PSYC-2900 Chapter 2.2

withdrawal reflex

composed of a sensory neurons, an excitatory interneuron, and a motor neuron

1. dendrites of sensory neuron detect stimulus

2. in the spinal cord, interneuron connected to axon of sensory neuron excites motor neuron connected to interneuron

3. motor neuron causes muscle contraction, muscle causes withdrawal from the source of stimulus

descending inhibitory control

a form of modulating reflexes, in which a cognitive signal decreases/stops a reflex. the same process occurs as if a reflex were activated, except the muscle contraction (reflex) is inhibited by an interneuron attached to the motor neuron in the spinal cord

communication along axons

generated by the movement of ions across the cell membrane (in/out) when:

• channels/transporters are available

• there is a concentration gradient (movement from high to low)

• electrical gradient (attraction to opposite charge)

membrane potential

the difference in electrical charge between the inside and outside of a neuron

resting membrane potential

the electrical charge of the axon when it is not firing an action potential (-70mV)

depolarization

reduction of membrane potential (i.e. the cell becomes more positive). positively charged cations move into the cell, or negatively charged anions move outside the cell

hyperpolarization

increase in membrane potential (i.e. the cell becomes more negative). negatively charged anions move into the cell, or positively charged cations move outside the cell

diffusion

the movement of molecules from regions of high concentration to regions of low concentration. it is completed when molecules attain equilibrium

electrostatic pressure (ion graidents)

a concentration and electrical gradient caused by the natural amounts of specific ions in inter and extracellular fluids

intercellular fluid

fluid within the cell that has higher levels of organic anions (A-) and potassium ions (K+)

extracellular fluid

fluid surrounding the cell that has higher levels of chloride ions (Cl-) and sodium ions (Na+)

sodium-potassium pump

a process that maintains resting membrane potential by using active transport: a pump pushes 3 Na+ out of the cell in exchange for 2 K+ into the cell using ATP

action potential

a brief electrical impulse that provides the basis for conduction of information along an axon. it is generated at the axon hillock, and regenerates & does not diminish as it travels down the axon. allows for communication within neurons as an electrical signal

threshold of excitation

a value of a membrane potential that must be reached to produce an action potential

(i.e. “all or none”)

rate law

the intensity of information being transmitted in an axon are presented by variations in the rate at which the axon fires

saltatory conduction

the process by which nerve impulses travel quickly down a myelinated axon. insulation from the myelin sheath allows the action potential to travel faster, and Na+/K+ pumps are only needed at the nodes of Ranvier