topic overview Flashcards
How do sensory receptors convert different types of stimuli into nerve impulses? (3)
- Act as transducers,
- Converting various forms of energy (e.g., light, chemical, mechanical),
- Into nerve impulses (electrical impulses)
What happens to a sensory receptor in its resting state? (4)
- There is a difference in charge between the inside and outside of the cell,
- Created by ion pumps and ion channels,
- Resulting in a potential difference across the membrane,
- Known as the resting potential
What is a generator potential, and how is it triggered? (3)
- A change in the potential difference caused by a stimulus,
- It is triggered when a stimulus excites the cell membrane, making it more permeable,
- Allowing ions to move in and out of the cell.
How does the strength of a stimulus affect the generator potential? (3)
- The bigger the stimulus,
- The more ions move, resulting in a larger change in potential difference,
- Producing a bigger generator potential
What happens if the generator potential reaches the threshold? (2)
- If the generator potential is big enough to reach the threshold potential,
- It triggers an action potential (nerve impulse) along a neurone
What happens if the stimulus is too weak? (3)
- If the stimulus is too weak,
- The generator potential won’t reach the threshold,
- No action potential is triggered
What type of stimuli do Pacinian corpuscles detect? (2)
- Mechanoreceptors that detect mechanical stimuli,
- Such as pressure and vibrations
How do Pacinian corpuscles generate a nerve impulse? (4)
- When stimulated, the lamellae in the corpuscle are deformed and press on the sensory nerve ending,
- This deforms stretch-mediated sodium channels in the sensory neurone’s membrane,
- Sodium ions diffuse into the cell, depolarising the membrane and creating a generator potential.,
- If the generator potential reaches the threshold, an action potential is triggered and transmitted to the CNS
What are some other types of sensory receptors? (3)
- Chemoreceptors (e.g., olfactory receptors in the nose),
- Thermoreceptors (e.g., end-bulbs of Krause in mucous membranes of the tongue),
- Photoreceptors (e.g., cone and rod cells in the eye)
What are the key components of all neurones? (4)
- A cell body with a nucleus, cytoplasm, and organelles,
- E.g., large amounts of endoplasmic reticulum and mitochondria for neurotransmitter production,
- Dendrons (short extensions from the cell body) and dendrites (smaller branches) carry nerve impulses towards the cell body,
- Axons carry nerve impulses away from the cell body
What are the characteristics of sensory neurones? (3)
- Short dendrites.,
- One long dendron carries nerve impulses from receptor cells to the cell body,
- One short axon carries nerve impulses from the cell body to the CNS
What are the characteristics of relay neurones? (2)
- Many short dendrites carry nerve impulses from sensory neurones to the cell body,
- Many short axons carry nerve impulses from the cell body to motor neurones
What are the characteristics of motor neurones? (2)
- Many short dendrites carry nerve impulses from the CNS to the cell body,
- One long axon carries nerve impulses from the cell body to effector cells
What is the typical pathway for a nervous response? (5)
- Receptor,
- Sensory Neurone,
- Relay Neurone,
- Motor Neurone,
- Effector Cell
What is the myelin sheath, and what is it made of? (3)
- An electrical insulator,
- Made of Schwann cells,
- Which grow around the axon many times to form layers of the phospholipid bilayer
What are the nodes of Ranvier, and why are they important in myelinated neurones? (4)
- Gaps between Schwann cells,
- Where sodium ion channels are concentrated,
- Depolarisation only occurs at the nodes,
- Allowing the impulse to jump from node to node (saltatory conduction)
What is saltatory conduction, and why is it faster than continuous transmission? (2)
- Saltatory conduction is when the impulse jumps from node to node,
- Which is much faster than continuous transmission along the axon
How do impulses travel in non-myelinated neurones? (3)
- In non-myelinated neurones,
- The impulse is transmitted continuously along the nerve fibre,
- Making it slower than in myelinated neurones
What is the resting potential in a neurone? (3)
- The potential difference across a neurone’s membrane when it is not transmitting an impulse,
- With the outside of the membrane being more positively charged than the inside,
- It is approximately -70mV
What happens when a stimulus triggers an action potential? (5)
- Voltage-gated Na⁺ channels open, and Na⁺ diffuses into the axon, making the inside less negative,
- If the threshold potential is reached (around -55mV), more Na⁺ channels open, causing rapid depolarisation (positive feedback),
- At +40mV, Na⁺ channels close, and voltage-gated K⁺ channels open, allowing K⁺ to diffuse out of the axon, leading to repolarisation,
- Hyperpolarisation occurs as too many K⁺ ions leave the axon, making the membrane more negative than the resting potential,
- The sodium-potassium pump restores the membrane to its resting potential
What is the refractory period? (2)
- A recovery period after an action potential during which the voltage-gated Na⁺ channels cannot open,
- Preventing the membrane from being excited again
How does myelination affect the speed of action potentials? (2)
- Myelination allows for saltatory conduction, where the impulse jumps from node to node,
- This is faster and more energy-efficient than continuous depolarisation along the entire length of the neurone
What is synaptic divergence, and what is its role? (2)
- When one neurone connects to many neurones,
- Allowing information to be dispersed to different parts of the body
What is synaptic convergence, and what is its role? (2)
- When many neurones connect to one neurone,
- Allowing information to be amplified
What is summation, and how does it enable a nervous response? (2)
- Occurs when low-level stimuli add together to release enough neurotransmitter,
- To produce an action potential in the postsynaptic neurone
What is spatial summation at a synapse? (3)
- Occurs when multiple presynaptic neurones release neurotransmitter to one postsynaptic neurone,
- The combined amount of neurotransmitter is enough to reach the threshold,
- To trigger an action potential
