BIO 348 Lecture 2: Cells of the Nervous System

2 classes of cells in the nervous system

neurons

glia

soma

includes nucleus (contains genetic material), mitochondria (energy to power functions of cells), golgi (modify, sort, and pack proteins), vesicles (packaged proteins)

Neurons are…

polarized cells, or compartments are specialized

Synapse

• site of neuronal communication

• presynaptic component (axon termina)

  • filled with vesicles containing neurotransmitters

• postsynaptic component (dendrite)

  • membrane dense with proteins, neurotransmitter receptors

Morphological Neuronal Classification

• based on number of processes originating from the soma

• Neuronal Diversity

  • unipolar, bipolar, ppsuedounipolar, and multipolar

• Dendritic morphology is highly diverse

  • Purkinje cell

  • Retinal ganglion cells

Motor Neurons

• transmit information away from the CNS

• Efferent (= exit) projections

• Acts on info from outside world into CNS

• Sends info out to the muscles

Sensory Neurons

• transmit information from the periphery toward the CNS

• Afferent (= arrive) projections

• Detect info from outside world into CNS

Interneurons

• Local

  • Within the same structure

• Relay

  • Between different structures

Excitatory

• glutamate as neurotransmitter (glutamatergic)

• projection neurons - cells that communicate to distant regions

  • form motor cortex to spinal cord to control involuntary motor control 

Inhibitory

• GABA

• Interneurons - cells that communicate to neighboring cells, local cells do not project beyond region

• Inhibitory neurons are not always interneurons

Neuromodulatory

• dopamine

• acetylcholine

• norepinephrine

• serotonin

• effects depend on the receptor

• modulate excitation or inhibition

Physiological classification

• can define neurons the way they fire (regular firing v burst firing)

Principle of Dynamic Polarization (Cajal)

• electrical signals flow in one direction

  • dendrite/soma → axon → dendrite/soma (pre-synaptic neurorn → postsynaptic neuron)

Dendrites receive…

• input

  • input spreads passively down the membrane

  • proportional to the stimulus/input strength and duration (strong stimulus, stronger response; stronger duration; response of dendritic proportional to stimulus)

  • degradable 

Trigger Zone/Axon Hillock

• integrates the signals received from all inputs

• high density of voltage-sensitive Na+ channels

• Facilitates reaching spike threshold

• Initiation of action potential

Axon

• propagates action potentials

• actively reproduced periodically as it travels down the axon

• not degradable (same hight and shape propagates all the way down the axon)

• can travel as fast as 100 m/2

Output signal

• neurotransmitter release

• frequency of action potential is proportional to the amount of transmitter that is released (weak stimulus = less release of neurotransmitters)

Glia are more than just nerve glue

• schwann cells (PNS) and oligodendrocytes (CNS)

  • insulate axons and facilitate efficient neuronal communication

• microglia

  • immune cells of CNS that eliminate excess synapses

• astrocytes

  • required for synapse formation and modulate synaptic activity

Saltatory Conduction

• jumping of action potentials

• action potentials propagates at Nodes of Ranvier

Multiple Sclerosis (MS)

• demyelinating disease

• selective degeneration of oligodendrocytes (CNS), but not Schwann cells

• disrupts neuronal communication

Guillain Barre syndrome

• demyelinating disorder of the PNS

• autoimmune disorder

• demyelination of peripheral myelin

• triggered by infection

Myelin is…

• necessary for neuronal function

  • mice lacking myelin basic protein have deficient myelin → exhibit tremors, seizures, early death

    • affects CNS, PNS myelin is largely normal

• protects axons from degeneration

• white matter is composed of myelin

• myelination is not uniform

Astrocytes

• distributed throughout the CNS

• blood brain barrier (keeps peripheral immune cells out of CNS)

• regulation of blood flow

• synapse formation

• neural system cells in adult brain

• mediate synaptic plasticity and function

• CNS response to injury or disease

• reactive astrocytes creates a glial scar

• create a border between spared and lesioned tissue

Inflammation is…i

inversely correlated with neuronal survival (inflammation high, neuronal survival low)

Tripartite synapse

synapse not just the pre and post synaptic neuron, but also the astrocyte

Microglia

• immune cells of CNS

• eliminate unwanted material by cleaning debris (dead tissue/cells and also prunes dead synapses)

  • make many synapses in development than you need, then microglia prunes those synapses that you don’t need

    • autism = excess synapse

    • schizophrenia = too few synapses

  • microglia prune by engulfing excess synapses

• change morphology in pathological state (different format of microglia near side of stroke compared to healthy side)

• are not neural cells and are derived from the yolk sac

• respond rapidly to injury