The structure of the nervous system

Question 1

The nervous system of all mammals has two divisions. What are they?

Answer 1

the central nervous system (CNS) and the peripheral nervous system (PNS).

Question 2

Describe what these terms refer to in regards to the orientation of the rat brain

1) Caudal
2) Posterior
3) Dorsal
4) Anterior
5) Ventral
6) Rostral

Answer 2

The direction, or anatomical reference, pointing toward the rat’s nose is known as anterior or rostral
The direction pointing toward the rat’s tail is posterior or caudal
The direction pointing up is known as dorsal, and the direction pointing down is ventral

Question 3

If we look down on the nervous system, we see that it may be divided into two equal halves. What is this known as?

Answer 3

The right side of the brain and spinal cord is the mirror image of the left side. This characteristic is known as bilateral symmetry.

Question 4

What is meant by the terms 1) midline 2) lateral and 3) medial

Answer 4

The invisible line running down the middle of the nervous system is called the midline, and this gives us another way to describe anatomical references. Structures closer to the midline are medial; structures farther away from the midline are lateral.

Question 5

What is meant by the terms ipsilateral and contralateral?

Answer 5

two structures that are on the same side are said to be ipsilateral to each other……… If the structures are on opposite sides of the midline, they are said to be contralateral to each other

Question 6

Describe what these terms refer to in regards to sections of the brain

1) Sagittal (and variations)
2) Horizontal
3) Coronal

Answer 6

The plane of the section resulting from splitting the brain into equal right and left halves is called the midsagittal plane. Sections parallel to the midsagittal plane are in the sagittal plane. The horizontal plane is parallel to the ground. A single section in this plane could pass through both the eyes and the ears. Thus, horizontal sections split the brain into dorsal and ventral parts. The coronal plane is perpendicular to the ground and to the sagittal plane. A single section in this plane could pass through both eyes or both ears but not through all four at the same time. Thus, the coronal plane splits the brain into anterior and posterior parts.

Question 7

What does the CNS consist of? (2)

Answer 7

The central nervous system (CNS) consists of the parts of the nervous system that are encased in bone: the brain and the spinal cord.

Question 8

What three parts of the brain are common to all mammals?

Answer 8

A side view of the rat brain reveals three parts that are common to all mammals: the cerebrum, the cerebellum, and the brain stem.

Question 9

Which brain area is the largest and rostral-most?

Answer 9

The Cerebrum

Question 10

What name is given to the division of the two hemispheres of the cerebrum?

Answer 10

sagittal fissure

Question 11

Describe the location and size of the cerebellum

Answer 11

Lying behind the cerebrum is the cerebellum. While the cerebellum is in fact dwarfed by the large cerebrum, it actually contains as many neurons as both cerebral hemispheres combined.

Question 12

What is the primary function of the cerebellum?

Answer 12

The cerebellum is primarily a movement control center that has extensive connections with the cerebrum and the spinal cord.

Question 13

Comment on the extent to which the cerebrum and cerebellum are contralateral

Answer 13

In general, the right cerebral hemisphere receives sensations from, and controls movements of, the left side of the body. Similarly, the left cerebral hemisphere is concerned with sensations and movements on the right side of the body.

In contrast to the cerebral hemispheres, the left side of the cerebellum is concerned with movements of the left side of the body, and the right side of the cerebellum is concerned with movements of the right side.

Question 14

In which plane is the brainstem best observed?

Answer 14

midsagittal view of the brain

Question 15

Describe the structure of the brain stem in relation to the cerebrum and the cerebellum?

Answer 15

The brain stem forms the stalk from which the cerebral hemispheres and the cerebellum sprout.

Question 16

Name two of the primary functions of the brain stem

Answer 16

The brain stem is a complex nexus of fibers and cells that in part serves to relay information from the cerebrum to the spinal cord and cerebellum, and vice versa. However, the brain stem is also the site where vital functions are regulated, such as breathing, consciousness, and the control of body temperature.

(Indeed, while the brain stem is considered the most primitive part of the mammalian brain, it is also the most important to life. One can survive damage to the cerebrum and cerebellum, but damage to the brain stem is usually fatal.)

Question 17

What function does the spine carry out?

Answer 17

The spinal cord is the major conduit of information from the skin, joints, and muscles of the body to the brain, and vice versa.

Question 18

What effects does a transection of the spinal cord have?

Answer 18

A transection of the spinal cord results in anesthesia (lack of feeling) in the skin and paralysis of the muscles in parts of the body caudal to the cut. Paralysis in this case does not mean that the muscles cannot function, but they cannot be controlled by the brain.

Question 19

How does the spinal cord communicate with the brain and body (be specific mentioning both types and their functions)

Answer 19

The spinal cord communicates with the body via the spinal nerves, which are part of the peripheral nervous system.

Each spinal nerve attaches to the spinal cord by means of two branches, the dorsal root and the ventral root ( the dorsal root contains axons bringing information into the spinal cord, such as those that signal the accidental entry of a thumbtack into your foot). The ventral root contains axons carrying information away from the spinal cord—for example, to the muscles that jerk your foot away in response to the pain of the thumbtack.

Question 20

What two parts is the PNS divided into?

Answer 20

the somatic PNS and the visceral PNS

Question 21

What makes up the somatic PNS?

Answer 21

All the spinal nerves that innervate the skin, the joints, and the muscles that are under voluntary control are part of the somatic PNS.

Question 22

What different types of axons are in the Somatic PNS and where do they join the nerves in the spinal cord?

Answer 22

The somatic motor axons, which command muscle contraction, derive from motor neurons in the ventral spinal cord.

The somatic sensory axons, which innervate and collect information from the skin, muscles, and joints, enter the spinal cord via the dorsal roots.

Question 23

Where do the cell bodies lie for both of these cells?

Answer 23

The cell bodies of the motor neurons lie within the CNS, but their axons are mostly in the PNS.

The cell bodies of these neurons lie outside the spinal cord in clusters called dorsal root ganglia. There is a dorsal root ganglion for each spinal nerve

Question 24

What does the visceral PNS consist of?

Answer 24

The visceral PNS, also called the involuntary, vegetative, or autonomic nervous system (ANS), consists of the neurons that innervate the internal organs, blood vessels, and glands.

Question 25

What functions do the two axons in the visceral PNS carry out?

Answer 25

Visceral sensory axons bring information about visceral function to the CNS, such as the pressure and oxygen content of the blood in the arteries. Visceral motor fibers command the contraction and relaxation of muscles that form the walls of the intestines and the blood vessels (called smooth muscles), the rate of cardiac muscle contraction, and the secretory function of various glands. For example, the visceral PNS controls blood pressure by regulating the heart rate and the diameter of the blood vessels.

Question 26

In addition to the nerves that arise from the spinal cord and innervate the body what nerves arise from the brain stem and innervate (mostly) in the brain?

Answer 26

12 pairs of cranial nerves that arise from the brain stem and innervate (mostly) the head.

Question 27

What systems are the cranial nerves part of?

Answer 27

Some of the cranial nerves are part of the CNS, others are part of the somatic PNS, and still others are part of the visceral PNS.

Question 28

Why is the nervous system encased in the skull and not damaged through contact with the bone?

Answer 28

The CNS, that part of the nervous system encased in the skull and vertebral column, does not come in direct contact with the overlying bone. It is protected by three membranes collectively called the meninges (singular: meninx)

Question 29

What are the names and positions of the three membranes?

Answer 29

The outermost covering is the dura mater; leatherlike consistency, The dura forms a tough, inelastic bag that surrounds the brain and spinal cord. Just under the dura lies the arachnoid membrane. This meningeal layer has an appearance and a consistency resembling a spider web. The pia mater, the “gentle mother,” is a thin membrane that adheres closely to the surface of the brain. Along the pia run many blood vessels that ultimately dive into the substance of the underlying brain

Question 30

If there is a gap between the dura mater and the arachnoid membrane what could this mean?

Answer 30

While there normally is no space between the dura and the arachnoid, if the blood vessels passing through the dura are ruptured, blood can collect here and form what is called a subdural hematoma. The buildup of fluid in this subdural space can disrupt brain function by compressing parts of the CNS. The disorder is treated by drilling a hole in the skull and draining the blood.

Question 31

How is the pia mater separated from the arachnoid membrane?

Answer 31

The pia is separated from the arachnoid by a fluid-filled space. This subarachnoid space is filled with salty clear liquid called cerebrospinal fluid (CSF). Thus, in a sense, the brain floats inside the head in this thin layer of CSF.

Question 32

Where else is this CSF found?

Answer 32

The fluid-filled caverns and canals inside the brain which constitute the ventricular system.

Question 33

How is CSF produced? How does it travel to the ventricles and subarachnoid space?

Answer 33

CSF is produced by a special tissue, called the choroid plexus, in the ventricles of the cerebral hemispheres. CSF flows from the paired ventricles of the cerebrum to a series of connected, central cavities at the core of the brain stem. CSF exits the ventricular system and enters the subarachnoid space by way of small openings, or apertures, located near where the cerebellum attaches to the brain stem. In the subarachnoid space, CSF is absorbed by the blood vessels at special structures called arachnoid villi.

Question 34

What is meant by grey matter?

Answer 34

A generic term for a collection of neuronal cell bodies in the CNS. When a freshly dissected brain is cut open, neurons appear gray.

Question 35

What is meant by a cortex?

Answer 35

Any collection of neurons that form a thin sheet, usually at the brain’s surface. Cortex is Latin for “bark.”

Question 36

How is a nucleus defined in the brain?

Answer 36

A clearly distinguishable mass of neurons, usually deep in the brain (not to be confused with the nucleus of a cell).

Question 37

What is a substantia?

Answer 37

A group of related neurons deep within the brain but usually with less distinct borders than those of nuclei.

Question 38

Define a locus in the brain?

Answer 38

A small, well-defined group of cells.

Question 39

What is a ganglion?

Answer 39

A collection of neurons in the PNS. (apart from basal ganglia)

Question 40

What is a nerve?

Answer 40

A bundle of axons in the PNS (apart from optic nerve)

Question 41

What is meant by white matter?

Answer 41

A generic term for a collection of CNS axons.

Question 42

What is a tract?

Answer 42

A collection of CNS axons having a common site of origin and a common destination.

Question 43

What is a bundle?

Answer 43

A collection of axons that run together but do not necessarily have the same origin and destination.

Question 44

What is meant by a capsule?

Answer 44

A collection of axons that connect the cerebrum with the brain stem.

Question 45

What is a commissure?

Answer 45

Any collection of axons that connect one side of the brain with the other side.

Question 46

What is meant by a lemniscus?

Answer 46

A tract that meanders through the brain like a ribbon

Question 47

Name the layers of which the embryo originally consists of and what they later form (3)

Answer 47

The embryo begins as a flat disk with three distinct layers of cells called endoderm, mesoderm, and ectoderm. The endoderm ultimately gives rise to the lining of many of the internal organs (viscera). From the mesoderm arise the bones of the skeleton and the muscles. The nervous system and the skin derive entirely from the ectoderm.

Question 48

What part of the ectoderm gives rise to the nervous system?

Answer 48

Neural plate

Question 49

Describe the process from a neural plate to tube

Answer 49

At this early stage (about 17 days from conception in humans), the brain consists only of a flat sheet of cells. The next event of interest is the formation of a groove in the neural plate that runs rostral to caudal, called the neural groove (Figure 7.10b). The walls of the groove are called neural folds, which subsequently move together and fuse dorsally, forming the neural tube (see copy/ docs)

Question 50

What develops from the neural tube?

Answer 50

The entire central nervous system develops from the walls of the neural tube

Question 51

How does the neural crest form and what derives from this?

Answer 51

As the neural folds come together, some neural ectoderm is pinched off and comes to lie just lateral to the neural tube. This tissue is called the neural crest. All neurons with cell bodies in the peripheral nervous system derive from the neural crest. All neurons with cell bodies in the peripheral nervous system derive from the neural crest.

Question 52

Outside of the ectoderm, hat does the neural crest develop in close association with and what derives from this

Answer 52

The neural crest develops in close association with the underlying me- soderm. The mesoderm at this stage in development forms prominent bulges on either side of the neural tube called somites. From these somites, the 33 individual vertebrae of the spinal column and the related skeletal muscles will develop.

Question 53

What is the process by which the neural plate becomes the neural tube called?

Answer 53

neurulation

Question 54

When does neurulation typically occur in development?

Answer 54

about 22 days after conception in humans

Question 55

What is the process by which structures become more complex and function- ally specialised during development called?

Answer 55

differentiation

Question 56

What is the first step in differentiation?

Answer 56

The first step in the differentiation of the brain is the development, at the rostral end of the neural tube, of three swellings called the primary vesicles The entire brain derives from the three primary vesicles of the neural tube.

Question 57

Describe the three primary vesicles by which most the brain develops

Answer 57

The rostral-most vesicle is called the prosencephalon. Pro is Greek for “before”; encephalon is derived from the Greek for “brain.” Thus, the pros- encephalon is also called the forebrain. Behind the prosencephalon lies another vesicle called the mesencephalon, or midbrain. Caudal to this is the third primary vesicle, the rhombencephalon, or hindbrain. The rhombencephalon connects with the caudal neural tube, which gives rise to the spinal cord.

Question 58

Describe the next important developments that occur in the forebrain

Answer 58

secondary vesicles sprout off on both sides of the prosencephalon. The secondary vesicles are the optic vesicles and the telencephalic vesicles.

Question 59

What is the central structure that remains after the secondary vesicles have sprouted off called?

Answer 59

The central structure that remains after the secondary vesicles have sprouted off is called the diencephalon, or “between brain”. Thus, the forebrain at this stage consists of the two optic vesicles, the two telencephalic vesicles, and the diencephalon.

Question 60

What happens to the optic vesicles at this point?

Answer 60

The optic vesicles grow and invaginate (fold in) to form the optic stalks and the optic cups, which will ultimately become the optic nerves and the two retinas in the adult. The important point is that the retina at the back of the eye, and the optic nerve containing the axons that connect the eye to the diencephalon and midbrain, are part of the brain, not the PNS.

Question 61

The telencephalic vesicles together form the telencephalon, or “endbrain,” consisting of the two cerebral hemispheres. The telencephalon continues to develop in four ways. Describe these four ways

Answer 61

(1) The telencephalic vesicles grow posteriorly so that they lie over and lateral to the diencephalon. (2) Another pair of vesicles sprout off the ventral surfaces of the cerebral hemispheres, giving rise to the olfactory bulbs and related structures that participate in the sense of smell. (3) The cells of the walls of the telencephalon divide and differentiate into various structures. (4) White matter systems develop, carrying axons to and from the neurons of the telencephalon.

Question 62

Why are the paired lateral ventricles a key landmark in the adult brain?

Answer 62

Whenever you see paired fluid- filled ventricles in a brain section, you know that the tissue surrounding them is in the telencephalon. The elongated, slit-like appearance of the third ventricle in cross section is also a useful feature for identifying the diencephalon.

Question 63

At this stage, the walls of the telencephalic vesicles appear swollen due to the proliferation of neurons. These neurons form two different types of gray matter in the telencephalon. Name these

Answer 63

the cerebral cortex and the basal telencephalon.

Question 64

Likewise, the diencephalon differentiates into two structures:

Answer 64

Thalamus and hypothalamus

Question 65

The neurons of the developing forebrain extend axons to communicate with other parts of the nervous system. These axons bundle together to form three major white matter systems. Name and describe these

Answer 65

The cortical white matter contains all the axons that run to and from the neurons in the cerebral cortex. The corpus callosum is continuous with the cortical white matter and forms an axonal bridge that links cortical neurons of the two cerebral hemispheres. The cortical white matter is also continuous with the internal capsule, which links the cortex with the brain stem, particularly the thalamus.

Question 66

Why is the thalamus often referred to as the gateway to the cerebral cortex?

Answer 66

Neurons in the olfactory bulbs receive information from cells that sense chemicals in the nose (odors), and relay this information caudally to a part of the cerebral cortex for further analysis. Information from the eyes, ears, and skin is also brought to the cerebral cortex for analysis. However, each of the sensory pathways serving vision, audition (hear- ing), and somatic sensation relays (i.e., synapses upon neurons) in the thalamus en route to the cortex. Thus, the thalamus is often referred to as the gateway to the cerebral cortex

Question 67

What does the term basal mean?

Answer 67

The term basal is used to describe structures deep in the brain, and the basal ganglia lie deep within the cerebrum.

Question 68

What functions does the hypothalamus carry out?

Answer 68

The hypothalamus performs many primitive functions; The hypothalamus controls the visceral (autonomic) nervous system, which regulates bodily functions in response to the needs of the organism. For example, when you are faced with a threatening situation, the hypothalamus orchestrates the body’s visceral fight-or-flight response (blood to muscles, heart rate etc) or when you're relaxing (blood to gastrointestinal tract, etc). The hypothalamus also plays a key role in motivating animals to find food, drink, and sex in response to their needs.

Question 69

Apart from its connections to the ANS how else does the hypothalamus direct bodily responses?

Answer 69

via connections with the pituitary gland located below the diencephalon. This gland communicates with many parts of the body by releasing hormones into the bloodstream.

Question 70

How does the midbrain differentiate during brain development? (3)

Answer 70

The dorsal surface of the mes- encephalic vesicle becomes a structure called the tectum The floor of the midbrain becomes the tegmentum. The CSF-filled space in between constricts into a narrow channel called the cerebral aqueduct. The aqueduct connects rostrally with the third ventricle of the diencephalon.

Question 71

How does the tectum differentiate?

Answer 71

The tectum differentiates into two structures: the superior colliculus and the inferior colliculus. The superior colliculus receives direct input from the eye, so it is also called the optic tectum. The inferior colliculus also receives sensory information but from the ear instead of the eye. The inferior colliculus serves as an important relay station for auditory information en route to the thalamus.

Question 72

What two important cell groups are located in the tegmenjtum? What are they involved in?

Answer 72

it contains both the substantia nigra (the black substance) and the red nucleus. These two cell groups are involved in the control of voluntary movement

Question 73

What three important structures does the hindbrain differentiate into?

Answer 73

the cerebellum, the pons, and the medulla oblongata

Question 74

Describe how the hindbrain forms the cerebellum and pons

Answer 74

At the three-vesicle stage, the rostral hindbrain in cross section is a simple tube. In subsequent weeks, the tissue along the dorsal–lateral wall of the tube, called the rhombic lip, grows dorsally and medially until it fuses with its twin on the other side. The resulting flap of brain tissue grows into the cerebellum. The ventral wall of the tube differentiates and swells to form the pons

Question 75

Describe the changes which form the medulla

Answer 75

The ventral and lateral walls of this region swell, leaving the roof covered only with a thin layer of non- neuronal ependymal cells. Along the ventral surface of each side of the medulla runs a major white matter system. Cut in cross section, these bundles of axons appear somewhat triangular in shape, explaining why they are called the medullary pyramids.

Question 76

In addition to being an important conduit for information passing from the fore- brain to the spinal cord, and vice versa, what functions do neurons in the hindbrain carry out?

Answer 76

contribute to the processing of sensory information, the control of voluntary movement, and regulation of the autonomic nervous system.

Question 77

What functions does the cerebellum carry out?

Answer 77

important movement control center. It receives massive axonal inputs from the spinal cord and the pons. The spinal cord inputs provide information about the body’s position in space. The inputs from the pons relay information from the cerebral cortex, specifying the goals of intended movements. The cerebellum com- pares these types of information and calculates the sequences of muscle contractions that are required to achieve the movement goals

Question 78

What function does the pons serve in relation to the cerebellum?

Answer 78

Of the descending axons passing through the midbrain, over 90%— about 20 million axons in the human—synapse on neurons in the pons. The pontine cells relay all this information to the cerebellum on the opposite site. Thus, the pons serves as a massive switchboard connecting the cerebral cortex to the cerebellum. (The word pons is from the Latin word for “bridge.”) The pons bulges out from the ventral surface of the brain stem to accommodate all this circuitry.

Question 79

What about the axons that do not terminate in the pons?

Answer 79

The axons that do not terminate in the pons continue caudally and enter the medullary pyramids.

Question 80

Where do most of the axons in the medullary pyramids originate?

Answer 80

Most of these axons originate in the ce- rebral cortex and are part of the corticospinal tract. Thus, “pyramidal tract” is often used as a synonym for corticospinal tract.

Question 81

Where does this pyramidal tract cross to the contralateral side?

Answer 81

Near where the medulla joins with the spinal cord, each pyramidal tract crosses from one side of the midline to the other. A crossing of axons from one side to the other is known as a decussation, and this one is called the pyramidal decussation.

Question 82

In addition to the white matter systems passing through, what functions do the neurons in the medulla carry out?

Answer 82

the medulla contains neurons that perform many different sensory and motor functions.

Question 83

Give three examples of sensory functions which neurons in the medulla carry out and their respective structures

Answer 83

the axons of the auditory nerves, bringing auditory information from the ears, synapse on cells in the cochlear nuclei of the medulla. The cochlear nuclei project axons to a number of different structures, including the tectum of the midbrain. Damage to the cochlear nuclei leads to deafness. Other sensory functions of the medulla include touch and taste. The medulla contains neurons that relay somatic sensory information from the spinal cord to the thalamus. Destruction of the cells leads to anesthesia (loss of feeling). Other neurons relay gustatory (taste) information from the tongue to the thalamus.

Question 84

Describe the differentiation of the spinal cord

Answer 84

With the expansion of the tissue in the walls, the cavity of the tube constricts to form the tiny CSF-filled spinal canal.

Question 85

When cut in cross section, what name is given to this tissue and how is it divided? (both grey and white matter)

Answer 85

Cut in cross section, the gray matter of the spinal cord (where the neurons are) has the appearance of a butterfly. The upper part of the butterfly’s wing is the dorsal horn, and the lower part is the ventral horn. The gray matter between the dorsal and ventral horns is called the intermediate zone. Everything else is white matter, consisting of col- umns of axons that run up and down the spinal cord. Thus, the bundles of axons running along the dorsal surface of the cord are called the dorsal columns, the bundles of axons lateral to the spinal gray matter on each side are called the lateral columns, and the bundles on the ventral surface are called the ventral columns.

Question 86

How do the two horns and intermediate zones differ in their functions?

Answer 86

As a general rule, dorsal horn cells receive sensory inputs from the dorsal root fibers, ventral horn cells project axons into the ventral roots that innervate muscles and intermediate zone cells are interneurons that shape motor outputs in response to sensory inputs and descending commands from the brain.

Question 87

How do the columns differ in the functions that they carry out?

Answer 87

The large dorsal column contains axons that carry somatic sensory (touch) information up the spinal cord toward the brain. The lateral column contains the axons of the descending corticospinal tract, which also cross from one side to the other in the medulla. These axons innervate the neurons of the intermediate zone and ventral horn and communicate the signals that control voluntary movement.

Question 88

the spinal cord is the major conduit of information from the skin, joints, and muscles to the brain, and vice versa. However, the spinal cord is also much more than that. How so?

Answer 88

The neurons of the spinal gray matter begin the analysis of sensory information, play a critical role in coordinating movements, and orchestrate simple reflexes (such as jerking away your foot from a thumbtack).

Question 89

Describe how you can identify the brain structure you're looking at by paying attention to the ventricles

Answer 89

Dorsal to the lateral ventricles, at the surface of the brain, lies the cortex. Ventral and lateral to the lateral ventricles lies the basal telencephalon. The lateral ventricles are continuous with the third ventricle of the diencephalon. Surrounding this ventricle are the thalamus and the hypo- thalamus. The third ventricle is continuous with the cerebral aqueduct. Dorsal to the aqueduct is the tectum. Ventral to the aqueduct is the midbrain tegmentum. The aqueduct connects with the fourth ventricle that lies at the core of the hindbrain. Dorsal to the fourth ventricle sprouts the cerebellum. Ventral to the fourth ventricle lie the pons and the medulla.

Question 90

Describe the similarities between the human and rat brain

Answer 90

Dorsal to the lateral ventricles, at the surface of the brain, lies the cortex. Ventral and lateral to the lateral ventricles lies the basal telencephalon. The lateral ventricles are continuous with the third ventricle of the diencephalon. Surrounding this ventricle are the thalamus and the hypo- thalamus. The third ventricle is continuous with the cerebral aqueduct. Dorsal to the aqueduct is the tectum. Ventral to the aqueduct is the mid- brain tegmentum. The aqueduct connects with the fourth ventricle that lies at the core of the hindbrain. Dorsal to the fourth ventricle sprouts the cerebellum. Ventral to the fourth ventricle lie the pons and the medulla.

Question 91

Name an immediate different between the structure of the rat and human cerebral cortex

Answer 91

the many convolutions on the surface of the human cerebrum. Sulci and gyri result from the tremendous expansion of the surface area of the cerebral cortex during human fetal development.

Question 92

The side views of the rat and human brains reveal further differences in the forebrain. One is the small size of the __________ in the human relative to the rat

Answer 92

Olfactory bulb

Question 93

What common features does the cerebral cortex of all vertebrae animals have in common? (3)

Answer 93

First, the cell bodies of cortical neurons are always arranged in layers, or sheets, that usually lie parallel to the surface of the brain. Second, the layer of neurons closest to the surface (the most superficial cell layer) is separated from the pia mater by a zone that lacks neurons; it is called the molecular layer, or simply layer I. Third, at least one cell layer contains pyramidal cells that emit large dendrites, called apical dendrites, that extend up to layer I, where they form multiple branches.

Question 94

What can we conclude about the cerebral cortex based on these three commonalities?

Answer 94

the cerebral cortex has a characteristic cytoarchitecture that distinguishes it, for example, from the nuclei of the basal telencephalon or the thalamus.

Question 95

Where can the hippocampus be found in the rat brain and how many cell layers does it have?

Answer 95

Medial to the lateral ventricle is a piece of cortex that is folded onto itself in a peculiar shape. This structure is called the hippocampus, which, despite its bends, has only a single cell layer

Question 96

What other type of cortex is connected to the hippocampus ventrally? How many cell layers does it have?

Answer 96

Connected to the hippocampus ventrally and laterally is another type of cortex that has only two cell layers. It is called the olfactory cortex because it is continuous with the olfactory bulb, which sits further anterior.

Question 97

The olfactory cortex is separated from a more elaborate type of cortex. Name the fissure, the cortex and how many layers this cortex has

Answer 97

The olfactory cortex is separated by a sulcus, called the rhinal fissure, from another more elaborate type of cortex that has many cell layers. This remaining cortex is called neocortex.

Question 98

What is unique about the mammal brain?

Answer 98

Unlike the hippocampus and olfactory cortex, neocortex is found only in mammals.

Question 99

What is meant by the connectome of the cortex?

Answer 99

Modern thinking is that the smallest functional unit of the neocortex is a cylinder of neurons 2 mm high—the distance from the white matter to the cortical surface—and 0.5 mm in diameter. This cylinder, usually described as a neocortical column, con- tains on the order of 10,000 neurons and 100 million synapses (approximately 10,000 synapses per neuron). We wish to understand the detailed wiring diagram of how these neurons connect with one another: the con- nectome of the neocortex.

Question 100

Why is understanding the connectome of the cortex a difficult challenge?

Answer 100

synapses can be identified with confidence only using electron microscopy, which requires very thin (􏰕50 nm) sections of tissue.

Question 101

How is the evolution of our brain studied?

Answer 101

The brain is a soft tissue, so there is not a fossil record of the cortex of our early mammalian ancestors. Nonetheless, considerable insight can be gained by comparing the cortex of different living species

Question 102

What are the thoughts on how the cortex has evolved over time?

Answer 102

The surface area of the cortex varies tremendously among species; for example, a comparison of mouse, monkey, and human cortex reveals dif- ferences in size on the order of 1:100:1000. On the other hand, there is little difference in the thickness of the neocortex in different mammals, varying by no more than a factor of two. Thus, we can conclude that the amount of cortex has changed over the course of evolution, but not its basic structure.

Question 103

Detailed comparisons of cortical structure and function in living species with diverse evolutionary histories suggest that the primordial neocortex of our common mammalian ancestor consisted mainly of three types of cortex. What are these?

Answer 103

The first type consists of primary sensory areas, which are the first to receive signals from the ascending sensory pathways. For example, area 17 is designated as primary visual cortex, or V1, because it receives input from the eyes via a direct path: retina to thalamus to cortex. The second type of neocortex consists of secondary sensory areas, so designated because of their heavy interconnections with the primary sensory areas. The third type of cortex consists of motor areas, which are intimately involved with the control of voluntary movement.

Question 104

What differences does the combination of the cortical expansion and the curved NS longtudinal axis cause between the human and rat brain in regards to the other structures

Answer 104

You get a different orientation of a number of cortex associated structures with regards to the whole brain and nuclei. (e.g lateral ventricles)