Central and Peripheral Nervous System

Learning Outcomes

• Review the structure and function of the Central Nervous System (CNS) and Peripheral Nervous System (PNS)
• Describe the components of a nerve cell
• Describe the difference between sympathetic and parasympathetic systems
• Outline the process of reflex arcs
• Explore associated health conditions and effects of exercise

Overview

• The nervous system can be subdivided into the central nervous system (CNS) and the peripheral nervous system (PNS).
• The two main cell types in the nervous system are neurons and neuroglia.
• Neurons are highly specialized nerve cells that generate and conduct nerve impulses.
• Neuroglia supports cells that provide physical support, remove debris, and offer electrical insulation.
• The nervous system coordinates and controls many body activities, like muscle contraction, awareness of the environment, and brain activity related to memory, emotions, and reasoning.

The Nervous System

• The nervous system sends electrical messages along nerves to and from different parts of the body.
• Stimuli are changes that can be detected by the nervous system.
• Receptors detect these changes.
• Effectors bring about the responses to the stimuli.
• Stimulus goes to Receptor then to Coordinator then, to Effector, resulting in a Response.
• The nervous system controls actions, coordinating different body parts for correct responses.
• The nervous system coordinates muscles for activities like walking, running, writing, and reading.
• The CNS connects to different body parts through nerves.
• Nerves consist of numerous nerve cells or neurons.
• The main parts of the nervous system (Brain and Spinal Cord) are together called the CNS.
• Sense organs are receptors, sending messages along sensor neurons.
• Muscles and Glands are effectors, receive instructions from Motor Neurons.

Nerve Impulses

• Messages carried by nerves are called nerve impulses, which are electrical signals.
• Nerve impulses pass quickly along the axon of the neuron.
• Impulses travel like a train along a track, each separate from the next.
• Some axons have a fatty sheath for insulation, which speeds up impulse travel.

Reflex Arcs

• A nerve impulse is triggered from a pain sensor
• The white matter consists of neuron axons
• The grey matter consists of neuron cell bodies

Sympathetic and Parasympathetic systems

• The Sympathetic division is for arousing the body
• The Parasympathetic division is for calming the body
• The Sympathetic system causes pupil dilation
• The Parasympathetic system causes pupil constriction
• The Sympathetic system is for Fight, flight or fright responses
• The Parasympathetic system is for Peace and contentment as well as Rest and Digest

Key Terms

• Nerve: Bundles of nerve fibres travelling together and wrapped in connective tissue.
• Nerve Impulse: Wave of electrical discharge passing along a nerve fibre.
• Motor Neuron: Nerve cell carrying information from the CNS, associated with muscles or glands as effectors.
• Sensory Neuron: Nerve cell associated with specialist receptors carrying information into the CNS.

Neurons

• Action potential arrives at the presynaptic nerve terminal
• Depolarization occurs, opening voltage-gated sodium (Na+) channels.
• Na+ ions enter, causing further depolarization.
• Repolarization occurs as K+ channels open and K+ ions exit.
• The membrane potential returns to its resting state.

How Exercise Impacts the Nervous System and Contributes to Central Nervous System (CNS) Fatigue

• Inflammatory responses during exercise can contribute to central nervous system (CNS) fatigue through cytokine release, binding of cytokines to receptors impacting sensory feedback, and afferent signaling.
• Central nervous system (CNS) fatigue can impair gains in maximum strength and muscle size by preventing the recruitment of high-threshold motor units.
• CNS fatigue develops during each set of a workout (and dissipates during rest periods) as well as over the course of the whole workout

Optimizing Workouts to Limit Central Nervous System (CNS) Fatigue

• As a workout progresses, CNS fatigue increases, reducing the effectiveness of later exercises for muscle growth.
• Exercises performed last yield inferior results due to accumulating CNS fatigue.
• By strategically selecting exercises and ordering them within a workout, the impact of CNS fatigue can be minimized.
• Exercises involving less muscle mass (single-joint, single-limb) generate less CNS fatigue and can be placed later to counter increasing fatigue.
• Multi-joint, two-limb exercises cause the most CNS fatigue.
• Single-joint, two-limb or single-limb multi-joint exercises, cause moderate CNS fatigue.
• Single-joint, single-limb exercises cause the least CNS fatigue

Explore the central and peripheral nervous systems and their functions. Learn about neurons and neuroglia, the main cell types. Understand how the nervous system coordinates body activities and its role in muscle contraction, environmental awareness, and brain functions.