topic 1

• central nervous system


  brain and spinal cord, integrative and control centers
• peripheral nervous system


  -cranial nerves and spinal nerves

  -communication lines between the CNS and the rest of the body

  -made up of the sensory and motor divisions

  -receives signals from the sensory division

  -sends signals to the motor division
• sensory division


  -somatic and visceral sensory nerve fibers

  -conducts impulses from receptors to the CNS
• motor division


  -motor nerve fibers

  -conducts impulses from the CNS to effectors (muscles and glands)

  -made of the somatic and autonomic systems
• somatic nervous system


  somatic motor, the voluntary movement

  conducts impulses from the cns to skeletal muscles
• autonomic nervous system


  -visceral motor (involuntary)

  -conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands

  -made up of the sympathetic and parasympathetic nervous systems
• sympathetic division


  mobilizes body system 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, and form part of glycocalyx.
• four methods of passive membrane transport

  simple diffusion

  carrier mediated facilitated diffusion

  channel mediated facilitated diffusion

  osmosis
• simple diffusion


  diffusion of fat soluble molecules directly through the phospholipid bilayer
• carrier mediated facilitated diffusion


  diffusion via protein carrier specific for one chemical; binding of substrate causes transport protein to change shape
• channel meditated facilitated diffusion

  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

  voltage gated

  mechanically gated
• chemically gated


  stimulated by chemicals; includes leakage channels
• voltage gated


  respond to changes in membrane potential
• mechanically gated


  respond to physical changes in the shape of the receptor by touch or pressure
• primary active transport


  the atp driven na+ - k+ pump stores energy by creating a steep concentration gradient for na+ entry into the cell
• active membrane transport mechanisms

  primary active transport

  secondary transport

  phagocytosis

  pinocytosis

  receptor meditated endocytosis
• secondary active transport


  as na+ diffuses back across the membrane through a membrane cotransporter protein, it drives glucose against its concentration gradient into the cell
• phagocytosis


  the cell engulfs a large particle by forming projecting pseudopods around it an enclosing it within a membrane sac called a phagosome. the phagosome is combined with a lysosome. undigested contents remain in the vesicle or are rejected by exocytosis. vesicle may or may not be protein coated but has receptors capable of binding to microorganisms or solid particles
• pinocytosis


  the cell "gulps" a drop of extracellular fluid containing solutes into tiny vesicles. no receptors are used, so the process is non specific. most vesicles are protein coated
• receptor mediated endocytosis


  extracellular substances bind to specific receptor proteins, enabling the cell to ingest an concentrate specific substances in protein coated vesicles. ligands may simply be released inside the cell, or combined with a lysosome to digest contents. receptors are recycled to the plasma membrane in vesicles.
• generating a resting membrane potential

  1) K+ diffuse 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 negative charge established on 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.
• ionic differences are the consequence of

  cell membranes differential permeability to Na+ and K+

  operation of the Na+/K+ pump
• depolarization


  inside the membrane is less negative
• repolarization


  membrane returns to its resting potential
• hyperpolarization


  inside the membrane becomes more negative than the resting potential
• resting state


  Na+ and K+ channels are closed

  leakage accounts for small amount of Na+ and K+ movement

  each Na+ channel has 2 voltage regulate gates

  activation gates closed

  inactivation gates open
• depolarization phase


  Na+ permeability increase; membrane potential reverses

  na+ gates are opened; k+ gates are closed

  leakage accounts for a small amount of K+ movement

  threshold = a critical level of depolarization

  at threshold depolarization becomes self generating
• repolarization phase


  na+ inactivation gates close

  membrane permeability to na+ declines to resting levels

  leakage accounts for small amount of na+ movement

  as sodium gates close voltage sensitive k+ gates open

  k+ exits the cell and the internal negativity of the resting neuron is restored
• hyperpolarization phase


  Na+ activation gates are closed

  na+ inactivation gates are closed

  leakage accounts for small amount of na+ movement

  k+ gates remain open, causing an excessive efflux of k+

  this efflux causes hyperpolarization of the membrane

  the neuron is insensitive to stimulus and depolarization during this time
• synapses


  a junction that meditates information transfer from one neuron to either another neuron or to an effector cell
• presynaptic neuron


  conducts impulses toward the synapse
• postsynaptic neuron


  transmits impulses away from the synapse
• chemical synapses


  transmit signals from one neuron to another using neurotransmitters