neuronal communication Flashcards
you will prefer stepping on legos once you complete this
describe the sensory neurones structure and function
- dendron from receptors in skin
- axon leading to another neurone
- cell body joining dendron and
axon - transmits impulse from sensory receptor cell to relay neurone, motor neurone or brain (CNS)
what is homeostasis?
maintenance of a stable internal environmental within tolerable limits
describe the structure and function of a relay neurone
- cell body in centre with lots of dendrites and axons coming out of it
- transmits impulses between neurones
describe the structure and function of a motor neurone
- cell body with dendrites coming off it
- one long axon in direction of impulse
- myelinated
- schwann cells and nodes of ranvier
- transmits impulse from sensory or relay neurone to effector
what are the key features of a neurone?
cell body
- DNA in a nucleus and lots of RER and mitochondria
dendrons
- protrusions from cell body connected to other cells
axons
- carry impulse away from cell body
what is the myelin sheath and why is it important?
- made of many layers of schwann cell membranes
- insulates the axon which helps increase speed of impulse
what are nodes of ranvier and why are they important?
- gaps between adjacent schwann cells where saltatory conduction occurs
- where axon depolarises
what is saltatory conduction?
- depolarisation of the axon
- impulse can “jump” from one node to another
what is the role of a receptor?
detect a stimulus
what structure are receptors?
specialised cells or peripheral endings of neurone
what transduction of energy occurs at receptors?
stimulus/mechanical energy (light, touch) to electrical energy
what are pacinian corpuscles?
mechanoreceptors found deep in skin of hands or feet
describe the structure of a pacinian corpuscle
- non myelinated terminal of a neurone
- surrounded by connective tissue
what ions channels are located in the neurone ending at the corpsucle?
stretch mediated ion channels
describe how a stretch mediated ion channel works in a corpuscle
- high conc sodium ions outside axon and is less positive inside
- when pressure is applied the gates open and sodium ions diffuse into sensory neurone down electrochemical gradient and becomes depolarised
- this creates a generator potential
- if enough pressure is applied, an action potential is produced
describe the components and events involved in a reflex arc
- receptor cells detect a stimulus and sends an electrical impulse along sensory neurone
- it passes over synapse to relay neurone in CNS and the motor neurone to effector cells which triggers them to react
describe how resting potential is generated
- active transport of 2 K+ into cell for every 3 Na+ out of cell which uses a sodium potassium pump
- results in more Na+ outside and more K+ inside
- the uneven distribution causes facilitated diffusiondown electrochemical gradient
- membrane is more permeable to K+ as more K+ ion channels are open than sodium ones so ends up more Na2+ and K+ outside than K+ inside
what is the value of resting potential?
-70mV
describe how an action potential is generated
- energy of stimulus causes Na+ voltage gated ion channels to open and increase membrane permeability to Na+
- sodium ions diffuse into axon making the outside less negative
- change of pd causes more voltage gated ion channels to open and more Na+ to diffuse in (positive feedback)
- continues until pd hits +40mV
describe the propagation of a nerve impulse as localised circuits
- depolarisation can only occur at nodes of ranvier where no myelin is present
- Na+ can pass through membrane at nodes
- longer localised circuits arise between nodes
- action potential jumps from nod to node
- repolarisation uses ATP so having fewer nodes makes the impulse more efficient
describe how a resting potential is re-established after and action potential
- once membrane reaches pd +40mV Na2+ channels close and K+ channels open
- more k+ outside the membrane causes hyperpolarisation
- eventually k+ channels close and sodium ions start diffusing down the electrochemical gradient
- sodium potassium pump starts working again and re-establishes the resting potential
how does myelination affect speed of impulse?
allowing depolarisation at certain points in the membrane makes transmission faster as it doesn’t have to occur at every point along the membrane
how does axon diameter affect speed of impulse?
large diameter means faster flow as there is less resistance to flow of ions in cytoplasm
how does temperature affect speed impulse?
- ions diffuse faster at a higher temperatures
- occurs up to 40C as proteins denature
what is the all or nothing principle?
if the stimulus is not strong enough then there is not enough depolarisation to reach threshold value so action potential doesn’t occur
what is the refractory period?
hyperpolarisation after the action potential which prevents a stimulus leading to a second action potential
what is the importance of the refractory period?
ensures action potential:
- are discrete impulses
- do not overlap
- are unidirectional
what is the synaptic cleft?
gap that separates axon of one neurone and dendrite of the next which is 20-30nm across
what is the synaptic knob?
swollen end of the presynaptic neurone that contains lots of endoplasmic reticulum and mitochondria
what are the two types of neurotransmitter?
excitatory and inhibitory
why are mitochondria and ER in abundance in knob?
bulk transport required energy and synthesis of vesicles
what does an excitatory neurotransmitter do?
results in the depolarisation of the postsynaptic neurone which results in an action potential if threshold is reached
what does an inhibitory neurotransmitter do?
results in the hyperpolarisation of the postsynaptic neurone which prevents an action potential
what is the process of synaptic signal transmission?
- action potential arrives at the presynaptic neurone and depolarises the membrane causing Ca2+ voltage gated ion channels to open
- ions diffusion into presynaptic knob which causes synaptic vesicles containing neurotransmitters to fuse to the membrane and release them via exocytosis
- they diffuse across the synaptic cleft and bind to specific receptor molecules on the post synaptic membrane
- Na+ ion channels open and sodium ions diffuse into postsynaptic neurone and cause a new action potential
what molecule breaks down ACh and into what?
acetylcholinesterase into acetate and choline
what is summation?
combination of graded potentials in postsynaptic neurone
what is spatial summation?
the sum of excitatory potentials from different neurones triggering an action potential
what is temporal summation?
many excitatory potentials from one neurone in quick succession
how do synapses ensure unidirectional impulses?
receptors are only present on postsynaptic membrane
what are the terms for impulses from a single neurone passing to many neurones and vice versa?
divergence and convergence
what is the benefit of filtering out background stimulation?
ensures that only stimulation that is strong enough will be passed on
outline the ways motor and sensory neurone are similar
both have
- dendrites
- axons
- cell body
- myelin sheath and schwann cells
suggest how the immune system causes damage to the nervous system
- antigens on neurones activate immune system
- antibodies against neurones are produced
where are acetylcholine receptors found ?
postsynaptic membrane
suggest and explain the effect that nicotine has on the nervous system
- nicotine slows down rate of transmission
- binds to receptors
- receptors remain in refractory period for longer
suggest how GABA is released from the inhibitory neurone and why an action potential may not occur if both GABA and acetylcholine are released
- nerve impulse causes influx of Ca2+ into presynaptic neurone
- causes vesicles to fuse with the membrane and release GABA via exocytosis to diffuse across the synaptic cleft
- binds to complementary receptors on post synaptic membrane
- causes Cl- ion channels to open and the influx of chloride ions causes postsynaptic neurone to become hyperpolarised
- when Na+ enters the postsynaptic membrane from acetylcholine, there isnt enough +ve charge to reach threshold voltage so no action potential occurs
describe structure of the mammalian nervous system
(mention CNS, PNS, brain, spinal cord, motor system, sensory system, somatic system, autonomic system, sympathetic, parasympatheticf)
what does the autonomic nervous system do?
controls involuntary processes using centres located near the medulla oblongata eg. swallowing, breathing, HR
what do sympathetic nerves do?
- release noradrenaline to mobilise body systems (fight or flight)
- increase HR
- open airways and dilate pupils
- vasodilation
- glucose release
what do parasympathetic nerves do?
- releases acetylcholine to relax body systems
- rest HR
- regular airways and pupils
- regular glycogen and insulin levels
how do reflexes increases survival?
- doesnt involve decision making so more rapid so brain can deal with more complex responses
- present from birth
- fast
what is a reflex?
an involuntary fixed response to a stimulus
explain the knee jerk patella reflex
- occurs when patellar tendon stretched
- reflex arc followed but relay neurone also inhibits motor neurone of flexor muscle
- extensor muscle contracts
- determines the presence of spinal lesion
explain the blinking corneal reflex
- cornea touched/light
- sensory neurone (5th cranial nerve) and motor neurone (7th cranial nerve) are involved
- very rapid response to close eyes
- tests brain stem function in unconscious patients
what is the structure of cardiac muscle?
- contract without stimulation (myogenic)
- branched allowing faster signal propagation and contractions in 3D
- connected by gap junctions at intercalated discs
- more mitochondria as reliant on aerobic respiration
what are the unique properties of cardiac muscles?
- longer period of contraction and refraction which is needed to maintain a viable heart beat
- tissue doesnt become fatigued allowing for continuous, lifelong contractions
- interconnected network of cells is separated between atria and ventricles allowing them to contract separately
what are the unique properties of smooth muscles?
- long but slow contractions
- controls involuntary contractions
- not striated
- spindle shape
- uninucleated
what are the unique properties of skeletal muscles?
- short, rapid contractions
- attached to the skeleton
- voluntary movement
- multinucleated tubular fibres that are heavily striated
how are skeletal muscles organised?
- muscular bundles containing multiple muscle fibres
- enclosed by the sarcolemma
- fibres are multinucleate and longer than normal cells
- have a shared cytoplasm called the sarcoplasm
- many mitochondria
- T-tubules connected by sarcoplasmic reticulum
how are muscle fibres formed?
individual embryonic muscle cells fusing together
what is the sarcolemma?
plasma membrane that envelopes muscle fibres
what are T-tubules?
points where membrane folds inwards to help spread electrical impulses throughout the sarcoplasm
why are there many mitochondria in muscle fibres?
provide ATP for muscle contractions
what is the sarcoplasmic reticulum?
modified ER that contains calcium ions for contraction
what are myofibrils?
long cylindrical organelles made of proteins specialised for contractions
what is the structure and function of myofibrils?
- lined up in parallel to provide maximum force when contracting together
- made of 2 different protein filaments (actin and myosin)
- divided into repeating sections called sarcomeres
what is in a sarcomere?
- Z disc
- I band
- A band
- H zone
- M line
describe the structure of a sarcomere
(refer to a diagram)
where is tropomyosin found?
wrapped around the actin filaments
where is the M line found?
down the centre of only the myosin filaments
where is the Z line found?
down the centre of only the actin filaments
where are I (light) bands found?
around where there are only actin filaments
where are A (dark) bands found?
around areas with only myosin and also where myosin and actin overlap
where are H zone found?
around areas with only myosin
which part of the brain controls learning, memory and conscious thoughts?
cerebrum
which part of the brain controls unconscious actions including posture and balance?
cerebellum
which part of the brain controls breathing rate and heart rate?
medulla oblongata
which part of the brain is the regulatory centre for temperature and water balance?
hypothalamus
what is the structure of myosin?
- globular heads that are hinged to allow them to move forwards and backwards
- one head binds to ATP and the other to actin
- two filaments wound around eachother
what is the structure of actin?
- binding sites for myosin (actin-myosin binding sites)
- these are blocked by tropomyosin and held in place by troponin
- two filaments wound around eachother
what happens at neuromuscular junctions?
- action potential initiated in motor neurone
- acetylcholine released into synaptic cleft
- depolarisation spreads along the sarcolemma and T-tubules
- Ca2+ are released from the sarcoplasmic reticulum
- sarcomere contraction is triggered, shortening the muscle fibres
how is tropomyosin removed from myosin binding site on actin?
- the arrival of an action potential means an impulse penetrates the muscle via transverse(T) tubules causing Ca2+ ion channels in the sarcoplasmic reticulum to open
- calcium ions diffuse into muscle fibres and bind to troponin molecules
- they change shape which causes the tropomyosin to move to a different position
what happens when tropomyosin moves away from binding site?
myosin head is free to bind to actin which forms an actinomyosin bridge
how does the actinomyosin birdge break?
- ATP binds to active site on one myosin head
- hydrolysed into ADP and Pi
- energy releases moves the head back down to the starting position
what is another name for the ATP binding myosin head?
ATPase
what is the sliding filament theory?
movement of calcium ions to move tropomyosin, and the hydrolysis of ATP in the myosin head to move the actin filament long the myosin
how does a sarcomere change when it contracts?
- whole sarcomere shortens
- I band and H zone become narrower
- Z lines move closer together
- A band remains the same
what is white matter?
bundles of myelinated axons
what is grey matter?
neuronal cell bodies and dendrites and unmyelinated nerve fibres
what is the role of creatine phosphate in muscle contraction?
act as backup supply of phosphate ions to reform ATP quickly during short bursts of high activity
energy from the hydrolysis of ATP is needed for what two processes during muscle contraction?
- movement of myosin heads
- active transport of calcium ions back into the sarcoplasmic reticulum
explain how it is possible for ACh to have an effect on cells in the skin of the squid
- secreted into the blood as it can be a hormone
- binds to receptors on cell surface membrane of skin
which subdivision of the peripheral nervous system supplies the SAN?
autonomic nervous system
which part of the brain are the nerves that the SAN attach to connected to?
medulla oblongata
explain how blocking calcium channels could inhibit insulin secretion
calcium ions cant enter the cell so dont trigger vesicles to release insulin via exocytosis
