Neural Communication

What does homeostasis require

coordinated communicatino among cells

What does the nervous system use

rapid signaling using electrical signals along neurons and neurotransmitters at synapses

What is the nervous system best suited for

fast and targeted control of muscles, glands, and moment-to-moment regulation

What does the endocrine system use

hormones that travel through the blood to distant targets

What is the endocrine system responsible for

often slower in onset and longer lasting

important for metabolism, growth, reproduction, and fluid/electrolyte balance

What is neural signaling

electrical transmission along a neuron and chemical transmission at most synapses

When does membrane potential change

when ion permeability changes

What is depolarization

net inward positive charge increases, commonly from Na entry

inside becomes less negative

What is hyperpolarization

net outward positive charge increases, commonly from K exiting

the inside becomes more negative

What changes ion movement across the cell

triggering events that open and close ion channels

What do the ion movements do

redistribute charge and make membrane potential fluctuate

What are the ion channels

ligand-gated, mechanically gated, always open, and voltage-gated

Wha are the 2 groups of ion channels

leak or gated

What are leak channels

channels that are open all the time

What do leak channels allow for

unregulated leakage of a specific ion across the membrane through the channels

What are gated channels

channels that gave gates that can be open or closed

what do gated channels do

permit ion passage through the channels when open and prevent when closed

When does gate opening and closing occur

in response to a triggering event that causes a change in conformation of the portein that forms the gated channel

What are the 4 types of gated channels

Voltage, chemically, mechanically, and thermally

What do voltage gated channels do

open or close in response to changes in membrane potential

What do chemically gated channels do

change in shape in response to the binding of a specific extracellular chemical messenger to a surface membrane receptor

What does a mechanically gated channel do

respond to stretching or other mechanical deformation

What does a thermally gated channel do

responds to local changes in temperature

What are the 2 basic electrical signals that excitable cells use

graded potentials and action potentials

What are graded potentials

local, short-distance signals that decrease with distance

What are examples of graded potentials

EPSP, IPSP, receptor/generator potentials, end-plate potentials, and pacemaker potentials

What are action potentials

long-distance propagated signals

Key distinction between action and graded potentials

graded potentials are variable and decremental; action potentials are all-or-nothing and nondecremental

Graded potentials occur in

varying grades or degrees of magnitude or strength

How are graded potentials produced

by a specific triggering event that causes gated ion channels to open, ion movement produces the graded potential

Most commonly is a depolarization of the membrane potential because of Na entry

Where are graded potentials

confined to a small region of the total plasma membrane

What are the 2 important characteristics for graded potentials

the stronger the triggering event, the larger the resultant graded potential

the longer the duration of the triggering event, the longer the duration of the graded potential

What happens when a graded potential occurs locally in a nerve or muscle cell membrane

the rest of the membrane remains at resting potential

What is the temporarily depolarized region called

an active area

Where is ion movement or current moving

along the membrane between regions next to each other on the same side of the membrane

What is ion current flow in contrast to

ion movement across the membrane through ion channels or carriers

When does the magnitude of the graded potential diminish

the farther it moves from the initial active area

The spread of a graded potential is

decremental; gradually decreases

What are graded potentials necessary for

the body’s function

Examples of graded potentials

post-synaptic potentials

receptor potentials

end-plate potentials

pacemaker potentials

slow-wave potentials

Where do action potentials begin

in a small patch of excitable membrane

What do the local currents trigger

a new action potential in adjacent membranes

What is the amplitude of action potentials

non-decremental

doesn’t fade with distance

What is the function of action potentials

faithful long-distance signaling

What do action potentials have

absolute refractory period

What is the absolute refractory period

Na channels ave opened and become inactivated

What cannot occur during the absolute refractory period

a second action potential cannot fire until depolarization resets them

What is the rising phase

rapid Na influx through voltage-gated Na channels after threshold is reached

What is the peak/early falling phase

Na channels inactivate as voltage gated K channels open

What is the falling phase

K efflux repolarizes the membrane

What happens after hyperpolarization

K channels close slowly so K efflux briefly drives the membrane potential below resting level

What happens when returning to resting potential

K channels close and resting ion gradients are maintained

What does a neuron consist of

cell body, dendrites, and axon

Where are nucleus and organelles located

cell body

Where do dendrites project from

cell body

What to dendrites increase

surface area

Dendrites carry signals

toward the cell body

What contain protein receptors that bind chemical messengers from other neurons

plasma membrane of cell body and dendrites

What is the space that receives and integrate incoming signals

input zone

What carries action potentials away from the cell body

axon

what is an axon

a single elongated tubular extension

What is the first portion of the axon and the cell body

axon hillock or initial segment

What is the axon hillock

the neuron’s trigger zone, sight where action potentials are triggered by graded potential

What is the output zone

axon terminals

How do action potentials propagate

self-perpetuating once threshold is reached

What are the 2 ways conduction can occur

continuous or saltatory

What is continuous conduction

the spread of the action potential along every patch of membrane down the length of the axon

What is saltatory conduction

the action potential jumps from one node of ranvier to the next in a myelinated neuron

Which method of conduction is faster

saltatory

What happens in the absolute refractory period of an action potential

cell will not elicit another action potential if stimulated; Na channels are inactive

What is the relative refractory period

late falling phase and hyperpolarization; K channels open

How do we differentiate between two stimuli of different strengths

frequency of the action potentials

When an AP is stated, what 2 things does the velocity depend on

whether the nerve fiber is myelinated or not

nerve fiber diameter, larger diameter, faster

Continuous conduction occurs for which fibers

unmyelinated fibers

Saltatory conduction occurs for which fibers

myelinated fibers

What is multiple sclerosis

pathophysiologic condition in which nerve fibers in various locations lose their myelin; autoimmune disease where the body’s defense system attacks the myelin sheath

What happens when an action potential reaches the axon terminals

they release chemical messengers that alter the activity of the cells where it terminates

What are the 3 structures a neuron can terminate

muscle, gland, or another neuron

What is the junction between two neurons

synapse

What is the junction between a neuron and muscle

neuromuscular junction

What are the two ways information can be transferred across synapses

electrically or chemically

How are adjacent neurons connected

adjacent neurons are coupled by gap junctions which allow ions/currents to pass directly between cells

Electrical synapses are

very rapid, often useful for synchronized activity

Direction of electrical synapse transmissions

bidirectional but an action potential in one cell does not necessarily guarantee an action potential in the next

Which synapse is more common

chemical

Where can an electrical synapse be found

specialized circuits in the retina

What happens at chemical synapses

neurotransmitter crosses a synaptic cleft and changes postsynaptic membrane potential

What receives thousands of synaptic inputs

dendrites and the cell body

Directionality of chemical synapses

one-way

presynaptic to postsynaptic

what triggers the neurotransmitter release

an action potential arriving at the presynaptic terminal

how do neurotransmitters cross the synaptic cleft

bind to postsynaptic receptors and change postsynaptic membrane potential

What is the synaptic delay

time for neurotransmitter release and receptor binding

What does an excitatory synapse do

Depolarizes the postsynaptic membrane and brings it close to threshold

increases likelihood of generating an action potential

What does an inhibitory synapse do

hyperpolarizes the postsynaptic membrane or stabilizes it below threshold

decreases the likelihood of generating an action potential

What does the postsynaptic effect depend on

the receptor and ion channels activated

What are EPSP and IPSP

local graded potentials that summate to determine whether the neuron fires

What is acetylcholine

excitatory or inhibitory depending on receptor subtype

What is dopamine

modulatory; effect depends on receptor subtype

what is norepinephrine

excitatory or inhibitory depending on receptor subtype

what is serotonin

modulatory; multiple receptor subtypes