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SNAB biology hoe > 8A Nervous and Hormonal Communication > Flashcards

8A Nervous and Hormonal Communication Flashcards

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1
Q

why do animals respond to changes in their external and internal env

A
  • ↑ chances of survival
  • to make sure conditions are always optimal for their metabolism
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2
Q

nerve impulse pathway

A

stimulus -> receptor -> sensory neurone -> CNS -> motor neurone -> effector

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3
Q

describe how eyes respond to dim light

(3 marks)

A
  1. dim light stimulus
  2. photoreceptors in eyes detect lack of light
  3. CNS processes this info
  4. radial muscles (effectors) in iris stimulated by motor neurones
  5. radial muscles contract to dilate pupils (make them bigger)

NOTE: reflex response as brain unconsciously processes this info

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4
Q

stimulus

A

change in internal or external env

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5
Q

receptors

A
  • detect stimuli
  • can be cells / proteins on cell surface membranes
  • communicate with effectors via nervous system / hormonal system or both
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6
Q

effectors

A
  • cells that bring about response to stimulus
  • to produce an effect
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7
Q

describe how eyes respond to bright light

(3 marks)

A
  1. bright light stimulus
  2. photoreceptors detect bright light
  3. CNS processes this info
  4. circular muscles (effectors) in iris are stimulated by motor neurones
  5. circular mucles contract to constrict pupils
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8
Q

describe the how motor neurones are adapted to their function

(2 marks)

A
  • one long axon -> carries nerve impulses from cell body to effector cells
  • many short dendrites carry nerve impulses from CNS to cell body
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9
Q

describe how sensory neurones are adapted to their function

A
  • one long dendron -> carries nerve impulses from receptor cells to cell body (located in middle of neurone)
  • one short axon -> carries nerve impulses from cell body to CNS
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10
Q

describe how relay neurones are adapted to their function

A
  • many short dendrites carry nerve impulses from sensory neurones to cell body
  • axon carries nerve impulses from cell body to motor neurones
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11
Q

explain the role of Schwann cells and myelination in neurones

A
  • axon insulated by fatty layer (myelin sheath)
  • myelin sheath made of schwann cells which wrap around axon
  • between schwann cells: uninsulated gaps of bare membrane (nodes of Ranvier)
  • Na⁺ channels concentrated at nodes
  • electrical impulses in myelinated cells don’t travel down whole axon -> jump from one node to another …
  • speeds up impulse transmission
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12
Q

conduction velocity

A

speed that impulse moves along neurone

↑ conduction velocity = impulse travelling quickly

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13
Q

gland

A

group of cells specialised to secrete a useful substance eg. hormone

eg. pancreas secretes insulin

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14
Q

hormones

A
  • chemical messengers
  • proteins / peptides eg. insulin
  • some hormones are steroids eg. progesterone
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15
Q

describe how a gland is stimulated

A
  • stimulated by change in conc of specific substance
  • can also be stimulated by electrical impulses

hormones secreted when gland stimulated

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16
Q

describe how the hormonal system plays a part in the response to low blood glucose conc

(4 marks)

A
  1. low blood glucose conc (stimulus)
  2. receptors on pancreas cells detect stimulus
  3. pancreas secretes hormone glucagon into blood
  4. target cells in liver detect glucagon and convert glycogen->glucose
  5. glucose released into blood -> so glucose conc ↑
17
Q

explain 4 differences in the nervous and hormonal systems

A
  • nervous uses electrical impulses / hormonal uses chemicals
  • nervous: faster response (electrical impulses v fast) / hormonal slower (hormones travel at speed of blood)
  • nervous: localised response (carry impulse to specific cells / hormonal: widespread response (target cells all over body)
  • nervous: short lived response (neurotransmitters removed quickly) / hormonal long lived response (hormones not broken down quickly)
18
Q

explain why myelinated axons conduct impulses faster than unmyelinated axons

A
  • saltatory conduction
  • impulse jumps from 1 node of Ranvier to another
  • depolarisation cannot occur where myelin sheath acts as electrical insulator
  • so impulse does not travel along whole axon length
19
Q

resting potential

A
  • potential diff (voltage) across neurone membrane when not stimulated

~ -70 mV in humans

  • created and maintained by Na/K pumps and K⁺ channels in neurone’s membrane
20
Q

how is resting potential established

A

membrane more permeable to K⁺ than Na⁺

  • Na/K pump actively transports 3Na⁺ out of cell and 2K⁺ into cell
  • establishes electrochemical grad
21
Q

describe why neurone cell membranes are polarised at rest

A
  • in resting state (not stimulated) -> outside the membrane is more +ve compared to inside
  • as more +ve ions outside cell than inside
  • so membrane polarised (diff in charge)
22
Q

describe synapses roles in the nervous system

A

allow info to be dispersed / amplified

  • synaptic divergence -> when 1 neurone connects to many neurones , info can be dispersed to diff parts of body
  • synaptic convergence -> when many neurones connect to 1 neurone, info can be amplified
23
Q

neurotransmitter

A

chemical subs

comes from vesicle that binds to presynaptic neurone

diffuses across synaptic gap

affects post synaptic membrane

24
Q

describe the seq of events known as an action potential

(6 marks)

A
  1. stimulus -> excites neurone cell membrane, causes Na⁺ channels to open
    -> membrane now more permeable to Na so Na⁺ diffuse into neurone down Na⁺ electrochemical grad (makes inside of neurone ↓ -ve)
  2. depolarisation -> if p.d reaches threshold (~ -55 mV) more Na⁺ channels open + more Na⁺ diffuse into neurone
  3. repolarisation -> at p.d of ~ +30 mV, Na⁺ channels close, K⁺ channels open
    -> membrane now more permeable to K so K⁺ diffuse out of neurone down K⁺ conc grad -> this starts to get membrane back to its resting potential
  4. hyperpolarisation -> K⁺ channels slow to close so slight overshoot where too many K⁺ diffuse out of membrane -> p.d becomes more -ve than resting potential (less than -70 mV)
  5. resting potential -> ion channels reset. Na/K pump returns membrane to resting potential + maintains it until membrane’s excited by another stimulus
25
Q

refractory period

A
  • period of recovery where neurone cell cannot get excited again straight after action potential
  • as ion channels are recovering and cant be made to open - Na⁺ channels closed during repolarisation + K⁺ channels closed closed during hyperpolarisation
26
Q

describe how neurotransmitters transmit nerve impulses between neurones

part 1

A

action potential triggers Ca influx

  1. a.p arrives at synaptic knob on presynaptic neurone
  2. a.p stimulates voltage-gated Ca²⁺ channels in presynaptic neurone to open
  3. Ca²⁺ diffuse into synaptic knob
27
Q

describe how neurotransmitters transmit nerve impulses between neurones

part 2

A

Ca influx causes neurotransmitter release

  1. causes synaptic vesicles to move to presynaptic membrane + fuse with it
  2. vesicles release neurotransmitter into synaptic cleft (exocytosis)
28
Q

describe how neurotransmitters transmit nerve impulses between neurones

part 3

A

neurotransmitter triggers action potential in postsynaptic neurone

  1. neurotransmitter diffuses across synaptic cleft + binds to specific receptors on postsynaptic membrane
  2. causes Na⁺ channels in postsynaptic neurone to open
  3. influx in Na⁺ into postsynaptic membrane causes depolarisation -> a.p on postsynaptic membrane made if threshold reached
  4. neurotransmitter removed from synaptic cleft so response doesn’t keep happening
29
Q

explain how synaptic knobs are adapted to their function

A
  • contain lots of mitochondria
  • which make ATP needed for active transport + movement of vesicles

SNAB biology hoe (15 decks)

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