lecture 1/2 - nervous tissue Flashcards
ramon y Cajal
father of neurobiology
nervous system works with _______ to maintain homeostasis
endocrine system
CNS stands for
central nervous system
CNS components
brain and spinal cord
PNS stands for
peripheral nervous system
PNS components (examples) 3
all nervous tissue aside from brain and spinal cord
- cranial nerves
- spinal nerves
- enteric plexuses of small intestine
- sensory receptors in skin
PNS 2 subcategories
somatic NS
autonomic NS
autonomic NS subcategories
sympathetic
parasymphathetic
enteric plexuses
sympathetic NS controls (3)
smooth muscle
cardiac muscle
glands
parasympathetic NS controls (3)
smooth muscle
cardiac muscle
glands
enteric plexuses control
smooth muscle and glands of GI tract
somatic NS controls
skeletal muscle
somatic NS is responsible for
voluntary movements/changes
autonomic NS is responsible for
involuntary changes
sympathetic NS is responsible for
fight of flight
- elevate HR etc
parasymphathetic NS is responsible for
rest and digest
- lowering HR etc
path of nervous system (neuron names, 3)
sensory neuron
interneuron
motorneuron
functions of the NS (3)
sensory function - detect
integrative function - analyze
motor function - initiate
functions of NS - sensory function
sensory neurons (receptors) detect changes in the internal and external environment
functions of NS - integrative function
interneurons analyze incoming sensory info, store info, and make decisions for appropriate behaviours
functions of NS - motor function
motor neurons initiate appropriate response to stimuli by activating effectors like muscles and glands
two types of cells in nervous tissue
neurons
neuroglia
neuron facts (2)
- electrically excitable
- does not undergo mitotic division
electrically excitable meaning (in this case)
can generate nerve impulses (action potential)
neuroglia facts (3)
- support protect nourish neurons
- maintain interstitial fluid
- undergo mitotic division
stimulus
a change in environment that triggers an action potential
nerve impulse
the signal sent between neurons
- travels across the membrane of a neuron
parts of a neuron (3, general)
cell body (soma)
dendrites
axons
cell processes are also known as
nerve fibres
examples of cell processes (nerve fibers)
axons, dentrites
dendrites facts (5)
- unmyelinated
- has neurofibrils and nissl bodies
- receiving part of axon
- conduct impulses to cell body
- has receptor sites (spines)
axon facts (6)
- has a trigger zone (axon hillock)
- has axoplasm and axolemma
- carries impulse away from body
- end in axon terminals
- can have divisions called axon collaterals
- terminals end with synaptic end bulbs that contain synaptic vesicles that store neurotransmitters
three structure types of neurons
multi polar
bipolar
psuedounipolar/unipolarm
multipolar neuron shape
traditional
- many dendrites, one axon
bipolar neuron shape
one dendrite, one axon
(doesnt matter if the dendrite is branched, only if it touches the body does it count)
psuedounipolar/unipolar neuron shape
one fused dendrite and axon
(cell body usually off to the side)
multipolar neuron locations
all motor neurons
- most CNS neurons (interneurons)
- most common
bipolar neuron locations
retina, inner ear olfactory area of brain
(think sensory related without taste or touch)
psuedounipolar/unipolar neuron location
notes say “dendrites act as sensory receptors for stimulus”
- assume touch?
functional classification of neurons (based on the direction of impulse propagation, 3)
- sensory (afferent)
- motor (efferent)
- interneurons (association neurons)
sensory neurons facts (3)
- may contain sensory receptor or be triggered by a receptor
- form nerve impulses
- sends impulse to CNS (via cranial/spinal nerves)
motor neurons facts (1)
- sends nerve impulses from CNS to muscles and glands (effectors) via cranial and spinal nerves
interneurons facts (2)
- processes incoming info and initiates motor response
- connects sensory to motor neurons in the CNS
neuroglia facts (7)
- make up half the volume of the CNS
- smaller + more numerous that neurons
- support, protect, nourish neurons
- maintain ISF
- undergo mitosis
- not electrically excitable
- 6 types
how many types of neuroglia are in the CNS
4/6
- astrocytes
- oligodendrocytes
- microglial
- ependymal cells
how many types of neuroglia are in the PNS
2/6
- schwann cells
- satellite cells
6 types of neuroglia
- astrocytes
- oligodendrocytes
- microglial
- ependymal cells
- schwann cells
- satellite cells
astrocytes appearance and how to remember
star shaped
- blue ones in the diagram if that helps
- largest and most numerous
- can hv short branched processes
or long unbranched (depending on type)
2 types of astrocytes
fibrous - long unbranched processes
protoplasmic - short branched processes
astrocytes function (5)
- provide structural support
- processes help form blood brain barrier
- regulate ion/neurotransmitter concentrations in ISF
- helps form neural synapse
- regulate chemicals needed for neuron development in embryos
oligodentrocytes appearance and how to remember
“o” for octopus
- smaller that astrocytes + less processes
- attached to axons via myelin sheath
oligodendrocytes function (1)
- form and maintain myelin sheath around CNS neurons
(one can myelinate several neurons)
microglial cells appearance and how to remember
- small cells
- slender processes
- like chihuahuas - small but killers (phagocytes)
microglial cells function (2+1)
- phagocytosis (remove cell debris, microbes, damaged tissues)
- refine synapses during development
- are the immune cells of the CNS
ependymal cells appearance and how to remember
- cuboidal / columnar cells
- have microvilli and cilia
- think “ep” is the same as epithelial - same shape and appearances
ependymal cells functions (3)
- line ventricles of the brain and central canal of spinal cord
- produce cerebrospinal fluid (CSF)
- form blood CSF barrier
satellite cell appearance and how to remember
youll find them surrounding clusters of cell bodies (ganglia) in PNS
- picture the starfish on the wall of the tank in nemo
satellite cells functions (2)
- provide structural support for neurons
- regulate material exchange between neuronal cell bodies and ISF
schwann cells appearance and how to remember
the liner on the axon in PNS
- axon condoms
schwann cell functions (2)
- form myeline sheath around some axons
- one cell = one axon (myelinated)
- one cell = up to 20 axons (unmyelinated)
- axon regeneration
very similar to oligodendrocytes but in the PNS instead of CNS
myelination in the PNS is done by
schwann cells
myelination in the CNS is done by
oligodendrocytes
myelination in PNS process
schwann cells wrap an axon segment
what does myelin sheath do
electrically insulates axons and increased the speed of nerve impulse
neurolemma function
aid in regeneration
myelination in the CNS process
oligodendrocytes myelinate parts of many axons
- processes wrap axons, but no neurolemma is formed because oligos dont have it
why is there limited cell regeneration in the CNS compared to the PNS?
because of the absence of neurolemma and inhibitory action of oligodendrocytes
myelination increases from birth to maturity (no answer, just remember it)
names for clusters of neuronal cell bodies in PNS /CNS
nucleus - ground of neuronal cells in CNS
ganglion - group in PNS
names for clusters of bundles of axon in PNS/CNS
tract - group of axons in CNS
nerves - group of axons in PNS
a tract functions to :
connect neurons in the spinal cord and brain
a nerve functions to : (2 answers (cranial and spinal))
cranial nerve- connect brain to periphery
spinal nerve - connect spinal cord to periphary
white matter contains:
primarily myelinated axons
grey matter contains:
cell bodies, dendrites, neuroglia, unmyelinated axons, axon terminals, nissl bodies
slides name all the parts of a neuron, might be able to just say neuron and then nissl bodies n shit
in the brain, grey matter is:
on the outside
graded potential type of communication
short distance
action potential type of communication
long distance
where do graded potentials occur? (2)
- sensory receptors
- between neurons
are neurons polarized
yes
what are the charges at resting membrane potential inside and out?
inside - negative ions
outside - positive ions
results in -70mV at rest
three factors that contribute to RMP
- difference in distribution of leak channels
- inability of most anions to leave cells
- activity of sodium potassium pump
sodium potassium pump ratio
3 Na out, 2 K in
leak channels
- randomly open and close
- more K than Na channels
4 types of ion channels
leak channels
ligand gated
mechanically gated
voltage gated
ligand gated channels
open and close in response to a chemical that binds to a receptor
mechanically gated channels
opens/closes in response to vibration or pressure
voltage gated channels
open / close in response to change in membrane potential
where are leak channels found/
nearly all cells
- dendrites
- cell bodies
- and axons
- alll types of neurons
- in other words, fuckin everywhere
where are ligand gates channels found
- dendrites of some sensory neurons like pain receptors
- cell bodies of inter/motor neurons
where are mechanically gated channels found
dendrites of some sensory neurons like touch receptors or pain receptors
where are voltage gated channels found
axons of all types of neurons
graded potentials
occur in response to stimulus
- differ in amplitude - “graded”
- can depolarize or hyperpolarize membrane
action potentials
all or nothing, triggered when depolarization reaches a threshold
- sequence of events that decreases, reverses, and restores membrane potential
graded potentials are found in (what parts of the neuron)
dendrites and cell body
what types of ion channels do graded potentials use/open?
mechanically/ligand gated
hyperpolarizing graded potential
more negative than resting
moves further from threshold
less likely for AP to occur
depolarizing graded potential
less negative than resting
closer to threshold
more likely for AP to occur
decremental conduction
when graded potentials disappear as they spread along membrane
summation of graded signals
(what is it and what does it do)
when graded potentials stack onto each other
- results in stronger and longer graded potential signals OR no graded potential
graded potentials differ in _______ based on _____-
amplitude, strength of stimulus
why does a stronger stimulus lead to a larger graded potential than a weaker one?
more ion channels are opened by stronger stimulus, and therefore a larger GP
where does an AP arise
in the axon hillock
strength of a nerve impulse/AP is:
always the same
what ion channels does an AP use/open?
Na and K channels
why does the Na channel have two gates?
when are they open? closed?
middle gate, determines whether the channel is open or closed
ball gate, determines whether channel in active or inactivated
resting potential
- mid gate - closed
- ball gate - open
“resting state”
depolarization
- both gates open
“activated
repolarization
- mid gate - open
- ball gate - closed
“inactivated”
what is happening with the Na channel during repolarization?
the gate is inactivated, NOT closed, just plugged by the ball gate
after hyperpolarizing phase
a more -ve potential due to K channels being open longer
refractory periods
absolute
relative
absolute refractory period
(what is Na gate doing)
no second AP in response to stimulus
- Na gate inactivated, not closed
relative refractory period
( what is Na/K gate doing)
second AP can occur in response to a very large stimulus
- Na gate is at rest, closed, unplugged
- K channel is still open
absolute refractory period starts and end where?
start - once threshold is reached
ends - when threshold is reached the second time during repolarization
if APs are all of nothing, how do we respond to light vs firmer touch stimuli/
- stronger stimulus - higher frequency of impulses = more sensory neurons activated = more neurons activated
why are nerve impulses only propogated in one direction?
because previous parts of the axon are in refractory period
three factors that determine the speed of propagation
amount of myelination - faster if more
axon diameter - faster in larger
temperature - faster if hotter
graded vs action potential comparison
graded
- from stimulus
- can lead to AP or inhibit AP
- in dendrites/cell body
action/nerve impulse
- from threshold being reached
- in axon hillock/axon
types of propagation
continuous
saltatory
continuous propagation (4)
- step by step
- occurs in unmyelinated axons
- slower
- even distribution of voltage gated channel
saltatory propagation (5)
- leap from gap to gap
- occurs in myelinated axons
- energy efficient
- faster
- uneven dist of voltage gated channels
(most at nodes on ranvier)
how can action potential be blocked and why might this be useful?
blockage of the voltage gated Na channels
this can be useful in anesthetics
cooler temperature slows propagation of APs
can be useful in reducing pain (icing)
synapse
junction between a neuron and another cell where communication occurs
axodendritic synapse
synapse froma axon to dendrite
axosomatic synapse
synapse from axon to cell body
axo axonal synapse
synapse from axon to axon
types of synapses
electrical
chemical
electrical synapse (4)
- ion current flow through gap junctions
- bi directional
- fast
- allows connected ground of cells to synchronize APs
chemical synapse (5)
- has synaptic cleft (fluid region between)
- one way
- release of neurotransmitters form presynapic neuron
- neurotransmitters bind to receptors on post synaptic neuron whihc produces a post synaptic potential which may form an AP
- slower (synaptic delay)
post synaptic potential
when a post synaptic neuron in a chemical synapse receives neurotransmitters from presynaptic neuron, may form an AP (keep signal going)
synaptic vesicles
carry neurotransmitters to synaptic end bulb so they can cross the synaptic cleft
7 steps of chemical synapse in super detail
- nerve impulse arrives as synaptic end bulb
- nerve impulse opens voltage gated Ca channels on membrane
- increased Ca triggers exocytosis of synaptic vesicles and release of neurotransmitters
- NTMs diffuse across cleft and bind receptors on ligand gates channels on post synaptic neuron
- binding open channels and ions flow in
- ion flow may result in postsynaptic potential (PP), can be depolarizing or hyperpolarizing (type of graded P)
- depolarizing PP reaches threshold an triggers nerve impulse of post synaptic neuron
EPSP
excitatory postsynaptic potential
- depolarization of postsynaptic membrane
IPSP
inhibitory postsynaptic potential
- hyperpolarization of postsynaptic membrane
can a post synaptic neuron receive EPSPs and ISPSs at the same time?
yes, combined effect determines result (summation)
types of summation
spatial
temporal
spatial summation
several end bulbs -. one neurons
same time
different sites on membrane
spatial summation analogy
many people pushing a car, when they work together, car moves
temporal summation
one end bulb -> one neuron
different times, rapid succession
same site on membrane
temporal summation analogy
popeye
one strong guy pushing a car by himself
types of circuits (4)
- diverging - one input, many output
- converging - many input, one output
- reverberating - one input, one output, loops back again and again
- parallel after discharge - many input from lots of pathways to one output
diverging circuit example
amplification of signals to brain regions
converging circuit example
effective stimulation of inhibition of postsynaptic neuron
reverberating circuit example
waking up from sleeping
parallel after discharge circuit example
for precise activities that require multiple pathways, like math problems or playing an instrument
postsynaptic neurons integrate signals at tigger zone as: (3)
EPSPs, IPSPs, nerve impulses (from summation of epsps and ipsps)
types of neurotransmitter receptors
ionotropic
metabotropic
ionotropic receptors
- contains a NTM binding site and an ion channel (2 in 1)
- ligand gated
metabotropic receptors
- two seperate proteins, one is a binding site for NTM, the other is an ion channel
- connected by a G protein, which opens/closes the ion channel (or a second messenger)
neurotransmitter classification is based on :
size
NTMs can be classified into two groups based on size:
small molecule NTMs
neuropeptides
examples of neuropeptides (2)
endorphins, substance p
neuropeptides
- 3-40 amino acids
- can be excitatory/inhibitory
- in CNS and PNS
- also act as hormones
3 ways NTMS are removed
- diffusion - move away from cleft
- enzymatic degradation - eg acetycholinesterase
- uptake - transported by into the same cell that released them
why is there limited nervous tissue repair in CNS? (3)
- inhibitory influences form neuroglia (oligodendrocytes)
- absence of growth stimulating cues
- rapid formation of scar tissue
in PNS, repair is possible if:
- cell body is intact
- schwann cells are functional
- scar tissue doesnt form too fast
steps involved in repair process of nervous tissue (3)
chromatolysis
wallerian degeneration
formation of regeneration tube
summary of regeneration and repair on PNS tissue
regeneration requires neurolemma, which forms the regeneration tube (neurolemma absent in CNS)
chromatolysis
nissl bodies breaking into fine masses
wallerian degeneration
axon area after damage breaks up and myelin sheath deteriorates
- neurolemma remains
multiple sclerosis
deterioration of myeline sheath
- loss of myelin function
- autoimmune disease
