Lecture 15 Impulse transmission 2

Postsynaptic Potentials

Neurotransmitters can activate different ion channels in the post synaptic membrane

Excitatory postsynaptic potential (EPSP

• Na+ channel activation (depolarization), nonspecific ion channels activation

• More Na+ than K+, (Depolarization), Ca2+ channel activation (Depolarization)

Inhibitory postsynaptic potential (IPSP)

K+ channels activation (hyperpolarizing)

Cl- channel activation (hyperpolarizing)

Synaptic Integration: Summation

• A single EPSP cannot induce Action Potential

• EPSPs can add together to influence postsynaptic neuron

• IPSPs can also add together

Most neurons receive both EXCITATORY and INHIBITORY inputs from thousands of other neurons

Action potentials are started ONLY if SPSP’s dominate and bring membrane potential to threshold

2 types of graded potential summation

Spatial summation of opposing stimuli

• changes in membrane potential can cancel each other out

Graded potentials vs Action potentials

Conduction velocity - Speed

Speed of electrical propagation depends on:

Axon diameter: larger diameter: FASTER (less resistance) ex. Squid giant axon

Degree of myelination

Myelin insulate and prevents leakage of charge

• action potentials traveling though myelinated neurons propagate about 30 times faster than unmyelinated neurons

Conductivity

Multiple sclerosis (MS) - demyelination

• Autoimmune disease primarily affects young adults

• Myelin sheaths in CNS destroyed through inflammation and scarring

• Immune system attacks myelin and turns it to hardened lesions called scleroses

• Impulse conduction slows and eventually ceases

Symptoms of multiple sclerosis

• visual and speech disturbances

• Weakness and loss of muscular control

• Urinary incontinence