Cells, synapses and neurotransmitters; Vision Flashcards
4 types of glial cells
Glial cells - provide support (chemical and physical) to neuronal cells
1. oligodendroglial cells (small dense dark circles on imaging)
- form the myelin sheath in the CNS, usually of several axons
- astrocytes (opaque lighter circles)
- help form BBB
- take up ions and neurotransmitters
- cover brain capillaries and parts of neurons - microglia (long and skinny, have weird hairs coming off them)
- originate in the blood and enter the brain during inflammation
- phagocytic activity - ependymal cells
- line surfaces of ventricles
- produce cerebrospinal fluid
components of a neuron
soma - main body
axon - extends from soma to synaptic terminal where info will be processed
dendrite - sensory “hairs” of neuron
cells in CNS vs PNS
CNS:
- oligodendrocyte
- astrocyte
- microglia
- neuron
PNS
- Schwann cell
- satellite glial cell
synaptic responses
excitatory post synaptic potential (EPSP)
- electrotonic response that decays with an exponential time course
- the last EPSP is larger because it happens before the previous EPSP has fully decayed
- channels and ions that create an EPSP: cation channels, or Na+
- glutamate: chief excitatory transmitter in CNS
inhibitory post synaptic potential (IPSP)
- postsynaptic cell is hyperpolarized
- result in increases in membrane permeability
- ions involved: K+ and Cl-
- GABA: chief inhibitory transmitter in adult CNS
absolute vs relative refractory period
absolute: Na+ is on coffee break, the cell is unable to generate a second action potential because there are not enough Na+ channels ready to open
relative: cell can generate a second action potential, but a stronger stimulus is required because some Na+ channels are inactivated AND K+ channels remain open
classes and examples of neurotransmitters
- Excitatory neurotransmitters (depolarization –> increases mV and crosses to positive voltage)
- acetylcholine: memory, learning, attention
- dopamine: happiness
- norepinephrine: fight or flight response
- glutamate: memory, cognition, mood regulation - Inhibitory neurotransmitters
- acetylcholine:
- serotonin: mood, sleep patterns, sexuality, anxiety, appetite and pain
- norepinephrine
- GABA:
acetylcholine in Alzheimer’s disease
- not enough acetylcholine (important for learning and memory)
- cholinesterase inhibitors increase the overall amount of acetylcholine available (drug) by blocking the action of acetylcholine, which breaks down acetylcholine
lens shape for achieving accomodation
- lens are a circular disk
- refractive power is 20 diopters, but can be increased to 34 diopters by making lens thicker
- it is connected to suspension ligaments which hold it in place
- contraction of ciliary muscle –> pulls ligament forward –> lens become thicker –> see things closer
- as we age, the flexibility of the lens decreases and thus we cannot see close as well
- solution is to make thick glasses which help see things close
organization of the retina
- retina is at the back of the eye, and the light it senses has been projected by the lens
from back of eye to front of retina
1. pigment layer
2. photoreceptor layer
3. outer nuclear layer
4. outer plexiform layer
5. inner nuclear layer
6. inner plexiform layer
7. ganglion cell layer
8. nerve fiber layer –> send signal through optic nerve
important parts of retina:
- optic disk - space where all the veins and arteries go, where ganglion cell axons exit the eye to form the optic nerve –> results in blind spot!
- macula lutea - yellow oval spot at the center of the retina, which is important for sharp, detailed central vision
- fovea - latin for “sinking point”, place where color is most specific and eye can sense things with high sensitivity because it is densely packed with only cones –> sits in the center of the macula lutea
comparing rods and cones
rods
- sensitive to light
- high sensitivity
- specialized for night vision (scotopic vision)
- high amplification; single photon detection
- slow response
- low acuity
- achromatic; one type of rod pigment (rhodopsin)
cones
- 3 different color cones (red, blue, green) which pick up on colors
- lower sensitivity - specialized for day vision (photopic vision)
- less amplification
- fast response
- more common in macula and fovea
neuronal pathway in vision
- light comes in and is projected by lens to the retina
- nasal retina (inner sides of eye) and temporal retina (outer sides of eye)
–> left sides of eye will connect to left brain
–> right sides of eye will connect to right brain - signal travels through optic nerve
- signal crosses at the optic chiasma –> fibers from nasal halves of retina have to cross
- fibers synapse in dorsal lateral geniculate nucleus (LGN) - important for relaying information to primary visual cortex via optical radiation AND “gate control” of information to primary visual cortex
diopter
measure of the power of a lens
- 1 diopter is the ability to focus parallel light rays at a distance of 1 meter
- eye has total refractive power of 59 diopters
signal transmission in the retina
- transmission of signals in retina is by electrotonic conduction
- the response is proportional to light intensity
- only the ganglion cells will fire the action potential to the brain
lateral inhibition
- horizontal cells only output inhibitory feedback
- horizontal cells inhibit the excitation of surrounding rods/cones to build contrast - contrast is enhanced with excitatory center and inhibitory surround
