Exam 1 Flashcards
basic features of Galen’s model
- the brain is the seat of sensations from the 5 external senses, the site of all mental or psychic functions, and source of voluntary movement
- Sensory function is supported by psychic pneuma flowing from sensory organs to lateral ventricles
- The three psychological functions of the rational soul (imagination, thought, and memory), are accomplished by psychic pneuma refined in the brain ventricles
- Voluntary movement effected by psychic pneuma flowing from fourth ventricle through motor nerves to the muscles
- Regarded the brain as a sort of pump
- Pneumatic-ventricular model was the first system of nervous system functional localization
3 cell theory as described by Nemesius
- The first cell (the right and left lateral ventricles together) subserve association of the 5 basic external cells along with the imagination
- The second cell (our third ventricle) subserves thinking or cognition
- The third cell (our fourth ventricle) subserves memory
- The three basic internal senses - memory, cogitation and imagination - were divided into at least 7 different faculties and then further refined in over 70 different ways
Vesalius’ contribution to neuroanatomy
- Systematically described the body through dissection, to correct previous errors, and to illustrate the body with best artistic methods
- Paid attention to the brain structure and the ventricular system but was careful not to speculate too much
- Distinguished between outer grey matter and inner white matter when drawing the cerebrum and cerebellum and illustrated the entire nervous system
Willis extended the view of the nervous system
- Psychic pneuma is generated in the grey matter of the cerebral and cerebellar cortices and circulates through the white matter of the brainstem and spinal cord from the sensory to the motor nerves
- Topographic separation of functionally distinct fiber types within white matter and its continuation in the nerves
- The cerebral grey matter controls voluntary behavior whereas the cerebellar cortex controls involuntary movements
- Certain white matter tracts known from that time interconnect the cerebral and cerebellar cortices
neuron doctrine (Cajal)
nerve cells interact by way of contact rather than continuity (axons and dendrites generally do not anastomose)
functional polarity law (Cajal)
in the context of normal neural circuits, impulses are generally transmitted from dendrites and soma to axon, and then from the axon to its terminals on other neurons or effector cells
four broad eras in the nervous system evolution (Cajal)
- First era - irritability - characterizes certain cells in plant and animals without a nervous system
- Second era - sensory and motor nerve cells derived from the outer covering of the first animals with a nervous system - coelenterates
- Third era - characterized by worms, where neurons between motor and sensory (interneurons) assume equally important role
- Fourth era - characterized by dominant role for second broad class of association neuron - a psychomotor or second order neuron
principles of nervous system evolution (Cajal)
- As evolution proceeds, products of earlier eras are preserved and integrated in more advanced forms
- Hierarchy of conditions required for psychological experiences is linked to the nature of differentiated sensory outputs
- The proliferation of neurons and their process increases the complexity of relationships that can be maintained between various organs and tissues
- Adaptive differentiation of neuronal morphology and fine structure increases their capacity for impulse conduction
- Progressive concentration of neural elements into gray matter masses results in shortening of many processes and consequently an increase in the rate of impulse conduction
- By forcing nervous system differentiation, there is refinement/enhancement of reflex activity which protects life of both individual and species
flatmap
2D schematic drawing to show general spatial relationships within the brain. A good way for showing the general organization, especially for neural circuitry and pathways
connection matrix
connection tables with “from” on one axis and “to” on the other, such as looking at gray matter regions
Swanson’s ideas of an ideal model of the nervous system, including his minimum requirements to move forward
•Ideal model would be systematic, complete, and internally consistent, and needs to have microscopic, macroscopic, mathematical and schematic descriptions
•Seven requirements:
1) hierarchically organized account of all nervous system parts
2) mathematically defined 3D computer graphics models of nervous system need to be developed and made available online
3) computer graphics atlases based on representative series of histological sections
4) nervous system flatmaps
5) schematic diagrams of neural circuitry
6) connection matrices
7) basic plan of nervous system circuitry must be described and analyzed in mathematical terms
optogenetics
- Optogenetics use brief pulses of light that enables the control of electrical potentials of neurons - either activated or silenced
- Takes a light-sensitive protein from algae - this protein is an ion channel that opens in response to blue light. Take the gene for this protein and insert DNA into certain neurons in the brain. Can flash blue light to make neurons fire (firing is an electrical signal created by opening and closing ion channels). With right combo of neurons, you can activate an entire brain circuit or region to control behavior such as movement.
Three classes of opsins used for optogentics
channelrhodopsins, halorhodopsins, and light-driven outward proton pump (eg. archaerhodopsins)
channelrhodopsin
light driven inward cation channels from green algae. They localize to the cell membrane when expressed in neurons, and when illuminated they open up a channel that lets in a positive charge which then depolarizes the cell
halorhodopsin
light-driven inward chlorine pumps. When expressed in neurons and illuminated, they pump chlorine ions into the cells which hyperpolarizes them
light-driven outward proton pump
archaerhodopsins - positively charged protons flow out of the cell, hyperpolarizing them
how are genes typically delivered?
Viral delivery. Once the neurons are infected, the neuron will express the opsin protein. By inserting a promotor (another piece of DNA) in front of the opsin gene, only a specific subset of neurons will have the correct machinery to express the algal protein in the cell membrane.
blindsight
- Cortical regions involved in conscious perception of visual stimuli are damaged but other visual pathways are intact
- Use subconscious vision to see, showing that perceptions don’t need to enter consciousness to affect our behavior
types of cerebral cortex and where they’re typically found
- Isocortex aka neocortex - 6 layers, 90% of cerebral hemisphere (sensory, motor and association areas)
- Mesocortex - 3-6 layers, transition area consisting of paralimbic areas, majority of the limbic lobe
- Allocortex - 3 layers, hippocampal formation (archicortex), primary olfactory areas (paleocortex)
- Corticoid areas - no layers but cortex-like appearance
criteria used to define Brodmann’s areas
Thickness of cortex, number and thickness of cortical layers, arrangement of cells, presence of specific cell types
What is the difference between primary, secondary, and association cortex in terms of the types of information they process?
- Primary cortex - first cortical input of sensory stimuli or last cortical input of movement commands
- Secondary cortex - 2nd cortical input or next-to-last cortical output (more abstract processing)
- Association cortex - processing of more than one sense and/or areas not strictly sensory or motor - multimodal areas, more complex functions
layers of cortex
I - molecular layer, contains very few neurons, and only fibers of cells from other layers rather than cell bodies
II - external granular layer, pyramidal cells, granule/stellate cells
III - external pyramidal layer, pyramidal cells, projection neurons
I-III: supragranular layers, primary origin and termination of the intracortical connections
IV - involved in specific sensations. Internal granular layer, receives thalamocortical connections, stellate or granule cells, interneuons
V - pyramidal cells, internal pyramidal layer, projects to basal ganglia, brain stem and spinal cord, has projection neurons
VI - multiform (fusiform) layer, these cells connect to thalamus, and also receive connections from thalamus, many types of cells
V-VI: infragranular layers, primarily connect cerebral cortex with subcortical regions
gene therapy using adenovirus vector
vector binds to cell membrane, vector is packaged inside the vesicle, vesicle breaks down releasing the vector, vesicle injects new gene into nucleus, cell makes protein using new gene
different portion of layers of cortex
primary motor cortex - majority of layers V and VI, very small IV
association cortex - slightly less V and VI, larger IV
primary sensory cortex - IV is more proportional to combination of V and VI
ways to classify cells in nervous system
- could classify as neurons or glial cells
- Shape, size function, location, number of connections, kinds of synapses, kinds of neurotransmitters
- Structure - multipolar, bipolar, monopolar
- Function - sensory, motor, interneurons
different structures of neuron
multipolar - have many dendrites and one axon, this is the typical neuron
bipolar - have one dendrite and one axon (receiving end of visual, vestibular and auditory systems)
monopolar/pseudo-unipolar have single branch that extends in two directions, often found in dorsal root ganglia
different functions of neuron
- sensory - receive environmental input because their dendrites are “specialized” for detecting physical stimuli. Carry signals from periphery to CNS
- motor - can make muscles contract or gland change, carry signals from CNS to outer parts of body
- interneurons - neurons that lie entirely within the CNS, receive input from and send output to other in brain and spinal cord
glia
surround neurons and hold them in place, control supply of nutrients, insulate neurons from one another
types of glia
1) microglia - respond to injury, act as phagocytes and engulf/breakdown dead and dying neurons, primary immune defense of CNS
2) macroglia
- astrocytes
- oligodendrocytes
- NG2 cells
- Schwann cells
functions of astrocytes
- Provide physical support to neurons
- Clean up debris in the brain
- Help control chemical composition of fluid surrounding neurons
- Involved in providing nourishment to neurons
- Help control extracellular K+ concentration
- Help control BBB along with capillaries
How neurons differ from other cells in body
Have distinctive structural components that serve purpose of:
•Signaling - both with other neurons and with outside world
•Integration of signals from other neurons
Parts of a typical neuron
- Dendrites - receive signal (input)
- Cell body - contains nucleus
- Axon hillock - combines/transforms input
- Axon - conducts signal, carries action potential
- Axon terminals - transmit signal to other cells (output), when AP reaches them they secrete neurotransmitter, form synapses with other neurons
interneuron
- Receive input from and send output to other neurons
- Enable communication between sensory or motor neurons and the CNS
- Local interneurons form circuits with nearby neurons and analyze small pieces of info
- Relay interneurons connect circuits of local interneurons in one region of the brain with those in other regions
