Homeostasis
Homeostasis is the tendency to resist change in order to maintain a stable, relatively constant internal environment. |
Many factors of the internal environment must be homeostatically maintained. For example: (Nutrients; O 2 and CO 2; Waste products; pH; Water, Salt, and other electrolytes; Volume and pressure; Temperature) |
Homeostasis is dependent on the communication of cells and body systems in order to perform regulatory actions |
Cells can communicate through Direct or Indirect Communication for the Nervous System and are relied on getting fast rapid responses accurately throughout the body |
Synaptic Transmission
Synapse: - junction between two neurons, or between a neuron and a muscle or gland that enables one cell to electrically and/or biochemically influence another cell |
Electrical synapses: neurons connected directly by gap junctions |
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Organization of Nervous System
The nervous system is organized into the central and peripheral nervous system |
Central nervous system (CNS): brain and spinal cord |
Peripheral nervous system (PNS): nerve fibers (Afferent and efferent divisions) |
Enteric nervous system (ENS): nerve network of the digestive tract |
Autonomic nervous system: fibers that innervate smooth muscle, cardiac muscle, and glands (Further subdivided into the sympathetic and parasympathetic nervous system) |
Sympathetic - division of the autonomic nervous system that prepares the body for strenuous physical activity. “Fight or flight response” |
Parasympathetic - division of the autonomic nervous system that maintains resting functions of the internal organs. “Maintaining homeostasis” |
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Diffusion
Diffusion is the process of movement of molecules under a concentration gradient. |
Rate of diffusion through a membrane depends on five factors: |
1) magnitude of the concentration gradient: as concentration gradient increases, rate of diffusion increases |
2) permeability of the membrane: as permeability increases, rate of diffusion increases |
3) surface area of the membrane: as surface area increases, rate of diffusion increases |
4) molecular weight of the substance: as molecular weight increases, rate of diffusion decreases |
5) distance (thickness) over which diffusion takes place: as distance increases, rate of diffusion decreases |
Membrane Potential
Membrane potential is a separation of opposite charges across the plasma membrane.(Vm) |
The grater the separation of charges across the membrane, the larger the potential |
Equilibrium potential for K+ (EK+= -90mV) |
Equilibrium potential for Na+ (ENa+= +60mV) |
Resting membrane potential (- 70mV) |
At the resting membrane potential, membrane permeability K+ > Na+ |
Leak channels permit ions to diffuse down concentration gradients |
Na/K ATPase establishes and maintains concentration gradients (pumps 3 Na + out of the cell for every 2 K + pumped into the cell) |
Action & Graded Potentials
Depolarization – change in membrane polarization to more positive values than resting membrane potential |
Hyperpolarization – change in membrane polarization to more negative values than resting membrane potential |
Repolarization - return to resting membrane potential after depolarization |
Action Potential - Brief all-or-nothing reversal in membrane potential (spike), lasting on the order of 1 millisecond, , that is brought about by rapid changes in membrane permeability to Na+ and K+ ions |
Graded potentials - are local changes in membrane potential, occur in varying grades or degrees of magnitude or strength, spread by passive current flow, and die over short distances |
Propagation - action potentials propagate when locally generated depolarizing current spreads to adjacent regions of membrane causing it to depolarize. |
Absolute refractory period - a brief period during a spike |
Relative refractory period - a brief period following a spike |
Refractory period prevents “backward” current flow |
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