neurones, electrical communication

Question 1

neuronal structure and functions:

Answer 1

• Cell body: Biosynthesis; signal integration
• Dendrites receives incoming signals;
  Ligand-gated and/or GPCR gated
  ion channels
• Axon Impulse conduction
  (action potentials);
  Voltage-gated Na and K channels
• Nerve termini Secretion of neurotransmitter; Voltage-gated
  Na, K and Ca channels

Question 2

types of neurones based on the number of poles:

Answer 2

slide 14

Question 3

types of neurones based on functions (afferent VS efferent):

Answer 3

• Motor or efferent neurons:
• Carry impulses from CNS to
  peripheral effector organs e.g.,
  muscles/glands/blood vessels
• Generally each motor neurons
  has long axon and short
  dendrites
• Sensory or afferent neurons:
• Carry impulses from periphery to
  CNS
• Generally each neuron has short
  axon and long dendri

Question 4

types of neurones based on the length of axon:

Answer 4

• Golgi Type I neurons:
• Have long axons
• Cell body situated in CNS and their axon reaches remote
  peripheral organs
• Golgi type II neurons:
• Have short axons
• Present in cerebral cortex and spinal cord

Question 5

soma are present in:

Answer 5

• Grey matter of CNS
• Nuclei of brain e.g., cranial N. Nuclei/Basal
  ganglia/Ganglia of CNS
• All neurons contain soma
• All processes do not survive without soma
  !!* Each neuron has centrally placed one nucleus in soma
• Prominent nucleoli which contains ribose nucleic acid
• No centrosome – loss power of division!!

Question 6

what is soma:

Answer 6

also known as the cell body or perikaryon, is the central part of a neuron that contains the nucleus
(contains genetic material)

Question 7

what are nissl granules/bodies:

Answer 7

• Small basophilic granules or membrane bound
  cavities found in clusters or clumps in soma
• Present in cell body and dendrites but absent in axon
  and axon hillock
  !! They are made up of rough endoplasmic reticulum (RER) and ribosomes. The primary role of Nissl granules is related to protein synthesis!!

Question 8

some components of neurones:

Answer 8

• Neurofibrillae (Microtubules &
  microfilaments):
• Thread like structure present all over cell
• Consists of microtubules and
  microfilament
• Mitochondria:
• Present in soma and axon
• Form the power house of the nerve cell
  where ATP is produced
• Golgi Apparatus
• Same of Golgi Apparatus of other cells
• Concerned with processing and packing of
  proteins into granules

Question 9

dendrites composition + function

Answer 9

• Tapering and branching extension of soma
• Dendrites of cerebral cortex and cerebellar cortex show
  knobby projections called dendritic spine
• May be absent. If present there is one or more
• Conduct impulses towards the cell body
• Generate local potential not action potential as well as
  integrate activity
• Has Nissl granules and neurofibrils
• Dendrites and soma constitute input zone

Question 10

axons composition + function:

Answer 10

• Each neuron has only one axon
• Arises from axon hillock of soma
• Carry impulses away from cell body
• Cannot synthesize own protein depends upon soma
• Branched only at its terminal end called synaptic knob,
  terminal button, axon telodendria
• Axon may be medullary or non medullary
• Contains granules or vesicles which contain synaptic
  transmitters
• Specialized to convert electrical signal (AP) to chemical signal

Question 11

Axis cylinder composition + function:

Answer 11

• Has long central core of cytoplasm- axoplasm
• Axoplasm covered by membrane – axolemma continuation of
  cell membrane of soma
• Axoplasm along with axolemma- axis cylinder
• Contains mitochondria, neurofibrils and axoplasm, vesicles
• Axis cylinder covered by neurilemma in non myelinated
  nerve fiber
• Nerve fiber insulated by myelin sheath – myelinated nerve
  fiber
  !! carries electrical signals from the cell body to the synaptic terminals, where the signals are transmitted to other neurons or target tissues !!

Question 12

Synapses:

Answer 12

neurones = connected to other cells/ neurones by synapses
(neuron-neuron, neuron-skeletal muscle, neuron-gland synapse)

Question 13

Neurones communication:

Answer 13

• electrical communication: mvmts of ions in and out of cell membrane
• chemical communication: release of neurotransmitters to nearby transmitter receptors at synapses

Question 14

Stimuli, activator of neurons:

Answer 14

• neurons = excitable, activated by stimuli to send signals to other cells

Question 15

what is stimulus?

Answer 15

any change in the environment that triggers a change in the neuron (mechanical, electrical, chemical)
- activation = through activation of channels on dendrites (stimulus = changes shape of channel = transmits via electrical or chemical changes inside the cell

Question 16

types of ion channels found in neurones:

Answer 16

• mechanically gated channels: in response to physical forces
• voltage-gated channels: in response to electrical forces
• ligand-gated channels: when chemicals or neurotransmitters bind
• leaky channels: always open
  (Ionic flux through a channel is always passive), when gate opens= conformational change that lets ionic flux across the membrane

Question 17

channels = selective for specific ions:

Answer 17

Channels are Selective for Specific Ions
Ion channel pores have selectivity filters
* Charge selectivity
- The aqueous pore of a channel may contain multiple amino acid residues with the opposite charge of the ion it’s selective for
- An intrapore positive charge would repel cations, thus making the channel selective for anions and vice versa
* Size selectivity
- Allows selectivity within a charge class (i.e., monovalent cation channels selective for Na+ vs K+ vs Li+)
(An anion selectivity filter
contains positive charge)

Question 18

ion channel gates criteria to opens

Answer 18

• Different ion channel proteins are classified by different
  gating mechanisms:
  1. Ligand-gated: a signal molecule binds to a receptor domain
  on the channel protein, leading to the conformational change,
  opening the channel
  2. Phosphorylation-gated: the ion channel is phosphorylated
  and remains open as long as the PO4- group is attached
  3. Voltage-gated: a change in membrane potential typically
  opens the channel
  4. Mechanically-gated: stretch or pressure opens the channel
  5. Non-gated: constitutively open

Question 19

ions channel and when the flow can change:

Answer 19

*Ions tend to flow from an area of high concentration to an area of low concentration.
*In the presence of a voltage gradient, there may be no flow of ions despite unequal
concentrations.
*Ion channels can be open or closed.
*Opening is brought about by changing the voltage across the membrane, or binding a
chemical substance to a receptor.
*Most important role is that they provide the neuron with electrical excitability.
*Found in all parts of the neuron and to a lesser extent in the neuroglial cells

Question 20

fundamental properties of an ion channel:

Answer 20

1.It is made up of a number of protein sub units, sitting
across the membrane, allowing ions to cross from one
side to the other. (Transmembrane pore)
2.The channel must be able to move from open to
closed state, and back.
3.Must be able to open in response to the appropriate
stimuli.
Some channels respond to chemical stimulus
(particularly at the synapse). These channels have
specific receptors for that chemical, that leads to
channel opening

Question 21

electrical communication=

Answer 21

occurs by movement of ions in and out of the membrane.
electrical gradients are measured as membrane potential

Question 22

membrane potential:

Answer 22

= amount of electrical charge present on the inside of the cell (ICF) compared to outside of cell (ECF)
- positive membrane potential = positive more inside than outisde (+ de K+ inside ou more Cl- outside)
- negative membrane potential:
(opposites ac Na+ et tralala)
slide 41 !!

Question 23

Ion accumulation membrane:

Answer 23

• normalement entre in and out of membrane electrical charge = 0 mais when there’s a difference = electrical gradient
• the ions will accumulate close to the membrane on either sides due to the attraction of negative charge to positive charge mais they can’t pass sans channel pcq hydrophobic (ions). donc they wait for signal et en attendant they’re stored very locally at the cell.

Question 24

Magnitude of membrane potential:

Answer 24

increasing number of ions that accumulate at the membrane = increases magnitude
- normalement magnitude at rest = negative pcq: proteins A- inside + K+ inside + Na+ outside
membrane potential at rest = -70mV
NOTHING MOVES WITHOUT CHANNELS

Question 25

depolarisation VS hyperpolarisation:

Answer 25

depo = positive
hyper = negative

Question 26

case of leaky K+

Answer 26

when at rest, passive, k+ channels let them leak to near to equilibrium
k+ PERMEABILITY = high at rest but not complete et le contraire pr Na+

Question 27

Electrical signaling types:

Answer 27

• Graded potential: ( = in response to stimulus, a graded potential is variable in strength and can either depolarize or hyperpolarize the membrane), small local change, can vary in size, does not travel far, can build-up to become a larger trigger)
• The amplitude of the voltage deflection is variable and dependent upon the
  stimulus intensity = graded potential
  excitatory = positive ions move IN, inhibitory = positive ions move OUT/ negative = move IN
  (* Graded potentials can occur in any part of the membrane in any cell
• Graded potentials also can result from the process of summation, where two or more stimuli affect the membrane potential over time or space.)
• Action potential: large, fast, long distance, same magnitude every time it occurs
  SLIDES 59- 60- 61

Question 28

graded potential then action potential:

Answer 28

• In membrane domains that contain voltage-gated channels, if the
  magnitude of the graded potential reaches threshold, an action potential is developed.
• This is a maximum, all-or-none voltage deflection (i.e., it’s not graded)

Question 29

action potential pattern:

Answer 29

1) membrane rest
2) treshold
3) rising phase: depolarisation
4) falling phase: repolarisation
5) DIP: hyperpolarisation
6) return to rest

Question 30

Voltage gated channels:

Answer 30

• Voltage gated Na+ channels: closed at -70mV, opens rapidly at -50/-55, closes by separate inactivation gate
• // // K+: closed at -70, opens slowly (same mV), closes slowly

Question 31

speed of impulse propagation:

Answer 31

slide 67

Question 32

Factors influencing Action potential:

Answer 32

thanks to conduction velocity: 2 factors that influence it:
- myelination: increased myelination = increased speed
- axon diameter: large diameter axons = fast conduction (large diameter = low resistance + fast conduction, small diameter = high resistance + slow conduction)
- space = limited, if axon needs fast transmission = will be both large and myelinated

Question 33

nervous system tissue:

Answer 33

the fatter the fibre, the faster it flies

Question 34

continuous vs saltatory conduction:

Answer 34

slide 73

Question 35

nerve transmission:

Answer 35

slide 76

Question 36

graded vs action potential

Answer 36

slide 77