Topic 8 Test

Question 1

role of neurones

Answer 1

nerve cells that coordinate communication with the nervous system

Question 2

Structure of Neurones

Answer 2

• cell body composed of the nucleus as well as organelles such as mitochondria within the cytoplasm. These provide the energy (in the form of ATP) needed for the active transport of ions into & out of the cell in an impulse (see below).
• extensions called dendrites involved in conducting impulses towards the cell body
• axons which conduct impulses away from the cell body.

Question 3

3 types of neurone

Answer 3

Motor neurones are involved in transmitting electrical signals from the central nervous system to muscles and glands in the body.
- Sensory neurones transmit impulses from receptors to the central nervous system whereas
- Relay neurones are located within the central nervous system are involved in transmitting the electrical impulses from sensory neurones to motor neurones.

Question 4

What is myelination

Answer 4

• a layer of fatty substance formed from Schwann cells wrapped around the neurone - can increase the speed of impulses by acting as an electrical insulator, and allowing impulses to travel by saltatory conduction

Question 5

what is the myelin sheath

Answer 5

an electric insulator of axons and dendrons) - produced by Schwann cells.

Question 6

What is saltatory conduction

Answer 6

mechanism by which the speed is increased is where the action potential jumps between gaps in the myelin sheath called nodes of Ranvier.

Question 7

Resting Potential

Answer 7

1. Nerve cells are in a resting state when not transmitting impulses.
2. They are polarized due to an imbalance of sodium (Na+) and potassium (K+) ions.
3. This imbalance creates a negative charge inside the cell compared to the outside.
4. Sodium-ion pumps actively remove Na+ ions from the cell cytoplasm.
5. Potassium ions (K+) diffuse out of the cell through ion channels.
6. An electrostatic force attracts K+ ions back into the cell due to the negative potential.
7. When the forces on K+ ions are balanced, no net movement occurs.
8. The resting potential is established, with a voltage of -70mV across the neurone membrane.

Question 8

Action Potential Process

Answer 8

1. Upon stimulation, the neurone cell membrane becomes depolarized.
2. The stimulus excites the neurone cell, causing sodium ion channels to open.
3. The membrane becomes more permeable to sodium ions (Na+), allowing them to diffuse into the neurone.
4. As Na+ ions enter, the inside of the neurone becomes less negative.
5. The membrane potential continues to become less negative until it reaches the threshold potential of -55mV.
6. Once the threshold is reached, more sodium channels open.
7. This results in a potential difference of +30mV, marking the end of depolarization and the start of repolarization.

Question 9

Repolarisation

Answer 9

1. Sodium channels close and potassium channels open.
2. Potassium ions diffuse out of the neurone.
3. The resting potential is restored, but hyperpolarization occurs due to delayed potassium channel closing.
4. The sodium-potassium pump returns the potential to -70mV.
5. A refractory period follows, preventing further excitation.
6. The action potential travels as sodium ions trigger local currents in adjacent regions.

Question 10

What is a synapse

Answer 10

junctions between two neurones.

Question 11

Process at synapse

Answer 11

1. An action potential arrives, causing the presynaptic membrane to depolarize.
2. Calcium channels open, allowing calcium ions to enter the neurone.
3. Calcium ions trigger the fusion of synaptic vesicles containing neurotransmitters (e.g., acetylcholine) with the presynaptic membrane.
4. Neurotransmitters are released into the synaptic cleft.
5. The neurotransmitter binds to receptors on the postsynaptic membrane, opening cation channels for sodium ions to enter.
6. The postsynaptic membrane depolarizes, potentially triggering a new action potential if the neurotransmitter is excitatory (EPSP).
7. If the neurotransmitter is inhibitory (IPSP), chloride ions enter, making it harder to trigger a new action potential.
8. Digestive enzymes in the synaptic cleft break down the neurotransmitter to prevent overstimulation.
9. The broken neurotransmitter is taken back up by the presynaptic membrane for reuse, ensuring the action potential travels in one direction.

Question 14

What are cells specialised for detection of stimuli called?

Answer 14

Receptors

Receptors are essential for sensing environmental stimuli.

Question 15

What is the function of sense organs like the eye?

Answer 15

They are composed of groups of receptors

Sense organs integrate multiple receptors to detect specific stimuli.

Question 16

What are photoreceptors?

Answer 16

Light receptors in the eye

Photoreceptors are crucial for converting light into neural signals.

Question 17

How does light enter the eye?

Answer 17

Through the pupil

The pupil’s size is adjusted by the iris to control light intake.

Question 18

What controls the amount of light entering the eye?

Answer 18

Muscles of the iris

The iris adjusts the pupil size to regulate light exposure.

Question 19

What is the role of the lens in the eye?

Answer 19

Focus the light on the retina

The lens adjusts its shape to focus images clearly on the retina.

Question 20

Where are photoreceptors located in the eye?

Answer 20

In the retina, specifically the fovea

The fovea is the region of the retina with the highest concentration of photoreceptors.

Question 21

What happens to nerve impulses received by photoreceptor cells?

Answer 21

They are carried via the optic nerve to the brain

This transmission allows the brain to process visual information.

Question 22

What is the blind spot in the eye?

Answer 22

The point where the optic nerve leaves the eye

There are no photoreceptor cells at the blind spot, leading to a lack of vision in that area.

Question 23

What are the two types of photoreceptors in the retina?

Answer 23

• Cones
• Rods

Cones are responsible for color vision, while rods are for monochromatic vision.

Question 24

What is the function of cones in the retina?

Answer 24

Involved in colour vision

Cones function best in bright light conditions and enable color perception.

Question 25

What is the function of rods in the retina?

Answer 25

Can only produce monochromatic vision ## Footnote Rods are more sensitive to light and are crucial for night vision.

Question 26

What do rod cells contain

Answer 26

Rods contain a light-sensitive pigment called rhodopsin which absorbs light energy and subsequently splits into cis- retinal and opsin.

Question 27

In the dark….

Answer 27

1. In the dark, sodium ion channels in rod cells remain open. 2. Sodium ions diffuse into the cell while being actively pumped out. 3. This results in the inside of the cell being slightly less negative, causing slight depolarization. 4. The slight depolarization leads to the release of the neurotransmitter glutamate. 5. Glutamate inhibits the neurones connected to the rod cells, creating an inhibitory postsynaptic potential (IPSP). 6. no information is transmitted to the brain.

Question 28

In the light….

Answer 28

1. When light is present, rhodopsin in the rod cells splits into cis-retinal and opsin. 2. Opsin binds to the cell membrane, causing sodium ion channels to close. 3. Although the sodium ions are still actively removed from the cell, the closure of the channels prevents sodium from entering. 4. This leads to hyperpolarization of the membrane, meaning that no neurotransmitter is released into the synaptic cleft. 5. As a result, an action potential can form, which is then transmitted to the brain via the optic nerve.

Question 29

What is tropsim

Answer 29

Plants respond to external stimuli to increase their chance of survival. - growth responses to a direction stimulus.

Question 30

Phototropism

Answer 30

phototropism where the direction of growth is determined by the direction of light. The shoots of the plant are positively phototropic and grow towards the lights whereas roots are negatively phototropic and grow away from the light. This allows them to maximise the light, for photosynthesis, captured by green parts of the plant whilst moving the roots away from the surface in search of minerals & water.

Question 31

Plant Growth - IAA

Answer 31

1. IAA is a hormone produced at the tips of plant shoots. 2. It helps control how plants grow towards light (tropism). 3. IAA makes cells elongate by loosening their walls. 4. Protons from inside the cell help to stretch the cell walls. 5. If light shines on all sides, IAA spreads evenly, and cells grow equally. 6. If light shines from one side, IAA moves to the shaded side, causing that side to grow longer. 7. This bending makes the plant grow towards the light.

Question 32

Brain Structure

Answer 32

Question 33

MRI

Answer 33

MRI (Magnetic Resonance Imaging) uses a magnetic field and radio waves to create detailed images of soft tissues, like the brain, aiding in the diagnosis of diseases and tumors.

Question 34

fMRI

Answer 34

fMRI (functional MRI) is a modified MRI that visualizes brain activity in real-time by monitoring oxygen uptake during tasks, useful for diagnosing conditions linked to abnormal brain function.

Question 35

CT Scan

Answer 35

CT (Computed Tomography) employs X-rays to generate cross-sectional images of the brain, allowing for the examination of brain structure and the identification of damage or abnormalities.

Question 36

PET scan

Answer 36

PET (Positron Emission Tomography) utilizes radioactive isotopes to track blood flow and brain activity, providing insights into brain function during various activities as the isotopes decay.

Question 37

Pros/Cons Animal Testing

Answer 37

Pros: - Similarity to humans leads to important discoveries (e.g., antibiotics). - Can be used if treated well and suffering is minimized. - Reduces ethical issues in drug trials. Cons: - Violates animal rights and prevents natural behaviors. - Some believe animals should never be used. - Others weigh benefits against the harm done to animals.

Question 38

Define Habituation

Answer 38

Habituation is a phenomenon where an organism becomes insensitive to repeated stimuli over time which does not threaten their survival or does not benefit them in any way.

Question 39

Process of Habituation

Answer 39

Habituation occurs when calcium channels in the presynaptic membrane become less responsive, resulting in reduced calcium ion influx and decreased neurotransmitter release, which prevents action potentials in the postsynaptic membrane.

Question 40

Studies to investigate brain function

Answer 40

- twin studies - longitudinal studies - cross cultural studies - experiments