Fig. 34-1, p.572

p.573a

Line of Communication stimulus receptors sensory neurons integrators interneurons motor neurons effectors muscles, glands response Fig. 34-2, p.574

Fig. 34-4, p.575

Vertebrate Nervous Systems Vertebrate nervous system divisions

Communication Lines Stimulus (input) Receptors (sensory neurons) Integrators (interneurons) motor neurons Effectors (muscles, glands) Response (output) Figure 34.5 Page 575

Neurons Fig. 34-6d2, p.576

Motor Neuron dendrites cell body Input Zone Trigger Zone Conducting Zone axon Output Zone axon endings Stepped Art Fig. 34-6d1, p.576

Neuron structure and function

Three Classes of Neurons Sensory neurons Interneurons Motor neurons

dendrites axon cell body Fig. 34-6a, p.576

dendrites dendrites cell body axon Fig. 34-6b,c, p.576

Structure of a Neuron dendrites input zone cell body trigger zone conducting zone axon endings axon output zone Fig. 34-6d1, p.576

How Ions Move across Membrane Interstitial fluid Cytoplasm Na+/K+ pump Passive transporters with open channels Passive transporters with voltage-sensitive gated channels Active transporters Lipid bilayer of neuron membrane Figure 34.7 Page 577

Pumping and Leaking Interstitial fluid Na+ pumped out Na+ leaks out Plasma membrane Na+ leaks in K + pumped in K+ leaks out Cytoplasm Figure 34.7 Page 577

Ion Movement Ion concentrations

Ion Concentrations at Resting Potential Potassium (K+) Higher inside than outside Sodium (Na+) Higher outside than inside

Action potential propagation

Positive Feedback more Na+ ions flow into the neuron more gated channels for Na+ open neuron becomes more positive inside

All or Nothing All action potentials are the same size If stimulation is below threshold level, no action potential occurs If it is above threshold level, cell is always depolarized to the same level

Repolarization Once peak depolarization is reached, Na+ gates close and K+ gates open Movement of K+ out of cell repolarizes the cell The inside of the cell once again becomes more negative than the outside

Measuring membrane potential

action potential +20 -20 Membrane potential (millivolts) threshold -40 resting membrane potential -70 1 2 3 4 5 Figure 34.9f Page 579 Time (milliseconds)

Propagation of Action Potentials An action potential in one part of an axon brings a neighboring region to threshold Action potential occurs in one patch of membrane after another

Chemical Synapse Gap between the terminal ending of an axon and the input zone of another cell plasma membrane of axon ending of presynapic cell plasma membrane of postsynapic cell synaptic vesicle synaptic cleft membrane receptor Figure 34.10a Page 580

Synaptic Transmission Action potential at end of presynaptic cell axon causes voltage-gated calcium channels to open Flow of calcium into presynaptic cell causes release of neurotransmitter into synaptic cleft

Synaptic Transmission Neurotransmitter diffuses across cleft and binds to receptors on membrane of postsynaptic cell Binding of neurotransmitter to receptors opens ion channels in the membrane of postsynaptic cell

Synaptic Transmission Synapse function

Chemical Synapse Chemical synapse

neuromuscular junction motor neuron axons from spinal cord to skeletal muscle cells transverse slice of spinal cord part of a skeletal muscle Fig. 34-11a, p.581

axon ending muscle fiber Fig. 34-11b, p.581

Neurotransmitters ACh Norepinephrine Epinephrine Dopamine Serotonin GABA Derived from amino acids

Neuroglia More than half the volume of the vertebrate nervous system A variety of cells that metabolically assist, structurally support, and protect the neurons

Nerve A bundle of axons enclosed within a connective tissue sheath myelin sheath nerve fascicle A bundle of axons enclosed within a connective tissue sheath Figure 34.15 Page 584

Myelin Sheath A series of Schwann cells Sheath blocks ion movements Action potential must “jump” from node to node Figure 34.15b Page 584

Nerve Nerve structure

Ion flow in myelinated axons

Reflexes Automatic movements made in response to stimuli In the simplest reflex arcs, sensory neurons synapse directly on motor neurons Most reflexes involve an interneuron

Stretch Reflex Figure 34.16 Page 585 STIMULUS Biceps stretches. sensory neuron motor neuron Response Biceps contracts. Figure 34.16 Page 585

Stretch Reflex Stretch reflex

Peripheral Nervous System Somatic nerves Motor functions (Shown in green) Autonomic nerves Visceral functions (Shown in red)

Two Types of Autonomic Nerves Sympathetic Parasympathetic Most organs receive input from both Usually have opposite effects on organ

Sympathetic Nerves Originate in the thoracic and lumbar regions of the spinal cord Ganglia are near the spinal cord Promote responses that prepare the body for stress or physical activity (fight-or-flight response)

Parasympathetic Nerves Originate in the brain and the sacral region of the spinal cord Ganglia are in walls of organs Promote housekeeping responses such as digestion

Both Systems Are Usually Active Most organs are continually receiving both sympathetic and parasympathetic stimulation For example, sympathetic nerves signal heart to speed up; parasympathetic stimulate it to slow down Which dominates depends on situation

Function of the Spinal Cord Expressway for signals between brain and peripheral nerves Sensory and motor neurons make direct reflex connections in the spinal cord Spinal reflexes do not involve the brain

Structure of the Spinal Cord ganglion nerve meninges (protective coverings) vertebra Figure 34.18 Page 587

Organization of the spinal cord

Vertebrate Brains olfactory lobe olfactory lobe (part of forebrain) midbrain hindbrain midbrain fish (shark) hindbrain reptile (alligator) mammal (horse) Figure 34.21 Page 589

Regions of the vertebrate brain Vertebrate Brains Regions of the vertebrate brain

Cerebrospinal Fluid Surrounds the spinal cord Fills ventricles within the brain Blood-brain barrier controls which solutes enter the cerebrospinal fluid Figure 34.20 Page 588

Anatomy of the Cerebrum Largest and most complex part of human brain Outer layer (cerebral cortex) is highly folded A longitudinal fissure divides cerebrum into left and right hemispheres

Limbic System Controls emotions and has role in memory (olfactory tract) cingulate gyrus thalamus amygdala hypothalamus Figure 34.24 Page 591 hippocampus

Prefrontal cortex activity when generating words Visual cortex activity when seeing written words Motor cortex activity when speaking Fig. 34-23b, p.590

Sensory Pathway Path to visual cortex