Transcript The Nervous System.ppt

The Nervous System
1
Objectives:
• Describe the functions of the nervous system
• Identify and describe the functions of various types
of nervous cells
• Describe how a nerve impulse is generated and
transmitted
• Identify and describe the divisions of the nervous
system
• Identify the major structures of the central nervous
system
• Describe the major structure of the peripheral
nervous system
• List and describe diseases and disorders of the
nervous system
2
Functions of the Nervous
System
• Sensory input – gathering information
– To monitor changes occurring inside and outside
the body
– Changes = stimuli
• Integration
– To process and interpret sensory input and
decide if action is needed
• Motor output
– A response to integrated stimuli
– The response activates muscles or glands
(effector organs)
3
Functions of the Nervous
System
4
Divisions of the Nervous
System
Structural classifications:
• Central nervous system (CNS)
– Brain
– Spinal cord
• Peripheral nervous system (PNS)
– Nerve outside the brain and spinal cord
– Sensory (afferent) and motor neurons
(efferent)
5
Divisions of the Peripheral Nervous
System
Functional classifications:
• Sensory (afferent) division
– Nerve fibers that carry information to the
central nervous system. Receptors of
stimulus.
• Motor (efferent) division
– Nerve fibers that carry impulses away from
the central nervous system to effector
organs.
6
Divisions of the Efferent Peripheral
Nervous System
• Motor (efferent) division continued
– Two subdivisions
• Somatic nervous system = voluntary
• Autonomic nervous system = involuntary
• The Autonomic nervous system has two
divisions:
– Sympathetic = Becomes active when body is
stressed, “fight of flight”
– Parasympathetic = Becomes active when the body is
relaxed or at rest.
7
Organization of the
Nervous System
8
Types of Neuroglial Cells and Their
Functions
• Microglia
– Spider-like
phagocytes
– Dispose of debris
• Ependymal cells
– Line cavities of the
brain and spinal cord
– Circulate
cerebrospinal
fluid
9
Types of Neuroglial Cells and Their
Functions
• Oligodendrocytes
– Produce myelin sheath
around nerve fibers in
the central nervous
system
• Satellite cells
– Protect neuron cell
bodies
• Schwann cells
– Form myelin sheath in
the peripheral nervous
system
10
Neuroglial Schwann Cells
 Schwann cells –
produce myelin
sheaths in jelly-roll
like fashion
 Nodes of Ranvier –
gaps in myelin
sheath along the
axon
Figure 7.5
11
12
Neurons
Neurons = nerve cells
– Cells specialized to transmit
messages
– Major regions of neurons
• Cell body – nucleus and metabolic
center of the cell
• Processes – fibers that extend from
the cell body (dendrites and axon)
13
Neurons
Classification of Neurons as it relates to
their functions:
– Sensory (afferent) neurons
• Carry impulses from the sensory receptors
– Cutaneous sense organs
» Nerve endings (pain and temperature),
Meissner’s corpuscle (touch), Pacinian corpuscle
(deep pressure)
– Proprioceptors – detect stretch or tension
– Motor (efferent) neurons
• Carry impulses from the central nervous
system
– Interneurons (association neurons)
• Found in neural pathways in the central
nervous system
• Connect sensory and motor neurons
14
Neurons
15
Neuron Structure
• Cell body (Soma)
– Nucleus
– Large nucleolus
– Nissl substance –
specialized rough
endoplasmic
reticulum
– Neurofibrils –
intermediate
cytoskeleton that
maintains cell shape
16
Neuron Structure
• Extensions outside the cell
body
– Dendrites – conduct impulses
toward the cell body
– Axons – conduct impulses away
from the cell body
• Axons end in axonal terminals
• Axonal terminals contain
vesicles with
neurotransmitters (Ach)
• Axonal terminals are
separated from the next
neuron by a gap
– Synaptic cleft – gap between
adjacent neurons
– Synapse – junction between
nerves
The black arrows indicate the
17
direction of the impulse movement
along the neuron.
18
Pop Quiz
Key Choices
Oligodendrocytes
Satellite Cells
Schwann Cells
1.
Microglia
Ependymal Cells
Neuroglia
Myelin Sheath
3.
4.
2.
5. The type of cells in the diagrams are _____.
19
Pop Quiz
Key Choices
1.
Node of Ranvier
Axonal Terminal
Dendrites
Schwann Cell
2.
5.
3.
Microglia
4.
Soma
20
Nerve Impulses
• Irritability – ability to respond to stimuli
• Conductivity – ability to transmit an
impulse
• The plasma membrane at rest is
polarized
– Fewer positive ions are inside the cell than
outside the cell
– resting potential difference is -70 millivolts
between the outside and inside of the cell
– inside of the cell’s axon contains K+ ions
and Na+ ions are found outside of the
21
axon’s membrane
22
Neuron Depolarization and Action
Potentials
• Depolarization – a stimulus
depolarizes the neuron’s
membrane
• A deploarized membrane
allows sodium (Na+) to flow
inside the membrane
through special proteins in
the membrane called
sodium channel proteins.
• The movement of the ions
initiates an action potential
in the neuron due to the
increase in voltage from -70
millivolts up to +30 millivolts
within the axon
• The action potential travels
down the axon like a wave.
23
Neuron Depolarization and Action
Potentials
• If the action potential (nerve impulse)
starts, it is propagated over the entire
axon (all or none response)
• When the axon’s internal charge
reaches + 40 millivolts, the Na+ channels
close and the K+ channels open;
potassium ions rush out of the neuron
after sodium ions have entered. The K+
ions move out until a negative charge of
-70 millivolts is reestablished in the
axon. Then the K+ channel proteins
close. This repolarizes the axons
membrane. However the Na+ and K +
ions are in opposite locations of where
they were before the neuron depolarized
• The sodium-potassium pump restores
the original configuration by pumping
Na+ ions out and K + ions back into the
axon.
– This action requires ATP
24
Action Potentials and Neural
Synapse
• The impulse continues to move toward
the cell body of the next neuron in the
pathway.
• Impulses are able to cross the synapse
to another nerve
– Neurotransmitter is released from a
nerve’s axon terminal
– The dendrite of the next neuron has
receptors that are stimulated by the
neurotransmitter
– An action potential is started in the
dendrite
25
Neural Synapse
26
Reflex Response
 Reflex – rapid, predictable, and
involuntary responses to stimuli
 Reflex arc – direct route from a
sensory neuron, to an interneuron, to
an effector
27
Reflex Response
• Autonomic reflexes – regulate involuntary
activity
• Somatic reflexes – all reflexes that
stimulate skeletal muscles
28
Central Nervous System
• CNS develops from the embryonic
neural tube (ectoderm)
– The neural tube becomes the brain and
spinal cord
– The opening of the neural tube becomes
the ventricles
• Four chambers within the brain
• Filled with cerebrospinal fluid - nourishes and
cushions the brain
29
CNS: The Brain
30
CNS: Brain: Cerebrum
• Right hemisphere controls
the left side of the body and
the left hemisphere controls
the right side of the body
• more than half of the brain
mass
• surface is made of ridges
(gyri) and grooves (sulci)
• Fissures (deep grooves)
divide the cerebrum into
lobes
• Surface lobes of the
cerebrum
–
–
–
–
Frontal lobe
Parietal lobe
Occipital lobe
Temporal lobe
31
CNS: Brain: Cerebrum
32
CNS: Brain: Diencephalon
• Sits on top of the
brain stem
• Enclosed by the
cerebral
hemispheres
• Made of three parts
– Thalamus
– Hypothalamus
– Epithalamus
33
Diencephalon: Thalamus
• relay station for sensory impulses; transfers
impulses to the correct part of the cortex for
localization and interpretation
34
Diencephalon: Hypothalamus
• autonomic nervous system center; regulates body
temperature, controls water balance, and regulates
metabolism
• an important part of the limbic system (emotions)
and the pituitary gland is attached to the
hypothalamus
35
Diencephalon: Epithalamus
• houses the pineal body (an endocrine gland).
• includes the choroid plexus which forms
cerebrospinal fluid
36
CNS: Brain: Brain Stem
• Attaches to the
spinal cord
• Parts of the brain
stem
– Midbrain
– Pons
– Medulla oblongata
37
Brainstem: Midbrain
• composed of tracts of nerve fibers
– two parts: cerebral peduncles and corpora
quadrigemina
– function - reflex centers for vision and hearing
38
Brainstem: Pons
• mostly composed of fiber tracts
• contains nuclei involved in the control of
breathing
39
Brainstem: Medulla oblongata
• lowest part of the brain stem
• merges into the spinal cord
• contains important control centers such as:
heart rate control, blood pressure
regulation, breathing, swallowing, and
vomiting
40
CNS: Brain: Cerebellum
• composed of two hemispheres with convoluted
surfaces
• provides involuntary coordination of body
movements
41
Meninges
• specialized membranes
below the bone
surrounding the brain and
spinal cord
• Dura mater (outer most
layer) “tough mother”
– Double-layered external
covering
• Periosteum – attached
to surface of the skull
• Meningeal layer – outer
covering of the brain
– Folds inward in several
areas
• Arachnoid layer
– Middle layer
– Web-like
• Pia mater “gentle mother”
– Internal layer
– Clings to the surface of the
brain
42
CSF: Cerebrospinal Fluid
• Similar to blood
plasma composition
• Forms a watery
cushion to protect
the brain
• Circulated in
arachnoid space,
ventricles, and
central canal of the
spinal cord
43
Location and Circulation of CSF
44
Spinal Cord Structure
45
Nerve Anatomy
• Nerve = bundle of
neuron fibers
• Neuron fibers are
bundled by connective
tissue
• Endoneurium
surrounds each fiber
• Groups of fibers are
bound into fascicles by
perineurium
• Fascicles are bound
together by epineurium
• Mixed nerves – both
sensory and motor
fibers
46
Quiz
Key Choices
Hypothalamus
1.
Cerebellum
Diencephalon
2.
Cerebrum
3.
Thalamus
4.
Pons
Brain Stem
Medulla Oblongata
5. Which part of the brain helps you to vomit when you are sick?
6. Which part of the brain helps you to regulate body temperature?
7. Which part of the brain helps you to see and smell?
8. Which area of the brain includes the pons and medulla oblongata?
9. The hypothalamus is part of which area of the brain?
10. Which areas of the brain are divided into left and right hemispheres?
47
Diseases and Disorders of the
Nervous System
• Cerebrovascular Accident:
CVA
• Commonly called a stroke
• The result of a ruptured
blood vessel supplying
(cerebral hemorrhage) a
region of the brain or a
vessel is obstructed by a
clot.
• Brain tissue supplied with
oxygen from that blood
source dies, swelling occurs
in the brain due to leaking of
blood from vessels.
• Loss of some functions or
death may result
• This is due often to elevated
blood pressure or
hypertension.
48
Diseases and Disorders of the
Nervous System
Epilepsy:
• This disease is due to
random, mis-firing of
neurons within the brain
affecting sensory and motor
regions of the brain.
• Ranging in effects from
sleep-like state of
consciousness (narcolepsy),
muscle paralysis and
spasms (Petit mal and Grand
mal seizures). Still not
understood why this disease
occurs. However in some
cases it can result from
brain trauma or injury.
49
Diseases and Disorders of the Nervous
System
• Concussion
– Slight brain injury
– No permanent brain damage
• Contusion
– Nervous tissue destruction
occurs
– Nervous tissue does not
regenerate
• Cerebral edema
– Swelling from the inflammatory
response or injury
– May compress and kill brain
tissue
– May be caused by infectious
agents such as viruses
(encephalitis) or bacteria which
cross the blood brain barrier or
infect the meninges or CSF
surrounding the brain
(meningitis)
50
Diseases and Disorders of the
Nervous System
• 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 called
plaques
• Can only be truly diagnosed
by autopsy and study of
brain tissue at death
• Victims experience memory
loss, irritability, confusion
and ultimately,
hallucinations and death
51
Diseases and Disorders of the
Nervous System
Parkinson’s Disease
• Normally effects those in 50’s & 60’s
• Dopamine releasing neurons degenerate
and this causes the dopamine targets to
become overactive
• Symptoms include persistent tremors at
rest, head nodding and pill-rolling
movement of fingers, stiff facial
expressions and forward bent walk
• Michael J. Fox has this disease
52
Diseases and Disorders of the
Nervous System
• Hydrocephalus
– “Water on the brain”
– Occurs mostly in babies
– CSF builds up in ventricles
• Multiple Sclerosis
– An autoimmune disease
– Body’s antibodies attack the myelin sheath of
the neuron, making impulses much slower
53