13 Neuronal Communication Flashcards
1 internal factor that cause a response in a plant and animal
Plant- water potential
Animal- blood glucose concentration
What responses do animals react through?
Electrical (via neurones)
Chemical (via hormones)
Why is coordination needed?
Coordinate functions of different cells and systems to operate in response to internal and external changes
Example of coordination ?
Muscle cells need to respire in order to contract. Thus need oxygen thus need red blood cells
What is homeostasis?
Constant internal environment.
What is cell signalling?
Communication at cellular level. Cells can transfer signals locally between neurones or synapses using a neurotransmitter or across large distances using hormones
Role of neurones?
Transmit electrical impulses rapidly around body so organism can respond to changes in internal and external environment
Structure of neurone?
Cell body (contains nucleus surrounded by cytoplasm. Cytoplasm contains many ER and mitochondria involved in production of neurotransmitters)
Dendrons (transmit e impulses towards cell body)
Axons (transmit e impulses away from cell body)
Types of neurone
Sensory
Relay
Motor
Function and makeup of sensory neurone
Transmit impulses from sensory reception to relay or motor or brain. One dendron one axon.
Function and makeup of relay neuron
Transmit impulses between neurones I.e sensory and motor. Many short axons and dendrons
Function and makeup of motor neurone
Transmit impulses from relay or sensory to an effector (muscle or gland). One long axon and many short dendrites
What are some axons of neurones covered in?
Myelin sheath made of layers of plasma membrane. Schwann cells produce these layers creating a double layer of phospholipid bilayer each time.
What does a myelin sheath do?
Acts as an insulating later and allows neurones to conduct electrical impulses at a faster rate of 100m per second
What is between each adjacent Schwann cell?
Node of ranvier (electrical impulse jumps from one node to the other)
Features of sensory receptors?
Specific to one type of stimulus
Act as a transducer converting stimulus into a nerve impulse (generator potential)
What is a pacinian corpuscle?
Mechanoreceptor. Detects mechanical pressure, located in skin
How does pacinian corpuscle convert mechanical pressure into a nervous impulse?
- ) in resting state the stretch-mediated sodium iron channels in membrane are too narrow to allow sodium to pass through them.
- ) when pressure applied= corpuscle changes shape which stretches membrane.
- ) membrane stretches, sodium iron channels widen and allow sodium ions to enter neurone
- ) influx of positive sodium ions causes membrane to become depolarised. Resulting in a generator potential
- ) generator potential causes action potential along sensory neurone to CNS
Explain how your body detects your finger has touched a pin!
- ) in resting state the stretch-mediated sodium iron channels in membrane are too narrow to allow sodium to pass through them.
- ) when pressure applied= corpuscle changes shape which stretches membrane.
- ) membrane stretches, sodium iron channels widen and allow sodium ions to enter neurone
- ) influx of positive sodium ions causes membrane to become depolarised. Resulting in a generator potential
- ) generator potential causes action potential along sensory neurone to CNS
Events creating a resting potential in axon
- ) 3 Na+ ions out and 2 K+ ions in axon by active transport
- ) thus Na+ ions diffuse back into axon down electrochemical gradient. k+ ions diffuse out.
- ) most gated sodium ion channels closed. Many potassium ion channels open so more K+ diffuses out. Thus more positively charged ions outside axon than inside- created resting potential of -70mV
Action potential of axon
1.) energy of stimulus opens sodium voltage-gated ion channels, allowing Na+ ions to diffuse into axon down electrochemical gradient
2.) change in charge causes more Na+ ions to open (positive feedback)
When potential reaches +40mV then the voyage gated sodium ion channels close and potassium open open. Na+ ions can no longer enter axon.
3.) K+ diffuses out down electrochemical gradient so the inside becomes more negative
4.) too negative = hyperpolarisation
5.) so K+ ion channels close and sodium- potassium pump cause Na+ ions to move out and K+ ions to move in. Axon returns to resting potential- repolarised
In an axon how is depolarisation continued along all regions? And what is this called?
Action potential in sensory receptor causes first region to be depolarised. This acts as a stimulus for depolarisation of next region. Process continues along length forming a wave of depolarisation
Why is a refractory period important in axon?
Makes sure all action potentials are unidirectional
And ensures action potential do not overlap
What is saltatory conduction?
Action potential jumps from one node to another on myelinated axons. Faster than wave of depolarisation. Long term s conduction is also more energy efficient as it reduces amount of repolarisstion (using ATP) needed
What three factors affect the speed at which an action potential travels?
1- myelinated neurone
2- axon diameter (bigger/ faster. Bc less resistance to flow of ions in cytoplasm)
3- temp (higher/faster. But obvs only up to 40•c
What is the all-or-nothing principle of nerve impulses?
Threshold value triggers a response. If threshold is reached there’s always an action potential. Strong stimulus creates same size action potential but occurs more frequently
What is the junction between two neurones called?
Synapse
How are impulses transmitted across synapse ?
Using neurotransmitters
The 6 features of a synapse ?
Synaptic cleft Presynaptic neurone Postsynaptic neurone Synaptic knob Synaptic vesicles Neurotransmitter receptors
What is a presynaptic neurone?
Neurone along which the impulse has arrived
What is a postsynaptic neurone
Neurone that receives neurotransmitter
What is a synaptic knob?
Swollen ;) end of presynaptic neurone. Contains many mitochondria and ER to make neurotransmitters
What is a synaptic vesicles
Vesicles containing neurotransmitters. They fuse w presynaptic membrane and release contents into synaptic cleft
What is a synaptic cleft
Gap which separates axon of one neurone from the dendrite of another
What are neurotrnsmitter receptors ?
Receptor molecules which the neurotransmitter binds to in the postsynaptic membrane
2 types of neurotransmitter?
1- excitatory (result in depolarisation of postsynaptic neurone. If threshold is reached in postsynaptic membrane then an action potential is triggered)
2- inhibitory (results in hyperpolarisation of postsynaptic membrane. Prevents action potential being triggered )
Example of a excitatory neurotransmitter?
Acetylcholine
Example of inhibitory neurotransmitter?
GAMA
Explain transmission of impulses across synapse
1.) action potential reaches end of presynaptic neurone
2.) depolarisation of presynaptic membrane causes calcium ion channels to open
3.) calcium ions diffuse into presynaptic knob
This causes presynaptic vesicles containing neurotransmitter to fuse w presynaptic membrane. Neurotransmitter released into synaptic cleft by exocytosis
4.) neurotransmitter diffuses across synaptic cleft and binds w it’s specific receptor molecule on postsynaptic neurone
5.) action potential triggered. Impulse is propagated along the postsynaptic neurone
Any neurotransmitter left in the synaptic cleft is removed. Why?
Prevents the response from happening again and allows the neurotransmitter to be recycled
What is the role of synapses? X3
Ensure impulses are unidirectional
Allow an impulse from one neurone to be transmitted to a number of neurones at multiple synapses. Results in a single stimulus creating a number of simultaneous responses
A number of neurones may feed into the same synapse with a single postsynaptic neurone. Results in a stimuli from different receptors providing a single result
What is spatial summation?
Occurs when a number of presynaptic neurones connect to one postsynaptic neurone. Each releases neurotransmitter which builds up to a high level in the synapse to trigger an action potential.
What is temporal summation?
Occurs when a single presynaptic neurone releases neurotransmitter as a result of an action potential several times over a short period. This builds up in the synapse until the quantity is enough to trigger an action potential
How do drugs work on synapses ?
Mimick shape of neurotransmitter (I.e nicotine has same shape as acetylcholine
Stimulates release of more neurotransmitter
Inhibiting the enzyme responsible for breaking down the neurotransmitter in synapse can result in loss of muscle control.
Explain how synapses ensure impulses are only transmitted in one direction?
Neurotransmitter receptors are only present on the postsynaptic membrane so can only cause depolarisation of this membrane resulting in action potential
Mammalian nervous system is organised structurally into two systems. What r they?
Central nervous system (brain and spinal cord)
Peripheral nervous system (consists of all neurones that connect CNS to rest of body)
Nervous system is functionally organised into two systems. What r they?
Somatic nervous system (under conscious control I.e move a muscle in arm)
Autonomic nervous system (works constantly. Under subconscious control. I.e heart beat or digesting food)
The autonomic nervous system further divided into what ?
Sympathetic (if outcome inc activity)- inc in ❤️ rate
Parasympathetic (if outcome Dec activity)- Dec in breathing or ❤️ rate after excersize
ONLY EXCEPTION IS PROCESSES TO DO W DIGESTION
State and explain one reason why many autonomic functions can also be controlled by the somatic nervous system?
Breathing can be controlled by holding breath when swimming as we can’t breath under water
5 main areas of the brain
Cerebrum- controls voluntary actions - conscious thought
Cerebellum- controls unconscious functions- posture, balance. If damaged causes jerky movements
Medulla oblongata- used in autonomic control - ❤️ rate and breathing rate.
Hypothalamus - regulatory centre for temp and water balance and produces hormones I.e ADH
Pituitary gland - stores and releases hormones (and releases hormones produced by hypothalamus). Divided into 2 sections- anterior pituitary (front section produces 6 hormones). Posterior pituitary (stores and releases hormones produced by Hypothalamus)
State the pathway followed by a nervous impulse produced by a sound wave?
Sound receptor in left ear
Sensory neurone
Temporal lobe in cerebral hemisphere
What is a reflex arc?
An involuntary response to a sensory stimulus
Pathway of reflex arc between stimulus and response
Stimulus
Receptor (detects stimulus and creates an action potential)
Sensory neurone (carries impulse to spinal cord)
Relay neurone (connects sensory n to motor n)
Motor neurone (carries impulse to effector to carry out response )
What type of reflex is a knee-jerk reflex ?
Spinal reflex
Why are reflexes essential to survival?
Avoid body being harmed/ less damage I.e iris contracts in pupil in bright light to prevent damage to the retina
How do reflexes increase survival? (Basically what features)
Being involuntary responses
Not having to be learnt
Extremely fast
Many reflexes are everyday actions I.e those keeping us upright
State the reflex arc which occurs when a doctor tests the knee -jerk reflex
Pressure receptor in skin
Sensory neurone
Relay neurone
Motor neurone
Muscle
3 types of muscle?
Skeletal (responsible for movement)
Cardiac muscle (in ❤️- these cells are myogenic meaning they contract without need for a nervous stimulus )
Smooth muscle (found in walls of stomach and blood vessels )
What is the structure of skeletal muscle?
Made of bundles of fibres enclosed in a plasma membrane called sarcolemma. Muscle fibres have lots of mitochondria to provide ATP for contraction. Also have modified version of ER called sarcoplasmic reticulum- contains calcium for contraction
Each fibre contains many myofibrils.
Myofribils are made up of two types of protein filaments
Actin- thinner, consists of 2 strands twisted round each other
Myosin- thicker, consists of rod shaped fibres
Structure of a myofibril
Light bands (I bands)- actin and myosin filaments don’t overlap
Dark bands(A bands)- myosin overlapped w actin
Z lines- at centre of each light band. Distance between adjacent z lines is called sarcomere l. Muscle contracts makes the sarcomere shorten
H zone- lighter coloured region found in centre of each dark and. Only myosin filaments present. When muscle contracts h zone decreases
Properties of slow twitch fibres
((Found in Calf muscles ))
Contract slowly
Less powerful contractions but over longer period
Gain Energy from Aerobic respiration
Rich in myogloblin (red) stores oxygen
Rich supply of blood vessels
Properties of fast twitch fibres
((Found in biceps and eyes))
Contract quickly
Powerful contractions but shorter time period
Gain energy from anaerobic respiration
Pale coloured- low levels of myogloblin and blood vessels
Contain more myosin filaments
How does skeletal muscle contract ?
Actin and myosin filaments within myofibrils slide past each other (sliding filament model)
During contraction myosin filaments pull the actin filaments inwards towards the centre of the sarcomere. What does this result in?
Light band becoming narrower
Z lines moving closer together, shortening sarcomere
H zone becoming narrower
Dark bands remain same width
