Heart rate, reflex, Receptors Flashcards
(95 cards)
1
Q
Myogenic Control of heart rate
A
2
Q
Before this topic have a good understanding of the cardiac cycle.
A
3
Q
Draw The heart and label the structures involved in the Myogenic control of heart rate?
A
- Sinoatrial node - in the wall of the right atrium
- AVN node in the middle of the ventricular system
- ventricular septum - prevents mixture of blood (oxy + deoxy)
4
Q
what is the heart muscle known as?
A
Cardiac muscle
5
Q
what is special about the cardiac muscle?
A
it is myogenic, so the contraction is initiated from the muscle itself. (it can contract on its own, without needing nerve impulses (stimulus))
6
Q
what is neurogenic?
A
contraction is initiated by nervous impulses from the outside. (the cardiac muscle is NOT neurogenic)
7
Q
what is the contraction in the heart initiated by?
A
the Sinoatrial node (SAN) (or pacemaker) in the wall of the right atrium
8
Q
what does the sinoatrial node determine?
A
the beat of the heart
9
Q
why is SAN referred to as a pacemaker?
A
it sets the rhythm of the heartbeat by sending out regular waves of electrical activity to the atrial walls
10
Q
Describe the process on how a heartbeat is initiated and co-ordinated? - MSA
A
- A single heart beat begins when the Sinoatrial node (SAN) sends a wave of electrical impulses from the wall of the right atrium across both atria, causing them to contract
- A layer of Non-conductive tissue (atrioventricular septum) prevents the wave crossing to the ventricles
- the wave of electrical impulses are passed/picked up by/enter a second group of cells called the Atrioventricular node (AVN) which lies between the atria
- But the AVN delays the impulses to allow blood to leave the atria before ventricles can contract
- the AVN sends a wave of electrical impulses between the ventricles (middle of the ventricular septum) along a series of specialised cardiac muscle fibres called Purkyne fibres which make up the ‘Bundle Of His’
- the Bundle of His’ divides into right and left branches, which spreads to the walls of the base of the ventricles
- from here the signal spreads from the walls of the ventricles through the Purkyne fibres
- impulses from the purkyne fibres cause the ventricle muscles to contract from the base upwards.
11
Q
when a wave of electrical activity reaches the AVN, there is a short delay before a new wave leaves the AVN. Explain the importance of this Short delay? - MSA
A
- Allows atria to empty and ventricles to fill
- before ventricles contract
OR - Delays contraction of ventricles
- until after atria has contracted/ ventricles have filled.
12
Q
Nervous control of heart rate
A
13
Q
What is the rate of the heart rate controlled by?
A
The nervous system
14
Q
Which main nervous system does the control of heart rate involve, and what are the two sub divisions of this system?
A
- Autonomic system consists of the parasympathetic and sympathetic nervous system
15
Q
What is the Autonomic system?
A
the autonomic system controls the involuntary (subconscious) activities of internal muscles and glands
16
Q
What is the parasympathetic and sympathetic nervous system?
A
Sympathetic NS - this stimulates effectors and so speeds up any activity. it helps us cope wit stressful situations by heightening our awareness and preparing us for activity/ potential danger (fight or flight)
Parasympathetic NS -This inhibits effectors and so slows down any activity. it controls activities under normal resting conditions. it is concerned with conserving energy and replenishing the body’s reserves. Rest and digest response.
17
Q
The actions of both the parasympathetic and Sympathetic nervous systems are..?
A
Antagonistic - if one system contracts, the other relaxes (therefore control of heart rate)
18
Q
When does the heart rate need to be altered to meet varying demands for oxygen?
A
During exercise, the resting heart rate may need more than double
19
Q
Which region of the brain Co-ordinates/controls the heart rate?
A
The Medulla (oblongata)
20
Q
What are the two centres associated with the Medulla Oblongata?
A
- A centre that increases the heart rate, which is linked to the SAN by the sympathetic nervous system (Cardiovascular centre)
- A centre that decreases the heart rate, which is linked to the SAN by the parasympathetic nervous system (Cardiovascular centre)
21
Q
Reflex And Nervous control of heart rate
A
22
Q
What is the rate of the heart beat affected by?
A
Although the beating of the heart is myogenic, the rate at which is beats can be affected by stimuli and increased or decreased in response
23
Q
Which part of the Nervous system does this involve?
A
Autonomic system (involuntary system)
24
Q
What is an external stimuli, which affects the heart rate?
A
Response to potential danger - Fight or flight
25
What hormone is released during flight or flight?
Adrenaline
26
Explain how Adrenaline affects the heart rate?
- Released in the blood it stimulates SAN to increase electrical impulses (and strength of contractions).
- SO INCREASES HEART RATE
27
What two examples of Internal stimuli affect the heart rate?
1) Changes in pH of blood
2) Changes in blood pressure
28
What lowers the pH of the blood, and increasing heart rate does what?
- High rate of respiration leads to high
CO2 in the blood (Lowers pH).
- Increasing heart rate increases the removal of CO2 and the supply of O2 to the tissues
29
What is a reflex?
Involuntary response to a sensory stimulus is a REFLEX
30
What is a reflex arc?
The pathway of neurones involved in a reflex is a REFLEX ARC
31
What are the three neurones involved in a reflex arc?
- sensory neurone
- Relay neurone
- Motor neurone
32
Describe how a reflex arc is carried out, when a person touches a hot object?
- stimulus - heat from the hot object
- receptor - temperature receptors (Thermoreceptors) in the skin, generates nerve impulses in the sensory neurone
- sensory neurone - passes nerve impulse to spinal cord
- relay neurone - this is the co-ordinator and links the sensory neurone to motor neurone
- motor neurone - carries nerve impulses from the spinal cord to a muscle in the upper arm
- effector - the muscle in the arm is stimulated to contract
- Response - pulling the hand away from the object
33
What is the importance of reflex arc's?
- Protect body from harmful stimuli e.g. Help escape from predators
- Effective from birth- INNATE so no need to learn
- Fast, Immediate , due to short neurone pathway with few synapses (1 or 2). This is important for withdrawal reflexes
- Involuntary, and rapid do not require decision of the brain, so the brain is bale to carry out more complex responses. Brain is not overloaded
- Inflexible- always the same
- Protect against damage to body tissues;
- Enable homeostatic control.
34
Which are the two main receptors which work to maintain the heart rate?
- chemoreceptors and baroreceptors
35
Where is are Chemoreceptors found, and what is their role?
Chemoreceptors (in the aorta, carotid artery and medulla): sensitive to changes in pH of blood, due to carbon dioxide dissolving in the blood plasma to form Carbonic acid.
36
Describe how Chemoreceptors detect low blood pH and return the blood pH back to normal?
- when blood has a higher than normal concentration of carbon dioxide, the pH is lowered
- the chemoreceptors in the carotid artery and aorta detect this and increase the frequency of nervous impulses
- to the cardiovascular centre in the Medulla Oblongata
- This centre increases the frequency of impulses via the sympathetic nervous system which secrete Noradrenaline, which binds to receptors on the SAN
- This increases the rate of production of electrical impulses by the SAN and therefore increases the heart rate
- This increases blood flow, leads to more carbon dioxide being removed by the lungs, so Carbon dioxide concentration of the blood return to normal
37
Describe how Chemoreceptors detect a decrease in pH and return the pH of the blood back to normal?
- when blood has a lower than normal concentration of carbon dioxide, the pH is increased
- the chemoreceptors in the carotid artery and aorta detect this and increase the frequency of nervous impulses
- to the cardiovascular centre in the Medulla Oblongata
- This centre increases the frequency of impulses via the sympathetic nervous system which secrete Acetylcholine, which binds to receptors on the SAN
- This decreases the rate of production of electrical impulses by the SAN and therefore decreases the heart rate
38
Why is it important to control the pH of the blood?
to prevent enzymes from denaturing
39
What are Baroreceptors, and where are they found?
Baroreceptors are found in the Carotid artery, Aorta and Vena cava, and they are sensitive to changes in blood pressure.
40
What type of receptor is a baroreceptor?
a type of stretch receptor
41
Describe how Baroreceptors detect a High blood pressure and return the Blood pressure to normal?
- When blood pressure is higher than normal, Baroreceptors and increase the frequency of nervous impulses
- to the Cardiovascular centre in the Medulla Oblongata
- This centre increases the frequency of impulses via the parasympathetic neurones.
- These secrete Acetylcholine, which binds to receptors on the SAN.
- This decreases the rate of production of electrical impulses by the SAN and therefore decreases the heart rate
42
Describe how Baroreceptors detect a low Blood pressure and return the blood pressure back to normal
- When blood pressure is lower than normal, Baroreceptors and increase the frequency of nervous impulses
- to the Cardiovascular centre in the Medulla Oblongata
- This centre increases the frequency of impulses via the sympathetic neurones.
- These secrete Acetylcholine, which binds to receptors on the SAN.
- This increases the rate of production of electrical impulses by the SAN and therefore increases the heart rate
43
why is it important that blood pressure is controlled?
- if blood pressure is too high could cause damage to walls of the arteries
- if blood pressure is too low , there may be an insufficient supply of oxygenated blood to respiring tissues and cells and removal of waste
44
Receptors
45
What are receptors?
Receptors are specialised cells that detect the changes in the body's environment (stimulus)
46
Why are receptors specific?
Usually only sensitive to one type of stimulus.
47
What is meant by Receptors are Transducers?
Receptors act as transducers. i.e. convert the energy of the stimulus into the start of a nerve impulse known as a generator potential (GP)
48
What features does the Pacinian Corpuscle have?
- is specific to one type of stimulus (only responds to pressure, and no other stimuli)
- Acts as a transducer Converts the energy of a stimulus into a nervous impulse known as a generator potential
49
What does the Pacinian corpuscle respond to?
Responses to changes in pressure
50
Where are the Pacinian Corpuscle receptors found?
- Found in deep in the skin, mainly in the fingers and feet
- they can also occur in joints, ligaments and tendons
51
Describe the appearance of a Pacinian Corpuscle receptor?
- at it's centre consists a single sensory neurone
- Which is wrapped in many layers of connective tissue called lamellae
- each of these layers are separated by viscous gel
52
What is the resting potential/ state?
- When the receptor is in it's resting state OR the potential difference when a cell is at rest
- When a nervous receptor is in it's resting state (not stimulated), there is a difference in charge between the inside and the outside - the inside is negative;y charged compared to the outside which is positively charged
53
What does this create across the membrane?
This means that there is voltage across the membrane. Voltage is the potential difference.
54
What is the resting potential generated by?
generated by ion pumps and ion channels
55
Describe the Pacinian Corpuscle in it's resting state?
- when the Pacinian Corpuscle is in it's resting state
- Stretch- mediated sodium ion channels are closed and are too narrow
- This means that there are more sodium ions outside the neurone, compared to inside the neurone
- This is called the resting potential
56
What happens when a Pacinian Corpuscle is stimulated by pressure?
This creates a generator potential
57
What is a Generator Potential?
A graded change in the voltage difference across the membrane of a sensory receptor that leads to excitation of a sensory neurone
58
How does the Pacinian Corpuscle receptor transduce the mechanical energy of the stimulus into a generator potential?
- a Pacinian Corpuscle is stimulated by pressure
- the lamellae is deformed, which causes greater deformation of of Stretch-mediated sodium ion channels
- the stretch mediated sodium ion channels open and Na+ diffuse (via facilitated diffusion) into the axon of the neurone
- the influx of Na+, leads to depolarisation of the axon
- The axon is now positive compared to the outside
- This forms/ creates a generator potential
59
When is an Axon potential produced?
If the generator potential is big enough, it will trigger an action potential (electrical impulse along a neurone)
60
An Axon potential will only be reached when..?
if the generator potential reaches a certain level called the threshold level.
61
What is the strength of a stimulus measured by?
the strength of a stimulus is measured by the frequency of action potentials.
E.g if the stimulus is too weak, the generator potential will not reach the threshold , so no action potential
62
Explain how the Pacinian Corpuscle allows an organism to distinguish between the levels of pressure? - MSA
- Greater pressure results in greater
deformation of layers/membranes/lamellae in the Pacinian corpuscle/more sodium channels open;
- Greater pressure produces a higher frequency of action potentials/impulses;
63
Why do we stop feeling pressure, when pressure is applied for a long time?
- When pressure is first applied to the corpuscle, it initiates a high number of impulses in its sensory neurone.
- However, with continuous pressure, the frequency of action potentials decreases quickly and soon stops.
- This is HABITUATION
64
Explain the importance of Habituation?
Useful as it prevents the nervous system from being bombarded with insignificant information.
65
Photoreceptors
66
What are photoreceptors?
Receptors in your eyes that detect light
67
Where are these Photoreceptors found?
Found on the retina, specifically the Fovea has a lot of photoreceptors. However, the Fovea has more Cone cells than Rod cells (because it receives the highest light intensity)
68
What is the function of the iris?
Controls how much light enters the pupil
69
What is the role of the lens?
focuses light on the retina
70
What is the function of the optic nerve?
Carries electrical impulses from the eye to the brain
71
What is the 'Blindspot'?
The place where the Optic nerve leaves the eye is called the 'Blindspot'. There are no Photoreceptors here.
72
What are the two types of Photoreceptors in the eye?
- Rods
- Cones
73
Where are Rods usually found?
Rods are mainly found in the peripheral parts of the retina/Fovea
74
How many rod cells are there in each eye?
120 million Rods in each eyes
75
What differs rod cells to Cone cells?
Rod cells can not distinguish different wavelengths of light and so processes images in black and white.
(Cones can distinguish between wavelengths of light and gives information/ images in colour)
76
What makes rods sensitive to to different wavelengths of light?
Rods contain a pigment called Rhodospin, which makes rods more sensitive to light.
77
Because Rhodospin is more sensitive to light, what does this mean?
Rhodospin breaks down/ Bleaches more easily at low light intensities i.e at nightime
78
Why do rod cells respond to low-intensity light?
Because there is enough energy from low intensity light to cause the break down/ bleaching of Rhodospin
79
What is the approximate wavelength of light hitting Rod cells and what colour?
Rods are mores sensitive to Blue-green wavelengths of light at approximately ≈ 500nm
80
Describe retinal convergence in rod cells?
there are multiple Rods that Synapse with one Bipolar cell
81
What increases as the number of rods cells connected to a single Bipolar cell increases?
there is a much greater chance that the threshold value will be exceeded than if a single rod cell were connected to each bipolar cell.
82
What is this due to?
This is due to summation (sum of all rods)
83
What is visual acuity?
the ability to tell apart points that are close together
84
What is a disadvantage to Rod cells?
They have a low visual Acuity - due to retinal convergence - many rods join together at the same bipolar neurone, which means that light from two points close together can't be told apart.
85
Where are Cones mostly found?
Cone are mainly found packed together at the Fovea.
86
How many cones are there in each eye?
much less than Rods - 6 million cones in each eye
87
What differs between Cones and Rods?
Cones respond to different wavelenghts of light, and depending on the proportion of each type that is stimulated, we perceive coloured images
88
What is the pigment found in Cone cells and how does this pigment differ from pigment found in Rod cells?
The pigment in Cone cells (Iodospin) requires a higher light intensity to break down/ Bleach and only and only light of high intensity will provide enough energy to break down/Bleach Iodospin and create a generator potential.
89
Why are cones less sensitive to rods?
Cones are less sensitive to Rods. This is because one cone synapses with a bipolar neurone, so it takes more light to reach the threshold and trigger an action potential.
90
What are the three different types of cones, what wavelength of light do they absorb?
- Blue - absorbs wavelength of ≈ 420nm
- Green - absorb wavelength of ≈ 534nm
- Red - absorb wavelength of ≈ 563nm
91
Describe the retinal Convergence of Cones?
One cone synapses with a single bipolar neurone
92
What is an advantage of Cone cells?
each cone cell has it's own connection to a single bipolar neurone , this means that if two were stimulated at the same time , the brain receives two separate impulses. therefore detect between 2 separate sources of light (that stimulated the two individual cones)
93
Describe the process by which Rods and Cones help us to see images?
1. Light enters the eye and hits the photoreceptor
2. Light-sensitive pigments in the photoreceptor (rhodopsin or iodopsin) are broken down/ BLEACHED
3. The light causes a chemical change and alters membrane permeability to sodium ions. causing the synaptic terminal to release neurotransmitters.
4. Neurotransmitters bind to bipolar cells
5. This creates a generator potential and if the threshold is reached then an impulse is sent along the bipolar neurone, then to the ganglion cell and finally to the optic nerve.
6. This is a large bunch of neurones that is connected to the brain. Where the optic nerve joins the eye there is a blind spot; there are no photoreceptors here so it cannot detect light.
94
When you move from bright light to low light, why does it take time for you to get accustomed to the dark?
In bright light all rhodopsin has been bleached - therefore there is no Rhodospin to react to dim light when you move into the dark (you are using your cone cells to see clearly, in colour). Time taken for rhodopsin to reform when is has been broken down in response to light.
95
DONE!!
