Transcript Nervous System - Creston High School

Nervous System
Anatomy and Physiology
What are the major functions of the nervous
system?
• The master controlling and communicating
system of the body
• Functions:
– Sensory input – monitoring stimuli occurring inside
and outside the body
– Integration – interpretation of sensory input
– Motor output – response to stimuli by activating
effector organs
How is the nervous system organized?
• Central nervous system (CNS)
– Brain and spinal cord
– Integration and command center
• Peripheral nervous system (PNS)
– Paired spinal and cranial nerves
– Carries messages to and from the spinal cord and
brain
What are the divisions of the
peripheral nervous system?
• Sensory (afferent) division
– Sensory afferent fibers – carry impulses from skin,
skeletal muscles, and joints to the brain
– Visceral afferent fibers – transmit impulses from
visceral organs to the brain
• Motor (efferent) division
– Transmits impulses from the CNS to effector organs
What are the parts of the
motor division?
• Somatic nervous system
– Conscious control of skeletal muscles
• Autonomic nervous system (ANS)
– Regulate smooth muscle, cardiac muscle, and
glands
– Divisions – sympathetic and parasympathetic
What are the functions of the
sympathetic and parasympathetic
divisions?
• Parasympathetic- “resting and digesting system”
• Most active in nonstressful situations
• Keeps energy use low and maintains vital
housekeeping activities running.
• Sympathetic division- “fight or flight” division
• Exercise, excitement, emergency, and
embarrassment division
• Prepares the body for action
What types of supporting cells
make up central nervous
tissue?
Known as neuroglia or glial cells
1. Astrocytes-star shaped cells that connect
neurons together and to their blood supply.
2. Microglia- function as phagocytes by engulfing
foreign invaders.
3. Ependymal- (epithelial-like) provide a barrier
between brain and spinal fluid.
4. Oligodendrocytes- connect thick neuronal fibers
and produce an important insulating material
called the myelin sheath.
What are neurons?
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Conduct messages in the form of nerve impulses
They number in the billions (much higher in
anatomy teachers)
Have extreme longevity
Most cannot divide (hippocampus is a rare
exception; it is involved in memory).
Have a high metabolic rate; require mucho oxygen
and glucose
3 basic regions: dendrites, cell body, and axons
Impulses travel from dendrites to cell body to
axons
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How is a nerve impulse
transmitted across a neuron?
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The sodium-potassium pump creates a resting
potential across the membrane of a neuron.
 When a threshold stimulus is applied to the
neuron, an action potential travels down the
neuron. (action potential=nerve impulse)
 The nerve impulse will jump from the axon to the
dendrite of another neuron across a synapse by the
use of neurotransmitters
What is the all-or-none
phenomenon?

An action potential either happens completely or
not at all.
 Many sub-threshold stimuli can cause an action
potential. Neurons can have different thresholds
(pain)
 It is similar to the flash point of a burning twig. As
a match is placed under a twig, the twig must get
hot enough to produce a flame on the twig.
What is saltatory conduction?

Myelin sheath found on the axon insulates and
doesn’t allow the depolarization of the membrane.
 The action potential must jump from one node of
Ranvier to the next. This makes the action
potential move faster down the axon.
 Some can reach speeds of 100 m/s.
 Unmyelinated neurons propagate slow action
potentials that must move from one site to the
next. This is called continuous conduction.
Saltatory conduction
What is a synapse?
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Synapses are gaps between neurons
Exists between the axon of one neuron and the
dendrite of another.
Neurons can have a large number connecting to
numerous other neurons. (This accounts for the
complexity of the nervous system)
When an action potential reaches the end of an
axon, neurotransmitters are stimulated to flood the
gap and bond to ion channels on the post synaptic
neuron.
This causes an action potential to be produced.
Vesicles with
neurotransmitters
Synapse
Page 409
What are neurotransmitters?
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Molecules that bridge the synapse
 Over 50 different types have been
discovered
 Some can be excitatory or inhibitory
 See page 416-417 for types
What are reflexes?
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Rapid, automatic responses to stimuli, in which a
particular stimulus always causes the same motor
response.
 Produces the simplest behaviors. Ex. Removing
hand from a hot object.
 Occur over neural pathways called reflex arcs.
 5 basic components: receptor, sensory neuron,
integration center, motor neuron, and effector.
What are the major parts of
the brain?
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Cerebral hemispheres, diencephalon, Brain
stem, and cerebellum
 Cerebrum and cerebellum have a gray
matter nuclei surrounded by white matter
and a gray matter cortex.
 Gray matter- unmyelinated neurons
 White matter- myelinated neurons
What are the functions of the
cerebral cortex?
 Interprets sensory impulses (including
auditory,visual, and olfactory), controls voluntary
and skilled skeletal muscle, functions in
intellectual and emotional processing.
 Shows lateralization of function
– Most people the left hemisphere is dominant and is
specialized for language and mathematical skills
– The right hemisphere is more concerned with visualspatial skills and creative endeavors.
– Right hemisphere controls the left side of the body
(motor control) and vice versa.
See page 436
What are the functions of the
diencephalon?
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Consists of the thalamus, hypothalamus and
epithalamus and encloses the third ventricle.
 Thalamus-Relay station for sensory and motor impulses to and
from the cerebrum. Functions in memory.
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Hypothalamus-Regulates hormonal output of the pituitary gland,
regulates body temp., food intake, water balance, thirst, and biological
rhythms and drives. (limbic system)
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Limbic System- functional system involving cerebral structures
and the diencephalon that mediates emotional responses and is also
involved in memory.
What are the parts and
functions of the brain stem?
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Medulla oblongata- respiratory rhythm, heart
rate, and blood pressure
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Pons- regulation of respiration
 Midbrain- visual and auditory reflex centers and
fear response
What is the function of the
cerebellum?
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Cerebellum processes and interprets
impulses from the motor cortex making
movements smooth and well timed.
(coordination)
What protects the brain?
 The brain is protected by bone, meninges,
cerebrospinal fluid, and the blood-brain barrier.
 Meninges have 3 layers:
– Dura mater- tough layer of fibrous connective tissue
– Arachnoid mater- filled with large blood vessels and
CSF
– Pia mater- delicate connective tissue with capillaries
 Blood-brain barrier- keep blood products separate from
neurons. Formed from tight capillary walls and ependymal cells that
form a tight membrane around capillaries.
 CSF- liquid cushion produced by the choroid plexus and fills the
cranial cavity.
Blood-brain barrier
What is the spinal cord?
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Two-way impulse conduction pathway and
a reflex center.
 Lies within the vertebral column
 Protected by meninges and CSF
 31 pairs of spinal nerve roots extend from
the cord.