neuronal communication + muscles Flashcards
(121 cards)
1
Q
main functions of the nervous system
A
send, receive and interpret information
2
Q
neurone definition
A
conductive excitable cells of the nervous system that are specialised to transmit nerve impulses
3
Q
nerve definition
A
elongated bundles of nerve fibres
4
Q
3 types of neurone
A
sensory neurone
relay neurone
motor neurone
5
Q
outline the structure of a sensory neurone
A
- cell body with nucleus is located in the centre of the neurone
- has both an axon and a dendron on each side of cell body
- axon leads to branched axon terminal nerve endings, where signal is transmitted
- dendron branches into dendrites which are connected to receptor cells
- the axon and dendron are myelinated
6
Q
what is the difference between an axon and a dendron
A
axon carries an impulse away from the cell body
dendrons carry an impulse to the cell body
7
Q
what is a myelin sheath
A
an insulating layer made of schwann cells which increases the efficiency of transmission of electrical impulses
no myelin sheath measn the signal would have to diffuse across the entire length of the neurone - this is too slow - and the action potential would have to be regenerated
8
Q
what are nodes of ranvier
A
these are gaps in the myelin sheath that allow the efficient movement of an electrical impulse along the neurone, as they allow the action potential to be propagated from one node to another - saltatory conduction
if the neurone was fully myelinated the body would still have to rely solely on diffusion
9
Q
why is saltatory conduction more efficient
A
less repolarisation (which requires ATP) is necessary
10
Q
where are sensory neurones located + what is their function
A
found in spinal cord in dorsal ganglia
these carry signals from receptors to the CNS
11
Q
outline the structure of a relay neurone
A
- small cell body with nucleus at the end of the neurone
- short highly branched dendrites stem from the cell body
- only contains an axon
- neurone is not myelinated - okay as they are very short, it also means they take up less space
- branched axon terminals at the nerve ending, where signal is transmitted
12
Q
where are relay neurones located + what is their function
A
found in brain and spinal cord
these allow sensory and motor neurones to communicate
13
Q
outline the structure of a motor neurone
A
- large cell body with nucleus at the end of the neurone - usually lies within spinal cord or brain
- highly branched dendrites stem from cell body
- only has an axon
- neurone is myelinated
- branched axon terminals at nerve endings which are connected to effector cells
14
Q
what are schwann cells
A
a type of cell that surrounds neurones to keep them alive + makes up the myelin sheath
15
Q
where are motor neurones located + what is their function
A
found in brain and travel to brain stem and spinal cord
carries signal from CNS to effectors
16
Q
why are dendrites and axon terminals highly branched
A
branching increases SA:V which increases efficiency of transmission from axon terminals to dendrites
17
Q
give 2 factors affecting the speed of conduction + explain how
A
axon diameter - larger axon diameter = faster transmission as there is less resistance to flow in cytoplasm
temperature - higher temps = faster transmission as ions diffuse faster at high temps, but only up to 40C because proteins get denatured
18
Q
outline the stages of a reflex arc
A
> stimulus - change in internal or external environment
receptors - organs or cells - detect stimulus + release signals which travel via sensory neurones
CNS detects signals and coordinates a response via motor neurones
relay neurones transmit signal from sensory to motor neurones, skipping brain
effectors - organs or cells - carry out the action/response to change
response
19
Q
reflex definition
A
simple and rapid autonomic responses to stimuli operated through the nervous system
20
Q
why are reflexes important
A
they are important to an animals survival
- they produce protective reactions, e.g. blinking, coughing, sneezing
- includes adjusting internal organ activity to suit the needs of the body
- includes adjusting tone of skeletal muscles to enable balance + maintain posture
- causes reciprocal inhibition within antagonistic muscles, allowing one to contract while another relaxes
21
Q
for a named reflex, outline the process from stimulus to response
A
knee jerk reflex
stimulus - hammer hits ligament by kneecap causing quadriceps to stretch
receptor - stretch receptors in quadricep muscles detects this and transmits a signal via sensory neurones
coordinator - spinal chord receives signal
effector - signal reaches quadriceps muscle via motor neurones
response - muscle contracts causing leg to straighten
22
Q
what is the purpose of the knee jerk reflex
A
useful for when you fall as this tends to propel you forwards
23
Q
what makes reflexes so fast
A
reflexes don’t involve the brain, and if the brain were involved the signals would have to pass through too many synapses, which delay impulse transmission - only one synapse between sensory and motor neurones is crossed during a reflex arc, which allows them to be so fast
24
Q
what are 3 advantages of reflexes
A
- simple pathway = quicker response
- brain can be used for more complex processing
- always the same reaction, successful + consistent
25
what are 3 disadvantages of reflexes
- response may not be appropriate to situation
- alternative outcomes may be possible or the reflex could cause further problems
26
what makes up the PNS
sensory and motor neurones
27
sensory receptor definition
receptors are organs or cells which detect stimuli and convert the energy they detect into a form of electrical energy - impulse / signal
essentially they are transducers
28
what are 6 types of receptors + examples
- photoreceptors detect light e.g. rod and cone cells in retina
- chemoreceptors detect chemicals e.g. olfactory cells in nasal cavity, taste buds on tongue
- mechanoreceptors / proprioreceptors detect force, pressure, movement or strain in limbs e.g. pacinian corpuscles in skin detect pressure changes
- baroreceptors detect blood pressure
- osmoreceptors detect body fluids and water potential e.g. in hypothalamus
- phonoreceptors detect sound waves / vibrations e.g. cochlea in ear
29
where are pacinian corpuscles found
in the skin of fingers, soles of feet, joints, tenodns and ligaments, at the ends of sensory neurones
30
what happens when pacinian corpuscles are stimulated
they are stimulated by pressure, which leads to the generation of an action potential
31
describe the structure of a pacinian corpuscle
- found at the end of sensory neurones
- made up of many layers of membrane and tissue called lamellae
- these layers are separated by a gel
- enclosed by a capsule
- the axon attached contains stretch mediated Na+ channels
32
outline how an action potential is generated by a pacinian corpuscle
- when no pressure has been applied, there is an excess of Na+ ions outside the axon
- when pressure is applied the layers of membrane and tissue are distorted and press on the sensory ending
- this causes the stretch mediated Na+ ion channels to open as they are deformed
- Na+ enters the axon of the sensory neurones
- a generator potential is established as Na+ ions cause depolarisation of the membrane
- if enough generator potentials are produced an action potential will be established and a nerve impulse will begin along the axon
33
outline the process of the generation of an action potential
1- resting potential= -60mV
here a Na+/K+ pump actively pumps ions through membrane, and leaky K+ channels allow some movement
2- a threshold potential = -55mV is met due to the energy of a stimulus, causing Na+ voltage gated channels to open
3- the membrane is depolarised as mV increases due to the influx of Na+
4- at +40mV the Na+ gates close and K+ voltage gated channels open, causing K+ to travel out due to repulsion from all the positive charged ions inside
5- membrane is repolarised
6- membrane is hyperpolarised = -80mV
this causes K+ channels to close again, now the only movement occurring is the Na+/K+ pump and the leaky K+ channels
7- resting potential is re established
in/out = in/out of axon through axon membrane
34
how do Na+/K+ pumps work
uses ATP to actively pump 3Na+ out and 2K+ in
35
what does the threshold potential imply about the energy of a stimulus
the stimulus must be above a minimum strength/energy for an action potential to be generated
36
what is the all or nothing principle
if threshold potential is not reached no action potential will be generates, meaning that there are some very small stimuli that the body may not need to react to
37
resting potential definition
the potential difference of the axon membrane when no impulse in being transmitted
38
refractory period
the short time period for which the neurone cannot generate another action potential
39
why must there be a short delay between stimuli for the body to react to them separately
an action potential can only be generated when the neurones are at resting potential, so some time so needed to allow the membrane to return to resting potential after hyperpolarisation
this refractory period prevents overlap of action potential and prevents action potential from moving backwards
40
synapse definition
where 2 neurones meet
41
what are the 2 types of synapse
inhibitory and excitatory synapses
42
what is the difference between inhibitory and excitatory synapses
inhibitory synapses are junctions where activity from presynaptic neurone in the form of an action potential reduces the probability of an action potential in the postsynaptic neurone, by releasing transmitters that lead to hyperpolarisation
excitatory synapses are junctions where activity from presynaptic neurone in the form of an action potential increases the probability of an action potential in the postsynaptic neurone,
43
what are the features of a cholinergic synapse
PRESYNAPTIC KNOB
- mitochondria
- voltage gated Ca2+ channels
- neurotransmitter reuptake pump
- synaptic vesicles containing neurotransmitter
- synaptic cleft
POST SYNAPTIC KNOB
- neurotransmitter receptors
- Na+ ion channels
44
what is the function of mitochondria in the presynaptic knob
generates ATP energy for the synthesis + transport + release of neurotransmitters, and to maintain Ca2+ conc gradients
45
what is the function of voltage gated Ca2+ channels in the presynaptic knob
allows Ca2+ to move in when an action potential has arrived, triggering the fusion of presynaptic vesicles with presynaptic membrane + the release of neurotransmitters into synaptic cleft
- this is because Ca2+ causes snare proteins connecting vesicle to membrane to contract so exocytosis can occur
- it ensures neurotransmitters cannot be released if there is no action potential
46
what is the function of the neurotransmitter reuptake pump in the presynaptic knob
allows broken down neurotransmitter than has diffused back across synaptic cleft from postsynaptic knob to enter presynaptic knob again to be reused
47
what is the function of the synaptic vesicles containing neurotransmitters in the presynaptic knob
contains + transports neurotransmitters from cell body to presynaptic terminal, then when an action potential reaches the vesicles release neurotransmitter into synaptic cleft via exocytosis
48
why does the presynaptic knob end in a bulb
to increase SA for release of acetylcholine by exocytosis
49
what is the function of neurotransmitter receptors in the postsynaptic knob
receives and binds to neurotransmitters, inducing changes - depolarising or hyperpolarising - in postsynaptic membrane potential, leading to either the generation or inhibition of an action potential
50
what is the function of Na+ ion channels in the postsynaptic knob
these open if neurotransmitter is bound to the receptor and cause the depolarisation of the postsynaptic membrane
51
what is the main neurotransmitter
acetylcholine
52
what are the roles of synapses
- one way signalling - different structures on pre/post terminals means unidirectionality
- spatial summation - many stimuli at the same time but different areas, having a cumulative effect upon membrane potential (e.g. of convergence)
- temporal summation - many stimuli in one place in close succession, having a cumulative effect on membrane potential
- convergence - many neurones send impulses to 1 postsynaptic terminal e.g. in the eye
- divergence - a single neurone sends impulses to many postsynaptic neurones e.g. adrenaline
- synapse becomes fatigued after repeated stimulation as it runs out of vesicles - why we get used to background noise
53
describe what occurs at a synapse
- action potential arrives at presynaptic knob
- Ca2+ channels open allowing ions to diffuse into presynaptic terminal
- this causes the synaptic vesicles to move and fuse with presynaptic membrane, releasing Ach into synaptic cleft
- Ach diffuses across cleft and binds to receptors on postsynaptic membrane
- Na+ channels open on postsynaptic terminal
- Na+ ions rapidly diffuse into post synaptic membrane, causing depolarisation
- action potential is generated in post synaptic membrane
- acytelcholinase breaks down Ach, allowing it to leave receptor and diffuse back across synaptic cleft to be reabsorbed back into presynaptic terminal
- Ach is reformed and packaged into vesicles
- Ca2+ pumped back out
- synaptic membrane repolarised + cycle repeats
54
what is tetanus
the continuous contraction of muscles
- this is what happens if the neurotransmitter is not broken down and so stays in the receptor
- this can be fatal if muscles around lungs + throat are affected as this prevents breathing
55
how do muscles work together during contraction/relaxation
they work in antagonistic pairs
e.g. 1 shortens and 1 elongates to bend a limb
56
by what model do muscles contract
sliding filament mechanism
57
outline the resting state of the muscle
when the muscle is relaxed:
troponin is attached to tropomyosin, which wraps around actin filaments - it holds tropomyosin in place, blocking actin-myosin binding sites
ADP + Pi is attached to myosin complex
Ca2+ is actively pumped into sarcoplasmic reticulum against conc gradient
58
outline the process of muscle stimulation
- impulse arrives at axon terminal
- causes an influx of Ca2+ ions which bind to snare proteins causing vesicles to move and release Ach via exocytosis
- Ach binds to cholergenic receptors on motor end plate
- action potential reaches muscle cells
- Na+ moves in causing depolarisation to occur across sarcolemma + down transverse tubules to sarcoplasmic reticulum
- here Ca2+ ions are released as voltage gated channels open and flood into muscle cells
- they bind to troponin causing a conformational change pulling tropomyosin along actin filament
- this exposes actin-myosin binding site so myosin heads bind to actin and form cross bridges
- causes a conformational change and ADP is released, myosin head can now change its shape
- myosin head flexes and flicks forward, pulling actin filaments causing them to move - powerstroke
- ATP then binds to myosin head causing a conformational change
- myosin is released from cross bridges and flicks back, now able to bind to a new area
- Ca2+ ions in sarcoplasm activate breakdown of ATP via ATPase
- Ca2+ is actively transported back into SR for contraction to end
59
what happens to the sections of the muscle fibres during the powerstroke
Z lines come together
I bands shorten
A bands stay the same
H bands narrow
sarcomeres shorten
length of myofibrils doesn't change, just the amount overlapping - but remember filaments don't touch
60
summarise the role of ATP in muscle contraction
- active transport of Ca2+ into sarcoplasmic reticulum
- breaking cross bridges between actin and myosin
- resetting myosin heads to original positions
61
neuromuscular junction definition
where neurones meet muscle tissue - where the motor end plate is
62
what is the motor end plate
the folded post synaptic membrane of the muscle cells
63
why is the motor end plate highly folded
increases SA allowing more receptors to be present
64
what is different about stimulation at the motor end plate than in other places
there is no threshold potential that needs to be reached, 1 single impulse will cause a contraction
65
neurotoxin definition
a substance which interferes with the ability of neurones to conduct nerve impulses
66
what are the 3 main types of muscle
cardiac muscle
smooth muscle
skeletal muscle
67
where is cardiac muscle found
heart walls - forms the myocardium
68
where is smooth muscle found
lining walls of blood vessels, digestive tract, within organ walls
69
where is skeletal muscle found
throughout the body, attached to bones via tendons
70
describe the structures and functions of cardiac muscle
- irregular arrangement
- specialised striated muscle due to arrangement of microfilaments
- spiral arrangement of muscle fibres to maximise pumping efficiency
- fibres are branched, with 1 nucleus, branched cells are interconnected by disks - useful for rapid communication + syncronisation
- contracts rhythmically + involuntarily
- myogenic - regulates its own beat
- intermediate contraction speed + length
- can contract without fatigue
71
describe the structures and functions of smooth muscle
- made up of muscle fibres, containing both actin and myosin filaments
- no banding or striation
- made of small elongated cells/spindle shaped fibres containing 1 nucleus
- vital for unconscious control of body parts
- contraction is slower + longer lasting
- allows for precise control
72
describe the structures and functions of skeletal muscle
- most regular arrangement
- highly specialised with contractile proteins arranged in cytoplasm
- sarcolemma had many tube like projections that fold in from outer surface - T tubules - which help to spread electrical impulses so whole fibre receives it at the same time
- sarcoplasm contains many mitochondria for ATP for muscle contraction
- also contains many myofibrils
- contain multiple nuclei as they are formed from the fusion of many embryonic muscle cells - this makes muscle stronger
- sarcoplasm is shared between muscle cells + fibres which allows for rapid communication
- proton pumps in sarcoplasmic reticulum that transport Ca2+ into SR lumen for contraction
73
myofibrils definition
long cylindrical organelles arranged in parallel lines to provide maximum force during contraction
made up of actin + myosin filaments arranged in bands and lines which slide past each other during muscle contraction
74
muscle fibre definition
highly specialised cell like units - many thousands of muscle fibres make up a muscle
75
sarcolemma definition
muscle cell surface membrane
76
sarcoplasm definition
muscle cytoplasm
77
sarcoplasmic reticulum definition
muscle endoplasmic reticulum
78
outline the difference between actin and myosin filaments
actin - thinner filaments, made of 2 strands twisted around each other
myosin - thicker filaments, long rod shaped fibres with bulbous heads that protrude on one side
79
what is the Z line
the middle of an actin band - as myofibrils are cylindrical, this is like a disc separating one sarcomere from another, also known as the Z disc
80
what is the M line
the middle of a myosin band
81
what is the sarcomere
the distance between adjacent Z lines, and 1 basic contractile unit of muscle fibre
82
what is the A band
the length of a single myosin/actin band including overlaps
83
what is the H band
myosin only - no overlaps with actin
84
what is the I band
actin only - no overlaps with myosin
85
why do muscles contain many mitochondria
they require lots of ATP for contraction
for the movement of myosin heads and also active transport of Ca2+ back into T-tubules
this means aerobic respiration rates must be very high
86
what is myoglobin
an oxygen carrying pigment in muscles with a very high oxygen affinity and that only releases O2 when the surrounding partial pressure is very low
it is a single chain like protein - like 1 haemoglobin subunit
87
how does myoglobin help when muscle ATP supplies run low during exercise
myoglobin only releases O2 when the surrounding concentration is very low, such as when respiration rate is very high and O2 is being used up - this means it acts as an emergency store of O2 for aerobic respiration
88
what type of respiration can take place in muscles
both aerobic and anaerobic respiration
89
why is anaerobic respiration less efficient for ATP generation in muscles than aerobic respiration
anaerobic respiration can provide almost all the energy needed for short bursts of energy but less ATP per glucose is obtained
90
what chemical in muscles provides another source of ATP
creatine phosphate - provides a phosphate to convert ADP >> ATP
- no lactate is produced so no muscle fatigue occurs
- there is only a limited store of creatine phosphate but enough is present to produce enough ATP for short bursts of activity, to keep muscles contracting until respiration catches up with ATP demands
91
give the equation for the reaction by which creatine phosphate provides energy to the muscles
ADP + creatine phosphate >> ATP + creatine
catalysed by enzyme creatine phosphokinase
92
what are the divisions of the nervous system
the nervous system is divided into the CNS and PNS - the PNS is then divided into the somatic and autonomic nervious systems - the autonomic nervous system is further divided into the sympathetic and parasympathetic nervous systems
93
what is the somatic nervous system
controls mostly voluntary actions, as well as some autonomic responses that involve skeletal muscle - e.g. the knee jerk reflex
94
what is the autonomic nervous system
controls involuntary responses affecting glands and muscles
95
what is the sympathetic nervous system
controls fight or flight responses
96
what is the parasympathetic nervous system
controls background maintenance of the body - rest and digest response
97
give some example responses of the sympathetic nervous system
- pupils dilate
- heart rate increases as impulses along accelerator nerve to SAN increase, and mostly norepinephrine is used as a neurotransmitter
- breathing rate increases
- digestion doesn't occur as blood flow is directed away
- muscles are contracting so blood is being directed here to maintain high O2 conc
98
give some example responses of the parasympathetic nervous system
- pupils are relaxed
- heart rate decreases as impulses along vagus nerve to SAN increase and acetylcholine is mostly used as a neurotransmitter
- breathing rate decreases
- digestion occurs
- muscles are relaxed
99
how does the autonomic nervous system control heart rate
the heart receives signals to the SAN, which controls heart beat, from different pathways to speed up and to rest
- to speed up, more norepinephrine impulses are sent to the SAN from the accelerator nerve
- to slow down, more acetylcholine impulses are sent to the SAN from the vagus nerve
100
what are the differences in structure and location of the neurones between sympathetic and parasympathetic nervous system
SYMPATHETIC
- short preganglionic neurones and long postganglionic neurones
- ganglia are closer to the spinal cord
- nerves are located in the thoracolumbar (thoracic + lumbar) region
PARASYMPATHETIC
- long preganglionic neurones and short postganglionic neurones
- ganglia are closer to target organs
- nerves are located in the craniosacral (cranial + sacral) region
101
what are the different regions of the spine and where are they located
cranial region - spine leading into skull
thoracic region - spine above ribcage
lumbar region - spine below ribcage
sacral region - bottom part of spine
102
what are the main regions of the brain
cerebral cortex
cerebrum
cerebellum
medulla oblongata
pituitary gland
hypothalamus
brain stem
103
what is the cerebral cortex
thin outer layer of the brain made of grey matter
104
what is the function of the cerebrum
- controls many movements
- processes sensory information
- involved in complex cognitive functions e.g. language, problem solving, memory
105
what is the structure of the cerebrum
- divided into 2 hemispheres which control opposite sides of the body
- these hemispheres are joined together with nerve fibres - corpus callosum
- each hemisphere is further divided into 4 lobes - frontal, parietal, temporal, occipital
- highly folded to increase SA:V + allow a greater no. of nerves, which increases its ability to carry out complex behaviour
106
what are the effects of damage to the cerebrum
- damage to frontal lobe can cause personality changes + impaired judgement
- damage to temporal lobe can cause memory loss + speech/language difficulties
- damage to the parietal lobe can cause issues with spatial awareness, + difficulties reading / writing
107
what is the function of the cerebellum
- receives information from sensory systems + spinal cord to regulate movements
- coordinates motor movement + maintains balance + motor learning
- functions are involuntary
108
what is the structure of the cerebellum
- lies below cerebrum
- made up of 2 hemispheres and a central vermis
- white matter + grey matter arranged in a distinctive tree like pattern
109
what are the effects of damage to the cerebellum
- ataxia - a lack of coordination
- dysmetria - difficulty judging distance
- hypotonia - loss of muscle tone, affecting posture and balance
110
what is the function of the medulla oblongata
- controls autonomic functions e.g. heartbeat, breathing rate, blood pressure
- serves as a relay station for information passing between spinal cord and other brain centres e.g. cardiac centre (controls heart rate) + vasomotor centre (controls blood pressure via smooth muscle contraction in vessel walls) + respiratory centre (controls breathing rate)
- controls nuclei for cranial nerves and in cardiovascular / respiratory centres
111
what is the structure of the medulla oblongata
- found at the base of the brain, where brain connects to spinal cord
- connected to spinal cord and pons
112
what are the effects of damage to the medulla oblongata
- respiratory failure + cardiac arrest can occur as vital functions are impaired
- difficulty swallowing + speaking
- loss of consciousness + coma
113
what is the function of the pituitary gland
anterior pituitary
- secretes hormones that regulate growth, reproduction, metabolism
posterior pituitary
- secretes hormones produces by hypothalamus, e.g. ADH, oxytocin
114
what is the structure of the pituitary gland
- split into the anterior and posterior pituitary
- located below hypothalamus at the bottom of the brain
- anterior and posterior lobes are connected by a thin stalk
- controlled by the hypothalamus which releases and inhibits hormones
- connected to hypothalamus via pituitary stalk
115
what are the effects of damage of the pituitary gland
- hormonal imbalances, especially affecting growth, reproduction and metabolism
- acromegaly - the enlargement of extremities, e.g. hands, feet - as a result of excess production of growth hormone
116
what is the function of the hypothalamus
- maintaining homeostasis by regulating body temp + hunger + thirst + circadian rhythms + blood flow
- controls pituitary gland + thus endocrine system
117
what is the structure of the hypothalamus
- located in the middle of the lower part of the brain
- part of the limbic system which is involved in emotion
- connected to the pituitary gland via the pituitary stalk
118
what is the effect of damage on the hypothalamus
- disruption of homeostasis e.g. temp not regulated + disrupted sleep/wake cycle
- changes in emotion - can effect mood + motivation
119
how does the brain regulate heart beat
- controlled by cardio regulatory centre in medulla, which is connected to the SAN via nerves
brain recognises:
- pH changes in blood as a result of lactic acid + CO2 conc (from anaerobic respiration) via chemoreceptors in aortic body + brain
- increased body temp
- stretch receptors in muscles send signals in more O2 is needed
- stretch receptors in aortic body that detects changes in blood pressure
120
outline the role of the brain + nervous system in the fight or flight response
the cerebrum uses sensory input from external threats detected by receptors in body - e.g. eyes, ears - as well as internal threats e.g. pain
if a threat is recognised it stimulates the hypothalamus which activates the sympathetic nervous system + the release of hormones from pituitary gland
121
what is the fight or flight response
an instinct that all mammals possess, in a potentially dangerous situation the body will trigger a serious of physical responses intended to help the individual survive by preparing the body to either run or fight
