BIOL 2220 Fall 2022 U4 Notes - Brain Development PDF
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2022
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These are lecture notes about the brain, covering its development, ventricles, surface anatomy, and functional regions. The notes detail the primary and secondary brain vesicles, different adult brain structures, the cerebral cortex, and functional areas.
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Lecture Objectives: The Brain . Describe the development of the brain, and relate embryonic regions to the structures 1 of the adult brain. Development of the Adult Brain The ectoderm thickens along the midline to form the neural plate ○ The neural plate is the...
Lecture Objectives: The Brain . Describe the development of the brain, and relate embryonic regions to the structures 1 of the adult brain. Development of the Adult Brain The ectoderm thickens along the midline to form the neural plate ○ The neural plate is the thickening of the ectodermal tissue Neural plate invaginates to form the neural groove with neural folds ○ The invagination of the neural plate is the neural groove ○ The sides of the neural groove are the neural folds The neural folds fuse and the neural tube forms ○ The brain and spinal cord derive themselves from the neural tube ○ The neural tube is made of ectodermal tissue and has a hollow center The neural tube descends The neural crest develops as offshoots of neural folds ○ The neural crest will later develop into neuroganglia The anterior portion of the neural tube begins to differentiate with swellings ○ These swellings will eventually differentiate into adult brain structures Primary Brain Vesicles (swellings) Prosencephalon ○ The most anterior portion of the developing brain ○ Also called the forebrain Mesencephalon ○ Also called the midbrain Rhombencephalon ○ Also called the hindbrain ★ The rest of the neural tube will develop into the spinal cord Secondary Brain Vesicles Telencephalon ○ Comes from the prosencephalon ○ Has the greatest development in the brain Diencephalon ○ Comes from the prosencephalon Metencephalon ○ Comes from the rhombencephalon Myelencephalon ○ Comes from the rhombencephalon ★ T he secondary brain vesicles will differentiate into adult brain structures ★ The mesencephalon does not differentiate into a secondary brain vesicle ○ It differentiates into a human adult brain structure Adult Brain Structures Cerebrum ○ Comes from the telencephalon ○ In humans, it is the part of the brain that has gone through the most change and development ○ It is so big that is wraps around other brain structures ○ Contains two hemispheres Left hemisphere and right hemisphere Hypothalamus ○ Comes from the diencephalon Thalamus ○ Comes from the diencephalon Epithalamus ○ Comes from the diencephalon Midbrain ○ Comes from the mesencephalon Pons ○ Comes from the metencephalon Cerebellum ○ Comes from the metencephalon Medulla oblongata ○ Comes from the myelencephalon ★ The diencephalon also gives rise to the retina of the eyeball ○ The sensory part of the eye (retina) starts out as brain tissue before detaching and moving away ★ The midbrain, pons, and medulla oblongata form the brainstem ○ Function in basilar activities ○ Ex: Breathing and digesting Development of the Brain ROADMAP Ex: Primary brain vesicle ○ Secondary brain vesicle Adult brain structures Prosencephalon ○ Telencephalon Cerebrum ○ Diencephalon Hypothalamus Thalamus Epithalamus Retina Mesencephalon ○ No secondary brain vesicle Midbrain Rhombencephalon ○ Metencephalon Pons Cerebellum ○ Myelencephalon Medulla oblongata 2. Identify the ventricles of the brain. Ventricle ○ Expansion of the hollow cavity of the neural tube ○ Ventricles are filled with cerebrospinal fluid (CSF) CSF functions to help the brain float CSF functions as a cushion to dissipate trauma to protect the brain ○ All ventricles are connected to each other The ventricles also connect to the CSF on the outside of the brain ○ Ventricles are lined with ependyma Brain Ventricles Lateral ventricles ○ Hollow cavities of the cerebrum ○ The septum pellucidum separates the two ventricles A thin membrane in between the ventricles that prevents fluid from going from one ventricle to another ○ The lateral ventricles connect indirectly via the third ventricle Third ventricle ○ Located in the diencephalon Located in the thalamuses ○ Connected to the lateral ventricles ○ Connected to the fourth ventricle Fourth ventricle ○ Located in the hindbrain ○ Connected to the third ventricle ○ Connected to central canal Connecting Channels of Brain Ventricles Interventricular foramen ○ Connects the lateral ventricles and the third ventricle Cerebral aqueducts ○ Connects the third ventricle to the fourth ventricle Openings for CSF Flow Lateral apertures ○ Opening on the sides of the fourth ventricle Connects CSF from ventricles to CSF that is around the brain Median aperture ○ On the roof of the fourth ventricle Connects the CSF from the ventricles to the CSF on the outside of the CNS 3. Describe the surface anatomy of the cerebrum, its lobes, and its functional regions. Surface Anatomy of the Cerebrum The hemispheres of the cerebrum are not smooth ○ The cerebrum is rough and bumpy ○ In general, the more folds/bumps on the brain, the more cognitive capability a human has Gyri ○ Single is gyrus ○ The bumps on the cerebrum Sulci ○ Single is sulcus ○ The depressions between the gyri Longitudinal fissure ○ Separates the two hemispheres from right and left Transverse cerebral fissure ○ Separates the cerebrum from the cerebellum Lobes of the Cerebrum rontal F Parietal Temporal Occipital Insula ★ The lobes of the cerebrum are named by the bones it’s associated with ○ The exception is the insula There is not an insula bone The insula is the deep lobe ★ Each hemisphere has a frontal, parietal, temporal, and occipital lobe ★ You can distinguish the lobes using the central and lateral sulci ○ The central and lateral sulci are deeper than the other sulci Regions of the Cerebrum Cortex ○ The superficial region of the cerebrum ○ Made of grey matter Consists of neuronal bodies and axons of unmyelinated neurons White matter ○ Deep to the cortex ○ Made of myelinated axons that are bundled together Basal nuclei ○ Located in the white matter . List the specific functional areas of the cerebral cortex, and identify their general 4 purpose. Cerebral Cortex The cortex varies in degrees of thickness and structure ○ Cortex varies from 2-4 mm in thickness ○ These areas are separated into domains ○ Domains are linked to function Each hemisphere controls the opposite side of the body ○ Ex: To wiggle the left index finger, the right side of the brain sends a signal telling the left finger to move The cerebral cortex has a lateralization of function ○ Some things only occur on one side of the brain ○ Linked to eye dominance Eye dominance is linked to hand dominance No area acts alone ○ No area of the cerebrum works by itself In front of the central sulcus relates to motor activity Behind the central sulcus relates to sensation The cortex is associated with high-level thinking, communication, memory, self-awareness, sensation, and conscious movement Functional Areas of the Cortex Motor areas ○ Involved with voluntary movement ○ Generates nervous impulses that activate skeletal muscle Sensory areas ○ Involved with conscious awareness of sensation ○ Receives sensory inputs Association areas ○ Connects and communicates from one area of the brain to another area of the brain ○ Ex: Connects a sensory area to a motor area ○ Ex: Connects a motor area to another motor area ★ A ll neurons in the cerebrum are interneurons ★ All neurons in the cerebrum are multipolar Motor Areas of the Cortex Primary motor cortex ○ Sends a signal/impulse to skeletal muscle to make it contract ○ Uses pyramidal cells Premotor cortex ○ Part of the brain that functions during learned skilled tasks ○ Sends signal to primary motor cortex ○ Ex: Writing, typing, playing an instrument Broca’s area ○ Found only in the left hemisphere ○ Associated with speech Involved with controlling the muscles for speech Ex: Activates muscles in the throat, tongue, lips, jaw etc ○ The analog on the right side deals with body language Frontal eye field ○ Controls the voluntary movement of our eyes ○ Ex: Follow the doctor’s finger without moving your head Sensory Areas of the Cortex Primary somatosensory cortex ○ Involved with spatial discrimination ○ Lets us determine which part of the body is being stimulated Somatosensory association cortex ○ Interprets all the sensory information ○ Uses past experience to determine what the sensory information is Primary visual cortex ○ Receives all the information from the retina Visual association cortex ○ Interprets information from the primary visual cortex ○ Uses past experiences to determine what we are seeing Primary auditory cortex ○ Receives all sensory information from the inner ear Auditory association area ○ Uses past experiences to determine what we are hearing Olfactory cortex ○ All information from odor receptors goes here ○ Does not have a specific association area ○ Linked strongly to memory and emotion Gustatory cortex ○ All information from taste receptors goes here Vestibular cortex ○ Located in the insula ○ Awareness of our balance Association Areas of the Cortex Prefrontal cortex ○ The most evolved of the brain structures ○ Also called the anterior association area ○ Part of the brain that is associated with intellect, cognition, complex learning, and recall Also associated with personality ○ Develops slowly and relies on social feedback Social feedback plays a crucial part during the development of the prefrontal cortex in middle/late teens Intellect, learning, and cognition have a social component Language areas ○ Broca’s area Only found in the left hemisphere Involved with speech ○ Wernicke’s area Only found on the left hemisphere Part of the brain (sensory portion) that is used when looking at complex words The analog on the right side is the sensory side for body language General interpretation area ○ Only found in the left hemisphere ○ Receives input from all of the sensory association areas Takes all the sensory information and turns it into a single thought Ex: Takes all stimuli and the brain thinks, “I am hungry.” Visceral association area ○ Gives us conscious perception of visceral sensation Conscious feeling of internal organs Ex: You can feel your stomach is upset before vomiting Ex: You can feel when your bladder is full 5. Name the structures and functions of the cerebral white matter and basal bodies. Cerebral white matter ○ Deep to cortical grey matter ○ Communicates/carries information between areas of the cerebrum ○ Carries information between the cortex and lower CNS centers ○ Consists of myelinated fibers bundled into large tracts ★ White matter are the communication links Types of White Matter Fibers Commissures ○ Carries information between the right and left hemispheres ○ The biggest commissure is the corpus callosum Association fibers ○ Connect one part of a hemisphere to another part of the same hemisphere ○ Ex: Connects the sensory area of the left hemisphere to the motor area of the left hemisphere Projection fibers C ○ onnect the cerebral cortex to other parts of the brain or the spinal cord ○ Connects the conscious brain to the rest of the nervous system Basal Nuclei The basal nuclei and the cerebellum work to fine tune motor activity ○ Ex: People with Parkinson’s have basal nuclei that do not function properly Fine motor skills are gone Tremors occur The basal nuclei do not have direct access to motor pathways ○ Instead, the basal nuclei work through the thalamus ○ Ex: The putamen would send a signal to the thalamus which would send a signal to the primary motor cortex or the premotor cortex Caudate nucleus Putamen Globus pallidus Amygdala ○ Highly linked to emotion ○ Functions in fear, danger, satation of hunger/sex ○ Functions in the limbic system 6. List the structures and functions of the diencephalons and brain stem. Structures and Functions of the Diencephalons (Thalamuses) Thalamus ○ Contains several nuclei (not related to DNA; just a cluster of neurons) Each nucleus has specialty functions Connects to specific regions of the cortex All sensory input is sorted here before being sent to the cortex All non-sensory inputs pass through here ○ The “doorway/gateway” to the cortex Hypothalamus ○ Regulates ANS activity Regulates involuntary activity The autonomic nervous system functions through the hypothalamus ○ Controls emotional responses Also controls the wake and sleep cycle (biorhythm) The “thermostat” of the body ○ Regulates body temperature ○ Controls food intake S ince we typically eat at the same times of the day, our body gets accustomed to eating at these times The hypothalamus lets the body know it is time to eat ○ Regulates water balance Uses sensory information from the kidneys to determine proper water volume in the body Controls sleep cycle ○ ○ Regulates hormone release The hypothalamus is the main link between the nervous system and the endocrine system ★ T he hypothalamus regulates heart rate, blood pressure, rate of breathing, act of digestion, size of pupils in the eyes etc ○ Regulate means modify ○ Other places in the brain cause these places to function, but the hypothalamus regulates the activity Epithalamus ○ The pineal gland is at the end of the epithalamus The pineal gland is reduced compared to the pineal gland of other organisms ○ The pineal gland secretes melatonin Therefore, the epithalamus functions in the sleep/wake cycle The pineal gland is inhibited by UV radiation When the sun is up, the pineal gland is inhibited ○ When the sun sets, melatonin is released and we become sleepy Melatonin affects mood Mood affects learning ○ The epithalamus contributes to the production of cerebrospinal fluid Affects the diameter of the choroid plexuses; therefore it affects the permeability of the choroid plexus Structures and Functions of the Brainstem In the brainstem, there is gray matter deep to white matter ○ There is white matter superficial to the gray matter ○ In the cerebrum, the gray matter is superficial to the white matter There are islands of gray matter embedded in white matter ○ The brain stem is continuous with the spinal cord The brain stem ends and the spinal cord begins when the islands of gray matter embedded in the white matter disappear Provides programmed automatic behaviors needed for survival ○ Ex: Breathing, digestion, heart rate The brainstem acts as a connection/pathway from higher brain centers to the rest of the body Midbrain ○ Contains motor tracts that connect to the spinal cord Also contains tracts that connect to the cerebellum Carries information from cerebrum to cerebellum to be refined Carries refined information from cerebellum back to cerebrum Carries refined information from the cerebrum to the spinal cord ○ Functions in pain suppression Pain is a survival mechanism, but sometimes we have to suppress pain to function to survive ○ Serves as the link between the amygdala and the ANS Controls fight or flight ○ Contains the visual reflex center Coordinates our head movement with where our eyes go Mostly due to the corpora quadrigemina This is a part of the midbrain that controls sight and sound ○ Functions as auditory relay-puts important info into perception Mostly due to the corpora quadrigemina This is a part of the midbrain that controls sight and sound Pons ○ Chiefly composed of conduction tracts Receives input from all other brain areas Takes all the information and conducts a signal Complete pathway between the higher brain centers and the spinal cord Relays information between the motor cortex and the cerebellum Medulla Oblongata ○ The major autonomic reflex center Controls heart rate and blood vessel diameter Controls rate/depth of breathing Regulates vomiting, hiccuping, swallowing, coughing, and sneezing ★ Moving your hand away from something hot is a skeletal muscle reflex ○ The medulla functions in autonomic reflexes . Describe the anatomy of the cerebellum, its functional areas and the mechanism of 7 cerebellar processing. Cerebellum ○ The anatomical composition of the cerebellum is similar to that of the cerebrum There is a gray cortex that is superficial to white matter ○ Refines skeletal muscle contractions P ○ lays a role in cognition, language, and problem solving ○ Activity occurs subconsciously ○ The arbor vitae is the white matter of the cerebellum Cerebellar Processing M otor association area of the cerebral cortex sends signals to the cerebellum of its intent to initiate voluntary muscle contraction ○ Cortex sends a signal to the cerebellum to be refined The cerebellum receives information from visual receptors, equilibrium receptors and proprioceptors throughout the body The cerebellar cortex calculates the best way to coordinate the force of contraction ○ The best possible way of performing the contraction is calculated The message is refined The cerebellum dispatches the message to the cerebral cortex The signal is sent from the cerebral cortex to the muscle 8. Describe the function of functional brain systems. Functional brain systems ○ Networks of neurons that work together but span relatively large distances in the brain ○ Cannot be localized to specific brain regions Limbic system ○ Known as the “emotional brain” Also linked in resolving mental conflict ○ Uses the amygdala and the diencephalon derivatives ○ Closely linked with the rhinencephalon The rhinencephalon is linked with odor Odor is strongly linked with emotions ○ Output is relayed through the hypothalamus The limbic system may send signals to the hypothalamus to change HR or BP (heart rate or blood pressure) Might send signal to the cortex to activate skeletal muscle ○ Strong link between feelings and thoughts There is a constant battle in the brain between emotion and logic Emotion beats logic Evolutionarily, emotion takes over logic because it is linked to the autonomic nervous system Ex: ○ See bear, get scared, immediately run without thinking ○ It is faster to run than logically think about the potential danger the bear might pose Assesses danger and elicits fear Reticular Formation ○ Loosely clustered neurons in the center of the medulla, pons, and midbrain (brainstem) ○ Governs arousal of the brain as a whole ○ When you are awake, the RAS (reticular activation system) sends a constant signal to the cerebrum to keep the cortex alert to receive sensory input and respond with motor output When the RAS is inhibited, we do not get information to the cortex, so we do not respond to the stimuli 9. Explain what EEGs measure and what information can be discerned from an EEG. EEG ○ Electroencephalogram Electro - electricity En - inside Ceph - head Gram - writing/recording The writings of electricity inside the head ○ Electroencephalograms record a person’s brain waves Brain waves are patterns of neuronal electrical activity Types of Brain Waves Alpha waves ○ Common in an “idle” brain ○ 8-13 waves/second Beta waves ○ Common in a “concentrating” brain ○ Anything more than 13 waves/second Theta waves ○ Common in children, not terribly common in adults ○ 4-8 waves/second Delta waves ○ Common in deep sleep Delta patterns when awake is indicative of brain damage ○ Anything less than 4 waves/second 10. Define consciousness, and differentiate the various levels of consciousness. Consciousness A ○ wareness of sensations and control of movement ○ There is a medical continuum for consciousness from most conscious to least conscious Alert, drowsy, lethargic, stupor, coma 11. Describe sleep, and discuss its importance. Sleep ○ A state of partial unconsciousness ○ The difference between sleep and a coma is the fact that you can be aroused from sleep You can wake up from sleep to become alert; in a coma, you cannot be aroused to become alert Types of Sleep Non-REM sleep ○ Restorative sleep REM sleep ○ Rapid Eye Movement sleep ○ Dreaming occurs during REM sleep Dreaming may be the brain working on problems that did not get completed during the day Whatever is on your mind during the day, you dream about it Dreaming may be reverse learning Throughout the day, the brain is bombarded with information Dreaming may be a way to sort out what was important during the day and what was not important during the day Our last dreams of the night are the most vivid of our dreams We are typically victorious in whatever challenge we face in the dream The cycle lasts about 90 minutes and beings with restorative sleep ○ As the cycles progress throughout the night, they get slightly longer The REM phase lasts a little longer each cycle 12. Define memory, and discuss the processes leading to the encoding of information. Memory ○ The storage and retrieval of information ○ All memory start as a stimulus The stimulus goes to the cortex ○ Since it has reached the cortex, we are aware of it All information goes through a buffer ○ W e lose some of the information, and some of the information goes into short term storage Short term memory can be retrieved for a short span of time ○ If we work with the information from short term memory, we can store it in long term memory almost indefinitely When long term memories is lost, it is easier to relearn that information and store it to long term memory again than it is to store new information How to Store Information into Long Term Memory 1. Repetition ○ Look at the information multiple times after putting it into short term memory 2. Mood ○ It is much easier to put information into long term memory if you are in a good mood 3. Association ○ By making connections between new information and information that you already know, it is easier to store the new information ★ Y ou are learning how the brain works. Use that to your advantage. This lecture objective is essentially explaining how to do better in school by learning how to put info to long term memory. Begin to practice it in your own other classes as well as this one. 3. Describe the structural and functional relationships of meninges, cerebrospinal fluid, 1 and the blood-brain barrier. T he meninges, cerebrospinal fluid, blood-brain barrier, and skull bones all play a role in protecting the brain Bone ○ Protects against trauma like a football helmet would Meninges ○ The membranes covering the brain and spinal cord Blood-brain barrier ○ Regulates what moves in and out of the brain Meninges Cover and protect the CNS ○ Cover and protect the brain and spinal cord ○ Leathery, fibrous, and tough ○ Function in protection Function in protection of the blood vessels of the brain ○ The blood vessels are located between layers of meninges Contain cerebrospinal fluid Dura Mater ○ German for “durable mother” ○ Outermost meninx (singular form of meninges) The strongest and most superficial covering ○ Two-layered sheet of fibrous connective tissue Double layered around the brain The superficial layer is the periosteal layer ○ This layer is attached to the skull ○ Functions to anchor the brain in place Single layered around the spinal cord Having one layer around the spinal cord allows for more movement and flexibility of the spinal cord Arachnoid Mater ○ The middle meninx Means “spider mother” ○ Creates the subarachnoid space The space between the arachnoid mater and the pia mater The subarachnoid space contains the blood vessels and the CSF ○ There is also a subdural space This is the space between the dura mater and the arachnoid mater This space also contains CSF Pia Mater ○ The deepest meninx Means “loving mother” ○ Immediately covers the brain and spinal cord ○ Covers the gyri and goes into the sulci Cerebrospinal Fluid (CSF) L iquid cushion around the brain and the spinal cord Reduces the brain weight by 97% ○ Prevents the brain from crushing itself Have approximately 150 mL of CSF Protects the CNS from physical trauma ○ When you hit your head, the energy is dissipated throughout the fluid Helps nourish the brain and carries chemical signals Formed by the choroid plexuses in each ventricle ○ The choroid plexuses are the capillary beds in the roofs of the ventricles These capillaries leak fluid The epithalamus sends a signal that causes dilation of the capillaries which make them permeable and leaky ○ The fluid leaked by the choroid plexus is modified by the ependyma to become CSF and goes into the ventricles Most of this fluid is in the subarachnoid space The CSF is replaced approximately every 8 hours, or 3x/day A spinal tap can be performed to assess the fluid for pathogens etc. Blood-Brain Barrier A protective mechanism for the brain to help maintain a stable environment within the brain The blood-brain barrier allows some things to penetrate it: ○ Glucose ○ Amino acids ○ Electrolytes Substances in the brain capillaries are separated from the brain by: ○ Capillary endothelium ○ Thick basal lamina on capillaries ○ Astrocytes Connect the neural cell to the blood vessel Acts as an exchange between the blood vessel and the neuron These three things function as a selective barrier There are regions of the brain where the blood-brain barrier is absent ○ Vomiting center If poisons/toxins/hazardous chemicals reach here, the vomiting center detects the chemicals in the blood and causes the body to vomit in an effort to get rid of the toxins ○ Hypothalamus Monitors the body temperature Monitors our water balance 14. Discuss the embryonic development of the spinal cord. Embryonic Development of the Spinal Cord T he spinal cord develops from the neural tube Two distinct clusters of neuroblasts are formed ○ Alar plate These neurons develop into interneurons F orms on the back/dorsal side Swelling on the dorsal side helps us distinguish anterior vs posterior portion of the spinal cord The swellings are called dorsal root ganglia ○ Contains the cell bodies of the sensory neurons Basal plate ○ These neurons become motor neurons Forms of the anterior/ventral side ★ The alar and basal plates become the gray matter of the spinal cord The axons of these neurons become the white matter of the spinal cord 15. Summarize the gross anatomy of the spinal cord. Gross Anatomy of the Spinal Cord The spinal cord extends from the foramen magnum to the first lumbar vertebrae (L-1) ○ The terminus/end of the spinal cord is called the conus medullaris The spinal cord is covered with meninges ○ There is a single layer of dura mater surrounding the spinal cord There is an epidural space superficial to the dura mater ○ The meninges extend beyond the conus medullaris The meninges are anchored to the coccyx by filum terminale Anchoring portions of the meninges are called filum terminale ○ The spinal cord is held to the dura mater by denticulate ligaments The cauda equina extends sacral and lumbar nerves beyond the conus medullaris There are cervical and lumbar enlargements where lots of nerves are to go to the upper and lower limbs The spinal cord is a two-way path ○ It has ascending and descending pathways The spinal cord also acts as a reflex center ○ A reflex occurs when sensory information arrives at the spinal cord and automatically triggers a motor pathway An interneuron may be used in the reflex pathway The spinal cord has two grooves that run the length of the cord and divide it into left and right halves ○ Anterior median fissure Deeper than the posterior median sulcus ○ Posterior median sulcus The spinal cord contains a central canal that has CSF in it 6. Explain the anatomy of the gray matter and the white matter of the spinal cord, 1 including the neuronal make-up and the spinal cord tracts. Gray Matter of the Spinal Cord Looks like the letter H ○ Contains anterior, posterior, and lateral horns The left and right halves are connected by gray commissure Each horn contains different neurons ○ Posterior horns Contain interneurons ○ Anterior horns Contain mostly cell bodies of somatic motor neurons The axons extend via ventral roots ○ Lateral horns Contain autonomic (sympathetic) motor neurons There is a division of labor within the posterior horn ○ The anterior portion of the posterior horn receives visceral sensory information ○ The posterior portion of the posterior horn receives somatosensory information White Matter of the Spinal Cord Divided into three white columns ○ The spinal cord contains a posterior, anterior, and lateral column Columns contain collections of fibers that run as multineuron tracts Neurons going to the same places run together in the same column Ascending Pathways Nonspecific Ascending Pathway ○ Sending sensory information to the brain about anything ○ Ex: Pain, temperature, touch etc ○ Has a three neuron chain ○ Information can go to the cortex of the reticular formation The RAS can wake up the brain using pain, coarse touch, temp etc ○ These pathways decussate in the spinal cord Specific Ascending Pathway ○ Sends information about a single type of sensory information using a single type of sensory receptor ○ Ex: Vibration, light touch, muscle stretch ○ These pathways decussate at the medulla oblongata Spinocerebellar Tracts ○ These tracts go to the cerebellum These tracts do not go to the cortex ○ Conveys sensory information, but not consciously Receives information about muscle and tendon stretch ○ These pathways do not decussate They stay on the same side (ipsilateral) Descending Pathways Direct (pyramidal) system ○ Regulates fast/fine skilled movements Indirect (extrapyramidal) system ○ Works with the axial muscles that regulate balance and coarse movement ○ Ex: Head, neck, and eye movement are coordinated to track things visually 17. Differentiate first, second, and third-order neurons. X-order Neurons First-order neurons ○ Cell bodies are located in ganglion Sensory info ○ Conducts impulses from sensory receptors and proprioceptors These are sensory neurons Second-order neurons ○ Cells bodies are in the dorsal horn of the spinal cord or in the medulla oblongata ○ Transmits impulses to the thalamus or the cerebellum Third-order neurons ○ Located in the thalamus ○ Conduct impulses to somatosensory cortex of the cerebrum ○ Takes info from the thalamus to the somatosensory cortex of the cerebrum ○ Interneurons Lecture Objectives: Sensory Receptors 1. Define sensory receptors, and identify their functions. Sensory Receptor ○ Neural structures that respond to stimuli A stimulus is some form of energy Heat, light, touch, pressure, pain etc. Sensory receptors function to take energy and convert it to an electrical signal A stimulus causes a graded potential on a sensory receptor If the stimulus is strong enough, it will cause an action potential ○ Can lead to, but do not provide themselves, sensation and perception The signal from the sensory receptor has to make it to the cerebral cortex in order for us to perceive the stimulus. Perception is a brain (cortex) function Sensation is a sensory receptor function ○ Classified based on: Type of stimuli they detect Location Structural complexity . Classify sensory receptors based on type of stimulus detected, structure, and body 2 location. Sensory Receptors Based on Type of Stimulus Detected Mechanoreceptor ○ Detects mechanical force ○ Ex: Touch, vibration, pressure, itch, stretch Thermoreceptor ○ Detects thermal energy Heat energy refer to temperature changes Chemoreceptor ○ Detects chemical energy ○ Ex: Taste and smell Photoreceptor ○ Detects light energy ○ Rods and cones in the eye Nociceptors ○ Detects potentially dangerous stimuli Detects painful stimuli ★ Any receptor can function as a pain receptor if overstimulated. Sensory Receptors Based on Location Exteroceptors ○ Detects stimuli outside the body ○ Located at or near the surface of the body ○ Ex: Touch, pressure, external temperature of the skin Interoceptors ○ Detects stimuli within the body ○ Ex: Stretch and internal body temperature Proprioceptors ○ Detects stimuli (stretch) within muscles, joints, tendons, ligaments, and connective tissue Sensory Receptors Based on Structural Complexity Simple receptors ○ Modified dendritic endings of sensory neurons The dendrites are modified to act as a sensory field ○ Most receptors are complex Complex receptors ○ Localized collections of cells associated with the special senses Special senses include sight, taste, smell, hearing, and balance are special senses ○ Used in the sense organs ○ Ex: Nose, tongue, eyeballs . Differentiate free nerve endings from encapsulated nerve endings, and list examples of 3 each of their functions. Free Nerve Endings F ree nerve endings do not have connective tissue wrapped around the dendrites Ex: ○ Merkel’s discs Located in the epidermis ○ Hair follicle receptors ○ Itch receptors Free nerve endings in the dermis Encapsulated Dendritic Endings T hese nerve endings are wrapped in connective tissue Ex: ○ Meissner’s corpuscles ○ Pacinian corpuscles ○ Ruffini’s corpuscles Detect stretch in connective tissue ○ Muscle spindles Detect stretch in muscles ○ Golgi tendon organs Detect stretch in tendons ○ Joint kinesthetic receptors Detect stretch in the synovial joint 4. Describe the actions of the somatosensory system. Somatosensory System Part of the sensory system that serves the body wall and the limbs ○ This system is so we can feel things at the surface of the skin Requires neural integration at: ○ Receptor level This involves the sensory receptors ○ Circuit level This involves the ascending pathways through the CNS ○ Perceptual Level This means the signal was delivered to the cerebral cortex and was perceived We are aware of the stimulus because it made it to the cortex . Differentiate receptor level processing, circuit level processing, and perceptual level 5 processing. Receptor Level Processing The receptor must be receptive to the stimulus ○ Receptors are specific to certain stimuli/energy ○ Receptors have specificity The stimulus must be applied within the receptive field ○ If the stimulus is applied outside the receptive field, the receptor won’t detect the stimulus The stimulus in transduced into receptor potential ○ All receptors do is convert one form of energy to another form of energy C hanging one form of energy to another form of energy is called transduction ○ Ex: Touch is the conversion of mechanical energy to an action potential An action potential is produced ○ When the stimulus is strong enough, you reach threshold stimulus An action potential occurs ○ When the stimulus is not strong enough, you get a generator potential or a subthreshold stimulus An action potential does not occur If an action potential is produced, neurotransmitter is released ○ Once an action potential occurs, the signal can then go from the receptor level to the circuit level Circuit Level Processing Ascending pathways carry impulses to appropriate regions of the cerebral cortex First-order neurons carry signals from the receptor to the spinal cord ○ These first-order neurons synapse will second-order neurons in the spinal cord or medulla oblongata If a spinal reflex occurs, a first-order neuron will synapse with a motor neuron to cause an action to occur Does not involve the cortex or perception Second-order neurons carry the impulse/signal to the thalamus or the cerebellum ○ The second-order neurons synapse with third-order neurons if the signal is delivered to the thalamus instead of the cerebellum Third-order neurons transmit the signal to the somatosensory cortex of the cerebrum Perceptual Level Processing Message to the cortex is always an action potential ○ Without an action potential, the message would not have left the receptor Perception is determined based on what part of the cortex receives the impulse ○ This is how we discriminate what part of our body and what type of sensation we are feeling This is called projection We project the information to the appropriate part of the cerebral cortex 6. Compare tonic and phasic receptors. Tonic Receptors G enerateGenerate nervous impulses at a constant rate, unless altered Constantly sending action potentials to the brain Ex: ○ Equilibrium receptors constantly send signals to the brain to tell us where we are in space ○ Can change when we lose balance ○ Really slow to adapt, but they still adapt Phasic Receptors N ormally off, unless activated Adapt very rapidly Ex: ○ Pacinian corpuscle When someone applies deep pressure, you can feel it Eventually the Pacinian corpuscle stops sending signals to the brain, so you do not feel the pressure 7. Define adaptation, and identify the classes of receptors that do not adapt. Adaptation ○ The reduction in sensitivity in the presence of a constant stimulus ○ Ex: Cold receptors adapt when you go outside, so when you come inside, cold water feels warm Salt receptors can adapt so you end up adding more salt onto your food Nociceptors (pain) and proprioceptors (related to balance) never adapt ○ Our survival depends on those receptors sending us information, so they do not adapt 8. Identify the main aspects of sensory perception. Aspects of Sensory Perception Perceptual detection ○ Detection that we have been stimulated ○ Ability to determine that a stimulus has been applied to our body ○ Ex: We hear a cough in the classroom anstude estimation A ○ relative impression of the strength of a stimulus ○ The brain looks at the number of action potentials it receives to determine the strength of the stimulus ○ Ex: We can determine how loud the cough was Spatial discrimination ○ We can know where we have been stimulated ○ Based on what part of the cortex the impulse was sent to Feature abstraction ○ Ex: Touch velvet Feels soft and cushioning ○ Ex: Touch sandpaper It has rough and grainy features as you rub your finger across it Quality discrimination ○ Certain stimuli have certain submodalities ○ Ex: Not only can we tell that we have tasted something, but we can tell what submodality it is Sweet versus bitter versus salty ○ Ex: Can also distinguish the submodalities of sound High pitch versus low pitch Pattern recognition ○ Ability to recognize a stimulus that follows a familiar pattern ○ Ex: Picking someone out of the crowd, picking something normal to us out of a random crowd ○ Ex: Distinguish a stranger in the group, picking someone odd out of a crowd you normally see ○ Ex: You can hear certain sounds that make a melody that is familiar to us We can recognize a song we know 9. Define nerve and ganglion. Nerve ○ A cordlike organ of the PNS Contains nervous tissue, blood vessels, lymphatic vessels, connective tissue, and myelin ○ Parallel bundles of peripheral neurons enclosed by successive wrappings of connective tissue Ganglion ○ Collections of neuronal cell bodies associated with peripheral nerves 10. List the classifications of nerves. Classifications of Nerves Sensory (afferent) nerves ○ Carry sensory information to the CNS Motor (efferent) nerves ○ Carry motor information away from the CNS Mixed nerves ○ Carry both sensory information to the CNS and motor information away from the CNS Cranial nerves ○ Come off the brain Spinal nerves ○ Come off the spinal cord 11. Discuss the process of nerve regeneration. N erve regeneration is limited to damage to areas other than the cell body Nerves have a better chance of regenerating when the damage is close to the axon terminal rather than when the damage is close to the axon hillock If a nerve cannot regenerate, the nerves following the damage nerve will degenerate and die as well Nerve Regeneration T he peripheral axon is damaged The separated ends of the axon seal and swell Wallerian degeneration occurs ○ Phagocytes degrade the axon, but the neruolemma withing the endoneurium remains intact The axon and myelin sheath degenerate due to the lack of nourishment and the phagocytes come and break it down Everything inside the plasma membrane is broken down Surviving Schwann cells proliferate (divide) and migrate to the injury site ○ The Schwann cells respond to the damage by dividing and migrating Schwann cells release growth factors and CAMS and form regeneration tube ○ CAM is cell-surface adhesion molecule Lecture Objectives: Motor Activity 1. Name the 12 pairs of cranial nerves, listing the general function of each. Cranial Nerves 1. Olfactory nerve ○ Runs to the olfactory cortex ○ Deals with information related to smell ○ Comes off the forebrain 2. Optic nerve ○ Deals with vision ○ Goes to the eyeball ○ Comes off the forebrain 3. Oculomotor Nerve ○ Associated with the movement of the eye ○ When intoxicated, there is a loss of control of this nerve Results in eye wiggling This is why police officers will have you follow their finger ○ Comes off the midbrain 4. Trochlear Nerve ○ Changes the focus of the lens Changes the diameter of the lens Pulley system of muscles changes the shape of the lens to focus/defocus ○ Comes off the midbrain 5. Trigeminal Nerve ○ Associated with facial sensations and chewing ○ Largest of the cranial nerves ○ Comes off the midbrain 6. Abducens ○ Allows for eye abduction ○ Comes off the midbrain 7. Facial nerve ○ Allows for facial expressions ○ Ex: Wrinkling of the nose Furreling of the forehead 8. Vestibulocochlear Nerve ○ Also called the auditory nerve ○ Deals with hearing and balance 9. Glossopharyngeal Nerve ○ Linked to the tongue and pharynx Allows movement of the tongue/pharynx for swallowing/speech 10.Vagus Nerve Controls heart rate ○ ○ Only cranial nerve that extends past the head/neck 11.Accessory Nerve ○ Runs with the Vagus nerve ○ Goes to the neck muscles Helps to twist and pivot the neck 12.Hypoglossal Nerve ○ Associated with tongue movement for speech ○ Also responsible for moving food around in the mouth using the tongue 2. Describe the general features of the spinal nerves; including the roots and rami. There are 31 pairs of spinal nerves ○ All pairs arise from the spinal cord ○ Spinal nerves go everywhere in the body except the head and neck Spinal nerves are based on their point of origin at the spinal cord All are mixed nerves Dorsal and Ventral Roots A ttachments for spinal nerves to the spinal cord Dorsal roots have sensory neurons ○ Carry sensory information Ventral roots have motor neurons ○ Ventral roots start as smaller components called rootlets ○ Carry motor information Dorsal and ventral roots fuse to make spinal nerves Nerve Rami orsal ramus goes to the posterior body trunk (back) D Ventral ramus goes to the rest of the trunk and the limbs When roots merge into a spinal nerve, the nerve splits into rami Contain both motor and sensory neurons Spinal Nerves of Interest Phrenic Nerve ○ Cervical plexus nerve ○ Runs to the diaphragm Associated with breathing Can also cause spastic contractions of the diaphragm These are hiccups Median Nerve ○ D etects sensation of skin of hand and controls flexors to allow us to wiggle the fingers ○ Also allows for opposition ○ Repeated tasks can cause Carpal Tunnel Syndrome The nerve gets inflamed and rubs on the aponeurosis and causes pain Ulnar Nerve ○ At the surface of the skin on the elbow ○ Responsible for the “funny bone” sensation when it's hit Sciatic Nerve ○ Thickest and longest nerve of the body ○ Controls the entire lower limb except the anterior medial thigh Pudendal Nerve ○ Goes to the muscles and skin of the perineum ○ Allows for voluntary bladder control ○ Also involved in erections 3. Define nerve plexus, and identify their adaptive significance. Nerve Plexus ○ Branching and linkage of ventral rami ○ Occurs only in the cervical, brachial, lumbar, and sacral regions ○ Primarily serves limbs Adaptive Significance of Nerve Plexus If there is damage to part of a nerve, you can reroute the information ○ Provide redundancy Ability to send the same message through multiple pathways ★ There are no thoracic plexus 4. Define dermatome, and explain their role in cutaneous reception. Dermatome ○ Area of skin innervated by the cutaneous branches of a single spinal nerve ○ All nerves except C1 go to a portion of the skin 5. Differentiate the nerve endings of somatic and autonomic nerve fibers. Somatic Nerve Endings H ave neuromuscular junctions that utilizes acetylcholine Highly modified structure Autonomic Nerve Endings Have swellings called varicosities that utilize different neurotransmitters 6. Outline the levels of hierarchy of motor control. Segmental Level O ccurs at the spinal cord Associated with spinal reflexes ○ Sensory neurons can synapse with motor neurons in the spinal cord ○ For a reflex, the stimulus will always cause the same reaction or motor activity Also controls Central Pattern Generator (CPG) ○ CPG is a motor activity that is done the same way all the time A pattern is produced ○ Ex: Moving left foot then right foot to walk ○ CPG can be overridden by the brain Ex: You can force your left arm to swing while the left foot moves, but it is awkward Projection Level O ccurs in the motor cortex or the brain stem Direct/pyramidal pathways ○ Motor impulse goes from the motor cortex of the cerebrum through the anterior horns of the spinal cord ○ Motor neuron causes voluntary skeletal muscle movement Indirect/extrapyramidal pathways ○ Motor tracts originate in the brain stem Precommand Level M otor impulse goes through the cerebellum and the basal nuclei Refines voluntary movement ○ No direct connection between motor activity and the precommand level The message from the cerebellum must go through the cortex 7. Contrast intrinsic and acquired reflexes. Intrinsic Reflex A rapid, predictable, motor response to a stimulus that is unlearned, unpremeditated (not planned), and involuntary ○ Predictable means that it will happen in the same way every time Acquired Reflex A rapid, predictable, motor response to a stimulus that results from practice or repetition Ex: ○ Athletics, martial arts When a boxer sees a punch coming to his face, his reaction is to duck out of the way This comes from repeated practice of the movement Ex: ○ Driving When you are going uphill, you automatically press harder on the break to maintain speed . Name the components of a reflex arc, and distinguish between autonomic and somatic 8 reflexes. Components of a Reflex Arc Receptor ○ Allows for the detection of a stimulus if it is a correct stimulus for that receptor Sensory neuron ○ The sensory neuron carries the message from the receptor to the CNS Integration center ○ The CNS Could be the spinal cord or the brain Motor neuron ○ Connects the integration center to the effector organ Effector ○ Could be a muscle or a gland ★ S omatic reflexes are mediated by the spinal cord ★ Autonomic reflexes utilize higher brain centers 9. Compare and contrast the various types of spinal reflexes discussed in class. Spinal reflex ○ Somatic reflexes are mediated by the spinal cord Rapid predictable skeletal muscle contractions in response to a stimulus Stretch Reflex Results in contraction due to excessive stretch on a muscle 1. The muscle spindle apparatus is stretched ○ The muscle spindle apparatus is a receptor 2. Sensory neurons (Type IA and Type 2) transmit the signal to the spinal cord 3. Sensory neurons synapse with motor neurons (Alpha efferent fibers) 4. Motor neurons carry the signal to extrafusal fibers of the muscle ○ Carries the signal to the contractile fibers of the muscle 5. Contraction occurs ★ T he stretch reflex is monosynaptic (does not involve interneurons) and ipsilateral (does not cross over the spinal cord, does not decussate) ★ Prevents the overstretching of the muscle to prevent tearing ★ Promotes reciprocal inhibition ○ Relaxation of an antagonistic muscle brought about by a stretch reflex Gamma Motor Neuron Reflex Arc A ccompanies a stretch reflex Refines the contractions promoted by the stretch reflex by affecting the muscle spindle apparatus Regulates response of spindle intrafusal fibers ○ Gamma efferent motor fibers stimulate intrafusal fibers to maintain tension Golgi Tendon Reflex Muscle relaxation and lengthening in response to over contraction ○ Always polysynaptic The Golgi tendon apparatus acts as the sensory receptor Motor neurons synapse with extrafusal fibers to cause them to stop contracting . C 1 ontraction or stretching of muscle increases muscle tension 2. The Golgi tendon organs activate 3. Afferent impulses transmitted to the spinal cord and the cerebellum ○ Sometimes the signal is sent to the spinal cord, sometimes it is sent to the cerebellum 4. Motor neurons supplying the muscles are inhibited 5. Antagonist muscles are activated ○ Reciprocal activation Withdrawal/Flexor Reflex P ainful stimulus causes an automatic withdrawal of the threatened body part away from the stimulus This is an ipsilateral and polysynaptic reflex Crossed Extensor Reflex Ipsilateral withdrawal reflex plus contralateral extensor reflex Extensor reflex helps you balance from with withdrawal reflex Superficial Reflexes Plantar Reflex ○ Caused by gentle cutaneous stimulation ○ Stroke the bottom of the foot, toes curl inwards, ○ If brain damage has occurred (usually after a stroke), toes will curl outwards This is called Babinski’s sign Babies do this without damage to the brain because the brain has not yet fully developed Abdominal Reflex ○ Cutaneous stimulation of the abdomen which causes the belly button to move towards the stimulus 0. Identify the anatomy of a muscle spindle, and identify the major contribution of each 1 component. Muscle Spindle Anatomy Intrafusal fibers ○ Noncontractile fibers ○ Lack myofilaments Except at the ends ○ Do not run the entire length of the muscle ○ Make up the muscle spindle apparatus These are the sensory receptors Extrafusal fibers ○ The contractile muscle fibers Type 1A fibers ○ Sensory neurons ○ Wrap around the center of the intrafusal fibers Type 2 fibers ○ Sensory neurons ○ Wrap around the ends of the intrafusal fibers Gamma efferent fibers ○ Motor fiber at the end of the muscle spindle ○ Sends signal to the ends of the intrafusal fibers Alpha efferent fibers ○ Motor fibers that send signals to the extrafusal fibers to contract Lecture Objectives: Autonomic Nervous System (ANS) 1. Identify the functions of the autonomic nervous system. T he ANS is a system of motor neurons that functions to involuntary innervate smooth muscle, cardiac muscle, and glands 2. Differentiate autonomic motor units from somatic motor units. Autonomic Motor Unit Contains a two neuron chain ○ Has a preganglionic neuron and a postganglionic neuron Preganglionic cell body is in the CNS ○ Synapses with the postganglionic neuron in the autonomic ganglion outside the CNS (away from the spinal cord) Postganglionic axon extends to the effector organ (muscle/gland) ○ Postganglionic axon can be unmyelinated ANS always uses ACh as the preganglionic neurotransmitter ○ May use ACh or norepinephrine (NE) as postganglionic NT Somatic Motor Unit Has a one neuron chain ○ Only has one motor neuron to the effector organ Motor neurons in the somatic nervous system are thicker and heavily myelinated ○ Rapid rate of signal transmission Somatic system always uses ACh and is always excitatory 3. Compare and contrast the sympathetic and parasympathetic divisions. Sympathetic Nervous System Fibers emerge from the thoracic and lumbar regions of the spinal cord ○ From T1-L2 Short preganglionic and long postganglionic fibers ○ Ganglia are located close to the spinal cord There is a SHORT distance from the CNS to the ganglia in the sympathetic nervous system Involved in fight/flight Parasympathetic Nervous System F ibers emerge from the brain and sacral region of the spinal cord Long preganglionic and short postganglionic fibers ○ Ganglia are located in the visceral effector organs Involved in maintenance, rest and digest . Identify the site of origin of preganglionic neurons and location of ganglionic neuron 4 cell bodies for all sympathetic and parasympathetic pathways Sympathetic Preganglionic neurons ○ Located in the lateral horn of the spinal cord (T1-L2) Ganglionic neurons ○ Located close to the spinal cord Parasympathetic Preganglionic neurons ○ Located in the cranial and sacral nerves Ganglionic neurons ○ Located away from the spinal cord 5. Discuss the neurotransmitters released by the ANS, including where they are released. Acetylcholine A ll preganglionic axons All parasympathetic postganglionic axons (cholinergic fibers) Sympathetic postganglionic axons innervating sweat glands, blood vessels in skeletal muscle, and external genitalia Norepinephrine Released by most sympathetic postganglionic axons (adrenergic fibers) 6. Define cholinergic and adrenergic fibers, and list their different types of receptors. Types of Fibers Cholinergic fiber ○ Release acetylcholine Adrenergic fiber ○ Release norepinephrine Cholinergic Receptors Nicotinic Receptors ○ On ALL ganglionic neurons ○ On adrenal medulla ○ Receptors on the motor end plate of skeletal muscle ○ ACh is always stimulatory Muscarinic Receptors ○ On all parasympathetic target organs ○ Eccrine sweat glands ○ Some blood vessels of skeletal muscles ○ Can be excitatory or inhibitory Adrenergic Receptors Alpha ○ N orepinephrine is usually excitatory Beta ○ Norepinephrine is usually inhibitory Extra Differences Between ANS Divisions Sympathetic ○ NE is slowly inactivated by reabsorption ○ NE acts more slowly and requires secondary messengers ○ NE is also released into the bloodstream by the adrenal medulla NE acts as a hormone here Parasympathetic ○ ACh is quickly inactivated by acetylcholinesterase ○ ACh acts directly and rapidly on effector organs 7. Describe ANS controls. Control of ANS Activity Reticular formation ○ Controls heart rate and respiratory rate when we wake up Hypothalamus ○ Modifies ANS activity Cerebral Cortex ○ Affects ANS through memory By seeing something that evokes emotion that we remember, the cortex affects HR etc Spinal Cord ○ Defecation and urination 8. Identify and explain some ANS disorders. Hypertension C aused by overactive sympathetic activity Causes constriction of blood vessels ○ As a result, blood pressure increases Increased blood pressure can cause damage to the blood vessels ○ Can lead to cardiac and renal problems ○ Blood vessels in the retina can burst resulting in the loss of vision Raynaud’s Disease With Raynaud’s Disease, blood vessels constrict in response to cold ○ Can lead to gangrene and frostbite Lecture Objectives: Special Senses 1 1. Describe the structure, location, and activation of the receptors for taste. Types of Papillae Fungiform Papillae ○ Taste buds ○ Cover the entire surface of the tongue ○ Gives the tongue its gripping texture Circumvallate Papillae ○ 7-12 of them ○ Located at the back of the tongue Structure of Taste Bud Gustatory cell ○ Actual sensory receptor ○ Reacts with chemicals and creates generator potentials Supporting cells ○ Support and nurture the gustatory cells Basal cells ○ Undifferentiated stem cells that produce more gustatory and supporting cells Taste pore ○ The opening of the taste bud Gustatory hairs ○ Extension of the gustatory cell that functions as the receptor that binds with chemicals ○ The actual reactive part of the gustatory cell ○ Determines taste Location of Taste Buds Taste buds are located in the mucosal papillae of the tongue ○ Also on soft palate, cheeks, pharynx, and epiglottis Activation of Taste Buds (Taste Physiology) Chemicals dissolve in saliva ○ Chemicals then bind to gustatory hairs This causes a generator potential If threshold is reached, an action potential occurs Gustatory cell membrane depolarizes ○ Salty/sour Direct mechanism of opening channels ○ Bitter/sweet/umami Use indirect mechanism to open channels Uses secondary messengers Neurotransmitter is released ○ Generator potentials are created Action potentials sent to the CNS through the cranial nerves ○ Signal first goes to medulla prior to thalamus Then it goes through the thalamus to the gustatory cortex Functions of Taste Trigger digestive reflexes ○ Causes activation of parasympathetic activity Gagging and Vomiting ○ Having an off taste can trigger gagging and vomiting to force the body to get rid of whatever was tasting like this ○ Extreme bitter flavors causes gagging and vomiting because nitrogenous compounds are toxic and taste bitter 2. Identify the basic taste sensations. Taste Sensations Sweet ○ Receptors bind to sugars and alcohols Salty ○ Binds to metal ions Sour ○ Binds to acids Bitter ○ Binds to alkaloids Ex: Nicotine and caffeine Aspirin is a non-alkaloid that is bitter Umami ○ Binds to the amino acid glutamate ○ Cooked meat flavor Had these receptors prior to us using fire to cook 3. Describe the structure, location, and activation of olfactory receptors. Structure of Olfactory Receptors Olfactory receptor cells ○ Sensory receptor Supporting cells ○ Supports and nourishes the olfactory receptor cells Basal cells ○ Divide and replace olfactory cells Olfactory cilia ○ Receptor cells have cilia to increase surface area of reception Filaments of olfactory nerve ○ Fasciculi of olfactory receptor cells ○ Fasciculi pass through the cribriform plate (holes in the ethmoid bone) and synapse with the olfactory bulb on Cranial Nerve 1. Location of Olfactory Receptors Olfactory epithelium is located in the mucosa on the roof of the nasal cavity Activation of Olfactory Receptors (Smell Physiology) G aseous molecules enter the nasal cavity when we breath Molecules dissolve in the epithelial mucous ○ For anything to be biologically active, it must be dissolved in solution Dissolved chemicals bind to receptor molecules on the olfactory cilia Receptor potential generated Action potential transferred through filaments Synapse with olfactory bulbs at glomeruli Action potentials sent to the CNS via olfactory tracts 1. Olfactory tract, thalamus, olfactory cortex ○ Interprets/identifies the smell 2. Olfactory tract, hypothalamus, amygdala and limbic system ○ Elicits an emotional response to an odor Functions of Smell Sympathetic activity ○ Bad chemicals cause fight or flight to initiate you to leave the location of the bad chemical Parasympathetic activity ○ Good chemicals can cause the mouth to water or the stomach to activate Sneezing and Coughing ○ Explosive pushes of air to rid the body of foreign/toxic molecules 4. List and explain the structure and function of the accessory eye structures. Accessory Eye Structures Eyebrows ○ Hair that covers the bony protuberance of the head ○ Functions to: Shade eyes; filter light Prevent salty sweat from entering the eyes Eyelids ○ Highly protective structure ○ Functions to: Cover eyes to filter light Blink Moves fluid over eyes to keep them lubricated ○ Eyelashes On eyelids Function to: Filter light Have root hair plexus associated with them ○ If something touches an eyelash, we blink to prevent something from entering the eyes Conjunctiva ○ Transparent mucous membrane that lines the eyelids and covers the surface of the eyeball ○ Two layers One layer covers the eye One layer covers the lid ○ Sac of fluid that works to wash and bathe the eye Lacrimal Apparatus
