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Essentials Ch 7 Nerves

Chapter 7
The Nervous System
Functions of the Nervous System
1. Sensory input—gathering information

Sensory receptors monitor changes, called
stimuli, occurring inside and outside the body
2. Integration

Nervous system processes and interprets
sensory input and decides what action is needed
3. Motor output

A response, or effect, activates muscles or
glands
Organization of the Nervous System
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Central nervous system (CNS)
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Brain and spinal cord
Integration and command center which
interprets incoming sensory information and
issues outgoing commands
Peripheral nervous system (PNS)

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Paired spinal and cranial nerves
Carries messages to and from the spinal cord
and brain
Peripheral Nervous System:
Two Functional Divisions
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Sensory (afferent; “carrying toward”) division

Motor (efferent; “carrying away”) division

Transmits impulses from the CNS to effector
organs (muscles and glands)
Motor Division: Two Main Parts

Somatic nervous system
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Conscious control of skeletal muscles
(voluntary nervous system)
Autonomic nervous system (ANS)

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Regulates smooth muscle, cardiac muscle, and
glands (involuntary nervous system)
Divisions – the ANS is further divided down
into the sympathetic and parasympathetic
which work in opposition to each other
Histology of Nerve Tissue

Two main cell types of the nervous system:

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Neurons – excitable cells that transmit
electrical signals
Supporting cells (neuroglia) – cells that
surround and wrap neurons
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Unable to conduct nerve impulses
Never lose the ability to divide
Support
Insulate
Protect neurons
Neurons (Nerve Cells)

Neurons send electrical signals in the
body. Composed of a body, axon, and
dendrites.
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Long-lived, generally amitotic (don’t divide)
high metabolic rate (need a lot of glucose and
oxygen)
Dendrite
Cell
body
Axon
Nucleus
One
Schwann
cell
Axon
terminal
Schwann cells,
forming the myelin
sheath on axon
Nerve Cell Components


Nerve Cell Body: Contains the nucleus
Dendrites: short, tapering, branches that
receive input for the neuron and conduct
impulses toward the cell body
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Neurons may have hundreds of dendrites
Axons: Neurons have only one axon arising
from the cell body

They conduct impulses away from the cell body
Nerve Cell Components

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Axonal terminal – the branched endings of
the axon that contain vesicles with
neurotransmitters
Axonal terminals release neurotransmitters
(signaling chemicals)
Axon terminals are separated from the next
neuron by a gap called the synaptic cleft

Synapse— junction between two nerves where a
nerve impulse is transmitted
Myelin Sheath

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Whitish, fatty segmented material surrounding
most long or thick axons
Created by the Schwann cells (support cell)
It functions to:



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Protect the axon
Electrically insulate fibers from one another
Increase the speed of nerve impulse
transmission
Found only with axons, never dendrites
Nervous Tissue: Neurons

Terminology

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Nuclei—clusters of cell bodies in the CNS
Ganglia—collections of cell bodies outside the CNS
in the PNS
Tracts—bundles of nerve fibers in the CNS
Nerves—bundles of nerve fibers in the PNS
White matter—collections of myelinated fibers
(tracts)
Gray matter— unmyelinated fibers and cell bodies
Neuron Classification:
Functional



Sensory (afferent) — transmit impulses toward
the CNS
Motor (efferent) — carry impulses away from
the CNS
Interneurons (association neurons) — lie
between motor and sensory neurons in neural
pathways and shuttle signals through CNS
pathways where integration occurs. Over 99% of
neurons in the body including those in the CNS are
interneurons.
Neurons classified by function
Sensory
neuron
Spinal cord
(central nervous system)
Dendrites
Afferent
transmission
Receptors Peripheral
nervous
system
Efferent transmission
Motor neuron
To effectors
(muscles and glands)
Interneuron
(association neuron)
PNS Tracts

Spinothalamic tract (anterior/lateral)

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Anterior: crude touch and pressure
Lateral: pain and temperature
Spinocerebellar tract (golgi tendon
organs/muscle spindles)

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Proprioception
Fine touch
Neurophysiology

Electrical conditions of a resting neuron’s
membrane

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The plasma membrane at rest is inactive
(polarized)
A resting, polarized neuron’s plasma membrane is
(+) on the outside and (-) inside of the membrane


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K+ is the major positive ion inside the cell
Na+ is the major positive ion outside the cell
As long as the inside of the membrane is more
negative than the outside, the cell remains inactive
Neurophysiology

Certain stimuli can change the neuron’s
permeability to sodium ions

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Sodium channels now open, and sodium (Na+)
diffuses into the neuron
The inward rush of sodium ions changes the
polarity at that site and is called depolarization
The depolarization initiates and generates an
action potential (electrical nerve impulse).
Neurophysiology
Resting membrane is polarized.
The external face of the membrane is
slightly positive; its internal face is
slightly negative. The chief extracellular
ion is sodium (Na+), whereas the chief
intracellular ion is potassium (K+). The
membrane is relatively impermeable to
both ions.
1
[Na+ ]
[K+]
Na+
Na+
Stimulus causes local
depolarization. A stimulus changes
the permeability of a local “patch” of
the membrane, and sodium ions diffuse
rapidly into the cell. This changes the
polarity of the membrane (the inside
becomes more positive; the outside
becomes more negative) at that site.
2
Depolarization – the inside of the
membrane becomes less negative

Na+ enters the cell making the inside more
positive (Depolarization)
Repolarization – the membrane
returns to its resting potential

K+ exits the cell and internal negativity of the
resting neuron is restored (Repolarization)
Action Potential:
Role of the Na+-K+ Pump

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Initial conditions of sodium and potassium ions
are restored using ATP driven the sodiumpotassium pump.
This restores the ionic original configuration.
https://www.youtube.com/watch?
v=_bPFKDdWlCg
Synapses


A synapse is a junction that mediates information
transfer from one neuron to an effector cell.
Effector cells are either:
 another neuron
 muscle
 gland
Synapses:
Neurotransmitters

Transmission of the signal at synapses


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When the action potential reaches the axon
terminal, the electrical charge causes the release
of neurotransmitters into the synaptic cleft
The neurotransmitter molecules diffuse across
the synaptic cleft and bind to receptors on the
membrane of the next neuron
Eventually an action potential (nerve impulse)
will occur in the neuron beyond the synapse
Synaptic Cleft:
Information Transfer
BioFlix: How Synapses Work
https://www.youtube.com/watch?v=Ibzfwtdtong
© 2018 Pearson Education, Inc.
Nervous Tissue: Reflexes

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Reflexes are rapid, predictable, and
involuntary responses to stimuli
Reflexes occur over neural pathways called
reflex arcs

Two types of reflexes:
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Somatic reflexes stimulate the skeletal muscles
Autonomic reflexes regulate smooth muscles,
the heart, and glands
Central Nervous System (CNS)

Brain regions
1. Paired (left and right) Cerebral
hemispheres

Lobes are named for the cranial bones that lie
over them
2. Diencephalon
3. Brain stem
4. Cerebellum
Regions of the Brain
Functional Anatomy of the Brain

Three main regions of cerebral hemisphere
1.
2.
3.
Cortex is superficial gray matter
White matter
Basal nuclei are deep pockets of gray matter
Left lateral view of the brain
Frontal lobe
Parietal lobe
Occipital lobe
Temporal lobe
Cerebellum
Cerebral cortex
(gray matter)
Medulla oblongata
Spinal
cord
Cerebral
white
matter
Functional Anatomy of the Brain:
Cerebral Cortex (Gray Matter)

Primary motor area (frontal lobe)
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Primary somatic sensory area (parietal lobe)
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Allows us to consciously move skeletal muscles
Receives impulses from the body’s sensory
receptors
Cerebral areas involved in special senses
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Visual area (occipital lobe)
Auditory area (temporal lobe)
Olfactory area (temporal lobe)
Primary motor area
Primary somatic sensory
area
Gustatory area (taste)
• Working memory
and judgment
• Problem
solving
• Language
comprehension
Broca’s area
(motor speech)
Olfactory
area
Visual area
Auditory area
Sensory and Motor Cortex
Anatomy of the Brain:
Diencephalon

Made of three structures:
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1. Thalamus
2. Hypothalamus
3. Epithalamus
Sits on top of the brain stem
Enclosed by the cerebral hemispheres
Important autonomic nervous system center
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Regulates body temperature
Regulates water balance
Regulates metabolism
Cerebral hemisphere
Corpus callosum
Occipital lobe
Thalamus
Pineal gland
Hypothalamus
Pituitary gland
Medulla oblongata
Spinal cord
Cerebellum
Anatomy of the Brain:
Brain Stem
Anatomy of the Brain:
Cerebellum
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Controls balance
Provides precise timing for skeletal muscle
activity and coordination of body
movements
Spinal Cord
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Extends from the foramen magnum of the
skull to the first or second lumbar vertebra
Provides a two-way conduction pathway to
and from the brain
31 pairs of spinal nerves arise from the
spinal cord
Cervical
enlargement
Cervical
spinal nerves
C8
Thoracic
spinal nerves
Lumbar
enlargement
T12
End of spinal cord
Lumbar
spinal nerves
L5
S1
S5
Sacral
spinal nerves
Peripheral Nervous System
(PNS)
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PNS consists of nerves and ganglia outside the
CNS
Nerves are bundles of neurons found outside
the CNS
Mixed nerves
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Sensory (afferent) nerves
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Contain both sensory and motor fibers
Carry impulses toward the CNS
Motor (efferent) nerves

Carry impulses away from the CNS
Axon
Myelin sheath
Endoneurium
Perineurium
Epineurium
Fascicle
Blood
vessels
Cranial Nerves
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12 pairs of nerves that arise from the brain
and serve mostly the head and neck
Only the pair of vagus nerves (X) extends
to thoracic and abdominal cavities
I. Olfactory – smell
II. Optic – vision
VIII. Vestibulocochlear – Hearing and balance
Testing Cranial Nerves
https://www.youtube.com/watch?v=jdRJqbB0ZyA
Spinal Nerves
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Spinal nerves
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31 pairs
Named for the region of the spinal cord from which they
arise
Plexus—networks of nerves serving motor and
sensory needs of the limbs
Four plexuses
1.
2.
3.
4.
Cervical
Brachial
Lumbar
Sacral
Cervical
nerves
Thoracic
nerves
Lumbar
nerves
Sacral
nerves
C1
2
3
4
5
6
7
8*
T1
2
3
4
5
6
7
8
9
10
11
12
L1
2
3
4
Cervical plexus
(C1 – C5)
Brachial plexus
(C5 – C8; T1)
No plexus
formed
(intercostal
nerves)
(T2 – T12)
Lumbar plexus
(L1 – L4)
5
S1
2
3
4
Sacral plexus
(L4 – L5; S1 – S4)
Axillary nerve
Humerus
Radial
nerve
Musculocutaneous
nerve
Ulna
Radius
Ulnar nerve
Median
nerve
(a) Brachial plexus,
anterior view
Femoral nerve
Femur
(b) Lumbar plexus,
anterior view
Sciatic nerve
Common fibular
nerve
Tibial nerve
(c) Sacral plexus, posterior view
Autonomic Nervous System

Motor subdivision of the PNS
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Consists only of motor nerves
Controls the body automatically (and is also
known as the involuntary nervous system)
Regulates cardiac and smooth muscles and
glands
Has two arms
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Sympathetic division
Parasympathetic division
Autonomic Functioning:
Sympathetic

Sympathetic—“fight or flight” division
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Response to unusual stimulus when
emotionally or physically stressed or
threatened
Takes over to increase activities
Remember as the “E” division
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Exercise
Excitement
Emergency
Embarrassment
Autonomic Functioning:
Parasympathetic
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Parasympathetic—“housekeeping”
activites
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“Rest-and-digest” system
Conserves energy
Maintains daily necessary body functions
Remember as the “D” division
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Digestion
Defecation
Diuresis
Parasympathetic vs.
Sympathetic
https://www.youtube.com/watch?v=7wFX9Wn70eM
Kahoot Chapter Review

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