Chapter 48 - Neurons, Synapses

and Signaling

By: Sam Biller + Ryan Coughlin

Overview of Neurons

• Neurons are nerve cells that transfer information within the body.

• The structure of Neurons allows them to use pulses of electrical current to receive, transmit, and regulate the flow of information over long distances.

• Neurons transmit sensory information, control heart rate, coordinate hand and eye movement, record memories, generate dreams and more.

 

Neuron Organization and Structure:Cnidaria - Sea Anemone

• Movements used by a net of nerves

• No Brain or Nervous System

• Cnidarians detect and respond to stimuli from all directions. Sensing objects by touch.

Neuron Organization and Structure:Annelida - Segmented Worm

• No brain, have a ganglionic mass

• Bundle of nerves running

down body

• Branches into other bundles

• Sensory organs on skin

Neuron Organization and Structure:Arthropoda - Crustaceans

• Very similar tothe annelidas.

• Have a brain thatbraches off into nerve

bundles and cord

• These each have a specific function

Neuron Organization and Structure:Mammalian - Humans

• Bigger more complexbrain

• Nerves branched allover body

• Messages travel from brain along nerves

• Electric signals traveldown the neurons

Action Potential

The Sodium and Potassium channels are closed.

• A reduction in the magnitude of the membrane potential is called a depolarization.

• Sodium Channels in a resting neuron to open, membrane's permeability to Sodium Ions increases.

• After the Membrane has been crossed the positive and negative feedback switch along the membrane because of the Sodium Ions positive charge.

• Potassium Channels remain closed.

• Sodium Channels become inactivated blocking the sodium ions flow.

• Most Potassium Channels become open switching the positive and negative feedback back to normal.

• The Sodium Channels remain closed, but are unblocked.

• Some Potassium remain open causing the membrane's permeability to potassium ions to be higher than at rest.

• As the Potassium channels begin to close and sodium channels remain closed the membrane returns to its resting state.

Neurons communicate with other cells at Synapses

• Action potentials are not transmitted from neurons to other cells.

• Transmission does occur at the synapses.

• Electrical and Chemical Synapses transmit information to other cells.

Electrical Synapses

• Allows the electrical current to flow directly from one neuron to the other.

• Vertebrates and Invertebrates, electrical synapses synchronize the activity of neurons for rapid behaviors.

• Electrical Synapses take place in the vertebrate brain.

Electrical Synapses

Chemical Synapses

Chemical Synapses continued...

1. The action potential arrives in the presynaptic membrane depolarizing it.

Chemical Synapses continued...

2. Depolarization opens voltage-gated channels, triggering Ca2+ in the membrane.

Chemical Synapses continued...

3. Increased Ca2+ concentration causes the synaptic vesicles to fuse with the presynaptic membrane, releasing the neurotransmitters into the synaptic cleft.

Chemical Synapses Continued...

4. The neurotransmitters then bind to the ligand-gated ion channels in the postsynaptic membrane which binding triggers opening, allowing Sodium and Potassium to diffuse through.

Chemical Synapses Continued...

• Neurotransmitter is not part of the ion channel

• Neurotransmitter binds to metabotropic receptor

• Activates a signal transduction pathway in the postsynaptic membrane involving a second messenger

Neurotransmitters

100 different types Acetylcholine – Amino Acids Biogenic Amines Neuropeptides Gases

Diseases

Motor Neuron Diseases (MND) - destroy neuron cells which are important in health and everyday life and functioning.

MND controls: voluntary muscle actions, such as swallowing, breathing, speaking, talking, hand gestures, and walking.

Examples of Diseases:

Amyotrophic lateral sclerosis (ALS or Lou Gehrig’s Disease)

Progressive Muscular Atrophy - Causes Weaknesses in the hands and the lower body.

Diseases

Epilepsy – a brain disorder in which a bunch of nerve cells start to signal abnormally

When the signals happen so fast, sometimes as quick as 500 times per second, a person has a seizure.

Diseases Continued...

There is no cure for Neuron related diseases.

There is no cause for Neuron related diseases, but some are inherited.

Work Cited

• "Motor Neuron Diseases." - Symptoms, Causes, Treatments. Web. 25 Mar. 2012. <http://www.localhealth.com/article/motor-neuron-diseases>.

• Reece, Jane B., and Neil A. Campbell. Biology. Boston, MA: Cummings, 2011. Print.

• "Google Images." Google Images. Web. 25 Mar. 2012. <http://images.google.com/>.

“MedicineNet.com.”MedicineNet. Web. 25 Mar.2012.<http://www.medicinenet.com/sizure/article.htm.