Midterm 2 Flashcards
In the central nervous system clusters of cell bodies are called what
Nuclei
Singular: nucleus
In the peripheral nervous system clusters of cell bodies are called what
Ganglia
Singular: ganglion
In the central nervous system, bundles of axons are called what
Tracks
In the peripheral nervous system, bundles of axons are called what
Nerves
What is an axon hillock
The cone shaped region at the junction between the axon and the cell body
What are synapses
The gaps between adjacent neurons across which chemical signals are transmitted
What are the two fundamentally different types of cells in the nervous system
Neurons and glia cells
What are myelin
Fatty insulating substance around many axons, the myelin sheath they form increase the speed and efficiency of axonal conduction.
-saltatory conduction>AP jumps from node to node down axon skipping over myelinated regions
What are oligodendrocytes
Type of glial cell with (usually myelin rich) extensions that wrap around the axons of some neurons of the central nervous system.
- myelination of CNS axons
- provide several myelin segments, often on more than one axon
What are Schwann cells
Another class of glial cells found in the PNS
- myelination of the PNS axons
- each Schwann cell constitutes one myelin segment
- can guide axonal regeneration (regrowth) after damage * this is why axons in brain/spinal cord usually cannot be repaired after damage (Schwann cells are only in the PNS)
What are microglia
Class of glial cells that are smaller than other glial cells
- respond to injury or disease by multiplying, engulfing cellular debris, and triggering inflammatory responses
- originate in bloodstream and migrate to the brain
- Phagocyte (removes waste, repairs damage)
- releases growth factor
What are astrocytes
- largest glial cells that are star shaped
- some extensions cover the outer surfaces of blood vessels that course through the brain
- can make contact with neuron cell bodies-allowing the passage of some chemicals in the blood into the CNS neurons and in blocking other chemicals (Control/create the blood brain barrier)
- provide physical structure to the CNS( helps keep things in place)
- serves as a bridge from blood to cells (nutrients in, waste out)
- scar tissue
What are synaptic vesicles
spherical cell membrane packages that store neurotransmitter molecules ready for release near synapses
what are neurotransmitters
Molecules that are released from active neurons and influence activity of other cells
- produce either excitation or inhibition, not both; but a few produce excitation under some circumstances and inhibition under others
- synthesized in the neuron
What are microtubules
Tubules responsible for the rapid transport of materials throughout neurons
What is a pyramidal cell
Multipolar neuron found in areas of the brain-many found in cerebral cortex
-type of interneuron
What is a purkinje cell
Neuron mainly found in cerebellum,
- elaborate dendritic tree heavily invested with dendritic spines.
- type of interneuron
What are sensory neurons (Afferent neuron)
-don’t have dendrites receive neurotransmitters
-interact with outside world converting physical impulse into electrical impulse
-can be bipolar or unipolar
-has receptors
Ex. Visual and olfactory cells (bipolar)
What are motor neurons (efferent neuron)
Release NT’s on muscles or glands
- has dendrites
- info flows from brain to muscles or glands
- usually multipolar
What are Interneurons or relay neurons
- connects neurons together (Connects sensory to motor>reflex arc)
- most neurons are interneurons
- in the brain(pyramidal&purkinje cells) and spinal cord
What are ependymal cells?
Glial cell along the walls of ventricles and central canal of spinal cord
- produce CSF
- shock absorber, brain cooling, Carries particles (nutrient/waste)
Describe multiple sclerosis
- demyelinating disease of glia in CNS
- oligodendrocytes are attacked. Myelin is damaged/destroyed(breaks down/breaks apart) and axon is exposed
- can no longer carry out electrical signal down to the end of axon to other cells
- mostly affects relay neurons/ interneurons
Describe Amyotrophic Lateral Sclerosis (ALS)
- Motor neurone disease (PNS)
- death of neurons which controls voluntary muscles
- Target Schwann cells
- gradual weakening do to shrinking of muscles
- myelin sheath is rotten away, signal can’t travel to muscles to make them contract> eventually they waste away in leads to cell death
How do Schwann cells aid in neuron regrowth
After axon is damaged, Schwann cells first shrink and then divide forming glial cells along the axons former path. The neuron sends out axon sprouts, one of which finds the Schwann cell path and becomes the new axon. Schwann cells envelop the new axon forming new myelin
What is membrane potential
The difference in electrical charge between the inside and outside of a cell
What are microelectrodes
Intercellular electrodes with tips that are too small to be seen by the naked eye. The tip can pierce the neural membrane without severely damaging it and can record membrane potential
What is a neurons resting potential? Where are the ions distributed?
In a neurons resting state, the charge build up across its membrane is -70 mV. The neuron is said to be polarized
- steady membrane potential of -70mV
- more Na+ ions outside the cell then inside and more K+ ions inside than outside
- Na+ ion channels are closed (but some still leak in)
- K+ ion channels are opened but few exit because they’re largely held inside by the negative resting membrane potential
- sodium potassium pump’s transport 3 sodium out for every two potassium they transport in
What is an excitatory postsynaptic potential? (EPSP)
When the postsynaptic neuron becomes depolarized (less negative/polar) due to excitatory NT’s and increase the likelihood that the neuron will fire
- type of graded response>amplitude proportional to the intensity of the signals that elicit them
- transmitted at great speed
- are decremental: decrease in amplitude as they travel through the neuron
What are Inhibitory postsynaptic potentials (IPSP)?
- postsynaptic hyper polarizations that decrease the likelihood that the neuron will fire
- type of graded response>amplitude proportional to the intensity of the signals that elicit them
- transmitted at great speed
- are decremental: decrease in amplitude as they travel through the neuron
What determines whether or not a neuron fires?
Depends on the balance between the excitatory and inhibitory signals reaching its axon
- AP’s are generated in the axon initial segment where EPSP and IPSP are conducted
- if the sum of the depolarizations and hyperpolarizations reaching the axon initial segment at any time is sufficient to depolarize the membrane to a level referred to as its threshold of excitation(~65mV) an AP is generated
Describe actions potentials
- massive but momentary(1ms) reversal of the membrane potential from about -70mV to ~+50mV
- all or none responses
- each multipolar neuron adds together(integrates) all the graded excitatory and inhibitory postsynaptic potentials reaching its axon and decides to fire or not to fire on the basis of their sum
- they do not grow weaker as they travel across the axonal membrane (except in myelinated axon)
- conducted more slowly than PSPs
What are the two ways that neurons integrate incoming signals?
-over space and time
- Spatial summation: local EPSPs produced simultaneously on different parts of the receptive membrane sum to form a greater EPSP and vice versa for IPSPs. EPSPs and IPSPs can also sum to cancel each other out
* Grade potential’s that occur closer to the axon hillock have a larger effect - Temporal summation: postsynaptic potentials produced in rapid succession at the same synapse sum to form a greater signal
- if two great potential to happen closer together, they are more likely to reach threshold and if they happened further apart
What happens during an action potential in unmylinated axon
When the threshold of excitation is reached by an EPSP, the membrane potential is depolarized. Voltage activated Sodium channels open and Na+ ions rush in causing the membrane potential to suddenly change from about -70 to about +50 mV. This activates voltage activated potassium channels to open and K+ ions near the membrane are driven out of the cell to repolarize the neuron. Once the neuron is re-polarized potassium channels gradually close and the neuron is left hyperpolarized for a brief period of time. Sodium potassium pump’s reestablish resting potential. (depolarized, repolarized, hyperpolarized)
- each sodium stores energy by holding back Na+ ions which are under pressure to move down their concentration and electrostatic gradients into the neuron> once one channel opens it triggers adjacent channels to open all the way to end of axon to axon terminals
- expenda a lot of energy
- requires pumps
What is the absolute refractory period
Brief period after the initiation of an action potential during which is impossible to elicit a second one
- during repolarization
- followed by the relative refractory period
What is the relative refractory period
Period during which it is possible to fire the neuron again only by applying higher than normal levels of stimulation
- during hyperpolarization
- K+ channels are still open
- occurs after the absolute refractory period.
What two important characteristics of neural activity is the refractory period responsible for?
- APs travel across axons in one direction(cannot reverse direction)
- section axon cannot fire again until it has been repolarized - The rate of neural firing is related to the intensity of the stimulation (intermediate levels of stimulation produce intermediate rates of neural firing)
What is antidromic conduction
Action potential generated in the direction from the terminal buttons to the cell body
What is orthodromic conduction
Axonal conduction in the natural direction> from the cell body to the terminal buttons
What is a concentration gradient and a voltage gradient (both are forces that act on neurons)
Concentration gradient: the tendency of substances to move (diffuse) from area of high concentration to an area of low concentration
voltage gradient: ions tend to move from areas of high(away from 0) charge to areas of lower charge
-opposite charges attract each other, similar charges repel each other
What are the four kinds of ions in resting potential? where they found?
1 anions: negative charged ions that stay inside cell but want to go outside cell (attracted to positive forces outside the cell)
2 sodium: positive charged ions mostly outside the cell and want to be inside the cell (leak in)
3 potassium: positive charged ions mostly inside the cell but want to go outside of cell (few leak out through channels)
4 chloride: negative charged ions in abundance that stay outside of cell, little on inside (want to move inside the cell but do not)
What is a graded potential or graded response?
Post synaptic potentials
- Small short lived voltage fluctuations between inside and outside of cell. Restricted to small area. Cell either gets more positive or more negative.
- can either be excited toilet or Vittori
Describe action potential in myelinated axon
- not a proper AP
- no exchange of ions
- faster conduction
- let energy expended (no pumps)
- however, strength of signal gradually decreases due to the fact that there is no ion exchange
- nodes of Ranvier replenish action potential and allows it to continue traveling across atonal membrane jumping from node to node
What are some differences in APs in different neurons
- some are longer or shorter
- threshold may very
- some fire faster than others
- some dendrites can conduct action potentials
- some neurons don’t display APs
What is the advantage of presynaptic facilitation and inhibition
Axoaxonic synapses selectively influence single synapses, rather than the entire neuron
What is a directed synapse
A synapse at which the site of neurotransmitter release and the site of neurotransmitter reception are in close proximity
Describe the two basic categories of neurotransmitter molecules
Small-molecule NTs: typically synthesized in the cytoplasm of the terminal button and packaged in synaptic vesicles by golgi complex. Once vesicles are filled with neurotransmitters they are stored in clusters next to the presynaptic membrane
-tend to be released into directed synapses and activate either ionotropic or metabotropic receptors that act directly on Ion channels
Large-molecule NTs(Neuropeptides): short proteins or chains of amino acids that are synthesized in cytoplasm of the cell body on ribosomes. They are packaged in vesicles by Golgi complex and transported by microtubules to the terminal buttons
-tend to be released diffusely(further away from receptor binding site) and bind to metabotropic receptors that act through second messengers
What is exocytosis
The process of neurotransmitter release into the synaptic cleft by the fusion of synaptic vesicles to the presynaptic membrane
-vesicles fuse to the membrane due to voltage activated calcium channels opening and calcium ions enter the button
What are receptor subtypes?
The different types of receptors to which a particular neurotransmitter can bind are called receptor subtypesfor that neurotransmitter
What is an ionotropic receptor?
- easy/simple kind of receptor
- binding site for neurotransmitter(receptor) is on ion channels
- changes are direct and fast
- when a NT molecule binds to an ionotropic receptor, the associated ion channel opens or closes immediately, inducing an immediate post synaptic potential by altering the flow of ions into or out of the neuron
What is a metabotropic receptor?
- more complex
- associated with signal proteins and G proteins
- affects are slower to develop, longer-lasting and more varied
- it is attached to a serpentine signal protein that winds its way back-and-forth through the cell membrane seven times
- The metabotropic receptor is attached to this signal protein outside the neuron, the G protein is attached to a portion of the signal protein inside the neuron
- changes or indirect and slow
What happens when a neurotransmitter binds metabotropic receptor
-A subunit of the associated G protein breaks away and it may bind to an ion channel inducing a posted synaptic potential or may trigger the synthesis of a second messenger