Unit 3.1 The Nervous System Flashcards
(276 cards)
1
Q
How much does the nervous system weigh and how much of the body mass does it account for?
A
The nervous system weighs barely 2 kilograms and only accounts for around 3% of the body mass, yet is perhaps the most complex of all the body systems.
2
Q
What does the nervous system use to coordinate the body and maintain homeostasis?
A
It uses electrical impulses.
3
Q
What are the specialised cells which are responsible for direct communication between different groups of cells called?
A
Never cells, or neurones.
4
Q
Neurones form a network of highly specific connections between different groups of cells in order to do what 3 things?
A
Gather information from sensory receptors.
Process information and create memory in the central nervous system (CN)
Stimulate effector cells (for example to cause voluntary movement, or to cause the release of secretions from a gland)
5
Q
What organ is the most anatomically complex system in the body?
A
The brain.
6
Q
What 2 ways does the brain function in?
A
As a coordination and control centre for many parts of the body (for example controlling the respiratory system)
And also as a self contained unit (for example in the development of memory)
7
Q
Although the brain and CNS are highly complexing the way they function, which 5 types of cell are they made up of?
A
Neurones, Glial cells, microglial cells, connective tissue and blood vessels.
8
Q
Neurones are specialised cells capable of developing electrical impulses and transmitting the impulses along the length of the cell. What do they all posess?
A
They possess a cell body, axons and dendrites (dendrons), myelin sheath, nodes of ranvier, synapse, synaptic knob.
9
Q
How many neurones are there in the body?
A
There are between 10 and 20 billion neurones in the body.
10
Q
What size do neurones range from?
A
Ranging in the size from a few thousandths of a millimetre (micron) to over a metre in length,
11
Q
Why do neurones have a high level of metabolic activity?
A
Energy is needed to maintain neurones in a state of readiness for conducting impulses.
12
Q
What do neurones contain many of?
A
They contain many mitochondria to supply the ATP they need for aerobic respiration.
13
Q
How are electrical impulses in neurones generated?
A
By changes in the permeability of the cell membrane to different ions.
14
Q
What can neurones be classified according to?
A
The direction in which they conduct impulses.
15
Q
What do sensory neurones transmit?
A
Sensory neurones transmit nerve impulses from sensory cells towards the spinal cord and the brain, also known as afferent neurones.
16
Q
What do motor neurones transmit?
A
Motor neurones transmit nerve impulses from the brain and the spinal cord towards the muscles and glandular organs, also known as efferent neurones.
17
Q
What does the cell body of a neurone contain?
A
The contains the nucleus and the normal organelles associated with cell metabolism.
18
Q
What are the axons of neurones?
A
These are fibres which conduct nerve impulse away from the cell body.
19
Q
How many axons per neurone?
A
A neurone has a single axon, which may be as long as a metre in length.
20
Q
What is at the end of an axon?
A
At the end of an axon there are hundreds or even thousands of branches that end at axon terminals called synaptic knobs.
21
Q
What are dendrites?
A
These are the connecting fibres of each neurone and look like branching hair lie processes.
22
Q
How many dendrites do each neurone have?
A
Each neurone has hundreds and sometimes many thousands of dendrites.
23
Q
What does the extensive branching allow dendrites to do?
A
The extensive branching allow dendrites to communicate with many different neurones.
24
Q
What is the function of the myelin sheath?
A
This is an insulating sheath around the axon which increases the speed at which an impulse is conducted.
25
What are the nodes of Ranvier?
The myelin sheath is interrupted at approximately one millimetre intervals by gaps known as the nodes of Ranvier.
26
What do the nodes of Ranvier provide?
The gaps increase the speed of transmission of impulses along the axon, as the change in potential jumps from one node to another.
27
What is the synapse?
The synapse is a very small gap between neurones. Often the gap its between 2 dendrites but it may be between a dendrite and the cell membrane of a cell body.
28
What does the synapse contain?
Interstitial fluid
29
Billions of never cells meet a synaptic junctions but do not touch, therefore what is the communication at the synapses?
The electrical nerve impulses cannot jump the gap so communications at the synapses is chemical.
30
What is the time taken to cross a synapse?.
0.5 milliseconds.
31
What is the synaptic knob?
This is the terminal end of the neurone.
32
What doe the synaptic knob contain?
It contains a chemical (neurotransmitter) which is released in response to nerve impulse arriving in the knob.
33
What do the neurotransmitters do?
The neurotransmitters diffuses across the gap and binds to receptors on the postsynaptic membrane stimulating never impulses in the postsynaptic neurone. Different synapses shave different neurotransmitters but they all facilitate communication between different neurone.
34
Around how many different neurotransmitters have been identified and how many in each neurone?
Many neurones contain two or three types of neurotransmitters each having different effects upon the postsynaptic cells. Around 100 different neurotransmitters have been identified, including acetylcholine, noradrenaline, serotonin and dopamine.
35
What are nerves often categorised on?
Nerves are often categorised on the main neurotransmitter they release, for example nerve cells that release acetylcholine are called cholinergic neurones.
36
A severed bacon accent be repaired or re-grown, but neurones do have a capacity to adapt, known as what?
Plasticity.
37
What does plasticity involve?
Plasticity involves the sprouting of new dendrites, synthesis of new proteins and changes in synaptic contact with other neurones.
38
In which nervous system its plasticity greater?
Plasticity is greater in the peripheral nervous system than it is in the central nervous system.
39
What do space do glial cells occupy?
Glial cells occupy the space between neurones and carry out support functions.
40
What is the function of glial cells?
In the case of injury or disease, neruoglial cell multiple and fill in spaces formally occupied by neurones..
41
What is bigger and more common in the nervous tissue, the neurones or glial cells?
Glial cells are vernally smaller than neurones and about 50 times more numerous in the nervous tissues.
42
What function do some glial cells have?
Some neuroglial cells have an immune system function.
43
What disease is commonly derived from glial cells?
Primary brain tumours.
44
What is a nerve impulse?
A nerve impulse is an electrical sign which is transmitted along the length of the neurone.
45
What are the two major functional properties of neurones?
Irritability and conductivity.
46
What is irritability the ability to do?
Irritability (seen mainly in sensory neurones) is the ability to generative nerve impulses in response to a stimulus,
47
What is conductivity the ability to do?
Conductivity is the ability to transmit the impulse to other neurones, muscles or glands.
48
What is the plasma membrane of an inactive neurone said to be?
Polarised - the inside of the cell is more negative than the outside.
49
What happens to the plasma membrane after a stimulus such as neurotransmitter being received?
The permeability of the plasma membrane to sodiums and potassium ions is altered for a very short time. Depolarisation occurs.
50
What state is a cell in when it has been depolarised?
The inside of the cell becomes positive compared with the outside.
51
What is depolarisation caused by?
Sodium ions flood into the cell through the cell membrane.
52
What does the entry of sodium ions into the cell cause?
An action potential.
53
What is the membrane of an axon relatively impermeable to and relatively freely permeably to?
The membrane of an axon is relatively impermeable to sodium ions (Na+) but relatively freely permeable to potassium ions (K+).
54
What does the difference in permeability gives the neurones?
They're conducting properties.
55
What pump dose the axon membrane also contain?
A very active sodium/potassium pump.
56
How does the sodium potassium pump work?
This pump uses ATP to move sodium ions out of the axon and potassium ion into the axon.
57
What is the result of the sodium/potassium pump?
As a result, the concentration of sodium ions inside the axon is lowered because the ions are pumped out but cannot move back into the axon bu diffusion.
58
What can the potassium ions do once pumped into the axon?
Although the sodium pump moves potassium ions into the axon, they diffuse out again through the membrane down a concentration gradient.
59
What is the result of the ion movement?
The inside of the axon is left slightly negative relative to the outside.
60
What does the polarised membrane have a potential difference of?
The polarised membrane has a potential difference of -70mV which is known as the resting potential.
61
What occurs when a nerve impulse travels along an axon, or any nevre fibre?
The big change is in permeability of the axon membrane to sodium ions.
62
In a sensory neurone, what does the change in permeability happen in response to?
A stimulus such as light, sound, touch, taste or smell.
63
In a motor neurone, what is an impulse triggered by?
A neurotransmitter chemical.
64
When happens when a neurone is stimulated and there is a sudden big increase in the permeability of the axon membrane to sodium ions?
Very specific sodium ion channels open and sodium ions diffuse rapidly into the axon down concentration and electrochemical gradients.
65
What does the diffusion of sodium into into the cell result in?
This results in a brief reversal of the potential across the axon membrane - it becomes depolarised with he inside of the cell become positive relative to the outside.
66
What is the potential difference across the membrane, what is is known as?
+40mV and this is the action potential.
67
How long does the action potential last for?
About one millisecond.
68
What does the all or nothing response mean in terms of the action potential?
Every action potential is exactly the same size, it either happens or it does not.
69
What needs to happen to the membrane after the action potential? What is this process called?
After the action potential the membrane needs to return to its resting state so that another impulse can be passed. This is the re-polarisation.
70
How does the re-polarisation take place?
The sodium ion channels close and the sodium/potasssium pump quickly pumps out the excess sodium ions, an active transport and therefore uses ATP.
71
In re-polarisation, what happens to the permeability of the membrane?
The permeability of the membrane to potassium increases briefly o potassium into also diffuse out of the axon down both concentration and electrochemical gradients.
72
After re-polarisation the inside of the cells is returned to its resting state, what is this?
With the inside negative compared to the outside, as the positive sodium and potassium ions leave the cell
73
How long does re-polarisation take and what is it known as?
It takes a few milliseconds and this is known as the refractory period.
74
During the refractory period, what can not happen to that area of the axon? What 2 things does this help make sure?
It cannot be simulated again. This helps to make sure that the impulse travels in only one direction along the axon and limits the number of impulses which can travel along a neurone in a given period of time.
75
For the nerve system to function, one neurone must be able to pass an impulse to another, they must be able to communicate - what are neurones linked by and what is the action potential conducted along until it reaches?
A synapse
76
The electrical impulse cannot jump across the synaptic gap to stimulate the next neurone, what chemicals are used to cross the gap?
Chemicals known as neurotransmitters are used to cross the gap.
77
When an impulse arrives in the synaptic knob, it increased the permeability of the pre-synpatic membrane to what?
Calcium ions (Ca 2+)
78
How do calcium ions move into the pre-synaptic knob?
Down a concentration gradient.
79
What effect does the movement of calcium ions into the pre-synaptic knob have on the neurotransmitters?
As a result, synaptic vesicles full of neurotransmitters move to the pre-synpatic membrane here they fuse with the membrane and release their transmitter molecules into the synaptic gap.
80
Once the neurotransmitters are in the synaptic gap, what happens next?
The diffuse across the gap and become attached to specific protein receptor sites on the post-synaptic membrane.
81
When neurotransmitters attach to protein receptor sites on the post synaptic membrane, what happens?
This opens sodium ion channels so sodium ions move into the post synaptic knob.
82
What happens if enough receptors are stimulated?
The threshold level of sodium ions inside the cell is reached and a new action potential is set up in the post synaptic cell. It usually needs a number of impulses to arrive in pre-synpatic neurones to trigger an action potential in the post synaptic neurone.
83
In healthy individuals, what happens to neurotransmitters in the synaptic cleft once they have done their job?
The are destroyed by enzymes in the synaptic clift so they do not continue to stimulate the post synaptic neurone.
84
What can affect the transmission of nerve impulses?
A range of drugs, including alcohol, sedatives and anaesthetics.
85
Some drugs affect the sodium ion channels in neurones, what affect can this have?
It can prevent the sudden inrush of sodium ions which causes the action potential.
86
Other drugs affect the sodium/potasium pump mechanism. without this, what cannot be maintained?
Without the sodium potassium pump the resting state of a neurone cannot be maintained and so it will not be able to transmit an impulse.
87
Some drugs affect the synapses between neurones, examples being?
They may replace natural neurotransmitters, destroy natural neurotransmitters or enhance their action.
88
What does cold or continuous pressure also obstruct impulse conduction?
Because it interrupts blood flow to neurones.
89
What various forms can information about the external world and the internal environment of the body exist?
Pressure, temperature, light, smell, sound waves.
90
What specialised cells can convert various stimulus into nerve impulses in sensory neurones?
Specialised receptor cells.
91
There are several different types of sensory receptors which respond to external and internal stimulus, what do exteroceptors receive?
Exteroceptors receive external stimuli (from outside the body) such as light, sound, chemical changes, temperature changes and pain.
92
What do Interoceptors receive?
Interoceptors receive internal stimuli such as water levels in the body (thirst) nutrient levels (hunger) carbon dioxide concentration in the blood and blood pressure.
93
What is adaption to a stimulus?
In the presence of a constant stimulus, neurones eventually top responding and sensitivity i great reduced - this is adaption to a stimulus - this is how we turn out repetitive low level sounds or chronic pain,.
94
What two types of adapting sensors are there?
There are fast-adapting sensors and slow adapting sensor.
95
What are nociceptors?
Nociceptors detect pain - these are slow adapting receptors are especially common in skin, joint capsules, bone and around the walls of blood vessels. Deep tissues and the visceral organs have few nociceptors.
96
What are thermoreceptors?
Thermoreceptos are fast-adapting and found in skin, skeletal muscles, the liver and the hypothalamus. Fat adaption means that when you enter an air-conditioned room, it feels initially quite cold but within a few minute you become conformation as the adaption process occurs.
97
Which thermoreceptors, hot or cold are more numerous?
Cold receptors are 3 or 4 times more numerous than heat receptors.
98
What are mechanoreceptors?
Mechanoreceptors are sensitive to stimuli that distort cell membranes, like a direct physical blow to a part of the body - these respond to forces that cause stretching, compression, twisting or other types of distortion to cell membrane.
99
What are the 3 types of mechanoreceptor?
Baroreceptors detect pressure changes in the walls of blood vessels - an interoceptor function.
Proprioceptors monitor the position of joints and muscles - these interoceptors are the most structurally complex of the mechanoreceptors.
Tactile receptor provide sensations to touch, pressure, vibration, itch or tickle - they are exteroreceptors.
100
What are chemoreceptors?
Chemoreceptors include exteroceptors that detect chemicals in the mouth (taste), nose (smell) and many interoceptors that detect chemicals in body fluids.
101
What bare osmoreceptors?
Osmoreceptors are interoceptors that detect the water potential (osmotic pressure) of body fluids.
102
What are photoreceptors?
Photoreceptors arre exteroceptors which detect light some of them adapt rapidly and some of them are very slow adapting.
103
What is the cause of every impulse in sensory neurones?
Stimulation of receptors.
104
What is the pathways of communication from stimulation to response?
Stimulation of receptors is the cause of eery impulse in sensory neurones, information is coordinated in the central nervous system and impulses pass along motor neurones to reach effectors, where as response is made to the original sensory input. Typical examples of effectors are glands and muscles.
105
What does the Central Nervous system consist of?
The brain and spinal cord.
106
How are the brain and spinal cord protected?
The brain and spinal cored are so essential that they are fully encased in bone: the brain with the cranial cavity of the skull and the spinal cord within the vertebral canal of the vertebrae.
107
How much does the brain weigh?
About 1.5kg
108
How many neurones and supporting glial cells does the brain contain?
Over 12 billion neurones and 50 billion supporting glial cells.
109
The brain is protected within the cranial cavity of the skull by which 3 membranes?
```
The Dura Mater (outer layer)
Arachnoid mater (middle layer)
Pia mater (inner layer)
```
110
What is the dura mater?
The dura mater is a tough, leathery membrane that forms an inelastic bag that surrounds the brain and spinal cord.
111
What does the Arachnoid mater resemble?
The term arachnoid is from the greek work for spider as it resembles a spiders web?
112
What is the pia mater?
The pia mater is a thin membrane that adheres closely to the surface of the brain.
113
What is the space between the arachnoid mater and the pia mater called and contains?
It is the sub-arachnoid space and contains cerebrospinal fluid (CSF)
114
What is the CFS, what functions do it have?
it is a clear colourless fluid similar to lymph, and has the following three primary functions:
- It acts as a buffer against the physical shock and protects the CNS from damage.
- It transports nutrients to the CNS
- It removes waste from the CNS.
115
The brain is a hollow organ, and the fluid filled canals and spaces within the brain constitute the ventricular system and are filled with CSF, what are the areas f the brain?
Cerebrum, thalamus, hypothalamus, pituitary gland, midbrain, pons, medulla oblongata, spinal cord, cerebellum, cavity in brain filled with fluid.
116
Where is the medulla oblongata located? what does it control?
This is the lowest part of the brain stem - it controls the basic functions of life, including regulation of cardiac and respiratory systems- the areas controlling the heart rate and breathing are also known as vital centres.
117
Where is the pons located? what does it control?
The pons bridges the two halves of the cerebellum - it is below the midbrain and above the medulla - facial expression and eye movement are controlled by the pons.
118
Where is the cerebellum located? What does it do? What is its appearance?
This consists of paired hemispheres which span both sides of the brain stem.
It receives inputs from motor and sensory areas of the cerebral cortex. it coordinates muscular activity, muscle tone or resistance to stretch and motor coordination (like balance and posture) The cerebellar surface has a distinctive ridged appearance.
119
Where is the midbrain located? what do it control?
The midbrain is the shortest segment of the brain stem, narrower than the pons but extended above it. It controls visual and auditory functions (sight and hearing)
120
What is the cerebrum (cerebral hemispheres)? What does it control?
The cerebrum is the largest part of the brain, it receives and interprets all sensory information and controls motor function. It is also the centre of intelligence, personality, judgement, decision making, consciousness and memory.
121
Where is the thalamus found and what does it do?
The thalamus is a relay station and links the areas of the cerebral cortex involved in sensory perception and movement with other parts of the brain and the spine.
It organises the sensory information and distributes it as appropriate. It is also involved in the control of sleep and wakefulness.
122
What is the hypothalamus, what does it coordinate?
This is a small area of the brain which coordinates hormonal and nervous functions, particularly those concerned with homeostasis. It controls water balance as well as regulating temperature and the release of hormones linked to the control fo the metabolism and reproduction
123
How many cranial nerves does the brain give rise to?
12 pairs.
124
What do the cranial nerves contain?
Some contain only motor fibres, some contain only sensory neurones and other contain a mixture of both.
125
How many pairs of spinal nerves stem from the spinal cord?
thirty one pairs of spinal nerves stem from the spinal cord, each with a motor and sensory component.
126
What does a cross section of the spinal cord appear as?
An oval plate with an H or butterfly shape in the middle.
127
What does the grey matter consist of?
The butterfly shape is the grey matter and this consists of nerve cells and cell bodies.
128
What does the white mater consist of?
The remaining matter is white matter which consists of nerve fibres.
129
What gives the characteristic white colour to white matter?
The myelin sheath around the nerve fibres.
130
What are bundles of nerve fibres existing in the spinal cord called?
Nerve tract.
131
What is a collection of nerve cell bodies called?
The structure is called a ganglion.
132
What can occur if the spinal cord is damaged?
It can lead to a loss of sensation, or muscle control or both.
133
The brain is the most sensitive body organ and relies on a constant internal environment. Other body organs can cope well with small fluctuations in the concentrations of hormones, nutrients and ions that occur after for example eating or exercise. If the brain were exposed to such chemical changes, uncontrolled neuronal activity could result in potentially dangerous outcomes, for examples seizures of black outs. What keeps the neurones of the brain separated from many blood borne substances, preventing these problems?
The blood-brain barrier.
134
What does the blood-brain barrier consist of?
The blood-brain barrier consists of a continuous layer of endothelial cells joined by tight junctions.
135
What does the blood brain barrier prevent?
It also prevents many drugs from reaching and affecting the brain.
136
What are the only water soluble substances that pass easily through the membranes of the blood brain barrier?
Water, glucose and essential amino acids.
137
What is the blood brain barrier virtually ineffective at preventing the passage of?
Fats and fat-soluble molecules into or out of the brain.
138
How are blood borne alcohol, nicotine and anaesthetics able to affect the brain?
Through fat and fat soluble molecules that the blood brain barrier is ineffective at preventing the passage of.
139
Which 2 gasses diffuse easily through all plasma membranes?
Oxygen and carbon dioxide.
140
What is the blood brain barrier an important adaption for?
protecting the brain, for example the exclusion of medicines such as penicillin protects the CNS against severely toxic effects.
141
In parts, the blood brain barrier is leaky, what does this mean?
The blood brain barrier is not consistently impermeable, in parts it is leaky and this enables some drug molecules to pass through which can be exploited by certain pharmacological agents.
142
Where is the blood brain barrier less effective?
In the hypothalamus.
143
There is little evidence of a blood brain barrier between what?
The circulation and the peripheral nervous system.
144
Where the blood brain barrier is less effective, what can these areas be used for?
These areas can be used to delivery medicines to the brain but it also means that some illegal drugs can reach, influence and sometimes damage the brain.
145
What does the peripheral nervous system consist of and what can it be divided into?
This consists of all the nervous tissue that does not belong to the CNS. It can be divided into the voluntary (somatic) nervous system, and the involuntary (autonomic) nervous system.
146
What is the somatic nervous system concerned with?
All activities that are under conscious control. When you decide to scratch your nose, shut a book or walk out the room, you will do so voluntarily and your somatic nervous system is in action.
147
What are most of the sensory receptors in the somatic nervous system?
Machnoreceptors.
148
Some other functions are also controlled by the somatic neurone activity, what are these?
Some involuntary functions such as breathing. The muscles that generate respiratory movements and skeletal muscles under the control of somatic motor neurones.
149
Somatic motor pathways always involve at least two of what? what are these?
At least 2 motor neurones, an upper motor neurone whose cell body is contained within a CNS processing centre and a lower motor neurone whose cell body is contained in a nucleus of the brain stem or spinal cord.
150
What happens if a lower motor is destroyed or damaged?
A person will lose both voluntary and reflex control over the motor unit (muscle) it controls and paralysis occurs.
151
What doe the autonomic nervous system control?
All the involuntary systems of the body, particularly the internal organs and the blood vessels.It is extremely differential to influence the autonomic system using the conscious brain although it can be done
152
What can influence how autonomic systems function?
Strong emotions.
153
What receptors are the most autonomic sensory neurones?
interoceptors.
154
What can intense activation of interoceptors cause?
For example, the pain sensations felt in angina pectoris. - the angina pain sensation is relayed into the autonomic nervous system by autonomic sensory neurones.
155
What two distinct and opposite systems is the autonomic system divided anatomically into?
The sympathetic and parasympathetic systems.
156
What is the sympathetic system?
Largely excitatory, the impact of the sympathetic systems clearly seen in the fight or flight response: it tends to speed up the heart and breathing rate and cause a rise in blood pressure.
157
What is the parasympathetic system?
Largely inhibitory, stimulation tends to slow down the heart and breathing rate and lower blood pressure. the many branches of the vagus nerve make up the major part of the parasympathetic system.
158
What function can the sensation of pain serve?
The sensation of pain may serve a protective function by indicating the presence of noxious, tissue damaging conditions.
159
What is pain detected by?
Nociceptors which are especially common in and just under the skin, in joint capsules and within the perineum membrane surrounding bones.
160
How are nociceptors activated?
Nociceptors are activated by specific substances released from damaged tissue - it is probabale that a number of chemical agents called algogens (pain producing substances)are released following injury to tissue.
161
What is agents are included in algogens?
ATP, bradykinin, histamine, serotonin, hydrogen ions and inflammatory mediators such as prostaglandins.
162
What is pain conveyed by?
Specific sets of sensory nerve fibres rather than by the massive stimulation of all sensory nerve fibres.
163
What two types of pain are there?
Fast and slow.
164
What is fast pain detected by?
The perception of fast pain occurs very swiftly after a stimulus such as a knife cut of skin being punctured by a needle. it is detected by A-delta nociceptors which are connected to myelinated A--delta nerve fibres - fast pain is not felt in the deeper tissues of the body.
165
When does slow pain perception begin?
A second or more after a stimulus is applied.
166
What detected slow pain?
Slow pain is detected by C-polymodal nociceptors and is conducted along unmyelinated C nerve fibre
167
What is slow pain often referred to as?
Throbbing, burins or aching pain.
168
What does C fibre sensations cause?
C fibre sensations cause the thalamus to become activated, the individual is aware of the pain sensation but only has a general idea of the area affected.
169
What do the sensory neurones that bring pain sensations into the CNA release as neurotransmitters?
Glutamate or substance P.
170
What is chronic pain known as?
Continued release of nerotransmitters can lead to slow pain which lasts for a few days, weeks or even months, way beyond the normal time for the healing process, this is known as chronic pain.
171
PAIN PROCESSING IN THE BRAIN:
| Where do impulses from nociceptors travel?
Travel up the spinal core ending up in various ears in the brain stem concerned with pain perception.
172
When impulse from nociceptors travel up the spinal cord ending up in various areas in the brain stem concerned with pain perception, the stimulation is processed here and send to which two brain areas?
The cortex (via the thalamus) and the limbic system deep inside the cerebrum.
173
What occurs in the cerebral cortex and the limbic system parts of the brain?
The cerebral cortex is the shining part of the brain where awareness of the unpleasant pain sensation is generated and awareness develops while the limbic system generates emotional responses such as sadness, tears and anger.
174
How can the level of pain felt be reduced?
The level of pain felt can be reduced by the release of peptides such as endorphins and enaphapine within the CNS.
175
These peptides are neuromodulators, what are these?
These are substances that do not act directly as neurotransmitters but increase or decrease the action of neurotransmitters.
176
What are neuromodulators structurally similar to?
Morphine.
177
Where are neuromodulators found?
They are faint in the limbic system the hypothalamus and the brainstem and they have powerful analgesic effects.
178
Where are impulses from the brain passed down?
Impulses from the brain are passed down descending nerve fibres to spinal ganglia where they can modular the incoming pain pathways.
179
What is the gate control theory of pain?
A normal pain response is self limiting, the brain quickly suppresses nerve pathways in the spinal cored while the deeper ache of the C-firbes resolves more solidly as tissue repair proceeds and inflammatory chemical disappear. This is the self regulating system down as the gate control therapy of pain.
180
What closes the gate, stopping pain transmission?
The defending nerve impulses generated by the brain close the gate, stopping pain transmission.
181
What can failure of the descending nerve impulses generated by the brain lead to?
Chronic pain, which persists after the removal of the cause of after completion of the healing process.
182
The nervous system allows us to respond to changes in both the world around us and in out body systems - to make these responses the CNS needs information about changes in the environment from what?
The sensory receptors which are often found together in sense organs -
183
What do the sense organs respond to and do?
Sense organs respond to changes in the environment and send impulses that travel along the sensory neurones to the CNS
184
What are the 5 main sensory systems in the body?
- Sight - the eyes.
- Sound and balance - the ears.
- Touch/pressure proprioception (special awareness of body position), temperature and pain - sensory receptors in the joints,skin, muscles and semi-circular canals of the ears.
- Taste - the tongue, closely linked to the sense of smell.
- Smell - the nose, closely linked to the sense of taste.
185
Where are the eyes positioned? How much is exposed and protected?
In a protective bony socket at the front of the skull. In the human, 80% of the eye is protected in this way, leaving 20% exposed to the outside world?
186
What allows for both voluntary and involuntary coordinated movement of each eye independently?
Three pairs of muscles attached to the outer coat of the eye allow for both voluntary and involuntary coordinated movement of each eye independently. Allowing us go focus both eyes on the same object.
187
What function do the eyelids have?
The eyelids protect the eyes from physical damage and spread tears as lubrication over the surface of the eye.
188
Where are tears made? what do they contain?
Tears are made in the lachrymal glands. They produce a salty fluid which also contains an antibacterial enzymes called lysozyme.
189
When light enters the eye, what is it bent or refracted by?
By the cornea through the pupil, the opening in the iris.
190
After light is refracted by the cornea, it passes through the lens (located behind the pupil) what does this do?
This fine tunes the focusing, bending the focused light onto the retina.
191
What does the retina contain?
The retina contains light sensitive cells called rods, which give black and white vision and sensitive to low light levels. And cones which give colour vision and clear focus in bright light.
192
When light fall on the retina, what does it cause in the light sensitive cells of the rods and cones of the retina?
Chemical changes.
193
What do the chemical changes in the cones and rods of the retina result in?
The chemical changes result in nerve impulses that are carried through the optic nerve to the visual cortex in the occipital lobe of the cerebral cortex of the brain, where the image is interpreted.
194
The eye issues a very complex sense organ comprising of which structures?
Sclera, cornea, chorus, aqueous humour, vitreous humous, lens, pupil, iris and retina.
195
What is the sclera? What does it do?
The outer coat of the eye (the white of the eye) The sclera protects the more sensitive underlying structures and preserves the shape of the eyeball.
196
What is the sclera attached to?
The optic muscles are attached to the sclear.
197
What is the cornea?
The cornea is at the front of the eye. The sclera converts into a transparent tissue called the cornea which bends (refracts or focus) the light coming into the eye towards the retina.
198
What is the choroid?
The middle layer of the eyeball containing blood vessels.
199
Where is the aqueous humous found and what do it do?
This fill the front (anterior) chamber of the eye and helps to refract incoming light rays.
200
What is the vitreous humour?
A transparent jelly which fills the whole back (posterior) chamber of the eye
201
What is the lens?
This changes shape to focus light onto the retina - it gives the fine focusing that enables us to see clearly.
It is short and fat to focus light from close object and long and thin to focus light from distant objects which needs less bending to bring them into focus.
202
What is the pupil?
The pupil is the hole in the middle of the iris. which changes diameter to control the amount of light entering the eye - in bright light the muscles of the iris shrined the pupil to limit the amount of light entering the eye. In dim light the muscles of the iris expand the pupil to allow more light in.
203
What is the iris?
A pigmented muscular diaphragm which controls the amount of light entering the eye by changing the diameter of the pupil.
204
What is the retina?
The retina contains the light sensitive cells, rods and cones. Each retina contains about 120 million rods and six million cones. Rods remain sensitive at low light levels are are more numerous at the edge of the retina. Cones are only stimulated by bright light. They are more numerous int he centre of the retina which is where objects can be brought into sharp focus.
205
The ear is two organs in one - what are these?
The organ of hearing and the organ of equilibrium (balance)
206
In order to hear, what needs to happen?
Sound waves from the outside need to be transmitted to the sensory receptors in the cochlea and then into nerve impulses in the auditory nerve to the brain, which then interpret the sound coming from the world.
207
The ear is divided into three parts, the outer ear, the middle ear and the inner ear. What is the outer ear made up of?
The outer ear is made up of the ear flap or pinna, and the outer ear (auditory) canal, which end at the eardrum.
208
What does the pinna do?
The pinna collects sound waves which travel down the external auditory cancel.
209
What is the canal protected by?
Hairs and also modified sebaceous glands which's secrete wax called cerumen.
210
What us the eardrum known as and what do it do?
The eardrum or tympanic membrane vibrates as sound waves hit it and passes these vibrations on into the middle ear.
211
Where is the middle ear?
The middle ear is the cavity between the eardrum and the inner ear.
212
What does the middle ear contain?
The ear ossicles, the three smallest bones in the body: the malleus (hammer), incus (anvil) and stapes (stirrup).
213
When the eardrum receives vibrations traveling up the auditory canal, what happens next?
It transferred to the tiny ossicles. They rock against each other to transfer the vibration to the oval window, the port into the inner ear, the eardrum is about 15 times larger than the oval window which amplifies the vibrations.
214
What is the inner ear? what does it contain?
The inner ear is a maze of bony chambers called the bony labyrinth, including the snail like cochlea, which is filled with fluid and contains the actual organ of hearing, the organ of Corti. The inner ear also contains the semi circular canals.
215
The inner ear can be through of as two organs: The cochlea and the semi-circular canals: What does the cochlea do?
The cochlea converts sound pressure impulses from the outer ear into electrical impulses which are passed to the brain via the auditory nerve.
216
What do the semi-circular canals do?
They contain fluid which moves against sensory hairs as the body turns and moves - this stimulates sensory cells which send nerve impulse to the brain via vestibular nerve and act as the body balance organs giving the brain information about the orientation of the head.
217
Olfaction (sense of smell) is a chemical sense, what is the sensation of smell caused by?
The interaction of certain molecules with olfactory receptors.
218
What does the olfactory mucosa do and where is it located?
It senses smell and also some aspects of taste and is located in the roof of the nose.
219
How big is the olfactory mucosa and what does it contain?
In an area the size of a postage stamp, the nose has around 10-100 million receptors for smell.
220
What are the olfactory hairs?
The site of olfactory transaction (smell) is the olfactory hairs which are cilia that project from cell dendrites.
221
How many different chemicals or odours do humans have the ability to identify?
Around 10,000
222
What is the structure of the olfactory receptor cells?
They have a larger central bulge containing the nucleus and two further cytoplasmic extensions.
223
Where do the two cytoplasmic extensions on the olfactory receptor cells extend to?
One of these extends to the surface epithelium of the nose (to detect smell) and the other penetrates in the other direction into the basement membrane to send impulses to the brain.
224
Several ears of the brain are involved in the interpretation of smell, including what?
The limbic system and the hypothalamus.
225
Scents and smells (olfactory impressions) are long lasting and therefore...
Form part of out memories and emotions.
226
The olfactory senses are extremely sensitive and Therefore how many ned to be present in the air to be perceived as an odour?
Sometimes only a few molecules of a certain substance. Methyl mercaptan, which smells like rotten cabbage can be detected in concentrations as low as one part per billion of air.
227
What can occur rapidly to odours?
Adaption (decreasing sensitivity) to odours occurs rapidly.
228
What important region of the brain for odour recognition if damages can often have trouble identifying different odours?
The orbito-frontal area.
229
At what age do anatomical and physiological changes in the nervous system begin?
Around the age of 30.
230
What are common age related anatomical changes in the nervous system?
- A reduction in brain size and weight, primarily from a decrease in the size of the cerebral cortex.
- A reduction in the number of cortical neurones (the brain stem is far less affected)
- A decrease in blood flow to the brain caused by fatty deposits accumulating gradually in the walls of blood vessels.
- Changes to the synaptic organisation of the brain. In many areas the number of dendritic branches and interconnections appears to decrease. Many neurones accumulate intracellular deposits.
231
The age related anatomical changes in the nervous system in the brain contribute to conditions often lined to ageing such as what?
Senile dementia, Alcheimers disease and parkinsons disease.
232
For around what percentage of the population do these changes not interfere significantly with the elderly populations ability to function in society?
Around 80%
233
Therefore, around what percentage of elderly people are affected by changes in their brain function to varying degrees?
Around 20%
234
Cerebrovasular accident, CVA or stroke is the name given to an illness where what occurs?
An illness in which pat of the brain is damaged or destroyed because of their a thrombus or haemorrhage which affects the blood supply.
235
What is the result of a rhombus or haemorrhage?
The oxygen supply to the affected area is reduced or completely cut off resulting in a loss of function in those parts of the body that are normally under control of the damaged area.
236
What can result from a stroke?
Firstly the extent of the stroke depends on the extent of the area of the brain that is damaged. Secondly depdending not he nerve tracts affected, there could be facial contortion or paralysis as well as tactile speech and visual problems. Symptoms often affect only one side of the body and tend to reduce after a few days as brain swelling reduces. They may however be so extensive and affect so many vital functions that the patient dies.
237
What type of condition is Multiple sclerosis (MS)?
It is an autoimmune disease where the immune system attacks the myelin sheaths of the neurones.
238
What does damage to the myelin and its stripping off the nerve fibres either partially or completely cause?
It leaves scars known as lesions or plashes and the myelin damage disrupts impulse traveling along nerve fibres - they can slow down, become distorted, pass from one nerve fibre to another (short circulating) or not get through at all.
239
With MS, as well as myelin loss what can also occur
There can also sometimes be damage to actual nerve fibres - it is this nerve damage that causes the onset of disability that can progress over time.
240
What is the term dementia used to describe?
The term dementia is used to describe various different brain disorders that feature a loser of brain function that is usually progressive and eventually severe.
241
There are over 100 different types of dementias what are the most common?
Alcheimers disease, vascular dementia and dementia with Lewy Bodies.
242
What do symptoms of dementia include?
Loss of memory, confusion, problems with speech and understanding and loss of the ability to carry out normal function in everyday life.
243
What is epilepsy defined as?
A tendency to have recurrent seizures (fits).
244
What is a seizure caused by?
A sudden burst of electrical activity in the brain, causing a temporary disruption in the normal impulses passing between brain cells. and there are different types of seizure leading to different effects.
245
What may a person suffering from a seizure have?
They may have Movements they cannot control, unusual sensations of feelings or suffer loss of consciousness.
246
What are the reasons for epilepsy to develop?
Due to brain damage caused by an injury, stroke to infection of the brain. However for most people around 60% there is no known cause, this is called idiopathic epilepsy.
247
What are mental disorders?
Illnesses in this category can be classified as psychosis, a severe disruption of brain physiology where the patient loses touch with reality or a neurosis, where the patient is still suffering exaggerated behavour but is aware of their clinical condition.
248
What are affective (mood) disorders?
Mood disorders are emotional disturbances consisting of prolonged periods of excessive sadness, low mood, lack of enjoyment or pleasure of excessive joyousness, or both.
249
What are mood disorders and depressive disordered and bipolar disordered characterised by?
Mood disorders are categorised as depressive (unipolar) or bipolar. Depressive disorders are characterised by major depressive episodes and bipolar disorders are characterised by depressive episodes and manic episodes.
250
What is schizophrenia?
When someone cannot tell the difference between what is real and what is imaginary, they may be described as having a psychotic illness. The most common type of psychosis is schizophrenia.
251
What does schizophrenia involve?
It is different for each person, but usually involves a dramatic disturbance in thrust and feelings and results in behaviour that may seem off to other people. Some people only experience one episode of psychosis and some recover from it. For other it is a long term illness but a combination or medication and talking therapies can help to control it.
252
What are the symptoms of schizophrenia classified as?
Positive, negative or cognitive.
253
What are positive symptoms?
These can be quite frightening and include hallucinations and delusions, the most common hallucination is auditory where suffered report hearing voices.
254
What are negative symptoms?
These can include withdrawal, a lack of communication and drive or detachment from people, places, family and jobs.
255
What are cognitive symptoms?
These include difficulty in understanding information and using it to make decisions, trouble focusing or paying attention and problems with working memory - the ability to use information immediately after learning it.
256
What are personality disorders?
These are conditions in which a person is likely to think, feel or behave in a way that is different to most other people, leading to difficulties in making and maintaining friendships and other relationships. Leading to the sufferer feeling isolated and distressed.
257
What are the main categories of personality disorders?
Suspicious, emotional and impulsive and anxious.
258
What is a cataract?
Cataract form when the normally transparent lens of the eye becomes progressively more cloudy and opaque as protein deposits build up, it causes a gradual loss in sight.
259
What is glaucoma?
Normal pressure inside the eyeball is 15-20mm Hg. Glaucoma is an abnormal condition where pressure inside the eyeball increases. it is usually caused by an obstruction in the anterior chamber which contains the aqueous humour. It can reduce or bloc the blood flow to the retina ultimately resulting in blindness.
260
What is macular degeneration?
A common condition in older people when the central part of the retina, the macula stops working properly. Side vision is not lost but people affected can no longer focus clearly or see what is directly ahead of them.
261
What is Otitis usually classified as?
Otitis externa or otitis media.
262
What does Otitis external usually refer to?
Inflammation or infection of the external canal resulting from allergy, bacteria, fungi, viruses and trauma.
263
What does Otitis media refer to?
Inflammation or infection of the middle ear, it can be caused by allergy, bacteria or viruses and may be preceded by an upper respiratory infection.
264
What its sinusitis?
This is inflammation of the mucous membranes lining the air filled sinuses. It may cause pressure, pain, headache, fever and local tenderness.
265
What is anosmia caused by?
Most anosmia (loss of sense of smell) result from head injuries or the after effects of nasal inflammation, it may be caused by ageing or smoking. In some cases anosmia may be caused by psychological factors such as a phobia or fear associated with certain smells. In a third of cases it is caused by zinc deficiency and is easily corrected once a sin supplement is prescribed.
266
What do nasal polyps result from?
These result either from chronic infective inflammation or chronic allergic inflammation. They consist of rounded elongated pieces of pulpy, connective tissue infiltrated with chronic inflammatory cells that project into the nasal cavity.
267
What are analgesics used for?
Analgesic medicines are used to relieve pain by interfering with the transmission of painful stimuli, either peripherally at the site of tissue damage or centrally where the painful stimulus are interpreted.
268
What are AChE inhibitors used for?
To improve some of the symptoms of relatively early alzheimer's disease and slow down the progression of the illness. No drug treatments can yet provide a cure for Alzheimers disease.
269
The symptoms of Parkinson's disease - typically tremor, slowness of movement and rigidity, occur because of what? How can medicines help?
The symptoms occur because levels of the neurotransmitter dopamine in the brain become too low. Medicines aim to increase the level of dopamine, prevent the dopamine that is produced in the body from being destroyed and stimulate the part of the brain where dopamine acts.
270
What is the objective of epilepsy treatment?
The objective is to stabilise the electrical activity of the brain and prevent seizures occurring - for about 8 in every 10 patients medication is very effective. Careful adjustment of the dose is required to avoid side effects.
271
What do hypnotics do?
Hypnotics are medicines that promote sleep - they include benzodiazepines, by far the most widely used hypnotic. Most anxiolytics (sedatives) will induce sleep when given at night and most hypnotics will sedate when given during the day. Prescriptions of these drugs is widespread for sleep disorders but dependence (both physical and psychological) and tolerance can occur.
272
What are antipsychotics used for?
To treat patients with schizophrenia, bipolar disorder, severe anxiety and depression, they affect neurotransmitters in the brain, especially dopamine and can be very effective at relieving symptoms.
273
How do antidepressants act?
By increasing the synaptic concentration of the neurotransmitters serotonin and or noradrenaline in the brain. They are effective in the treatments of moderate and major depression also ffective for lower grade chronic depression, not generally effective in milder forms of acute depression.
274
What is the most widely prescribed anti depressant medicine?
Selective serotonin re-uptake inhibitors (SSRIs)
275
What are motifs used to treat?
Glaucoma - they help improve the drainage of the aqueous humour and so lower pressure inside the eye - this reduces the risk of long-term damage and blindness.
276
What can antibiotics be used to treat?
Any bacterial infection of the nervous system including otitis media, and sinusitis.
