Topic 6 - Nervous Coordination Flashcards
What are neurons?
Specialised cells that transmit electrical impulses throughout the body enabling communication with the nervous system.
What are the six structures in a neuron?
- Dendrites.
- Axon.
- Axon terminal.
- Cell body.
- Schwann cells
- Notes of Ranvier.
What is the cell body?
Contains the nucleus and cytoplasm with organelles such as mitochondria and ribosomes to produce proteins and energy required for impulse transmission. The site of metabolic activity within the neurone.
What are dendrites?
- branched extensions from the cell body
- Conduct nerve impulses towards the cell body.
What are axons?
- A long single extension that transmits impulses away from the cell body to the next neuron or effector.
- Enclosed in a myelin sheath neurons to increase the speed of impulse transmission
What the axon terminal?
- End of the axon that forms synapses with other neurons or factors such as muscles or glands.
What are Schwann cells?
- surround the axon in myelinated neurones producing the myelin sheath which acts as an electrical insulator.
What are notes of ranvier?
- gaps in the myelin sheath
- Enable a faster transmission.
What is a sensory neuron?
Carries impulses from receptors to the central nervous system.
What is a motor neuron?
Transmits impulses from the CNS to factors such as muscles or glands.
What is a relay neuron?
Found in the CNS and connect sensory neurons to motor neurones.
What is meant by a neurons resting potential?
The state of a neuron when it is not transmitting an impulse at this state the neurons membrane is polarised due to a different in electrical charge between inside and outside of the membrane.
The resting potential is maintained at approximately 70 my by what three different ways?
Sodium potassium pumps
Potassium channels
Neuron is negatively charged inside
Explain how a sodium potassium pump maintains a neurons resting potential.
Actively transport three sodium ions out and two potassium irons in creating an electro chemical gradient.
Explain how potassium channels maintain arresting potential in a neuron
Allow potassium to diffuse out further contributing to the positive charge outside.
Explain how the inside of the neuron being negatively charged maintains a resting potential.
The inside of the neuron is negatively charged compared to the outside due to the presence of large negatively charged proteins and fewer positive ions.
What is an action potential?
Rapid temporary reversal of a neuron membrane potential triggered when the cells reach a threshold, allowing an electrical signal to travel along the neuron.
When stimulated how does the membrane of a neuron become depolarised?
- Sodium channels open allowing sodium ions to flood into the cell making the inside more positive.
- If the stimulus is strong enough it reaches the threshold potential and triggers a full action potential
- The action potential propagate along the neuron transmit the signal
What are the two key features of resting potential?
- Voltage difference.
- Ion distribution.
Explain voltage different in resting potential
- The inside of the neuron has a negative charge relative to the outside with a typical resting potential of 70 my.
- This is caused by an imbalance of ions across the membrane.
Explain ion distribution during resting potentials
There is a higher concentration of sodium ions outside the axon and a higher concentration of potassium ions inside the axon
What is the role of the sodium potassium pump?
The sodium potassium pump actively transport ions:
- three sodium irons are pumped out of the neuron
- Potassium irons are pumped into the neuron
Create an electro chemical gradient with more positive ions outside the neurone.
How does membrane permeability affect ion diffusion?
- The membrane is in permeable sodium ions so sodium cannot diffuse back into the axon.
- The membrane is partially permeable to potassium ions allowing some potassium to diffuse out the potassium ion channels contributing to the positive charge outside.
How does the sodium potassium pump work?
It uses ATP for active transport maintaining the resting potential.
What are nerve impulses?
Electrical signals transmitted along neurons, enabling communication within the nervous system. They occur due to changes in the voltage across the neuron membrane, caused by the movement of ions.
What is an action potential?
- a nerve impulse is initiated when the neuron membrane becomes depolarised creating an action potential.
- An action potential occurs if the stimulus exceeds the threshold.
What are the four phases of an action potential?
Depolarisation
Repolarisation
Hyperpolarisation
Resting potential reestablished
What is the polarisation in action potential?
- when stimulated voltage gated sodium ion channels open allowing sodium ions to diffuse into the neuron
- The inside becomes less negative and can reach a value of approximately 40 mV
What is the repolarisation phase of an action potential potential?
- sodium ion channels close and voltage gated potassium ion channels open allowing potassium ions to diffuse out
- This restores the inside of the neuron to a negative charge
What is the hyperpolarisation phase of an action potential?
Potassium ion channels remain open longer than necessary causing the potential to drop below the resting potential.
What is the resting potential reestablished phase of an action potential?
The sodium potassium pump restores the resting potential by actively transporting three sodium iron out and two potassium ions in.
What is the refractory period?
- After an action potential there is a short period where the neuron cannot generate another impulse.
- This ensures impulses are unidirectional and prevent overlap.
What is propagation of nerve impulses?
- The action potential causes localised changes in the membrane potential triggering adjacent sections of the membrane to depolarise.
- this result in the impulse moving along the neuron.
What is meant by saltatory conduction?
- In myelinated neurons, the action potential jumps between the notes of ranvier significantly increasing the speed of transmission.
- in non-myelinated neurons, the impulse travels continuously along the membrane which is slower.
What is the significance of nerve impulses?
- They enable rapid communication between sensory receptors the central nervous system and effectors
- They are central responses to stimuli such as reflex actions and voluntary movement.
What is the absolute refractory period phase of the refractory period?
- During this phase, no action potential can be generated regardless of the strength of the stimulus.
- This occurs because the sodium ion channels remain closed preventing depolarisation
What is the relative refractory period phase of the refractory period?
- during this phase and new action potential can be generated but only if the stimulus is stronger than usual.
- This is because the membrane is hyper polarised
What are the three functions of the refractory period?
- Ensures that action potentials travel in One Direction only by preventing the propagation of a backwards impulse.
- Produces discrete impulses by ensuring that each action potential is separate from the next
- Limits the frequency of nerve impulses ensuring the neuron has time to recover
What is the all or nothing principle?
- an action potential is only generated if the stimulus reaches a threshold value.
- If the threshold is not reached, no action potential is produced
- All action potential generated have the same magnitude regardless of stimulus strength
What is a myelin sheath?
Axon surrounded by myelin sheet conduct impulses much faster than non-myelinated axons.
How can temperature affect action potentials?
Higher temperatures increase the kinetic energy of ions which accelerates their diffusion across the axon membrane during action potentials.
How can temperature influence the ATP yield?
Temperature can also influence the rate of respiration which produces the ATP required for the sodium potassium pump to restore resting potentials.
What is the formula for maximum frequency of impulses?
Maximum impulse frequency (Hz) = 1/refractory period (s)
What are cholinergic synapses?
Junctions between two neurons or between a neuron and an effect that use the neurotransmitter acetylcholine to transmit nerve impulses.
What are the four key features of the cholinergic synapse?
- Pre-synaptic neuron.
- Synaptic left.
- Post synaptic neuron.
- Enzyme action.
Explain the pre-optic neuron in the cholonergic synapse?
- Contains vesicles filled with acetylcholine
- when an action potential arrives at the synaptic knob voltage gated calcium ions channel allowing calcium ions to diffuse into the knob
Explain the synaptic cleft during cholinergic synapse
- A gap between the presynaptic and post-synaptic membranes.
- acetylcholine it released into this cleft by excytosis and diffuses across the to the post membrane.
Explain the post an Arctic neuron in the choloergic synapse.
- The post synaptic membrane contains specific receptors that bind acetylcholine
- finding open ligand-gated sodium ion channels causing sodium ions to enter and polarised the membrane
Explain enzyme action during the cholonergic synapse
- acetylcholine is broken down by the enzyme acetylcholinesterase into choline and ethanoic acid.
- These products are reabsorbed by the presynaptic neuron to re-synthesise acetylcholine using ATP.
