Grey Matter Flashcards
(43 cards)
Neurones
Dendrons:
Extend from the cell body of the neuron, denrons brand off even further to form the dendrites
Dendrites:
Receive signals
Cell body:
Contains nucleus and other organelles, carry out normal functions of the cell, like protein synthesis
Axon:
Carries electrical signal away from the cell body to the synapses
Synapses:
Lie at the end of the axon and pass the electrical signal on to the next cell
Myelin sheath:
Layers of fat that covers the axon
Schwann Cells:
Membrane encircles the axon many times forming the myelin sheath. Its presence increases the speed of impulse conduction. They also engulf debris and neuronal regeneration.
Nodes of Ranvier:
The gaps between the myelin sheaths
Which direction do dendrites travel?
Towards the cell body.
Which direction do axons travel?
Away from the cell body.
Describe a reflex arc.
Rapid short-lived, automatic and involuntary Stimulus receptor sensory neurone Synapses CNS Relay neuron Synapses Motor neuron Effector
Describe the pupil reflex.
Reflex Pathway Light is picked up by photoreceptors in the retina of the eye This is passed on to sensory neurons which pass the signal back to the brain Midbrain sensory neurons target a coordinator The co-ordinator changes the activity of motor neurones targeting muscles in the eye. Dark light - Contraction of radial and relaxation of circular muscles.
Describe the resting potential.
-70mV. Neurones have a negative resting potential across their cell (negative inside compared to outside). So negative ions inside the cell have a tendency to leave the cell and positive ions outside the cell have a tendency to enter the cell. Resting potential is about -70mV Sodium-potassium pump Uses ATP to pump 3 sodium ions (+ charge) out of the cell and 2 potassium ions (+ charge) into the cell to maintain the resting potential. Net loss of 1 positive from inside the cell. The membrane is permeable to potassium ions through potassium channels but not to sodium. Potassium ions leave the cell through facilitated diffusion down the concentration gradient Potassium ions have an electrical gradient (into cell) and concentration gradient (out of cell).
Describe an action potential (depolarisation, repolarisation and hyperpolarisation).
Depolarisation (positive feedback)
If a sodium channel opens then there is an influx of sodium ions and the membrane potential is reduced. This then causes more voltage-gated sodium channels to open. If the membrane potential exceeds the threshold potential then action potential will occur. This causes all the gates of the sodium channel to open (all or nothing principle) causing the membrane polarity to reverse.
Repolarisation
When the axon becomes positive,voltage-gated potassium channels open (at +40). Voltage-gated sodium channels close. Potassium ions leave the cell and therefore reduce the membrane potential. The potassium channels remain open and leads to the undershoot
Hyperpolarisation
There is a high amount of potassium outside the cell and high amount of sodium inside the cell. The action of the sodium potassium pump restores the ion concentrations back to its resting potential.
Refractory period
In this period it is impossible to initiate another action potential as the axon can’t be depolarised. Allows the action potential to only travel in one direction Action potentials are discrete (only one after the other can occur)
Refractory period
It is impossible to initiate another action potential as the axon is unable to be depolarised. - Action potential only one direction - Action potential discete
Action Potential Graph
What does the size of a stimulus affect?
Frequency of impulses. Number of neurons in a nerve conducting impulses.
Define saltatory conduction.
Myelin sheaths increase the speed of conduction because action potential can’t occur where the myelin sheath is present. So the action potential jumps between the nodes of Ranvier.
Describe speed of conduction.
Determined by the diameter of an axon. Speed is quicker for normal squid but slower for a giant squid. The myelin sheath acts as an electrical insulator and the depolarisation occurs in the nodes of Ranvier.
Synapses workings
- action potential reaches the synaptic nob
- calcium channels open and calcium (from the synaptic cleft) in to the pre-synaptic nob
- the the vesicles with the neurotransmitters moves to the cell membrane and the transmitter is release through exocytosis
- neurotransmitters move to the post-synaptic through the cleft and binds to the receptors on the post synaptic membrane
- neurotransmitter stimulates action potential through depolarizing (sodium channels open)
How are neurotransmitter are removed from the synapse
The neurotransmitter breaks down at the receptors and there is a large concentration gradient causing the parts to move back to the pre-synaptic nob and form vesicles so the NT are ready to be used again.
What are synapses used for?
Control of nerve pathways. Integration of information from different neurons.
Acetylcholine
Found in all nerves of the voluntary and the parasympathetic autonomic system
Describe excitatory synapses.
Post-synaptic membrane is more permeable to Na+ ions.
Describe inhibitory synapses.
Less likely for there to be an action potential. Cl- and K+ channels are opened. Greater potential difference leads to hyperpolarisation.
What are the differences between nervous and hormonal control?
Nerves transmit signals electrically, hormones transmit signals chemically. Nerves are fast acting, hormones are slow acting. Nerves create short-term changes, hormones create long-term changes. Nerves are transmitted in action potentials, hormones are transported in blood. Nerves have a local response, hormones have a widespread response.
Rod cells at rest
Sodium diffuse in through open cation channels
The sodium moves down the concentration gradient to the inner segment
The sodium is actively pumped out causing it to be depolarised to -40mV
The membrane is slightly depolarised which triggers a neurotransmitter (glutamate) to be released.
This diffuses across the synaptic cleft to a bipolar cell, preventing it from depolarising,
Rod cells detect light
Light is absorbed by rhodopsin in the rod cell.
Rhodopsin breaks down into opsin and retinal.
Cation channel to close.
This means that the inner segment continues to pump sodium ions out of the cell so the membrane becomes hyperpolarized.
So glutamate is not released across the synapse so an action potential forms and is transmitted to the brain.
The information from the optic nerve is processed by the brain in the visual cortex.
How does auxin work?
Stimulates growth in response to cell elongation.
Light –> Found at the shaded side so grows to the sun
Gravity –> Found against gravity so it grows down
Describe phytochromes.
Pr absorbs red light. Pfr absorbs from infrared light.
Pr inhibits growth
Pfr promotes growth
Phytochrome and Germination
Phytochromes are first synthesized in the young seed at the inactive Pr form.
Exposed to light, Pr is converted to Pfr
The Pfr form allows chlorophyll molecules to be synthesized so the growing seed can start to photosynthesise.
The Pfr form also promotes growth and flowering by active as a transcription factor
