Transcript Nervous_system_Tissue_Overview0

The Nervous System
Functions of the Nervous System
 Sensory input – gathering information
 Uses sensory receptors to monitor changes
(stimuli) occurring inside and outside the
body
 Integration
 To process and interpret sensory input and
decide if action is needed
Functions of the Nervous System
 Motor output
 A response to integrated stimuli
 The response activates muscles or glands
Neuroglia



“Cell Glue”
Generally assist, segregate, and
insulate neurons
Neuroglia can replicate but cannot
conduct
Neurofibromatosis

Overproduction of
Schwann cells
Nervous Tissue: Neurons
 Neurons = nerve cells
 Cells specialized to transmit messages –
can conduct but cannot replicate
 Have 3 specialized characteristics
 Longevity: with nutrition, can live as long
as you do
 Amitotic: unable to reproduce
themselves (so cannot be replaced)
 High metabolic rate: require continuous
oxygen & glucose (due to lots of activity)
Neuroglia vs. Neurons
Neuroglia divide. Neurons do not.
 Most brain tumors are “gliomas.”
 Involve the neuroglia cells, not the
neurons.
 As neuroglia grow out of control, they
press on the neurons impairing their
function
Neurolemma

Why is the plasma membrane
(neurolemma) of a neuron so
important?
 It is the site of electrical signaling –
plays a crucial role in cell to cell
interactions during development as
well
Major Regions of Neurons
 Cell body
 Contains the metabolic/biosynthetic center
of the cell (location of the nucleus)
 Does not contain centrioles (reflects
amitotic nature) but has the other
organelles
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Neuron Anatomy
 Dendrites
 hundreds per cell –
diffusely branched
– close to cell body
 Receptive sites
conduct impulses
toward the cell
body
 Immense surface
area for reception
Figure 7.4a
Slide 7.10
Neuron Anatomy
 Axons
 Transmit
impulses away
from cell body
 Vary in length
and diameter
 Larger diameter
= faster
conduction
Figure 7.4a
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Slide 7.10
Neuron Anatomy
 Axons
 Axon collaterals
– right angle
branches
connecting other
neurons
 Axon terminals
located at end of
axon branches
Figure 7.4a
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Slide 7.10
Axon terminals
 Contain vesicles with
neurotransmitters –
chemicals which
transmit electrical
impulses
 Axonal terminals are
separated from the next
neuron or effector by
the Synaptic cleft
 Synapse -junction between
nerves
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Slide 7.11
Myelin Sheath
 Function:
 Protects & insulates
fibers
 Increases speed of
transmission
 Formed by Schwann
Cells (add to notes)
Figure 7.5
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Slide 7.12
Functional Classification of
Neurons
 Sensory (afferent)
 Nerve fibers that carry information from
sensory receptors to the central nervous
system (CNS)
 Ends of dendrites associated with
specialized receptors – know examples in
your notes!
Sensory Receptors
Ends of dendrites are associated
with specialized receptors
Cutaneous receptors: pressure,
pain, heat, cold
Proprioceptors: muscles &
tendons: amount of stretch or
tension
Specialized receptors in sense
organs: sight, hearing, smell,
taste, equilibrium
Functional Classification
 Motor (efferent) division
 Nerve fibers that carry impulses from the
central nervous system to muscles &
glands
Functional Classification
Association or Interneurons
• Responsible for integration & reflex –
connect motor & sensory neurons
• Make up over 99% of neurons
End of Quiz #1 Material
Study for quiz!!!
Functional Properties of Neurons
Two major functional properties
of neurons resulting in
electrochemical event
Irritability - ability to respond to
stimuli & convert it into a nerve
impulse
Conductivity – ability to transmit an
impulse to other neurons, muscles,
or glands
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Slide 7.17
Synapse – know the diagram
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Slide 7.11
Stages of the Chemical Event
 The action potential (electrical signal)
reaches the axon terminals
 Neurotransmitter is released into the synaptic
cleft when the vesicle fuses with the
membrane (presynaptic neuron)
 NT diffuses across the cleft and binds to the
receptors on the dendrite of the next neuron
(postsynaptic neuron)
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Slide 7.21
Stages of the Chemical Event
 An action potential is started in the next
neuron (or muscle or gland)
 In order to prevent continuous stimulation, NT
is removed from the synapse through:
 Re-uptake
 Enzymatic breakdown
 Synapse Animation
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Slide 7.21
Development Aspects of the
Nervous System
 As you learn:
Axon terminal gets wider so
more NT can be released (more
surface area)
Synaptic cleft get narrower
More NT gets across to
receptors
Faster & more efficient process
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Slide
Reflex Activity
 Reflex: rapid predictable motor
response to stimuli that the body is
programmed to do
Unlearned, unpremeditated,
involuntary
 Withdrawal from pain
Learned or acquired reflexes result
from repetition or practice.
 Example: experienced driver drives a car
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Slide 7.58
Reflex Activity
 Two types:
Autonomic: regulate the activity of
smooth muscles, the heart, and
glands
Examples: salivary reflex, pupilary
reflex, digestion, blood pressure
Somatic reflexes: skeletal muscle
reflexes
Example: knee jerk reflex
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Slide 7.58
Reflex – define 5 elements of
Know your diagram
Regeneration
 Mature neurons are incapable of
mitosis. However, PNS nerve axons
can regenerate if cell body is not
destroyed.
 The uninjured cell body gets larger in
order to synthesize proteins needed for
regeneration
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Slide
7.14b
Regeneration
 Axons regenerate at a rate of 1.5 mm/day
 The greater the distance between severed
nerve endings, the less chance of
recovery. Axonal sprouts may grow into
surrounding areas and form a mass called
a neuroma.
 Surgical realignment can help. Retraining
may be necessary once the connection is
completed
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Slide
7.14b
Neuroma

Acoustic
neuroma MRI
Regeneration
 PNS vs CNS
In PNS axon regeneration,
macrophages clean out the debris
from the injury.
Schwann cells will form a tunnel of
neurolemma to guide severed nerve
ending together. A growth factor is
also released
In CNS – No Schwann cells to do this.
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Organization of Nervous System
Memorize the info on the chart provided you need to understand how it all fits
together
Classification of the Nervous System
 Central nervous system (CNS)
 Brain & Spinal cord
 Integrative & control centers
 Bundles of neurons called “Tracts”
 Peripheral nervous system (PNS)
 Outer regions of nervous system
 Has “nerves” not tracts
 Cranial & Spinal Nerves (outside the brain and
spinal cord)
 Communication lines between the CNS and the
rest of the body
Distribution of Cranial Nerves
Figure 7.21
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Slide 7.59
Spinal Nerves
Figure 7.22a
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Slide 7.64
Functional Classification of the
Peripheral Nervous System
• Afferent: Sensory, impulses towards CNS
• Efferent: Motor (efferent) division; from CNS
 Two subdivisions
 Somatic nervous system = voluntary
 Conducts impulses to skeletal muscles
 Autonomic nervous system = involuntary
 Conducts impulses to cardiac and smooth
muscle, & glands
Functional Classification of the
Peripheral Nervous System
 Autonomic: Involuntary, From CNS to skeletal;
2 parts
• Sympathetic division: “Fight or flight” system
•
•
Speeds up HR, respiration rate, increases
cardiac output
Slows down digestive system
• Parasympathetic division: “Feed and Breed”
Resting system
Activates digestive, slows other systems
Autonomic system takes care of the 4 F’s of the body
Fight
Feed
Flight
Mating
Organization of the Nervous
System
Figure 7.2
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Slide 7.4
End of Quiz #2 Material
Central Nervous
System
What causes a “hangover”?
Protection of the CNS
 Scalp, hair, and skin- Cushions
 Bone: Skull and vertebral column
– Surrounds & Protects
 Meninges – membranes fig 7.16
Figure 7.16a
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Meninges
 Epidural space:
 Found around spine only-contains fat
& CT
 Dura mater – “tough mother”
 Dural sinuses – venous blood
collected from brain and shunted into
internal jugular vein
 Double-layered external covering
fused together except where dural
sinuses are enclosed
Meninges
 Subdural space
Contains serous fluid
 Arachnoid layer
 Spider web-like
 Middle layer
 Subarachnoid space
 Contains CSF & major arteries &
veins
Meninges
 Pia mater:
“little mother”
 Clings directly
to the surface
of the brain
 Internal layer
of delicate CT
Blood Brain Barrier
 Function: ensures
stable environment by
endothelial tight
junctions(the least
permeable capillaries
of the body)
 Excludes many
potentially harmful
substances and
metabolic waste
products
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Slide 7.48
Blood Brain Barrier
 Useless against some substances
 Fats and fat soluble molecules
 Respiratory gases
 Alcohol
 Nicotine
 Anesthesia
****Medical Implication (add to notes):
Hard to get antibiotics through BBB so
hard to treat brain infections
Blood Brain Barrier
 Not identical in all regions
In the hypothalamus region, the
BBB is almost non-existent so
chemical composition of blood
can be monitored
 Different in newborns vs. adult
 Kernicterus: description on next
page
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Slide 7.48
Kernicterus
Hemoglobin is released into blood as RBC’s
recycle
Hemoglobin breaks down into bilirubin which is
normally cleared from the body by the liver
Newborns have an immature liver so bilirubin
will build up and cause jaundice of body and
of brain
Infant will have diminished reflexes, lethargy,
reduced muscle tone, and a high pitched
abnormal cry as external symptoms.
UV light treatment
helps dissolve
excess bilirubin.
Cerebrospinal Fluid
 Function:
Support, protect, & exchange of
materials
Forms a watery cushion to
protect the brain
Circulates to monitor levels of
CO2, O2 , pH – triggers feedback
mechanism if necessary
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Cerebrospinal Fluid
 Similar to blood plasma
composition
 Location: subarachnoid space and
4 ventricles in brain and central
canal of SC
 Formed by the choroid plexus
(network of capillaries) in brain
ventricles: seeps from capillaries
into ventricles
 ~800 ml formed daily
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Slide 7.46
Hydrocephalus
•Define: something blocks
Slide 7.47b
circulation/drainage of CSF, fluid
accumulates & puts pressure on brain
•Adult:skull bones are fused, fluid
compresses BV and soft brain tissue – result
is brain damage
•Child:skull bones not fused, head may
enlarge, brain damage still a possibility
•Treatment: insert a shunt to go around
blockage
Figure 7.17b
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Hydrocephalus
Do not need to copy this info
Shunt drains excess fluid
from ventricles into
abdominal cavity where
body can reabsorb it.
Pressure then does not
build up in the brain
Brain Development (CNS)
 CNS develops from the embryonic
neural tube
 The neural tube becomes the brain
and spinal cord
 The opening of the neural tube
becomes the ventricles
 Malformations of neural tube lead to
several defects such as spina bifida
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Major Regions of the Brain
 Cerebral
hemisphere
 Diencephalon
 Brain stem
 Cerebellum
Figure 7.12
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Slide 7.27
Cerebrum
 The surface is
made of ridges
(gyri) and
grooves (sulci)
 Purpose: triple
surface area
Slide
7.28b
Figure 7.13a
Lobes of the Cerebrum
 Fissures (deep sulci) divide the
cerebrum into lobes
Longitudinal fissure: separates 2
hemispheres
Transverse fissure: separates
cerebellum
Lateral fissure:on side of brain
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Lobes of the brain
Surface lobes of the Cerebrum
•
•
•
•
Frontal Lobe
Parietal Lobe
Occipital Lobe
Temporal Lobe
Lobes of the Cerebrum
Figure 7.15a
Slide
7.29b
The Cerebrum
Cerebral cortex:
 Gray matter: cell bodies
 ~40% of brain mass
 Voluntary motion
 Higher order thinking skills
Slide 7.30
Sensory and Motor Areas of the
Cerebral Cortex
Figure 7.14
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Slide 7.31
Layers of the Cerebrum
 White matter
 Fiber tracts inside
the gray matter
 Example: corpus
callosum connects
hemispheres &
allows them to
communicate
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Figure 7.13a
Slide
7.33b
Layers of the Cerebrum
 Basal nuclei – internal islands of
gray matter w/in white matter
 Indirectly helps initiate and
control slow stereotyped muscle
movement
 When impaired, postural
disturbances, muscle tremors
uncontrolled contractions result
Figure 7.13a
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Slide
7.33c
Cerebral Nuclei
Diencephalon
 Sits on top of the brain stem
 Enclosed by the cerebral
hemispheres
 Made of three parts
 Thalamus
 Hypothalamus
 Epithalamus
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Slide
7.34a
Brain Stem
 Attaches to the spinal cord
 Rigidly programmed
automatic behaviors
necessary for survival
 Parts of the brain stem
 Midbrain
 Pons
 Medulla oblongata - If
damaged severely, death
will result
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Slide
7.38a
Cerebellum
 Two hemispheres with convoluted
surfaces
 Provides involuntary smooth,
coordinated body movements
 Likened to the control system of an
automatic pilot to constantly
monitor and adjust muscle
functioning
 Ataxia
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Slide
7.43a