Biol-182 Dunlap Quiz 4: Neurons

Neurotransmitter

chemical messengers that cross the synaptic gaps between neurons

Cortisol

steroid hormone released by the adrenal cortex in response to stress; mobilizes internal fuel for quick use and narrows capillary pores to preserve energy

Chronic Stress

Long term elevated levels of cortisol; leads to muscle wasting, reproductive inhibition, and immunosuppression

Brain

The mass of nerve tissue that is the main control center of the nervous system; highly connected, electrically active

Evolution of Nervous System

only animals have one; neurons generate electric siganls almost exactly the same way in all animals, but number of neurons and patterns of connections differ greatly

Dendrite

highly branches extensions off neurons that receive signals

Axon

extension that transmits signals to other cells

Neuron

cell units of the brain that send and receive signals

Resting potential

the state of the neuron when not firing a neural impulse; high K+ and low Na+ in cell; cell has net negative charge

Permeability

K+ leaks out more than Na+ leaks in; more ions are leaving the cell than are entering thus establishing a more negative cell interior

Sodium -Potassium Pump

2K+ in for 3Na+ out

Depolarization

The process during the action potential when sodium is rushing into the cell causing the interior to become more positive

Absolute threshold

the minimum intensity of stimulation that must occur before you experience a sensation

Action Potential

a neural impulse; a brief electrical charge that travels down an axon

Resting/Action Potential Process

1. Resting state: ion channels are closed

2. depolarization: stimulus opens Na+ channels

3. Rising phase: depolarization opens more Na+ channels, while K+ remains closed; cell interior becomes more positive than outside

4. Falling phase: most Na+ inactivate, but most K+ channels stay open allowing K+ to exit the cell so it becomes more negative again

5. Undershoot: Na+ channels close, K+ channels stay open, returning cell membrane to resting state

How are action potentials propogated?

One part of the neuron triggers the next in a chain reaction; the positive charge travels down the axon at roughly 60mph

Myelin Sheath

A layer of fatty tissue segmentally encasing the fibers of many neurons; enables faster transmission speed of neural impulses to 200mph

Synapse

the junction between the axon tip of the sending neuron and the dendrite or cell body of the receiving neuron

Excitatory Neurotransmitter Process

1. Ca2+ within synaptic gap enters sending neuron to trigger synaptic vesicles to release neurotransmitters

2. Neurotransmitter binds onto receptor, opening ion channel

3. Na+ rushes into sending cell, making it more positive

4. Neurotransmitter unlatches from cell, closing ion channel

Inhibitory Neurotransmitter

Causes K+ to exit cell, making electrical charge of a cell more negative

Knee Reflex

1. Sensory receptors in knee receives signal of being hit

2. Sensory neurons in brain passes message to knee muscles

3. Excitatory neuron causes quadriceps muscles to contact

4. Inhibitory neurons inhibits flexors from moving, forcing the knee to move in a forward motion

Temporal summation

One neuron transmits impulses in rapid-fire order, add up together to trigger action potential

Spatial summation

The sum of multiple synapses firing at different locations at one time to create an action potential

Acetylcholine (ACh)

neurotransmitter that triggers muscle contractions; is inhibited by botox

Sarin gas

inhibits acetylcholine esterase (enzyme that breaks down ACh), forcing repeated muscle contractions; can be fatal

Sensory Transduction

converting a stimulus into an electrical charge in a cell

Modality

kind of stimulus

Intensity

how much stimulus