THE NERVOUS SYSTEMChapter 35

Body Organization

• Cell- basic unit of structure and function• Specialized- made for a particular function

• Tissues• Epithelial-• Connective- • Nervous• Muscle-

• Organs and organ systems

• Homeostasis- the process by which organisms keep internal conditions relatively constant despite changes in external environments

• Feedback Mechanisms—Utilized by the nervous system to help maintain homeostasis. Feedback mechanisms help to keep the body “on track”.• Positive Feedback—Ex: Blood clotting, Fever.• Negative Feedback—Ex: Blood pressure, Metabolic

“set point”.

The nervous system controls and

coordinates functions throughout the body,

enabling organisms to respond to internal

and external stimuli.

NEURONS•Nerve Cells•Units of the nervous system•Transmit electrical signals called impulses throughout the body.

3 TYPES of NEURONS• Sensory• Motor • Interneurons

IMPORTANT STRUCTURES OF NEURONS

•Cell body-•Dendrites- •Axon- •Myelin Sheath•Nodes-

“RESTING” NEURONS• Resting Potential—

The electrical charge across the cell membrane of a neuron in its “resting” state.

• Sodium (Na+) ions are actively pumped out of the cell.

• Potassium (K+) ions are pumped into the cell.

• Permeable cell membrane = Leaky K+ leaving cell

MOVING IMPULSE• A neuron remains in its resting state until it receives a stimulus large enough to start a nerve impulse.

• Action Potential—Occurs when Na+ channels open, causing sodium ions to flood into the cell.

• Impulse termination—Occurs when the sodium gates close, and K+ channels open. Returns to resting potential.

ACTION POTENTIAL

THRESHOLD POTENTIAL

• Remember—the strength of an impulse is always the same. The stimulus causing the impulse, however, may vary!

• Threshold—The potential that a stimulus must reach in order to be ‘strong’ enough to transmit an impulse. Causes action potential.

• All-or-None Principle—Either a stimulus will produce an impulse or not.

Nerve Impulse Animation• http://highered.mcgraw-hill.com/sites/0072495855/student

_view0/chapter14/animation__the_nerve_impulse.html

• http://highered.mcgraw-hill.com/olc/dl/120107/anim0013.swf

IMPULSE TRANSMISSION• Synapse• Synaptic cleft• Neurotransmitters

DIVISIONS OF THE NERVOUS SYSTEM

• Central Nervous System• Peripheral Nervous System

• Sensory Division• Motor Division

• Somatic Nervous System• Autonomic Nervous System

• Sympathetic Nervous System• Parasympathetic Nervous System

CENTRAL NERVOUS SYSTEM

THE BRAIN

• Cerebrum• Cerebellum• Brain Stem• Hypothalamus• Thalamus

THE CEREBRUM• Largest part of the human brain.• Responsible for voluntary actions; is the site for intelligence, learning, and judgment.

• 2 Hemispheres—Right and Left, each divided into lobes.

• Corpus Callosum—Band of tissue connecting the hemispheres.

• 2 Layers• Outer—Cerebral cortex, consisting of gray matter. Gray matter consists of densely packed nerve cell bodies.

• Inner—Made up of white matter. White matter consists of bundles of axons & their myelin sheaths.

• Cerebellum—2nd largest portion of the human brain, responsible for coordination and balance of muscle action.

• Brain Stem—Connects the brain to the spinal cord. Neural “switchboard” that regulates the flow of info between the brain and the body.• Blood pressure, heart rate, breathing, swallowing.

• Thalamus and Hypothalamus—Found between the brainstem and the cerebrum.• Thalamus—Receives messages from sensory receptors

throughout the body.• Hypothalamus—Recognizes sensations of hunger, thirst,

fatigue, anger, and body temperature. Coordinates nervous and endocrine systems. Located above Thalamus.

• Spinal Cord—Main communications link between the brain and the rest of the body.

• Reflex—Some reflexes are processed directly in the spinal cord. A reflex is a quick, automatic response to a stimulus.

• Reflex Arc—The pathway that an impulse travels from a sensory receptor to an effector.

ReceptorSensoryNeuroninterneuron in spinal cord →Motor NeuronEffector

PERIPHERAL NERVOUS SYSTEM

• Sensory Division of PNS—Transmits impulses from sense organs to the Central Nervous System (CNS).

• Motor Division of PNS—Transmits impulses from the CNS to muscles or glands. Subdivisions:• Somatic Nervous System—regulates activities that are under voluntary control, such as muscle movement.(but also includes reflexes)

• Autonomic Nervous System—Regulates activities that are automatic, or involuntary. Composed of Sympathetic and Parasympathetic Nervous Systems.

Sympathetic Nervous System

Extends from thoracic to lumbar vertebrae-nerves originate in spinal columnOrgan

Associated with “fight-or-flight” response-sense of danger or excitementEffect

Eye Dilates pupil

Heart Increases rate and force of contraction

Lungs Dilates bronchioles

Blood Vessels Constricts

Sweat Glands Activates sweat secretion

Digestive tract Inhibits peristalsis

Kidney Increases renin secretion

Parasympathetic Nerves• Usually related to “housekeeping” tasks, like digestion, or

decreasing heart rate• Not much outside stimulation• After response of sympathetic nerves to return to normal

after the sympathetic nerves have responded to a stressful or exciting situation