Chapter 11-13 In Text Questions

What is a transient ischemic attack (TIA) and how is it different from a stroke?

A TIA is a temporary loss of blood supply to brain tissue, and it differs from a stroke in that the resulting impairment is fully reversible.

Which type of neuroglia controls the extracellular fluid environment around neuron cell bodies in the CNS? In the PNS?

Astrocytes control the extracellular environment around neuron cell bodies in the CNS, whereas satellite cells perform this function in the PNS.

What structure joins two neurons at an electrical synapse?

At an electrical synapse, neurons are joined by gap junctions.

Which structural and functional type of neuron is activated first when you burn your finger? Which type is activated last to move your finger away from the source of heat?

Burning a finger will first activate unipolar (pseudounipolar) neurons that are sensory (afferent) neurons. The impulse to move your finger away from the heat will be carried by multipolar neurons that are motor (efferent) neurons.

What is CSF? Where is it produced? What are its functions?

CSF, formed by the choroid plexuses as a filtrate of blood plasma, is a watery "broth" similar in composition to plasma. It protects the brain and spinal cord from blows and other trauma, helps nourish the brain, and carries chemical signals from one part of the brain to another.

Which type of fiber allows the two cerebral hemispheres to "talk to each other"?

Commissural fibers (which form commissures) allow the cerebral hemispheres to "talk to each other."

Why does a myelinated axon conduct action potentials faster than a nonmyelinated axon?

Conduction of action potentials is faster in myelinated axons because myelin allows the axon membrane between myelin sheath gaps to change its voltage rapidly, and allows current to flow only at the widely spaced gaps.

What is the function of convolutions of the brain?

Convolutions increase the surface area of the cortex, which allows more neurons to occupy the limited space within the skull.

Why is cyclic AMP called a second messenger?

Cyclic AMP (cAMP) is called a second messenger because it relays the message between the first messenger (the original chemical messenger) outside of the cell and effector molecules that will ultimately bring about the desired response within the cell.

On the cross section of the spinal cord below, label the central canal, and dorsal and ventral roots and horns. Draw in a sensory neuron, showing the location of its cell body and axon terminals. What is in the central canal?

Make sure that the sensory neuron you drew has a unipolar shape (there should be a clear "T-shaped junction" of the axon attached to the cell body with the central and peripheral axons; see also p. 397). The central canal contains CSF.

Mrs. Lee, a neurology patient, seldom smiles, has a shuffling, stooped gait, and often spills her coffee. What degenerative brain disorder might she have?

Mrs. Lee might have Parkinson's disease.

Name the components of the basal nuclei.

The caudate nucleus, putamen, and globus pallidus together form the basal nuclei.

What anatomical landmark of the cerebral cortex separates primary motor areas from somatosensory areas?

The central sulcus separates primary motor areas from somatosensory areas.

Which parts of the nervous system ultimately plan and coordinate complex motor activities?

The cerebellum and basal nuclei, which form the precommand level of motor control, plan and coordinate complex motor activities.

Which ventricle is surrounded by the diencephalon?

The third ventricle is surrounded by the diencephalon.

After his horse-riding accident, the actor Christopher Reeve was unable to breathe on his own. Which ventral rami, nerve plexus, and major nerve were involved?

The ventral rami were C3-C5, the nerve plexus was the cervical plexus, and the major nerve was the phrenic nerve. The phrenic nerve is the sole motor nerve supply to the diaphragm, the primary muscle for respiration.

The graph below shows an intracellular recording of an action potential. For the x and y axes, what is being measured and in what units? Name phases a, b, and c. For each phase, state the permeability change(s) responsible.

The x axis indicates time measured in milliseconds (ms). The y axis indicates membrane potential (which is the difference in voltage between the inside and outside of the cell) in millivolts (mV). Phase (a) is depolarization, which is due to an increase in permeability to Na+. Phase (b) is repolarization, which is due to both a decrease in permeability to Na+ and an increase in permeability to K+. Phase (c) is hyperpolarization, which is due to delayed closure of K+ channels, which means that the membrane is still more permeable to K+ than it is at rest.

What is the explanation for the cervical and lumbar enlargements of the spinal cord?

The nerves serving the limbs arise in the cervical and lumbar enlargements of the spinal cord.

What is the structural classification of the neuron shown below? What is its usual functional classification? Name the parts labeled a-d.

The neuron is a unipolar (or pseudounipolar) neuron that acts as a sensory neuron. The parts of this neuron are (a) receptive endings, (b) peripheral process (part of the axon), (c) cell body, and (d) axon terminals.

Name the cranial nerve(s) most involved in each of the following: moving your eyeball; sticking out your tongue; controlling your heart rate and digestive activity; shrugging your shoulders.

The oculomotor (III), trochlear (IV), and abducens (VI) nerves control eye movements. Sticking out your tongue involves the hypoglossal nerve (XII). The vagus nerve (X) influences heart rate and digestive activity. The accessory nerve (XI) innervates the trapezius muscle, which is involved in shoulder shrugging.

What pattern of neural processing occurs when we smell freshly baked apple pie and remember Thanksgiving at our grandparents' house, the odor of freshly cooked turkey, sitting by the fire, and other such memories?

The pattern of neural processing is parallel processing.

What pattern of neural processing occurs when your finger accidentally touches a hot grill? What is this type of pathway called?

The pattern of neural processing is serial processing. The response is a reflex arc.

Three-year-old Jessica proudly shows you how she can wiggle her left big toe in the sand. Where precisely are the pyramidal cells that allow her to perform this movement? (Name the side, lobe, and region of the brain.) Where are the cell bodies of the neurons that these pyramidal cells synapse with?

The pyramidal cells controlling left big toe movement are in the right primary motor cortex in the frontal lobe. They synapse with the cell bodies of ventral horn neurons in the spinal cord.

What determines the size of a graded potential?

The size of a graded potential is determined by the strength of a stimulus.

What is meant by "integration," and does it primarily occur in the CNS or the PNS?

Integration involves processing and interpreting sensory information, and making a decision about motor output. Integration occurs primarily in the CNS.

Five-year-old Kayla in the pediatric neurology ward has a brain tumor that is interfering with her cerebellar function. What problems would you expect her to have?

Kayla would likely have problems with executing smooth, coordinated movements. This would affect her balance so she might fall over when walking or running, and might have trouble keeping up with her peers. Her motor tone would also likely be decreased so her limbs might seem "floppy."

Draw a chemical synapse, showing the locations of voltage-gated and chemically gated ion channels. What causes each to open?

As shown in the diagram, voltage-gated ion (Ca2+) channels are found in the presynaptic axon terminal. They open when an action potential reaches the axon terminal. Chemically gated ion channels are found in the postsynaptic membrane and open when neurotransmitter binds to the receptor protein.

The hypothalamus oversees a branch of the peripheral nervous system. Which branch?

The hypothalamus oversees the autonomic nervous system.

What are the pyramids of the medulla? What is the result of decussation of the pyramids?

The pyramids of the medulla are the corticospinal (pyramidal) tracts, the large voluntary motor tracts descending from the motor cortex. The result of decussation (crossing over) is that each side of the motor cortex controls the opposite side of the body.

What are the three levels of sensory integration?

The three levels of sensory integration are receptor level, circuit level, and perceptual level.

Why is the thalamus called the "gateway to the cerebral cortex"?

Virtually all inputs ascending to the cerebral cortex synapse in the thalamus en route.

Which subdivision of the PNS is involved in (a) relaying the feeling of a "full stomach" after a meal, (b) contracting the muscles to lift your arm, and (c) increasing your heart rate?

(a) This "full stomach" feeling would be relayed by the sensory (afferent) division of the PNS (via its visceral afferent fibers). (b) The somatic nervous system, which is part of the motor (efferent) division of the PNS, controls movement of skeletal muscle. (c) The autonomic nervous system, which is part of the motor (efferent) division of the PNS, controls the heart rate.

Which part of the neuron is its fiber? How do nerve fibers differ from the fibers of connective tissue (see Chapter 4) and the fibers in muscle (see Chapter 9)?

A nerve fiber is a long axon, an extension of the cell. In connective tissue, fibers are extracellular proteins that provide support. In muscle tissue, a muscle fiber is a muscle cell.

What is in a nerve besides axons?

Nerves also contain connective tissue, blood vessels, lymphatic vessels, and the myelin surrounding the axons.

You've cut your finger on a broken beaker in your A&P lab. Using stimulus type, location, and receptor structure, classify the sensory receptors that allow you to feel the pain.

Nociceptors respond to painful stimuli. They are exteroceptors that are nonencapsulated (free nerve endings).

Which two types of neuroglia form insulating coverings called myelin sheaths?

Oligodendrocytes and Schwann cells form myelin sheaths in the CNS and PNS, respectively.

What is the key difference between tonic and phasic receptors? Why are pain receptors tonic?

Phasic receptors adapt, whereas tonic receptors exhibit little or no adaptation. Pain receptors are tonic so that we are reminded to protect the injured body part.

When Taylor begins to feel drowsy while driving, she opens her window, turns up the volume of the car stereo, and sips ice-cold water. How do these actions help keep her awake?

Taylor is increasing the amount of sensory stimuli she receives, which will be relayed to the reticular activating system, which, in turn, will increase activation of the cerebral cortex.

In what ways are the cerebellum and the cerebrum similar? In what ways are they different?

There are many possible answers to this question—here are a few: Structurally, the cerebellum and cerebrum are similar in that they both have a thin outer cortex of gray matter, internal white matter, and deep gray matter nuclei. Also, both have body maps (homunculi) and large fiber tracts connecting them to the brain stem. Both receive sensory input and influence motor output. A major difference is that the cerebellum is almost entirely concerned with motor output, whereas the cerebrum has much broader responsibilities. Also, while a cerebral hemisphere controls the opposite side of the body, a cerebellar hemisphere controls the same side of the body.

Juan injured his back in a fall. When his ER physician stroked the bottom of Juan's foot, she noted that his big toe pointed up and his other toes fanned out. What is this response called and what does it indicate?

This response is called Babinski's sign and it indicates damage to the corticospinal tract or primary motor cortex.

What is the difference between temporal summation and spatial summation?

temporal summation is summation in time of graded potentials occurring in quick succession at the postsynaptic membrane. It can result from EPSPs arising from just one synapse. Spatial summation is summation in space—a postsynaptic neuron is stimulated by a large number of terminals at the same time.

Trevor was tackled while playing football. After hitting the ground, he was unable to move his lower limbs. What is a loss of motor function called? What level of his spinal cord do you think was injured (cervical, thoracic, lumbar, or sacral)? Is this a permanent injury?

A loss of motor function is called paralysis. Lower limb paralysis could be caused by a spinal cord injury in the thoracic region (between T1 and L1). If the spinal cord is transected, the result is paraplegia. If the cord is only bruised, he may regain function in the limbs.

Figure 12.34 shows both tracts and nerves, as well as nuclei and ganglia. How do tracts and nerves differ? How do nuclei and ganglia differ? (Hint: See Chapter 11, pp. 394-395.)

A nerve is a bundle of axons in the PNS, whereas a tract is a bundle of axons in the CNS. A nucleus is a collection of neuron cell bodies in the CNS, whereas a ganglion is a collection of neuron cell bodies in the PNS.

How does a nucleus within the brain differ from a nucleus within a neuron?

A nucleus within the brain is a cluster of neuron cell bodies, whereas the nucleus within each neuron is a large organelle that acts as the control center of the cell.

ACh excites skeletal muscle and yet it inhibits heart muscle. How can this be?

ACh interacts with more than one specific receptor type, and this explains how it can excite at some synapses and inhibit at others.

Which is bigger, a graded potential or an action potential? Which travels farther? Which initiates the other?

Action potentials are larger than graded potentials and travel farther. Graded potentials generally initiate action potentials.

Amber, your 2-year-old patient, has no pain receptors (a condition called congenital insensitivity to pain). What problems would you expect Amber to have over the course of her life?

Amber is likely to suffer from numerous undetected injuries. These could lead to infection (and possibly amputation).

An action potential does not get smaller as it propagates along an axon. Why not?

An action potential is regenerated anew at each membrane patch.

When would you see delta waves in an EEG?

Delta waves are typically seen in deep sleep in normal adults.

Which two states of consciousness are between alertness and coma?

Drowsiness (or lethargy) and stupor are stages of consciousness between alertness and coma.

What are ganglia?

Ganglia are collections of neuron cell bodies in the PNS.

Your cortex decodes incoming action potentials from sensory pathways. How does it tell the difference between hot and cold? Between cool and cold? Between ice on your finger and ice on your foot?

Hot and cold are conveyed by different sensory receptors that are parts of separate "labeled lines." Cool and cold are two different intensities of the same stimulus, detected by frequency coding—the frequency of APs would be higher for a cold stimulus than for a cool one. Action potentials arising in the fingers and foot arrive at different locations in the somatosensory cortex via their own "labeled lines" and in this way the cortex can determine their origin.

Which ions flow through chemically gated channels to produce IPSPs? EPSPs?

IPSPs result from the flow of either K+ or Cl− through chemically gated channels. EPSPs result from the flow of both Na+ and K+ through chemically gated channels.

If an axon receives two stimuli close together in time, only one AP occurs. Why?

If a second stimulus occurs before the end of the absolute refractory period, no AP can occur because sodium channels are still inactivated.

Your PNS mostly consists of nerves. What else belongs to your PNS?

In addition to nerves, the PNS also consists of sensory receptors, motor endings, and ganglia.

How is a myelin sheath formed in the CNS, and what is its function?

In the CNS, a myelin sheath is formed by oligodendrocytes that wrap their plasma membranes around the axon. The myelin sheath protects and electrically insulates axons and increases the speed of transmission of nerve impulses.

Where are the cell bodies of the first-, second-, and third-order sensory neurons in the spinothalamic pathway located?

In the spinothalamic pathway, the cell bodies of first-order sensory neurons are outside the spinal cord in a ganglion, cell bodies of second-order sensory neurons are in the dorsal horn of the spinal cord, and cell bodies of third-order sensory neurons are in the thalamus. (See also Figure 12.34b.)

Using the spinal cord cross section below, draw and label the five components of a reflex arc. Make sure the cell bodies are placed correctly. Name the structure that contains the cell body of the sensory neuron.

Make sure that in your drawing (as in the diagram), the cell body of the sensory neuron is in the dorsal root ganglion, the cell body of the interneuron is in the dorsal horn, and the cell body of the motor neuron is in the ventral horn.

During which sleep stage are most skeletal muscles actively inhibited?

Most skeletal muscles are actively inhibited during REM sleep.

Mike, who is left-handed, decided to wear his favorite T-shirt to his anatomy class. On his T-shirt were the words "Only left-handed people are in their right minds." What does this statement mean?

Motor functions on the left side of the body are controlled by the right hemisphere of the brain because motor tracts from the right hemisphere cross over (in the medulla oblongata) to the left side of the spinal cord to go to the left side of the body.

Which types of neural circuits would give a prolonged output after a single input?

Reverberating circuits and parallel after-discharge circuits both result in prolonged output.

Spinal nerves have both dorsal roots and dorsal rami. How are these different from each other in location and composition?

Roots lie medial to spinal nerves, whereas rami lie lateral to spinal nerves. Dorsal roots are purely sensory, whereas dorsal rami carry both motor and sensory fibers.

Will's femoral nerve was crushed while clinicians tried to control bleeding from his femoral artery. This resulted in loss of function and sensation in his leg, which gradually returned over the course of a year. Which cells were important in his recovery?

Schwann cells, macrophages, and the neurons themselves were all important in healing the nerve.

The limbic system is sometimes called the emotional-visceral brain. Which part of the limbic system is responsible for the visceral connection?

The hypothalamus is part of the limbic system and also an autonomic (visceral) control center.

Which two areas of the adult brain have an outside layer of gray matter in addition to central gray matter and surrounding white matter?

The cerebral hemispheres and the cerebellum have an outside layer of gray matter in addition to central gray matter and its surrounding white matter.

Which region of the brain stem is associated with the cerebral peduncles and the superior and inferior colliculi?

The cerebral peduncles and the colliculi are associated with the midbrain.

For an open channel, what factors determine in which direction ions will move through that channel?

The concentration gradient and the electrical gradient—together called the electrochemical gradient—determine the direction in which ions flow through an open membrane channel.

Which component of the reflex arc brings about the response?

The effector (muscle or gland) brings about the response.

Recall (from Chapter 9) that, at a neuromuscular junction, the AP in the muscle fiber is also triggered by a graded potential. Name that graded potential.

The graded potential at the junctional folds of the sarcolemma is called an end plate potential (EPP). It triggers an action potential in the adjacent sarcolemma.

Your patient, Ms. Young, has failing kidneys that cause an increase in her extracellular fluid K+ concentration. What would this do to the resting membrane potential of her neurons and muscle cells? Explain.

The resting membrane potential depends on both the concentration gradients of K+ and Na+ across the membrane and the permeability of the membrane to K+ and Na+. An increase in the extracellular K+ concentration will decrease the concentration gradient for K+ and this will decrease the resting membrane potential of neurons and muscle cells. In other words, the inside of these cells will become less negative (be depolarized).

Identify structures a-f on the section of skin below. For each structure, state the type of stimulus to which it best responds. (Note that structure b is not normally found in hairy skin.)

The sensory structures are as follows: (a) epithelial tactile complexes, which detect light pressure; (b) tactile corpuscle, which also detects light pressure (usually on hairless skin); (c) lamellar corpuscle, which detects deep pressure, stretch, and vibration; (d) bulbous corpuscle, which detects deep pressure and stretch; (e) free nerve endings, which detect pain and temperature; and (f) hair follicle receptor, which detects hair movement.

A technician is drawing blood from your arm for blood tests. As you feel the pain of the needle, you suppress your flexor reflex. Name the ascending pathway that carries pain signals and the region of the cortex that receives them (use Figure 12.34 on p. 477). Next, name the descending pathway you would use to inhibit the flexor reflex (use Figure 12.35 on p. 479).

The spinothalamic pathway carries pain signals to the somatosensory cortex in the parietal lobe. The pyramidal pathways carry voluntary motor information and would be involved in inhibiting the flexor reflex.

What is the role of the stretch reflex? The flexor reflex?

The stretch reflex is important for maintaining muscle tone and adjusting it reflexively by causing muscle contraction in response to increased muscle length (stretch). It maintains posture. The flexor or withdrawal reflex is initiated by a painful stimulus and causes automatic withdrawal of the painful body part from the stimulus. It is protective.

Identify structures a-e in the frontal section below. What is the function of structure (b)? Between which two structures would you find CSF? Name the two parts of structure (c).

The structures are (a) dural venous sinus (if you said superior sagittal sinus, that's also correct), (b) arachnoid granulation, (c) dura mater, (d) arachnoid mater, and (e) pia mater. Arachnoid granulations absorb CSF into venous blood. You would find CSF in the subarachnoid space between structures (d) and (e). The two parts of the dura mater are the superficial periosteal layer next to the bone and the deeper meningeal layer.

For which cation are there the largest number of leakage channels in the plasma membrane?

There are more leakage channels for K+ than for any other cation.

Name three factors that can enhance transfer of information from short-term memory to long-term memory.

Transfer of memory from STM to LTM is enhanced by (1) rehearsal, (2) association (tying "new" information to "old" information), and (3) a heightened emotional state (for example, alert, motivated, surprised, or aroused).

What are varicosities and where would you find them?

Varicosities are the series of knoblike swellings that are the axon endings of autonomic motor neurons. You would find them on axon endings serving smooth muscle or glands.