How Nerves Work Flashcards
What are the sub-divisions of the nervous system?
Brain
Spinal Cord
Peripheral nerves - Sympathetic and Autonomic nervous systems
What lobes does the cerebrum consist of?
From front to back;
Frontal
Parietal
Occipital
and Temporal below Frontal and Parietal
What is in the forebrain?
Cerebellum
Diencephalon - thalamus and hypothalamus
What is in the brain stem?
Midbrain
Pons - fibres connecting brain hemispheres
Medulla Oblongata
Besides from the 12 cranial spinal nerves - what are the rest?
8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal
In the spinal cord, why is grey matter grey and white matter white?`
Grey due to cell bodies
White as it is mainly axons
What re the differences between the dorsal and ventral horns in the spinal cord?
Dorsal - sensory info in
Ventral - motor info out
In a neuron what does the cell body/soma contain?
The nucleus
What do dendrites do in a neuron?
Is an important route for info from other neurons
What does the initial segment/axon hillock do?
It arranges the information for making action potentials and is where the action potential is triggered.
Is the critical threshold region.
What does the axon do?
Is what the action potential travels down
What are the terminals in a neuron?
Connects with other nerves/muscles and releases neurotransmitters.
What does the gila make up?
90% of all cells in the CNS
What are the three types of gila?
Astrocytes
Ogliodendrocytes
Microgila
What do astrocytes do?
Maintains the external environment of neurons by surrounding the blood vessels
Creates the blood-brain barrier
What do oligodendrocytes do?
From the myelin sheaths in the CNS
What do microgila do?
Phagocytic hoovers that mop up infection
What is the typical resting membrane potential of neurons?
-70mV
What is the main factor in creating the resting potential?
Leaky K channels.
Describe how the resting potential is created…
Na/K pump, pumps K into cells and Na out.
Leaky ion channels in the membranes allow K to flow out down the conc. gradient
This creates an electrical gradient pulling the K back in - meaning K ions don’t move out half and half to even out the conc. gradient
Eventually, the electrical gradient becomes equal to the conc. gradient pushing the ions of the cell
Equilibrium potential is reached.
What happens if we have a high intake of K ions?
K conc. outside the cell would increase
conc. gradient pushing K ions out of leaky channels gets smaller
electrical gradient also gets smaller to compensate
cell depolarises and RMP reduces.
What happens if the RMP reduces too far?
Heart can fail
Brain unaffected as blood brain barrier protects it
How do graded potentials vary in intensity?
In response to how intense the stimulus was
Are graded potentials decremental or self propagating?
What does this mean for the distance transmitted?
Decremental - can only transmit over short distances
Can graded potentials be inhibitory AND excitatory?
Yes;
How is a graded potential inhibitory?
Causes hyperpolarisation when Cl- or K+ channels open
How is a graded potential excitatory?
Causes depolarisation when Na channels open or K channels close
Can graded potentials summate?
Yes
What is temporal summation?
When the cell fires quickly before the cell fully repolarises
What is spatial summation?
When the cell fires a second greater graded potential after cell fully repolarises from the first
What are the 4 types of graded potentials and where are they found?
Generator potentials - at sensory receptors
Postsynaptic potentials - at synapses
Endplate potentials - at neuromuscular junction
Pacemaker potentials - in pace maker tissues
What happens when the graded potential reaches threshold?
Action potential fires
Describe an action potential
Voltage gated Na channels open and flood cell with Na, depolarizing it.
This causes K+ channels to open, causing cell to repolarise then hyperpolarise slightly.
What is the voltage of an AP?
+40mV
How is intensity shown in an AP? Why this way?
In the frequency of fired APs as its an all or nothing event.
What does it mean that the AP is self propagating?
Charge can spread through the axon without re-firing.
Does this by spreading up the axon opening more voltage gated channels along the way.
What are the 3 nerve fibre types?
Afferent (sensory)
Interneurons - decides what to do with the info
Efferent (motor)
What are two ways of using up less voltage gated channels thus speeding up transmission time?
Using large axons, less resistance so charge can travel further before fading.
Insulating the axon via myelin sheaths.
In both cases voltage gated channels can be spread further apart
What makes up myelin sheaths?
Schwann cells or oligodendrocytes in the CNS
Consequences of demyelinating diseases?
Results in the rapid decay of action potentials, preventing them from reaching the next node and from propagating, thus conduction fails.
Do APs and GPs both have refractory periods?
No, just APs
Steps in neuromuscular transmission?
- Action potential in motor neurone
- Opens voltage-gated Ca2+ channels in presynaptic terminal
- Triggers fusion of vesicles
- Acetylcholine (ACh) released
- Diffuses across synaptic cleft
- Binds to ACh (nicotinic) receptors
- Opens ligand-gated Na+/K+ channels
- Evokes graded (local) potential (end plate potential)
- Always depolarises adjacent membrane to threshold
- Opens voltage-gated Na+ channels - evokes new AP
- ACh removed by acetylcholinesterase
What is the action of tetrodoxin on the NMJ?
blocks the Na channels, blocking the AP
What is the action of Joro spider toxin on the NMJ?
blocks Ca2+ release, stopping neurotransmitter release
What is the action of Botulinum toxin on the NMJ?
disrupts release mechanism, stops n.transmitter release
What is the action of curare toxin on the NMJ?
blcoks Ach receptos, prevents end plate potential
What is the action of anticholinesterases on the NMJ?
blocks Ach breakdown, causing increases transmission at the NMJ
