The photograph, made with the aid of an electron microscope, reveals actual cell bodies, dendrites, and axons in a cluster of neurons. Schwann cell – a non-neural cell that generates the myelin

Resting potential The imbalanced electrical charge of the axon in its inactive state (when the neuron is ready to fire) The inside of cell is negative relative to the outside of the axon OBJECTIVE 4-3| Describe parts of a neuron and explain how its impulses are generated.

The typical neuron receives hundreds of messages…some of these messages are excitatory (saying “FIRE”) while others are inhibitory (saying “DON’T FIRE”) e e e e e e When there are more excitatory than inhibitory messages, the cell body exceeds its threshold and creates an electric impulse… e i i i e e i

A neural impulse that consists of a brief electrical charge that travels down an axon generated by the movement of positively charged atoms in and out of channels in the axon’s membrane. All-or-Nothing Response: When depolarizing current exceeds the threshold a neuron will fire, and below threshold it will not – there is NO HALFWAY. Intensity (strength) of an action potential remains the same, throughout the length of the axon – in other words it doesn’t get weaker or stronger

Depolarization occurs, when positive sodium (Na+) ions enter the neuron, making it more susceptible to fire an action potential. Refractory Period After a neuron has fired an action potential it pauses for a short period to recharge itself to fire again – at this time the inside potassium ions move out of the cell & cannot fire

Other Action Potential Info… This graph depicts the change, with time, in the electrical charge across a given point on the axon membrane as an action potential passes through that point. To transmit the “message” the length of the axon takes less than one hundredth of a second!! With each action potential, a small amount of sodium enters the cell and a small amount of potassium leaves it – to maintain the original balance of these elements, each portion of the axon has a sodium-potassium pump that continuously moves sodium out of the cell and potassium into it

We are going to take a trip to the boys’ restroom for a neural-firing demonstration Remember the firing-process and pay close attention during the demonstration! This WILL help you remember the process…I promise! 

Synapse -- a junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron. This tiny gap is called the synaptic gap or cleft. OBJECTIVE 4-4| Describe how nerve cells communicate. Synapse was coined by Lord Sherrington (1857-1952) who inferred it through behavioral experiments. Cajal (1852-1934) described the synapse based on his anatomical studies of the brain.

Neurotransmitters (chemicals) released from the sending neuron, travel across the synapse and bind to receptor sites on the receiving neuron, thereby influencing it to generate an action potential.

Neurotransmitters in the synapse are reabsorbed into the sending neurons through the process of reuptake. Reuptake basically has the effect of “turning the volume down” on message being transmitted between neurons Once the neurotransmitters have done their job, reuptake keeps the message from being sent again

OCD High blood pressure

Neurotransmitters bind to the receptors of the receiving neuron in a key-lock mechanism. OBJECTIVE 4-6| Explain how drugs and other chemicals affect neurotransmission, and describe the contrasting effects of agonists and antagonists. Each neurotransmitter has an unique chemical configuration… Neurotransmitters attach to specific receptors…like a puzzle piece fitting into its proper place, receptors will only accept or recognize one type of neurotransmitter

Similar enough in structure that it mimics the neurotransmitters effect on the receiving neuron – often agonists INCREASE activity by inhibiting reputake “Master Key” Similar enough to occupy the receptor site and block its action, but not similar enough to stimulate activity “Other Key”