524- Nervous System A

Question 1

Explain the process of stimuli through to effector organs

Answer 1

Stimuli are changes detected by sensory receptors inside or outside the body. These receptors make action potentials (electric signals) that gets sent along the sensory neurons to the CNS.
The sensory info is processed in the CNS. More action potentials (for instructions) gets sent through motor neurons this time to an effector (muscle or gland).
When the effector is stimulated, a response is created.

Question 2

What are the 2 cell types found in the nervous tissue?

functions?

Answer 2

> Neurons:
create and transmit electrical and chemical signals
Glial Cells (“neuroglia”):
provide support, nutrition, insulation for neurons and help signal transmission.
(10 glial cells per neuron!)

Question 3

What is a myelin sheath?

Answer 3

those little oval looking cells wrapped around the length of the axon. They’re filled with myelin (fatty substance) that provide insulation.

Question 4

What is an axon?

Answer 4

single long extension that transmits signals

Question 5

What is the difference between structural and functional classifications of neurons?

Answer 5

> Structural- how many processes (projections) extend out from the cell body.

> Functional- if the neuron is transporting nerve impulses toward, within or away from the CNS.

Question 6

What are unipolar, bipolar, and multipolar neurons? (differences?)

Answer 6

> UNIPOLAR:
have 1 process, mostly found in sensory receptors transmitting nerve impulses towards CNS.

> BIPOLAR:
have 2 processes (axon + dendrite), these are uncommon but tend to be sensory neurons.

> MULTIPOLAR:
have 3+ processes (1 axon + 2 or more dendrites), makes up 99% of ALL neurons nd are mostly motor and interneurons.

Question 7

1) What is the neurons role?
2) What are the electric signals called?
3) What is synaptic transmission?

Answer 7

1) to create and transmit electrical & chemical signals that allow communication between body parts!!!
2) action potentials (“nerve impulses”)
3) action potentials are sent through chemical signals and are passed onto other neurons, muscles and glands.

Question 8

Why do we need to keep positive and negative charges apart? (benefit?)

Answer 8

to stop attraction and keep it separate through barriers (like membranes) to build potential!

Question 9

1) What is voltage? (V, mV)

2) What is membrane potential?

Answer 9

1) it is the potential energy made when you separate opposite charges. (Usually V but in the body it is mV due to small amounts)
2) difference in charge (bigger difference=higher potential)

Question 10

What is current?

equation?

Answer 10

the flow of electricity from 1 point to another.

Current= Voltage / Resistance

Question 11

What is Resistance? (example)

Answer 11

whatever is getting in the way of the current.

plastic: high resistance
conductor (metal): low resistance

Question 12

1) What are the charges inside and outside of a resting neuron?
2) What is a resting membrane potential?

Answer 12

1)> negative inside (K+ but more bigger -vely charged proteins)
>positive outside (Na+)

2) V across the neuron’s membrane (-70mV)

Question 13

What is the sodium potassium pump? (what does it do?)

Answer 13

lots of protein along the axon that straddles the membrane of a neuron.

It creates and maintains the resting membrane potential. For every 2 K+ ions it pumps into the cell, 3 Na+ ions is pumped out. This causes a difference in charge (membrane potential) and concentration of Na+ and K+ making the outside of a neuron (ECF) more positive!)

Question 14

What is the electrochemical gradient?

Answer 14

difference in charges =electrical and

difference in conc. of ions (Na+ and K+) =chemical

Question 15

1) What must ions do to maintain the balance of charges?

2) What regulates this?

Answer 15

1) MUST PASS the MEMBRANE

2) ion channels (large proteins) that allow movement of ions across the membrane when their respective gates are open!

Question 16

What are the 3 types of gated channels? (how do they open?)

Answer 16

> Voltage gated:
specific membrane potentials (Na+ channels at -55mV)

> Ligand gated
specific chemical binds to receptors on its surface

> Mechanically gated
physically stretching the membrane

Question 17

1) What are action potentials?

2) What do they do?

Answer 17

1) electrical signals (“nerve impulses”) made and conducted by neurons!)
2) they send information through neurons from 1 part of the body through another and is done through ion movements across the axonal membrane

Question 18

What is a graded potential?

Answer 18

This is when there’s only a few channels open and only a few ions enter the cell, creating a SMALL change in the membrane potential in a LOCALIZED part of the cell.

Question 19

What are the 3 stages that happen during specific voltage changes and ion movements? (briefly describe)

Answer 19

⭐Depolarization:
to reduce difference in charge (V) across the membrane
>-70mV to -55mV to +30mV
⭐Repolarization:
to recreate a difference in charge across the membrane

⭐Hyperpolarization:
to increase the difference in charge across the cell’s membrane

Question 20

What is Depolarisation?

How does an action potential relate to this?

Answer 20

> When a stimulus occurs, it causes a few sodium voltage ion channels to open, allowing Na+ to move into the neuron. This increases the charge inside the neuron and decreases V across the membrane.

> if the stimulus is strong enough to reach and breach the threshold, an action potential is created. Once it begins, it continues all the way to the end of an axon to +30mV.

Question 21

What is repolarisation?

Answer 21

After depolarisation– as we reach +30mV, this causes the voltage gated K+ channels to OPEN, letting the K+ to flow out (electrochemical gradient) to try and rebalance the charges and the Na+ v gated channels close!
(+30mV > -70mV)

> it briefly goes below -70mV

Question 22

What is hyperpolarisation?

Answer 22

This happens because of the voltage gated K+ ion channels being too slow to close, causing extra K+ to leak out of the neuron.

So it briefly goes below -70mV before returning to it.

Question 23

How do we restore the resting membrane potential after depolarisation, repolarisation and hyperpolarisation?

Why do we need to restore it?

Answer 23

> Through the sodium-potassium pump moving (3) Na+ out and (2) K+ in.

> IT MUST BE RESTORED to the original distribution to be able to make more action potentials.

Question 24

1) What is propagation of action potentials?

2) Explain process

Answer 24

1) Actions potentials need to move along the ENTIRE length of a neuron’s axon (axon hillock to axon terminal) so it can relay the info from 1 part of the body to another (synaptic transmission!)

2) in the axon hillock, once the threshold is reached, the Na+ v. gated channels open and Na+ flows in the axon making it depolarize to +30mV. Once it reaches +30mV, that section closes off its Na+ v. gated channels to prevent backflow.
Depolarization acts as a wave and moves towards the axon terminal in sections by making them reach the threshold. Again, this makes the Na+ v. gated channels open and depolarize. Synaptic transmission occurs when the action potential reaches the axon terminal.

Question 25

1) What is refractory period?

2) What are the 2 periods?

Answer 25

This is when the neuron cannot respond to another stimulus due to an axon going through the transmission of action potentials. It must finish the action potential it is on 1st.

2)
⭐Absolute refractory period:
(depolarisation to repolarisation) another action potential cannot start during this

⭐Relative refractory period:
(repolarisation to hyperpolarisation back to resting potential).

only a STRONG stimulus can start another action potential (it’ll be hard because of the lowered threshold)

Question 26

What factors (2) affect neuron transmission speed? Why?

What is saltatory conduction?

Answer 26

> Myelin sheath present
Axons with larger diameters.

Axons with larger diameters and thicker myelin sheaths have higher conduction velocities.
The larger diameter offers less resistance and myelination triggers saltatory conduction. This is when a current leaps from one gap (nodes of ranvier) in the myelin sheath to the next (skips the chain reaction of activating one channel at a time)

Question 27

1) What is a synapse?

2) What are the 2 types? (differences)

Answer 27

1) point where 2 neurons communicate

2) >Electrical synapse:
fast, general info, not common

>Chemical synapse: slow, specific info, more common

Question 28

How does synaptic transmission occur at the chemical synapse?

Answer 28

Action potential arriving at axonal terminal of a presynaptic neuron causes the calcium v. gated channels to open! This allows Ca+ to move into the axonal terminal where it causes the synaptic vesicles (in the terminal) that contain neurotransmitters to move towards the synaptic cleft and release it.
The neurotransmitters can then diffuse across the synaptic cleft and bind with receptors in the post synaptic neuron and either excite (depolarize to reach threshold) or inhibit (hyperpolarize) the postsynaptic neuron which determines if the message is relayed or not.

Question 29

What is a neurotransmitter?

Answer 29

a chemical messenger secreted by a neuron that may excite or inhibit other neurons or effector organs.

Question 30

How are neurotransmitters removed from the synaptic cleft?

Answer 30

They only bond to their receptors for a few milliseconds, after the message is released they are released and can go through these:
>reuptake- recycled. presynaptic neuron reuses it.

> degradation- specific enzymes breaks it down

> diffusion- diffuses away from the synapse

Question 31

What are the differences between the somatic and autonomic reflexes?

Answer 31

⭐Somatic:
skeletal muscle (effector) and 1 neuron between CNS (spine) and effector

⭐Autonomic:
smooth/cardiac muscle or glands and 2 motor neurons between CNS (spine) and effector

Question 32

What are the 5 components of the reflex arc?

Answer 32

> Stimulus: (pain)

> Sensory/Afferent neuron: pain receptor in sensory neuron sends action potentials to CNS.

> Interneuron in CNS: connects sensory neuron to motor neuron and leaves spinal cord (CNS) at the same level sensory neuron entered.

> Motor/efferent neuron: action potential made stimulates effector (skeletal) to contract

> Effector: muscle contracts and moves away from painful stimulus..

->only after the response has occurred is when info reaches the brain and tells you you got hurt.