Lecture 2 - Communication within the Nervous System Flashcards
Does the human brain have more neurons or glial cells?
glial cells (10-50 x more than neurons)
T/F: It is always one-on-one communication between neurons.
False: 1 neuron can communicate with multiple neurons
List the 4 main functions of neurons.
- receive and integrate incoming information from sensory receptors or other neurons
- generate a nerve impulse (action potential)
- conduct the action potential
- transmit information to target cell (other neurons, muscles, glands)
How does information get passed along within the nervous system?
Action Potential
What is the basic functional unit of the nervous system?
Neuron cells
What are the 3 main features of a typical neuron?
cell body, dendrites, axons
Differentiate between dendrites and axons.
Dendrites carry signals towards the cell body, axons carry signals away from the cell body.
What are neurites?
axons and dendrites
What 2 ways are neurons classified?
structure and function
How are neurons structurally classified?
by number of a neuron’s processes extending from cell body
What are the 4 types of structural neuron classifications?
unipolar neurons
pseudo-unipolar neurons
bipolar neurons
multipolar neurons
Describe a unipolar neuron.
single process from cell body, characteristic of invertebrates
Describe a pseudo-unipolar neuron and list an example.
Short single process from cell body that splits into two processes (like a “T‟)
•Example: sensory neurons within dorsal root ganglion
Describe a bipolar neuron and list an example.
2 processes:one dendrite, one axon
•Examples: some sensory
neurons, including those of retina of eye and olfactory epithelium
Describe a mulitpolar neuron Where are they abundant? List an example of one.
a single axon and one or more dendritic branches emerge from all parts of the cell body
•characteristic of most neurons in brain and spinal cord
•Examples: motor neurons in spinal cord, Purkinje neurons of cerebellum, pyramidal neurons of motor cortex
Of the 4 structural classifications of neurons, which are the most abundant in the human nervous system?
multipolar
What are the 4 morphological characteristics of a multipolar neuron?
dendrites, cell body, axon, pre-synaptic terminal
Describe the nerve cell body.
Contains mitochondria, nucleus, neurofibrils and nissl substances; metabolic centre of the nerve.
Describe dendrites.
main apparatus for receiving information from other nerve cells; relatively short processes
often branch extensively (resemble branches of a tree)
What can you devise when you come across a neuron that has an extensive dendrite branching?
That the nerve is capable of receiving more information and is able to perform more complex tasks.
What is the main conducting unit of a neuron?
axons
Describe axons.
Can vary in length (1mm -> 1m), branch extensively before terminating, ends of the branches are enlarged and called the pre-synaptic terminals
Describe presynaptic axon terminals.
where axons make contact to transmit information, point of contact is the synpase.
What are the 3 components of a synpase?
presynaptic membrane + synaptic cleft + post synaptic membrane
How are neurons functionally classified?
based on connections to different tissue types
What are the 3 functional classifications of neurons?
- Primary sensory or afferent neurons
- Motor or efferent neurons
- Interneurons
You just wrapped your hands around your mug of coffee and found it to be warmer than you expected. Trace the action potential through the 3 functional classification of neurons.
- Primary sensory/afferent neurons: registered the temperature stimulus and passed it onto the interneuron
- Interneuron: sorted through the incoming information and realized that the best course of action is to let go of the mug. The interneurons passed this message in to the motor/efferent neurons.
- Motor neuron/efferent neurons: received the message from the interneurons and activated the appropriate muscles in the hand let go of the mug.
Differentiate between Golgi Type 1 neurons and Golgi Type 2 neurons. Where can each be found?
Golgi Type 1: • have long axons • form the long fibre tracts of brain and spinal tracts • form the nerve fibres of peripheral nerves Golgi Type 2: • have short axons that terminate near cell body • have short dendrites, with a starshaped appearance • found in large numbers in cerebral and cerebellar cortex and in retina
What is a synapse? What are the 2 most common areas for synapses?
A point of functional contact between two neurons or between a neuron and an effector cell;
axo-dendritic and axo-somatic
What are the 2 types of synapses?
chemical and electrical
Describe the synaptic transmission at a chemical synapse.
- a chemical substance, the neurotransmitter, is released from presynaptic terminals of neuron
- neurotransmitter binds to neurotransmitter receptors in postsynaptic membrane of another neuron
- produces either excitation or inhibition of postsynaptic neuron
The neurotransmitters at the axon terminal are housed in what structure?
vescicles
What is the resting membrane potential?
potential difference across nerve fiber cell membrane is -70 to - 80 mV
• produced by diffusion of sodium and potassium ions through plasma membrane which is maintained by active sodium-potassium pump and passive leakage
When are action potentials generated?
when excitatory synaptic inputs
excite a neuron
Describe the different stages of an Action Potential.
- nerve impulse (AP) is initiated at initial segment of axon
- AP acts as a stimulus to adjacent point along cell membrane
- this stimulus alters permeability of membrane to sodium ions (-55 mv)
- sodium ions rapidly enter axon, producing depolarization of membrane potential
- repolarization
- refractory period
- resting membrane potential
What is the purpose of the refractory period?
Ensures that action potential propagation occurs unidirectionly & avoids a continuous excitatory state of the nerve and limits the frequency of the impulses
Trace the movement of the neurotransmitters following the arrival of action potential at presynaptic axon terminal.
membrane of presynaptic terminal depolarizes, causing opening of voltage-gated Ca2+ channels, influx of Ca2+ causes synaptic vesicles to fuse with presynaptic membrane triggers release of neurotransmitters into synaptic cleft
T/F: Once the neurotransmitter binds to the receptor on the post-synaptic membrane the signal will always be excitatory.
False: depends on the type of neurotransmitter
______ synaptic potentials tend to generate excitatory postsynaptic potentials (EPSP).
depolarizing
______ synaptic potentials inhibit production of action potentials -> inhibitory postsynaptic potentials (IPSP)
hyperpolarizing
______ is a neurotransmitter found at neuromuscular junction and parasympathetic nerve endings.
acetylecholine
_____ is a neurotransmitter that acts on postsynaptic membrane in the sympathetic nervous system
norepinephrine
How do neurotransmitters released into the synapse allow for communication between neurons?
By either producing EPSPs or IPSPs
What are neuromodulators? Give an example of a neuromodulator.
modulate and modify activity of post-synaptic neurons, they’re not neurotransmitters. Neuromodulators released into synaptic cleft enhance, prolong, inhibit, or limit the effect of principal neurotransmitter on postsynaptic membrane.
Example: dopamine
Describe how action potentials travel along unmyelinated neurons.
slow conduction rate and AP occurs on one direction; usually seen on small-diameter neurons.
T/F: All myelin sheath is produced by Schwann cells.
F: Oligodendrocytes (CNS) Schwann cells (PNS).
The small space of axon not covered by myelin sheath is called the ____ _ ____.
Node of Ranvier
List the 4 functions of myelin sheath.
- insulates the axonal membrane
- reduces ability of current to leak out of the axon
- thus, myelin increases the distance that a current can flow passively
- greatly increases speed of AP conduction
How are the Nodes of Ranvier able to depolarize the membrane?
b/c they have a high density of voltage-gated sodium channels
How does AP propagation occur along myelinated neurons?
through saltatory conduction - jumping from one Node of Ranvier to the next
Describe the etiology of Multiple Sclerosis.
plaques of demyelination are accompanied by inflammation of axons
may lead to permanent axonal damage
eventually blocked transmission of signals
Electrical synapses use ___ ____ for communication.
gap junctions
Describe how electrical synapses work.
mode of information transmission through ionic current
ion channels extend from cytoplasm of presynaptic neuron to cytoplasm of postsynaptic neuron
channels permit very rapid flow of ionic current from one cell to another e.g. defense reflexes
T/F: Both chemical and electrical synpases allow only for unidirectional communication.
False.
Chemical: unidirectional.
Electrical: bidirectional
List the 4 types of glial cells found in the CNS.
- Microglia
- Astrocytes
- Ependymal cells
- Oligodendrocytes
What is the function of microglia?
smallest of glial cells
•function as phagocytes to remove cell debris, wastes and pathogens; protect brain against micro-organisms
What are the 4 functions of astrocytes?
star-shaped glial cells; numerous in CNS
- maintain blood-brain barrier
- regulate the chemical environment of the extra-cellular space
- provide structural support to neurons
- absorb and recycle neurotransmitters
What is the function of ependymal cells?
line ventricles of brain and central canal of spinal cord
•assist in production and circulation of Cerebrospinal Fluid (CSF)
What is the function of oligodendrocytes?
form a myelin sheath around CNS axons
•one oligodendrocyte contributes myelin to several axons
•provide structural framework
What are the 2 types of glial cells found in the PNS.
Schwann and Satellite cells
What is the function of Schwann cells?
form myelin sheaths around axons in PNS
•each Schwann cell myelinates only a single axon
•participate in repair process after injury
Compare and contract Oligodendrocytes and Schwann cells.
Oligodendrocytes: 1. Produce myelin sheath 2. Found in the CNS 3. 1 oligodendrocyte cell can make myelin sheath on many axons Schwann cells: 1. Produce myelin sheath 2. Found in the PNS 3. 1 Schwann cell per axon
What is the function of satellite cells?
surround neuron cell bodies in PNS ganglia
•regulate O2, CO2, nutrient and neurotransmitter levels around ganglia
