Neurons, Neurotransmitters, Receptors

Question 1

How many more glial cells are there than neurons?

Answer 1

over 3x

Question 2

Who was Golgi?

Answer 2

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)

Question 3

Who was Cajal?

Answer 3

proposed the Neuron Doctrine
that states each neuron is an individual entity

said things communicate by series of cells

Question 4

Summarize actions in a neuron

Answer 4

Dendrites are information gathering portion of the neuron, summarized in cell body (Soma), action potential then travels down axon and produces synaptic event

Question 5

Why is the myelin important

Answer 5

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)

Question 6

Whats the difference between neurons and nerves?

Answer 6

nerves are a bundle of neural axons

neurons are a neural cell

Question 7

Whats the most dense type of neuron

Answer 7

cerebellum Purkinje nerve cells

Question 8

What does bipolar cells mean?

Answer 8

Bipolar cells means they have 2 processes and a cell body, one in the dendrites and one in the axons.

Question 9

Describe action potentials

Answer 9

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

Question 10

As it passes through the axon, the signal jumps from node to node in a process known as

Answer 10

Saltatory Conduction

Question 11

what is the node of Ranvier?

Answer 11

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.

Question 12

Describe what constitutes a reflex?

Answer 12

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

Question 13

Where in the cell are neurotransmitters made?

Answer 13

Golgi apparatus and endoplasmic reticulum

Question 14

What picks up and repackages neurotransmitters after synaptic cleft actions?

Answer 14

Glial cells

Question 15

What are the 2 categories of neurotransmitters (based on size)?

Answer 15

Small molecule NT:

  * ACh
  * Amino Acids
  * Purines
  * Biogenic Amines (catecholamines)

Neuropeptides (3-30 amino acids long)

Question 16

Where is ACh found?

Answer 16

neuromuscular junctions, ganglia of visceral motor system, CNS

Question 17

What is the most prevalent neurotransmitter in the brain?

Answer 17

Glutamate

Question 18

What determines whether certain NT are excitatory or inhibitory?

Answer 18

the receptor type

Question 19

Which NTs are only excitatory?

Answer 19

Glutamate
epinephrine
norepinephrine
Serotonin (5 – HT)
Histamine

Question 20

Which NTs can be excitatory or inhibitory?

Answer 20

Dopamine
ACh (Nicotinic is excitatory, Muscarinic can be either)
Neuropeptides
Nitric Oxide (NO)

Question 21

Which NTs are only inhibitory?

Answer 21

GABA

Glycine

Question 22

Compare Ionotropic to Metabotropic receptors

Answer 22

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

Question 23

Which NTs have Ionotropic receptors?

Answer 23

Ach (nicotinic receptor)
Glutamate
(NMDA, AMPA, Kainate)
 GABA (A and C subtypes)
 Glycine

Question 24

Which NTs have Metabotropic receptors?

Answer 24

ACh (muscarinic receptor)
 Glutamate
 GABA (B subunit)
 Catecholamines
 Serotonin
 Histamine

Question 25

What are neurons that use ACh as a transmitter called?

Answer 25

cholinergic neurons

Question 26

What was the first substance identified as a NT?

Answer 26

ACh

Question 27

What ion does Muscarinic ACh receptors eventually activate?

Answer 27

Potassium to a potassium channel

Question 28

What are 2 ACh toxins?

Answer 28

``` Curare is an Ach receptor antagonist so it blocks Ach from binding postsynaptically to the receptor Botulinum toxin (Botox) blocks postsynaptic receptor ```

Question 29

What ion does glutamate receptors let into the channel?

Answer 29

Potassium

Question 30

Where are GABA and Glycine found?

Answer 30

• Most inhibitory synapses in the CNS use GABA Glycine is found mostly in the spinal cord. Strychnine is antagonist that leads to seizures.

Question 31

Most interneurons and Purkinje cells of cerebellum contain...?

Answer 31

GABA

Question 32

How is GABA synthesized?

Answer 32

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.

Question 33

Which types of GABA are ionotropic?

Answer 33

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

Question 34

All known amines are derived from which amino acid?

Answer 34

tyrosine Roles in homeostatic functions, cognition (attention), psychiatric disorders

Question 35

Where is dopamine produced? Simarly, where does parkinsons attack?

Answer 35

Substantia Nigra and Ventral tegmental area

Question 36

Where is Norepinephrine produced?

Answer 36

Locus Coeruleus

Question 37

What role does norepinephrine play?

Answer 37

Arousal, attention, feeding behavior Sympathetic visceral motor system Agonists are amphetamines

Question 38

Where is epinephrine (adrenaline) produced?

Answer 38

Medullary epinephrine neurons

Question 39

Where is serotonin produced and what role does it play?

Answer 39

Produced in Raphe nuclei and pontine nuclei Arousal (sleep/wake), mood

Question 40

What are the different types of neuropeptides?

Answer 40

• 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

Question 41

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?

Answer 41

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

Question 42

What law is Weber’s law?

Answer 42

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

Question 43

What is Stephens Law?

Answer 43

I = K(S – So)^n ``` where: I = intensity of sensation, S = stimulus strength, So = threshold amplitude of the stimulus, n = system exponent ```

Question 44

What is Sensory Physiology?

Answer 44

1) Studies relationship between physical stimulus and neural response 2) Quantifies stimulation parameters, transduction, neural coding, and information processing in the CNS…

Question 45

What did Psychophysics show?

Answer 45

demonstrated that perception and behavior | could be described and studied empirically

Question 46

What are 3 common properties of receptors?

Answer 46

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

Question 47

What is the Doctrine of specific nerve energies?

Answer 47

If an afferent neuron stimulates the receptor, the receptor will respond by creating the sensation of the afferent neuron that stimulated it.

Question 48

What type of potentials do receptors respond with?

Answer 48

Receptors respond with graded linear summation potentials

Question 49

What is Neural adaptation?

Answer 49

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

Question 50

Describe receptive fields?

Answer 50

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

Question 51

Neural noise gives rise to what?

Answer 51

Neurons have noise. Neural noise gives rise to uncertainty. Must use population of cells to better discriminate.

Question 52

Neural sensitivity and noise level affects signal code. How?

Answer 52

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

Question 53

Convergence produces what?

Answer 53

Convergence produces large receptive fields and loss of specificity, but can also increase sensitivity

Question 54

What do inhibitory interneurons do?

Answer 54

Inhibitory interneurons increase contrast and sharpen signal/noise

Question 55

What encodes intensity and temporal resolution of sensation?

Answer 55

Neural firing rate, duration, and number of cells in synchrony together encode intensity and temporal resolution of sensation

Question 56

Why do axons in sensory systems cross the midline?

Answer 56

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.