Brain & Cranial Nerves
The nervous system consists of the Central Nervous System (CNS) and Peripheral Nervous System (PNS).
Afferent: Sensory, carries impulses to the CNS. Conveying toward the center. Carrying inward to a central organ (eg brain) or section, as nerves that conduct impulses from periphery of the body to the brain or spinal cord. They are sensory.
Efferent: motor carries impulses away from the CNS. Conducting or progressing away from CNS or specific site. Nerve impulse outwards the PNS.
Central Nervous System is made up of:
- Spinal Cord
It combines information from the entire body & coordinates activity across the whole organism. Uses 20% of our oxygen we breathe in. There is an estimated 100 billion neurons with each connected to even more. There are four main lobes: parietal, temporal, occipital, and frontal. Brain is protected by the skull. Spinal cord travels down the spine. Brain is housed within the meninges. The spinal cord carries info between the body and brain. It connects to the PNS (skin, muscles, and joints).
Temporal Lobe is important for processing sensory input and assigning it emotional meaning: long-term memories; language (some)
Occipital Lobe is for visual processing
Parietal Lobe integrates sensory information including touch, spatial awareness, & navigation; language processing (some)
Frontal Lobe contains most of the dopamine; sensitive neurons; involved in attention; reward, short-term memory, motivation, & planning
The brain is the central control module of the body. It is the most complex organ. Some sections are dedicated. Others functions involve working together. There are twelve nerves. Eight of them appear to be along the brain stem.
Neuroglia cells support the nervous tissue.
Peripheral Nervous System is made of:
- All the nerves and ganglia outside of the brain and spinal cord
They are the exterior system of the brain. The PNS consists of 31 pairs of nerves. Outside of the brain and spinal cord there are two parts: the somatic, autonomic and enteric. The somatic nervous system is made up of nerves that connect to voluntary skeletal muscles & to sensory receptors. It is composed of afferent nerves that carry info to the CNS (spinal cord) & efferent fibers that carry neural impulses away from the CNS. The sensor neurons convey info from receptors in body to brain. The SNS motor neurons conduct voluntary impulses from brain to skeletal muscles.
Autonomic nervous system consists of sympathetic and parasympathetic division. Sympathetic mobilizes the body to respond to emergencies. Parasympathetic generally helps to conserve body energy & normal operations. Eg. digestion and blood pressure. The ANS sensory neurons convey info from receptors in organs to brain. The motor ANS conduct impulses from brain to smooth muscle cardiac muscle & glands (involuntary).
The nervous system which works with the GI tract is called Enteric Nervous System (ENS). Many books still have this system as part of the autonomic parasympathetic nervous system. But, many are going away from that thought. The ENS has both sensory and motor neurons in the GI tract (involuntary).
The meninges makes us the protective structures of the spinal cord and brain. It is composed of three parts (dura mater, arachnoid, and pia mater). The dura mater is the thickest and the outer most part. The middle layer is the arachnoid which is a thin avascular layer. It allows space for the spinal fluid to flow between the two membranes. It is a web like structure. The innermost layer is the pia mater which is attached to the brain’s nervous tissue and is molded close to the brain’s tissues. This thin delicate transparent structure has the most blood vessels of all of the meninges. Nutrients and oxygen are supplied by these blood vessels. It has the denticulate ligaments which extend laterally to secure and suspend the spinal cord.
Within the meninges the subarachnoid and epidural space is found. The subarachnoid space, which contains the Central Spinal Fluid (CSF), is between the arachnoid mater and pia mater. The epidural space is above the dura mater & bone. It consists adipose tissue between vertebrae and meninges.
Cerebrum is for intelligence, communication, learning, memory and thinking. It is the largest part of the brain and is divided into two hemispheres or halves. The word “cerebrum” is Latin for brain. The Romans used the same word to refer to the “skull” (which houses the brain) and the “head” which houses the “head” which houses the skull. And in Rome “cerebrum” meant understanding and fiery temper.
Cerebellum is equilibrium and muscular coordination. It is not only involved in precise motor control, but, also, language and attention. The corpus callosum (white myelinated axon) bridges the two hemispheres. It is part of the mind that allows communication between the two hemispheres of the brain. It is responsible for transmitting neural messages between both the right and left hemispheres.
The cerebellum is made up of the vermis (which connects both hemispheres), arbor vitae (“tree of life” which is the white matter), and folia (which are slender folds that add more surface area).
Diencephalon contains the thalamus, hypothalamus, epithalamus, and pituitary gland. The thalamus is the main rely station (think Grand Central station) to the cerebral cortex. It contains the intermediate mass. The hypothalamus helps to maintain homeostasis, and body functions. It controls the pituitary glands, hormonal functions. In addition, it helps regulate emotions, temperature, eating, and drinking, smell & taste reflexes, and mammillary bodies. It contains the infundibulum (which is the little “canal” which connects to pituitary gland). Pineal gland secretes melatonin that controls sleep/wake cycles.
The limbic system is for emotions. It consists of the amygdale, hippocampus, thalamus, hypothalamus, basal ganglia & cingulated gyrus. It combines higher mental functions and more primitive into a single system (called the emotional nervous system). It is the reason we enjoy eating and why we experience high blood pressure due to mental stress.
The brain stem has three parts: midbrain, pons and medulla oblongata. Each of these are composed of various parts which have specific functions.
- Cerebral pedunclesa is axons which transfer info
- Corpora quadrigemini 4 count
- Superior colliculi is located posterior of the midbrain. Receives visual signals from the retina of the eyes; helps with orientation of eyes & head; visual reflexes
- Inferior colliculi is located posterior of the midbrain. The lower layer processes multiple signals from various other parts of the brain. Main purpose is signal integration, frequency recognition, and patch discrimination; auditory reflexes
- Neural pathways or tracts; Respiratory centers that assist with the medulla oblongata; relays info to diencephalon
- cardiac, respiratory, vomiting and vasomotor (blood vessel rates) centers; is a very vital area; extends below the skull. It is involved in involuntary functions such as vomiting, breathing, sneezing, & maintaining the correct blood pressure.
The central sulcus separates the frontal lobe from the parietal lobe. Directly in from of the central sulcus is the precentral gyrus, and directly behind is the postcentral gyrus. The lateral sulcus runs between the temporal lobe and the parietal/frontal lobe. The transverse fissure separates the cerebellum from the cerebrum.
The functional areas of the cerebral cortex are the central sulcus, motor & sensory areas as well as the Wernicke’s area. In the motor areas, there is the primary motor area (precentral gyrus), and Broca’s speech area (on left side of brain). Broca’s speech area is putting thoughts into speech. The sensory areas consist of primary sensory area (postcentral gyrus), primary auditory and visual areas. The Wernicke’s area interprets speech into thought.
Always motor is always in the front.
The cranial meninges is made up of dura mater, arachnoid mater and pia mater. The dura mater consists of Falix cerebri (extends into the longitudinal fissure between cerebral hemisphere), and Falx cerebelli (extends between cerebellar hemispheres), and Tenetorium cerebelli (extends into the transverse fissure). The arachnoid mater lies between the dura mater and pia mater. The pia mater hugs the brain tightly.
There are four ventricles, (two lateral, third ventricle and below that the fourth ventricle which proceeds to the subanrachnoid space, then onto arachnoid villi of dural venous sinuses to the heart & lungs which pushes it out to through the arterial blood to the fourth ventricle and over again. The septum pellucidum is a thin membrane that separates the lateral ventricles.
Spinal Cord and Spinal Nerves
There are thirty-one spinal nerves. It consists of the cervical & lumbar enlargement, conus medullaris, cauda equine, and filum terminale. The cervical enlargement is runs from C4-T1 and goes to the upper extremities via the brachial plexuses. The lumbar enlargement (also called lumbosacral enlargement) is located from T9-T12. It forms the sacral and lumbar plexuses which goes to the lower extremities. The conus medullaris which is of the end of the spinal cord forms a cone shape. It is followed by a bundle of nerves called cauda equine before ending at the filum terminale.
The phrenic nerve innovates the spinal cord and aids the diaphragm. It is located within the cervical plexus of the spine. It is located between C3-C5. Remember the saying–“Cervical nerves 3, 4, and 5 keep the diaphragm alive.” Brachial plexus contains five main nerves which axillary nerve (shoulder region), musculocutaneous nerve (anterior of the upper arm), median nerve (most anterior of forearm), ulner nerve (most hand muscles), and radial nerve (all of the posterior muscles of the arm and forearm). The brachial plexus is located between C5-T1.
The thoracic (or intercostal) nerves do not have any plexuses. But, the lumbar plexus has two nerves which it innovates. There are the femoral nerve which goes to the quadriceps and the obturator nerve which goes to the adductor muscles (medial thigh). The sacral plexus contains the largest nerve in the body called sciatic nerve which goes to the hamstrings (posterior thigh) and pudendal nerve which goes to the perineum muscles of the genital area.
The spinal cord is composed of the dorsal & ventral root as well as the spinal cord. The dorsal root consists of the somatic & autonomic sensory axons which enter the spinal cord via this root. The bump on the side of the root is called the dorsal root ganglion. It is composed of cell bodies of sensory neurons. The ventral root as well has a somatic and autonomic axons, but they are sensory. They exit the spinal cord via ventral root. The spinal nerve is where the ventral and dorsal root converge and exit the intervertebral foramen. It is called mixed because it contains both the sensory and motor fibers.
The dorsal root ramus innervates the skin and deep muscles of the back and trunck. The anterior root ramus innervates the muscles and skin of our arms and legs as well as the anterior and lateral body parts. The meningeal rami works with the vertebraes & their ligaments as well as the meninges and spinal cord’s blood vessels.
The spinal cord has the posterior median sulcus and the anterior median fissure as well as the central canal and gray & white commissure. The fissure is a wide groove while the sulcus is narrow. The central canal extends the length of the spinal cord. The gray and white commissure joins the left and right sides.
The white matter columns (or funiculi) contains the ascending sensory tract and the descending motor tract which consists of CNS axon bundles. There is a anterior, lateral, and dorsal side to the columns.
The gray matter has the ventral, dorsal, and lateral horns. The somatic motor neurons cell bodies is located in the ventral horn. The dorsal horn contains the interneuron cell bodies. In the lateral horn of ANS motor neurons cell bodies exist except in the cervical region.
There are three protective connective tissues which cover each spinal cord:
- Epineurium which surrounds the whole nerve
- Perineurium which surrounds the fascicle (which is a smaller nerve bundle)
Endoneurium which cover the axon (myelinated and unmyelinated)
We used the below for our final.
Here is a video from Texas Women’s University UT Southwestern Medical Center that help us study. There is one additional song created by Joseph Reger —Cranial Nerve Song.
NOTE: THE NERVES ARE USUALLY WRITTEN IN ROMAN NUMERALS
CN#1 Olfactory nerve is for smell.
CN#2 Optic nerve is for sight (rods & cones)-vision
CN#3 Oculomotor nerve moves the eyelids & eyeballs
CN#4 Trochlear nerve moves eyeballs
CN#5 Trigeminal nerve for facial muscles (example chewing)
CN#6 Abducens nerve moves the eyeballs
CN#7 Facial nerve for taste, tears, saliva & facial expression
CN#8 Vestibulocochlear or Acoustic nerve is for auditory (vestibular nerve-equilibrium; cochlear nerve for hearing)
CN#9 Glossopharyngeal nerve is motor sensory nerve-swallowing, saliva, taste, viscera
CN#10Vagus nerve controls the PNS-Motor control of the heart and viscera, sensation from the thorax, pharynx, and abdominal viscera
CN#11Accessory nerve moves the head & shoulders
CN#12Hypoglossal nerve works the tongue muscles (speech & swallowing), some skeletal muscles, some viscera, sensation form skin and viscera
There are eight pairs of cervical spinal nerves, twelve pairs of thoracic, five pairs of lumbar, five pairs of sacral, and one pair of coccyx spinal nerves.
Music video on the digestive system by biological music video
The digestive system goes from the mouth to the anus. The mouth is used for mastication which is the process of chewing.. It breaks down food. It is made up of multi-layer stratified squamous. There are three sets of salivary glands which secrete saliva which contain bicarbonate. It maintains a pH between 6.5 – 7.5. Through peristalsis the bolus (a ball of masticated food) passes between the mouth to the stomach. Peristalsis is the movement of food through the alimentary tract by means of contractions. Food generally stays in the alimentary tract for three days.
Parotid gland is located in the front and below the ear. It secretes a clear, watery amylase. Amylase breaks down carbohydrates. The Stensen’s duct is attached to it. The second gland is called Submandibular and is located on the inside surface of the mandible. It secretes a serous, and some mucous with the Whaton’s duct attached to it.
The cells within the alimentary canal changes every three days. Of which the majority these cells are simple columnar epithelium. There are four layers of alimentary tract.
Four Layers of Alimentary Tract
- Mucosa is the inner most layer of the alimentary tract. It is made up primarily of Epithelium and Mucus Cell. The lumen is the tube in the center of the alimentary tract.
- Submucosa is the 2nd layer. It contains blood vessels, nerves and the lacteals. Lacteals are the lymph vessel.
- There are two layers of muscle which comes next.
- The inner most layer called circular fibers
- Longitudinal Fibers
- Serosa is the outer most layer
- Visceral Peritoneum which covers the organs
- Parietal Peritoneum which lines the peritoneal cavity
The tongue manipulates the food by aiding in the chewing and swallowing. The tongue is anchored by the lingual frenulum. It has papillae (vallate, fungiform, and filiform) located on the surface. Vallate are located near the back of the tongue in a V-shape form and have taste buds on them. Fungiform can distinguish a change in temperature and has the sour taste buds located on it. Filiform gives the tongue its rough texture and helps in gripping the food. It does not have taste buds.
The uvula is the u-shaped structure which hangs in the back of the mouth. According to Mercola, it has five purposes.
- It prevents excessive nasal sound.
- Keeps throat lubricated
- Helps prevent food from going up into the nose and aid in mucous drainage
- Gag Reflex
- Aid in the immune responses
There are three sets of tonsils (palatine, pharyngel and lingual). The Palatine swell when there is infection. Pharyngeal is the same as the adenoids. Linguals is located in the bottom portion of the mouth (upper potion of the throat). It has been discovered that the tonsils help prevent infection from getting into the rest of the body. Some authorities question whether the tonsils should be removed.
The pharynx is comprised of three parts: nasopharynx, oropharynx, and laryngopharynx. It is runs from the base of the skull to the inferior cricoid cartilage where it connects to the esophagus. Its primary purpose is for deglutition (swallowing) and respiration.
The esophagus is approximately 9 inches (25 cm) long and is lined with stratified squamous and mucous cells. It connects the pharynx to the stomach. It is located behind the trachea.
The stomach is made of three muscle layers, oblique, circular and longitudinal. The oblique is the innermost layer. The stomach is lined with columnar epithelium cells. Within the stomach, there are ruga(e) which are made up of columnar epithelial cells. Basically, rugae is folds with in the stomach which aid in digestion. Water, glucose, salts, alcohol, and drugs is absorbed by the stomach (gastric absorption).
The stomach contains three different gastric glands which start at the beginning of the stomach and end at the stomach’s lumen. They secretes gastric juice and mucus. Each gland has a specific purpose. The cardiac gland, located at the top, and the pyloric gland, located at the bottom, both secrete mucus. The intermediate gastric glands does most of the secreting. It is composed of three types of cells, chief, parietal, mucus neck cells. The intermediate gastric glands secretes HCl or hydrochloric acid. It is needed to activate some enzymes. Dr. Iram Tassaduq has a nice computerized slide show on the stomach.
The various secretions of the gastric glands are:
- Pepsinogen–secreted by chief cells and forms pepsin
- Pepsin is formed when HCl reacts with pepsinogen. It aids in digestion
- HCl–secreted by the parietal cells. It reacts with pepsinogen.
- Mucus–secreted by both the goblet cells and mucus glands. Mucus is used to protect the lining. It is alkaline.
- Intrinsic Factor–secreted by the parietal cells and aids in the absorption of vitamin B12 which is needed for blood production Pernicious anemia is caused by the lack of B12.
Gastrin is a polypeptide hormone which is secreted by the pylorus in the stomach. It increases gastric activity and pepsin production. Frequently when there is an over productivity of gastrin a peptic ulcer will form.
The parasympathetic and sympathetic nervous system both are involved in gastric activity. The parasympathetic increases it while the sympathetic decreases it. It is believed that sadness, fear, and withdrawal increases gastric juices.
The proteolytic enzyme breaks down proteins into smaller peptides. It goes by numerous other names such as protease, proteinase, and peptidase. Proteins are somewhat broken down as they are leaving stomach to the small intestines. Upon leaving they are broken down even more by the proteolytic enzyme which is secreted by the pancreas.
The enterogastric reflex (stomach & small intestines) starts in the intestines and goes to the stomach. It slows down peristalsis when impulses from the intestine to the Central Nervous System (CNS), then to stomach via the Vagus Nerve (Cranial Nerve #10).
Cholecystokinin is secreted by the small intestine in response to Chyme (paste-like substance which is passed from the stomach to the small intestines) with a high fat content. Cholecystokinin causes the stomach to slow down the Peristaltic Activity.
There are two sphincters, lower esophageal and pylorus. They are found in their respective areas. Please refer to the above picture. They pylorus sphincter is a valve which closes off the stomach from the duodenum. The lower esophageal sphincter closes off the esophagus from the stomach.
The small intestine measure in a cadaver to eighteen to twenty feet long. It is divided into three sections (duodenum, jejunum, and ileum). The duodenum is the only fixed portion. It measures 2″ x 12″. The jejunum has a thicker wall and has a greater diameter than the ileum. The longest part of the small intestines is the ileum.
Mesentery is a fold of membrane which holds the stomach to the intestine so that it stays in place. It contains a network of blood vessels, nerves, and lymphatic vessels. Scientists are trying to decide if it should be consider an organ. The greater omentum is a layer of fat which purpose is to prevent the peritoneal surface from being harmed, store fat, and decrease any infection spreading to the peritoneal cavity.
Within the intestines there are three ways to increase absorption of nutrients which are via microrvilli, villi, and plicae circulares. Plicae circulares is a circular fold within the intestinal lining. The villi are fingerlike folds which are found within the intestinal lining. In addition, microvilli are fine extensions of individual columnar cells (at free surface) which increase surface area.
The Intestinal glands (found in the mucous lining between adjacent villi) secrete a watery fluid to aid in absorption. The Brunner’s glands (in proximal part of duodenum) secrete a viscid, alkaline mucus.
Microvilli secretes sucrase (which breaks down sucrose), peptidase (which breaks down protein), lactase (which breaks down lactose), and lipase (which breaks down triglycerides “fat”).
Absorption in the small intestine takes place via facilitated diffusion, active transport or simple diffusion. Carbohydrates are absorbed via active transport or facilitated diffusion, proteins via active transport, and lipids via simple diffusion.
Lipids have two methods which are used to be absorb in the small intestines. Micelles which are created by bile salt are lipid sphere which are formed in an aqueous solution. They make it possible for lipase to do job. It helps to cleanse the system. Chylomicrons have lipoprotein coating which aids in the absorption into the blood. Typically there are vitamins and proteins present in chylomicrons.
The large intestine’s main function is to absorb water and electrolytes. The colon consists of the ascending, transverse, descending sigmoid.
The cecum is the blind pouch found at the junction of the large and small intestines. It is considered the first place in the large intestines. The appendix/vermiform is located on the lower right of the abdomen. The ileocecal valve is a sphincter muscle valve which located between the ileum and cecum. Approximately two liters of liquid enter the valve via the ileocecal valve.
The tenia coli is three muscle bands found in the wall of the colon. Haustra are pouches which are formed as the result of tenia coli. Information on this will be at the end.
Epiploic appendage are small pouches in the peritoneum which are filled with fat. Within the colon, there are numerous mucous cells. Bacteria can be found within the colon. It breaks down cellulose for energy (A carbohydrate and synthesize vitamin K, B12, Thiamine, and Riboflavin).
Colostomy is a surgical procedure in which the a hole is created to bring the large intestine out of the body so that the stoma can drain into a bag. Diarrhea (peristaltic rush) is the condition where one has three or more bowel movements per day. It usually lasts a few days and disappears as quickly as it comes. Dysentery is an infection in the intestine which causes the passage of bloody stools. It can be caused by a parasite or bacteria.
There are four types of symbiosis: Mutualism, Commensalism, Parasitism, and Amensalism. Commensalism is called mess mates. It is where one organism receives benefits from another without it affecting the other either way. Mutualism is when both benefit from their association. Parasitism is when the parasite harms the host. Amensalism is very rare. It occurs when where organism may not receive show any direct benefit from the relationship.
Taenia saginata is a beef tapeworm while Taenia solium is a pork tapeworm. In addition, Ascaris lumbricoides is roundworm. Diphyllobothrium latum is a fish eating mammal. Broad fish tapeworm can reach up to 60 feet long. It is a intestinal parasite which absorbs vitamin B12 from its host. Entamoeba histolvtic is an intestinal parasite which causes “Amoebic Dysentery”. Entamoeba gingivalis is commensal of gums. It lives in a person’s mouth and reproduces asexually. Giardia intestinalis is a parasite of the small intestines which causes “Giadiasis”.
Cirrhosis is caused by fatty liver and/or too much alcohol. Hepatitis A, B, C, D is of the liver. A and B predominately from dirty food or dishes. C and D can be found with semen.
The average blood volume of human beings is about 5 liters. Blood consists of cells, proteins, oxygen, and nutrients in addition to other components. Hematocrit is made up of plasma, erythrocyte, leukocytes, and thrombocytes.
Plasma makes up 55% of total blood volume. It makes up half of the bloods volume. It is ninety percent water with 10% being proteins, minerals, waste products, clotting factors, hormones, and immunoglobin. It is separated from the rest of blood through centrifuge. Erythrocyte (red blood cells) is stored in the spleen. It is a biconcave disk which doesn’t contain a nucleus and lives on about 120 days. It transport oxygen and carbon dioxide maintain normal acid base balance. The aged RBCs are devoured macrophages which are found in the liver and the spleen. Leukocytes account for about one percent of blood. They aid in protection from outside environs such as illness and disease. They are also called white blood cells. Another name for thrombocytes is platlets and aid in blood clotting. They are anucleated cell fragments. Buffy Coat is the white layer of white blood cells and platlets once blood has been centrifuged. They are in the middle between plasma and red blood cells.
Hemoglobin which is a protein molecule carries oxygen from the lungs to human tissue then eventually returns it to the lungs. It is made up of four protein molecules which in the adult human has two alpha-globulin chains and two beta-globulin chains. It helps to maintain the shape of red blood cells. It makes up one third of the RBCs. It is about 7.5 microns in diameter and 2.5 micron in thickness. It can not be reproduced and is anucleated.
What is the life cycle of an erythrocyte? Hematopoiesis is the process from the birth of the cell to the end. It goes on throughout a person life from conception to death. The stages are:
- hemocytoblast – is the stem cell which produces the red blood cell and can be found in the red blood marrow.
- erythroblast – an immature red blood cell which has a nucleus.
- reticulocyte – a young red blood cell which contain basophilic cytoplasmic network. It develops into the erythrocyte.
- Erythrocyte is the mature red blood cell.
Erythropoietin is a hormone which is produced by the kidneys (and liver to a lesser degree) in response to decreased oxygen. It stimulates the red bone marrow to produce red blood cells. Erythropoietin is also called epo.
Destruction of “Dead” Red blood cells
- Phagocytosis is done by the Kuffer cells which star shaped and found within the liver.
- Breakdown of Hemogloblin is the process by which hemoglobin degrades RBCs into smaller components.
- Ferritin is iron which is stored in the liver
- Bile pigments – biliverdin and bilirubin