nervous coordination Flashcards
what are the series of steps involved in coordinating a nervous response
-stimulus - receptor - coordinator (CNS) - effector - response
-sensory neuron bwt receptor and coordinator
-relay neuron in CNS
-motor neuron in bwt coordinator and effector
how can the nervous system be categorised
-Central nervous system - recive info, process info and send response back
-peripheral - nerves leading to and from the brain and spinal cord
these can then be further split into the somatic and autonomic system
what is the somatic nervous system
controls skeletal muscles and external senory receptors - voluntary actions - conscious
what is the autonomic system
automatic and not conscious and controls internal organs
can be further categorized into sympathetic and parasympathetic - antagonistic
what is the sympathetic system
speeds up the system
what is the parasympathetic system
slows down the system
what are sensory neurons
carry impulses from receptors to the CNS
what do all neurons contain
cell body
-contains nucleus most of the cytoplasm and organelles
Neurones have a long fibre known as an axon
-The axon of some neurones is insulated by a fatty sheath with small uninsulated sections along its length (called nodes of Ranvier) - stretched out cytoplasm
The sheath is made of myelin, a substance made by specialised cells known as Schwann cells
-Myelin is made when Schwann cells wrap themselves around the axon along its length
The presence of Schwann cells means that the electrical impulse does not travel down the whole axon, but jumps from one node to the next
-The ‘jumping’ of the electrical impulse between nodes of Ranvier is called saltatory conduction
This speeds up the conduction of the impulse and its transfer from one cell to another
Neurone cell bodies contain many extensions called dendrites
-This means they can connect to many other neurones and receive impulses from them, forming a network for easy communication
what are motor neurons
carry impulses from the CNS to the effectors
what are relay neurons
transmit impulses within CNS
how to distinguish bwt motor and sensory
motor - cell body at the end
sensory - cell body in middle
what is the reflex arc
shortest route nwt a receptor and an effector
designed to give a rapid response to limit damage
not conscious and does not need to be learned
what are the electrical impulses like in a neuron
change in charge at the end of neuron caused by rapid movement of sodium and potassium ions into and out of the axon
-polarised
what is the resting potential
-when a neuron is not conducting a nerve impulse
-uneven distribution of ions inside and out of the axon
-more +ve charge outside than in
what is the value of the resting potential
-70 mV
what are the 2 ways in which the resting potential of a neuron is maintained
-by active transport using sodium-potassium pump
-by facilitated diffusion using carrier proteins
how does resting potential work
-in neuron there is a charge of -70 mV at rest
-sodium-potassium pump actively transports 3 Na+ out and 2 K+ in to the cell at expense of ATP
-K+ ions can diffuse back out of the cell via open gated K+ channels
-very few Na+ can diffuse back in the cell because Na+ gated channels are closed
-so net effect in the cytoplasm of the neuron is -ve charged compared with outside of the cell to a value of -70 mV
what is the action potential
where a neuron is stimulated with an electric current and there is a sudden change in potential difference bwt -70 mV and +40 mV
and is said to be depolarised
how to describe the action/resting potential graph
-Na+ gated channels open at the point of stimulation
-higher conc of Na+ outside the axon than inside - creating a conc gradient
-Na+ ions move along an electrical gradient and the axon becomes +ve charged to +40 mV
-at this point the increase in charge causes there to be a change in the tertiary structure of the channel protein and so the Na+ close and K+ open
-so K+ diffuse out of axon down conc gradient
-outward movement of +ve charge returns to normal and thus is repolarisation
-since the K+ ions leave the axon the pd becomes even more -ve than the normal resting value and causes a brief overshoot of -70 mV - hyperpolarisation
-K+ gates close and begins to act as normal
what is the refractory period and why is it important
when both the Na+ and K+ channels remain closed and the membrane cannot be repolarised
-this keeps the action potential discrete
-ensure action potentials can only pass in one direction
when will depolarisation take place
when the stimulus exceeds the threshold level required to open the Na+ channels -therefire it is called all or nothing law as it needs to be max to happen
what happens when an action potential is stimulated
-Na+ gated channels in the axon membrane open
-Na+ pass into the axon down the electrochemical gradient
-reducing the potential difference across the axon membrane as the inside becomes less negative - depolarises - to +40 mV
-continues to allow more gated channels to open
how are action potentials transmitted and why does it only go in one direction
-depolarisation causes Na+ to move in and they attract the -ve charge region
-depolarisation at the membrane of the stimulus/ first action potential causes Na+ to diffuse along the axon depolarising the next section of the axon - causes more Na+ channels to open
-the action potential can only go in one direction as the area behind it is still in the refractory period and is hyperpolarised so not able to generate another action potential
what is the speed of a neuron transmission affected by
-diameter of axon - wide axons conduct impulses more quickly than narrow ones as there is less leakage of ions from wider neurons
-myelin sheath
-tempurature
how does the myelin sheath affect transmission of a neuron
-myelinated neurons tend ot pass impulses ore quickly than unmyelinated ones
-in non-myelinated the impulse is transmitted along the neuron when each section of the membrane causes the next to become depolarised - slow
-myelinated nuerons conduct quickly because of the action potentials that only occur at the nodes of Ranvier
-local currents are stet up in which Na+ move from one node to the next - saltatory conductin
why is saltatory conduction more effiecient
ions only exchanged at the nodes
-this greatly reduces the energy needed for the active transport of Na+ and K+
-wide myelinated neurons can carry impulses for as quick as 120 ms-1 whereas unmyelinated giant axons of the squid - 25 ms-1
how does temperature affect the rate of transmission of neurons
-higher temp the faster the nerve impulses as the ions are bale to diffuse faster
-if temp becomes too high the membrane proteins denature as will the enzymes of respiration which produce ATP that is required for the active transport by the Na-K pump impulses then fail
what starts off an action potenital
-generated by a wide variety of stimuli such as light,sound,touch and temp or chemicals
-structures which respond to these are sensory receptors
-some are specialised cells found in sensory organs such as the rods and cones in the eye
-other receptors are simply the ends of sensory neuron themselves eg the pacinian corpuscles found int the dermis of the skin
how does the pacinian corpuscles work
-pressure is applied to the corpuscle the sensory neuron inside becomes deformed opening the Na+ and K+ channels
-allows Na~+ in and K+ out causing depolarisation
-the harder the pressure the more channels open until eventually the threshold value is reached and an action potential is triggered
-as pressure increases action potentials are triggered more frequently
what is the space in between 2 neurons known as
synapse that contains
-synaptic cleft
-pre-synaptic neuron
-post-synaptic neuron
-synaptic knob/bulb - this contains vesicles which have neurotransmitters in them
what happens when an action potential reaches a synapse
arrives at pre-synaptic bulb and causes the release of the transmitter substance which then diffuses across the synaptic cleft and binds to receptors on the post-synaptic membrane causing it to become depolarised and triggering an action potential in the post-synaptic neuron
describe the process of action potential transmission in a synapse
-action potential arrives at the pre-synaptic bulb
-Ca2+ gated channels open in the pre-synaptic membrane
-Ca2+ diffuse into the pre-synaptic bulb
-causing vesicles containing neurotransmitters to move to and fuse with to pre-synaptic membrane
-neurotransmitter binds to complementary receptors on the post-synaptic membrane
-Na+ gated channel proteins in the post-synaptic membrane open so Na+ diffuse in
-causing an action potential (depolarisation_
-enzyme breaks down neurotransmitter - sub for the specific neurotransmitter and enzyme - into component parts
-these diffuse back across the synapse and are repackaged in the vesicles
what are synapse and enzymes that use acetylcholine called
cholinergic synapse
-enzyme that breaks this down is acetylcholinesterase
what is the synapse called for noradrenaline
-adrenergic
what are inhibitory synapses
-release of transmitter cause the post-synaptic membrane to be hyperpolarised
-this is known as inhibitory postsynaptic potential
-prevent impulses passing to the next nueron
what is synapse fatigue
-when many action potentials arrive at the synapse in a short period of time the neuron runs out of transmitter substance
-post-synaptic neuron will not be stimulated and the response will be lost
-this is known as adaption and allows organisms to ignore repeated stimuli which are harmless
what is the neuromuscular junction
-the post-synaptic membrane of the synapse is a muscle fibre membrane called the sarcolemma
-synaptic transmission works in the same way
how does the sarcolemma work
-depolarised when acetylcholine -released by the presynaptic membrane of the neuron diffuses across the synapse and binds to the protein receptors in the sarcolemma
-this leads to the depolarisation of the membranes
-causing muscle contraction
what are the 3 roles of the synapse
-ensure one-way transmission of nerve impulse
-increase possible range of actions in response to the stimuli
-involved in memory and learning
how does the synapse ensure one-way transmission
-only pass from pre-synaptic neuron to the post-synaptic neuron
-this allows impulses to be directed to specific goals rather than randomly spreading throughout the nervous system
how does the synapse increase the range of actions in response to a stimuli
-allow a wider range of behaviour then what would be possible if neurons were directly linked to each other
-each neuron in the brain synapses thousands of other therefore thousands of different responses are possible
what happens when the amount of neurotransmitter released by the pre-synaptic neuron is not enough to cause depolarisation
-spatial summation
-temporal summation
what is spatial summation
-several action potentials arrive at a synapse from different neurones at the same time
-each release some neurotransmitter and the combined amount is now enough to depolarise the post-synaptic neuron an trigger an action potential;
what is temporal summation
-action potentials arrive at the synapse from one neuron but in a very rapid succession
-increase the amount od neurotransmitter release is enough to depolarise the post-synaptic neuron and trigger an action potential
how do drugs affect transmissipn at synapse
Chemical or drugs can have a major impact on the functioning of the brain and nervous system
Some prescription drugs can have a beneficial effect on those suffering from neurological disorders while recreational drugs can have a damaging or even fatal effect
Many drugs have been found to produce a specific effect on synaptic transmission
They can have different modes of action such as:
-Stimulating the release of a neurotransmitter
-Providing the chemicals needed to synthesise neurotransmitters
-Acting in the same way as a neurotransmitter by binding to the same specific receptor
-Preventing the reuptake of the neurotransmitter by the presynaptic neurone
-Research is ongoing to further understand how several drugs work in the hopes that they can be used to treat nervous disorders
what is the effect of dopamine on synapses
Dopamine is a neurotransmitter involved in muscle control
Individuals that suffer from Parkinson’s disease produce insufficient amounts of dopamine
There are two types of drugs that are used to treat this disease
A dopamine agonist - produces the same effect as dopamine by binding to the same receptors
A dopamine precursor - this can be used to synthesise dopamine in the neurones
what are the 2 types of neurotransmitters and their function
There are many different neurotransmitters that bind to specific receptor molecules
They are often restricted to certain regions of the brain so that they have a specific function
Some are excitatory and some are inhibitory
Excitatory neurotransmitters result in the production of an action potential
Inhibitory neurotransmitters prevent the production of an action potential. They do this by causing potassium ions to leave the postsynaptic membrane
what is the effect of morphine
Dopamine also plays a vital role in pain relief
Chemicals called endorphins which are produced in the brain can stimulate the release of dopamine
The endorphins attach to opioid receptors found on presynaptic neurones that release dopamine molecules
Exercise is a natural way to cause the release of endorphins
Morphine is a chemical very similar in structure to endorphins and so it can provide pain relief by stimulating the release of dopamine
what is the effect fo cocaine on synapse
Cocaine also affects levels of dopamine
It binds to the dopamine transporter protein
This prevents dopamine from binding to the transporter so it is not able to move through the membrane back into the presynaptic neurone
As a result dopamine builds up in the synapses which can lead to feelings of pleasure
what is the effect of cannabinoids on synapse
Cannabinoids are compounds found in cannabis
Cannabinoid receptors are located in the pre-synaptic membrane of neuromuscular junctions
When a cannabinoid molecule binds to its specific receptor, it closes the calcium ion channels
This leads to decreased muscle contraction
There is currently research investigating whether cannabinoids could be an effective drug in treating multiple sclerosis (MS)
MS is a disease that involves damage to the myelin sheaths of neurones. Sufferers struggle to control muscle contraction
what is the effect of MDMA on synapses
MDMA stimulates the release of multiple neurotransmitters most notably, serotonin
Serotonin can affect people in many ways including their mood, anxiety and sleep
When an individual takes MDMA they may feel extreme euphoria and enhanced touch and bodily sensations
what is the affect of nicotine
-heightened activity in cholinegric pathways in the brain
-improve reaction times
-stimulation of cholinergic neurons promote release of neurotransmitter in reward passages for the brain
-release og glutamate -enhances the connections bwt sets of neurons and increase memory by strengthening these connections
how is resting potential maintained - exam answer
-sodium-potassium pump operates by active transport using ATP
-3Na+ out and 2K+ in
-gated Na+ ion channel closed
-K+ ion gated channel open- some K+diffuse back out
-70 mV maintained
what is occuring when the resting potential is 0mV
-equal disrubution of Na+ and k+ either side of the membrane
