Nervous System PDF

CHAPTER 11 The Nervous System Parts of neurons Resting potential of a neuron Stimulatory and inhibitory signals Action potentials Divisions of the nervous system Parts of the brain Nervous system disorders Neurons: for electrical transmission of signals Dendrites: Receives signals into c...

CHAPTER 11 The Nervous System Parts of neurons Resting potential of a neuron Stimulatory and inhibitory signals Action potentials Divisions of the nervous system Parts of the brain Nervous system disorders Neurons: for electrical transmission of signals Dendrites: Receives signals into cell Cell body: with nucleus, organelles Axon: transmits signal away from cell Axon bulbs (endings): contain neurotransmitters, when released these stimulate or inhibit other cells: neurons, muscle and gland cells. 50 different neurotransmitters, Acetylcholine A for muscle stimulation, for example. Myelin sheaths: produced by fatty neuroglial cells. Support and protect some neurons, increase electrical signal transmission speed A myelinated neuron (motor neuron) Neuroglial cells 90% of all nervous system cells. Cells specialized for support and protection of neurons and maintaining proper ion balance for neurons. Cells that create myelin sheaths: Schwann cells: myelin sheaths of peripheral nervous system. Oligodendrocytes: myelin sheaths of central nervous system. Myelin sheaths speed up the transmission of impulses (120 m / sec.!!! vs. 2.3 m / sec.) Help damaged or severed axons regenerate in peripheral nervous system, not central nervous system Types of neurons Sensory neurons Information brought to brain and spinal cord (central nervous system) dendrites directly attach to axon. Interneurons In central nervous system. Receive and process information from sensory neurons. Stimulate other interneurons and motor neurons. Motor neurons Receive information from interneurons. Transmit signals from central nervous system to muscles and glands. 3 Types of neurons  Resting potential of a neuron At rest, there is a –70 mV voltage difference between inside and outside of neurons. Why? 1) The sodium-potassium pump: Pumps 3 sodium out and 2 potassium in. Both are + ions. 2) Potassium diffuses out of channel proteins faster than sodium diffuses in. These 2 factors combined means that: Outside of neurons are more positive than inside of cells  voltage difference of –70mV Maintenance of the resting membrane potential Faster than Na+ diffusion Only when a “threshold” is passed, the neuron experiences an action potential (it “fires”) Threshold is approximately –50 mV If depolarization passes the threshold (> -50mV) the neuron fires, and the electrical signal (action potential) travels down the axon. Synaptic integration information from multiple other neurons is tallied Neurons can receive stimulatory or inhibitory signals from other neurons. Neurotransmitters released by other neurons cause Na+ or K + gated protein channels to open on the receiving neuron. Na+ channels opened : depolarization (a stimulatory signal), K + channels opened: hyperpolarization (an inhibitory signal) A stimulatory signal: Na+ gated channels open Synaptic integration Sensory neurons generate an electrical signal (“fire”) after a certain threshold is exceeded. Interneurons and motor neurons receive information from many other neurons. These signals may be stimulatory or inhibitory. These neurons “fire” if the sum of inhibitory and stimulatory input exceeds a certain threshold (-50 mV) (integration of information).  Synaptic integration Many excitatory signals and few inhibitory signals: receiving neuron fires. Increased frequency of sending a stimulatory signal by a neuron  more likely that receiving neuron will fire. Resting membrane potential, stimulatory and inhibitory signals, and an action potential  Action potential: 3 steps After the –50 mV threshold is exceeded: 1) Depolarization occurs: sodium gated channels open  sodium moves into the axon, then gated channels close (+30 mV) 2) Repolarization: potassium gated channels open (in response to voltage change)  potassium moves out of the axon, then these gated channels close (less than -70 mV) 3) Reestablishment of the resting potential: sodium-potassium pump restores normal resting potential quickly (-70 mV) Resting state Na in K out Resting state Stimulation Threshold crossed Na/K pumps restore resting state  Action potential facts Depolarization in one region causes depolarization further down the axon. Myelin sheaths = action potential skips from node to node = faster transmission (120 m / sec. vs. 2.3 m / sec.) Self-propagating: action potential always travels entire length of neuron. All or none: no “degrees of firing” the neuron either fires or it does not. If the threshold is exceeded the cell fires. Frequency of firing can vary. A myelinated neuron (motor neuron)  Divisions of the nervous system Central Nervous System (CNS): brain and spinal cord Receives, processes, and transfers information Peripheral Nervous System (PNS): nerves outside CNS Sensory nerves: carries information toward the CNS Motor nerves: carries information away from CNS 1) Somatic subdivision: stimulates skeletal muscles 2) Autonomic subdivision: stimulates smooth muscles / glands a) Sympathetic nerves b) Parasympathetic nerves Components of the Nervous System Figure 11.1 Slide 11.1 Nervous system function: Input, integration, output Sensory neurons receive data from outside and inside the body, and transmit this information to interneurons of the central nervous system. Central nervous system receives and processes this information, arrives at an action plan then causes action by stimulating motor neurons Motor neurons execute the action plan, by stimulating muscle contraction or glands. Motor neurons: somatic Voluntary: conscious control of skeletal muscles. Signal from primary motor cortex. Involuntary: spinal reflexes = quicker response. Withdrawing your foot from A sharp object, for example. Slide 11.9B  Motor neurons: autonomic Not under conscious control, stimulates smooth muscles and glands. Important for maintaining homeostasis (controls heart rate, breathing rate, blood pressure, etc.) Sympathetic nerves Function: for “fight or flight” reaction; opposes parasympathetic division Parasympathetic nerves Function: for relaxation, normal body functions Motor neurons: autonomic, sympathetic nerves Releases epinephrine / norepinephrine neurotransmitters, opposes parasympathetic nerves “Fight or flight” response : better mental alertness and physical activity: heart rate up, respiratory rate up, blood pressure up, pupils dilated, more blood flow to skeletal muscles, liver releases glucose = “Ready for action!!” Immediately non-essential activities shut down: intestines, kidneys. Epinephrine / norepinephrine released from adrenal gland for sustained signal. (act as a hormone, felt after 20 sec.) Motor neurons: autonomic, parasympathetic nerves Releases acetylcholine neurotransmitter, opposes sympathetic division Relaxation: Lower heart rate, lower respiration rate, increased digestion, lower blood pressure. = “rest and digest”  Central nervous system: spinal cord Spinal cord: relays information between brain and peripheral nervous system Responsible for reflexes Sensory nerves enter on dorsal side Motor nerves leave on ventral side White matter: myelinated neurons ascending and descending spinal cord Grey matter: unmyelinated axons,dendrites, cell bodies, some synapses form here Sensory nerves enter on dorsal side Motor nerves exit on ventral side  Brain: hindbrain Medulla oblongata (brain stem): Monitors hydrogen ion (= carbon dioxide) / oxygen of blood Controls heart rate and breathing rate Controls blood pressure Controls movements of digestive system Controls reflexes like coughing, sneezing, swallowing Joins spinal cord and the rest of the brain. Medulla oblongata  Brain: hindbrain Cerebellum: Coordinates basic movements and balance Maintains posture (upright) Learned motor programs that become automatic (like juggling, hitting a tennis serve, driving a car, walking) Drunk people: cerebellum affected, so a person cannot walk properly and certainly cannot drive properly Cerebellum  Brain: forebrain Hypothalamus: Regulates hormone secretions of pituitary gland. Helps with homeostasis by monitoring body temperature, hunger and thirst (monitors blood solute concentration). Important for sex drive Hypothalamus  Brain: forebrain Thalamus: Relays touch sensory input from the body to the cerebral cortex for proper interpretation. Processes some outgoing motor signals. Parkinson’s disease: A degenerative disease in which dopamine-releasing neurons in thalamus die over many years. Smooth motions become increasingly difficult: tremors, poor balance, slow movements, rigidity. Dementia and depression can occur too. Thalamus Brain: forebrain Limbic system: involved in emotions and short term memory. Limbic system associated with strong emotions and instincts (love, fear, rage and sorrow). Linked with the hypothalamus (basic desires: hunger, thirst, sex). “Impulses” of limbic system and hypothalamus pass through thalamus to the cerebral cortex. Cerebral cortex can control both strong emotions and basic desires. Limbic System Brain: forebrain Limbic system: Short term memory (up to several hours): limbic system. Transferring short-term to long term memory: Saying information out loud Writing down information Reading information Using information in conversation repeatedly, Information transmitted to: long term memory in cerebral cortex. Four primary regions of the cerebral cortex Frontal lobe: creates voluntary movement including speech, also: planning, decision making, abstract thought, personality traits, long term memory. Parietal lobe: primary somatosensory region receives skin sensory information, interpretation of sense of touch. Also receives and interprets taste information. Occipital lobe: primary visual cortex receives visual input, interpretation of visual data Temporal lobe: primary auditory cortex receives auditory input, including speech, interpretation of auditory data. Also receives and interprets smell information.  Also taste Also smell Alzheimer’s disease Degenerative disease that usually starts late in life (65 or older): Frontal lobe and limbic systems affected: protein amyloid “plaque” deposited in brain, kills neurons. As it proceeds only tangled remains of neurons and protein plaque remain. Progressive memory loss occurs, irritability and personality change. Eventually the person cannot care for themselves.  chiras fig 11.18  Generating words: Broca’s area.. Hearing words: primary auditory cortex and Wernicke’s area Seeing words: primary visual cortex and visual association cortex. Musicians “interpret” music similar to words, non-musicians don’t Hearing foreign language: Wernicke’s area not active Seeing a foreign script: visual association cortex not as active  Primary motor cortex, part of the frontal lobe: Generates movement in specific regions of the body. There are many motor neurons associated with parts of the body with fine motor control (like the fingers and the face). More motor neurons = fine movements = more brain devoted to moving these regions Primary sensory cortex, part of the parietal lobe: receives sensory input from specific regions of the body. Some parts of the body are more sensitive to touch (like fingertips and lips), because they have more dense sensory neurons there. More sensory neurons = more sensitive to touch = more brain devoted to receiving information from these regions.  Disorders of the Nervous System Concussion: blow to the head disrupts brain’s normal electrical activity: often results in blurred vision, headaches, problem balancing and short-term memory loss. Sometimes people lose consciousness. Epilepsy Leads to seizure episodes: abnormal electrical activity with many neurons firing at once. Person falls to the ground and moves uncontrollably. Caused by drugs, brain injuries or inherited. Usually can be treated with anti-convulsants.  Disorders of the Nervous System Infections: Encephalitis (inflammation of brain due to viral infection), usually leads to fever and headache. More serious problems can arise like seizures, confusion, behavior changes and inability to control movements. Coma and death can occur. Meningitis (inflammation of tissues surrounding brain due to viral or bacterial infection of fluid surrounding brain) leads to high fever, severe headache and painful, stiff neck. Other symptoms are possible like confusion and seizures. Can lead to permanent brain damage and can be fatal.  Disorders of the Nervous System Infections: Rabies Virus infects neurons and travels up to brain killing cells. Causes hallucinations, seizures, coma then death. Mammal bites may cause rabies, once symptoms appear (4-6 weeks) there is no cure.  Chiras, DD Human biology, health, homeostasis, and the environmentJones and Bartlett, 2002