Neuronal Communication Flashcards
1st to 5th second during action potential
1- polarised resting potential difference 2- depolarisation 3- repolarisation 4- hyper polarisation 5- repolarised resting potential
Nervous response electrical impulse pathway
Receptor, sensory neurone, relay neurone, motor neurone , effector cell
Node of ranvier
Found between each adjacent Schwann cell
In myleniated neurones this creates gaps in the myelin sheith, allowing electrical impulses to jump between gaps
Sensory neurone
Transmit impulses from sensory receptor cells to a relay neurone, motor neurone or the brain
They have one dendron, carries impulse to cell body
They have one axon, carries impulse away from cell body
Relay neurones
Transmit impulses between neurones
E.g between sensory neurones and motor neurones
Many short axons and dendrons
Motor neurones
Transmit impulses from relay or sensory neurone to an effector, such as a muscle or a gland
One long axon and many short dendrites
Myelinated neurones
Axons covered in myelin sheith, made of many layers of plasma membrane
Schwann cells produce these layers of membrane by growing around the axon many times
Each time they grow around the axon a double phospholipid bilayer is laid down
20 layers when Schwann cell stops growing
Mylien sheith acts as an insulator meaning electrical impulses travel and much faster speeds
What is resting potential
Minus 70 milli volts
Resting potential is the difference in charge between the inside and the outside of the axon
Membrane is said to be polarised
What is the pacinian corpuscle
Specific sensory receptors that detect mechanical pressure, and convert it into electrical energy
Enable you to know which joints are changing direction
End of the sensory neurone is found within the centre of the corpuscle, surrounded by layers of connective tissue, each layer is separated by a layer of gel
Creation of resting potential
- Na+ are actively transported out of the axon while K+ is transported in by a specific intrinsic protein known as the sodium potassium pump
- movement of sodium out (3)> potassium in (2)
- sodium ions outside the membrane diffuse back in down an electrochemical gradient, whereas potassium ions diffuse out
- most of the gated sodium channels are closed whereas the potassium channels are open allowing k+ to move out
- meaning there are more positively charged ions outside the axon than in the cell
What is action potential
When a stimulus is detected by the sensory receptor the energy reverses charges on the axon membrane causing the membrane to become positively charged +40mv
Stages of action potential (1-3)
- neurone has resting potential, potassium channels are open , sodium voltage gated ion channels are closed
- energy from the stimulus triggers some sodium voltage gated ion channels to open, sodium therefore diffuses into the axon down their electrochemical gradient making the inside less negative
- this change in charge causes more sodium ion channels to open, allowing more sodium ions to diffuse into the axon
Stages of action potential (4-6)
- When the potential difference reaches +40mv the voltage gated sodium channels close and potassium channels open
- potassium ions diffuse out of the axon down their electromagnetic gradient reducing the charge inside the axon
- inside becomes more negative than usual resting state “ hyper-polarisation” , potassium pumps close. Sodium potassium pump restores resting potential
What is the refractory period
After an action potential has been stimulates the membrane enters a refractory period where it cannot be stimulated
Importance of refractory period
- creates discrete impulses, meaning each action is separate from each other
- ensures action potential travels in one direction
Limits number of impulses travelling, preventing overstimulation
Propagation of action potential
axon is at resting potential
Stimulus causes a sudden influx of sodium ions, membrane is depolarised
Localised electrical Circuits established by the influx of sodium ions cause sodium voltage gated channels to open further down the axon
Behind this sodium gates close and potassium gates open leading to potassium ions leaving the axon down an electrochemical gradient
Action potential is propagated along the whole way
Membrane becomes hyper polarised then reaches resting
Benefits of salutatory conduction
Faster
More efficient due to less ATP use
Factors effecting speed at which an action potential travels
Axon diameter- wider = faster due to less resistance of flow of ions in the cytoplasm
Temperature- higher temp, faster the nerve impulse as ions diffuse faster at higher temperatures, pumps and channels may become denatured at temperatures too high
Myelinatation
What is the all or nothing principle
A certain level of stimulus , threshold value, always triggers a response
If threshold is reached membrane is depolarised , action potential is then generated
Synaptic cleft
Gap which separates the axon of one neurone from the dendrite of the next neurone
Presynaptic neurone
Neurone along which impulse has just traveled
Postsynaptic neurone
Neurone that receives the neurotransmitter
Synaptic knob
Swollen end of the presynaptic neurone
Contains many mitochondria and large amounts of endoplasmic reticulum to enable it to manufacture neurotransmitters
Synaptic vesicles
Vesicle containing neurotransmitters.
The vesicles fuse with the presynaptic membrane and release their contents into the synaptic cleft
Neurotransmitter receptors
Receptor molecules which the neurotransmitter binds to in the postsynaptic membrane
Excitatory neurotransmitter
Results in the depolarisation of the postsynaptic neurone
If the threshold is reached in the postsynaptic membrane an action potential is triggered
E,g acetylcholine
Inhibitory neurotransmitter
Neurotransmitter results in the hyperpolarisation of the postsynaptic membrane
This prevents an action potential being triggered
GABA is an example
Transmission of impulses across synapses
Action potential reaches the end of the presynaptic neurone
Depolarisation of the presynaptic membrane causes calcium ion channels to open
Calcium ions diffuses into the presynaptic knob
Synaptic vesicles containing neurotransmitter to fuse with the presynaptic membrane, neurotransmitter is released into the synaptic cleft by exocytosis
Neurotransmitter diffuses across the synaptic cleft and binds with specific receptor molecule on postsynaptic membrane
Sodium channels open
Sodium ions diffuse into the postsynaptic neurone
Triggers an action potential and the impulse is propagated along the postsynaptic neurone
5 main gross structures in the brain
Cerebrum Cerebellum Medulla oblongata Hypothalamus Pituitary gland
Cerebrum
Controls voluntary actions such as learning, memory, personality, and conscious thought
Split into left and right halves which control different sides of the body
Highly convoluted which increases surface area and therefore ability to carry out complex activity
Cerebellum
Control of muscular movement, body posture, balance.
It does not initiate movement
If this area is damaged a person suffers from jerky uncoordinated movement
Medulla oblongata
Contains many important regulatory centres of the autonomic nervous system
Controls reflex activities such as ventilation and heart rate
Swallowing, digestion , coughing
Hypothalamus
Main controlling region for the autonomic nervous system
Has 2 centres one for the parasympathetic and one for the sympathetic
- controlling complex patterns of behaviour, such as feeding, sleeping and aggression
-monitors the composition of blood plasma, such as the concentration of water and blood glucose, therefore has rich blood supply
- producing hormones, as it is an endocrine gland
Pituitary gland
Found at the base of the hypothalamus, divided into 2 sections
- anterior pituitary, which produces 6 hormones including FSH
- posterior pituitary- stores and releases hormones produced by hypothalamus such as ADH
Events at neuromuscular junctions
- AP arrives, voltage gated calcium channels open, ca2+ influx
- Ca2+ cause vesicles containing ACH to fuse with presynaptic membrane
- ACH is released and diffuses across the synaptic cleft
- ACH bind with lingand gated sodium channels causing them to open and therefore na+ influx
- this depolarisation the membrane and initiates an action potential which spreads along the membrane
- depolarisation of sarcolemma spread down T-tubules
- ca2+ channels open and ca2+ ions diffuse out of the sarcoplasmic reticulum
How is strength of stimulus communicated
Frequency of action potentials
Knee jerk reflex
Works to quickly straighten leg, helps maintain posture and balance
-stretch receptors in the quadricep detect the muscle is being stretched
- nerve impulses are passed along a sensory neurone, which communicates directly with a motor neurone in the spinal cord
- motor neurone carries the nerve impulses to the effector (quad muscle)
Causing it to contract and shorten
Blinking reflex
When your body detects something that could damage your eye
- sensory nerve endings in cornea are stimulated by touch
- a nerve impulse is sent along the sensory neurone to a relay neurone in the CNS
- the impulse is passed from the relay neurone to motor neurones
- motor neurones send impulses to effectors, orbicularis oculi muscles that move your eye lids causing a contraction
How muscle contraction is triggered by action potential
- Action potential from motor neurone depolarisation the sarcolemma
- depolarisation spreads down T-tubules to the sarcoplasmic reticulum
- sarcoplasmic reticulum releases ca2+ into sarcoplasm
- ca2+ bind to troponin causing it to change shape and pull the tropomyosin out of the actin-myosin binding sites
- myosin head binds forming actin myosin cross bridge
How muscle contracts
- Calcium ions that are released from sarcoplasmic reticulum bind to troponin causing it to change shape
- as a result the tropomyosin molecule pulls away from the binding sites on the action molecule
- myosin head now attaches to the binding sites on the actin filament, forming actin myosin cross bridges
- myosin head flexes pulling the actin filament along, a molecule of ADP bound to myosin head is released
- ATP molecule can now bind to the myosin head causing it to detach from the actin filament
- hydrolysis of ATP to ADP provides energy for myosin head to resume its normal position
- head of myosin reattaches to a binding site further along the actin filament, cycle is repeated
A band
Anywhere where there’s myosin
I band
Just actin
light band
H zone
Just myosin
M line
Middle of myosin
Z line
End of a sarcomere
Sacromere
Single unit of a microfibril
Skeletal muscle
Bulk of body muscle tissue
Responsible for movement
Striated, voluntary action, regularly arranged so muscle contracts in 1 direction rapidly, short contraction,
Fibres are tubular and multinucleate
Cardiac muscle
Only found in heart
Myogenic, meaning they contract without need for nervous stimulus, causing heart to beat
Specifically striated ( less visible than skeletal) , involuntary, cells branch and interconnect resulting in simultaneous contraction
Length and speed of contraction intermediate
Fibres are branch and uninucleated
Involuntary muscle
Found in many parts of the body e.g stomach, blood vessels, digestive tracks
Non striated, involuntary, no regular arrangement
Slow contraction speed but remain contract for long length of time
Use of creatine phosphate
- Body can generate ATP by using chemical creatine phosphate, which is stored in muscle.
- to form ATP, ADP must be phosphorylated, a phosphate group must be added, creatine phosphates acts as a reserve supply of phosphate
Why are action potentials not constantly generated by wearing cloths
Sodium ion channels remain open therefore resting potential is never established
Role of synapses
Allow action potentials to be passed from one neurone to another
Allows convergence of impulses
Divergence of impulses
Ensures 1 direction of travel for an impulse
Allows low level stimuli to be amplified
effects of adrenaline
- secreted from the adrenal gland ( sometimes the medulla oblangata )
- transported in blood stream and has rapid effect
e. g vasoconstriction/dilation, relaxing of smooth muscle to increase air flow,, stimulates the breakdown of glycogen into glucose in the liver cells ( glycogenolysis)
describe the second messenger model, action of adrenaline
- when adrenaline binds to its receptor the enzyme adenylyl cyclase (present in membrane) is activated
- adenylyl cyclase triggers the conversion of ATP into cyclic AMP
- increase in cAMP levels activates specific enzymes called protein kinases which phosphorylate and hence activate other enzymes
Difference between dendron and dendrite
Dendrites are appendages designed to receive communication from other neurones
Dendrons conduct impulse towards cell body
Heart rate of a calm mammal compared to one exhibiting flight or fight responses
Calm - heart rate is slow, contracting with less force
Fight/flight - faster, contracting with greater force
Neurotransmitters involved para/sympathetic
Parasympathetic- acetylcholine
Sympathetic - noradrenaline
Differences between CNS and Peripheral nervous system
- CNS contains relay neurones, spinal chord and brain whereas peripheral contains all other neurones connecting the CNS to the rest of the body ( effectors )
- peripheral can be divided into somatic / autonomic whereas CNS cannot
- CNS has a role in coordinating whereas peripheral has roles in sensing stimuli and conducting impulses
Where would you find the myelin sheath
Around the membrane of Schwann cells
How do potassium ions leave the axon
Facilitated diffusion out of potassium ion channels
