Neuronal Communication

Question 1

Coordination

Answer 1

Co-ordination is the way all the organs and systems of the body are made to work efficiently together.

Question 2

Examples of changes in external environment?

Answer 2

1. Light intensity
2. External temperature
3. Humidity
4. New or sudden sound

Question 3

How do animals respond to changes in environment?

Answer 3

Animals react through electrical responses (neurons) and chemical responses (via hormones)

Question 4

How do plants respond to changes in environment?

Answer 4

Have a number of chemical communication systems including plant hormones.

Question 5

Why is coordination needed?

Answer 5

Cells become specialized to perform specific functions and these functions

Question 6

Why is coordination needed?

Answer 6

Cells become specialized to perform specific functions and organisms need to coordinate the function of different cells and systems to operate effectively.

Question 7

Examples of coordination in animals?

Answer 7

1. Red blood cells transport oxygen effectively but have no nucleus. A constant supply of red blood cells is maintained by haematopoietic stem cells.
2. In order to contract muscle cells need to constantly respire and are dependent of red blood cells for a consistent supply of oxygen.

Question 8

Examples of coordination in plants?

Answer 8

Plants need to coordinate with seasons and pollinators need to coordinate with the plants.
In temperature sensitive climates light sensitive chemicals enable plants to coordinate development of flower buds with the lengthening days that signal the approach of spring and summer.

Question 9

Homeostasis in relation to coordination?

Answer 9

Different functions of the organs need to be coordinated in order to maintain a constant internal environment. For example digestive organs for the maintenance of blood glucose concentration.

Question 10

What is cell signalling?

Answer 10

One cell releases a chemical which has an effect on another cell known as the target cell.

Question 11

How does coordination rely on cell signalling?

Answer 11

Coordination relies on communication at a cellular level through cell signalling

Question 12

How do cells transfer signals locally?

Answer 12

Between neurons at synapses. The signal is used as a neurotransmitter.

Question 13

How do cells transfer signals across large distances?

Answer 13

Using hormones the cells of the pituitary gland secrete ADH which act on cells to maintain water balance of the body.

Question 14

Coordination in plants

Answer 14

Plants survive by responding to internal and external changes to their environment. For example, plant stems grow towards a light source to maximize their rate of photosynthesis which is achieved by plant hormones.

Question 15

What is the nervous system responsible for?

Answer 15

Detecting stimuli in the internal and external environment.

Question 16

Neurons

Answer 16

Specialized nerve cells which transmit electrical impulses rapidly around the body so the organism can respond to the changes in its internal and external environment.

Question 17

Cell Body

Answer 17

Contains a nucleus surrounded by cytoplasm. the cytoplasm contains large amounts of endoplasmic reticulum and mitochondria which are involved in the production of neurotransmitters ( chemicals used to pass on signals from one neuron to the next)

Question 18

Dendrons

Answer 18

Short extensions which come from the cell body. These extensions divide to smaller branches called dendrites

Question 19

Axons

Answer 19

Singular elongated nerve fibers that transmit impulses away from the cell body. The fibers are long and are cylindrical in shape consisting of a narrow region of cytoplasm surrounded by a plasma membrane

Question 20

Sensory neurons

Answer 20

Neurons transmit impulses away from a sensory receptor cell to a relay neuron, motor neuron or the brain. They have one dendron which carries impulses to the cell body and an axon which carries an impulse away from the cell body

Question 21

Relay neurons

Answer 21

Neurons transmit impulses between neurons. For example, between sensory neurons and motor neurons. They have one long axon and many short dendrons

Question 22

Motor Neurons

Answer 22

Neurons transmit impulses from a relay or sensory neuron to its effector (gland or muscle). They have a long axon and many short dendrites

Question 23

Myelin sheath

Answer 23

Made of many layers of a plasma membrane (produced by Schwann cells). The myelin sheath acts as an insulating layer and allows myelinated neurons to conduct electrical impulses at a faster speed

Question 24

Schwann cells

Answer 24

Schwann cells produce these layers of membrane in the myelin sheath by growing around the axon many times. Each time they grow a double layer of phospholipid bilayer is laid down.

Question 25

Node of ranvier

Answer 25

Allows electrical impulses jump from node to node. Which allows impulses to travel faster.

Question 26

Non mylienated axons

Answer 26

Impulses do not jump and transmit continuously along the nerve fibre.

Question 27

Sensory receptors

Answer 27

Specialized cells that detect change in it’s environment . They convert the stimulus into a nerve impulse. Information is passed through the nervous system to the CNS (Brain). The brain then coordinates the required responses and sends an impulse to the effectors (glands and muscles) for a desired response.

Question 28

Two main features that sensory receptors have?

Answer 28

1. Specific to a single type of stimulus

2. Act as a transducer (convert a stimulus into a nerve impulse)

Question 29

Role of a sensory receptor as a transducer?

Answer 29

The receptor converts stimuli into a nerve impulse called the generator potential.

Question 30

Pacinian Corpuscle

Answer 30

Specific sensory receptors that detect mechanical pressure. They are located deep in the skin and are also found in joints.

Question 31

Structure of the pacinian corpuscle?

Answer 31

The end of the sensory neuron is found within the centre of the corpuscle, surrounded by layers of connective tissue. Each layer of tissue is separated by gel.

Question 32

What can be found within the membrane of the neuron

Answer 32

Sodium ion channels

Question 33

What are sodium ion channels responsible for?

Answer 33

Transport sodium ions across the membrane . The neuron ending in the pacinian corpuscle has a stretch mediated sodium channels which change shape (when they stretch their permeability to sodium changes)

Question 34

How does the pacinian corpuscle convert mechanical pressure into a nervous impulse?

Answer 34

1. In resting state the stretch mediated sodium ion channels in the sensory neurons membrane are too narrow to allow sodium ion channels to pass through them. The neuron of the pacinian corpuscle has a resting potential.
2. When pressure is applied the corpuscle changes shape which causes the membrane surrounding the neuron to stretch
3. When the membrane stretches the sodium ions channels widen and sodium ions can now diffuse into the neuron.
4. The influx of positive sodium ions changes the potential of the membrane - so it becomes depolarized. Which results in generator potential
5. Generator potential creates an action potential that passes along the sensory neuron. And the action potential will be transmitted along neurons in the CNS

Question 35

What happens when a sensory neuron detects a change in the environment?

Answer 35

An impulse is sent along the neuron temporarily changing the potential difference across the axon membrane. As a result, the axon membrane switches between two states: resting potential and action potential

Question 36

Resting Potential

Answer 36

When a neuron is not transmitting an impulse the potential difference across its membrane is the resting potential. The outside of the membrane is more positively charged than the inside of the membrane. The membrane is polarised as the potential difference is -70mv

Question 37

How does the resting potential occur?

Answer 37

Occurs via the movement of sodium and potassium ions across the axon membrane. The phospholipid bilayer prevents ions from diffusing across the membrane so they have to diffuse via channel proteins. Most of the channels are gated and must be opened to allow specific ions to pass through them. Other channels are open so ions can diffuse in anytime.

Question 38

Steps for Resting potential.

Answer 38

1. Sodium ions are actively transported out of the axon, whereas potassium ions are actively transported into the axon by an intrinsic protein - sodium-potassium pump. Every 3 sodium ions out 2 potassium ions are pumped in.
2. More sodium ions are on the outside of the membrane than the axon cytoplasm, whereas more potassium ions in the cytoplasm than the outside. Therefore sodium ions diffuse back into the axon via an electrochemical gradient.
3. Some sodium gated channels are closed preventing sodium ions from moving but potassium channels are open so potassium can diffuse out of the axon. There more positively charged ions outside the axon than in the cell. Creating a resting potential of -70mv

Question 39

The process of an Action Potential.

Answer 39

1. The neuron has a resting potential. Some sodium ions are open (not voltage-gated) but sodium voltage-gated ion channels are closed.
2. The energy of the stimulus triggers some sodium voltage-gated ion channels to open, making the membrane more permeable to sodium ions. Sodium ions, therefore, diffuse into the membrane via an electrochemical gradient. So the inside of the membrane is less negative.
3. The change in charge causes more sodium ion channels to open allowing more sodium channels to diffuse into the membrane (positive feedback).
4. When the potential difference reaches +40mv the voltage-gated sodium ion channels close and voltage-gated potassium ion channels open. Sodium can’t enter the axon so the membrane is now permeable to potassium ions
5. Potassium ions diffuse out of the axon down an electrochemical gradient. This reduces charge , so the inside of the axon is more negative than the outside.
6. Hyperpolarisation: