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The Nervous System: Integration and Control
11 The Nervous System: Integration and Control 1
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Nervous System Overview
Characteristics of the nervous system Receives information from many sources Integrates information (processes, compiles, makes sense of this information) Initiate specific responses such as muscle contraction, glandular secretion, conscious control over movement Extremely fast—can receive, integrate, and respond in tenths of a second
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Nervous System Has Two Principal Parts
Central nervous system (CNS) Components: brain and spinal cord Functions: receives, processes, and transfers information Peripheral nervous system (PNS) Components: nerves outside CNS Sensory division: carries information toward the CNS Motor division: carries information away from CNS Somatic and autonomic divisions
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Nervous System Has Two Principal Parts
CNS Brain Sensory (input) Spinal cord Motor (output) PNS Signals from external environment Signals from skin, tendons, and muscles Signals from internal organs Somatic division (control of skeletal muscle) Autonomic division (autonomic control of smooth muscle, cardiac muscle, and glands) Figure 11.1 Components of the nervous system. Parasympathetic Sympathetic 4
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Neurons Are the Communication Cells of the Nervous System
Neurons are specialized cells for communication Generate and conduct electrical impulses Types of neurons Sensory neurons: neurons found in the PNS that receive stimuli and transmit information to the CNS Interneurons: transmit information between motor & sensory Motor neurons: neurons found in the PNS that transmit information away from the CNS
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Neurons Are the Communication Cells of the Nervous System
Three parts of the neuron Cell body: main part of the cell, has the nucleus and most of the cytoplasm and organelles Dendrites: small extensions of the cell body, receive incoming information Axon: long slender extension, conducts electrical impulses away from the cell body
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Skin Muscle Sensory neuron Motor neuron Brain and spinal cord Receptor
Figure 11.2 Skin Receptor Dendrite Axon Muscle Axon bulb Sensory neuron Axon terminals Cell body Axon Motor neuron Impulse direction Figure 11.2 Types of neurons in the nervous system. Axon hillock Dendrites Interneuron Cell body Dendrites Axon Cell body Brain and spinal cord 7
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Neurons Initiate Action Potentials
Neurons generate and transmit action potentials An action potential is basically an electrical impulse Action potentials are the primary means of communication throughout the nervous system
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Anmation: The Nerve Impulse Right-click and select Play
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Neuroglial Cells Support and Protect Neurons
Neuroglial cells make up 80% of nervous system cells Function Support Protection Glial cells do NOT transmit action potentials Two types Schwann cells Oligodendrocytes
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Neuroglial Cells Support and Protect Neurons
Schwann cells: form myelin sheaths in PNS Role of myelin sheath: Speed up the transmission of impulses Saltatory conduction: leaping pattern of action potential conduction Help damaged or severed axons regenerate Oligodendrocytes Form myelin sheaths in CNS
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A myelinated motor neuron of the peripheral nervous system
Figure 11.7 In saltatory conduction, the nerve impulse jumps from node to node. A myelinated motor neuron of the peripheral nervous system Node of Ranvier Schwann cell Myelin sheath Neuron axon Figure 11.7 A myelinated motor neuron of the peripheral nervous system. TEM cross section of part of an axon (yellow) and its surrounding myelin sheath (beige). 12
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Animation: Myelinated Neurons and Saltatory Conduction Right-click and select Play
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Information Is Transferred from a Neuron to Its Target
Targets: another neuron, muscle cell, or gland Synapse: special junction between axon end and target cell Synaptic transmission Process of transmission of impulse from sending (presynaptic neuron) across synaptic cleft to receiving (postsynaptic) target Involves release and diffusion of chemical neurotransmitters
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Neurotransmitter Is Released
Events that occur during synaptic transmission: Action potential arrives at axon end, causing Ca2 to diffuse into axon bulb Ca2 causes release of neurotransmitter from vesicles Neurotransmitter diffuses across synaptic cleft Neurotransmitter binds to receptors on target (postsynaptic) membrane and opens gated ion channels Electric signals result from ion movement through opened channels
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Animation: The Synapse Right-click and select Play
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Neurotransmitters Exert Excitatory or Inhibitory Effects
Response of postsynaptic target cell depends on Type of neurotransmitter (50 types) Type of receptors Type of gated ion channels Examples of some neurotransmitters: Acetylcholine Norepinephrine Dopamine endorphins
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Peripheral Nervous System Relays Information Between Tissues and CNS
Nerve contains axons of many neurons wrapped together in a protective sheath Carries information to and from the CNS Cranial nerves 12 pairs Connect directly to brain Spinal nerves 31 pairs Connect to spinal cord
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Animation: Cranial and Spinal Nerves Right-click and select Play
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The Somatic Division of PNS Controls Skeletal Muscles
Functions Voluntary- conscious control of skeletal muscles ( targets) Involuntary reflexes Spinal reflexes: Involuntary responses mediated primarily by spinal cord and spinal nerves, with little brain involvement Example withdrawal reflex
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The Autonomic Division of PNS controls Automatic Body Functions
Part of the motor division of the PNS Controls automatic body functions of many internal organs Consists of two divisions 1. Sympathetic division 2. Parasympathetic division Targets: smooth muscle, cardiac muscle, internal organs
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The Sympathetic and Parasympathetic Divisions Oppose Each Other
Norepinephrine is the key neurotransmitter Produces fight-or-flight response Increases heart rate and respiration Raises blood pressure Dilates pupils Opposes parasympathetic division
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The Sympathetic and Parasympathetic Divisions Oppose Each Other
For peacetime activities Opposes sympathetic division Acetylcholine is the key neurotransmitter Actions: lowers heart rate and respiration, increases digestion, permits defecation and urination Sympathetic and parasympathetic divisions work antagonistically to maintain homeostasis
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Thoracic nerves Lumbar nerves Sacral nerves Stimulates secretion of
Figure 11.12 SYMPATHETIC DIVISION PARASYMPATHETIC DIVISION Dilates pupil Constricts pupil Decreases salivation Increases salivation Cranial nerves Increases respiration rate Decreases respiration rate Increases heart rate Thoracic nerves Decreases heart rate Constricts blood vessels Dilates blood vessels Inhibits digestive processes Stimulates digestive processes Lumbar nerves Figure The sympathetic and parasympathetic divisions of the autonomic nervous system. Inhibits digestive processes Stimulates digestive processes Sacral nerves Relaxes bladder muscles Contracts bladder muscles Stimulates secretion of epinephrine and norepinephrine Inhibits defecation Stimulates defecation Causes salt and water retention Synapse between neurons Ganglion 24
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Animation: The Autonomic Nervous System Right-click and select Play
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The Brain and Spinal Cord Constitute the CNS
CNS protection Bone: skull and vertebrae Meninges: protective membranes Dura mater, arachnoid, and pia mater Cerebrospinal fluid: bathes the brain, spinal cord Shock absorber Produced within the ventricles of the brain Blood-brain barrier: prevents entry of certain chemicals and pathogens
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Central Nervous System; Brain and Spinal cord
Figure 11.13
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The Spinal Cord Relays Information
Spinal cord is a superhighway for communication between the brain and the rest of the body White matter Outer portion of spinal cord Consists of ascending (sensory) and descending (motor) nerve tracts Gray matter Center portion of spinal cord Contains neuron cell bodies
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The Brain Major divisions
Cerebrum (right and left cerebral hemispheres) Right cerebral hemisphere controls left side of body Left cerebral hemisphere controls right side of body Cerebellum Brainstem: for communication between brain and spinal cord Consists of: midbrain, pons, medulla oblongata Thalamus, hypothalamus
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Brain: command center of the body :processes and acts on information
Figure 11.15 Cerebrum • controls voluntary movement •language, thinking, speech Midbrain • visual and auditory reflexes Corpus callosum • connects the two cerebral hemispheres Thalamus • Receives, and transfers information/sensations Pons • Connects spinal cord with higher brain centers • Medulla oblongata • Has vital centers Cerebellum • coordinates movements Q: Which part of the brain classifies humans as “intelligent” beings?
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Brain Cerebrum Structure: grey matter outside, white matter inside
Right and left hemispheres Hemispheres connected by corpus callosum (nerve tracts) allow two hemispheres to share information Cerebral cortex: gray matter, the outer layer of the cerebrum Contains areas for motor control (movement), sensation, language, decision making, conscious thought White matter Inner region is receiving/sending signals
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A Closer Look at the Cerebral Cortex
Functions: memory storage, thought, conscious awareness, conscious control of skeletal muscle Divided into four lobes Occipital lobe: interprets visual information Temporal lobe: interprets auditory information, comprehends spoken/written language Parietal lobe: receives and interprets sensory information from the skin Frontal lobe: initiates motor activity, responsible for speech, conscious thought Area for language only in dominant cerebral hemisphere ( left cerebral hemisphere in most people)
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Outer layer of cerebrum is grey matter ( for processing, etc.)
Cerebral cortex Outer layer of cerebrum is grey matter ( for processing, etc.) Parietal lobe Interprets sensory information Occipital lobe Processes visual information Temporal lobe Interprets auditory information Frontal lobe Initiates motor activity Responsible for speech Conscious thought Figure 11.16b
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MOTOR SENSORY Leg Trunk Hip Arm Hip Trunk Neck Elbow Arm Wrist Elbow
Figure 11.17 Leg Trunk Hip Arm Hip Trunk MOTOR Neck Elbow SENSORY Arm Wrist Elbow Fingers Hand Forearm Thumb Fingers Neck Thumb Brow Toes Genitals Eye Eye Face Primary somatosensory area Nose Primary motor area Lips Face Jaw Lips Tongue Teeth Thumb Gums Swallowing Frontal lobe Tongue Pharynx Figure Primary somatosensory and motor areas of the cerebral cortex. Left hemisphere Right hemisphere Parietal lobe Posterior 34
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Brainstem Midbrain: Pons
Coordinates reflex movements of the head related to vision and hearing Controls movement of eyes and size of pupils Pons Connects higher brain centers and the spinal cord Aids medulla oblongata in regulating respiration
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Brainstem Medulla oblongata Connects to spinal cord
Contains vital centers Cardiovascular center: regulates heart rate and blood pressure Respiratory center: controls breathing
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Cerebellum Coordinates body movements Maintains balance and posture
Excessive alcohol consumption disrupts normal cerebellum function
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Hypothalamus Thalamus Helps regulate homeostasis
Example; has the food, thirst, temperature control centers Thalamus Receiving and transfers information to cerebral cortex
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Limbic System Involved in emotions Fear, anger, sorrow, pleasure...
Figure 11.19
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Nervous system Disorders
Meningitis Encephalitis Epilepsy Alzheimer’s disease Parkinson’s disease Multiple sclerosis Hemophilia
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