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+ BIOL 371 > Lecture 1: Nervous System – Structure and Function > Flashcards

Lecture 1: Nervous System – Structure and Function Flashcards

1
Q

How can we prove that the brain/nervous system is actually important?

A

damage to something in head and/or brain (and nowhere else) can result in problems with using other body parts

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2
Q

What is the vertebrate CNS entirely encased in?

A

protective bony armour

except retina

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3
Q

What are the protective structures of the central nervous system? (5)

A
  • skull
  • vertebral column
  • meninges (membranes)
  • cerebrospinal fluid (CSF)
  • blood brain barrier (BBB)
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4
Q

How does the skull protect the CNS?

A

cranium – casing made of 8 bones cemented together with sutures (special joints) that supports and protects brain

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5
Q

What sort of injuries does the skull protect the brain from?

A

blunt injuries

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6
Q

What is the spinal/vertebral column?

A

group of bones (vertebrae) that support spinal cord

each vertebrae has hole that contains the running spinal cord

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7
Q

What are the components of the central nervous system?

A
  • brain
  • spinal cord

(everything inside bony shells)

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8
Q

What sort of injuries does the vertebral column protect the brain from?

A

puncturing injuries

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9
Q

What sort of injuries does the vertebral column NOT protect the brain from?

A

blunt injuries (there are so many processes that can be cracked)

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10
Q

What are meninges?

A

three layers of protective membranes that lie between skull and brain

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11
Q

What are the 3 meninges?

A
  • dura mater
  • arachnoid mater
  • pia mater
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12
Q

What do meninges primarily consist of?

A

elastic collagen fibres

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13
Q

What is the dura mater?

A

outer layer – thickest and toughest

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14
Q

What is the arachnoid mater?

A

middle layer – has extra structures to separate from third layer

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15
Q

What is the pia mater?

A

inner layer – thinnest and softest

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16
Q

Between which meninges can CSF be found?

A

in the space between arachnoid and pia layers

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17
Q

What does CSF do?

A

cushions brain from skull (and vertebrae)

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18
Q

What sort of injuries would meninges protect the brain from?

A
  • friction – layers of membranes allow organs to slide around
  • puncturing injuries
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19
Q

What are the contents of CSF?

A
  • carefully balanced ionic concentrations

- variety of neurotrophic factors, other proteins, and nutrients

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20
Q

What is CSF produced by?

A

secreted by cells in choroid plexus within brain’s ventricular system

choroid plexus is associated with blood vessels

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21
Q

Where does CSF circulate/flow?

A
  • flows within subarachnoid space, through ventricles, and drains back into bloodstream at sagittal sinus
  • percolates through brain tissue via glymphatic system
  • some CSF flows into spinal cord, but most flows out and surrounds outside
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22
Q

What is the glymphatic system?

A

system of blood vessels that forces CSF into brain tissue

lined by glial cells that modify rate of flow

(system is also under circadian control – highest during sleep)

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23
Q

What sort of protection could be provided by CSF?

A

acts as cushion – when soft brain tissue slams against hard bony shells

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24
Q

What extra protection would come from forcing CSF to flow directly through brain tissue (glymphatic system)?

A

remove metabolic waste – brain does not have lymphatic system

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25
Q

Can CSF production be altered?

A

yes – it is a dynamic, responsive process

can depend on the state of the animal (ie. awake vs. asleep, mutation vs. wild type)

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26
Q

TRADE-OFF: What’s the disadvantage in having a rigid skull encasing fluid-producing structures?

A

in adults, bones of skull are fused, therefore blockages to CSF (or bleeding in brain) cannot increase volume, so intracranial pressures rise

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27
Q

What is hydrocephalus?

A

complication seen in very young children (before skull sutures close) when blockages prevent CSF circulation or draining, causing overly large head growth and neurological symptoms

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28
Q

What is trephination/trepanation?

A

drilling of holes in skull – used to release intracranial pressure

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29
Q

Are brain capillaries less permeable than other capillaries in the body (ie. heart capillaries)?

A

yes – HRP diffuses from capillary lumen into tissue beyond endothelial cells in heart, but does not reach brain tissue or even perivascular space in brain tissue

30
Q

What kind of anatomical specializations do capillaries in the brain have?

A

specializations that control and seal them tightly

31
Q

What is the blood brain barrier (BBB) created by?

A

tight junctions between capillary endothelial cells that prevent water and solute movement

32
Q

What is the function of the blood brain barrier (BBB)? (2)

A
  • prevents entry into brain of circulating cells in blood

- limits diffusion of many molecules which circulate in blood into CNS

33
Q

What type of barrier is the blood brain barrier (BBB)?

A

selective barrier – some molecules can cross it and enter the brain

  • free diffusion across endothelial cell membranes
  • facilitated diffusion across capillary cell membranes
34
Q

What is the blood brain barrier (BBB) created by?

A

tight junctions between capillary endothelial cells that prevent water and solute movement

35
Q

What are astroglia?

A

support cells within brain that surround brain-side of capillary

36
Q

What are the functions of astroglia? (2)

A
  • contribute to formation and maintenance of BBB

- can locally control capillary diameter

37
Q

What sort of protection could be provided by the BBB?

A
  • protect from microbiological hazards
  • protect from toxins
  • keep out certain medications
  • protect from messenger molecules that may be circulating the blood that could influence what goes on in brain
38
Q

What does the brain need to do in order to keep its metabolism going?

A

needs molecules carried in blood to get across BBB

39
Q

What affects molecules’ ability to diffuse across cell membranes?

A

their chemical properties

40
Q

TRADE-OFF: What does the brain do for metabolism if the BBB keeps polar substances out?

A
  • free diffusion (across endothelial cell membranes)

- facilitated diffusion (across capillary cell membranes)

41
Q

What molecules use free diffusion (across endothelial cell membranes)?

A

small and hydrophobic molecules

42
Q

What molecules use facilitated diffusion: (across capillary cell membranes)?

A

polar and/or large key nutrient and signalling molecules that cannot diffuse on their own

43
Q

What is required for facilitated diffusion?

A

endothelial cells must express specific transporter proteins for each molecule that needs to cross BBB

44
Q

BBB is a key factor that affects…

A

efficacy of drugs in the brain

45
Q

Imagine you are working for Big Pharma: You need to create a drug that can be swallowed or injected, but will still have effects on the brain. What properties should it have? Why?

A

soluble in water – needs to be able to go through blood
- blood can be the transport system into brain

soluble in lipids – this is the only way it will get across BBB
- there is no transporter since it is an invented drug

46
Q

How does BBB look different when looking at live vs. preserved tissue? Why?

A

in vivo: perivascular space between astrocyte end feet and capillary wall is clearly visible

post mortem (fixed) tissue: perivascular space is greatly reduced or fully absent

this is because process of fixing tissue (with formalin or alcohol) involves some level of dehydration and tissue shrinkage

47
Q

Where are the semi-impermeable barriers?

A

there are separate semi-impermeable barriers between blood, choroid, CSF and brain

48
Q

How does each semi-impermeable barrier differ?

A

each barrier has slightly different gross anatomy and cell biology (ie. different levels of tight junction and transporter proteins), therefore limit ion and fluid flow differently

49
Q

What are the 4 semi-impermeable barriers?

A
  • blood brain barrier (BBB)
  • blood-CSF barrier
  • brain-CSF barrier
  • CSF-brain barrier
50
Q

Where is the blood brain barrier (BBB)?

What is it the source of?

A

occurs between blood and brain tissue

source of O2 and glucose into brain

51
Q

Where is the blood-CSF barrier?

What is it the source of?

A

occurs between blood and choroid plexus (CSF secreting cells)

source of water into brain

52
Q

Where is the brain-CSF barrier?

What is its function?

A

occurs between subarachnoid space and brain surface

keeps wastes from getting back into brain

53
Q

Where is the CSF-brain barrier?

A

occurs between ventricles and brain tissue

glymphatic system

54
Q

What is the permissibility of the CSF-brain barrier?

A

fairly permissive in most adults, but can vary

55
Q

Can gross structure reveal the function of the nervous system?

A

yes, it is possible to learn about nervous system’s role from its gross anatomy – if you are careful

56
Q

How is the PNS connected to CNS?

A

PNS radiates from CNS in hub-and-spoke organization, which originate and/or terminate in many locations throughout the rest of the body

57
Q

PNS vs. CNS

A

PNS: outside the bones – everything that is nervous tissue connected to CNS

CNS: inside the bones

58
Q

What does afferent mean?

A

relating to nerves that run from periphery into CNS

59
Q

What function do all afferent nerves have?

A

sensory function

60
Q

What does efferent mean?

A

relating to nerves that run from CNS to peripheral structures – including (but not only) muscles

61
Q

What is the somatic nervous system?

A

portion of nervous system that innervates muscles and integument (skin, tendons, etc.)

62
Q

What is the autonomic/visceral nervous system?

A

portion of nervous system that innervates viscera and other non-somatic organs – organs that you control, that is not skeletal muscle

63
Q

What does this view of the nervous system as a whole suggest to you about its function?

A

nervous system’s function is coordination of the rest of the body – the rapid and specific integration and transfer of information between different body systems and different regions

  • constantly collecting information from afferents about what is going on in the body
  • can target what it’s saying to various places
  • to understand how it does this, need to take a closer look at brain and spinal cord
64
Q

What type of protection do the protective structures and adaptations of the CNS have?

A

both physical and chemical protection and isolation

65
Q

What is the BBB?

A

complex and dynamic ‘fence’ between CNS and rest of body

66
Q

What does the BBB do?

A
  • controls access of blood born molecules into CNS

- locally regulates blood flow to different regions of CNS

67
Q

Is the BBB highly regulated?

A

yes, by specialized cells

68
Q

What does the BBB have profound consequences for?

A

practical manipulation of vertebrate brain (ie. by metabolic fuel, drugs)

69
Q

When are relationships in gross anatomy meaningful?

A

CNS and PNS are a connected whole – it is only when considering the diverse and ubiquitous innervations by the PNS that structure-function relationships in gross anatomy are meaningful

function of brain cannot be considered in isolation

70
Q

What effects might breakdown of the BBB have on the CNS? (4)

A
  • immune cells enter CNS and disrupt its function
  • chemicals from blood enter CNS and disrupt its function
  • ionic composition of CNS ECF is disrupted by mixing with plasma
  • neurotrophic factors from CNS leach out through the BBB
71
Q

What are some reasons why it would be dangerous for an animal if the flow of CSF through this system is disrupted by a blockage?

A
  • increased pressure can cause seizures/neurological dysfunction
  • failure to remove waste products from neurons
  • failure to keep brain supplied with neurotrophic factors
  • less shock absorption

+ BIOL 371 (22 decks)

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