CHAPTER 13 - NEURONAL COMMUNICATION Flashcards
Coordination, Neurones, Sensory receptors, Nervous Transmission, Synapses, Organisation. of Nervous system, Structure and function of the brain, reflexes, Voluntary and involuntary muscles and Sliding Filament Model
1
Q
What are some internal environments that needs to be maintained
A
Blood glucose concentration
internal temperature
Water Potential
Cell pH
2
Q
Name Some external environments
A
Humidity
External temperature
Light intensity
New or Sudden sound
3
Q
How do animals and plants respond to changes?
A
Electrical responses - neurones
Chemical responses - Hormones
4
Q
What is Homeostasis?
A
Functions of body coordinating to maintain a relatively constant internal environment
5
Q
What organs work together to maintain a constant blood glucose concentration
A
Exocrine pancreas, duodenum, ileum, liver and endocrine pancreas
6
Q
What is cell signalling
A
Coordinating responses by releasing chemicals to cause a change or effect on another cell
7
Q
How can cell signalling be used locally and over long distances
A
Locally - neurotransmitters at a synapse
Long distances - Hormones eg. ADH from Pituitary gland to kidneys to maintain water balance
8
Q
State one internal factor which causes a response in A plant and an animal
A
A plant - Water potential in cells
Animal - Blood pH
9
Q
Describe how cells are able to communicate with one another
A
Cell releases a chemical
which has an effect on a target cell
10
Q
Using examples, explain how and why coordination is required in a multicellular organism
A
Organism needs to respond to internal/external changes for survival
occurs by electrical impulses/nervous system in animals
chemicals/hormones/hormonal system in plants/animals
/ named example of hormone or chemical
different cells rely on others for materials/removal of waste
named example e.g., glucose/oxygen
different organs work together to ensure homeostasis
named example e.g., brain and skin in temperature control
cells communicate through cell signalling
named example of where this occurs
11
Q
What do neurones do?
A
Transmit electrical impulses rapidly around the body so that the organism can respond to changes in internal and external environment
12
Q
What is a Neurone comprised of?
A
Cell body - contains nucleus, with lots of endoplasmic reticulum and mitochondria to produce neurotransmitters
Dendrons - Short extensions from the cell body, divides into dendrites, takes impulse towards cell body
Axons - Elongated nerve fibres that take impulse away from cell body
13
Q
What type of Neurones are there
A
Sensory
Relay
Motor
14
Q
What do sensory neurones do?
A
Transmit impulses from sensory receptor cell to a relay neurone, motor neurone or the brain, containing 1 dendron and 1 axon
15
Q
What do relay neurones do?
A
Transmit impulses between neurones eg from sensory neurones to motor neurones
Containing many short axons and dendrons
16
Q
What do motor neurones do?
A
Transmit impulses from a relay neurone or sensory neurones to an effector, such as a muscle or gland - containing one long axon and many short dendrites
17
Q
What is the electrical impulse pathway?
A
Receptor - Sensory Neurone - Relay Neurone - Motor Neurone - Effector Cell
RSRME
18
Q
What are myelin sheaths made out of?
A
Schwann Cells
19
Q
What do myelin sheaths do?
A
Provides electrical insulation and allows for Neurones to conduct the electrical impulse at faster speeds
20
Q
What speeds can myelinated and unmyelinated neurones transmit impulses at?
A
100 metres per second myelinated
1 metre per second unmyelinated
21
Q
What are Nodes of Ranvier
A
Small gaps between Schwann cells so the electrical impulse jumps from one node to another as it travels across the neurone
22
Q
Why is jumping across nodes of ranvier fasrer than a non-jumping impulse
A
Continuous transmission along the nerve fibre is much slower
23
Q
State the difference between the function of a motor neurone and a sensory neurone
A
Sensory neurones transmit impulses to the CNS from receptor,
motor neurones transmit impulses away from the CNS / to an effector
24
Q
Describe the difference in structure between a myelinated and non-myelinated neurone and how this affects the speed a nerve impulse is transmitted
A
Axon of a myelinated neurone is covered in myelin
myelin is an electrical
insulator
the sheath is formed by Schwann cells growing around the axon several times
there
are gaps in the myelin sheath known as nodes of Ranvier
electrical impulse moves in a series of
‘jumps’ from one node to the next/saltatory conduction
impulse transmitted much faster than
along an unmyelinated axon
25
What is MS (multiple sclerosis)
MS is an autoimmune disease which affects nerves in the brain and spinal cord, causing a wide range of symptoms, including problems with muscle movement, balance and vision`
26
Why is MS an autoimmune disease
Immune system attacks healthy body tissue, leading to a thinning or complete loss of myelin sheath - eventually leading to a breakdown of axons
27
State what is meant by an autoimmune disease
A disease causing the body’s immune system to attack its own cells
28
Describe the role of myelin in the body
Speeds up transmission of nerve impulses
29
One of the symptoms of MS is the loss of vision normally in only one eye. Suggest why a damaged myelin sheath could prevent a person from being able to see
Light energy detected by sensory receptor/rod/cone cell in eye
impulse does not reach CNS/brain or impulse received too slowly
due to sensory neurone axon being broken down
30
What do sensory receptors do?
Convert stimulus they detect into a nerve impulse
31
What are the two main features of sensory receptors
Specific to a single type of stimulus
Acts as transducer - convert a stimulus into a nerve impulse
32
What are the 4 main types of sensory receptor present in an animal?
Mechanoreceptor
Chemoreceptor
Thermoreceptor
Photoreceptor
33
What is the stimulus, example of receptor and example of sense organ for a mechanoreceptor
S: Pressure and movement
R: Pacinian corpuscle (detects pressure)
O: Skin
34
What is the stimulus, example of receptor and example of sense organ for a Chemoreceptor
S: Chemicals
R: Olfactory receptor (detects smells)
O: Nose
35
What is the stimulus, example of receptor and example of sense organ for a Thermoreceptor
S: Heat
R: End-bulbs of Krause
O: Tongue
36
What is the stimulus, example of receptor and example of sense organ for a Photoreceptor
S: Light
R: Cone cells (detects different light wavelengths)
O: Eye
37
What are Pacinian corpuscles?
Specific sensory receptors that detect mechanical pressure, located deep within skin
38
What type of sodium ion channel do pacinian corpuscles have?
Stretch-mediated sodium channels
39
How do pacinian corpuscles convert mechanical pressure into a nervous impulse?
In normal state, stretch-mediated sodium ion channels are too narrow to allow sodium ions through them, at resting potential
When pressure is applied, corpuscle changes shape, causing membrane to stretch
Causes Na+ channels to widen - Na+ can now diffuse into neurone
Influx of sodium ions causes membrane depolarisation - creating generator potential
Generator Potential creates action potential (nerve impulse) that passes along the sensory neurone (transmitted all the way through to CNS)
40
Describe the role of a sensory receptor in the body
Detect stimuli
convert energy into a nervous impulse
41
State the transformation that takes place in a cone cell
Light energy is converted into a nervous impulse/action potential
42
Explain how your body detects that your finger has touched a pin
When you touch the pin it exerts mechanical pressure on your skin
Pacinian corpuscle found within skin detects pressure
pressure changes shape of Pacinian corpuscle
stretch-mediated sodium channel in neuronal membrane stretches
channel widens
sodium ions diffuse into membrane
membrane is depolarised/generator potential created
generator potential creates an action potential
action potential transmitted along neurones to CNS/brain
43
What is resting potential
When neurone isn't transmitting an impulse, the difference in charge between inside and outside of axon is the resting potential
Outside of membrane is more positively charged than inside of axon
Membrane is polarised as there is a potential difference across it = -70mV
44
What events result in the creation of a resting potential
Na+ are actively transported out of the axon whereas K+ are actively transported into the axon by Sodium-potassium pump (3 Na+ out, 2 K+ in)
Results in more Na+ outside the membrane than inside axon cytoplasm, but more K+ inside than outside - hence more sodium ions can diffuse back into the axon down its electrochemical gradient whereas potassium ions diffuse out
Most of the gated Na+ channels are closed - prevents movement of sodium ions but K+ channels are open, so K+ can diffuse out - more positive charged ions outside the axon than in, creating the -70mV resting potential
45
What happens to the membrane when a stimulus is detected
Potential difference across the membrane rapidly changes and becomes +40MV - depolarisation
46
What happens when the impulse passes?
Repolarisation occurs - postive back to negative
47
How do action potentials occur
When protein channels in axon membrane change shape as a result of the change of voltage across its membrane, results in opening or closing (voltage-gated ion channels)
48
What events take place during an action potential
Neurone at resting potential - no impulse transmitted, K+ channels open, Na+ closed
Energy of the stimulus causes Na+ volatge-gated ion channels to open - increase permeability to Na+ - more enter - less negative
This charge causes more Na+ to diffuse into axon - positive feedback
Potential difference reaches +40mV - Voltage gated Na+ channels close and K+ open
K+ ions diffuse out of axon, reducing charge, axon more negative than the outside
Loss of K+ results in becoming more negative than resting state - Hyperpolarisation - leading to closing of K+ channels, and only Sodium-potassium pump causes removal of sodium ions - leading to return to resting potential - Repolarised
(Page 350 for graph)
49
Describe the series of events in the propogation of action potentials
At resting potential, the [Na+] outside the axon are higher than inside, where as [K+] is higher inside than outside. The overall [+ve] is greater outside than inside (polarised membrane)
Stimulus causes influx of Na+ and depolarisation of membrane - action potential created
Localised electrical circuits established by the influx of Na+ in region causes depolarisation. behind this region, Na+ channels close and K+ channels open
Action potential is propagated along the axon, inward influx of K+ causes repolarisation behind section
Following repolarisation of axon membrane ,the axon membrane returns to its restin gpotential in readiness for new stimulus
(pg 351 for diagram)
50
What is the refractory period?
The period of time where the axon cannot be excited again, Na+ channels remain closed preventing movement of Na+ into axon
51
Why is a refractory period important?
Prevents propagation of an action potential backwards as well as forwards, makes sure unidirectional and that action potentials dont overlap
52
Why can depolarisation only occur at nodes of ranvier
No myelin present so Na+ channels are in membrane `
53
What is saltatory conduction?
Action potential jumping from one node to another due to localised circuits
54
Why is saltatory conduction faster than a wave of depolarisation
Every time channels open, it takes for ions to move,
saltatory conduction reduces the amount of times the channels open
55
Why is saltatory conduction more efficient than wave of depolarisation?
Less ATP needed during repolarisation as less of the axon is depolarised
56
What 3 factors affect the speed at which an action potential travels
Myelination
Axon diameter - the bigger the diameter, the faster the impulse - less resistance to the flow of ions in a cytoplasm
Temperature - Higher temp, quicker impulse, Ions have higher KE, diffuse quicker
57
What is the all or nothing principle?
If the threshold is reached, an action potential will always be created,
if the threshold is not reached, no action potential will be triggered
58
What affect does the size of a sufficient action potential have upon stimuli
Greater action potential, increased number of stimulus in a given time
59
State how the body detects the difference between a small and a large stimulus
The larger the stimulus the more frequent the nerve impulses/action potentials
60
State the difference between depolarisation, repolarisation and hyperpolarisation
Depolarisation – voltage/potential difference becomes more positive;
repolarisation – voltage/potential difference becomes more negative
hyperpolarisation – when potential difference is lower than resting potential
61
Describe what would happen if the refractory period didnt exist?
The axon could be immediately depolarised after an action potential
therefore the action
potential could travel backwards / in both directions / not reach target cell
62
Describe how the movement of ions establishes the resting potential in an axon
Sodium potassium pump actively transports sodium and potassium ions
three sodium ions moved out
two potassium ions moved in
potassium ions can diffuse out through
open potassium ion channels / sodium ions cannot diffuse in as sodium ion channels closed
more positive ions outside than inside the axon / outside of the cell is more positively charged
cell/axon membrane is polarised / there is a difference in voltage across it
63
Explain how temperature receptors in the hand generate an action potential in the sensory neurone to tell the body that you are touching a hot object
Heat energy acts a stimulus
stimulus causes (voltage–gated) sodium ion channels
to open
sodium ions diffuse into axon
down electrochemical gradient
inside of axon
becomes less negative/more positive/depolarises
an action potential is triggered
along a sensory neurone to the CNS/Brain
64
What is a synapse?
The junction between two neurones (or a neurone and an effector)
65
How are impulses transmitted across a synapse
Neurotransmitters (chemical)
66
What are the 6 components of the synapse structure
Synaptic cleft
Presynaptic neurone
Postsynaptic neurone
Synaptic knob
Synaptic vesicle
Neurotransmitter receptors
67
What is the synaptic cleft?
The gap which separates the axon of one neurone from the dendrite of the next - 20-30nm across
68
What is a presynaptic neurone
Neurone along which the impulse has arrived
69
What is the postsynaptic neurone
Neurone that receives the neurotransmitter
70
What is the synaptic knob
The swollen end of the synaptic neurone, containing many mitochondria and large amounts of endoplasmic reticulum to enable it to manufacture neurotransmitters
71
What is the synaptic vesicle
Vesicles containing neurotransmitters, which fuse with the presynaptic membrane and release their contents into the synaptic cleft
72
What are neurotransmitter receptors
Receptor molecules which the neurotransmitter binds to in the postsynaptic membrane
73
What are the types of neurotransmitters
Excitatory and inhibitory
74
What do excitatory neurotransmitters do
Result in the depolarisation of the postsynaptic neurone. If the threshold is reached in the postsynaptic membrane an action potential is triggered - eg. acetylcholine
75
What do Inhibitory neurotransmitters do
Result in hyperpolarisation of the postsynaptic membrane. This prevents action potential being triggered. eg. Gamma-aminobutyric acid (GABA)
76
How do transmission of impulses across synapses occur
Action potential reaches end of presynaptic neurone
Depolarisation of the presynaptic membrane - Ca2+ channels open
Ca2+ ions diffuse into the presynaptic knob
Causes synaptic vesicles containing neurotransmitters to fuse to presynaptic membrane
Neurotransmitters released by exocytosis
NTs Diffuse across the synaptic cleft and binds to receptor on postsynaptic membrane
Causes Na+ diffusion into the postsynaptic neurone
Triggers an action potential and the impulse is propagated along the postsynaptic neurone
77
Why is it important to remove action potential after it as passed
So another stimulus can arrive at the synapse and affect it
78
How are action potentials stopped
Any neurotransmitter left in synaptic cleft is removed, acetylcholine is released from receptors on postsynaptic membrane and is broken down by enzymes, RECYCLING
79
What are cholinergic synapses?
Synapses that use acetylcholine as the neurotransmitter
80
What enzyme hydrolyses acetylcholine
Acetylcholinesterase
81
Describe the events that occur at a cholinergic synapse
Arrival of action potential at Presynaptic neurone causes Ca2+ channels to open and ions to enter synaptic knob
Influx of Ca2+ ions causes vesicles to fuse with Presynaptic membrane, acetylcholine released into cleft
Acetylcholine fuses with receptor on postsynaptic neurone, causing Na+ channels to open, causing an influx in sodium ions
which generate an action potential in postsynaptic neurone
Acetylcholinesterase hydrolyses acetylcholine (also released by receptors) into choline and ethanoic acid (acetyl), so it can be recycled
ATP released by Mitochondria used to recombine choline and acetyl to recycle, Na+ channels close due to lack of Acetylcholine in receptors
pg 357
82
What is the role of synapses
Ensure impulses are unidirectional - receptors only present on postsynaptic neurone
Can allow one neurone transmitted to multiple synapses - many simultaneous responses
Many neurones can feed into one synapse - many receptors to produce single result
83
What is summation
If the amount of neurotransmitter builds up sufficiently to reach the threshold then this will trigger an action potential
84
What are the two types of summation
Spatial and temporal
85
What is spatial summation
Many presynaptic neurones connect to one postsynaptic neurone. Each releases neurotransmitter which builds up to a high enough level in the synapse to trigger an action potential in the single postsynaptic neurone
86
What is temporal summation
When a single presynaptic neurone releases neurotransmitter as a result of several action potentials over a short period, Builds up until the quantity is sufficient to trigger an action potential
87
How do stimulant drugs work?
Mimicks shape of neurotransmitter, so they can bind to receptors on postsynaptic membrane to trigger action potentials in postsynaptic neurone (eg. nicotine and acetylcholine)
Or
Stimulates release of more Neurotransmitter (amphetamines)
Or
Inhibits the enzyme responsible for the breakdown of neurotransmitter in the synapse - can result in loss of muscle control (nerve gases stop breakdown of acetylcholine)
88
How do inhibitor drugs work?
Blocks receptors so neurotransmitter (eg. curare and acetylcholine) can no longer bind to the receptor and no action potentials can be created, no muscle stimulant - paralysis
Binds to only specific receptors on some of the neurones changing the shape of the receptor so that binding of neurotransmitter increases (eg. Alcohol and GABAa receptors)
89
State the difference between the result of an inhibitory and a stimulatory drug that acts on the nervous system
An inhibitory drug results in less action potentials being created
A stimulatory drug creates more action potentials
90
Explain how amphetamines (stimulant) will affect the nervous system
Amphetamines stimulate the release of more neurotransmitter
from the presynaptic neurone
therefore it will bind to more receptors/more receptors activated
on the postsynaptic membrane
threshold is reached
more action potentials generated in the post synaptic neurone
greater response to stimulus
91
Explain how alcohol affects the nervous system
Alcohol binds to GABA receptors
this changes shape of receptor allowing more A
neurotransmitter (GABA) to bind
this increases activity of the neurotransmitter
GABA decreases the activity of the brain by preventing nervous transmission
92
Serotonin is a neurotransmitter involved in the regulation of sleep and other emotional states. Low levels of serotonin are found in patients suffering from depression. Prozac is an example of a drug used to treat depression. It works by blocking the reuptake of serotonin into the presynaptic neurone. Using your knowledge of synapses, explain how Prozac works
Serotonin would normally be taken back into the presynaptic neurone to be used again
prozac would prevent this occurring resulting in higher levels of serotonin in synapse
more serotonin can bind to neurotransmitter receptors
on postsynaptic membrane
depolarisation threshold reached
more action potentials
nervous system more stimulated, reducing depression symptoms
93
State what is meant by a synapse
Junction between one neurone and another (or neurone and effector cell)
94
Explain how synapses ensure impulses are only transmitted in one direction
Neurotransmitter receptors are only present on the postsynaptic membrane
so can only cause depolarisation of this membrane resulting in action potential
95
Describe one similarity and one difference between temporal and spatial summation
Similarity –
both result in a build-up of neurotransmitter in the synapse / both result in an action potential being triggered
difference –
spatial is a result of neurotransmitter being released from many neurones into the same synapse, temporal is a result of small amounts of neurotransmitter being released from a neurone several times in a short period
96
Explain in detail how a motor neurone causes a postsynaptic neurone to depolarise
The action potential reaches the end of the pre-synaptic/motor neurone
depolarisation of the pre-synaptic membrane causes calcium ion channels to open
calcium ions diffuse into the presynaptic knob
synaptic vesicles fuse with the presynaptic membrane and release neurotransmitter / exocytosis takes place
neurotransmitter diffuses across the synaptic cleft /binds with receptor on the postsynaptic membrane
sodium ion channels open and sodium ions diffuse into the post-synaptic neurone
threshold potential reached / depolarisation triggers an action potential
muscle cell contracts
97
What are the two systems that the nervous system is organised into
Central nervous system (CNS) - Brain and Spinal Cord
Peripheral Nervous system (PNS) - all the neurones that connect the CNS to the rest of the body
(pg 361)
98
What are the two types of functional organisation of the nervous system
Somatic and autonomic nervous systems (pg 360+361)
99
What is the Somatic nervous system
The system is under conscious control, when you decide to voluntarily do something eg. moving a muscle in your arm. Somatic nervous system carries impulse to the body's muscles
100
What is the Autonomic Nervous system
A constant and subconscious part of the nervous system, used when the body does something automatically without you deciding to do it - involuntary eg. Heart to beat, digestion of food
Autonomic nervous system carries nerve impulses to glands, smooth and cardiac muscles
101
What is the autonomic nervous system further divided into
The Sympathetic (Increase in activity) and Parasympathetic (decrease of activity)
(pg 360)
102
State the difference between the peripheral and the Central nervous system
The CNS is the brain and the spinal cord
the PNS is all other neurones
103
Sort the following activities into those which are controlled by the somatic nervous system and those which are controlled by the autonomic nervous system
Pupil dilation, Blood pressure, Throwing a ball, Walking
Somatic - Throwing a ball, walking
Autonomic - Pupil dilation, Blood pressure
104
State and explain why many autonomic functions can also be controlled by the somatic nervous system
for example:
breathing can be controlled
so that a person can hold their breath underwater
as it is not possible to breathe normally in this environment
105
What is an advantage of having a central control centre for the whole body
Communication between the billions of neurones is a lot faster than if many control centres for different functions were distributed around the body
106
What is the only nervous reaction that isn't processed by the brain
Reflex actions
107
How is the brain protected?
Skull and protective membranes (meninges)
108
What are the 5 main structures in the brain
Cerebrum, Cerebellum, medulla oblongata, Hypothalamus and Pituitary gland
109
What does the cerebrum control?
Control voluntary action, such as learning, memory, personality and conscious thought
110
What does the cerebellum control?
Controls unconscious functions such as posture, balance, and non-voluntary movement
111
What does the Hypothalamus control?
Regulatory centre for temperature and water balance
112
What does the pituitary gland control?
Stores and releases hormones that regulate many body function
113
Why is the cerebrum highly convoluted
Increasing its surface area, increases capacity for complex activity
114
What is the cerebrum split into two of
Cerebral hemispheres, each controlling one half of the body
115
What is the outer layer of the cerebral hemisphere known as
Cerebral cortex
116
Where do sophisticated processes such as reasoning and decision making occur?
Frontal and prefrontal lobe of the cerebral cortex (in cerebral hemisphere/cerebrum)
117
How many lobes are there in the cerebrum and what are they
4 - Frontal, Parietal, occipital and temporal
118
What side of the body does the right brain control
Left (and vice versa)
119
What does the cerebellum do and what happens if the brain is damaged
Control of muscular movement, body posture and balance - but doesn't initiate movement, coordinated it, receives information from organs of balance in the ears and information about the tone of muscles and tendons. Then relays information to cerebral cortex which controls motor action
If this area of the brain is damaged, suffers from jerky uncoordinated movement
120
What does the medulla oblongata do
Regulates Autonomic nervous system which controls actions like breathing rate and heart rate. Also controls activities such as swallowing, peristalsis and coughing
121
What are the functions of the hypothalamus
Has centres of parasympathetic and sympathetic nervous systems,
Controls complex patterns of behaviour, such as feeding, sleeping and aggression
Monitors composition of blood plasma, such as the concentration of water and blood glucose - therefore it has a very rich blood supply
Produces hormones - it is an endocrine gland
122
What do the two sections of the pituitary glands do
Anterior pituitary gland (front section) - Produces six hormones including follicle-stimulating hormone (FSH) involved in reproduction and growth hormones
Posterior pituitary (back section) - Stores and releases hormones produced by the hypothalamus, such as ADH involved in urine production
123
State the difference between the function of the anterior pituitary and the posterior pituitary
Anterior pituitary produces hormones,
posterior pituitary stores and secretes hormones produced by the hypothalamus
124
Sounds are interpreted by the auditory area in the temporal lobe. State the pathway followed by a nervous impulse produced by a sound wave
Sound receptor in left ear ---------> sensory neurone ----> temporal lobe in right cerebral hemisphere
125
A patient displays 3 symptoms: Asynergia - a lack of coordination in their motor movement, Adiadochokinesia - an inability to perform rapid movements and ataxic gait - staggering movements. Suggest and explain which part of the brain may have been damaged to explain which part of the brain may have been damaged to cause these symptoms
Cerebellum
because this region of the brain is responsible for muscular movement, body posture, and balance
126
What is the Reflex arc pathway
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)
Receptor - Sensory Neurone - Relay neurone - Motor Neurone - Effector
127
What is the spinal cord
Column of nervous tissue running up the back, surrounded around the spine for protection
128
What is the knee-jerk reflex
Spinal reflex testing neural circuit
Leg tapped just below the kneecap, stretching patellar tendon and acts as stimulus
Stimulus initiates reflex arc that causes the extensor muscle on the top of the thigh to contract.
At the same Time, the relay neurone inhibits the motor neurone of the flexor muscle causing it to relax
This contraction coordinated with the relaxation of the antagonistic flexor hamstring muscle causes the left to kick
If this doesn't occur, it my be a sign of a cerebellar disease
129
Describe the blinking reflex and what can cause it
Occurs when cornea is stimulated, to keep the cornea safe from damaged due to foreign bodies (dust, insects etc...) entering the eye.
Blink reflex occurs when sounds greater than 40-60 dB are head,
Occurs when in very bright light to protect the lens and the retina
Impulse passes through a relay neurone in the lower brain stem, sent along motor neurone to initiate a motor response to close eyelids in a consensual response (both eyes are closed in response to stimulus)
If the reflex is not seen, the patient may be brain-dead
130
plan an investigation into how the concentration affects a person's reaction time
Reaction time should be tested before a caffeine drink is given
this should be repeated many times / with many people to obtain reliable results
caffeine drink of known concentration is given to subjects
after a fixed time period, reaction time test is repeated in an identical way to the initial test
a range (ideally 5+) of caffeine concentrations should be investigated
control group / use of placebo caffeine drink
131
Why are reflexes essential for survival?
Help body avoid harm, or reduce severity of damage
132
How do reflexes increase survival
Being involuntary - prevents an overload of stimulus and Brian can deal with more complex responses
Not learnt - provides immediate protection and is present at birth
Extremely fast - reflex arc is short, only involving a few synapses
Many reflexes are everyday actions such as keeping upright and controlling digestion
133
State the reflex arc which occurs when a doctor test the knee-jerk reflex
pressure receptor in skin ----- sensory neurone ---- relay neurone ---- motor neurone --- (extensor) muscle
134
Which of the following actions are reflexes - Gagging, speaking, jumping pupil dilation
Gagging and pupil dilation
135
State and explain how a reflex action can improve an organisms chances of survival
eg. hand placed over burning material, reflex arc formed does not include the brain / it is an involuntary response
which decreases the time taken for the body to react to the situation
136
State and explain the considerations a researcher should take into account when planning an investigation into the effect of drugs, such as caffeine on a group of human volunteers
Researcher should take into account: Health benefits / risks
the drug administered could have an effect on the subject’s body
which could be positive or negative
Ethical considerations
when employing a placebo, people may believe that they have received a drug which has a beneficial effect which may or may not be the case
exemplification on the use of a placebo – for example, an experimental drug may be able to cure a condition; use of a placebo means that some of the sample group would not receive the drug
137
What are the 3 types of muscle and what do they do
Skeletal - Most of body muscle tissue responsible for movement eg. Biceps and Triceps
Cardiac - Cardiac muscle only found in heart - myogenic (contract without nervous stimulus) causing heart to beat in regular rhythm
Involuntary (Smooth) muscle - Found in many areas eg. walls of hollow organs such as stomach and bladder, and in walls of blood vessels and digestive tract
138
How do the muscles types vary in Fibre appearance, control, arrangement, contraction speed, length of contraction and structure compare
pg369 table
139
How are skeletal muscle structured
Bundles of muscle fibres, which are enclosed within a plasma membrane known as the sarcolemma
140
Why do muscle fibres win skeletal muscle contain Long nuclei
Formed as a result of many individual embryonic muscle cells fusing together, which makes the muscle stronger as there are no gaps between adjacent cells so no weaknesses and ensure the whole fibre contracts at the same time
141
Why do skeletal Muscle fibres have a lot of mitochondria
to provide the ATP needed for muscle contraction
142
What is sarcoplasmic reticulum
Modified endoplasmic reticulum which extends throughout the muscle fibre and contains calcium ions required for muscle contraction
143
What are myofibrils
Long cylindrical organelles made of proteins and specialised for contraction, which collectively are very powerful
Lined up in parallel to provide maximum force
144
What two protein filaments are myofibrils made up
Actin - the thinner filament. Consisted of two strands twisted around each other
Myosin - The thicker filament, consisting of long rod-shaped fibres with bulbous head that project to one side
145
What are the 4 components to a myofibril
Light bands - regions where actin and myosin filaments don't overlap (I-bands)
Dark Bands - presence of thick myosin filaments overlapped by actin (A-bands)
Z-line - Line found at the centre of light band (the distance between two Z lines is called a sarcomere)
H-Zone - a lighter coloured region found in the centre of each dark band - only myosin filaments are present at this area
146
Why are there light bands within a sarcomere
These are areas where actin and myosin filaments to not overlap.
pg.371, 372
147
What are the properties of slow-twitch fibres
Slow contraction
Less powerful contractions
Long period
Dont tire easily
Gain energy from aerobic respiration
Rich in myoglobin (red protein which stores oxygen)
Rich supply of blood vessels and mitochondria
148
Properties of fast-twitch fibres
Fibres contract very-quickly
Produce powerful contractions
Short period
Easily tire
Gain energy from Anaerobic respiration
Pale coloured - low levels of myoglobin and blood vessels
Contain more myosin filaments
Stores Creatine Phosphate to rapidly generate ATP from ADP in anaerobic conditions
149
State and explain how you could tell the difference between areas of fast-twitch and slow twitch muscle when observing skeletal muscle under the microscope
Slow twitch muscle fibres would appear redder in colour
due to more myoglobin/blood vessels
there would be more blood capillaries and more mitochondria
as these cells carry out aerobic respiration
150
State and explain any differences in composition which may exist in the skeletal muscles of marathon runners and sprinters
Marathon runners will have a higher proportion of slow twitch fibres
as these fibres provide contraction over long periods of time
without tiring
marathon runners mainly use aerobic respiration during exercise
which provides the energy for slow-twitch muscles
151
Describe simply the structure of skeletal muscle
Muscles are made up of bundles of muscle fibres
each fibre is made up of bundles of myofibrils
each myofibril is made up of protein filaments / actin and myosin
152
Describe the similarities and differences in the structure and function of cardiac and involuntary muscle
Similarities:
Both involuntary / unconscious control
both uninucleated / one nucleus per cell
Differences:
Cardiac striated, involuntary not
Cardiac – fibres branched, involuntary – fibres spindle shaped
involuntary are slower to contract
involuntary can contract for longer
153
What model is used to describe muscle contraction
Sliding Filament model
(pg 374)
154
What happens to the bands of muscle fibres when the muscle contractions and why
Myosin filaments pull actin filaments inwards towards centre of sarcomere
Light bands become narrower
Z-lines move closer together, shortening sarcomere
H-zone becomes narrower
155
What part of the structure of myosin filaments allow them to move backwards and forwards
Hinged Globular heads with binding sites for actin and ATP
156
What are present on actin filaments
Binding sites for Myosin heads
157
What inhibits the binding sites for myosin heads on actin filaments
Tropomyosin, held in place by troponin
158
What is a neuromuscular junction?
The point where a motor neurone and skeletal muscle fibre meet
Triggers muscle contraction when an action potential arrives at it
159
How do neuromuscular junctions help to ensure muscle fibres contract simultaneously
There are many along the length of a muscle, if only one existed, there would be a wave of contraction and would be slower
160
What is a motor unit
All the muscle fibres supplied by a single motor neurone
161
How does force required relate to motor unit stimulation
If a strong force is needed, a large number of motor units are stimulated, if a weak force is needed, a small force is required
162
Where does the depolarisation spread to in the sarcolemma
T-tubules
163
What are the T-Tubules in contact with
Sarcoplasmic reticulum, which contains Ca2+ absorbed actively from the sarcoplasm
164
What happens in the sarcoplasm when an action potential occurs
Sarcoplasmic reticulum stimulates Ca2+ channels to open, Ca2+ diffuse down conc gradient flooding sarcoplasm with Ca2+
Ca2+ bind to troponin, causing it to change shape - hence moving away from the Actin-Myosin binding sites, which then allow The bonding of Actin+Myosin
Once myosin head is attached to actin filament, it flexes, pulling actin filament along.
ADP bound to Myosin head is released, ATP binds to myosin head causing detach from actin filament
Ca2+ in sarcoplasm also activate ATPase in myosin, causing hydrolysis of ATP to ADP and Pi, releasing energy for myosin to return to original state
Cycle repeats
(pg 377)
165
How is the energy provided for muscle contraction
ATP hydrolysed into ADP and Phosphate group (Pi)
166
What pathways is ATP Generated from
Aerobic respiration
Anaerobic respiration
Creatine Phosphate
167
What type of reaction forms ATP in Aerobic respiration, where does it take place and what does it need to occur
Oxidative phosphorylation
Mitochondria (Plentiful in muscle)
Oxygen is required (Aerobic respiration used for long periods of low-intensity exercise)
168
How is ATP formed from Anaerobic respiration and what is the drawbacks from it
Glycolysis
No oxygen present, pyruvate produced converts to lactic acid which builds up and leads to muscle fatigue (Anaerobic used for short high intensity exercise eg. sprinting)
169
How is ATP produced from Creatine Phosphate
ADP is phosphorylated by creatine phosphate, which acts as a reserve supply to immediately combine with any ADP present.
Stores of creatine are used up rapidly as it generates ATP quickly so it is used for short bursts of vigorous exercise (eg tennis serve)
Creatine phosphate store replenished using phosphate from ATP
170
Maybe make flashcard of EMGs
171
State two differences in the appearance of a sarcomere in a relaxed and contracted muscle when observed through a microscope
In a contracted muscle the light band is narrower
Z lines closer together
H- zone becomes narrower
172
Professional sprinters have high levels of creatine phosphate in their muscle cells. Describe why this is advantageous
During a sprint, muscles work so hard oxygen cannot be replaced as quickly as it is used up
aerobic respiration alone can’t be used / anaerobic respiration required
creatine phosphate is a source of phosphate
the more creatine phosphate, the more ADP can be phosphorylated
muscles can perform at maximum rate for longer
173
After a persons death, their body can no longer produce ATP. This results in the stiffening of muscles (Rigour Mortis). Explain why a lack of ATP prevents muscles relaxing
ATP is needed to break bond/cross-bridge between actin and myosin
if no ATP available actin remains bonded to myosin
filaments remain in contracted state / filaments can’t slide back to original position
174
Bepridil is a drug that can be used to treat angina, a form of heart disease. It works by partially blocking Calcium ion channels. Explain the effect of bepridil upon heart muscle contraction
Muscles do not contract as much
as fewer calcium ions released into sarcoplasm/from sarcoplasmic reticulum
fewer calcium ions bind to troponin
less troponin moves/pulls tropomyosin
myosin-actin binding sites remain blocked
myosin cannot bind to actin to pull filament
