Module 5 Flashcards
What part of a neurone transmits away from its cell body?
The axon
What are the main (structural) differences between motor and sensory neurones?
Motor neurones have no dendron, only dendrites, and sensory neurones have their cell bodies in the ‘middle’ of the cell, with axons and dendrons and roughly equal length
What does a Schwann cell do?
It lays down up to twenty phospholipid bilayers around some neurones, forming a ‘myelin sheath’
What are the gaps called between the sheaves of myelinated neurones?
Nodes of Ranvier
What do sensory receptors do?
Act as a transducer - they each convert one specific type of stimulus into a nerve impulse
Name the four broad types of sensory receptor?
Mechanoreceptor
Chemoreceptor
Thermoreceptor
Photoreceptor
Describe and explain the role of the Pacinian Corpuscle and how it works
The Pacinian Corpuscle is a mechanoreceptor abundant in the skin, fingers and feet, which detects pressure. When pressure is applied to the receptor, it stretches the stretch-mediated sodium ion channels in the membrane, causing sodium ions to flood into the dendron and fire an action potential
What is the approximate potential difference across a resting potential, and how is it maintained?
About -70mV. The sodium-potassium ion pump pumps 3 sodium out for every 2 potassium it pumps in. Almost all of the voltage-gated sodium ion channels are closed but most potassium ion channels are open - making an overall charge gradient across the axon. The neurone is ‘polarised’
Describe the events of an action potential
Stimulus triggers voltage-gated sodium ion channels to open - causing sodium ions to flood in. If the ‘threshold’ is exceeded, this influx causes other ion channels to open and more ions to flood in (positive feedback loop, at about +40mV the membrane, is considered depolarised
How is the membrane of a neurone repolarised?
The membrane becomes more permeable to potassium ions and hence, they diffuse out of the membrane down their electrochemical gradient, reducing the charge in the axon until ‘hyperpolarisation’ occurs (axon < -70mV) causing the potassium channels to close and allows the resting potential to be restored
How does the mechanism of action potential propagation ensure a unidirectional impulse?
The action potential propagates a ‘wave of depolarisation’ through the neurone, followed by its repolarization (known as the refractory period) stopping the impulse being conducted backwards. Think of it like a Mexican wave!
What is saltatory conduction?
When depolarization occurs only across the nodes of Ranvier, creating ‘local circuits’ to more efficiently transmit the impulse (It effectively ‘jumps’ the myelin sections)
Which 3 factors have the highest influence on an axon’s speed?
Presence of myelin sheath, Diameter and temperature
What is the strength of an impulse related to?
It’s frequency of impulse, NOT it’s speed or anything
What is the neurotransmitter released from cholinergic synapses, and what is the basic nature of the neurotransmitter?
AcetylCholine (ACh), excitatory (depolarises the membrane)
Name an Inhibitory neurotransmitter
GABA, inhibitory (hyperpolarizes the membrane)
What happens when an action potential reaches a typical synapse?
The action potential’s ‘wave of depolarisation’ causes voltage-gated calcium ion channels on the presynaptic knob to open, allowing calcium ions to flood in. The influx of calcium ions causes the vesicles in the presynaptic knob to fuse to the presynaptic membrane and release the neurotransmitter (say, ACh) by exocytosis, to diffuse over the synaptic cleft
What happens at the post-synaptic membrane when a neurotransmitter has been released?
The neurotransmitter (probably ACh) will attach to sodium ion channels on the postsynaptic membrane and cause them to open, thus allowing sodium ions to flood in and propagate the action potential
What happens to ACh after it has propagated the action potential?
It is hydrolysed by Acetylcholinesterase, which returns acetate and choline to the presynaptic knob to be regenerated
What are the two forms of neuronal summation?
Spatial and temporal
Describe briefly the main organisation of the mammaliam nervous system
CNS and PNS. From PNS leads Autonomic (subconscious) and Somatic. From Autonomic leads Sympathetic Motor (flight or flight) and Parasympathetic Motor (relax/slowing)
What are the features of somatic neurones?
Heavily myelinated
ACh transmitter
What are the features of autonomic sympathetic neurones?
Lightly myelinated preganglionic neurones
Unmyelinated postganglionic neurones
NA transmitter
What are the features of autonomic parasympathetic neurones?
Lightly myelinated preganglionic neurones
Unmyelinated postganglionic neurones
ACh transmitter