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Bio11: The Nervous System Body control systems Nervous system Endocrine system What parts of your brain are you using right now? Frontal lobe x orcy or te x ns Moto rco r te Somat ose area Senses; reading Work together to regulate body activities Speech Somatosensory association area Reading Taste The brain processes and acts on information Each of the Speech four lobes has distinct functions Hearing Smell Auditory association area Hearing and smell Temporal lobe Visual association area Vision Sends a hormone as a messenger to the target organ Can target several organs Slower acting Longer lasting response The human brain Parietal lobe Movement and conscious thought; Frontal speech association Quick Sends message directly to target organ Vision It receives information from nerves and the spinal cord integrates it and generates the appropriate response. Occipital lobe Figure 27.12 The human brain Cerebrum – largest part of the brain Central processing center where learning, remembering and reasoning takes place The cerebral cortex a highly folded layer of tissue that forms the surface of the cerebrum The Cerebrum Cerebrum Right and left cerebral hemispheres Connected by the corpus callosum Are you left-brained or rightbrained? Right = artistry Left = logic Little about life is that clear and distinct. The traits associated with each side of the brain are matters of degree 1 White matter: the brain’s connections The Cerebrum Gray matter makes up the cerebral cortex mainly cell bodies and nonmyelinated (naked) axons and dendrites. White matter Myelinated axons that connect neurons in different regions of the cerebral cortex MRI scan The brain: Cerebellum Coordinates basic movements: Maintains posture and balance Essential for motor coordination and precision. Learns and remembers new motor skills (tying a shoe, playing the piano or hitting a baseball) The brain stem The central nervous system (CNS) Breathing Heart rate Temperature control Brain stem What protects the CNS? The Central Nervous System Connects the brain to the spinal cord Controls basic body functions: brain spinal cord Bone and protective membranes called the meninges a series of 3 coverings between the nervous tissue and bone Spaces filled with cerebrospinal fluid Liquid shock absorber 2 Cerebrospinal fluid provides a constant environment 1. 2. 3. 4. CSF protects the brain Superhighway for nerve impulses traveling between the brain and rest of body Vertebra protect the spinal cord Signal direction astrocyte Protects the brain from bacterial and viral infections Glucose is actively transported across the barrier Neurons are unique cells Direction of Signal Movement nerves Structure of a neuron Signal direction Dendrites Cell body Separates the circulating blood from the brain CSF Tight junctions around the capillaries restrict the entry of bacteria and large molecules into the cerebrospinal fluid Cushions the brain Prevents the fragile surface of the brain from striking the skull Maintains consistent chemical environment Allows the brain to be bathed in CSF rather than blood, to avoid bloodborne infection Spinal cord relays information Blood-brain barrier Direction of electrical signal: Dendrite → cell body → axon Can be many feet in length! Conduct electrical signals Dendrites, Cell Body, Axon Dendrites Cell body An axon ends in a cluster of branches, each with a bulb-like synaptic terminal that relays signals to Axon Supporting cell Signal pathway Axon Synaptic terminals Supporting cell Another neuron A muscle Signal pathway Synaptic terminals Nucleus Nucleus Myelin sheath Forms insulating material around an axon Increases the speed of the electrical signal Myelin sheath Figure 27.2 3 Types of neurons Bring messages into brain/spinal cord SENSORY INPUT Sensory receptor Sensory neuron INTEGRATION SENSORY INPUT Sensory neuron Sensory receptor Interneuron MOTOR OUTPUT Motor neuron Effector cells Types of neurons MOTOR OUTPUT Motor neuron Brain and spinal cord Peripheral nervous system (PNS) Central nervous system (CNS) Effector cells Types of neurons Peripheral nervous system (PNS) INTEGRATION Interneuron Transfer Brain and spinal cord messages within brain/spinal cord Central nervous system (CNS) Nerves SENSORY INPUT Sensory receptor Sensory neuron INTEGRATION Interneuron MOTOR OUTPUT “Cables” or bundles of axons Extend from the CNS to various parts of the body. Motor neuron Effector cells Take messages Brain and spinal cord from brain/spinal cord to muscles or Peripheral nervous Central nervous glands system (PNS) system (CNS) The other brain cells (Neurons are not alone) Neurons Neuron carry electrical signals 100 billion in brain Myelin sheath Glia Trillions of support cells Several different types of glia cells help optimize brain function Insulates axons Covering formed by a type of glia called Schwann cells Cells wrap themselves around the axon several times 4 What happens if the myelin sheath is damaged? Nerves no longer conduct impulses normally Multiple sclerosis Central Nervous System (CNS) Inflammatory disease that destroys the myelin sheath The brain Spinal cord Peripheral nervous system All nervous tissue outside the CNS MS “short circuits” the nervous system Peripheral Nervous System: sensory and motor nerves The nervous system has two parts Sensory nerves bring info from the body to the CNS Information is integrated by interneurons in brain and spinal cord Response PNS: motor nerves Other nerves serve muscles and glands But not skeletal muscle Controls “automatic” functions of the body’s internal organs Involuntary Autonomic Nervous System Peripheral Nervous System Voluntary Carries signals to and from skeletal muscles Involuntary Fight or flight Neurons work by carrying electrical signals Neurons are specialized for carrying electrical signals from one part of the body to another axon cell body Rest and digest Controls smooth and cardiac muscles, organs and glands dendrites 5 The electrical signals are called action potentials An action potential is a brief change in electrical charge at a membrane When a neuron “fires”, the charge across the neuron’s membrane suddenly reverses polarity Action potentials are “all or nothing” events axon cell body dendrites http://www.youtube.com/watch?v=R0TdXkxBOkE&NR=1 Action potentials spread down the axon What happens when a neuron “fires”? Outside Cell Inside Cell At rest, the Na+ When the neuron fires, channels are closed. the Na+ channels Inside of cell has open negative charge Electrical currents involve movement of charged (+ or -) particles Analogy: Power Plant Creates Charge Power Lines Move that Charge (electrical current) To Your House Signal is propagated down the axon like an electrical current down a wire How is the action potential passed to the next cell? Particles don’t move much, they hand their charge off to the next particle What happens at the Synapse? Electrical Chemical Electrical Electrical signals can’t cross the gap between two neurons or synapse The signal is transmitted by chemicals called neurotransmitters Stored in vesicles at the end of the axon Bind to receptors on the next cell Neurotransmitters 6 Synaptic terminal of sending neuron Neurotransmitters Dendrite of receiving neuron SYNAPSE Sending neuron Action potential arrives. Vesicles Synaptic terminal What happens after the action potential is passed to the next neuron? Neurotransmitter Receptor Ions Vesicle fuses with plasma membrane. More than 100 small molecules Either excite or inhibit the receiving neuron Most widely studied Acetylcholine (ACh), norepinephrine (NE), dopamine, serotonin, and GABA Neurotransmitter is released into synaptic cleft. Synaptic cleft Receiving neuron Ion channels Neurotransmitter molecules Neurotransmitter binds to receptor. Ion channel opens and triggers or inhibits a new action potential. Ion channel closes. Neurotransmitter is broken down and released. Dendrites Myelin sheath Receiving cell body Axon Synaptic terminals Neurons integrate many signals Neurons and how they work 4:43 http://www.youtube.com/watch?v=FR4S1BqdFG4&feature=endscreen&NR=1 SEM A neuron may receive input from hundreds of other neurons via thousands of synaptic terminals Recap: How neurons work How do motor nerves control muscle contraction? Motor neurons carry nerve impulse to a muscle fiber Neurotransmitter ACh is released, diffuses across the synapse and binds to receptors on muscle cell Muscle fiber contracts 7