The mammalian nervous system Flashcards
What is the nervous system made up of
Interconnected neurons specialized for the rapid transmissions of impulses throughout the body
What do neurons carry
Impulses from special receptor cells and specialized effector cells
Where are sense organs
Eyes, ear
What are sensory neurons
Neurons that only carry information from the internal or external environment into the central processing areas of the nervous system
What happens as animals increase in size and complexity
They develop more specialized concentrations of nerve cells, which form the central nervous system
What is the central nervous system (CNS)
Incoming information from sensory neurons is processed, and from where impulses are sent out through motor neurons
Where is the CNS in vertebrates
Brain and spinal cord
What are neurons made up of
Individual cells and each one has a long nerve fibre that carries the nerve impulse
What are nerves
Bundles of nerve fibres called axons and dendrons
What are:
motor nerves
sensory nerves
Nerves that only carry motor fibres
Nerves that only carry sensory fibres
What is the peripheral nervous system (PNS)
The parts of the nervous system that are not within the central nervous system
What are neurons
The basic unit of a nervous system
What are nerve impulses
Neuron cells specialized in the transmission of electrical signals
What is the structure of a neuron
Why does it contain these components
The cell body contains: cell nucleus mitochondria RER Needed for the synthesis of the neurotransmitter molecules
What are dendrites
What does it do
The cell body of the neurons have slender finger-like processes
connects to the neighboring nerve cells
What is the most distinctive feature on a nerve cell
How does it look
Nerve fibre
extremely long and thin and carries the nerve impulse
What are axons
Fibres that carry impulses away from the nerve cell body
What are dendrons
Fibres that transmit impulses towards the cell body
What connects the motor and sensory neurons
Short relay neurons that are found in the CNS
What does a Schwann cell do
What is a myelin sheath
The membrane wraps itself repeatedly around the nerve fibre, forming a fatty layer known as a myelin sheath
What are the nodes of Ranvier
Gaps between the Schwann cell
Give two reasons why the myelin sheath is important
1) It protects the nerves from damage
2) Speeds up the transmission of nerve impulse
What is the role of the nervous system
To quickly carry electrical impulses from one area of the body to another
What two factors do the speed at which impulses can be carried in the nervous system depend on
1) Diameter of the nerve fibre (The thicker the fibre, The more rapidly impulses travel)
2) Presence or absence of the myelin sheath (myelinated nerve fibes carry impulses faster)
Which of the two don’t have myelin sheath on the nerves:
Invertebrates
Vertebrates
Invertebrates hence the reason they travel so slow
In Vertebrate animals which neurons are myelinated
and which are unmyelinated
Voluntary motor neurons
Autonomic neurons
What is one of the most effective ways you can investigate nerve impulses
Nerve impulses are electrical so to record and measure the tiny electrical changes
What is the basis of nerve impulse
The fact that the concentration of sodium ions, potassium ions, and other charged particles outside the axon is different from the inside
Is the membrane of the axon permeable
YES
What gives the axon its special conducting properties
The difference in permeability of this membrane to positively charged sodium and potassium ions
Explain the partial permeability of the axon membrane
It’s impermeable to the sodium ions but quite freely permeable to potassium ions
When is the axon ‘at rest’
When it is not conducting a nerve impulse
What’s greater than the concentration in the cytoplasm of the axon
The extracellular concentration of ions
How is the gradient in the axon created
By a very active sodium/potassium ion pump
What enzyme does the sodium/potassium pump have and how does this help
Na+/K+ ATPase that uses ATP to move sodium ions out of the axon and potassium ions in
What is a resting potential
The potential difference across the membrane of around -70mV
What is the key event when an impulse travels along an axon
A change in the permeability of the cell membrane to sodium ions
What causes a change in the permeability of the cell membrane to sodium ions
Either response to a stimulus or the arrival of a neurotransmitter in a motor neuron
What happens when a neuron is stimulated
The axon membrane shows a sudden or dramatic increase in its permeability to sodium ions
When sodium gates open what does it allow to happen
Allows sodium ions to diffuse rapidly down their concentration and electrochemical gradient
How long does the depolarisation last
A millie second
What is the action potential
The potential difference across the membrane at this point
What happens at the end of the depolarization
Sodium ion channels close again and excess sodium ions are rapidly pumped out by the active sodium pump
Why do potassium ion channels open
As a result of repolarisation
What happens as a result of repolarisation
What happens to the axon after this
Potassium ions diffuse out of the axon down the concentration gradient and an electrochemical gradient attracted by the negative charge on the outside of the membrane
The axon becomes negatively charged relative to the outside
How can the event of the action potential be recorded
It can be recorded clearly using the internal/external electrode combinations you already have
What is the threshold for any nerve fibre
The point when sufficient sodium ion channels open for the rush of the sodium ions into the axon to be greater than the outflow of potassium ions
What happens once the threshold is reached
The action potential occurs
What is the refractory period
The time it takes for an area of the axon membrane to recover after an action potential, that is the time it takes for ionic movements to repolarise the membrane and restore the resting potential
What does the refractory period depend on
Both on the sodium/potassium pump and the membrane permeability to potassium ions.
What happens after the first millisecond or so after the action potential
What is this known as
it is impossible to restimulate the fibres
the sodium channels are completely blocked and the resting potential has not been restored
This is known as the absolute refractory period
What is the relative refractory period
After the absolute refractory period, there is a period where the action potential is restored for a millisecond and the threshold has been effectively raised
Why is the refractory period important in the functioning of the nervous system
It limits the rate at which impulses may travel to 500-1000 per second
ensures impulses flow in one direction along nerves
What cannot take place until the resting potential is restored?
The part of the nerve fibre that impulse has just left cannot conduct another impulse
What happens once the action potential is set up in response to the stimulus
It will travel the entire length of the nerve fibre
What is the movement of the nerve impulse along the fibre a result of
Local currents set up by the ion movements at the action potential itself
Why can’t the sodium ion channels behind the action potential open
Due to the refractory period of the membrane behind the spike
Where can ions pass through in the myelinated neurons
What does this mean
The node of Ranvier
This means that action potential can only occur at the nodes
What is the Saltatory conduction
Speed up the transmission as the ionic movements associated with the action potential occurs much less frequently, taking less time
Where must receptors pass their information
The sensory nerves, which in turn must pass the information to the CNS
What happens wherever two neurons meet
They are linked by a synapse
What is every cell in CNS covered with
Synaptic knobs from other cells
What increases the permeability of the presynaptic membrane to calcium ions as calcium ion channels open up
The arrival of an impulse at the synaptic knob
What is the effect of the influx of calcium ions
to cause the synaptic vesicles to move to the presynaptic membrane
What do some of the vesicles fuse with
The presynaptic membrane and release the transmitter substance into the synaptic cleft.
What opens the sodium channels
Molecules diffuse across the gap and become attached to specific protein receptor sites on the sodium channels of the post-synaptic membrane
What are the excitatory post-synaptic potentials (EPSP)
The potential difference across the post-synaptic membrane caused by an influx of sodium ions into the nerve fibres, as the result of the arrival of a molecule of a neurotransmitter on the receptors of the post-synaptic membrane that makes the inside more positive than the normal testing potential, increasing the chance of a new action potential
What are the inhibitory post-synaptic potentials (IPSP)
The potential difference across the post-synaptic membrane caused by an influx of negative ions as a result of the arrival of a molecule of neurotransmitters on the receptors of the post-synaptic membrane that makes the inside more negative than the normal testing potential, decreasing the chance of a new action potential
What is one of the most common neurotransmitters found in humans
acetylcholine (ACh)
Where is acetylcholine (ACh) synthesized
In the synaptic knob using ATP produced in the many mitochondria present
What are cholinergic nerves
Nerves using acetylcholine as their transmitters
What happens to the acetylcholine once it has done its job
It is rapidly hydrolyzed by the enzyme acetylcholinesterase
What happens once the neuroreceptors have bounded to the receptor and initiated a response
What does it ensure
It is rapidly hydrolysed into acetate and choline.
That it no longer affects the postsynaptic membrane and releases the components to be recycled
Where do the components rapidly diffuse
Across the synaptic cleft down a concentration gradient and are taken back to the synaptic knob through the presynaptic membrane
What happens in the presynaptic membrane
They are resynthesized into more acetylcholine
What is Acetylcholine
The neurotransmitter in all motor neuron, the parasympathetic nervous system, and cholinergic synapses in the CNS
What does nicotine do
Mimics the effect of acetylcholine and binds to specific acetylcholine receptors in post-synaptic membranes known as nicotinic receptors
What does nicotinic receptors trigger
An action potential in the post-synaptic neuron, but then the receptors remain unresponsive to more stimulation for some time
What does nicotine cause
What does it trigger
Causes raised heart rate and blood pressure
The release of another type of neurotransmitter in the brain called dopamine
What is dopamine associated with
Pleasure sensations
Is nicotine bad at high doses only
No even at low it releases a large amount of dopamine and still has a big effect on your acetylcholine
What is Lidocaine and when is it used?
A drug used as a local anesthetic
commonly used by dentists when drilling or removing a tooth
What does Lidocaine do
what two things does it prevent
Block voltage-gated sodium channels, preventing the production of an action potential in sensory nerves and so preventing you from feeling pain
What does Lidocaine block
It blocks sodium channels, raising the depolarization threshold
What is cobra venom
A substance made by several species of a cobra that is toxic and often fatal in snake bite
What does Cobra venom do?
It binds reversibly to the acetylcholine receptors in the post-synaptic membrane and neuromuscular junctions between motor neurons and muscles. Makes people paralyzed as a result
What happens once the toxin from cobra venom reaches the muscles involved in breathing
You will die
Is cobra venom always bad
No, in low concentrations it can relax the muscle of the trachea and bronchi in severe asthma attacks
What do sensory receptors play a vital role in
Providing an animal with information about both its internal and external environment
What are simple sensory receptors
Neurons with a dendrite that is sensitive to one particular stimulus
What happens when the dendrite in simple sensory receptors receive a stimulus
What is this type of cell known as
Chemical events occur that result in an action potential in the nerve fibre of the neuron
Primary receptor
What is a secondary receptor
It consists of one or more completely specialised cells that are sensitive to a particular type of stimulus
What do secondary receptor cells do
Give an example of a secondary receptor
These cells synapse with a normal sensory neuron, which carries the impulse to the central nervous system
The retinal cells in the retina of the eye
What happens to the sensory systems as animals become more complex
The sensory systems are more complex
What do receptor cells 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
What happens when receptor cells receive a stimulus
What does this generate
Sodium ions move rapidly across the cell membrane along with concentration and electrochemical gradient, and this sets up a generator potential
What happens if the generator potential is not large enough
There will be no action potential, the action potential obeys the all or nothing rule whereas the general potential doesn’t
What is the common process in most sensory receptors
Stimulus –> Local change –> Gernerator —-> action
in permeability potential potential
What happens if the generator potential for a single receptor cell is insufficient to set up a synapse
What is this known as
The potential from several may add together or summate and trigger an action potential
Convergence
What is Convergence useful for
It is a useful adaption for increasing the sensitivity of a sensory system to low-level stimuli
What does a weak stimulus result in
A low frequency of action potentials along a sensory neuron
What does a strong stimulus result in
What happens as a result of this
A rapid stream of action potentials being fired along the sensory neuron
The axon obeys the all or nothing rule in terms of action potential
What is our eye sensitive to
What does this allow
EM radiation with a wavelength of 400-700nm
It allows clear and sophisticated vision
What does the retina do
.Focusing light
.Preceive the light and provide the brain with info needed to make sense of the image
What does the retina contain
What are the two main ones
Photoreceptors (light-sensitive cells)
Rods and cones
What are rods and cons described as
Secondary exteroceptors- they signal changes in the external environment
Where are there no rods
In the fovea
What do rods provide
What are they mainly used for
Greyscale vision
To see low light intensities or at night
Why do rods not give clear vision
They are not tightly packed together and several of them synapse with the same sensory neuron
What can trigger an action potential to the CNS
Several small generator potentials
Where are cones found
How many cones are there
They are found tightly packed together in the fovea
6 million cones
What are cones
They are receptors in the retina that are used mainly for vision in bright light and they also provide color vision
Why do cones provide a great visual acuity in bright lights
They have tight packing in the fovea and has its own sensory neurons
Why is the arrangement of the retina seen as weird
It appears to be arranged back to front
Explain the structure of the retina
The outer segments are next to the choroid, and the neurons are the interior edge of the eyeball
The light needs to pass through the synapses and the inner segments before reaching the outer segments containing visual pigments.
What is the reason for the weird arrangement of the retina
The origin of the retinal cells in the embryo and the way in which the eye is formed during the embryonic development
What is the visual pigment in the rod
What is it formed from
rhodopsin (visual purple)
opsin and retinal
What is Opsin
A lipoprotein and retinal is a light-absorbing derivative of vitamin A
What two forms of retinal exists
What form is it in the dark
cis-retinal and trans-retinal
In the cis form in the dark
What happens to the cis-retinal when a small unit of light hits it
What effects does it have
It converts the cis-retinal to trans-retinal
It changes the shape of the retinal and puts a strain the bonding between the retinal and opsin
What are rod cell membranes permeable to
Sodium Ions
What is bleaching
The breaking up of the molecule rhodopsin
Explain how rods work?
What is hyperpolarisation known as
1) Sodium ions move into the rod cells through Sodium ion channels, and sodium pump moves them out again
2) When rhodopsin is bleached, it triggers a cascade of reactions that results in the closing of the sodium ion channels, so the rod cell membranes become much less permeable to sodium ions and fewer sodium ions diffuse into the cell
3) The sodium pump continues to work at the same rate, pumping sodium ions out the rod cell, so the interior becomes more negative than usual.
4) This hyperpolarisation is known as the generator potential in the rod
What does the size of the general potential depend on
The amount of light hitting the rod, and therefore the amount of rhodopsin bleaching that takes place
What happens if the general potential is large enough to reach the threshold
What is then set up
Neurotransmitter substances are released into the synapse with the bipolar cell
An action potential is then set up
What forms the optic nerve leading to the brain
All the sensory neurons leave the eye at the same point to form the optic nerve
Once the visual pigment has been bleached, When can the rod be stimulated
The rods cannot be stimulated again until the rhodopsin is resynthesised
How do you convert the trans-retinal back to cis-retinal
ATP produced by the mitochondria in the inner segment of the rod to convert the trans-retinal to cis-retinal and rejoin it to the opsin to form rhodopsin again
Why can’t rods respond to daylight
They are almost entirely bleached
What is the Cods visual pigment
iodopsin
How many types of iodopsin are there and what are they sensitive to
Three
Sensitive to one of the primary colors of light
How can iodopsin be broken down
If it hit it with light that has more energy than rhodopsin
How do cones provide color vision
The brain interprets the number of different types of cones stimulated by different colors
How did the brain form
As a swelling in the hallow neutral tube at the front or anterior end of a vertebrate embryo that folds back on itself
What are the three distinct areas of the brain
Forebrain, midbrain, and hindbrain
Why is the brain hard to see
The cerebrum is folded back over the entire brain
What is the brain made up of
Made up of a combination of grey matter, neuron cell bodies, and white matter
What does the brain contain
Centers or nuclei made up of cell bodies that make intercommunication between million of cells possible
What does the nerve from the spinal cord do and why
They cross over as they enter and leave the brain so that the left-hand side of the brain receives information from and control the righthand side of the body and vice versa
What does cerebrum consist of
Two cerebral hemispheres
How is the cerebrum described
The biggest and developer of the human brain
What abilities does the cerebrum give us
See, think learn and feel emotions
What does the cerebrum control
Our motor function (all the conscious movements)
Whats the outer layer of the cerebral and explain the structure
Cerebral cortex 2-4nm thick made up of grey matter nerve cell bodies dendrites synapses deeply folded to give a large surface area divided into lobes eg: frontal lobe
What is the corpus callosum
The left and right cerebral hemisphere are connected by a band of axons known as the corpus callosum
What does the hypothalamus do in the brain
Coordinates the autonomic nervous system and plays a major role in thermoregulation (Regulation of core temperature of the body)
monitors chemistry of the blood
controls hormone secretion in the pituitary gland
Controls thirst, hunger, aggression and reproductive
What does the medulla oblongata do
The most primitive part of the brain
contains reflux centers that control functions such as breathing rate, heart rate, blood [presusre and saliva production
What is the spinal cord
A tube made up of a core of grey matter surrounded by white matter, which runs out from the base of the brain through the vertebra
Approx. 43-45cm
What is an important function that the spinal cord carries out
Important coordination centre in its own right
What are most of the actions in the complex animal result of
Result of the unconscious reflux actions
Give examples of human refluxes
Touching something hot and moving your hand
blinking when something goes in your eye
What are reflex arcs
They are nerves that control unconditioned reflexes
What is the function of the reflex arc
To bring about an appropriate response to a particular stimulus as rapidly as possible without the time delay that occurs when the conscious centers become involved
What are the two main reflexes
spinal reflexes (hand moving from a hot object) cranial reflexes (blinking, pupil reflex)
What do the sensory nerves carry in the peripheral nervous system
Impulses from the receptors about changes in both the internal and external environment into the CNS
What does the motor nerve carry in the peripheral nervous system
Impulses out from the CNS to the effectors of the body
What are the two main types of motor nerves
The voluntary nervous system and autonomic nervous system
What is a voluntary nervous system
It involves motor neurons that are under voluntary or conscious control involving the cerebrum,
Give an example of something that is controlled by the voluntary nervous system
Carrying things such as a drink
What is the autonomic nervous system
Involves motor neurons that are not under the control of the conscious area of the brain
Give an example of something that is controlled by the autonomic nervous system
heart rate and breathing
What can the autonomic nervous system be subdivided into
Sympathetic nervous system and parasympathetic nervous system
What are the structural differences between sympathetic and parasympathetic nervous systems
What does this tell you about the fibres
In sympathetic, the ganglia are very close to the CNS
.Preganglionic fibres are short and postganglionic fibres are long
In parasympathetic, the ganglia are near to or in the effector organ
.Preganglionic fibres are long and postganglionic fibres are short
What are the similarities between sympathetic and parasympathetic nervous systems
Myelinated preganglionic fibres leave the CNS and synapse in the ganglion with unmyelinated post-ganglionic fibre
What are the functional differences between the sympathetic and parasympathetic nervous systems
Sympathetic produce noradrenaline at the synapse. It is referred to as the fight or flight response
When under physical or psychological stress the sympathetic pathway shall take over
Parasympathetic is slower and produces acetylcholine at the synapse
Restores calm after a stressful situation
it is sometimes referred to as the rest or digest system
Give an example of how the parasympathetic and sympathetic nervous system act antagonistically
the sympathetic system speeds up the heart rate whereas parasympathetic slows it down
