Section 14: Neurons, Synapses, and Signaling (Part A)

Neurons

Nerve cells that transfer information within the body

1. electrical signals

2. chemical signals

Neurons use these types of signals to communicate: [2]

Electrical signals

neurons use these signals for long distances

chemical signals

neurons use these signals for short distances

1. simple cluster of neurons called ganglia

2. more complex organization of neurons (brain)

processing information takes place in either: [2]

Axon

neuron receives information and transmits it along this extension

Synapses

information travels along axon and transmits it to other cells via THESE specialized junctions

1. sensory information or output from OTHER neurons

input to neuron iis:

One direction.

Electrical impulses travel in how many directions?

every electical impulse is identical but the FREQUECY of signalling varies.

How does electrical signaling vary?

1. muscles

2. glands

3. other neurons

output from neurons is received by: [3]

cell body

where are most neuron organelles

dendrites

highly branched extensions of neurons that transmit signals to other cells at synapses

axon

longest extension that transmits signals to other cells at synapses

axon hillock

cone shaped base of axon is called:

synaptic terminal

passes information across the synapses as chemical messengers

neurotransmitters

chemical messengers that pass across synapse as chemical messengers

synapse

junction between an axon and another cell

presynaptic cell

information is transmitted from a ______cell to a ______celll

neuron

presynaptic cell is:

1. neuron

2. muscle

3. gland cell

postsynaptic cells are: [3]

1. sensory input

2. integration

3. motor output

three stages of nervous system processing

sensory neurons

sensors detect external stimuli and internal conditions and transmit information along:

info sent to brain or ganglia

interneurons integrate

sensory information is sent HERE, where THESE integrate the information from sensory neurons

motor neurons

motor output leaves the brain via these, which trigger muscle or gland activity

central nervous system

system where integration takes place

peripheral nervous system (PNS)

system that carries information in and out of CNS

nerves

neurons of the peripheral nervous system are are bundled together

glia cells

mot neurons are nourished and insulated by:

gated ion channels

channels that open or close in response to stimuli

neurons respond to gated ion channels

how do membrane potential changes occur?

the net moveent of ions in and out of the cell

the resting membrane potential of a neuron depends on:

less polarized, or DEPOLARIZED

when POSITIVE ions move into the cell (or negative move OUT), the membrane becomes….

sodium channel opens and Na+ diffuses into cell

example of depolarization:

more polarized, or HYPER polarized

when posittive ions move OUT of the cell (or NEGATIVE moves in), the membrane becomes:

potassium channels in the neurons open, K+ diffuses out.

hyperpolarization occurs if:

graded potentials

changes in polarization where the magnitude of the change varies with the strength of the stimulus

The generation of nerve signals

Graded potentials are not nerve signals that travel along axons, but they do have an effect on:

action potential

If depolarization shifts the membrane potential sufficiently, it results in a massive change in membrane voltage called:

has constant magnitude, and transmit signals over long distances

action potential magnitude:

because some ion channels are voltage gated, opens or closes when the membrane potential passes a certain level

why do action potentials arise?

most voltage gated sodium and potassium channels are closed.

describe resting potential stage

1. volage gated sodium channels open first, Na+ diffuses in

what happens at voltage gated channels when an action potential is generated?

Na+ diffuses in and the threshold is crossed, and membrane potential is increasing

what happens during rising phase of action potential:

Voltage-gated sodium channels become inactivated

voltage gated Potassium channels open, K+ flows into the cell

what happens during falling phase of action potential generation?

membrane permeability to K+ is at first higher than therest, then voltage gated potassium channels close and resting potential is restored.

what happens during the undershoot of action potential generation?

A second action potential cannot be initiated.

What happens during refractoryperiod after action potential?

temporary inactivation of the sodium channels

the refractory period is a result of what?

axon hillick

where are action potentials usually generated

toward synaptic terminal in one direction

direction of action potential travel:

inactivation of sodium channels behind the zone of depolarization

what prevents the action potential from traveling backward?

diameter

the speed of action potential increases with the axon’s..

myelin sheath

In vertebrates, axons are insulated by:

increase

myelin sheath causes action potential’s speed to…

glia - oligodendrocytes

myelin cells in CNS

Schwann cells

myelin cells in PNS

at nodes or ranvier

Only place where action potentials are formed (verts)

Node of ranvier

gaps in the myelin sheath where voltage-gated sodium channels are found

Saltatory conduction

Action potentials in myelinated axons jump between nodes or ranvier in this process:

gap junctions

at electrical synapses, the electrical current flows from one neuron to another through:

neurons

at chemical synapses, a chemical neurotransmitter carries information between:

chemical

most synapses are: (chemical or electrical)

1. action potential arrives, depolarizes the presynaptic membrane

2. depolarization opens voltage gated channels, triggering influx of calcium

3. elevated calcium concentration causes synaptic vesicles to fuse with presynaptic membrane, releasing neurotransmitter into the synaptic cleft

4. the neurotransmitter binds to ligand-gated ion channels in post-synaptic membrane,

four steps that happen at a chemical synapse: