Chapter 9 Nervous system
Types of neurons Sensory neurons -
(aka afferent) - Carry impulses to the spinal cord & brain from all parts of the body
Types of neurons Interneurons -
(aka central connecting neurons) Conduct impulses from sensory neurons to motor neurons. They also connect with each other to form complex central networks of nerve fibers
Types of neurons Motor neurons -
(aka efferent) - Carry impulses away from the brain & spinal cord. - They DO NOT conduct impulses to all parts of the body - Only two types of tissue : Muscle tissue & glandular epithelial tissue
Withdrawal reflex -
(example) Application of an irritating stimulus to the skin of the thigh initiates a three-neuron reflex response that causes contraction of muscles to pull the leg away from the irritant -a three neuron arc reaction.
Microglia -
- Are smaller than astrocytes. They usually remain stationary, but in inflamed or degenerating brain tissue, they enlarge, move about and act as microbe eating scavengers - Help to clean up cell damage resulting from injury & disease
Reflex arc -
- Basic type of neuron pathway & is important to nervous system functioning - the simplest kind of reflex arc is a two-neuron arc "so called" because it consists of only two types of neurons : sensory & motor neurons
Neuron structure Axon -
- One elongated projection from the cell body - They are the processes that carry impulses away from the neuron cell body
Neuron structure Dendrites -
- One or more branching projections from the cell body. - They are the process or projections that carry impulses to the neuron cell body
Transmission of signals from one neuron to the next -__________- is an important part of the nerve conduction process..
Across the synapse
Nerve impulses is also known as...
Action potentials
Blood brain barrier (BBB) -
Along with the walls of the blood vessels, astrocytes branches form a two layer structure. BBB separates the blood tissue & nerve tissue to protect vital brain tissue from harmful chemicals that might be in the blood
reflex -
An involuntary response to impulse conduction over a reflex arc
Nodes of Ranvier -
Are gaps between adjacent Schwann cells.
Glial cells are also known as _________. They attach to neurons and blood vessels holding these structures together
Astrocytes
Three main types of glia cells:
Astrocytes, Microglia, & Oligodendrocytes
What are three types of glia cells?
Astrocytes, microglia, & Schwann cells
Pons -
Bulges out a bit more than the medulla forming a bridge to the narrower midbrain
Neuron structure Each neuron consist of three parts :
Cell body , Dendrites, & Axon
Because there are no Schwann cells in the __________________, axons in the brain & spinal cord have no neurilemma
Central nervous system (CNS)
What is the difference between the central nervous system and the peripheral nervous system?
Central nervous system is the brain and spinal cord; Peripheral nervous system is the rest of the body
Neurotransmitters-
Chemicals by which neurons communicate; at least 30 different compounds have been identified as "it"
The nervous system & the endocrine system
Control of the body's trillion of cells is mainly accomplished by two body-wide communication systems :
Glia -
Do not specialize in transmitting impulses. Instead, they're special types of supporting cells
Each axon in a nerve is surrounded by a thin wrapping of fibrous connective tissue called __________ . Groups of these wrapped axons are called fascicles. Each fascicles is surrounded by a thin, fibrous perineurium. A tough fibrous sheath called epineurium covers the whole nerve
Endoneurium
Each axon in a nerve is surrounded by a thin wrapping of fibrous connective tissue called endoneurium . Groups of these wrapped axons are called _________. Each fascicles is surrounded by a thin, fibrous perineurium. A tough fibrous sheath called epineurium covers the whole nerve
Fascicles
How are glial cells different from neurons?
Glial cells are smaller than neurons, as well as more numerous . They can be metastatic & also act as glue by holding functioning neurons together as well as protecting them.
Most common type of brain tumor called _________ develops from the glial cell
Glioma
Nerve -
Group of peripheral nerve fibers (axons) bundled together like the strands of a cable.
Oligodendrocytes -
Help hold nerve fibers together. They produce the fatty myelin sheath that envelops nerve fibers located in the brain & spinal cord. The myelin sheath affects nerve conduction speed.
Saltory conduction -
If the traveling impulse encounters a section of membrane covered with insulating myelin, it simply "jumps" around the myelin to the next gap in the myelin sheath. This type of impulse travel is much faster than is possible in nonmyelinated sections.
Reticular formation -
In the brainstem, small bits of gray matter mix closely & intricately with white matter to form the "it". In the spinal cord, gray & white matter do not intermingle. Gray matter forms the interior core of the spinal cord, & white matter surrounds it
Also known as Central connecting neurons
Interneurons
Hypothalamus -
Located below the thalamus. The posterior pituitary gland , the stalk that attaches it to the under surface of the brain, & areas of gray matter located in the side walls of a fluid-filled space called the third ventricle are extensions of the "it"
Also known as effernt neurons
Motor neurons
The most common primary diseases of the CNS is a myelin disorder called _______
Multiple sclerosis (MS)
The ___________ affects nerve conduction speed
Myelin sheath
Organization of the Nervous system Peripheral nervous system :
Nerves that extend to the outlying parts of the body
Cells of the nervous system ____________ is the major component of the nervous system
Nervous tissue
Nodes of Ranvier are gaps between adjacent Schwann cells. The outer wrapped layer of a Schwann cell is called the...
Neurilemma
Cells of the nervous system Two types of cell s are found in the nervous system :
Neurons & Glia
Oligodendrocyte can form part of the myelin sheath around several axons -BUT schwann cels wrap around ____________ axon
Only one
The simplest kind of reflex arc is a two-neuron arc because it consists of two types of neurons :
Sensory & motor neurons
Also known as afferent neurons
Sensory neurons
Three-neuron arcs are the next simplest kind of arcs after two-neuron arcs. They consists of all 3 kinds of neurons :
Sensory, interneurons & motor neurons
Endocrine system transmits info _________ by chemicals secreted by ducted glands into the blood stream & then circulates to other parts of the body
Slowly
The nerve impulse ________ at the synapse, chemical signals are sent across the gap & then a new impulse continues along the dendrites, cell body, & axon of the motor neuron. The motor neuron axon forms a synapse with a structure called an effector, an organ that puts nerve signals "into effect". Effectors are usually muscles or glands & muscle contractions & gland secretions are the kind of reflexes operated by these effectors
Stops
Cells of the nervous system Glia supports....
Supports neurons
Organization of the Nervous system Central nervous system :
The brain & the spinal cord
Brainstem -
The lowest part of "it" is the medulla oblongata. Immediately above the medulla lies the pons & above that the midbrain. Together these three structures are called the "it"
Neuron pathways -
The routes traveled by nerve impulses
Reflex arc are like one way streets :
They allow impulse conduction in only one direction
Reflex arcs are like one-way streets :
They allow impulse conduction in only one direction.
Organization of the Nervous system Autonomic nervous system :
Toomatic or involuntary functions (heart rate, stomach contractions, intestines, & secretions of chemical compounds by glands)
The simplest kind of reflex arc is a _________ arc because it consists of two types of neurons : Sensory & Motor neurons
Two-neuron
Bundles of axons are called tracts, also are myelinated & thus form ___________ of the brain & spinal cord
White matter
A synaptic knob is -
a tiny bulge at the end of a terminal branch of a presynaptic neuron's axon.
...other well known neurotransmitters include, nonrepinephrine, dopamine, & serotonin. They belong to a group of compounds called______, which plays a role in sleep, motor function, mood, & pleasure recognition
amines
Some neurons in the hypothalamus function in a surprising way; they make the hormones that the posterior pituitary gland secretes into the blood. Because of these hormones (called _______________) affects the volume of urine excreted, the hypothalamus plays an essential role in maintaining the body's water balance
antidiuretic hormone or ADH
Schawnn cells
are glial cells that also form myelin sheaths, but only do so in the peripheral nervous system (PNS)
Receptors -
are the beginning of dendrits of sensory neurons. They are often located far from the spinal cord (examples : in tendons, skin, mucous membranes)
Nerve impulses do not continually race along every nerve cells surface. They 1st have to be initiated by a stimulus, a change in the neuron's environment, pressure, temperature, & _____________ are the usual stimuli
chemical changes
In three-neuron reflexes, the end of the sensory neuron's axon synapses 1st with an interneuron before ________________ are sent across a second synapse resulting in conduction through the motor neuron
chemical signals
Cells of the nervous system Neurons conduct....
conduct impulses
Nerve impulses do not.....
continually race along every nerve cells surface. They 1st have to be initiated by a stimulus, a change in the neuron's environment, pressure, temperature, & chemical changes are the usual stimuli.
The cerebellum may assist the cerebrum & other parts of the brain, perhaps having an overall __________ for the whole brain
coordinating function
In the spinal cord, gray & white matter__________
do not intermingle
...other well known neurotransmitters include, nonrepinephrine, __________, & serotonin. They belong to a group of compounds called amines, which may plays a role in sleep, motor function, mood, & pleasure recognition
dopamine
The axon of the sensory neuron travels from the cell body in the ______ _______ ganglion & ends near the dendrites of another neuron located in the gray matter of the spinal cord
dorsal root
The nerve impulse stops at the synapse, chemical signals are sent across the gap & then a new impulse continues along the dendrites, cell body, & axon of the motor neuron. The motor neuron axon forms a synapse with a structure called an ________, an organ that puts nerve signals "into effect". Effectors are usually muscles or glands & muscle contractions & gland secretions are the kind of reflexes operated by these effectors
effector
Two morphinelike neurotransmitters called ________ & ______ are released at various spinal cord & brain synapses in the pain conduction pathway. These neurotransmitters inhibit conduction of pain impulses. They are natural painkillers
endorphins, enkephalins
Each axon in a nerve is surrounded by a thin wrapping of fibrous connective tissue called endoneurium . Groups of these wrapped axons are called fascicles. Each fascicles is surrounded by a thin, fibrous perineurium. A tough fibrous sheath called ____________ covers the whole nerve
epineurium
It is important to know that there are NO neurilemma in the CNS, because the neurilemma plays an essential role in the regeneration of cut and injured axons. Therefore, the potential for regeneration of damaged axons in the brain &b spinal cord is _______ than it is in the PNS
far less
One function of ___________ is to hold the functioning neurons together & protect them
glia cells
Glia in Greek means..
glue
Brain & spinal tissue composed of cell bodies & unmyelinated axons & dendrites is called...
gray matter
Measured by size, it is one of the least significant parts of the brain, but measured by its contribution to ______________, it is one of the most important brain structure
healthy survival
Each dorsal root ganglion contains ______ of sensory neuron cell bodies
hundreds
Hypothalamus exerts major control over virtually all ____________. Among the vital functions that it helps to control are the heartbeat, constriction & dilation of blood vessels & contractions of the stomach & intestines
internal organs
Some reflexes involve three rather than two neurons. In these complex types of responses, an ____ addition to a sensory & a motor neuron, is involved.
interneuron
Gray matter forms the H- shaped inner core of the spinal cord. Because of the presence of an.....
interneuron, three-neuron reflex arcs have two synapse. However, a two-neuron reflex arc has only a sensory neuron & a motor neuron with one synapse between them
Ganglion -
is a group of nerve cell bodies located in the PNS
Nerve impulse -
is a self-propagating wave of electrical disturbance that travels along the surface of a neuron's plasma membrane. (visualize this as a tiny spark sizzling its way along a fuse)
Medulla oblongata -
is an enlarged, upward extension of the spinal cord. It lies just inside the cranial cavity, above the large hole in the occipital bone called the foramen magnum
Cerebellum -
is the second largest part o the human brain. It lies under the occipital lobe of the cerebrum. In the "it" folded gray matter composes the thin outer layer & forms a large surface area of nervous connections that allow for a huge amount of information processing. White matter tracts form most of the interior.
Nerve signals If all impulse conduction ceases,.....
life itself ceases
arbor vitae literally means
living tree
Neuron structure Cell body -
main part of a neuron
The brain is protected by the skull, the spinal cord is surrounded in the spinal cavity by the vertebral column. In addition, the brain & spinal cord are also protected by three membranes called...
meninges
In the brain stem, small bits of gray matter _______& intricately with white matter to form reticular formation
mix closely
All three parts of the brainstem functions as two-way conduction paths. Sensory fibers conduct impulses up from the spinal cord to other parts of the brain, & ___________ conduct impulses down from the brain to the spinal cord
motor fibers
Hormones are the other kind of signal the body can use to send information with, however, this method is ___________ than nerve signals. They can move from one body part to another via blood circulation.
much slower
The nerve impulse stops at the synapse, chemical signals are sent across the gap & then a new impulse continues along the dendrites, cell body, & axon of the motor neuron. The motor neuron axon forms a synapse with a structure called an effector, an organ that puts nerve signals "into effect". Effectors are usually muscles or glands & ________ & ________ are the kind of reflexes operated by these effectors
muscle contractions & gland secretions
The nerve impulse stops at the synapse, chemical signals are sent across the gap & then a new impulse continues along the dendrites, cell body, & axon of the motor neuron. The motor neuron axon forms a synapse with a structure called an effector, an organ that puts nerve signals "into effect". Effectors are usually __________ or _________ & muscle contraction & glands secretions are the kind of reflexes operated by these effectors
muscles or glands
Many diseases are associated with disorders of the oligodendrocytes . Because these glial cells are involved in myelin formation, these diseases are called _______
myelin disorders
Bundles of axons are called tracts, also are ______ & thus form white matter of the brain & spinal cord (because myelin is white peripheral nerves often look white)
myelinated
Neurons with myelin-wrapped axons are called ...
myelinated fibers
reticular means
netlike
When a nerve impulse arrives at the synaptic knob, _____________ are released from vesicles into the synaptic cleft.
neurotransmitter molecules
...other well known neurotransmitters include, _________, dopamine, & serotonin. They belong to a group of compounds called amines, which plays a role in sleep, motor function , mood, & pleasure recognition
nonrepinephrine
The cerebellum plays a essential part in the production of ....
normal movements
Each axon in a nerve is surrounded by a thin wrapping of fibrous connective tissue called endoneurium . Groups of these wrapped axons are called fascicles. Each fascicles is surrounded by a thin, fibrous _________. A tough fibrous sheath called epineurium covers the whole nerve
perineurium
Microglia surround the microbes, draw them into cytoplasm, & digest them. (What is this an example of?)
phagocytosis
By definition, a synapse is the place where impul;ses are transmitted from one neuron, called the presynaptic neuron, to another neuron called the ______ neuron.
postsynaptic
Nerve impulses do not continually race along every nerve cells surface. They 1st have to be initiated by a stimulus, a change in the neuron's environment, __________, temperature, & chemical changes are the usual stimuli
pressure
By definition, a synapse is the place where impulses are transmitted from one neuron, called the ____________ neuron, to another neuron called the postsynaptic neuron.
presynaptic
Nerve signals Only neurons can provide the _____________ between cells that is necessary for maintaining life
rapid communication
Nervous system transmits info________ by nerve impulses
rapidly
impules conduction normally starts in ...
receptors
It is important to know that there are NO neurilemma in the CNS, because the neurilemma plays an essential role in the _________ of cut and injured axons. Therefore, the potential for regeneration of damaged axons in the brain &b spinal cord is far less than it is in the PNS
regeneration
Glial cells perform many different functions, one including the __________ of neuron function
regulation
This type of impulse travel is much faster than is possible in nonmyelinated sections
saltory conduction
All three parts of the brainstem functions as two-way conduction paths. ______________ conduct impulses up from the spinal cord to other parts of the brain, & motor fibers conduct impulses down from the brain to the spinal cord
sensory fibers
...other well known neurotransmitters include , nonrepinephrine, dopamine, & __________. They belong to a group of compounds called amines, which plays a role in sleep, motor function, mood, & pleasure recognition
serotonin
Diencephalon -
small but important part of the brain located between the mid-brain below & the cerebrum above. It consist of three major parts : Hypothalamus, thalamus, & pineal gland
The word astrocyte means
star cell
A microscopic separates the axon ending of one neuron from the dendrites of another neuron. This gap serves as a junction between nerve cells called a ....
synapse
Three structures make up a typical synapse: a synaptic knob, a _________, & the plasma membrane of a postsynaptic neuron.
synaptic cleft
Three structures make up a typical synapse : a ______________, a synaptic cleft, & the plasma membrane of a post synaptic neuron.
synaptic knob
Nerve impulses do not continually race along every nerve cells surface. They 1st have to be initiated by a stimulus, a change in the neuron's environment, pressure, ____________, & chemical changes are the usual stimuli
temperature
Receptors are....
the beginning of dendrites of sensory neurons. They are often located far from the spinal cord ( i.e. in tendons, skin, & mucous membranes)
Produces smooth coordinated movements, maintains equilibrium, & sustains normal posture
the cerebellum
All interneurons lie entirely within ___________ of the brain or spinal cord
the gray matter
Three structures make up a typical synapse : a synaptic knob, a synaptic cleft, & __________ of a post synaptic neuron
the plasma membrane
Synaptic cleft -
the space between a synaptic knob & the plasma membrane of a postsynaptic neuron -it is an incredibly narrow space- only about two-millionths of a centimeter in width. "It" is filled w/ extracellular matrix that holds the synaptic structure in place
Neuron structure Each neuron consist of _______ parts.
three
Bundles of axons are called _________
tracts
The nervous system and the endocrine system both ...
transmit info throughout the body
Each synaptic knob contains many small sacs of
vesicles. Each vesicle contains a very small quantity of a chemical compound called a neurotransmitter
Many important reflex centers lie in the brainstem. The cardiac, respitory, & vasomotor centers ( collectively called the _________), for example are located in the medulla
vital centers
Some neurons in the hypothalamus function in a surprising way; they make the hormones that the posterior pituitary gland secretes into the blood. Because of these hormones (called antidiuretic hormone, or ADH) affects the volume of urine excreted, the hypothalamus plays an essential role in maintaining the body's water balance
water balance