6. Nerve Flashcards
Name the 4 lobes of the brain
Frontal
Parietal
Temporal
Occipital
What are the ridges and valleys of the brain called?
Ridges= Gyri Valleys= Sulci
What are the 3 parts of the brainstem?
Midbrain
Pons
Medulla
Why is the brainstem important?
Its the target or source of all cranial nerves
What is the cerebellum responsible for?
Motor coordination
Balance
Posture
Where does the spinal cord descend from?
Medulla
Role of spinal cord
Conduit for neural transmission
Co-ordinates some reflex actions
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
What are the 3 types of multipolar cells?
Pyramidal
Golgi
Purkinje
Neurones
Excitable cells of CNS
Heterogeneous morphology
Non-dividing cells
What are the 3 main parts of a neurone?
Soma (cell body)
Axon (only 1)
Dendrites (numerous)
Describe the soma
Contains nucleus and ribosomes
Has neurofilaments for structure and transport
Although neurones can differ by morphology, all only have 1
Axon
Describe the axon
Long process (aka nerve fibre)
Originates from soma at axon hillock
Can branch off into ‘collaterals’
Usually myelinated
Describe dendrites
Highly branched
NOT myelinated
Receive signals from other neurons
What are neuroglia?
All cell types in CNS that aren’t neurones
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
