GENERAL PRESENTATION SPECIAL SENSES 1

Topics: Nervous system, Neuron, Action potential Pages: 22 (839 words) Published: January 22, 2015
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

12-2

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

12-3

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

12-4

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)

12-5

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

– Visceral motor division (autonomic nervous system)—carries signals to glands, cardiac and smooth muscle
• Its involuntary responses are visceral reflexes

12-6

Overview of the Nervous System
• Visceral motor division (autonomic nervous system)
– Sympathetic division
• Tends to arouse body for action
• Accelerating heart beat and respiration, while inhibiting digestive and urinary systems

– Parasympathetic division
• Tends to have calming effect
• Slows heart rate and breathing
• Stimulates digestive and urinary systems

12-7

Subdivisions of the Nervous System

12-8

Figure 12.1

Subdivisions of the Nervous System
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Central nervous system

Brain

Peripheral nervous system

Spinal
cord

Visceral
sensory
division

Sensory
division

Somatic
sensory
division

Figure 12.2
12-9

Motor
division

Visceral
motor
division

Sympathetic
division

Somatic
motor
division

Parasympathetic
division

Functional Classes of Neurons
• Sensory (afferent) neurons
– Detect stimuli and transmit information about them toward the CNS

• Interneurons (association neurons)
– Lie entirely within CNS connecting motor and sensory
pathways (about 90% of all neurons)
– Receive signals from many neurons and carry out integrative functions (make decisions on responses)

• Motor (efferent) neuron
– Send signals out to muscles and gland cells (the effectors)

12-10

Classes of Neurons
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Peripheral nervous system

Central nervous system

1 Sensory (afferent)
neurons conduct
signals from receptors
to the CNS.

3 Motor (efferent)
neurons conduct
signals from the CNS
to effectors such as
muscles and glands.

2 Interneurons
(association
neurons) are
confined to
the CNS....
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