Nervous System Flashcards
Information flow through neurons
Dendrites
Cell body (Soma)
Axon
Specialised Glial Cells
Astrocytes
Schwann cells
Astrocytes
Most numerous cells in the brain
Fills spaces between neurons
Regulates chemical content of the extracellular space
Schwann cells
Oligodendroglial cells
Provides myelination of axons
Myelin sheath
Insulates the axonat intervals in order to speed up action potential propagation
Central Nervous Systym (CNS)
The brain and the spinal chord
Peripheral Nervous System (PNS)
Radiates form CNS
Afferent vs Efferent Axons
Brain vs Spinal Chord funtions
Brain:
Cognition, motivation, voluntary movement, learning and memory
Spine:
Reflexive actions, fast acting that doesn’t require the brain
Transport of electricity in biology
Ions in solution (biology is based on water)
Na+,K+,Cl-,Ca2+
Potassium Sodium Which Has Higher Concentration Inside/Outside of cell?
Memomic: You do K you stay inside, if you are outside you are Na
Resting Membrane Potential
-65mV
How the resting membrane potential is set
K+ ions leave via the potassium leak channels due to there being a lower concentration outside.
This leads to a drop in the charge inside the cell. As the charge inside become lower and lower a potnetial force builds up between the inside and the postive charge outside.
Eventually this equals the force due to concentration difference and while the channel is still open equilibrium is reached around -65/70mV
How to record resting membrane potential
Can use microelectrode
Action potential
Neurons fire action potentials when stimulated.
It is a binary unit, it either propegates or it doesn’t
Action potential trains and firing rate
The frequency of the train encodes information e.g. the harder the touch the faster the train will occure
What are the 4 phases of an action potential
What is threshold potential?
This is the potential required for an action potential to occur, if this isn’t reached nothing happens.
This is around -55mV
What is a voltage gated sodium channel?
These are sodium channels which open when the threshhold potential is reached and quickly close up after approx 1ms. They are responsible for the rapid depolarisation during an action potential. They can be only be opened again when the resting potential is once again reached
What is a voltage gated potassium channel?
These are potassium channels which open approx 1ms after the threshhold potential is reached, these are responsible for the rapid reploarisation of the axon. They close up again once resting potential is reached.
These are different to the two pore potassium channels which set the resting potential, the two pore ones are always open
How does action potential propegate in an unmyelinated axon?
The axon is like a tube so it passively propagates down as the nearby action potential stimulates the next part to threshhold potential
What is the myelin sheath and how does it increase signal propagation?
Shwann cells joins together to make the myelin sheath, the gaps inbetween sections of sheath are called nodes of Ranvier. Polarisation of the axon can jump from node to node resulting in much faster propagation
What is saltatory conduction?
Saltatory conduction is the rapid node to node conduction of action potentials along myelinated axons
The different axons for sensory input
Mechanosensitive ion channels
This are the channels present around mechanorecptors are they are gated depending on the stretch of the surrounding membrane
4 main sensory input modalities from the skin
- Temperature
- Touch
- Pain
- Pressure
What is a synapse?
A terminal between neurons in which they communicate through neurotransmitters.
It consists of a presynaptic terminal where the transmitters are synthesised and a postsynaptic terminal where transmitters are recieved
How are neurotransmitters sythesised?
Enzymes produced in the neuron cell body travel down the axon, these then react with precursors to make the neurotransmitters
How does an action potential release neurotransmitters?
What is a vesticle?
This holds neurotransmitter for release during exocytosis
Exocytosis vs endocytosis
- Exocytosis is the fusion of a vesticle to the cell membrane thus releasing neurotransmitters
- Endocytosis is the generation of new vesticles by pinching them from the membrane
Exocytosis/Endocytosis cycle
Two types of receptors
- Ionotropic - fast acting, ion channels open as soon and neuroreceptor binds
- Metabotropic - slower acting, activation of a second messenger e.g. via g-protiens
Excitatory vs Inhibitory neurotransmitters
Excitatory neurotransmitters increase the excitability of the post synaptic neuron, inhibitatory neurotransmitters deacrease the excitability of the postsynaptic neuron
What is the quantal hypothesis of neurotransmission?
This is that the postsynaptic response will be quantised or discrete as opposed to continuous. This is due to the vesticles. The response will be proportional to vesticles released e.g. (1,2,3…)vesticles
How do excitatory neurotransmitters work?
They act on ion channels which increase the charge within the postsynaptic terminal
How do inhibitory neurotransmitter work?
They act on ion channels which decrease the charge within the postsynaptic terminal
How can multiple inputs add together to excite a neuron?
There are two different types of summation of EPSPs
Spatial summation is the summation of EPSPs generated at different synapses
Temporal summation os the summation of EPSPs generated at the same synapse
What EPSP stand for
Excitatory postsynaptic potential
Describe how the excitatory and inhibitatory synapses interact and balance
The excitatory synapse produces a depolarisation in the dendrite which passively propagates towards the soma, if there is an active inhibitory synapse present this will counteract the depolarisation produced by the excitatory synapse therefore at the soma no depolarisation is detected and the threshold potential is not reached in order to produce an action potential down the axon.
With regards to neuropharmocology what is an agonist and an antagonist
An agonist acts to mimic an endogenous neurotransmitter
An antagonist acts to block an endogenous neurotransmitter
What does ANS stand for and what are it’s two sub branches
Autonomic nervous system
Sympathetic and parasympathetic nervous system
What muscles does the somatic nervous system control?
Skeletal muscle
What muscles does the sympathetic nervous system control and what is it’s general purpose
Smooth muscle, cardiac muscle and gland cells.
It is responsible for fight or flight responses
What muscles does the parasympathetic nervous system control and what is it’s general purpose
Smooth muscle, cardiac muscle ad gland cells.
Responsible for rest and digest functions and acts to counter the sympathetic nervous system
The origins and features of the SNS
- Short preganglionic fibres originating from the thoracic and lumbar region
- These act on many different long postganglionic fibres making it very general (all or nothing)
What is a ganglion
A synaptic relay station between nerves
The origins and features of the PSNS
- Long preganglionic fibres originating from the cranial and sacral areas
- These act on select short postganglionic fibres resulting in more sleective functions (e.g. can act to increase digestion while leaving heart rate alone)
How does the SNS and PSNS affect the different body function?
SNS
- Increases heart rate
- Increases breathing
- Decreases digestion and urination
- Stimulates energy(glucose) production and release
- Constrics blood vessels
PSNS
- Slows heart rate
- Slows breathing and constricts airways
- Stimulates digestion
- Stimulates energy(glucose) storage
What is ACh
Acetylcholine
Used for muscle contraction in the somatic nervous system
In the ANS released by all preganglionic neurons and the postganglionic neurons of the PSNS
What is released by the SNS from the postganglionic neurons?
Noradrenaline
Uppermotor neurons vs lower motor neurons
- Upper motor neurons are found within the spinal chord
- Lower motor neurons are the ones from the spinal chord to the peripheries
What is a motor neuron pool
A collection of alpha motor neurons all responsible for the same muscle, if damage to one occurs then the muscle can still be innervated
What is the predicable organisation of lower motor neurons within the ventral horn
Ones that innervate distal muscles occur lateral to ones that innervate axial
Ones that innervate flexors occur posterior to those that innervate extensors
What is this and what is it’s function?
Sarcolemma
Is the excitable cell membrane covering the muscle fibre
What is this and what is it’s function?
Sarcoplasmic reticulum
Stores calcium which when released causes contraction
Describe how calcium interacts with tropinins and in order for muscles to contract
Calcium binds to tropinins which in turn open up the actin filament to binidng with the myosin filament. The myosin head bends thus sliding the actin filament
Describe the whole story of excitation-contraction coupling from an action potential in an alpha neuron to a muscle contraction
- AP occurs in alpha neuron
- Motor neurons release ACh at synapses
- ACh triggers depolarisation of the sarcolemma
- In response to this the sarcoplasmic reticulum releases Ca2+
- This triggers the sliding of the actin/myosin filaments resulting in muscle contraction
What is a muscle twitch?
This is the response due to a single action potential
If these stack you end up with full contraction
Where are reflexs processed?
In the spinal chord
What is an inhibitory interneuron
This is a neuron in the spinal CNS that inhibits an antagonist muscle while the agonist muscle is activated
