Chapter 12: Basic Principles of Neurophysiology

• central nervous system (CNS)

  • brain and spinal cord
  • integrative and control system
  • sends and receives signals from the peripheral nervous system
• peripheral nervous system (PNS)

  • cranial nerves and spinal cord
  • communication lines between the central nervous system and the body
  • made up of two divisions: sensory and motor
• sensory (afferent) division of the pns

  • somatic and visceral sensory nerve fibers
  • conducts impulses from receptors to CNS
  • from skin, from stomach ect
• motor (efferent) division of the PNS

  • motor nerve fibers
  • conducts impulses from the cns
  • muscles and glands
  • made up of somatic nervous system and autonomic nervous system
• somatic nervous system

  • voluntary movement / somatic motor
  • conducts impulses from the CNS to skeletal muscles
• autonomic nervous system

  • involuntary movement / visceral motor
  • conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands
  • made of two parts: sympathetic and parasympathetic
• sympathetic division

  • mobilizes body systems during activity
  • fight or flight
• parasympathetic division

  • conserves energy
  • promotes house keeping functions during rest
  • rest and digest
• plasma membrane - biomolecular layer of lipids and proteins in a constantly changing fluid mosaic
• the plasma membrane is a selective barrier that allows sufficient passage of oxygen, nutrients, and waste to service the volume of every cell
• integral proteins function

  • transport proteins (channels and carriers), enzymes or receptors
• peripheral proteins function

  • enzymes, motor proteins, cell to cell links, provide support on intracellular surface
• passive membrane transport mechanisms:

  • simple diffusion
  • carrier mediated facilitated diffusion
  • channel meditated facilitated diffusion
  • osmosis
• simple diffusion of fat soluble molecules move through the phospholipid bilayer
• carrier meditated facilitated diffusion via protein carrier specific for one chemical; binding of substrate causes transport protein to change shape
• channel mediated facilitated diffusion through a channel protein; mostly ions selected on basis of size and charge
• osmosis - diffusion of a solvent such as water through a specific channel protein or through the lipid bilayer
• types of ion channels

  • chemically gated / ligand gated
  • voltage gate
  • mechanically gated
• chemically gated ion channels ; stimulated by chemicals; includes leakage channels, open in response to binding of the appropriate neurotransmitter
• voltage gated: respond to changes in membrane potential
• mechanically gated : respond to physical changes in the shape of the receptor by touch or pressure
• active membrane transport mechanisms:

  • primary active transport
  • secondary active transport
• primary active transport

  • the ATP driven Na+ - K+ pump stores energy by creating a steep concentration gradient for Na+ entry into the cell
• secondary active transport

  • As Na+ diffuses back across the membrane through a membrane cotransporter protein, it drives glucose agaisnt its concentration gradient into the cell
• plasma membrane : generate a resting membrane potential

  1. K+ diffuses down their steep concentration gradient via leakage channels. loss of K+ results in a negative charge on the inner plasma membrane face
  2. K+ also move into the cell because they are attracted to the inner plasma membrane face
  3. a negative membrane potential is established when the movement of K+ out of the cell equals K+ movement into the cell. at this point the concentration gradient promoting K+ exit exactly opposes the electrical gradient for K+ entry
• neuron - individual nervous system cell
• nerve - many neurons working together
• neurons are either sensory or motor
• nerves can be sensory, motor, or a mixture
• perikaryon or soma is the cell body, the biosynthetic center
• dendrites are the receptive region, typically where neurons are stimulated
• antero grade - toward axon terminal
• retro grade - away from axon terminals
• leakage channel - always open never closed
• general range for cells in our body from -50mV to -100mV
• nerves and muscles are -70mV
• sodium potassium pump puts 3 na in for every 2 k out
• depolarization : inside of the membrane is less negative
• repolarization : membrane returns to its resting potential
• hyperpolarization : inside the membrane becomes more negative than the resting potential