Topic 6A and 6B Flashcards
What is an Axon?
A single long fibre that carries nerve impulses away from the cell body.
What are dendrons and dendrites
Extensions of the cell body that carry nerve impulses
Dendrites are smaller divisions of dendrons
What is a neurone?
A specialised cell adapted to rapidly carrying nerve impulses.
What is a cell body?
Associated with production of proteins and neurotransmitters
What are Schwann cells used for?
protecting the axon and providing electrical insulation. they also carry out phagocytosis + help nerve regeneration
What are the two main forms of coordination in animals?
The nervous system
The hormonal system
What is a myelin sheath for?
covers the axon, made up of membranes of Schwann cells.
What are nodes of Ranvier ?
constrictions between adjacent schwann cells where there’s no myelin sheath.
Name 3 classifications of neurone
Sensory neurones
Motor neurones
Intermediate/ relay neurones
Neurones are adapted to carry electrochemical charges called…
Nerve impulses
Each neurone comprises a cell body that contains a ….. and large amounts of ………. …… ……
Each neurone comprises a cell body that contains a nucleus and large amounts of rough endoplasmic reticulum.
Axons are surrounded by ……… cells which protect and provide ……. because their membranes are rich in a lipid known as ……
Axons are surrounded by Schwann cells which protect and provide insulation because their membranes are rich in a lipid known as Myelin.
3 types of neurone. Those that carry nerve impulses to an effector are called ……. neurones. Those that carry impulses from a receptor are called ……. neurones and those that link the other two types are called …… neurones.
3 types of neurone. Those that carry nerve impulses to an effector are called motor neurones. Those that carry impulses from a receptor are called sensory neurones and those that link the other two types are called relay neurones.
List three ways in which a response to a hormone differs from a response to a nerve impulse
Hormone response is slow, widespread and long-lasting. Nervous response is rapid, localised and short-lived.
What do synapses do?
Transmit information, from one neurone to another or an effector.
What separates neurones?
Synaptic Cleft
Which neurone releases the neurotransmitter?
Presynaptic neurone
Axon of presynaptic neurone ends in a swollen portion called ……
Synaptic knob
Where is the neurotransmitter stored?
In the synaptic vesicles
What is the general path for a reflex arc?
Stimulus -> Receptor -> Sensory Neuron -> Relay Neuron -> Motor Neuron -> Effector -> Response
What are the extensions of neurones called?
dendrites (towards cell body)
How are nerve cells polarised in their resting state?
Imbalance between sodium ions and potassium ions, resulting in more negative inside of axon tha outside
As a result of polarisation there is a difference in the ……. across the axon membrane with a value of …. known as resting potential
As a result of polarisation there is a difference in the voltage across the axon membrane with a value of -70mV
The resting potential is generated as well as maintained by the help of the ………-……. ……..
The resting potential is generated as well as maintained by the help of the sodium-potassium pump
For ever …. sodium ions that are pumped out of the axon …. potassium ions are pumped in.
For every 3 sodium out
2 potassium in
Resting potential is maintained by…
Active transport and passive diffusion
During resting potential the plasma membrane of the axon is more permeable to …. ions
Membrane more permeable to K+ ions
The process where a neurone is depolarised and returns to resting potential is called….
an action potential
Where do motor neurones carry impulses?
From the CNS —> effector organs
Where do sensory neurons carry impulses?
From receptors –> CNS
Where do relay neurones carry impulses?
From sensory neurones –> motor neurone
What do receptors do?
Detect stimuli
What do effectors do?
Produce a response
Give some examples of receptors
cells/proteins on cell membranes
Give some examples of effectors
muscle cells and cells found in glands
What does the autonomic nervous system control?
Unconscious activities e.g. digestion
What 2 parts is the autonomic nervous system split into?
Sympathetic- ready for response, fight/flight
Parasympathetic- calms body down
What does the somatic nervous system control?
Conscious activities e.g. running
What is a reflex?
An involuntary response to a stimulus
What is a tropism?
the growth of a plant in response to a directional stimulus.
What is the difference between positive and negative tropisms?
Positive = growth towards stimulus Negative = growth away from stimulus
What is phototropism?
The growth of a plant in response to light
….. are positively phototropic and grow ….. light
Shoots are positively phototropic and grow towards light
…. are negatively phototropic and grow ……. light
Roots are negatively phototropic and grow away from light
What is gravitrotropism?
The growth of a plant in response to gravity.
Shoots are …… gravitropic and grow ……..
shoots are negatively gravitropic and grow upwards
Roots are ……. gravitropic and grow …….
Roots are positively gravitropic and grow downwards
What is auxin?
a growth factor that stimulates the growth of shoots by elongation
What is cell elongation?
cell walls becoming loose and stretchy, so the cells get longer
Name an important auxin that’s produced in the tips of shoots in flowering plants
Indoleacetic acid (IAA)
In phototropism IAA moves to the more….. parts of the shoots and roots resulting in …..
During phototropism IAA moves to the more shaded parts of the shoots and roots resulting in uneven growth
In gravitrotropism IAA moves to the ……… of shoots and roots so there’s ……
In gravitrotropism IAA moves to the underside of shoots and roots so there’s uneven growth
Receptors only detect one particular stimulus so they are…
specific
What happens if a stimulus is too weak?
The generator potential won’t reach the threshold so there’s no action potential
Why do organisms respond to changes in environment?
To increase their chance of survival
What do Pacinian corpuscles detect?
mechanical stimuli e.g. pressure and vibrations
Photoreceptors convert light into what?
An electrical impulse
Neurone cell membranes become …….. when they’re stimulated.
depolarised
What is the value for the threshold?
-55mV
Describe what happens during depolarisation
If potential difference reaches the threshold (-55mV) then more sodium ion channels open and more sodium ions rapidly diffuse into neurone
Describe what happens during repolarisation
At a potential difference of around +30mV the sodium ion channels close and K+ channels open. The membrane is more permeable to potassium so potassium diffuses out down the conc grad to regain resting potential.
Describe what happens during hyperpolarisation
Potassium ion channels are slow to close so there’s an overshoot as too many potassium ions diffuse out of neurone. Potential difference becomes more negative than resting potential (less than 70mV)
Describe resting potential
The ion channels are reset. The sodium-potassium pump returns the membrane to its resting potential and maintains until another stimulus excites the membrane.
why don’t action potentials overlap or move in more than one direction?
During the refractory period ion channels can’t be opened. Therefore it acts as a time delay
Why are action potentials described as all or nothing responses?
As once the threshold is reached an action potential will always fire with the same change in voltage no matter how big the stimulus
A bigger stimulus won’t cause a bigger action potential but it causes …..
them to fire more frequently
What is the gap between neurons called?
Synaptic Cleft
Where are neurotransmitters stored?
Synaptic vesicles
What is a synapse?
The point where one neuron communicates with another or an effector
What is the neurone called that releases the neurotransmitters?
Presynaptic neurone
What is the synaptic knob? What does it contain lots of?
Swollen portion at the end of an axon.
Mitochondria and Endoplasmic reticulum
What are Pacinian Corpuscles
Pressure receptors in your skin
Pacinian corpuscles contain the end of ….. …..
a sensory neurone surrounded by lamellae
What happens when pressure is applied to a Pacinian corpuscle?
The tissue is deformed and pressues the sensory nerve ending causing the membrane of neurone to stretch, deforming the stretch mediated Na+ channels which opens them so Na+ ions diffuse in and a generator potential is made.
Photoreceptors convert …… into an ……… …….
light into an electrical impulse
Spatial Summation
many different neurones collectively trigger a new action potential by combining the neurotransmitter they release to exceed the threshold value.
Temporal summation:
One neurone releases neurotransmitter repeatedly over a short period of time to add up to enough to exceed the threshold value.
Name the two types of photoreceptors found in your eye
rods and cones
List features of Rods
Rods = black and white low intensity light many rods to 1 bipolar cell pigment = rhodopsin low visual acuity
List features of Cones
Cones= Colour high intensity 1 cone to 1 bipolar pigment= iodopsin high visual acuity
Explain the importance of reflex actions (3)
- involuntary/automatic response
- prevents damage to tissues/injury
- Escape from predators
What is a tactic response (taxes)
When an organism moves towards or away from a directional stimulus e.g light
What is a kinetic response (kineses)
When the organisms movement is affected by non-directional stimulus e.g. humidity
What is summation?
the effect of a neurotransmitter released from many neurones is added together.
What is a neuromuscular junction?
a synapse between a motor neurone and a muscle cell
Which neurotransmitter is found at neuromuscular junctions?
Acetylcholine
What receptors does Acetylcholine bind to?
Cholinergic receptors
Acetylcholine is always ……. at a muscular junction
Excitatory
What enzyme breaks down Acetylcholine?
Acetylcholinesterase
Rods can generate an action potential in ……. …… whereas cones require ….. …. to generate an action potential
Rods can generate an action potential in dim light whereas cones require brighter light to generate an action potential
How is a generator potential established in a Pacinian Corpuscle?
Deformation of stretch-mediated sodium ion channels in a Pacinian corpuscle leads to the establishment of a generator potential.
Function of SAN?
Acts as pacemaker, sends electrical activity to atria so they contract
Function of Purkyne tissues
sends electrical activity through ventricle muscles so that they contract.
Outline the Resting Cardiac cycle
SAN sends electrical activity. Atria contract. AVN receives electrical activity from SAN and slightly delays and then sends to bundle of His onto Purkyne tissue, into muscular ventricle walls for ventricular contraction.
Why does the AVN delay passing on the waves of electrical activity?
So that the atria empty before ventricles contract
What is the rate of the SAN controlled by?
The medulla oblongata UNCONSCIOUSLY controls rate
Why do animals need to alter their heart rate?
To respond to internal stimuli i.e make sure heart rate is high enough to supply the body with enough oxygen
What are the pressure receptors in the aorta and carotid arteries called?
Baroreceptors
What are the pressure receptors in the aorta and carotid arteries called? What are they stimulated by?
Baroreceptors stimulated by high and low blood pressure
What are the chemical receptors called that are found in aorta, medulla and carotid arteries? What are they stimulated by?
Chemoreceptors monitor oxygen levels in blood, and CO2 and pH (indicators of O2 level)
Light inhibits … …….. in the tip so it is only produced on the ….. …..
IAA production
shaded side
Why does Axon diameter affect speed of conduction?
The bigger the diameter the less resistance to flow of ions therefore depolarisation reaches other parts of neurone quicker.
Why does temperature affect speed of conduction?
Ions diffuse faster at higher temperatures (after 40”c they denature)
Name the cell membrane of muscle fibres
Sarcolemma
Name the cytoplasm of muscle fibres
Sarcoplasm
What is the network of internal membranes called in a muscle? What do they do
Sarcoplasmic reticulum (store and release calcium ions)
Compare slow and fast twitch muscle fibres
Slow = contract slowly, endurance, long time without tiring, aerobic resp, lots of mitochondria Fast= contract quickly, tired v quickly, short bursts of speed and power, few mitochondria, anaerobic resp
