exam 3

• Functions of Nervous system

  • Controls voluntary and involuntary movement of the body
  • Homeostasis
  • Sensing stimuli
  • Responding to stimuli
• Central Nervous system (CNS)


  Brain and spinal cord
• Types of nerves in PNS

  • Afferent (sensory)
  • Efferent (motor)
  • Somatic nervous system (voluntary motor)
  • Autonomic nervous system (involuntary motor)
• Divisions of Autonomic Nervous System

  • Parasympathetic (rest and digest)
  • Sympathetic ("fight or flight")
• Characteristics of nervous tissue

  • Excitable
  • Able to send/receive electrochemical signals that provide body with info
• Anatomy of a neuron

  • Cell body
  • Dendrites
  • Axons (nerve fiber)
  • Axon hillock
• Nissl bodies


  Help in protein synthesis of neurons, discrete clumps of rough endoplasmic reticulum and free ribosomes in nerve cells
• Axolemma


  Conveys signals between the neuron and its Schwann cells
• Axon terminals


  Ends of axons which transmit messages to other cells via use of neurotransmitters at synapses
• Myelin sheath


  Protects axons and helps speed nerve transmissions
• Nodes of Ranvier


  Specialized, unmyelinated regions in the axonal membrane
• Structural classification of neurons

  • Multipolar
  • Bipolar
  • Unipolar
• Functional classification of neurons

  • Sensory
  • Motor
  • Interneurons
• Types of glial cells

  • Astrocytes
  • Microglial cells
  • Ependymal cells
  • Oligodendrocytes
  • Schwann cells
  • Satellite cells
• Ganglia


  Groups of nerves or brain cells that are closely related
• Tracts


  A system of body parts or organs that act together to perform some function
• Nerves


  Cables that carry electrical impulses between your brain and the rest of your body
• White matter


  Made up of myelinated axons
• Gray matter


  Made up of neuronal cell bodies
• Neurophysiology is the study of how the nervous system works
• Neurons use electrical signals and chemicals to communicate
• Electrical signals are produced when ions move across membranes
• Types of gated ion channels

  • Ligand-gated
  • Mechanically gated
  • Voltage-gated
• Membrane potential


  The charge difference across a membrane
• Resting membrane potential


  About -70 millivolts (negative membrane potential means inside is more negative than outside)
• Resting membrane potential


  1. Na+/K+ pump pumps 3 Na+ ions out of cell for every 2 K+ ions pumped in

  2. Inside of cell has fewer positive charges (or more negative) than outside of membrane
• Resting membrane potential


  No electrical signal
• Electrical signals


  • Graded potentials are short-distance signals
  • Action potentials are long-distance signals
• Graded potentials


  1. Occur when ligand-gated or mechanically-gated ion channel opens

  2. Decrease with distance
• Action potentials


  1. Transient reversals of the membrane potential

  2. Occur when voltage-gated ion channels open

  3. Occur along axolemma and sarcolemma
• Action potentials


  • All-or-none events caused by the diffusion of Na+ and K+ ions
  • Threshold (about -55 millivolts) is the membrane potential that must be reached for AP to begin
• Phases of an action potential

  1. Depolarization (Na+ channel opens, Na+ enters cell)

  2. Repolarization (K+ channel opens, K+ leaves cell)

  3. Hyperpolarization (K+ channels close slowly, membrane potential becomes more negative)
• Action potential propagation


  1. Starts at axon hillock

  2. Continuous conduction (slower) in unmyelinated axons

  3. Saltatory conduction (faster) in myelinated axons, jumping over myelinated regions
• Action potential conduction speed

  • Depends on axon diameter (thicker is faster)
  • Depends on amount of myelination (heavily myelinated is fastest, unmyelinated is slowest)
• Synapse


  Junction between two neurons or between neuron and effector cell
• Types of synapses


  • Electrical synapses (rare in nervous system)
  • Chemical synapses (most common, neurotransmitter released)
• Neurotransmitters


  Chemical messengers released by the nervous system
• Examples of neurotransmitters


  • Dopamine (motor control)
  • Serotonin (moods, sensory perception)
• Main neurotransmitters in PNS

  • Acetylcholine (stimulates skeletal muscle contractions)
  • Norepinephrine (released by certain autonomic neurons)
• Central Nervous System


  • Consists of brain and spinal cord
  • Brain has about 100 billion neurons (99% of nervous system)
  • Brain weighs about 3-3.5 lbs
  • Main integration and control center