How Nerves Work Flashcards by Zain Aslam

What are the sub-divisions of the nervous system?

Brain

Spinal Cord

Peripheral nerves - Sympathetic and Autonomic nervous systems

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What lobes does the cerebrum consist of?

From front to back;

Frontal
Parietal
Occipital

and Temporal below Frontal and Parietal

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What is in the forebrain?

Cerebellum

Diencephalon - thalamus and hypothalamus

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What is in the brain stem?

Midbrain

Pons - fibres connecting brain hemispheres

Medulla Oblongata

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Besides from the 12 cranial spinal nerves - what are the rest?

8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal

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In the spinal cord, why is grey matter grey and white matter white?`

Grey due to cell bodies

White as it is mainly axons

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What re the differences between the dorsal and ventral horns in the spinal cord?

Dorsal - sensory info in

Ventral - motor info out

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In a neuron what does the cell body/soma contain?

The nucleus

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What do dendrites do in a neuron?

Is an important route for info from other neurons

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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.

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What does the axon do?

Is what the action potential travels down

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What are the terminals in a neuron?

Connects with other nerves/muscles and releases neurotransmitters.

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What does the gila make up?

90% of all cells in the CNS

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What are the three types of gila?

Astrocytes
Ogliodendrocytes
Microgila

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What do astrocytes do?

Maintains the external environment of neurons by surrounding the blood vessels

Creates the blood-brain barrier

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What do oligodendrocytes do?

From the myelin sheaths in the CNS

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What do microgila do?

Phagocytic hoovers that mop up infection

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What is the typical resting membrane potential of neurons?

-70mV

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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