Neuronal communication Flashcards
Outline how receptors work
- transducers
- convert energy from one form to another
Outline the types of receptors there are and what kind of stimulus is detected and where
- Photoreceptor = light/in cone cells
- Chemoreceptor = chemicals/ olfactory receptor
- Thermoreceptor = heat/end bulbs of krause
- Mechanoreceptor = pressure/movement/pacinian corpuscle
- Prophoreceptor = movement/position/muscle spindle
- Baroreceptor = pressure/stretch receptors in arteries
Whats the pacinian corpuscle
- specific sensory receptors that detect mechanical pressure found deep in the skin
- abundant in fingers, soles of feet and joints
- have special Na+ channels called stretch-mediated Na+ channels that when the channel changes shape the permeability to Na+ changes ]
What happens in the pacinian corpuscle
- At resting state, stretch mediated Na+ channels are too narrow to allow Na+ through. The neurone of the pacinian corpuscle has a resting potent
- pressure is applied to PC changing the shape - membrane bound neurone stretches
- Membrane stretches, widening Na+ channels. Na+ diffuse into neurone
What are the characteristics of motor, sensory and relay neurones
MOTOR - Cell body in CNS - Long axon that carries AP to the effector SENSORY - short axon that carries AP into CNS - long dendron RELAY - Connect sensory and motor neurones - cell body in CNS - many short dendrites and short axon
Whats the perineurium
- protective layer that surrounds bundles of axons of neurones
Whats myelin and its function
- axons of some neurones covered in myelin sheath made of layers of plasma membrane
- schwann cells produce the membrane layers by growing around the axon many times (each time they wrap around axon they lay down double layer of phospholipid bilayer)
- acts as an insulating layer and allow neurones to conduct the electrical impulse at a faster speed
What is saltatory conduction
- action of impulses jumping from each node to the next
Why at resting potential is the inside of the neurone negatively charged and what is resting potential’s value (in mv)
- there are large negatively charged proteins inside the neurone
- distribution of ions (Na+ and K+) across the membrane
- -60mv - -70mv
How is resting potential maintained?
- sodium potassium pump actively transports 3Na+ out and 2K+ in
- Na+ can’t diffuse back across creating an electrochemical gradient
- K+ can diffuse through channels back out neurone, further increasing potential difference
How is generator potential produced
- stimulus detected
- Na+ channels open
- Na+ move in my diffusion down a conc gradient and electrochemical gradient
- influx of Na+ causes potential difference to become less negative = generator potential
- larger the stimuli the more Na+ channels open
Describe the all or nothing principle
- if the potential difference reaches over -50mv then there will be a large GP, the voltage-gated Na+ channels open and AP will be triggered
- However if the potential difference is below -50mv the Na+ channels won’t open resulting in AP not happening
Describe the process of polarisation, depolarisation, repolarisation and hyperpolarisation
- membrane starts at resting state of -70mV (POLARISED)
- Na+ channels open and some Na+ ions diffuse into the cell
- membrane DEPOLARISES becoming less negative until the threshold value of -50mV
- Voltage-gated Na+ channels open and Na+ ions flood in making cell more +ve until it reaches +40mV
- Na+ channels close and K+ channels open, K+ ions diffuse out of the cell bringing potential difference back to negative inside (REPOLARISED)
- Potential difference overshoots slighting making cell HYPERPOLARISED and original potential difference is restored so cell returns to resting state
How is a local current produced
- when membrane is stimulated, Na+ ions travel through normal voltage gated Na+ channels
- Na+ ions diffuse sideways
- area behind is depolarised and even when hyper polarised its unlikely it will reach threshold value
- area ahead is in resting state so as Na+ ions diffuse it causes a small increase in positive change so the next Na+ channels open
- process repeats along axon so AP travels to synapse
What is the refractory period
- time delay of a few milliseconds after an AP before another one is possible… has two parts:
1) ABSOLUTE REFRACTORY PERIOD- Na+ channels closed so movement Na+ (-1ms)
2) RELATIVE REFREACTORY PERIOD: - Period of 2-5ms where Na+ channels are starting to recover but resting potential hasn’t been re-established yet
- Na+ channels closed so movement Na+ (-1ms)
Whats the importance of the relative refractory period
- limits frequency of action potential
- prevents action potential going backwards
How are messages transported through the synapse
- action potential arrives at synaptic knob of presynaptic neurone
- AP stimulates voltage gated Ca2+ channels to open and Ca2+ diffuses in
- Influx of Ca2+ causes synaptic vesicles to fuse with presynaptic membrane and release ACh into synaptic cleft by exocytosis
- ACh diffuses across synaptic cleft and binds to cholinergenic receptors on post-synaptic neurone causing Na+ channels to open and Na+ diffuses in
- Influx of Na+ causes depolarisation and an action potential is generated if the threshold value reached and ACh broken down by acetylcholinesterase
Describe the difference between endocrine, paracrine and autocrine glands
ENDOCRINE: communication between distant cells mediated by hormones e.g. adrenaline
PARACRINE: communication between local cells e.g. neurotransmitters
AUTOCRINE: cell producing signal and receiving are the same e.g. interleukins
Describe what temporal summation is
- when two or more nerve impulses arrive in quick succession from the same presynaptic neurone making AP more likely because more neurotransmitter is released into synaptic cleft
Describe what spatial summation is
- Where two or more presynaptic neurones converge and release their neurotransmitters at the same time onto the same presynaptic neurone
- allows signals from multiple stimuli to be coordinated into a single response
What is synaptic divergence and synaptic convergence
DIVERGENCE: when one neurone connects to many neurones meaning information can be dispersed to diff parts of the body
CONVERGENCE: when many neurones connect to one neurone information can be amplified
Outline the difference between excitatory and inhibitory synapses
EXCITATORY: neurotransmitter triggers AP in next neurone e.g. ACh
INHIBITORY: neurotransmitter prevents AP in next neurone causing hyper polarisation by opening K+ channels (e.g. GABA: stretch reflex in antagonistic muscles)
How do synapses make sure impulses are unidirectional?
- neurotransmitters are only released from presynaptic neurones
- receptors for neurotransmitters are only on postsynaptic neurones
Describe how nicotine affects the CNS
- absorbed into lungs and travels through blood to brain where it behaves like ACh
- it binds to receptors resulting in a stimulating effect causing its highly addictive potential
- symptoms are relaxation, sharpness and calmness
Describe how botox affects the CNS
- inhibits exocytosis of ACh at cholinergic motor and autonomic neurone terminals
- prevents AP from being transferred to post-synaptic neurone which results in partial to complete muscle paralysis
Describe how organophosphates (insecticides) affect the CNS
- Interfere with chemical neurotransmission or ion channels and cause reversible neurotoxin effects
- Also cause organophosphate poisoning which involves inhibition of AChE leading to ACh build up in the body
Describe how myelination affects speed of conduction of impulses
- in myelinated neurone depolarisation happens at nodes of Ranvier and neurones cytoplasm conducts enough electrical charge to depolarise the next node so impulse jumps from node to node (saltatory conduction) = very fast
- in unmyelinated neurones impulse travels as a wave along whole length of axon which is slow
Describe how axon diameter affects speed of conduction of impulses
- AP’s conducted quicker along axons with larger diameters because theres less resistance to the flow of ions than in the cytoplasm of a smaller axon
- less resistance = depolarisation reaches other parts of neurone cell membrane quicker
Describe how temperature affects speed of conduction of impulses
- speed of conduction increases as temp does because ions diffuse faster
- only speeds up to 40 degrees celsius as after proteins begin to denature
Describe the structure of the neurone
- Synaptic cleft: gap which separates the axon of one neurone from the dendrite of the next neurone
- Presynaptic neurone: neurone along which the impulse has arrived
- Postsynaptic neurone: neurone that receives the neurotransmitter
- Synaptic knob: the swollen end of the presynaptic neurone containing many mitochondria and large amounts of ER to enable it to manufacture neurotransmitters
- Synaptic vesicles: vesicles containing neurotransmitters which 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
Describe the two types of neurotransmitter
- Excitatory: these neurotransmitters result in the depolarisation of the postsynaptic neurone e.g. ACh
- Inhibitory: these neurotransmitters result in the hyperpolarisation of the postsynaptic neurone preventing an AP being triggered e.g. GABA
Describe the transmission of impulse across synapses
- AP arrives at the synaptic knob of the presynaptic neurone
- AP stimulates voltage-gated Ca2+ channels to open and Ca2+ diffuses in
- Influx of Ca2+ causes synaptic vesicles to fuse with presynaptic membrane and release ACh into synaptic cleft by exocytosis
- ACh diffuses across synaptic cleft and binds to cholinergic receptors on post-synaptic neurone causing Na+ channels to open and Na+ diffuses in
- Influx of Na+ causes depolarisation and an AP is generated if the threshold is reached and the ACh is broken down by acetylcholinesterase
Whats the difference between the CNS and the PNS
- CNS: Consists of brain and spinal cord
* PNS: consists of all the neurones that connect the CNS to the rest of the body
Whats the difference between the somatic and autonomic nervous system
- Somatic nervous system: system under conscious control – used when you voluntarily decide to do something e.g. moving muscles in your arm
- Autonomic nervous system: system works constantly and under subconscious control and is involuntarily e.g. smooth in the walls of the intestine
Describe the roles of the sensory and motor neurone system
- Sensory: detects the stimulus and sends impulses along sensory neurones to CNS
- Motor: sends impulse from CNS along the motor neurone to the effector
What does antagonistic mean
• Systems that have opposite effects
Describe the effects of the sympathetic system
- If outcome increases activity generally it involves the sympathetic system
- e.g. increase in heart rate, increased ventilation rate, orgasm, pupil dilation
- Most active in times of stress
- Secrete noradrenaline
- Preganglionic neurones v short
Describe the effects of the parasympathetic system
- If outcome decreases activity it is generally parasympathetic
- e.g. decrease in breathing rate after a period of exercise, sexual arousal, pupil constriction
- secrete ACh
- Most active in sleep and relaxation
- Preganglionic neurones vary in length
Describe the gross structure of the brain
• Cerebrum: controls voluntary actions e.g. learning, memory, personality and conscious thought
o Split into two hemispheres connected by tracts of neurones called the corpus callosum
• Cerebellum: controls unconscious functions e.g. posture, balance and non-voluntary movement
• Medulla oblongata: used in autonomic control e.g. controls heartrate and breathing rate
• Hypothalamus: regulatory centre for temp and water balance
• Pituitary gland: stores and releases hormones that regulate many body functions
Describe the parts of the cerebrum
- Temporal lobe: auditory info e.g. hearing, sound and recognition of speech
- Occipital lobe: Processing info from eyes e.g. vision, colour, shape and perspective
- Parietal lobe: Concerned with orientation, movement, sensation, calculation and types of recognition
- Frontal lobe: Involved with conscious emotion, decision making and reasoning. Includes motor cortex which stores info on how to carry actions
Describe the reflex arc
- Receptor: detects stimulus creating an AP 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 effector to carry out the appropriate response
Whats the spinal cord
• Column of nervous tissues surrounded by spine for protection, at intervals along th spine neurones emerge in pairs
Whats the knee-jerk reflex
- It’s a spinal reflex - doesn’t go up to brain
- When leg tapped just below kneecap it stretches patella tendon acting as a stimulus
- Stimulus initiates reflex arc causing extensor muscle on top of thigh to contract and at same time the relay neurone inhibits motor neurone of flexor muscle to relax
- Absence of this reflex indicates nervous problems and multiple oscillations of the leg may be a sign of a cerebellar disease
- Reflex used by body to maintain posture and balance
Describe the blinking reflex
- Reflexes increase survival chances
- Involuntary response – decision making parts of brain not involved so brain is able to deal with more complex responses
- Doesn’t have to be learnt – present at birth therefore provide immediate protection
- Fast – reflex arc short
What are slow twitch muscles
o Fibres contract slowly
o Less powerful contractions but over a longer period
o Used for endurance – don’t tire easily
o Rich in myoglobin (stores oxygen) – making fibres appear red
o Rich supply of blood vessels and mitochondria
o E.g. back and calf muscles
What are fast twitch muscles
o Fibres contract quickly
o Powerful but short contractions
o Used for short bursts of speed and power – tire easily
o Gain energy from anaerobic respiration
o Pale coloured due to low levels of myoglobin and blood vessels
o Contain more, thicker myosin filaments
o Stores creatine phosphate – molecule that rapidly generates ATP from ADP in anaerobic conditions
o E.g. biceps and eyes
Describe the action at the neuromuscular joint
- Synapse between a motor neurone and muscle cell
- Muscle contraction triggered when an action potential arrives at a neuromuscular junction
- Ca2+ channels are stimulated and Ca2+ ions diffuse into the synaptic knob causing synaptic vesicles to fuse with the presynaptic membrane
- ACh is released into the synaptic cleft by exocytosis and diffuses across the synapse
- ACh binds to receptors on sarcolemma (postsynaptic membrane) opening Na+ channels resulting in depolarisation
- ACh broken down by AChE into choline and ethanoic acid preventing the muscle from being overstimulated
- Choline and ethanoic acid diffuse back into neurone and recombine with ATP to form ACh
- Depolarisation of sarcolemma travels deep into a muscle spreading through T-tubules which are in contact with the sarcoplasmic reticulum
- The SR contains stored Ca2+ which it actively absorbs from sarcoplasm
- When an AP reaches the S.R. it stimulates the Ca2+ channels to open and Ca2+ diffuse down conc gradient flooding sarcoplasm
- Ca2+ bind to troponin causing it to change shape pulling on the tropomyosin moving it away from the actin-myosin binding sites on the actin filament
- Binding sites are exposed and the myosin head binds to the actin filament forming n actin-myosin cross-bridge
- Once attached to the actin filament, myosin head flexes pulling actin filament along and a molecule of ADP bound to the myosin head is released
- ATP molecule can now bind to the myosin head causing the head to detach from the actin filament and Ca2+ also activate ATPase stimulating the hydrolysis of ATP to ADP releasing energy that the myosin head uses to return to its original position
- The myosin head can now attach itself to another atcin-myosin bindsite along the actin filament
- This cycle is then repeated
Describe how the structure changes as the sliding filament model is in action
• During contraction myosin filaments pull the actin filaments toward the centre of the sarcomere meaning:
o Light band becomes narrower
o Z lines move closer together – shortening sarcomere
o H-zone becomes narrower
o Dark band remains same width as myosin filaments themselves haven’t shortened but overlap actin filaments further
Describe the structure of myosin
o Globular heads hinged allowing them to move back and forward
o On head there is a binding site for actin and ATP
Describe the structure of actin
o Have binding sites for myosin heads – often blocked by protein called tropomyosin held in place by protein troponin
o When a muscle is in resting state the actin-myosin sites are blocked by tropomyosin
How is the supply of ATP maintained in muscle contraction
• Creatine phosphate: stored in the muscle and acts as a reserve supply of phosphate to phosphorylate ADP into ATP
o This system generates ATP rapidly but store of phosphate is used up quickly
o Used for short bursts of vigorous exercise e.g. tennis serve
• Anaerobic respiration: oxygen used up more quickly than the blood in very active muscle so ATP has to be generated anaerobically
o But can cause lactic acid build-up leading to muscle fatigue
o Used for short periods of high intensity exercise e.g. sprinting
How do reflexes increase survival rates
- Reflexes increase survival chances
- Involuntary response – decision making parts of brain not involved so brain is able to deal with more complex responses
- Doesn’t have to be learnt – present at birth therefore provide immediate protection
- Fast – reflex arc short
Describe the structure and function of cardiac muscle
STRUCTURE:
- specialised striated, cells branch and interconnect resulting in simultaneous contraction, muscle shows striations much finer than those in skeletal muscle, fibres branched and uninucleated
FUNCTION:
- involuntary, intermediate contractions
Describe the structure and function of skeletal muscle
STRUCTURE:
- striated, regularly arranged so muscle contracts in one direction, muscle shows cross striations and fibres are tubular and multinucleated
FUNCTION:
- under conscious control, rapid short contractions
Describe the structure and function of smooth muscle
STRUCTURE:
- non-striated, no regular arrangement - diff cells can contract in different directions, muscles show no cross striations and fibres and spindle shaped and uninucleated
FUNCTION:
- involuntary, slow long contractions
