Download Notes Chapter 50 Nervous and Sensory Systems

50 Nervous System
1) Identify the two main organs of the central nervous system.
a) Mental and physical activity and many aspects of homeostasis are controlled by the
nervous system, a complex network of cells that communicate with one another.
b) The nervous system includes two major divisions: the central nervous system and the
peripheral nervous system.
i) The brain and spinal cord make up the central nervous system.
ii) The spinal cord carries messages from the body to the brain, where they are analyzed
and interpreted.
iii) Response messages are then passed from the brain through the spinal cord and to the
rest of the body.
c) The peripheral nervous system consists of the neurons that are not included in the brain
and spinal cord.
i) Some peripheral neurons collect information from the body and transmit it toward the
central nervous system.
(1) These are called afferent neurons.
ii) Other peripheral neurons transmit information away from the central nervous system.
(1) These are called efferent neurons.
2) Identify the parts of the brain and their functions.
a) The brain is responsible for maintaining homeostasis by controlling and integrating the
various systems of the body.
b) Protection of the nervous system
i) The delicate neurons of the brain and spinal cord are protected by 3 layers called the
meninges.
(1) The outer layer, the dura mater, consists of connective tissue, blood vessels, and
neurons.
(2) The middle layer called the arachnoid layer is elastic and web-like.
(3) The inner layer is called the pia mater and it adheres to the brain and spinal cord.
ii) A clear liquid called CSF cushions and protects the brain and spinal cord.
(1) It separates the middle and inner meninges and fills four interconnected ventricles
(cavities) of the brain.
c) The cerebrum is the largest part of the brain.
i) It is composed of 2 cerebral hemispheres which are connected via the corpus callosum.
(1) Other folds divide the brain in 4 hemispheres: the temporal, the parietal, the frontal,
and the occipital.
ii) The folded outer layer of the cerebral hemispheres is called the cerebral cortex. .
(1) It is important in sensory and motor perception, such as auditory, visual, and motor
movements/functions.
iii) Below the cerebral cortex lies the white matter.
(1) Composed of axon which link specific regions of the cortex together.
d) Below the cerebrum is the diencephalon (the brain stem).
i) The upper brain stem contains important relay centers for information entering and
exiting the brain.
(1) The upper relay center is the thalamus, which directs sensory signals to the cortex.
(2) The hypothalamus is below the thalamus and it maintains homeostasis by playing a
role in the body's hormone production.
ii) The limbic system is made up of the thalamus, the hypothalamus, and certain portions
of the cerebral cortex, and some parts of the temporal lobes.
(1) The limbic system plays a role in emotion, memory, and motivation.
e) Below the upper brain stem is the lower brain stem, of which there are 3 main divisions.
i) The midbrain is involved in visual and auditory transmission.
ii) The pons is a relay center between the neurons of the cerebral hemispheres and the
cerebellum.
iii) The medulla oblongata serves as a relay and a control center, as well as playing a role
in controlling heart rate and respiration rate.
f) Lying throughout the brain stem is a diffuse network of neurons called the reticular
formation.
i) The reticular formation acts as a filter for incoming sensory information as well as
controlling circulation and respiration.
g) Below the occipital lobe lies the cerebellum.
i) It controls muscle coordination, particularly the timing of muscle contractions.
3) Describe the structure of the spinal cord.
a) The spinal cord is a column of nerve tissue that starts in the medulla oblongata and runs
down through the vertebral column.
b) The spinal cord is composed of an outer sheath of white matter and an inner layer of gray
matter.
c) As it does in the brain, the white matter contains primarily the axons of neurons.
i)
The white matter surrounds a rigid inner core of gray matter, which is composed of
the cell bodies of neurons.
d) Thirty-one pairs of spinal nerves, part of the peripheral nervous system, originate in the
spinal cord and branch out to both sides of the body.
i) Recall that neurons have long axons that enable them to transmit signals rapidly.
ii) When bundled together, these axons form a nerve.
iii) Each spinal nerve consists of a dorsal root and a ventral root.
(1) The dorsal roots contain neurons that carry signals to the central nervous system
from various kinds of sensory receptor neurons.
(2) The ventral roots contain the axons of motor neurons, which are neurons that
contact and carry information to muscles and glands.
4) Distinguish between sensory receptors, motor neurons, and interneurons.
a) Sensory neurons
i)
Sensory receptors acquire information from the external and internal environments
of the body.
ii)
A sensory receptor is a neuron that is specialized to detect a stimulus, such as
pressure or heat.
b) Motor neurons
i)
The ventral roots contain the axons of motor neurons, which are neurons that
contact and carry information to muscles and glands.
c) Interneurons
i)
Within the spinal cord and elsewhere in the body are interneurons, which are
neurons that connect other neurons to each other.
5) Name the two divisions of the peripheral nervous system and describe their function.
a) There are 12 pairs of cranial nerves and 31 pairs of spinal nerves that connect the CNS to
the rest of the body.
b) Sensory Division
i)
The sensory division of the peripheral nervous system is composed of sensory
receptors and the interneurons that connect them to the central nervous system.
ii)
Spinal and cranial nerves enable the flow of sensory information to the central
nervous system.
c) Motor Division
i) The motor division of the peripheral nervous system allows the body to react to the
sensory information.
ii) The motor division is composed of two independent systems--the somatic nervous
system and the autonomic nervous system.
6) Distinguish between the somatic nervous system and the autonomic nervous system.
a) Somatic Nervous System
i)
The somatic nervous system of the motor division consists of motor neurons that
control the movement of skeletal muscles.
ii)
The somatic system is said to be voluntary-that is, skeletal muscles can be moved at
will.
iii) The somatic system can also operate automatically, as it does when you maintain
your balance.
b) Autonomic Nervous System
i)
The autonomic nervous system of the motor division consists of nerves that control
the body's internal conditions by affecting smooth muscles, both in blood vessels and
in organs - It is under involuntary control.
ii)
The main function of the autonomic nervous system is the control of respiration,
heartbeat, and other functions involved in homeostasis.
iii) There are 2 divisions of the ANS - the sympathetic and the parasympathetic.
7) Distinguish between the sympathetic division and the parasympathetic division.
a) Stimulation and inhibition of body systems are the responsibility of two different
subdivisions of the autonomic system-the sympathetic division and the parasympathetic
division.
b) A major function of the sympathetic division is the shunting of blood from one part of the
body to another.
i)
The sympathetic division of the autonomic nervous system is activated by
conditions of physical or emotional stress.
ii)
For example, the threat of a physical attack would cause your sympathetic division
to redirect the flow of blood away from your digestive organs and toward your heart
and skeletal muscles.
iii) This is often called the "fight-or-flight" response.
iv) The sympathetic division stimulates activities that consume large amounts of
energy.
c) The parasympathetic division of the autonomic nervous system controls the internal
environment during routine conditions.
i)
After a threat of danger has passed, nerves from the parasympathetic division signal
organs to revert to normal levels of activity.
ii) Blood flow to the heart and skeletal muscles is decreased and their function slows.
iii) The action of the parasympathetic division induces the body to. conserve energy.
iv) Under normal conditions, both systems usually are activated to some degree.
v) The balance of actions of the sympathetic division and the parasympathetic division of
the autonomic nervous system help the body maintain homeostasis.
8) Describe the structure of a neuron.
a) The nucleus of a neuron, along with most of its organelles, is located in the cell body.
b) Extending out from the cell body in different directions are membrane-covered extensions
called dendrites.
i) Dendrites receive action potentials from other neurons.
c) The axon is a long, membrane-bound projection that transmits the action potentials away
from the cell body.
i) A neuron may have a single axon or branching axons that contact several other
neurons.
ii) The end of the axon is called the axon terminal.
iii) It may lie near a muscle, a gland, or the dendrite or cell body of another neuron.
iv) The axons of most neurons are covered with a lipid layer known as the myelin sheath.
(1) The myelin sheath both insulates the axon much like the rubber coating of an
electrical cord and speeds up transmission of action potentials through the axon.
(2) In the peripheral nervous system, myelin is produced by cells called Schwann
cells, which surround the axon.
(3) Gaps in the myelin sheath along the length of the axon are known as the nodes of
Ranvier.
d) Neurons do not touch each other.
i) Instead, a small gap, called a synaptic cleft, is present between the end of the axon of
one neuron and the dendrite or cell body of another neuron.
ii) In most neurons, electrical activity in the neuron causes the release of chemicals into
the synaptic cleft.
(1) These chemicals, called neurotransmitters, in turn elicit electrical activity in a
second neuron.
(2) Thus, the signaling activity of the nervous system is composed of electrical
activity within neurons and chemical flow between neurons.
9) Distinguish between sensory neurons.
a) Sensory Organs
i) There are many kinds of sensory neurons:
(1) Mechanoreceptors - respond to movement, pressure, and tension
(2) Photoreceptors - respond to variations in light
(3) Chemoreceptors - respond to chemicals
(4) Thermoreceptors - respond to changes in temperature
(5) Pain receptors - respond to tissue damage
b) All are found in high concentrations in the sensory organs; the eyes, ears, nose, mouth,
and skin.
i) When a particular sense organ receives a stimuli, the sensory receptor converts that
stimuli into an electrical signal, which is then sent to a specific region of the brain.
Chapter 50 Nervous System and Sense Organs
 The central nervous system (CNS) includes the brain and spinal cord.
 Main divisions of the brain include the cerebrum and the brain stem—including the
diencephalon—and the cerebellum. The cerebral cortex forms the outer layer of the
cerebrum.
 The cerebellum coordinates muscle action and helps the body maintain its balance.
 The lower brain stem has three main sections—the midbrain, the pons, and the medulla
oblongata.
 Thirty-one pairs of spinal nerves each consist of a dorsal root containing sensory neurons and
a ventral root containing motor neurons.
 The peripheral nervous system (PNS) links the central nervous system and the rest of the
body. The PNS is composed of a sensory division and a motor division.
 The motor division of the PNS is divided into the somatic nervous system and the autonomic
nervous system.
 The somatic nervous system controls skeletal muscles and is under voluntary control.
 In a reflex, a signal is routed from sensory neurons, through the spinal cord and out through
motor neurons.
 In autonomic control of internal conditions, the sympathetic division and the parasympathetic
division have largely opposite effects.
 A neuron consists of a cell body, dendrites, and an axon. The transmission of a signal through
a neuron is called an action potential.
 In a neuron at rest, K+ ions are concentrated inside the membrane while Na+ ions are
concentrated outside the cell membrane. The inside of the cell membrane has a negative
charge relative to the outside.
 During an action potential, the polarity of the membrane is reversed briefly as Na+ ions
diffuse into the neuron and K+ ions diffuse out of the neuron through gated channels.
 When an action potential reaches the presynaptic membrane of the next neuron,
neurotransmitter molecules diffuse across the synapse, where they can either stimulate or
inhibit the start of an action potential in the postsynaptic neuron.
 Sensory receptors include mechanoreceptors, photoreceptors, chemoreceptors,
thermoreceptors, and pain receptors.
 The eye receives light through the pupil. The lens focuses this light on the retina, which is
composed of photoreceptors. The optic nerve that exits at the back of the retina carries a
signal to the brain.
 In the ear, vibrations pass through the auditory canal, the tympanic membrane, the bones of
the middle ear, the oval window, and the cochlea of the inner ear. Hair cells in the organ of
Corti produce signals that travel through the auditory nerve to the brain.
 Hair cells in the semicircular canals of the inner ear monitor the body’s position in space.
 Stimulation of neurons that line the inner surface of a taste bud initiates signals that travel to
the brain, where they are interpreted as taste. Likewise, olfactory receptors in the nasal
passage transmit signals to the brain, where they are interpreted as odor.
Vocabulary List
Action potential
Afferent neuron
Autonomic nervous system
Axon
Axon terminal
Central nervous system
Dendrite
Efferent neuron
Interneuron
Limbic system
Motor division
Motor neuron
Myelin sheath
Nerve
Neurotransmitter
Node of Ranvier
Olfactory receptor
Parasympathetic division
Peripheral nervous system
Potential
Reflex
Refractory period
Resting potential
Schwann cell
Sense organ
Sensory division
Sensory receptor
Somatic nervous system
Spinal reflex
Sympathetic division
Synaptic cleft