Download Understanding Neural Signaling: Electrical Signals & Cell Transmission and more Slides Biology in PDF only on Docsity! Chapter 40 Neural Signaling Communication Docsity.com Nervous System • General Scheme, fig 40-1 – Stimulus excites a receptor (sensor) – Name some stimuli. – Receptor sends info via sensory neuron (nerve cell) to an… – Integration center (CNS) that processes info (interneurons) and sends instructions via a… – Motor neuron to an effector (skeletal muscle, etc.) 2 Docsity.com Nervous System • Neuroglia = helper cells that nourish and protect neurons. Examples: – Microglia – – Astrocytes – – **Schwann cells (PNS) and oligodendrocytes (CNS) form myelin sheaths = insulation. 5 Docsity.com How Do Cells Generate Electrical Signals? • Review: – Atoms that lose electrons become positive ions – Atoms that gain electrons become negative ions. • Ions of opposite charges are attracted to each other. To separate them requires energy. Charge separation represents potential energy – like your car battery. 6 Docsity.com How Do Cells Generate Electrical Signals? • Membrane potentials (electrical) – In cells, different concentrations of ions on each side of a membrane produces an electrical potential or voltage. – Ions must move through channels – 3 types: • Ligand gated – • Voltage gated – • “Leak channels” – 7 Docsity.com How Do Cells Generate Electrical Signals? • Because the charges on either side of the plasma membrane are different, cell membranes are said to be polarized. When the charge difference changes… – and the potential decreases or becomes less negative, the membrane is said to be depolarized. – and the potential increases or becomes more negative, the membrane is said to be hyperpolarized. 10 Docsity.com How Do Cells Generate Electrical Signals? • Action Potential = rapid, transient depolarization, also called a nerve impulse. This occurs only at the axon hillock of a nerve cell. • Sequence, fig 40-7. – A stimulus causes a small depolarization by allowing Na+ to enter the cell through Na channels. – If the depolarization reaches a certain voltage (=threshold potential), voltage-gated Na channels open. – Na rushes into the cell causing a large, transient depolarization. 11 Docsity.com How Do Cells Generate Electrical Signals? • Action Potential sequence cont’d • At the peak of the large depolarization, the voltage gated Na+ channels close and voltage gated K+ channels open. • K+ moves out of the cell and the membrane potential returns toward resting membrane potential = repolarization. • K+ channels are slow to close and membrane potential falls below resting levels = hyperpolarization or undershoot. 12 Docsity.com How are Action Potentials Propagated? • Action potentials take place at a discreet spot on the cell membrane. Neighboring areas have a different voltage and an electrical current to flow between the 2 spots – like a battery. • Adjacent areas depolarize, voltage gated Na+ channels open and – the action potential sequence is repeated, fig 40.8. 15 Docsity.com How are Action Potentials Propagated? • The process continues until the action potential moves over the entire cell. • In large neurons with myelin sheaths, the action potential is regenerated at each Node of Ranvier, fig 40-9. – Cause action potential to “jump” from node to node down the axon and move faster = saltatory conduction. – Maintains strength of action potential. 16 Docsity.com How are Electrical Impulses Transmitted Between Cells? • Connection = synapse – Fluid filled gap or space between 2 neurons or between a neuron and another cell = synaptic cleft, fig 40-10. – The neuron sending the impulse is the presynaptic cell, the cell receiving the impulse is the postsynaptic cell. • The “message” is sent across the synapse via chemicals called neurotransmitters. 17 Docsity.com
