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A-level Biology > 5.13 - Neuronal communication > Flashcards

5.13 - Neuronal communication Flashcards

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1
Q

Homeostasis

A

The maintenance of a constant internal environment

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2
Q

Cell signalling

A

Cells can release chemicals that have an effect on other cells. They can:
- transfer signals locally or across large distances
- transfer signals between neurones at synapses using neurotransmitters
- transfer signals using hormones

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3
Q

Sensory neurones

A
  • transmit impulses from a sensory receptor cell to a relay neurone, motor neurone or the brain
  • the cell body is in the middle of the neurone, with the dendron and axon either side
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4
Q

Structure of a neurone

A
  • a cell body contains a nucleus surrounded by cytoplasm, with ER and mitochondria for neurotransmitter production
  • dendrons transmit electrical impulses towards the cell body, they divide into smaller branches called dendrites
  • axons transmit impulses away from the cell body
  • myelinated
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5
Q

Relay neurone

A
  • transmit impulses between neurones
  • contain many axons and dendrons (are spider-like with a cell body in the middle)
  • non-myelinated
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6
Q

Motor neurone

A
  • transmit impulses from a relay neurone or sensory neurone to an effector, such as a muscle or gland
  • the cell body is at the end of the neurone, surrounded by dendrites, it has one long axon
  • myelinated
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7
Q

Myelinated neurones/ saltatory conduction

A
  • Schwann cells wrap around the axon many times
  • creating many layers of phospholipid membrane around the neurone
  • acting as an insulator
  • white appearance
  • can conduct the impulse at a much faster speed
  • as the impulse jumps between the small gaps between adjacent Schwann cells known as nodes of Ranvier
  • because the sodium ions can only pass through at the nodes of Ranvier
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8
Q

Non-myelinated neurone

A
  • many neurones sit in one Schwann cell
  • grey appearance
  • the impulse transmits continuously along the nerve fibre, so is much slower
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9
Q

Mechanoreceptor

A
  • stimulated by pressure and movement
  • for example the Pacinian Corpuscle in the skin organ
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10
Q

creating a generator potential in the Pacinian corpuscle

A
  • pressure receptor found in the skin
  • converts mechanical pressure into a nerve impulse
    Resting potential (-70mV):
  • transporting 3Na+ out of neurone for every 2K+ out of neurone
  • by active transport through specific carrier proteins
  • stretch-mediated sodium ion channels are closed so an electrochemical gradient is built up
    Stimulus:
  • pressure causes Pacinian corpuscle to change shape, changing shape of the neurone membrane
  • the membrane stretched causing the stretch-mediated sodium ion channels to open
  • sodium ions flood into the neurone causing it to depolarise, creating a generator potential
  • the generator potential causes an action potential/ electrical impulse in the neurone
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11
Q

The creation of an action potential

A
  • at resting potential, voltage gated ion channels are closed, Na+ stays out of the cell, K+ stays in the cell. There is a difference between charge inside and outside the cell (-70mV)
  • stimulus; some Na+ moves into the neurone. If the threshold is reached, the potential difference across the membrane is changes
  • this causes the Na+ voltage gate to open, letting Na+ flood into the neurone (depolarisation +30mV)
  • the potential difference changes again, so the Na+ voltage gates close and the K+ voltage gates open
  • K+ floods out of the cell (repolarisation)
  • this reduces the charge, the inside of the axon becomes more negative than its normal resting state (hyperpolarisation)
  • this prevents another stimulus creating an action potential (refractory period)
  • the K+ channels close and the sodium-potassium pump ensures it returns to its resting potential (repolarised)
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12
Q

What is the all or nothing principle in generating an action potential

A
  • the action potential is the same value whether there is a strong stimulus or a weak stimulus
  • strength of stimulus affects number of action potentials
  • threshold potential must be reached by the stimulus to trigger an action potential
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13
Q

Synapse structure

A
  • Presynaptic neurone where the impulse arrives
  • synaptic knob is the swollen and of the presynaptic neurone that contains lots of mitochondria and ER to manufacture neurotransmitters
  • synaptic vesicles contain neurotransmitters and are released from the presynaptic neurone through exocytosis
  • synaptic cleft is the gap that separates the presynaptic and postsynaptic neurone
  • postsynaptic neurone recieves the neurotransmitter
  • neurotransmittor receptors are on the postsynaptic membrane, where neurotransmitters fuse to
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14
Q

What are the two types of neurotransmitter

A
  • Excitatory neurotransmitters result in the depolarisation of the postsynaptic neurone, triggering an action potential
  • Inhibitory neurotransmitters result in the hyperpolarisation of the postsynaptic membrane, preventing an action potential being triggered
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15
Q

The transmission of impulses across synapses

A
  • the action potential reaches the end of the presynaptic neurone
  • depolarisation of the presynaptic membrane causes calcium ion channels to open
  • calcium ions diffuse into the presynaptic knob
  • this causes synaptic vesicles containing neurotransmitters to fuse with the presynaptic membrane and release neurotransmitters into the synaptic cleft through exocytosis
  • neurotransmitters diffuse across synaptic cleft and bind to specific receptors on the postsynaptic membrane
  • this causes sodium ion channels to open, letting sodium ions diffuse inot the postsynaptic neurone, triggering an action potential
  • the action potential is propagated across the postsynaptic neurone
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16
Q

Transmission across cholinergic synapses

A
  • uses neurotransmitter acetylcholine
  • when ACh is released from from the presynaptic knob, is diffuses across the synaptic cleft to the postsynaptic membrane to fuse with receptors
  • the sodium ion channels are opened and the postsynaptic neurone becomes depolarised
  • acetylcholinesterase (AChE) breaks down the ACh in the cleft for absorption back into the presynaptic neurone to be reformed back into ACh (via protein channels or endocytosis)
  • this means another action potential can be carried out as the postsynaptic neurone can become repolarised
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17
Q

Convergence (neurones)

A
  • multiple neurones connect to one neurone
  • results in stimuli from different receptors interacting to produce a single action potential (spatial summation) - (balance between inhibitory and excitatory impulses)
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18
Q

Divergence (neurones)

A
  • one neurone connects to multiple neurones
  • results in a single stimulus creating a number of simultaneous responses e.g. muscle contraction
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19
Q

Why are synapses important in transporting an impulse

A

They ensure impulses are unidirectional as the neurotransmitter receptors are only present on the postsynaptic membrane, so impulses can only travel in one direction

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20
Q

Spatial summation

A

occurs when a number of presynaptic neurones connect to one postsynaptic neurone. The neurotransmitters released from all of the presynaptic neurones builds up to a high enough level to trigger an action potential in the postsynaptic neurone

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21
Q

Temporal summation

A

Occurs when a single presynaptic neurone releases neurotransmitters as a result of an action potential several times over a short period, building up in the synapse until there is sufficient quantity to trigger an action potential in the postsynaptic neurone

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22
Q

Drugs that alter synaptic transmission

A

Stop action potentials from being generated:
- Botox prevents release of ACh from presynaptic membrane
- nicotine is similar shape to ACh to triggers action potentials but not broken down as quickly in cleft
- organophosphate insecticides inhibit AChE

23
Q

central nervous system (CNS)

A

brain and spinal chord

24
Q

peripheral nervous system

A

all the neurones that connect the CNS to the rest of the body (sensory and motor neurones)

25
Q

Somatic nervous system

A
  • under conscious control
  • used when you voluntarily decide to do something e.g. move muscles in your arm
  • input from sense organs
  • output to skeletal muscles
26
Q

Autonomic nervous system

A
  • works constantly
  • under subconscious control
  • used to do automatic things you don’t think about like food digestion
  • input from internal receptors
  • output to glands and smooth muscle
  • 2 types, sympathetic and parasympathetic
27
Q

Sympathetic motor system

A
  • fight or flight responses
  • neurotransmitter is noradrenaline
  • ACh is an excitor
28
Q

Parasympathetic motor system

A
  • rest and digest (relaxing responses)
  • neurones from brain via vagus nerve and base of spinal chord
  • ACh is an inhibitor
29
Q

Function of the cerebrum

A
  • receives sensory information
  • interprets sensory information with respect to information stored from previous experiences
  • send impulses along motor neurones to effectors to produce an appropriate response
  • responsible for coordinating all voluntary responses and some involuntary ones
  • carries out a variety of functions associated with conscious activities including vision, hearing, speech, thinking, memory
30
Q

Structure of the cerebrum

A
  • largest part of the brain (in humans)
  • Consists of five lobes
  • Divided into two halves, the cerebral hemispheres
  • joined together by a band of nerve fibres, known as the corpus callosum
  • right hemisphere controls the left side of the body and the left one controls the right side
  • thin outer layer, the cerebral cortex or ‘grey matter’
  • consists of the cell bodies of neurones
  • highly folded, which increases its surface area and allows it to contain a greater number of neurones
  • With more neurones in the brain, more connections between neurones can be made
  • the more connections between neurones in the brain, the greater the ability of the brain to carry out more complex behaviours
  • Beneath the cerebral cortex or grey matter layer is the ‘white matter’
  • The white matter consists of the myelinated axons of neurones
31
Q

Function of the cerebellum

A
  • the control of muscular movement, body posture and balance
  • does not initiate movement but coordinates it
  • if damaged, a person suffers from jerky, uncoordinated movement
  • receives information from the organs of balance from the ears and information about the tone of muscles and tendons
  • relays information to the areas of the cerebral cortex that are involved in motor control
32
Q

function of the medulla oblongata

A
  • contains regulatory centres of the autonomic nervous system
  • control reflex activities such as breathing and heart rate
  • controls activities such as swallowing, coughing and peristalsis (muscle contraction involved in digestion)
33
Q

Function of the hypothalamus

A
  • main controlling region of the autonomic nervous system
  • has two centres for the sympathetic and parasympathetic nervous system
  • controls complex patterns of behaviour such as sleeping, feeding and aggression
  • monitors the composition of blood plasma (water and glucose concentration, has a rich blood supply)
  • producing hormones as it is an endocrine gland (e.g.ADH)
34
Q

The pituitary gland

A
  • found at the base of the hypothalamus
  • controls most of the glands in the body
    Anterior (front) pituitary:
  • produces six hormones
  • produces follicle stimulating hormones (FSH) involved in reproduction and growth hormones
    Posterior (back) pituitary:
  • stores and releases hormones produced in hypothalamus such as ADH (urine production)
35
Q

steps in the reflex arc

A
  • receptor detects stimulus and creates an action potential 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 the effector to carry out the appropriate response
36
Q

knee-jerk reflex

A

A spinal reflex, so the neural reflex only goes up to the spinal cord, not the brain. Is used by the body to help maintain posture and balance
- a leg is tapped just below the kneecap
- the patellar tendon is stretched and acts as a stimulus
- the stimulus initiates a reflex arc that causes the extensor muscle on the top of the thigh to contract
- a relay neurone inhibits the motor neurone of the flexor muscle at the same time, causing it to relax
- causes the leg to kick
-

37
Q

why does the blinking reflex happen

A

Involuntary blinking of the eyelids when the cornea is stimulated. Prevents damage to the cornea from bodies such as dust or flying insects entering the eye
- also occurs when loud sounds are heard or because of a very bright light

38
Q

How does the blinking reflex occur as a result of a foreign body entering the eye

A
  • cornea of the eye is irritated by a foreign body
  • stimulus triggers an impulse along a sensory neurone
  • the impulse travels through a relay neurone in the lower brain stem
  • impulses are sent along branches of the motor neurone to initiate a motor response to close the eyelids
  • The effectors for the blinking reflex include the superior levator palpebrae muscle, which lowers the upper eyelid, and the orbicularis oculi muscle, which pulls the eyelids inwards and helps to close them
39
Q

How do reflexes increase the chance of survival

A
  • being involuntary responses, the decision making regions of the brain are not involved, therefore the brain is able to deal with more complex responses at the same time. Prevents the brain being overloaded with situations in which the response is always the same
  • not having to be learnt, present at birth so therefore provide immediate protection
  • extremely fast as the reflex arc is very short (normally only involves one or two synapses)
  • many reflexes are everyday actions such as digestion and keeping us upright
40
Q

How to measure reaction time

A
  • measuring the time to catch a falling object
  • use a ruler with a suitable scale
  • one person drops, with the other person’s hand at the zero line of the ruler
  • the distance on the ruler corresponds to the reaction time
  • can be done with caffeine and a placebo to investigate how the concentration of caffeine affects a persons reaction time
41
Q

skeletal muscles

A

Cells responsible for movement, make up the bulk of the body.
- striated
- multinucleated
- tubular
- conscious/voluntary movements
- regularly arranged so muscle contracts in one direction
- rapid contraction speed
- short contraction length

42
Q

cardiac muscles

A

Cells found only in the heart, Myogenic, so contract without the need for a nervous stimulus, causing the heart to beat in a regular rhythm
- specialised striated (fainter than skeletal)
- mononucleated
- branching
- many mitochondrion
- intercalated discs
- involuntary control
- intermediate contraction speed
- intermediate contraction length

43
Q

smooth (involuntary) muscle

A

Found in the walls of hollow organs such as the stomach and bladder, in blood vessels and in the digestive tract
- non-striated
- spindle shaped and wavy
- mononucleated
- involuntary control
- no regular arrangement
- slow contraction speed
- can remain contracted for a relatively long time

44
Q

structure of skeletal muscle

A
  • made of bundles of muscle fibres enclosed within a plasma membrane called the sarcolemma
  • muscle fibres are made up of bundles of fused elongated muscle cells with multiple nuclei and a shared cytoplasm called sarcoplasm
  • muscle fibres have a lot of mitochondria and a modified version of the endoplasmic reticulum (sarcoplasmic reticulum) that extends throughout the muscle fibre
  • the sarcoplasmic reticulum contains calcium ions required for muscle contraction
  • each muscle fibre contains many myofibrils lined up in parallel to provide maximum force when they all contract together
45
Q

myofibrils

A
  • made up of two different types of protein filament, actin and myosin
  • have alternating light and dark bands resulting in a striped appearance
  • the light bands appear light as they are the region where actin and myosin do not overlap. Also known as I bands
  • the dark bands appear dark because of thick myosin filaments, the edges overlap with actin. Also known as A bands
  • Z line, found at centre of each light band.
  • Sarcomere, the distance between each Z band, shortens when the muscle contracts
  • H zone, where only myosin fibres are fond at the centre of each dark band. The H zone decreases when the muscle contracts
46
Q

actin

A

ia thin globular protein surrounded by tropomyosin and troponin. It consists of two strands twisted around each other

47
Q

myosin

A

a thick fibrous protein of long rod-shaped fibres with bulbous projections called myosin heads

48
Q

sliding filament model

A
  • during contraction, myosin filaments pull actin filaments inwards towards the centre of the sarcomere
  • the light band becomes narrower
  • the Z lines move closer together, shortening the sarcomere
  • the H-zone becomes narrower
  • the dark band remains the same width as the actin filaments are overlapping the myosin
49
Q
  1. How is muscle contraction triggered (neuromuscular junction)
A
  • when an action potential reaches the neuromuscular junction, it stimulates calcium ion channels to open
  • calcium ions diffuse from the synapse into the synaptic knob, where they cause synaptic vesicles containing acetylcholine to fuse with the presynaptic membrane
  • acetylcholine is released into the synaptic cleft by exocytosis and binds to receptor proteins on the sarcolemma (surface membrane of the muscle fibre cell)
  • This stimulates ion channels in the sarcolemma to open, allowing sodium ions to diffuse in
  • This depolarises the sarcolemma, generating an action potential
  • acetylcholine broken down by acetylcholinesterase into choline and ethanoic acid
50
Q

motor unit

A

all the muscle fibres supplied by one singular motor neurone

51
Q

neuromuscular junction

A
  • where a motor neurone and a skeletal muscle fibre meet
  • there are many neuromuscular junctions along the length of a muscle to ensure all the muscle fibres contract simultaneously
52
Q
  1. How is muscle contraction triggered (sarcoplasm)
A
  • depolarisation of sarcolemma travels deep into muscle fibre by spreading through the T-tubules
  • the action potential reaches the sarcoplasmic reticulum, stimulating calcium ion channels to open
  • the calcium ions diffuse down the concentration gradient flooding the sarcoplasm with calcium ions
  • calcium ions bind to troponin and causes it to change shape
  • causes the tropomyosin molecule to pull away from the binding sites on the actin molecule
  • the myosin head can now attach to the binding site on the actin filament
  • the head of myosin changes angle, moving the actin filament along as it does so
  • an ADP molecule bound to the myosin head is released
  • ATP molecule fixes to myosin head, causing it to detach from the actin filament
  • hydrolysis of ATP to ADP by myosin (it is an ATPase) provides the energy for the myosin head to resume its normal position
  • Head of myosin reattaches to a binding site further along the actin filament
  • the cycle is repeated, shortening the sarcomere and causing the muscle to contract
53
Q

creatine phosphate

A
  • another way the body can generate ATP
  • stored in muscle
  • acts as a reserve supply of phosphate, which is available immediately ton combine with ADP, reforming ATP
  • the store of phosphate is used up quickly, so it is only used for short bursts of vigorous exercise
  • when the muscle is relaxed, the creatine phosphate store is replenished using phosphate from ATP

A-level Biology (24 decks)

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