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GI physiology > Synapses, chemical communication > Flashcards

Synapses, chemical communication Flashcards

1
Q

neurones communication: electrically VS chemically:

A
  • electrical communication = movements of ions in an out of cell membranes
  • chemical communication = release of neurotransmitters to nearby receptors at synapses
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2
Q

neurone communication process:

A
  • at the connection btw 2 neurones = space (synaptic cleft, the synapse is where the conversion from an electrical signal to a chemical one occurs, particularly in chemical synapses), does not allow electrical current to flow, so a chemical signal = required as an intermediate.
    (after becoming chemical, graded or AP in 2nd (post-synaptic cell).
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3
Q

Structures of synapses:

A

Presynaptic neurone
synaptic cleft
postsynaptic neurone

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4
Q

Presynaptic neurone:

A

neurone that transmits a signal to the synapse
- synaptic vesicle: sacs of chemicals released when signal reaches axon terminal
- neurotransmitters: chemicals found in synaptic vesicles that will excite postsynaptic neurone, muscle or gland

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5
Q

Synaptic cleft:

A

space between axon terminal + postsynaptic cell
- electrical signal can’t pass but chemical can !!

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6
Q

Postsynaptic neurone:

A

the neurone that receives the signal from the synapse
- neurotransmitter receptors = proteins found in postsynaptic cell membrane that bind to chemical neurotransmitter
- ion channels: proteins in postsynaptic cell membrane that open to allow electrical impulses to conduct through
SLIDE 11

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7
Q

Events at the synapse:

A
  • pre-synaptic events at the axon terminal:
    1) action- potential
    2) Ca2 entry (voltage-gated Ca2 channels open and calcium enters axon terminal)
    3) NT release (in synaptic vesicles) (it’s the Ca2 entry that causes exocytosis of vesicles and release of neurotransmitter at axon terminal)
  • post-synaptic events at the dendrites:
    4) NT receptor activation
    5) ions enter (neurotransmitter binding to receptor causes ion channel to open et they move to post-synaptic cell membrane)
    6) graded potential (influx of ions in post-synaptic cell = graded potential at dendrite)
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8
Q

Post-synaptic potential (PSP):

A

graded potential in post-synaptic cell
- if positive ions flow in post-synaptic membrane = excitatory PSP
- if negative = inhibitory PSP
type of ion channel depends on neurotransmitter + its receptor

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9
Q

PSP’s:

A

their combination of activity determines whether cell reaches threshold for action potential.
also they can do it only if summed (not only one EPSP

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10
Q

axon hillock keeps score of:

A

all graded potentials received at dendrites

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11
Q

Temporal VS Spatial summation:

A
  • temporal = 1 presynaptic = increases frequency of impulses = more neurotransmitters = released in quick succession (same location, stimulation increases timing)
  • spatial summation = postsynaptic neurone = stimulated by multiple pre-synaptic neurones at the same time
    (same timing, simulation increases locations)
  • IPSP and EPSPS can also be summed and cancel eachother out.
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12
Q

neurones normally = one neurotransmitters, but a lot can respond to several neurotransmitters

A

slide 29

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13
Q

Classification of neurotransmitters by chemical structure:

A
  • AcH (has both excitatory and inhibitory effects) (slide 31)
  • Biogenic amines: catecholamine + serotonin
  • Amino acids: glutamine, glycine, GABA
  • Peptides: endorphins, substance p
  • Chemical messengers: ATP + dissolved gases NO
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14
Q

neurotransmitters that open ion channels = direct:

A
  • promote rapid response (fast synapses)
  • ex: AA’s + AcH
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15
Q

neurotransmitters that act through 2nd messenger = indirect:

A
  • promote long lasting effects “slow synapses”
  • ex: biogenic amines + peptides + dissolved gases
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16
Q

effects of neurotransmitters:

A

mediate changes in membrane depending on: amount of neurotransmitters released + amount of time neurotransmitter = bound to receptor
neurotransmitters = always affect the receptor donc must be deactivated

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17
Q

Deactivation of neurotransmitters effects:

A
  • Active transport: neurotransmitter = actively pumped back to pre-synaptic or nearby neuroglia
  • Enzymes: present in synaptic cleft = will breakdown neurotransmitter to stop signal
  • Diffusion: neurotransmitter = diffuses away enough from cleft for signal to stop (slide 36)
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18
Q

AcH enzymes:

A

Acetylcholinesterase: enzyme in synaptic cleft that degrades AcH
AcH = transferred back to presynaptic terminal to make more AcH with the help of enzyme ChAT
(AcH = made by AcetylCoA + choline)

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19
Q

drug synaptic activity altering actions:

A
  • synthesis, storage, release of neurotransmitters
  • modifying neurotransmitter interaction with its receptor
  • influencing neurotransmitter reuptake or destruction
  • replacing deficient neurotransmitter with a substitute
    (ex: SSRI + tetanus toxin)
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20
Q

Convergent pathways:

A

one cell = influenced by many others

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21
Q

Divergent pathways:

A

one cell = influences many others

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22
Q

sensory processing functions:

A
  • Attention + arousal
  • perception of the world around us
  • memory
  • emotion
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23
Q

Perception =

A

conscious interpretation of the external world created by patterns in our brain.

24
Q

perception = limited by:

A
  • receptor types: humans can’t sense UV lights…
  • level of sensitivity: humans can’t hear certain frequencies
  • level of central processing and filtering: what grabs your attention in a room depends on your past experiences
25
Q

Processing at the perception level:

A

(outer region), cortex = responsible for:
- sensation: awareness of stimuli
- perception: interpretation of stimuli

26
Q

Sensory processing:

A
  • sensory neurones = cells in afferent division of PNS,+ receive info from PSR
  • sensory nerves = bundles of sensory axons in PNS that contact neurones in CNS
27
Q

Main divisions of sensory processing are:

A
  • Somatic
  • Visceral
  • Special senses
28
Q

Peripheral nervous system organisation:

A
  • (afferent) sensory division: (carries info from receptor to CNS)
  • somatic afferent nerves = carry impulses from skin, skeletal muscles, joints
  • special sense afferent nerves: eyes, ears, taste, smell
  • visceral afferent nerves: impulses from organs within ventral body cavities (NOT) consciously perceived
29
Q

Sensory receptor location:

A
  • as a specialised ending of peripheral sensory neurone
  • as a separate receptor cell closely associated with peripheral ending of a sensory neurones
    (slide 49)
30
Q

sensory receptor action:

A
  • converts information into electrical signal:
  • stimulus: change detectable by body
  • receptor: structure within an afferent neurone that responds to stimuli by producing depolarising GP
  • sensory transduction: conversion of stimulus energy (ex: light, heat, sound), into electrical energy
31
Q

Receptor potentials:

A
  • depolarising GP’s that activate sensory neurones
  • no refractory period, summation to rapidly successive stimuli possible
  • converted into action potential at sensory neurone level:
  • if receptor = part of afferent neurone = voltage Na+ ion channel change local flow
  • if receptor = next to afferent neurone, neurotransmitter release depolarised after neurone
    ( this trigger zone = on dendrite not axon hillock)
32
Q

sensory receptor on afferent neurone (slide 52)

A

Stimulus (yellow circle): The sensory receptor, which is the modified ending of the afferent neuron, detects a stimulus. This could be any form of physical, chemical, or mechanical stimulus, like pressure or temperature.

Stimulus-sensitive nonspecific cation channel (labeled 1): In response to the stimulus, stimulus-sensitive channels open, allowing sodium ions (Na⁺) to enter the neuron. This causes depolarization, making the inside of the neuron more positive.

Voltage-gated Na⁺ channels (labeled 2): Once the membrane reaches a certain level of depolarization (threshold potential), voltage-gated Na⁺ channels open, allowing more Na⁺ ions to rush into the neuron.

Action potential (labeled 3): As more sodium ions enter, the neuron becomes further depolarized, leading to the generation of an action potential. This electrical signal then travels along the afferent neuron fiber to the central nervous system for further processing.

33
Q

sensory receptor next to afferent neurone (slide 53) (look at slide 54)

A

Stimulus (yellow circle): A stimulus triggers the activation of the sensory receptor (a separate receptor cell).

Stimulus-sensitive nonspecific cation channel (labeled 1): The stimulus opens channels that allow sodium ions (Na⁺) to enter the receptor cell, causing depolarization (increased positive charge inside the cell).

Voltage-gated Ca²⁺ channel (labeled 2): As the depolarization increases, voltage-gated calcium channels open, allowing calcium ions (Ca²⁺) to enter the receptor cell.

Neurotransmitter release (labeled 3): The influx of calcium triggers the release of neurotransmitters from the receptor cell into the synaptic cleft, the space between the receptor and the afferent neuron.

Chemically gated receptor-channel (labeled 4): On the afferent neuron, chemically gated channels respond to the neurotransmitter by allowing Na⁺ ions to enter the neuron, causing depolarization.

Voltage-gated Na⁺ channel (labeled 5): If the depolarization in the afferent neuron reaches the threshold, voltage-gated sodium channels open, leading to further Na⁺ influx.

Action potential (labeled 6): The depolarization triggers an action potential, which propagates along the afferent neuron fiber, transmitting the signal to the central nervous system.

34
Q

sensory receptor types:

A
  • photoreceptors: wavelenghts of light
  • mechanoreceptors: mechanical movement: muscle stretch, touch, sound, blood pressure
  • thermoreceptors: heat and cold
  • osmoreceptors: concentration of solutes
  • chemoreceptors: presence of specific chemicals: taste, smell
  • nociceptors: tissue damage
35
Q

adequate stimulus:

A
  • sensory receptors = activated by specific stimulus with different sensitivities = adequate stimulus
  • adequal stimulus at receptor = changes in electrical activity in sensory neuron
  • some receptors = respond weakly to other stimuli in addition to their adequate stimuli
    ex!!: photoreceptors = respond to light, but they can weakly respond to “mechanical touch”, although it’s not their ADEQUATE stimuli
36
Q

stimulus intensity:

A
  • number of receptors stimulated: stronger stimuli = affect larger areas
  • frequency of action potentials: stronger stimuli = larger receptor potential = greater frequency of action potentials
37
Q

Stimulus- response changes:

A
  • body = able to adjust to stimulus as more info = brought in
  • response to stimulus can be altered in 3 ways: receptor adaptation, neurone habituation, neurone sensitivity
38
Q

Sensory receptor adaptation:

A

receptors can “adapt” to stimuli by decreasing the extent of depolarization to sustained or repeated stimuli.
if stimulus = repeated enough = frequency of AP = generated to same stimulus = decreased = receptor no longer reacts to same degree as before
(ex: smell that goes away after a while cos u don’t “smell” it anymore)

39
Q

Types of receptor adaptation:

A
  • Tonic receptors: do not adapt, or adapt very slowly + continue to generate AP’s even after a lot of stimuli + used for maintenance functions, balance + posture information = always relayed to CNS via stretch receptors
  • Phasic receptors: rapidly adapting + stop responding quickly when stimulus is repeated + used for signaling stimulus changes + intensity (ex: touch receptors adapt differently to things worn)
40
Q

Phasic receptors:

A

= fast adapting
report changes in the environment
burst of firing at beginning + end of stimulus

41
Q

Tonic receptors:

A

= slow adapting or not at all
constant firing rate
for situations where continuous info about stimulus = valuable

42
Q

Neurone habituation:

A

habituation: neurones will reduce their response to repeated stimuli by depressing synaptic activity
(ex: repeated stimulus = reduces activity through changes in voltage gated Ca2+ channels in the presynaptic terminal)

43
Q

Neurone sentisization:

A
  • neurones = increase their responsiveness to stimuli following strong or noxious stimulus
44
Q

Orders of sensory processing:

A

1st order sensory neurone: peripheral sensory neurone that first detects the stimulus
2nd = in spinal cord, medulla oblongata
3rd = in CNS and thalamus of the brain
(slides 67-68-69)

45
Q

labeled lines:

A

info from receptors = follow specific paths + locations + organised into regions of the brain
info + stimuli = conveyed to CNS via these organised “labeled lines”

46
Q

Coding of a stimulus:

A

determining type of stimulus or receptor activated depends on:
pathway it takes + area of cerebral cortex it travels to
amount of area of the cortex devoted to each region = related to the regions sensitivity

47
Q

Sensory discrimination:

A
  • sensory neurones respond to stimulus information within small regions of input = receptive fields
  • sensitivity of area = determined by amount of receptors per area,
    where most receptors in small area = highest sensitivity
48
Q

lateral inhibition:

A

helps increase sensory discrimination + loca when receptive fields = dense
receptive field closest to stimulus = most active et le nearby = weakly activated
- this occurs at level of receptors and CNS via inhibitory neurone activation + increase contrast of stimuli perception

49
Q

The special senses:

A

= located in specialised sense organs + bring in sensory information from environment to CNS:
olfactory, gustatory, auditory, vestibular, visual

50
Q

mucosas + anatomical structures of diff senses:

A
  • olfactory: stimulus: dissolved in olfactory mucosa, anat: olf epithelium + bulb + nerve (CN I) + limbic + hypothalamus + olf cortex
  • gustatory: s: dissolved in saliva, anat: tongue + facial nerve (CN VII, glossopharyngeal nerve CN IX, vagus nerve CN X) + medulla + thalamus + gustatory cortex
  • auditory system: s: fluid vibration in inner ear, (receptor = hair cells in cochlea), anat: ext ear + int ear + middle ear + vestibulocochlear nerve (CN VIII) + thalamus + auditory cortex
  • vestibular system: s: head movement, fluid movement in inner ear, (receptor = hair cells in semicircular canals), anat: inner ear + vestibulocochlear nerve (CN VIII) + pons + medulla + cerebellum + cerebral cortex
  • visual system: s: light, (receptors = photoreceptors), anat: eye + accessory structure of eye + optic nerve (CN II) + thalamus + visual cortex + brainstem + pineal gland (day/night cycles)
51
Q

Visual pathway:

A
  • ganglion cell axons travel through optic nerves, where some fibres cross at optic chiasm
  • optic tracts travel to thalamus, then visual cortex, hypothalamus, superior colliculus, or pineal gland
52
Q

Reflexes:

A

= simplest nervous system ac simple pathways:
stimulus = receptors, sensory cell, CNS cell = motor cell = (puis) muscle
- few cells = minimal synapses = fast, immediate and involuntary responses
(exaggerated or absence of reflexes = neurological problems)

53
Q

General reflex arc:

A

receptor = detects stimulus = sensory neurone = relays info to CNS = integration neurone = in spinal cord = motor neurone = carries response away from CNS to effector, effector carries out response to muscle or gland

54
Q

Reflex classification:

A
  • spinal reflex: in spinal cord independant of brain
  • cranial reflex: in brain
  • aquired: habitual repetitions of activities become reflexive
  • innate: present regardless of experience
  • monosynaptic: single sensory to motor neurone synapse (fast)
  • polysynaptic: more than 1 intermediate neurone entre sensory and motor neurones (slow)
  • somatic: controls skeletal muscle
  • visceral: controls organs/ glands
55
Q
A

GI physiology (12 decks)

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