Chapter 15 Sensory Pathways and the Somatic Nervous System
If the primary sensory cortex were damaged or the projection fibers cut, a person would be able to detect light touch but would be unable to determine __________. A-the source of the stimulus B-the amount of pressure C-the magnitude of the stimulus D-All of the listed responses are correct.
A
Which of the following terms refers to a number of disorders affecting voluntary motor performance that may be caused by trauma during birth? A-paresthesia B-cerebral palsy C-aphasia D-anencephaly
B
which three pairs of descending tracts make up the corticospinal pathway?
Corticobulbar tract Lateral corticospinal tract Anterior corticospinal tract
Which of the following receptors are stimulated when a stiff breeze blows across the skin of your arm and moves some of the hairs? A-lamellated corpuscles B-Golgi tendon organs C-Ruffini corpuscles D-root hair plexuses
D
Identify six types of tactile receptors located in the skin, and describe their sensitivities
Free nerve endings- sensitive to touch and pressure Root hair plexus- monitors distortions and movements across the body surface Tactile discs- detect fine touch and pressure Bulbous corpuscle (ruffini corpuscles)- sensitive to pressure and distortion of the skin Lamellar corpuscle (pacinian corpuscles)- sensitive to pulsing or vibrating stimuli (deep pressure) Tactile corpuscle (meissner corpuscle)-detect find touch and pressure
Harry, a construction worker, suffers a fractured skull when a beam falls on his head. Diagnostic test indicate severe damage to the primary motor cortex. His wife is anxious to know if he will ever be able to move or walk again. What would you tell her?
Injuries to the primary motor cortex eliminate the ability to produce fine control of motor unites. However, as long as the cerebral nuclei are function, gross movements would still be possible. He should still be able to walk, maintain his balance, and perform voluntary and involuntary movements using the rubrospinal and reticulospinal tracts in place of the corticospinal tracts. Although these movements may be awkward or difficult, they will still be possible
Why does the sensory homunculus appear distorted in the face and hands?
It is a representation of the number of sensory neurons in the given body areas.
List the major types of general sensory receptors, and identify the nature of the stimulus that excites each type
Nociceptors (pain) Thermoreceptors (temperature) Mechanoreceptors (physical distortion) Chemoreceptors (chemical concentration)
_____________ receptors are normally inactive, but become active for a short time whenever there is a change in the modality that they monitor
Phasic
Receptor A has a circular receptive field on the skin surface with a diameter of 2.5 cm. Receptor B has a circular receptive field 7.0 cm in diameter. Which receptor provides more precise sensory information?
Receptor A provides more precise sensory information because it has a smaller receptive field on the skin surface
What do we call the body's specialized cells that monitor specific internal or external conditions
Sensory receptors
what are the three major somatic sensory pathways and their functions?
Spinothalamic pathway-provides conscious sensations of poorly localized (crude) touch, pressure, pain and temperature Posterior column pathway-provides conscious sensations of highly localized (fine) touch, pressure, vibration, and proprioception Spinocerebellar pathway- carries proprioceptive information about the position of skeletal muscles, tendons, and joints to the cerebellum
Identify the three classes of mechanoreceptors
Tactile receptors Baroreceptors Proprioceptors
what three types of mechanoreceptors respond to stretching, compression, twisting, or other distortions of their plasma membrane
Tactile receptors Baroreceptors Proprioceptors
Is it possible for somatic motor commands to occur at the subconscious level?
Yes
what is a motor homunculus? How does it differ from a sensory homunculus?
a motor homunculus is a mapped-out area of the primary motor cortex, provides an indication of the degree of fine motor control available a sensory homunculus indicates the relative density of peripheral sensory receptors
An individual would lose two-point discrimination at 3-5 mm on which region or regions of the body?
backs of hands and feet
Which type of receptor detects volumes of digestive materials in the colon? A-thermoreceptor B-proprioceptor C-chemoreceptor D-baroreceptor
baroreceptor
The background patterns of movement involved in voluntary motor activities are controlled by the __________.
basal nuclei
Visceral sensory information is distributed primarily to reflex centers in the __________.
brain stem and diencephalon
Chemoreceptors in the medulla oblongata would be sensitive to changes in pH and PCO2 in __________.
cerebrospinal fluid
The three integrated pathways controlling conscious and subconscious motor commands in skeletal muscle are the __________.
corticospinal, medial, and lateral
The spinothalamic pathway relays impulses associated with __________.
crude sensations of touch, pressure, pain, and temperature
The spinocerebellar pathway carries information concerning the __________.
position of muscles, tendons, and joints to the cerebellum
The three major somatic sensory pathways are the __________.
posterior column, spinothalamic, and spinocerebellar
The integrative activities performed by neurons in the cerebellar cortex and cerebellar nuclei are essential to the __________
precise control of voluntary and involuntary movements
The primary sensory cortex of the cerebral hemispheres or areas of the cerebellar hemispheres receives __________.
somatic sensory information
If a tract name begins with spino-, it must start in the __________.
spinal cord and end in the brain, carrying sensory information
When someone touches a hot stove, the rapid, automatic, preprogrammed response that preserves homeostasis is provided by the __________
spinal reflex
If the name of a tract ends in -spinal, its axons must __________.
start in the higher centers and end in the spinal cord, bearing motor commands
explain the phenomenon of referred pain in terms of labeled lines and organization of sensory tracts and pathways
strong pain sensations arriving at a particular segment of the spinal cord can cause simulations of the interneurons of the spinothalamic pathway. This stimulation is interpreted by the somatsensory cortex as originating in the region of the body surface associated with the origin of the same labeled line or pathway
which spinal tract carries action potentials generated by nociceptors?
the lateral spinothalamic tracts
Tactile receptors provide sensations of __________.
touch, pressure, and vibration
What would happen to you if the information from proprioceptors in your legs were blocked from reaching the CNS?
your movements would be uncoordinated and you likely could not walk
what are the two primary functional roles of the cerebellum?
1- integrates proprioceptive sensations with visual information from the eyes and equilibrium-related sensations from the internal ear 2- adjusts the activities of the voluntary and involuntary motor centers on the basis of sensory information and the stored memories of previous experiences
what three steps are necessary for transduction to occur?
1-an arriving stimulus alters the membrane potential of the receptor cell 2-the receptor potential directly or indirectly affects a sensory neuron 3-action potentials travel to the CNS along an afferent fiber
The axons of the posterior column ascend within __________. A-the fasciculus gracilis and fasciculus cuneatus B-the posterior and lateral spinothalamic tracts C-the posterior and interior spinocerebellar tracts D-all of the listed tracts
A
The posterior column pathway receives sensations associated with which of the following? A-highly localized fine touch, pressure, vibration, and position B-pain and temperature C-crude touch and pressure D-All of the listed responses are correct.
A
the corticospinal tract A- carries motor commands from the cerebral cortex to the spinal cord B-carries sensory information from teh spinal cord to the brain C- starts in the spinal cord and ends in the brain D-does all of these
A
Describe the relationship among first-order, second-order, and third-order neurons in a sensory pathway
A sensory neuron that delivers sensations to the CNS is a first-order neuron. Within the CNS< the axon of the first-order neuron synapses on a second-order neuron, which is an interneuron located in the spinal cord or brainstem. The second-order neuron synapses on a third-order neuron in the thalamus. The axons of third-order neurons synapse on neurons of the primary somatosensory cortex of the cerebral hemispheres
Differentiate between a tonic receptor and a phasic receptor
A tonic receptor is always active a phasic receptor is normally inactive and becomes active only when a change occurs in the condition (modality) being monitored
The CNS interprets information entirely on the basis of the A-number of action potentials that it receives B-kind of action potentials that it receives C-line over which sensory information arrives D-intensity of the sensory stimulus E-Number of sensory receptors that are stimulated
C
Which of the following correctly defines referred pain? A-pain localized to a specific, small area of the body where injury has occurred B-pain felt as being received from an amputated limb C-pain felt in an uninjured body area when the injury has actually occurred in another location D-pain generalized all over the body, such as the pain accompanying a fever
C
the larger the receptive field, the A-larger the stimulus needed to stimulate a sensory receptor B-fewer sensory receptors there are C-harder it is to locate the exact point of stimulation D-larger the area of the somatosensory cortex in the brain that deals with the area E-closer together the receptor cells
C
"Itch spots" can be found in all EXCEPT which of the following areas of the body? A-inner surface of eyelids B-skin C-nasal mucous membranes D-trachea
D
The area of primary somatosensory cortex devoted to a body region is relative to the A-size of the body area B-distance of the body area from the brain C-density of motor units in the area of the body D-density of sensory receptors in the area of the body E-size of the nerves that serve the area of the body
D
by which structures and in which part of the brain is the level of muscle tone in the body's skeletal muscles controlled? how is this control exerted?
Muscle tone is controlled by the basal nuclei, cerebellum, and red nuclei through commands distributed by the reticulospinal and rubrospinal tracts
The upper motor neuron of a somatic motor pathway has a cell body that lies in __________.
a central nervous system (CNS) processing center
Ruffini corpuscles and Golgi tendon organs are similar in their __________.
ability to detect tension and distortion
Judith is receiving messages in her brain from baroreceptors in the stomach, chemoreceptors detecting PO2 levels in the blood, and tactile receptors in the skin. All this information must be transmitted in what type of format to be detected by the central nervous system (CNS)?
action potentials
an injury involving the superior portion of the motor cortex affects which region of the body?
affects the ability to control the muscles in the upper limb and the proximal portion of the lower limb
what effect does injury to the primary motor cortex have on peripheral muscles?
affects the ability to exert fine control over motor units. Gross movements are still possible however because they are controlled by the basal nuclei that use the reticulospinal or rubrospinal tracts. Thus, walking and other voluntary and involuntary movements can be performed with difficulty, and the movements are imprecise and awkward
The basal nuclei contain two populations of neurons. Neurons in the first group release acetylcholine (ACh), which has __________ effect on the neurons they synapse with; neurons in the second group release gamma aminobutyric acid (GABA), which has __________ effect.
an excitatory; an inhibitory
Somatic motor pathways always involve __________.
an upper and lower motor neuron
A condition in which the brain of a newborn infant has failed to develop is called __________.
anencephaly
The spinocerebellar pathway includes the __________.
anterior and posterior tracts
The center of somatic motor control that coordinates complex motor patterns is the __________.
cerebellum
The center of somatic motor control that plans and initiates voluntary motor activity is the __________.
cerebral cortex
Denzel had to have his arm amputated at the elbow after an accident. He tells you that he can sometimes still feel pain in his fingers even though the hand is gone. He says this is especially true when he bumps the stub. How can this be?
he is experiencing phantom pain. Since pain perception occurs in the somatosensory cortex of the brain, he can still feel pain in his fingers if the brain projects feeling to that area. When he bumps the arm at the elbow, sensory receptors are stimulated to send impulses to the somatsensory cortex. The brain perceives a sensation from a general area, and projects that feeling to a body part. Since more sensory information reaches the brain from the hands and fingers, it is not unusual for the brain to project to this area
what effect would increased stimulation of the motor neurons of the red nucleus have on muscle tone?
increase stimulation of the skeletal muscles in the upper limbs, increasing their muscle tone
Define adaptation
it is a decrease in receptor sensitivity or a decrease in perception during constant stimulation
An individual whose primary motor cortex has been destroyed retains the ability to walk and maintain balance, but the movements __________
lack precision and are awkward and poorly controlled
The primary goal of the vestibular nuclei is __________.
maintaining posture and balance
The center of somatic motor control that controls basic respiratory reflexes is the __________.
medulla oblongata
Amyotrophic lateral sclerosis (ALS) is a degenerative disorder that affects __________.
motor neurons and their associated skeletal muscles
A sensory first-order neuron traveling along the posterior column pathway from the arm would synapse in the __________.
nucleus cuneatus
Nociceptors, common in the skin, in joint capsules, and around the walls of blood vessels, are sensory receptors for __________.
pain
The efferent division of the nervous system that includes nuclei, motor tracts, and motor neurons controls __________.
peripheral effectors
The receptors that provide information about the intensity and rate of change of a stimulus are called __________.
phasic receptors
Which part of the brain is responsible for the highest level of motor command in terms of complexity and voluntary motion?
primary motor cortex
In the thalamus, data arriving over the posterior column pathway are integrated, sorted, and projected to the __________.
primary sensory cortex
Voluntary and involuntary somatic motor commands issued by the brain reach peripheral targets by traveling over the __________
pyramidal and extrapyramidal systems
If a sensation arrives at the wrong part of the sensory cortex, you will __________.
reach an improper conclusion about the source of the stimulus
Free nerve endings can be stimulated by many different stimuli because they exhibit little __________.
receptor specificity
The reticulospinal tract is involved with __________.
regulation of involuntary reflex activity and autonomic functions
A person demonstrating anesthesia in a given area has lost __________.
sensation of touch, sensation of pressure, and sensitivity to pain and temperature
The motor neurons and pathways that control skeletal muscles form the __________.
somatic nervous system
what is the anatomical basis for the fact that the left side of the brain controls motor functions on the right side of the body?
the anatomical basis for opposite-side motor control is crossing over (decussation) of axons, so the motor fibers of the corticospinal pathway innervate lower motor neurons on the opposite side of the body
as a result of pressure on her spinal cord, Jill cannot feel fine touch or pressure on her lower limbs. Which spinal tract is being compressed?
the gracile fasciculus in the posterior column of the spinal cord, which carries information about touch and pressure from the lower limbs to the brain would be compressed
which cerebral hemisphere receives impulses carried by the right gracile fasciculus?
the left cerebral hemisphere (specifically, the primary somatosensory cortex)
Kayla is having difficulty controlling her eye movements and has lost some control of her facial muscles. After an examination and testing, Kayla's physician tells her that her cranial nerves are perfectly normal but that a small tumor is putting pressure on certain fiber tracts in her brain. This pressure is the cause of Kayla's symptoms. Where is the tumor most likely located?
the tumor is most likely adjacent to the corticobulbar tracts. The axons of those tracts carry action potentials to motor nuclei of the cranial nerves, which control eye muscles and muscles of facial expressions.
Thermoreceptors are phasic receptors because they are __________
very active when the temperature is changing
which three motor tracts make up the medial pathway?
vestibulospinal tract tectospinal tract reticulospinal tract
The motor tracts in the spinal cord controlling subconscious regulation of balance and muscle tone are the __________.
vestibulospinal tracts
damage to the posterior spinocerebellar tract on the left side of the spinal cord at the L1 level would interfere with the coordinated movement of which limb(s)
would interfere with the coordinated movement of the left leg
