Body control systems. Nervous system. Organization of Nervous Systems. The Nervous System. Two types of cells. Organization of Nervous System

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1 Body control systems Nervous system Nervous system Quick Sends message directly to target organ Endocrine system Sends a hormone as a messenger to the target organ Slower acting Longer lasting response Work together to regulate body activities The Nervous System Controls the muscular system Works with the endocrine system to maintain homeostasis Organization of Nervous Systems Two main divisions: The central nervous system (CNS) brain and spinal cord The peripheral (PNS) nerves that carry signals into and out of the CNS Organization of Nervous System Two types of cells Two main divisions: The central nervous system (CNS) brain and spinal cord The peripheral (PNS) nerves that carry signals into and out of the CNS Neurons cells specialized for carrying electrical signals from one part of the body to another Neuroglia Cells that support and nourish s Outnumber s 9 to 1 axon cell body dendrites Neuron

2 Myelin sheath Covering formed by a type of neuroglia called Schwann cells Cells wrap themselves around the axon several times Insulates axons Sensory receptor Effector cells Three types of s SENSORY INPUT Sensory MOTOR OUTPUT Motor Peripheral nervous system (PNS) INTEGRATION Inter Brain and spinal cord Central nervous system (CNS) Nerves Axons bundle up into nerves that extend from the CNS to various parts of the body. Signal direction Nucleus Structure of a motor Dendrites Cell body Axon Supporting cell Direction of electrical signal: Dendrite cell body axon Signal pathway terminals Myelin sheath Forms insulating material around an axon Helps increase the speed of the electrical signal The nerve impulse The nerve impulse When a is at rest, the inside of the axon is negatively charged compared to the outside. More positive ions outside than inside the membrane recording reference electrode electrode inside axon outside axon axonal membrane A rapid, short-lived reversal in the charge across the membrane Sodium channels in the membrane open letting Na into the axon Signal is propagated down the axon like an electrical current direction of signal open Na channel b. Stimulus causes the axon to reach its threshold; the axon potential increases from -65 to -40. The action potential has begun.

3 Axon Passing the nerve impulse to the next cell Action potential A synapse is the gap between two s The nerve impulse can t cross the gap The signal is transmitted by chemicals called neurotransmitters Action potential Electrical signal travels down the axon Action potential Stored in vesicles at the end of the axon terminal of sending s They can either excite or inhibit the postsynaptic cell More than 25 small molecules act as neurotransmitters Most widely studied Acetylcholine (ACh), norepinephrine (NE), dopamine, serotonin, and GABA Dendrite of receiving SYNAPSE Sending Action potential arrives. Vesicles terminal Receptor Ions Vesicle fuses with plasma membrane. is released into synaptic cleft. cleft Receiving Ion channels molecules binds to receptor. Ion channel opens and triggers or inhibits a new action potential. Ion channel closes. is broken down and released. Figure 27.5 Dendrites Integration Myelin sheath Receiving cell body A may receive input from hundreds of other s via thousands of synaptic terminals Axon terminals It integrates signals SEM Control of muscle contraction Motor s carry nerve impulse to a muscle fiber ACh is released, diffuses across the synapse and binds to receptors on muscle cell Muscle fiber contracts

4 How do recreational drugs work? Many drugs affect the levels of neurotransmitters. Mimic the action of a neurotransmitter Block its receptor Interfere with removal of a neurotransmitter from the synapse Cocaine Prevents the uptake of dopamine at the synapse Dopamine remains in the synapse longer and continues to stimulate the postsynaptic cell. The user experiences a rush sensation Methamphetamine Marijuana A synthetic drug made by adding a methyl group to amphetamine Its structure is similar to dopamine Stimulatory effect mimics cocaine anadamide Anadamide receptor THC binds to a receptor for the neurotransmitter anadamide feeling of peaceful contentment, mild euphoria Nicotine The Central Nervous System Nicotine acts as a stimulant by mimicking acetylcholine it binds to and activates ACh receptors The brain and spinal cord Protected by bone; wrapped in protective membranes called the meninges Spaces filled with cerebrospinal fluid Cushions the CNS Supplies nutrients, hormones

5 Spinal cord The human brain Conducts signals to and from the brain Gray matter contains cell bodies of s White matter contains myelinated axons that run together in bundles called tracts White matter Cerebrum largest portion of the brain Responsible for reasoning, learning and memory, language The cerebral cortex Spinal nerve Gray matter Cerebrum Is a highly folded layer on the surface of the cerebrum Gray matter contains over 1 billion cell bodies ry ya sor ry ma ma P ri P ri Taste The Cerebral Cortex Parietal lobe sen mo to r a re a Frontal lobe re a Cerebrum - divided into four lobes The right and left cerebral hemispheres interconnected by the corpus callosum Speech Smell Hearing Vision Temporal lobe Bridge of nerve tracts Indicates that the hemispheres work together Occipital lobe Figure The brain: Cerebellum Functions: Maintains posture and balance Coordinates body movement Helps us learn new motor skills (i.e. playing the piano or hitting a baseball) The brain stem Connects the brain to the spinal cord Regulates breathing, heartbeat and blood pressure Brain stem

6 The Peripheral Nervous System Contains the nerves Cranial nerves carry signals to and from the brain Spinal nerves carry signals to and from the spinal cord Two components: The somatic The autonomic Somatic (voluntary) PERIPHERAL NERVOUS SYSTEM Autonomic (involuntary) Parasympathetic division (rest and digest) Sympathetic division (fight or flight) Voluntary leg muscles Involuntary heart muscle LM Figure 27.9 Peripheral Alzheimer s disease The somatic (voluntary) Carries signals to and from skeletal muscles Mainly responds to external stimuli The autonomic (involuntary) Regulates the internal environment Controls Smooth and cardiac muscles Organs and glands Most common form of dementia Neurodegeneration Entire brain regions are demolished Destroys memory and thinking skills Metabolic function of the brain Alzheimer s disease PET allows for noninvasive tests of brain function using radioactive tracers that target specific molecules Here the FDG tracer is used to measure the metabolic activity. Note the decrease in metabolic function in patients with Alzheimer's Healthy Alzheimer's Possible causes Reduced synthesis of neurotransmitter acetylcholine Dangerous buildup of amyloid protein inflammation Breakdown of myelin in brain demyelination