GENERAL PRESENTATION SPECIAL SENSES 1

SPECIAL SENSES
GENERAL PRESENTATION

Overview of the Nervous System
• Endocrine and nervous systems maintain internal coordination – Endocrine system: communicates by means of chemical messengers (hormones) secreted into to the blood
– Nervous system: employs electrical and chemical means to send messages from cell to cell

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Overview of the Nervous System
• Nervous system carries out its task in three basic steps
• Sense organs receive information about changes in the body and external environment, and transmit coded messages to the brain and spinal cord (CNS: central nervous system)
• CNS processes this information, relates it to past experiences, and determines appropriate response
• CNS issues commands to muscles and gland cells to carry out such a response

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Overview of the Nervous System
• Two major subdivisions of nervous system
– Central nervous system (CNS)
• Brain and spinal cord enclosed by cranium and vertebral column

– Peripheral nervous system (PNS)
• All the nervous system except the brain and spinal cord; composed of nerves and ganglia
• Nerve—a bundle of nerve fibers (axons) wrapped in fibrous connective tissue
• Ganglion—a knot-like swelling in a nerve where neuron cell bodies are concentrated

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Overview of the Nervous System
• Peripheral nervous system contains sensory and motor divisions each with somatic and visceral subdivisions
– Sensory (afferent) division: carries signals from receptors to
CNS
• Somatic sensory division: carries signals from receptors in the skin, muscles, bones, and joints
• Visceral sensory division: carries signals from the viscera (heart, lungs, stomach, and urinary bladder)

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Overview of the Nervous System
• Motor (efferent) division—carries signals from CNS to effectors (glands and muscles that carry out the body’s response) – Somatic motor division: carries signals to skeletal muscles
• Output produces muscular contraction as well as somatic reflexes—involuntary muscle contractions

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