Biology - Topic 8 Grey Matter

What are neurones?

Nerve cells that transmit electrical signals within the nervous system.

What are the three types of neurones and their functions?

• Sensory neurones → Carry impulses from receptors to CNS.

• Relay neurones → Transmit impulses within the CNS.

• Motor neurones → Carry impulses from CNS to muscles/glands.

What is myelination and its function?

• The myelin sheath insulates axons, increasing impulse speed via saltatory conduction.

What is resting potential?

• The neurone is polarised at -70mV due to an imbalance of sodium (Na⁺) and potassium (K⁺) ions.

What happens during an action potential?

• Depolarisation → Sodium channels open, Na⁺ enters, making inside positive.

• Repolarisation → Potassium channels open, K⁺ leaves, restoring negativity.

• Hyperpolarisation → Excess K⁺ leaves, making it too negative temporarily.

• Resting potential restored by the Na⁺/K⁺ pump.

How does saltatory conduction work?

• Impulses jump between Nodes of Ranvier, speeding up transmission.

What happens at a synapse?

• Action potential arrives, depolarising the presynaptic membrane.

• Calcium ions (Ca²⁺) enter, causing vesicles to release neurotransmitters.

• Neurotransmitters bind to receptors on postsynaptic membrane.

• Sodium channels open, triggering an action potential in the next neurone.

• Neurotransmitters are broken down by enzymes or reabsorbed.

What is the difference between excitatory and inhibitory synapses?

• Excitatory synapses → Increase likelihood of action potential (e.g., acetylcholine).

• Inhibitory synapses → Decrease likelihood of action potential (e.g., GABA).

What are the two types of photoreceptors?

Feature	Rods	Cones

Colour

Black & white

Colour

Sensitivity

High (work in dim light)

Low (need bright light)

Location

Peripheral retina

Fovea (center of retina)

Visual Acuity

Low (many rods per neurone)

High (one cone per neurone)

What is rhodopsin?

The light-sensitive pigment in rods that absorbs light and breaks down into cis-retinal and opsin, triggering an impulse.

What is the blind spot?

The point where the optic nerve leaves the eye, containing no photoreceptors.

How is plant growth affected by changes in day length?

Plants are also affected by changes in day length . This kind of sensitivity is known as photoperiodism where the plants flower and germinate in response to day length. This response is coordinated by a photoreceptor called phytochrome. The phytochrome exists in two states, P R which is the inactive form and P FR which is the active form. Pfr (phytochrome far red) is converted to Pr (phytochrome red) in the dark/low light levels and if exposed to light of far-red light wavelengths, whilst the reverse will occur in daylight or if Pr is exposed to red light

Plant growth is also controlled by…

Plant growth is also controlled by indoleacetic acid (IAA) which is an important auxin produced in the ps and shoots of flowering plants . The distribution of IAA around the plant controls tropism. IAA causes cell elongation - as opposed to physical growth - brought about by the ‘loosening’ of cell walls, which go on to take in water by osmosis & stretch (elongate). Protons pumped into the cell wall from the cell cytoplasm disrupt the bonds between cellulose molecules, allowing the cell wall to be stretched.

When the shoot is illuminated from all sides…

the auxins are distributed evenly and move down the shoot tip thus causing elongation of cells right across the zone of elongation . Whereas if the shoot is only illuminated from one side, the auxins move towards the shaded part of the shoot thus causing elongation of the shaded side only which results in bending of the shoot towards the light.

What are the main parts of the brain and their functions?

Brain Part	Function
Cerebrum	Higher thinking, memory, voluntary movement.
Cerebellum	Balance & coordination.
Medulla oblongata	Controls heart rate, breathing, blood pressure.
Hypothalamus	Regulates temperature & hormones.

How is the brain studied?

• MRI scans → Show brain structure using magnetic fields.

• fMRI scans → Show brain activity while performing tasks.

• PET scans → Detect blood flow using radioactive isotopes.

What is a critical window?

A specific time period where the nervous system must receive a stimulus to develop properly.

What was Hubel and Wiesel’s experiment?

Found that visual cortex neurons need light exposure during early development or vision is permanently affected.

How do cataracts support critical windows?

Babies born with cataracts must have surgery early, or they may never develop normal vision.

What is habituation?

When an organism stops responding to repeated stimuli that are not harmful.

What happens at the synapse during habituation?

Less calcium enters, reducing neurotransmitter release, meaning fewer action potentials occur.

How is learning linked to synapses?

• Strengthened synapses = More efficient learning (e.g., long-term potentiation).

What are the ethical concerns of using animals in research?

✅ For → Similarity to humans, helps develop medicine.
❌ Against → Animal rights, unnatural conditions.

What is utilitarianism in research ethics?

• Harm is justified if benefits outweigh suffering (e.g., using animals for drug testing).

What is the nature vs. nurture debate?

• Nature → Genetics determine behaviour.

• Nurture → Environment shapes behaviour.

What studies support nature?

Twin studies show identical twins share more traits than fraternal twins.

What studies support nurture?

Cross-cultural studies show upbringing affects intelligence and behaviour.