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BIOL_Final review > Chapter 12 Neural Tissue > Flashcards

Chapter 12 Neural Tissue Flashcards

1
Q

the functions of the nervous system (3)

A
  1. monitors variables inside and outside body
  2. processes & interprets sensory information
  3. generates a response by telling different parts of the body what to do
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2
Q

What are the effectors?

A

Glands and muscles = effectors
> the items tell what to do

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3
Q

Organization of the Nervous System

A

1. Central Nervous system (CNS)
: Brain and spinal cord
- information processing: integrates, processes, and coordinates sensory input and motor commands

2. Peripheral Nervous System (PNS)
: Nervous tissue outside the CNS and the ENS (digestive tract) = all the nerves outside of brains & spinal cord
A) sensory information within afferent division = “receptor”
- special sensory receptors (smell, taste, vision, balance, and hearing)
- visceral sensory (monitor internal organs)
- somatic sensory receptors (skeletal muscles, motor neuron system; skeletal muscles, joints and skin surface)

B) motor commands (neurons) within efferent division
- somatic nervous system (SNS)
= skeletal muscle
- Autonomic nervous system (ANS)
a) parasympathetic nervous system (slow down)
b) sympathetic nervous system
(speed up)
Both influence…
* smooth muscle
* cardiac muscle
* gland
* adipose tissue

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4
Q

What is Central Nervous System (CNS)?

A

Central Nervous System (CNS)
: includes the brain and the spinal cord

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5
Q

What is peripheral nervous system (PNS)?

A

Peripheral nervous system (PNS)
: consists of the nerves outside the CNS, including the spinal nerves, which interact with the spinal cord, and cranial nerves, which interact with the brain directly
- the nerves of the PNS are further classified as:
1. sensory (afferent) - they convey impulses to the CNS
2. Motor (efferent) - they convey impulses from the CNS

  • Motor nerves can be either voluntary or involuntary. Voluntary nerves make up the Somatic Nervous System and involuntary nerves make the Autonomic Nervous System (ANS)
  • The ANS consists of two divisions that often work complementary to one another:
    1. the sympathetic nervous system
    2. parasympathetic nervous system
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6
Q

Two types of cells in the nervous system:

A
  1. Neurons (nerve cells) - excitable cells; most lack centrioles & are long-lived except in adults (nose & hippocampus)
  2. Neuroglia = glial cells - supporting cells

CNS = Brain + Spinal cord
Out of CNS = PNS + ENS

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7
Q

The parts of neurons

A
  1. a nucleus
  2. nucleolus
  3. Nissl bodies (clusters of REER and free ribosomes)
  4. mitochondrion
  5. cell body
  6. perikaryon (cytoplasm)
  7. neurofilaments (proteins)
  8. Dendritic spines of dendrites
  9. axon hillock**
  10. axon
  11. axolemma (plasma membrane of axon)
  12. axoplasm (cytoplasm within the axolemma)
  13. telodendria (= like telephone)
  14. synaptic terminals

anterograde (kinesin; axonal transport) <-> retrograde (dynein)

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8
Q

What do neurotubules in the axoplasm do?

A

Use ATP to fast/ slow transport vesicles

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9
Q

What is Synapse?

A

Synapse
: junction between two neurons that mediates the transfer of information from one neuron to the next

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10
Q

2 types of synaptic neurons

A
  1. presynaptic neurons: sends the message
  2. postsynaptic neurons: **receives* the message
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11
Q

What happens if the neurotransmitter binds to receptors on the postsynaptic cell?

A
  • conveys the signal from the presynaptic cell to the postsynaptic cell
  • passes on the Action Potential
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12
Q

4 categories of neurons

A
  1. an anaxonic neuron (e.g. in the brain (CNS))
  2. a multipolar neuron (e.g. somatic motor neurons)
    - brain stem
    - spinal cord
    = signals to skeletal muscles
  3. a unipolar neuron (e.g. sensory neurons)
  4. a bipolar neuron (rare)
    (e.g. special sense neurons, small/ hearing)
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13
Q

What is a neuron?

A

the specialized cells of the nervous system that convey electrical impulses are called neurons

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14
Q

3 types of Neurons

A
  1. Interneurons
  2. Motor Neurons
  3. Sensory Neurons
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15
Q

What are interneurons?

A

Neurons that connect Motor and Sensory neurons to make Pathways are called interneurons.
- their cell bodies are within the CNS

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16
Q

what are motor neurons?

A

Neurons that carry signals from the CNS to muscles, viscera or glands are called Motor neurons.
- their cell bodies are located in the CNS

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17
Q

What are sensory neurons?

A

Neurons that carry signals toward the CNS are called Sensory neurons.
- their dendrites are associated with receptors, and their somas are located in Ganglion outside the CNS

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18
Q

Glial cells in CNS

A
  1. Astrocyte
    : support neurons by anchoring them to capillaries and protect them from harmful substances
    - maintain blood-brain barrier (physically & chemically)
    - provide structural support
    - regulate ions, nutrients and dissolved gas concentration
    - absorb and recycle neurotransmitters
    - form scar tissue after injury
    - role in synaptogenesis during embryogenesis
  2. Microglia: Phagocytic cells in the nervous tissue of the CNS
  3. Ependymal cells: simple cuboidal epithelial cells lining ventricles (in the brain) and the central canal (in the spinal cord)
    - assist in producing, circulating, & monitoring cerebrospinal fluid
  4. Oligodendrocyte
    : myelinate CNS axons; provide structural framework

only in CNS

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19
Q

what is the function of astrocyte?

A

: support neurons by anchoring them to capillaries and protect them from harmful substances
- maintain blood-brain barrier (physically & chemically)
- provide structural support
- regulate ions, nutrients and dissolved gas concentration
- absorb and recycle neurotransmitters
- form scar tissue after injury
- role in synaptogenesis during embryogenesis

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20
Q

what is microglia?

A

: Phagocytic cells in the nervous tissue of the CNS
- very small; gobble up any type of infections (debris, bacteria and dead cells)

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21
Q

what is ependymal cells?

A

: simple cuboidal epithelial cells lining ventricles (in the brain) and the central canal (in the spinal cord)
- assist in producing, circulating, & monitoring cerebrospinal fluid

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22
Q

What is oligodendrocyte?

A

: myelinate (formation surrounding the axons) CNS axons; provide structural framework

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23
Q

Glial cells in PNS (not in CNS)

A
  1. Satellite cell: surround neuron cell bodies in ganglia
    - regulate O2, CO2, nutrient and neurotransmitter levels around neurons in the ganglia*
    *Ganglia: a collection of neuronal bodies found in the somatic and autonomic branches of PNS
  2. Schwann cells: surround all axons in PNS
    - responsible for myelination of peripheral axons; participate in repair process after injury
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24
Q

What is the function of Satellite cell?

A

: protect and cushion int he PNS and regulate the exchange of materials between neuronal cell bodies & extracellular fluid
- regulate O2, CO2, nutrient and neurotransmitter levels around neurons in the ganglia*

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25
Q

What is the function of Schwann cells?

A

: form the myelin sheaths in the PNS
- responsible for myelination of peripheral axons; participate in repair process after injury

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26
Q

The function of myelin:

A

: an insulating sheath around an axon that increases impulse propagation rate along the axon
-> speeds up the electrical impulse proration

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27
Q

where are Neuroglia found in?

A

Peripheral Nervous system (PNS)
1. satellite cells (surround neuron cell bodies in ganglia)
- regulate O2, CO2, nutrients and neurotransmitter levels around neurons in the ganglia
2. Schwann cells
- responsible for myelination of peripheral axons; participate in repair process after injury

Central Nervous System (CNS)
1. ependymal cells (line ventricles (brain), and central canal (spinal cord) - assist in producing circulating, and monitoring cerebrospinal fluid
2. oligodendrocytes
- myelinate CNS axons
- provide structural framework
3. astrocytes
- maintain blood-brain barrier
- provide structural support
- regulate ion, nutrient, and dissolved gas concentrations
- absorb and recycle neurotransmitters
- form scar tissue after injury
4. microglia
- Phagocytic cells in the nervous tissue of the CNS

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28
Q

What is Ganglion?

A

= a collection of neural cell bodies outside the CNS (i.e. in the PNS)

Plural of ganglion: ganglia

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29
Q

What is nuclei?

A

= a collection of neural cell bodies inside the CNS

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30
Q

An important difference between Schwann cells and oligodendrocytes?

A

Schwann cells can direct the regrowth of severed axons
> can help axons’ regrowth

while…

Oligodendrocytes cannot, likely due to many axons more involved; astrocyte scar tissue & astrocyte chemical release that blocks axonal regrowth

consequences: if axons in the brain or spinal cord are severed, the neurons can not be repaired, and paralysis and loss of sensation occur in the region that had been innervated.

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31
Q

What happens if the axon gets injured? 4 steps

A
  1. fragmentation of axon and myelin occurs in the distal stump
  2. Schwann cells form the cord, grow into cut, and untie stumps. Macrophages engulf degenerating axon and myelin
  3. axon sends buds into network of Schwann cells and then starts growing along cord of Schwann cells
  4. axon continues to grow into distal stump and is enfolded by Schwann cells
32
Q

Ion movements and Electrical signals in neurons

A

like all cells, neurons maintain a transmembrane potential
- inside of cell (K+, protein-) is slightly negative relative to outside (Na+, Cl-)

when the cell is at rest this is called a potential difference or an electrochemical gradient

33
Q

what is resting membrane potential?

A

= -70 mV
the unequal distribution of charges inside and outside the plasma membrane, which produces a transmembrane potential

If a cell is left undisturbed, it will maintain a resting membrane potential indefinitely

33
Q

How do ions cross cell membranes without use of ATP?

A
  1. leakage channel
    - leak either Na+ and K+
  2. Gated Channel
    - voltage-gated
    - chemical (ligand) gated (need ACh ligand)
    - mechanically gated
  3. Na+/ K+ ATPase pump
    - pump 3 Na+ ions out of cell & 2K+ ions into cell for every ATP used
34
Q

How does Gated channels work?

A

a) Chemically regulated channel
1. resting state (closed)
2. Presence of ACh (still closed)
3. ACh binds in the binding site (channel open)

b) Voltage-regulated channel
1. resting state; -70mV (activation site closed/ inactivation site closed)
2. -60mV (channel open)
3. +30mV;Channel inactivated (activation site open/ inactivation site closed)

c) Mechanically regulated channel
1. channel closed
2. pressure applied on the membrane (channel open)
3. pressure removed (channel closed)

35
Q

What are the concentration gradient and the electrical gradient?

A

When an ion channel is open, the ions will move according to both the concentration gradient and the electrical gradient.

The direction of movement due to concentration gradient =
Na+ will move into the cell
K+ will move out of the cell

The direction of movement due to electrical gradient =
positive ion towards the inside of cell (Na+ & K+)
negative ion towards the outside of cell (Cl- & protein)

36
Q

What is electrochemical gradient

A

the tendency of the ions to move as a result of both these gradients influencing the ions at the same time

37
Q

Potassium Ion Gradient (K+)

A

At a neuron’s resting membrane potential, the chemical and electrical gradients are opposed for potassium ions (K+). The net electrochemical gradient tends to force potassium ions out of the cell.

If the plasma membrane were freely permeable to potassium ions, the outflow of K+ would continue until the equilibrium potential (-90mV) was reached. Note how similar it is to the resting membrane potential.

38
Q

Sodium Ion Gradient (Na+)

A

At a neuron’s resting membrane potential, the chemical and electrical gradients for sodium ions (Na+) are combined. The.net electrochemical gradient forces sodium ions into the cell.

If the plasma membrane were freely permeable to sodium ions, the inflow of Na+ would continue until the equilibrium potential (+66mV) was reached. Note how different it is from the resting membrane potential.

*sodium electrical gradient was toward the inside of the cell at resting membrane potential, however, it turned toward the outside of the cell at equilibrium potential.

39
Q

When ion channels are mostly closed?

A

At rest, most ion channels are closed
except: leaky channel

40
Q

where is the net loss of +charge derived from? (leaky Na+/ K+ channels)

A

There are
a) a very few leaky Na+ channels
b) a few more leaky K+ channels
» net loss of +charge from inside cells

In addition, the Na+/ K+ pump moves both ions back in the opposite direction, preventing changes in concentrations
» Further net loss of positive charge from inside the cell

*all of these movement (K+leak channel/ Sodium-potassium exchange pump/ Na+ leak channel) contribute to generating the resting membrane potential

41
Q

what does it mean the cell is polarized?

A

If the cell is left undisturbed, it will maintain the resting membrane potential indefinitely.

In this condition, the cell is said to be polarized

42
Q

Factors that can change the membrane potential from resting?

A
  1. anything that changes the permeability of the membrane to a particular ion
    i.e. opening of ion channels
  2. anything that changes the Ion concentration on the two sides of the membrane
    - normally, the opening or closing of ion channels (adjusting the negativity)
43
Q

The cell is said to be depolarized when…

A

it becomes more positive than the resting potential (above -70mV; closer to ‘0’)

44
Q

The cell is said to be hyperpolarized when…

A

it becomes more negative than the resting potential (below -70mV)

45
Q

when the current and released potential energy can be seen?

A

if the cell is stimulated, such that the membrane potential changes from resting we have generated a current and released potential energy.

Changes in membrane potential act as a stimulus
(i.e. changes above/ below resting potential)

46
Q

How does a neuron generate an Electrical impulse (Action Potential)?

A

Depolarization can lead to a graded potential and the development of an action potential: effect of neurotransmitter at a synapse between two neurons

47
Q

what happens in Resting stage

A

resting membrane with closed chemically regulated sodium ion channels = -70mV

48
Q

Steps for generating Action potential: Step 1

A

Neurotransmitter binds to the receptor, which is part of a chemical (ligand) gated sodium channel

Sodium moves into the cell, depolarizing a small area. the spread of sodium produces a local current that depolarizes adjacent portions of the cell membrane.

sodium moves into the cell=depolarizing

49
Q

Steps for generating Action potential: Step 2

A

The Spread of sodium ions inside the cell membrane produces a local current that depolarizes adjacent portions of the cell membrane

this small depolarization is an example of Graded potential

50
Q

the characteristics of Graded potential

A
  • most affects locally and the effect decreases with distance = used for short distance communication
  • effect spreads passively owing to local currents
  • may cause depolarization or hyperpolarization depending on which ion channels are stimulated to open
  • the stronger the stimulus the greater the change in transmembrane potential, and the larger the area affected
50
Q

the three that the degree of change in potential varies with

A

1) graded depolarization of axon hillock
2) degree of synaptic vesicles secreted
3) degree of chemical gated ion channels open

51
Q

What is the action potential?

A

if the cell is depolarized beyond a critical threshold level, an action potential is generated.

An action potential is diff from a graded potential in that it is an “all or none” event

52
Q

the diff between action potential and graded potential

A

Graded potentials are variable-strength signals that can be conveyed over small distances, whereas action potentials are massive depolarizations (rapid change) that can be transferred over long distances.

53
Q

The characteristics of the action potential

A

a) all or nothing - degree of depolarization doesn’t vary with the strength of the stimulus
b) once started, passes all the way down the axon without fading

54
Q

Generation of Action potential: resting stage

A

at rest:

all gated Na+ and K+ channels are closed

Na+ activation gate is closed
Na+ inactivation gates is opened
K+ gate is closed

55
Q

Generation of Action potential: step 1 (-60mV)

A

Depolarization to threshold
an initial stimulus starts to depolarize the membrane to -60mV, triggering the Na+ voltage-sensitive gate to open

  • to generate an action potential that will travel down the axon, first a graded potential must occur in the axon hillock
  • graded potential (stimulus is a neurotransmitter e.g. ACh)
56
Q

Generation of Action potential: step 2 (+10mV)

A

Activation of sodium channels and rapid depolarization
Depolarization causes voltage-sensitive Na+ channels to open; only the most sensitive open at first
- Na+ rushes into the cell, depolarizing it further to +30mV

57
Q

Generation of Action potential: step 3 (+30mV)

A

Inactivation of sodium channels and activation of potassium channels
Na+ channels close (inactivation) at +30mV
- Slower-acting voltage-sensitive K+ channels open

58
Q

Generation of Action potential: step 4 (-90mV)

A

the return to normal permeability
As the cell repolarizes to -90mV, K+ channels close

59
Q

Generation of Action potential: resting stage again (-70mV)

A

The cell has now returned to the resting state

60
Q

where does the action potential typically start? (p54)

A

In a neuron, the action potential typically starts at initial segment and travels down the axon

*The graded potential stars at the axon hillock

61
Q

How is the action potential conducted without fading out like a graded potential?

A

b/c it is an all-or-none event - that is mediated by voltage-gated channels and Na+/ K+ ion pumps

62
Q

Why does it normally only move in one direction?

A

b/c the axon hillock does not have any voltage-gated Na+ channels, it can’t respond with an action potential, so to begin with, the action potential propagates in one direction only.
- it can never reverse as it travels down the axon as the previous segment is always still int eh absolute refractory period

63
Q

conduction along the membrane: 4 steps

A
  1. as an action potential develops in the initial segment, the transmembrane potential depolarizes to +30mV
  2. a local current depolarizes the adjacent portion of the membrane to threshold
  3. An action potential develops at this location, and the initial segment enters the refractory period
  4. a local current depolarizes the adjacent portion of the membrane to the threshold, and the cycle is repeated
64
Q

What is nodes of Ranvier

A

Many neurons are myelinated = wrapped with many layers of cell membrane of a glial cell. The spaces between the sheath formed by individual cells are called the nodes of Ranvier

  • in cells that are myelinated, the action potential skips the internodes, and so travels **rapidly from node to node **
65
Q

Saltatory propagation, conduction in a myelinated neuron…

A
  • no voltage-sensitive Na+ channels under the myelin
  • no leakage of ions across the membrane
66
Q

The steps for saltatory propagation, conduction in a myelinated neurons

A
  1. action potential at the initial segment
  2. depolarization to threshold at node 1
  3. action potential at node 1
  4. depolarization to threshold at node 2
67
Q

Conduction velocity depends on…

A
  1. presence of myelin sheath
    - saltatory conduction = very rapid
  2. Axon diameter
    - larger diameter axons conduct faster than smaller ones
68
Q

Three types of nerve fibers (in terms of conduction velocity)

A

a) type A:
- the largest axon (4-20Mm diameter)
- fastest AP speed of 120m/s or 268mph
[function]: conduct sensory info from skin, joints, and skeletal muscle into CNS and conduct instructions to skeletal muscle

b) type B
- small (2-4Mm diameter)
- intermediate speed; AP speed of 18m/s or 40 mph
- myelinated axons

c) type C
- small (2Mm diameter)
- unmyelinated axons
- AP speed of 1m/s or 2mph (the slowest)

[function] for both B &C
- transmit sensory info from sensory visceroreceptors and from some pain, temp, general touch and pressure receptors
- carry instructions to smooth & cardiac muscle, glands

69
Q

Homeostatic imbalance: what is multiple sclerosis?

A

involves: immune system attacking myelin

symptoms: any neurological symptoms
1. muscle weakness or spasms
2. coordination problems
3. visual problems
4. fatigue, chronic pain
5. bladder, bowel problems
6. cognitive impairment
= the propagation of active potential is affected, leading to a slow-down

70
Q

two kinds of synapses

A

a) electrical: less common depolarization spread from cell to cell through direct ion flow through channel way-fastest
(similar looks to gap junction)
b) chemical synapse
1. axon terminal = excitatory/ inhibitory neurotransmitters
2. receptor region on the postsynaptic membrane

71
Q

how to transfer information at chemical synapses; an example of a cholinergic synapse (i.e. one that uses ACh as the neurotransmitter)
= 4 steps

A
  1. an action potential arrives and depolarizes the synaptic knob
  2. extracellular Ca2+ enters the synaptic cleft triggering the exocytosis of ACh
  3. ACh binds to receptors and depolarizes the postsynaptic membrane
    - graded potential generated at postsynaptic membrane spreads along the membrane to the initial segment
  4. ACh is removed by AChE (acetylcholinesterase)
72
Q

Events Occurring at Synapse

A
  1. an arriving action potential depolarizes the synaptic knob
  2. calcium ions enter the cytoplasm, and after a brief delay. ACh is released through the exocytosis of synaptic vesicles
  3. ACh binds to sodium channel receptors on the postsynaptic membrane, producing a graded depolarization
  4. depolarization ends as ACh is broken down into acetate and choline by AChE
  5. The synaptic knob reabsorbs choline from the synaptic cleft and uses it to synthesize new molecules of ACh
72
Q

What is Synaptic Delay?

A

Synaptic Delay (0.2-0.5msec)
= time between the arrival of the AP at the synaptic knob and the effect on the postsynaptic membrane
- includes: neurotransmitter release & Ca+ influx

73
Q

what is Synaptic Fatigue

A

Synaptic Fatigue
: under intense stimulation, resynthesis and transport may be unable to keep pace with the demand for neurotransmitter

74
Q

How do neurotransmitters and neuromodulators work? (p.73)

A

a) direct effects: opening/ closing chemically gated ion channel (ionotropic) or
b) indirect effects by G protein: indirectly through activating G protein-coupled receptors (GRCRs)
c) indirect effects by intracellular enzymes: indirectly through activating/ inhibiting intracellular enzymes/ channels

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