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Biology > Nervous coordination > Flashcards

Nervous coordination Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What is a neurone?

A

A single nerve cell

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2
Q

What is a nerve?

A

A bundle of axons surrounded by connective tissues which binds them together

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3
Q

What is the structure of a neruone?

A
  • cell body
  • dendrons - extensions of the cell body which subdivide into smaller branches called dendrites, which carry nerve impulses towards the cell body
  • axon - a single long fibre that carries nerve impulses away from the cell body
  • schwann cells - surround the axon to build up a layer of myelin sheath which provides electrical insulation
  • nodes of Ranvier - gaps between adjacent schwann cells where there is no myelin sheath
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4
Q

What are the 3 types of neurone and what are their functions?

A
  • sensory - transmit nerve impulses from a receptor to an intermediate neurone in the CNS
  • intermediate - transmit nerve impulses from a sensory neurone to a motor neurone across the CNS
  • motor - transmit impulses from an intermediate neurone to an effector
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5
Q

What is the structure of a sensory neurone?

A

one dendron that carries an impulse towards the cell body and one axon that carries it away. Synaptic knobs connect to other neurones

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6
Q

What is the structure of an intermediate neurone?

A
  • unmyelinated
  • numerous short processes
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7
Q

What is the structure of a motor neurone?

A

A long axon and many short dendrites

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8
Q

What do cell bodys contain and why?

A

A nucleus and a large amount of RER used in the production of proteins and neurotransmitters

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9
Q

What is a nerve impulse?

A

A wave of electrical activity that travels along the axon membrane. It is a temporary reversal of the electrical potential differences across the axon membrane

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10
Q

What is resting potential and how is it established?

A

The inside of the axon is negatively charged relative to the outside - the axon is described as polarised

  • 3 sodium ions are actively transported out of the axon by sodium-potassium pumps
  • 2 potassium ions are actively transported into the axon
  • the outward movement of sodium ions is greater than the inward movement of potassium ions which creates an electrochemical gradient (around -70mV)
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11
Q

How is movement across the membrane controlled?

A
  • phospholipid bilayer prevents sodium and potassium ions from diffusing across it
  • sodium and potassium channel proteins
  • sodium-potassium pumps
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12
Q

What is an action potential and how is it caused?

A

When a stimulus is detected by a receptor, it causes a temporary reversal of charges in the axon, causing it to become depolarised

  • the energy of the stimulus causes sodium voltage-gated channels in the axon membrane to open, and sodium ions diffuse into the axon through channels along their electrochemical gradient
  • as more sodium ions diffuse into the axon, more sodium channels open causing a greater influx of sodium ions by diffusion
  • this causes a reversal in charge because the inside of the axon becomes more positive relative to the outside (around +40mV)
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13
Q

How do axons become repolarised?

A
  • once an action potential of around +40mV has been established, the voltage gates on sodium ion channels close preventing further sodium ions from entering
  • voltage gate potassium ion channels begin to open, so potassium ions diffuse out of the axon membrane, causing it to begin to repolarise as the charge becomes more positive outside the axon relative to the inside
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14
Q

What is hyperpolarisation?

A
  • potassium ion channels are slow to close and this causes potassium ions to diffuse out of the axon, making the charge inside the axon more negative
  • this causes a temporary overshoot of the electrical gradient
  • K+ channels then close and the sodium potassium pump will increase Na+ entering into the axon, meaning the charge inside becomes less negative, and resting potential is restored
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15
Q

By what process do sodium ions move in during an action potential?

A

Diffusion

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16
Q

By what process do sodium ions move during resting potential?

A

active transport

17
Q

How does action potential change as it moves along an axon?

A

Stays the same

18
Q

What is the passage of action potential along an unmyelinated axon?

A
  • at resting potential, the axon membrane is polarised because the outside of the membrane is more positively charged than the inside of the membrane
  • A stimulus causes a sudden influx of sodium ions which causes the charges to be reversed - membrane becomes depolarised
  • The localised electrical currents established by the influx of sodium ions cause the opening of voltage-gated sodium ions further along the axon causing a wave of depolarisation
  • behind this wave of depolarisation, sodium ion channels close and potassium ion channels open. The outward movement of potassium ions causes this section of membrane to become repolarized
  • repolarisation allows sodium ions to be actively transported out, as so resting potential is restored
19
Q

What is the passage of action potential along a myelinated axon?

A

process known as saltatory conduction

  • action potentials can only occur at the nodes of ranvier, so electrical impulses will skip along the axon without having to depolarise the entire length of the axon, making this much faster conduction
20
Q

Which factors affect the speed at which an action potential travels?

A
  • myelin sheath - provide electrical insulation and lead to saltatory conduction, which speeds up conductance
  • axon diameter - greater axon diameter = faster conductance - less leakage of ions from a large axon - making it more difficult to maintain membrane potentials in smaller axons
  • temperature - higher temperature = faster rate of diffusion of ions so faster nerve impulses. Active transport also requires ATP which requires enzymes, faster production of ATP at higher temperatures
21
Q

What are the absolute and relative refractory periods?

A

absolute = the interval during which a second action potential absolutely cannot be initiated, no matter how large the stimulus

relative = the interval immediately following during which initiation of a second action potential is inhibited but not impossible

22
Q

Why is there a refractory period?

A

Inward movement of sodium ions is prevented because voltage-gated sodium ion channels are closed, meaning it is impossible for a further action potential to be generated

23
Q

What is the purpose of the refractory period?

A
  • ensures that action potentials occur in one direction only - they cannot move backwards as the membrane is in the refractory period
  • produces discrete impulses - ensures that action potentials are separated from each other due to refractory period
  • limits the number of action potentials - limits the number of action potentials that can pass along an axon at a given time
24
Q

Why do neurones contain a large amount of RER?

A

used to produce proteins and neurotransmitters

25
Q

What is the all-or-nothing principal?

A

as long as the stimulus allows enough sodium ions to move in to reach threshold, action potential is always the same

stronger stimulus = more frequent action potentials

26
Q

What are the stages of synaptic transmission?

A
  • action potential arrives at the end of the presynaptic neurone and the membrane of the presynaptic membrane depolarizes
  • calcium ion channels open and calcium ions enter into the synaptic knob
  • calcium ions cause synaptic vesicles to fuse with the presynaptic membrane and release acetlycholine (a neurotransmitter)
  • acetylcholine diffuses across the synaptic cleft and attaches to receptors on the postsynaptic membrane
  • sodium ion channels open and sodium ions enter the postsynaptic membrane leading to depolarisation
  • an action potential is produced in the postsynaptic neurone if threshold is reached
27
Q

Why is synaptic transmission unidirectional?

A

there are only vesicles in the presynaptic membrane and only receptors on the postsynaptic membrane

28
Q

What is temporal summation?

A

accumulation of neurotransmitters due to several action potentials occuring over a short time period, leading to neurone reaching threshold

29
Q

What is spatial summation?

A

accumulation of neurotransmitters due to several neurones producing an action potentials over a short time period, releasing more neurotransmitters and leading to neurone reaching threshold

Biology (25 decks)

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