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Biology Unit 8 > Structure and function of Nerve tissue and Responses to stimuli > Flashcards

Structure and function of Nerve tissue and Responses to stimuli Flashcards

1
Q

State the three types of functional neurons.

A

Sensory neurons, motor neurons and relay neurons.

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2
Q

Describe the structure of a sensory neuron.

A

Usually unipolar, transmits impulses from receptors to CNS. The cell body is in the centre of the axon. It has dendrites and a long axon.

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3
Q

State the function of a sensory neurone

A

Carries nerve impulses from the receptors to the CNS via the dorsal root.

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4
Q

Describe the structure of a motor neurone

A

Short dendrites carry impulses from CNS to cell body. The cell body is at the end of the neuron and a long axon carries impulses from cell bodies to effectors.

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5
Q

State the function of a motor neurone.

A

Carries nerve impulses from the CNS to the effectors via the ventral root.

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6
Q

Describe the structure of a relay neurone.

A

Usually bipolar, transmits impulses between neurons. They’re found in the CNS. They have highly branched dendrites and axon terminals.

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7
Q

State the function and location of a relay neurone

A

It’s located in the spinal cord and links the sensory neurone to the motor neurone.

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8
Q

What are Schwann cells?

A

Cells that form the myelin sheath around nerve cells in the peripheral nervous system.

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9
Q

Explain why myelinated axons conduct impulses faster than un myelinated axons.

A

Saltatory propagation. Impulse ‘jumps’ from one node of Ranvier to another because depolarization can’t occur where the myelin sheath acts as an electrical insulator. The impulse does not travel along the whole axon length.

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10
Q

Why do neurons need nodes of Ranvier?

A

The sodium ions would diffuse and dissipate and the concentration wouldn’t be high enough to allow the action potential to propagate along the entire neurone. The nodes of Ranvier provide gaps where there are ion channels to boost the action potential.

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11
Q

Name the two main divisions of the nervous system

A

Central nervous system and peripheral nervous system.

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12
Q

Outline the gross structure of the mammalian nervous system.

A

Central: spinal cord and brain.
Peripheral: voluntary and autonomic (divided into parasympathetic and sympathetic)

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13
Q

What is the central nervous system?

A

Brain and spinal cord.

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14
Q

What is the peripheral nervous system?

A

Pairs of nerves that originate from the CNS and carry nerve impulses into and out of the CNS.

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15
Q

What is an effector?

A

An organ, tissue or cell that produces a response to a stimulus.

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16
Q

What is a stimulus?

A

An internal or external change or factor which triggers a response.

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17
Q

What is grey matter?

A

The darker tissue of the central nervous system which lies centrally and consists of relay and motor neurone cell bodies.

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18
Q

What is white matter?

A

The lighter tissue of the CNS which surrounds grey matter and consists of myelinated axons.

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19
Q

What is the ventral root?

A

A root that emerges from the spinal cord. Motor neurons leave the spinal cord via the ventral root.

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20
Q

What is the dorsal root?

A

A root that emerges from the spinal cord. It travels to the dorsal root ganglion. Sensory neurons enter the spinal cord via the dorsal root.

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21
Q

What is a reflex?

A

A rapid, automatic response to a sensory stimulus by the body. It serves as a protective mechanism

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22
Q

Outline a simple reflex arc

A

stimulus - receptor - sensory neurone - relay neurone in CNS - motor neurone - effector - response

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23
Q

What is resting potential?

A

Potential difference (voltage) across neuron membrane when not stimulated. Usually about -70 mV in humans.

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24
Q

How is resting potential established?

A
  1. Membrane is more permeable to calcium than sodium ions.
  2. Sodium-potassium pump actively transports 3Na+ out of the cell and 2K+ into the cell.

Establishes electrochemical gradient: cell contents more negative than outside

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25
Q

Name the stages in generating an action potential

A
  1. depolarization
  2. repolarization
  3. hyperpolarisation
  4. return to resting potential
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26
Q

What happens during depolarization?

A
  1. Stimulus - facilitated diffusion of Na+ into cell down gradient
  2. p.d. across membrane becomes more positive
  3. If membrane reaches threshold potential, voltage-gated Na+ channels open (positive feedback mechanism).
  4. Significant influx of Na+ ions reverses p.d. to +40mV
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27
Q

What happens during repolarization?

A
  1. Voltage-gated Na+ channels close and voltage-gated K+ channels open.
  2. Facilitated diffusion of K+ ions out of the cell down their electrochemical gradient.
  3. P.D. across membrane becomes more negative.
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28
Q

What happens during hyperpolarisation?

A
  1. Overshoot when k+ ions diffuse out. P.d. becomes more negative than resting potential.
  2. Refractory period: no stimulus is large enough to raise membrane potential to threshold.
  3. Voltage-gated potassium pump re-establishes resting potential.
29
Q

Describe the all-or-nothing law

A

Principle that states that all stimuli above a certain threshold value will generate the same size of action potential, regardless of the strength of the stimulus.

30
Q

What is saltatory conduction?

A

Setting up of localized circuits between nodes of Ranvier which allows for the rapid propagation of an action potential.

31
Q

Describe the structure of a synapse.

A

Presynpatic neurone ends in synaptic knob.
Synaptic knob contains a lot of mitochondria, endoplasmic reticulum and vesicles of neurotransmitter.
Synaptic cleft, a 20-30 nm gap.
Postsynaptic neurone has complementary receptors to the neurotransmitter.

32
Q

What is the synaptic cleft?

A

A small gap between neurons across which a nerve impulse is transmitted via neurotransmitters.

33
Q

Describe the synaptic transmission in the presynaptic neurone

A
  1. Wave of depolarization travels down presynaptic neuron, causing voltage-gated Ca2+ channels to open.
  2. Ca2+ cause vesicles of acetylcholine to move towards and fuse with presynaptic membrane.
  3. Exocytosis of neurotransmitter into synaptic cleft.
34
Q

How do neurotransmitters cross the synaptic cleft?

A

Via simple diffusion

35
Q

How is the merging of impulses prevented during synaptic transmission?

A

-Active transport of Ca2+ out of synaptic knob
-Role of cholinesterase
-Reabsorption of neurotransmitters

36
Q

Describe the role of cholinesterase in synaptic transmission

A

Hydrolyses acetylcholine in the postsynaptic neurone and products diffuse back across the cleft.

37
Q

What is the refractory period?

A

The short period of time following an action potential where another action potential can’t be generated no matter how large the stimulus

38
Q

What causes the refractory period?

A

The voltage gated sodium channels become inactivated for a period of time following an action potential and can’t open regardless of stimulus size.

39
Q

Why is it important that nerves have a refractory period?

A

To ensure that nervous transmission is unidirectional. It also ensures that each nervous impulse is separate from each other so they can be individually interpreted by the brain.

40
Q

What is the iris and what is its function?

A

The colored ring around the pupil that controls its diameter.

41
Q

What is the pupil and what is its function?

A

It’s the hole in the middle of the iris that lets light into the eye.

42
Q

Explain the response of the eye to bright light.

A

The radial muscle contracts and the circular muscle relaxes, making the pupil smaller.

43
Q

State the response of the eye to a lack of light.

A

The pupil increases in diameter to allow more light to hit the retina.

44
Q

State the response of the eye to bright light.

A

The pupil decreases in diameter to reduce the amount of light which hits the retina

45
Q

Explain the response of the eye to a lack of light.

A

The radial muscle relaxes and the circular muscle contracts making the pupil larger.

46
Q

How does nicotine affect nervous transmission?

A

It mimics acetylcholine and binds to receptors in cholinergic synapses involved in the reward centres of the brain. Binding of nicotine triggers dopamine release and so nicotine can be an addictive drug.

47
Q

What is nicotine?

A

A drug found in tobacco which contributes to the addictive properties of cigarettes

48
Q

What is lidocaine?

A

A drug which can be used as a local anesthetic or to treat heart arrhythmias

49
Q

How does lidocaine work as a local anesthetic?

A

It prevents the propagation of action potentials by blocking Na+ ion channels in nerve cells. This prevents impulses in response to pain from being generated in the area affected by the drug.

50
Q

What is alpha-cobratoxin?

A

A type of neurotoxin which is found in the venom of Nana cobras

51
Q

What effects does a-cobratoxin have?

A

It causes muscle paralysis which may lead to death from respiratory failure

52
Q

How does a-cobratoxin cause muscle paralysis?

A

It reversibly blocks acetylcholine receptors at cholinergic synapses.

53
Q

How might drugs increase synaptic transmission?

A

By inhibiting AChE and mimicking the shape of a neurotransmitter.

54
Q

How might drugs decrease synaptic transmission?

A

-Inhibit the release of a neurotransmitter
-decrease permeability of postsynaptic membrane to ions
-hyperpolarise postsynaptic membrane

55
Q

How is L-dopa used to treat Parkinson’s disease?

A

L-dopa is a dopamine precursor that can cross the brain blood barrier. It’s used to produce more dopamine in the brain to replace the neurotransmitter lost by the death of neurons.

56
Q

What is MDMA?

A

Chemical in ecstasy. It interacts with transmembrane proteins that transport serotonin, a neurotransmitter that regulates mood. It increases serotonin level in synaptic clefts in the brain.

57
Q

Describe the distribution of rods and cones in the human eye

A

Typically more rods than cones evenly distributed in the retina, however in the fovea there are no rods an only cones.
There are no photoreceptors at the blind spot where ganglion axon fibers form the optic nerves.

58
Q

What is the fovea?

A

An area of the retina with lots of photosensitive cells so it has the highest visual acuity.

59
Q

What is the function of rods?

A

They function in low light intensities (black and white)

60
Q

What is the function of cones?

A

To detect color. There are 3 different types of cone cells.

61
Q

Describe the pigments in rod and cone cells.

A

Rod: rhodopsin absorbs all wavelengths of light = monochromatic vision.
Cone: three types of iodopsin which absorb red, blue or green light = tricolor vision

62
Q

Explain why rod cells don’t generate action potentials in the dark.

A
  1. Na+ enters outer segment of rod cell via non-specific cation channels. Active transport of Na+ out of inner segment = rod cell is slightly depolarised.
  2. Action potential = voltage-gated Ca2+ channels open. Triggers exocytosis of glutamate.
  3. Glutamate acts as inhibitory neurotransmitter to hyperpolarise bipolar neuron.
63
Q

Explain how rod cells generate an action potential in the light.

A
  1. Rhodopsin pigment bleaches when it absorbs light & breaks down into opsin + retinal
  2. Opsin closes cation channels via a hydrolysis reaction. Active transport of Na+ out of inner segment continues.
  3. Rod cell becomes hyperpolarised. No glutamate is released, so no inhibitory signal
  4. Bipolar neuron depolarises
64
Q

Outline the pathway of light from photoreceptor to the brain

A

photoreceptor - bipolar neuron - ganglion cell of optic nerve - brain

65
Q

Describe the visual acuity of rod and cone cells

A

Rod: many rod cells synapse with 1 bipolar neurone, so low resolution.
Cone: 1 cone cell synapses with 1 bipolar neuron so there is no retinal convergence. High resolution.

66
Q

Describe the light sensitivity of rod and cone cells

A

Rod: very sensitive due to spacial summation of sub threshold impulses - vision in low-light conditions.
Cone: less sensitive - vision in bright light

67
Q

What is bleaching?

A

Sudden exposure to high light intensity causes rhodopsin to break down faster than it can reform.

68
Q

Describe the process of light and dark adaptation in the eye.

A

Light adaptation: as rhodopsin reforms after bleaching, retinal sensitivity decreases.
Dark adaptation: rod cells become functional, retinal sensitivity increases.

69
Q
A

Biology Unit 8 (3 decks)

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