A dendrite is an extension of the cell body from a neuronal cell. This the site where communication from other neurones is recieved. It is also at this point where it is determined whether or not an action potential is transmitted down the axon . In a dendrite, when neurotransmitters cross the synaptic cleft and bind to receptors on the membrane, a signal is transferred. Unlike in the axon of a neuronal cell, the signal is not an action potential, but in fact a graded potential. Graded potentials can be of varying strengths and depending on the strength of the graded potential when it reaches the axon hillock. If the graded potentials exceed the threshold level then an action potential is passed down the axon.
There are two types of graded potentials: excitatory and inhibitory. The excitorary potential is known as an EPSP. This is initiated by Na+ ion channel opening and the Na+ ions entering the membrane, causing depolarisation to occur. The inhibitory potential, the IPSP is initiated by the Cl- ion channel opening. This hyperpolarises the membrane potential and could thus cancel out the EPSP, preventing the action potential from being passed on.
- ↑ Alberts et al., 5th edition, G:10