EDU2HBS Human Body Systems 1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin...

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EDU2HBS Human Body Systems

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

The Nervous Systems

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The Nervous System

– Is the primary coordinating and controlling system of the body

– Uses impulses to fulfill its functions

General functions include

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Divisions of the Nervous SystemAnatomical divisionsCentral nervous system (CNS)

• Body’s neural control center

Peripheral nervous system (PNS)

Consists of nerves and sensory receptors

ReceptorsEffectors

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Functional divisions– Sensory division

– Motor division

• Divided into 2 divisions

1. Somatic nervous systemVoluntary control of skeletal muscle

2. Autonomic nervous systemInvoluntary control of cardiac muscle, smooth muscle, and glands

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Nerve TissueNeurons

– Specialized to transmit neural impulses– Structural and functional units of nervous

system– Though they vary in size and shape, neurons

have many common features

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Structure of a neuron

Dendrites

Cell Body

Axon

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Synapse

• The junction across which a nerve impulse passes from an axon terminal to the dendrite of another neuron.

Threshold stimulus is needed to activate a neuron

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Steps in synaptic transmission

• An impulse travels down the axon

• When the impulse reaches the axon terminal, Ca+ ions are released.

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Steps in synaptic transmission (cont)

• The neurotransmitters alter the membrane surface to allow sodium into the dendrites

• This causes an action potential to start if threshold is reached

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Types of neuronsSensory neurons

Motor neurons• Carry impulses from CNS to effectors to

produce an action

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Protection for the Central Nervous System• Bones

– Cranial bones– Vertebrae

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Meninges: three fibrous membranes

Pia Mater

• Contain blood vessels to nourish brain and spinal cord

Arachnoid Mater

• Filled with cerebrospinal fluid

Dura Mater

• Attached to cranial bones

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The Brain

• Four major components: cerebrum, cerebellum, diencephalon, brain stem

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1. Cerebrum• Largest portion of the brain• Left and right cerebral hemispheres• Performs higher brain functions

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Hemisphere specialization– Each hemisphere performs basic functions

• Receiving sensory output• Initiating voluntary motor output

– Some functions are only performed by one hemisphere

• Left hemisphere

• Right hemisphere

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Cerebral hemisphere is divided into 4 lobes• Frontal lobe• Parietal lobe• Temporal lobe• Occipital lobe

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2. Cerebellum• Second largest brain region

• Controls posture, balance, and muscle coordination

• Damage results in loss of equilibrium, muscle coordination, and muscle tone

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3. Diencephalon• Lies between the brain stem

and midbrain• Consists of two major areas

Thalamus

relay station for sensory impulses

Hypothalamus a role in regulation of body temperature and water balance the centre for many drives and emotions (thirst, appetite, sex, pain and pleasure)

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4. Brain Stem

• About the size of a thumb and 3 inches long• Provides a pathway for spinal cord• Functions

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Spinal Cord• A continuation of the brain stem• 17 inches long

• Functions– Transmit impulses to and from brain

• Ascending (sensory) tracts• Descending (motor) tracts

– Reflex center for spinal reflexes

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Peripheral Nervous System

• Consists of nerves found outside the CNS

• Main function

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Reflexes

– Maintain homeostasis and increase chances for survival

– Reflex pathways are called reflex arcs

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Autonomic Nervous System• Consists of parts of central and peripheral

nervous systems

• Purpose – to maintain homeostasis• The ANS affects heart rate, digestion,

respiration rate, salivation, perspiration, sexual arousal

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Disorders of the Nervous System

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• Alzheimer’s disease– Characterized by progressive loss of memory,

disorientation, and mood swings– Exhibit loss of neurons in brain– Also have reduced ability to secrete acetylcholine

• Concussion– Caused by severe jarring of brain due to blow to the

head– Can be accompanied by unconsciousness, amnesia,

and confusion

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• Dyslexia– Person reverses letters or syllables in

words or words within sentences– Due to malfunctioning language center

• Fainting– Loss of consciousness due to sudden

reduction in brain blood supply– Physical or psychological causes

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• Headaches– Various causes

• Most due to dilation of blood vessels within the meninges

• Some are caused by tension in head and neck muscles

• Paralysis– Permanent loss of motor control over body

parts– Common cause is injury to CNS

EDU2HBS Human Body Systems 1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin...

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