Lecture 8: Nerve 1 Flashcards
Describe the structure of a nerve from out to in:
Whole nerve -> fascicles -> bundles of neurons -> axon
Describe the structure of a neuron:
A neuron is a single cell
Dendrites -> cell body (soma) -> axon -> synaptic terminals
What are the 3 different types of neurons?
- Multipolar - multiple local inputs at soma (motor neurons, CNS)
- Unipolar - dendrites distal from soma (sensory neurons)
- Anaxonic - no distinct axon, axonless (CNS neurons)
How do neurons communicate with eachother?
- The pre-synaptic neuron contains neurotransmitter vesicles and releases these in the electrical-chemical conversion
- A chemical synapse occurs between the 2 neurons which allows for regulation (dampening or potentiation) of the signal
- The post-synaptic neuron contains neurotransmitter receptors - this is where the chemical-electrical conversion occurs
Where is the input zone of a neuron?
Dendrites and cell body (soma)
* Receives input - local potentials
* Chemically-gated ion channels
Where is the integration zone of a neuron?
Axon hillock
* Summates the local potentials -> generates action potential
* Voltage-gated ion channels
Where is the action potential zone of a neuron?
Axon
* Sends an action potential down the axon
* Voltage-gated ion channels
Where is the output zone of a neuron?
Axon terminals
* Releases neurotransmitter to initiate a response in target cell
* Voltage-gated ion channels
Describe the ion gradients in bioelectricity:
- There are concentration gradients and electrostatic forces
- Both can act simultaneously in the same or opposite direction
- If they exactly balance, ions will stop moving - EQUILIBRIUM
What are the relative levels of Na+ and K+ in the ECF and ICF?
ECF:
High Na+ - 142mM
Low K+ - 4mM
ICF:
Low Na+ - 12 mM
High K+ - 150mM
What is equilibrium potential?
The membrane potential when the 2 opposing forces of an ion are balanced
What is resting membrane potential (RMP)?
The combined permeabilities and gradients of all the ions (Na+, K+, Cl-, & others) involved, and is approximately -70mV
What is the threshold value for an action potential?
-60mV
What is depolarisation?
Becoming more positive
What is repolarisation?
Becoming more negative but still above RMP
What is hyperpolarisation?
More negative than RMP
What is overshoot?
More positive than zero
What are local potentials?
- Small (graded) local changes – depolarises or hyperpolarises the membrane to different levels (can cause action potential)
- Does not propagate, amplitude decreases with distance – short distances
- Temporal and spatial summation
- Chemically gated ion channels
What are action potentials?
- All or nothing – either the same size action potential or no action potential at all
- Depolarizes to the same level (+30 mV) each time
- Propagates down the axon without loss of amplitude - long distances
- Voltage-gated ion channels
Give 3 examples of different stimuli and their receptors:
- Touch on a skin pressure receptor
- Pain on a nociceptor
- Light hits photoreceptor
Describe the local depolarisation between neurons:
- Neurotransmitter from the pre-synaptic cell binds to the receptor on the postsynaptic cells
- Chemically gated Na+ channels will open
- Na+ will flow into cell
- Causes a local depolarisation
What happens if an excitatory neurotransmitter binds?
Adrenaline/epinephrine:
Na+ enters neuron bringing membrane potential closer to threshold - depolarising
What happens if an inhibitory neurotransmitter binds?
Serotonin:
Cl- enters neuron moving membrane potential away from threshold - hyperpolarising
