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A2 BIOLOGY OCR > Neuronal communication > Flashcards

Neuronal communication Flashcards

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1
Q

Outline how receptors work

A
  • transducers

- convert energy from one form to another

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2
Q

Outline the types of receptors there are and what kind of stimulus is detected and where

A
  • Photoreceptor = light/in cone cells
  • Chemoreceptor = chemicals/ olfactory receptor
  • Thermoreceptor = heat/end bulbs of krause
  • Mechanoreceptor = pressure/movement/pacinian corpuscle
  • Prophoreceptor = movement/position/muscle spindle
  • Baroreceptor = pressure/stretch receptors in arteries
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3
Q

Whats the pacinian corpuscle

A
  • specific sensory receptors that detect mechanical pressure found deep in the skin
  • abundant in fingers, soles of feet and joints
  • have special Na+ channels called stretch-mediated Na+ channels that when the channel changes shape the permeability to Na+ changes ]
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4
Q

What happens in the pacinian corpuscle

A
  • At resting state, stretch mediated Na+ channels are too narrow to allow Na+ through. The neurone of the pacinian corpuscle has a resting potent
  • pressure is applied to PC changing the shape - membrane bound neurone stretches
  • Membrane stretches, widening Na+ channels. Na+ diffuse into neurone
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5
Q

What are the characteristics of motor, sensory and relay neurones

A 
MOTOR
- Cell body in CNS
- Long axon that carries AP to the effector
SENSORY
- short axon that carries AP into CNS
- long dendron
RELAY 
- Connect sensory and motor neurones
- cell body in CNS 
- many short dendrites and short axon
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6
Q

Whats the perineurium

A
  • protective layer that surrounds bundles of axons of neurones
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7
Q

Whats myelin and its function

A
  • axons of some neurones covered in myelin sheath made of layers of plasma membrane
  • schwann cells produce the membrane layers by growing around the axon many times (each time they wrap around axon they lay down double layer of phospholipid bilayer)
  • acts as an insulating layer and allow neurones to conduct the electrical impulse at a faster speed
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8
Q

What is saltatory conduction

A
  • action of impulses jumping from each node to the next
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9
Q

Why at resting potential is the inside of the neurone negatively charged and what is resting potential’s value (in mv)

A
  • there are large negatively charged proteins inside the neurone
  • distribution of ions (Na+ and K+) across the membrane
  • -60mv - -70mv
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10
Q

How is resting potential maintained?

A
  • sodium potassium pump actively transports 3Na+ out and 2K+ in
  • Na+ can’t diffuse back across creating an electrochemical gradient
  • K+ can diffuse through channels back out neurone, further increasing potential difference
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11
Q

How is generator potential produced

A
  • stimulus detected
  • Na+ channels open
  • Na+ move in my diffusion down a conc gradient and electrochemical gradient
  • influx of Na+ causes potential difference to become less negative = generator potential
  • larger the stimuli the more Na+ channels open
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12
Q

Describe the all or nothing principle

A
  • if the potential difference reaches over -50mv then there will be a large GP, the voltage-gated Na+ channels open and AP will be triggered
  • However if the potential difference is below -50mv the Na+ channels won’t open resulting in AP not happening
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13
Q

Describe the process of polarisation, depolarisation, repolarisation and hyperpolarisation

A
  • membrane starts at resting state of -70mV (POLARISED)
  • Na+ channels open and some Na+ ions diffuse into the cell
  • membrane DEPOLARISES becoming less negative until the threshold value of -50mV
  • Voltage-gated Na+ channels open and Na+ ions flood in making cell more +ve until it reaches +40mV
  • Na+ channels close and K+ channels open, K+ ions diffuse out of the cell bringing potential difference back to negative inside (REPOLARISED)
  • Potential difference overshoots slighting making cell HYPERPOLARISED and original potential difference is restored so cell returns to resting state
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14
Q

How is a local current produced

A
  • when membrane is stimulated, Na+ ions travel through normal voltage gated Na+ channels
  • Na+ ions diffuse sideways
  • area behind is depolarised and even when hyper polarised its unlikely it will reach threshold value
  • area ahead is in resting state so as Na+ ions diffuse it causes a small increase in positive change so the next Na+ channels open
  • process repeats along axon so AP travels to synapse
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15
Q

What is the refractory period

A
  • time delay of a few milliseconds after an AP before another one is possible… has two parts:
    1) ABSOLUTE REFRACTORY PERIOD
    • Na+ channels closed so movement Na+ (-1ms)
      2) RELATIVE REFREACTORY PERIOD:
    • Period of 2-5ms where Na+ channels are starting to recover but resting potential hasn’t been re-established yet
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16
Q

Whats the importance of the relative refractory period

A
  • limits frequency of action potential

- prevents action potential going backwards

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17
Q

How are messages transported through the synapse

A
  • action potential arrives at synaptic knob of presynaptic neurone
  • AP stimulates voltage gated Ca2+ channels to open and Ca2+ diffuses in
  • Influx of Ca2+ causes synaptic vesicles to fuse with presynaptic membrane and release ACh into synaptic cleft by exocytosis
  • ACh diffuses across synaptic cleft and binds to cholinergenic receptors on post-synaptic neurone causing Na+ channels to open and Na+ diffuses in
  • Influx of Na+ causes depolarisation and an action potential is generated if the threshold value reached and ACh broken down by acetylcholinesterase
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18
Q

Describe the difference between endocrine, paracrine and autocrine glands

A

ENDOCRINE: communication between distant cells mediated by hormones e.g. adrenaline
PARACRINE: communication between local cells e.g. neurotransmitters
AUTOCRINE: cell producing signal and receiving are the same e.g. interleukins

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19
Q

Describe what temporal summation is

A
  • when two or more nerve impulses arrive in quick succession from the same presynaptic neurone making AP more likely because more neurotransmitter is released into synaptic cleft
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20
Q

Describe what spatial summation is

A
  • Where two or more presynaptic neurones converge and release their neurotransmitters at the same time onto the same presynaptic neurone
  • allows signals from multiple stimuli to be coordinated into a single response
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21
Q

What is synaptic divergence and synaptic convergence

A

DIVERGENCE: when one neurone connects to many neurones meaning information can be dispersed to diff parts of the body
CONVERGENCE: when many neurones connect to one neurone information can be amplified

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22
Q

Outline the difference between excitatory and inhibitory synapses

A

EXCITATORY: neurotransmitter triggers AP in next neurone e.g. ACh
INHIBITORY: neurotransmitter prevents AP in next neurone causing hyper polarisation by opening K+ channels (e.g. GABA: stretch reflex in antagonistic muscles)

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23
Q

How do synapses make sure impulses are unidirectional?

A
  • neurotransmitters are only released from presynaptic neurones
  • receptors for neurotransmitters are only on postsynaptic neurones
24
Q

Describe how nicotine affects the CNS

A
  • absorbed into lungs and travels through blood to brain where it behaves like ACh
  • it binds to receptors resulting in a stimulating effect causing its highly addictive potential
  • symptoms are relaxation, sharpness and calmness
25
Q

Describe how botox affects the CNS

A
  • inhibits exocytosis of ACh at cholinergic motor and autonomic neurone terminals
  • prevents AP from being transferred to post-synaptic neurone which results in partial to complete muscle paralysis
26
Q

Describe how organophosphates (insecticides) affect the CNS

A
  • Interfere with chemical neurotransmission or ion channels and cause reversible neurotoxin effects
  • Also cause organophosphate poisoning which involves inhibition of AChE leading to ACh build up in the body
27
Q

Describe how myelination affects speed of conduction of impulses

A
  • in myelinated neurone depolarisation happens at nodes of Ranvier and neurones cytoplasm conducts enough electrical charge to depolarise the next node so impulse jumps from node to node (saltatory conduction) = very fast
  • in unmyelinated neurones impulse travels as a wave along whole length of axon which is slow
28
Q

Describe how axon diameter affects speed of conduction of impulses

A
  • AP’s conducted quicker along axons with larger diameters because theres less resistance to the flow of ions than in the cytoplasm of a smaller axon
  • less resistance = depolarisation reaches other parts of neurone cell membrane quicker
29
Q

Describe how temperature affects speed of conduction of impulses

A
  • speed of conduction increases as temp does because ions diffuse faster
  • only speeds up to 40 degrees celsius as after proteins begin to denature
30
Q

Describe the structure of the neurone

A
  • Synaptic cleft: gap which separates the axon of one neurone from the dendrite of the next neurone
  • Presynaptic neurone: neurone along which the impulse has arrived
  • Postsynaptic neurone: neurone that receives the neurotransmitter
  • Synaptic knob: the swollen end of the presynaptic neurone containing many mitochondria and large amounts of ER to enable it to manufacture neurotransmitters
  • Synaptic vesicles: vesicles containing neurotransmitters which fuse with the presynaptic membrane and release their contents into the synaptic cleft
  • Neurotransmitter receptors: receptor molecules which the neurotransmitter binds to in the postsynaptic membrane
31
Q

Describe the two types of neurotransmitter

A
  • Excitatory: these neurotransmitters result in the depolarisation of the postsynaptic neurone e.g. ACh
  • Inhibitory: these neurotransmitters result in the hyperpolarisation of the postsynaptic neurone preventing an AP being triggered e.g. GABA
32
Q

Describe the transmission of impulse across synapses

A
  • AP arrives at the synaptic knob of the presynaptic neurone
  • AP stimulates voltage-gated Ca2+ channels to open and Ca2+ diffuses in
  • Influx of Ca2+ causes synaptic vesicles to fuse with presynaptic membrane and release ACh into synaptic cleft by exocytosis
  • ACh diffuses across synaptic cleft and binds to cholinergic receptors on post-synaptic neurone causing Na+ channels to open and Na+ diffuses in
  • Influx of Na+ causes depolarisation and an AP is generated if the threshold is reached and the ACh is broken down by acetylcholinesterase
33
Q

Whats the difference between the CNS and the PNS

A
  • CNS: Consists of brain and spinal cord

* PNS: consists of all the neurones that connect the CNS to the rest of the body

34
Q

Whats the difference between the somatic and autonomic nervous system

A
  • Somatic nervous system: system under conscious control – used when you voluntarily decide to do something e.g. moving muscles in your arm
  • Autonomic nervous system: system works constantly and under subconscious control and is involuntarily e.g. smooth in the walls of the intestine
35
Q

Describe the roles of the sensory and motor neurone system

A
  • Sensory: detects the stimulus and sends impulses along sensory neurones to CNS
  • Motor: sends impulse from CNS along the motor neurone to the effector
36
Q

What does antagonistic mean

A

• Systems that have opposite effects

37
Q

Describe the effects of the sympathetic system

A
  • If outcome increases activity generally it involves the sympathetic system
  • e.g. increase in heart rate, increased ventilation rate, orgasm, pupil dilation
  • Most active in times of stress
  • Secrete noradrenaline
  • Preganglionic neurones v short
38
Q

Describe the effects of the parasympathetic system

A
  • If outcome decreases activity it is generally parasympathetic
  • e.g. decrease in breathing rate after a period of exercise, sexual arousal, pupil constriction
  • secrete ACh
  • Most active in sleep and relaxation
  • Preganglionic neurones vary in length
39
Q

Describe the gross structure of the brain

A

• Cerebrum: controls voluntary actions e.g. learning, memory, personality and conscious thought
o Split into two hemispheres connected by tracts of neurones called the corpus callosum
• Cerebellum: controls unconscious functions e.g. posture, balance and non-voluntary movement
• Medulla oblongata: used in autonomic control e.g. controls heartrate and breathing rate
• Hypothalamus: regulatory centre for temp and water balance
• Pituitary gland: stores and releases hormones that regulate many body functions

40
Q

Describe the parts of the cerebrum

A
  • Temporal lobe: auditory info e.g. hearing, sound and recognition of speech
  • Occipital lobe: Processing info from eyes e.g. vision, colour, shape and perspective
  • Parietal lobe: Concerned with orientation, movement, sensation, calculation and types of recognition
  • Frontal lobe: Involved with conscious emotion, decision making and reasoning. Includes motor cortex which stores info on how to carry actions
41
Q

Describe the reflex arc

A
  • Receptor: detects stimulus creating an AP in the sensory neurone
  • Sensory neurone: carries impulse to spinal cord
  • Relay neurone: connects the sensory neurone to the motor neurone within the spinal cord or brain
  • Motor neurone: carries impulse to effector to carry out the appropriate response
42
Q

Whats the spinal cord

A

• Column of nervous tissues surrounded by spine for protection, at intervals along th spine neurones emerge in pairs

43
Q

Whats the knee-jerk reflex

A
  • It’s a spinal reflex - doesn’t go up to brain
  • When leg tapped just below kneecap it stretches patella tendon acting as a stimulus
  • Stimulus initiates reflex arc causing extensor muscle on top of thigh to contract and at same time the relay neurone inhibits motor neurone of flexor muscle to relax
  • Absence of this reflex indicates nervous problems and multiple oscillations of the leg may be a sign of a cerebellar disease
  • Reflex used by body to maintain posture and balance
44
Q

Describe the blinking reflex

A
  • Reflexes increase survival chances
  • Involuntary response – decision making parts of brain not involved so brain is able to deal with more complex responses
  • Doesn’t have to be learnt – present at birth therefore provide immediate protection
  • Fast – reflex arc short
45
Q

What are slow twitch muscles

A

o Fibres contract slowly
o Less powerful contractions but over a longer period
o Used for endurance – don’t tire easily
o Rich in myoglobin (stores oxygen) – making fibres appear red
o Rich supply of blood vessels and mitochondria
o E.g. back and calf muscles

46
Q

What are fast twitch muscles

A

o Fibres contract quickly
o Powerful but short contractions
o Used for short bursts of speed and power – tire easily
o Gain energy from anaerobic respiration
o Pale coloured due to low levels of myoglobin and blood vessels
o Contain more, thicker myosin filaments
o Stores creatine phosphate – molecule that rapidly generates ATP from ADP in anaerobic conditions
o E.g. biceps and eyes

47
Q

Describe the action at the neuromuscular joint

A
  • Synapse between a motor neurone and muscle cell
  • Muscle contraction triggered when an action potential arrives at a neuromuscular junction
  • Ca2+ channels are stimulated and Ca2+ ions diffuse into the synaptic knob causing synaptic vesicles to fuse with the presynaptic membrane
  • ACh is released into the synaptic cleft by exocytosis and diffuses across the synapse
  • ACh binds to receptors on sarcolemma (postsynaptic membrane) opening Na+ channels resulting in depolarisation
  • ACh broken down by AChE into choline and ethanoic acid preventing the muscle from being overstimulated
  • Choline and ethanoic acid diffuse back into neurone and recombine with ATP to form ACh
  • Depolarisation of sarcolemma travels deep into a muscle spreading through T-tubules which are in contact with the sarcoplasmic reticulum
  • The SR contains stored Ca2+ which it actively absorbs from sarcoplasm
  • When an AP reaches the S.R. it stimulates the Ca2+ channels to open and Ca2+ diffuse down conc gradient flooding sarcoplasm
  • Ca2+ bind to troponin causing it to change shape pulling on the tropomyosin moving it away from the actin-myosin binding sites on the actin filament
  • Binding sites are exposed and the myosin head binds to the actin filament forming n actin-myosin cross-bridge
  • Once attached to the actin filament, myosin head flexes pulling actin filament along and a molecule of ADP bound to the myosin head is released
  • ATP molecule can now bind to the myosin head causing the head to detach from the actin filament and Ca2+ also activate ATPase stimulating the hydrolysis of ATP to ADP releasing energy that the myosin head uses to return to its original position
  • The myosin head can now attach itself to another atcin-myosin bindsite along the actin filament
  • This cycle is then repeated
48
Q

Describe how the structure changes as the sliding filament model is in action

A

• During contraction myosin filaments pull the actin filaments toward the centre of the sarcomere meaning:
o Light band becomes narrower
o Z lines move closer together – shortening sarcomere
o H-zone becomes narrower
o Dark band remains same width as myosin filaments themselves haven’t shortened but overlap actin filaments further

49
Q

Describe the structure of myosin

A

o Globular heads hinged allowing them to move back and forward
o On head there is a binding site for actin and ATP

50
Q

Describe the structure of actin

A

o Have binding sites for myosin heads – often blocked by protein called tropomyosin held in place by protein troponin
o When a muscle is in resting state the actin-myosin sites are blocked by tropomyosin

51
Q

How is the supply of ATP maintained in muscle contraction

A

• Creatine phosphate: stored in the muscle and acts as a reserve supply of phosphate to phosphorylate ADP into ATP
o This system generates ATP rapidly but store of phosphate is used up quickly
o Used for short bursts of vigorous exercise e.g. tennis serve
• Anaerobic respiration: oxygen used up more quickly than the blood in very active muscle so ATP has to be generated anaerobically
o But can cause lactic acid build-up leading to muscle fatigue
o Used for short periods of high intensity exercise e.g. sprinting

52
Q

How do reflexes increase survival rates

A
  • Reflexes increase survival chances
  • Involuntary response – decision making parts of brain not involved so brain is able to deal with more complex responses
  • Doesn’t have to be learnt – present at birth therefore provide immediate protection
  • Fast – reflex arc short
53
Q

Describe the structure and function of cardiac muscle

A

STRUCTURE:
- specialised striated, cells branch and interconnect resulting in simultaneous contraction, muscle shows striations much finer than those in skeletal muscle, fibres branched and uninucleated
FUNCTION:
- involuntary, intermediate contractions

54
Q

Describe the structure and function of skeletal muscle

A

STRUCTURE:
- striated, regularly arranged so muscle contracts in one direction, muscle shows cross striations and fibres are tubular and multinucleated
FUNCTION:
- under conscious control, rapid short contractions

55
Q

Describe the structure and function of smooth muscle

A

STRUCTURE:
- non-striated, no regular arrangement - diff cells can contract in different directions, muscles show no cross striations and fibres and spindle shaped and uninucleated
FUNCTION:
- involuntary, slow long contractions

A2 BIOLOGY OCR (11 decks)

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