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pr3153 COPY (Adeline) > ic2 and ic3 - neurophysiology > Flashcards

ic2 and ic3 - neurophysiology Flashcards

1
Q

what comprises the peripheral and central nervous systems

A

peripheral comprises of nerves arising from spinal cord

central nervous system encompasses the brain and spinal cord

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2
Q

what is the brain and spinal cord covered by

A

brain covered by skull

spinal cord covered by vertebral column or spine

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3
Q

how are the spinal nerves sectioned

A

cervical spinal nerves, thoracic spinal nerves, lumbar spinal nerves, sacral spinal nerves and coccygeal nerve

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4
Q

what do nerves consist of

A

nerves consist a number of nerve fibers

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5
Q

locate the cranium, cerebral hemispheres and cerebellum

A

cranium is the bone that forms the head

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6
Q

what are the different types of nerve fibers and how do you differentiate them

A

afferent and efferent

afferent nerve fibers are fibers that carry info from PNS to CNS, passes info to cells in neurons in CNS for processing

efferent nerve fibers are fibers that originate from within the CNS and neurons generate signals to convey via the efferent fibers to reach the PNS

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7
Q

list examples of afferent nerve fibers

A

pacinian corpuscle, nociceptors

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8
Q

draw how afferent and efferent fibers lead to various effects (sensation/ perception, emotion/ cognition, behavior and homeostasis)

A
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9
Q

what is a receptor field

A

an area on the skin where the stimulus will excite a receptor

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10
Q

what is the structural features of the pacinian corpuscle

A

pacinian corpuscle receptor is embedded in skin which has a receptor field

pacinian corpuscle is an enclosed nerve ending with layers of connective tissue

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11
Q

what is the process of signal transduction in the pacinian corpuscle

A

the pacinian corpuscle is specialised and will convert physical energy from an external pressure into an electrical signal

the afferent fiber carries the information through long fibers (axons) to reach the spinal cord in the CNS which may then break up into branches (collaterals)

collaterals further break up into branches that end as a knob like structure called axon terminals

upon reaching the CNS, the information is transferred to neurons across synapses

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12
Q

what is the structural property of the pacinian corpuscle axon

A

it is A-beta myelinated

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13
Q

compare the structure of the panician corpuscle to the nociceptor

A

panician corpuscle is an enclosed nerve ending vs the nociceptor is a free nerve ending

panician corpuscle also has a myelinated axon (Abeta) vs the nociceptor has mostly an unmyelineated axon (C fiber) (and some THINLY myelinated axon which is Adelta fiber)

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14
Q

how do nociceptors sense its stimuli

A

nociceptors has Trpv1 protein molecule which is a pharmacological receptor which allows free nerve endings to sense tissue damaging stimuli

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15
Q

how do neurons receive information

A

when information is conveyed from receptors along afferent to CNS, information is transferred to neurons across synapses in CNS

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16
Q

what is the presynaptic structure and what is the postsynaptic structure

A

presynaptic is axon terminals

postsynaptic is dendrites of neurons that are excitatory in nature or soma (for inhibitory synapse)

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17
Q

what happens when information reaches neurons

A

neurons generate another signal that is conveyed to the efferent

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18
Q

where are efferent nerve fibers mostly located in

A

cell bodies efferent nerve fibers are mostly located in ventral horn of the spinal cord and they exit through the ventral root of the spinal cord (travel through spinal nerves and ultimately synapse with the skeletal muscle cells found in the NMJ)

efferent nerve fibers are mostly in the grey matter

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19
Q

what kind of membranes do afferent, efferent and neurons have that allows for communication as part of signalling

A

excitable membranes thus generation of action potential allows for communication as mode of signalling

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20
Q

which part of the spinal cord is the ventral horn

A

it is located in the lumbar section of the spinal cord

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21
Q

what does the force of muscle contraction depend on

A

each efferent can control multiple fibers and the force of muscle contraction depends on the number of motor units the efferent activates

“motor unit” is the combination of an individual motor neuron and all of the muscle fibers that it innervates

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22
Q

what does it mean by “signalling” and what types of “signalling” are there

A

involves neurons sending electrical signals (action potentials) along axons to achieve long distance, rapid communication to reach its own terminals through a mechanism called conduction

signalling intracellularly or intercellularly

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23
Q

when are action potentials generated

A

it is generated in two scenarios

  1. when an external stimulus is applied
  2. when information is transferred to neuron
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24
Q

what are the principles behind generating an action potential

A
  1. skeletal and cardiac muscles are excitable membranes that exhibit resting membrane potentials
  2. when perturbed these membranes are able to generate action potentials due to electrical changes that are depolarising in nature
  3. action potentials occur due to opening of voltage gated channels that alter the membrane permeability of Na+ and K+
  4. the depolarisation is due to the net efflux of cations to inside of cell
  5. action potential involves a rapid and large depolarisation from a threshold membrane potential
  6. threshold membrane potential is more positive than the resting membrane potential
  7. after peak of depolarisation, the membrane rapidly repolarises back towards the resting membrane potential
  8. action potential is still generated even if the depolarisation does not reach the threshold membrane potential at the trigger point but it means that the neuron will not fire the action potential
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25
Q

compare how does the action potential travel between a myelinated and unmyelinated axon

A

for a myelinated axon, the action potential jumps from node to node (nodes of ranvier)

for an unmyelinated axon, the action potential is generated from point to point

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26
Q

what are nodes of ranvier

A

empty spaces between the myelin sheath

the action potential jumps over the myelin sheath for myelinated axons instead of across it

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27
Q

does the action potential travel faster in myelinated or unmyelinated axons

A

the action potential travels faster in myelinated axons as the presence of nodes of ranvier speeds up conduction of action potential

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28
Q

what is the type of conduction called when the action potential is sent through a myelinated axon

A

saltatory conduction

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29
Q

describe the different phases part of generating an action potential

A

phase 1: RMP (neuron at rest at -60mV which is determined by distribution of K+, Na+ and Cl-, Na+ conc outside of cell while K+ conc inside of cell)

phase 2: depolarising stimulus (action potential begins when a depolarising potential reaches the trigger zone and depolarises the membrane, the action potential is generated by the opening of the ligand gated channels by the excitatory neurotransmitter at the NMJ and synapses within the CNS due to excitatory synaptic transmission)

phase 3: threshold membrane potential aka the voltage required to open the Na channel (as the cell depolarises, voltage gated Na+ channels are activated, making the membrane more permeable to Na+)

phase 4: rising phase - upstroke of action potential (as the Na channel opens, Na rapidly enters the cell which depolarises the cell)

phase 5: overshoot phase - upstroke of action potential (inside of the cell becomes more positive than outside due to entry of Na+ thus reversing the membrane potential polarity)

phase 6: falling phase - downstroke of action potential (voltage gated Na channels become inactivated while voltage gated K channels open, which makes membrane more permeable to K and as K moves out of the cell, the membrane potential rapidly repolarises)

phase 7: recovery phase (membrane potential returns to normal which occurs as the voltage gated K channels close)

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30
Q

what kind of channels do ions affect vs what kind of channels do neurotransmitters affect

A

ions -> voltage gated channels

neurotransmitters -> ligand gated channels

31
Q

what is the threshold membrane potential

A

the voltage required to activate the opening of Na channels

32
Q

what is resting membrane potential (RMP)

A

voltage difference across membrane

RMP usually -60mV -> negative membrane potential reflects unequal distribution of charges and the inside of cell is more negative than outside

33
Q

is there movement of ions at resting membrane potential

A

yes, there is continuous diffusion of ions but RMP reflects a balance of movement of ions (no equilibrium but net movement of ions at steady state)

34
Q

what is meant by “equilibrium potential” (explain using K+ ions)

A

it means that the movement of an ion is at equilibrium

at -65mV, there is more K+ inside and less outside which establishes chemical concentration gradient whereby ions from inside diffuse to outside across the membrane

K+ also experiences an electrical gradient as RMP is negative while K+ is positive thus causing attraction and pulling of K+ from outside to inside

overall, K+ experiences concentration gradient and electrical pull thus combined K+ experiences electrochemical gradient which facilitates its movement

K+ has an equilibrium potential of -97mV whereby at this potential, the movement along concentration gradient is balanced by movement along electrical gradient and at this point if there is a change in membrane potential it triggers the movement of K+ ions leading to either a net influx or efflux

35
Q

what happens when there is hypokalemia

A

hypokalemia means decrease in serum K+ aka outside of cell

this causes the chemical gradient to be sharper and K+ diffuses along the chemical concentration gradient (thus K+ move out of the cell -> membrane becomes more -ve charged) which causes hyperpolarisation of membrane

hyperpolarisation of membrane indicates less excitability as it moves membrane away from threshold

36
Q

what does hyperpolarisation of a membrane indicate

A

hyperpolarisation of a membrane indicates less excitability of a membrane as it moves the membrane away from its threshold potential

37
Q

what does the generation of action potential in neurons require

A

generation of action potential in neurons require the release of excitatory neurotransmitters into synaptic cleft which will combine with receptor of the postsynaptic membrane causing depolarisation of the membrane at the excitatory postsynaptic potential (EPSP)

38
Q

what is the process of synaptic transmission in triggering the contraction of skeletal muscles

A

action potential (nerve impulses) travel from brain or spinal cord and propagates down a motor neuron to reach a skeletal muscle fiber whereby the excitation occurs at the NMJ

this transmission of messages from the brain or spinal cord can trigger the contraction of skeletal muscles

39
Q

what is meant by “neuromuscular joint”

A

NMJ is a chemical synapse where axon terminals of a motor neuron meets the motor end plate of a skeletal muscle fiber

40
Q

where are the steps involved in synaptic transmission

A

receptive step and translating step

[receptive step] the arrival of the action potential at the presynaptic cell (presynaptic axon terminal) which activates the receptive step and starts the process -> action potential depolarises the synaptic membrane which leads to the opening of voltage gated Ca channel -> influx of Ca into presynaptic terminal and then fusion of synaptic vesicle with the presynaptic membrane leads to a release of neurotransmitter ACh into synaptic cleft

[translating step] ACh binds to postsynaptic ligand gated receptor (ie. nicotinic receptor) to trigger opening of Na channels (and thus influx of Na) when membrane potential reaches threshold potential

41
Q

what are sensory receptors and list examples of sensory receptors

A

sensory nerve ending that recognises a stimulus and in response to the stimuli initiate sensory transduction in the same cell or in an adjacent one -> receptors then send their info to CNS via afferent nerve fibers

mechanoreceptor, nociceptor, chemoceptor, photoreceptor, thermoceptor, proprioceptor

42
Q

what is sensory transduction

A

sensory transduction is the conversion of a sensory stimuli into a neuronal signal/ activity

43
Q

how does processing of sensory information occur

A

sensory transduction occurs where external stimuli converted into action potential (greater stimulus strength gives greater frequency of action potential)

phase 1: application of stimulus to the receptor generally results in depolarisation of the receptor membrane

phase 2: receptor potential travels to trigger zone and when depolarisation reaches trigger zone, action potential generated

phase 3: action potential propagated along axon

phase 4: action potential reaches axon terminal resulting in release of transmitter which affects the neuron next in line

44
Q

what do seizures and epilepsy result from

A

seizures and epilepsy result from hyperexcitability (rhythmic firing of a relatively large population of neurons)

abnormal activity in small areas of cortex (called foci) provide triggers for seizures which then spreads to other synaptically connected regions

45
Q

what is epilepsy

A

epilepsy is when there are multiple unprovoked seizures

46
Q

how are seizures controlled

A

seizures can be controlled by enhancing the function of inhibitory synapse -> limit action potential firing by using drugs that act on voltage gated Na channels

inhibition involves hyperpolarisation of the membrane to further away from the threshold that can be induced by inhibitory transmitters like GABA (inhibitory postsynaptic potential)

47
Q

what do diseases generally result from

A

diseases generally result from interruption of signal through

  1. disruption of action potential
  2. lesion of the region due to trauma and thus no action potential thus affecting comunication
  3. degeneration of cells (alteration of neurochemistry due to aging or disease)
48
Q

what is the unique feature of the somatosensory cortex

A

the somatosensory cortex is contralateral in nature

it comprises of two separate pathways for pain and touch (spinothalamic pathway and dorsal column pathway respectively)

49
Q

what are the two pathways the somatosensory cortex has, and outline these pathways

A

[spinothalamic pathway: pain pathway from spinal cord] starting on left side, from nociceptor receptor travel through Adelta and C afferent into spinal cord -> first order neuron reaches second order neuron in the gray matter in the dorsal horn of spinal cord -> crosses midline -> travel up to thalamus where second order neuron meets third order neuron -> third order neuron meets forth order neuron in somatosensory cortex -> sensation perceived

[dorsal column pathway: touch pathway] starting on left side, from pacinian corpuscle travel through Abeta fibers to reach spinal cord -> first order neuron reaches second order neuron (still on left side) in the medulla -> crosses midline -> second order neuron meets third order neuron in the thalamus -> third order neuron meets forth order neuron in the somatosensory cortex -> sensation perceived

50
Q

what is a laminae, how many laminae does the spinal cord have and which laminae are the dorsal horn

A

laminae are spaces between an arbiturary line drawn to segment the spinal cord and dorsal horn

ten

dorsal horn is laminae I to VI

51
Q

what does sensory processing rely on

A

sensory processing relies on using action potential as signal to relay information

52
Q

what is somatosensory homunculus

A

map along the cerebral cortex of where each part of the body is processed

53
Q

what is meant by “touch allodynia”

A

touch allodynia is when there is pain sensation to a normally non painful stimulus (pain to a stimulus normally sensed as touch)

(shown by new graph)

54
Q

what is meant by “hyperalgesia”

A

hyperalgesia is when there is increased pain to a given noxious stimulus

(shown by shifts in graph)

55
Q

explain how touch allodynia occurs (compare the spinothalamic tract when in normal condition vs in touch allodynia)

A

in normal conditions, the touch and pain signals follow its normal paths (dorsal column tract and spinothalamic tract) respectively without interfering with either paths

in touch allodynia, there is alteration in inhibitory neurons which may result in an increase or decrease inhibition of spinothalamic tract neuron by touch pathway

the inhibitory neuron now excites and transmits signal along spinothalamic tract which suggests that the phenotype of the neuron has now changed

normally, inhibitory neurotransmitter GABA acts on spinothalamic neuron by opening Cl channels -> Cl moves along electrochemical gradient from outside to inside and hyperpolarises the spinothalamic tract neuron thus making it less excitable -> when there is chronic pain, Cl gradient is altered so much such that when inhibitory neuron releases GABA, Cl may move out of neuron instead, and since Cl is negatively charged, its outward movement causes neuron to polarise and excite -> spinothalamic tract neuron becomes sensitised (normally c fiber has low activity else we would always be feeling pain vs now transmitters are released in excessive amounts so when there is tissue damage, properties of spinothalmic neuron is altered which affects the threshold and makes it more excitable)

56
Q

how might there be modulation of pain (enhancement or suppression of pain)

A

occurs through segmental modulation (gate theory) or through descending pathway

[gate theory] stimulation of large diameter afferents (aka Abeta afferents - for touch) (gate for pain signal closes) excites inhibitory interneuron that in turn decreases transmission of pain signal in spinal cord (activation of Abeta fibers can help reduce and inhibit the transmission in small diameter Adelta and C fibers)

[descending pathway] stress/ morphine/ expectation/ context -> stimulation of midbrain periaqueductal gray (PAG) activates medullary regions (nucleus raphe magnus) which excites interneuron (interneuron enkephalin) in spinal cord thus inhibiting transmission of pain signal (inhibit txf of signal from interneuron in spinal cord to spinothalamic neuron) (stimulating PAG releases endogenous opioid which may play a role in suppressing pain)

57
Q

what are the properties of morphine

A

mimic effect of enkephalin (an interneuron in the spinal cord) and thus excite neurons in the midbrain periaqueductal gray to activate the inhibition of pain

58
Q

what are the different types of motor behavior and what do each type of motor behavior mean

A

reflexes, rhythmic motor patterns, voluntary

reflexes are involuntary movements
rhythmic motor patterns require voluntary initiation and termination, voluntary movements are goal directed

59
Q

what are the various brain parts and its corresponding function regarding motor behavior

A

cortex -> voluntary movement
brainstem -> postural reflexes, rhythmic motor patterns
spinal cord -> site of motor neurons, control of muscle activity through efferent fibers

60
Q

what does the brain stem comprise of

A

midbrain, pons, medulla

61
Q

what is the significance of an efferent nerve fiber in terms of motor behaviour (esp reflexes)

A

it is the final common pathway as all signals from cortex or brainstem to become behavior must reach spinal cord and the efferents will control the muscles to bring about behavior

for reflexes there is direct excitation of the efferents without going to the cortex

62
Q

what are the main functions of the cerebellum

A

coordination of limb and eye movement, maintain balance and muscle tone

63
Q

what is the effect if there are lesions in the cerebellum

A

any lesions will disrupt its function and indirectly affect movement by adjusting the output of the efferent via cortex and brainstem

64
Q

what is the function of the basal ganglia

A

the normal functions of basal ganglia includes initiation and selection of motor programme that is appropriate

the basal ganglia also interacts with the cortex

65
Q

the basal ganglia has a special type of neuron, what is it

A

it has dopamine neuron

66
Q

what does it mean by “input region” and “output region” of the basal ganglia? also differentiate the input and output regions of the basal ganglia (and draw the location)

A

input regions receives information while output regions initiates movement

input regions: caudate, putamen
output regions: globus padillus, subthalamic nucleus, substantia niagra

67
Q

what are the effects if basal ganglia is damaged

A

disorder of movement: tremor at rest, rapid flicking movements/ chorea, violent failing movements/ ballism, slow writhing or twisting movement (athetosis/ dystonia), bradykinesia (slowness of movement)

disorder of posture: rigidity

68
Q

what is “chorea”

A

movement disorder that causes sudden, unintended, and uncontrollable jerky movements of the arms, legs, and facial muscles

69
Q

what is “ballism”

A

a severe form of chorea characterized by involuntary, violent flinging movements of the limbs

70
Q

what is “bradykinesia”

A

slow movements

71
Q

what are the ingredients for a voluntary movement

A
  1. knowledge of where the body is in space (mental body image is generated by inputs from somatosensory, proprioceptive and visual inputs to the posterior parietal cortex)
  2. where it intends to go (importance of prefrontal cortex (anterior frontal lobes) that is assoc with abstract thought and decision making)
  3. selection of a plan to get there (importance of premotor cortical areas along with cerebellum for movement coordination triggered by motor cortex and basal ganglia)
  4. memory of plan until appropriate timing for it to be carried out
  5. instruction for implementation of the plan (go command given by primary motor cortex along with basal ganglia and cerebellum)
72
Q

map out the locations of the various important regions for voluntary movements

A

posterior parietal cortex
prefrontal cortex
premotor cortex
primary motor cortex (and supplementary motor area SMA)

73
Q

what are the principles of sensory processing in determining the location, quality and intensity of a stimuli

A

[location] signal travels along topographic lines (different population of afferents will relay information from different locations - receptors from hand and food remain separate from each other and will receive diff information, separation of topography is retained all the way until cortex - relay from each organ will relay to its assigned area in somatosensory cortex presented as somatosensory homunculus)

[quality] signal travels along topographic (labelled) lines whereby receptors and its primary afferent normally respond to only one type of stimulus which also needs to be adequate -> allows identification of modality (type/ quality) - each receptor has its own selective stimulus

[intensity] signal travelling along topographic lines encode for properties of the stimuli and includes intensity -> more intense stimulus will have more number of action potentials per unit time bc more intense stimulus cause more receptors to be affected thus more neurons generating action potential (frequency code aka population code)

pr3153 COPY (Adeline) (18 decks)

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