Neurons, Neurotransmitters, Receptors Flashcards
How many more glial cells are there than neurons?
over 3x
Who was Golgi?
reticularist view
that nerve cells fuse into a continuous network
of cytoplasmic continuity
thought everything was connected in one network. His view competed with Cajal (neuron doctrine, each neuron is an individual entity, things communicate by series of cells)
Who was Cajal?
proposed the Neuron Doctrine
that states each neuron is an individual entity
said things communicate by series of cells
Summarize actions in a neuron
Dendrites are information gathering portion of the neuron, summarized in cell body (Soma), action potential then travels down axon and produces synaptic event
Why is the myelin important
The myeline is important for keeping electrical events insulated from passing from one cell to the other (bad), and also for faster conduction velocity (fastest neurons are down to toes, slowest are pain fibers)
Whats the difference between neurons and nerves?
nerves are a bundle of neural axons
neurons are a neural cell
Whats the most dense type of neuron
cerebellum Purkinje nerve cells
What does bipolar cells mean?
Bipolar cells means they have 2 processes and a cell body, one in the dendrites and one in the axons.
Describe action potentials
Neuron is excited (positive current) or inhibited (negative current) by injecting current
Resting potential is -65mV
Threshold at -50mV
AP are around 1 ms long, can only have about 1000 action potentials in a second. Exception is eye muscle cells
As it passes through the axon, the signal jumps from node to node in a process known as
Saltatory Conduction
what is the node of Ranvier?
Area of polarity reversal
periodic gap in the myelin on the axon of certain neurons that serves to facilitate the rapid conduction of nerve impulses.
Myelin insulates, at nodes of Ranvier, the axonal membrane is uninsulated and therefore capable of generating electrical activity.
Describe what constitutes a reflex?
Sensory to spinal cord -> 2 pathways: 1. to interneuron and also 2. to motor neuron. Motor neuron to muscle to flex it. Interneuron to inhibitory to opposite muscle to relax it.
Motor neuron fires after delay because sensory neuron to motor takes time. Because of synapse time and AP limits
Where in the cell are neurotransmitters made?
Golgi apparatus and endoplasmic reticulum
What picks up and repackages neurotransmitters after synaptic cleft actions?
Glial cells
What are the 2 categories of neurotransmitters (based on size)?
Small molecule NT:
* ACh * Amino Acids * Purines * Biogenic Amines (catecholamines)
Neuropeptides (3-30 amino acids long)
Where is ACh found?
neuromuscular junctions, ganglia of visceral motor system, CNS
What is the most prevalent neurotransmitter in the brain?
Glutamate
What determines whether certain NT are excitatory or inhibitory?
the receptor type
Which NTs are only excitatory?
Glutamate epinephrine norepinephrine Serotonin (5 – HT) Histamine
Which NTs can be excitatory or inhibitory?
Dopamine
ACh (Nicotinic is excitatory, Muscarinic can be either)
Neuropeptides
Nitric Oxide (NO)
Which NTs are only inhibitory?
GABA
Glycine
Compare Ionotropic to Metabotropic receptors
Ionotropic are direct receptors that open channels. Only allow a few ions to enter and then closes again. Metabotropic are receptors that activate Gproteins that eventually open channels.
Ionotropic are fast, Metabotropic are slow. Metabotropic has more control, allows for modulation over long periods of time
Which NTs have Ionotropic receptors?
Ach (nicotinic receptor) Glutamate (NMDA, AMPA, Kainate) GABA (A and C subtypes) Glycine
Which NTs have Metabotropic receptors?
ACh (muscarinic receptor) Glutamate GABA (B subunit) Catecholamines Serotonin Histamine
What are neurons that use ACh as a transmitter called?
cholinergic neurons
What was the first substance identified as a NT?
ACh
What ion does Muscarinic ACh receptors eventually activate?
Potassium to a potassium channel
What are 2 ACh toxins?
Curare is an Ach receptor antagonist so it blocks Ach from binding postsynaptically to the receptor Botulinum toxin (Botox) blocks postsynaptic receptor
What ion does glutamate receptors let into the channel?
Potassium
Where are GABA and Glycine found?
• Most inhibitory synapses in the CNS use GABA
Glycine is found mostly in the spinal cord. Strychnine is antagonist that leads to seizures.
Most interneurons and Purkinje cells of cerebellum contain…?
GABA
How is GABA synthesized?
GABA is synthesized in the neurons from glucose to glutamate then to GABA using the enzyme glutamic acid decarboxylase (GAD). GAD requires a co-factor, pyridoxal phosphate, that is derived from Vitamin B6.
Which types of GABA are ionotropic?
GABAa & GABAc are ionotropic: GABAb is metabotropic
- GABAa and c channels allow Cl- to enter the cell
- GABAa and GABAc agonists include benzodiazepines (valium, librium), barbituates, steroids
- GABAb opens K+ channels
All known amines are derived from which amino acid?
tyrosine
Roles in homeostatic functions, cognition (attention), psychiatric disorders
Where is dopamine produced? Simarly, where does parkinsons attack?
Substantia Nigra and Ventral tegmental area
Where is Norepinephrine produced?
Locus Coeruleus
What role does norepinephrine play?
Arousal, attention, feeding behavior
Sympathetic visceral motor system
Agonists are amphetamines
Where is epinephrine (adrenaline) produced?
Medullary epinephrine neurons
Where is serotonin produced and what role does it play?
Produced in Raphe nuclei and pontine nuclei
Arousal (sleep/wake), mood
What are the different types of neuropeptides?
• Brain-gut peptides
Substance P – spinal cord: inhibited by opiates to block pain
*Opioid peptides - depressants
Morphine & fentanyl – analgesics
Endorphin – released from brain to block substance P
Using psychophysics, It was discovered that all sensory systems
encode four attributes of a stimulus and when combined, these four attributes give rise to
sensation.
Who discovered this and what are the 4 attributes of a stimulus?
Weber and Fechner
a) modality – vision, touch, audition, taste,
smell, vestibular (motion)
b) intensity – level of stimulation
c) duration – temporal sequence
d) location – spatial topography
What law is Weber’s law?
Delta S = K x S
Delta S is the change in magnitude of stimulus. K is constant
Intensity of sensation depends upon strength of stimulus
Later replaced by Stephens Law
What is Stephens Law?
I = K(S – So)^n
where: I = intensity of sensation, S = stimulus strength, So = threshold amplitude of the stimulus, n = system exponent
What is Sensory Physiology?
1) Studies relationship between physical stimulus
and neural response
2) Quantifies stimulation parameters, transduction, neural coding, and information processing in the CNS…
What did Psychophysics show?
demonstrated that perception and behavior
could be described and studied empirically
What are 3 common properties of receptors?
1) Specialized cells (neural and non-neural) that perform a
transduction from modal stimulus to change in
membrane voltage.
2) Connects to primary afferent neurons, bipolar or pseudo-
polar cells, whose somas lie in ganglia, then project
to CNS
3) Receptors are ordered across the sensory epithelium
in a topographic map. Neurons innervating receptors
project to CNS and maintain topography
What is the Doctrine of specific nerve energies?
If an afferent neuron stimulates the receptor, the receptor will respond by creating the sensation of the afferent neuron that stimulated it.
What type of potentials do receptors respond with?
Receptors respond with graded linear summation potentials
What is Neural adaptation?
a) All sensory receptors and nerve fibers adapt to constant stimulation. Adaptation varies from slow to rapid.
b) Adaptation allows for:
Slow = sustained stimuli
Rapid = stimulus on/off
time derivative
of stimulation (velocity,
acceleration of stimulus)
c) Intensity encoded by number of action potentials per second (rate code) and by the number of neurons activated by a stimulus.
Rapidly adapting cant encode duration, slow adapting can
Slow adapting will continue firing as long as pressure is applied, rapidly adapting will only fire and onset and offset
Rapidly is following rate of change, doesn’t fire in steady state
Describe receptive fields?
Size of receptive fields vary across body regions. Size of fields also depends on receptor type. Very small receptive field in fingertips
a) Receptive field determines location
b) Each neuron only responds to stimuli
in it’s receptive field
c) Receptors have excitatory receptive field center and inhibitory surround. Such a mechanism serves to enhance contrast: each neuron responds optimally to a stimulus that occupies most of its center but little of its surround.
d) No response to stimulation outside of receptive field
e) Across a population of neurons with neighboring receptive fields, a topographic map of body space is created
Neural noise gives rise to what?
Neurons have noise. Neural noise gives rise to uncertainty. Must use population of cells to better discriminate.
Neural sensitivity and noise level affects signal code. How?
Low sensitivity -> Regular firing neurons:
temporal code
The temporal information in a stimulus is carried by the time-varying pattern of activity in small groups of receptors and central neurons.
High sensitivity -> Irregular firing neurons:
rate code
Convergence produces what?
Convergence produces large receptive fields and loss of specificity, but can also increase sensitivity
What do inhibitory interneurons do?
Inhibitory interneurons increase contrast and sharpen signal/noise
What encodes intensity and temporal resolution of sensation?
Neural firing rate, duration, and number of cells in synchrony together encode intensity and temporal resolution of sensation
Why do axons in sensory systems cross the midline?
These decussations serve the broad functions of bringing together all axons carrying visual informa- tion from half the visual world or of bringing somato- sensory information into alignment with motor output, which is itself a largely crossed system.
