6. Nerve Flashcards by Georgia Leggett

Name the 4 lobes of the brain

Frontal
Parietal
Temporal
Occipital

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What are the ridges and valleys of the brain called?

Ridges= Gyri
Valleys= Sulci

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What are the 3 parts of the brainstem?

Midbrain
Pons
Medulla

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Why is the brainstem important?

Its the target or source of all cranial nerves

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What is the cerebellum responsible for?

Motor coordination
Balance
Posture

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Where does the spinal cord descend from?

Medulla

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Role of spinal cord

Conduit for neural transmission

Co-ordinates some reflex actions

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What are the 4 broad types of cells in the nervous system?

Named based on their appearance

Unipolar: 1 axonal projection
Pseudo-unipolar: single axonal projection that divides into 2
Bipolar: 1 axon, 1 dendrite projection
Multipolar: 1 axon, many dendrites

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What are the 3 types of multipolar cells?

Pyramidal
Golgi
Purkinje

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Neurones

Excitable cells of CNS
Heterogeneous morphology
Non-dividing cells

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What are the 3 main parts of a neurone?

Soma (cell body)
Axon (only 1)
Dendrites (numerous)

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Describe the soma

Contains nucleus and ribosomes

Has neurofilaments for structure and transport

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Although neurones can differ by morphology, all only have 1

Axon

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Describe the axon

Long process (aka nerve fibre)
Originates from soma at axon hillock
Can branch off into ‘collaterals’
Usually myelinated

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Describe dendrites

Highly branched
NOT myelinated
Receive signals from other neurons

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What are neuroglia?

All cell types in CNS that aren’t neurones

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What is the difference between axons and dendrites?

Axons are myelinated and dendrites are not

There is only 1 axon but there are many dendrites

Name 5 neuroglia

Astrocytes
Ogliodendrocytes
Schwann cells
Microglial cells
Ependymal cells

What is the most abundant cell type in the CNS?

Astrocytes

Functions of astrocytes

Structural cells
Cell repair
Immune cells and are considered ‘facultative macrophages’
Neurotransmitter release and re-uptake – help maintain homeostasis

Name 2 myelin producing cells

Ogliodendrocytes

Schwann cells

Describe ogliodendrocytes

Provide myelin for other axons
Variable morphology and function
Numerous projections that form internodes of myelin
In CNS 
1 oligodendrocyte myelinates many axons

Describe Schwann cells

Produce myelin for peripheral nerves

1 Schwann cell myelinates 1 axon segment

Describe Microglial cells

Specialised cells - similar to macrophages

Perform immune functions in CNS

Describe Ependymal cells

Epithelial cells - line fluid filled ventricles | Regulate production and movement of cerebrospinal fluid (CSF)

What is the usual resting membrane potential?

Between -40 and -90mV

What are the intracellular and extracellular concentrations of the 4 main ions involved in action potentials?

Na+ - inside: 10 outside: 140 K+ - inside: 150 outside: 4 Cl- - inside: 5 outside: 120 Ca2+ - inside: 0.1 outside: 2

Why is transport of the main ions regulated by channels and pumps?

Cell membranes are impermeable to these ions

Describe the uneven ion distribution which creates a potential difference across the cell membrane

High extracellular: Na+ & Cl- Low extracellular: K+ High concentration gradient for Ca2+ (into cell)

What is the charge inside neuronal cells compared to outside?

Negative charge inside compared to outside

At resting membrane potential, what state are the voltage gated sodium and potassium channels in?

VGSCs: Closed VGKCs: Closed

Membrane depolarisation

Opening of VGSCs Sodium influx Further depolarisation

What happens to VGKCs in an action potential?

VGKCs open at a slower rate | Potassium efflux out of cell

Hyperpolarisation

Getting more and more negative

What does an action potential leave?

Sodium and Potassium imbalance | Needs to be restored

What restores the ion gradients after an action potential?

Na+-K+-ATPase (pump) restores the ion gradients | transporter, not channel

Describe the process of depolarisation

Na+/K+-ATPase uses ATP hydrolysis to move 3 Na+ out (vestibule phosphorylated), changing shape Then 2 K+ bind and are moved into cell as pump returns to resting configuration

What is saltatory conduction?

Action potentials jump between adjacent nodes of ranvier | This increases the speed of transmission

How does myelin prevent action potentials spreading?

Myelin has high resistance and low capacitance (doesn’t store charge)

When is an action potential unable to 'jump'?

Across the gap at the axon terminal (synapse)

Describe what occurs when an action potential reaches a synapse

AP activates VGCCs at synaptic terminal: Ca2+ influx Ca2+ influx causes vesicle exocytosis and NT release NT binds to postsynaptic receptors transmitting the signal NT is either metabolised within the synaptic cleft or recycled by transporter proteins