lecture 4 notes

Lecture 4:  

Depolarization = excitatory (more positive) 

Hyperpolarization = inhibitory (more negative) 

The resting membrane potential is more positive than Ek (potassium equilibrium potential) because it includes sodium permeability as well 

Local potentials 

• small 

• Graded --> vary in size and duration in relation to the strength and duration of the stimulus   

• Localized --> occur close to the site of their initiation; does not get actively conducted away from that site 

• Decremental --> decrease in size with distance away from the site of initiation  

• Either depolarizing or hyperpolarizing 

• Capable of summation --> can add together ; summed over both time (temporal summation – if they occur close together in time) or space (spatial summation – if they arise in close physical proximity) 

• Local potentials spread passively, dissipates exponentially within the cell and known as electrotonic spread 

• Local potentials are typical precursors of action potentials that constitute rapid long distance neural communication 

• The fact that local potentials can be excitatory or inhibitory and can summate over time and space, they are crucial to the nervous system's ability to integrate (filter) information 

Where do local potentials arise  

• Synapses – on dendrites and cell body of neurons  

• Sites of sensory reception – skin, sensory organs, internal organs  

What causes local potentials 

• Opening of ion channels