Cells, Synapses, and Neurotransmitters Flashcards
List the 4 types of glial cells, and describe their function
- astrocytes
- hold neurons together in proper spatial relationship
- induce brain capillaries to form tight junctions for blood-brain barrier
- enhance synapse formation
- strengthen synaptic transmission via chemical signalling with neurons
- take up and degrade released neurotransmitters into raw materials
- take up excess K+ to maintain proper brain-ECF [ion] and regular neural excitability - oligodendrocytes
- creates myelin in CNS (found in white matter) - ependymal cells
- cells that line the internal, fluid filled cavities of the CNS
- helps create cerebrospinal fluid
- neural stem cells (can make new neurons and glial cells) - microglia
- immune cells of CNS (phagocytic savengers)
Describe the different cell types in the central and peripheral nervous system
IN CNS:
- neuron
- microglia
- astrocyte
- oligodendrocyte
IN PNS:
- schwann cell
- satellite glial cell
Briefly describe the classes of neurotransmitters and their receptors
- Acetylcholine (both)
Receptors:
- nicotinic acetylcholine (ionotropic)
- muscarinic acetylcholine receptor (metabotropic)
- Glutamate (excitatory)
Ionotropic Receptors:
a. NMDA
b. AMPA
c. Kainate
(allows flow of Na+ ions into the cell membrane –> depolarizes)
Metabotropic receptors (can be both inhibitory or excitatory)
- GABA (inhibitory)
Receptors
GABA-a (ionotropic)
- allows influx of Cl- (hyperolarizes neuron)
GABA-b (metabotropic)
- allows efflux of K+ (hyperolarizes neuron)
4.Serotonin (inhibitory)
Receptors (7):
6 G-coupled (metabotropic)
1 ligand gated ion channels (ionotropic)
Describe the effect of the interplay between excitatory and inhibitatory signals
Excitatory post synaptic potential (EPSP) –> depolarizes cell
- ANS: cation channels (Na+, K+, Ca2+)
- Glutamate: opens cation channels and is chief excitatory transmitter in CNS
Inhibitatory post synaptic potential (IPSP) –> hyperpolarizes cell
- K+ / Cl- ions
- GABA: opens Cl- channels and is chief inhibitory transmitter in CNS
- Temporal Summation
- successive EPSP/IPSP from same synapse add together (adding incentive + frequency) - Spatial Summation
- overlapping EPSP/IPSP from different distant synapses (peer pressure) - EPSP - IPSP cancellation
Describe how lens shape changes to achieve accommodation
Lens:
- Relaxed = spherical
- held by ligaments (when ligaments are relaxed, lens is flat)
Achieving accomodation:
- parasympathetic stimulation causes ciliary muscles to contract
- the suspensory ligaments are pulled forward == lens becomes thicker
Describe the organization of the retina
Composed of many layers:
(1 == at the back of the eye, 8 == closest to lens)
- pigment layer
- contains pigment epithelium - photoreceptor layer
- contains bases of rods and cones - outer nuclear layer
- contains the rest of the rods and cones - outer plexiform layer
- location of synaptic connections between photoreceptor cells and horizontal cells/ bipolar neurons - inner nuclear layer
- contains:
- amacrine cell: visual signal processing (feedback, averaging, noise reduction)
- bipolar neuron: translate light signals into electrical signals
- horizontal cell: “lateral inhibition” inhibitory feedback to rods/cones/and bipolar cells (only detects signal outputs from specific photorectpors) - inner plexiform layer
- location of synaptic connections between amacrine cell/ bipolar neuron and amacrine cell - ganglion cell layer
- (optic) nerve fiber layer
Compare the major features of rods and cones
Cones: see color
- common in fovea and macula
- three types of cones (red, blue, green)
- sensitive to direct light
- fast response (short integration)
- low amplification + sensitivitiy
Rods: see in low-light settings
- common in periphery
- one type of rod
- sensitive to scattered light
- slow response (low integration)
- high amplification + sensitivity (ability to see in dark)
Describe the neuronal pathway in vision
- Retina receives light signals
- travel through optic nerve
- Intersect at optic chiasm
- nasal retina nerves cross over and join fibers from the opposite temporal retina
- temporal retina does not cross sides - synpase at dorsal lateral geniculate nucleus (LGN) of thalamus
- LGN sends signals to primary visual cortex via optic radiation (relay)
Components (3) of a neuron
Components:
1. Soma (main body)
- Axon (effector)
- nerve fibre: initates, propagates, and transmits action potentials AWAY from soma - Dendrite (sensory)
- nerve fibre: conducts action potentials to the soma
Types of neurotransmitter receptors (2)
- Iontropic receptor
- cation / anion channels
- rapid response
- small molecular transmitters
Function: directly modulates ion activity in neurons by opening its channels - Metabotropic receptor (g-coupled)
- mutliple resonse
- prolonged responses
- neuropeoties
Functions of 2nd messenger:
a. opens channels
b. activates enzymes (both membrane and intercellular)
c. activates gene transcription
How does action potential cross the synaptic cleft?
- Stored in synaptic vesicles
- action potential reaches axon terminal –> pre-synaptic terminal opens voltage-gated Ca 2+ ions
- Ca 2+ influx into the cell and depolarizes it
- Ca 2+ binds to synaptotagmin –> causes the fusion of vesicles w/ pre-synaptic membrane
- neurotransmitter diffuses across synaptic cleft
- binds to receptors on post-synaptic cell membrane
Describe the steps required for the body to shut down a neurotransmitter signal
- enzymatic destruction of neurotransmitter
- diffusion away from receptors
- reuptake by transporters and sent to astrocytes or pre-synaptic cell
(ex.
Glutamine is taken up by glial cells via the excitatory amino acid transporters –> converted into glutamin by glutamase –> sent into presynaptic cell body to be made into glutamine)
Why do dendrites have few voltage gated Na+ channels?
Signal transmittion and summation
- transmits signals via electrotonic conduction (transmits via conduction in fluids)
- large spatial area allows for summation of signals
- voltage gated Na+ channels are primarily used for signal propagation therefore few are found in dendrites
Why does hyperpolarization occur?
Mechanical answer:
- voltage gated K+ channels (that were open to start repolarization), do not close quickly enough
- leads to extra K+ ions outside of the cell membrane –> hyperpolar environment
Results in a refractory period:
- Absolute
- cell unable to generate second action potential –> not enough Na+ channels can be open
- occurs during repolarization - Relative
- cell can generate second action potential but requires stronger stimulus –> some Na+ channels are inactive
- occurs during hyperpolarization
Why is accomodation important?
diopter: measure of power of lens (1 diopter = ability to focus parallel light rays at dist of 1 m; large diopter = ability to focus at smaller dist)
Accomodation: changing the diopter of the lens by modifying its thickness
- used to help focus images on retina
