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Human Biology Concepts and Current Issues Seventh Edition Michael D. Johnson 11 The Nervous System: Integration and Control © 2014 Pearson Education, Inc. Lecture Presentations by Robert J. Sullivan Marist College Nervous System Overview Characteristics of the nervous system 1. Receives information from many sources simultaneously 2. Integrates information (processes, compiles, makes sense of this information) 3. Extremely fast—can receive, integrate, and respond in tenths of a second 4. Can initiate specific responses such as muscle contraction, glandular secretion, conscious control over movement © 2014 Pearson Education, Inc. 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 © 2014 Pearson Education, Inc. Figure 11.1 CNS Brain Sensory (input) Spinal cord Signals Signals Signals from internal from external from skin, environment tendons, and organs muscles PNS Motor (output) Somatic division Autonomic division (control of skeletal muscle) (autonomic control of smooth muscle, cardiac muscle, and glands) Parasympathetic © 2014 Pearson Education, Inc. Sympathetic 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 components of the CNS – Motor neurons: neurons found in the PNS that transmit information away from the CNS © 2014 Pearson Education, Inc. 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 slender extensions of the cell body, receive incoming information – Axon: long slender extension, specialized to conduct electrical impulses away from the cell body © 2014 Pearson Education, Inc. Figure 11.2 Skin Receptor Dendrite Axon Muscle Axon bulb Sensory neuron Axon terminals Cell body Axon Impulse direction Motor neuron Axon hillock Dendrites Interneuron Cell body Dendrites Cell body Axon Brain and spinal cord © 2014 Pearson Education, Inc. 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 © 2014 Pearson Education, Inc. Sodium-Potassium Pump Maintains Resting Potential Functions of Na/K pump – Maintains cell volume – Establishes and maintains resting potential by ongoing active transport of three Na out of the cell and two K into the cell Resting potential: measurable difference in voltage across the cell membrane in a resting cell – 70 mV – Interior of cell negative relative to the exterior © 2014 Pearson Education, Inc. Figure 11.3 Interstitial fluid Na Sodium(3) Na potassium pump K Resting potential: 70 mV (inside negative) Membrane (2) K Axon cytoplasm © 2014 Pearson Education, Inc. Na K Graded Potentials Alter the Resting Potential Graded potential – Transient local changes in the resting potential – May depolarize or hyperpolarize the membrane Summation – Graded potentials can add up in space or time – This additive effect may reach a “trigger point” or threshold, which initiates an action potential © 2014 Pearson Education, Inc. An Action Potential Is a Sudden Reversal of Membrane Voltage Initiated when graded potentials reach a certain threshold (triggering point) Depolarization: Voltage-sensitive Na channels open, Na moves into the axon (this reverses the voltage across the membrane, interior becomes ) Repolarization: Na channels close, K channels open, K moves out of the axon (this restores the initial polarity, actually becomes temporarily hyperpolarized) Reestablishment of the resting potential: K channels close, the normal activity of the sodiumpotassium pump restores resting potential © 2014 Pearson Education, Inc. Membrane potential in millivolts (mV) Figure 11.4 30 20 A depolarizing 10 graded potential 0 10 Resting A hyperpolarizing 20 membrane graded potential 30 potential 40 Summation 50 60 70 80 0 20 40 60 80 Time (milliseconds) © 2014 Pearson Education, Inc. Action potential Threshold 100 120 140 Figure 11.5 Interstitial fluid Axon cytoplasm 1 Interstitial fluid Na Na K Na K Na Axon cytoplasm 2 DEPOLARIZATION K K REPOLARIZATION • Sodium channels close • Potassium channels open • Potassium diffuses out • Membrane repolarizes • Sodium channels open • Sodium diffuses in • Membrane depolarizes Membrane potential (mV) 30 0 PNa Threshold PK 70 0 1 2 4 3 5 6 Time (milliseconds) 3 RESTING POTENTIAL • Potassium channels close Interstitial fluid Interstitial fluid Axon cytoplasm © 2014 Pearson Education, Inc. REESTABLISHMENT OF RESTING POTENTIAL • Sodium and potassium channels closed • Na-K pump matches rate of leakage Na Na K K Axon cytoplasm Na Na K K Action Potentials Are All-or-None and SelfPropagating All-or-none – Individual neuron threshold sets extent of stimulus needed – If threshold is achieved, it triggers – Once triggered, an action potential is always the same in speed and voltage Self-propagating – Continues to propagate itself in the next region of the axon – Moves like a wave down the axon, with constant speed and amplitude © 2014 Pearson Education, Inc. Action Potentials Are All-or-None and SelfPropagating The number of action potentials/unit time encodes the strength of the stimulus – Stronger stimuli generate more action potentials/unit time Speed of action potential – Always the same for a particular neuron – Can be different in different neurons – In larger diameter axons, action potentials travel at greater speed © 2014 Pearson Education, Inc. 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 © 2014 Pearson Education, Inc. Neuroglial Cells Support and Protect Neurons Schwann cells: form myelin sheaths in PNS – Role of myelin sheath: – Save the neuron energy – 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 © 2014 Pearson Education, Inc. Figure 11.7 In saltatory conduction, the nerve impulse jumps from node to node. A myelinated motor neuron of the peripheral nervous system Myelin sheath Neuron axon TEM cross section of part of an axon (yellow) and its surrounding myelin sheath (beige). © 2014 Pearson Education, Inc. Node of Ranvier Schwann cell Disorders Associated with Degeneration of Myelin Sheaths Multiple sclerosis (MS) – Progressive damage to myelin sheaths in brain and spinal cord – Weakness, visual impairment, incontinence Amyotrophic lateral sclerosis (ALS) – Progressive damage to myelin sheaths in motor area of spinal cord – Progressive weakening and wasting of skeletal muscle © 2014 Pearson Education, Inc. Information Is Transferred from a Neuron to Its Target Targets: another neuron, muscle cell, or gland Synapse: special junction between axon terminus 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 neurotransmitter © 2014 Pearson Education, Inc. Neurotransmitter Is Released Events that occur during synaptic transmission Action potential arrives at axon terminus, 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 channels Graded potential results from Na movement through opened channels © 2014 Pearson Education, Inc. Figure 11.8 Axon bulbs form synapses with a postsynaptic neuron 1 An action potential arrives, causing Ca2 to diffuse into the axon bulb. Action potential 2 Ca2 causes vesicles containing neurotransmitter to fuse with the cell membrane releasing neurotransmitter. Axon of presynaptic neuron Ca2 Synaptic cleft Mitochondrion Vesicles containing neurotransmitter Neurotransmitter Axon bulb Na Presynaptic neuron Synaptic cleft Dendrite or cell body of postsynaptic neuron Close-up of a synapse Cytoplasm of postsynaptic cell Presynaptic membrane Postsynaptic membrane © 2014 Pearson Education, Inc. Na 3 4 Neurotransmitter binds to receptors on chemically gated sodium channels, causing the channels to open. Diffusion of sodium produces a graded potential in the local region of the synapse. 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 Excitatory neurotransmitters – Depolarize the postsynaptic cell, approaching or exceeding threshold Inhibitory neurotransmitters – Hyperpolarize the postsynaptic cell © 2014 Pearson Education, Inc. Table 11.1 © 2014 Pearson Education, Inc. Postsynaptic Neurons Integrate and Process Information Response in postsynaptic cell depends on – How many neurons are forming synapses with it – Whether the neurons forming synapses with it are excitatory or inhibitory Convergence: occurs when one neuron receives input from many others Divergence: occurs when one neuron sends action potentials to multiple other neurons © 2014 Pearson Education, Inc. Figure 11.9 Convergence Divergence © 2014 Pearson Education, Inc. 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 © 2014 Pearson Education, Inc. Sensory Neurons Provide Information to the CNS Provide information for both the somatic and autonomic motor divisions of the PNS Incoming information arrives at the CNS as action potentials from sensory neurons located throughout the body © 2014 Pearson Education, Inc. The Somatic Division Controls Skeletal Muscles Functions – Voluntary – Conscious control of skeletal muscles – Involuntary (reflexes) – Spinal reflexes: Involuntary responses mediated primarily by spinal cord and spinal nerves, with little brain involvement – Flexor (withdrawal) reflex – Crossed extensor reflex – Stretch reflex: important in maintaining upright posture, movement © 2014 Pearson Education, Inc. Figure 11.10 3 To brain Interneurons (gray) stimulate specific motor neurons on both sides of the body and send signals to the brain. Dorsal root (sensory) Cell body of sensory neuron Ventral root (motor) 2 Sensory neurons carry the signal to the spinal cord. Spinal cord Motor neuron Motor neuron 4a Flexor reflex: withdraws the right leg. 1 A painful stimulus is applied to the right foot. © 2014 Pearson Education, Inc. Effector muscles (thigh) 4b Crossed extensor reflex: extends the left leg. The Autonomic Division Controls Automatic Body Functions Part of the motor output of the PNS Controls automatic body functions of many internal organs Consists of two divisions 1. Sympathetic division 2. Parasympathetic division Both sympathetic motor neurons and parasympathetic neurons enervate each organ Targets: smooth muscle, cardiac muscle, internal organs © 2014 Pearson Education, Inc. The Sympathetic and Parasympathetic Divisions Oppose Each Other Sympathetic division – Prepares the body for emergencies – Norepinephrine is the key neurotransmitter – Produces fight-or-flight response – Increases heart rate and respiration – Raises blood pressure – Dilates pupils – Slows digestion and urine production – Generally produces a unified response in all organs at once – Opposes parasympathetic division © 2014 Pearson Education, Inc. The Sympathetic and Parasympathetic Divisions Oppose Each Other Parasympathetic division – – – – Relaxes the body 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 © 2014 Pearson Education, Inc. Figure 11.12 SYMPATHETIC DIVISION PARASYMPATHETIC DIVISION Constricts pupil Dilates pupil Decreases salivation Increases salivation Cranial nerves Decreases respiration rate Increases respiration rate Increases heart rate Thoracic nerves Decreases heart rate Constricts blood vessels Dilates blood vessels Inhibits digestive processes Stimulates digestive processes Lumbar nerves Inhibits digestive processes Sacral nerves Relaxes bladder muscles Inhibits defecation © 2014 Pearson Education, Inc. Stimulates digestive processes Stimulates secretion of epinephrine and norepinephrine Ganglion Causes salt and water retention Synapse between neurons Contracts bladder muscles Stimulates defecation Table 11.2 © 2014 Pearson Education, Inc. 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 © 2014 Pearson Education, Inc. Figure 11.13 Right ventricle Skull Left ventricle Hair Scalp Skull Dura mater Arachnoid Meninges Pia mater Brain tissue Third ventricle Cerebrospinal fluid Meninges Spinal canal Spinal cord Fourth ventricle Right ventricle Left ventricle Third ventricle Cerebral aqueduct Fourth ventricle Anterior view. © 2014 Pearson Education, Inc. Sagittal view. Cerebrospinal fluid The Spinal Cord Relays Information Spinal cord is a superhighway for action potentials between the brain and the rest of the body White matter – Outer portion of spinal cord – Consists of myelinated ascending (sensory) and descending (motor) nerve tracts Gray matter – Center portion of spinal cord – Contains cell bodies, dendrites © 2014 Pearson Education, Inc. Figure 11.14 Spinal cord Gray matter Central canal White matter Ganglion Nerve Intervertebral disc Pia mater Arachnoid A transverse slice of the cord, showing white and gray matter. Meninges Dura mater Spinal cord Vertebra The spinal cord lies within the vertebral column. © 2014 Pearson Education, Inc. A closer look at the spinal cord and its relationship with a vertebra. Superior view of vertebra. The Brain Processes and Acts on Information Brain: command center of the body Three major anatomical/functional divisions – Hindbrain: coordinates basic, automatic, and vital tasks – Midbrain: coordinates muscle groups and responses to sight and sound – Forebrain: receives, integrates sensory input, determines complex behavior © 2014 Pearson Education, Inc. Figure 11.15 FOREBRAIN Cerebrum • Coordinates language • Controls decision making • Produces conscious thought MIDBRAIN • Relays visual and auditory inputs • Coordinates movement Corpus callosum • Bridges the, two cerebral hemispheres Thalamus • Receives, processes, and transfers information HINDBRAIN Pons • Connects cerebellum, spinal cord with higher brain centers • Aids medulla in regulating respiration © 2014 Pearson Education, Inc. Medulla oblongata • Controls automatic functions of internal organs Cerebellum • Controls basic and skilled movements Hindbrain: Movement and Automatic Functions Oldest, most primitive part of brain, from an evolutionary perspective Three basic parts – Medulla oblongata – Cerebellum – Pons © 2014 Pearson Education, Inc. Hindbrain: Movement and Automatic Functions Medulla oblongata – Connects to spinal cord – Controls vital automatic functions of internal organs – Cardiovascular center: regulates heart rate and blood pressure – Respiratory center: adjusts respiration in response to CO2 and O2 levels – Motor nerves cross over in medulla oblongata – Right forebrain controls left side of body – Left forebrain controls right side of body © 2014 Pearson Education, Inc. Hindbrain: Movement and Automatic Functions Cerebellum – Coordinates basic body movements – Stores and replicates sequences of skilled movements – Examples – Tying a shoe – Swinging a bat – Using a keyboard – Excessive alcohol consumption disrupts normal cerebellum function © 2014 Pearson Education, Inc. Hindbrain: Movement and Automatic Functions Pons – Connects higher brain centers and the spinal cord – Coordinates the flow of information between the cerebellum and higher brain centers – Aids medulla oblongata in regulating respiration © 2014 Pearson Education, Inc. Midbrain: Vision and Hearing Coordinates movements of the head related to vision and hearing Controls movement of eyes and size of pupils Reticular formation: group of neurons that extend through medulla oblongata, pons, and midbrain – Works with cerebellum to control skeletal muscle activity related to posture/balance – Maintains wakefulness © 2014 Pearson Education, Inc. Forebrain: Emotions and Conscious Thought Receives and integrates information concerning emotions and conscious thought Hypothalamus – Helps regulate homeostasis Thalamus – Receiving, processing, and transfer center Limbic system – Pathways involved in emotions and memory Cerebrum – Language, decision making, conscious thought © 2014 Pearson Education, Inc. Forebrain: Emotions and Conscious Thought Cerebrum – Structure – Right and left hemispheres – Hemispheres connected by corpus callosum – Nerve tracts in corpus callosum allow two hemispheres to share information – Cerebral cortex: gray matter, the outer layer of the cerebrum © 2014 Pearson Education, Inc. A Closer Look at the Cerebral Cortex Functions: memory storage, abstract thought, conscious awareness, conscious control of skeletal muscle Divided into four lobes – Occipital lobe: processes 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 All four lobes: memory storage © 2014 Pearson Education, Inc. Figure 11.16 Parietal lobe Right cerebral hemisphere Surface fold • Interprets sensory information from skin Occipital lobe • Processes visual information Posterior Corpus callosum Anterior Cerebral white matter Cerebral cortex (gray matter) Temporal lobe Left cerebral hemisphere The cerebral cortex (gray matter; outer layer, shown in four colors) consists of interneurons that integrate and process information. White matter (inner core) consists of ascending and descending nerve tracts. The two separate hemispheres are joined by the corpus callosum. © 2014 Pearson Education, Inc. Frontal lobe • Initiates motor activity • Responsible for speech • Conscious thought • Interprets auditory information • Comprehends language • Perceptual judgment The functions of the four lobes of the cerebral cortex are location-specific. Figure 11.17 Leg Trunk Hip Trunk Hip Arm Neck Elbow Arm Wrist Elbow Fingers Hand Forearm Thumb Fingers Neck Thumb Toes Brow Genitals Eye Eye Face Primary somatosensory area Primary motor area Lips Nose Face Lips Jaw Teeth Tongue Thumb Gums Frontal lobe Swallowing Tongue Pharynx Right hemisphere Left hemisphere Parietal lobe Posterior © 2014 Pearson Education, Inc. Brain Activity Continues During Sleep Reticular activating system (RAS) – Group of neurons within the reticular formation – Controls levels of sleep and wakefulness – Sleep center in RAS – Releases the neurotransmitter serotonin – Induces sleep by inhibiting arousal – To return to wakefulness, norepinephrine (secreted by another area in the brain) inhibits the serotonin © 2014 Pearson Education, Inc. Brain Activity Continues During Sleep Sleep stages – Based on electroencephalograms (EEGs) – Stage 1: transitional, random small waves on EEG – Stage 2: skeletal muscles relax, little eye or body movement, EEG shows sleep spindles – Stage 3: heart and respiration slower, EEG shows slow wave sleep – Stage 4: difficult to awaken, heart and respiration slowest, body temperature decreased – REM (rapid eye movement) sleep: dreaming, EEG same as awake – Typical night’s sleep: cycle through stages © 2014 Pearson Education, Inc. Figure 11.18 Awake Stage (Sleep spindles) Stage Stage Awake Stage 0 10 seconds EEG recordings in an awake person and during Stages 1-4 and REM sleep. Note the similarity between REM sleep and wakefulness. © 2014 Pearson Education, Inc. 1 2 3 4 5 6 7 Hours Patterns of sleep during a typical night. 8 The Limbic System Is the Site of Emotions and Basic Behaviors Includes all neuronal structures that together control emotional behavior and motivational drives Hypothalamus serves as a gateway to and from limbic system Emotions – Fear, anger, sorrow, love, etc. Basic behavior – Seeking food, satisfying thirst – Sexual gratification Behaviors modified by cerebrum Short-term memory © 2014 Pearson Education, Inc. Figure 11.19 Cerebrum Limbic system Thalamus Corpus callosum Hypothalamus Cerebellum © 2014 Pearson Education, Inc. Memory Involves Storing and Retrieving Information Short-term – Working memory – Information from previous few hours – Stored in the limbic system Long-term – Information from previous days to years – Involves permanent changes in neurons and synapses in the cerebral cortex © 2014 Pearson Education, Inc. Psychoactive Drugs Affect Higher Brain Functions Psychoactive drugs – Affect states of consciousness, emotions, or behavior Action – Able to cross blood-brain barrier – Influence concentrations or actions of neurotransmitters – Affect higher brain functions © 2014 Pearson Education, Inc. Psychoactive Drugs Affect Higher Brain Functions Psychological dependence – User craves the feeling associated with the drug Tolerance – Requires more of the substance to achieve the same effect Addiction – The need to continue obtaining and using a substance – No free choice Withdrawal – Physical symptoms that occur upon stopping the drug © 2014 Pearson Education, Inc. Disorders of the Nervous System Trauma – Physical injury to brain or spinal cord – Concussion – Blow to the head may lead to unconsciousness – Disruption of electrical activity in the brain – Risk of subdural hematoma – Spinal cord injuries – Impairment of sensation and function below site of injury © 2014 Pearson Education, Inc. Disorders of the Nervous System Infections: Caused by viruses or bacteria that manage to pass through the blood-brain barrier – Encephalitis – Inflammation of the brain caused by viral infection – Meningitis – Inflammation of the meninges caused by viral or bacterial infection – Rabies – Infectious viral disease – Spread by bite or saliva of infected animal – Virus spreads from bite to brain via sensory neurons Brain tumors: abnormal growth in or on the brain © 2014 Pearson Education, Inc. Disorders of the Nervous System Disorders of neural and synaptic transmission – Epilepsy – Recurring episodes of abnormal electrical activity (seizures) – Alzheimer’s disease – Most common cause of dementia – Accumulation of abnormal protein, beta amyloid – Progressive memory lapses and dementia – Parkinson’s disease – Loss of dopamine-releasing neurons – Progressive degenerative disorder affecting motor activity © 2014 Pearson Education, Inc. Figure 11.21 A PET scan of a healthy brain. © 2014 Pearson Education, Inc. A PET scan of a patient with Alzheimer’s disease, showing decreased activity and an irregular pattern.