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The Nervous System Ch. 12-17 The Nervous System Introduction Composed of Brain Spinal Cord Nerves 2 Major Subdivisions CNS (Central Nervous System) Brain, Spinal Cord PNS (Peripheral Nervous System) Cranial and Spinal Nerves 2 Major Subdivisions Afferent incoming pathways Efferent Outgoing pathways Neurons Remember neuron structure: The Cell Body or Soma Contains a nucleus surrounded by cytoplasm along with all other organelles found within a cell The Dendrites Extensions from Cell Body/Soma Receives information The Axon Single, long extension from Cell Body/Soma Branch out into telodendria and end at synaptic/axon terminals Structure of a Neuron The Synapse Each synaptic/axon terminal is part of a synapse Site where the neuron communicates with another cell Presynaptic Cell: sends the message (usually a neuron) Postsynaptic Cell: receives the message (any cell type) After a series of electrical signals is transmitted through the neuron, the axon/synaptic terminals release chemicals or neurotransmitters to the dendrite of another cell to continue the message Synaptic Cleft Synapse Neuron Video http://www.youtube.com/watch?v=r71Ro Ikftd4 Neuroglia Higher quantity and variation in CNS than PNS Central Nervous System 1. Ependymal Cells 2. Astrocytes 3. Microglia 4. Oligodendrocytes Peripheral Nervous System 1. Schwann Cells 2. Satellite Cells CNS Neuroglia Ependymal Cells Line ventricles in the brain and spinal cord Aid in producing, circulating and monitoring of cerebrospinal fluid Microglia Removes cell debris, wastes, and pathogens by phagocytosis CNS Neuroglia Astrocytes Provide structural support Regulate ion, nutrient, and dissolved gas concentrations Absorb and recycle neurotransmitters Form scar tissue after injury Oligodendrocytes Myelinate axons Provide structural framework PNS Neuroglia Schwann Cells Surround all axons Responsible for myelination Participate in repair process after injury Satellite Cells Surround neuron cell bodies Regulate gas, nutrient, and neurontransmitter levels Synaptic Activity Messages move from 1 location to another in the form of action potentials along neurons Also known as nerve impulses Messages move across the synapse Can be electrical Can be chemical (use of neurotransmitter) Electrical Synapses Presynaptic and postsynaptic cell membranes are locked together Local electrical currents and directly transferred from cell to cell = very rapid electrical impulse Efficient action potential transfer from cell to cell Chemical Synapses Presynaptic and postsynaptic cell membranes are NOT locked together Message not guaranteed to be transferred to the next cell dependent on the amount of neurotransmitters released Different neurotransmitters: Acetocholyne: found at neuromuscular junction Norepinephrine: excitatory effect, adrenaline Dopamine: Parkinson’s disease (rigidity of muscles) Serotonin: attention, emotion, responsible for depression GABA: reduce anxiety Spinal Cord and Spinal Nerves Chapter 13 Spinal Cord Anatomy Posterior/Anterior/Lateral Anterior Horn of Gray matter Median Fissure Posterior Median Sulcus Spinal Nerve (Posterior/Anterior Roots) Spinal Ganglion Spinal Cord Anatomy Adult – 18 inches in length Only reaches down to L1-L2 Spinal Meninges: specialized membranes that surround the spinal cord Dura Mater Arachnoid Pia Mater Bacterial or vial infections of the Meninges Meningitis Meninges Dura Mater Tough, fibrous outermost layer Collagen fibers Covered with blood vessels and adipose tissue Epidural Space Pia Mater Meshwork of connective tissue Dense area of vessels Arachnoid Filled with cerebrospinal fluid (SPF)—shock absorber Spinal tap Nerve Plexuses Complex 1. interwoven network of nerves Plexus. Cervical Plexus 1. 2. Brachial Plexus 1. 3. C5-T1 (muscles of pectoral girdle and upper limb) Lumbar Plexus 1. 4. C1-C5 (muscles of neck, thoracic cavity) T12-L4 Sacral Plexus 1. L4-S4 Day 2 Refluxes Chapter 13 Reflexes Rapid automatic responses to a specific stimuli made by a receptor Preserve homeostasis Rapid adjustments The Reflex Arc: wiring of a single reflex Beings at the receptor Ends at peripheral effector (ex: muscle fiber) Reflexes Sensory Receptors Proprioreceptors: provide info about body position and muscle control Vestibular Receptors: provide a sense of equilibrium Cutaneous Receptors: touch, pressure, heat and cold Photoreceptors: respond to light Chemoreceptors: respond to taste Nocioreceptors: pain receptors Reflexes 1. 2. 3. 4. 5. Arrival of a stimulus and activation of receptor (pain) Activation of a Sensory Neuron (action potential along axons of neurons spinal cord) Information Processing (neurotransmitter released and sensation related to brain) Activation of Motor Neuron (axons carry action potential back towards the origin of pain) Response of Peripheral Effector (release of neurotransmitter to skeletal muscle fiber contraction pulls hand away from pain) http://www.youtube.com/watch?v=wLrhYzdbbpE Reflexes Receptor Density More dense the receptors = more “sensitive” the area Upon stimulation… Phasic: receptors respond with an initial burst of action potentials and rapidly decrease, even though stimulus continues Tonic: receptors firing at a constant rate as long as the stimulus is applied 1. Lab on reflexes The Brain and Cranial Nerves Chapter 14 Human Brain Contains 98% of neural tissue Weighs about 3 lbs Covered by a neural cortex (superficial layer of gray matter Main Areas Cerebrum Cerebellum Diencephalon Brain Stem Cerebrum Largest portion of the brain 2 hemispheres Controls thoughts, sensations, intellect, memory, and complex movements Lobes (correspond with cranial bones) Frontal Parietal Occipital Temporal Cerebrum Landmarks Longitudinal fissure (separates the 2 hemispheres) Central Sulcus (separates the frontal from parietal lobes) Lateral Sulcus (separates the frontal from temporal) Parieto-occipital sulcus (separates the parietal from the occipital) White Matter Dense region of axons Cerebrum Motor and Sensory Areas Frontal Lobe = Voluntary control of skeletal muscles Parietal Lobe = conscious perception of touch, pressure, vibration, pain, temperature, and taste Occipital Lobe = conscious perception of visual stimuli Temporal Lobe = conscious perception of auditory and olfactory stimuli, speech All Lobes = Integration and processing of sensory data and motor activities stop Cerebellum 2nd Largest portion of the brain 2 hemispheres 2 Primary Functions Adjusting Postural muscles of the body Programming and fine-tuning movements Other Major Regions of the Brain Diencephalon: Thalamus: relay and processing centers for sensory information Hypothalamus: emotions, autonomic function, hormone production, body temp regulation Other Major Regions of the Brain Brain Stem :link between cerebrum and brain stem Mesencephalon: aka “midbrain”; visual and auditory information Pons: sleep & respiration Medulla Oblongata: regulate heart rate, blood pressure, digestion Ventricles of the Brain Chambers fluid (CSF) filled with cerebrospinal Lateral Ventricles (2 in each hemisphere of cerebrum) Third Ventricle Interventricular Foramen (connection between the lateral ventricles and third ventricle) Cerebral Aqueduct (connection between the third ventricle and fourth ventricle) Fourth Ventricle Narrows cord and opens into the spinal Protection and Support Protected 1. 2. by Bones of cranium: mechanical protection (car) Cranial Meninges: anchor (seat belt) Dura Mater: outer layer Arachnoid: middle layer Pia Mater: surface of brain 3. Cerebrospinal Fluid: cushions against shocks/jolts (air bag) Cerebrospinal Fluid (CSF) Function: Cushion Support Transport nutrients/chemical messengers/waste products Formation: Choroid plexus (in all ventricles): specialized cells that produce CSF Blood Supply to the Brain Brain requires a tremendous amount of blood Receives 15-20% of blood pumped by heart Interruption unconsciousness/irreversible brain damage Dependent on constant supply of oxygen & glucose Receives blood through arteries Hydrocephalus Condition with infants Prior to fusion of cranial bones Excess CSF (due to blockage or constriction of the meninges)causes the skull to enlarge Infants suffer some degree of mental retardation Cranial Nerves Part of the PNS Connected to the brain and branch out 12 of them Attaches the brain near a sensory or motor neuron 2 of each Cranial Nerves 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. Olfactory Nerves smell Optic Nerves Vision Oculomotor Nerves Eye Movements Trochlear Nerves Eye movements Trigeminal Nerves Sensory/Motor to face Abducens Nerves Motor eye movements Facial Nerves Sensory/Motor to face Vestibulocochlear Nerves balance/equilibrium and hearing Glossopharyngeal Nerves Sensory/Motor to head and neck Vagus Nerves Sensory/Motor to thorax and abdomen Accessory Nerves Motor to muscles of neck and upper back Hypoglossal Nerves Motor for tongue movements “Oh, once one takes the anatomy final, very good vacations are heavenly” Sleep Conscious/Unconscious Conscious = state of awareness of external stimuli Unconscious = number of conditions, deep, unresponsive state drifting into sleep Levels of Sleep 2 1. levels, patterns of brain activity Slow wave sleep Deep sleep/non-REM sleep Entire body relaxed Cerebral cortex activity at minimum Heart rate, blood pressure, respiratory rate, energy utilization decline by 30% 2. Rapid Eye Movement (REM sleep) Active dreaming Changes in blood pressure/respiratory rate Muscle tone decreases Neurons controlling eye muscles stop regulation = eyes move rapidly as dream events unfold Sleeping Cycles REM and Deep sleep alternate throughout the night Starts with Deep sleep = 1.5 hours REM last on average 5 minutes Determined by an EEG Electroencephalogram: graphic record of the electrical activities of the brain Alzheimer’s Disease Loss of cerebral functions Symptoms appear around 50-60 years old Can affect younger individuals but is rare Currently affects 2 million ppl in USA 100,000 deaths each year Chromosome 14, 19, and 21 Majority of Downs Syndrome develop it (21) Composed of: Brain Spinal Cord Nerves Sense of smell activity Sense of smell options Cinnamon Cherry Orange Baby Lemon Rootbeer Strawberry Grapes Peppermint powder Rose Sense of Smell Key 1. Baby 6. Cherry powder 7. Root beer 2. Cinnamon 8. Peppermint 3. Rose 9. Orange 4. Lemon 10.Grape 5. Strawberry Action Potential = The membrane potential of a neuron that is conducting an impulse (nerve impulse) Action potential is an all-or-none response Resting membrane potential (RMP) at -70mV. Na+ on outside and K+ on inside of cell Stimulus at dendrites triggers Na+ channels to open, causing local depolarization. If the opening is sufficient to drive the interior potential from -70 mV up to -55 mV, the process of depolarization continues. As depolarization reaches threshold of -55mV, the action potential is triggered and Na+ rushes into cell until membrane potential reaches +30mV on action potential Propagation of the action potential at 100 m/sec (which is 225 mph) Repolarization occurs with K+ exiting the cell to return to -70mV RMP Return of ions (Na+ and K+) to their extracellular and intracellular sites by the sodium potassium (Na+K+) pump Continues until RMP is met Action Potential Video Video 2