Figure 11.2 Schematic of levels of organization in the nervous system. 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

(a) Astrocytes are the most abundant CNS neuroglia. Figure 11.3a Neuroglia. Capillary Neuron Astrocyte (a) Astrocytes are the most abundant CNS neuroglia.

(b) Microglial cells are defensive cells in the CNS. Figure 11.3b Neuroglia. Neuron Microglial cell (b) Microglial cells are defensive cells in the CNS.

(c) Ependymal cells line cerebrospinal fluid-filled cavities. Figure 11.3c Neuroglia. Fluid-filled cavity Ependymal cells Brain or spinal cord tissue (c) Ependymal cells line cerebrospinal fluid-filled cavities.

Myelin sheath Process of oligodendrocyte Nerve fibers Figure 11.3d Neuroglia. Myelin sheath Process of oligodendrocyte Nerve fibers (d) Oligodendrocytes have processes that form myelin sheaths around CNS nerve fibers.

(forming myelin sheath) Figure 11.3e Neuroglia. Satellite cells Cell body of neuron Schwann cells (forming myelin sheath) Nerve fiber (e) Satellite cells and Schwann cells (which form myelin) surround neurons in the PNS.

Figure 11.4 Structure of a motor neuron. 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 (b) Terminal branches

Figure 11.4a Structure of a motor neuron. Neuron cell body (a) Dendritic spine

Figure 11.4b Structure of a motor neuron. Dendrites (receptive regions) Cell body (biosynthetic center and receptive region) Nucleolus Axon (impulse generating and conducting region) Impulse direction Nucleus Node of Ranvier Nissl bodies Axon terminals (secretory region) Axon hillock Schwann cell (one inter- node) Neurilemma (b) Terminal branches

Figure 11.5a Nerve fiber myelination by Schwann cells in the PNS. 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)

Figure 11.5b Nerve fiber myelination by Schwann cells in the PNS. sheath Schwann cell cytoplasm Axon Neurilemma (b) Cross-sectional view of a myelinated axon (electron micrograph 24,000X)

Figure 11.10 The spread and decay of a graded potential. Stimulus Depolarized region Plasma membrane (b) Spread of depolarization: The local currents (black arrows) that are created depolarize adjacent membrane areas and allow the wave of depolarization to spread. (a) Depolarization: A small patch of the membrane (red area) has become depolarized. Active area (site of initial depolarization) –70 Resting potential Distance (a few mm) (c) Decay of membrane potential with distance: Because current is lost through the “leaky” plasma membrane, the voltage declines with distance from the stimulus (the voltage is decremental). Consequently, graded potentials are short-distance signals.

Figure 11.11 Action Potential (1 of 2) The big picture 1 Resting state 2 Depolarization 3 Repolarization 3 Membrane potential (mV) Action potential 4 Hyperpolarization 2 Threshold 1 1 4 Time (ms) The AP is caused by permeability changes in the plasma membrane 3 Action potential Relative membrane permeability Na+ permeability 2 Membrane potential (mV) K+ permeability 1 1 4 Time (ms)

Axodendritic synapses Dendrites Axosomatic synapses Cell body Figure 11.16a Synapses. Axodendritic synapses Dendrites Axosomatic synapses Cell body Axoaxonic synapses (a) Axon

Figure 11.17 Chemical Synapse (1 of 3) Presynaptic neuron Presynaptic neuron Postsynaptic neuron Action potential arrives at axon terminal. 1 Voltage-gated Ca2+ channels open and Ca2+ enters the axon terminal. 2 Mitochondrion Ca2+ Ca2+ Ca2+ Ca2+ Ca2+ entry causes neurotransmitter- containing synaptic vesicles to release their contents by exocytosis. 3 Synaptic cleft Axon terminal Synaptic vesicles Neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the postsynaptic membrane. 4 Postsynaptic neuron

Figure 11.22a Types of circuits in neuronal pools.

Figure 11.22b Types of circuits in neuronal pools.

Figure 11.22c-d Types of circuits in neuronal pools.

Figure 11.22e Types of circuits in neuronal pools.

Figure 11.22f Types of circuits in neuronal pools.

Figure 11.23 A simple reflex arc. Stimulus Interneuron 1 Receptor 2 Sensory neuron 3 Integration center 4 Motor neuron 5 Effector Spinal cord (CNS) Response

Table 11.2 Comparison of Action Potentials with Graded Potentials (4 of 4)