The nervous system Flashcards
1
Q
What are the two major divisions of the nervous system
A
1) The central nervous system (CNS)
2) The peripheral nervous system (PNS)
2
Q
What is the central nervous system (CNS) made up of
A
The brain and spinal chord
3
Q
What is the peripheral nervous system (PNS) made up of
A
Pairs of nerves that originate from either the brain or spinal cord.
4
Q
What is the peripheral nervous system divided into
A
- Sensory neurones
- Motor neurones
5
Q
What do sensory neurones do
A
Carry nervous signals from receptors to the central nervous system
6
Q
What do motor neurones do
A
Carry nervous impulses from the central nervous system to the effectors
7
Q
What can the motor nervous system be divided into
A
1) The voluntary nervous system
2) The autonomic nervous system
8
Q
What does the voluntary nervous system do
A
Carries nerve impulses to body muscles and is under conscious control .
9
Q
What does the autonomic nervous system do
A
Carries nerve impulses to glands, smooth muscle and cardiac muscle and is subconscious
10
Q
What is a reflex
A
An involuntary and rapid response to a stimulus
11
Q
What is the reflex arc
A
The neural pathway responsible for the involuntary, rapid and automatic response of the body to a stimulus.
12
Q
List the four key features of the reflex arc
A
1) Immediate- it is a very quick response as only 3 neurones are involved. The fewer the number of synapses, the faster the response.
2) Specific- one stimulus leads to one response
3) Involuntary/automatic- it happens without conscious thought
4) Innate- it is present from birth.
13
Q
List each of the stages in the reflex arc
A
- Stimulus
- Receptor
- Sensory neurone
- Coordinator/relay neurone
- Motor neurone
- Effector
- Response
14
Q
What are two features of all sensory receptors
A
- They are specific to a single type of stimulus
- They produce a generator potential by acting as a transducer.
15
Q
What stimulus does the pacinian corpuscle respond to
A
Mechanical pressure
16
Q
How does the pacinian corpuscle act as a transducer
A
It transduces the mechanical energy of the stimulus into a generator potential.
17
Q
How do all receptors in the nervous system act as transducers
A
They convert the energy of the stimulus into a nervous impulse known as the generator potential.
18
Q
Where are pacinian corpuscles most abundant
A
The fingers, the soles of the feet and external genitalia
19
Q
What is the function of the pacinian corpuscles that occur in joints, ligaments and tendons
A
They enable the organism to know which joints are changing direction.
20
Q
Describe the structure of a pacinian corpuscle
A
- The single sensory neurone of a pacinian corpuscle is at the centre of layers of tissue, each separated by a gel.
- The sensory neurone ending at the centre of the Pacinian Corpuscle has a stretch-mediated sodium channel in its plasma membrane.
21
Q
Why are stretch-mediated sodium channels called that
A
Because their permeability to sodium changes when they are deformed (eg. By stretching).
22
Q
Describe how the Pacinian corpuscle functions
A
- In its normal (resting) state, the stretch-mediated sodium channels of the membrane around the neurone of a Pacinian Corpuscle are too narrow to allow sodium ions to pass along them.
- In this state, the membrane of a pacinian corpuscle has a resting potential.
- When pressure is applied to the pacinian corpuscle, it is deformed and the membrane around its neurone becomes stretched.
- The stretching widens the sodium channels in the membrane and sodium ions diffuse into the neurone.
- The influx of sodium ions changes the potential of the membrane- it becomes depolarised.
- This produces a generator potential.
- The generator potential in turn creates an action potential that passes along the neurone and then,via other neurones, to the central nervous system.
23
Q
How do cone and rod cells act as transducers
A
They conserve light energy into the electrical energy of a nerve impulse.
24
Q
Describe the differences between rod and cone cells
A
- Rod cells are rod-shaped and cone cells are cone-shaped.
- Rod cells are in greater numbers than cone cells.
- Rod cells are present at the periphery of the retina and absent at the fovea whereas cone cells are concentrated at the fovea while there are fewer at the periphery of the retina.
- Rod cells give low visual acuity whereas cone cells give good visual acuity
- rod cells are sensitive to low-intensity light whereas cone cells are not sensitive to low-intensity light
- there is only one type of rod cell whereas there are three types of cone cell each of which responds to different wavelengths of light.
25
How many types of cone cell are there
Three
26
Why do rod cells give low visual acuity
- Because many rod cells link to a single bipolar cell, light received by rod cells sharing the same neurone will only generate a single impulse travelling to the brain regardless of how many of the neurones are stimulated.
- This means that, in perception, the brain cannot distinguish between the separate sources of light that stimulated them.
- Two dots close together therefore cannot be resolved and so appear as a single blob.
- This means rod cells give a low visual acuity.
27
Explain why rod cells respond to low-intensity light
- In order to create a generator potential the pigment rhodopsin must be broken down.
- There is enough energy from low-intensity light to cause this breakdown.
28
What is the purpose of rod cells
To allow us to see in low light intensity
29
Describe the structure and function of rod cells
- Many rod cells are connected to a single sensory neurone in the optic nerve.
- Rod cells are used to detect light of very low intensity.
- A certain threshold value has to be exceeded before a generator potential is created in the bipolar cells to which they are connected.
- As a number of rod cells are connected to a single bipolar cell (retinal convergence) there is a greater chance that the threshold value will be exceeded than if only a single rod cell were connected to a single bipolar cell.
- As a result, rod cells allow us to see in low light intensity although only in black and white.
30
Why do cone cells only respond to high light intensity
- Each cone cell is connected to their own separate bipolar cell and then to a sensory neurone in the optic nerve.
- This means that the stimulation of a number of cone cells cannot be combined to help exceed the threshold value and so create a generator potential.
- As a result, cone cells only respond to high light intensity and not low light intensity.
31
Why is each type of cone cell sensitive to a specific range of wavelengths
- The pigment iodopsin that is found in cone cells requires a higher light intensity for its breakdown.
- Only light of high intensity will therefore provide enough energy to break it down and create a generator potential.
- There are three different types of cone cell, each containing a specific type of iodopsin.
- As a result, each cone cell is receptive to different wavelengths of light.
32
Why do cone cells give a high visual acuity
- Each cone cell has its own connection to a single bipolar cell which means that, if two adjacent cone cells are stimulated, the brain receives two separate impulses.
- The brain can therefore distinguish between the two separate sources of light that stimulated the two cone cells.
- This means that two dots close together can be resolved and appear as two dots.
- Therefore cone cells give very accurate vision/high visual acuity.
33
What does having different types of light receptor (cone and rod cells) allow mammals to do
Benefit from good all-round vision both day and night
34
What are the two divisions of the autonomic nervous system
1) The sympathetic nervous system
2) The parasympathetic nervous system
35
What is the role of the sympathetic nervous system
- The sympathetic nervous system stimulates effectors and so speeds up any activity.
- It controls effectors when we exercise or experience strenuous emotions.
- It helps us to cope with stressful situations by heightening our awareness and preparing us for activity (fight or flight response).
36
What is the role of the parasympathetic nervous system
- The parasympathetic nervous system inhibits effectors and so slows down any activity.
- It controls activities under normal resting conditions.
- It is concerned with conserving energy and replenishing the bodies reserves.
37
What does it mean when we say that the actions of the sympathetic and parasympathetic nervous systems are antagonistic
- They normally oppose one another.
- If one system contracts a muscle, then the other relaxes it.
- The activities of internal muscles and glands are therefore regulated by a balance of the two systems.
38
What does the cardiac muscle being myogenic mean
Its contraction is initiated from within the muscle itself rather than by nervous impulses from outside (neurogenic)
39
Where is the sinoatrial node SAN (pacemaker) located
Within the wall of the right atrium
40
Describe the sequence of events that controls the basic heart rate
- A wave of electrical excitation spreads out from the sinoatrial node 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 excitation enters a second group of cells called the atrioventricular node (AVN), which lies between the atria.
- The atrioventricular node, after a short delay, conveys a wave of electrical excitation between the ventricles along a series of specialised muscle fibres called Purkyne tissue which collectively makes up a structure called the bundle of His.
- The bundle of His conducts the wave through the atrioventricualr septum to the base of the ventricles, where the bundle branches into smaller fibres of Purkyne tissue.
- The wave of excitation is released from the Purkyne tissue, causing the ventricles to contract quickly at the same time, from the bottom of the heart upwards.
41
What is the resting heart rate of a typical adult human
70 beats per minute
42
What region of the brain controls changes in heart rate
Medulla oblongata
43
Name and describe the two centres that the medulla oblongata has that are concerned with heart rate
1) A centre that increases heart rate which is linked to the sinoatrial node by the sympathetic nervous system.
2) a centre that decreases heart rate which is linked to the sinoatrial node by the parasympathetic nervous system.
44
What determines which of the centres in the medulla oblongata is stimulated when controlling heart rate
Nerve impulses received from chemoreceptors and pressure receptors in the blood
45
Describe how chemoreceptors control heart rate
- when the blood has a higher than normal concentration of carbon dioxide, its pH is lowered.
- The chemoreceptors in the walls of the carotid arteries and the aorta detect this and increase the frequency of nervous impulses to the centre in the medulla oblongata that increases heart rate.
- This centre increases the frequency of impulses via the sympathetic nervous system to the sinoatrial node.
- This, in turn, increases the rate of production of electrical waves by the sinoatrial node and therefore increases the heart rate.
- The increased blood flow that this causes leads to more carbon dioxide being removed by the lungs and so the carbon dioxide concentration of the blood returns to normal.
- As a consequence the pH of the blood rises to normal and the chemoreceptors in the wall of the carotid arteries and aorta reduce the frequency of nerve impulses to the medulla oblongata.
- The medulla oblongata reduces the frequency of impulses to the sinoatrial node, which therefore leads to a reduction in the heart rate.
46
What are chemoreceptors and where are they found
- Chemoreceptors are sensitive to changes in the pH of the blood that result from changes in carbon dioxide concentration.
- In solution, carbon dioxide forms an acid and lowers pH
- chemoreceptors are found in the walls of the carotid arteries (the arteries that serve the brain).
47
Where are pressure receptors found
In the walls of the carotid arteries and the aorta
48
Describe how pressure receptors control heart rate
- When blood pressure is higher than normal, pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that decreases heart rate.
- This centre sends impulses via the parasympathetic nervous system to the sinoatrial node of the heart, which leads to a decrease in the rate at which the heart beats.
- When blood pressure is lower than normal, pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that increases heart rate.
- This centre sends impulses via the sympathetic nervous system to the sinoatrial node, which increases the rate at which the heart beats.
49
Compare the nervous system and the hormonal system
- The nervous system uses nerve cells to pass electrical impulses along their length whereas the hormonal system produces chemicals (hormones) that are transported in the blood plasma to their target cells.
- The nervous system stimulates its target cells by secreting chemicals known as neurotransmitters directly onto them whereas the target cells of the hormonal system are stimulated by the change in concentration of hormones picked up by the receptors on their cell surface membranes.
- A nervous response is fast whereas a hormonal response is slower
- A nervous response is very specific whereas a hormonal response is less specific.
- A nervous response is short lived and restricted to a localised region of the body whereas a hormonal response is longer and more widespread.
- The effect of a hormonal response may be permanent and irreversible whereas the effect of a nervous response is usually temporary and reversible.
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