graded potentials

what are the 2 excitable tissues and what do they do (2)

• neurons and muscles

• 2 cell types that can change the RMP in order to create an AP to enable them to communicate – can undergo rapid changes in their RMP

what are the 2 types of potential change that the excitable tissues and explain

• graded potentials - small changes - serve as short-distance signals

• action potentials - large changes - serve as long-distance signals

what is the fastest way to move ions across cell membranes

• through ion channels

• As channels eg Na+ channel can transport up to 1x10^7 substances per second compared to other ways like the sodium potassium pump which is only 5 x 10^2

4 characteristics of ion channels

• Pores in cell membranes

• Selective for a particular ion (Na+ channel)

• Passive – no energy is required – ions flow down their electrochemical gradient

• Gated – can be in an open/closed state – prevents/allows passage of ions

what is the function of the neuron

to transport impulses around the body, allowing communication

The neuron contains the same fundamental structures as other cells of the body such as (4)

–      plasma membrane

–      nucleus

–      endoplasmic reticulum and Golgi apparatus

–      mitochondria etc.

how is the neuron is specialized for its function in three ways and explain each one

–      axon – long but variable in length – depends on location in body and height

–      dendrites – cytoplasmic processers that come out of the cell body of the neuron – allow it to make connections with other neurons

–      myelin sheath – lipid layer wrapped around axon – improves speed of impulses in the neuron

what does motor neuron do

takes information from the brain / spinal cord to the muscles

what does interneuron do

– found within CNS – consists of brain and spinal cord – connects information from sensory neuron to the motor neuron

what point is the impulse / AP generated at

axon hillock (start of the axon near the cell body) - and then travels down axon

what is synaptic transmission

process by which the information passes onto another neuron

explain the characteristics of graded potentials (4)

•       short lived, localized changes in RMP

•       triggered by changes in environment which cause opening of gated ion channels (change in pressure / any stimulus)

•       may be either hyper- or depolarization

• A graded potential is a small change in RMP (up to 15mV) that is proportional to the stimulus and propagated decrementally

   

explain what local currents do (3)

• small change in RMP spreads to next portion of the membrane – local currents - cause the change in RMP to occur in next portion of the membrane

• initial stimulus depolarizes small area of membrane

• local currents created depolarize adjacent membrane areas, wave of depo spreads

describe the magnitude of GPs

• Magnitude of GPs varies directly with the magnitude of the stimulus

•       Magnitude of a GP can be up to 15mV

•       Magnitude / graded potential declines with distance – doesn’t travel very far

state some examples of GPs (4)

–      excitatory postsynaptic potentials (EPSPs)

–      inhibitory postsynaptic potentials (IPSPs)

–      above: small GPs which are created at the synapse

–      Receptor potentials

–      Pacemaker potentials