Neural Signalling and Communication

What is the resting potential voltage?

-65mV

What 4 factors contribute to establishing a resting potential?

1) anionic intracellular proteins that can't leave

2) Sodium/ potassium pumps

3) K+ ion gradients equilibrium

4) Na+ ion gradient causing small inward diffusion

Describe the K+ ion gradient equilibrium found at a resting potential:

K+ leaves the cell down a concentration gradient and is also pulled back in by the negative charge creating a balance of movement

What is the name of the equation used to work out ion equilibrium potential?

Nernst equation

True or false: at resting potential, there is more Na+ outside the cell than inside

True

True or false: at resting potential, there is more K+ outside the cell than inside

false

What is the voltage of an action potential?

+35mV

Describe how depolarisation of a neurone takes place:

Na+ channels open and if the threshold potential is reached, voltage gated Na+ channels open, creating an action potential

Describe how repolarisation of a neurone takes place:

Na+ ion channels close and voltage gated K+ ion channels open so K+ flows out of the cell

What is hyperpolarisation?

when the membrane potential becomes more negative that its resting potential

What does the All or Nothing Principle state? (2 points)

1) all excitable cells have a threshold magnitude which must be passed for an action potential to be generated

2) a further increases over the threshold results in a higher frequency of action potentials rather than a large action potential amplitude

What is meant by absolute refractory period?

no further action potentials can be elicited, allowing for unidirectional action potentials

What is meant by relative refractory period?

a larger stimulus can result in an action potential

What is propagation?

movement of an action potential along the nerve axon

Describe propagation of an action potential in a non-myelinated neurone:

Na+ influx causes other voltage gated Na+ channels to open further down causing an action potential in the next membrane section

Describe propagation of an action potential in a myelinated neurone:

the nodes of Ranvier are the only area where current can pass through the membrane so the impulse jumps making it faster

Where are sensory receptors found?

at the ends of sensory nerves

Give 3 examples of sensory modalities:

1) light

2) vibration

3) chemicals

What is signal transduction?

the conversion of environmental or internal signals into electrochemical energy

What is the role of sensory receptors?

to detect a stimulus and create a receptor potential

Describe how a sensory receptor creates an action potential down a sensory neurone:

a sensory receptor produces a receptor potential which if large enough will create an action potential

What determines the magnitude of a receptor potential?

the strength of the stimulus

Give two examples of sensory receptors in muscles:

1) muscle spindle

2) Golgi tendon organ

What stimulates muscle spindles?

passive stretching of muscles

What switches of muscle spindle receptors?

contraction or shortening of the muscle

What is the role of muscle spindles?

preventing muscles from being overstretched

Describe the role of muscle spindles in the knee jerk reflex:

stretching the knee stimulates the muscle spindle leading to firing from the sensory neurone into the spinal cord and down the motor neurone, causing a jerk

How is the knee jerk reflex monosynaptic?

no interneuron is involved

Where are Golgi tendon organs found?

tendons

What stimulates Golgi tendon organs?

muscle contraction or stretching

What do Golgi tendon organs protect us from?

muscle and connective tissue injury

Describe the neural pathway stimulated by the the Golgi tendon organ:

an action potential from the sensory neurone passes into an inhibitory interneuron preventing further motor neurone depolarisation

Describe how electrical synapses transmit action potentials:

through the direct passage of current via ions flowing through gap junctions

Describe how chemical synapses transmit action potentials:

through the release of vesicles containing chemical neurotransmitters

Give 4 key groups of neurotransmitters:

1) acetylcholine

2) amines

3) amino acids

4) peptides

Give 5 example of amine neurotransmitters:

1) dopamine

2) noradrenaline

3) adrenaline

4) serotonin

5) histamine

Give 3 examples of amino acid neurotransmitters:

1) GABA

2) Glycine

3) glutamic acid

What are the two types of neurotransmitter receptors?

1) ionotropic

2) metabotropic

Describe ionotropic neurotransmitter receptors:

clusters of similar subunits forming ion channels

Describe metabotropic neurotransmitter receptors:

7 transmembrane molecules coupled to intracellular proteins that transduce a signal to the cell interior

Give 2 examples of neurotransmitters that give rise to EPSPs:

acetylcholine and glutamic acid

What are EPSPs?

excitatory postsynaptic potentials created by neurone depolarisation at a synapse

What are IPSPs?

inhibitory postsynaptic potentials created by an influx of Cl- ions giving rise to hyperpolarisation

Give 2 examples of neurotransmitters that give rise to IPSPs:

GABA and glycine

True or false: EPSPs and IPSPs have no refractory period

true