BIOL CHAP 39- Neurons and Synapses

Neural signaling

How a neuron communicates; response to stimulus

reception

detection of stimulus by sensory neurons; see ball coming at you

input

integration

brain processes sensory neurons and decides what to do

processing

response

signals sent to muscles by brain about what to do

action

cell body

houses nucleus

eukaryotic

genes transcribed here

protiens made here

Nerve fibers

dendrites and axons

dendrites

receive information

sends info to the cell body

less than 1 mm

call dendritic tree or dendritic arbor

axon hillock

start of the action potential

axon

take signal to axon terminal

surrounded by myelin sheath

axon terminal

send signal to other neurons or muscles by sending signal to effector

effector

nerves, cell, glands or muscles that respond to signals from axon terminal

interneurons

Axon has axon terminals that sprout out

used for neuron-to-neuron communication

terminal less than 1 mm

Projection Neurons

Used for long distance communication

Axon terminals are longer than 1 mm

gilia cells

Provide support to neurons

can multiply and replace dead cells

loss of gliia regulation = brain tumor

types of gilia cells

Astrocytes cover blood vessels. CNS

Oligodendrocytes make myelin. CNS

Schwann cells- make myelin. PNS

Synapse

after the axon terminal, the period where neurons make connections to effector

presynaptic cell

cell or neuron that sends signal

post synaptic cell

effector that receives signal

Chemical synapse

Presynaptic and postsynaptic cells are separated by a gap. Neurotransmitters in axon terminal go from pre to post to transmit a signal

synaptic cleft

in chemical synapse, 25 nm gap between pre and post synaptic cells

Electrical Synapse

Pre and post-synaptic cells touch and gap junctions allow ion signals to flow to post synaptic cell

exocytosis

Only for a chemical synapse. vesicle and membrane fuse to let neurotransmitters bind to receptors in post synaptic cell. After binding, ion channels open or close

chemical synapse

Electrical synapse

cytosol

A jelly-like substance in a cell made of cations and anions

Animals have more anions in cytosol

lots of K+

cytoplasm

everything in cell besides nucleus

cytosol and organells

membrane potential

electrical change inside the cell vs outside the cell

ICF is more negative bc K+ leaves the cell

ECF is more positive

An action potential leads to ICF depolarization; ECF stays the same

Charge measured in mV

equilibrium membrane potential is -98 mV

ICF

intracellular fluid

made of water, ions and protiens

includes all fluid inside cell as well as cytosol

Lots of Na+

ECF

Fluid outside the cell

includes blood plasma, lymph and intercellular fluid (Middle ground fluid in between tissue kida)

Main ions are NA+ and CL-

leak ion channels

Ion channels that are always open so ions can pass thru

gated ion channels

channels that can close to regulate which ions come thru

How do small organic molecules (like amino acids) cross the membran

With carrier proteins, but this is slower than channels

How does a carrier protein work

carrier proteins are attached to the plasma membrane. On the outside of the cell they bind to non-lipid things and then change shape and push thing inside cell

Na+/K+ pump

Helps to keep sodium and potassium levels different inside and outside of cell.

3 Na+ out of cell

2 K+ inside of cell

Uses about half of brains ATP

without pump, neurons cant send electrical signals

ionic driving force

chemical vs electrical force

when will K+ stop leaving the cell/ when will cell have charge of 0 mV and how

it will stop when ICF and EFC are balanced. this can happen because K+ will leave until K= wants to come back because it attracts to more negative, or the ICF. 

equilibrium potential

electrical energy needed to balance out chemical energy (electrical energy needed to balance the K+ that left)

threshold potential

-50 mV

depolarization

Na+ ions rush in, caused by Na+ gates opening. after reaching threshold, ICF becomes positive in less than 1mS

repolarization

After reaching about 30 mV, K+ leaves or Cl- comes in and goes to hyper polarization, or less than -70

Refractory Period

Reaction potential can’t be generated for a few milliseconds. Starts at the peak of the action potential. The cell can’t be restimulated. The threshold required for another action potential is higher than normal. 1-4 mS for 1 action potential cycle. makes sure action potential is 1-way movment

all-or-nothing principle

Action potential is produced only if the threshold is met. if its 1 above or even 100 threshold, action potential size is same

explain action potential from start to finish

starts at axon hillock. The resting potential is -70 mV. Stimulus makes Na+ channels open and depolarization happens. reaches about 30 mV, then repolarization happens, or K+ leaves cell, or Cl- comes in. The refractory period happens, then back to resting potential.

Hyperpolarization

goes below to about -80 mV

voltage-gated ion channels

open/ close in response to changes in membrane potential

found on axon hillock and axon

depolarization-activated ion channels

activated after depolariation, and its the K+ channels opening tso K+ can leave.

Reflexes

Does not require brain to process

Involuntary

respond to stimuli faster than voluntary movment

Propagation/ how action potential propagates

Moving or spreading

Action potential propagates down the axon bc positive charges influence axon segments to make an action potential, helping action potential travel down the axon

frequency of action potentials

More action potentials cause more neurotransmitters to be released at the synapse (10 above threshold produces more frequency than 1 above threshold)

anesthetics effects

Procaine and lidocaine bind to Na+ channels and block their ability to let ions flow. Sensory nerves in this region can’t send pain signals fully. Tetrodotoxin also blocks Na+ channels, leading to muscle paralysis or death. 

what is ganglion

neuron chunks in PNS

Nuceli

Neuron chunks in CNS. Found in gray matter or brain

inside of cell membrane is charged

negatively

what is resting potential range

-40 to -90 mV. average is -70

membrane potential

separation of positive and negative charges across the plasma membrane

Neuronal membrane doing nothing is called

polarized

what is an action potential

a neuron sending electrical signal causing membrane potential change

why is refractory period important

so action potential doesnt reverse direction along axon

action potential is considered as an

all or nothing principle

what happens to magnitude of action potential as propagates

remains the same

the intensity of a stimulus is reflected in

frequency. greater stimulus is more AP per second

myelin

speed up in axon