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12 HUMAN BIO ATAR > CH 3 NEURONS COMMUNICATE QUICKLY > Flashcards

CH 3 NEURONS COMMUNICATE QUICKLY Flashcards

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Biology 101 flashcards
1
Q

define neuron

A
  • nerve cell

- highly specialised cells perfectly designed for rapid communication of messages in the body

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2
Q

name the 4 main parts of a neuron

A
  • cell body
  • axon
  • dendrite
  • nucleus
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3
Q

functions of the cell body

A
  • contains nucleus
  • responsible for controlling the functioning of the cell
  • contains cytoplasm surrounding nucleus
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4
Q

functions of the dendrites

A
  • usually fairly short extensions of the cytoplasm of the cell body
  • often highly branched
  • carry messages or nerve impulses to the cell body
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5
Q

functions of the axon

A
  • single extension of the cytoplasm carries nerve impulses away from the cell body
  • divided into many small branches which terminate at the axon terminal
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6
Q

functions of the myelin sheath

A
  • acts as an insulator
  • protects the axon from damage
  • speeds up the movement of nerve impulses along the axon
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7
Q

functions of the Shwann’s cell

A
  • the Shwann’s cell forms the myelin sheath outside of the brain and spinal cord
    (myelin created by oligodendrocytes in spinal cord)
  • the outermost coil forms the neurilemma
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8
Q

functions of the neurilemma

A
  • helps repair the injured fibres

- protects the myelin sheath

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9
Q

how does myelin relate to white and grey matter?

A
  • the fatty nature of the myelin means that the areas containing myelinated fibres appear white and are called white matter
  • the areas that are made up of cell bodies and unmyelinated fibres are called grey matter due to their grey colour
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10
Q

what is a synapse?

A
  • the junction where the axon terminals of one neuron meets the dendrites or the cell body of another
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11
Q

define neurotransmitters

A
  • molecule that carries nerve impulses across the small gap between the branches of adjacent nerve cells
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12
Q

what is a neuromuscular junction?

A
  • synapse where an axon meets a skeletal muscle cell
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13
Q

what is the function of a sensory neuron?

are there any other names for it?

A
  • carry messages from receptors in the sense organs or in the skin, to the central nervous system
  • other names include; afferent or receptor neuron
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14
Q

what is the function of a motor neuron?

are there any other names for it?

A
  • carry messages from the central nervous system to the effectors, the muscles and the glands
  • other names include; efferent or effector neurone
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15
Q

what is the function of an interneuron?

are there any other names for it?

A
  • link between sensory and motor neurons (located in central nervous system
  • other names include; association neurons, connector neurons or relay neurons
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16
Q

what is a multipolar neuron?

A
  • one axon and multiple dendrites extending from the cell body
  • most common
  • includes most of the interneurons in the brain and spinal cord as well as the motor neurons that carry messages to the skeletal muscles
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17
Q

what is a bipolar neuron?

A
  • have one axon and one dendrite
  • both the axon and dendrite may have branches at their end
  • occur in the eye, ear and nose, where they take impulses from the receptor cells to other neurons
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18
Q

what is a unipolar neuron?

A
  • have just one extension, the axon

- not found in humans or other vertebrates

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19
Q

what is a psuedounipolar neuron?

A
  • have properties of both unipolar neurons and bipolar neurons
  • single axon from cell body, which then separates into two extensions.
  • one extension connects to dendrites, other extends to axon terminals
  • the arrangement of the cell body and axon means that the cell body lies to one side of the main axon
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20
Q

define nerve

A
  • groups of nerve fibres outside the brain and spinal cord
  • nerve fibres are arranged in bundles half together by connective tissue, with multiple bundles joining together to form a nerve
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21
Q

define nerve impulse

A
  • electrochemical message that travels along a nerve fibre

- transmitted quickly

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22
Q

why is a nerve impulse described as an electrochemical change?

A
  • involves a change in electrical voltage

- that is brought out by changes in chemicals (specifically the ions inside and outside the cell membrane of the neuron

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23
Q

explain what is meant by the term “potential difference”

A

when + and - charges come together, energy is released. if a group of + and - charges are separated, they have the potential to come together and release energy. this can be measured in voltage.

24
Q

define ion

A

electrically charged particle

25
Q

define extracellular fluid

A
  • the fluid outside the cell containing high concentrations of sodium chloride
  • most charged particles = positive sodium ions and negative chloride ions
26
Q

define intracellular fluid

A
  • fluid inside the cell containing low concentrations of sodium ions and chloride ions.
  • main positive ions are potassium, negative ions come from a variety of organic substances made by the cell
27
Q

define membrane potential

A

the differences in concentration of ions means that there is a potential between inside and outside of the cell

28
Q

resting membrane potential of nerves is…

A
  • -70mV
  • potential of unstimulated cells
  • means that potential on inside of membrane is 70mV less than outside
29
Q

differentiate between leakage channels and voltage-gated channels

A
  • ions are unable to diffuse through phospholipid bilayers of cell membrane directly, instead, they travel through channels
    LEAKAGE: open all the time
    VOLTAGE: only open when nerve is stimulated
30
Q

describe the concentration of Na, K, Cl ions inside and outside of the cell

A

Na: 10 times higher OUTSIDE. cell membrane only slightly permeable to Na. limits facilitated diffusion of Na ions

K: 30 times greater INSIDE. large number of K leakage channels = cell highly permeable to K

Cl: higher OUTSIDE. cell membrane highly permeable to Cl, allowing diffusion through protein channels

negatively charged ions: large ions higher INSIDE than outside. CM impermeable to these ions; they stay inside the cell

31
Q

how might Na and K ions move across the cell membrane?

A

channels: voltage gated & leakage
sodium-potassium pump: 2 K into cell, 3 Na out of cell
- pump movement is against conc. gradient; is a form of active transport (ATP)

32
Q

process of sodium-potassium pump

A
  1. pump binds 3 Na ions and ATP molecule
  2. splitting of ATP provides energy to change shape of channel. Na ions driven through channel
  3. Na ions released to outside, new channel shape allows 2 potassium ions to bind
  4. release of PO allows channel to revert to original form, releasing K ions on inside of CM
33
Q

what does it mean for a cell membrane to be polarised?

A

the concentration of negative ions inside the cell is higher than outside of the cell, producing a negative resting membrane potential.
additionally, the intracellular fluid is therefore less positively charged than extracellular fluid

34
Q

action potential

A
  • if a stimulus to a neuron is sufficient, signal will be passed along neuron
  • this occurs due to opening and closing of voltage-gated channels, causing rapid depolarisation and repolarisation of the membrane
  • this lasts approx. 1 millisecond
35
Q

depolarisation

A
  • sudden increase in membrane potential
  • occurs if level of stimulation exceeds about 15 mV (reaching threshold of -55mV)
  • when neuron stimulated by a neurotransmitter, ligand and mechanical gated channels open, causing more sodium ions to move into cell. this makes intracellular fluid less negative, increasing potential difference.
  • if stimulus strong enough to increase potential to -55mV, voltage gated sodium channels open, producing movement of Na cells into cells that proceeds independently of stimulus.
    ; the size of the response is not related to strength of the stimulus = all-or-none response
  • inward movement of sodium ions too great to be balanced by an outward movement of potassium ions, making inside of membrane more positive than the outside. original polarity of membrane increases, reaching approx. +40 mV.
    ; membrane said to be depolarised
36
Q

repolarisation

A
  • short period after depolarisation
  • sodium channels close, stopping influx of Na ions
  • at same time, voltage-gated K channels open, increasing flow of K ions out of cell
    ; inside of cell becomes more negative than outside & decreases membrane potential

HYPERPOLARISATION

  • potassium channels remain open longer than needed
  • causes membrane potential to drop lower than resting membrane potential
37
Q

refractory period

A
  • sodium channels open again, quickly becoming inactivated.
  • means they are unresponsive to stimulus.
    ; for a brief period after being stimulated, membrane will not undergo another action potential. this period lasts from when membrane reaches threshold of -55 mV until it returns to resting membrane potential of -70mV
38
Q

does a single action potential run across a whole neuron?

A

no,
a single action potential occurs in a section of a membrane and triggers an action potential in the adjacent membrane. this process continues along cell membrane and is called a nerve impulse.

thus, an action potential does not travel along a nerve fibre, it is the message/nerve impulse that travels along the fibre. one action potential produces a domino effect. energy is transmitted from first domino to the last

39
Q

how does a nerve impulse travel across unmyelinated fibres

A
  • in unmyelinated nerve fibre, depolarisation of one area of the membrane causes a movement of Na ions into adjacent areas. movement stimulates opening of voltage gated Na channels in next part of membrane, initiating action potential across that area of a membrane, and so on
  • if stimulus should occur in middle of a fibre, impulse travels in both directions [unusual] but is prevented from going backwards by refractory period
40
Q

how does a nerve impulse travel across myelinated fibres

A
  • myelin sheath insulates nerve fibre from extracellular fluid
  • where nerve fibre is surrounded by myelin (not node of Ranvier), ions cannot flow between inside and outside of membrane; action potential cannot form.
  • instead, action potential jumps from one node of Ranvier to the next. this ‘jumping’ conduction, ‘saltatory conduction’ allows nerve impulse to travel much faster along myelinated fibres than unmyelinated ones.
  • large myelinated fibre can conduct impulses up to 140m/s, unmyelinated; max 2m/s
41
Q

steps of transmission across a synapse (5 steps)

A
  1. action potential arrives at axon terminal, activating voltage gated Ca channels
  2. higher conc. of Ca ions in extracellular fluid causes ions to flow into the cell at pre-synaptic axon terminal
  3. synaptic vessels fuse with membrane, releasing special chemicals via exocytosis
  4. neurotransmitters diffuse across gap and attach to receptors in membrane of next neuron
  5. ligand gated channels stimulated to open, allowing influx of sodium ions and initiating action potential in post-synaptic membrane
42
Q

which chemicals can have an effect on the transmission of nerve impulses?

A
  • caffeine and benzedrine stimulate transmission
  • anaesthetics and hypnotics depress transmission
  • venom affects neuromuscular junction
  • nerve agents/gases contain organophosphates, which cause the build up of acetylcholine at neuromuscular junction. all muscles in body then try to contract and the loss of muscle control prevents breathing
43
Q

find the connection between receptor and sense organ

A

a receptor is a structure that is able to detect a change in the body’s internal or external environment. sometimes receptor cells of a particular type are grouped together in a sense organ.

(other receptors are simple nerve endings and may be spread through parts of the body or whole body e.g. pain receptors in skin)

respond via an automatic reflex or complex response

44
Q

thermoreceptors

A
  • heat and cold
  • skin receptors inform hypothalamus and cerebrum of change outside body
  • skin has sensitive hot and cold receptors (not both in same place)
  • core temp monitored by receptors in hypothalamus, which detect temp of blood flowing through brain.
  • hypo. regulated body temp
45
Q

osmoreceptors

A
  • osmotic pressure determined by conc. of substances dissolved in water of blood plasma. higher conc = higher osmotic pressure
  • receptors (located in hypothalamus) sensitive to changes in osmotic pressure.
  • can stimulate hypo. so that body’s water content is maintained within very narrow limits
46
Q

chemoreceptors

A
  • stimulated by particular chemicals
  • nose, mouth, internal structures, some blood vessels
  • blood vessel receptors sensitive to pH of blood and conc. of oxygen and carbon dioxide.
  • involved in regulation of heartbeat and breathing
47
Q

touch receptors

A
  • aka mechanoreceptors/pressure receptors
  • mainly in skin; lips fingertips, eyelids, external genital organs
  • nerve endings also associated with base of each hair follicle, sensitive to light touch that bends the hair
  • follicle receptors very sensitive, we become used to them
  • deeper receptors detect pressure and vibrations
48
Q

pain receptors

A
  • aka nociceptors
  • stimulated by large damage to the tissues (poor blood flow to a tissue)
  • receptors for pain concentrated in skin and mucous membranes
  • occur in most organs, not in the brain
  • adapt little or not at all
49
Q

four properties of a reflex

A
  • requires stimulus
  • involuntary
  • rapid response
  • stereotyped response (occurs in same way every time it occurs)
50
Q

explain steps of a reflex arc (5)

A
  1. STIMULUS pain receptors in skin detect the stimulus and produce a nerve impulse
  2. sensory neuron conducts the nerve impulse from the receptor to spinal cord
  3. info processed in CNS. one or more interneurons pass the message to appropriate motor neurons
  4. motor neuron carries nerve impulse to effector
  5. effector, e.g. bicep muscle contracts, moving hand from painful stimulus
51
Q

which root in reflex arc carries the impulse to the spinal cord?

A

dorsal root with ganglion

52
Q

which root in reflex arc carries the impulse away from the spinal cord?

A

ventral root

53
Q

main 5 components to a reflex arc

A
  • receptor reacts to change
  • sensory neuron carries impulses from receptor to spinal cord or brain
  • at least one synapse involves
  • motor neuron carries nerve impulse to effector
  • effector receives nerve impulse, carries out a response (muscle cells or secretory cells)
    people are only consciously aware of a reflex after it is carried out
54
Q

differentiate between innate and acquired reflexes

A

innate determined genetically; suckling, chewing, following movements with eyes
acquired are learnt complex motor patterns; adjustments made to maintain balance on a bike, jamming brakes on a car, catching a ball

55
Q

characteristics of nervous system

A

nature of message: electrical impulses and neurotransmitters
transport of message:along membrane of neurons
cells affected: muscle and gland cells; other neurons
type of response: usually local and specific
time taken to respond: rapid - within milliseconds
duration of response: brief - stops quickly when stimulus stops

56
Q

characteristics of endocrine system

A

nature of message: hormones
transport of message:by the bloodstream
cells affected: all body cells
type of response: may be very general and widespread
time taken to respond: slower - from seconds to days
duration of response: longer lasting - may continue long after stimulus has stopped

12 HUMAN BIO ATAR (13 decks)

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