Nervous Control Flashcards
What is the central nervous system made up of ?
The brain and the spinal cord
What is the peripheral nervous system made up of ?
made up of pairs of nerves originating from the brain or the spinal cord.
what is the motor nervous system divided into ?
the voluntary nervous system
the autonomic nervous system
What is the autonomic nervous system divided into ?
the sympathetic nervous system
the parasympathetic nervous system
what is the role of the sympathetic nervous system ?
stimulates effectors
speeds up activity
preparation for stressful activities ‘fight or flight’
increase heart rate
dilate pupils
inhibit activity of intestines and stomach
What is the role of the parasympathetic nervous system ?
inhibits effectors slows down activity
Controls activities at rest
conserves energy and replenishes the bodies reserves
slow heart rate
constrict pupils
stimulate activity of stomach
What 3 neurones does a REFLEX ARC involve ?
Sensory neurone
Intermediate neurone
Motor neurone
What are the main stages of a spinal reflex arc when touching a hot object ?
Stimulus is the heat from the hot object
Receptors detect temperature change in the skin and generate a nerve impulse.
Sensory neurone passes the nerve impulse to the spinal cord.
Intermediate neurone links the sensory neurone to the motor neurone in the spinal cord.
Motor neurone carries the nerve impulse from the spinal cord to a muscle in the upper arm.
The muscle in the upper arm which is stimulated to contract.
What is the effector in a simple reflex arc when touching a hot object ?
the muscle in the upper arm which is stimulated to contract.
What is the response in a simple reflex arc when pulling the hand away from the hot object ?
pulling the hand away from the hot object.
What is the role of reflex actions ?
Avoiding damage to tissues and prevents injury
Used to escape from predators
Describe the importance of REFLEX ARCS
protect the body from harmful stimuli
Make survival more likely
What is resting potential ?
In a resting axon (one that is not transmitting impulses), the inside of the axon always has a negative electrical potential compared to outside the axon.
Describe the structure of a neurone.
They have :
a cell body : contains a nucleus with large amounts of Rough ER associated with the production of neurotransmitters.
Dendrons and dendrites :This means they can connect to many other neurones and receive impulses from them, forming a network for easy communication
An axon : a single long fibre that carries nerve impulses away from the cell body
A myelin sheath and Nodes of Ranvier - allows nerve impulses to travel by saltatory conduction which speed up the rate of transmission.
What is the numerical value for the resting potential of the axon membrane ?
-70mv
Explain how resting potential is maintained in a neurone.
Sodium-potassium pumps are present in the membranes of neurones
These pumps use ATP to actively transport 3 sodium ions out of the axon for every 2 potassium ions that they actively transport in.
This means that there is a larger concentration of positive ions outside the axon than there are inside the axon
The movement of ions via the sodium-potassium pumps establishes an electrochemical gradient.
The cell-surface membrane of neurones has selective protein channels that allow sodium and potassium ions to move back across the membrane by facilitated diffusion.
The protein channels are less permeable to sodium ions than potassium ions
This means that potassium ions can diffuse back down their concentration gradient, out of the axon, at a faster rate than sodium ions.
What is the defintion of an Action Potential ?
The change that occurs in the electrical charge across the membrane of an axon when it is stimulated and a nerve impulse passes.
also known as a ‘wave of depolarisation along the axon membrane’
What causes the production of an action potential ?
a stimulus
Explain how an action potential is produced when a stimulus arrives at a resting neurone.
Sodium ion channels in the axon membrane open
Sodium ions pass into the axon down the electrochemical gradient.
This reduces the potential difference across the axon membrane as the inside of the axon becomes less negative (depolarisation)
Depolarisation triggers more channels to open, allowing more sodium ions to enter and causing more depolarisation (positive feedback)
If the potential difference reaches around -55mV (known as the threshold potential), many more channels open and many more sodium ions enter causing the inside of the axon to reach a potential of around +40mV
An action potential is generated
The depolarisation of the membrane at the site of the first action potential causes sodium ions to diffuse to along the axon, depolarising the membrane in the next section of the axon and causing sodium ion voltage-gated channel proteins to open there. (conduction)
What happens during repolarisation ?
Voltage gated sodium ion channels close
Voltage gated potassium ion channels in the axon membrane open.
This allows the diffusion of potassium ions out of the axon, down their concentration gradient
This returns the potential difference to normal resting potential (-70mv)
What is Hyperpolarisation ?
This is when the potential difference across this section of axon membrane briefly becomes more negative than the normal resting potential
What is the Refractory Period ?
Once an action potential has been generated there is a period when sodium ions cannot move into the axon because the voltage gated sodium ion channels are closed. (unresponsive)
During this time it is impossible to generate a new action potential.
(a period of recovery)
What is the importance of the Refractory Period ?
Ensures that an action potential is propagated in one direction only
Produces discrete impulses
It limits the frequency of impulses that can pass along an axon in a given time.
What is the ALL-OR-NOTHING LAW ?
An impulse (action potential) is only transmitted if the initial stimulus is sufficient to increase the membrane potential above a threshold potential
How can an organism perceive the size of a stimulus ?
the larger the stimulus, the more nerve impulses are generated in a given time.
In unmyelinated Neurones the speed of conduction is very slow. Why is this ?
This is because depolarisation must occur along the whole membrane of the axon
What is a myelin sheath made from ?
Schwann cells
What does the myelin sheath act as ?
an electrical insulator
How does a myelin sheath increase the speed at which action potentials can travel ?
In sections of the axon that are surrounded by a myelin sheath, depolarisation cannot occur, as the myelin sheath stops the diffusion of sodium ions and potassium ions
Action potentials can only occur at the nodes of Ranvier
The presence of Schwann cells means the action potentials ‘jump’ from one node to the next, this is known as saltatory conduction.
What are nodes of Ranvier ?
Small uninsulated sections of the axon
What is SALTATORY CONDUCTION ?
Jumping of action potentials across the nodes of Ranvier.
What is the speed of conductance like if the axon diameter is thicker ?
The speed of conductance is faster. This is due to less resistance of flow so ions can be pushed into the next section faster.
greater surface area over which the diffusion of ions can occur
This increases the rate of diffusion of sodium ions and potassium ions through protein channels, which in turn increases the rate at which depolarisation and action potentials can occur
How does temperature affect the speed of conduction along an axon ?
Colder conditions can slow down the conduction of nerve impulses.
The colder temperatures mean there is less kinetic energy available for the facilitated diffusion of potassium and sodium ions during an action potential.
Some animals, such as mammals, maintain very stable body temperatures. Temperature does not usually affect the speed of nerve impulses in these animals
What is the name for synapses which use acetylcholine as a neurotransmitter ?
Cholinergic synapses.
Describe the sequence of events following a nerve impulse arriving at a cholinergic synapse
The arrival of an action potential at the presynaptic membrane causes depolarisation of the membrane
This stimulates voltage-gated calcium ion channel proteins to open
Calcium ions diffuse down an electrochemical gradient from the tissue fluid surrounding the synapse (high concentration of calcium ions) into the cytoplasm of the presynaptic neurone (low concentration of calcium ions)
This stimulates ACh-containing vesicles to fuse with the presynaptic membrane, releasing ACh molecules into the synaptic cleft
The ACh molecules diffuse across the synaptic cleft and temporarily bind to receptor sites on sodium ion channels in the postsynaptic membrane
This causes the sodium ion channels to open allowing sodium ions to diffuse down an electrochemical gradient into the the cytoplasm of the postsynaptic neurone.
The influx of sodium ions generates a new action potential in the post synaptic neurone.
Acetylcholine is broken down into choline and Acetate by the enzyme Acetylcholineesterase The choline is absorbed back into the presynaptic membrane and reacts with acetyl coenzyme A to form ACh, which is then packaged into presynaptic vesicles ready to be used when another action potential arrives.
Why must Acetylcholine be broken down by acetylcholineesterase in the synaptic cleft ?
To prevent the sodium ion channels staying permanently open and to stop permanent depolarisation of the postsynaptic membrane, the ACh molecules are broken down and recycled.
Why can synapses only pass impulses in one direction ?
(They are Unidirectional)
Vesicles containing neurotransmitter only found in the presynaptic neurone.
Post synaptic neurone only has receptors for the neurotransmitter.
When an impulse arrives at a synapse it does not always cause impulses to be generated in the next neurone. What are reasons for this ?
Only a small amount of acetylcholine is released into the synaptic cleft
A small number of the gated ion channels are opened in the axon membrane
An insufficient number of sodium ions pass through the membrane
The threshold potential is not reached
The small amount of acetylcholine attached to receptors is broken down rapidly by acetylcholinesterase
What is temporal summation ?
If multiple impulses arrive within quick succession the effect of the impulses can be added together to generate an action potential
What is spatial summation ?
Multiple impulses arriving simultaneously at different synaptic knobs stimulating the same cell body can also generate an action potential through spatial summation.
How does summation allow an action potential to be generated in the postsynaptic neurone ?
A large amount of acetylcholine is released into the synaptic cleft
A large number of the gated ion channels open
A sufficient number of sodium ions pass through the membrane
What are the benefits of summation ?
It allows for the effect of a stimulus to be magnified
A combination of different stimuli can trigger a response
It avoids the nervous system being overwhelmed by impulses
Other neurotransmitters can prevent the generation of an action potential in a postsynaptic neurone. What is this process known as ?
Inhibition
Explain what happens If the cell body of a motor neurone is subject to both excitatory and inhibitory synapses
Sodium ions enter the cell body following stimulation by the excitatory synapse.
The stimulation of the inhibitory synapse causes potassium ions to diffuse out of the cell body as the voltage gated potassium ion channels are opened.
This cancels out the effect of the sodium ions entering
The threshold potential is not reached so no action potential is generated
Why is inhibition important ?
They prevent random impulses from being sent around the body
They allow for specific pathways to be stimulated
How can drugs stimulate the nervous system ?
They stimulate the nervous system by creating more action potentials in the post synaptic neurone.
A drug may mimic a neurotransmitter or may inhibit the enzyme that breaks down the neurotransmitter so more impulses are produced in the post synaptic neurone.
How can drugs inhibit the nervous system?
They can inhibit the nervous system by creating fewer action potentials.
A drug may inhibit the release of neurotransmitters or block the receptors on the sodium/potassium ion channels which reduces the frequency of impulses in the postsynaptic neurone.
What are the Key facts about drugs and synapses ?
Drugs that have similar shapes to neurotransmitters can affect the protein receptors in postsynaptic membranes
Some drugs bind to postsynaptic receptors, causing gated ion channels to remain open or stay closed.
some drugs inhibit the action of acetylcholineesterase
Some drugs may inhibit the reabsorption of transmitter substances from synapses.
Explain transmission across a neuromuscular junction.
An impulse arrives at the pre -synaptic membrane of the neuromuscular junction and causes depolarisation of the membrane. This stimulates voltage-gated calcium ion channel proteins to open.
Calcium ions diffuse down an electrochemical gradient from the tissue fluid surrounding the synapse (high concentration of calcium ions) into the cytoplasm of the presynaptic neurone.
This stimulates vesicles containing the neurotransmitter acetylcholine (ACh) to fuse with the presynaptic membrane
The ACh that is released diffuses across the neuromuscular junction and binds to receptor proteins on the sarcolemma
This stimulates ion channels in the sarcolemma to open, allowing sodium ions to diffuse in.
This depolarises the sarcolemma, generating an action potential that passes down the T-tubules towards the centre of the muscle fibre.
These action potentials cause voltage-gated calcium ion channel proteins in the membranes of the sarcoplasmic reticulum to open.
Calcium ions diffuse out of the sarcoplasmic reticulum (SR) and into the sarcoplasm surrounding the myofibrils
Calcium ions bind to troponin molecules, stimulating them to change shape
This causes the troponin and tropomyosin proteins to change position on the actin filaments
The myosin head-binding sites are exposed.
The process of muscle contraction (known as the sliding filament model) can now begin
Where is a neuromuscular junction located ?
They are located between a (motor) neurone and a muscle cell
What is the sequence of events that occurs at a neuromuscular when an action potential stops ?
Acetylcholine destroyed at neuromuscular junction by acetylcholineesterase.
Stops stream of action potentials along sarcolemma.
Sarcoplasmic reticulum stops releasing calcium ions.
Calcium ions pumped back into sarcoplasmic reticulum- uses ATP
Fall in level of calcium ions causes tropomyosin to move back to its original position.
Actin-binding sites are now blocked so myosin heads cannot bind with actin.
Muscle contraction stops.
Compare and Contrast Cholinergic synapses and neuromuscular junctions.
Chlolinergic synapse:
uses acetylcholine as a neurotransmitter
Found between neurones
Can be excitatory or inhibitory
Stimultated by an action potential on the presynpatic membrane.
Neuromuscular junction:
uses acetylcholine as a neurotransmitter
found between a motor neurone and a muscle
can only be excitatory
stimulated by an action potential on the presynaptic membrane,
What is a Pacinian corpuscle ?
a receptor found deep in the skin ( especially the fingers and soles of feet )
What is the function of a Pacinian Corpuscle ?
respond to mechanical stimuli such as pressure and changes this mechanical energy into a generator potential.
What does the Pacinian corpuscle surround ?
the end of a sensory neurone.
What is the name of the protein channels found in the plasma membrane of the Pacinian corpuscle ?
Stretch-mediated sodium channels
A Pacinian corpuscle is said to have a resting potential why is this ?
In the resting state, the stretch-mediated sodium channels are too narrow to allow sodium ions into them.
What happens when pressure is applied to a Pacinian corpuscle ?
When pressure is applied it changes shape (is deformed) and the membrane becomes stretched/deformed.
The stretch-mediated sodium channels widen and open, and sodium ions diffuse into the neurone
The greater the pressure, the more channels open
The influx of sodium ions changes the potential of the membrane, it is depolarised, and therefore produces a generator potential
The generator potential creates an action potential that passes along the neurone to the CNS.
What part of the brain controls heart rate ?
The CARDIO-REGULATORY CENTRE in the MEDULLA OBLONGATA
What are the two different regions of the cardio-regulatory centre ?
the ACCELERATORY CENTRE
the INHIBITORY CENTRE
What does the ACCELERATORY centre do to heart rate?
increases heart rate
is linked to the SA node of the heart by the sympathetic nervous system,
What does the INHIBITORY centre do to heart rate ?
decreases heart rate
and is linked to the SA node by the parasympathetic nervous system.
What is the name of the receptors that detect if the heart rate needs to increase or decrease?
CHEMORECEPTORS
Where are chemoreceptors found ?
are found in the walls of the carotid arteries and the wall of the aorta.
What are chemoreceptors sensitive to ?
Sensitive to changes in pH
For example, When exercising, more carbon dioxide is produced which lowers blood pH
How is Heart rate increased ?
Increased muscular activity.
increase in carbon dioxide produced by tissues from increased respiration
Fall in blood pH
Detected by chemoreceptors in the carotid arteries
More nerve impulses sent to the acceleratory centre of cardiac centre in the medulla
more nerve impulses sent along the sympathetic nerve to the sinoatrial node
sinoatrial node stimulated by the neurotransmitter noraadrenaline
Increase in frequency of waves of electrical activity across the atria and the ventricles which increases heart rate.
Increase in blood flow removes carbon dioxide faster in the lungs,
Carbon dioxide levels return to normal.
Describe the events involved in the electrical coordination of the heartbeat
Cells in the SAN depolarise and produce a wave of electrical stimulation that spreads across the atria causing them to contract
The signal passes down the atrial septum. It does not reach the ventricles due to a thin layer of collagen at the base of the atria.
The electrical stimulation instead passes to the AVN located between the atria.
The AVN passes the impulse down to the bundle of HIS.
There is a slight delay here. So that there is time for the atria to completely empty before the ventricles contract.
The bundle of HIS the the transmits the impulse to the apex of the heart. Here it splits into purkyne fibres and these branch up each ventricle
The impulse passes up the purkyne fibres. This causes the ventricles to contract from the base upwards. Allows ventricles to completely empty.
How is Heart rate decreased ?
decreased carbon dioxide produced decreases the stimulation of the chemoreceptors
The inhibitory centre in the medulla sends impulses via the parasympathetic nerves
The SA node is stimulated by the neurotransmitter acetylcholine
reduced frequency of waves of electrical activity and the heart rate decreases.
What are the name of the pressure receptors which can control heart rate ?
Baroreceptors
Where are baroreceptors found ?
in the walls of the carotid arteries and the aorta
How is heart rate decreased when blood pressure is too high ?
When blood pressure is higher than normal, baroreceptors detect the rise and impulses are sent to the cardiac centre in the medulla;
impulses are then sent via the parasympathetic nervous system to the SA node of the heart which decreases heart rate.
How is heart rate increased when blood pressure it lower than normal ?
baroreceptors detect the decrease and fewer impulses are sent to the medulla.
The medulla sends impulses via the sympathetic nervous system to the SA node to increase heart rate.
What is cardiac muscle described as ?
myogenic
Why is heart muscle described as myogenic ?
the cardiac muscle is able to contract without any external stimuli.
What are Receptors ?
Receptors are groups of specialised cells that can generate an electrical impulse in a sensory neurone
The eye contains two different types of receptor cells what are these called ?
Rod cells
Cone cells
What is the function of the eye ?
The purpose of the eye is to receive light and focus it onto the retina at the back of the eye
What part of the eye are Rod and Cone cells located ?
The Retina
What optical pigment do Rod cells contain ?
Rod cells contain rhodopsin
What optical pigment do Cone cells contain ?
Cone cells contain iodopsin
What happens when the optical pigments are broken down ?
a generator potential is produced
Receptors have different Sensitivities to light. What is the definition of sensitivity ?
Sensitivity refers to the amount of light required to stimulate the receptor
What are the properties of Rod cells ?
120 million in each eye
Distributed widely across the retina, but few at the centre of the eye, the fovea and none at the BLIND SPOT (where the optic nerve leaves the eye)
Sensitive to low intensity (dim light)
Enable us to distinguish light from dark in dim light
Do not allow us distinguish different colours,
Contain a pigment called RHODOPSIN- low light intensity breaks down rhodopsin and creates a generator potential.
What are the properties of CONE cells ?
6 million in each eye
Mainly concentrated in the centre of the retina (FOVEA)but none at the blindspot
Sensitive to different wavelengths of light so we can distinguish colour.
Cones contain a pigment called IODOPSIN. High intensity light is needed to break it down an create a generator potential.
There are three cone types found in human eyes, each contains a different optical pigment. What are these ?
Red-sensitive cones are sensitive to wavelengths of light that correspond to the colour red
Blue-sensitive cones are sensitive to wavelengths of light that correspond to the colour blue
Green-sensitive cones are sensitive to wavelengths of light that correspond to the colour green
The combined effect of all three pigments allows humans to observe all the other colours that are on the visible spectrum
What is visual Acuity ?
how far apart two spots of light can be seen as being separate; this is affected by the way in which the receptors are connected to the optic nerve fibres.
Explain why Cone cells have high visual acuity
A single cone cell synapses with a single bipolar cell
A single bipolar cell synapses with a single ganglion cell
If two cones are stimulated to send an impulse the brain is able to interpret these as two different spots of light
Explain why Rod cells have low visual acuity
Multiple rod cells synapse with a single bipolar cell
Multiple bipolar cells synapse with a single ganglion cell
The brain is not able to interpret which impulses are sent by specific rods
If multiple rod cells connected to the same bipolar cell detect light, only one impulse from the bipolar cell is sent
For example several dots of light would only generate one nerve impulse and the dots would appear as a single point of light.
Explain how Rod cells show summation.
There is a benefit to how each rod cell is connected to the optic nerve.
Each rod is very sensitive to light however a single stimulated rod is unlikely to produce a large enough generator potential to stimulate the bipolar cell for the conduction of nerve impulses.
When a group of rods are stimulated at the same time the combined generator potentials are sufficient to reach the threshold and stimulate the bipolar cell for the conduction of nerve impulses onwards towards the optic nerve
Summation produces a less sharp image but enables organisms to see in much dimmer light than cones allow.
How do Rod cells show retinal convergence ?
Several rods synapse with one bipolar cell and one ganglion cell (optic nerve neurone)
One rod on its own cannot produce a large enough generator potential to stimulate the bipolar cell to transmit a nerve impulse.
Do cone cells show Retinal Convergence ?
NO
Are cone cells used for day or night vision ?
Day vision
Are rod cells used for day or night vision ?
Night vision
Explain difference between spatial and temporal summation
During temporal summation several impulses reach the same synaptic knob in quick succession; [1 mark]
During spatial summation several impulses arrive simultaneously at different synaptic knobs stimulating the same cell body; [1 mark]
