Exam 1 Flashcards
Brain Lobes
Lobes:
Names of folds on brain
- gyri
- sulci
- fissures
Bell and Magendie
Dorsal and ventral roots carry information in opposite directions
Galen
- Cerebrum = sensation
- cerebellum = motor
- ventricles = ‘communicating fluids’
Hippocrates
Believed the brain was the seat of intelligence and involved in sensation.
–Charles Bell
- Cerebellum: Origin of the motor fibers
- Cerebrum: Destination of sensory fibers
–Marie-Jean-Pierre Flourens
•Experimental ablation method
–Paul Broca
•Discrete region of the human cerebrum for speech
–Franz Joseph Gall
•Phrenology: Bumps on the surface of skull reflect brain surface and related personality traits
SUPER WRONG
Goal of neuroscience
•To learn how the nervous system functions
–Brain’s activity reflected in behavior
–Computer-assisted imaging techniques
–New treatments for nervous system disorders
–Non-invasive methods
– Experiments in live tissue
–Levels of analysis
- Molecular
- Cellular
- Systems
- Behavioral
- Cognitive
Glia
Insulates, supports, and nourishes neurons
–Neurons
- Process information
- Sense environmental changes
- Communicate changes to other neurons
- Command body response
–The Nissl Stain
•Facilitates the study of cytoarchitecture in the CNS
•Golgi-stain (Developed by Camillo Golgi) shows two parts of neurons:
–Soma and perikaryon
–Neurites: Axons and dendrites
•Differences between the cytoplasm of axon terminal and axon
- No microtubules in terminal
- Presence of synaptic vesicles
- Abundance of membrane proteins
- Large number of mitochondria
•Classification Based on Dendritic and Somatic Morphologies
–Stellate cells (star-shaped) and pyramidal cells (pyramid-shaped)
–Spiny or aspinous
Classification based on –Based on axonal length
- Golgi Type I (projection neurons)
- Golgi Type II (local interneurons)
•Astrocytes
–Most numerous glia in the brain
–Fill spaces between neurons
–Influence neurite growth
–Regulate chemical content of extracellular space
•Myelinating Glia
–Oligodendroglia (in CNS)
–Schwann cells (in PNS)
–Insulate axons
4 Important points Equilibrium Potentials
- Large changes in Vm
- Miniscule changes in ionic concentrations(Q=CV)
- Net difference in electrical charge
- Inside and outside membrane surface
- Rate of movement of ions across membrane
- Proportional Vm – Eion
- Concentration difference known: Equilibrium potential can be calculated
–Inside positively charged relative to outside
The Nernst Equation
E =61.5 mV log ([Ion]o /[Ion]i)
• The Distribution of Ions Across The Membrane
–K+ more concentrated on inside, Na+ and Ca2+ more concentrated outside
Na-K Pump
Ca2+ pump actively pumps calcium out of cell
Membrane @ Rest
–Selective permeability of potassium channels - key determinant in resting membrane potential
–Resting membrane potential is close to EK because it is mostly permeable to K+
–Membrane potential sensitive to extracellular K+
–Increased extracellular K+ depolarizes membrane
–Oscilloscope to visualize an AP
image
The Action Potential, In Theory
- Depolarization (influx of Na+) and repolarization (efflux of K+)
- Membrane Currents and Conductances
–Current
•The net movement of K+ across membrane
–Potassium channel number
•Proportional to electrical conductances
–Membrane potassium current
•Flow and driving force
–Hodgkin and Huxley
- Voltage Clamp: “Clamp” membrane potential at any chosen value
- Rising phase à transient increase in gNa, influx of Na+ ions
- Falling phase à increase in gK, efflux of K+ ions
Existence of sodium
–Functional Properties of the Sodium Channel
- Open with little delay
- Stay open for about 1 msec
- Inactivation: Cannot be opened again by depolarization
–Potassium vs. sodium gates
- Both open in response to depolarization
- Potassium gates open later than sodium gates
–Delayed rectifier
•Potassium conductance serves to rectify or reset membrane potential
–Structure: Four separate polypeptide subunits join to form a pore
•Factors Influencing Conduction Velocity
–Spread of action potential along membrane
•Dependent upon axon structure
–Path of the positive charge
- Inside of the axon (faster)
- Across the axonal membrane (slower)
–Axonal excitability
- Axonal diameter (bigger = faster)
- Number of voltage-gated channels
–Myelin: Layers of myelin sheath facilitate current flow
- Myelinating cells
- Schwann cells in the PNS
- Oligodendroglia in CNS
CNS Synapses
–Axodendritic: Axon to dendrite
–Axosomatic: Axon to cell body
–Axoaxonic: Axon to axon
–Dendrodendritic: Dendrite to dendrite
–Gray’s Type I: Asymmetrical, excitatory
–Gray’s Type II: Symmetrical, inhibitory
Principles of Chemical Synaptic Transmission
–Neurotransmitter synthesis
–Load neurotransmitter into synaptic vesicles
–Depolarization à Vesicles fuse to presynaptic terminal
–Neurotransmitter spills into synaptic cleft
–Binds to postsynaptic receptors
–Biochemical/Electrical response elicited in postsynaptic cell
–Removal of neurotransmitter from synaptic cleft
Neurotransmitters
–Amino acids: Small organic molecules
•e.g., Glutamate, Glycine, GABA
–Amines: Small organic molecules
•e.g., Dopamine, Acetylcholine, Histamine
–Peptides: Short amino acid chains (i.e. proteins) stored in and released from secretory granules
•e.g., Dynorphin, Enkephalins
•Neurotransmitter Synthesis and Storage
image
•Neurotransmitter Release ()
–Mechanisms
- Process of exocytosis stimulated by release of intracellular calcium, [Ca2+]i
- Proteins alter conformation - activated
- Vesicle membrane incorporated into presynaptic membrane
- Neurotransmitter released
- Vesicle membrane recovered by endocytosis
•Neurotransmitter receptors:
–Ionotropic: Transmitter-gated ion channels
Metabotropic: G-protein-coupled receptor
•Excitatory and Inhibitory Postsynaptic Potentials:
- EPSP:Transient postsynaptic membrane depolarization by presynaptic release of neurotransmitter
- IPSP: Transient hyperpolarization of postsynaptic membrane caused by presynaptic release of neurotransmitter
•Neurotransmitter Recovery and Degradation
–Diffusion: Away from the synapse
–Reuptake: Neurotransmitter re-enters presynaptic axon terminal
–Enzymatic destruction inside terminal cytosol or synaptic cleft
–Desensitization: e.g., AChE cleaves Ach to inactive state (to prevent desensitization)
Neuropharmacology
–Effect of drugs on nervous system tissue
–Receptor antagonists: Inhibitors of neurotransmitter receptors
•Curare
–Receptor agonists: Mimic actions of naturally occurring neurotransmitters
•Nicotine
–Defective neurotransmission: Root cause of neurological and psychiatric disorders
•EPSP Summation
–Allows for neurons to perform sophisticated computations
–Integration: EPSPs added together to produce significant postsynaptic depolarization
–Spatial: EPSP generated simultaneously in different spaces
–Temporal: EPSP generated at same synapse in rapid succession
•IPSPs and Shunting Inhibition
–Excitatory vs. inhibitory synapses: Bind different neurotransmitters, allow different ions to pass through channels
–Membrane potential more negative than -65mV = hyperpolarizing IPSP
•Shunting Inhibition: Inhibiting current flow from soma to axon hillock
•The Geometry of Excitatory and Inhibitory Synapses
–Excitatory synapses
- Gray’s type I morphology
- Spines: Excitatory synapses
–Inhibitory synapses
- Gray’s type II morphology
- Clustered on soma and near axon hillock
•Chemical synaptic transmission
–Rich diversity allows for complex behavior
–Provides explanations for drug effects
–Defective transmission is the basis for many neurological and psychiatric disorders
–Key to understanding the neural basis of learning and memory
Somatic PNS
Innervates skin, joints, muscles
Visceral PNS
Innervates internal organs, blood vessels, glands
Dorsal root ganglia
–Clusters of neuronal cell bodies outside the spinal cord that contain somatic sensory axons
•Cranial Nerves
–12 nerves from brain stem
–Mostly innervate the head
–Composition: Axons from CNS, somatic PNS, visceral
–Advantages of MRI over CT
- More detail
- Does not require X-irradiation
- Brain slice image in any angle
•The Spinal Cord
–Conduit of information (brain body)
- Skin, joints, muscles
- Spinal nerves
- Dorsal root
- Ventral root
•Neurotransmitter - three criteria
–Synthesis and storage in presynaptic neuron
–Released by presynaptic axon terminal
–Produces response in postsynaptic cell
•Mimics response produced by release of neurotransmitter from the presynaptic neuron
•Catecholaminergic Neurons
–Involved in movement, mood, attention, and visceral function
–Tyrosine:
– Precursor for three amine neurotransmitters that contain catechol group
- Dopamine (DA)
- Norepinephrine (NE)
- Epinephrine (E, adrenaline)
•Serotonergic (5-HT) Neurons
–Amine neurotransmitter
•Derived from tryptophan
–Regulates mood, emotional behavior, sleep
•Selective serotonin reuptake inhibitors (SSRIs) - Antidepressants
–Synthesis of serotonin
•Amino Acidergic Neurons
–Amino acidergic neurons have amino acid transporters for loading synaptic vesicles.
–Glutamic acid decarboxylase (GAD)
- Key enzyme in GABA synthesis
- Good marker for GABAergic neurons
- GABAergic neurons are major of synaptic inhibition in the CNS
•The Basic Structure of Transmitter-Gated Channels
–Pentamer: Five protein subunits
(except glutamate receptors- tetramer)
Glutamate-Gated Channels
–Glutamate-Gated Channels
•AMPA, NMDA, kainite
–Voltage dependent NMDA channels
–GABA-Gated and Glycine-Gated Channels
- GABA mediates inhibitory transmission
- Glycine mediates non-GABA inhibitory transmission
- Bind ethanol, benzodiazepines, barbiturates
–Five steps in G-protein operation
- Inactive: Three subunits - a, b, and g - “float” in membrane (a bound to GDP)
- Active: Bumps into activated receptor and exchanges GDP for GTP
- Ga-GTP and Gbg - Influence effector proteins
- Ga inactivates by slowly converting GTP to GDP
- Gbg recombine with Ga-GDP
•Tip of the tongue
Sweetness
•Back of the tongue
Bitterness
•Sides of tongues
•Saltiness and sourness
•Tastes Receptor Cells
–Apical endsà Microvillià Taste pore
–Receptor potential: Voltage shift
–Transduction process
- Taste stimuli (tastants)
- Pass directly through ion channels
- Bind to and block ion channels
- Bind to G-protein-coupled receptors
•Mechanisms of Taste Transduction
–Saltiness
- Salt-sensitive taste cells
- Special Na+ selective channel
- Blocked by the drug amiloride
- Serotonin released (new)
•Mechanisms of Taste Transduction
–Sourness
- Sourness- acidity – low pH
- Protons causative agents of acidity and sourness
- Depolarize by Blocking K channels, pass through amiloride-sens Na channels
•Mechanisms of Taste Transduction
–Bitterness
- Families of taste receptor genes – T1R and T2R
- Block K channels (e.g., quinine), Bind to G-protein coupled receptors (T2R class).
- ATP = Transmitter (new)
•Mechanisms of Taste Transduction
–Sweetness
- Sweet tastants natural and artificial
- Sweet receptors
- T1R2+T1R3
- Expressed in different taste cells
- G protein-coupled receptors, 2nd messenger-mediated transduction (cAMP, IP3)
cAMPà phosphorylates (& closes) K channel
•Mechanisms of Taste Transduction
–Umami
- Umami receptors:
- Detect amino acids
- T1R1+T1R3
- Ionotropic & metabotropic
•Central Taste Pathways
–Localized lesions
•Ageusia- the loss of taste perception
–Gustation
- Important to the control of feeding and digestion
- Hypothalamus
- Basal telencephalon
–Labeled line hypothesis
- Individual taste receptor cells for each stimuli
- In reality, neurons broadly tuned
- Population coding
- Roughly labeled lines
- Temperature
- Textural features of food
–Olfactory epithelium
• Olfactory receptor cells, supporting cells, and basal cells
•The Organs of Smell
–Odorants: Activate transduction processes in neurons
–Olfactory axons constitute olfactory nerve
–Cribriform plate: A thin sheet of bone through which small clusters of axons penetrate, coursing to the olfactory bulb
–Anosmia: Inability to smell
–Humans: Weak smellers
•Due to small surface area of olfactory epithelium
–Olfactory Transduction
decreased response despite continued stimulus.
•Central Olfactory Pathways (Cont’d)
–Axons of the olfactory tract: Branch and enter the forebrain (pyriform cortex)
–Neocortex: Reached by a pathway that synapses in the medial dorsal nucleus
•Gross Anatomy of the Eye
–Pupil: Opening where light enters the eye
–Sclera: White of the eye
–Iris: Gives color to eyes
–Cornea: Glassy transparent external surface of the eye
–Optic nerve: Bundle of axons from the retina
•Cross-Sectional Anatomy of the Eye
•Direct (vertical) pathway:
–Ganglion cells
–Bipolar cells
–Photoreceptors
•Retinal processing also influenced lateral connections:
–Horizontal cells
•Receive input from photoreceptors and project to other photoreceptors and bipolar cells
–Amacrine cells
•Receive input from bipolar cells and project to ganglion cells, bipolar cells, and other amacrine cells
•Photoreceptor Structure
–Converts electromagnetic radiation to neural signals
–Four main regions
- Outer segment
- Inner segment
- Cell body
- Synaptic terminal
–Types of photoreceptors
• Rods and cones
•Phototransduction in Rods
–Dark current: Rod outer segments are depolarized in the dark because of steady influx of Na+
–Photoreceptors hyperpolarize in response to light
–Calcium’s Role in Light Adaptation
- Calcium concentration changes in photoreceptors
- Indirectly regulates levels of cGMPà channels
–Photoreceptors release less neurotransmitter when stimulated by light
•On-center Bipolar Cell
–Light on (less glutamate); Light off -> more glutamate
•M-type (Magno) and P-type (Parvo)ganglion cells in monkey and human retina
•The Optic Nerve, Optic Chiasm, and Optic Tract
•Right and Left Visual Hemifields
field errors
•Nonthalamic Targets of the Optic Tract:
–Hypothalamus: Biological rhythms, including sleep and wakefulness
•
–Pretectum: Size of the pupil; certain types of eye movement
•
–Superior colliculus: Orients the eyes in response to new stimuli
The Lateral Geniculate Nucleus (LGN)
•Inputs Segregated by Eye and Ganglion Cell Type
•Receptive Fields LGN
–Receptive fields of LGN neurons: Identical to the ganglion cells that feed them
–Magnocellular LGN neurons: Large, monocular receptive fields with transient response
–Parvocellular LGN cells: Small,monocular receptive fields with sustained response
•Nonretinal Inputs to the LGN
–Primary visual cortex provides 80% of the synaptic input to the LGN
–
–Brain stem neurons provide modulatory influence on neuronal activity
Anatomy of the Striate Cortex
•Lamination of the Striate Cortex
–Layers I - VI
–Spiny stellate cells: Spine-covered dendrites; layer IVC
–Pyramidal cells: Spines; thick apical dendrite;
layers III, IVb, V, VI
–Inhibitory neurons: Lack spines; All cortical layers; Form local connections
•Inputs to the Striate Cortex
–Magnocellular LGN neurons: Project to layer IVCa
–Parvocellular LGN neurons: Project to layer IVCb
–Koniocellular LGN axons: Bypasses layer IV to make synapses in layers II and III
•Inputs to the Striate Cortex binocular
–First binocular neurons found in striate cortex - most layer III neurons are binocular (but not layer IV)
•Outputs of the Striate Cortex:
–Layers II, III, and IVB: Project to other cortical areas
–Layer V: Projects to the superior colliculus and pons
–Layer VI: Projects back to the LGN
•Monocular Receptive Fields
–Layer IVC: Similar to LGN cells
–Layer IVCa: Insensitive to the wavelength
–Layer IVCb: Center-surround color opponency
•Binocular Receptive Fields
–Layers superficial to IVC: First binocular receptive fields in the visual pathway
–Two receptive fields - one for each eye
Orientation Selectivity
Parallel Pathways: Magnocellular; Koniocellular; Parvocellular
•Hierarchy of complex receptive fields
–Retinal ganglion cells: Center-surround structure, Sensitive to contrast, and wavelength of light
–Striate cortex: Orientation selectivity, direction selectivity, and binocularity
–Extrastriate cortical areas: Selective responsive to complex shapes; e.g., Faces
•The Dorsal Stream (V1, V2, V3, MT, MST, Other dorsal areas)
–Area MT (temporal lobe)
•Most cells: Direction-selective; Respond more to the motion of objects than their shape
–Beyond area MT - Three roles of cells in area MST (parietal lobe)
- Navigation
- Directing eye movements
- Motion perception
–Area V4
•Achromatopsia: Clinical syndrome in humans-caused by damage to area V4; Partial or complete loss of color vision
–Area IT
- Major output of V4
- Receptive fields respond to a wide variety of colors and abstract shapes
