neuronal communication chp 13 Flashcards
How do animals and plants react to changes in environments
- Animals react through electrical responses (via neurones) and through chemical responses (via hormones).
- Plants react through purely chemical responses (via hormones)
Why is coordination needed within animals and plants
- coordination between cells and organs are needed for efficent operation
What is an example of coordination in animals and plants
- bone marrow produces red blood cells as red blood cells cannot reproduce themselves
(haematopoietic stem cells) - flowering plants needs to coordinate with seasons, and pollinators must coordinate with the plants
What is homeostasis
- maintainence of internal conditions while adjusting to changing external conditions
What does coordination (especially between organ systems) rely on
- communication between cells
Through cell signalling process what can be done
- transfer signals locally (within cell) or across large distances (entire body often hormones)
which is faster and more targeted, hormonal or neuronal communication
Neuronal communication is generally much faster and more targeted response than that produced by hormonal communication
What is the role of neurones
- transmit electrical impulses around the body
What are the components of the reflex arc
- Receptor
- sensory
- relay
- motor
neurones
What are they key structures of mammalian neurones
- cell body
- dendrons
- axons
Why is the cell body a key feature of mammalian neurones
- contains nucleus surrounded by cytoplasm
- cytoplasm contain endoplasmic reticulum and mitochondria
^involved in the production of neurotransmitters
Why is the dendron a key feature of mammalian neurone
- divide into smaller branches called dendrites.
- detect chemical messengers and propagates impulse towards cell body
structure of mammalian neurone axons
- single, thin, long nerve fibre
- carries impulse away from cell body
in most nervous systems the electrical impulse follows which pathway
receptor->sensory neurone->relay neurone->motor neurone->effector cell
What are sensory neurones
Draw one
- transmit impulses from sensory receptor cell to a relay/motor neurone or the brain.
- myelinated neurone
What are relay neurones
draw one
- transmit impulses between neurones
- have many short axons and dendrons.
What are motor neurones
Draw one
- These neurones transmit impulses from a relay neurone or sensory neurone to an effector, such as a muscle or a gland.
- They have 1 long axon and many short dendrites
What are myelin sheaths made up of
they are made up of many layers of plasma membrane
what is the function of Schwann cells
- produce myelinated sheaths as grow and produce many layers of phospholipids bilayer
what is the function of myelin sheaths
- increase speed of electrical impulse transmission
What are nodes of ranvier
- gaps between adjacent myelin sheaths on axons and dendrons
How does the myelin sheath allow the impulse to travel faster and how does it link to the node of ranvier
- myelin sheath is electrical insulator.
- ^In myelinated neurones, the electrical impulse ‘jumps’ from one node to the next
^allows impulse to be transmitted much faster. - In non-myelinated neurones the impulse does not jump
- ^it transmits continuously along the nerve fibre, so is much slower.
What are some features of sensory receptors
- specific to single stimulus
- create generator potential
What is a generator potential
a nervous impulse created from activation of sensory receptors
What is the function of the pacinian corpuscle
detect mechanical pressure on skin
Where can pacinian corpuscle be found
- deep layers of the skin (especially hands and soles) and joints
what is the structure of the pacinian corpuscle
- dendron of sensory neurone found surrounded by layers of connective tissues
- dendron in a pacinian corpuscle has stretch-mediated sodium channel (open in responsed to pressure)
What is the function of sodium ion channels
These are responsible for transporting sodium ions across the membrane.
What are the steps to how a pacinain corpuscle converts mechanical pressure into a nervous impulse
- at rest stretch mediated sodium ion channel is closed, so neruone is at resting potential
- When pressure applied, the Pacinian corpuscle changes shape.
- change in shape stimulates stretch-mediated sodium ion channels to open
- influx of sodium ions depolarizatises neurone, generator potential generated
- generator potential triggers an action potential
What occurs to the pacinain corpuscle when there is an influx of sodium ions
It becomes depolarised
What is a potential difference
A voltage
What is resting potential
outside of membrane is more positive than axon interior
resting potential is -70 mV and so is called polarised
Why does resting potential occur and how is it maintained
- result of movement of sodium and potassium ions across axon membrane via channel proteins
- Some channels are gated and others are perpetually open
How is a resting potential created
- 3 Na+ ions pumped out while 2 K+ pumped into axon using Na-K pump
- most Na+ channels closed, K+ channels open, so K+ diffuses out
- ^this means outside of axon more negative than in,side
What is the electrochemical gradient
this is the name given to a concentration gradient of ions
What occurs in the axon of a sensory neurone when a stimulus is detected
- reverses the charges on the axon membrane.
- potential difference changes and becomes positively charged at +40 mV.
^This is known as depolarisation (a change in potential difference from negative to positive)
When does an action potential occur
- occurs when ion channels in axon open/close as result of change of potential difference
What actually is a nerve impulse
- an action potential that starts at one end of a neurone and is propagated to the other end
What is depolarisation
- when the axon goes from positive to negative due to an influx of cations
What is repolarisation
- repolarization refers to the change in membrane potential that returns it to a negative value just after the depolarization phase of an action potential
what is hyperpolarisation, what is its function
- Hyperpolarization is a change in a cell’s membrane potential that makes it more negative. It is the opposite of a depolarization.
- It inhibits action potentials by increasing the stimulus required to move the membrane potential to the action potential threshold.
when does the refractory period occur
- after an action potential
What physcially occurs during the refractory period
- voltage-gated sodium ion channels closed
^no action potential can form
why is a refractory period important
- makes sure action potential are unidirectional and non overlapping
on myelinated neurones where can depolarisation occur, why is this important
- depolarisation of the axon membrane can only occur at the nodes of ranvier where no myelin is present.
- This allows myelinated axons to transfer electrical impulses much faster
how does saltatory coduction work
- at nodes of ranvier, sodium ions can pass though membrane
- Longer localised circuits arise between adjacent nodes.
- action potentials can jump from one node to next
What are the benfits of saltatory conduction
- quicker
- more energy efficent as not as much ATP used for depolarisation
Apart from myelination what affects the speed at which an action potential travels
- Axon diameter
- Temperature
How and why does axon diameter affect the speed of action potentials
- bigger axon diameter, faster impulse is transmitted
- because there is less resistance to flow of ions in cytoplasm compared with those in a smaller axon
- How does temperature affect the speed of action potential
- why
- the higher the temperature the faster the nerve impulse.
- because ions diffuse faster
- only occurs up to certain temperature as channel proteins become denatured
what is meant when nerve impulses are said to be all or nothing responses
- certain level of stimulus, the threshold value, always tiggers same response.
- If this threshold is reached an action potential will be created.
- If threshold isn’t reached, no action potential will be triggered.
What would the effect of stimulus intensity be on impulse frequency
The sizeof the action potential is always the same, but the frequency increases
What is the junction between 2 neurones called
it is called a synapse
What are the key structures of all synapses
- Synaptic cleft
- presynaptic neurone
- postsynaptic neurone
- synaptic knob
- synaptic vesicles
- neurotransmitter receptors
What is the synaptic cleft
The gap which separates the axon of one neurone from the dendrite of the next neurone. It is approximately 20-30 nm across
What is the presynaptic neurone
- neurone that delivers nervous impulse to synaptic cleft
define postsynaptic neurone
Neurone that receives the neurotransmitter
What is the synaptic knob, what does it contain
- The swollen end of the presynaptic neurone.
- contains lots of mitochondria and endoplasmic reticulum so can make neurotransmitters
- contains calcium ion channels in it membrane
- contains vesciles of neutrotransmitter
what is the synaptic vesicle
- vesicles containing neurotransmitters.
- the vesicles fuse with the presynaptic membrane and release their contents into the synaptic cleft
what are neurotransmitter receptors
receptor molecules which the neurotransmitter binds to in the postsynaptic membrane
what are the 2 types of neurotransmitters
- excitatory
- inhibitory
what is a excitatory neurotransmitter, what is an example of one
- neurotransmitters that result in depolarisation of postsynaptic neurone.
- If threshold is reached in postsynaptic membrane action potential triggered
- Acetylcholine is an example
what is an inhibitory neurotransmitter
- these neurotransmitters result in the hyperpolarisation of the postsynaptic membrane.
- ^this prevents an action potential being triggered.
- Gamma-aminobutyric (GABA) acid is an example in the brain
what takes place for a synaptic transmission to occur
1) action potential reaches the end of the presynaptic neurone
2) Depolarisation of the presynaptic membrane causes calcium ion channels to open
3) calcium ions diffuse into the presynaptic knob
4) This causes synaptic vesicles containing neurotransmitters to fuse with the presynaptic membrane. Neurotransmitter is released into the synaptic cleft by exocytosis
5) Neurotransmitter diffuses across the synaptic cleft and binds with its specific receptor molecule on the postsynaptic membrane
6) This causes sodium ion channels to open
7) sodium ions diffuse into the postsynaptic neurone
8) This triggers an action potential and the impulse is propagated along the postsynaptic neurone
why is it important that a neurotransmitter is removed after triggering an action potential
- It is important that it is removed so the stimulus is not maintained, and so another stimulus can arrive at and affect the synapse.
- The neurotransmitter can be recylced
How is the neurotransmitter that is left in the synaptic cleft removed
- is it removed
- acetylcholine is broken down by enzymes,
^which also releases them from the receptors on the postsynaptic membrane. - The products are taken back into the presynaptic knob
what synapses use acetylcholine as a neurotransmitter
Cholinergic synapses
where are cholinergic synapses most commonly found
In the CNS of vertebrates and at neuromuscular junctions
what is a neuromusclar junction
where a motor neurone and a muscle cell meet
What steps are there in the transmission across a cholinergic synapses
1)Action potential arrive at the end of presynaptic neurone makes calcium ion channels open and calcium ion enter the synaptic knob
2)influx of calcium ions into presynaptic neurone make synaptic vesicles to fuse with the presynaptic membrane, acetylcholine is released into synaptic cleft
3)Acetylcholine molecules fuse with sodium ion channels on postsynaptic membrane, this causes sodium ion channels to open and sodium diffuses in rapidly by diffusion
4)The influx of sodium ion creates a new action potential in postsynaptic neurone
5)Acetylcholinesterase hydrolyses acetylcholine into choline and acetic acid, which diffuse back across the synaptic cleft into the presynaptic neurone (recycling), also stops new action potentials from being created in post
6)ATP released by mitochondria is used to recombine choline and ethanoic acid into acetylcholine, stored in presynaptic neurone, sodium ion channels close in the absence of acetylcholine
what are the roles of synapses in the nervous system
- they ensure impulses are unidirectional
- allow for summation
what is meant by summation
when small amounts of neurotransmitter build up to trigger an action potential in the postsynaptic neuron
what are the 2 types of summation in neural communication
- spatial summation
- temporal summation
what is spatial summation
- this occurs when multiple presynaptic neurones connect to 1 postsynaptic neurone.
- Each releases neurotransmitter which builds up to a level that an action potential is triggered in the single postsynaptic neurone
What is temporal summation
- this occurs when a single presynaptic neurone releases neurotransmitter as a result of an action potential several times over a short period.
- It builds up until a action potential can be triggered
what are the effects of some drugs on the synapses
- mimicking the shape of neurotransmitters
- stimulating the releases of more neurotransmitter
- inhibiting the enzyme responsible for breaking down the neurotransmitter in the synapse
- blocking receptors
- binding to specific receptors on the post synaptic membrane to increase or decrease binding of the neurotransmitter
what are the 2 structural systems into which the nervous system is organised
- Central nervous system (CNS)
- Peripheral nervous system (PNS)
what does the CNS consist of
the brain and spinal cord
what does the PNS consist of
- consists of all neurones that connect the CNS to the rest of the body.
- ^sensory and motor neurones
what functional difference between motor and sensory neurones
- sensory brings impulses to the CNS from the receptor
- Motor neurones take the impulse from the CNS to the effector
what are the 2 functional systems into which the PNS is organised
- somatic nervous system
- autonomic nervous system
what is the somatic nervous system
- system under conscious control
- used when you voluntary decide to do something, like moving a muscle
what is the autonomic nervous system
- works constantly, under subconscious control
- it causes the heart to beat, digestion of food
- carriers nerve impulses to glands, smooth muscle (walls of intestine) and cardiac muscle
what are the 2 sub-divisions of the autonomic nervous system
sympathetic and parasympathetic nervous system
what does the sympathetic nervous system control
- if outcome increases activity it involve’s sympathetic nervous system
- such as an increase in heart rate
what is the parasympathetic nervous system
- if the outcome decreases activity it is parasympathetic nervous system
- such as decrease in heart rate after a period of exercise
whats the full organisation of the mammalian nervous system
How many neurones are in an adult human brain on average
86 billion
what is the advantage of having a central control centre
the communication between billions of neurones involved is much faster than if control centres were for each individual function
what is the protective membrane that surrounds the brain
meninges
what are the 5 main areas of the brain
- cerebrum
- cerebellum
- medulla oblongata
- hypothalamus
- pituitary gland
what is the function of the cerebrum
- receives sensory info
- interprets it with respect to previous experiences
- sends impulses to effectors
- responsible for coordination of all voluntary responses as well as some involuntary ones (
what is the structure of the cerebrum
- highly convoluted, increases surface area for complex activity to occur
- spilt into left and right halves (cerebral hemispheres)
- Each hemisphere has discrete areas which perform specific functions (mirrored in each hemisphere)
- outer layer of the cerebral hemispheres is called cerebral cortex (2-4mm thick), were reasoning and decision-making occur in cerebral cortex
what does the size of a sensory area within the cerebral hemisphere depend on
- it is proportional to the relative number of receptor cells present in the body part
once an impulse has reached a sensory area within the cerebral hemisphere where does it go
it is passed onto an associated area to be analysed and acted upon
what is the function of the cerebellum
- controls muscular movement, body posture, balance
- It does not initiate movement, only coordinates it
- it relays information to the areas of the cerebral cortex that are involved in motor control
what can happen to a person if there cerebellum is damaged
- can suffer from jerky uncoordinated movement
from what does the cerebellum receive information
- from organs of balance in the ears
- also receives info about tone of muscles and tendons
what is the function of the medulla oblongata
- regulatory centre of the autonomic nervous system
- controls involuntary activates such as breathing rate, heart rate, swallowing, coughing and vomiting
What is the function of the hypothalamus
- controls the autonomic nervous system
- controls complex patterns of behaviour (feeding, sleeping, aggression)
- monitors composition of blood plasma
- produce & secretes hormones (it is an endocrine gland)
what is the structure of the hypothalamus
- it has 2 centres
- ^one for both parasympathetic and sympathetic nervous systems
- it has a rich blood supply
what is the function of the pituitary gland
it controls mosts of the glands in the body
what is the structure of the pituitary gland
- split into 2 sections
- ^anterior pituitary & posterior pituitary
what is the function of the anterior pituitary
- produces 6 hormones
- ^ including follicle-stimulating hormone (FSH)
what is the function of the posterior pituitary
- stores and releases hormones produced by the hypothalamus
- ^such as ADH involved in urine production
what are the steps between the stimulus and the response
- receptor: detects stimulus and creates an action potential in the sensory neurone
- sensory neurone: carries impulse to spinal cord
- relay neurone: connects the sensory neurone to the motor neurone within the spinal cord or brain
- motor neurone: carries impulse to the effector to carry out the appropriate response
what is the spinal cord
- column of nervous tissue running up the back
- surrounded by the spine for protection
- At intervals along the spinal cord pairs of neurones emerge
what type of reflex is the knee-jerk reflex
spinal reflex
What is a spinal reflex
this means that the neural circuit only goes up to the spinal cord, not the brain
explain the knee-jerk reaction
- when patella tapped, it stretches the patella tendon
- ^this stimulus initiates a reflex arc
- causes quadracep to contract
- ^at same time, relay neurone inhibits motor neurone of quadracep, causing it to relax
- both contraction and relaxation cause leg to kick
What could the absence of the knee-jerk reaction indicate
- may indicate nervous problems
- multiple oscillation of the leg may be a sign of a cerebellar disease
what is the knee-jerk reaction used for in the body (why have it)
- used by body to help maintain posture and balance with little effort or conscious thought
when does the blinking reflex occur, what is its purpose
- when cornea is stimulated (for example by being touched)
- Purpose is to keep cornea safe from damage due to foreign bodies (e.g dust, flying insects, loud sounds or bright light)
What type of reflex is the blinking reflex
- cranial reflex: occurs in the brain not the spinal cord
explain how the blinking reflex actually occurs
- eye is irritated by foreign body
- stimulus made sent along sensory neurone, goes to relay neurone in brain stem
- impulse sent to motor neurones to illicate response to close eye
what does the presence of the blinking reflex indicate what is it used to test for
- if present , lower brain stem is functioning
- used to test wether patient is brain-dead, if corneal response present patient cannot be classified as brain-dead
what is an experiment that can be used to test reaction time
- ruler drop test
- converts distance dropped into reaction time
How do reflexes increase your chance of survival
- being involuntary responses: prevents brain from being overloaded as decision making regions not involved
- not having to be learnt: provide immediate protection as present at birth
- extremely fast: usually only involved 1-2 synapses
- many reflexes are used everyday such as maintaining balance and controlling digestion
what are the 3 types of muscles
- skeletal muscle
- cardiac muscle
- involuntary muscle (smooth muscle)
what is skeletal muscle
- makes up the bulk of body muscle tissue
- cells responsible for movement (e.g. biceps and triceps)
What is cardiac muscle
- cells found only in heart
- cells are myogenic (self-exciting, causing heart to beat in regular rhythm)
features of involuntary muscle (smooth muscle)
- found in walls of hollow organs and blood vessels
- different cells contract in different directions
- slow contraction speed
- not striated
what are the differences in structure and function of the 3 different muscle types
skeletal:
- multinucleated
- tubular fibres
- striated/striped
Cardiac:
- lightly striated
- branched fibres
- uninucleated
smooth muscle:
- non-striated
- spindle shaped fibres
- uninucleated
structure of skeletal muscle
- made up of bundles of muscle fibres
- ^enclosed within plasma membrane known as sarcolemma
structure of muscle fibres
- contain number of nuclei
- are much longer than normal cells
- ^as they are formed from individual embryonic muscle cells fusing together
- ^makes muscle stronger, as junction between adjacent cells would act as weak point
- shared cytoplasm within a muscle fibre is known as sarcoplasm
- contain lots of mitochondria to provide ATP needed for muscle contraction
- have modified versions of endoplasmic reticulum called sarcoplasmic reticulum
- ^this extends throughout the muscle fibre and contains calcium ions required for muscle contraction
structure of sarcolemma
- parts of the sarcolemma fold inwards (known as transverse or T tubules)
- ^helps spread electrical impulses throughout the sacroplasm
- ^this ensures that whole fibre receives the impulse to contract at the same time
what are myofibrils, what is the (macro) structure & function
- long cylindrical organelles made of protein and specialised for contraction
- individually provide almost no force but collectively very powerful
- myofibrils line up parallel to each-other to provide maximum force own they contract together
- made up of actin and myosin
- actin: thinner filament, consists of 2 strands twisted around eachother
- myosin: thicker filament, consists of long rod shaped fibres with bulbous heads that project to one side
What are the H-zone of myofibrils
- H-zone: lighter coloured region found in centre of each dark band, only myosin filaments are present at this point, when muscle contracts the H zone decreases
what are the light bands of myofibrils
- also called I-band or isotopic band
- regions where myosin filaments and actin do not overlap
- what are the dark bands of myofibrils made up of
- what is another name for them
- also known as anisotropic bands or A-band
- appear darker because presence of thick myosin filaments
- edges are particularly dark as myosin is overlapped with actin
What are the Z-lines of myofibrils
- line found at centre of each light band
- distance between adjacent Z-lines is sarcomere
what features are visible from a microscope view of skeletal muscle
- individual muscle fibres
- highly structured arrangement of sarcomeres, dark and light bands
- streaks of connective and adipose tissue
- capillaries running in between the fibres
what are properties of slow-twitch muscle fibres
- fibres contract slowly
- provide less powerful contractions but over longer period
- used for endurance activities (do not tire easily)
- gain energy from aerobic respiration
- rich in myoglobin (protein that stores oxygen, red colour)
- rich supply of blood vessels and mitochondria
properties of fast twitch muscle fibres
- fibres contract very quickly
- produce powerful contractions (short periods)
- used for short bursts of speed&power as tire easily
- gain energy from anaerobic respiration
- low levels of myoglobin and blood vessels (pale)
- contain more, thicker myosin filaments
- store creatine phosphate
what is the sliding filament model used to describe
muscle contractions
What occurs to the sarcomere during muscle contraction
- the light band becomes narrower
- Z-lines move closer together, shortening the sarcomere
- H-zone becomes narrower
- the dark band remains the same width, as the myosin filaments themselves have not shortened
what happens when the sarcomere returns to its original length
the muscle relaxes
what is the structure of myosin filaments
- have globular heads that are hinged
- ^allows them to move back and forward
- on the head is a binding site for actin and ATP
- the tails of several hundred myosin molecules come together to form myosin filaments
structure of actin
- have binding sites for myosin heads
- ^called actin-myosin binding sites
- these binding sites often blocked by protein tropomyosin
- ^held in place by protein troponin
what is happening to actin when a muscle is relaxed
- actin-myosin sites are blocked by tropomyosin
- ^myosin heads cannot bind to actin and filaments cannot slide past each other
What is happening to actin when a muslce is stimulated to contract
- myosin heads form bonds with actin filaments known as actin-myosin cross-bridges
- myosin heads then flex (change angle) in unison, pulls actin filaments along myosin filaments
- ^myosin then detaches from actin and head returns to original angle using ATP
- myosin then reattaches further along and pulls again
- ^this is repeated up to 100 times per second
when does muscle contraction occur
- triggered when action potential arrives at a neuromuscular junction (point where motor neurone and a skeletal muscle fibre meet)
what are the muscle fibres that are supplied by a single motor neurone called
- called motor units, fibres act as single unit
What is the difference in motor units stimulated when a large and small force are needed
- if strong force needed, large number of motor units stimulated
- if small force, small number of motor units stimulated
Once a action potential arrives at a neuromuscular junction what happens
- it stimulated calcium ion channels to open
- ^calcium ions diffuse from synapse into synaptic knob
- ^cause synaptic vesicles to fuse with presynaptic membrane
- Acetylcholine released into synaptic cleft (exocytosis), diffuses across synapse
- binds to receptors on postsynaptic membrane (the sarcolemma)
- ^opens sodium ion channels (depolarisation occurs)
- acetylcholine breaks down, prevents overstimulisation
- choline and ethanoic acid (products of acetylcholine breakdown) diffuse back to presynaptic neurone, recombined into acetylcholine
what happens when the action potential reaches the sarcoplasmic reticulum
- stimulates calcium ion channels to open
- ^calcium ions diffuse down concentration gradient flooding the sarcoplasm with calcium ions
- calcium ions bind to troponin causing it is change shape
- ^this pulls on tropomyosin moving it away from actin-myosin binding sites
- now binding sites are exposed, sliding filament model occurs
- the cycle continues as long as muscle is stimulated
How does depolarisation of the sarcolemma travel through the muscle fibre
- Spreads through T-tubule
- ^they are in contact with sarcoplasmic reticulum
what does the sarcoplasmic reticulum contain
- contain calcium ions which it actively absorbs from the sarcoplasm
what provides the energy for muscle contraction
- provided by the hydrolysis of ATP into ADP & phosphate
what part of muscle contraction needs energy
- Energy required for movement of myosin heads back to original shape after is has pulled actin filament
- to enable sarcoplasmic reticulum to actively reabsorb calcium ions from the sarcoplasm
How can creatine phosphate be used to generate ATP
- Acts as reserve supply of phosphate for phosphorylation of ADP to ATP
- it allows for immediate ATP generation
- reserve stores are used up quickly
- used for short burst of vigorous exercise (tennis serves)
- when muscle is relaxed, creatine phosphate store is replenished using phosphate from ATP
What is the sequence of events that takes place for an action potential to occur
- Resting Membrane Potential:
Neuron at -70 mV. - Depolarization:
Stimulus opens Na+ channels. - Threshold Reached:
-55 mV threshold crossed. - Rapid Sodium Influx:
Na+ floods in, neuron becomes positive. - Repolarization:
Na+ channels close, K+ channels open. - Hyperpolarization:
K+ outflow overshoots briefly. - Sodium-Potassium Pump:
Restores resting potential. - Refractory Period:
Temporarily less responsive.
How is an action potential propagated
Neurone is at resting potential
Initiation:
Action potential starts at the axon hillock.
Depolarization:
Na+ channels open, causing local depolarization.
Propagation:
Positive charge triggers adjacent Na+ channels to open.
Conduction:
Action potential travels down the axon.
Refractory Period:
Prevents backward transmission.
Continuous Process:
Repeats along the entire length of the axon.
