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Neuroscience Test 1
Lectures 1-7
190
Anatomy
Undergraduate 3
02/12/2013

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Cards

Term
What are the two major divisions of the Nervous System?
Definition

Central (CNS): neurons whose cell bodies, axons, & dendrites lie entirely within the cranium or vertebral canal

 

Peripheral (PNS): neurons that link the CNS to the peripheral tissues/organs

Term
What makes up the CNS?
Definition
brain and spinal cord
Term
What makes up the PNS?
Definition
nerves connecting CNS to muscles & organs
Term
List the 3 Functional Classes of neurons:
Definition
sensory, motor, & interneurons
Term
Define sensory:
Definition
sensory receptors TO the CNS
Term
Define motor:
Definition
FROM the CNS to muscles & organs
Term
Define interneurons:
Definition
connections w/n CNS
Term
What are the 2 branches of the PNS?
Definition
somatic & autonomic
Term
What are the 2 branches of the autonomic system?
Definition
sympathetic & parasympathetic
Term
List the four regions of the brain:
Definition
  • cerebral hemispheres (cerebrum)
  • Diencephalon
  • Brainstem
  •  Cerebellum
Term
Define Rostral:
Definition
toward the nose (anterior)
Term
Define Caudal:
Definition
toward the tail (posterior)
Term
Define dorsal:
Definition
superior
Term
Define ventral:
Definition
inferior
Term
What are the characteristics of the cerebral hemispheres?
Definition
largest part of brain
2 hemispheres separated by longitudinal cerebral fissure
cavity in each hemisphere = lateral ventricle
connected by transverse fiber bundle (corpus callosum)
Term
Define sulci:
Definition
grooves on surface of cerebral hemispheres
Term
Define gyri:
Definition
twisted elevated ridges b/n sulci
Term
Define fissures:
Definition
deep grooves that separate major regions of brain
Term
What does the transverse fissure separate?
Definition
cerebrum & cerebellum
Term
What does the longitudinal fissure separate?
Definition
cerebral hemispheres
Term
What are the five lobes of the cerebral hemispheres?
Definition
  1. frontal
  2. temporal
  3. parietal
  4. occipital
  5. limbic
Term
What is the frontal lobe responsible for?
Definition
  • higher mental function (judgment, planning, reason, conscience)
  • speech & language center
Term
What is the temporal lobe responsible for?
Definition
memory, hearing, & speech
Term
What is the parietal lobe responsible for?
Definition
perception
Term
What is the occipital lobe responsible for?
Definition
visual cortex
Term
What is the limbic lobe responsible for?
Definition
emotion & motivation (particularly in reference to survival)
Term
What are the three main parts of the Diencephalon?
Definition
epithalamus, thalamus, & hypothalamus
Term
Describe the physiology of Thalamus:
Definition
  • relay station for sensory impulse
  • transfers impulse to correct part of cortex for localization & interpretation
Term
Describe the physiology of Hypothalamus:
Definition
  • autonomic nervous system center
  • regulates body temp & metabolism
  • controls water balance
  • hunger center
  • limbic system (i.e. emotions)
  • where pituitary gland attached

 

Term
Describe the physiology of Epithalamus:
Definition
  • forms roof of 3rd ventricle
  • houses pineal body & endocrine gland
  • includes choroid plexus
  • forms cerebrospinal fluid 
Term
What are the three subregions of the Brainstem?
Definition
midbrain, pons, & medulla oblongata
Term
What are additional features that make up the brainstem?
Definition
  • gray matter (sensory & motor nuclei of cranial nerves)
  • white matter nerve tracts
  • 3rd & 4th ventricles
  • cerebral aqueduct
Term
Describe the physiology of Cerebellum:
Definition
  • maintenance of balance, posture, & coordination
  • timing & strength of muscle contractions
Term
What is the purpose of meninges and what are its three layers?
Definition

provide protection of brain & spinal cord

 

 

dura mater, arachnoid, & pia mater

Term
Define dura mater:
Definition
outermost & heaviest layer of meninges
Term
Define epidural space:
Definition
space above dura mater that contains fat
Term
Define subdural space:
Definition
space b/n dura & arachnoid
Term
Define arachnoid:
Definition
thin, membranous covering that does not conform to the irregularities of surfaces
Term
Define subarachnoid space:
Definition
space under arachnoid that contains cerebrospinal fluid
Term
Define pia mater:
Definition
thin, membranous covering that adheres smoothly to surface & confokms to all irregularities of surfaces
Term
At spinal levels, what does the pia mater do?
Definition
gathers laterally, pierces arachnoid, & attaches to dura which stabilizes the spinal cord
Term
Characteristics of cerebrospinal fluid:
Definition
  • similar in content to blood, but less protein
  • maintains balance of extracellular fluid in brain
  • about 400 mL/day of CSF circulates through ventricular system then drains into venous circulation
Term
Define blood brain barrier:
Definition

protective feature composed of extensive capillaries & sinuses that:

 

  • protects brain from hormones & circulating chemicals
  • has tight junctions to limit permeability
  • has astrocyte processes to secrete paracrines
  • has glucose transporters 
Term
Define a neuron and its function:
Definition
cell specialized for rapid communication that receives info in the form of electrochemical signals from 1 neuron & relays it to the next in sequence
Term
Describe the structural characteristics of a neuron:
Definition
  • cell body (soma)
  • specialized slender processes (axons/dendrites)
  • receptive/input region (dendrites/soma)
  • conducting component (axon)
  • secretory/output region (axon terminal)
Term
What are glial cells?
Definition
neuroglia are support cells for every neuron (10-50 per)
Term
List the subclasses of glial cells in the CNS:
Definition
  • astrocytes
  • oligodendrocytes
  • microglia
  • ependymal cells 
Term
List the subclasses of glial cells outside the CNS (periphery):
Definition
  • Schwann cells
  • satellite cells

 

Term
Define astrocytes:
Definition

help neurons survive by providing structural & metabolic support

 

(this can include taking up excess K+ & neurotransmitters)

Term
Define oligodendrocytes:
Definition
help insulate axons (aka myelination)
Term
Define microglia:
Definition
immune defense cells related to macrophages
Term
Define ependymal cells:
Definition
line fluid-filled ventricles where CSF circulates w/n CNS
Term
Define Schwann cells:
Definition
myelinate or support axons in peripheral nerves
Term
Define satellite cells:
Definition
support nerve cell bodies in peripheral ganglia (collections of neurons outside CNS)
Term
Define nerve:
Definition

bundles of neurons that form discrete white, flat, or circular threads visible to naked eye in PNS

 

(usually include sensory & motor fibers)

Term
Define tract:
Definition
  • comparable to nerve, except runs w/n CNS
  • composed of bundles of axons of interneurons
  • either ascending or descending

 

Term
Describe the arterial supply to the brain:
Definition

Internal carotid artery:

  • arises in neck
  • enters cranial cavity via carotid canals
  • terminates as anterior & middle cerebral arteries
  • joined to posterior cerebral artery by posterior communicating artery 
Term
What are the areas supplied by the anterior cerebral artery?
Definition
  • medial brain
  • superior brain
  • frontal pole
Term
What are the areas supplied by the middle cerebral artery?
Definition
  • lateral brain
  • temporal pole 
Term

What are the areas supplied by the posterior cerebral artery?

 

Definition
  • inferior brain
  • occipital pole 
Term
How many pairs of spinal nerves are there in the spinal cord?
Definition

31 pairs

 

(1 less cervical vertebra than cervical spinal nerves)

Term

What are the enlargements of the spinal cord and what are they due to?

 

Definition
  • cervical (C5-C8) & lumbosacral (L4-S1)
  • due to large # of axons entering & leaving spinal cord to innervate the extremities
Term
Define conus medullaris:
Definition
  • "medullary cone"
  • terminal end of spinal cord
  • near lumbar vertebral levels 1 & 2
Term
Define cauda equina:
Definition
  • continuation of spinal nerves as dangling nerve roots after spinal cord tapers out
Term
Define filum terminale:
Definition
terminal nerve root tail
Term
Define gray matter:
Definition

integrates information

 

= cell bodies, neuroglia, unmyelinated axons, & dendrites of motor neurons

Term
What are the three kinds of gray matter horns?
Definition
  1. posterior horn
  2. lateral horn
  3. anterior horn

(all shaped like an "H")

Term
Define white matter:
Definition
  • information travels to and from brain
  • myelinated axons
  • white matter of spinal cord divided into columns/funiculi by gray matter horns
Term
What are the three kinds of white matter columns/funiculi?
Definition
  1. anterior white columns
  2. posterior white columns
  3. lateral white columns

(all columns contain tracts that carry information)

Term
Define ascending tracts:
Definition
sensory; carry information TO brain
Term
Define descending tracts:
Definition
motor; carry signals FROM brain
Term
Characteristics of tactile corpuscles:
Definition
  • aka Meissner's corpuscles
  • type of mechanoreceptor
  • responsible for sensitivity to light touch
  • skin; especially fingers & lips
Term
Characteristics of Kraus end bulbs:
Definition
  • bulbous capsules in the skin containing sensory nerve endings
  • can be mechanoreceptors or thermoreceptors
  • sensitive to cold (< 20 C)
Term
Characteristics of lamellated corpuscles:
Definition
  • aka pacinian corpuscle
  • numerous small oval bodies
  • sensitive to pressure
  • concentric layers of connective tissue
Term
Characteristics of free nerve ending:
Definition
  • unspecialized, afferent nerve ending
  • cutaneous receptors
  • used by vertebrates to detect pain in skin
Term
Characteristics of Merkel discs:
Definition
  • aka Merkel's corpuscle
  • disklike expansion of nerve fiber end
  • tactile function
  • associated w/ sense of light touch to discriminate shapes & textures
Term
Define Merkel cells:
Definition

oval receptor cells found in the skin of vertebrates that have synaptic contacts w/ somatosensory afferents

 

(associated w/ Merkel discs)

Term
What is the structural classification of neurons?
Definition
multipolar neurons, bipolar neurons, & unipolar neurons
Term
Define multipolar neurons:
Definition
  • most common
  • includes interneurons & motor neurons
Term
Define bipolar neurons:
Definition
restricted to a few special sense organs such as the retina for vision (also in olfactory pathway)
Term
Define unipolar neurons:
Definition
peripheral somatic sensory neurons such as from skin & muscles in limbs
Term
What are the three components of the PNS?
Definition
  1. Peripheral Nerves
  2. Ganglia
  3. Nerve Plexuses
Term

What are the somatic and visceral components of peripheral nerves?

 

(spinal: 31 & cranial: 12)

Definition

Somatic:

supply the sensory & motor innervation of skin & muscle

 

 

 

Visceral:

supply the sensory & motor innervation of internal organs

 

 

Term
Define ganglia:
Definition
clusters of nerve cell bodies located entirely outside the CNS
Term
Define nuclei:
Definition
clusters of nerve cell bodies located entirely within the CNS
Term
Describe the two branches of ganglia:
Definition
  • Somatic - (sensory only); dorsal root ganglia
  • Autonomic - (motor to viscera); paravertebral, prevertebral, & enteric
Term
Define nerve plexuses:
Definition
networks of nerves formed from ventral primary rami
Term
What are the branches of the nerve plexuses:
Definition
  • cervical
  • brachial
  • lumbar
  • sacral
  • coccygeal
Term
Define afferent:
Definition
carrying information INTO the CNS from receptors
Term
What are the afferent branches of the PNS?
Definition
  • General somatic - skin, sensors, body positions
  • Special somatic - vision, hearing, balance
  • General visceral - organ distention
  • Special visceral - taste, smell
Term
Define efferent:
Definition
carrying information OUT of the CNS to effectors
Term
What are the efferent branches of the PNS?
Definition
  • General somatic - to skeletal muscle
  • General visceral - to smooth, cardiac muscle
  • Special visceral - to facial & speaking muscle
Term
The Autonomic Nervous System is classified into what divisions?
Definition
  • parasympathetic
  • sympathetic
  • enteric
Term
What is the function of the Autonomic Nervous System?
Definition
  • maintain homeostasis
  • fight or flight response
  • rest & digest response
Term
Characteristics of the Sympathetic Nervous System:
Definition
  • fight or flight
  • release adrenaline & noradrenaline
  • increase heart rate, blood pressure, & blood flow to skeletal muscles
  • inhibition of digestive functions
Term
Characteristics of the Parasympathetic Nervous System:
Definition
  • rest & digest
  • calms body to conserve/maintain energy
  • lowers heart & breathing rates
  • lowers blood pressure
Term
Autonomic Differences in relation to eyes:
Definition
  • Sympathetic - pupils dilate
  • Parasympathetic - pupils constrict
Term
Autonomic Differences in relation to salvation:
Definition
  • Sympathetic - decreases
  • Parasympathetic - increases
Term
Autonomic Differences in relation to skin:
Definition
  • Sympathetic - perspires
  • Parasympathetic - dries
Term
Autonomic Differences in relation to respiration:
Definition
  • Sympathetic - increases
  • Parasympathetic - decreases
Term
Autonomic Differences in relation to heart:
Definition
  • Sympathetic - accelerates
  • Parasympathetic - slows
Term
Autonomic Differences in relation to digestion:
Definition
  • Sympathetic - inhibits
  • Parasympathetic - activates
Term
Autonomic Differences in relation to adrenal glands:
Definition
  • Sympathetic - secretes stress hormones
  • Parasympathetic - decreases secretion of stress hormones
Term
Define preganglionic neurons:
Definition
originate in the brainstem & spinal cord
Term
Define postganglionic neurons:
Definition
originate peripherally in an autonomic ganglion
Term
Where are the sympathetic autonomic ganglion located?
Definition
some distance from the organ they innervate, close to CNS
Term
Where are the parasympathetic autonomic ganglion located?
Definition
in, on, or near the tissues/organs they innervate
Term
The Sympathetic preganglionic fibers use what neurontransmitter?
Definition
Acetylcholine
Term
The Sympathetic postganglionic fibers use what neurontransmitter?
Definition
Norepinephrine
Term
The Parasympathetic preganglionic fibers use what neurontransmitter?
Definition
Acetylcholine
Term
The Parasympathetic postganglionic fibers use what neurontransmitter?
Definition
Acetylcholine
Term
What are the three types of eyes?
Definition
simple, complex, & compound
Term
Define simple eyes:
Definition
  • detect whether it is light or dark
  • have a single lens
Term
Define complex eyes:
Definition
can detect color, motion, depth, height, width, length, & distance
Term
Define compound eyes:
Definition
  • found in insects, crustaceans, arachnids, & other multi-jointed legged creatures
  • combine what they see into single image or multiple images
Term
What are the three main coats (tunics) of the human eye?
Definition
  1. fibrous coat - cornea, sclera
  2. vascular coat - choroid, ciliary body, & iris
  3. retina
Term
Anatomy of the Sclera:
Definition
  • tough, white outer coat of eyeball covering approximately the posterior 5/6ths of surface
  • continuous anteriorly w/ cornea & posteriorly w/ external sheath of optic nerve
  • forms principal part of outer fibrous coat
Term
Physiology of Sclera:
Definition
  • protects intraocular contents
  • maintains shape of the globe when distended by intrinsic intraocular pressure
  • relatively avascular, has irregular connective tissue, & matrix collagen
Term
Anatomy of Cornea:
Definition
  • transparent part of the coat of the eyeball that covers the iris & pupil
  • transparency due to regularity & smoothness of epithelium covering, avascularity, & components of stroma
Term
Physiology of Cornea:
Definition
  • responsible for most of eye refraction
  • admits light to interior
  • refracts light, yielding 2/3rds of eye's optical power
Term
What is the nerve supply of the Cornea?
Definition
sensory fibers form ophthalmic division of trigeminal via long ciliary nerves
Term
Anatomy of Choroid:
Definition
vascular layer of eye lying b/n retina & sclera
Term
Physiology of Choroid:
Definition
  • provides oxygen & nourishment to outer layers of retina
  • along w/ ciliary body & iris, forms uveal tract
Term
Physiology of the Iris:
Definition
reponsible for controlling the amount of light entering the eye by controlling the diameter of the pupil
Term
Anatomy of Ciliary Body:
Definition
  • composed of ciliary muscle & ciliary processes
  • ciliary muscles attached to the lens by connective tissue structure called zonule of Zinn
Term
Physiology of Ciliary Body:
Definition
controls the shape of the lens via the muscles & the production of aqueous humor via the epithelial cell coating
Term
What are the two types of photoreceptors in the retina?
Definition
rods & cones
Term
Characteristics of Rods:
Definition
  • responsible for black & white vision
  • low light levels
  • more numerous (120 million)
  • chemical is rhodopsin
Term
Characteristics of Cones:
Definition
  • responsible for color vision
  • high light levels
  • less numerous (6-7 million)
  • chemical is one of three cone pigments
Term
What are the four functional segments of Rods & Cones?
Definition
  1. Outer segment - contains chemicals that decompose upon exposure to light & excite nerve fibers leading to optic nerve
  2. Inner segment
  3. nucleus
  4. synaptic body
Term
What is the Optic Nerve?
Definition
  • made up of continuation of axons & ganglion cells
  • transmits visual information from the retina to brain
Term
What is the Macula Lutea?
Definition
  • yellowish circle in the center of the retina
  • responsible for clear, distinct vision
  • sharp visual acuity
Term
What is the Fovea Centralis?
Definition
  • lies within the macula lutea
  • area with only cones
  • responsible for sharpest visual acuity
Term
What is the Optic Disc?
Definition
  • small circular region of retina where axons of the ganglia (as fibers of the optic nerve) emerge from the eyeball
  • contains no rods or cones
  • optically insensitive
  • aka blind spot
Term
Anatomy of Vitreous Body:
Definition
  • transparent jelly-like substance behind the lens
  • largest structure of the eye (80% of globe)
  • unique connective tissue
  • up to 98.5% water
  • spherical shape
Term
Physiology of Vitreous Body:
Definition
allows for light to pass through & gives rigidity
Term
What is the Anterior Chamber?
Definition
  • b/n the iris & corneal endothelium (most inner surface of cornea)
  • filled w/ aqueous humor produced by epithelium of ciliary body
Term
What is the Aqueous Humor?
Definition
  • nourishes cornea & lens
  • secreted by the ciliary body
Term
What is the Posterior Chamber?
Definition
  • behind edge of iris & suspensory ligaments of lens & ciliary processes
  • aqueous humor first passes through here on its way to the anterior chamber
  • is not the vitreous chamber
Term
Define Canal of Schlemm:
Definition
canal in anterior chamber through which aqueous humor is delivered to it by the systemic circulation
Term
What is Trabecular Network?
Definition
  • spongy tissue around base of cornea near ciliary body
  • guards the entrance to the Canal of Schlemm
  • responsible for most of resistance to flow of aqueous humor through the canal
Term
Characteristics of a Visual Field:
Definition
  • part of the world seen by the patient with both eyes and looking straight ahead
  • total area that can be seen in peripheral vision when the eyes are focused on a central point
Term
Define the binocular zone:
Definition
seen by both eyes; overlapping
Term
Define monocular zone:
Definition
seen only by corresponding eye
Term
How is the visual field divided?
Definition
into hemifields - nasal & temporal halves, each of which is divided into upper & lower parts (results in quadrants)
Term
Describe how the retinotopic map works:
Definition
  • light from the right visual world strikes the left temporal and right nasal retinas
  • light from inferior world strikes superior retina (and vice versa)
Term
What is the Receptive Field?
Definition
  • region of the visual field whose stimulation affects the activity of a single neuron
  • arranged in central area (center) & concentric circle (surround) which respond oppositely to light
  • detects edges & contrast (i.e. center is depolarized so surround is hyperpolarized)
Term
Characteristics of the Visual Cortex:
Definition
  • almost 1/2 of cerebral cortex devoted to processing visual information
  • located in occipital lobe
  • 2 broad divisions are primary & secondary visual cortexes

 

Term
How does the visual cortex work?
Definition
  • left visual cortex receives input from right visual field (& vice versa)
  • superior cortex receives input from interior visual field (& vice versa)
Term
What are the two pathways out of the visual cortex?
Definition
  1. Mangocellular - "Where?" : conceptualising movement of objects & their position in space
  2. Pavocellular - "What?" : detailed visual information used for the recognition of objects
Term
Define Conjugate Eye Movements:
Definition
motor coordination of eye movement such that both eyes remain focused on a single object
Term
Characteristics of Binocularity/Binocular Vision:
Definition
  • in animals w/ 2 forward-facing eyes
  • 2 retinal images go through series of sensory & motor processes resulting in the perception of singleness & depth
Term
What components aid in the effectiveness of binocular vision?
Definition
  • two corresponding retinal points (2 foveae)
  • retinotopic mapping
  • 6  EOM in each eye create version
  • visual motor feedback (i.e. fusion)
  • medial rectus contraction & lateral rectus relaxation
Term
What is stereopsis?
Definition
  • sensation for depth
  • ability to perceive the relative distances of separate objects
  • judgement of distance/depth can occur w/ monocular cues
  • refers exclusively to binocular retinal disparity
Term
Define wavelength discrimination:
Definition

color vision is the result of absorption of light by different classes of cones

 

  • short (S-cones): 440nm
  • middle (M-cones): 545nm
  • long (L-cones): 565 nm
Term
Define spatial resolution:
Definition
measure of visual acuity or the ability of the eye to see fine detail
Term
Define depth perception:
Definition
the ability to perceive the world in 3-dimensions; both binocular clues (stereopis & parallax) & monocular clues (perception of size)
Term
What is temporal discrimination?
Definition
  • when eye samples information of images on retina, info is integrated so the objects appear to be stable
  • intermittent stimuli can be perceived as separate or continuous depending on rate
  • slow rate = perceived as separate; image stays on but changes in intensity (flicker)
Term
Define refraction:
Definition

the change in direction of a ray of light (i.e. bending) when passing from one medium to another

 

the eye refracts light to create an image on the retina

Term
How is Nearsighted Vision Corrected?
Definition
To correct for myopia in which light rays are focused in front of the retina, a concave lens is used
Term
How is Farsighted Vision corrected?
Definition
In order to correct for hyperopia in which light rays are focused behind the retina, a convex lens is used
Term
Define simple diffusion:
Definition
movement of a molecule (typically oxygen, carbon dioxide, or water) from an area of high concentration to an area of low concentration
Term
Define facilitated diffusion:
Definition
  • similar to simple diffusion, but process is aided by a protein which functions as a pump or channel
  • protein responds to its binding molecule (ligand)
Term
How is a channel opened or gated?
Definition
  • gated channel is opened by various signals & named for those
  • initiating stimulus can be an electric current, ligand, or mechanical stress
Term
Define Active Transport:
Definition
  • molecule is pumped from area of low concentration to an area of high concentration
  • requires expenditure of energy in the form of ATP
Term
What is signal transduction?
Definition
  • process that occurs from receptor activation to cellular response
  • signal generally a molecule which binds specifically to a protein receptor (that be intra- or extra- cellular)
Term
What happens to a molecule that can pass through the cell membrane?
Definition
the molecule binds to an intracellular receptor & eventually affects protein synthesis at the DNA level
Term
What happens to a molecule that cannot pass through the cell membrane?
Definition
the molecule binds to an extracellular membrane receptor which is linked by a cytoplasmic transducer
Term
Describe the process known as signal cascade:
Definition
  • activated transducer stimulates primary effector which stimulates production of second messenger
  • second messenger stimulates secondary effector
  • initiates series of steps...eventually leads to cellular response
Term
The transducer is usually a what?
Definition
G-protein
Term
The secondary effector is usually a what?
Definition
protein kinase (enzyme which phosphorylates specific proteins)
Term
Why is the method of signal transduction said to have the property of amplication?
Definition
  • a phosphorylated protein can activate a different protein kinase & so on until cell effect achieved
  • each signal molecule can activate thousands of second messengers
Term
What is a common second messenger system?
Definition
Guanylate cyclase - cGMP system
Term
Describe the processes of the cGMP system:
Definition
  1. signal molecules bind to receptor initiating activation of G-protein
  2. G-protein activates guanylate cyclase which catalyzes formation of cGMP from GTP
  3. cGMP is second messenger
  4. enzyme phosphodiesterase hydrolyzed cGMP, destroys it, & ends process
Term
Differentiate betwen the outer and inner segments of rods & cones:
Definition
  • connected through thin connecting cilium
  • outer filled w/ dense stack of membrane discs
  • discs carry visual pigment & other transduction components
  • inner contains endoplasmic reticulum & Golgi & packed with mitochondria
Term
Characteristics of Phototransduction with respect to darkness:
Definition
  • synaptic terminal transmits light signal to 2nd order neurons in the retina (bipolar & horizontal cells)
  • in darkness: steady inward current through cation conductance on outer-segment membrane
  • this depolarizes rod/cone & maintains synaptic release of glutamate
Term
Characteristics of Phototransduction with respect to light:
Definition
  • light closes cation conductance (consists of cGMP-gated channels) to stop dark current
  • produces membrane hyperpolarization which decreases/terminates dark glutamate
Term
Describe the photochemistry of vision with respect to the Na+/K+ Channel:
Definition
  • Na+/K+ pump on inner segment of rod
  • pumps 3 Na+ out for every 2 K+ in (results in inside negative charge)
  • outer segment contains Na+ channels; when open allow Na+ to travel down gradient into this portion of cell (negates much of charge)
Term
How are Na+ channels opened?
Definition
  • open under dark conditions
  • resulting charge about -40 mV (average is -70 mV)
Term
What happens when rhodopsin is exposed to light?
Definition
  • Na+ permeability is decreased but Na+ is still being pumped out
  • results in greater inside negativity of the cell
  • this is known as hyperpolarization
Term
Define hyperpolarization:
Definition
electrical signal transmitted by the ganglion cells to the optic nerve
Term
Describe the overall conversion/decay of Rhosopsin:
Definition
  • Rhodopsin (scotopsin + 11-cis-retinal) absorbs light
  • converted to bathorhodopsin
  • this decays to lumirhodopsin
  • further decays to metarhodopsin I then metarhodopsin II
  • this splits completely into scotopsin and all-trans-retinal
Term
Describe the overall conversion/formation of Rhosopsin:
Definition
  • rhodopsin all-trans-retinal converted to 11-cis-retinal via retinal isomerase
  • this combines w/ scotopsin to make rhodopsin
Term
What is transducin?
Definition
a protein present in the celll membrane that is activated by the catalyzation of Metarhodopsin II
Term
Activated transducin activates what?
Definition
phosphodiesterase
Term
What happens when phosphodiesterase hydrolyses cGMP?
Definition
  • it destroys it
  • since cGMP was holding Na+ channels of outer segment open, the channels close resulting in hyperpolarization
Term
What happens after Na+ channels close and hyperpolarization?
Definition
  • within seconds, rhodopsin kinase inactivates the activated rhodopsin & entire process reverses
Term
When does Amplication occur?
Definition
at the level of transducin activation, phosphodiesterase activation, & cGMP hydrolysis
Term
A single photon of light results in what?
Definition
the inhibition of the influx of millions of Na+ molecules
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