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Biology > The Nervous System > Flashcards

The Nervous System Flashcards

1
Q

What are the two systems that make up the nervous system?

What do each consist of?

A

Central nervous system:

  • Brain
  • Spinal cord

Peripheral nervous system

  • Sensory nerves
  • Motor nerves
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2
Q

What systems make up the peripheral nervous system?

A

Autonomic nervous system

  • Involuntary
  • Stimulates smooth muscle, cardiac muscle and glands

Somatic nervous system

  • Voluntary
  • Stimulates skeletal muscle
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3
Q

What two systems can the autonomic nervous system be divided into?

A

Sympathetic nervous system
-‘fight or flight’ responses

Parasympathetic nervous system
-‘rest and digest’ responses

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4
Q

When would a gland be stimulated?

A
  • When there is a change in the concentration of a specific substance
  • If they receive an electrical impulse
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5
Q

What do hormones bind to?

A

Target cells

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6
Q

What is a nervous system receptor like in the resting state?

A
  • Difference in charge between the inside and outside of the cell
  • This means there is a voltage across the membrane
  • The membrane is said to be polarised
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7
Q

What is potential difference?

A

The voltage across the membrane

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8
Q

What happens in a receptor when a stimulus is detected?

A
  • Permeability of the cell membrane to ions changes
  • This stops the movement of ions in or out of the cell
  • This causes a change in the potential difference, which, if large enough, will trigger an action potential
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9
Q

What is an action potential?

A

An electrical impulse along a neurone

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10
Q

What pigment do rod cells contain?

A

Rhodopsin

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11
Q

What is rhodopsin made from?

A

Retinal and opsin

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12
Q

What happens when rod cells are stimulated?

A
  • Light energy causes rhodopsin to break down into retinal and opsin in a process called bleaching
  • The bleaching of rhodopsin causes the sodium ion channels to close
  • Sodium ions are moved out of the cell via active transport but can’t diffuse back in
  • Na+ ions build up outside the cell making the inside of the membrane more negative than the outside
  • The cell membrane is hyperpolarised
  • This stops the cell releasing neurotransmitters which means there is no inhibition of the bipolar molecule
  • The bipolar molecule depolarises which causes a change in potential difference
  • If the change in potential difference is large enough, an action potential is transmitted to the brain via the optic nerve
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13
Q

What do dendrites do?

A

Carry nerve impulses towards the cell body of a neuron

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14
Q

What do axons do?

A

Carry nerve impulses away from the cell body of a neuron

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15
Q

Describe the structure of a motor neuron

A
  • Many short dendrites

- One long axon

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16
Q

Describe the structure of a sensory neuron

A
  • One long dendrite

- One short axon

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17
Q

Describe the structure of a relay neuron

A
  • Many short dendrites

- Many short axons

18
Q

What is the voltage across the membrane when it’s at rest?

A

-70 mV

19
Q

How is the resting potential created and maintained?

A
  • Sodium-potassium pumps move Na+ ions out of the neuron and K+ ions into the neuron
  • This creates a sodium ion electrochemical gradient as the sodium ions can’t re-enter the neuron
  • Membrane is permeable to K+ ions so they diffuse back out of the neuron through potassium ion channels
20
Q

Describe the sequence of events that make up an action potential

A

Stimulus

  • Neuron cell membrane becomes excited causing sodium ion channels to open
  • The membrane becomes more permeable to sodium, so Na+ ions diffuse into the neuron down the sodium ion electrochemical gradient
  • This makes the inside of the neuron less negative

Depolarisation

  • If the potential difference reaches the threshold, around -55 mV, more sodium ion channels open
  • This causes more Na+ ions to diffuse into the neuron

Repolarisation

  • When the potential difference is around +30 mV, the sodium ion channels close and the potassium ion channels open
  • K+ ions diffuse out of the neuron down the potassium ion concentration gradient
  • Membrane starts to return to its resting potential

Hyperpolarisation

  • Potassium ion channels are slow to close so too much K+ ions diffuse out of the neuron
  • The potential difference becomes more negative than the resting potential (less than -70 mV)

Resting potential

  • The ion channels are reset
  • The sodium-potassium pump returns the membrane to its resting state
21
Q

What happens in the refractory period?

A
  • The sodium and potassium ion channels are recovering and can’t open again for a while
  • Therefore the neuron cell membrane can’t become excited again straight away
22
Q

How does the action potential move along a neuron?

A

In a wave of depolarisation

23
Q

Compare nerve impulses and hormones

A

Nervous communication:

  • Uses electrical impulses
  • Fast response
  • Localised response
  • Short acting

Hormonal communication:

  • Uses chemical messengers in the blood
  • Slower response
  • Widespread response
  • Longer acting
24
Q

Describe the sequence of events​ from the action potential arrival at the presynaptic membrane of a synapse to the generation of a new action potential at the postsynaptic membrane (6)

A
  • Action potential arriving at the presynaptic membrane stimulates voltage gated Ca2+ ion channels to open
  • Ca2+ ions diffuse into the neuron
  • This causes synaptic vesicles, containing neurotransmitter, to move the to the presynaptic membrane
  • The vesicles fuse with the membrane and release the neurotransmitter into the synaptic cleft via exocytosis
  • The neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane
  • This causes Ca2+ ion channels to open in the postsynaptic membrane
  • There is an influx of Ca2+ ions which causes depolarisation
  • This triggers a new action potential to be generated at the postsynaptic membrane
25
Q

What is a reflex?

A

A rapid, involuntary response to a stimulus

26
Q

Describe the reflex arc

A
  • Receptors detect a stimuli and generate an impulse
  • Sensory neurons conduct the impulse to the centre nervous system (CNS) by entering the spine through the dorsal route
  • Sensory neurone forms a synapse with a relay neurone
  • Relay neurone forms a synapse with a motor neurone
  • Motor neurone carries the impulse out of the spinal cord through the ventral route to effectors
  • Effectors produce a response
27
Q

What is the advantage of the reflex pathways?

A
  • They produce rapid responses

- Important for survival

28
Q

Describe the nervous pathways involved in the increase of heart rate when starting to exercise

A
  • Cardiovascular control centre in brain detects increase in CO2 and lactate in the blood
  • Sensory receptors in muscles send impulses to cardiovascular control centre along sensory neurons
  • Impulses sent from cardiovascular control centre to SAN via sympathetic nerve
  • Impulses from SAN to heart muscles increases in frequency, causing heart rate to rise
29
Q

Where are dendrons found?

A

Before the cell body in a sensory neuron

30
Q

Where are axons found in neurons?

A
  • After the cell body

- Carrying the impulse away

31
Q

Where are the cell bodies of sensory neurons found?

A

-In the Ganglia

32
Q

What is the Ganglia? Where is it?

A
  • The place where cell bodies of sensory neurons are found

- Near the spinal cord

33
Q

What are on the ends of sensory neurons?

A

Dendrites

34
Q

Compare and contrast the structure of motor and sensory neurones

A
  • Both have a long nerve fibre
  • In a motor neurone this nerve fibre is an axon
  • In a sensory neurone it is a dendron
  • Sensory neurones have their cell body in the middle of neurone while motor neurones have the cell body at the start of the neurone
35
Q

Explain how the parasympathetic and sympathetic branches of the autonomic nervous system work antagonistically

A
  • Antagonistic means working in opposition to each other
  • Changes made by the sympathetic system can be reversed by the parasympathetic system
  • They allow changes to be made, for example when regulating heart beat
36
Q

What is the motor-end plate?

A

Where a neurone and muscle meet

37
Q

What are Schwann cells? What do they do?

A

-Forms a myelin sheath around an axon

38
Q

Where are nodes of Ranvier found?

A

In between Schwann cells on the myelin sheath

39
Q

How does a myelin sheath increase the speed of impulses?

A
  • Acts as an electrical insulator
  • Ensures depolarisation only happens at the nodes of Ranvier
  • Impulse travels from node to node, decreasing the points at which depolarisation can take place along an axon
40
Q

What is it called when an impulse is insulated by a myelin sheath?

A

Saltatory conduction

41
Q

Why is an impulse along a non-myelinated neurone slower than an impulse along a myelinated one?

A
  • In a non-myelinated neurone the impulse travels as a wave along the whole length of the axon membrane
  • In a myelinated neurone, the impulse can only travel from node to node, reducing the amount of axon membrane that the impulse travels along
42
Q

Why is the refractory period important?

A
  • In the refractory period, an impulse cannot travel along a neuron until the resting potential has been reached
  • This keeps the wave of depolarisation moving forward as the membranes behind the impulse cannot carry the impulse as they have not reached the resting potential yet

Biology (20 decks)

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