Nerves Flashcards
What two systems do animals have
Nervous and hormonal/endocrine
What are the chemical coordinators of the Endocrine system and where are they secreted
Hormones which are secreted into the blood
What are the chemical coordinators of the Nervous system
Neurotransmitters
Which of the endocrine and nervous system is longer lasting
Endocrine system
Which of the endocrine and nervous system have a faster speed of effect
Nervous system
What order does a stimulus move down the nervous system
Stimulus
Receptor
Sensory neurone
Co-ordinator
Motor neurone
Response
What is a motor neurone
A nerve cell that carries out an impulse from the CNS to an effector
What is a stimulus
A change in the external or internal environment that brings about a response in an organism
What is a co-ordinator
Region of Central nervous system where sensory information is interpreted
What is a receptor
a structure that detects a stimulus and generates a nerve impulse
What is a response
Action behavior brought about by an effector
What is a sensory neurone
A nerve cell that carries an impulse from a receptor to the CNS
What does the CNS consist of
Brain, Spinal cord,
Cranial nerves
Spinal nerve
Peripheral nerves
Sensory neurons
Motor neurons
Describe how the component part of the nervous system bring about a reflex
The stimulus activate receptors
An electron impulse travels along the sensory neuron to the closest CNS
An electrical impulse travels to the motor neuron to the effector
The response is brought out
What 5 structures make up a myelinated axon
Cell body
Dendrites
Axon
Myelin Sheath
Nodes of Ranvier
What is the cell body in the myelinated sheath
Contains the nucleus, cytoplasm, Endoplasmic reticulum and neurotransitters
What are the dendrites in the myelinated sheath
Finger-like projections of cytoplasm of cell body
What are the Axons in the myelinated sheath
Extension of cytoplasm which transmits impulses away from the cell body
What are the nodes of Ranvier in the myelin sheath
Junctions between Schwann cells
What do axons do
take information away from the cell body
What are some structural features of an axon
No ribosomes
Smooth surface
Branched further from the cell body
can have myelin insulation
What do dendrites do
Bring information towards the cell body
How many axons per cell
1 generally
How many dendrites per cell
many dendrites per cell
What are some structural features of a dendrite
Rough surface
Has ribosomes
never has myelin insulation
branched near cell body
What is resting potential difference across the membrane
-70mv
Is the interior axon positive or negative
negative
How is resting potential maintained
Active transport in the sodium potassium pump- 3Na+ out and 2K+ in
Facilitated diffusion - more K+ ions leak out than Na+ ions leak in through the closed facilitated diffusion channels
What is meant by a reflex action
The rapid response carried out by the unconscious part of the brain
An innate reaction which occurs everytime
How does the hormonal system differ from the nervous system
Slower than neuron
Chemical not electrical
Long lasting not short lasting
You smell
I know
How long does active potential last
about 3 milliseconds
What is action potential
When neurons are stimulated by a change in the resting potential
What is seen in the axon membrane during action potential
The voltage inside axon raises from -70mv to +40mv which is caused by voltage gated channels opening which allow ions to diffuse
What happens during depolarisation
Voltage gated Na+ ion channels open
This leads to Na+ ion flooding down the conc gradient into the axon
So the inside of axon becomes positive
What happens during repolarisation
Na+ voltage gated channels close
K+ voltage gated channels open and K+ ions flood down conc gradient of axon
Inside the axon returns to -70mv
What is repolarisation
Where the axon recovers its resting potential after the membrane reaches +40mv
What happens during hyperoplarisation
Too many K+ ions leave the axon so cytoplasm temporarily more negative than -70mv until the k+ vgc ions close
What is the all or nothing principal
Action potential can only be generated if the stimulus reaches a certain threshold intensity and below the threshold action potential won’t be reached
How does size change between action potentials
It doesn’t all action potentials are the same size
How does a strong stimulus differ in production in action potential to a weaker stimulus
A strong stimulus produces more action potentials and is likely to cause action potential in more neurones
What is a refractory period
for a brief time after an impulse where
The k+ channels close and so do the Na+ channels
No matter what stimulus is applied they will not reopen to allow Na+ in
This means no impulse can pass
What is the importance of the refractory period
No overlapping of potentials
Ensures a.p only travels in one direction
Limits the number of a.ps
What are the effects of myelination
The myelin sheath greatly increases the speed at which impulses are conducted over the axon
How does the myelin sheath help to increase speed
Insulates the axon so depolarisation can only occur at nodes of Ranvier and the impulse jumps from node to node
How are unmyelinated sheaths slower
The entire axon membrane is exposed and it all must undergo depolarisation so impulse conduction is slower
What are the effects of the diameter of an axon
Impulse will be conducted at a higher speed along neurones with thicker axons
they have a greater Surface area over which diffusion of ions can occur
What are the effects of temperature on an axon
Doesn’t usual affect the speed of nerve impulses
However colder conditions can slow down the conduction of nerve impulses
The blink reflex is caused by what type of stimuli
(7)
Pressure
light
touch
temperature
chemicals
smell
noise
What event starts depolarisation
Sodium channels open
Why would a hydrophobic molecule be able to pass into neurones
they are lipid soluble
Why might damage to myelin sheaths lead to problems controlling muscle contraction
Causes hyperpolarisation or preventing depolarisation
Why would a myelinated axon conduct impulses faster than a non-myelinated axon
In myelinated action potential only at nodes so impulses jump from node to node and action potential does not travel whole length
Give 3 factors that effect the speed of nerve impulses
Temperature
Axon diameter
Myelination
Why is it important that a neurotransmitter is transported back out of synapses?
If it isn’t removed it will keep binding to receptors
This means it will keep causing depolarisaion in post synaptic membranes
Explain how resting potential is reestablished
Active transport of sodium out of axon and
Active transport of potassium into axon
Describe how resting potential is established in an axon
Pump Na+ ions out of axon and diffusion of K+ into axon
Little diffusion of Na+ into axon
Why can Na+ and K+ only pass through the axon membrane through proteins
Can not pass through phospholipid bilayer as they are charged
Describe the sequence of events leading to the acetylcholine and its binding to the postsynaptic membrane
calcium ions enter synaptic knob
Vesicles fuse with membrane
Acetylcholine diffuses across synaptic cleft
Binds to receptors
Explain the importance of reflex actions
Automatic/involuntary
Reducing damage to tissues
Posture and balance
Escaping from predators
Finding food
Describe the sequence of events which allows information to pass from one neurone to the next neurone across a cholinergic synapse
Impulse causes calcium ions to enter axon
Vesicles fuse with presynaptic membrane
This releases acetylcholine
Acetylcholine diffuses across the synaptic cleft where it binds with receptors on the postsynaptic membrane
Sodium ions enter neurone
Depolarisation of postsynaptic membrane
If above the threshold action potential is produced
What are agonist drugs
Drugs that stimulate a nervous system
What are antagonist drugs
Drugs that inhibit a nervous system
Describe temporal summation
A number of impulses arriving in quick succession
Describe summation
A number of synaptic neurons synapsing with one Post synaptic neuron
Their effects add up together
What does unidirectionally synapse mean
Synapses can only pass information in one direction
Describe inhibitory ion channel synapses
Neurotransmitters released bind to chloride ions channel protein on the Post synaptic membrane
Chloride ions move into Post synaptic membrane by facilitated diffusion
The binding of the neurotransmitter causes openings of nearby K+ vgc
K+ move out of the Post synaptic membrane neuron into the synapse
Inside of he Post synaptic neurone is more negative making that the threshold is harder to reach
Name types of receptors in humans
Photoreceptors
Mechanoreceptors
Chemoreceptors
Thermoreceptors
Describe photoreceptors
Detect light and other forms of E.M
Desribe mechanoreceptors
Detect movements, pressure, tension, gravity and sound waves
Describe chemoreceptors
Detect specific chemicals
