Download Ch. 7 - Nervous System

Chapter 7
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The nervous system allows the body to
detect, interpret and respond to stimuli.
◦ A stimulus is any change in the external or internal
environment.
Functions of the Nervous System
1. Sensory input
 To monitor changes occurring inside and outside the
body using sensory receptors
2. Integration
 To process and interpret sensory input
3. Motor output
 To produce a response, if needed, that activates
muscles or glands (effectors)
Organization of the Nervous
System
• Two main divisions:
• Central nervous system
(CNS)
• Brain
• Spinal cord
• Peripheral nervous
system (PNS)
• Nerves outside the
brain and spinal cord
Organization of the Nervous System
•
Nervous tissue is made up of neuroglial
(supporting ) cells and neurons.
• Neuroglial cells outnumber neurons.
• Neuroglial cells do not conduct impulses; neurons do.
• Neuroglial cells generally support, insulate and protect
delicate neurons.
• Neuroglial cells are capable of dividing; neurons are
not.
Supporting Cells
Neurons
•
Neurons = nerve cells
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Specialized to transmit messages (impulses)
Major regions of neurons:
•
Cell body – nucleus and metabolic center of the cell
•
Processes – fibers that extend from the cell body
•
Dendrites – carry impulses towards the cell body
•
Axon – carries impulse away from the cell body
Neurons
Neurons
 Myelin sheath – fatty material
surrounding axons produced
by Schwann cells
 Insulates axons
 Speeds up transmission
Classification of Neurons
 Sensory (afferent) neurons
 Carry impulses from sensory receptors to the CNS
 Motor (efferent) neurons
 Carry impulses from the CNS to muscles or glands
(effectors)
 Interneurons (associative neurons)
 Connect sensory and motor neurons
Classification of Neurons
The Nerve Impulse
 The plasma membrane at rest is polarized (resting
potential)
 Fewer positive ions are inside the cell than outside the
cell
 Active transport by the sodium-potassium pump
maintains this polarity
Starting the Nerve Impulse
• A stimulus depolarizes the
neuron’s membrane
• Sodium ions (Na+) rush
inside the membrane
• This initiates an impulse
(action potential) in the
neuron
Continuing the Nerve Impulse
 The impulse continues to
move toward the cell body
 Potassium ions rush out of
the neuron which repolarizes
the membrane
 The sodium-potassium pump
then establishes the original
polarity
The Threshold
 A minimum stimulus (threshold) is needed to start an
impulse
 If the threshold is met, a nerve impulse starts, and
continues over the entire axon (all or none response)
 Impulses travel faster when fibers have a myelin sheath
Neuron to Neuron Communication
• Neurons do not touch each other because of a gap
called the synapse.
• Impulses cross the synapse with the help of chemicals
called neurotransmitters.
• Neurotransmitters released from the axon terminal
diffuse across the synapse
• The dendrite of the next neuron has receptors that are
stimulated by the neurotransmitter
• An action potential (impulse) is started
Neuron to Neuron Communication
The Central Nervous System
 Brain and spinal cord
Regions of the Brain
 Cerebral
hemispheres
 Diencephalon
 Brain stem
 Cerebellum
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Cerebrum
◦ Voluntary activities (motor initiation), intelligence,
learning, judgment, sensory interpretation
◦ Two hemispheres connected by the corpus
callosum
 Right hemisphere controls the left side of the body and
visa-versa
◦ Deep folds and grooves increase surface area
 Gray matter – outer layer of dense nerve cell bodies
 White matter – inner layer of myelinated nerve fibers
Lobes of the Cerebrum
 Fissures (deep grooves)
divide the cerebrum into
lobes
 Surface lobes of the
cerebrum
 Frontal lobe
 Parietal lobe
 Occipital lobe
 Temporal lobe
Specialized Areas of the Cerebrum
 Primary sensory area (postcentral gyrus)–
receives impulses from the body’s sensory
receptors
 Primary motor area (precentral gyrus)– sends
impulses to skeletal muscles
Sensory and Motor Areas of the
Cerebral Cortex
Specialized Area of the Cerebrum
 Cerebral areas involved in special senses
 Broca’s area – speech
 Gustatory area - taste
 Visual area - sight
 Auditory area - hearing
 Olfactory area – smell
 Interpretation areas of the cerebrum
 Speech/language region
 Language comprehension region
 General interpretation area
Specialized Area of the Cerebrum
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Two hemispheres with convoluted surfaces
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Provides involuntary coordination of body movements
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http://www.youtube.com/watch?feature=player_detailpage&v=F7Yw26zHoEw
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Sits on top of the brain stem
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Enclosed by the cerebral
hemispheres
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Made of three parts
 Thalamus – sensory relay
station
 Hypothalamus – controls
hunger, thirst, fatigue,
anger, temperature,
coordinates with endocrine
system
 Epithalamus – pineal gland
and choroid plexus (forms
cerebrospinal fluid)
•
Attaches to the spinal cord
•
Controls vital functions – blood pressure, heart rate,
breathing, swallowing, vomiting
•
Parts of the brain stem
• Midbrain
• Pons
• Medulla oblongata
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Scalp and skin
Skull and vertebral column
Meninges
Cerebrospinal fluid (CSF)
Blood-brain barrier
Skin of scalp
Periosteum
Bone of skull
Superior
sagittal sinus
Subdural
space
Subarachnoid
space
Periosteal
Meningeal
Dura
mater
Arachnoid mater
Pia mater
Arachnoid villus
Blood
vessel
Falx cerebri
(in longitudinal
fissure only)
(a)
Figure 7.17a
Occipital lobe
Tentorium
cerebelli
Cerebellum
Arachnoid mater
over medulla
oblongata
Skull
Scalp
Superior
sagittal sinus
Dura mater
Transverse
sinus
Temporal
bone
(b)
Figure 7.17b
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Similar to blood plasma composition
Formed by the choroid plexus
◦ Choroid plexuses–capillaries in the ventricles of the
brain
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Forms a watery cushion to protect the brain
Circulated in arachnoid space, ventricles, and
central canal of the spinal cord
Lateral ventricle
Anterior horn
Septum
pellucidum
Interventricular
foramen
Inferior
horn
Third ventricle
Lateral
aperture
Cerebral aqueduct
Fourth ventricle
Central canal
(a) Anterior view
Figure 7.18a
Lateral ventricle
Anterior horn
Posterior
horn
Interventricular
foramen
Third ventricle
Inferior horn
Cerebral aqueduct
Median
aperture
Fourth ventricle
Lateral
aperture
Central canal
(b) Left lateral view
Figure 7.18b
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Includes the least permeable capillaries of the
body
Excludes many potentially harmful
substances
Useless as a barrier against some substances
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Fats and fat soluble molecules
Respiratory gases
Alcohol
Nicotine
Anesthesia
Traumatic Brain Injuries (TBI)
 Concussion
 Slight or mild brain injury
 Bleeding & tearing of nerve fibers
 Recovery likely with some memory loss
 Contusion
 A more severe TBI
 Nervous tissue destruction occurs
 Nervous tissue does not regenerate
 Cerebral edema
 Swelling from the inflammatory response
 May compress and kill brain tissue
Cerebrovascular Accident (CVA)
 Commonly called a stroke
 The result of a ruptured blood vessel supplying a region
of the brain
 Brain tissue supplied with oxygen from that blood source
dies
 Loss of some functions or death may result
Alzheimer’s Disease
 Progressive degenerative brain disease
 Mostly seen in the elderly, but may begin in middle age
 Structural changes in the brain include abnormal protein
deposits and twisted fibers within neurons
 Victims experience memory loss, irritability, confusion
and ultimately, hallucinations and death
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Twelve pairs of nerves that mostly serve the head
and neck
Only the pair of vagus nerves extend to thoracic
and abdominal cavities
Most are mixed nerves, but three are sensory only
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I Olfactory nerve—sensory for smell
II Optic nerve—sensory for vision
III Oculomotor nerve—motor fibers to eye muscles
IV Trochlear—motor fiber to one eye muscle
V Trigeminal nerve—sensory for the face; motor fibers to
chewing muscles
VI Abducens nerve—motor fibers to eye muscles
VII Facial nerve—sensory for taste; motor fibers to the face
VIII Vestibulocochlear nerve—sensory for balance and hearing
IX Glossopharyngeal nerve—sensory for taste; motor fibers to
the pharynx
X Vagus nerves—sensory and motor fibers for pharynx, larynx,
and viscera
XI Accessory nerve—motor fibers to neck and upper back
XII Hypoglossal nerve—motor fibers to tongue
III Oculomotor
IV Trochlear
VI Abducens
I Olfactory
II Optic
V Trigeminal
V Trigeminal
VII Facial
Vestibular
branch
Cochlear
branch
VIII Vestibulocochlear
X Vagus
IX Glossopharyngeal
XII Hypoglossal
XI Accessory
Figure 7.24
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Oh – Olfactory
Oh – Optic
Oh – Oculomotor
To – Trochlear
Touch – Trigeminal
And – Abducens
Feel – Facial
Very – Vestibulocochlear
Green – Glossopharyngeal
Vegetables – Vagus
Ah – Accessory
Ha – Hypoglossal
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Extension of brain stem
Controls reflexes
Surrounded by meninges (membranes)
Central canal is filled with spinal fluid
Protected by vertebrae.
Gray matter – mostly cell bodies
White matter – myelinated cell fibers
Spinal Cord
 Extends from the medulla
oblongata to the region of T12
 Below T12 is the cauda equina
(a collection of spinal nerves)
 Enlargements occur in the
cervical and lumbar regions
Spinal Cord
 Central canal filled with cerebrospinal fluid
The Reflex Arc
 Reflex – rapid, predictable, and involuntary responses to
stimuli
 Reflex arc – direct route from a sensory neuron, to a
spinal cord interneuron, to an effector
 No brain involvement
Peripheral Nervous System
 Nerves and ganglia outside the central nervous system
 A nerve consists of neuron fibers bundled by connective
tissue
 There are twelve pairs of cranial nerves and 31 pairs of
spinal nerves.
 Somatic nerves control voluntary functions and
autonomic nerves control involuntary functions
A nerve has layers of
connective tissue.
The endoneurium is a delicate
connective tissue wrapping around
each fiber.
The perineurium is a coarser
wrapping around a bundle of fibers
(fascicle).
The epineuriun is a tough
connective tissue wrapping around
all the fascicles.
Nerves may contain just sensory
neurons, just motor neurons, or
both (mixed).
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There is a pair of spinal nerves at the level of
each vertebrae.
Formed by the combination of the ventral and
dorsal roots of the spinal cord
Named for the region from which they arise
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Plexus–networks of nerves serving motor and
sensory needs of the limbs
Form from ventral rami of spinal nerves in the
cervical, lumbar, and sacral regions
Four plexuses:
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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
Ventral rami form
cervical plexus
(C1 – C5)
Ventral rami form
brachial plexus
(C5 – C8; T1)
No plexus
formed
(intercostal
nerves)
(T1 – T12)
12
L1
2
3
4
Ventral rami form
lumbar plexus
(L1 – L4)
5
(a)
S1
2
3
4
Ventral rami form
sacral plexus
(L4 – L5; S1 – S4)
Figure 7.25a
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Motor subdivision of the PNS
◦ Consists only of motor nerves
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Also known as the involuntary nervous
system
◦ Regulates activities of cardiac and smooth muscles
and glands
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Two subdivisions
◦ Sympathetic division
◦ Parasympathetic division
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Sympathetic—“fight or flight”
◦ Response to unusual stimulus
◦ Takes over to increase activities
◦ Remember as the “E” division
 Exercise, excitement, emergency, and embarrassment
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Parasympathetic—“housekeeping” activites
◦ Conserves energy
◦ Maintains daily necessary body functions
◦ Remember as the “D” division
 digestion, defecation, and diuresis
Anatomy of the Autonomic Nervous
System
Comparison of Somatic and
Autonomic Nervous Systems