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Mammalian Physiology > Slide 4 > Flashcards

Slide 4 Flashcards

1
Q

What are the three components of the nervous system?

A
  1. brain
  2. spinal cord
  3. peripheral nerves
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2
Q

How is the nervous system anatomically subdivided?

A

CNS: brain +spinal cord - integrates sensory information, evaluates and sends outgoing response
PNS: (peripheral areas of the body)
cranial nerves - originates form brain
spinal nerves - originate from spinal cord

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3
Q

How can the nervous be subdivided by the organs they innervate?

A

SNS - somatic
-motor division carries division to somatic effectors
-sensory division carries feedback to somatic integration centres (relays PNS to CNS)
ANS - (autonomic) no voluntary control
-afferent division: incoming msgs from visceral receptors
-efferent division: outgoing of ANS to visceral effectors (smooth and cardiac muscles and glands)

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4
Q

How can the ANS efferent pathway be further categorized?

A

The EFFERENT pathway can be subcategorized by:

  1. sympathetic
    - fight or flight response
    - prepares for immediate threats
  2. parasympathetic
    - normal resting activities
    - rest and repair
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5
Q

How does the sympathetic system control heart rate?

A

Where there is greater need for blood flow:

  • stimulates SA node by the release of norepinephrine which acts by accelerating inactivation of K+ channels
  • > less able to leave the cell
  • cell becomes less negative
  • so there is a swifter drift to action potential
  • meaning the heart beats more forcefully and squeezes more blood out
  • it also vasoconstriction effect on the blood vessels so there is more blood flow in that direction.
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6
Q

What is the parasympathetic control over the stomach?

A

-the presence of food triggers parasympathetic reflexes via distension of stomach (outward expansion)
-more gastric juices are secreted
How?
-in response to amino acids, parasympathetic :
causes gastrin (digestive hormone secreted by mucosa in the presence of food) to increase secretion of gastric juice.

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7
Q

What are the two major cell types in the nervous system? Please describe them.

A

neurons: excitable cells that conduct electrical impulse, required for all nervous system activities
glial cells: do not conduct information but support the function of neurons

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8
Q

Describe the nervous structure (the structure of a nerve cell).

A

input of signal= structure: dendrites (receive incoming signals)
integration= structure: cell body, axons carry outgoing information
output of signal= structure: axon terminal

The (presynaptic) axon terminal is in contact with the post synaptic dendrites/neuron, the space in between is called the synaptic cleft. All three structures compose the synapse.

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9
Q

Describe the basic nervous structure (the structure of a nerve cell).

A

input of signal= structure: dendrites (receive incoming signals)
integration= structure: cell body, axons carry outgoing information
output of signal= structure: axon terminal

The (presynaptic) axon terminal is in contact with the post synaptic dendrites/neuron, the space in between is called the synaptic cleft. All three structures compose the synapse.

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10
Q

Describe the transport structures within the neuron.

A

cytoskeleton: microtubules, microfilaments and neurofibrils -allow rapid transport of small organelles
- vesicles contain the neurotransmitters and mitochondria (both are motor molecules that shuttle organelles to and from the extremities of the neuron)

How does it work within the axon?
Motor molecules move proteins on the cytoskeleton on the highway to be released at the synaptic knobs.

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11
Q

What are the five major types of glial cells?

Which types are part of the CNS and which are part of the PNS?

A
  1. astrocytes
  2. microglia
  3. ependymal cells
  4. oligendendrocytes
  5. schwann cells

Only the schwann cells are part of the PNS.

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12
Q

What is the purpose for astrocytes?

A
  • star shape
  • connect neurons to capillaries so transfer nutrients from blood to neurons (take up K+, water, neurotransmitters)
  • for tight sheaths around brain capillaries with tight junctions between capillary endothelial cells make up the blood brain barrier (BBB)
  • substrate for ATP production
  • neural stem cells
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13
Q

What does the blood brain barrier do? And how is it achieved?

A
  • selectively supplies brain with nutrients to function properly
  • strictly limits transport via physical (tight junctions) and metabolic enzymes barriers

This can be achieved due to 2 specializations:
1. BBB capillaries are held together by tight junctions (which act as a barrier against molecules as they cannot permeate the cracks between cells like glue)
2. involved the feet of the astrocytes = forms a web of tight sheets around
=> the 2 specializations make the DOUBLE barrier of astrocyte feet + endothelial cells of the capillary walls

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14
Q

What can/not cross the barrier?

A
  • it does allow receptor specific mechanisms like:
    1. lipid soluble molecules can penetrate through easily via membrane lipids
    2. water soluble molecules like ions are unable to cross without specialized carrier
    3. liposome A: spherical vesicle with PL bilayer membrane, can be used to deliver drugs and genetic material into a cell as it fuses with other bilayers to delivering liposome contents
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15
Q

What is the function of microglia?

A

It is like the macrophage of the brain.

  • stationary cells, small
  • except when in inflamed brain tissues: they enlarge, move and phagocytosis to remove microorganisms and debris
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16
Q

What are ependymal cells for?

A

They are like epithelial cells.

  • form thin sheets that lin fluid filled cavities like cerebral spinal fluid in the CNS
  • some produce fluid while other aid circulation (using cilia)
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17
Q

What are oligodendrocytes used for?

A
  • smaller than astrocytes
  • hold nerve fibres together
  • produce myelin sheath in CNS
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18
Q

Which glial cells are in the spinal cord?

A

microglia, ependymal cells, oligodendrocytes and astrocytes.

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19
Q

Multiple sclerosis is a disorder of?

A 
oligodendrocytes.
A common CNS disease characterized by myelin loss and destruction. 
-plaque like lesions form
-nerve conduction fails
-communication is interrupted
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20
Q

What are the glial cells in the PNS?

A
  1. schwann cells

2. satellite cells (still a type of schwann cell)

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21
Q

What do schwann cells do?

A
  • found in the PNS only and function like an oligodendrocyte
  • form myelin sheaths
  • gaps in the sheaths = nodes of ranvier-nodes and myelin sheat are important for efficient conduction of impulses on nerve fibres

Satellite cells:

  • a type of schwann cell that cover and support neuron cell bodies in PNS
  • -> just like a protective covering…
  • DO NOT form myelin sheath
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22
Q

What are grey fibres and white fibres?

A

Grey fibres: solely support, do NOT form myelin sheath (like a connective tissue between nerve fibres)

White fibres: form myelin sheaths that wraps around the nerve fibre forming many layers of plasma membrane made of myelin (phospholipid)

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23
Q

How do PNS schwann cells form?

A

A schwann cell envelops an axon.

  • nucleus is pushed to the outside of the myelin sheath
  • the myelin consists of multiple layers of the cell membrane contouring the axon.
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24
Q

What is the node of ranvier?

A

It is a section on the axon membrane that is unmyelinated.
Between two schwann cells.
1 axon = 1 schwann cell (that formed the myelin)

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25
Q

Identify the functional regions in a neuron.

A
  1. Input zone (receives information) = dendrites + part of the cell body
  2. Summation zone (nerve impulse combine and may trigger an action potential that will be conducted along axon) = axon hillock
  3. Conduction zone (has many voltage gated channels Na+ and K+) = axon
  4. Output zone (contains many Ca2+ channels, where the nerve impulse triggers release of neurotransmitters) = synaptic knobs of axon
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26
Q

How are neurons classified?

A
  • afferent : incoming sensory conduct the impulse TO spinal cord and brain
  • efferent : outgoing, conduct impulse AWAY from spinal cord or brain TO muscles or glandular tissue
  • interneurons: lie only inside CNS (brain and spinal cord). They conduct (link) impulses from sensory neurons to motor neurons.
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27
Q

Name the three neuron arc.

A

Reflex arc: signal conduction route to and from CNS.

  1. sensory receptor send msg to CNS
  2. reached interneuron
  3. interneurons initiate outgoing response at motor neuron
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28
Q

What are nerves and tracts?

A

Neurons are bundled in nerves ( for PNS nerve fibres) and tracts (for CNS nerve fibres).

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29
Q

Describe the anatomical structure of a nerve.

A

Nerve fibre:
Neurons contains axons.
Many neurons are wrapped with endoneurium and bundled into one fascicle with a perineurium covering.
Several fascicles are bundled together with artery, veins, lymph space and fat within the nerve fibre. It is covered by epineurium.

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30
Q

Describe the process of a nerve fibre repair.

A
  • mature neurons are not capable of cell division so nervous tissue damage can be permanent.
  • limited capacity for reparations (PNS: little, CNS: none)
  • nerve FIBRES can be repaired if:
    1. damage is not extensive/ cell body
    2. neurilemma - schwann cell cytoplasm of nerve fibre- are intact
    3. no scarring.
31
Q

What does study on long term neuronal survival after implantation show?

A

sciatic nerve regenerates- regrowth

32
Q

What is a nerve impulse?

A

electrical signal = means of communication

  • electrical fluctuation that travels along plasma membrane
  • excite neurons
  • propagated
33
Q

What is the RMP?

A

Resting membrane potential.

  • when neuron is not conducting an electrical impulse.
  • naturally produces an ionic imbalance of -70 mV
  • the interior of cell is negative in comparison to outside
34
Q

What promotes the RMP?

A
  1. ion transport mechanisms
    - Na+/K+ ATPase: active transport mechanism that transports them in opposite directions at different rates
    - pumps: 3 Na+ out and 2K+ in = maintaining an imbalance of more positive ions out
  2. membrane’s permeability characteristic
    - plasma channels for anions may not be there or are closed
    - No passage in nor out of cell:
    a) . anionic proteins are trapped within the cell
    b) . likewise, chloride ions, dominant on the outside of cell, are repelled by intracellular anions as they are trapped outside the cell.

The cell is more permeable to K+ than Na+ (only ions that move efficiently across membrane)

  • Na+ channels are close so none moves into cell
  • there are some closed and some OPEN K+ channels that can slowly leak K+ out of cell
35
Q

Which ions does the membrane potential depend on?

A 
potassium
sodium
chloride
calcium
protein anions
36
Q

How is it achieved?

A
  1. sodium is a primary determinant
    - there is active transport of Na+ ions OUT of cell to create a gradient = making inside more negative
  2. membrane is more permeable to K+ than Na+
    - small amount of Na+ leaks out
    - Na/K pump contributes by 3Na out for 2K in
37
Q

What do terms like depolarization, repolarization and hyperpolarization refer to?

A

Depol: membrane becomes more positive (less negative)

Repol: membrane returns to RMP

Hyperpol: RMP moves even further than -70mV

38
Q

Name gated channels that control ion permeability.

A

mechanically gated

  • sensory neurons
  • physical trigger

chemically gated

  • respond to ligand
  • most neurons

voltage gated

  • threshold voltage must be attained
  • changes in cell membrane potential
39
Q

What does channelopathies mean?

A

Disturbed ion channel function or dysfunction in the proteins that regulate them.

40
Q

Which way does K+ move?

A

Slowly leaks out of cell.

41
Q

What is an action potential?

A

Change in RMP.

-nerve impulse (electrical signal form one neuron to another)

42
Q

How a neuron stimulated to produce an action potential?

A
  • membrane potentials fluctuate above or below RMP in response to stimuli
  • excitation: when stimulus triggers opening of more Na+ channels allowing enough to cause a membrane potential to move toward zero (more positive=depolarization)
  • more Na+ opening channels = more Na+ entering cells
  • as they enter, the overall the charge changes across the membrane (reduced meaning the inside of cell is reduced)
  • depolarization
43
Q

What is a local potential?

A

slight shift away from RMP in a specific region on the plasma membrane

44
Q

How is a neuron inhibited?

A

When a stimulus triggers the opening of K+ channels at chemical synapse.

  • this increases the membrane potential at the plasma membrane since more K+ diffuses out of cell
  • the excess K+ moving out of cell, hyperpolarizes the cell since the membrane potential is now below -70mV.
45
Q

What is the step by step mechanism of an action potential?

A
  • an adequate stimulus (chemical or electrical from adjacent neuron or gap junction) applied to a neuron
  • Na+ channels open in response to stimulus
  • if magnitude of local depolarization reaches threshold potential (-59 mV, voltage-gated Na+ channels open = more Na+ enters cell so there is MORE depolarization
  • many voltage gated Na+ channels and K+ channels are in the summation and conduction zone
46
Q

What is important for an action potential to trigger the firing of a neuron?

A

A minimum threshold potential where local stimulus can be summed at the summation zone to produce firing to the conduction zone.

47
Q

What are two possibilities at the summation zone?

A

Since the action potential is an all or none response: voltage gated Na+ channels either open or remain closed (do not open)

a) if local depolarization fails to reach -59 mV, Na+ channels does not open. It moves back to RMP.
b) if it is reached, the voltage gated Na+ channels stay open for 1 milisecond before automatically closing
- so there is always the same magnitude of action potential reached.

48
Q

What happens when the action potential peaks?

A

The membrane begins to move back toward the resting membrane potential.

How?
- there is an opening of K+ channels to allow outward diffusion of K+ = repolarization

-brief period of repolarization: when K+ channels remain open even after RMP is reached (because it is very slow channel)

49
Q

Once the membrane depolarizes, what is the difference between the voltage gated Na+ channels and the K+ channels?

A

Na+ channels: open rapidly so there is a rush of Na+ into cell

K+ channels: open at the same but slowly and then close very slowly causing the hyperpolarization.
once they close, the RMP is maintained.

50
Q

What are the two gates the Na+ channels have?

A
  1. activation gate
    - closed at RMP
    - opens during depolarization = Na+ enters
  2. inactivation gate
    - closes after peak is reached = Na+ entry stops
    - reset to original position during repolarization (which is caused by K+ leaving cell)
51
Q

Describe the positive feedback cycle during depolarization.

A

Depolarization triggers local Na+ channel activation gates to open rapidly, Na+ enter cell, more depolarization - opens the Na+ channel activation gates in the next cell… etc.

It also triggers slow K+ channels to open so it slowly leave cell causing repolarization.

52
Q

What is the refractory period?

A
  1. absolute refractory period
    - brief period where local area of a neuron’s membrane resists restimulation and WILL NOT respond to a stimulus no matter what
    - starts once it is above threshold potential until hyperpolarization
  2. relative refractory period
    - membrane is repolarized and trying to restore RMP
    - WILL respond to a very strong stimulus
    - starts when hyperpolarization starting to recover back to RMP
53
Q

How is conduction of an action potential propagated?

A

At peak action potential, the plasma membrane polarity is now reverse of RMP (positive in local region inside cell instead of negative).

  • reversal causes electrical current to flow to adjacent regions to trigger voltage gated Na+ channels in the next segment to open.
  • continues to repeat
  • domino effect: never moves backwards due to the absolute refractory period (and relative) which prevents restimulation from the same mechanism that is propagating the signal forward
  • myelinated fibres insulate resisting ion movement and local flow of current
  • the depolarization is conserved during the myelin sheaths
  • so action potentials occur only at the nodes of Ranvier = called salutatory conduction (where impulse regeneration leaps from node to node.
54
Q

What happens to the conduction in demyelinating diseases?

A

The depolarization signal leaks since the myelin sheaths are deficient.

  • depolarization occurs at one node where the myelin sheath normal but then there is
  • slow current conduction + leak
55
Q

What does the positive feedback loop do in terms of action potentials?

A

action potentials begins at trigger zone and depolarizes by opening of Na+ channels.
-positive charge from depolarization spreads to adjacent zones
Why?
because K+ is repelled by the rush of Na+ into cell and cell’s depolarization
It is therefore attracted to the adjacent negative charge.
So as the next cell region becomes more positive due to the K+ repelled there, it makes for swifter drift to depolarization.

The spread causes more depolarization = positive feedback.

56
Q

What is a synapse?

A

A gap where neurotransmitters are released.

  • chemical synapse: presynaptic cell releases a chemical transmitter across synaptic cleft to the postsynaptic cell
  • the plasma membrane of the postsynaptic neuron has protein molecules as receptors for neurotransmitters.
57
Q

Where can a neuron terminate? (send signal to)

A
  1. muscle
  2. gland
  3. neuron
58
Q

What is a synaptic knob?

A

The end of the terminal branch of a presynaptic neuron’s axon where it contains vesicles with neurotransmitters.

59
Q

What are the arrangement of synapses?

A
  1. axodendritic
    - axon signals postsynaptic dendrite
    - common
  2. axosomatic
    - axon signals postsynaptic soma (the cell body)
    - common
  3. axoaxonic
    - axon signals postsynaptic axon
    - regulates action potentials of postsynaptic axon
60
Q

What is the mechanism of transmission of a pre-synaptic neuron?

A
  • action potential depolarizes axon terminal
  • depolarization causes a+ gated channels to open and calcium enters cell (presynaptic neuron)
  • calcium entry triggers exocytosis of synaptic vesicles
  • neurotransmitters diffuse across synaptic cleft and bind to receptors on post synaptic cell
  • neurotransmitter binds and initiates postsynaptic cell response
61
Q

How is the signal transmitted to post synaptic neuron?

A

the opening of ion channels produces potential

  • can be excitatory (EPSP-Na)
  • or inhibitory (IPSP, CI)

After: transmitters are inactivated or removed from cleft
-transmission is brief

62
Q

What are neurotransmitters?

A

means by which neurons communicate with one another.

63
Q

What are the classifications of neurotransmitters?

A
  1. function = determined by postsynaptic receptor
  2. chemical structure =
    -excitatory or inhibitory
    or
    -direct receptor opening of channel or uses second messenger with G proteins and in cell signal
64
Q

What are the four chemical classes of neurotransmitters?

A
  1. ACh - junctions with motor effectors (muscles + glands)
    salivary and sweat ANS: fight or flight response
    excitatory for PNS and CNS
  2. Amines: monamines like serotonin is inhibitory for moods and emotion in CNS
  3. aminoacids: like glycine is a common inhibitory neurotransmitter in the spinal cord
  4. other small molecules like nitric oxide which can signal from post to pre-synaptic neuron
65
Q

Which are rapid or slow synaptic potentials?

A

chemically gated ion channel = fast, short acting

G-protein coupled = slow synaptic potentials, long-term effects

66
Q

How can neurotransmitters have a direct stimulation on post synaptic receptor?

A

it binds one or two sites on ion channel (by itself) and directly affects closing/opening.

67
Q

What is an indirect stimulation of a post-synaptic receptor?

A

Neurotransmitters can activate G protein
eg. norepinephrine binds G protein linked receptor triggering adenylyl cyclase )ATP to cAMP) second messengers, PKA, cascade!

68
Q

How is neurotransmitter action terminated? Give an example ACh.

A

By enzymes.

  1. NT returned to axon terminal for reuse or transported to glial cells.
  2. Enzymes inactivate NT.
  3. NT can diffuse out of synaptic cell to nearby glial cell.

eg. ACh is broken down by actylcholine esterase.

  1. ACh is made from choline + acetyl CoA.
  2. synaptic cleft ACh is rapidly broken down by enzyme AChase
  3. choline is transported back to axon terminal and is used for more ACh.
69
Q

What are endogenous opioids?

A
  • neuropeptides
  • distributed in CNS and PNS.
  • natural pain killers produced by our own bodies.
  • crucial for functioning of motor coordination, learning and memory, gastrointestinal function, seizure and reproductive system.
  • pain modulation

eg. pain killers like morphin, demorol = narcotic street drugs like heroin: act at receptors for these neuropeptide NTs.

70
Q

What is the anatomy of the neuromuscular junction?

A

Somatic motor neuron contacts muscle fibre = called a neuromuscular junction.

The motor neuron is covered by schwann cell sheath, the axon terminal is in close proximity to the motor end plate (the end of the muscle fibre).

71
Q

What kind of receptors are at the motor end plates?

A

nicotinic ACh receptors. They are receptors for ACh.

72
Q

What is a graded action potential? (When a neuron receives info from many sources)

A

When more than one excitatory neuron fire that can be below threshold, when summed together at the trigger zone create a suprathreshold signal. (above threshold)
therefore, an action potential is generated.

73
Q

If a neuron receives opposing info from many sources what happens?

A

1 inhibitory, 2 excitatory neurons fire, summed potentials are below threshold so no action potential is generated.

Mammalian Physiology (17 decks)

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