Cells of the Nervous System Flashcards
What does the CNS consist of?
two cerebral hemispheres, the brainstem, the cerebellum and the spinal cord
What are the ridges of the brain called?
gyri (singular gyrus)
What are the valleys of the brain called?
sulci (singular sulcus)
What are the 4 lobes of the brain?
Frontal
Parietal
Temporal
Occipital
What is the function of the frontal lobe?
Responsible for executive functions such as personality
What is the function of the parietal lobe?
Contains the somatic sensory cortex responsible for processing tactile information
What is the function of the temporal lobe?
Contains important structures such as the hippocampus (short term memory), the amygdala (behaviour) and Wernicke’s area (auditory perception & speech)
What is the function of the occipital lobe?
Processing of visual information
What does the brainstem consist of in descending order?
midbrain, pons and medulla
these structures are the target source of all cranial nerves
What does the cerebellum have an important role in?
motor coordination, balance and posture
What are the main types of neurone morphologies?
Unipolar
Pseudo-unipolar
Bipolar
Multipolar
Describe a unipolar neurone
cell body containing nucleus, and a single axonal
projection from the cell body
Describe the structure of a pseudo-unipolar cell
Cell body with nucleus and a single projection. However, the single projection is able to fork into two different branches, therefore forming two different projections from one original projection from the cell body
Describe the structure of a bipolar neurone
Cell body with the nucleus and the two projections from the cell body.
One will be an axon and the other one is commonly referred to as a dendrite
Describe the structure of a multi-polar neurone
Most common type of neurone
Numerous projections from cell body
Only one of these projections will be an axon and rest are dendrites
Name the 3 types of multipolar neurone types
Pyramidal cells
Purkinje cells
Golgi cells
Define a mature neuron
non-dividing excitable cell whose main function is to receive and transmit information in the form of electrical signals
Give 4 characteristics of neurones
Excitable cells of CNS
Heterogenous morphology
Non-dividing cells
Share common features
What are some common features of neurones?
Soma (cell body, perikaryon)
Axon
Dendrites
What does the soma (cell body) contain?
Nucleus and ribosomes
What are neurofilaments important for?
Maintaining structure of neuron and transportation of proteins (e.g. to end our axons or dendrites
What is an axon?
Single projection from cell body and it projects from an area known commonly as the Axon hillock
Axon has collateral elements, which can project to different areas or different neurones
What substance usually covers the axon?
Myelin
What is the purpose of myelin?
Allow signals to be transmitted from axons at a faster rate
What are dendrites?
projections from the cell body, but unlike axons there are numerous dendrites from the cell body
What are dendrites important for?
Receiving signals from other neurons
What are astrocytes?
Astrocytes are the most abundant cell type in the mammalian brain. They function as structural cells and are known to play an important role in cell repair, synapse formation, neuronal maturation and plasticity
What are oligodendrocytes?
Myelin producing cells of CNS. Each oligodendrocyte cell body sends out numerous projections that form internodes of myelin covering the axon of neurones
What are the myelin producing cells of the of the PNS?
Schwann cells
How many axons can each Schwann cell myelinate?
Only a single axonal segment
What are microglia?
Specialised cells that are similar to macrophages and they perform immune functions in the CNS.
What are ependyma?
Ependymal cells are epithelial cells that line the fluid filled ventricles regulating the production and movement of CSF
What is said to be the resting membrane potential of neurones?
-70mV
What does hyperpolarised mean?
membrane potential becomes more negative
What does depolarised mean?
membrane potential becomes more positive
What happens when a cell is sufficiently depolarised?
Action potential is generated
What are 4 major physiological ions?
Potassium, sodium, chloride and calcium
How do ions impermeable to the cell membrane get transported across it?
Transportation regulated by channels and pumps (ion channels)
What does the activity of ion channels lead to?
Uneven ionic distributions
Which ions are more abundant extracellularly?
Na+ and Cl-
Which ions are more abundant intracellularly?
K+
In which direction would calcium be transported?
Into the cell down its concentration gradient
What is the range of a RMP?
-40 to -90 mV
Which ions are important in the generation of neuronal action potential?
Na+ and K+
At RMP are VGSCs and VGKCs closed or open?
They are closed
What is membrane depolarisation?
Membrane potential becomes more positive leading to the opening of VGSC and VGKC
What leads to membrane repolarisation?
efflux of K+ from cells
Which channel opens faster?
VGSCs
What is the purpose of the Na+-K+-ATPase (pump)?
restoring the Na+ and K+ gradients
Why does myelin prevent the AP from spreading?
Myelin has high resistance and low capacitance
What are the areas where there are no myelin called?
Nodes of Ranvier (high concentration of sodium and potassium channels)
What happens in saltatory conduction?
AP jumps between Nodes of Ranvier to the presynaptic terminal
Much faster than cable transmission
What are the small gaps that exist between neurones known as?
Synapse
What does the synapse itself consist of?
pre-synaptic nerve terminal, which is separated from the postsynaptic cell by an extracellular space known as the synaptic cleft
Why is the electrical signal turned into a chemical signal?
So that it can cross the synapse (turns back into an electrical signal on the post-synaptic cell)
What does an action potential open at the presynaptic terminal?
voltage gated Ca2+ channels (influx via vesicle exocytosis)
What is released from the pre-synaptic terminal that binds to the post-synaptic terminal?
Neurotransmitter
How can you remove the neurotransmitter afterwards?
Enzymes (e.g. cholinesterase) break it down and allow re-uptake back into the pre-synaptic terminal
Outline chemical transmission at a synapse.
1) Propagation of the AP: AP is propagated by VGSCs opening. Na+ influx → membrane depolarisation → AP ‘moves along’ neurone. VGKC opening → K+ efflux → repolarisation
2) NT release from vesicles: AP opens VGCC at presynaptic terminal. Ca2+ influx → vesicle exocytosis
3) Activation of postsynaptic receptors - NT binds to receptors on post-synaptic membrane. Receptors modulate post-synaptic activity
4) NT reuptake - NT dissociated from receptor and can be: Metabolised by enzymes in synaptic cleft. Recycled by transporter proteins
Outline synaptic organisations between neurones.
Axodendritic synapse - Connection between presynaptic terminal → neuronal dendrite
Axosomatic synapse - connection between presynaptic terminal → neuronal soma
Axoaxonic synapse - connection between presynaptic terminal → neuronal axon
What is the NMJ?
Specialised structure incorporating axon terminal and muscle membrane allowing unidirectional chemical communication between peripheral nerve and muscle.
Describe communication between nerve and effector cells.
Paracrine - NT release
Outline transmission across NMJ.
AP propagated along axon → Ca2+ entry at presynaptic terminal
Ca2+ entry → ACh release into synapse
ACh binds to nicotinic ACh receptors (nAChR) on skeletal muscle → change in end plate potential (EPP)
Miniature EPP: quantal ACh release
What is sarcolemma?
Skeletal muscle membrane
nAChR activation → depolarisation -AP
What are T-tubules?
Continuous with sarcolemma and closely connected to SR
AP travels through T-tubules
Where is SR located?
Surrounds myofibrils (contractile units of muscle)
What is the function of SR?
Ca2+ storage → Ca2+ release following sarcolemma depolarisation
Effect: Ca2+ → myofibril contraction and muscle contraction
List and explain 3 disorders of the NMJ.
Botulism - Botulinum toxin - irreversible disrupts stimulation - induced ACh release from presynaptic nerve terminal
Myasthenia Gravis - Autoimmune disorder - antibodies directed against ACh receptor. Cause fatiguable weakness
Lambert-Eaton myastenic syndrome (LEMS) - Autoimmune disorder - Abs directed against VGCC
