Chapter 33 Notes,
The Nervous System
Nervous System
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A neuron is a cell of the nervous system that
carries nerve impulses through the body.
There are three kinds of neurons in the body.
Interneurons are neurons that are found in the
brain and the spinal cord.
Interneurons process information received from
the sensory neurons, and transmit that
information to motor neurons.
Nervous System
• Sensory neurons send information to the
interneurons and they are found mostly in the
skin, but they are also connected to organs.
• Motor neurons receive information from the
interneurons to produce a response in the
muscles and glands.
Neurons
The Nervous System
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The nervous system consists of two divisions.
The central nervous system (CNS) includes
the interneurons of the brain and spinal cord.
The peripheral nervous system consists of
the sensory neurons and motor neurons that
carry information to and from the CNS.
The Central and Peripheral Nervous Systems
Reflexes
• Sometimes an impulse triggers an involuntary
reflex that does not involve the brain.
• The sensory neurons send information to the
spinal cord, and the spinal cord sends
information directly back to a motor neuron
without processing the information in the brain.
• This is known as a reflex arc.
(Patellar Reflex) Reflex Arc
The Brain
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The largest part of the brain is called the
cerebrum. It is divided into two halves called
the cerebral hemispheres.
The cerebrum is responsible for learning,
memory, language, speech, voluntary body
movements and sensory perception.
The many folds and grooves on the surface of
the cerebrum increase surface area and allow
more complicated thought processes.
The Cerebrum
The Brain
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The next largest part of the brain, located near
the back of the brain, is called the cerebellum.
The cerebellum is responsible for balance,
posture, and coordination.
The brain stem connects the brain to the spinal
cord. The brain stem is made up of two parts;
the medulla oblongata and the pons.
The medulla oblongata relays signals between
the brain and the spinal cord, and it controls the
breathing rate, heart rate, and blood pressure.
Cerebellum, Medulla Oblongata, and the Pons
The Brain
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The pons relays information between the
cerebrum and the cerebellum.
A small region of the brain called the
hypothalamus maintains homeostasis.
The hypothalamus maintains body temperature,
thirst, appetite, and water balance.
Additionally, the hypothalamus regulates sleep,
and some emotions like aggression, and fear.
The Hypothalamus
The Nervous System
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Nerves of the body that are under voluntary
control, and use skeletal muscles are part of the
somatic nervous system.
The somatic nervous system relays information
from the sensory receptors to the CNS.
Somatic motor nerves relay information from
the CNS to the skeletal muscles.
A reflex arc is also an involuntary response of
the somatic nervous system.
The Nervous System
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The part of the nervous system that controls the
internal organs that are under involuntary control is
called the autonomic nervous system.
If you have ever woken up from a nightmare and your
heart was pounding, this is a response caused by the
autonomic nervous system.
If you ever came close to running into a moose while
driving or you were involved in a car accident, you
probably felt your body's fight-or-flight response.
Organization of the Nervous System
The Nervous System
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The fight-or-flight response is a response
created by the autonomic nervous system.
The autonomic nervous system has two
divisions; they are called the sympathetic and
parasympathetic nervous system.
The sympathetic nervous system is most active
in times of emergency or stress. The heart rate
and breathing rate is elevated, pupils dilated.
The parasympathetic nervous system is most
active when the body is relaxed.
Sympathetic vs. Parasympathetic
Nervous System
The Sensory Organs
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A region of the brain that has special sensory
neurons responsible for the sense of smell is
called the olfactory bulb. The nerves of the
olfactory bulb are called olfactory nerves.
Areas of chemical receptors on the tongue
responsible for taste are called taste buds.
Taste buds are connected to sensory neurons.
The olfactory nerves and taste buds
communicate with one another to enhance the
flavor of food. Without smell, food loses flavor.
Taste and Smell
Taste and Smell
The Sensory Organs
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When light enters the eye it first travels through
a transparent layer of cells called the cornea.
The amount of light entering the eye is
controlled by muscles of the iris, which is the
part of the eye that is colored.
Behind the iris is the lens. The lens inverts the
image and projects it onto the retina.
The retina contains receptor cells called rods
and cones. Rods help to see in low-light.
Cones function in bright light and detect color.
Anatomy of the Eye
The Sensory Organs
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The two functions of the ear are hearing and balance.
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Sound waves enter the auditory or ear canal.
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Sound waves cause the eardrum or tympanum to
vibrate. These vibrations cause three bones in the
middle ear called the malleus (hammer), incus
(anvil), and stapes (stirrup) to vibrate.
Vibrations from these bones cause fluid inside the
cochlea to move tiny hairs. These tiny hairs send
nerve impulses to the brain that interpret sounds
generated by sound waves.
Anatomy of the Ear
The Sensory Organs
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Inside the inner ear, located near the cochlea
are three canals called semicircular canals.
The semicircular canals are also filled with fluid
and tiny hairs. These hairs in the canals are
responsible for balance.
As you move, the fluid in the canals causes the
hairs to bend in response to gravity. The way
the hairs bend sends signals to the brain that
allows us to achieve balance and equilibrium.
Anatomy of the Ear