Nervous system Flashcards
what is an anion and a cation?
Anion= A negativly charged ion
Cation= A positvely charged ion
What is the resting membrane potential of a nerve and what is it set by?
-65mV
Due to -80mV of potassium moving moving out of the cell, but also a Cl- charge acting the other way.
Where is an action potential created?
In the axon hillock, or inital segment of an axon.
Action potentials are generated by special types of voltage-gated ion channels embedded in a cell’s plasma membrane.
What happens to sodium pores in an action potential?
At rest the Na+ channels are closed. As the membrane potential becomes depolarised and reaches threshold voltage it induces a conformational change of the protein structure, opening a pore. Sodium ions flood into the cell, rapidly depolarising the cell.
These are open for 1 ms before inactivating
What happens to potassium channels in an action potential?
Requires depolarisation to open, slow to open (1ms after depolarisation). K+ ions leave the cell.
This delay in opening gives them their name a delayed rectifier. Channels close when the membrane potential returns to rest.
At rest in neurone cells, what ions flow in and out of cells? And what causes the negative resting membrane potential in neurones?
K+ ions would be moving out of the cells, while Na+ and Cl- ions would be moving into the cell.
In neurons, K+ ions have high concentration inside, and Na+ outside. The cell has K and Na leakage channels that allow diffusion down concentration gradients. There is far more K leakage channels however, so more cations leave the cell than enetering and this causes a negative charge. The actions of the sodium-potassium pump help to maintain the resting potential, once it is established.
What happens in the falling phase of an action potential?
- Na+ channels inactivate
- K+ channels open
What happens in the undershoot phase?
- Na+ channels are already closed
- K+ channels close
What are the absolute refractory period and the relative refractory period of an action potential?
ARP- between 0-1ms
RRP- between 1ms and until the membrane potential returns to rest.
What are the 4 phases of an action potential called?
How do action potentials propagate along axons?
As the sodium flows through the membrane, it can also depolarise the membrane close to another area. That will reach threshold and get another explosive activation of sodium channels at a point downstream of the initial action potential.
Therefor it takes time for an action potential to propegate along the axon.
What are the symptoms and life expectancy of ALS?
Early symptoms of ALS is slight weakness in hands and limbs. As the disease progresses (weeks- month) get twitching, cramping and loss of control of muscles. Increased incidence of falling, persistent fatigue and slurred speech. Late stage symptoms ( >1 year) are difficulty breathing, swallowing and then paralysis.
Life expectancy after diagnosis is 3-5years.
What are the symptoms and life expectancy of MS (multiple sclerosis)?
There is a wide range of symptoms such as blurred vision, loss of sensation and balance and uncontrolled voluntary movement. However life expectancy is only slightly reduced and it can be managed.
What causes MS?
Formations of lesions in the CNS called plaques, then there is an autoimmune response which leads to inflammation and then destruction of myelin. This leads to signals being disrupted.
What are astrocytes?
Fill the extracellulae space that surrounds neurones regulate the chemical content of the the extracellular space. they stop the ‘spill out’ of chemical content to the extracellular space.
What are schwann cells?
Produce myelin, the insulating sheath which wraps around the axon, acting as a insulating ‘cable’ and allows faster and effcient propogating of info down the nerve stream.
What are efferent and afferent axons?
sesnory (afferent) axons take info from the periphery to the CNS.
Motor (efferent) axons take info from the CNS to the muscles.
What types of nerves are in dorsal roots, ventral roots and the spinal nerve?
- Dorsal roots contain afferent axons
- ventral roots contain efferent axons
- spinal nerve contains a mix of afferent and efferent nerves
What different functions do the brain and spinal cord have?
The brain= cognition, motivation, emotion, learning, memory and volitional movement.
Spinal cord= reflexive actions which are automatic and do not require the brain.
How do ions move through the phospholipid membrane and why?
They are hydrophillic- cannot pass directly through the membrane, so move through ion pumps (active) or ion channels (passive).
What is the structure of a neurone?
Has a middle soma and long fibrous attachments called dendrites. The dendrites collect electric signals from many upstream neurones and sum that info to the cell body. if significant info has been given, the cell body will release a signal to the axon.
What are ventral and dorsal roots?
Each spinal nerve has two roots, a dorsal or posterior (meaning “toward the back”) one and a ventral or anterior (meaning “toward the front”) one. The dorsal root is sensory, the ventral is motor.
What are the 4 main sensory types of axon?
A-alpha, a-beta and a-gamma are all myelinated. C is not.
How are vesicles replenished with neurotransmitter?
This is called the exocytosis/endocytosis cycle. Starts with the invasion of the AP into the terminal, opening the Ca gates. This facilitates docking of the vesicles to the presynaptic membrane, which then release their contents. A little bit of the membrane is ‘pinched of’ to form another empty vesicle, then through enzymes there is a loading of that vesicle with transmitter.
How do ionotropic receptors work?
◊ Ionotropic receptors, ion channels which open when neurotransmitter binds. Very fast response (micro-milli seconds).
◊ Neurotransmitter will bind to a receptor pocket which causes a pore, so ions can flow into the cell and depolarisation occurs, creating an action potential.
How do postsynaptic metabolic receptors work?
There is an activation of a second messanger, take take ms-s.
Neurotransmitter bind to a protein, causing the release of an alpha subunit called a g-protein subunit which moves across the cell and interacts with an effector protein, or will bind to an ion channel.
What are spartial and temporal summation?
Spatial summation- summation of EPSPs generated at the different synapses.
Temporal summation- summation of EPSPs generated at the same space.
How do reflex actions occur?
A reflex is a involuntary near instantaneous movement that does not require the brain.
Info comes to the periphery and is processed in the spinal cord to ensure quick action.
The spinal cord will excite alpha motor neurons that go back to area of the sensory nerve which will initiate a muscle movement. At the same time another neuron excites an inhibitory interneuron in the spinal cord which inhibits the extensor that travels to the antagonist muscle
