(1103) 261 Ch 7 p1

Chapter 7: The Nervous System

Introduction to the Nervous System

  • The nervous system is often perceived as a passive component in physical activities such as Olympic lifting.

  • Despite muscle being essential for weightlifting, the nervous system plays a crucial role in control and coordination of movements.

  • Observations of Lydia Valentine’s Olympic lifts highlight the importance of the nervous system in sports performance:

    • Joint movements (ankles, knees, hips, shoulders) are coordinated by the nervous system.

    • Timing, force, speed, and balance are managed by neural commands.

    • Optimal training of the nervous system is necessary for enhancing muscle performance.

Organization of the Nervous System

  • Two Main Branches:

    • Central Nervous System (CNS):

      • Comprises the brain and spinal cord.

    • Peripheral Nervous System (PNS):

      • Sensory part brings information to the CNS (afferent).

        • Includes senses such as vision and proprioception (position and movement of body).

      • Motor part sends commands from CNS to body (efferent).

        • Divided into somatic (musculoskeletal) and autonomic (involuntary functions).

        • Autonomic includes sympathetic (fight or flight) and parasympathetic (rest and digest).

Neurons and Nerves

  • Structure of Nerves:

    • Composed of bundles of neurons (nerve cells).

    • Neurons send signals throughout the body.

    • The human brain consists of approximately 150 billion neurons.

  • Neuron Functions:

    • Cell Body: Contains nucleus; processes incoming information.

    • Dendrites: Receive signals from other neurons; highly branched for maximum connectivity.

    • Axon: Transmits signals away from the cell body to other neurons or muscle fibers.

    • Myelin Sheaths: Formed by Schwann cells, allowing faster signal transmission by enabling signals to jump between nodes (Nodes of Ranvier).

Neuronal Communication

  • Action Potential: The process by which neurons communicate through electrical impulses.

    • Directional flow from the cell body down the axon, culminating at the synapse.

    • Involves production of electrical and concentration gradients.

  • Polarity Maintenance: Essential to send messages.

    • Differences in charge across the neuron's membrane (Resting Membrane Potential).

    • Resting potential maintained through sodium-potassium pumps:

      • 2 potassium ions in & 3 sodium ions out.

      • Essential for generating an action potential when a stimulus is received.

  • Phases of Action Potential:

    • Resting Potential: Typically remains around -70mV due to ionic distribution.

    • Depolarization: Positive sodium influx occurs, reversing the charge.

    • Repolarization: Returns to resting potential by moving potassium back out.

Disorders Affecting Neurons

  • Multiple Sclerosis: A condition involving damage to myelin sheaths, disrupting signal transmission and affecting motor control.