Neuronal communication Flashcards
3 key features of a neurone
Cell body, dendrons and axons
what are the 3 types of neurone and their order?
Receptor-sensory neurone-relay neurone-motor neurone-effector
What makes a myelinated neurone
Schwann cells which wrap around the axon leaving gaps in between called the nodes of Ranvier.
What does Myelinated neurones allow?
Quicker transmission of electrical impulses as the electrical impulse jumps from one node to the next
2 features of sensory receptors
-Specific to a single type of stimulus
-Acts as a transducer (concerts a stimulus into a nerve impulse-produces a generator potential )
What is the stimulus for a mechanoreceptor?
pressure or movement
What is a pacinian corpuscle?
They are nerve endings in the skin, responsible for sensitivity to deep pressure touch and high frequency vibration.
What type of sodium channel does pacinian corpuscle have?
stretch-mediated sodium channel (when they stretch their permeability to Na changes)
5 steps involved in generating an action potential in the Pacinian corpuscle
- the neurone has a resting potential as the Na channel is too narrow
- When pressure is applied the corpuscle changes shape and the membrane around the neurones stretches
- Where the membrane stretches the Na channels widen allow Na+ to diffuse into neurone
- The influx Na+ depolarises the membrane creating a generator potential
- Generator potential creates an action potential
What is the resting potential (value)
-70mV
What causes the resting potential?
- 3 Na+ are actively transported out of the axon and 2 K+ are actively transported into the axon by sodium- potassium pump
- most of the sodium ion channels are voltage-gated so they cannot diffuse back into the axon
-potassium ion channels are open so they can freely diffuse out of the axon - negatively charged proteins in the axon
What value does depolarisation occur at
+40mV
6 steps of creating an action potential
- neurone has a resting potential
- The energy of a stimulus triggers some voltage-gated sodium channels to open, therefore allowing Na+ to diffuse into the axon down electrochemical gradient
- positive feedback occurs so more sodium channels open
- Once +40mV has been reached, Na voltage gated channels close and K voltage gated channels to open
- K+ diffuse out making the inside of the axon more negative again known as hyperpolarisation, now both voltage gated channels are closed
- the axon returns to resting potential- repolarised
How does an action potential cause an electrical impulse?
Positive feedback when the voltage gated sodium channels open. So when an action potential depolazizes the membrane it activates adjacent ones too. Refractory period means it can only be propagated forwards.
What is the refractory period?
a period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation.
It prevents the propagation of action potentials backwards along the axon
What is salatory conduction?
- the action potential cannot occur where the myelin sheath is present as it is insulated
- increased influx at nodes
- As a result it jumps between the nodes of ranvier
What are the advantages of salatory conduction?
- faster
-more energy efficient as reduces the amount of repolarisation needed
What other two factors affect the speed of action potentials
axon diameter- the bigger the faster because less resistance from the cytoplasm
temperature- higher temp the faster as ions diffuse quicker until 40 degrees plus denature occurs
What is the all or nothing principle?
Any stimulus that causes the membrane to reach threshold potential will generate an action potential. All action potentials have same magnitude. However if it is a strong stimulus it will cause more frequent action potentials
Give 5 features of a synapse
- synaptic cleft
-presynaptic neurone
-postsynaptic neurone
-synaptic knob
-synaptic vesicles
-neurotransmitter receptors
2 types of neurotransmitters
excitatory and inhibitory
4 steps involved in transmission across a cholinergic synapse
- action potentials arrives at end of presynaptic neurone causing Ca channels to open and Ca to enter presynaptic knob
- Ca2+ ions cause the vesicles to fuse with presynaptic membrane releasing acetylcholine into synaptic cleft
- Acetylcholine diffuses across the cleft and fuse with receptor sites on Na+ channels on the postsynaptic membrane causing them to open and Na+ to diffuse in
- Na+ influx causes action potential
What happens to acetylcholine once it has fused with sodium channels?
Acetylcholinesterase hydrolyses it into choline and ethanoic acid so it diffuses back across. These products also prevent the continuous production of new action potentials
ATP released by mitrochondria is used to recombine choline and ethanoic acid and is stored in vesicles
Where is a cholinergic synapse found?
junction between motor neurone and a muscle cell
What is the role of synapses
make sure impulses only travel one way and they allow one neurone to transmit impulse to multiple neurones and vice versa
What is spatial summation?
several different presynaptic neurons connect to one postsynaptic neurone which all release neurotransmitters which builds up to be enough to generate an action potential
What is temporal summation?
several impulses from one neuron over time which builds up to be enough neurotransmitter to cause an action potential
What is summation?
in some synapse the amount of neurotransmitter isn’t enough to reach threshold level so they build up
What two systems is the mammalian nervous system split into?
- Central nervous system (brain and spinal cord)
- Peripheral nervous system (all neurones)
What 2 systems does the peripheral nervous system split into?
- somatic nervous system (conscious)
-autonomic nervous system (subconscious)
What 2 systems makes up the autonomic nervous system?
-sympathetic motor system (‘fight or flight’) neurotransmitter = noradrenaline
-parasympathetic motor system (relaxing responses) neurotransmitter = acetylcholine
5 parts of the brains structure and their roles
- Cerebrum: controls voluntary actions e.g memory, personality
-Cerebellum: controls unconscious functions e.g balance, posture
-Medulla Oblongata: autonomic control e.g heart rate, breathing - Hypothalamus: regulatory centre for temperature and water balance
- Pituitary gland: stores and releases hormones that regulate body functions
What is the structure of cerebrum?
it is split into two halves- hemispheres and each one controls one side of the body. The outer layer of the cerebrum is called cerebral cortex. This is split into frontal and prefrontal lobe which is where reasoning and decision making occurs. The main region which controls movement is primary motor cortex located at the back of the frontal lobe.
What part of the brain initiates movement?
cerebrum
Which part of the brain controls muscular function?
cerebellum
What part of the brain controls sleeping and aggression?
Hypothalamus
What part of the brain monitors blood composition?
Hypothalamus
What part of the brain produces hormones?
hypothalamus and anterior pituitary gland (produces 6)
What part of the brain stores and releases hormones?
posterior pituitary
what is the reflex arc pathway
stimulus -> receptor ->sensory neuron -> relay neuron -> motor neuron -> effector -> response.
Which reflex can be used to check damage to spinal cord?
knee jerk
How does the knee jerk reflex work?
Leg tapped just below the patella, stretches the patellar tendon, initiates the reflex arc, extensor muscle on top of the thigh contracts, relay neurone inhibits motor neurone of the flexor muscle so it relaxes, contraction of the extensor muscle causes the leg to kick. muscles work antagonistically
How does the blinking reflex work?
Sensory nerve endings in the cornea are stimulated by touch,light or sound. An impulse is sent to relay neurone in the CNS the impulse is passed from the relay neurone to motor neurones. The motor neurones cause the orbicularis oculi muscles to contract, closing the eyelid. Consensual response (both close)
Why are reflexes important for survival?
-involuntary so the brain doesn’t become overloaded
-don’t have to be learnt
-extremely fast
What are the frequency of action potentials measured with?
Oscilloscope
