(Neuro)Glial cells- why are they important? Make up 85% of the nervous system Clear away cellular debris Microglia repair Astrocytes create the blood brain barrier Oligodendrocytes help with the myelin sheaths 10

Ready… Aim… FIRE! Neurons have a negative “Resting Potential” Nerve impulse = Action Potential Resting potential= -70 mV Action potential= All or none law 5

The nerve impulse: 100 million messages per second 50 billion neurons 10, 000 miles of fibers in 1 cubic inch. Stretched out goes to the moon and back.

The Myelin sheath (formed by Schwann cells and oligodendrites) why is it important? Myelin sheath is provided by which two neuroglia cells? – Schwann and oligodendrocytes Acts as insulation Action potential occurs only at the unmyelinated regions called the nodes of Ranvier. This is where the sodium channels are located Insulated with myelin for speed ----Unmyelinatd axons speed of AP is 10 m/s. Myelin sheath has spaces= Nodes of Ranvier. ----The AP jumps from node to node (speed 120 m/s).

Functional Properties of Neurons Irritability – ability to respond to stimuli Conductivity – ability to transmit an impulse The plasma membrane at rest is polarized Fewer positive ions are inside the cell than outside the cell

Starting a Nerve Impulse Depolarization – a stimulus depolarizes the neuron’s membrane A depolarized membrane allows sodium (Na+) to flow inside the membrane The exchange of ions initiates an action potential in the neuron Figure 7.9a–c

The Action Potential If the action potential (nerve impulse) starts, it is propagated over the entire axon K+ rush out of the neuron after Na+ ions rush in, which repolarizes the membrane The Na+ - K+ pump restores the original configuration This action requires ATP

http://www.sumanasinc.com/webcontent/ animations/content/synapse.html http://www.sumanasinc.com/webcontent/ animations/content/carrier_proteins.html

Nerve Impulse Continues b/w Neurons Impulses are able to cross the synapse to another nerve Neurotransmitter is released from a nerve’s axon terminal The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter Action potential is started again in the dendrite

How Neurons Communicate Figure 7.10

Disease Multiple sclerosis destroys myelin sheaths. Sodium (Na) channels are only at nodes. Neuron can’t have an action potential or nerve impulse. Disease that impact the myelin sheath, like MS, affect the action potential which impacts the action potential of that neuron. People with MS ultimately experience pain and decrease motor function in the areas of their body where the myelin sheath of the neurons has been effected.

Anesthetics = action potential Local (Novocain, Xylocaine) attach to Na+ channel. Na+ can’t enter cell. Anesthetia stops the action potential, stop the action potential and do you feel pain? – NO why? – the signal fro pain is stopped. Both local and general anesthesia prevent the change in polarity along the axis of the neuron. General anesthetic (ether, chloroform) open K + channels, K + exits as fast as Na+ enters

The Reflex Arc Reflex – rapid, predictable, and involuntary responses to stimuli Reflex arc – direct route from a sensory neuron, to an interneuron, to an effector Figure 7.11a

Types of Reflexes and Regulation Autonomic reflexes Smooth muscle regulation Heart and blood pressure regulation Regulation of glands Digestive system regulation Somatic reflexes Activation of skeletal muscles

Reflex Arc

Reflex Arc Receptors Sensory neuron Relay neuron Motor neuron Effectors