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Biology - Unit 3 > Nervous System > Flashcards

Nervous System Flashcards

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1
Q

Define stimulus

A

Any detectable change n the internal or external environment of the organism

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2
Q

Define Receptor Cells

A

Act as transducers detecting energy in one form and convert it to electrical energy

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3
Q

What happens at the neurones ?

A

Electrical energy travels along them as a nerve impulse, this impulse initiates a response in an effector

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4
Q

Recall the pathway from stimulus to response.

A

Stimulus - Receptor - Sensory neurone - CNS - Motor Neurone - Effectors - Response

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5
Q

What happens at the sensory neurone?

A

Carries nerve impulses from the receptor cell in the organs to the CNS

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6
Q

What happens at the relay neurone?

A

Found in the CNS, connects the sensory and motor neurones

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7
Q

What happens at the motor neurone?

A

Transports nerve impulses from the CNS to the effector ( muscle/ Glands )

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8
Q

What do the sensory and motor neurone contain which the relay does not?

A

The myelin sheath, formed by the Schwann cells which wraps itself around the nerve fibres, creating several layers of cell membrane.

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9
Q

What are the small spaces between the Shwann cells called?

A

The nodes of ranvier

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10
Q

What is saltatory conduction?

A

The rapid method where nerve impulses move down a myelinated axon with excitation occurring only at nodes of Ranvier

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11
Q

Name the parts for the sensory neurone?

A

Dendrite - carries impulses towards the cell body
Axon - long fibre carries impulses away from the cell body
Ganglion - The cell body, to one side, causing a swelling in the spinal nerve
Synaptic Bulbs - pass the impulses onto another neurone/ effector.

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12
Q

Name some parts of the motor neurone

A

Short dentrites - carry impulses from CNS to cell body
cell body found at one end of neurone
Long Axon - carries impulses from the cell body to effector

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13
Q

Name the parts of a relay neurone

A

Dendrites
Dendron
Cell body
Nucleus
Axon
Synaptic bulbs

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14
Q

What are the 2 distinct areas inside the spinal cord ?

A

1) The central grey matter containing the cell bodies. In the centre of the grey matter is the spinal canal, through which the cerebrospinal fluid circulates.
2) the outer white matter containing myelinated axons, running up and down the spinal cord to the brain

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15
Q

What is the dorsal root ?

A
  • One of the 2 roots that emerged from the spinal cord
  • Travels to the dorsal root ganglion
    Sensory neurones enter the spinal cord via the dorsal root
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16
Q

What is the ventral root ?

A
  • One of the two roots that emerges from the spinal cord
  • Motor neurones leave the spinal cord via the ventral root
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17
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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18
Q

Outline a simple reflex arc

A

Stimulus - receptor - sensory neurone - relay neurone - motor neurone - effector - response

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19
Q

How does a reaction differ from a reflex ?

A

Reaction= voluntary and coordinated by brain
Reflex = non-voluntary and does not involve the brain

20
Q

What is a nerve net?

A
  • Simplest form of nervous system
  • Consists of interconnected nerve cells with short extensions allowing a response to a limited number of stimuli
21
Q

What is the function of the axon ?

A

A long fibre that conducts nerve impulses away from the cell body

22
Q

Define action potential

A

Temporary change in electrical potential across the membrane of an axon in response to the transmission of a nerve impulse

23
Q

What is resting potential ?

A

Potential difference across a neurone membrane when not stimulated (-70mV)

24
Q

How is resting potential established ?

A

Membrane is more permeable to potassium then sodium
- Sodium-potassium pumps actively transport 3Na out of the cell and 2K into the cell.
- As a result an electrochemical gradient is established.
- Some potassium ion channels are left open meaning some will leak out

25
Q

Stages of an action potential being fired.

A

Depolarisation
Repolarisation
Hyperpolarisation
Returns to resting potential

26
Q

Explain depolarisation when action potential is fired

A

1) stimulus causes a change in the voltage across an axon membrane, opening voltages gated sodium channels
2) Sodium diffuse into the axon
3) Potential differences across the membrane become more positive, meaning the membrane depolarises

27
Q

Explain what happens during repolarisation of firing action potential

A

1) Membrane potential reaches +40mV (action potential reached)
2) Voltage gated sodium channels close and voltage gated potassium channels open
3) Facilitated diffusion of potassium ions out of the cell down the electrochemical gradient
4) Potential differences across membrane becomes more negative, membrane is repolarised

28
Q

What happens during hyper polarisation when firing an action potential?

A

1) overshoot when potassium ions diffuse out
2) potential difference becomes more negative then resting potential
3) Membrane hyperpolarises preventing another impulse occurring

29
Q

What is a refractory period and why are they important

A

Time period after an action potential during which further action potentials are prevented
Ensures that action potential can only propagated in one direction.

30
Q

What is the ‘all or nothing’ law?

A

All stimuli above a certain threshold value will generate the same size action potential, regardless of the strength of the stimulus

31
Q

What factors affect the speed of conduction of a nervous impulse?

A
  • Temperate = increased temperature, increases kinetic energy therefore greater rate of conduction
  • Axon diameter = the greater the diameter, the faster the rate of transmission. Larger surface area for ion exchange to take place
  • Myelin Sheath = Myelinated nerve fibres conduct faster than non. Saltatory conduction
32
Q

Why do myelinated axons conduct impulses faster than non?

A

Saltatory Propogation- Impulses can jump from one node of ranvier to another, therefore not travelling the whole length of the axon.

33
Q

What is a synapse?

A

Junction between two nerve cells or a nerve cell and effector.

34
Q

Explain the function of the synapse.

A
  • Electrical impulses can’t cross the junction
  • Neurotransmitters send impulses between neurones or from neurone to effectors
35
Q

What parts make up the Synpase?

A
  • Presynaptic membrane
  • synaptic knob
  • Vesicles containing neurotransmitters
  • Synaptic cleft
  • Postsynaptic membrane
  • Receptors
36
Q

Describe the synaptic transmission.

A

1) Wave of depolarisation travels down the presynaptic neurone, causing voltage gated calcium channels to open.
2) the influx of calcium in the synaptic knob causes vesicles containing acetylcholine to move towards and fuse with the presynaptic membrane.
3) The neurotransmitters leave via exocytosis into the synaptic cleft
4) Acetylcholine diffuses across the cleft and binds to specific receptors, this is only temp, on the postsynaptic membrane
5)Binding opens up sodium channels in the postsynaptic membrane.
6) Sodium ions flood in by diffusion and depolarise the membrane creating action potential in the postsynaptic neurone.

37
Q

What is the role of cholinesterase in synaptic transmission and what does it prevent?

A
  • hydrolyses acetylcholine into choline and Ethanoic acid, then these products of acetylcholine diffuse back across the cleft into the presynaptic neurone and re-form acetylcholine.
    Prevents acetylcholine remaining in the cleft and constantly initiating new impulses in the postsynatic membrane
38
Q

What are some properties of the synapse ?

A
  • Transmits info between neurones
  • Pass impulses in one direction only, generating precision
  • Filters out low level stimuli, only generate A.P when reaching threshold value.
39
Q

What is a drug?

A

A molecule that has a physiological effect on the body when ingested, inhaled, absorbed or injected.

40
Q

What’s are the 2 types of drugs ?

A

Sedatives
Stimulants / agonists

41
Q

How do sedatives effect the synaptic transmissions?

A

Inhibits the nervous system, creating fewer action potential in post synaptic neurone.
Prevents the calcium channels opening and thus preventing exocytosis blocking receptors

42
Q

How do stimulants effects synaptic transmission ?

A

Stimulate the nervous system allowing more action potentials in post synaptic neurones
Inhibits the enzyme that breaks down the neurotransmitters

43
Q

Describe the mechanism of drug action ( mimicking neurotransmitters )

A

They may have the same shape and bind to the post synaptic receptors in the same way as a neurotransmitter, increasing the frequency of action potentials
Drugs such as nicotine is not removed by hydrolysis so it continues to initiate impulses

44
Q

What is grey matter?

A

Found in the spinal cord, it contains many cell bodies and nuclei

45
Q

What is the spinal cord surrounded by ?

A

Membrane called meninges

Biology - Unit 3 (11 decks)

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