The Nervous System

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The Nervous System
Neurons (Nerve Cells) – Cells that are
specialized to carry messages throughout the
body
Structure of a Neuron
 Cell body – rounded area with two types
of extensions
 Dendrites – receive messages
 Axons – send messages
Three Major Groups of Neurons
 Sensory neurons – carry impulses from
the peripheral body to the brain/spinal
cord
 Interneurons – transmit impulses from
one part of the brain to another
 Motor neurons – carry nerve impulses
out of the brain/spinal cord
Neuroglial Cells – Supporting cells of the
nervous system– fill spaces – provides
structure – produces myelin (lipoprotein)
Central Nervous System (CNS)
 Brain/Spinal Cord
Peripheral Nervous System (PNS)
 Nerves that connect the CNS to other
body parts
Functions of the Nervous System
 Sensory Function – convert information
into nerve impulses
 Motor Function – impulses are carried to
effectors (muscles or glands)
o Consciously controlled motor
neurons – somatic nervous system
o Involuntarily controlled motor
neurons – autonomic nervous system
Nerve Impulse
 Resting Potential – nerve cell is resting
and is polarized (outside of the cell
membrane is in excess of NA+ ions –
inside has excess K+ - inside is negative
compared to outside)
 Threshold stimulus is received
 Na+ channels open
 Na+ depolarize the inside of the cell
 K+ channels open
 K+ moves out repolarizing the cell
 Causes a bioelectric current that
stimulates adjacent portions of the
membrane
 Wave of action potential travels the
length of the axon as a nerve impulse
Nerve impulses travel from neuron to
neuron along nerve pathways – junction
between two neurons is called a synapse
 Impulse travels across the synaptic cleft
by releasing neurotransmitters
Reflex Arcs
 Reflexes – automatic subconscious
responses to changes within or outside
the body
 Involve a small number of neurons
Brain – 3 Major Portions
 Cerebrum
 Diencephalon
 Cerebellum
Structure of the Cerebrum
 2 Large masses – left and right cerebral
hemispheres
 corpus callosum – deep bridge of
nerve fibers that connects the two
 Ridges (convolutions) separated by
grooves (shallow grooves – sulcus, deep
grooves – fissures)
Lobes of the Cerebral Hemispheres
 Frontal Lobe
 Parietal Lobe
 Temporal Lobe
 Occipital Lobe
 Insula – deep within the sulcus –
covered by frontal, parietal, and
temporal lobes
 Cerebral cortex – thin layer of gray
matter (lacks myelin – appears gray)
forms the outermost portion of the
cerebrum
Functions of the Cerebrum
 Interpreting sensory impulses
 Initiating voluntary muscular
movements
 Stores, information of memory and
utilizes it to reason
 Responsible for intelligence and
personality
Diencephalon – located between the cerebral
hemispheres and above the midbrain
 Thalamus – central relay station for
incoming sensory impulses
 Hypothalamus – maintains homeostasis
 Limbic system – produces emotions and
modifies behavior
Brain Stem – nervous tissue that connects
the cerebrum to the spinal cord
Parts of the Brain Stem
 Midbrain – contains reflex centers
associated with eye and head movements
 Pons – transmits impulses between the
cerebrum and other parts of the nervous
system – contains centers that help
regulate the rate and depth of breath
 Medulla oblongata – transmits all
ascending and descending impulses and
contains several vital and nonvital reflex
centers
Cerebellum – large mass of tissue located
below the occipital lobes of the cerebrum
and posterior to the pons and medulla
oblongata
 2 hemispheres
 functions primarily as a reflex center for
integrating sensory information required
in the coordination of skeletal muscle
movements and maintenance of
equilibrium
Peripheral Nervous System
 12 pairs of cranial nerves that connect
the brain to parts in the head, neck, and
trunk
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