neuronal communication Flashcards
(42 cards)
What is coordination in multicellular organisms and why is it necessary?
Coordination is the process by which different organs and systems communicate to work together effectively. It is necessary because cells and tissues in multicellular organisms are specialised and may rely on other cells for substances or functions, requiring a communication system to integrate activities.
What are the two main systems involved in coordination?
The nervous system – Uses electrical impulses for rapid, short-term communication.
The hormonal system – Uses hormones transported in the blood for slower, longer-lasting responses.
What is a neurone and what are its basic structural features?
A neurone is a specialized cell that transmits electrical impulses. Key features include:
Dendrites to receive impulses from other neurones or receptors
A dendron, which carries impulses toward the cell body and branches into dendrites
A cell body containing the nucleus
An axon to transmit impulses away from the cell body
Gated ion channels in the axon membrane, which open or close to allow specific ions (e.g., Na⁺ or K⁺) to pass through, enabling electrical impulse generation and propagation
Myelin sheath for insulation
Nodes of Ranvier to speed up transmission through saltatory conduction. The myelin sheath is an electrical insulator, so the impulse jumps from one node of Ranvier to the next as it charges (known as saltatory conduction)
What is the function of the myelin sheath and how does it work?
The myelin sheath is an insulating layer around the axon made of Schwann cells. The plasma membrane of the schwann cells grow around the axon forming a thick layer. It speeds up nerve impulse transmission by allowing saltatory conduction—impulses jump from one node of Ranvier to the next.
What are the three types of neurones and their roles?
Sensory neurones – Carry impulses from receptors to the CNS.
Relay neurones – Connect sensory and motor neurones within the CNS.
Motor neurones – Carry impulses from the CNS to effectors (muscles or glands).
How does cell signalling occur in coordination?
Cell signalling involves one cell releasing a chemical that causes a response in another cell. It can occur:
Between adjacent cells (e.g., synaptic transmission)
Between distant cells (e.g., hormones in the blood)
What is the structure and function of a sensory neurone?
Sensory neurones have a long dendron and a short axon. They transmit impulses from sensory receptors to the CNS. The cell body is located midway along the neurone, just outside the CNS.
What is the role of a sensory receptor?
A sensory receptor detects a change in the environment (stimulus) and converts the energy from the stimulus into a nerve impulse (generator potential). This process is called transduction.
What are the features of sensory receptors?
They are specific to a single type of stimulus.
They act as transducers: they convert the stimulus energy into a nerve impulse (generator potential).
What are the four types of sensory receptors and what do they detect?
There are four types of sensory receptors, each detecting a specific type of stimulus and converting one form of energy into an electrical nerve impulse:
Mechanoreceptors – detect pressure and movement. Example: Pacinian corpuscle in the skin. They convert mechanical energy into an electrical impulse.
Chemoreceptors – detect chemicals. Example: Olfactory receptors in the nose. They convert chemical energy into an electrical impulse.
Thermoreceptors – detect heat. Example: End-bulbs of Krause in the skin. They convert heat energy into an electrical impulse.
Photoreceptors – detect light. Example: Cone cells in the retina of the eye. They convert light energy into an electrical impulse.
Describe the role of a Pacinian corpuscle.
Back:
Located deep in the skin (especially fingers and soles of feet).
Detects mechanical pressure.
Only responds to pressure changes, not constant pressure.
Functions as a mechanoreceptor converting mechanical energy into a nervous impulse (electrical energy).
How does a Pacinian corpuscle work as a transducer?
Back:
In a resting state, stretch-mediated sodium ion channels in the sensory neurone membrane are too narrow for Na⁺ to pass through; membrane has a resting potential.
When pressure is applied, the membrane stretched and the sodium channels to widen.
Sodium ions diffuse into the neurone, creating a potential difference across the neurone so it is depolarised which creates a generator potential.
the generator potential creates an action potential that passes along the sensory neurone
the action potential will then be transmitted along the neurones to the CNS
What is the resting potential and how is it maintained?
Back:
Resting potential = the difference in charge across the neurone membrane when not stimulated; inside is about –70 mV relative to the outside.
Maintained by:
- Sodium-potassium pump actively transports:
3 Na⁺ ions out of the neurone
2 K⁺ ions into the neurone
This creates a higher concentration of Na⁺ outside and K⁺ inside.
The potassium gated ion channels in the membrane remain open to K⁺ but the sodium gated ion channeles remain closed to Na⁺, so some K⁺ diffuses out of the neurone down its concentration gradient.
As more positive ions leave than enter, the inside becomes negatively charged compared to the outside.
This maintains a negative resting potential across the membrane.
Why does a Pacinian corpuscle only respond to changes in pressure?
Because when pressure is constant, the stretch-mediated sodium channels remain closed, and no further generator potential is created.
Explain how the nervous system transmits information from sensory receptors to the CNS.
Sensory receptor detects stimulus → creates generator potential.
If threshold is reached → action potential is triggered.
Action potential passes along sensory neurone to CNS for processing
How is an action potential initiated and what is depolarisation?
When a stimulus is detected, it triggers voltage-gated Na⁺ channels to open.
Na⁺ ions rush in due to the electrochemical gradient, making the inside less negative.
More Na⁺ channels open via positive feedback, causing further depolarisation.
The membrane potential reaches around +40 mV.
What happens during repolarisation?
At +40 mV, Na⁺ channels close and K⁺ channels open.
K⁺ ions diffuse out of the axon, causing the membrane potential to become negative again.
What is hyperpolarisation and how is resting potential restored?
Due to excessive K⁺ efflux, the membrane becomes more negative than the resting potential (hyperpolarisation).
Voltage-gated K⁺ channels then close.
The sodium-potassium pump restores the resting potential by re-establishing ion balance.
What is the all-or-nothing principle in neural transmission?
An action potential is only triggered if the stimulus exceeds a certain threshold.
If the threshold isn’t met, no action potential is generated.
The size of the action potential remains the same regardless of stimulus strength, as long as the threshold is exceeded.
How does the strength of a stimulus affect action potentials?
A stronger stimulus does not increase the size of the action potential.
It increases the frequency of action potentials — more are fired per second.
This allows the nervous system to interpret stimulus intensity.
How does the action potential propagate along an unmyelinated axon?
Sodium ions move sideways to adjacent regions (like region B), creating a localised electrical circuit, which opens sodium channels in that region and spreads the depolarisation.
What is the refractory period and why does it occur?
The short period after an action potential during which the membrane cannot transmit another action potential.
it occurs because:
The membrane must reestablish Na⁺ and K⁺ electrochemical gradients (repolarisation).
Voltage-gated sodium channels remain temporarily inactive and cannot reopen immediately.
Why is the refractory period important?
Ensures unidirectional flow of the action potential.
Prevents overlapping of action potentials.
Limits the maximum frequency of impulses — hence the maximum stimulus strength detected
What are the steps of synaptic transmission using acetylcholine as an example neurotransmitter
Action potential arrives at the presynaptic knob.
Voltage-gated calcium ion channels open.
Calcium ions (Ca²⁺) diffuse into the synaptic knob.
Ca²⁺ triggers vesicles to fuse with the presynaptic membrane to undergo exocytosis.
Acetylcholine is released into the synaptic cleft.
Acetylcholine diffuses across the cleft and binds to receptors specific to acetylcholine and sodium ion channels on the postsynaptic membrane.
Sodium channels open, Na⁺ enters the postsynaptic neuron.
Depolarisation occurs — an action potential is triggered in the postsynaptic neuron.
Acetylcholinesterase breaks down acetylcholine into choline and ethanoic acid.
These are reabsorbed into the presynaptic neuron.
ATP is used to reform acetylcholine, which is stored in vesicles for reuse.
