Neurons, Synapses, and Signaling

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An axon joins the cell body at the axon hillock.

Slide 10

Neurons

Dendrites

Stimulus

Nucleus

Cell

body

Axon

hillock

Presynaptic cell

Axon

Synaptic terminals

Synapse

Postsynaptic cell

Neurotransmitters

Slide 11

A synapse is a junction between cells.

The synaptic terminal of one axon passes information across the synapse in the form of chemical messengers called neurotransmitters.

Information is transmitted from a presynaptic cell (a neuron) to a postsynaptic cell (a neuron, muscle, or gland cell).

Most neurons are nourished or insulated by cells called glia.

Slide 12

Structural diversity of neurons

Dendrites

Axon

Cell

body

Sensory neuron

Interneurons

Portion

of axon

Cell bodies of

overlapping neurons

80 µm

Motor neuron

Slide 13

Ion pumps and ion channels maintain the resting potential of a neuron

Every cell has a voltage (difference in electrical charge) across its plasma membrane called a membrane potential.

Messages are transmitted as changes in membrane potential.

The resting potential is the membrane potential of a neuron not sending signals.

Slide 14

Formation of the Resting Potential

In a mammalian neuron at resting potential, the concentration of K+ is greater inside the cell, while the concentration of Na+ is greater outside the cell.

Sodium-potassium pumps use the energy of ATP to maintain these K+ and Na+ gradients across the plasma membrane.

These concentration gradients represent chemical potential energy.

Slide 15

The opening of ion channels in the plasma membrane converts chemical potential to electrical potential.

A neuron at resting potential contains many open K+ channels and fewer open Na+ channels; K+ diffuses out of the cell.

Anions trapped inside the cell contribute to the negative charge within / inside the neuron.

Slide 16

The Basis of the Membrane Potential

OUTSIDE

CELL

[K+]

5 mM

Na+

150 mM

[Cl–]

120 mM

INSIDE

CELL

K+

140 mM

[Na+]

15 mM

[Cl–]

10 mM

[A–]

100 mM

(a)

(b)

OUTSIDE

CELL

Na+

Key

K+

Sodium-

potassium

pump

Potassium

channel

Sodium

channel

INSIDE

CELL