Upon registering your anatomy model by simply scanning the label, you will also have access to a free three-day trial to the full Complete Anatomy platform. Once the trial period has ended, 3B Scientific customers can of course continue using the 3B Smart Anatomy Courses for free and have the option of installing the full app (again) at a 10%. Gross anatomy deals with things that can be seen with the naked eyes, whereas microscopic anatomy deals with the things that can only be viewed under a microscope. How is human anatomy relevant? Human anatomy helps us to understand the structure and relationship of all parts of the body.
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Anatomical names for body parts
Muscle and bone work together to create movement, Designua/Shutterstock.com
Anatomy (Lesson 3.1) study guide by sciencechick143 includes 11 questions covering vocabulary, terms and more. Quizlet flashcards, activities and games help you improve your grades. Gross anatomy deals with things that can be seen with the naked eyes, whereas microscopic anatomy deals with the things that can only be viewed under a microscope. How is human anatomy relevant? Human anatomy helps us to understand the structure and relationship of all parts of the body. 3D modeled by physicians and anatomy experts. Using the International Anatomical Terminology. +6000 anatomical structures. Add, Delete and Combine anatomical structures.
Anatomy names reveal place, shape and direction of use for that body part. In anatomy class you will see many pictures of bones and muscles with labels. You will handle models of body parts that mysteriously fit together like a puzzle. You will hear lectures about how the body parts function.
But, the real key to learning anatomy is to understand anatomical names in terms of the movement they control. Think of the body moving in three dimensions. Anatomic charts are static. The body parts and models in anatomy laboratory are fixed. Yet, human anatomic names describe their size, shape, placement and direction of movement.
Anatomical locations
Where does this body part fit? Directional terminology for anatomical location often gives students problems right from the beginning. Is the disassembled bone from the right side or left side of the skeleton? Am I viewing this arm from the front or the back?
Even whether an arm is a right or left one can be puzzling. Do not feel bad if you have trouble with the right and left designation. Even hospitals must go to great lengths to make sure a surgeon does not get mixed up between right and left appendages.
We all think of right and left in terms of our own right and left. Our brains have unconscious memory traces for automatic actions that are hard to overcome when we try to think of the movements of another person. It takes a conscious effort to reverse right and left for a person we are facing.
Human anatomical position
Mapping out anatomical direction of body parts can be very frustrating. If you become exasperated by sorting out the terms medial, lateral, caudal and distal, think of them in terms of a map. If you want to plan a route from New York City to San Francisco, first you must know which city is your starting point. You also need to have the concept of north, south, east and west under control to get where you want to go.
Anatomy is much the same way in that you need a fixed starting point—not an obvious thing with a body as lanky and flexible as that of a human. The starting point you must learn first is the human ‘anatomical position’. All body parts and connections are named relative to a standing person facing the observer with arms out from his/her side and palms of the hands facing the observer.
Human Anatomical Position, Alex Luengo/Shutterstock.com
Remember always that the ‘right’ and ‘left’ of a person in the anatomical position are opposite your own right and left. For your right and left side to match that of someone else, you must have your back to them.
In order to map the movement of a body away from the anatomical position, you need directional terms. Because road maps are flat representations of Earth’s static surface four directions suffice. To map body movement away from the anatomical position in three dimensions, more than 4 directional words are needed.
It is critical to your success in anatomy to study human body directional terms until they are second nature to you. Many students pass over this early part of the course because it seems boring. Yet, directional terms will appear repeatedly as you proceed with learning the names and locations of body parts. You need to work on the directional concepts used in anatomy until your brain becomes programmed to think of anatomy in that language.
Translating anatomical names
Anatomical names are descriptions. Anatomic names were decided long ago when scientists worked in the Latin language. But Latin can be translated into your own language with the help of Google. Once translated you will see that anatomical names make sense. Click here to find Google translations.
You will also notice that anatomical names appear in layers. For example, muscle names reflect the names of the bone they are connected to. The blood vessels and nerves run together in bundles and reflect the name of the muscle they course through. Even if your exams are not cumulative, if you make your learning cumulative as you proceed through your anatomy and physiology course you will find it much easier. And, your exam grades will be much higher.
Further Reading:
Do you want to know more about the role movement plays in naming anatomical parts? Please put your questions in the comment box or send me an email at [email protected]. I read and reply to all comments and email.
If you think this description of mapping out the location of human body parts is helpful, share it with your fellow students or send it to your favorite social media by clicking one of the buttons below.
Margaret Thompson Reece PhD, physiologist, former Senior Scientist and Laboratory Director at academic medical centers in California, New York and Massachusetts and CSO at Serometrix LLC is now CEO at Reece Biomedical Consulting LLC.
Dr. Reece is passionate about helping students, online and in person, pursue careers in life sciences. Her books “Physiology: Custom-Designed Chemistry”, “Inside the Closed World of the Brain”, the workbook companion to her online course “30-Day Challenge: Craft Your Plan for Learning Physiology”, and “Busy Student’s Anatomy & Physiology Study Journal” are written for those new to life science. More about her books is available at https://www.amazon.com/author/margaretreece.
Dr. Reece offers a free 30 minute “how-to-get-started” phone conference to students struggling with human anatomy and physiology. Schedule an appointment by email at [email protected].
Functions of the Brain Stem
The brainstem regulates vital cardiac and respiratory functions and acts as a vehicle for sensory information.
Learning Objectives
Describe the functions of the brainstem
Key Takeaways
Key Points
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- In vertebrate anatomy, the brainstem is the posterior part of the brain adjoining, and structurally continuous with, the spinal cord.
- Though small, the brainstem is an extremely important part of the brain, as the nerve connections from the motor and sensory systems of the cortex pass through it to communicate with the peripheral nervous system.
- The brainstem also plays an important role in the regulation of cardiac and respiratory function, consciousness, and the sleep cycle.
- The brainstem consists of the medulla oblongata, pons, and midbrain.
Key Terms
- pons: Contains nuclei that relay signals from the forebrain to the cerebellum, along with nuclei that deal primarily with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture.
- midbrain: Associated with vision, hearing, motor control, sleep and wake cycles, alertness, and temperature regulation.
- medulla: The lower half of the brainstem that contains the cardiac, respiratory, vomiting, and vasomotor centers and regulates autonomic, involuntary functions such as breathing, heart rate, and blood pressure.
Examples
Diseases of the brainstem can result in abnormalities in cranial nerve function, leading to visual and hearing disturbances, changes in sensation, muscle weakness, vertigo, coordination problems, swallowing and speech difficulty, and voice changes.
Location and Basic Physiology
In vertebrate anatomy, the brainstem is the most inferior portion of the brain, adjoining and structurally continuous with the brain and spinal cord. The brainstem gives rise to cranial nerves 3 through 12 and provides the main motor and sensory innervation to the face and neck via the cranial nerves. Though small, it is an extremely important part of the brain, as the nerve connections of the motor and sensory systems from the main part of the brain that communicate with the peripheral nervous system pass through the brainstem. This includes the corticospinal tract (motor), the posterior column-medial lemniscus pathway (fine touch, vibration sensation, and proprioception ) and the spinothalamic tract ( pain, temperature, itch, and crude touch). The brain stem also plays an important role in the regulation of cardiac and respiratory function. It regulates the central nervous system (CNS) and is pivotal in maintaining consciousness and regulating the sleep cycle.
Components of the Brainstem
The three components of the brainstem are the medulla oblongata, midbrain, and pons.
Brainstem Anatomy: Structures of the brainstem are depicted on these diagrams, including the midbrain, pons, medulla, basilar artery, and vertebral arteries.
The medulla oblongata (myelencephalon) is the lower half of the brainstem continuous with the spinal cord. Its upper part is continuous with the pons. The medulla contains the cardiac, respiratory, vomiting, and vasomotor centers regulating heart rate, breathing, and blood pressure.
The midbrain (mesencephalon) is associated with vision, hearing, motor control, sleep and wake cycles, alertness, and temperature regulation.
The pons (part of metencephalon) lies between the medulla oblongata and the midbrain. It contains tracts that carry signals from the cerebrum to the medulla and to the cerebellum. It also has tracts that carry sensory signals to the thalamus.
Brainstem Function
The brainstem has many basic functions, including regulation of heart rate, breathing, sleeping, and eating. It also plays a role in conduction. All information relayed from the body to the cerebrum and cerebellum and vice versa must traverse the brainstem. The ascending pathways from the body to the brain are the sensory pathways, including the spinothalamic tract for pain and temperature sensation and the dorsal column, fasciculus gracilis, and cuneatus for touch, proprioception, and pressure sensation. The facial sensations have similar pathways and also travel in the spinothalamic tract and the medial lemniscus.
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Descending tracts are upper motor neurons destined to synapse on lower motor neurons in the ventral horn and intermediate horn of the spinal cord. In addition, upper motor neurons originate in the brain stem’s vestibular, red, tectal, and reticular nuclei, which also descend and synapse in the spinal cord. The brainstem also has integrative functions, including cardiovascular system control, respiratory control, pain sensitivity control, alertness, awareness, and consciousness.
Human Brain with Cranial Nerves: Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of cranial nerves. Only the first and the second pair emerge from the cerebrum; the remaining ten pairs emerge from the brainstem.
Medulla Oblongata
Anytrans 6 4 for mac free download. The medulla oblongata controls autonomic functions and connects the higher levels of the brain to the spinal cord.
Learning Objectives
Describe the location and function of the medulla oblongata region of the brain stem
Key Takeaways
Key Points
- The medulla oblongata is the lower half of the brainstem. It controls autonomic functions and connects the higher levels of the brain to the spinal cord.
- The medulla oblongata is responsible for regulating several basic functions of the autonomic nervous system, including respiration, cardiac function, vasodilation, and reflexes like vomiting, coughing, sneezing, and swallowing.
Key Terms
- tuberculum cinereum: A raised area between the rootlets of the accessory nerve and posterolateral sulcus that overlies the spinal tract of trigeminal nerve.
- cerebellar peduncle: The structure that connects the medulla to the cerebellum.
- sympathetic system: The division of the autonomic nervous system responsible for stimulating the body’s fight-or-flight response.
- olivary body: Either of a pair of prominent oval structures in the medulla oblongata containing the olivary nuclei. These structures are involved in cerebellar motor learning and the perception of sound.
- parasympathetic system: The division of the autonomic nervous system responsible for the relaxation or inhibition of various body functions.
Examples
A stroke can injure the pyramidal tract, medial lemniscus, and the hypoglossal nucleus. This causes a syndrome called medial medullary syndrome, a type of alternating hemiplegia characterized by recurrent episodes of paralysis on one side of the body.
The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla. The medulla contains the cardiac, respiratory, vomiting, and vasomotor centers and regulates autonomic, involuntary functions such as breathing, heart rate, and blood pressure.
The Brain Stem with Pituitary and Pineal Glands: Medulla oblongata labeled at bottom left, in relation to the pons, pituitary gland, spinal cord, pineal gland and cerebellum.
The medulla is often divided into two parts:
- An open or superior part where the dorsal surface of the medulla is formed by the fourth ventricle.
- A closed or inferior part where the metacoel (caudal part of fourth ventricle) lies within the medulla oblongata.
Structure of the Medulla Oblongata
The region between the anterior median and anterolateral sulci is occupied by an elevation on either side known as the pyramid of medulla oblongata. This elevation is caused by the corticospinal tract. In the lower part of the medulla, some of these fibers cross each other, thus obliterating the anterior median fissure. This is known as the decussation of the pyramids. Other fibers that originate from the anterior median fissure above the decussation of the pyramids and run laterally across the surface of the pons are known as the external arcuate fibers.
The region between the anterolateral and posterolateral sulcus in the upper part of the medulla is marked by a swelling known as the olivary body, caused by a large mass of gray matter known as the inferior olivary nucleus.
The posterior part of the medulla between the posterior median and posterolateral sulci contains tracts that enter it from the posterior funiculus of the spinal cord. These are the fasciculus gracilis, lying medially next to the midline, and the fasciculus cuneatus, lying laterally.
The fasciculi end in rounded elevations known as the gracile and cuneate tubercles. They are caused by masses of gray matter known as the nucleus gracilis and the nucleus cuneatus. Just above the tubercles, the posterior aspect of the medulla is occupied by a triangular fossa, which forms the lower part of the floor of the fourth ventricle. The fossa is bounded on either side by the inferior cerebellar peduncle, which connects the medulla to the cerebellum.
The lower part of the medulla, immediately lateral to the fasciculus cuneatus, is marked by another longitudinal elevation known as the tuberculum cinereum. It is caused by an underlying collection of gray matter known as the spinal nucleus of the trigeminal nerve. The gray matter of this nucleus is covered by a layer of nerve fibers that form the spinal tract of the trigeminal nerve.
The base of the medulla is defined by the commissural fibers, crossing over from the ipsilateral side in the spinal cord to the contralateral side in the brain stem; below this is the spinal cord.
Embryonic Development
During development, the medulla oblongata forms from the myelencephalon. The final neuroblasts from the alar plate of the neural tube produce the sensory nuclei of the medulla. The basal plate neuroblasts give rise to the motor nuclei.
Function of the Medulla Oblongata
The medulla oblongata controls autonomic functions and connects the higher levels of the brain to the spinal cord. It is also responsible for regulating several basic functions of the autonomic nervous system, including:
- Respiration: chemoreceptors
- Cardiac center: sympathetic system, parasympathetic system
- Vasomotor center: baroreceptors
- Reflex centers of vomiting, coughing, sneezing, and swallowing
Pons
The pons is a relay station between the forebrain and cerebellum that passes sensory information from the periphery to the thalamus.
Learning Objectives
Describe the role and location of the pons region of the brainstem
Key Takeaways
Key Points
- The pons is a structure located on the brainstem, named after the Latin word for “bridge.”
- This white matter includes tracts that conduct signals from the cerebrum down to the cerebellum and medulla, as well as tracts that carry the sensory signals up into the thalamus.
- The pons contains nuclei that relay signals from the forebrain to the cerebellum, along with nuclei that deal primarily with sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture.
- Within the pons is the pneumotaxic center, a nucleus that regulates the change from inspiration to expiration.
- The pons also contains the sleep paralysis center of the brain and plays a role in generating dreams.
- The functions of these four nerves include sensory roles in hearing, equilibrium, taste, and in facial sensations such as touch and pain. They also have motor roles in eye movement, facial expressions, chewing, swallowing, urination, and the secretion of saliva and tears.
Key Terms
- pons: Contains nuclei that relay signals from the forebrain to the cerebellum, along with nuclei that regulate sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture.
- pneumotaxic center: A network of neurons in the rostral dorsal lateral pons that regulates the respiratory rate; also known as the pontine respiratory group (PRG).
- Basal plate: The region of the neural tube ventral to the sulcus limitans and containing primarily motor neurons.
- alar plate: Also called the alar lamina, it is a neural structure in the embryonic nervous system; the caudal part later becomes the sensory axon aspect of the spinal cord.
Pons/Brainstem: Structure of the brainstem showing the location of the pons in relation to the midbrain and medulla.
The pons is a structure located on the brainstem, named after the Latin word for “bridge.” It is above the medulla, below the midbrain, and anterior to the cerebellum. The white matter of the pons includes tracts that conduct signals from the cerebrum down to the cerebellum and medulla, and tracts that carry the sensory signals up into the thalamus.
Structure
The pons measures about 2.5 cm in length in adults. Most of it appears as a broad anterior bulge rostral to the medulla. Posteriorly, it consists mainly of two pairs of thick stalks called cerebellar peduncles. These connect the cerebellum to the pons and midbrain.
The pons contains nuclei that relay signals from the forebrain to the cerebellum, along with nuclei that regulate sleep, respiration, swallowing, bladder control, hearing, equilibrium, taste, eye movement, facial expressions, facial sensation, and posture. Within the pons is the pneumotaxic center, a nucleus that regulates the change from inspiration to expiration. The pons also contains the sleep paralysis center of the brain and also plays a role in generating dreams. Due 1 2 3.
Development
During embryonic development, the metencephalon develops from the rhombencephalon and gives rise to two structures: the pons and the cerebellum. The alar plate produces sensory neuroblasts, which will give rise to the solitary nucleus and its special visceral afferent column, the cochlear and vestibular nuclei (which form the special somatic afferent fibers of the vestibulocochlear nerve), the spinal and principal trigeminal nerve nuclei (which form the general somatic afferent column of the trigeminal nerve), and the pontine nuclei, which is involved in motor activity. Basal plate neuroblasts give rise to the abducens nucleus (forms the general somatic efferent fibers), the facial and motor trigeminal nuclei (form the special visceral efferent column), and the superior salivatory nucleus, which forms the general visceral efferent fibers of the facial nerve.
Cranial Nerves of the Pons
A number of cranial nerve nuclei are present in the pons:
- The chief or pontine nucleus of the trigeminal nerve sensory nucleus (V)- mid-pons
- The motor nucleus for the trigeminal nerve (V)-mid-pons
- Abducens nucleus (VI)-lower pons
- Facial nerve nucleus (VII)-lower pons
- Vestibulocochlear nuclei (VIII)-lower pons
Functional Characteristics
The functions of the four nerves of the pons include sensory roles in hearing, equilibrium, taste, and facial sensations such as touch and pain. They also have motor roles in eye movement, facial expressions, chewing, swallowing, urination, and the secretion of saliva and tears. Central pontine myelinosis is a demyelination disease that causes difficulty with sense of balance, walking, sense of touch, swallowing, and speaking. If it is not diagnosed and treated, it can lead to death or locked-in syndrome (a condition in which a person is conscious but cannot move or communicate).
Midbrain
The midbrain plays a major role in both wakefulness and regulation of homeostasis.
Learning Objectives
Describe the location and functions of the midbrain
Key Takeaways
Key Points
- The midbrain or mesencephalon is a portion of the central nervous system (CNS) associated with vision, hearing, motor control, sleep and wake cycles, arousal (alertness), and temperature regulation.
- Anatomically, the midbrain comprises the tectum (or corpora quadrigemina), tegmentum, ventricular mesocoelia (or “iter”), and cerebral peduncles, as well as several nuclei and fasciculi.
- During embryonic development, the midbrain arises from the second vesicle, (mesencephalon) of the neural tube.
- The mesencephalon is considered part of the brainstem.
Key Terms
- mesencephalon: A part of the brain located rostral to the pons and caudal to the thalamus and the basal ganglia, composed of the tectum (dorsal portion) and the tegmentum (ventral portion).
- substantia nigra: Brain structure located in the midbrain that plays an important role in reward and movement.
- tectum: The dorsal part of the midbrain, responsible for auditory and visual reflexes.
- tegmentum: The ventral portion of the midbrain, a multisynaptic network of neurons involved in many unconscious homeostatic and reflexive pathways.
The midbrain or mesencephalon (from the Greek mesos, middle, and enkephalos, brain ) is a portion of the central nervous system (CNS) associated with vision, hearing, motor control, sleep and wake cycles, arousal (alertness), and temperature regulation. Anatomically, it comprises the tectum (or corpora quadrigemina), tegmentum, ventricular mesocoelia (or “iter”), and the cerebral peduncles, as well as several nuclei and fasciculi. Caudally (posteriorly) the mesencephalon adjoins the pons (metencephalon), and rostrally it adjoins the diencephalon (eg., thalamus, hypothalamus). The midbrain is located below the cerebral cortex and above the hindbrain placing it near the center of the brain.
Primary Midbrain Components
Brainstem Anatomy: Brainstem anatomy showing the location of the midbrain in relation to the midbrain, pons, medulla, basilar artery, and vertebral arteries.
The tectum (Latin for “roof”) is formed by the superior and inferior colliculi and comprises the rear portion of the midbrain. The superior colliculus regulates preliminary visual processing and eye movement, while the inferior colliculus is involved in auditory processing. Collectively, the colliculi is referred to as the corpora quadrigemina.
The tegmentum is involved in many unconscious homeostatic and reflexive pathways, and is the motor center that relays inhibitory signals to the thalamus and basal nuclei to prevent unwanted body movement. It extends from the substantia nigra to the cerebral aqueduct (also called the ventricular mesocoeli). The nuclei of cranial nerves III and IV are located in the tegmentum portion of the midbrain.
The substantia nigra is closely associated with motor system pathways of the basal ganglia. The human mesencephalon is archipallian in origin, sharing its general architecture with the most ancient of vertebrates. Dopamine produced in the substantia nigra plays a role in motivation and habituation of species from humans to the most elementary animals such as insects. The midbrain is the smallest region in the brain and helps to relay information for vision and hearing.
The cerebral peduncles are located on either side of the midbrain and are its most anterior part, acting as the connectors between the rest of the midbrain and the thalamic nuclei. The cerebral peduncles assist in motor movement refinement, motor skill learning, and converting proprioceptive information into balance and posture maintenance.
Embryonic Development
During embryonic development, the midbrain arises from the second vesicle, also known as the mesencephalon, of the neural tube. Unlike the other two vesicles (the prosencephalon and rhombencephalon), the mesencephalon remains undivided for the remainder of neural development. It does not split into other brain areas while the prosencephalon, for example, divides into the telencephalon and the diencephalon. Throughout embryonic development, the cells within the midbrain continually multiply and compress the still-forming aqueduct of sylvius or cerebral aqueduct. Partial or total obstruction of the cerebral aqueduct during development can lead to congenital hydrocephalus.
Reticular Formation
The reticular formation assists in regulation of the sleep cycle and detecting sensory salience.
Learning Objectives
Describe the functions of the reticular formation region of the pons
Key Takeaways
Key Points
- The reticular formation is a region in the pons involved in regulating the sleep-wake cycle and filtering incoming stimuli to discriminate irrelevant background stimuli.
- The reticular formation consists of more than 100 small neural networks with varied functions including motor control, cardiovascular control, pain modulation, sleep, and habituation.
- Bilateral damage to the reticular formation of the midbrain may lead to coma or death.
- Traditionally, the nuclei of the reticular formation are divided into three columns: the median column or the Raphe nuclei, the medial column or the magnocellular nuclei, and the lateral column or parvocellular nuclei.
Key Terms
- magnocellular nuclei: Nuclei within the reticular formation involved in motor coordination.
- parvocellular nuclei: Nuclei within the reticular formation that are involved in the regulation of expiration during breathing and other motor functions.
- raphe nuclei: Located in the pons of the brainstem, the principal site of the synthesis of the neurotransmitter serotonin. Serotonin plays an important role in mood regulation, particularly when stress is associated with depression and anxiety.
The reticular formation is a region in the pons involved in regulating the sleep-wake cycle and filtering incoming stimuli to discriminate irrelevant background stimuli. It is essential for governing some of the basic functions of higher organisms, and is one of the phylogenetically oldest portions of the brain.
Divisions of the Reticular Formation
Traditionally, the nuclei are divided into three columns:
- Raphe nuclei (medium column)
- Magnocellular red nucleus (medial zone)
- Parvocellular reticular nucleus (lateral zone)
Sagittal division reveals more morphological distinctions. The raphe nuclei form a ridge in the middle of the reticular formation, and directly to its periphery, there is a division called the medial reticular formation. The medial reticular formation is large, has long ascending and descending fibers, and is surrounded by the lateral reticular formation. The lateral reticular formation is close to the motor nuclei of the cranial nerves and mostly mediates their function. The raphe nuclei is the place of synthesis of the neurotransmitter serotonin, which plays an important role in mood regulation.
The medial reticular formation and lateral reticular formation are two columns of neuronal nuclei with ill-defined boundaries that send projections through the medulla and into the mesencephalon (midbrain). The nuclei can be differentiated by function, cell type, and projections of efferent or afferent nerves. The magnocellular red nucleus is involved in motor coordination, and the parvocellular nucleus regulates exhalation.
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The original functional differentiation was a division of caudal and rostral, based on the observation that damage to the rostral reticular formation induces a hypersomnia in the cat brain. In contrast, damage to the more caudal portion of the reticular formation produces insomnia in cats. This study led to the idea that the caudal portion inhibits the rostral portion of the reticular formation.
Cross Section of the Pons: A cross section of the lower part of the pons showing the pontine reticular formation labeled as #9.
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Functions
The reticular formation consists of more than 100 small neural networks, with varied functions including:
- Somatic motor control: Some motor neurons send their axons to the reticular formation nuclei, giving rise to the reticulospinal tracts of the spinal cord. These tracts play a large role in maintaining tone, balance, and posture, especially during movement. The reticular formation also relays eye and ear signals to the cerebellum so that visual, auditory, and vestibular stimuli can be integrated in motor coordination. Other motor nuclei include gaze centers, which enable the eyes to track and fixate objects, and central pattern generators, which produce rhythmic signals to the muscles of breathing and swallowing.
- Cardiovascular control: The reticular formation includes the cardiac and vasomotor centers of the medulla oblongata.
- Pain modulation: The reticular formation is one means by which pain signals from the lower body reach the cerebral cortex. It is also the origin of the descending analgesic pathways. The nerve fibers in these pathways act in the spinal cord to block the transmission of some pain signals to the brain.
- Sleep and consciousness: The reticular formation has projections to the thalamus and cerebral cortex that allow it to exert some control over which sensory signals reach the cerebrum and come to our conscious attention. It plays a central role in states of consciousness like alertness and sleep. Injury to the reticular formation can result in irreversible coma.
- Habituation: This is a process in which the brain learns to ignore repetitive, meaningless stimuli while remaining sensitive to others. A good example of this is when a person can sleep through loud traffic in a large city, but is awakened promptly by the sound of an alarm or crying baby. Reticular formation nuclei that modulate activity of the cerebral cortex are part of the reticular activating system.
Effects of Damage
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Mass lesions in the brainstem cause severe alterations in the level of consciousness (such as coma) because of their effects on the reticular formation. Lesions in the reticular formation have been found in the brains of people who have post-polio syndrome. Some imaging studies have shown abnormal activity in this area in people with chronic fatigue syndrome, indicating a high likelihood that damage to the reticular formation is responsible for the fatigue associated with these syndromes.