#4: Nervous & Chemical Communication

Question 1

nerve signal

Answer 1

electrochemical message, or action potential, produced by nuerons

Question 2

action potential

Answer 2

“all-or-none” phenomenon. Once threshold potential is reached, membrane events are no longer dependent upon stimulus strength

Question 3

All action potentials have same amplitude

Answer 3

so the only way a nerve fiber can var its signal intensity is by changing the frequency of action potentials

Question 4

Electrochemistry of Action Potential

Answer 4

At rest, intracellular fluid of a neuron maintain a high concentration of K+ ions and a low concentration of Na+ ions (by way of selective permeability & ATP driven Na+-K+ pump). Outside the neuron, the reverse ratio is maintained. Inside neuron is negative w/ respect to outside: “resting membrane potential”

Question 5

Depolarization of action potential

Answer 5

Na+ channels open, Na+ diffuses into cell from outside; inside becomes > + relative to before

Question 6

Repolarization (synchronous w/ absolute refractory period)

Answer 6

Following depolarization, cells starts returning to its resting potential.
However, cell briefly becomes more negative than its resting potential (called hyperpolarization) synchronous with relative refractory period

Question 7

Synapses

Answer 7

small gap between two neurons; neurotransmitters carry action potential from presynaptic to postsynaptic neuron

Question 8

Acetylcholine (Ach)

Answer 8

Arrival of Action Potential at Presynaptic cell causes Ca2+ ions to diffuse into it, inducing exocytosis of Ach. The binding of Ach to receptors on the postsynaptic cell opens ion channels on it, causing a depolarization

Question 9

Types of synapses

Answer 9

Convergence: many presynaptic cells affect a single postsynaptic cell (allows info from many sources to affect one cell)
Divergence: a single presynaptic cell affects many postsynaptic cells (allows one info source to affect multiple paths)

Question 10

Reflex arc

Answer 10

Fundamental unit of neural operation, consisting of a group of neurons working together:

1. Receptor, a sense organ, perceives a stimulus
2. Afferent (sensory) neuron carries impulse to Central Nervous System (CNS)
3. CNS, where the impulse is received and processes
4. Efferent (motor) neuron carries impulses away from CNS
5. Effector, the organ that responds to the stimulus

Question 11

Sense organs

Answer 11

1. Transducers that transform energy of a specific kind into electrical signals.
2. Adequate stimulus: where each receptor is specific to a certain type of stimulus
3. Electrical signals received and processed at different regions of brain are perceived as different sensations

Question 12

Chemoreception

Answer 12

1. Oldest and most universal:
chemotaxis
smell
olfaction
2. Depends on receptor potentials from the binding of chemicals on receptor proteins

Question 13

Mechanoreception

Answer 13

1. Touch
2. Pain: depends on receptor potentials from pressure, chemicals released from injured tissue
3. Hearing
4. Equilibrium: depends on receptor potentials from movement of hair cells in Organ of Corti (structure in cochlear membrane of inner ear)

Question 14

Photoreception

Answer 14

Depends on receptor potentials from light absorption by the photopigment rhodopsin

Question 15

Chemical coordination

Answer 15

1. Hormones released into blood by endocrine glands; transported to distant target cells; alter rate of biochemical processes
2. Slow acting compared to nerve signals. Used for long lasting, sustained effect.
3. In spite of widespread distribution, hormones only engage their specific target cells by virtue of their receptor molecules
4. Most hormones are controlled by negative feedback. if they are to disrupt stable points, positive feedback is used.