a reaction (Example : muscle twitch to remove hand).

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