Unit 9- Nerve Transmissions

Question 1

Wha 2 control systems do humans have?

Answer 1

Nervous system
Endocrine system (hormonal system)

Question 2

What 3 basic steps make up the nervous system?

Answer 2

• detecting a stimuli
• coordinating a response
• effecting a response

Question 3

What is a stimuli? Give an example involving the eye

Answer 3

Changes in the internal or external environment

Light waves which stimulate the pupils to dilate or contract

Question 4

What is the role of the coordinator?

Answer 4

The network of interneurones connecting the sensory and motor systems, in humans this is the CNS
- receive impulses from sensory neurones and transmit impulses to motor neurones

Question 5

What is the effector? And what 2 kinds are there?

Answer 5

The cells that effect a response

• muscles
• hormone secreting glands

Question 6

What are exocrine and endocrine glands? And examples of them in action

Answer 6

Endocrine- secrete hormones into the blood stream eg insulin

Exocrine- secrete hormones the the outside of the body eg sweat, milk

Question 7

What is a nerve?

Answer 7

A bundle of several thousand neurone axons and dendrons

Question 8

Structure of a neurone:

Answer 8

• cell body
• dendrites(fingers) and dendrons (arm) carry impulses towards the cell body
• axon carries nerve impulse away from the cell body
• axon and dendrons are also coated in a myelin sheath formed from Schwann cells

Question 9

Purpose of dendrites?

Answer 9

• to provide a large surface area for connecting with other neurones
• carry impulses towards the cell body

Question 10

How is the myelin sheath formed and what is its purpose?

Answer 10

• Schwann cells are wrapped around the axon many times forming a thick lipid layer (myelin sheath)
• provides physical protection and electrical insulation

Question 11

What are gaps in the myelin sheath surrounding the axon called?

Answer 11

Nodes of ranvier

Question 12

What types of neurones do we have?

Answer 12

• sensory
• effector
• interneurones

Question 13

What are the differences between the 3 kinds of neurones

Answer 13

Sensory- long dendrons(sensory receptors -> CNS)
Effector- long axon (CNS->muscle/gland)
Interneurone- smaller, many inter connections, make up the CNS 99.9% of neurones

Question 14

What does the Na+K+ATPase protein pump do?

Answer 14

• simultaneously pumps 3 sodium ions out of the cell

- while pumping 2 potassium ions into the cell

Question 15

What do the ion channels do? Refer to leaking

Answer 15

• sodium channels let the Na+ ions diffuse into the cell
• potassium channels let the K+ ions diffuse out of the cell
• they are normally closed but still leak so ions continue to diffuse

Question 16

Are there more sodium or potassium channels in the membrane?

Answer 16

• more potassium ion channels, so potassium diffuses out the cell much faster to increase the rate of depolarisation

Question 17

What is the membrane potential?

Answer 17

A stable imbalance of Na+ ions and K+ ions across the cell membrane

Question 18

What charge is the membrane potential held at?

Answer 18

Normally -70mV but can range in different cells, however its always negative

Question 19

What is an action potential:

Answer 19

A change in the potential difference at a point on the membrane of a nerve cell

Question 20

What 2 phases make up the action potential?

Answer 20

• depolarisation

- repolarisation

Question 21

What occurs in depolarisation?

Answer 21

-The sodium channels open, sodium ions diffuse quickly into the cell down the conc. gradient
-Inside of the cell gets more positive
- Na+ gates then close
(Charge in cell is reversed, negative -> positive)

Question 22

What happens in repolarisation?

Answer 22

• potassium channels open, potassium ions diffuse quickly out the cell down the conc. gradient
• charge inside cells gets more negative
• K+ gates close again
  (Repolarisation is return to -70mV)

Question 23

What happens in the recovery period?

Answer 23

• K+ ions are attracted back into the cell by negative charge when membrane is hyperpolarised
• resting potential is restored

Question 24

How is an action potential started?

Answer 24

• special receptor cells containing sodium gate receptor proteins that open to a specific stimulus
• stimulus causes the sodium gate to open
• sodium ions diffuse into the cell causing depolarisation
• this affects voltage gated sodium channels nearby starting the action potential

Question 25

Give an example of a specialised sodium gate receptor protein:

Answer 25

Chemical gated sodium channels in the tongue

Mechanically gated sodium channels in the hair cells of ears that are opened by vibrations

Question 26

How is a nerve impulse propagated?

Answer 26

• sodium ions entering during an action potential flow along the inside of the nerve fibre
• the addition of sodium ions makes the charge less negative reducing the potential difference to the threshold
• this opens nearby voltage-dependant sodium gates

Question 27

What features do ion channels have that help the nerve impulse work effectively?

Answer 27

• Na+ ions will flow both ways along the membrane but the refractory period prevents the impulse from returning upstream as the channels cannot open again
• the ion channels are either open or closed, so action potential always reaches 40mV along the axon and this never reduces

Question 28

How do nerve impulses convey strength?

Answer 28

• strength of an stimulus is indicated by frequency of the nerve impulse
  A strong stimulus will cause a high frequency impulse along a sensory neurone

Question 29

What 3 factors affect speed of conduction in nerves?

Answer 29

1- Temperature
2- Axon diameter
3- myelin sheath

Question 30

Why do squids have such thick axons?

Answer 30

• live in freezing cold conditions

- thicker axons result in faster nerve conduction

Question 31

Why do warm blooded animals tend to have faster responses to a stimulus?

Answer 31

• warmer blood, so higher body temperature and faster nerve conduction

Question 32

How dos the myelin sheath speed up nerve conduction?

Answer 32

• voltage gated ion channels are only found at nodes of ranvier
• myelin sheath electrically insulates the axon
• action potential can jump from node to node (saltatory conduction)