Understanding brain structure through develop: Barr's/Bear Flashcards
Why do neurons (nerve cells) exist?
To transfer information rapidly from one part of the animal’s body to another
What is the nervous system?
All the neurons of an organism, together with their supporting cells
How do neurons carry out its communicative function?
-Conduction of signal from one part of the cell to another
- and synaptic transmission, which is communication between adjacent cells
What is an impulse (action potential)?
Wave of electrical depolarization that is propagated within surface membrane of the neuron. A stimulus applied to one part of the neuron initiates an impulse that travels to all other parts of the cell
What are neurites?
Long cytoplasmic processes end close to surfaces of other cells.
They are dendrites and axons
What is myelin
Wrapped around some axons, lipid-rich material composed of tightly packed membranous layers
Where are the cell bodies of neurons in the CNS?
Gray matter regions
What is a nucleus? (in terms of brain not nucleus of cell)
A compact aggregation of gray matter
What is the white matter of the CNS?
contains axons but not neuronal cell bodies
Where are the cell bodies in the PNS?
Occur in nodular structures called ganglia (singular: ganglion)
Where does the neurons and other cells develop from in the early embryo?
The dorsal ectoderm
Where is the epidermis derived from?
Epidermis is also derived from the ectoderm
What is the first indication of the future nervous system?
The neuroectoderm, consisting of the neural plate
Where does the neural plate appear?
In the dorsal mid-line of the embryo at the 16th-17th day after fertilization. Consists only of a flat sheet of cells
What makes the neural plate become taller than the ordinary ectoderm?
The underlying mesodermal cells
What comes after the neural plates, and in how long?
In 2 days the neural plate becomes the neural groove with a neural fold along each side
When is pregnancy timed?
from the 1st day of the last menstrual period, about 14 days before fertilization
the age of the embryo stated…?
from the known or estimated time of fertilization
When is the embryo renamed a fetus?
8 weeks and all the organs are formed
What is the embryonic period broken down into for exact description?
23 Carnegie stages, based on the studies of anatomical development in the large collection of embryos of the Carnegie Institution for science.
When do neural folds appear?
stage 8, when embryo is 1 - 1.5mm long
What happens at the 3rd week (stage 10) of development?
neural folds have begun to fuse with one another, thereby converting the neural groove into a neural tube.
Where does the transformation of neural groove to neural tube begin and proceed from there?
begins in the middle (in what will eventually be the cervical segments of the spinal cord)
Then proceed rostrally and caudally.
As the neural groove transforms into the neural tube from the middle, what are the openings called at each end and when do the openings close?
-Rostral neuropore at 24th day (stage 11)
-Caudal neuropores at about 27th day (stage 12)
Where does the brain and spinal cord develop from?
neural tube, the cells lining the tube will constitute the neuroepithelium, which will give rise to all the neurons and most of the other cells in the CNS
What is the neural crest?
Junction between the neural plate and ectodermal cells (that will be epidermis), not incorporated into the neural tube. Come together at midline. Dorsal to the tube. Some neural ectoderm pinched off. Cells from neural crests migrate laterally and ventrally.
What does the neural crest form? (neuronal)
-all neurons with cells bodies in the PNS
-Dorsal root ganglia of spinal nerves
-Some of the neurons in the sensory ganglia of cranial nerves
-Autonomic ganglia
-nonneuronal cells (neuroglia) of peripheral nerves
-Secretory cells of adrenal medulla
What are some of the nonneuronal elements that the neural crest differentiates into?
- Melanocytes of skin
- Calcitonin- secreting cells of thyroid gland,
- Chemosensory cells in the carotid and aortic bodies
- Odontoblasts of teeth
- Some of the bones, muscles, and other structures of mesenchymal origin in the head
Where are the connective tissue cells in the nerves and ganglia derived from?
Local mesoderm
What are placodes?
Thickened regions of ectoderm of the embryonic head. Some neurons and other cells in peripheral sense organs and ganglia derived from placodes.
(e.g., olfactory neurosensory cells)
What is the first populations of cells produced in neural tube
Neurons
when are most of the neurons are produced?
between the 4th and 20th weeks
The number of neurons formed in the neural tube…
Exceeds the number in the adult brain and spinal cord. Large numbers of neurons die in the normal course of development. (cell death or apoptosis)
what is apoptosis?
cell death
The cell death is genetically programmed in…
invertebrates
In vertebrates. the cells that died were those that…
failed to make synaptic connections
Where do the sensory ganglia derived from the neural crest send the neurites?
into the peripheral and into the neural tube
What happens by the 8th week of intrauterine life.
The centrally directed neurites have extensive synaptic connections with neurons in the spinal cord. The number and complexity of synapses continue to increase until well after birth, as does the generation of neuroglial
What are neuroglia (glia)?
comprises the cells of the nervous system that are not neurons.
What are the first glial cells that develop alongside the first neurons? And describe their processes
Radial glia, having cytoplasmic processes that extend from the lumen to the outside surface of the neural tube
What do the processes of radial glia do?
Guide the migration of the young neurons
Where are astrocytes and oligodendrocytes generated from?
The neuroepithelium during the fetal period
Where do microglial cells arise from? And Where do they go?
Arise from hemopoietic tissue (pertaining to the formation of blood or blood cells) and enter brain though the walls of blood vessels
In PNS where are neurons (in sensory and autonomic ganglia) and glial cells are (satellite cells in ganglia and Schwann cells in nerves) derived?
Neural crest
What does the caudal neuropore form?
upper lumbar segments of spinal cord
Further caudally from the caudal neuropore what is formed and how is it formed?
The spinal cord by secondary neurulation.
What is secondary neurulation?
The coalescence of a chain of vesicles that become continuous with the lumen (cavity) of the neural tube about 3 weeks after the closure of the caudal neuropore
Where is the vesicles from the secondary neurulation derived from?
The caudal eminence
What is the caudal eminence?
a mass of pluripotent cells located dorsal to the developing coccyx.
What are the 3 major divisions (or vesicles) of the brain that appear at the end of the 4th week of development?
-Prosencephalon (forebrain)
-Mesencephalon (midbrain)
-Rhombencephalon (hindbrain)
What does the prosencephalon develop into during the 5th week of development? (also referred to as the secondary vesicles)
-Telencephalic vesicles –>together both form the Telencephalon (endbrain)
-Diencephalon
-optic vesicles
What does the rhombencephalon (hindbrain) develop into during the 5th week of development?
- Metencephalon
- Myelencephalon
Does the mesencephalon differentiate into?
Doesn’t differentiate, eventually becomes the midbrain
What are neuromeres?
The early embryonic brain CNS divides longitudinally into smaller segments. The neuromeres become indistinguishable as the complex structure of the brain develops, but segmental organisation of the spinal cord persists throughout life.
What is the sulcus limitans
Longitudinal groove that appears along the inner aspect of each lateral wall in the neural tube as the cellular proliferation and differentiation proceed.
What does the sulcus limitans do?
separates dorsal alar plate from a ventral basal plate
What connections does the dorsal alar plate acquire?
afferent connections
What connections does the ventral basal plate acquire?
efferent connections
What are the left and right basal plates separated by?
By thin floor plate
What do the basal plate cells become?
Some differentiate into motor neurons, with axons that grow out into the developing muscles
What axons enter the alar plate?
The growing axons of neurons of the sensory ganglia
What does the myelencephalon (came from rhombencephalon) become?
Medulla oblongata.
What does the metencephalon (came from rhombencephalon) become?
pons and cerebellum
What is the mesencephalon of the mature brain called?
midbrain
What does the diencephalon become?
- Thalamus
- epithalamus
- hypothalamus
- subthalamus
What does the telencephalon become?
-Cerebral cortex and the basal telencephalon
-Cerebral hemispheres, each containing olfactory system, corpus striatum (a mass of gray matter with motor functions) , cerebral cortex, and white matter
What does the lumen of the neural tube become?
The ventricular system.
Where do the lateral, third and fourth ventricles located.
-lateral ventricle - in each cerebral hemisphere
-third ventricle - diencephalon
-fourth ventricle - bounded by the medulla, pons and cerebellum
(key landmarks in adult brain)
What connects the third and fourth ventricle?
narrow channel called the cerebral aqueduct (located in and running through midbrain)
What is the central/spinal canal?
the narrow lumen that runs down the middle of the spinal cord, continuous with the lumen of the caudal medulla .
What helps accommodate the initially cylindrical brain in what will eventually be a round head?
The flexures, which allow the brain to bend. Because neural tube growth at certain points is limited
Where is the cervical flexure?
Forms at the junction of the rhombencephalon with the spinal cord
Where is the mesencephalic flexure (aka cephalic flexure)?
at the level of the midbrain
Where is the pontine flexure?
in the metencephalon
What do the flexures do in order to contrast us with quadrupedal animals?
necessary feature of the erect posture of humans, in quadrupedal animals there is no abrupt bend at the junction of the midbrain with the forebrain
When does the membranous coverings of the brain and spinal cord first appear and what is it?
4th week appears as a single mesodermally derived primary (or primitive) meninx.
What happens 1 week later after the meninx is formed (5th week)?
Formation of the 3 layers that constitute the meninges:
-dura mater
-arachnoid membrane
-pia mater
What fluid is contained in the subarachnoid space, and where is it?
cerebrospinal fluid (CSF), between the inner 2 meningeal layers (arachnoid membrane and pia mater)
What is the least differentiated component of the CNS?
spinal cord
How is the segmented nature of the spinal cord reflected?
In a series of paired spinal nerves, each of which is attached to the cord by dorsal sensory root and a ventral motor root
Where is the neuronal cell bodies located in the spinal cord and what is the shape it makes?
The central Gray matter contain the neuronal cell bodies, and has a roughly H-shaped outline in a transverse section
Describe the white matter in the spinal cord
The white matter consists of myelinated axons running longitudinally, occupies the periphery of the cord (parts that are not the H-shaped outline)
where is the neuronal connections for spinal reflexes located?
The spinal gray matter
Where are the axons that convey sensory data and impulses to the brain, typically the ones of motor significance?
The spinal white matter
Where does the spinal cord fibre tract continue at the top?
in the medulla, where it also contains clusters of neurons (nuclei)
Describe the inferior olivary nuclei
located in the medulla, most prominent nuclei. Sends fibres to the cerebellum through the inferior cerebellar peduncles, which attach the cerebellum to the medulla
What are some of the smaller nuclei of the medulla?
some are components of the cranial nerves
What are the distinct parts the pons consists of?
-The dorsal portion - tegmentum
-The ventral portion - basal pons
describe the dorsal portion of the pons (tegmentum)
(tegmentum)
Has features shared with the rest of the brainstem, therefore it includes the ascending and deending tracts, together with some of the nuclei of cranial nerves
describe the ventral portion of the pons (basal pons)
Special part of the brainstem, provides extensive connections between the cerebral cortex (cortex) of the cerebral hemisphere and that of the contralateral cerebellar hemisphere (the hemispheres of the cerebellum). These connections contribute to maximal efficiency of motor activities. A pair of middle cerebellar peduncles attaches the cerebellum to the pons
What pathways does the midbrain contain?
Ascending and descending pathways, together with 2 cranial nerves
Describe the role of the dorsal region of the midbrain/mesencephalic vesicle (the roof or tectum)
Concerned principally with the visual and auditory systems
What are the red nucleus and substantia nigra in the midbrain/mesencephalic vesicles responsible for? And where are they located in midbrain? (tegmentum or floor)
Ventral region of midbrain,
motor control
How is the cerebellum attached to the midbrain?
By the superior cerebellar peduncles
What data does the cerebellum receive?
Data from most of the sensory systems and the cerebral cortex
What does the cerebellum influence?
The motor neurons that supply the skeletal musculature
What is the function of the cerebellum? And structure
-Produce changes in muscles tone in relation to equilibrium, locomotion, and posture and to coordinate the timing, force and extent of contraction of muscles being used for skilled movements.
-spinal cord inputs provide information about body’s position in space
-Operates at a subconscious level
-Left side of cerebellum for left side of body
-right side of cerebellum for right side
-contains as many neurons as both the cerebral hemispheres
-has extensive connections with cerebrum and spinal cord
What does the diencephalon form?
-Forms the central core of the cerebrum
-thalamus
-subthalamus
-epithalamus
-pineal gland
-hypothalamus
describe the role and connections of the thalamus.
Consists of several regions or nuclei, some of which receive data from sensory systems and project to sensory areas of the cerebral cortex.
Part of the thalamus has connections with cortical areas that are concerned with complex mental processes. Other regions participate in neural circuits related to emotions, and certain thalamic nuclei are incorporated into pathways from the cerebellum and corpus striatum to motor areas of the cerebral cortex.
What does the epithalamus include?
Small tracts and nuclei, and pineal gland (an endocrine organ)
What does the hypothalamus have controlling influence over?
-Autonomic visceral nervous system –> Sympathetic and parasympathetic systems, which supply internal organs, exocrine glands, and blood vessels
-responsible for fight or flight response
What happens to the hormones synthesized by the neurosecretory cells in the hypothalamus?
Enter the bloodstream
What do the hormones synthesized by the neurosecretory cells in the hypothalamus act on?
Some act on the kidneys and other organs; others influence the hormonal output of the anterior lobe of the pituitary gland through a special portal system of blood vessels
Where do SOME of the neurosecretory cells in the hypothalamus and in the immediately adjacent part of the telencephalon get derived from, the ones of which that are not derived from the epithelium of the neural tube?
olfactory placode
What does the neurosecretory cells in the hypothalamus contain and secrete? **
A polypeptide known as gonadotrophin-releasing hormone
Where does the gonadotrophin-releasing hormone of the neurosecretory cells of the hypothalamus migrate to after being releasing?
Migrate along the terminal nerve (cranial nerve 0) into the forebrain
What is the terminal nerve (cranial nerve 0)?
The terminal nerve is a tiny cranial nerve rostral to the olfactory nerves
What does the subthalamus include?
Sensory tracts that proceed to the thalamus, axons that originate in the cerebellum and corpus striatum, and the sub- thalamic nucleus, which has motor functions.
Where is the retina produced from?
Is produced from the diencephalon; therefore, the optic nerve and the visual system are intimately related to this part of the brain.
Describe the cerebral cortex
-Much of it folded, with ridges (gyri) separated by grooves (sulci).
-Major sulci separate the frontal, parietal, occipital, and temporal lobes of the cerebral hemisphere, which are named after the overlying bones of the skull.
-cell bodies of cortical neurons always arranged in layers (lie parallel to surface of brain)
Different modalities of sensation and motor functions are represented in…
Distinct areas of the cortex, and there are also large expanses of association cortex, in which the highest levels of neural function take place, including those inherent in intellectual activity.
What is the corpus striatum?
A large mass of gray matter with motor functions situated near the base of each hemisphere
What does the corpus striatum consist of?
the caudate and lentiform nuclei, which are parts of a system known as the basal ganglia
Describe the cerebral/cortical white matter
Consists of fibres that connect cortical areas of the same hemisphere, fibres that cross the midline (most are in a large commissure known as the corpus callosum) to connect cortical areas of the two hemispheres, and fibres that pass in both directions between the cortex and subcortical parts of the CNS.
What is the internal capsule?
Continuous with cortical white matter, fibres that pass in both directions between the cortex and subcortical parts of the CNS converge to form the compact internal capsule in the region of the thalamus and corpus striatum
What is the average brain weight at birth and what is the further increase in size attributed to?
400g, attributed to continuing formation of synaptic connections, production of neuroglial cells, and thickening of the myelin sheaths around axons
When does most rapid growth of brain occur?
during first 20 postnatal weeks
How much does an average brain weigh at age 3? And when does it continue to?
The average weight (1,200 g) of the brain is almost that of an adult, although slow growth continues until age 18 years
When does the brain begin to decline in size? and does this lead to intellectual deterioration?
After age 50 years, there is a slow decline in brain size. This decrease in size does not lead to intellectual deterioration unless there is considerable atrophy caused by disease
What are the factors that varies the mature brains weight?
Age and stature
What is the normal range of weight for men and women?
Men - 1,100 to 1,700 g (mean 1,360 g)
Women - 1,050–1,550 g (mean 1,275 g
(women have smaller because of smaller stature)
Is there evidence if a relation between brain weight, within normal limits and level of intelligence?
No
What is the cerebrum?
-The rostral-most and largest part of the brain, has 2 hemispheres separated by the deep sagittal fissure
-Right hemisphere receives sensations and controls movement of left
-left “” of the right
What is the purpose of brainstem?
-Serves to relay information from the cerebrum to the spinal cord and vice versa.
-site where vital functions are regulated: breathing, consciousness, body temp
Describe the spinal cord
-Encased in bony vertebral column
-attached to brainstem, major conduit of information from the skin, joints and muscles of body to brain and vice versa
How does the spinal cord communicate with the body? And where is it located?
Via the spinal nerves, which are part of PNS, they exit the spinal cord through notches between each vertebrae of vertebral coloumn
What are the 2 branches of the spinal nerves?
Dorsal root and ventral root
What are the dorsal root responsible for?
bringing information into the spinal cord
What are the ventral root responsible for?
carry information away from the spinal cord (e.g., to muscles)
What are the 2 parts of the PNS?
Somatic PNS, and Visceral PNS
What is the somatic PNS?
All the spinal nerves that innervate the skin, joints and muscles (under voluntary control)
What are the somatic motor axons? Where are the somatic motor axons derived from? And where do the cell bodies lie?
-Command muscle contraction.
Derived from motor neurons in the ventral spinal cord.
-Cell bodies of these neurons lie within the CNS, but their axons are mostly in the PNS
What are the somatic sensory axons? Where do they enter? And where do their cell bodies lie?
-Innervate and collect the information from the skin, muscles and joints.
-Cell bodies lie outside the spinal cord in clusters called dorsal root ganglia (there is a dorsal root ganglion for each spinal nerve)
What is the visceral PNS?
-Also called involuntary, vegetative or autonomic nervous system (ANS)
-Consists of the neurons that innervate the internal organs. blood vessels and glands
What are the visceral sensory axons?
They bring information about visceral function to the CNS, such as the pressure and oxygen content of the blood in the arteries
What are the visceral motor fibres?
Command the contraction and relaxation of muscles that form the walls of the intestines and blood vessels (smooth muscles), the rate of cardiac muscle contraction, and the secretory function of various gland
How does the visceral PNS control the blood pressure?
by regulating the heart rate and the diameter of the blood vessels
What is afferent?
“carry to”. carry information to the CNS
What is efferent?
“carry from”. Carry information from the CNS
How many cranial nerves are there, where do they arise from, and what do they mostly innervate?
12 pairs of cranial nerves,
arise from the brainstem innervate (mostly) the head
What is the meninges?
3 membranes that protect the CNS:
Dura mater
arachnoid membrane
pia mater.
What is the dura mater?
outermost part of meninges; tough, inelastic, surrounds brain and spinal cord
What is the arachnoid membrane
meningeal layer below the dura mater; appearance resembling spider web
What is the subdural hematoma?
Blood vessel passing between the dura mater and arachnoid membrane ruptured, blood collecting here; the build-up of fluid in this subdural space can disrupt brain function by compressing part of CNS, treated by drilling hold in skull and draining blood
What is the pia mater?
-meningeal layer; thin membrane that adheres closely to the surface of the brain
-along the pia run many blood vessel the dive into the substance of the underlying brain
What separates the arachnoid membrane and the pia mater?
Fluid filled space called the subarachnoid spaced, filled with clear fluid called cerebrospinal fluid (CSF)
What is the ventricular system?
Fluid-filled caverns and canals inside the brain, filled with cerebrospinal fluid (CSF). Contains ventricles, choroid plexus
What is the choroid plexus? And where is it located?
Specialised tissue in the ventricles that produces cerebrospinal fluid (CSF). Located in all the ventircles
Where does the CSF that’s produced by the choroid plexus go?
Circulates through the ventricles, from lateral ventricle to third ventricle to fourth ventricle and then exiting the ventricular system to enter through small openings (median aperture or foramen of magendie) located near where the cerebellum attaches to the brain stem to the subarachnoid space
What is the CSF absorbed by?
blood vessel at special structures called arachnoid villi in the subarachnoid space
What is the method CLARITY?
-Allows visualization of deep structures without section brain.
-Soak brain in a solution that replaces light-absorbing lipids with water-soluble gel that turns brain transparent
-if this “clarified” brain contains neurons that are labelled with fluorescent molecules, like GFP, then illumination will revel location of these cells deep in the brain
What is a limitation to the CLARITY method?
A clarified brain is still dead brain, limits usefulness in diagnosing neurological disorders in living individuals
What does the embryo begin as?
Flat disk with 3 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 skeleton and the muscles
Where is the nervous system and skin derived from?
Entirely from the ectoderm, and then walls of the neural tube
where do the somites form from and what do the somites form?
Somites come from the mesoderm at either side of the neural tube, from the somites 33 individual vertebrae of the spinal column and the related skeletal muscles develop. (nerves that innervate the skeletal muscles therefore called somatic motor nerves)
What is the process by which neural plate becomes the neural tube called? and when does this happen?
Neurulation, occurs very early in embryonic development, 22 days after the conception in humans.
How can the birth defect of the failure of appropriate closure of the neural tube be avoided?
in most cases ensuring the proper maternal nutrition
What is differentiation?
Process by which structures become more complex and functionally specializes during development
What happens to optic vesicles?
grow and invaginate to form the optic stalks and optic cups, which will ultimately become the optic nerves and the 2 retinas (retina part of forebrain not PNS)
How do the telencephalic vesicles grow?
in 4 ways:
1.) Grows posteriorly, lay over and lateral diencephalon
2.) olfactory bulbs vesicles sprout from ventral surface
3.) Cells of walls of the telencephalon divide and differentiate into various structures
4.)White matter system develop, carrying axons to and from the neurons of the telencephalon
What are the major white matter systems of the brain?
Axons that extend from developing forebrain to other parts of the nervous system
-cortical/cerebral white matter
-corpus callosum
-internal capsule
What is the role of the forebrain (prosencephalon)?
Seat of perceptions, conscious awareness, cognition, and voluntary action. All depends on extensive interconnectedness with sensory and motor neurons of brain stem and spinal cord.
What is commonly referred to as the “gateway to the cerebral cortex” and why?
Thalamus, because sensory pathways from the eye, ear, and skin all relay in the thalamus before terminating in the cerebral cortex
What does the thalamus send messages to the cortex with?
Via internal capsule
As a general rule where do the axons of the internal capsule carry information?
Carry information to the cortex about the contralateral side of the body
(Therefore, if a thumbtack entered the right foot, it would be relayed to the left cortex by the left thalamus via axons in the left internal capsule)
Where do axons from the cortex to the thalamus pass through?
The internal capsule as well. And back to the brain stem
What does the corticospinal/pyramidal tract do?
command voluntary movement
describe the basal ganglia
-A collection of cells in the basal telencephalon
- involved in the control of voluntary movement. Damages to basal ganglia disrupts ability to initiate voluntary movement.
The hypothalamus directs bodily responses via..
connections with the pituitary gland, this gland communicates with many parts of the body by releasing hormones into the bloodstream
What is a good landmark for identifying the midbrain
cerebral aqueduct
Does the midbrain contain neurons that contribute to sensory systems and control of movement?
Yes, contains axons descending from cerebral cortex to brain stem and spinal cord, e.g., the corticospinal tract
What does the tectum differentiate into?
The superior colliculus and inferior colliculus
Describe the superior colliculus
Received direct input from the eye, so it also called the optic tectum. control eye movement, via synaptic connections with motor neurons that innervate eye muscles
Where do cranial nerves iii (3) and IV (4) originate from? and what do they do
in the midbrain, axons that supply eye muscles
Describe the inferior colliculus
Receives sensory information from ear, serves as important relay station for auditory information en route to the thalamus
What does the tegmentum in the midbrain contain? and what are they involved in?
-substantia nigra (the black substance) and The red nucleus
-involved in control of voluntary movement
What do other cell groups beside the tegmentum and tectum of the midbrain do?
Have axons that project widely throughout much of the CNS and function to regulate consciousness, mood, pleasure, and pain
What does the hindbrain (rhombencephalon) become?
cerebellum, pons and medulla oblongata (medulla)
Describe the rhombic lip what does it form?
At 3 vesicle stage, the rostral hindbrain in cross section is simple tube. in subsequent weeks, the tissue along the dorsal-lateral wall of the tube, of hindbrain, grows dorsally and medially until it fuses with its twin on other side.
-The resulting flap of brain tissue grows into cerebellum.
-The ventral wall of the tube (not the rhombic lips, but lower down differentiated and swells to form the pons
How does the caudal half (lower half) of developing structure form?
-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, called medullary pyramids
What is the function of the hindbrain (rhombencephalon)?
-important conduit for information passing from forebrain to the spinal cord and vice versa
- neurons of the hindbrain contribute to the processing of sensory information, control of voluntary movement and regulation of autonomic nervous system
What is pyramidal decussation?
near where the medulla joins with the spinal cord each pyramidal tract cross from one side to the other. explains why one side of brain controls movement of opposite side of body
What are the functions of the medulla?
-Contains neurons that perform many different sensory and motor functions. (touch and taste and hearing)
-e.g., bring auditory information from ear and synapse on cells in cochlear nuclei of medulla
-the medulla contains neurons that relay sensory information from spinal cord to the thaladmus
control tongue via cranial nerve XII (12)
What is the dorsal horn?
-upper part of the H-outline of gray matter of spinal cord, above this in the white matter is the dorsal columns,
-receive sensory inputs from dorsal root fibres
what is the ventral horn?
-lower part of the H-outline of gray matter of spinal cord. Below this in the white matter is the ventral column
-project axons into the ventral roots that innervate muscle
What is the gray matter between the dorsal and ventral horns? and what is it responsible for?
-intermediate zone, lateral to this in the white matter is the lateral columns
-interneurons that shape motor outputs in response to sensory inputs and descending commands from the brain
What is the dorsal column responsible for?
-contains axons that carry somatic sensory (touch) information up the spinal cord toward the brain.
-speeds information from the ipsilateral side of body up to nuclei in medulla where postsynaptic neurons in medulla give rise to axons that decussate and ascend to the thalamus on contralateral side
What is the lateral column responsible for?
-contains axons of descending corticospinal tract, which decussate at the level of medulla
-These axons innervate neurons of the intermediate zone and ventral horn and communicate the signals that control voluntary movement
What are the differences in rat and human brain?
-convolutions on human cerebral cortex surface
-size of olfactory bulk (bigger in rats)
-growth of cerebral hemispheres: temporal, frontal, parietal, occipital (human brain arcs posteriorly, ventrolaterally and then anteriorly)
What does the central sulcus mark?
marks posterior border of frontal lobe, caudal to which lies the parietal lobe
What is the surface layer (layer I) of neurons separated from?
The pia mater, by a zone that lacks neurons.
What are apical dendrites?
At least one layer in cerebral cortex contains cell that emit large dendrites called apical dendrites, that extend up to layer I, where they form multiple branches
What is the connectome of the neocortex (cerebral cortex)
A detailed wiring diagram of connections
What is the smallest function unit of the neocortex?
-a cylinder of neurons 2 mm high (which is the distance from the white matter to the cortical surface) and 0.5mm in diameter
-contains approx. 10,000 neurons and 100 millions synapses
How long did Brenner’s work on flatworms of 7000 synapses and 302 neurons take?
over a dozen years
What is the 3 types of motor and sensory cortex according to evolutionary histories of common ancestors?
-The primary sensory areas (first to received signals from ascending sensory pathways)
-the secondary sensory area (heavy interconnections with primary sensory areas)
- Motor areas (intimately involves with control of voluntary movement, receive inputs from thalamic nuclei that relay information from the basal telencephalon and the cerebellum and send outputs to motor control neurons in the brain stem and spinal cord)
What has mainly expanded in the cortex?
-Regions between motors areas, the secondary sensory areas devoted to analysis of sensory information
-cortex amount has evolved, not structure
