Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Chapter 48 The Neurons Cells Communicate • Gap Junctions: communication only between adjacent cells • Hormones: distant cells but very slow & broad. • Neurons: fast & to specific cells Different types of neurons • Sensory Neurons: carry impulses from receptors to the spinal cord. • Motor Neurons: carry impulses from the spinal cord to the effectors. • Association Neurons: = interneurons, maintain connections within the spinal cord Reflex actions • Reflex actions: involuntary and usually self protective movements. • Reflex arc: the spinal cord is responsible for transmitting the response that pulls your hand away. Structure of a Neuron • Neuron: nucleated cell body and 2 kinds of threadlike extensions, dendrites and axons. • Dendrites: receive impulses from other neurons or receptors and carry impulses to the cell body. • Axon: carries impulses away from the cell body. • Synapses: small space between 2 neurons • Schwann cells: cells organized on layers that surround the axons. These cells form a structure know as myelin sheath, which insulates and protects the axon. • Nodes of Ranvier (ask Mr. Miller for the pronunciation): gaps in the myelin sheath. NEURON Nerve Impulses • Resting Neuron Na K K Na + + + + + + + + + + + + + + - + + - + + • Active Neuron + + - + + - + + - + + + + + + + + + + + + + + + + + - - - - - - - - + + + + + + + Impulse conduction • When a neuron is stimulated, its membrane become permeable to Na+. • As a result the inner surface becomes more positively charged than the outer surface. This process is called depolarization. • K+ ions diffuses out of the cell. Transmission across the synapses • Impulses are carried across a synapse by chemical messengers called neurotransmitters. • Acetylcholine • After transmission of an impulse, neurotransmitters in the synapse are destroyed by enzymes. PERIPHERAL NERVE CELLS • RECEPTORS:RECEIVE INFO FROM BOTH INTERNAL & EXTERNAL STIMULI • CONDUCTORS:TRANSMIT MESSAGES FROM RECEPTORS TO CNS • EFFECTORS: RECEIVE MESSAGES FROM CNS & CARRY THEM TO AN AREA OF THE BODY Senses: Receptors and sense organs • Mechanoreceptors: detect movement, pressure, or tension. • Photoreceptors: detect variations in light. • Chemoreceptors: detect chemicals • Thermoreceptors: respond to both internal and external heat and cold • Pain receptors: respond to tissue damage. NERVOUS SYSTEM NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM SPINAL CORD PERIPHERAL NERVOUS SYSTEM BRAIN AUTONOMIC NERVOUS SYSTEM SYMPATHETIC NERVOUS SYSTEM SCARED FRIGHTENED PARASYMPATHETIC NERVOUS SYSTEM SOMATIC NERVOUS SYSTEM BRAIN • CEREBRUM: 4 LOBES..1) FRONTAL, 2)PARIETAL, 3) OCCIPITAL, 4)TEMPORAL, THOUGHTS, CONVOLUTIONS- FOLDS • LEFT & RIGHT HEMISPHERE • CEREBELLUM: COORDINATION & BALANCE • BRAIN STEM: THE MIDBRAIN, MEDULLA and PONS PROTECTION OF BRAIN • MENINGES: THREE PROCTECTIVE LAYER THICK *DURA MATER: OUTER LAYER *ARACHNOID: MIDDLE LAYER *PIA MATER: INNER LAYER CEREBROSPINAL FLUID: FLUID CUSHION BETWEEN THE MIDDLE & INNER LAYERS Divisions of the peripheral nervous system • Somatic nervous system consists of nerves that control the voluntary movement movement of the skeletal muscles. • Automatic nervous system consists of the nerves that control involuntary actions, such as respiration and heart rate. Divisions of the Automatic NS • The sympathetic nervous system controls the stimulation of internal organs during conditions of high stress or increased activity. • The parasympathetic nervous system controls internals organs during routine conditions.