neuronal communication + muscles Flashcards
main functions of the nervous system
send, receive and interpret information
neurone definition
conductive excitable cells of the nervous system that are specialised to transmit nerve impulses
nerve definition
elongated bundles of nerve fibres
3 types of neurone
sensory neurone
relay neurone
motor neurone
outline the structure of a sensory neurone
- 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
what is the difference between an axon and a dendron
axon carries an impulse away from the cell body
dendrons carry an impulse to the cell body
what is a myelin sheath
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
what are nodes of ranvier
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
why is saltatory conduction more efficient
less repolarisation (which requires ATP) is necessary
where are sensory neurones located + what is their function
found in spinal cord in dorsal ganglia
these carry signals from receptors to the CNS
outline the structure of a relay neurone
- 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
where are relay neurones located + what is their function
found in brain and spinal cord
these allow sensory and motor neurones to communicate
outline the structure of a motor neurone
- 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
what are schwann cells
a type of cell that surrounds neurones to keep them alive + makes up the myelin sheath
where are motor neurones located + what is their function
found in brain and travel to brain stem and spinal cord
carries signal from CNS to effectors
why are dendrites and axon terminals highly branched
branching increases SA:V which increases efficiency of transmission from axon terminals to dendrites
give 2 factors affecting the speed of conduction + explain how
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
outline the stages of a reflex arc
> 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
reflex definition
simple and rapid autonomic responses to stimuli operated through the nervous system
why are reflexes important
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
for a named reflex, outline the process from stimulus to response
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
what is the purpose of the knee jerk reflex
useful for when you fall as this tends to propel you forwards
what makes reflexes so fast
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
what are 3 advantages of reflexes
- simple pathway = quicker response
- brain can be used for more complex processing
- always the same reaction, successful + consistent
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
what makes up the PNS
sensory and motor neurones
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
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
where are pacinian corpuscles found
in the skin of fingers, soles of feet, joints, tenodns and ligaments, at the ends of sensory neurones
what happens when pacinian corpuscles are stimulated
they are stimulated by pressure, which leads to the generation of an action potential
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
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
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
how do Na+/K+ pumps work
uses ATP to actively pump 3Na+ out and 2K+ in
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
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
resting potential definition
the potential difference of the axon membrane when no impulse in being transmitted
refractory period
the short time period for which the neurone cannot generate another action potential
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
synapse definition
where 2 neurones meet
what are the 2 types of synapse
inhibitory and excitatory synapses
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,
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
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
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
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
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
why does the presynaptic knob end in a bulb
to increase SA for release of acetylcholine by exocytosis