Ch.3: Cells of the Nervous System

neuron

electrically excitable cells that processes & transmits info

sensory neuron

detect stimuli from environment (light, sound, touch) and transmit info to CNS

visual, touch, auditory neurons

motor neuron

control muscles and organs; transmits from CNS to muscles, whether to contract or relax

upper/lower motor neurons

interneuron

• connect sensory neurons and motor neurons

• help process info and coordinate activity of different parts of nervous system

soma (cell body)

• provides metabolic (energy) and synthetic (protein) support

dendrites

receives info from other neurons

dendrite spine

can rapidly change in response to environmental stimuli (neural plasticity)

axon

sends info to axon terminal

• vary in length and diameter

  • larger diameter = faster signal

glia cells

• “glue” - support neurons

• non-electrical cells

Macroglia:

• astrocytes

• oligodendrocytes

• microglia

• Schwan cells

astrocytes

• maintains BBB

• structural & nutritional support for neurons

• wraps around synapse so info. flows through and doesn’t leak

oligodendrocytes

• myelinate CNS axons

• multiple neurons

microglia

immune system of NS

• removes dead cells and pathogens by phagocytosis

Schwann cells

• myelinate neurons in PNS

• one neuron

Resting Potential

• -70 mV

• more Na+ outside cell; more K+ inside cell → diffusion = Na goes in; K goes out

• ion (leak) channels: does not use energy; passive flow

• ion pump: uses energy to move ions against gradient (puts Na out and K in)

• more negative inside cell = 3 Na+ = 2 K+

Action Potential

• threshold = -55mV

• rising phase: Na+ opens → depolarization

• 40mV → Na closes

• falling phase: K+ gate opens

• hyperpolarization: past resting potential → K gate closes

absolute refractory period

no stimulus can produce another AP during a specific time of an AP

relative refractory period

cell can produce another action potential with a stronger stimulus

all-or-none

either you have an AP that reaches +40mV or you don’t (higher frequency, NOT amplitude)

Propagation of AP

• myelinated = faster, jumps from node to node

• unmyelinated = slower

synapse

electrical synapse

• small synaptic cleft

• very fast

• transmission by direct movement of ions

chemical synapse

• large synaptic cleft

• transmission takes up to many milisec.

• transmission by release of neurotransmitters

  • neurotransmitter must bind to receptor to let ions flow

1. neurotransmitter in vesicles while AP reaches pre-synaptic terminal

2. AP opens voltage-gated Ca2+ channels, neurotransmitters released to synaptic cleft by exocytosis

3. transmitter binds to post-synaptic receptor (ligand-gated ion channels), ions flow

4. Post-synaptic response: EPSP, IPSP, neuromodulation

EPSP (excitatory post-synaptic potential)

• brief electrical change to excite neuron (depolarization)

• AP more likely

IPSP (inhibitory post-synaptic potential)

• brief electrical change to inhibit neuron (hyperpolarization)

• AP less likely

neuromodulation

• changes in intracellular signaling that modulates neuronal function more long-term

post-synaptic potentials

• spatial summation: inputs from multiple neuron trigger an AP

• temporal summation: when large amounts of presynaptic APs trigger postsynaptic APs

Deactivation of neurotransmitters

• diffusion

• degradation

• reuptake