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Nervous System = communication conduit b/w brain and body Because neurons do not regenerate, spinal cord injuries can result in: a) paraplegia = paralysis of lower half of body b) quadriplegia = paralysis from neck down Neuron = nerve cell Three Main Regions of a Neuron: a) dendrites = receive impulses from other neurons & conduct them to cell body b) cell body = contains nucleus/organelles c) axon = carries impulses from cell body to other neurons & muscles Neuron Sketch (see textbook) Three Types of Neurons: a) sensory neurons = send impulses from receptors in skin & sense organs to interneurons b) interneurons = found in CNS – take impulse from sensory neuron & transmit to motor neuron c) motor neurons = carry impulse away from CNS to a gland or muscle, which results in a response Reflex Arc = nerve pathway that consists of a sensory neuron, an interneuron, and a motor neuron Nerve Impulse = electrical charge traveling length of a neuron (results from a stimulus – ex: touch) Neuron At Rest: There are more Na+ ions outside of neuron than inside, more K+ ions inside than out. Negatively charged proteins in neuron act as a Na+/K+ pump – working to counteract diffusion. Pumps Na+ out & K+ in. For every 2 K+ pumped into neuron, three Na+ are pumped out. This creates unequal distribution of (+) charged ions, resulting in a (+) charge outside neuron and a (-) charge inside neuron. Action Potential = another name for nerve impulse Threshold = minimum stimulus to cause an action potential When a stimulus reaches threshold, channels in plasma membrane open. Na+ rush into neuron’s cytoplasm through these channels. This causes a temporary reversal in electrical charge. Inside is now (+). This causes other channels to open. K+ leaves cell through these channels, restoring (+) charge outside of cell. This change in charge moves like a wave along the length of the axon. Speed Of An Action Potential: Some axons have myelin sheath (insulating layer) Myelin sheath has gaps (nodes of Ranvier) along axon Na+/K+ cannot diffuse through myelin but they can reach plasma membrane at these nodes This allows action potential to jump from node to node, increasing speed of impulse as it travels length of axon. Some neurons have myelin, some do not Neurons with myelin carry impulses associated with sharp pain. Neurons that lack myelin carry impulses associated with dull, throbbing pain. Action potential in these neurons travels much more slowly than they do in neurons with myelin. Synapse = small gap between axon of 1 neuron & dendrite of another neuron. When an action potential reaches the end of an axon, vesicles (small sacs) carrying neurotransmitters fuse with plasma membrane and release neurotransmitter by exocytosis. When a motor neuron synapses with a muscle cell, the released neurotransmitter crosses synapse and causes muscle to contract. Neutrotransmitter = chemical that diffuses across synapse and binds to receptors on the dendrite of a neighboring neuron. This causes channels to open up on the neighboring cell and creates a new action potential. Two most common neurotransmitters in human body: acetylcholine, epinephrine Two Major Divisions of Nervous System: 1) Central Nervous System (CNS) 2) Peripheral Nervous System (PNS) CNS = brain & spinal cord PNS = sensory neurons & motor neurons (carry info to and from CNS) CNS: made up mainly of interneurons. CNS relays messages, processes info., and analyzes responses Brain = control center of body 100 billion + neurons major sections (cerebrum, cerebellum, brain stem) Cerebrum = largest part of brain divided into two hemispheres two hemispheres connected by bundle of nerves cerebrum carries out thought processes involved with learning, memory, language, speech, voluntary body movements, & sensory perception. Folds/grooves increase surface area – allowing more complicated thought processes. Cerebellum = located at back of brain controls balance, posture, and coordination controls smooth & coordinated movement of skeletal muscles and is involved with motor skills (ex: riding bike) Brain Stem = connects brain to spinal cord Two regions of brain stem: Medulla oblongata = relays signals b/w brain & spinal cord Controls breathing, heart rate, BP Pons = relays signals b/w cerebrum & cerebellum, also helps control breathing rate Hypothalamus = located b/w brain stem & cerebrum maintaining homeostasis regulates body temp, thirst, appetite, and water balance. Partially regulates BP, sleep, aggression, fear, & sexual behavior. Spinal Cord: nerve column extending from brain to lower back protected by vertebrae spinal nerves extend from spinal cord to parts of body Nerve = bundle of neurons 12 cranial nerves = lead to and from brain 31 spinal nerves = lead to and from spinal cord Peripheral Nervous System (PNS): all neurons not part of CNS including sensory neurons & motor neurons classified as part of somatic nervous system or autonomic nervous system Somatic Nervous System (Voluntary) relays info. from sensory receptors to CNS & from CNS to skeletal muscle Autonomic Nervous System (Involuntary) (not under conscious control) carries impulses from CNS to internal organs (ex: heart) fight or flight response ex: scary nightmare – heart rate quickens Two Branches of Autonomic Nervous System: Sympathetic Nervous System (active in stressful times when heart rate/breathing rate increase) Parasympathetic Nervous System (most active when body is relaxed, counterbalances effects of sympathetic nervous system and restores body to a resting state after a stressful situation)