Bear et al: Chapter 7 Flashcards
Why does the human brain appear complicated when compared to the brains of other mammals?
It is distorted as a result of the selective growth of some parts within the confines of the skull
What brain structure is unique to mammals and proportionately largest in humans?
Cerebral neocortex
What are the two divisions of the nervous system of all mammals?
- Central Nervous System (CNS)
2. Peripheral Nervous System (PNS)
Anterior
Anatomical reference meaning toward the nose or rostral
Rostral
From the Latin for “beak”
Anatomical reference meaning toward the nose or anterior
Posterior
Anatomical reference meaning toward the tail, or caudal
Caudal
From the Latin for “tail”
Anatomical reference meaning toward the tail, or posterior
Dorsal
From the Latin for “back”
Anatomical reference meaning toward the back
Ventral
From the Latin for “belly”
Anatomical reference meaning toward the belly
Bilateral symmetry
Property where the right side of the brain and spinal cord is a mirror image of the left side
Midline
An invisible line that bissects the nervous system into right and left halves
Medial
An anatomical reference meaning toward the midline
Lateral
An anatomical reference meaning away from the midline
Ipsilateral
An anatomical reference meaning on the same side of the midline
Contralateral
An anatomical reference meaning on opposite sides of the midline
In the language of anatomists, what is a slice called?
Section
In the language of anatomists, how would you say ‘to slice’?
To section
What is the standard approach to cut into a brain?
Parallel to one of the three anatomical planes of section
What are the three anatomical planes of section?
- Midsaggital plane
- Horizontal plane
- Coronal plane
Midsaggital plane
An anatomical plane of section
through the midline that is perpendicular to the
ground. A section in the midsagittal plane divides
the nervous system into right and left halves.
Saggittal plane
An anatomical plane of section that is
parallel to the midsagittal plane
Horizontal plane
An anatomical plane of section
that divides the nervous system into dorsal and
ventral parts
Coronal plane
An anatomical plane of section
that divides the nervous system into anterior and
posterior parts
Central nervous system (CNS)
- The brain (including
the retinas) and spinal cord - Consists of parts of the nervous system that are encased in bone (i.e. the brain lies entirely within the skull)
What three parts of the brain are common to all mammals?
- Cerebrum
- Cerebellum
- Brain stem
Cerebrum
- Largest part of the forebrain; also called telencephalon
2. Rostral-most and largest part of the brain
Cerebral hemispheres
The two sides of the cerebrum,
derived from the paired telencephalic
vesicles
What structure separates the two cerebral hemispheres?
Deep sagittal fissure
What is the function of the right cerebral hemisphere?
Receive sensations from and control movements of the LEFT side of the body
What is the function of the left cerebral hemisphere?
Receive sensations from and control movements of the RIGHT side of the body
Cerebellum
- Derived from the Latin for “little brain”
- A structure derived from the rhombencephalon,
attached to the brain stem at the pons; an important movement control center
What are the two primary functions of the cerebellum?
- Movement control center
2. Extensive connections with the cerebrum and spinal cord
Does the cerebrum or the cerebellum have more neurons?
Cerebellum contains as many as both cerebral hemispheres combined
What is the function of the left side of the cerebellum?
Concerned with movements of the LEFT side of the body
What is the function of the right side of the cerebellum?
Concerned with movements of the RIGHT side of the body
Brain stem
- The diencephalon, midbrain, pons, and medulla. (Some anatomists exclude the diencephalon.)
- Complex nexus of fibers and cells that forms the stalk from which the cerebral hemispheres and the cerebellum sprout
From what view is the brain stem best observed?
Midsagittal view
What are the two main functions of the brain stem?
- Site where vital functions are regulated, such as breathing, consciousness, and the control of body temperature
- Relay information from the cerebrum to the spinal cord and cerebellum,
and vice versa
What is considered the most primitive part of the mammalian brain?
Brain stem
What part of the mammalian brain is most vital to life and why?
Brain stem–because one can survive damage to the cerebrum and cerebellum, but damage to the brain stem is usually fatal
Spinal cord
The part of the central nervous system encased in the bony vertebral column and attached to the brain stem
What is the primary function of the spinal cord?
It is the major conduit of information from the skin, joints, and muscles of the body to the brain, and vice versa
What does a transection of the spinal cord result 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.
The spinal card communicates with the body via the _____?
The spinal card communicates with the body via the SPINAL NERVES
Spinal nerves
A nerve attached to the spinal cord
that innervates the body
How do spinal nerves exit the spinal cord?
Through notches between each vertebra of the vertebral column
How does each spinal nerve attach to the spinal cord?
By means of two branches:
- Dorsal root
- Ventral root
Dorsal root
A bundle of sensory neuron axons that emerges from a spinal nerve and attaches to the dorsal side of the spinal cord. Dorsal root axons bring information
into the spinal cord.
Ventral root
A bundle of motor neuron axons that
emerges from the ventral spinal cord and joins sensory fibers to form a spinal nerve. Ventral root axons carry information away from the spinal cord.
Through which branches do axons enter and exit the spinal cord respectively?
Enter via the dorsal root
Exit via the ventral root
Peripheral Nervous System (PNS)
The parts of the nervous system other than the brain and spinal cord. The PNS includes all the spinal ganglia and nerves, cranial nerves III–XII, and the auto- nomic nervous system.
What are the two parts of the peripheral nervous system?
- Somatic PNS
2. Visceral PNS
What commands muscle contraction?
Somatic motor neurons
Where do the somatic motor axons derive from?
Motor neurons in the ventral spinal cord
Where do the cell bodies and axons of motor neurons lie?
The cell bodies of motor neurons lie within the CNS but their axons are mostly within the PNS
What is the function of somatic sensory axons?
Innervate and collect information from the skin, muscles, and joints
Through what branch do sensory somatic axons enter the spinal cord?
Via the dorsal roots
Where do the cell bodies of somatic sensory neurons lie?
Outside the spinal cord in clusters called dorsal root ganglion
There is _____ dorsal root ganglion for each spinal nerve
There is ONE dorsal root ganglion for each spinal nerve
Dorsal root ganglion
A collection of cell bodies of the sensory neurons that are part of the somatic PNS. There is one dorsal root ganglion for each spinal nerve.
Visceral peripheral nervous system
The part of the peripheral nervous system that innervates the internal organs, blood vessels, and glands; also called autonomic nervous system.
Autonomic nervous system (ANS)
A system of central and peripheral nerves that innervates the internal organs, cardiovascular system, and glands; also called visceral PNS. The ANS consists of sympathetic, parasympathetic, and enteric divisions.
What are three other names for the visceral peripheral nervous system?
- Autonomic nervous system (ANS)
- Involuntary nervous system
- Vegetative nervous system
What do visceral sensory axons do?
Bring information about visceral functions to the CNS, such as the pressure and oxygen content of the blood in arteries
What do visceral motor fibers do?
Command the contraction and relaxation of muscles that form the walls of intestines and 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 heart rate and the diameter of blood vessels
What part of the nervous system mediates emotional responses beyond voluntary control (i.e. “butterflies in the stomach”, blushing)?
Visceral PNS (the ANS)
Afferent
Derived from Latin “carry to”
An axon coursing toward and innervating a given structure
Efferent
Derived from the Latin “carry from”
An axon originating in and coursing away from a given structure
Cranial nerves
Twelve pairs of nerves that arise from each side of the brain stem, innervate (mostly) the head) and are numbered from anterior to posterior. Cranial nerve I is actually the olfactory tract, and cranial nerve II is the optic nerve; both are parts of the central nervous system. Cranial nerves III–XII, which are in the peripheral nervous system, perform many diverse functions.
Who were the cranial nerves originally numbered by and how long ago?
Galen, 1800 years ago
Does the central nervous system come in direct contact with the overlying bone?
No
What is the singular form of meninges?
meninx
Meninges
From the Greek for “covering”
Three membranes that cover the surface of the central nervous system: the dura mater, arachnoid membrane, and pia mater. Singular: meninx.
What protects the surface of the central nervous system?
Meninges
Dura mater
From the Latin words “hard mother,” an accurate description of the dura’s leather-like consistency.
The outermost of the three meninges, the membranes that cover the surface of the central nervous system.
Forms a tough, inelastic band that surrounds the brain and spinal cord.
Arachnoid membrane
From the Greek for “spider”, appropriately named for its appearance and consistency resembling a spider web.
The middle of the three meninges, the three membranes that cover the surface of the central nervous system.
Is there space between the dura and arachnoid?
Normally no BUT if the blood vessels passing through the dura are ruptured, blood can collect here and form what is called a subdural hematoma
What is a subdural hematoma, what does it do and how is it treated?
If blood vessels passing through the dura are ruptured, they can collect here and form a subdural hematoma.
Can disrupt brain function by compressing parts of the CNS.
Treated by drilling a hole in the skull and draining the blood.
Pia mater
“Gentle mother”
The innermost of the three meninges, the membranes that cover the surface of the central nervous system.
A thin membrane that adheres closely to the surface of the brain.
Along the _____ run many blood vessels that ultimately dive into the substance of the underlying brain.
Along the PIA MATER run many blood vessels that ultimately dive into the substance of the underlying brain.
Is the arachnoid separates from the pia mater?
Yes, by a fluid-filled space (called the subarachnoid space)
Cerebrospinal fluid (CSF)
In the central nervous system, the salty, clear fluid produced by the choroid plexus that flows through the ventricular system to the subarachnoid space.
Ventricular system
The cerebrospinal fluid–filled spaces inside the brain, consisting of the lateral ventricles, third ventricle, cerebral aqueduct, and fourth ventricle
What fluid runs in the ventricular system?
Cerebrospinal fluid (CSF), the dame fluid that runs in the subarachnoid space
What produces cerebrospinal fluid (CSF)?
A special tissue, called the choroid plexus, in the ventricles of the cerebral hemispheres
What is the normal flow of cerebrospinal fluid?
paired ventricles of the cerebrum—> series of connected, central cavities at the core of the brain stem—> exits the ventricular system and enters the subarachnoid spaces by way of small openings, or apertures, located near where the cerebellum attaches to the brain stem—> in the subarachnoid spaces, CSF is absorbed by blood cells at special structures called arachnoid villi
What special structures in blood vessels absorb cerebrospinal fluid in subarachnoid spaces?
Arachnoid villi
What happens if the normal flow of CSF is disrupted?
Brain damage…
Fluid will backup causing a swelling of the ventricles. This condition is called hydrocephalus, a term originally meaning “water head.”
How did anatomists initially investigate the internal structures of the brain for centuries? (hint: four steps)
- Removed the brain from the skull
- Sectioned it in various planes
- Stained the sections
- Examined the stained sections
What is the main limitation of the initial method in which anatomists investigated the internal structures of the brain?
Seeing how parts deep in the brain fit together in three dimensions
CLARITY
A new method introduced by researchers at Stanford University in 2013 that allows for visualization of deep structures without sectioning the brain
How does CLARITY work?
- Soak the brain in a solution that replaces light-absorbing lipids with a water-soluble gel that turns the brain transport
- If such a “clarified” brain contains neurons that are labeled with fluorescent molecules, such as green fluorescent protein (GFP), then appropriate illumination will reveal the location of these cells deep inside the brain
Hydrocephalus
When flow of cerebrospinal fluid from the choroid plexus through the ventricular system to the subarachnoid space is impaired leading to fluid backing up and causing a swelling of the ventricles
What happens when a baby is born with hydrocephalus?
Because the skull is soft and not completely formed, the head will expand in response to the increased intracranial fluid, sparing the brain from damage. Often this condition goes unnoticed until the size of the head reaches enormous proportions.
Why is hydrocephalus much more serious in adults?
Because the skull cannot expand and intracranial pressure is increased as a result. The soft brain tissue is then compressed, impairing function and leading to death if left untreated. Typically, this “obstructive” hydrocephalus is also accompanied by severe headache, caused by distension of nerve endings in the meninges.
How is hydrocephalus treated?
By inserting a tube into the swollen ventricle and draining off the excess fluid
In treatment of hydrocephalus, where is the tube inserted through and where is the drainage tube usually introduced?
Tube is inserted into the ventricle through hole in skull
Drainage tube is usually introduced into peritoneal cavity and (if applicable) with extra length to allow for the growth of the child
What is the entire central nervous system derived from and when is that formed?
The entire CNS is derived from the walls of a fluid-filled tube that is formed at an early stage in embryonic development. The inside of the tube becomes the adult ventricular system.
What are six common names for describing collections of neurons?
- Gray matter
- Cortex
- Nucleus
- Substantia
- Locus
- Ganglion
What are seven common names for describing collections of axons?
- Nerve
- White matter
- Tract
- Bundle
- Capsule
- Commissure
- Lemniscus
Gray matter
A generic term for a collection of neuronal cell bodies in the CNS. When a freshly dissected brain is cut open, neurons appear gray.
Cortex
Any collection of neurons that form a thin sheet, usually at the brain’s surface. Cortex is Latin for “bark.”
Example: cerebral cortex, the sheet of neurons found just under the surface of the cerebrum.
Nucleus
A clearly distinguishable mass of neurons, usually deep in the brain (not to be confused with the nucleus of a cell). Nucleus is from the Latin word for “nut.”
Example: lateral geniculate nucleus, a cell group in the brain stem that relays information from the eye to the cerebral cortex.
Substantia
A group of related neurons deep within the brain but usually with less distinct borders than those of nuclei.
Example: substantia nigra (from the Latin for “black substance”), a brain stem cell group involved in the control of voluntary movement.
Locus
A small, well-defined group of cells. Plural: loci.
Example: locus coeruleus (Latin for “blue spot”), a brain stem cell group involved in the control of wakefulness and behavioral arousal.
Ganglion
A collection of neurons in the PNS. Ganglion is from the Greek for “knot.”
Example: the dorsal root ganglia, which contain the cell bodies of sensory axons entering the spinal cord via the dorsal roots. Only one cell group in the CNS goes by this name: the basal ganglia, which are structures lying deep within the cerebrum that control movement
Nerve
A bundle of axons in the PNS.
Only one collection of CNS axons is called a nerve: the optic nerve.
White matter
A generic term for a collection of CNS axons. When a freshly dissected brain is cut open, axons appear white.
Tract
A collection of CNS axons having a common site of origin and a common destination.
Example: corticospinal tract, which originates in the cerebral cortex and ends in the spinal cord.
Bundle
A collection of axons that run together but do not necessarily have the same origin and destination.
Example: medial forebrain bundle, which connects cells scattered within the cerebrum and brain stem.
Capsule
A collection of axons that connect the cerebrum with the brain stem.
Example: internal capsule, which
connects the brain stem with the cerebral cortex.
Commissure
Any collection of axons that connect one side of the brain with the other side
Lemniscus
A tract that meanders through the brain like a ribbon.
Example: medial lemniscus, which brings touch information
from the spinal cord through the brain stem.
How does the embryo begin?
As a flat disk with three distinct layers of cells called endoderm, mesoderm, and ectoderm
What does the endoderm give rise to?
Lining of many of the internal organs (viscera)
What does the mesoderm give rise to?
Bones of the skeleton and muscles
What does the ectoderm give rise to?
Nervous system and skin
What is the first important step in the development of the nervous system?
Formation of a groove in the neural plate that runs rostral to caudal, called the neural groove
Neural folds
Walls of the neural grooves
What comes together and fuses to form the neural tube?
Neural folds
Neural crest
The bits of neural ectoderm that are pinched off and come to lie lateral to the neural tube when the neural tube rolls up
All neurons with cell bodies in the peripheral nervous system derive from the neural crest
What does the peripheral nervous system (PNS) develop from?
Neural crest
Somites
Mesoderm that will give rise to much of the skeletal system and the muscles
Prominent bulges on either side of the neural tube
From which the 33 individual vertebrae of the spinal column and related skeletal muscles will develop
What part of the ectoderm gives rise to the nervous system?
Neural plate
At about 17 days from conception in humans, what does the brain consist of?
Only a flat sheet of cells
Neural groove
Groove in the neural plate that runs rostral to caudal
How is the neural tube formed?
When the walls of the neural groove, neural folds, move together and fuse dorsally thus forming the neural tube
True or False?:
All neurons with cell bodies in the peripheral nervous system (PNS) derive from the neural crest.
True
True or False?:
All neurons with cell bodies in the peripheral nervous system (PNS) derive from the neural crest.
True
What does the neural crest develop in close association with?
Underlying mesoderm which, at this stage in development, forms prominent bulges on either side of the neural tube called somites
From what does do the 33 individual vertebrae of the spinal column and related skeletal muscles will develop?
Somites
What are the nerves that innervate the related skeletal muscles to the 33 individual vertebrae of the spinal column called?
Somatic motor nerves
Neurulation
The formation of the neural tube from the neural ectoderm during embryonic development; the process by which the neural plate becomes the neural tube
About how many days after conception does neurulation occur in humans?
Very early in embryonic development, about 22 days (~3 weeks) after conception in humans (when a mother may be unaware she is pregnant)
True or False?:
A common birth defect is the failure of appropriate closure of the neural tube.
True
What does recent research suggest about avoiding neural tube defects?
Most cases of neural tube defects can be avoided by ensuring proper maternal nutrition during this period (of neurulation)
How common is the birth defect of failure of appropriate closure of the neural tube?
Approximately 1 out of every 500 live births
What does a recent discovery of enormous public health importance trace many neural tube defects to?
Deficiency of the vitamin folic acid (or folate) in the maternal diet during the weeks immediately after conception. It has been estimate that dietary supplementation of folic acid during this period could reduce the incidence of neural tube defects by 90%.
What does the formation of the neural tube depend upon? (List 3)
- Precise sequence of changes in the three-dimensional shape of individual cells as well as on changes in the adhesion of each cell to its neighbours.
- Timing of neurulation must be coordinate must be coordinated with simultaneous changes in non-neural ectoderm and mesoderm.
- At the molecular level, successful neurulation depends on specific sequences of gene expression that are controlled, in part, by the position and local chemical environment of cells.
* Note: This process is highly sensitive to chemicals, or chemical deficiencies, in the maternal circulation.
What is the order of fusion of the neural folds to form the neural tube?
Occurs first in the middle, then anteriorly and posteriorly
What condition is a result of the failure of the anterior neural tube to close?
Anencephaly
Anencephaly
Condition characterized by degeneration of the forebrain and skull that is always fatal
What condition is a result of the failure of the posterior neural tube to close?
Spina bifida
What is spina bifida characterized by in its most severe form?
Failure of the posterior spinal cord to form from the neural plate
What Latin word meaning is bifida from?
Cleft in two parts
What is spina bifida characterized by in its less severe forms?
Defects in the meninges and vertebrae overlying the posterior spina cord
Is spina bifida fatal?
Spina bifida is usually not fatal but it does require extensive and costly medical care
What is the role of folic acid?
Plays an essential role in a number of metabolic pathways, including the biosynthesis of DNA, which naturally must occur during development as cells divide
Why does folic acid deficiency increase the incidence of neural tube defects?
We do not precisely understand why folic acid deficiency increase the incidence of neural tube defects but it is easy to imagine how it could alter the complex choreography of neurulation
What Latin word is the name folic acid derived from and what does this reflect?
Derived from the Latin word for “leaf”
Reflects the fact that folic acid was first isolated from spinach leaves
What are six good dietary sources of folic acid?
- Green leafy vegetables (i.e. spinach)
- Liver
- Yeast
- Eggs
- Beans
- Oranges
What food is commonly fortified with folic acid?
Many breakfast cereals
What is the folic acid intake of the average American and how does it compare to the recommended amount to prevent birth defects?
Folic acid intake of the average American is only half of what is recommended to prevent birth defects (0.4 mg/day)
What does the U.S. Centers for Disease Control and Prevention recommend women take before planning pregnancy?
Multivitamins containing 0.4 mg of folic acid
What does the U.S. Centers for Disease Control and Prevention recommend women take before planning pregnancy?
Multivitamins containing 0.4 mg of folic acid
Differentiation
During embryonic development, the process by which structures become more complex and functionally specialized
What is the first step in differentiation of the brain?
Development, at the rostral end of the neural tube, of three swellings called the primary vesicles
The entire brain derives from the _____ _____ _____ of the neural tube.
The entire brain derives from the THREE PRIMARY VESICLES of the neural tube.
Prosencephalon
Rostral-most of the three primary vesicles
Pro is Greek for “before”; encephalon is derived from the Greek for “brain”
Also called the forebrain
Forebrain
Region of the brain derived from the rostral primary embryonic brain vesicle
Also called prosencephalon
Forebrain structures include the telencephalon and the diencephalon
What vesicle lies posterior to the prosencephalon?
Mesencephalon or midbrain
What vesicle lies posterior to the mesencephalon?
Rhombencephalon or hindbrain
Midbrain
Region of the brain derived from the middle primary embryonic brain vesicle
Also called mesencephalon
Midbrain structures include the tectum and the tegmentum
Hindbrain
Region of the brain derived from the caudal primary embryonic brain vesicle
Also called rhombencephalon
Hindbrain structures include the cerebellum, pons, and medulla
The _____ connects with the _____ _____ _____, which gives rise to the _____ _____.
The RHOMBENCEPHALON connects with the CAUDAL NEURAL TUBE, which gives rise to the SPINAL CORD.
Where do the next important developments after the development of the three primary brain vesicles?
Forebrain, where secondary vesicles sprout off on both sides
What are the two secondary vesicles that sprout off on both sides of the prosencephalon called?
- Optic vesicles
2. Telencephalic vesicles
What is the central structure that remains after the secondary vesicles have sprouted off?
Diencephalon or “between brain”
After the sprouting of secondary vesicles off both sides of the prosencephalon, what does the forebrain consist of?
- Paired (two) optic vesicles
- Paired (two) telencephalic vesicles
- Diencephalon
Diencephalon
“Between brain”
A region of the brain stem derived from the prosencephalon (forebrain). Diencephalic structures include the thalamus and hypothalamus.
How do optic vesicles become the optic nerves and the two retinas in the adult?
Optical vesicles grow and invaginate (fold in) to form the optic stalks and the optic cups. The optic stalks will become the optic nerves, and the optic cups will become the retinas.
What part of the nervous system do the retina and the optic nerve belong to?
Brain; NOT the PNS
Where is the retina located?
Back of the eye
What does the optic nerve contain?
Axons that connect the eye to the diencephalon and midbrain
The _____ _____ develop into eyes.
The OPTIC VESICLES develop into eyes.
Telencephalon
“Endbrain”
A region of the brain derived from the prosencephalon (forebrain). Telencephalic structures include the paired cerebral hemispheres
that contain cerebral cortex and the basal telencephalon.
What four ways does the telencephalon?
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.
