Lecture 3 Flashcards
What are the two types of cells in the nervous system?
Neurons; They receive and transmit information to other cells.
Glia; They have many functions, some of those support neurons in their functions.
What is the structure of a neuron?
It consists of a soma, dendrites, an axon, a myelin sheath and a presynaptic terminal.
Discuss terminology in relation to a neuron
An afferent axon is one that carries electrical information to a structure.
An efferent axon is one that carries electrical information away from a structure.
This is relative.
A sensory neuron is afferent to the CNS and a motor neuron is efferent.
A nucleus is a cluster of cells in the CNS.
A ganglion is a cluster of cells in the PNS.
A tract is a cluster of axons in the CNS.
A nerve is a cluster of axons in the PNS.
Describe what a glia is
A glia is part of the nervous system, it’s smaller but more numerous than neurons. They don’t submit information across long distances. There are 4 types; astrocytes (they help synchronise the activity of neurons and they remove waste materials), microglia (They remove microorganisms and other waste materials), oligodendrocytes and schwann cells (they build the myelin sheaths) and radial glia (they guide the migration of neurons). (The last two occur during development)
How is the nervous system protected?
It’s protected by the skull, backbone, meninges (membranes surrounding the CNS), a blood-brain barrier which prevents viruses, bacteria etc. entering the brain. This all depends on the epithelial cells lining capillaries.
This is all needed as neurons struggle to regenerate.
What can pass through the epithelial barrier/membrane of a capillary?
Passively: Small uncharged molecules, water and fat soluble molecules.
Actively: Glucose, amino acids and certain vitamins.
Large molecule cannot pass through the barrier!
Discuss the nerve impulse
The neurons conduct electrical impulses extremely fast. This all depends on the resting and action potential.
Discuss resting potential
The neurons are more negative than outside the cell when resting. -70 mV. This is because of an uneven distribution of negatively charged CL- and protein ions and positively charged NA+ and K+.
How is the resting potential maintained?
It’s maintained by 4 factors:
2 homogenising factors;
1. Concentration gradients (move from areas of high to low concentration).
2. Electrical gradient (accumulation of a positive charge repels positive ions and vice versa with negative ions. Opposite charges attract each other).
Non-homogenising factors;
1. Membrane permeability (chloride and potassium pass through, sodium passes with difficulty and protein doesn’t).
2. Sodium-potassium pumps (3 sodium are transported out and 2 potassium in).
Discuss action potentials (not on a molecular level)
This happens when a neuron is stimulated above a certain threshold. The neuron can respond quickly thanks to the resting potential. The neuron becomes less negative and becomes depolarised. It must go beyond the threshold of excitation. After depolarisation, repolarisation and hyperpolarisation occurs. If it doesn’t reach the right potential then the subthreshold potential produces depolarisation that’s proportional to the stimulation strength.
Define the all or nothing law
This refers to the amplitude and velocity of an action potential being independent of the stimulus. So, no matter the strength of stimuli, as long as it goes above the excitation threshold, then the same strength action potential will be generated.
Discuss the molecular basis of an action potential
Sodium ions rush into the neuron and then potassium rushes out. The pump then restores it to resting potential.
Discuss the refractory period
It occurs just after an action potential, it means that the neuron cannot produce another action potential. There’s an absolute refractory period and a relative one where an action potential can be created as long as the stimuli is stronger than normal. During the refractory period, sodium channels are closed and potassium is flowing out the neuron.
Discuss the propagation of an action potential
It begins at the axon hillock and then travels along the axon via saltatory conduction. The direction of propagation is determined by the refractory period.
Discuss an action potential’s conduction speed
It depends on the diameter of the axon, thicker axons are slower. The myelin sheath also speeds up conduction thanks to the nodes of ranvier allowing saltatory conduction to occur (when the AP jumps from node to node).
Define synapse
When information flows from one neuron to another. It has 3 parts: the presynaptic terminal, the synaptic cleft and the postsynaptic neuron.
What happens when an action potential reaches a synapse?
It arrives at the terminal, then calcium ions cause the vesicles of neurotransmitters to be released into the synaptic cleft. The neurotransmitters attach to receptors via a lock and key system. This alters the activity which creates an AP in the post-synapse. The NT are then taken back to the cell.
What type of receptors are in the post-synaptic membrane?
Ionotropic receptors, these are fast and short. The neurotransmitter causes the sodium channels to open. Glutamate and GABA are types of this receptor. This type of receptor is relevant for vision and hearing.
There’s also metabotropic receptors. These are slow and long. The neurotransmitter activates the G-protein in the cell. The G-protein then binds to ion channels or stimulates the synthesis of the second messengers. These are relevant for hunger, thirst, fear etc.
Discuss the reuptake of NT
An enzyme breaks it down and then is absorbed by the presynaptic membrane to be reused.
Discuss temporal summation
The summation of excitatory postsynaptic potentials from one source. This all depends on the size, time and threshold of the EPSP. If the stimuli is too small but several EPSP occur (depolarisation of post-synapse) then an action potential will be generated.
Discuss spatial summation
This is the summation of EPSPs from different sources. These need to be simultaneous rather than one after another.
Briefly discuss an antagonistic and agonistic effect of drugs
Give examples of these psychoactive drugs
Antagonistic: When a drug blocks a receptor or stops the release of the neurotransmitter.
Agonistic: The drug binds to the receptor and activates it or it increases the release of neurotransmitters.
Cocaine is a dopamine/norepinephrine agonist, it blocks the reuptake of it. This causes euphoria.
Benzodiazepines (valium) is a GABA agonist which reduces anxiety.
