APPP 02: Gross Anatomy of the CNS – Gross Anatomy and Cellular Anatomy Flashcards
What are the major cell types of the CNS? (3)
- neurons
- glial cells
- cells of the blood brain barrier (BBB)
What is the basic unit of the nervous system?
nerve cell (neuron)
Describe the structure of nerve cells (neurons).
- cell body: contains nucleus and cytoplasm, site of transcription and translation
- dendrites: (nerve fibre) branched extensions of cell body, function to conduct impulses towards the cell
- axon: (nerve fibre) one elongated extension, functions to send messages as electrical impulses
What are oligodendrocytes?
myelinating glia of the central nervous system
- extend dendritic processes and wrap around the axon of nerve fibres to create myelin sheaths
- myelin is unique among plasma membrane equivalents in its usually high lipid content (around 70%)
What is the function of myelin?
insulates and supports CNS axons
- insulation increases the speed of nerve conduction
- results in the accumulation of voltage-gated Na+ channels at the nodes of Ranvier
What are nodes of Ranvier?
gaps on the axon in between the myelin sheaths
Defects in myelination and myelin structure have been observed in what population?
adults exposed to cocaine, cannabinoids, alcohol, methamphetamines
- affects nerve conductivity
- usually reversible, but depends on the length of drug use
- high dose of cannabinoids deteriorates myelination (causes inflammation), but low dose supports myelination
What is multiple sclerosis (MS)?
immune-mediated destruction of myelin that results in interrupted electrical nerve signals
- the most common demyelinating disease of the CNS
What are the symptoms of multiple sclerosis (MS)?
- numbness
- weakness
- cognitive difficulties
What is the therapy for multiple sclerosis (MS)?
aimed at slowing disease progression and improving quality of life
- high-dose corticosteroids are used to dampen inflammation
What are the 3 most common neuron structures?
- multipolar neuron
- bipolar neuron
- pseudounipolar neuron
What are multipolar neurons?
characterized by one axon and many dendrites that can originate from different regions of the cell body
- vary greatly in size, shape, and complexity of their dendritic tree
- the most common type of neuron in the central nervous system – ie. motor neurons
What are bipolar neurons?
two processes – one axon, one dendrite
- dendrite that receives signals usually from the periphery and an axon that propagates the signal to the central nervous system
- found in sensory organs – ie. retina, olfactory epithelium, auditory system
- least common type of neuron
What are pseudounipolar neurons?
variations of bipolar neurons – have two processes which fuse during their development into one short common axon
- axon splits into one branch that terminates in the periphery while the second branch terminates in the spinal cord – this way, stimuli from the periphery bypass the cell body and reach the axon terminal without delay
- found in sensory ganglion of cranial and spinal nerves
What are the 3 classifications of neurons?
(based on function)
- sensory neurons
- motor neurons
- interneurons
What is the function of sensory neurons?
convey signals from sensory receptors to the CNS via afferent nerves
What is the function of motor neurons?
convey information from CNS or ganglia to effector cells via efferent nerves
What is the function of interneurons?
form a communicating network between sensory and motor neurons
- make up > 99.9% of all neurons
Briefly describe the flow of information through neurons.
communication between neurons in the CNS occur through synapses
- dendrites collect
- cell body integrates
- axon passes
What are the 3 main types of ion channels and receptors that control synaptic transmission?
- voltage-gated ion channel
- ligand-gated ion channel
- metabotropic receptor
What are voltage-gated channels?
- respond to changes in membrane potential
- directly opens ion channels
What are ligand-gated channels?
- respond to neurotransmitters
- directly opens ion channels
What are metabotropic receptors?
- respond to neurotransmitters
- indirectly opens ion channels
Describe the membrane potential at resting state of a neuron.
- all voltage-gated Na+ channels and most voltage-gated K+ channels closed
- resting membrane potential: -70 mV
- Na+/K+ transporter pumps K+ ions into the cell and Na+ ions out
- inside net negative
- outside net positive
How does an action potential get generated?
- ligands bind receptors (ligand-gated ion channel or metabotropic receptor)
- changes to membrane potential as channels open
- when net charge increases to -55 mV, this sensitizes Na+ voltage-gated ion channels
- concentration of Na+ channels at axon hillock initiates action potential
- depolarization spreads down the axon, repolarization follows
- depolarization of presynaptic terminal opens Ca2+ channels, resulting in neurotransmitter release
How do voltage-gated Na+ ion channels work?
- open at -55 mV
- inactivated at +40 mV
- after inactivation, it takes time for the protein to return to resting state (unavailable for reactivation)
How do voltage-gated K+ ion channels work?
- slow to open
- once open, K+ flows out
- causes hyperpolarization
- occurs during repolarization stage
What do Na+/K+ pumps do?
active transport ions to maintain resting levels
How does synaptic transmission occur?
- Ca2+ binds to specific proteins (SNARE proteins), which triggers the complete fusion of the vesicle with the target membrane
- this results in neurotransmitter release from vesicles at the terminal bouton into the synaptic cleft, and either activation or inhibition of the neuron
How does vesicle loading (monoamine/amino acid) occur?
- carrier vesicles containing membrane transporter proteins are moved along microtubules
- small molecule (ie. acetylcholine) produced in the cell are taken into vesicles
- loaded vesicles are store at the presynaptic membrane
- depolarization leads to docking of vesicles and exocytosis into the synapse
What is orexin?
one of the many neuropeptides functioning in the CNS
Neurotransmitters
Dopamine
- mechanism
- type
- mechanism: inhibitory or excitatory
- type: monoamine
Neurotransmitters
Norepinephrine
- mechanism
- type
- mechanism: inhibitory or excitatory
- type: monoamine