Nervous System Basics

Nervous System - Basic Function

• The nervous system is composed of the central nervous system (CNS) and peripheral nervous system (PNS)
• CNS: brain and spinal cord
• PNS: nerves that connect CNS to the rest of the body

Structure of a Neuron

• Neuron: basic functional unit of the nervous system
  • Dendrites: receive signals
  • Cell body: contains nucleus
  • Axon: transmits signals
  • Myelin sheath: insulates and speeds up signal transmission

Types of Neurons

• Multipolar neurons: multiple processes extending from the cell body (most common type)
• Bipolar neurons: two processes extending from the cell body (some special sense neurons)
• Unipolar neurons: single short process extending from the cell body (most sensory neurons)
• Anaxonic neurons: processes are only dendrites, no axon present (interneurons of the CNS)

Important Attribute of Neurons

• Neurons are excitable and easily excited

Membrane Potential

• Resting membrane potential: -70mV (difference in electric potential between exterior and interior of cell membrane)
• Formed by unequal concentrations of K+ and Na+ ions
• Ion channels: allow ions to pass through the cell membrane
• Na+/K+ pump: active transport counter to ions concentrations, requires energy from ATP

Generation of Action Potential

• Stimulus: chemical, physical, or electrical signal
• Depolarization: stimulus raises membrane potential, threshold is -55mV
• Action potential: signal that carries information along the axon (1-2 msec)
• All-or-none response: action potential either occurs or it doesn't, no intermediate responses

Synapses

• Chemical synapse: transmission occurs through neurotransmitters
• Electrical synapse: transmission occurs through electrical signals
• Synaptic transmission: process of transmitting information from one neuron to another
• Postsynaptic potential: response of the postsynaptic cell to neurotransmitters (excitatory or inhibitory)

Synapse Functioning

• Summation of impulses: multiple signals combined to produce a response
• Summation of stimulus: multiple stimuli combined to produce a response