Lecture 4 Myelin and Autoimmune Conditions Flashcards
Myelin Sheath
Lipid material
* Covers and insulates nerve fibers
* Produced by
Oligodendroglia celss in CNS and Scwann cells in PNS
* Forms segments separated by nodes of Ranvier
Myelin Sheath (cont.)
* Acts as
Acts as insulator of axon
* Facilitates speed of nerve conduction
* ___Saltatory Conduction_______________: propagation of signal through
depolarization at each node of Ranvier
* Myelin insulates signal so the charge at each node is
enough to depolarize the following segment/node to
propagate the signal toward the terminal boutons.
Saltatory conduction
propagation of signal through
depolarization at each node of Ranvier
the rapid method by which nerve impulses move down a myelinated axon with excitation occurring only at nodes of Ranvier
from google
Myelin and Autoimmune Disease
* Multiple sclerosis (MS)
Multiple sclerosis (MS)
* Autoimmune condition, onset 30–40 years, females two times as likely as males
* Antibodies attack CNS myelin myelin degenerates but initially spares axon
* Glial proliferation and myelin debris contribute to plaque formulation in CNS
* Plaques may cause axon to degenerate more severe, progressive disability
* Relapse-remit pattern (not with all patients), variable symptoms
* No cure, treatment with corticosteroids, anti-inflammatories, other
pharmaceuticals
Myelin and Autoimmune Disease
Guillain-Barre syndrome (GBS)
Guillain-Barre syndrome (GBS)
* Peripheral myelin—demyelinating auto-immune condition—recoverable!
* Slows speed of nerve conduction
* Ascending deficits in sensorineural information
Transmission of Information
* Neurotransmitters
Neurotransmitters
* Chemicals that transmit signals across the neurons
* Help to regulate brain mechanisms that control
* Cognition – Attention
* Language – Memory
* Speech – Personality
* Hearing – Motivation
* Mood – Physiological tuning of brain
Neurons transmit nerve
impulses by
Neurons transmit nerve
impulses by synaptic
transmission
* Synapse
* Connection point that
permits a neuro to pass a
signal to another neuron
* The receptive ends of the
cell are chemically
activated and generate
electric impulses
Acetylcholine
Primary neurotransmitter in PNS
* In PNS: controls voluntary movement of spinal and
cranial nerves
* Implications Myasthenia gravis (deficient ACH at
neuromuscular junction)
* Also in CNS: forebrain and reticular formation
* Implications Alzheimer’s disease (deficient
cholinergic projections in hippocampus and
orbitofrontal cortex—atrophy of neocortex—but
questionable cause)
Dopamine
Dopamine
* Produced by substantia nigra cells in midbrain and
project ipsilaterally to basal ganglia structures
* Degeneration of substantia nigra reduces dopamine
production (associated with Parkinson disease)
* Projections to cortex involved in cognition
* Excessive dopamine in forebrain associated
with Schizophrenia
* Drug abuse and addiction-related
* Part of reward system
Norepinephrine
Norepinephrine
* A primary neurotransmitter in PNS: fight or flight
* In CNS: in pons and medulla—paradoxical sleep, random
eye movement, attention
Serotonin
Serotonin
* In CNS and PNS
* Levels vary with sleep/wake cycle—associated with
arousal, contributes to pain-control system; associated
with depression
Glutamate
Glutamate
* Excitatory neurotransmitter in CNS and mediates fast
synaptic transmission
GABA:
Major transmitter for CNS
* Inhibitory (a calming effect) – reduce stress, relieve
anxiety
* Implicated in Huntington’s disease/chorea
* Reduction of GABA produces abnormal movement
Important neurotransmitters
Acetylcholine in both PNS and CNA
Dopamine in the Cns
GABA in the Cns
Norepinephrine in both PNS and CNS
Serotonin in the CNS and PNS
Glutamate in the CNS
