Ch.7: The Nervous System Flashcards
1
Q
What are the functions of the nervous system?
A
- Sensory input
- Integration
- Motor output
2
Q
What is sensory input?
A
- Gathering information
* Sensory receptors monitor changes, called stimuli, occurring inside and outside the body
3
Q
What is integration?
A
Nervous system processes and interprets sensory input and decides whether action is needed
4
Q
What is motor output?
A
A response, or effect, activates muscles or glands
5
Q
Concept Link 1
A
These three overlapping nervous system functions are very similar to a feedback loop (Chapter 1, p. 19). Recall that in a feedback loop, a receptor receives sensory input, which it sends to the brain (control center) for processing (integration); the brain then analyzes the information and determines the appropriate output, which leads to a motor response.
6
Q
What are nervous system classifications based on?
A
- Structures (structural classification)
* Activities (functional classification)
7
Q
What is the structural classification of the central nervous system (CNS)?
A
Organs • Brain • Spinal cord Function • Integration; command center • Interprets incoming sensory information • Issues outgoing instructions
8
Q
What is the structural classification of the peripheral nervous system (PNS)?
A
Nerves extending from the brain and spinal cord
• Spinal nerves—carry impulses to and from the spinal cord
• Cranial nerves—carry impulses to and from the brain
Functions
• Serve as communication lines among sensory organs, the brain and spinal cord, and glands or muscles
9
Q
What is the functional classification of the nervous system?
A
- Sensory (afferent) division
* Motor (efferent) division
10
Q
What is sensory (afferent) division?
A
- Nerve fibers that carry information to the central nervous system
- Somatic sensory (afferent) fibers carry information from the skin, skeletal muscles, and joints
- Visceral sensory (afferent) fibers carry information from visceral organs
11
Q
What is motor (efferent) division?
A
• Nerve fibers that carry impulses away from the central nervous system organs to effector organs (muscles and glands)
12
Q
What are the two subdivisions of the motor (efferent) division?
A
- Somatic nervous system = voluntary
• Consciously (voluntarily) controls skeletal muscles - Autonomic nervous system = involuntary
• Automatically controls smooth and cardiac muscles and glands
• Further divided into the sympathetic and parasympathetic nervous systems
13
Q
Support cells in the CNS are grouped together as:
A
Neuroglia
14
Q
What are the general functions of support cells?
A
- Support
- Insulate
- Protect neurons
15
Q
Nervous tissue is made up of which two principal cell types?
A
Supporting cells (called neuroglia, or glial cells, or glia) • Resemble neurons • Unable to conduct nerve impulses • Never lose the ability to divide Neurons
16
Q
What are CNS glial cells (astrocytes)?
A
- Abundant, star-shaped cells
- Brace and anchor neurons to blood capillaries
- Determine permeability and exchanges between blood capillaries and neurons
- Protect neurons from harmful substances in blood
- Control the chemical environment of the brain
17
Q
What are CNS glial cells (microglia)?
A
- Spiderlike phagocytes
- Monitor health of nearby neurons
- Dispose of debris
18
Q
What are CNS glial cells (ependymal cells)?
A
- Line cavities of the brain and spinal cord
* Cilia assist with circulation of cerebrospinal fluid
19
Q
What are CNS glial cells (oligodendrocytes)?
A
- Wrap around nerve fibers in the central nervous system
* Produce myelin sheaths
20
Q
What are PNS glial cells?
A
Schwann cells
• Form myelin sheath around nerve fibers in the PNS
Satellite cells
• Protect and cushion neuron cell bodies
21
Q
What are neurons?
A
• Nerve cells
• Cells specialized to transmit messages (nerve impulses)
• Major regions of all neurons
*Cell body—nucleus and metabolic center of the cell
*Processes—fibers that extend from the cell body
22
Q
The cell body is the ______ of the neuron.
A
• Metabolic center • Nucleus with large nucleolus • Nissl bodies *Rough endoplasmic reticulum • Neurofibrils *Intermediate filaments that maintain cell shape
23
Q
What are examples of processes (fibers) in the nervous system?
A
- Dendrites
* Axons
24
Q
What are dendrites?
A
- Conduct impulses toward the cell body
* Neurons may have hundreds of dendrites
25
What are axons?
* Conduct impulses away from the cell body
* Neurons have only one axon arising from the cell body at the axon hillock
* End in axon terminals, which contain vesicles with neurotransmitters
* Axon terminals are separated from the next neuron by a gap
26
What is a synaptic cleft?
Gap between axon terminals and the next neuron
27
What is a synapse?
Functional junction between nerves where a nerve impulse is transmitted
28
What is myelin and what is its function?
* White, fatty material covering axons
* Protects and insulates fibers
* Speeds nerve impulse transmission
29
What are examples of myelin sheaths?
Schwann cells—wrap axons in a jelly roll–like fashion (PNS) to form the myelin sheath
• Neurilemma—part of the Schwann cell external to the myelin sheath
• Nodes of Ranvier—gaps in myelin sheath along the axon
Oligodendrocytes—produce myelin sheaths around axons of the C N S
• Lack a neurilemma
30
What are nuclei?
Clusters of cell bodies in the CNS
31
What are ganglia?
Collections of cell bodies outside the CNS in the PNS
32
What are tracts?
Bundles of nerve fibers in the CNS
33
What are nerves?
Bundles of nerve fibers in the PNS
34
What is white matter?
Collections of myelinated fibers (tracts)
35
What is gray matter?
Mostly unmyelinated fibers and cell bodies
36
What are sensory (afferent) neurons?
• Carry impulses from the sensory receptors to the CNS
• Receptors include:
*Cutaneous sense organs in skin
*Proprioceptors in muscles and tendons
37
What are motor (efferent) neurons?
Carry impulses from the central nervous system to viscera and/or muscles and glands
38
What are interneurons (association neurons)?
* Cell bodies located in the CNS?
| * Connect sensory and motor neurons
39
Structural classification is based on:
• The number of processes extending from the cell body
40
What are multipolar neurons?
* Many extensions from the cell body
* All motor and interneurons are multipolar
* Most common structural type
41
What are bipolar neurons?
* One axon and one dendrite
* Located in special sense organs, such as nose and eye
* Rare in adults
42
What are unipolar neurons?
* They have a short single process leaving the cell body
* Sensory neurons found in PNS ganglia
* Conduct impulses both toward and away from the cell body
43
What are the functional properties of neurons?
* Irritability
| * Conductivity
44
What is irritability?
Ability to respond to a stimulus and convert it to a nerve impulse
45
What is conductivity?
Ability to transmit the impulse to other neurons, muscles, or glands
46
What are the electrical conditions of a resting neuron’s membrane?
• The plasma membrane at rest is inactive (polarized)
• Fewer positive ions are inside the neuron’s plasma membrane than outside
*K+ is the major positive ion inside the cell
*N a+ is the major positive ion outside the cell
• As long as the inside of the membrane is more negative (fewer positive ions) than the outside, the cell remains inactive
47
What is action potential initiation and generation?
* A stimulus changes the permeability of the neuron’s membrane to sodium ions
* Sodium channels now open, and sodium (N a+) diffuses into the neuron
* The inward rush of sodium ions changes the polarity at that site and is called depolarization
* A graded potential (localized depolarization) exists where the inside of the membrane is more positive and the outside is less positive
* If the stimulus is strong enough and sodium influx great enough, local depolarization activates the neuron to conduct an action potential (nerve impulse)
48
What is propagation of the action potential?
* If enough sodium enters the cell, the action potential (nerve impulse) starts and is propagated over the entire axon
* All-or-none response means the nerve impulse either is propagated or is not
* Fibers with myelin sheaths conduct nerve impulses more quickly
49
What is repolarization?
* Membrane permeability changes again—becoming impermeable to sodium ions and permeable to potassium ions
* Potassium ions rapidly diffuse out of the neuron, repolarizing the membrane
* Repolarization involves restoring the inside of the membrane to a negative charge and the outer surface to a positive charge
* Initial conditions of sodium and potassium ions are restored using the sodium-potassium pump
* This pump, using A T P, restores the original configuration
* Three sodium ions are ejected from the cell while two potassium ions are returned to the cell
* Until repolarization is complete, a neuron cannot conduct another nerve impulse
50
What are the steps of transmission of the signal at synapses?
• Step 1: When the action potential reaches the axon terminal, the electrical charge opens calcium channels
• Step 2: Calcium, in turn, causes the tiny vesicles containing the neurotransmitter chemical to fuse with the axonal membrane
• Step 3: The entry of calcium into the axon terminal causes pore-like openings to form, releasing the neurotransmitter into the synaptic cleft
• Step 4: The neurotransmitter molecules diffuse across the synaptic cleft and bind to receptors on the membrane of the next neuron
• Step 5: If enough neurotransmitter is released, a graded potential will be generated
*Eventually an action potential (nerve impulse) will occur in the neuron beyond the synapse
• Step 6: The electrical changes prompted by neurotransmitter binding are brief
*The neurotransmitter is quickly removed from the synapse either by reuptake or by enzymatic activity
51
Transmission of an impulse is:
Electrochemical
52
Transmission down neuron is:
Electrical
53
Transmission to next neuron is:
Chemical
54
Reflexes are rapid, predictable, and involuntary responses to:
Stimuli
55
Reflexes occur over neural pathways called:
Reflex arcs
56
What are the two types of reflexes?
* Somatic reflexes
| * Autonomic reflexes
57
What are somatic reflexes?
* Reflexes that stimulate the skeletal muscles
* Involuntary, although skeletal muscle is normally under voluntary control
* Example: pulling your hand away from a hot object
58
What are autonomic reflexes?
* Regulate the activity of smooth muscles, the heart, and glands
* Example: regulation of smooth muscles, heart and blood pressure, glands, digestive system
59
What are the five elements of a reflex arc?
1. Sensory receptor—reacts to a stimulus
2. Sensory neuron—carries message to the integration center
3. Integration center (CNS)—processes information and directs motor output
4. Motor neuron—carries message to an effector
5. Effector organ—is the muscle or gland to be stimulated
60
What are two-neuron reflex arcs?
* Simplest type
| * Example: patellar (knee-jerk) reflex
61
What are three-neuron reflex arcs?
* Consists of five elements: receptor, sensory neuron, interneuron, motor neuron, and effector
* Example: flexor (withdrawal) reflex
62
What are the four main regions of the brain?
* Cerebral hemispheres
* Diencephalon
* Brain stem
* Cerebellum
63
Cerebral hemispheres are paired:
* (Left and right) superior parts of the brain
* Include more than half of the brain mass
* The surface is made of ridges (gyri) and grooves (sulci)
* Fissures are deeper grooves
* Lobes are named for the cranial bones that lie over them
64
What are the three main regions of cerebral hemisphere?
1. Cortex is superficial gray matter
2. White matter
3. Basal nuclei are deep pockets of gray matter
65
Which areas are in the cerebral cortex?
* Primary somatic sensory area
* Primary motor area
* Broca's area (motor speech area)
66
What are the cerebral areas involved in special senses?
* Visual area (occipital lobe)
* Auditory area (temporal lobe)
* Olfactory area (temporal lobe)
67
What is the primary somatic sensory area?
• Located in parietal lobe posterior to central sulcus
• Receives impulses from the body’s sensory receptors
*Pain, temperature, light touch (except for special senses)
• Sensory homunculus is a spatial map
• Left side of the primary somatic sensory area receives impulses from right side (and vice versa)
68
What is the primary motor area?
* Located anterior to the central sulcus in the frontal lobe
* Allows us to consciously move skeletal muscles
* Motor neurons form pyramidal (corticospinal) tract, which descends to spinal cord
* Motor homunculus is a spatial map
69
What is the Broca's area (motor speech area)?
* Involved in our ability to speak
| * Usually in left hemisphere
70
What are other specialized areas of the cerebral cortex?
* Anterior association area (frontal lobe)
* Posterior association area (posterior cortex)
* Speech area (for sounding out words)
71
What is cerebral white matter?
* Composed of fiber tracts deep to the gray matter
* Corpus callosum connects hemispheres
* Tracts, such as the corpus callosum, are known as commissures
* Association fiber tracts connect areas within a hemisphere
* Projection fiber tracts connect the cerebrum with lower C N S centers
72
What is basal nuclei?
* “Islands” of gray matter buried deep within the white matter of the cerebrum
* Regulate voluntary motor activities by modifying instructions sent to skeletal muscles by the primary motor cortex
73
What is the diencephalon?
* Sits on top of the brain stem
| * Enclosed by the cerebral hemispheres
74
What are the three structures which compose the diencephalon?
1. Thalamus
2. Hypothalamus
3. Epithalamus
75
What is the function of the thalamus in the diencephalon?
* Encloses the third ventricle
* Relay station for sensory impulses passing upward to the cerebral cortex
* Transfers impulses to the correct part of the cortex for localization and interpretation
76
What is the function of the hypothalamus in the diencephalon?
```
• Makes up the floor of the diencephalon
• Important autonomic nervous system center
*Regulates body temperature
*Regulates water balance
*Regulates metabolism
• Houses the limbic center for emotions
• Regulates the nearby pituitary gland
• Houses mammillary bodies for olfaction (smell)
```
77
What is the function of the epithalamus in the diencephalon?
* Forms the roof of the third ventricle
* Houses the pineal body (an endocrine gland)
* Includes the choroid plexus—forms cerebrospinal fluid
78
The brain stem attached to the:
Spinal cord
79
What are the three parts of the brain stem?
1. Midbrain
2. Pons
3. Medulla oblongata
80
What is the function of the midbrain in the brain stem?
* Extends from the mammillary bodies to the pons inferiorly
* Cerebral aqueduct (tiny canal) connects the third and fourth ventricles
* Two bulging fiber tracts, cerebral peduncles, convey ascending and descending impulses
* Four rounded protrusions, corpora quadrigemina, are visual and auditory reflex centers
81
What is the function of the pons in the brain stem?
* The rounded structure protruding just below the midbrain
* Mostly composed of fiber tracts
* Includes nuclei involved in the control of breathing
82
What is the function of the medulla oblongata in the brain stem?
• The most inferior part of the brain stem that merges into the spinal cord
• Includes important fiber tracts
• Contains important centers that control:
*Heart rate
*Blood pressure
*Breathing
*Swallowing
*Vomiting
• Fourth ventricle lies posterior to pons and medulla
83
What is reticular formation in the brain stem?
• Diffuse mass of gray matter along the brain stem
• Involved in motor control of visceral organs
• Reticular activating system (RAS)
*Plays a role in awake/sleep cycles and consciousness
*Filter for incoming sensory information
84
What is the cerebrum?
* Two hemispheres with convoluted surfaces
* Outer cortex of gray matter and inner region of white matter
* Controls balance
* Provides precise timing for skeletal muscle activity and coordination of body movements
85
What are the protection mechanisms of the central nervous system?
* Meninges
* Cerebrospinal fluid (CSF)
* Blood-brain barrier
86
What are the three main parts of the meninges in the central nervous system?
* Dura mater
* Arachnoid layer
* Pia mater
87
What is dura mater in the central nervous system?
• Outermost leathery layer
• Double-layered external covering
*Periosteum—attached to inner surface of the skull
*Meningeal layer—outer covering of the brain
• Folds inward in several areas
*Falx cerebri
*Tentorium cerebelli
88
What is the arachnoid layer in the central nervous system?
* Middle layer
* Web-like extensions span the subarachnoid space to attach it to the pia mater
* Subarachnoid space is filled with cerebrospinal fluid
* Arachnoid granulations protrude through the dura mater and absorb cerebrospinal fluid into venous blood
89
What is pia mater in the central nervous system?
* Internal layer
| * Clings to the surface of the brain and spinal cord
90
What is cerebrospinal fluid?
• Similar to blood plasma in composition
• Formed continually by the choroid plexuses
*Choroid plexuses—capillaries in the ventricles of the brain
• CSF forms a watery cushion to protect the brain and spinal cord
• Circulated in the arachnoid space, ventricles, and central canal of the spinal cord
91
What is the process of cerebrospinal fluid circulation?
1. CSF is produced by the choroid plexus of each ventricle
2. CSF flows through the ventricles and into the subarachnoid space via the median and lateral apertures. Some CSF flows through the central canal of the spinal cord
3. CSF flows through the subarachnoid space
4. CSF is absorbed into the dural venous sinuses via the arachnoid villi
92
What is the blood-brain barrier?
* Includes the least permeable capillaries of the body
* Allows water, glucose, and amino acids to pass through the capillary walls
* Excludes many potentially harmful substances from entering the brain, such as wastes
* Useless as a barrier against some substances
93
What are the types of traumatic brain injuries?
* Concussion
* Contusion
* Cerebrovascular accident (CVA), or stroke
* Transient ischemic attack (TIA)
94
What is a concussion?
* Slight brain injury
| * Typically little permanent brain damage occurs
95
What is a contusion?
* Marked nervous tissue destruction occurs
| * Coma may occur
96
Death may occur after head blows due to:
* Intracranial hemorrhage
| * Cerebral edema
97
What is a cerebrovascular accident (CVA), or stroke?
• Results when blood circulation to a brain area is blocked and brain tissue dies
• Loss of some functions or death may result
*Hemiplegia—one-sided paralysis
*Aphasia—damage to speech center in left hemisphere
98
What is a transient ischemic attack (TIA)?
* Temporary brain ischemia (restriction of blood flow)
| * Numbness, temporary paralysis, impaired speech
99
The spinal cord extends from the _____ of the skull to the first or second _____.
* Foramen magnum
| * Lumbar vertebra
100
_____ is a collection of spinal nerves at the inferior end of the spinal cord.
Cauda equina
101
The spinal cord provides a _____ pathway to and from the _____.
* Two-way conduction
| * Brain
102
__ pairs of spinal nerves arise from the spinal cord.
31
103
What is gray matter of the spinal cord and spinal roots?
• Internal gray matter is mostly cell bodies
• Dorsal (posterior) horns house interneurons
*Receive information from sensory neurons in the dorsal root; cell bodies housed in dorsal root ganglion
• Anterior (ventral) horns house motor neurons of the somatic (voluntary) nervous system
*Send information out ventral root
• Gray matter surrounds the central canal, which is filled with cerebrospinal fluid
104
What is white matter of the spinal cord?
* Composed of myelinated fiber tracts
* Three regions: dorsal, lateral, ventral columns
* Sensory (afferent) tracts conduct impulses toward brain
* Motor (efferent) tracts carry impulses from brain to skeletal muscles
105
The PNS consists of
| _____ outside the CNS.
Nerves and ganglia
106
Nerves are bundles of _____ found outside the CNS.
Neurons
107
_____ is a connective tissue sheath that surrounds each fiber of a nerve.
Endoneurium
108
Perineurium wraps groups of fibers bound into a:
Fascicle
109
Epineurium binds groups of:
Fascicles
110
Concept Link 2
The terms for the connective tissue coverings of a nerves should seem familiar: We discussed similar structures in the muscle chapter (Figure 6.1, p. 183). Names of muscle structures include the root word mys, whereas the root word neuro tells you that the structure relates to a nerve. For example, the endomysium covers one individual muscle fiber, whereas the endoneurium covers one individual neuron fiber.
111
What are mixed nerves?
Contain both sensory and motor fibers
112
What are sensory (afferent) nerves?
Carry impulses toward the CNS
113
What are motor (efferent) nerves?
Carry impulses away from the CNS
114
__ pairs of cranial nerves serve mostly the head and neck.
* 12
| * Only the pair of vagus nerves extends to thoracic and abdominal cavities
115
Most cranial nerves are mixed nerves, but what are the three which are sensory only?
* Optic
* Olfactory
* Vestibulocochlear
116
Cranial nerves mnemonic device
* Oh – Olfactory
* Oh – Optic
* Oh – Oculomotor
* To – Trochlear
* Touch – Trigeminal
* And – Abducens
* Feel – Facial
* Very – Vestibulocochlear
* Green – Glossopharyngeal
* Vegetables – Vagus
* A – Accessory
* H – Hypoglossal
117
What are spinal nerves?
* 31 pairs
* Formed by the combination of the ventral and dorsal roots of the spinal cord
* Named for the region of the spinal cord from which they arise
118
Spinal nerves divide soon after leaving the spinal cord into a _____ and a _____.
* Dorsal ramus
| * Ventral ramus
119
What is the ramus of a spinal nerve?
Branch of a spinal nerve; contains both motor and sensory fibers
120
What is the dorsal rami of a spinal nerve?
Serve the skin and muscles of the posterior trunk
121
What is the ventral rami (T1–T12) of a spinal nerve?
Form the intercostal nerves that supply muscles and skin of the ribs and trunk
122
What is the ventral rami (except T1–T12) of a spinal nerve?
Form a complex of networks (plexus) for the anterior
123
What are plexuses?
Networks of nerves serving motor and sensory needs of the limbs
124
Plexuses form from ventral rami of spinal nerves in the _____, _____, and _____ regions.
* Cervical
* Lumbar
* Sacral
125
What are the four plexuses of the spinal nerves?
* Cervical
* Brachial
* Lumbar
* Sacral
126
What is the motor subdivision of the PNS?
* Consists only of motor nerves
* Controls the body automatically (and is also known as the involuntary nervous system)
* Regulates cardiac and smooth muscles and glands
127
What is the somatic nervous system?
* Motor neuron cell bodies originate inside the CNS
| * Axons extends to skeletal muscles that are served
128
What is the autonomic nervous system?
• Chain of two motor neurons
*Preganglionic neuron is in the brain or spinal cord
*Postganglionic neuron extends to the organ
• Has two arms
*Sympathetic division
*Parasympathetic division
129
Parasympathetic division is also known as the:
Craniosacral division
130
Preganglionic neurons originate in:
* Cranial nerves III, VII, IX, and X
| * S2 through S4 regions of the spinal cord
131
Preganglionic neurons synapse with _____; from there, _____ extend to organs that are served.
* Terminal ganglia
| * Postganglionic axons
132
Sympathetic division is also known as the:
Thoracolumbar division
133
In sympathetic division, preganglionic neurons originate from __ through __.
* T1
* L2
* Axons pass through a ramus communicans to enter a sympathetic trunk ganglion
* Sympathetic trunk, or chain, lies near the spinal cord
134
After synapsing at the _____, the axon may synapse with a _____ at the same or different level, or the _____ may pass through the ganglion without synapsing and form part of the _____.
* Ganglion
* Second neuron
* Preganglionic neuron
* Splanchnic nerves
* Splanchnic nerves travel to the collateral ganglion
* Collateral ganglia serve the abdominal and pelvic organs
135
Body organs served by the _____ receive fibers from _____.
* Autonomic nervous system
* Both divisions (sympathetic division and parasympathetic division)
* Exceptions: blood vessels, structures of the skin, some glands, and the adrenal medulla
* These exceptions receive only sympathetic fibers
136
When body divisions serve the same organ, they cause _____ effects due to different _____.
* Antagonistic
| * Neurotransmitters
137
Parasympathetic (cholinergic) fibers release:
Acetylcholine
138
Sympathetic postganglionic (adrenergic) fibers release:
Norepinephrine
139
Preganglionic axons of both divisions release:
Acetylcholine
140
What is the sympathetic (fight or flight) division?
```
• Response to unusual stimulus when emotionally or physically stressed or threatened
• Takes over to increase activities
• Remember as the “E” division:
*Exercise
*Excitement
*Emergency
*Embarrassment
```
141
What are parasympathetic (housekeeping) activities?
```
• “Rest-and-digest” system
• Conserves energy
• Maintains daily necessary body functions
• Remember as the “D” division:
*Digestion
*Defecation
*Diuresis
```
142
The nervous system is formed during the first month of:
* Embryonic development
| * Any maternal infection can have extremely harmful effects
143
_____ destroys brain cells.
Oxygen deprivation
144
The _____ is one of the last areas of the brain to develop.
Hypothalamus
145
Severe congenital brain diseases include:
* Cerebral palsy
* Anencephaly
* Hydrocephalus
* Spina bifida
146
Premature babies have trouble _____ because the _____ is one of the last brain areas to mature prenatally
* Regulating body temperature
| * Hypothalamus
147
Development of _____ indicates the _____ and maturation of a child’s nervous system
* Motor control
| * Progressive myelination
148
Brain growth ends in:
* Young adulthood
| * Neurons die throughout life and are not replaced; thus, brain mass declines with age
149
_____ is low blood pressure due to changes in _____.
* Orthostatic hypotension
| * Body position
150
Healthy aged people maintain nearly optimal:
Intellectual function
151
What is the major cause of declining mental function with age?
Disease—particularly cardiovascular disease
152
What is arteriosclerosis?
Decreased elasticity of blood vessels
