Lecture 2: Neuro Flashcards
What principal does the action potential follow
All or nothing
- a cell will either fire or not
What initiates the action potential
The sum (graded signal) of the inputs at the cell of the dendrites or the cell body
What can generate input that initiates action potential
- Neighbouring neurons
- direct stimulation (heat,light,chemicals,etc) that work on the opening and closing of sodium channels
The sum of all the inputs must be large enough to overcome what in order for action potential to take place and travel along the axon
Firing threshold
What are the 4 steps of action potential
- Resting state
- Depolarization
- Repolarization
- Hyperpolarization
What is the resting state step
- the membrane is maintained at its resting potential
- no net movement of ions
What is depolarization step of action potential
- loss of the difference in charge btw the inside and outside of the plasma membrane
- influx of sodium
What is the repolarization step of action potential
-change in membrane potential that returns it to a negative value just after the depolarization
What is the hyperpolarization step of action potential
- is a change in cell’s membrane potential that makes it more negative
- it is the opposite of a depolarization
Typically the action potential generates a voltage change of how much in the membrane
110-120 mV (0.1V)
- membrane potential arises from disparity of ions
How long do action potentials last
approx. 1 msec (1/1000 of a second)
What is the energy that corresponds to the voltage generated in typical action potential
~10(-20exponent) J
What do you call the period during an action potential when another action potential cannot be generated
Refractory periods
-reload times
During what steps in the action potential is the refractory period
from the beginning of depolarization until the end of repolarization
(same duration as the action potential proper)
What occurs with the sodium and potassium channels during refractory period
- sodium channels are inactive
- potassium channels are open
If there is a potent input signal during refractory period will it generate a second action potential
NO
- no matter how potent there can be no other action potential generated
When is the relative refractory period
from the end of repolarization to the end of hyperpolarization
What happens at the end of hyperpolarization
resting membrane potential is reached
Can an action potential be produced during relative refractory period
It is possible but the stimulation must be stronger than when the neuron is at rest
Why does relative refractory period require stronger stimuli to produce AP
- the membrane is hyperpolarized so it is farther away from the threshold
- many channels have not returned to their resting state
What does the ALL or NONE principle stipulate about action potentials
-they have similar intensities (same change in membrane potential)
What 2 characteristics do you examine to differentiate between a weak or a strong stimulus
- frequency
- summative
What is frequency affect on intensity of the stimulus
- it varies in function with the intensity of the stimulus
- greater the frequency of an AP the greater the intensity
What is summative affect on intensity of the stimulus
- an intense stimulus can often stimulate more sensory neurons
- recruitment of many neurons increases the intensity of the stimulus
What 2 factors affect the speed of propagation of the AP
- diameter of the axon
- degree of myelination (saltatory conduction)
Physics states:
-the resistance to the passing of an electric current is inversely proportional to …
the diameter of the canal where it is transmitted
Physics states:
-the greater the diameter..
the less resistance to current (=the more conduction)
What do the synapses allow for
-transfer of info from 1 neuron to the next or from 1 neuron to an effector cell
in the neurons from the boundaries of the synapse what are presynaptic and postsynaptic
- presynaptic (neurons that send info)
- postsynaptic (neurons that receive info
How to the neurons from the boundaries of the synapse work
1 neuron receives information from millions of presynaptic neurons & sends them to millions of postsynaptic neurons
What are the 3 names of synapses based on where they connect
- axodendritic
- axosomatic
- axoaxonal
What are the 2 classes of synapse
- electrical
2. chemical
What is structure of electrical synapse
- less abundant
- separation is ~ 2nm
- formed of proteins (connexons) which join adjacent membranes (++in myocytes of heart)
What are electrical synapses also known as
gap junctions
-as their separation is so small
What is functions of electrical synapse
allows the AP to propagate as if it were generated in the same cell
- syncytium
- unidirectional and bidirectional communication
what is a characteristic of electrical synapses
- low resistance
- extremely electrically labile (easily broken down or changed)
- intimately linked to seizure and epilepsies
What is the separation between chemical synapse cell
~1 um (~500 times further apart than gap junctions)
What are the presynaptic axon terminals of chemical synapses
the sender
-it creates vesicles which release neurotransmitters
What are the postsynaptic terminals of chemical synapses
the receiver
-they have the receptors specific to a given neurotransmitter
What happens in chemical synapse cells
the synaptic cleft prevents the AP from directly coupling w/ the postsynaptic cell
-next cell is activated by neurotransmitters
Where are neurotransmitters in the chemical synapse
they are floating
where are the neurotransmitters released from in chemical synapse
postsynaptic proteins
what process do neurotransmitters go through in chemical synapse
presynaptic RE-UPTAKE
-recycling process
what do SSRI antidepressants do
block the chemical synapse presynaptic re-uptake
What are neurotransmitters
they are chemicals which are created within the brain in order to modulate and activate chemical synapses
What are 2 main functions of neurotransmitters
- inhibition
2. Excitation
What do excitatory neurotransmitters produce
excitatory postsynaptic potentials (EPSPs)
What do EPSPs do
- opens sodium channels that also let Calcium enter
- Ex: glutamate, dopamine, epinephrine
- Brings membrane potential closer to threshold
What do inhibitory neurotransmitters produce
inhibitory postsynaptic potentials (IPSPs)
What do IPSPs do
- opens channels which allow potassium to exit OR chloride to enter
- EX: GABA, acetylcholine
- Brings membrane potential farther from threshold
Neurotransmitters are classified according to?
their structure/ from where they originated
what are the 6 classifications of neurotransmitters
- biogenic amines
- amino acids (glutamate, glycerin)
- Neuropeptides (endorphins, oxytocin)
- Purines (adenosine)
- Gases and lipids (nitric oxide, endocannabinoids)
- Other (acetylcholine)
What are 2 subcategories of Biogenic amines
- catecholamines (dopamine, noradrenalin)
- indolamines (serotonin, histamine)
What is action of neurotransmitter that involves secondary messengers
the neurotransmitter will bind to the receptor that starts the internal mechanisms for a response to the stimulus that can lead (or not) to , a postsynaptic action potential
What is the simpler action of neurotransmitters
Certain channels open with the binding of neurotransmitter to receptors
how many cranial nerves serve to bring peripheral info to the CNS
12
-numbered in roman numerals
What does the # of cranial nerve reflect
the position of the nerve along the ventral surface of the brain
what kind of function can the cranial nerves have
- sensory
- motor
- sensorimotor
how to they become integrated at the level of the brain
interface with specific nuclei
Olfactory nerve : # , function and nucleus
I.
- sensory: smell
- motor: none
- nucleus: olfactory bulb
Optic nerve: # , function and nucleus
II.
- sensory: vision
- motor: none
- nucleus: lateral geniculate, superior colliculus
Occulomotor nerve: # , function and nucleus
III.
- sensory func: none
- motor: eye movement, pupil constriction
- nucleu: oculomotor nucleus, Edinger-Westphal nucleus
Trochlear: # , function and nucleus
IV.
- sensory f.: none
- motor f.: eye movements
nucleus: trochlear nucleus
Trigeminal: # , function and nucleus, 3 divisions
V.
- sensory f.: sensations frm the skin of face, nose, mouth
- 3 divisions: ophthalmic (eyes and nose), maxillary (upper lip), mandibular (lower jaw, largest, dentists favorite)
- motor f.: chewing & swallowing
- nucleus: spinal & sensory Trigeminal nuclei, mesencephalic nucleus
Abducens: # , function and nucleus
VI.
-sensoryf.: none
Motor f.: eye movements
-nucleus: abducens nucleus
Facial: # , function and nucleus
VII.
- sensory f.: taste frm anterior 2/3 of mouth
- motor f.: facial expressions, crying, salivation
- nucleus: spinal trigeminal, nucleus of the solitary tract, superior salivatory nucleus, facial motor nucleus
Auditory (vestibulocochlear): # , function and nucleus
VIII.
- sensory f.: hearing, balance
- motor f: none
- nucleus: cochlear and vestibular nuclei
Glossopharyngeal: # , function and nucleus
IX.
- sensory f.: taste frm posterior tongue and throat
- motor f.: swallowing, salivation
- nucleus: spinal trigeminal nucleus, nucleus of the solitary tract, inferior salivatory nucleus, nucleus ambiguous
Vagus: # , function and nucleus
X.
- sensory f.: taste sensation frm neck and abdo
- motor f.: swallowing, control of larynx, parasympathetic nerves to heart and viscera
- nucleus: spinal trigeminal nucleus, nucleus of the solitary tract, dorsal motor nucleus, nucleus ambiguous
Spinal Accessory
XI.
- sensory f.: none
- Motor f.: movement of shoulders and head
- nucleus: accessory nucleus
Hypoglossal
XII.
- sensory f.: none
- motor f.: movement of the tongue
- nucleus: hypoglossal nucleus
Structure of meninges
- consists of 3 diff. CT membranes
- they differ according to thickness & toughness of the T
What are the 3 membranes of meninges (from skull to brain)
- DURA MATER
- ARACHANOID MATER
- PIA MATER
What is the function of meninges
- protection
- separation of tissues
What is structure of the DURA MATER
- least malleable, most rigid
- has 2 layers that are fused across the brain except at the DURAL SINUSES (where venous blood collects and is sent into internal jugular)
What are the 2 layers of the DURA MATER
- External / Periosteal layer:
- attaches to the interior of the cranium bone - Internal/ Menigeal layer:
- external layer of the CNS
Where do certain extensions of the dura mater introduce themselves
-btw the hemispheres or other separations of the brain parts
(falx cerebri, falx cerebelli, tentorium cerebelli)
What is the function of dura mater
- fixes brain to the cranium
-limits movement of the brain
NOTE:
The dura mater can actually
cause damage to the underlying
cortex when the brain sustains
an injury
What is structure of arachnoid mater
-flexible envelope
-Separated from dura mater by the subdural space and from the pia mater by the subarachnoid space
Filled with CSF
-attached to the pia mater by filamentous extensions
What allows the passage of the venous blood of the Dural sinuses
The arachnoid villi cross the dura mater & penetrate in the Dural sinuses located in the superior portion of the cranial cavity
What is the PIA Mater: structure/ function
- vascularized
- firmly adheres to CNS (follows each convolution of the brain)
- location of meningiomas
Where is CSF generated and flows through
within the ventricles
-open spaces within the brain
How many ventricles are there in the brain
4
- 2 lateral (w/ several landmark divisions like the horns)
- 3rd and 4th ventricles
How do ventricles communicate w/ each other
through specialized passageways called :
- interventricullar foramen (of Monroe)
- Cerebral Aqueduct (of Sylvius)
What lines the ventricles
ependymal cells
-give rise to CSF
What is function of CSF
- ensures that the CNS float
- provides nutrients and recycles debris frm the CNS
What produces CSF
Produced by the choroid plexus that are a cluster of porous capillaries surrounded by a layer of ependymal cells linked by tight junctions & bearing numerous microvilli
Structure and function of choroid plexus
There is a plexus on the roof of every ventricle
Blood filtrate passes with ease through the endothelium of the capillaries because of the large fenestration
The ependymal cells monitor substances that pass in the CSF because they have pumps controlling ions
How much CSF is produced per day
1 Liter/ day
capacity: 150ml
renewal: every 3-4 hrs
circulation of CSF
- lateral ventricles
- interventricular foramen (of monroe)
- 3rd ventricle
- cerebral aqueduct (of sylvius)
- 4th ventricle
- median & lateral aperture
- central canal
- subarachnoid space
- dumps into dural venous sinuses and lymphatic vessels
