Transcript Nervous System: Nervous Tissue and Brain

Nervous System: Nervous Tissue
and Brain
Chapter 10
Lisa Ochs RN, BSN 2008
Structure of the Nervous System
• Central Nervous System (CNS)
– Brain
– Spinal cord
• Peripheral Nervous System (PNS)
– Outside of the CNS
– Includes nerves that connect the CNS with the rest
of the body
Figure 10-1 Nervous system: central nervous system and peripheral nervous system.
Elsevier items and derived items © 2007, 2003, 2000 by Saunders, an imprint of Elsevier Inc.
Function of the Nervous System
• Sensory
– Gather information from inside and outside the
body and transmit back to the CNS
• Integrative
– Processing and interpreting information received
from the sensory nerves
• Motor
– Causing an action or movement in response to the
information received
Figure 10-2 Three functions of the nervous system: A, Sensory function. B, Integrative function. C, Motor function.
Elsevier items and derived items © 2007, 2003, 2000 by Saunders, an imprint of Elsevier Inc.
Types of Cells
• Neuroglia
– Also called glial cells; mostly found in the CNS
– Support, protect, insulate and “care for” neurons
– Do not conduct nerve impulses
– Include astrocytes (most abundant), ependymal
cells (secrete CSF), Schwann cells,
oligodendrocytes
Figure 10-3 Neuroglia, or glia; astrocytes and ependymal cells.
Elsevier items and derived items © 2007, 2003, 2000 by Saunders, an imprint of Elsevier Inc.
Types of Cells
• Neurons
– Transmits information in the form of nerve
impulse
– Various shapes, sizes and lengths
– Do not replicate (nonmitotic); cannot replace
themselves when injured
Types of Cells
• Parts of a neuron
– Dendrites
• Tree like structures that receive information
– Cell body
• Contains the nucleus of the cell
– Axon
• Long extension that transmits information away from
the cell body
• Includes myelin sheath, nodes of Ranvier, & axon
terminals
Figure 10-4 Structure of a neuron: A, Dendrites, cell body, axon, and axon terminals. B, Structure surrounding the axon, showing the
myelin sheath, the nodes of Ranvier, and the neurilemma.
Elsevier items and derived items © 2007, 2003, 2000 by Saunders, an imprint of Elsevier Inc.
Types of Cells
• Types of neurons
• Sensory
– Carries information from the periphery to the CNS
– Also called afferent
• Motor
– Carries information from the CNS to the periphery
– Also called efferent
– Remember S.A.M.E.
Nerve Impulse
• An electrical signal that conveys information
along a neuron
• Also called an action potential
• Inside the cell, normal resting state is negative
(polarized)
• The cell changes to a positive state
(depolarization) when stimulated
• Returns to resting state of negative
(repolarization)
Figure 10-5 Nerve impulse (action potential): A, Polarization, B, depolarization, and C, repolarization.
Elsevier items and derived items © 2007, 2003, 2000 by Saunders, an imprint of Elsevier Inc.
Movement of Nerve Impulse
• The nerve impulse travels along the length of
the axon in a wave like manner
• Each impulse depolarizes the next section of
membrane
• Each nerve impulse fires in an “all or nothing”
manner; this ensures that the nerve impulse
does not weaken as it travels along the axon
Speed of Nerve Impulse
• Most axons are wrapped in myelin sheaths;
the spaces between the myelin are the nodes
of Ranvier; nerve impulses cannot travel
through myelin
• The nerve impulse jumps across the myelin to
the bare nodes
• This is called saltatory conduction
• Myelinated fibers are considered fastconducting fibers
Figure 10-8 Jumping from node to node. A, A myelinated axon and the nodes of Ranvier. B, The nerve impulse jumps from node to
node toward the axon terminal. C, The jumping of the nerve impulse resembles the jumping of a kangaroo.
Elsevier items and derived items © 2007, 2003, 2000 by Saunders, an imprint of Elsevier Inc.
Structure of Synapse
• Synapse is the place where two neurons meet
• Includes:
– Synaptic cleft (space between the neuron &
dendrite)
– Neurotransmitters (most common is ACh and
norepinepherine)
– Inactivators (stop the activity of
neurotransmitters)
– Receptors (on the dendrite where the
neurotransmitters attach)
Events at Synapse
• The nerve impulse of the first (presynaptic) neuron
causes the release of neurotransmitter into the
synaptic cleft.
• The neurotransmitter diffuses across the synaptic
cleft and binds to the receptors on the second
(postsynaptic) membrane.
• The activation of the receptors stimulates a nerve
impulse in the second neuron.
Figure 10-9 The synapse. Steps in the transfer of information across the synapse.
Elsevier items and derived items © 2007, 2003, 2000 by Saunders, an imprint of Elsevier Inc.
The Brain
Brain Structure
• Control center of the body- emotions, actions,
memory, sleep/ wake, etc.
• 2% of total body weight; requires 20% of
body’s oxygen supply
• Primary source of energy is glucose
• 4 major areas: cerebrum, diencephalon, brain
stem and cerebellum
Figure 10-10 Four major areas of the brain: cerebrum, diencephalon, brain stem, and cerebellum.
Elsevier items and derived items © 2007, 2003, 2000 by Saunders, an imprint of Elsevier Inc.
Cerebrum
• Largest portion of the brain
• Right and left hemispheres joined by the
corpus callosum (allows the separate sides to
communicate)
• Each hemisphere has four lobes
– Frontal
– Parietal
– Temporal
– Occipital
(sound familiar?)
Lobes & Function
• Frontal
– Motor, personality, behavior, emotion, intellect
• Parietal
– Somatosensory (skin/ muscle, taste, speech, reading)
• Temporal
– Hearing, smell, memory, some speech
• Occipital
– Vision and vision functions (reading, distance, 3D)
Specific Functions
• Decussation: crossing of fibers from one side of the brain to
the other
• Frontal lobe includes Broca’s area (left hemisphere);
responsible for motor speech; patients with a stroke here
suffer from expressive aphasia
• Temporal & parietal lobes include Wernicke’s area; broad
area that involves translating thoughts into words;
damage here can result in severe language deficits
(Wernicke’s aphasia)
Markings on the Cerebrum
• Gyri (sing. gyrus)
– “bumps” or elevations on the surface
• Sulci (sing. sulcus)
– “grooves”
• The extensive folding of the cerebral tissue
increases its surface area; the greater the
number of folds and grooves, the more
intelligent the species
Hmmmm…
• There are time-keeping neurons in our
brains. Specifically in the prefrontal cortex and
striatum of the cerebrum. Discovered recently in the
brains of monkeys by researchers at MIT, these timekeeping neurons fire consistently at certain rhythms .
..
– thus helping our brains to figure out when things are
happening. This helps us with rhythmic activities, of
course, but also with any number of tasks and memories
that rely on knowing what came first, in what order, and so
on.
Hmmmm…
Researchers speculate that damage to these
neurons, or damage to the mechanisms that
read the timing pattern, may contribute to
disorders (such as Parkinson Disease) that
involve ill-timed movements and other
functions.
From http://theapprofessor.blogspot.com/, retrieved December 30,
2009
Hmmmm…
In their paper, researchers failed to speculate
whether this is why A&P students know
exactly when to start slamming their books
shut moments before a class is scheduled to
end.
Diencephalon
• 2nd main area of the brain, beneath the
cerebrum and above the brain stem
• Includes the thalamus and the hypothalamus
Diencephalon
• Thalamus
– Relay station for sensory fibers traveling from
lower brain & spinal cord to sensory areas of
cerebrum
• Hypothalamus
– Regulates many processes in the body- body
temperature, water balance, metabolism
– “thermostat” of the body
Brain Stem
• Connects the spinal cord with higher brain
structures
• Includes midbrain, pons and medulla
oblongata
Brain Stem
• Midbrain
– Relays sensory and motor information; reflex centers for
vision and hearing
• Pons
– “bridge”; relays information; very important in regulating
breathing rate and rhythm
• Medulla Oblongata
– Relays information; very important in regulating heart rate,
blood pressure and respiration; called the “vital center”;
also contains vomiting center
Cerebellum
• Located under the occipital lobe and the base
of the skull; “little brain”
• Primarily concerned with coordination of
voluntary muscle activity; balance and
coordination
• Persons with damage to the cerebellum may
appear intoxicated
Other Structures
• Not confined to specific lobes
• Limbic system
– “emotional brain”; responsible for various
emotional states and behaviors
• Reticular formation
– Concerned with the sleep-wake cycle and
consciousness
– Sensitive to certain drugs and alcohol
Other Structures
• Memory areas
– Many lobes involved in recalling thoughts and
images
– Short term (seconds to hours)
– Long term (years to decades)
Protection of the CNS
• BONE
• First layer of protection for the brain and
spinal cord
• Cranium and vertebral column
Types of
skull
fractures
Protection of the CNS
• MENINGES
• Three layers of membranes that surround the brain and spinal cord
• Dura mater (“tough mother”)
– Tough connective tissue
• Arachnoid (“spider-like”)
– Weblike membrane
• Pia mater (“soft mother”)
– Delicate, thin; lies directly over the brain and spinal
cord
Figure 10-14 The three layers of meninges are the dura mater, arachnoid, and pia mater.
Elsevier items and derived items © 2007, 2003, 2000 by Saunders, an imprint of Elsevier Inc.
Protection of the CNS
• CEREBROSPINAL FLUID
• Third layer of protection; formed from the
blood within the brain; clear fluid that
resembles plasma
• Composed of water, glucose, protein and ions
(esp. Na+ and Cl-)
• Acts as a cushion and shock absorber, also
delivers nutrients and removes waste.
Protection of the CNS
• CEREBROSPINAL FLUID
• Formed in the choroid plexus of the ventricles
in the brain
• Circulates around and through the brain and
spinal cord; continuously produced and
drained
• Rate of production must equal rate of
drainage, otherwise increased ICP will result
Protection of the CNS
• BLOOD BRAIN BARRIER
• An arrangement of cells (glial astrocytes)
associated with blood vessels that supply the
brain and spinal cord
• Act as gate keepers- allows only certain
substances to cross. Most harmful substances
cannot cross this barrier
• Pharmacology can be difficult- most antibiotics
do not cross blood-brain barrier
NCLEX Question
• After a brain stem infarction, a nurse would
observe for which condition?
1.
2.
3.
4.
Aphasia
Bradypnea
Contralateral hemiplegia
Numbness and tingling in the face
Rationale
• 2. Bradypnea, or slowed respiratory rate,
would result from damage to the brain stem.
The brain stem contains the control center for
vital functions such as breathing, heart rate
and blood pressure.
NCLEX Question
• The nurse is caring for a client with a cerebral
injury that has impaired his speech and
hearing. The client most likely experienced
damage to the:
1.
2.
3.
4.
Frontal lobe
Parietal lobe
Occipital lobe
Temporal lobe
Rationale
• 4. The temporal lobe contains the primary
control centers for speech and hearing
NCLEX Question
• A client is experiencing problems with balance
and fine gross motor function. Which area of
the brain has been affected?
1.
2.
3.
4.
Cerebellum
Brain stem
Diencephalon
Cerebrum
Rationale
• 1. The cerebellum contains the control center
for voluntary muscle activity and balance.
Disorders of the CNS
Bell’s Palsy
Types of hematomas
Coronal section of brain illustrating large cerebral hemorrhage that has
compressed and displaced the cerebral ventricles.
Normal CT- Brain
Intracerebral Bleed
Subdural Hematoma
With midline shift
Intracerebral Bleed
43 year old male
Transcranial gunshot wound
Knife vs. cranium