The Nervous System

Organization of the Nervous SystemStructural Classification• Central Nervous System (CNS): Consists of the brain and spinal cord• Peripheral Nervous System (PNS): Consists of nerves that connect the CNS to the rest of the bodyFunctional Classification• Sensory (Afferent) Division: Carries impulses to the CNS from nerve endings• Motor (Efferent) Division: Carries impulses from the CNS to nerve endings• Somatic Nervous System: Controls skeletal muscles; voluntary• Autonomic Nervous System (ANS): Controls "automatic" activities like blood pressure and heart rate; involuntaryNervous Tissue: Structure and FunctionNeurons• Neuron: Excitable impulse-conducting cell• Cell Body: Control center of neuron containing the nucleus• Dendrite: Receives signals and transmits them to the cell body• Axon: Conducts impulses away from the cell body• Axon Terminal: End of axon containing synaptic knob where neurotransmitters are released• Synaptic Cleft: Narrow gap between neurons where neurotransmitters travel• Myelin: Insulating layer around axons; formed by Schwann cells in PNS and oligodendrocytes in CNS• Nodes of Ranvier: Sites of ion exchange during nerve impulse• White Matter: Consists of myelinated axons• Grey Matter: Contains nerve cell bodies and dendritesNeuron Types• Interneuron: Receives and processes information, stores and retrieves it, makes decisions on how to respond• Efferent Neuron: Issues outgoing signals, sends to muscles or gland cells• Afferent Neuron: Responds to stimuli, generates signals, carries to spinal cord or brainNerve Physiology• Irritability: Ability to respond to stimuli• Conductivity: Ability to transmit impulses• Action Potential: Electrical signal that travels along neurons• Depolarization: Initial event when stimulus causes sodium ions to enter the cell• Repolarization: Return to resting state• Synapse: Process where neurotransmitters are released from one neuron to affect anotherReflex Arc• Purpose is to protect the body• Involves sensory input, processing, and motor outputCentral Nervous SystemBrain AnatomyCerebral Hemispheres• Consists of gyri (thick ridges), sulci (shallow grooves), and fissures (deep grooves)• Connected by corpus callosum, which allows communication between left and right hemispheres• Central sulcus separates primary motor cortex from primary sensory cortexLobes and Functions• Frontal Lobe: Voluntary movements, memory, emotion, social judgment, decisions, reasoning• Parietal Lobe: Bodily sensations (touch, temperature, pressure, pain)• Temporal Lobe: Hearing, smell, learning, memory, emotional behavior• Occipital Lobe: Analyzing and interpreting visual information• Broca's Area: Associated with speech and articulationDiencephalon• Thalamus: Connection between limbic system and other parts of brain• Hypothalamus: Regulates body temperature, hunger, thirst, and other homeostatic functions• Epithalamus: Includes pineal gland; regulates circadian rhythms through melatonin secretion• Limbic System: Connects hypothalamus with hippocampus; involved in emotionsBrain Stem• Midbrain: Connects forebrain to hindbrain• Pons: Relays signals to and from different parts of the brain; several cranial nerves originate here• Medulla Oblongata: Controls vital functions like breathing and heart rateCerebellum• Coordinates movement and balanceProtection of the CNSMeninges (from outside to inside)• Dura Mater: Tough outer layer; epidural space contains fat, blood vessels, and connective tissue• Arachnoid Mater: Middle layer resembling a web• Pia Mater: Innermost layer; clings to surface of spinal cord and brain; contains cerebrospinal fluidCerebrospinal Fluid (CSF)• Contains water, proteins, electrolytes, glucose, neurotransmitters, vitamins• Flows through ventricles (lateral ventricles, third ventricle, fourth ventricle)• Created by choroid plexus• Functions to cushion and protect the brainBlood-Brain Barrier• Protects brain tissue by preventing harmful substances from enteringSpinal Cord• Carries information from body to brain and vice versa• Contains both gray matter (cell bodies) and white matter (myelinated axons)Peripheral Nervous SystemNerve Types• Sensory Nerve: Carries information from body to brain and spinal cord• Motor Nerve: Carries commands from brain to other parts of body• Mixed Nerve: Contains both motor and sensory fibersCranial Nerves1. Olfactory (I): Sensory - smell, olfactory bulbs above nasal cavity2. Optic (II): Sensory - vision3. Oculomotor (III): Motor - eyelid and eyeball movement, pupil constriction4. Trochlear (IV): Motor - eyelid and eyeball movement5. Trigeminal (V): Mixed - sensation in face and motor functions for chewing6. Abducens (VI): Motor - eyelid and eyeball movement7. Facial (VII): Mixed - taste, facial expression, tears, saliva8. Vestibulocochlear (VIII): Sensory - hearing and balance9. Glossopharyngeal (IX): Mixed - taste and throat functions10. Vagus (X): Mixed - heart, lung, digestive, urinary functions11. Accessory (XI): Motor - neck and shoulder movements12. Hypoglossal (XII): Motor - tongue movementSpinal Nerves• Cervical: C1-C8• Thoracic: T1-T12• Lumbar: L1-L5• Sacral: S1-S5• Coccygeal: Co1Autonomic Nervous SystemParasympathetic Division ("Rest and Digest")• Decreases heart rate• Decreases respiratory rate• Increases digestion• Contracts bladder, relaxes sphincters• Dilates blood vessels to increase blood flow• Primary neurotransmitter: AcetylcholineSympathetic Division ("Fight or Flight")• Increases heart rate• Increases respiratory rate• Decreases digestion• Constricts blood vessels to decrease blood flow• Primary neurotransmitters: Norepinephrine/epinephrine