1
Q
Outline how receptors work
A
- transducers
- convert energy from one form to another
2
Q
Outline the types of receptors there are and what kind of stimulus is detected and where
A
- 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
3
Q
Whats the pacinian corpuscle
A
- 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 ]
4
Q
What happens in the pacinian corpuscle
A
- 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
5
Q
What are the characteristics of motor, sensory and relay neurones
A
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
6
Q
Whats the perineurium
A
- protective layer that surrounds bundles of axons of neurones
7
Q
Whats myelin and its function
A
- 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
8
Q
What is saltatory conduction
A
- action of impulses jumping from each node to the next
9
Q
Why at resting potential is the inside of the neurone negatively charged and what is resting potential’s value (in mv)
A
- there are large negatively charged proteins inside the neurone
- distribution of ions (Na+ and K+) across the membrane
- -60mv - -70mv
10
Q
How is resting potential maintained?
A
- 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
11
Q
How is generator potential produced
A
- 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
12
Q
Describe the all or nothing principle
A
- 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
13
Q
Describe the process of polarisation, depolarisation, repolarisation and hyperpolarisation
A
- 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
14
Q
How is a local current produced
A
- 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
15
Q
What is the refractory period
A
- 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)
16
Q
Whats the importance of the relative refractory period
A
- limits frequency of action potential
- prevents action potential going backwards
17
Q
How are messages transported through the synapse
A
- 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
18
Q
Describe the difference between endocrine, paracrine and autocrine glands
A
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
19
Q
Describe what temporal summation is
A
- 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
20
Q
Describe what spatial summation is
A
- 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
21
Q
What is synaptic divergence and synaptic convergence
A
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
22
Q
Outline the difference between excitatory and inhibitory synapses
A
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)
23
Q
How do synapses make sure impulses are unidirectional?
A
- neurotransmitters are only released from presynaptic neurones
- receptors for neurotransmitters are only on postsynaptic neurones
24
Q
Describe how nicotine affects the CNS
A
- 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
25
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
26
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
27
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
28
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
29
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
30
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
31
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
32
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
33
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
34
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
35
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
36
What does antagonistic mean
• Systems that have opposite effects
37
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
38
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
39
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
40
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
41
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
42
Whats the spinal cord
• Column of nervous tissues surrounded by spine for protection, at intervals along th spine neurones emerge in pairs
43
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
44
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
45
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
46
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
47
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
48
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
49
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
50
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
51
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
52
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
53
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
54
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
55
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
