Nervous system - Lectures 1-3 Flashcards
How many cells in body?
- how many neurons?, glial cells?
- how many synapses?
- 37 trillion cells
- 100 billion neurons
- 900 billion glial cells
- 1000 trillion synapses
Efferent vs afferent division
- afferent –> PNS –> sends info from sensory receptors to the CNS
- efferent –> PNS –> takes info from CNS to target cells
Autonomic vs somatic neurons?
- autonomic –> involuntary control (heart, digestion, glands, adipose tissue)
- somatic –> skeletal muscles
sympathetic vs parasympathetic
- sympathetic
- parasympathetic
what is the enteric nervous system?
- network of neurons in the walls of the digestive tract
- a unique part of the nervous system that can act autonomously or can be controlled by CNS through autonomic division of the PNS
3 functions of the nervous system
- receive signals from outside (Afferent)
- integration of signals
- output (sending out signal for action)
Central vs peripheral nervous system
- central: brain + spinal cord
- peripheral: sensory (afferent) neurons + efferent neurons
What are neurons + their function?
neurons = functional unit of the nervous system
- carry electrical signals
6 parts of a neuron + functions
- cell body: nucleus + important organelles
- axon: sending out signal
- dendrites: receive signals
- collaterals: axon branches out to send signal to dif. cells
- axon terminals: interact with other neurons/target cells + store/release neurotransmitters
- varicosities: swirl around axon + store/release neurotransmitters
3 types of neurons separated by function
- afferent: sends into to CNS
- interneuron: between sensory and efferent neurons –> integrate and send info
- efferent: take info from CNS to target cell
4 types of neurons based on structure
- multipolar: highly branched interneurons, lack long extensions
- peudounipolar: sdendrites and axon fused together. like bipolar but 2 “axons” exit the same place in cell body
- bipolar: 2 relatively equal fibers extending off central cell body (from 2 different places)
- anaxonic neurons: interneuron with no apparent axon
what is a synapse?
- 2 types?
region where axon terminal communicates with its postsynaptic target cell
- electrical (direct contact ish) VS chemical synapses (via neurotransmitters)
nucleus vs ganglion?
both are masses of cell bodies
- nucleus in CNS
- ganglion in PNS
White vs gray matter?
- white: phospholipids + myelin from axons! = lots of axons
- grey: lots of dendrites, cut into nucleus (cell bodies)
nerve vs tract?
- nerve: collection of nerve fibers (axons, white matter) in PNS
- tract: collection of nerve fibers (axons) (white matter) in CNS
Signal transfer from what to what to what for somatical motor neurons?
VS for autonomic neurons
- somatical: afferent (body + axon in PNS, axon terminals in CNS) –> interneuron (CNS) –> efferent (cell body in CNS, rest in PNS)
VS
autonomic neurons: afferent (body + axon in PNS, axon terminals in CNS) –> interneuron (CNS) –>efferent cell (body in CNS, rest in PNS) –> another effector neuron to get to target
Axonal transport:
- fast (3)
- slow (2)
FAST:
- moves organelles and proteins at rates of up fo 400 mm/day
- anterogade transport: from cell body to axon terminal
- retrogade transport: from axon terminal to cell body
SLOW:
- moves material by axoplasmic/cytoplasmic flow at 0.2-2.5mm/day
- only 1 direction! anterogade
3 sizes of cytoplasmic protein fibers + examples
- associated with what?
- involved in (2)
- microfilaments –> actin fibers
- intermediate filaments: keratin + neurofilament
- microtubules –> tubulin
- associated with accessory proteins (that carry neurotransmitters?)
- in structural support and cell movement with motor proteins
what (2) allows developing neurons to find their targets?
- fixed for life?
- growth cones and neurotrophic factors
- not fixed for life –> can be rearranged
6 types of glial cells + where
- Schwann cells (PNS)
- Oligodendrocytes (CNS)
- Satellite cells (PNS)
- Astrocytes (CNS)
- Microglia (CNS)
- Ependymal cells
Schwann cells vs oligodendrocytes vs satellite cells
- Schwann cells (PNS) and Oligodendrocytes (CNS) –> wrap around axon and form insulating myelin sheaths
- schwann: 1 cell wraps around 1 axon vs oligo: 1 cell can warp around more than 1 axon
- Satellite cells (PNS): non-myelinating Schwann cell + wrap around cell bodies!
astrocyte vs microglia vs ependymal cells
- astrocyte (CNS): source of stem cell + take up water, neurotransmitters, secrete neurotrophic factors, help form blood-brain barrier, provide substrates for ATP production
- microglia (modified immune cells): act like macrophages and eat dead cells
- ependymal cells: creates barrier between compartments (cerebral spinal fluid) + source of neural stem cells
what are the spaces between the myelin sheaths/gaps in insulation called?
Nodes of Ranvier
- if cell body dies, neuron ______
- if axon is severed, (what) survives and (what) degenerates –> sensory vs motor neuron
- regeneration most likley in __NS than __NS
- neuron dies
- if axon is severed, cell body and attached segment survives, severed portion degenerates
- motor neuron: target muscle = permanent paralysis
- sensory neuron: loss of sensation from innervated area
- more likley in PNS than CNS
Do all cells have a resting membrane potential?
- at how much?
- do they all change?
yes!
around -70mV for neurons
- other types can have -40, -80 mV…
- RMP changed only for muscle cells and nervous tissue!
Resting membrane potential is created because of (2)
- en résumé: (2)
- due to unequal distribution of ions inside/outside cells –> leaking channels allow diffusion
- due to sodium potassium ATPase pump –> pumps 3 sodium out and 2 potassium in
- concentration of ions + electrical gradient
2 types of open-channels
3 types of gated channels
OPEN:
- leak channels (always open!)
- pores
GATED:
- chemically gated (ligand)
- voltage gated (can be locked/inactivated)
- mechanically gated (temp, touch…)
Intracellular vs extracellular –> more or less of:
- potassium
- sodium
- chlorine
- calcium
Intracellular:
- more potassium (150 mM)
- less sodium (15 mM)
- less chlorine (10 mM)
- more calcium (1mM)
Extracellular:
- less potassium (5 mM)
- more sodium (145 mM)
- more chlorine (108 mM)
- less calcium (0.0001 mM)
what is:
- depolarization (3)
- repolarization
- hyperpolarization
- depolarization: positive charge spread along adjacent sections of axon by local current flow –> cell becomes more positive (sodium enters cell = more positive) –> dependant on voltage-gated Na+ channels
- repolarization: goes back to normal negative (potassium leaves cell –> becomes more negative)
- hyperpolarization: cell becomes even more negative than normal RMP (potassium continues to exit = cell becomes super negative)
2 types of electrical signals:
graded potential vs action potential
- over what distance?
- strength?
graded:
- variable strength, if exceeds threshhold, causes action potential
- over short distance communication
action potentials:
- very brief, large depolarizations
- rapid signaling over long distances
Can graded and action potentials have summation?
2 types
only graded potentials can be summed!
- spatial summation = 2 or more neurons simultaneously fire and have an additive effect (ie a lot of people hit at the same time) –> cause postsynaptic inhibition: release of neurotransmitter is inhibitory instead of excitatory
- temporal summation = summation occurring when graded potentials overlap in time and having an additive effect (ie hit again and again before it comes down)
How can graded potential cause action potential? (4 steps)
- ligand and mechanical channels open/close –> sodium and potassium move in/out of cell
- if it reaches threshold voltage –> voltage gated channels open (IMPORTANT!)
- Potassium goes out + Sodium comes in
- induces action potential
Local current flow is a ______ of _______ that moves through the ______
wave of depolarization that moves through the cell
graded potentials lose/gain strength as they move through the cell
- bc of 2 reasons
lose strength
- current leak
- cytoplasmic resistance
if strong enough, graded potentials reach the ________ zone in the ______ ________ and initial segment
- trigger zone
- axon hillock
what is the cell’s excitability?
its ability to fire and action potential
action potential begins when?
when graded potential reaching trigger zone depolarizes to threshold
- rising phase of action potential (1)
- falling phase of action potential (4)
- voltage gated Na+ channels open and Na+ entry depolarizes cell
- at peak, Na+ channels close, slower voltage gated K+ channels open
- K+ exit repolarizes then hyperpolarizes cell
- voltage-gated K+ channels close, less K+ leaks out of the cell
- cell returns to resting membrane potential of -70 mV
does action potential alter ion concentration gradient?
no
2 types of refractory period
- absolute refractory period are due to voltage-gated Na+ channels resetting: after sodium voltage channels open and close, they lock! (inactivated) –> even if super strong stimulus, won’t have another AP
- relative refractory period: some sodium channels become activated again + not all potassium channels are closed –> SO you need a stronger stimulus if you want to induce another AP
Why are there refractory periods? (2)
to give cells enough time to recover! + they prevent backward conduction
- potential delay of 1-2 msec btw action potentials independent of intensity of trigger
In the axon, each _______ of the membrane is experiencing a _________ phase of the action potential
section
different
Chemical synapses occur when?
common?
occurs where presynaptic cells release chemical transmitters (neurotransmitters) across a tiny gap to the postsynaptic cell
- neurotransmitters bind to receptor of postsynaptic cell –> opens voltage gated channels –> induce another AP
- more common type of synapse in nervous system
a neuron may terminate on 1 of which 3 structures?
- muscle
- gland
- neuron
3 types of cell junctions:
- communicating junctions
- occluding junctions
- anchoring junctions
Communicating junctions:
- allow direct cell to cell communication
Occluding junctions:
- block movement of material between cells
Anchoring junctions:
- hold cells to one another and to the extracellular matrix
action potentials will NOT fire during ________ refractory periods
absolute
CONDUCTION OF ACTION POTENTIAL
1. ________ potential above threshold reaches the ________ zone
2. what type of Na+ channels open?
3. ________ charge flows into adjacent sections of axon by _______ ________ ________
4. Local current flow causes new section of the membrane to ___________.
5. When that happens, positive/negative charges move by local current flow into adjacent sections of the cytoplasm.
6. On the extracellular surface, current flows towards/against depolarized region.
7. Loss of what from cytoplasm repolarizes membrane (on left side of active region)
- Graded potentials, trigger zone
- voltage gated Na+ channels
- Positive charge –> local current flow
- depolarize
- positive charges
- toward
- potassium
Why can’t there be backward flow?
because the Na+ channels are inactivated –> refractory period prevents backward conduction
2 things that make action potentials conducted faster?
- larger neuron
- myelinated neurons –> less ion leakage from axon membrane + saltatory conduction!
why do myelinated neurons conduct action potentials faster? (2)
- myelin = plasma membrane/phospholipids = insulation –> leaking of electric signal is blocked
- action potential has saltatory conduction from one node of Ranvier to another!
what happens if 2 action potentials/stimuli at 2 ends of axon?
both action potentials will die out because of absolute refractory period
what 2 chemical factors alter electrical activity of neuron?
- variety of chemicals
- alterations in extracellular fluid concentration of ions (Ca+ and K+)
hyperkalemia vs hypokalemia
- which brings neuron closer/further from threshold?
- hyperkalemia = excess potassium in blood! = more positive outside = moves closer to threshold –> can cause irregular hearbeat
- hypokalemia = low potassium in blood = more positive inside = moves neuron further from threshold
Electrical synapses:
- pass electrical signals through what?
- signal can be single or bi-directional?
- ___________ activity of a network of cells
- gap junctions
- bi-directional
- synchronizes
3 types of neurocrines + differences
- neurotransmitters –> 1 neuron affects 1 neuron. mostly paracrine but can be autocrine
- neuromodulators –> 1 neuron can affect a group of neurons. mostly paracrine but can be autocrine
- Neurohormones –> circulate within blood. endrocrinology
- ionic receptors are also called ________-channels
- metabotropic receptors are ____(what type)__________ receptors for ___(which type of neurocrine)____________
- neurotransmitters bind to random/specific receptors except for ___________
- receptor-channels
- G protein coupled receptors for neuromodulators
- specific receptors except for nitric oxide (NO)
5 steps of classical model of neurotransmitter release
- AP depolarizes axon terminal
- depolarization opens voltage-gated Ca2+ channels and Ca2+ enters cell
- Ca2+ binds to regulatory proteins –> triggers exocytosis of synaptic vesicle contents (vesicle membrane merges with plasma membrane)
- Neurotransmitter diffuses across synaptic cleft and binds with receptors on postsynaptic cell
- neurotransmitter binding initiates a response in the postsynaptic cleft
Difference between classical model pathway and kiss-and-run pathway for neurotransmitter release
Kiss and run
- vesicles fuse with presynaptic membrane to form fusion pore –> neurotransmitters pass through a channel
- vesicle membrane doesn’t become part of the plasma membrane –> closes after and can be recycled!
where are neurotransmitters synthesized?
cell body and axon terminal
3 ways to terminate neurotransmitter activity (in synaptic cleft ish)
- prozac example
- diffusion away from synaptic cleft = not binding to receptors
- enzymatic breakdown (ie: acetylcholinesterase)
- uptake into cells (presynaptic axon terminal for reuse OR into glial cells)
- prozac: drug that blocks serotonin reuptake back into presynaptic neuron –> helps for depression
synthesis and recycling of acetylcholine (5 steps)
- Ach is made from choline and acetyl-coa
- in synaptic cleft, Ach is rapidly broken down by enzyme acetylcholinesterase
- choline is transporte back into axon terminal by cotransport with Na+
- Acetate is used to provide energy
- recycled choline is used to make more Ach
what 2 things impact the amount of neurotransmitter released?
- number of neurons involved (ie: if touch harder = more neurons)
- frequency of AP (even with refractory period)
what is synaptic plasticity?
- occurs primarily where?
- short or long term?
- may reduce or enhance synaptic activity?
- change of activity at the synapses (ie increase/decrease neurotransmitters, receptors, vesicles)
- in CNS
- both
- both
divergent vs convergent pathway
- divergent: 1 presynaptic neuron branches to affect large number of postsynaptic neurons
- convergent: many presynaptic neurons provide input to influence a smaller number of post-synaptic neurons
- slow synaptic potentials involve (2)
- fast synaptic potentials involve opening of (1)
- G-protein coupled receptors and second messengers
- opening of ion channels
EPSP vs IPSP
- depolarizing or hyperpolarizing?
- excitatory postsynaptic potential (EPSP) = depolarizing –> ie Na+ goes into cell
- inhibitory postsynaptic potential (IPSP) = hyperpolarizing –> is Cl- goes into post-synaptic neuron
synaptic activity can be modified –> __________ neuron terminates on the ______synaptic cell and modulates the release of _______(A)___________
- presynaptic facilitation vs inhibition favors/prevents release of (A)
- modulatory neuron
- presynaptic cell
- release of neurotransmitters
- facilitation –> favors release
- inhibition –> prevents release
how to inhibit a synapse?
- global vs selective
when an EPSP and IPSP sum together and cancel each other out
- global: EPSP + IPSP sum together at cell body –> no AP
- selective: EPSP fires –> AP generated –> IPSP fires at one dendrite blocking release of neurotransmitter BUT AP reaches 2 other dendrites where neurotransmitters released reached target cell
What is long term potentiation?
- potentiation similar to ________
- depression similar to _________
- probably responsible for what?
- _________ is a key element for potentiation (2 receptors)
when activity at a synapse induces sustained changes in quality or quantity of connection –> will “adapt” and become more effective ish
- facilitation
- inhibittion
- probably responsible for acquired behaviour
- glutamate (AMPA and NMDA receptors)
Parkinson’s disease, schizophrenia and some depressions are caused by disorders of _____________ ___________
synaptic transmission
