Brain Lec1-3: Nervous System, Reflexes, NTs

What is the Golgi Method that led to the reticular theory?

Staining nervous tissue with silver nitrate → visualization of single neurons

What is the reticular theory?

All neurons are connected by one long neuron

What is the neuron theory?

Gaps between neurons exist (but at the time, communication across synapses was unknown)

Name the four common types of neurons and where they are found.

• Unipolar → invertebrates

• Bipolar → retina

• Pseudounipolar → dorsal root ganglia of the spinal cord

• Multipolar → CNS

What are the two types of nervous system cells?

Neurons and glia

Name the four types of CNS glial cells and their functions.

• Microglia → prunes synapses, responsible for brain immunity

• Astrocytes → control levels of neurotransmitters

• Oligodendrocytes → produce myelin in the CNS

• Ependymal cells → create CSF

Name the two types of PNS glial cells and their functions.

• Schwann cells → produce myelin in the PNS

• Satellite cells → regulate chemical environment

What are the two components of the CNS?

Brain and spinal cord

Name the three major brain areas and their functions.

• Cerebrum → cognition, motor function, emotion

• Cerebellum → balance, coordination

• Brainstem → involuntary functions

Name the four parts of the spine and how many vertebrae are in each segment.

• C7

• T12

• L5

• Sacrum

What is a Hangman’s Fracture?

Spinal cord damage at C1-C2 → loss of function below this level → loss of diaphragm function → death by inability to breathe

What is a spinal tap and where is it performed?

Lumbar puncture at L3-L5 (because spinal cord ends right above) to obtain CSF for testing, decrease pressure, inject anesthetics during pregnancy

In a spinal cord cross section, what is white matter?

Myelin

In a spinal cord cross section, what is gray matter?

Nerve cell bodies

What type of neurons are in the dorsal horn?

sensory/afferent fibers

What type of neurons are in the ventral horn?

motor/efferent fibers

Describe the five steps of the reflex arc.

Receptor → afferent → integration center → efferent → effector

What are the two divisions of the PNS and what do they do?

• Somatic → voluntary actions

• Autonomic → involuntary actions

What is decerebrate posturing?

Brainstem lesion that tenses all muscles

How did Galvani/Volta prove that information travels through neurons via electricity?

Stimulated pair of frog legs by connecting two metal plates and flowing current through them

What does the Bernstein membrane theory say?

• Resting membrane is permeable to K+

• K+ is more concentrated inside the cell

• K+ tends to diffuse outward

• The inside of the cell becomes negative → resting membrane potential is approx. -60-70 mV

Where in the neuron is the largest density of voltage-gated channels?

Axon hillock

In MS, the myelin sheath is damaged. How does this impact signal propagation?

Signal slows down and gets weaker → no muscle firing

How are the two types of synapses different? Where are they located?

• Chemical synapses –– neurotransmitter binding triggers EPSP/IPSP, signal is all-or-nothing triggered by temporal/spatial summation

• Electrical synapses — gap junctions allow instantaneous bidirectional ion flow that is not modifiable, common in cardiac muscle

What are the six major neurotransmitters and their roles?

• Glutamate — learning, memory

• Dopamine — reward, motivation

• ACh — muscle contraction, attention, memory

• GABA — anti-anxiety

• Serotonin — mood, sleep, appetite, social behavior

• NE — arousal, attention

What is the NT failure that causes Parkinson’s?

Loss of dopaminergic neurons → tremor, slow movement

What is the NT failure that causes depression?

Dysregulation of serotonin, NE, and dopamine → low mood, cognitive impairment

What is the NT failure that causes epilepsy?

Glutamate/GABA imbalance that causes too much firing → seizures

What is the NT failure that causes Myasthenia gravis?

Antibodies attack ACh receptors → muscle weakness

What are the three ways NTs are removed from the synapse?

• reuptake

• enzymatic degradation

• diffusion

How does preferential treatment apply to signals that generate EPSPs?

Synapses closer to axon hillock get preferential treatment because:

1. Few voltage-gated channels in dendrites and cell body to propagate signal

2. Current decreases with time and distance in cell body

What does it mean for EPSPs to be all or nothing?

More neurons firing increases probability of AP getting generated (threshold must be reached)

What is the main excitatory NT for EPSPs? What ion does it release into the cell?

Glutamate

What is the main inhibitory NT for IPSPs? What ion does it release into/out of the cell?

GABA (or glycine), releases Cl- in or K+ out

What are four traits of the action potential (digital output) that gets converted from EPSPs and IPSPs?

• Binary (all or nothing)

• Fixed amplitude

• Doesn’t decay

• Noise-resistant

What are the two classes of receptors on the post-synaptic membrane? Which is faster?

• Ion channel (inotropic), faster

• G-coupled protein receptor (metabotropic)

Where do EPSPs occur and what type of postsynaptic receptors do they use?

• On dendritic spines

• Inotropic receptors

Where do IPSPs occur and what type of postsynaptic receptors do they use?

• Axon hillock, some dendrites (strategic placement allows for targeted inhibition)

• Inotropic or metabotropic receptors

What happens when there is too much EPSP and loss of IPSP?

Seizures

What kind of receptors does ACh act on and where?

• Nicotinic (inotropic) — skeletal muscle

• Muscarinic M1/M2 (metabotropic) — CNS and PNS (Parasympathetic)

Atropine is an ACh antagonist that blocks muscarinic receptors. What happens when a heart pre-treated with atropine is given ACh?

Nothing

Organophosphates inhibit ACh-ase at both receptors. What happens to the amount of local ACh?

ACh builds up

Succinylcholine acts as ACh to bind to nicotinic receptors. What happens to a patient given succinylcholine?

Paralysis (immediate contraction followed by relaxation)

What kind of receptor is at the neuromuscular junction?

Nicotinic ACh receptor

Which class of receptors do GABA and glutamate bind to?

Both inotropic and metabotropic

Which class of receptors does dopamine bind to?

Metabotropic