Results for "the nucleus"

The Nucleus, Nuclear Decay, Energy, Fission + Fusion

DNA Packaging and the Nucleus

Separation of the nucleus and cytoplasm

DNA, Chromosomes, and the Nucleus

the nucleus

CELL 201 - UNIT 3: DNA & the Nucleus

Chapter 10 (parts 1 and 2): The Nucleus

Chapter 10 (parts 1 and 2): The Nucleus

The nucleus

Lecture 13: The Nucleus

Chapter 10 - The Nucleus

The Nucleus

DNA, Chromosomes, Genome, and the Nucleus

Nuclear Stability: Forces in the Nucleus

Chapter 15 - Cell Theory, Prokaryotes, and the Nucleus

DNA and the nucleus

Question: Bile is a substance secreted to help digest fats. Bile is stored in the: Answer: Gallbladder Question: Which element in the protein hemoglobin, found in red blood cells, is responsible for binding oxygen? Answer: Iron Question: When a blood vessel is injured, which of the following is responsible for clotting? Answer: Platelets Question: If CaCl2 is mixed with Na2SO4 in aqueous solution, which of the following is a possible product? Answer: NaCl Question: The Earth is about 4.5 billion years old. About how many years ago did life first appear? Answer: 3.5 billion years Question: The sun’s energy reaches the Earth’s surface primarily in the form of: Answer: Visible light radiation Question: Which type of rock would likely be found at the bottom of a river bed? Answer: Sedimentary Question: Which of the following statements about the Earth is true? Answer: The mantle makes up the largest percentage of the Earth’s volume Question: If an unbalanced force acts on an object, then the object will begin to accelerate according to: Answer: Newton’s Second Law Question: In meiosis, one parent cell becomes how many daughter cells? Answer: 4 Question: The potential energy of an object with a mass of 5kg that is placed 20 meters above the surface of the earth is most nearly: Answer: 981 Joules Question: One of the reasons bacteria can be so deadly is because they multiply very quickly. E. coli has a doubling time of around 15 minutes. This means that if 100 bacteria are left alone for 2 hours, they will multiply to become: Answer: 25,600 Bacteria Question: Organisms which help one another survive by providing a mutual benefit to each other are known as: Answer: Symbionts Question: In taxonomy, which classification comes after ‘family’? Answer: Genus Question: All of the following are phenotypic traits except for: Answer: Missing 22nd chromosome Question: The cell membrane is a structure composed primarily of: Answer: Lipid Question: Of the following layers of the atmosphere, which is the closest to the earth’s surface and contains the majority of clouds? Answer: Troposphere Question: Which of the following body systems is most closely associated with the immune system? Answer: Lymphatic System Question: One of the primary characteristics of a bacteria is its: Answer: Lack of a nuclear membrane Question: Which of the following planets has a perfectly circular orbit? Answer: None Question: Sound waves will travel the fastest in a medium that is: Answer: The most dense Question: A calorie is actually a measure of energy, and is equivalent to how many Joules? Answer: 4.18 Question: What is the molecular weight of the compound C2H5O? Answer: 45 Question: Craig ran 2.5 miles on his afternoon run. How many feet did he run? Answer: 13,200 feet Question: The earth’s surface is covered by approximately what percent water? Answer: 70% Question: Blood that flows back from the body will enter the heart through the: Answer: Right Atrium Question: A nerve impulse is transmitted through your nervous system primarily by: Answer: An electric potential Question: All magnets have two poles which can be used to predict the direction of their magnetic waves. These two poles are the: Answer: South and North Question: Approximately how many bones exist in the human body? Answer: 200 Question: The nucleus of an atom is composed of: Answer: Protons and neutrons Question: What is the second most abundant gas in the atmosphere? Answer: Oxygen Question: As light passes through a substance, the incident angle changes, meaning the light’s entering angle is different than its exiting angle. This is an example of: Answer: Refraction Question: If one tectonic plate slides under another, the process is known as: Answer: Subduction Question: Carbon dioxide can be consumed and converted into glucose by what type of organism? Answer: Plants Question: Two separate weather fronts will have air that is of different: Answer: Density Question: Plants are autotrophs, meaning that they: Answer: Are able to produce their own food Question: Plant and animal cells both have cell membranes and nuclear membranes. However, plant cells have a structure that animal cells do not, known as a: Answer: Cell Wall Question: Muscles in the human body require what energy compound to function? Answer: ATP Question: When a human cell divides in mitosis, the two daughter cells will each have: Answer: 46 Chromosomes Question: In an electromagnetic wave, as the frequency of the wave becomes greater, what becomes shorter? Answer: The wavelength Question: Which of the following time periods is the longest? Answer: Eon Question: In the lily flower, the red color is dominant and the white color is recessive. This means that if you cross a homozygous red flower with a white one, the offspring will be: Answer: All red Question: Which of the following is a characteristic of the tundra ecological biome? Answer: Landscape dominated by shrubs and short trees Question: A train travels at 25 mph for 3 hours. How far did the train move? Answer: 75 miles Question: A solution contains 0.1 molar hydrogen ions (H+). This means the solution is likely: Answer: Around pH 1

Breeding and Selection Breeding: the mating and production of offspring by animals. The activity of controlling the mating and production of offspring of animals Selection: the act of choosing something or someone from a group Geneus species of livestock European cattle- Bos taurus Zebu Cattle- Bos Indicus Swine- Sus Scrofa Sheep- Ovis Aries Horse- Equus Cabellus Goat- Capra Hircus Dog- Canis Familaris Cat- felis catus Principles of Breeding and Genetics Phenotype: the characteristic of an animal that can be seen or measured Genotype: the genetic makeup of an individual (DNA) Phenotype= Genotype + Environment Genotype= phenotype - Envoromet Selection: differently producing what one wants in a herd. Allowing only certain mating to occur. Inheritance: transmission of genes from parents to offsprings Basic Cell Information Chromosomes: in the nucleus and contains genetic material Gene: an active area in the chromosome that codes for trait DNA: complex molecule of the chromosomes which is the coding mechanism of inheritance Gametogenesis: Process that the gonads produce cells that become gametes(ova and sperm) Spermatogenesis: production of sperm Oogenesis: production of egg or ova Meiosis- special type of nuclear division in which germ cells contain one member of each chromosomes pair Fertilization: when an egg and sperm unite from embryo Each contributes one chromosome per pair to new life Homosygous: an individual whose genes for a particular trait are identical or alike Heterozygous: individual who possesses unlike genes for particular trait Dominant: a gene that overpowers and prevents the expression of its recessive allele when the two alleles are present in a heterozygous individual Recessive: a gene that its expression is masked by dominant allele Allele: gene occupying corresponding loci on homologus chromosomes that affect the same trait What traits should one select? Only traits that contribute to productive efficiency and consumer acceptance are of economic importance Ex: reproduction, growth(pre-weaning, post weaning) Basis of Selection Appearance Genetic abnormalities Estimate carcas merit Fit standard for herd Reproduction record Individuals records Progeny testing Pedigree family Factors affecting genetic progress Selection differential Heritability Genetic interval Accuracy of records Genetic correlation Number of traits in selection program Things to remember about traits Heritability: amount of the phenotypic expression of a trait that is transmitted to offspring (enviroments have big effect) (h2) Heterosis: the tendency of a crossbred individual to show qualities superior to those of both parents Generation interval The average age of the parents when offsprings are born The shorter the generation interval, the faster the genetic interval Selection Methods Tandem Selection: Selection for one trait at a time Least effective: mattes rapid gain in a single trait, but is slow to reach selection goal involving several traits Independant culling: establishes minimum culling levels for each trait makes SLOWER gain for each trait, but reaches goals faster. Most effective when few traits are involved. Selection Index: each animal is rated numerically by combining performance of several traits into a single index New Mexico Ram Test Selection Index Index=12 + 40 (ADG) + 30(CWF) + SL - 12 (DIA) - o.5 (VAR) All variables expressed as ratio of individual to the average ADG= average daily grain CWF= clean wool fibers SL= staple length DIA= Fiber diameter VAR= difference between dide and Britch Breeding Systems Purebred breeder: develop breeding stock that pocessess the highest predictability for transmitting the most desirable inheritance possible purebred animal: meets the requiramnets of a recognized breed and whose ancestors are registered in the herd book of that breed Breed: race or variety of livestock where the members are related by descent and are similar Purebred breeders may use: Linecrossing: crossing different lines or unrelated animals of the same breed, it is also used as outcrossing for outbreeding systems. It results in an increased heterozygosity and heterosis (offspring will not breed true). Heterosis: increase in production in the offspring over average of parents. Inbreeding: mating of related individuals( sires and dams share at least one ancestor) results in a increase of homozygosisty Inbreeding coefficient: measures of how inbred an animal is( the probability two genes of a pair in an individual will be homozygous because they are replicates of a single ancestor gene Coefficient ranges from 0-1. 0=no change, 1=absolute certenity Increase inbreeding usually detrimental to: reproductive performance, pre-weaning growth, post-weaning growth, increase susceptibility to environmental stress Commercial Producers: make use of available genetic material in a manner to maximize production or give most efficient, rapid and economical prodyction possible Systems used by commercial producers Species crossing- how many result in nonfertile offsprings Crossbreeding- mating animals of different established breeds and takes advantage of complementary and heterosis(hybrid vigor) oucrossing/ linerarcrossing- mating of unrelated animals of same breed Grading up- making purebred sires to commercial grade females and their female offspring for several generations Most common species crosses Jack to mare= mule Stallion to jennet= hinny Zebu to european cattle= brangus cattle American bison to cattle= buffalo Cross breeding system- designed to maximize hybrid vigor(heterosis) and produce replacement females throught the rotation of different sire breeds Terminal Static crossbreding system Produces replacement females throught the rotation while taking advantage of producing crossbred offspring Also know as “terminal crossbreeding system” Replacament females can be purchased from or produced in separate population Composiste breeding system Combines desirable traits of two or more breeds of cattle into one package Composition must be carefully planed in order to achieve genetic merit Utilizes hybrid vigor without crossbreeding Systems of mating Determied by: type of facilities, breeding schedule, method of heat detection, genetic program, market target hand/Stud mating Purebred breeders use to control breeding Females are kept apart from the males until desire time of breeding, Horse, Rabbit and Poultry advantages prevents overse of particule sire certainity of mating and to which Sire can increase conception rate by 5-10%. Disadvantages increases labor estrus detection becomes a seven-day a week job Pen mating Males and females coexist throught the breeding seasons or year rounds Used mostly by commercial breeders advantages Minimum labor Heat detection is the responsibility of the sire disadvantages Uncertainty of mating and date of conception Uncertainty of infertile sires and of un-bred females May overwork sires Artificial Insemination referred as AI Process by which semen from male is placed into the reproduction tract of the female using mechanical means rather than by natural source advantages Decrease spreed fo disease Increase number of offspring from superior male Identifies the fertility of sire Reduces number of sires needed Allows mating of small females to larger males Genetic diversity disadvantages Requires trained level of management Increases time and supervision of the female herd for estrus detection Sire training Semen handling and special breeding facilities More costly Embryo transfer Removal of early pregnancy embryos from a genetically superior female and placement of these embryos into reproduction tract of a suitable recipient for gestation and parturition Reproduction defined: process by which animals produce offsrpings for the purpose of continuing the species. The process of reproduction begins with copulation, which is the mating of a male and female of the species Sperm cells from the male are deposited in the female reproduction tract and try to unite with an egg cell When fertilization( a sperm cell and an egg cell units) occurs, an embryo begins The embryo attaches to the wall of the uterus where it is protected, recieves nourishment, and develops When the new offspring reaches the end of the gestation period, it is delivered from the female reproductive tract in a process called parturition

biology 2.1Unit 2.1: Mitosis and Meiosis Introduction By the end of this section, you should be able to: Define a chromosome. Define DNA as the genetic material. Define genes. Describe the structure of chromosomes. Describe the components of DNA. Define mitosis and describe its stages. Define meiosis and describe its stages. Relate the events of meiosis to the formation of sex cells. Compare mitosis and meiosis. Chromosomes, Genes, and DNA Almost all the cells of your body—except for mature red blood cells—contain a nucleus, which acts as the control center of the cell. The nucleus holds all the information needed to make a new cell and, ultimately, a new individual. Inside the nucleus are chromosomes, thread-like structures that store genetic information passed from parents to offspring. Chromosomes are made up of DNA (deoxyribonucleic acid), a molecule that carries the instructions needed to make all the proteins in your body. Many of these proteins are enzymes, which control the production of other chemicals and affect everything about how your body functions. Each species has a specific number of chromosomes: Humans have 46 chromosomes (23 pairs). Tomatoes have 24 chromosomes (12 pairs). Elephants have 56 chromosomes (28 pairs). Half of your chromosomes come from your mother, and the other half from your father. These chromosomes are arranged in homologous pairs, meaning they contain matching sets of genes. A karyotype is a special photograph that arranges chromosomes into their pairs. In humans, 22 pairs of chromosomes are called autosomes, which control most body functions. The 23rd pair is the sex chromosomes, which determine whether you are male or female: Females have two X chromosomes (XX). Males have one X and one Y chromosome (XY). DNA Structure DNA is a long, twisted molecule shaped like a double helix (a spiraled ladder). Each strand of DNA is made up of smaller molecules called nucleotides, which consist of: A phosphate group A sugar (deoxyribose) A nitrogen base The four nitrogen bases in DNA are: Adenine (A) → Always pairs with Thymine (T) Cytosine (C) → Always pairs with Guanine (G) Genes are small segments of DNA that carry instructions for making proteins. The sequence of these bases acts like a biological code, directing the cell to create specific proteins. In 1953, James Watson and Francis Crick, using data from Rosalind Franklin’s X-ray photographs, discovered the double-helix structure of DNA. Their discovery led to a huge increase in genetic research, including the Human Genome Project, which mapped all human genes. Mitosis (Cell Division for Growth and Repair) All body cells (somatic cells) divide using mitosis, a type of cell division that creates two identical daughter cells. Mitosis is essential for: Growth (producing new cells). Tissue repair (replacing damaged or old cells). Asexual reproduction (producing offspring with identical DNA). Stages of Mitosis Interphase The cell prepares for division by copying its DNA. Chromosomes are not visible under a microscope. Prophase Chromosomes condense and become visible. The nuclear membrane breaks down. Metaphase Chromosomes line up in the center of the cell. Spindle fibers attach to each chromosome. Anaphase The spindle fibers pull the sister chromatids apart to opposite ends of the cell. Telophase A new nuclear membrane forms around each set of chromosomes. The cell is almost ready to split. Cytokinesis The cytoplasm divides, forming two identical daughter cells. Mitosis is constantly occurring in areas like your skin and bone marrow, where new cells are needed regularly. Meiosis (Cell Division for Reproduction) Unlike mitosis, meiosis occurs only in the reproductive organs (testes in males, ovaries in females) and produces gametes (sperm and egg cells). Gametes have half the number of chromosomes (haploid, n=23) so that when fertilization occurs, the new cell has the correct chromosome number (diploid, 2n=46). Stages of Meiosis Meiosis consists of two rounds of cell division, resulting in four non-identical cells. Meiosis I: Prophase I – Chromosomes pair up and exchange genetic material (crossing over). Metaphase I – Chromosome pairs line up in the center of the cell. Anaphase I – Chromosome pairs separate and move to opposite ends of the cell. Telophase I & Cytokinesis – The cell splits into two haploid daughter cells. Meiosis II (similar to mitosis): 5. Prophase II – Chromosomes condense again. 6. Metaphase II – Chromosomes line up in the center. 7. Anaphase II – Sister chromatids separate and move to opposite sides. 8. Telophase II & Cytokinesis – Four unique haploid gametes are formed. Each gamete is genetically different due to crossing over and random chromosome distribution. Mitosis vs. Meiosis: Key Differences Importance of Mitosis and Meiosis Mitosis ensures that cells grow, repair damage, and replace old cells. Meiosis allows genetic diversity, which is essential for evolution and survival. Summary Chromosomes carry genetic information in the form of DNA. Genes are sections of DNA that code for proteins. Mitosis produces two identical daughter cells for growth and repair. Meiosis creates four non-identical sex cells for reproduction. Mitosis ensures genetic stability, while meiosis introduces genetic diversity

EXTERNAL AND INTERNAL STRUCTURE OF THE BRAIN STEM DR A. A. NWAKANMA THE BRAINSTEM •The brainstem is made up of the medulla oblongata, pons and midbrain •It is stalklike in shape and connects the narrow spinal cord with the expanded forebrain •Occupies the posterior cranial fossa of the skull Loading… FUNCTIONS OF BRAINSTEM •It serves as a conduit for the ascending and descending tracts connecting the spinal cord to the different parts of the higher centers in the forebrain •It contains important reflex centers associated with the control of respiration and CVS. •It is also associated with the control of consciousness •It contains important nuclei of cranial nerves II through XII EXTERNAL FEATURES OF MEDULLA OBLONGATA • The medulla oblongata connects the pons superiorly with the SC inferiorly •The junction of the medulla and SC is at the origin of the anterior and posterior roots of the first cervical nerve which corresponds approximately to the level of the foramen magnum Loading… EXTERNAL FEATURES OF MEDULLA •The medulla oblongata is piriform in shape •It has a broad superior part – open part •And a lower closed part •The central canal of the SC continues upward into the lower half of the medulla •In the upper half of the medulla it expands as the cavity of the fourth ventricle EXTERNAL FEATURES OF MEDULLA •On the ant. Surface of the medulla is the anterior median fissure which is continous inferiorly with the ant. Median fissure of the SC •On each side of the median fissure is a swelling called the pyramid EXTERNAL FEATURES OF MEDULLA •The pyramids are composed of bundles of nerve fibers, corticospinal fibers which originate in large nerve cells in the precentral gyrus of the cerebral cortex •The pyramids tapers inferiorly and majority of the descending fibers cross over to the opposite side forming the decussation of the pyramids here •The ant. External arcuate fibers are a few nerve fibers that emerge from the ant. Median fissure above the decussation and pass laterally over the medulla oblongata to enter the cerebellum EXTERNAL FEATURES OF MEDULLA •Posterolateral to the pyramids are the OLIVES which are oval elevations produced by the underlying inf. Olivary nuclei •In the groove b/w the pyramid and olive emerges the rootlets of the hypoglossal nerve •Post. To the olives are the inf. Cerebellar peduncles which connect the medulla to the cerebellum EXTERNAL FEATURES OF MEDULLA •In the groove b/w the olive and the inf. Cerebellar peduncle emerges the roots of the glossopharyngeal and vagus nerves and the cranial roots of accessory nerve •The post. Surface of the sup. Half of the medulla forms the lower part of the floor of the 4th ventricle External features of medulla •The post surface of the inf. Half continues with the post. Aspect of the SC and possesses a post. Median sulcus •On each side of the median sulcus is an elongated swelling , the Gracile tubercle produced by the underlying gracile nu. •Lat. To the gracile tubercle is the cuneate tubercle produced by the underlying cuneate nu. Loading… INTERNAL STRUCTURE OF MEDULLA •The internal structure of the medulla oblongata is usually considered at 3 levels •Level of pyramidal decussation •Level of olive •Level of sensory or lemniscal decussation T/S OF MEDULLA AT THE LEVEL OF OLIVE •This level corresponds to the floor of the 4th ventricle and the cranial n. Nuclei seen include •Hypoglossal n. • Vestibular nuclei •Dorsal nu. Of vagus •Solitary tract and its nu. •Nu. Ambigus • dorsal and ventral cochlear nu. T/S OF MEDULLA AT THE LEVEL OF OLIVE •The other masses of gray matter seen at this level include •The medial and dorsal accessory olivary nu. •Lat. Reticular nu. •Arcuate nu. •The descending tracts seen include •Pyramid •Rubrospinal tract •Spinal nu. And •Tract of trigeminal n. T/S OF MEDULLA AT THE LEVEL OF OLIVE •The ascending tracts include •Medial lemniscus lying in the middle and is L shaped •Spinothalamic T •Spinocerbellar T. •Spinotectal T. •The reticular formation and the inf. Olivary nu. Are also prominent features found at this level T/S OF THE MEDULLA AT THE LEVEL OF LEMNISCAL DECUSSATION •The level represented by this section lies a little above the level of the pyramidal decussation •The structures found at this level include •Central canal surrounded by gray matter •Medial lemniscus •The pyramids the nu. And fasciculus cuneatus •Spinal nu. Of trigeminal n. •The reticular formation T/S OF THE MEDULLA AT THE LEVEL OF LEMNISCAL DECUSSATION •Internal arcuate fibers which arise from the nu. Gracilis and cuneatus and arch forward on the medial side of the gray matter crossing in the midline to form the lemniscal or sensory decussation •Accessory cuneate nu. Lying dorsolateral to the cuneate nu. T/S OF THE MEDULLA AT THE LEVEL OF LEMNISCAL DECUSSATION •The cranial nerve nuclei seen at this level include •Hypoglossal nu. •Dorsal motor nu. Of vagus •Arcuate nu. •Nu. Of solitary tract •Nu. Ambigus •Other structures include •Lower part of inf. Olivary nu. •Lat. Reticular nu. •Arcuate nu. •Lat. & ventral spinothalamic tr. •Doral and ventral spinocerebella tr. •Spino-olivary tr. •Pyramids •Vestibulospinal tr. •Corticospinal tr. •Medial longitudinal fasciculus Connections of the Inferior Olivary Complex • The main afferents of the inferior olivary nucleus are from the cerebral cortex and from the spinal cord • The main efferents are to the cerebellar cortex. • An olivospinal tract is traditionally described, but some authorities hold that the inferior olivary nuclei do not send any fibres to the spinal cord. •The nucleus may be regarded as a relay station on the cortico-olivo-cerebellar and spino-olivo-cerebellar pathways. • The accessory olivary nuclei are connected to the cerebellum by parolivo-cerebellar fibres. THE PONS •The pons is the middle part of the brainstem •Its continuous below with the medulla oblongata and above with the midbrain •It is seperated from the cerbellum by the 4th ventricle •Pons has two surfaces: •Ventral and dorsal External Features Of Ventral Surface Of Pons •The ventral surface of pons shows the following features •The ventral surface is convex and has a shallow groove in the midline called the basilar groove which lodges basillar artery •Transvesely running fibers connecting the pons to the cerebellum thru the middle cerebellar peduncle •The two roots of trigeminal nerve (sensory and motor) emerge at the jxn b/w the ventral surface of pons and middle cerebellar peduncle EXTERNAL FEATURES OF DORSAL PONS •The dorsal surface of pons shows the following features •Median sulcus in the median plane •Medial eminence – shows rounded elevation in the lower part called facial colliculus which overlies the nu. Of abducent n. •Sulcus limitans – is lat. To the medial eminence and seperates medial eminence from vestibular area T/S THROUGH CAUDAL PART OF PONS •The features seen at this level include •Medial lemniscus in the most ant. Part of the tegmentum •The facial nu. Lies post to the lat. Part of the medial lemniscus •The fibers of the facial nerve wind around the nu. Of the abducent nerve producing the facial colliculus T/S THROUGH CAUDAL PART OF PONS •The medial longitudinal fasciculus is situated beneath the floor of the 4th ventricle on either side of the midline •The medial longitudinal fasciculus is the main pathway that connects the vestibular and cochlear nuclei with the nuclei controlling the extraocular muscles (oculomotor, trochlear and abducent) •The medial vestibular nu. Is situated lat. To the abducent nu. And in close relationship to the inf. Cerebellar peduncle T/S THROUGH CAUDAL PART OF PONS •The sup. Part of the lat. And inf. Part of sup. Vestibular nu. Are found at this level •Post. And ant. Cochlear nu. Are also found at this level •The spinal nu.of trigeminal nerve and tract lie on the anteromedial aspect of the inf. Cerebellar peduncle T/S THROUGH CAUDAL PART OF PONS •The trapezoid body is made up of fibers derived from the cochlear nuclei and the nuclei of trapezoid body •They run transversely in the ant. Part of the tegmentum •The basilar part of the pons at this level contain masses of nervr cells called pontine nuclei T/S THROUGH CAUDAL PART OF PONS •The axons of these cells give origin to the transverse fibers of the pons which cross the midline and intersect the corticospinal and corticonuclear tracts breaking them up into small bundles Loading… INTERNAL STRUCTURE OF CRANIAL PART OF PONS •The internal structure of the cranial part of pons is similar to that seen at the caudal level but contains the motor and principal sensory nuclei of the trigeminal nerve •The motor nu. Of the trigeminal nerve is situated beneath the lat. Part of the 4th ventricle within the reticular formation INTERNAL STRUCTURE OF CRANIAL PART OF PONS •The principal sensory nu. Of the trigeminal nerve is situated lateral to the motor nu. •The sup. Cerebellar peduncle is situated posterolat. To the motor nu. Of trigeminal nerve EXTERNAL FEATURES OF MIDBRAIN •Midbrain measures about 2cm in length and connects the pons and cerebellum with the forebrain •The midbrain is traversed by a narrow channel – the cerebral aqueduct ( which is filled with CSF) •On the posterior surface are four rounded eminences that are divided into superior and inferior pairs •The sup. Colliculi are centers for visual reflexes while the inf. Are lower auditory centers •In the midline below the inf. Colliculi emerges the trochlear nerves EXTERNAL FEATURES OF MIDBRAIN •Each colliculi is related to a ridge called brachium •The sup. Brachium passes from the sup. Colliculus to the lat. Geniculate body and the optic tract •The inf. brachium connects the inf colliculus to the medial geniculate body EXTERNAL FEATURES OF MIDBRAIN •On the anterior aspect of the midbrain is a deep depression in the midline called the interpeduncular fossa which is bounded on either side by the crus cerebri •Many blood vessels perforate the floor of the interpeduncular fossa and this region is termed the post. Perforated substance INTERNAL STRUCTURE OF MIDBRAIN •The midbrain is divided into two parts – •An upper tectum and •A lower part called cerebral peduncles •The upper part (tectum) contains mainly the colliculi of the two sides and represents the dorsal part of the midbrain •The cerebral peduncles are subdivided by the substantia nigra into •The tegmentum and •Crus cerebri STRUCTURE OF MIDBRAIN AT OF INF. COLLICULUS •The structures seen at this level include •Crus cerebri- this contain descending fibers from different parts of the cerebral cortex •The medial 1/6 contain frontopontine fibers •The intemediate 2/3 contain corticospinal and corticonuclear fibers •The lat. 1/6 contain temporopontine fibers •Other structures include •Substantia nigra •Cerebral aqueduct : this is surrounded by the central gray matter. •Ventral to this aqueduct is the oculomotor and trochlear nerves STRUCTURE OF MIDBRAIN AT OF INF. COLLICULUS •Reticular formation b/w the substantia nigra and gray matter •Inferior colliculus •Mesocephalic nu. Of trigeminal nerve •Compact bundle of fibers lies in the tegmentum dorsomedial to the substantia nigra •This bundle consistsof the medial lemniscus, trigeminal lemniscus and spinal lemniscus •Medial longitudinal fasciculus •Superior cerebellar peduncle •Rubrospinal tract Structure of midbrain at the level of sup. colliculus •The following structures are seen at this level •Sup. Colliculus in the tectum •Red nu. In the tegmentum dorsomedial to the substantia nigra •Oculomotor nuclei near the central gray matter •Bundles of ascending fibers consisting of medial lemniscus, spinal lemniscus and trigeminal lemniscus Structure of midbrain at the level of sup. colliculus •Dorsal tegmental decussation : this consists of fibers originating in the sup. Colliculus, it crosses to the opp. Side and descend as the tectospinal tract •Ventral tegmental decussation : this originates in the red nu