The Mammalian Nervous System Flashcards
(126 cards)
1
Q
What are neurones?
A
Cells specialised for the rapid transmission of impulses throughout an organisms
2
Q
What are receptor cells?
A
Specialised neurones that respond to changes in the environment
3
Q
What are effector cells?
A
Specialised cells that bring about a response when stimulated by a neurone
4
Q
What are the simplest nervous systems made up of?
A
Receptor cells, neurones and the nerve endings associated with effectors
5
Q
What are sense organs?
A
Groups of receptors working together to detect changes in the environment such as the eyes and ears
6
Q
What are sensory neurones?
A
Neurones that only carry information from the internal or external environment into the central processing areas of the nervous system
7
Q
What is the central nervous system? (CNS)
A
A specialised concentration ot nerve cells where incoming information is processed and from where impulses are sent out through motor neurones which carry impulses to effector organs. E.g. in vertebrates it consists of the brain and spinal cord
8
Q
What is an axon?
A
The long nerve fibre of a motor neurone which carries the nerve impulse. It carries it away from the cell body
9
Q
What is a dendron?
A
The long nerve fibre of a sensory neurone which carries the nerve impulse. It carries it towards the cell body
10
Q
What are nerves?
A
Bundles of nerve fibres called axons or dendrons. Some are motor nerves which only carry motor fibres. Some are sensory nerves which only carry sensory fibres and some carry a mixture of both
11
Q
What is the peripheral nervous system?
A
It includes the parts of the nervous system that spread through the body and are not involved in the central nervous system
12
Q
What are nerve impulses?
A
The electrical signals transmitted through the neurones of the nervous system
13
Q
What is the structure of neurones?
A
- They have a cell body that contains the cell nucleus, mitochondria, other organelles and the rough endoplasmic reticulum (ER) and the ribosomes which are needed for the synthesis of neurotransmitter molecules.
- The cell body has slender finger like processes called dendrites that connect to neighbouring nerve cells.
- the most distinctive feature of all nerve cells is the nerve fibre which is extremely long and carries the nerve impulse
14
Q
What do connecter neurones do?
A
They connect motor and sensory neurones
15
Q
Where are connector neurones found?
A
In the CNS
16
Q
Why are connector neurones also known as bipolar neurones?
A
Because two fibres leave the same cell body
17
Q
What is the current model of a nerve impulse?
A
A minute electrical event due to charge differences between the outside and inside of the neurone membrane. It is based on ion movement through specialised protein pores and by an active pumping mechanism
18
Q
What is the schwann cell?
A
A specialised type of cell associated with myelinated neurones. It forms the myelin sheath
19
Q
What is the myelin sheath?
A
A fatty insulating layer around some neurones produced by the shwann cell
20
Q
What are the nodes of ranvier?
A
Gaps between the Schwann cells that enable saltatory conduction
21
Q
What are the two reasons the myelin sheath is important?
A
It protects the nerves from damage and speeds up the transmission of the nerve impulse
22
Q
What does the speed at which the nerve impulses can be carried depend on?
A
- the diameter of the nerve fibre. The thicker the fibre the quicker the impulse travels
- the presence of a myelin sheath. Myelinated nerve fibres carry impulses much faster than unmyelinated ones
23
Q
Invertabrates do not have myelin sheaths. How do they get quick nerve impulses when they need to react quickly?
A
Many invertebrate groups have evolved a number of giant axons with diameters of around 1mm which allow nerve impulses to travel fast
24
Q
Why is much of the work into how axons work done of giant axons from invertebrates?
A
- they are relatively easy to work with
* fewer ethical issues with working with invertebrates
25
What is the effect of a myelin sheath?
To speed up the transmission of the nerve impulse without the need for giant axons
26
Taking into consideratuon that nerve impulses are electrical events what would be an effective way of investigating them and how is this shown with early work on nerve impulses?
One of the most effective ways is to record and measure tiny electrical changes.
Early work was done using a pair of recording electrodes placed on a nerve which was then given a controlled stimulus. The impulses that resulted were recorded by electrodes and displayed on a screen. External electrodes however recorded the response of the entire nerve so the results of the recordings can be difficult to interpret correctly
26
Taking into consideratuon that nerve impulses are electrical events what would be an effective way of investigating them and how is this shown with early work on nerve impulses?
One of the most effective ways is to record and measure tiny electrical changes.
Early work was done using a pair of recording electrodes placed on a nerve which was then given a controlled stimulus. The impulses that resulted were recorded by electrodes and displayed on a screen. External electrodes however recorded the response of the entire nerve so the results of the recordings can be difficult to interpret correctly
27
Why are motor axons easier to access than sensory nerve fibres?
Because sensory nerve fibres often run from a sense organ in the head directly to the brain or from individual sensory receptors in the skin to the spinal cord making them difficult to access. Motor axons often run directly into muscles often in latge motor nerves this makes them relatively easy to get at and the effect of stimulating them can be seen immedietly with the twitch of a muscle
28
What technique is now used to study nerve fibres?
Using internal electrodes as well as external ones
29
What is the basis of the nerve impulse?
The concentration of sodiym ions, potassium ions and other charged particles is different from that inside the axon
30
What does the difference in permeability if the cell surface membrane to sodium and potassium ions give axons? And what is the axom membrane permeable and impermeable to?
The difference in permeability gives it special conducting properties.
It is relatively impermeable to sodium ions but quite freely permeable to potassium ions
31
What is the resting potential?
The potential difference across the membrane of around -70 mV when the neurone is not transmitting an impulse
32
How is the resting potential of a neurone created?
The extracellular concentration of ions is greater than the concentration in the axons cytoplasm. This gradient is created by an active sodium/potassium pump. This pump has an enzyme called Na+/K+ ATPase that uses ATP to move sodium ions out of the axon and potassium ions into the axon, lowering the concentration of sodium ions inside the axon and due to the relative impermeability of the membrane to the sodium ione they cannot move back in. At the same time pitassium ions are actively moved into the axon by the pump but then passively diffuse out again along the concentration gradient through open potassium ion channels. As a result the inside of the cell is left slightly negative to the outside and the membrane is polarised
33
When an impulse travels across an axon what is the ket event and why does this occur?
The key event is a change in the permeability of the cell membrane to sodium ions. This change occurs in response to a stimulus - for example light, sound, touch, taste or smell in a sensory neurone or the arrival of a neurotransmitter in a motor neurone. In the experimental situation the stimulus is usually a minute and precisely controlled electrical impulse
34
What is a neurotransmitter?
A chemical which transmits an impulse across a synapse
35
What are sodium gates?
Specific sodium ion channels in the nerve fibre membranes that open up when a neurone is stimulated allowing sodium ions to diffuse rapidly doen their concentration gradients and electrochemical gradients.
36
What is depolarisation?
The condition of the neurone when the potential difference across the membrane is briefly reversed when the neurone is stimulated during an action piteikntual with the cell becoming positive on the inside with respect to the outside for about 1 millisecond
37
What is the action potential?
Whe the potential difference across the membrane is briefly reversed to about +40mV on the inside with respect to the outside for about 1 millisecond
38
What happens at the end of the brief depolarisation?
The sodium ion channels close again and the excess sodium ions are rapidly pumped out by the active sodium pump. Also the permeability of the membrane to potassium ions is temporarily increased as voltage-dependent potassium ion channels open as a result of the repolarisation. As a result potassium ions diffuse out of the axon down their concentration gradient and electrochemical gradient attracted by the negative charge on the outside of the membrane. The inside of the axon becomes negative relative to the outside again
39
What is the threshold?
The point when sufficient sodium ion channels open for the rush of sodium ions into the axon to be greater than the outflow of potassium ions, resulting in an action potential
40
What is the refractorary period and what does it depend on?
The refeactory period is the time it takes for ionic movements to repolarise an area of the membrane and restore the resting potential after an action potential
It depebds both on the sodium/potassium pump and on the membrane permeability to potassium ions
41
What is the absolute refractorary period?
The first millisecond or so after the action potential when it is impossible to re-stimulate the fibre - the sodium ion channels are completely blocked and the resting potential has not yet been restored
42
What is the relative refractorary period?
A period of several milliseconds after an action pitentual and the absolute refractorary period when an axon may be stimulated but only by a much stronger stimulus than before. The threshold has effectively been raised
43
Why is the refractorary perjod important in the functioning of the nervous system as a whole,
It limits the rate at which impulses may flow along a fibre to 500-1000 each second. It also ensures that impulses only flow one direction across the nerve. Until the resting potential is restored the part of the nerve fibre that the impulse has just left cannot conduct another impulse. This means the impulse can only continue travelling in the same direction
44
Why do action potentials appear to jump from node to node in myelinated neurones?
Because ions can only pass in and out of the axons freely at the nodes of ranvier this means that action potentials can only occur at the nodes so they appear to jump from one to the next. The effect of this is to speed up transmission as the ionic movements associated with the action potential occur much less frequently taking less time. It is known as saltatory conduction
45
What is a synapse?
The junction between two neuroned that nerve impulses cross via neurotransmitters
46
What is a synapyic knob?
Synaptic knobs are the bulges at the end of the presynaptic neurones where the neurotransmitters are made
47
What are two neurones linked by?
A synapse
48
What is the path from receptor to effector?
Receptors pass their information to the sensory nerves which then relay the information to the CNS. Information needs to pass freely around the CNS and the impulses sent along the motor nerves must be communicated to the effector organ so action can be taken
49
What does the functioning of synapses depend on?
The movement of calcium ions
50
What happens when an impulse arrives at the synaptic knob?
* It increases the permeability of the presynaptic membrane to calcium ions as calcium ion channels open up. Calcium ions then move into the synaptic knob down their concentration gradient.
* This causes the synaptic vesicles which contain a neurotransmitter to move to the presynaptic membrane and release ybe transmitter substance into the synaptic cleft.
* These molecules diffuse across the gap and become attached to specific protein receptor sites on the sodium channels of the post-synaptic membrane.
* This opens sodium ion channels in the membrane resulting in an influx of sodium ions into the nerve fibre, causing a change in the potential difference across the membrane and an excitatory post - synaptic potential (EPSP) to be set up. If there are sufficient if these EPSPs the positive charge in the post synaptic cell exceeds the threshold level and an action potential is set up which then travels along the post-synaptic neurone
51
What is the presynaptic membrane?
The membrane on the side of the synapse where the impulse arrives and from which the neurostransmitters are released
52
What are the synaptic vesicles?
Membrane bound sacs in the presynaptic vesicle which contain about 3000 molecules of neurotransmitter and move to fuse with the presynaptic membrane when an impulse arrives in the presynaptic knob
53
What is the synaptic cleft?
The gap between pre-synaptic and post-synaptic membranes
54
What is the synaptic cleft?
The gap between pre-synaptic and post-synaptic membranes
55
What is the excitatory post-synaptic potential (EPSP)?
The potential difference across the post-synaptic membrane caused by an influx of sodiym ions in the nerve fibre as the result of the arrival of neurostransmitter on the receptors of the post synaptic membrane that makes the inside more positive than the normal resting potential, increasing the chance of a new action potential
56
What is the inhibitory post - synaptic potential?
The potential difference across the post-synaptic membrane caused by an influx of negative io s as the result of a molecule of neurotransmitter on the receptors of the post synaptic membrane, which makes the inside more negative than the normal resting potential, decreasing the chance of a new action potential
57
What happens once the transmitter has an effect?
It is destroyed by enzymes in the synaptic cleft so that the receptors on the post-synaptic membrane are emptied and can react to a subsequent impulse
58
What us acetylcholine?
A neurotransmitter found in the synapses of motor neurones, the parasympathetic nervous system and cholinergic synapses in the brain. It usually results in an excitation
59
Where is acetylcholine synthesised?
In the synaptic knob using ATP produced in the many mitochondria present
60
What are cholinergic nerves?
Nerves that use acetylocholine as the neuortransmitter in their synapses
61
What is acetylcholinesterase?
An enzyme found embedded in the post-synaptic membrane of cholinergic nerves that breaks down acetylcholine in the synapses after it has triggered a post-synaptic potential
62
What is acetylcholine broken down into and what happens to these?
It is hydrolysed by acetylcholinerase into acetate and choline. The components diffuse across the synaptic cleft down a concentration gradient and are taken back into the synaptic knob through the presynaptic membrane. In the presynaptic knob they are synthesised into more acetylcholine
63
What is noradrenaline?
A neurotransmitter found in the synapses of the sympathetic nervous system and adrenergic synapses of the brain. It is used often in the sympathetic nervous system and in adrenegenic synapses in the brain
64
What are adrenergic nerves?
Nerves that use noradrenaline as the neurotransmitrer in their synapses
65
What does the binding of noradrenaline to the receptors in the post-synaptic membrane depend on? What happens if levels are low?
The concentration of neurotransmitter in the synaptic cleft. As the release of noradrenaline from the presynaptic knob stops levels in the synaptic cleft fall. Noradrenaline is then released from the post synaptic receptors back into the synaptic cleft. Up to 90% of the noradrenaline is then taken up by the presynaptic knov where much of it is repacked and reused
66
What are the main effects that drugs have on increasing the effect of synapses?
* increases rhe amount of neurotransmitter synthesised
* increases the release of neurotransmitter from the vesicles at the presynaptic membrane
* Binds to post synaptic receptors and activates them or increases the effect of the normal transmitter
* prevents the degradation of neurotransmitters by enzymes or prevents reuptake into presynaptic knob
67
What are the main effects that drugs have on increasing the decreasing the response of synapses?
* blocks the synthesis of neurotransmitter
* causes neurotransmitter to leak from vesicles and be destroyed by enzymes
* prevents the release of neurotransmitter from vesicles
* blocks the receptors and prevents neurotransmitter binding
68
How does nicotine have an effect on the nervous system?
It mimics the effect of acetylcholine and binds to specific acetylcholine recpetors in post-synaptic membranes known as nicotine receptors. It triggers an action-potential in the post-synaptic neurone, but the receptor remains unresponsive to more stimulation for some time. Nicotine causes raised heart rate and blood pressure. Ut also triggers the release of another neurotransmitter in the brain called dopamine. This is associated with pleasure sensations. At a low dose nicotine has a stimulating effect but at a high dose blocks the acetylcholine receptoes and can kill
69
How does lidocaine effect the nervous system?
It is used as a local anaesthetic. Lidocaine molecules block voltage gated sodium channels, preventing the production of an action potential in sensory nerves and so preventing you from feeling pain. It is also used to prevent heart arrhythmias by blocking sodium channels raising the depolarisation threshold. In this way it reduces or prevents early or extra action potrntuals from the pacemaker region that can cause arrhythmias
70
How does cobra venom have an effect on the human nervous system?
It binds reversibly to acetylcholine receptors in post-synaptic membranes and neuromuscular junctions between motor neurones and muscles. As a result muscles are not stimulated to contract and gradually the person affected becomes paralysed. When the toxin reaches the muscles involved in breathing it causes death. In very low concentrations however can relax the muscles of the trachea and bronchi in severe asthma attacks and so save lives
71
How does cobra venom have an effect on the human nervous system?
It binds reversibly to acetylcholine receptors in post-synaptic membranes and neuromuscular junctions between motor neurones and muscles. As a result muscles are not stimulated to contract and gradually the person affected becomes paralysed. When the toxin reaches the muscles involved in breathing it causes death. In very low concentrations however can relax the muscles of the trachea and bronchi in severe asthma attacks and so save lives
72
What is a primary receptor and how does it work?
A neruone with a dendrite that is sensitive to one particular stimulus. When the dendrite recieves a stimulus, chemical events occur that result in an action potential in the nerve fibre of the neurone
73
What is a secondary receptor and give an example
A secondary receptor consists of one or more complicated specialised cells (not neurones) that are sensitive to a particular type of stimulus. These cells synapsw with a normal sensory neurone which carries the impulse to the CNS. The retinal cells in the retina of the eye are an example of these secondary receptors
74
How do sensory receptors work?
* They have a resting potential that depends on maintaining the charge of the cell interior negative in relation to the outside by using membrane sodium pumps.
* when a receptor cell recieves a stimulus, sodium ions move rapidly across the cell membrane along concentration and electrochemical gradients and this sets up a generator potential
* a small stimulus results in a large generator potential, a large stimulus results in a small generator potential
* if the generator potential produced is large enough to reach the threshold of the sensory neurone, an action potential will result in that neurone
75
What is the process that is common in one form or another to most sensory receptors?
Stimulus -> local change in permeability -> generator potential -> action potential
76
What is convergence and give an example of when it is used
In sense organs such as the eye several receptors may synapse with a single sensory neurone. If the generator potential from an individual receptor cell is insufficient to set up a synapse the potentials from several may add together or summate and trigger an action potential. It is an important feature of the light-sensitive cells of the retina of the eye
77
What is convergence a useful adaptation for?
Increasing the sensitivity of a sensory system to low-level stimuli
78
Why are we aware of not only the differences between light and dark but also the varying degrees of light and shade?
A weak stimulus results in a low frequency of action potentials along the sensory neurobe. A strong stimulus results in a rapid stream of action potentials being fired along the the sensory neurone. Although each axon obeys the all or nothing rule in terms of each individual action potential a graded response is still possible giving information about the strength of the stimulus
79
Which wavelengths of electromagnetic radiation are our eyes sensitive to?
Between 400 and 700 nm
80
What is the brain?
The area of the CNS where information can be processed and from where instructions can be issued as required to give fully coordinated responses to a whole range of situations
81
What are the two main types of photoreceptors along the retina?
The rods and cones
82
What are rods?
The photoreceptors found in the retina which contain the visual pigment rhodopsin. They respond to low light intensities, give black and white vision amd are very sensitive to movement
83
What are cones?
Photoreceptors found in the forvea of the retina which contain the visual pigment iodopsin. They respond to bright light, give great clarity of vision and colour vision
84
What are secondary exteroceptors?
Cells that signal changes in the external environment such as the photoreceptors on the retina
85
When are rods usually used and how many of them are there?
They are usually used in low light intensities or at night. There are around 120 million in each eye
86
Why are rods very sensitive to both low light levels and to movements in the visual field?
Because often several of them synapse with the same sensory neurone so many small generation potentials can trigger an action potential to the CNS by summation
87
How many cones are there?
Around 6 million in each eye
88
Why do cones provide great visual acuity in bright light?
Because they are tightly packed in the forvea and each cone usually has it's own sensory neurone. It's only when light is focused directly on the forvea that the image is clearly in focus
89
What is the arrangement of the retina?
It appears to be 'back to front'. The outer segments are next to the choroid and the neruones are at the interior endge of the eyeball. The light has to pass through the synapses and the inner segments before reaching the outer segments containing the visual pigments. The reason for this is the origin of the retinal cells in the embryo and the way the eye is formed during embryonic development
90
How is rhodopsin formed?
From two components opsin and retinal. Opsin is a lipoprotein and retinal is a light-absorbing derivative of vitamin A
91
How do rods work?
* A.retinal exists as two different isomers: cis-retinal and trans-retinal
* when a photon of light hits a molecule of rhodopsin it converts the cis-retinal into trans-retinal. This changes the shape of the retinal, and puts a strain on the bonding between opsin and retinal. As a result the rhodopsin breaks up into opsin and retinal. This breaking up of the molecules is reffered to as bleaching.
* rod cells unlike most neurones are very permeable to sodium ions. Sodium ions move into the rod cell through sodium ion channels and the sodium/potassium pump moves them out again.
* when rhodopsin is bleached it triggers a cascade reaction that results in the closing of the sodium ion channels so the rod cell membrane becomes much less permeable to the sodium ions and fewer sodium ions diffuse into the cell. Meanwhile the sodium/potassiym pump continues to work at the same rate so the interior of the cell becomes very negative with respect to the outside. This hyperpolarization is known as the generation potential in the rod.
* the size of the generator potential depends on the amount of light hitting the rod and so the amount of bleaching that takes place.
* if it is large enough to reach the threshold or if several rods are stimulated at once neurotransmitter substances are are released into the synapse with the bipolar cell which synapses both the photreceptor and the nerve fibre. An action potential is set up in the bipolar cell which passes across the synapse to cause an action potential in the sensory neurpne. All the sensory neurones leave the eye at the same point to form the optic nerve leading to the brain.
92
What happens after a rod is used?
After rhodopsin has been bleached the rod cannot be stimulated again until the rhodopsin is resynthesised. It takes ATP produced by the many mitochondria in the inner segment of the rod to to convert the trans-retinal back to cis-retinal and rejoin it to the opsin to form rhodopsin again
93
What does it mean when the eye is said to be light adapted?
When in normal daylight the rods are almost entirely bleached and can no longer respond to dim light
94
What does it mean when the eye is dark - adapted?
After about 30 minutes in the darkness the rhodopsin will be fully reformed and so the eye is sensitive to dim light
95
How do cones work?
In a very similar way to rods except their visual pigment is known as iodopsib. There appear to be three types of iodopsin each sensitive to one of the primary colours of light. Iodopsin needs to be hit with more light energy than rhodopsin in order to break down and so is not sensitive to low light intensities. The cones provide colour because the brain interprets the numbers of different types of cones stimulated as different colours
96
What does the CNS include?
* the brain where information can be processed and from where instructions can be issued as required to give fully coordinated responses to a whole range of situations
* the spinal cord which careies the nerve fibres into and out of the brain and also coordinates many unconcious reflex actions
97
What are the three distinct areas in the baisic brain pattern?
* forebrain: contains olfactorary lobes and in higher vertebrates forms the cerebral hemispheres
* midbrain: contains the optical lobes
* hindbrain: forms the cerebellum and the medulla
98
What is the cerebrum?
The area of the brain responsible for conscious thought, personality, control of movement ect.
99
What are the cerebral hemispheres?
The two parts of the cerebrum joined by the corpus callosum
100
Why is the original simple areangement of the brain very difficult to see in humans?
Because the cerebrum is folded back over the entire brain
101
What is grey matter?
It consists of the cell bodies of the neurons in the CNS
102
What is white matter?
It consists of the nerve fibres of neurones in the CNS
103
Why does the left hand side of the brain control the right side of the body and vice versa?
Because the great nerve tracts from the spinal cord cross over as they enter and leave the brain
104
What is the outer layer of the cerebrum?
The cerebral cortex
105
Give features of the cerebral cortex
* is made up almost entirely of grey matter- nerve cell bodies, dendrites and synapses
* deeply folded to give a huge surface area
106
What is the corpus callosum?
The band of axons (white matter) that join the left and right cerebral hemispheres of the brain
107
What are the left and right cerebral cortexes divided into?
A number of lobes whifh have been found to be associated with a number of functions
108
What is the frontal lobe associated with?
The higher brain functions such as emotional responses, planning ahead, reasoning and decision making
109
What does the hypothalamus do?
* Coordinates the automatic nervous system. •It plays a major part in thermoregulation and osmoregulation.
* It monitiors the chemistry of the blood
* controls hormone secretions in the pituitary gland
* controls many basic drives such as thirst, hunger, aggresion and reproductive behaviour
110
What does the cerebellum do?
Coordinates smooth movements. It uses the information from the muscles and the ears to control balance and maintain posture
111
What does the medulla oblongata do?
It is the most primitive part of the brain. I5 contains reflex centres that control functions such as the breathing rate, heart rate, blood pressure, coughing, sneezing, swallowing, saliva production and peristalsis. This region maintains the basic life responses
112
What is the structure of the spinal cord?
* it is a tube made up of a core grey matter surrounded by white matter which runs out from the base of the brain through the vertebra
* it is approximately 43-45cm long.
113
How are messages translated from the spinal cord to the brain a vice versa?
* impulses from sensory receptors travel along sensory nerve fibres into the spunal cord through the dorsal roots and then travel up the cord to the brain
* Instructions from the brain travel as impulses down motor fibres in the spinal cord and out in motor neurones through the ventral roots to the effector organs
114
What are reflex responses?
Rapid responses that take place with no conscious thought involved
115
What is a reflex arc?
The simplest type of nerve pathway in the body. In veertebrates this includes a receptor, a motor neurone, sensory neurone and sometimes a relya neurone located in the CNS. The function of the reflec arc is to bring about an appropriate response to a particular stimulus as rapidly as possible without the time delay that occurs when the conscious centres become involved
116
What are the two main type of reflexes?
* spinal reflexes, e.g. hand withdrawing from a hot object
| * cranial reflexes, e.g. blinking
117
How do you know that you have just performed a reflex action?
Sensory neurones will aldo relay information to the conscious areas of the brain so you know what had happened
118
What is the role of the peripheral nervous system?
Changes in the internal or external environment picked up by sensory receptors must be carried to the CNS and instructions from the CNS must be carried to the effector organs for nervous coordination to work
119
What are the two systems of the peripheral nerves?
* the voluntary nervous system
| * the autonomic nervous system
120
What does the voluntary nervous system involve?
Motor neurones that are under voluntary or conscious control involving the cerebrum. Voluntary motor neurones function as a result of conscious thought. When you consider an action the instructions that need to be issued to the muscles will be carried along the voluntary nerve fibres
121
What does the automatic nervous system involve?
Motor neurones that are not under the control of the conscious areas of the brain. They control bodily functions that are normally involuntary. E.g. control of the heart, breathing rate, the movements and secretions of the gut, sweating ect.
122
What can the automatic nervous system be subdivided into?
The sympathetic nervous system and the parasympathetic nervous system
123
What are the structural similiarities and differences between the parasympathetic and sympathetic nervous systems?
* in both of them myelinated preganglionic fibres leave the CNS and synapse in a ganglion (a collection of cell bodies) with unmyelinated post-ganglionic fibres
* in the sympathetic nervous system the ganglia are very close to the CNS so the preganglionuc fibres are very short and the post ganglionic fibres are long
* in the parasympathetic system the situation is reversed. The ganglia are near or in the effector organ so the preganglionic fibres are long amd the postganglionic fibres are short
124
What are the two functional differences beteen the sympathetic and the parasympathetic nervous systems?
* the sympathetic nervous system produces noradrenalune at the synapses and usually produces a rapid respinse in the target organ system. This is why it is sometimes referred to as the fight or flight syste.
* the parasympathetic nervous system often has a slower, damping down or inhibitory affect on organ systems and the neurotransmitter produced at the synapses is acetylcholine. The parasympathetic system maintains normal functioning of the body and restores calm after a stressful situation
125
Do the sympathetic and parasympathetic nervous systems act antagonistically or synergetically and give an example
Antagonistically. E.g. the sympsthetic system speeds up the breathing rate and heart rate whilst the parasympathetic system slows it down
