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Cecie Starr Christine Evers Lisa Starr www.cengage.com/biology/starr Chapter 29 Neural Control (Sections 29.9 - 29.11) Albia Dugger • Miami Dade College 29.9 The Spinal Cord • The spinal cord serves as a highway for information traveling to and from the brain, and as the integrating center for reflexes that do not involve the brain • The brain and spinal cord together constitute the central nervous system (CNS) • spinal cord • Portion of central nervous system that connects peripheral nerves with the brain Meninges and Cerebrospinal Fluid • The spinal cord and brain are enclosed by membranous meninges and cushioned by cerebrospinal fluid • meninges • Three membranes that cover and protect the central nervous system (brain and spinal cord) • cerebrospinal fluid • Fills the space between the meninges, the central canal of the spinal cord, and ventricles within the brain Structure of the Spinal Cord • The outer part of the spinal cord is white matter, consisting of bundles of myelin-sheathed axons (tracts) • Tracts carry information from one part of the CNS to another • Gray matter makes up the bulk of the CNS; it consists of cell bodies, dendrites, and many neuroglial cells • In cross-section, the spinal cord’s gray matter has a butterfly-like shape Key Terms • white matter • Tissue of brain and spinal cord consisting of myelinated axons • gray matter • Tissue in brain and spinal cord that consists of cell bodies, dendrites, and neuroglial cells The Spinal Cord The Spinal Cord white matter ventral root of spinal nerve (axons of motor neurons) spinal nerve spinal cord gray matter dorsal root of spinal nerve (axons of sensory neurons) meninges vertebra location of intervertebral disk Fig. 29.15, p. 480 Animation: Organization of the Spinal Cord To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Reflex Pathways • Reflexes are simple, ancient paths of information flow • Sensory signals flow to the spinal cord or the brain stem, which calls for a response by way of motor neurons • Spinal reflexes involve peripheral nerves and the spinal cord • reflex • Automatic response to stimulation that occurs without conscious thought or learning A Spinal Reflex A Spinal Reflex STIMULUS Biceps stretches. 1 Fruit being loaded into a bowl puts weight on an arm muscle and stretches it. Will the bowl drop? NO! Muscle spindles in the muscle’s sheath also are stretched. white matter gray matter 2 Stretching stimulates sensory receptor endings in this muscle spindle. Action potentials are propagated toward spinal cord. 3 In the spinal cord, axon 4 The stimulation is strong enough to generate action potentials that self-propagate along the motor neuron’s axon. 5 ACh released from the motor neuron’s axon terminals stimulates muscle fibers. terminals of the sensory neuron release a neurotransmitter that diffuses across a synaptic cleft and stimulates a motor neuron. RESPONSE Biceps contracts. 6 Stimulation makes the muscle spindle synapse of motor neuron with muscle cell stretched muscle contract. Ongoing stimulations and contractions hold the bowl steady. Fig. 29.16, p. 481 Animation: Stretch Reflex To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Spinal Cord Injury • An injury that interrupts tracts of the spinal cord can cause a loss of sensation and paralysis • Unlike axons of peripheral nerves, spinal cord axons do not grow back and restore function • Spinal injuries cause permanent disability – worldwide, more than 2.5 million people are disabled by a spinal injury Multiple Sclerosis • The autoimmune disorder multiple sclerosis (MS) also impairs spinal cord function • White blood cells attack and destroy oligodendrocytes (neuroglial cells) that produce the insulating myelin that wraps around axons in the spinal cord and brain • Symptoms include dizziness, numbness of hands and feet, muscle weakness, fatigue, and visual problems 29.10 The Vertebrate Brain • The brain is the main integrating organ in the vertebrate nervous system • In vertebrates, the embryonic neural tube develops into a spinal cord and brain • During development, the brain is organized as three functional regions: the forebrain, midbrain, and hindbrain Brain Development Brain Development forebrain midbrain hindbrain 7 weeks 9 weeks At birth Fig. 29.17, p. 482 Brain Evolution • The hindbrain is continuous with the spinal cord, and largely responsible for reflexes and coordination • Fishes and amphibians have the most pronounced midbrain; in birds and mammals, the midbrain is reduced • In birds and mammals, an expanded forebrain took over what were previously midbrain functions Vertebrate Brains Vertebrate Brains olfactory lobe forebrain midbrain hindbrain Fish (shark) Amphibian (frog) Reptile (alligator) Bird (goose) Fig. 29.18, p. 482 Ventricles and the Blood–Brain Barrier • The space in embryonic neural tubes develops into a system of cavities and canals filled with cerebrospinal fluid • A blood–brain barrier controls the composition and concentration of cerebrospinal fluid • The blood–brain barrier is not perfect; some toxins such as nicotine, alcohol, caffeine, and mercury slip across Key Terms • cerebrospinal fluid • Fluid around brain and spinal cord • blood–brain barrier • Protective barrier that prevents unwanted substances from entering cerebrospinal fluid Key Concepts • Vertebrate Nervous System • The central nervous system of vertebrates consists of the brain and spinal cord • The peripheral nervous system includes many pairs of nerves that connect the brain and spinal cord to the rest of the body The Human Brain • The portion of the hindbrain just above the spinal cord is the medulla oblongata • Controls heartbeat strength, breathing rhythm, and reflexes such as swallowing, coughing, vomiting, and sneezing • medulla oblongata • Hindbrain region that controls breathing rhythm and reflexes such as coughing and vomiting The Human Brain (cont.) • Above the medulla oblongata lies the pons, which also affects breathing • Pons means “bridge,” a reference to the tracts that extend through the pons to the midbrain • pons • Hindbrain region between medulla oblongata and midbrain; helps control breathing The Human Brain (cont.) • The cerebellum lies at the back of the brain and is about the size of a plum • The cerebellum is densely packed with neurons, having more than all other brain regions combined • cerebellum • Hindbrain region that controls posture and coordinates voluntary movements The Human Brain (cont.) • The forebrain contains the cerebrum, the largest part of the human brain • Each hemisphere has an outer layer of gray matter (cerebral cortex) which is responsible for our unique capacities such as language and abstract thought • cerebrum • Forebrain region that controls higher functions The Human Brain (cont.) • Most sensory signals destined for the cerebrum pass through the thalamus, which sorts them and sends them to the proper region of the cerebral cortex • thalamus • Forebrain region that relays signal to the cerebrum The Human Brain (cont.) • The hypothalamus (“under the thalamus”) is the center for homeostatic control of the internal environment • hypothalamus • Forebrain region that controls processes related to homeostasis • Control center for endocrine functions The Human Brain The Human Brain corpus callosum hypothalamus thalamus cerebrum midbrain cerebellum pons medulla oblongata Fig. 29.20b, p. 483 Brain Components and Functions Animation: Human Brain Development To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE 29.11 The Human Cerebrum • Our capacity for voluntary action, language, and conscious thought arise from activity of the cerebral cortex • The cortex interacts with other brain regions in shaping emotional responses and making memories Functions of the Cerebral Cortex • The cerebral cortex is a 2-millimeter-thick, highly folded layer of gray matter – the outer layer of the cerebrum • Prominent folds in the cortex define the cerebrum’s frontal, parietal, temporal, and occipital lobes • cerebral cortex • Outer gray matter layer of the cerebrum • Region responsible for most complex behavior Functions of Cerebral Cortex (cont.) • Frontal lobes contain association areas devoted to integrating information and governing conscious actions • A primary motor cortex near the rear of each frontal lobe controls skeletal muscles • Each hemisphere controls and receives signals from the opposite side of the body • primary motor cortex • Region of frontal lobe that controls voluntary movement Functions of Cerebral Cortex (cont.) • Sensory areas of the cerebral cortex allow us to perceive sensations • Primary somatosensory cortex of the parietal lobe receives sensory input from skin and joints • Primary visual cortex in the occipital lobe integrates incoming signals from both eyes. • Primary sensory areas of the temporal lobe process sounds and odors Primary Receiving and Integrating Centers Primary Receiving and Integrating Centers frontal lobe (planning of motor movements, aspects of memory, inhibition of unsuitable behaviors) primary motor cortex primary somatosensory cortex parietal lobe (visceral sensations) Broca’s area temporal lobe (hearing, advanced visual processing) occipital lobe (vision) Fig. 29.21, p. 484 Primary Motor Cortex Primary Motor Cortex toes lips Fig. 29.22, p. 484 Connections With the Limbic System • The limbic system (“emotional-visceral brain”) governs emotions, assists in memory, and correlates organ activities with self-gratifying behavior such as eating and sex • limbic system • Group of brain structures that govern emotion • Encircles the upper brain stem • Includes the hypothalamus, hippocampus, amygdala, and adjacent structures Limbic System Components Limbic System Components (olfactory tract) cingulate gyrus thalamus hypothalamus amygdala hippocampus Fig. 29.23, p. 485 Making Memories • Memory forms in stages: • Short-term memory holds a few bits of information (numbers, words of a sentence, etc.) for seconds to hours • Long-term memory stores larger chunks of information, more or less permanently • Emotions influence memory retention • Epinephrine released during stress helps place short-term memories into long-term storage Stages in Memory Processing Stages in Memory Processing Sensory stimuli, as from the nose, eyes, and ears Temporary storage in the cerebral cortex Input forgotten SHORT-TERM MEMORY Recall of stored input Emotional state, having time to repeat (or rehearse) input, and associating the input with stored categories of memory influence transfer to long-term storage LONG-TERM MEMORY Input irretrievable Fig. 29.24, p. 485 Stages in Memory Processing Sensory stimuli, as from the nose, eyes, and ears Temporary storage in the cerebral cortex Input forgotten SHORT-TERM MEMORY Recall of stored input Emotional state, having time to repeat (or rehearse) input, and associating the input with stored categories of memory influence transfer to long-term storage LONG-TERM MEMORY Input irretrievable Stepped Art Fig. 29.24, p. 485 Types of Memories • Different types of memories are stored and brought to mind by different mechanisms: • Skill memories (repetition of motor tasks) involve the cerebellum, and are highly persistent • Declarative memories (facts and impressions) involve the temporal lobe; inputs are screened by the amygdala, and some signals are sent to the hippocampus Key Concepts • A Closer Look at the Human Brain • The cerebral cortex is the part of the brain that evolved most recently • In humans, it governs conscious behavior and interacts with the limbic system in forming and retrieving memories In Pursuit of Ecstasy (revisited) • The active ingredient in Ecstasy (MDMA) harms brain interneurons that produce the neurotransmitter serotonin • Neurons do not divide, so damaged ones are not replaced • MDMA also damages the blood–brain barrier, which allows harmful molecules to slip into cerebrospinal fluid