hormonal and neuronal communication 2 Flashcards
Excitatory neurotransmitters
Excitatory neurotransmitters makes post-synpatic cells more likely to fire
-> done when binding to its receptors and causing an excitatory post-synpatic potential (EPSP)
Inhibitory neurotransmitters
Inhibitory neurotransmitters makes post-synpatic cells less likely to fire
-> done when binding to its receptors, causing an inhibitory post-synpatic potential (IPSP)
Synaptic transmission
Synaptic transmission:
1). The action potential reaches end of pre-synaptic neurone
2). Doplarisation of membrane causes calcium ion channels to open
3). Calcium ions diffuse into pre-synaptic knob
4). Vesicles containing neurotransmitters fuses with presynaptic membrane and releases into cleft by exocytosis
5). Neurotransmitter diffuses across cleft and binds with receptor on postsynaptic membrane
6). Sodium ion channels open
7). Triggers the action potential and impulse is propagated along the postsynaptic neurone
How are neurotransmitters removed that are left in the synaptic cleft after transmission?
Remaining neurotransmitters are broken down by enzyme Acetycholine - releases them from receptors and back into knob
-> This prevents response occuring again and allowing neurotransmitter to be recycled
Cholinergic synapses
Cholinergic synapses uses neurotransmitter acetycholine
Transmission across cholinergic synapses
Transmission across cholinergic synapses:
1). Action potential arrives at end of presynaptic neurone + calcium ion channels open and ions enter knob
2). Influx of calcium ions causes vesicles to fuse with membrane and acetycholine releases into cleft
3). Acetycholine fuses with receptor sites on sodium channel in postsynaptic membrane, causing sodium ion channels to open and ions diffuse in
4). Sodium ions generate new action potential
5). Acetycholinesterase hydrolyses acetylcholine into choline and ethanoic acid which diffuse back into cleft (recycled + prevents new aciton potential)
6). ATP used to recombine these into acetycholine, stored in vescles, and sodium channels close
The role of synapses
The role of synpases:
-Ensures impulses are unidirectional
-Can allow an impulse from one neurone to be transmitted to number of neurones at multiple synapses - results in singal stimulus creating number of simultaneous responses
-Number of neurones could feed into signal neurone - results in stimuli from diff receptors interacting to produce a single result
What is summation?
Summation is where an amount of neurotransmitteres build up sufficiently to reach the threshold and trigger an action potential
Two ways that summation can occur
Two ways that summation can occur:
-Spatial summation
-Temporal summation
What is spatial summation?
Spatial summation occurs when a number of presynaptic neurones connect to one postsynaptic neurone - each releases neurotransmitter which builds up to a high enough level in the synapse to trigger an action potential in the single postynatpic neurone
Temporal summation
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 sufficient to trigger an action potential
Role of synapses
Role of synapses:
-Transmits infro across the gaps between neurones via neurotransmitters in one direction only
-Connects neurones for cell signalling
-Allows convergence/impulses from more than one neurone to be passed to a single neurone
-Allows divergence/impulses from a single neurone to be passed to more than one neurone
Convergence in synapses
Convergence in synapses - impulses from more than one neurone to be passed to a single neurone
Divergence in synapses
Divergence in synpases - impulses from a single neurone to be passed to more than one neurone
Organisation of the human nervous system
Organisation of the human nervous system:
-CNS and PNS
-PNS splits into somatic and autonomic systems
-Autonomic splits into sympathetic and parasympathetic nervous systems
Steps of a reflex arc
Steps of a reflex arc:
1). Stimulus
2). Sensory receptor detects stimulus
3). Nerve impulse to spinal cord (ensures transmission is quick)
4). Relay neurone passes impulse across spinal cord
5). Motor neurone passes impulse to muscle
6). Effector contracts
7). Response initiated
Knee jerk reflex
Knee jerk reflex:
-Leg tapped (stretches the patellar tendon)
-Initiates reflex which causes flexor muscles to relax and extensor muscles to contract
-Absence of this reflex is an indicator of nerve damage
Blinking reflex
Blinking reflex:
-Occurs when cornea is stimulated
-Causes eyelids to close to minimise damage
-Can also be stimulated by light or sudden sounds
-Triggers an impulse along sensory neurone (5th cranial nerve)
-Motor impulse sent along the 7th cranial nerve to the eyelids
Survival importance of reflexes
Survival importance of reflexes:
-Involuntary, brain less overloaded
-Doesn’t have to be learnt
-Extremely fast
-Controls everyday things
Types of muscle
Types of muscle:
-Involuntary/smooth (eg blood vessel walls)
-Cardiac (heart, myogenic)
-Skeletal (makes up bulk of muscle tissue)
Involuntary/smooth muscle features
Involuntary/smooth muscle features:
-Involuntary
-Slow contraction
-Long lasting contraction
-Non striated (striped) fibres
Cardiac muscle features
Cardiac muscle features:
-Involuntary
-Intermediate contraction speed and length
-Specialised striated fibres
Skeletal muscle features
Skeletal muscles features:
-Conscious/voluntary
-Rapid contraction and short
-Striated fibres
Skeletal muscle makeup
Skeletal muscle is made up of muscle fibres (myofibrils) enclosed within a plasma membrane called a sarcolemma
->Contains nuclei and are long (due to being formed from multiple embryonic muscle cells fusing together) -> makes it stronger
Shared cytoplasm within muscle fibre
Shared cytoplasm within muscle fibre = Sarcoplasm
Sarcoplasm features
Sarcoplasm (the shared cytoplasm within muscle fibres) folds inwards (known as transverse/T tubulues) -> helps spread impulses throughout sarcoplasm -> whole fibre recieves impulse to contract at the same time
Filaments that make up myofibrils
Filaments that make up myofibrils:
-Actin = thin, 2 stransds twisted
-Myosin = thick, long rod-shaped with bulbous heads that project to one side
What are myofibrils?
-Myofibrils are long organelles made up of protein and specialised for contraction
-Lined up larallel for maximum force
Structure of myofibrils
Myofribril structure:
-Light bands
-Dark bands
-Z-line
-H-zone
Lights bands in myofibrils
Light bands in myofibrils:
-Appears light as it is the region where filamens don’t overlap
-Also known as isotopic/I bands
Dark bands in myofibrils
Dark bands in myofibrils:
-Appears dark due to thick myosin filaments
-Also known as anisotropic/A bands
Z-line in myofibrils
Z-line in myofibrils:
-Found at light band centres
-Distance between Z-lines = sarcomeres = functional unit of the myofibrils (shortens during contraction)
H-zone in myofibrils
H-zone in myofibrils:
-Light region in dark band centre
-Only myosin filaments present here
-H-zone decreases in muscle contraction
Histology of skeletal muscle fibre
Histology of skeletal muscle fibre:
-Capillaries running in between fibres
-Streaks of connective and adipose tissue
-Highly structured arrangement of sacomeres that appear as dark/A bands and light/I bands
Sliding filament model
The sliding filament model is used to describe the movement of myosin filaments across eachother in order for muscles to contract
How does the sliding filament model work?
Sliding filament model:
-Myosin filaments pull the actin filaments inwards towards centre of the sarcomere
-Results in light band and H zone narrowing, z lines moving closer shortening sacromere
-Simultaneous contraction means myofibrils and muscle fibres contract -> results in enough force to initiate movement
Actin filament structure
Actin filament structure:
-Binding sites for myosin heads
-Binding sites often blocked by tropomyosin molecule at resting state
-Actin filaments spiral around eachother
Interaction between actin and myosin filaments
Interaction between actin and myosin filaments:
-Myosin binding sites blocked by tropomyosin molecules when actin is at resting state
-When contracted, myosin heads form bonds with actin filaments (actin-myosin cross-bridge)
-Heads flex in unision, pulling actin closer to myosin
-Myosin detaches and head returns to original angle using ATP
Describe the sliding filament theory
Sliding filament theory:
-Myosin heads split ATP and become reorientated and energized
-Myosin heads bind to actin, forming crossbridges
-Myosin heads roate toward centre of the sarcomere (power stroke)
-As myosin heads bind ATP, the crossbridges detach from actin
What makes filaments slide past eachother in the sliding filament theory?
Sliding filaments:
-Energy for movement comes from splitting ATP
-ATPase that does this is located in myosin heads
-Energy from ATP causes angle of myosin heads to change
-Myosin heads can attach to actin
-Movement of myosin heads from causes causes filaments to slide relative to eachother - movement reduces sarcomere length
Functions of skeletal muscle
Functions of skeletal muscle:
-Force production for locomotion and breathing
-Force production for postural support
-Heat production during cold stress
Peripheral nervous system
Peripheral nervous system = consists of all the nruones that conenct the CNS to the rest of the body
Somatic nervous system
Somatic nervous system - conscious control - voluntary decisions
Autonomic nervous system
Autonomic nervous system - subconscious control - always working - involuntary - eg heart beating
Sympathetic nervous system
Sympathetic nervous system - increases activity
Parasympathetic nervous system
Parasympathetic nervous system - decreases activity
Pathway from stimulus leading to hormone release
Stimulus detected by sensory receptor -> impulses travels via neuronal pathways and across synapses -> to target gland which is then stimulated to release the hormone directly into the bloodstream -> to the target cell -> where it binds to the plasma membrane receptor and initiates the reaction
Effects of hormones in a stressful situation
Stressful situation:
-Detected by sympathetic nervous system -> triggers adrenal glands to secrete adrenaline/noradrenaline from the adrenal medulla -> effects increases survival eg increase respiration and muscle work -> effects such as increase blood glucose conc, heart rate an dbreathing rate, pupil widening, vasoconstriction to blood vessels
Appearance of islet of langerhans under a microscope
Appearance of islet of langerhans under a microscope:
-Lightly coloured
-Cluster of cells
-Surrounded by acini/exocrine tissue
Changes which take place inside a beta cell to cause release of insulin in the presence of high blood glucose concentration: (process)
The changes which take place inside a beta cell to cause release of insulin in the prescence of high blood glucose concentration:
-Glucose enters cells by transporter
-Glucose metabolised inside mitochondria, resulting in ATP production
-ATP binds to potassium channels and they close (ATP-sensitive potassium channels)
-Potential reduces and depolarisation causes, meaning voltage-gated calcium channels open and calcium ions enter cell -> causes secretory vesicles to release insulin by exocytosis
Interactions of the neuronal and hormonal systems in the fight or flight response (process)
-Hypothalamus communicates with sympathetic nervous system and adrenal-corticol system
-Sympathetic system uses neuronal pathways to initiate body reactions and adrenal-corticol system uses hormones in the blood stream
-Sympathetic -> activates adrenal medulla to release adrenaline and noradrenaline into bloodstream + impulses activate glands and smooth muscles.
-Adrenal-coritcol system -> activated -> pituitary gland secretes hormone ACTH -> ACTH arrives at adrenal cortex and releases hormones into bloodstream
Receptor + effect when blood pressure is high
High blood pressure:
-Baroreceptor
-Parasympathetic nervous system
-Heart rate decreases
Receptor + effect when blood pressure is low
Receptor + effect when blood pressure is low:
-Baroreceptor
-Sympathetic nervous system
-Heart rate increases
Receptor + effect when blood carbon dioxide concentration low
Receptor + effect when blood carbon dioxide concentration low:
-Chemoreceptor
-Parasympathetic nervous system
-Heart rate increases as carbon dioxide levels decrease -> so blood flows more quickly to lungs to be exhaled
Receptor + effect when carbon dioxide concentration high in blood
Receptor + effect when carbon dioxide concentration high in blood:
-Receptor = chemoreceptor
-Sympathetic nervous system
-Heart rate decreases as carbon dioxide level increases -> pH decreasing because carbonic acid forms when carbon dioxide reacts with water in blood
Why does an increase in blood pH decrease heart rate?
Increased blood pH -> decreases heart rate -> as a result of decreased carbon dioxide levels -> detected by chemoreceptors -> results in reduced frequency of impulses to SAN via sympathetic system therefore decreasing heart rate back to its normal level
Difference between taking a transverse and longitudinal section of muscle
Difference between taking a transverse and longitudinal section of muscle =
-Longitudinal = sample taken in the orientation of muscle fibres
-Transverse = sample taken across the muscle fibres
Difference between cardiac and involuntary muscle
Cardiac and involuntary muscle:
-Similarities = Both involuntary, contain uninucleated fibres
-Differences = Cardiac are found only I heart whereas involuntary are found in many parts of the body, involuntary is non-striated whereas cardiac is striated, involuntary is slower to contract but contracts for longer than cardiac
Function of the cerebrum?
The cerebrum is responsibe for the conscious/voluntary action of the brain -> thought, speech, memory -> consists of 5 lobes -> 2 halves (cerebral hemispheres) - consists of grey matter (cerebral cortex) and white matter (myelinated axons of neurones)
Function of the cerebellum?
The cerebellum is responsible for muscle coordination and movement
Function of medulla oblongata?
Medulla oblongata is responsible for involuntary actions -> increasing heart rate and breathing rate
Function of the pituitary gland?
The pituitary gland -> master gland -> controls gland activity
-Consists of anterior pituitary (releases certain hormones) and posterior pituitary (releases hormones produced by the hypothalamus - ADH)
Function of the hypothalamus?
The hypothalamus -> Regulates blood conc, body temp, endocrine functions (works with pituitary gland by stimulating it) and homeostasis
Medulla oblongata consists of which three centres?
Three centres of the medulla oblongata:
-Cardiac -> controls HR
-Vasometer -> controls BP
-Respiratory -> controls BR
What is an accelerator nerve?
The accelerator nerve is part of the sympathetic nervous system and delivers a higher than usual frequency of impulses to the SAN to increase the heart rate.
What is a vagus nerve?
The vagus nerve is opposite to the accelerator nerve as it is part of the parasympathetic nerve and works to decrease the heart rate by delivering a lower than usual frequency of impulses to the SAN.
