Ch. 39 Neurons

Afferent Neurons

Sensory receptors→ interneurons

Interneurons

Integrates message in CNS

Efferent neurons

Carries signals away from Interneurons to effectors (muscles and glands)

Motor neurons

Efferent neurons that carry signals to skeletal muscles

Dendrites

Recieves signals

Axon

Carries signals away from cell body to another neuron/effector

Axon terminal

Connects neurons with another

Glial cells

Non-neuronal cells that provide nutrition and support to neurons

Astrocytes

In CNS. Covers surface of blood vessels to provide physical support

Oligodendrocytes

In CNS. Wrap around axons to for myelin sheaths and nodes of ranvier

Schwann cells

In PNS. Form myelin sheaths

Resting potential

When neuron isn’t stimulated.

Range from -40 to -90mV

Avg: -70mV

• created by sodium-potassium pump: 2 K+ in, 3 Na+ out

• Ion leak channels- allows more K+ to diffuse out than Na+ in

Action potential

When neuron transmits electrical impulse and a change in membrane potential occurs.

• positive charges outside the membrane flow in (depolarization)

• Eventually it reaches threshold (10-20mV)

Voltage gated Channels

When neurons are stimulated, K+ and Na+ channels open and close causing membrane potential changes

• found on axon and axon hillock

Channel Timing

Action potential explained

Once threshold is reached, action potential fires and membrane potential increases.

Hyperpolarization

Potential Dallas dropping below -80mV

Refractory Period

Cell can’t be restimulated

Frequency of Action potentials

The greater the stimulus, the more action potentials per second

Saltatory conduction

Allows action potentials to hop rapidly along myelin-coated axons.

voltage gated channels at nodes of ranvier allows action potentials to happen at these points

Synapse

When neuron communicates with another neuron/effector.

• occurs by direct electrical flow or through a neurotransmitter

Electrical Synapses

Plasma membranes of presynaptic and postsynaptic cells are in direct contact.

When electrical impulse arrives at axon terminal, gap junctions allow ions to flow between cells

Chemical Synapses

Pre and postsynaptic cells are separated by a synaptic cleft.

• an neurotransmitter is released, and the postsynaptic cell can create a new electrical impulse

Neurotransmitters

Open and close ligand-gated ion channels

Excitatory Postsynaptic Potential

Change in membrane potential that pushes neuron closer to threshold.

• occurs when ligand-gated Na+ channel opens, causing depolarization

Inhibitory Postsynaptic Potential

A change in membrane potential that pushes neuron farther from threshold.

• occurs when ligand-gated ion channel opens and allows Cl- to flow in and K+ out (hyperpolarization)

Summation

Sum of EPSP and IPSPs