Neurons and Synapses

Question 1

Central nervous system (cns)

Answer 1

Brain and spinal cord

Question 2

Peripheral nervous system (pns)

Answer 2

Peripheral nerves outside the brain and spinal cord (cranial nerves: emerge directly from the brain stem - 12 pairs; spinal nerves: emerge directly from the spinal cord - 31 pairs)

Question 3

Stimulus response pathway

Answer 3

Stimulus - transmit - response (for the transmission of electrochemical signals)
Change the neurons membrane potential

Question 4

Stimulus (external or internal)

Answer 4

Detected by a sensory receptor in the peripheral nervous system (skin, eyes, ears, etc)

Question 5

Transmit

Answer 5

Sensory neurons (nerves in PNS) transmit the signal (via electrical impulses) to the central nervous system (to relay neurons)

Question 6

Response

Answer 6

“Selected” by CNS (conscious or unconscious) and a signal is sent (via relay neurons in the CNS to motor neurons in the PNS) to effectors (muscles or glands) to generate a response

Question 7

What is a response

Answer 7

Change in an organism due to detection of a stimulus

Question 8

Neurons (function)

Answer 8

To transmit electrical impulses

Question 9

Basic structure of a neuron

Answer 9

Dendrite, cell body (soma), axon

Question 10

Dendrite (what is it, function)

Answer 10

Short branched fibers (branch off the cell body)
Function: receive chemical signals (from sensory or other neurons) and transform them into electrical signals which are sent to cell body (into neuron)

Question 11

Cell body (soma; what is it, function)

Answer 11

Nucleus and cytoplasm + organelles

Function: metabolism and summation of input cells

Question 12

Axons (what is it, function)

Answer 12

Carry signals away from cell body to the end of the axon (axon terminal)

Question 13

Axon terminal

Answer 13

Where neurotransmitters are released for communication with other neurons or effectors

Question 14

Schwann cells

Answer 14

Supporting cells that form the myelin sheath

Question 15

Myelin sheath

Answer 15

Insulating layer on the axon: increases the speed of the saltatory conduction

Question 16

Saltatory conduction

Answer 16

Signal along the axon

Question 17

Sensory neurons (peripheral)

Answer 17

Transmit impulses from body to CNS

Question 18

Motor neurons (peripheral)

Answer 18

Transmit impulses from CNS to body (effectors)

Question 19

Relay neurons (central)

Answer 19

Transmit impulses within CNS

Question 20

Nerve

Answer 20

Bundle of neurons grouped together into a single structure (can be sensory, motor, or mixed)

Question 21

Role of neurons

Answer 21

Pump sodium and potassium ions across their membranes to generate a resting potential

Question 22

Membrane potential

Answer 22

The difference in electrical charge across the plasma membrane

Question 23

Resting potential

Answer 23

The difference in electrical charge across the plasma membrane when s neuron is at rest (not sending an impulse) = -70mV

Question 24

Inside of the cell at rest

Answer 24

More negative
Cations: lots of K+ and few Na+
Anions: proteins, sulfate, phosphate (collectively A-) and few chloride (Cl-)

Question 25

Outside of cell at rest

Answer 25

More positive Cations: lots of Na+ and few K+ Anions: chloride (Cl-)

Question 26

Resting membrane potential steps

Answer 26

1) sodium-potassium pumps in the membrane of the axon maintain the resting potential 2) using active transport (atp) sodium potassium pumps pump 3 Na+ ions out of the axon while pumping 2 K+ ions into the axon

Question 27

Result of resting potential membrane steps

Answer 27

Outside of neuron is more positive compared to the inside | Outside of axon and inside of neuron are polarized (negative resting potential of -70mV)

Question 28

Role of cytoplasm inside axon in resting membrane potential

Answer 28

Contains negatively charged ions that are permanently fixed there (A-) help maintain -70mV

Question 29

Nerve impulse

Answer 29

Action potentials propagated along the axons of neurons

Question 30

Action potential is generated and sent down the axon ONLY WHEN:

Answer 30

A stimulus caused a voltage gated ion (Na+) channel to open in the axon membrane Threshold voltage is reached

Question 31

An action potential is…

Answer 31

ALL OR NOTHING

Question 32

Action potential consists of…

Answer 32

Depolarization and repolarization of the neuron

Question 33

Depolarization

Answer 33

Voltage-gated Na+ channels open when threshold potential of -55mV is reached Na+ rushes into axon (more Na+ outside the cell) Causing more Na+ channels to open Domino effect down the axon Membrane potential becomes more positive

Question 34

Repolarization

Answer 34

K+ channels open (Na+ channels close) K+ rushes out of the axon Domino effect down the axon Membrane potential becomes more negative (hyperpolarized)

Question 35

Resting potential restored

Answer 35

Sodium potassium pumps: 3 Na+ out for every 2 K+ in (Refractory period: reset stage - action potential can’t be fired until this is done; the resting potential and Na+/K+ ion concentration gradients need to be restored

Question 36

In myelinated neurons, actions potentials travel…

Answer 36

Faster down the axon bc ion channels are only positioned between myelinated portions (saltatory conduction) Also require less atp to return to resting potential

Question 37

Synapse

Answer 37

Junction between two neurons (axon to dendrite) Transmitting cell- presynaptic neuron Receiving cell- post synaptic neuron

Question 38

Synaptic cleft

Answer 38

Gap that separated the neurons

Question 39

Neurotransmitters

Answer 39

Chemically Transmit messages across the synaptic cleft | Either excitatory or inhibitory

Question 40

Excitatory neurotransmitter

Answer 40

``` Open ion channels (Na+ into post-synaptic cell) Cause depolarization (action potentials) Ex: acetylcholine ```

Question 41

Inhibitory neurotransmitter

Answer 41

Open ion channels (Cl- into post synaptic cells) Prevent depolarization (action potentials) Hyperpolarize post-synaptic cell Example GABA

Question 42

Acetylcholine (Ach)

Answer 42

Neurotransmitter | Made by combining choline and an acetyl group

Question 43

Ach is usually released by presynaptic neurons at…

Answer 43

Neuromuscular junctions in order to trigger muscle contractions by binding to receptors (cholinergic/nicotinic) in the membrane of postsynaptic muscle fibers to allow Na+ ions to diffuse into postsynaptic muscle fiber cells

Question 44

Acetylcholinesterase (enzyme)

Answer 44

Released by presynaptic cell or found in membrane of postsynaptic cell Continually breaks down Ach into choline and an acetyl group

Question 45

Overstimulation of muscle fibers by Ach can lead to…

Answer 45

Fatal convulsions and paralysis. Break down in necessary

Question 46

Reabsorption

Answer 46

Choline is taken back into the presynaptic cell to be used to make Ach again

Question 47

Pesticides: blocking synaptic transmission at cholinergic synapses is done by…

Answer 47

Irreversibly Binding neonicotinoid pesticides to acetylcholine receptors (in postsynaptic muscle fiber cell membranes)

Question 48

It’s an effective pesticide bc…

Answer 48

Ach receptors in insects are different than in mammals, so the neonicotinoid binds stronger to the receptor

Question 49

When the neonicotinoid binds to Ach receptors…

Answer 49

It blocks normal Ach binding (block synaptic transmission) | AchE cant break down neonicotinoids, so it’s effect is permanent (paralysis/no muscle contraction/death)

Question 50

Environmental considerations of neonicotinoids

Answer 50

Reduces bees and bird populations