CHAPTER 28 Nervous Systems Modules 28.1 – 28.9

Can an Injured Spinal Cord Be Fixed? The spinal cord is the central communication conduit between the brain and the body It consists of a bundle of nerves

Spinal cord injury disrupts communication between the central nervous system and the rest of the body Paraplegia is paralysis of the lower half of the body Quadriplegia is paralysis from the neck down Research on nerve cells is leading to new therapies

NERVOUS SYSTEM STRUCTURE AND FUNCTION 28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands The nervous system has three interconnected functions Sensory input Integration Motor output

Peripheral nervous system (PNS) Central nervous system (CNS) SENSORY INPUT INTEGRATION Sensory receptor MOTOR OUTPUT Brain and spinal cord Effector Peripheral nervous system (PNS) Central nervous system (CNS) Figure 28.1A

The nervous system can be divided into two main divisions The central nervous system (CNS) : the brain the spinal cord (in vertebrates) The peripheral nervous system (PNS) : nerves ganglia (carry signals into/out of the CNS)

Central nervous system Peripheral nervous system B1. Somatic nervous system B2. Autonomic nervous system   1. Cerebrum 2. Brainstem 3. Cerebellum 4. Spinal cord

Three types of neurons correspond to the nervous system’s three main functions Sensory neurons convey signals from sensory receptors into the CNS Interneurons integrate data and relay signals Motor neurons convey signals to effectors

1 2 3 4 Sensory receptor Sensory neuron Brain Ganglion Motor neuron Spinal cord Quadriceps muscles 4 Interneuron CNS Nerve Flexor muscles PNS Figure 28.1B

28.2 Neurons are the functional units of nervous systems Neurons are cells specialized to transmit nervous impulses They consist of a cell body dendrites (highly branched fibers) an axon (long fiber)

Supporting cells protect, insulate, and reinforce neurons The myelin sheath is the insulating material in vertebrates It is composed of a chain of Schwann cells linked by nodes of Ranvier It speeds up signal transmission Multiple sclerosis (MS) involves the destruction of myelin sheaths by the immune system

Signal direction Dendrites Cell body Cell body Node of Ranvier Myelin sheath Signal pathway Axon Schwann cell Nucleus Nucleus Nodes of Ranvier Schwann cell Myelin sheath Synaptic knobs Figure 28.2

FIGURE 38-1 A nerve cell, showing its specialized parts and their functions

28.3 A neuron maintains a membrane potential across its membrane NERVE SIGNALS AND THEIR TRANSMISSION 28.3 A neuron maintains a membrane potential across its membrane The resting potential of a neuron’s plasma membrane is caused by the cell membrane’s ability to maintain a positive charge on its outer surface a negative charge on its inner (cytoplasmic) surface Voltmeter Plasma membrane Microelectrode outside cell –70 mV Microelectrode inside cell Axon Neuron Figure 28.3A

Resting potential is generated and maintained with help from sodium-potassium pumps These pump K+ into the cell and Na+ out of the cell OUTSIDE OF CELL K+ Na+ K+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+ channel Na+ Plasma membrane K+ Na+ - K+ pump K+ channel Na+ K+ K+ K+ Protein K+ K+ K+ K+ K+ K+ K+ INSIDE OF CELL Figure 28.3B

28.4 A nerve signal begins as a change in the membrane potential A stimulus alters the permeability of a portion of the plasma membrane Ions pass through the plasma membrane, changing the membrane’s voltage It causes a nerve signal to be generated

An action potential is a nerve signal It is an electrical change in the plasma membrane voltage from the resting potential to a maximum level and back to the resting potential

Neuron interior Neuron interior Figure 28.4 3 4 5 2 1 1 Na+ K+ Na+ K+ Additional Na+ channels open, K+ channels are closed; interior of cell becomes more positive. 4 Na+ channels close and inactivate. K+ channels open, and K+ rushes out; interior of cell more negative than outside. Na+ Action potential 3 4 2 The K+ channels close relatively slowly, causing a brief undershoot. Na+ Threshold potential 5 2 A stimulus opens some Na+ channels; if threshold is reached, action potential is triggered. 1 1 5 Resting potential Neuron interior Neuron interior 1 Resting state: voltage gated Na+ and K+ channels closed; resting potential is maintained. 1 Return to resting state. Figure 28.4

28.5 The action potential propagates itself along the neuron Axon Action potential Axon segment 1 Na+ K+ Action potential 2 Na+ K+ K+ Action potential 3 Na+ K+ Figure 28.5

An action potential is an all-or-none event Its size is not affected by the stimulus strength However, the frequency changes with the strength of the stimulus

FIGURE 38-5 Signaling stimulus intensity The intensity of a stimulus is signaled by the rate at which individual sensory neurons produce action potentials and by the number of sensory neurons activated. In this example, increasing pressure on the skin first causes faster firing and then causes an adjacent receptor to be activated.

28.6 Neurons communicate at synapses The synapse is a key element of nervous systems It is a junction or relay point between two neurons or between a neuron and an effector cell Synapses are either electrical or chemical Action potentials pass between cells at electrical synapses At chemical synapses, neurotransmitters cross the synaptic cleft to bind to receptors on the surface of the receiving cell

1 2 3 4 5 6 SENDING NEURON Action potential arrives Axon of sending neuron Vesicles Synaptic knob SYNAPSE 2 3 Vesicle fuses with plasma membrane Neurotransmitter is released into synaptic cleft SYNAPTIC CLEFT 4 Receiving neuron Neuro- transmitter binds to receptor RECEIVING NEURON Neurotransmitter molecules Ion channels Neurotransmitter Neurotransmitter broken down and released Receptor Ions 5 Ion channel opens 6 Ion channel closes Figure 28.6

FIGURE 38-4 (part 1) Structure and operation of the synapse A synaptic terminal contains many neurotransmitter-filled vesicles. When an action potential enters the synaptic terminal, the vesicles release their neurotransmitter into the space between the neurons. The neurotransmitter diffuses rapidly across the gap and binds to receptors on the postsynaptic cell. In many cases, transmitter binding to receptors causes a change in the resting potential of the postsynaptic cell, called a postsynaptic potential (PSP).

28.7 Chemical synapses make complex information processing possible Excitatory neurotransmitters trigger action potentials in the receiving cell Inhibitory neurotransmitters decrease the cell’s ability to develop action potentials The summation of excitation and inhibition determines whether or not the cell will transmit a nerve signal

A neuron may receive input from hundreds of other neurons via thousands of synaptic knobs Dendrites Synaptic knobs Myelin sheath Receiving cell body Axon Synaptic knobs Figure 28.7

28.8 A variety of small molecules function as neurotransmitters Most neurotransmitters are small, nitrogen-containing organic molecules Acetylcholine Biogenic amines (epinephrine, norepinephrine, serotonin, dopamine) Amino acids (aspartate, glutamate, glycine, GABA) Peptides (substance P and endorphins) Dissolved gases (nitric oxide)

28.9 Connection: Many drugs act at chemical synapses Drugs act at synapses and may increase or decrease the normal effect of neurotransmitters Caffeine Nicotine Alcohol Prescription and illegal drugs Figure 28.9

NERVOUS SYSTEMS 28.10 Nervous system organization usually correlates with body symmetry Radially symmetrical animals have a nervous system arranged in a nerve net Example: Hydras Nerve net Neuron A. Hydra (cnidarian) Figure 28.10A

B. Planarian (flatworm) Most bilaterally symmetrical animals exhibit cephalization, the concentration of the nervous system in the head end centralization, the presence of a central nervous system Eye Brain Brain Brain Brain Ventral nerve cord Ventral nerve cord Nerve cord Transverse nerve Ganglia Giant axon Segmental ganglion B. Planarian (flatworm) C. Leech (annelid) D. Insect (arthropod) E. Squid (mollusk) Figure 28.10B-E

28.11 Vertebrate nervous systems are highly centralized and cephalized CENTRAL NERVOUS SYSTEM (CNS) PERIPHERAL NERVOUS SYSTEM (PNS) Brain Cranial nerve Spinal cord Ganglia outside CNS Spinal nerves Figure 28.11A

The brain and spinal cord contain fluid-filled spaces Dorsal root ganglion (part of PNS) Gray matter Meninges BRAIN White matter Central canal Spinal nerve (part of PNS) Ventricles Central canal of spinal cord SPINAL CORD (cross section) Spinal cord Figure 28.11B

28.12 The peripheral nervous system of vertebrates is a functional hierarchy Sensory division Motor division Sensing external environment Sensing internal environment Autonomic nervous system (involuntary) Somatic nervous system (voluntary) Sympathetic division Parasympathetic division Figure 28.12A

Referred pain is when we feel pain from an internal organ on the body surface This happens because neurons carrying information from the skin and those carrying information from the internal organs synapse with the same neurons in the CNS Heart Lungs and diaphragm Lungs and diaphragm Liver Gallbladder Heart Stomach Liver Pancreas Small intestine Appendix Ovaries Kidney Colon Urinary bladder Ureters Figure 28.12B

The motor division of the PNS The autonomic nervous system exerts involuntary control over the internal organs The somatic nervous system exerts voluntary control over skeletal muscles

28.13 Opposing actions of sympathetic and parasympathetic neurons regulate the internal environment The autonomic nervous system consists of two sets of neurons that function antagonistically on most body organs The parasympathetic division primes the body for activities that gain and conserve energy The sympathetic division prepares the body for intense, energy-consuming activities

PARASYMPATHETIC DIVISION Brain Eye Constricts pupil Dilates pupil Salivary glands Stimulates saliva production Inhibits saliva production Lung Constricts bronchi Relaxes bronchi Accelerates heart Slows heart Heart Adrenal gland Stimulates epinephrine and norepi- nephrine release Liver Spinal cord Stomach Stimulates stomach, pancreas, and intestines Pancreas Stimulates glucose release Inhibits stomach, pancreas, and intestines Intestines Bladder Stimulates urination Inhibits urination Promotes erection of genitals Promotes ejacu- lation and vaginal contractions Genitals Figure 28.13

THE HUMAN BRAIN 28.14 The vertebrate brain develops from three anterior bulges of the neural tube The vertebrate brain evolved by the enlargement and subdivision of three anterior bulges of the neural tube Forebrain Midbrain Hindbrain Cerebrum size and complexity in birds and mammals correlates with sophisticated behavior

Embryonic Brain Regions Brain Structures Present in Adult Cerebrum (cerebral hemispheres; includes cerebral cortex, white matter, basal ganglia) Forebrain Diencephalon (thalamus, hypothalamus, posterior pituitary, pineal gland) Midbrain Midbrain (part of brainstem) Pons (part of brainstem), cerebellum Hindbrain Medulla oblongata (part of brainstem) Diencephalon Cerebral hemisphere Midbrain Midbrain Pons Hindbrain Cerebellum Medulla oblongata Spinal cord Forebrain Embryo one month old Fetus three months old Figure 28.14

28.15 The structure of a living supercomputer: The human brain Table 28.15

Cerebrum Forebrain Thalamus Cerebral cortex Hypothalamus Pituitary gland Midbrain Pons Hindbrain Medulla oblongata Spinal cord Cerebellum Figure 28.15A

Most of the cerebrum’s integrative power resides in the cerebral cortex of the two cerebral hemispheres Left cerebral hemisphere Right cerebral hemisphere Corpus callosum Basal ganglia Figure 28.15B

28.16 The cerebral cortex is a mosaic of specialized, interactive regions The motor cortex sends commands to skeletal muscles The somatosensory cortex receives information about pain, pressure, and temperature Several regions receive and process sensory information (vision, hearing, taste, smell)

The association areas are the sites of higher mental activities (thinking) Frontal association area (judgment, planning) Auditory association area Somatosensory association area (reading, speech) Visual association area

FRONTAL LOBE PARIETAL LOBE Somatosensory association area Somatosensory cortex Motor cortex Speech Frontal association area Taste Reading Speech Hearing Smell Visual association area Auditory association area Vision TEMPORAL LOBE OCCIPITAL LOBE Figure 28.16

In lateralization, areas in the two hemispheres become specialized for different functions “Right-brained” vs. “left-brained”

28.17 Connection: Injuries and brain operations have provided insight into brain function Much knowledge about the brain has come from individuals whose brains were altered through injury, illness, or surgery The rod that pierced Phineas Gage’s skull left his intellect intact but altered his personality and behavior Figure 28.17A

A radical surgery called hemispherectomy removes almost half of the brain It demonstrates the brain’s remarkable plasticity Figure 28.17B

28.18 Several parts of the brain regulate sleep and arousal Sleep and arousal are controlled by the hypothalamus the medulla oblongata the pons neurons of reticular formation Input from ears Eye Motor output to spinal cord Reticular formation Input from touch, pain, and temperature receptors Figure 28.18A

Two types of deep sleep alternate An electroencephalogram (EEG) measures brain waves during sleep and arousal Two types of deep sleep alternate Slow-wave (delta waves) and REM sleep Awake but quiet (alpha waves) Awake during intense mental activity (beta waves) Delta waves REM sleep Delta waves Asleep Figure 28.18B, C

28.19 The limbic system is involved in emotions, memory, and learning The limbic system is a functional group of integrating centers in the cerebral cortex, thalamus, and hypothalamus It is involved in emotions, memory (short-term and long-term), and learning The amygdala is central to the formation of emotional memories The hippocampus is involved in the formation of memories and their recall

Thalamus CEREBRUM Hypothalamus Prefrontal cortex Smell Olfactory bulb Hippocampus Amygdala Figure 28.19

28.20 The cellular changes underlying memory and learning probably occur at synapses Memory and learning involve structural and chemical changes at synapses Long-term depression (LTD) Long-term potentiation (LTP)

1 2 2 4 3 3 Repeated action potentials Sending neuron Sending neuron Synaptic cleft 2 2 4 Ca2+ Cascade of chemical changes 3 Ca2+ 3 Receiving neuron LTP Figure 28.20