Central nervous system (CNS) Peripheral nervous system (PNS) Brain and spinal cord Cranial nerves and spinal nerves Integrative and control centers Communication lines between the CNS and the rest of the body Sensory (afferent) division Motor (efferent) division Somatic and visceral sensory nerve fibers Motor nerve fibers Conducts impulses from the CNS to effectors (muscles and glands) Conducts impulses from receptors to the CNS Somatic sensory fiber Somatic nervous system Autonomic nervous system (ANS) Skin Somatic motor (voluntary) Visceral motor (involuntary) Conducts impulses from the CNS to skeletal muscles Conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands Visceral sensory fiber Stomach Skeletal muscle Motor fiber of somatic nervous system Sympathetic division Parasympathetic division Mobilizes body systems during activity Conserves energy Promotes house- keeping functions during rest Sympathetic motor fiber of ANS Heart Structure Function Sensory (afferent) division of PNS Parasympathetic motor fiber of ANS Bladder Motor (efferent) division of PNS

Capillary Neuron Astrocyte

Myelin sheath Process of oligodendrocyte Nerve fibers

Neuron Microglial cell

Fluid-filled cavity Ependymal cells Brain or spinal cord tissue

Satellite cells Cell body of neuron Schwann cells (forming myelin sheath) Nerve fiber

Dendrites Cell body Neuron cell body (receptive regions) (biosynthetic center and receptive region) Nucleolus Axon (a) Dendritic spine (impulse generating and conducting region) Nucleus Impulse direction Nissl bodies Node of Ranvier Axon terminals (secretory region) Axon hillock Schwann cell (one inter- node) Neurilemma Terminal branches

rotates around the axon, wrapping its plasma membrane loosely around Schwann cell plasma membrane Schwann cell cytoplasm A Schwann cell envelopes an axon. 1 Axon Schwann cell nucleus The Schwann cell then rotates around the axon, wrapping its plasma membrane loosely around it in successive layers. 2 Neurilemma The Schwann cell cytoplasm is forced from between the membranes. The tight membrane wrappings surrounding the axon form the myelin sheath. 3 Myelin sheath (a) Myelination of a nerve fiber (axon)

Receptor Neurotransmitter chemical attached to receptor Na+ Na+ Chemical binds K+ K+ Closed Open (a) Chemically (ligand) gated ion channels open when the appropriate neurotransmitter binds to the receptor, allowing (in this case) simultaneous movement of Na+ and K+.

Na+ Na+ Membrane voltage changes Closed Open (b) Voltage-gated ion channels open and close in response to changes in membrane voltage.

Voltmeter Plasma membrane Ground electrode outside cell Microelectrode inside cell Axon Neuron

Na+-K+ ATPases (pumps) maintain the concentration The concentrations of Na+ and K+ on each side of the membrane are different. Outside cell The Na+ concentration is higher outside the cell. Na+ (140 mM ) K+ (5 mM ) The K+ concentration is higher inside the cell. K+ (140 mM ) Na+ (15 mM ) Na+-K+ ATPases (pumps) maintain the concentration gradients of Na+ and K+ across the membrane. Inside cell The permeabilities of Na+ and K+ across the membrane are different. Suppose a cell has only K+ channels... K+ loss through abundant leakage channels establishes a negative membrane potential. K+ leakage channels K+ K+ K+ K+ Cell interior –90 mV Now, let’s add some Na+ channels to our cell... Na+ entry through leakage channels reduces the negative membrane potential slightly. K+ K+ Na+ K K+ Na+ Cell interior –70 mV Finally, let’s add a pump to compensate for leaking ions. Na+-K+ ATPases (pumps) maintain the concentration gradients, resulting in the resting membrane potential. Na+-K+ pump K+ K+ Na+ K+ K+ Na+ Cell interior –70 mV

The concentrations of Na+ and K+ on each side of the membrane are different. Outside cell The Na+ concentration is higher outside the cell. Na+ (140 mM ) K+ (5 mM ) The K+ concentration is higher inside the cell. K+ (140 mM ) Na+ (15 mM ) Inside cell Na+-K+ ATPases (pumps) maintain the concentration gradients of Na+ and K+ across the membrane.

K+ K+ The permeabilities of Na+ and K+ across the membrane are different. Suppose a cell has only K+ channels... K+ loss through abundant leakage channels establishes a negative membrane potential. K+ leakage channels K+ K+ Cell interior –90 mV K+ K+

Stimulus Depolarized region Plasma membrane (a) Depolarization: A small patch of the membrane (red area) has become depolarized.

Spread of depolarization: The local currents (black arrows) that are created depolarize adjacent membrane areas and allow the wave of depolarization to spread.

SHINGLES