13 - Neuronal communications

Question 1

Define stimulus and response

Answer 1

Environmental change is stimulus

the way organism changes its behaviour or physiology is the response

Question 2

Why are communication systems needed to maintain the constant internal environment in a changing external environment?

Answer 2

As the external environment changes, it places stress on living organisms. For example, a cooler environment will increase heat loss.

In order to survive these changes must be monitored and the organism must change its behaviour and physiological process to reduce the stress.

This occurs through the hormonal system. More immediate changes in the external environment require quicker response, and thus a quicker communication of the stimulus through the neuronal system.

Question 3

how do communication systems allow organisms to coordinate their activities in order to respond to a changing internal environment?

Answer 3

The metabolic processes of cells alter the internal environment, reducing the concentration of substrates, and increasing the concentration of products, which may be toxic.

In order for the metabolic processes to be maintained, these changes must be offset, requiring detection of the changing conditions and communication between cells to offset the changing internal environment.

For example, if carbon dioxide levels increase in the blood, it lowers the pH of the tissue fluid, which can disrupt the action of enzymes. Communication between chemoreceptors in the blood, the brain, and the gaseous exchange system are required to offset this change.

Question 4

Why is coordination needed in the body?

Answer 4

• organisms need to coordinate the function of different cells and systems to operate effectively
• e.g. red blood cells transport oxygen effectively, however they have no nucleus, therefore cant replicate. So the circulatory system relies on haematopoietic stem cells to maintain RBCs

Question 5

What is homeostasis?

Answer 5

-s the maintenance of a constant internal environment despite changes in external and internal factors

Organisms continuously monitor and respond to any deviation from the set point.​

—CO2 concentration, body temperature, blood glucose, salt, and water potential, as well as pressure must be maintained within a small range of variables.

Question 6

What is negative feedback?

Answer 6

a deviation from the optimum is detected and a mechanism reverses the change

Question 7

What is cell signalling and give the types?

Answer 7

is the process by which cells communicate with each other to coordinate various functions, the release of a chemical from one cell that has an effect on another

-> transfer signals locally- such as between neurone, using neurotransmitters
-> transfer signals over large distances using hormones

Question 8

What is positive feedback?

Answer 8

occurs where a deviation increases the original deviation, so is a mechanism whereby a change is increased.

For example, during pregnancy the dilation of the cervix causes the posterior pituitary gland to release oxytocin which increase uterine contractions which stretch the cervix more, causing more oxytocin to be secreted, increasing the dilation of the cervix.

Question 9

The need for a constant internal environment

Answer 9

1. Cellular activities depend on the action of enzymes which need a:​

-specific temperature and pH​
-specific concentration (water potential) aqueous environment​
-absence of toxins / inhibitors​

2. The internal environment includes the cell cytoplasm and tissue fluid. Cellular activity can alter this environment​
   -Uses up substrates​
   -Production of waste acts as a stimulus to cause the removal of these wastes
3. Changes in the external environment are called stimuli and the way in which the organism changes its behaviour or physiology is its response to the stress.

Question 10

Using examples, explain why coordination is required in a multicellular organism.​

Answer 10

Organism needs to respond to internal/external changes for survival (1); ​

different organs work together to ensure homeostasis (1); e.g., muscles/skin/blood/hypothalamus in temperature control (1);​

liver and pancreas in blood sugar regulation (1); ​

occurs by different types of cell signalling (1) (with e.g.) (1);​

named example of hormone or chemical (1)​

Question 11

Outline the ways in which the structures of a sensory neurone and a motor neurone are similar

Answer 11

both have

dendrite(s);

an axon;

a cell body with a, nucleus / named organelle;

myelin sheath / myelinated / (covered with) Schwann cell / nodes of Ranvier;

voltage-gated channels / sodium-potassium (ion) pump;

Question 12

Multiple sclerosis (MS) is an autoimmune disease that damages the nervous system.

Suggest how the immune system causes damage to the nervous system.

Answer 12

1. antigens on , neurones / nerve cell / Schwann cells / myelin sheath (activate immune system) ✓
2. antibodies against , neurones / nerve cells / Schwann cells / myelin sheath ( are produced)✓
3. phagocytes / neutrophils / macrophages / T(killer) cells, attack / break down, neurones / nerve cells / Schwann cells / myelin sheath ✓

Question 13

The cell body of neurones

Answer 13

contains the nucleus, surrounded by cytoplasm containing large amounts of endoplasmic reticulum and mitochondria to produce neurotransmitters used at the synapses of all three neurones

Question 14

The Dendrons of neurones

Answer 14

are short extensions which carry action potentials toward the cell body where dendrites of relay neurons synapse with sensory receptors, or relay neurons synapse with motor neurones.

Question 15

The Axons of neurone

Answer 15

singular, elongated nerve fibres that carry action potential potentially long distances away from the cell body.

Question 16

Sensory neurons

Answer 16

carry the action potential from a sensory receptor to the relay neurone, motor neurone or the brain. Sensory neurones have one long dendron carrying the impulse to the body and an axon carrying the impulse away from the cell body

Question 17

Relay neurons

Answer 17

transmit impulses between neurones e.g. sensory and motor neurons. They have many short dendrites to receive impulse transmissions from a number of sensory receptors and a short axon with variable numbers of synaptic endings to carry the action potential to the cell bodies of motor neurones in the CNS.

Question 18

Motor neurons

Answer 18

carry an action potential from the sensory or relay neurone to an effector such as cells in a muscle or gland. they have one long axon and many short dendrites

Question 19

Sensory receptors
- functions and features

Answer 19

Detect changes in the surroundings (stimulus)​

Each receptor is specific to a single type of stimulus​

Act as transducers - Convert energy from a stimulus into electrical energy (nerve impulse)

Question 20

transducers

Answer 20

Convert energy from a stimulus into electrical energy (nerve impulse)

Question 21

Describe the role of a sensory receptor in the body

Answer 21

Detect stimuli (1); convert energy into a nervous impulse (1) ​

Question 22

State the transformation that takes place in a cone cell (1 mark)

Answer 22

Wavelength of light is converted into a nervous impulse/action potential (1) ​

Question 23

Explain how your body detects that your finger has touched a pin (use the Pacinian corpuscle in your answer) (6 marks)

Answer 23

When you touch the pin it exerts mechanical pressure on your skin (1); ​

Pacinian corpuscle found within skin detects pressure (1); ​

pressure changes shape of Pacinian corpuscle (1); ​

stretch-mediated sodium channel in neuronal membrane stretches (1); ​

channel widens (1); ​

sodium ions diffuse into membrane (1); ​

membrane is depolarised/generator potential created (1); ​

generator potential creates an action potential (1); ​

action potential transmitted along neurones to CNS/brain (1). ​

Question 24

at resting potential, what channeles are open and closed, how do the ioons move?

Answer 24

Sodium-Potassium pumps in the plasma membrane actively transport Na+ ions out of the axon, and K+ ions into the axon.​

Open potassium channels allow the K+ ions to move back out (down concentration gradient).​

losed sodium channels prevent Na+ ions from re-entering the axon.​

Question 25

Resting potential is produced via the following mechanism:​

Answer 25

Sodium-Potassium pumps in the plasma membrane actively transport Na+ ions out of the axon, and K+ ions into the axon.​

For every 3 Na+ ions pumped out, 2 K+ ions are pumped in.​

Open potassium channels allow the K+ ions to move back out (down concentration gradient).​

Closed sodium channels prevent Na+ ions from re-entering the axon.​

As a result, there is a higher concentration of cations outside the axon than inside.

Question 26

Voltage gated ion channel?

Answer 26

change in potential difference across the membrane causes there to be a change in shape of the ion channel resulting in it either opening or closing.​

Question 27

the neurone have integral proteins:

Answer 27

• sodium/potassium pumps (Na+/K+ pump or Na+/K+ATPase)​ (active= requires ATP)​

Voltage-gated sodium (Na+/K+) channels (passive)​

Voltage-gated potassium (K+) channels (passive)​

Non-voltage-gated potassium channels (passive)

Question 28

Phases of an action potential?

Answer 28

Depolarisation – potential difference across axon membrane increases rapidly from –70mv to +40mv​

Repolarisation – potential difference across the axon membrane decreases from positive back to negative​

Hyperpolarisation – potential difference across membrane ‘undershoots’​

Restoration of resting potential – potential difference across membrane returns to -70mv

Question 29

Action potentialphase 1 -depolarisation

Answer 29

Stimulus detected by sensory receptor​

Energy of the stimulus triggers some voltage-gated Na+ channels to open​

Na+ ions enter; inside of the axon becomes LESS NEGATIVE​

More voltage-gated Na+ channels open – positive feedback​

More Na+ ions enter; inside of axon becomes MORE POSITIVE​

Inside of the axon rises to approx. +40 mV​

Question 30

Action potential phase 2 - repolarisation

Answer 30

Voltage across the membrane reaches +40 mV​

Voltage-gated Na+ channels CLOSE and voltage-gated K+ channels OPEN​

Na+ ions no longer enter, K+ ions can DIFFUSE OUT down their electrochemical gradient​

Membrane potential becomes negative​

​

Question 31

Action potential phase 3 - hyperpolarisation

Answer 31

Voltage-gated K+ channels stay open​

K+ ions continue to diffuse out of the axon​

Membrane potential becomes MORE negative than resting potential​

Membrane becomes HYPERPOLARISED ​

​

Question 32

Restoration of resting potential

Answer 32

Voltage-gated K+ channels close​

Na+/K+ pump returns the K+ ions inside and Na+ ions outside​

Membrane is repolarised​

Resting membrane potential of -70 mV restored ​

Question 33

refactory period?

Answer 33

hyperpolarisation and subsequent restoration of the resting potential constitute the refractory period​

Question 34

Propagation of action potentials in unmyelinated neurones

Answer 34

Circuits of action potentials form ‘waves of depolarisation’ in which sodium ions form localised electrical circuits​

Once sodium ions are inside the axon, they are attracted by the negative charge ahead, so they diffuse forwards along inside the axon, triggering depolarisation of the next section

Question 35

Significance of the refractory period:​

Answer 35

This is a period of approximately 1ms of hyperpolarisation and the subsequent recovery period that occurs after de/repolarisation. ​

Voltage-gated Na+ ion channels remain CLOSED and cannot immediately be excited again.​

During the refractory period no further action potentials can be generated​

This ensures action potentials are:​

DISCRETE​

DO NOT OVERLAP​

UNIDIRECTIONAL

Question 36

All or nothing principle​

Answer 36

Initial stimulus lower than threshold – no AP generated – results in failed initiations​

​

Initial stimulus meets or exceeds threshold – AP generated​

​

Initial stimulus strongly exceeds threshold – still generates same size AP… although it does increase the frequency of the action potentials

Question 37

What does myelination do?​

Answer 37

Forces longer localised circuits between adjacent nodes meaning the action potentials ‘jump’ from node to node​

… Saltatory conduction

Question 38

the process that happens during repolarisation of a neurone during the action potential?

Answer 38

Sodium channels - closed

Potassium channels - open

Membrane potential - decreasing

Question 39

Describe how an action potential is produced and transmitted along the sensory neurone if your hand is pinched. (9marks)​

Answer 39

Pressure receptors cells in your skin would detect the external stimuli (1)​

In response to this the Na+ channels in that area would open up (1), allowing Na+ ions to flood into the cell and thus reducing the resting potential of the cells and result in depolarisation. (1)​

If depolarisation reaches the threshold level, then an action potential has been generated and an impulse will be fired. (1)​

Once an impulse is made, a local current is set up between the area where there is an action potential and the resting area next to it. (1)​

​
Na+ flow down the concentration gradient and depolarise the next adjacent area (1)​

​
Repolarisation occurs behind the action potential (1)as K+ ions flow out resulting in a refractory period (1)​

Impulse is unidirectional. (1)

Question 40

stuctural organisation of the nervous system?

Answer 40

Central nervous system- Brain and spinal cord​

Peripheral nervous system - All other neurones (motor & sensory)​

Question 41

functional organisation of the nervous system

Answer 41

• autonomic
• somatic

Question 42

Somatic Nervous System​

Answer 42

“voluntary” Transmission of sensory information, movement of skeletal muscles, somatic reflex arcs, usually can be controlled consciously

conscious and mostly voluntary (except reflexes)

Question 43

Autonomic Nervous System​

Answer 43

involuntary movement of smooth/cardiac muscle, or control of glands

Question 44

what is the autonomic nervous system divided into?

Answer 44

The sympathetic nervous system ​
The parasympathetic nervous system​

Question 45

The parasympathetic nervous system​
neurotransmitter?

Answer 45

Rest and digest​
- acetylcholine
- increased gastric juices, saliva production, bronchial muscles contracted

Question 46

The sympathetic n​ervous system ​

Answer 46

Fight or flight​
- noradrenaline
- peristalsis reduced, decreased urine, bronchia muscles relaxed

Question 47

explain two types of neurones in the sympathetic nervous system, what neurotransmitter do they use, who is there effectors?

Answer 47

• neurones from CNS to effector organs
  -> lightly myelinated preganglionic axon, that meets a ganglion, leading to an unmyelinated postganglionic axon
  ->lightly myelinated preganglioniic axon that meets the adrenal medulla, where noradrenaline is released into the blood vessels
• noradrenaline
• smooth muscles (gut, glands and cardiac muscle)

Question 48

explain the type of neurones in the parasympathetic nervous system, what neurotransmitter do they use, who is there effectors?

Answer 48

neurones from CNS to effector organs
lightly myelinated preganglionic axon that meets a ganglion, reaching an unmyelinated postgaglionic axon
- uses accytlecholine
- smooth muscle

Question 49

explain the type of neurones in the somatic nervous system, what neurotransmitter do they use, who is there effectors?

Answer 49

• single neurone from CNS to effector
• heavily myelinated axon
• uses acetylcholine
• skeleta muscle
• stimulatory

Question 50

explain the spinal cord?

Answer 50

• Is a long, thin, tubular bundle of nervous tissue that extends from the brain

Protected by the vertebral column

The spinal cord function is the transmission of neural signals between the brain and the rest of the body but it also contains neural circuits that can independently control numerous reflexes. ​

Neurones emerge in pairs from the spinal cord at specific intervals​

Question 51

What are reflexes?​

Answer 51

These are rapid, predictable, automatic responses to a stimulus​

Unlearned, involuntary, not premeditated

Reflex actions happen without involving the brain. This is because the central nervous system sends electrical signals to the muscles before the brain can pick up the message.​

Two types:​

Somatic – effector is skeletal muscle​

Autonomic – effector is smooth muscle, cardiac muscle or glands​