Lectures 16-18A: The Visual System (PDF)

**Lectures 16-18A** **[THE VISUAL SYSTEM -- the eye and central]** **[pathway]**\ What is the human visual perception range? What is ultraviolet and infrared? The perception range is visible light, visual field is 150 degrees with one eye We cannot see infrared, past red is longer than 700 nm Ul...

**Lectures 16-18A** **[THE VISUAL SYSTEM -- the eye and central]** **[pathway]**\ What is the human visual perception range? What is ultraviolet and infrared? The perception range is visible light, visual field is 150 degrees with one eye We cannot see infrared, past red is longer than 700 nm Ultraviolet is shorter than violet ROY G BV -- 700 nm longest to 400 nm to shortest This structure allows light to enter into the eyes? Pupil is the opening where light enters the eyes Pupil sclera (white of the eye) iris (eye color) cornea (external surface of eye) optic nerve (bundle of axons from the retina) The axons come from the retina and exit through the optic disk which is also where we have a blind spot, and this area cannot process information *[Gross anatomy: ]* **Pupil**: opening that allows light to enter the eye and reach the retina, it appears dark due to the light absorbing pigments on the retina **Iris**: surrounds the pupil; pigmentation provides eye color; it contains two muscles that vary the size of the pupil, one makes the pupil smaller by contracting it and the other makes it larger **Cornea**: a glassy transparent external surface which covers the surface iris and pupil **Sclera:** the white of the eye which is continuous with the cornea **Optic nerve:** carries axons from the retina, exits the back of the eye, passes through the orbit, and reaches the base of the brain near the pituitary gland What types of lenses are used to correct for myopia and hyperopia?\ **Accommodation**, additional focusing power is provided by changing the shape of the lens **Emmetropia** -- ciliary muscles are relaxed, and the lens is flat, parallel light rays from a distant point source are focused sharply on the back of the retina and no accommodation needed **Myopia** -- eyeball is too long, and rays converge before the retina, cross, and again be imaged on the retina as a blurry circle; nearsightedness needs concave lenses **Hyperopia** -- the eye is too short from front to back, without glasses light rays are focused on a point behind the eye so farsightedness, need for convex lenses **Visual acuity -** distinguish two nearby points Describe the basic retinal circuit components. What is the only output from the retina? Photoreceptors to bipolar to ganglion Retinal processing is also influenced by lateral connections Most direct pathway is from **photoreceptors** to **bipolar cells** to **ganglion cells,** and will form the cranial nerve 2 axons of the optic nerve Besides these main cells, there are two types which influence the retinal processing: **Important**: - With one exception, only light-sensitive cells in the retina are the rod and cone photoreceptors; all other cells are influenced by light - **The ganglion cells are the only source of output from the retina** - Ganglion are the only retinal neurons that fire APs and this is essential for transmitting information outside the eye Laminated organization **Ganglion cell layer** -- inner most retinal layer, cell bodies of the ganglion cells **Inner plexiform layer** -- synaptic contacts between bipolar amacrine and ganglion cells **Inner nucleus layer** -- (contains neurons) bodies of bipolar, horizontal, and amacrine **Outer plexiform layer** -- PRs make synaptic contact with the bipolar and horizontal cells **Outer nuclear layer** -- (contains neurons) bodies of PRs Layer of PRs outer segments **Pigmented epithelium** -- maintenance of PRs and photopigments, absorbs any light that passe through the retina Where does phototransduction take place? PRs convert electromagnetic radiation to neural signals *[Rods]* In the dark rods are active, theres dark currents and sodium Is coming and theres presence of the cyclic GMP Sodium is fluxing into the rods, cell membrane is depolarized When rods are light exposed, rods become hyperpolarized because when light hits the rod its PRs will convert cyclic GMP into GMP and there will no longer be sodium influx Resting state in darkness - Rods are depolarized at about -30 mV due to a steady inflow of sodium ions through cGMP-gated channels - "dark current" is sustained by high levels of cGMP, produced in the PR by the enzyme guanylyl cyclase, which keeps sodium channels open Light activation 1. Light absorbed by rhodopsin 2. Retinal changes conformation which activates rhodopsin in a process called *bleaching* 3. Activated rhodopsin stimulates the G-protein *transducing* 4. Transducin activates the enzyme phosphodiesterase (PDE) 5. PDE reduces cGMP levels in the rod Result of light stimulation - Lower cGMP levels cause sodium channels to close, stopping the inflow of sodium - The MP hyperpolarizes, becoming more negative Signal amplification - Each rhodopsin activates many transducing - Each PDE breaks down multiple cGMP molecules - This biochemical cascade allows rods to detect single photons of light Sensitivity of Rods vs Cones - Rods are more sensitive because they contain more photopigment and amplify light responses more effectively - Which makes rods essential for vision in low light conditions *[Cones -- AFTER TRANSDUCING THE SIGNAL]* Cone function - In bright light, **rods become saturated**, so vision relies entirely on **cones** - Cones need more light to activate because their pigments are less sensitive than rods Phototransduction - Light reduces **cGMP levels**, closing sodium channels causing **hyperpolarization** - Difference lies in the **types of opsins**, which determine their sensitivity to specific Types and sensitivities - Short-wavelength or **blue** cones 430 nm - Medium wavelength or **green** 530 nm - Long wavelength or **red** cones 560 nm What are some of the differences in anatomy and functions between rods and cones? RODs -- long, cylindrical outer segment with many disks, these disks are free floating inside the rods since they have their own membrane - Large surface area for each disk, loaded with photopigments with photosensitive receptors CONEs -- shorter outer segments, tapering out and fewer disks, store light snesisitve molecules Rods are over 1000 times more sensitive to light than cones; rods used in the dark and cones used in the light Duplex retina -- cones process color information and rods are achromatic Cones are high visual acuity while rods are low and activated in dim light Fovea - Mostly cones no rods - Specialized for sharp central vision and color discrimination - Light reaches PRs directly, maximizing visual acuity Peripheral Retina - More rods than cones - Specialized for detecting dim light and motion, not fine detail or color Daylight (photopic vision) - Fovea excels in detail and color perception - Peripheral vision is less sharp and has poor color discrimination Low light - Peripheral retina dominates due to rod sensitivity to dim light - Central vision is ineffective in low light because rods are absent in the fovea Color perception -- perceived by cones; at night, rods are active, so perception is lost What are the three types of cones? S- cones (short): blue 420 nm M-cones: green 530 nm L-cones: red 560 nm Describe how light hyperpolarizes rod photoreceptors.\ In the dark rods are active, theres dark currents and sodium Is coming and theres presence of the cyclic GMP Sodium is fluxing into the rods, cell membrane is depolarized When rods are light exposed, rods become hyperpolarized because when light hits the rod its PRs will convert cyclic GMP into GMP and there will no longer be sodium influx - repeat What other cells in the retina, apart from photoreceptors, are also sensitive to light?\ Apart from rods and cones, **intrinsically photosensitive retinal ganglion cells (ipRGCs)** are light-sensitive cells in the retina. They contain the photopigment **melanopsin**, respond to ambient light (especially blue light at \~480 nm), and are involved in: - **Regulating circadian rhythms** by signaling the brain's biological clock. - **Controlling the pupillary light reflex**. - Supporting **non-image-forming vision** like mood and alertness. These cells are less sensitive than rods and cones and focus on ambient light detection rather than image formation What is On-center, Off-surround or Off-center, On-surround mean? The receptive field is an area of retina where light changes neuron's firing rate, these fields change in shape and stimulus specificity, connect indirectly to the ganglion cell Area within the field is divided into two regions: **ON center/OFF surround cell**: flashing a small bright spot in the center increases cells response. Flashing a spot in the surround region inhibits the cells response. There is little to no response to a full field spot of light which covers the cetner and surround because excitation in the center cancels the inhibition from the surround (lateral inhibition) **OFF center/ON surround**: opposite effect, the inhibition occurs by a small spot in the center and excitation from an annulus in the surround What are the differences between Parvo, Magno, and non-M/P retinal outputs? **Color-opponent cells**: some P and non-M/P are sensitive to differences in wavelength, the response to one color in the R field center is canceled by showing another color in the surround - Red versus green - Blue versus yellow Structure-function ganglion cell properties: **Magno (M-type):** larger, 5% of the population **Magnocellular** layers -- first two layers of LGN **Parvo (P-type):** smaller, 90% of the pop **Parvocellular** -- layers 3-6 **Non-M/P:** variety 5% M cells have larger R fields, they conduct AP more rapidly in the optic nerve and are more sensitive to low-contrast stimuli. They also respond to stimulation of their R field centers with a transient burst of APs P cells respond with sustained discharge as long as the stimulus is on Outside of the LGN, what other brain areas receive retinal input?\ [80% of everything that **goes into the LGN** comes from the **CORTEX**] [90% of everything that **comes out of the retina** goes to the **LGN**], give rise to axons that project to the primary visual cortex, where does the rest of the 10% go **Hypothalamus** -- direct projection play a role in synchronizing rhythms **Midbrain (pretectum)** -- control size of the pupil and certain eye movements **Midbrain (superior colliculus)** -- generating saccadic eye movement What causes 'tunnel vision'? Damage to optic chaism, lose peripheral vision Describe what happens when parts of the visual system are inactive. Damage to left optic nerve loss of the visual field like closing your left eye Damage to left optic tract loss of half of the right visual field What is a retinotopic map? **Retinotopy** is an organization whereby neighboring cells in the retina feed information to neighboring places in their target structures, the two-dimensional surface of the retina is mapped onto the two-dimensional surface of the subsequent structures Describe: thalamocortical projections, intracortical and lateral excitatory projections, and corticothalamic outputs from V1. **LAYER 4 OF THE NEOCORTEX** Thalamocortical projections - from in the LGN of the thalamus and terminate in V1 for cortical processing - Relay visual information from the retina (via LGN) to V1 for initial cortical processing. - Maintain retinotopic organization, ensuring that adjacent points in the visual field map to adjacent neurons in V1. - Magno LGN project to layer 4C-alpha - Parvo LGN project to layer 4C-beta - Konio LGN axons make synapses in layers 2 and 3 Intracortical and lateral -- connection between diff layers in V1 - IC: projects to layers 2,3, 4B cells project to other cortical areas - IC: layers 5 project to the superior colliculus and pons and 6 signal back to 4, recurrent processing - LE: Integrate information over larger regions of the visual field, helping process context, contours, and features that span multiple receptive fields. - Important for phenomena like **orientation selectivity** Corticothalamic -- projections from layers 5 and 6 - L5: Projects to subcortical structures, including the **superior colliculus**, which is involved in eye movements and attentional shifts - L6: sends feedback to LGN - shaping how sensory input is processed and influencing subsequent visual perception. Why does long-term visual deprivation causes reorganization of the cortical connections? Describe orientation and direction-selectivity. **Orientation** -- property of cell in the V1 which responds to a limited range of stimulus orientations, best response to a spot of light matched in size to the R field center **Direction** -- cells in V1 which respond only when stimuli move within a limited range of directions, respond when a bar of light at the optimal orientation moves perpendicular to the orientation in one direction but no the opposite Describe two techniques that can be used to image neuronal activity in the cortex using dyes and one without any dyes. **Image intrinsic signals -** When neurons are active, blood volume and oxygenation change to a degree correlated with neural activity. Blood flow and oxygenation influence the reflection of light from brain tissue, and reflectance changes can be used to indirectly assess neural activity. Light is projected onto the brain, and a video camera records the reflected light. Thus, when intrinsic signals are used to study brain activity, membrane potentials for action potentials are not directly measured. **Voltage-sensitive dye -** applied to the surface of the brain. The molecules in the dye bind to cell membranes, and an array of photo detectors or a video camera records changes in the optical properties that are proportional to variations in membrane potential **CALCIUM IMAGING** What is a cortical module and what are its key structures?\ A 2x2 chunk of striate cortex, processes information about a small patch of the visual field Each cortical module contains ocular dominance columns, orientation column, and cytochrome oxidase blobs (mitochondrial enzyme used for cell metabolism; blobs are stained pillars and each blob centered on an ocular dominance in layer 4 receive koniocellular inputs from LGN) Describe two major visual streams outside of V1: their projections and the dominant functions they are responsible for. **Dorsal Stream** -- serve analysis of visual motion and visual control of action - Begins in V1 and extends to - **2** and **V3** (initial processing of motion and spatial attributes). - **MT (V5):** Processes object motion. - **MST:** Processes complex motion patterns (e.g., radial and circular motion). - **Parietal Cortex:** Integrates visual information with spatial and motor systems for navigation and action. - **Dominant Functions:** - **Motion Perception:** - Detects object movement, speed, and direction. - Neurons in MT are specialized for analyzing motion and are highly direction-selective. - **Spatial Awareness:** - Helps locate objects in space and understand their spatial relationships. - **Visually Guided Actions:** - Assists in coordinating movements, such as reaching for or tracking objects. - Output -- parietal lobe Ventral stream - Begins in V1 and extends to: - V2 and V3 processing of form and color - V4: focuses on color and shape perception - Inferior temporal cortex (IT): analyzes object features - Fusiform gyrus: contains fusiform face area for facial recognition - Dominant functions: - Object recognition - IT - Color perception -- V4 - Visual memory -- stores and compares visual information - Output -- temporal lobe **Lecture 18B** **[THE AUDITORY SYSTEM]** What is the human hearing range? What is ultrasound and infrasound? Sound goes into the ear middle ear inner ear auditory nerve (CN 8) projects to cochlear nuclei inferior colliculus MGM of thalamus primary auditory cortex Human hearing range is 20 Hz to 20000 Hz **Ultrasound** -- above 20 kHz, high frequencies which many animals can hear **Infrasound** -- below 20 Hz, lower than what humans can hear What is the anatomy of the middles ear and the function of ossicles and muscles? Outer ear funnels sound to the **middle ear,** an air-filled cavity containing the first elements which respond to sound - **Tympanic membrane**: conical shape with its point extending into the cavity of the middle - **Ossicles**: (1) **malleus**, attached to the tympanic; (2) **incus**, rigid connection with 1 and forms a flexible connection with; (3) **stapes**, the flat bottom portion of it is called the foot plate and moves in and out like a piston at the **oval window** - Those movements transmit vibration to the fluids of the cochlea in the inner ear - Two tiny muscles attached to the ossicles - **Tensor tympani muscles:** anchored to bone in the cavity at one end of the middle and attaches to the malleus at the other end - **Stapedius muscles:** extend from a fixed anchor of bone and attaches to the stapes When these muscles contract, the chain of ossicles become rigid, and sound is diminished in the inner ear; onset of loud sound triggers a response which causes the muscles to contract called **attenuation reflex** - Greater pressure at oval window than tympanic membrane moves fluid - [Function]: adapts ear to loud sounds, protects inner ear, enables us to understand speech better Air in the middle ear is continuous with air in the nose via **eustachian tube**, typically a valve keeps it closed - People blow their noses to pop their ears and equalize the pressure - Common sight of infection Anatomy of the inner ear Cochlea -- spiral shape - At the base there are two membrane-covered holes: - Oval window - **Round window** - Contains three small parallel chambers (**scalae,** wrap around inside the cochlea**)** are separated by Reissner's membrane (scala vestibuli from scala media) and the **basilar membrane** (scala tympani from scala media) - On the **BMembrane,** sits the **organ of corti,** which contain auditory receptor neurons -- base of the organ of Corti - Hanging above this organ is the **tectorial membrane --** roof over the structure - at the base of cochlea; Media is closed off, Vestibuli meets the oval window, tympani meets the round window - fluid in the vestibuli and tympani is called **perilymph,** similar to ionic content LOW K HIGH Na - media is filled with **endolymph,** unusual extracellular fluid LOW NA HIGH K Where is endolymph located? What ion the highest concentration in the endolymph? - Found in the scala media, Low in sodium and high in potassium - Stria vascularis (the endothelium lining one wall of the media and contacting the endolymph) absorbs sodium from and secretes potassium into endolymph - Because of the ionic content differences and permeability of Reissner's membrane, it has an electric potential of about 80mV more positive than perilymph; this is called the **endocochlear potential** What's up in the organ of Corti? - Consists of hair cells, rods of Corti, and supporting cells - Auditory receptors are called **hair cells** since each one has a **stereocilia** extending from the top, HAIR CELLS ARE NOT NEURONS BUT RATHER ARE SPECIALIZED EPITHELIAL CELLS - Hair cells between modiolus and rods of Corti are called **INNER HAIR CELLS** - Those further out than the rods are **OUTER HAIR CELLS** - Reticular membrane between the basil and tectorial holds onto the hair cells - The auditory nerve is a branch of the **auditory-vestibular nerve (CN 8),** which projects to the cochlear nuclei in the medulla What is a 'tip link' and how does it regulate potassium channels on hair cell cilia? - In transduction channels, a stiff filament connects each to the upper wall of the adjacent cilium - When the cilia are pointing up, the tension on the link causes the channel to be opened, allowing a small amount of K+ to move from the endolymph into the hair cell - Displacement of the cilia in one direction increases tension on the tip link, increasing the rate of channel openings and the amount of inward K+ current - Displacement in the opposite direction relieves tension on the tip link which causes the channel to close reducing K+ movement - The entry of K into the hair cell causes depolarization, which in turn activates voltage-gated calcium channels What function do motor proteins serve in the outer hair cells? - More than 95% of the spiral ganglion neurons communicate with the relatively small number of inner hair cells, and less than 5% receive synaptic input from the more numerous outer hair cells - one spiral ganglion fiber receives input from only one inner hair cell: moreover, each inner hair cell feeds about 10 spiral ganglion neurites. The situation is the opposite with outer hair cells. Because they outnumber their spiral ganglion cells, one spiral ganglion fiber synapses with numerous outer hair cells outer hair cells act like tiny motors which amplify movement of the B. membrane cochlear amplifies; there are two types of mechanism which contribute: 1. **motor proteins** -- change the length of the hair cells which respond to sound with both a receptor potential and change in length - The motor is driven by the receptor potential and doesn't use ATP - its primary motor is a protein called prestin, which are tightly packed into the membranes of the outer bodies and are needed so that they move in response to sound 2. Myosin located in the hair bundles and attached to the end of the tip links, they enhance the movement in response to weak sounds The auditory component of cranial nerve VIII has most of it connections to these types of hair cells? The auditory nerve has axons of neurons located in the spiral ganglion; the ganglion neurons which are first in the auditory pathway to fire APs provide all the info sent to the brain Vast majority of info leaving the cochlea comes from the inner hair cells When does auditory information become biaural along its projections to the cortex? - Each cochlear nucleus gets input from just one ear so its ipsilateral; yet all other auditory nuclei in the brain stem receive input from both ears so they're binaural - This explains the fact that the only way by which brain stem damage can create deafness in one ear is if a cochlear nucleus (or auditory nerve) on one side is damaged What is a tonotopic map? They exist on the basilar membrane and within each auditory relay nuclei, the MGN and auditory cortex\ Systematic organization of sound frequency within the auditory structure What is the difference between conduction vs sensory neural hearing impairment? How can ears ring and otoacoustic measurement determine hearing loss? How do cochlear implants take advantage of the tonotopic map? Auditory pathways: Spiral ganglion -- (auditory nerve) ventral cochlear nucleus + superior olive -- (lateral lemniscus) inferior colliculus MGN Auditory cortex - Neural signals travel from the spiral ganglion to the auditory cortex - Cells in the ventral cochlear nucleus send axons that project to the **superior olive binaurally** - axons ascend in the **lateral lemniscus** and innervate the **inferior colliculus** of the midbrain - all ascending auditory pathways converge into the colliculus - The neurons then send axons to the **MGN** **of the thalamus** which projects to **auditory cortex** Projections and brain stem nuclei contribute to the pathways There is feedback in the auditory pathways Response properties of neurons? - Characteristic frequency -- frequency at which a neuron is more responsive (cochlea to cortex) - Response properties are more complex and diverse beyond the brain stem. - Binaural neurons are present in the superior olive. - Encoding info about stimulus intensity - Firing APs only in response to wound within limited frequency range, due to hair cells excitement by deformations of the basilar membrane Primary auditory cortex: - Axons leaving MGN project to auditory cortex via internal capsule in array called acoustic radiation. - Structure of A1 and secondary auditory areas: similar to corresponding visual cortex areas - Layer 1 contains cell bodies - Layers 2 and 3 contain small pyramidal cells - Layer 4 where MGN axons terminate, is of densely packed cells - Layers 5 and 6 are pyramidal cell Neuronal sensitivity: Cells closest to the base of the cochlea are most responsive to high frequency Those closest to middle are responsive to the median frequency Closest to the top are responsive to the lowest Hz - Ex: - Sound from the left side initiates activity in the left cochlear nucleus which is sent to the superior olive - Sound reaches the right ear initiating activity, while the first impulse has traveled farther along its axon - Both impulses reach olivary neuron 3 at the same time and summation of the synaptic potentials and generates a AP Auditory impairments: - **Conduction deafness** - Loss due to disturbance in the conduction of sound from outer ear to cochlea - Treated surgically - **Nerve deafness** - Loss of either neurons in auditory nerve or hair cells in cochlea - Tumors affecting the inner ear - If loss of either is definite, deafness is absolute - Partial loss, fixed by hearing aid to amplify sound for remaining hair cells - Hearing loss is bilateral and auditory is intact, cochlear implants help **Lecture 19** **[SOMATOSENSORY SYSTEM]** Hairy skin and glabrous (hairless) skin have a variety of sensory receptors within the dermal (inner) and epidermal (outer) layers - Each receptor has an axon, except for free nerve endings, all of them have associated on-neural tissues Functions of skin - Protects from the environment. - Prevents evaporation of body fluids - Provides direct contact with world MECHANORECEPTORS - Epidermal - Merkel's Disk -- consist of nerve terminal and a flattened no-neural epithelial cell (Merkel cell) - Free nerve ending - Dermis - Epidermal-dermal border - Meissner's corpuscle -- 1/10 the size of Pacinian and located in the ridges of glabrous skin - Hair follicle receptor - Pacinian corpuscle -- largest, lies deep in the dermis, about 2500 - Ruffini's Ending -- found in both hairy and glabrous skin smaller than Pacinian - Krause end bulbs, which lie in the border regions of dry skin and mucous membrane, the nerve terminals look like knotted balls of string Imagine rubbing your fingertips across a pane of smooth glass and then across a brick. What kinds of skin receptors help you distinguish between the two surfaces? As far as your somatic sensory system is concerned, what is different about the two surfaces? Smooth glass might produce a stimulus with no vibrations and no changes in pressure, whereas a brick has a rough surface that changes rapidly as the finger runs across it. Because these surface changes are small, we might expect that smaller receptors, closer to the surface of the skin, to be important in detecting the changes. Furthermore, because we want to sense the rapidly changing nature of the brick vs. the glass, we would suspect that the Meissner\'s corpuscles, with small receptive fields and rapidly adapting responses would show differing activity in both cases. Merkel\'s disks, being close to the surface, and Pacinian corpuscles, which are also rapidly adapting may be involved as well. What is a two-point discrimination test?\ Two point discrimination is the ability to discern that two nearby objects touching the skin are truly two distinct points, not one. It is often tested with two sharp points during a neurological examination and is assumed to reflect how finely innervated an area of skin is. How are receptive field sizes and adaptation dynamics differ for the nerve endings? A diagram of a rectangle Description automatically generated Mechanosensitive ion channels: - mechanoreceptors of the skin all have unmyelinated axon terminals, and the membranes of these axons have mechanosensitive ion channels that convert mechanical force into a change of ionic current - stimuli may trigger release of second messengers - specific types of channels in most somatic sensory receptors still unidentified \(a) Some membrane ion channels are sensitive to stretching of the lipid membrane; tension in the membrane directly induces the channel to open and allow cations to flow. \(b) Other ion channels open when force is applied to extracellular structures linked to the channels by peptides. \(c) Mechanically sensitive channels may also be linked to intracellular proteins, especially those of the cytoskeleton; deformation of the cell and stress on its cytoskeleton generate forces that regulate channel gating What are the four types of primary sensory afferents and their main functions? Which ones are fastest and largest, slowest and smallest? **Primary afferent axons** -- axons bringing info from the somatic receptors to the spinal cord or brain stem They enter the spinal cord through dorsal root and they lie in the dorsal root ganglia **A α** -- myelinated, largest, fastest, proprioceptors of skeletal muscle **A β** -- myelinated, mechanoreceptors of skin, mediates touch sensations **Aδ** -- myelinated, pain and temperature **C** -- unmyelinated, smallest, slowest, temperature pain and itch  Spinal Cord: - attached to the brain stem - most PNs communities with CNS via the spinal cord - 30 spinal segments divided into 4 parts - Cervical 1-8 - Thoracic 1-12 - Lumbar 1-5 - Sacral 1-5 What are dermatomes and how do shingles highlight them? Area of skin innervated by the right and left dorsal roots of a single spinal segment One to one correspondence with spinal segments - When a dorsal root is cut its corresponding on that side of the body doesn't lose sensation - To lose all sensation in one dermatome, three adjacent dorsal roots must be cut Skin innervated by the axons of one dorsal root is plainly revealed by a condition called **SHINGLES,** where all neurons of a single dorsal root ganglion become infected with a virus - reactivated virus increases the excitability of the sensory neurons, leading to very low thresholds of fi ring as well as spontaneous activity Dorsal Column-medial lemniscal pathway Pathway serving touch to the brain Spinal gray matter -- pathway of A β axons into the ipsilateral dorsal column - dorsal horn - receives sensory inputs from primary sensory neurons - plays role in initial processing and integration of sensory information before it ascends or connects to local reflex circuits - intermediate zone - contains interneurons involved in integrating sensor input and coordinating reflexes and motor output - may relay information to higher centers in the brain or facilitate communication between sensory and motor pathways - ventral zone (ventral horn) - associated with motor function - contains motor neurons whose axons exit the spinal cord via ventral roots to innervate muscles - less involved in processing tactile sensory info but essential for reflexive motor responses **Dorsal Columns**: - Carry tactile and proprioceptive information toward the brain. - Composed of primary sensory axons and second-order axons from neurons in spinal gray matter. **Dorsal Column Nuclei**: - Located at the junction of the spinal cord and medulla. - Primary axons terminate here. - This is where signals are still represented ipsilaterally. **Decussation**: - Axons from the dorsal column nuclei cross to the opposite side of the medulla. - This creates contralateral representation in the somatic sensory system (right-side sensations are processed by the left brain and vice versa). **Medial Lemniscus**: - A white matter tract where axons ascend through the medulla, pons, and midbrain. - Axons synapse in the **ventral posterior (VP) nucleus** of the thalamus. **Thalamus to Cortex**: - VP nucleus neurons project to the primary somatosensory cortex (S1). - This completes the processing pipeline for tactile information. How is somatic sensory information form the face area is being processed? Which cranial nerve is involved? - Large mechanoreceptors activated by touch **Trigeminal Touch Pathway** - Face sensation supplied by cranial nerve 5, trigeminal nerves, which enter the brain at the pons - Twin nerves, one on each side, which breaks into 3 peripheral nerves that innervate the face, mouth, the outer 2/3s of the tongue, and dura mater covering the brain - The nerve synapses on to second-order neurons in the ipsilateral trig nucleus, which is analogous to a dorsal column nucleus - The axons then decussate and project into the medial part of the VP nucleus of the thalamus - Information is relayed to the somatosensory cortex. What is homunculus? A somatic map, generated by electrical simulation and neuronal recordings, they roughly resemble a body with its legs and feet at the top of the postcentral gyrus and its head at the opposite lower end It may be discontinuous and disproportional What is 'barrel cortex'? How can one demonstrate that blocking glutamate transmission can stop activation of one of the barrels?\ Area of the S1 in rodents that processes tactile information from their whiskers - Each whisker on a rodent's snout is represented by a distinct group of neurons in the cortex, forming a "barrel" structure - These barrels are part of the system and as a model for studying neural circuits, sensory processing, and plasticity Can somatic sensory cortical map get reorganized with a loss of a digit or an overly extensive use of a digit? - remove digits or overstimulate, examine the map before and after - Cortical structure and activity maps are dynamic - Ex: the cortex originally devoted to the amputated digit now responded to stimulation of the adjacent digits, so there's been a major rearrangement of the circuitry underlying cortical somatotopy - Ex: representation of the stimulated digits had expanded in comparison with the adjacent, unstimulated ones What are some of the chemicals that mediate pain? **Nociceptors**, the free, branching, unmyelinated nerve endings that signal that body tissue is being damaged or is at risk of being damaged - Selective activation of nociceptors can lead to the conscious experience of pain Nociceptors: transduction of pain - Ion channels opened by: - Strong mechanical stimulation, temperature extremes, oxygen deprivation, chemicals - Substances released by damaged cells - Proteases (-\> bradykinin), ATP, K^+^ ion channels - Histamine - Heat-sensitive high temps activates leading to pain What are first and second pains? What is hyperalgesia? 1. **First Pain**: - **Characteristics**: Sharp, fast, and localized. - **Fibers Involved**: Mediated by **Aδ fibers**, which are myelinated and conduct signals quickly. - **Stimulus**: Typically mechanical or thermal stimuli, such as stepping on a sharp object or touching something hot. 2. **Second Pain**: - **Characteristics**: Dull, throbbing, and diffuse. - **Fibers Involved**: Mediated by **C fibers**, which are unmyelinated and conduct signals more slowly. - **Stimulus**: Associated with prolonged pain and inflammatory processes. **Hyperalgesia** - **Definition**: An increased sensitivity to pain, where stimuli that would normally be mildly painful become significantly more painful. - **Types**: - **Primary Hyperalgesia**: Occurs at the site of injury. - **Secondary Hyperalgesia**: Occurs in surrounding uninjured tissue. - **Mechanisms**: - Release of inflammatory mediators (e.g., prostaglandins, bradykinin, histamine) sensitizes nociceptors. - Changes in the central nervous system (e.g., increased synaptic strength in spinal cord neurons) amplify pain signals. **Inflammatory Soup** -- released when skin is damaged - NTs, peptides, lipids, proteases, etc - Together they trigger **inflammation** - Certain components can modulate the excitability of nociceptors **Types of Nociceptors:** Nociceptors are specialized nerve endings that respond to painful stimuli, and they are classified based on the type of stimulus they detect: 1. **Polymodal Nociceptors**: - Respond to mechanical, thermal, and chemical stimuli. 2. **Mechanical Nociceptors**: - Selectively respond to strong pressure. 3. **Thermal Nociceptors**: - Respond to extreme temperatures, such as burning heat or extreme cold. 4. **Chemical Nociceptors**: - Respond to chemicals like histamine and other pain-inducing substances. Nociceptors are found throughout the body, including in the skin, bone, muscle, organs, blood vessels, and heart, but are absent in the brain (except for the meninges). They transmit pain signals via **C fibers** (unmyelinated) and **Aδ fibers** (lightly myelinated). Itch sensation: - Disagreeable sensation that induces desire or reflex to scratch - Usually brief, minor annoyance---can become chronic, debilitating condition - Triggered by skin conditions or non-skin disorders - Similarities to and differences from pain - Signaling molecules and receptors mediating itch not yet identified What is the major difference between the ascending spinothalamic and dorsal lemniscal pathways? **Ascending Spinothalamic Pathway**: - **Function**: Carries pain, temperature, and crude touch information. - **Pathway**: - Nociceptors detect stimuli and send signals via **C fibers** and **Aδ fibers** to the **dorsal horn** of the spinal cord. - Second-order neurons synapse in the **dorsal horn** and cross to the opposite side (decussate). - These fibers ascend through the **spinothalamic tract** in the spinal cord to the **thalamus**, and then to the **somatosensory cortex**. **Dorsal Lemniscal Pathway**: - **Function**: Carries information about touch, vibration, and proprioception. - **Pathway**: - Sensory signals travel via **Aβ fibers** to the **dorsal columns** of the spinal cord. - These fibers ascend ipsilaterally (on the same side) until they reach the **medulla**, where they synapse in the **dorsal column nuclei**. - The second-order neurons cross over (decussate) and ascend through the **medial lemniscus** to the **thalamus**, and then to the **somatosensory cortex**. **Major differences** - The **spinothalamic pathway** primarily transmits **pain**, **temperature**, and **crude touch** sensations, and its fibers cross to the opposite side of the spinal cord at the **dorsal horn**. - The **dorsal lemniscal pathway** transmits **fine touch**, **vibration**, and **proprioception** information, and its fibers ascend **ipsilaterally** (same side) until they reach the **medulla**, where they decussate. Regulation of Pain - Afferent Regulation - pain evoked by activity in nociceptors can also be reduced by simultaneous activity in low-threshold mechanoreceptors (A beta fibers) - Bottom-up: modulation of pain through mechanisms that begin at the level of the **sensory input** and travel **upward** through the nervous system. This process focuses on the initial detection and transmission of painful stimuli from peripheral nociceptors to the brain. - Gate theory: certain neurons of dorsal horns, which project an axon up the spinothalamic tract are excited by both large-diameter sensory axons and unmyelinated pain axons - Descending regulation - Top-down: **Top-down pain regulation** refers to the modulation of pain that originates in the **brain** and travels **downward** through descending pathways to influence the processing of pain signals in the spinal cord and periphery. This is an example of how the central nervous system actively suppresses or amplifies pain based on context, attention, and emotional state. - Endogenous opioids: Natural peptides (e.g., endorphins, enkephalins) that bind to μ, κ, and δ receptors to inhibit pain signals. They act in the spinal cord, brainstem, and periphery to reduce neurotransmitter release and hyperpolarize neurons. Basis for opioid medications but carry a risk of dependency. - Endocannabinoids: Lipid-based molecules (e.g., anandamide, 2-AG) that bind to CB1 (CNS) and CB2 (immune system) receptors. They suppress pain signals, reduce inflammation, and activate descending inhibitory pathways. Non-addictive and form the basis for cannabis-based pain treatments. - **Difference**: Opioids primarily inhibit central pain processing, while endocannabinoids also target inflammation and peripheral pain pathways. Both systems interact and can work synergistically for pain relief. What is a top-down modulation of pain? What areas of the brain are involved? - Higher brain regions, like the cortex, actively influence and can decrease the perception of pain signals coming from the body by sending descending inhibitory signals to the spinal cord, essentially \"gating\" the pain signal before it reaches the brain - Key areas involved in this process include the periaqueductal gray (PAG) in the midbrain and the rostral ventromedial medulla (RVM) in the brainstem, which then project to the spinal cord to modulate pain transmission What receptors are responsible for thermal sensations? Is temperature pathway similar to pain pathway? How can we distinguish between the two? - Thermoreceptor TRP channels - Yes they are similar to each other - Cold receptors are coupled to Adelta and C fibers - Warm receptors are couped to only C fibers - Axons of second-order neurons decussate - They both utilize the spinothalamic tract BUT distinguished by the specific TRP channels activated and intensity of the stimulus, with extreme temps triggering pain receptors alongside thermoreceptors Posterior Parietal Cortex: - Involved in somatic sensation, visual stimuli, movement planning, attentiveness - Damage to posterior parietal areas causes neurological disorders. - Agnosia -- inability to recognize objects even though simple sensory skills are normal - Astereognosia -- cannot recognize common objects by feeling them although their touch sense is normal - Neglect syndrome - "The Man Who Fell Out of Bed" - Parietal cortical lesions - Part of the body or visual field is ignored or suppressed **Lecture 20-22** Describe these three syndromes (Capgras delusion -- Phantom Limb -- Synesthesia) with the following details in mind: causes; parts of the brain involved; mechanisms; testing or healing devices used by Dr. Ramachandran - **Capgras Delusion** - Result of damage to the fusiform gyros, found inside the inner surface of the temporal lobes, is called the face area in the brain as it helps you to recognize people's face. - Someone believes heir loved ones or others they know have been replaced with imposters. - Psychiatric interpretation: Oedipus complex of Freud, at the developmental stage sons produce a sexual desire for their mother as they don't recognize her to be their mother - Investigated the phenomenon through detailed interviews and observations, highlighting the disconnect between visual recognition and emotional response, sometimes using facial recognition tests to assess the severity of the delusion. - psychiatric disease in which a person endures a delusion that a friend, spouse, parent, or other close family members (or pet) has been substituted by an indistinguishable impostor. People experience Capgras syndrome by a dilemma within the brain, like atrophy, lesions, or cerebral dysfunction. - **Phantom Limb** - Still feeling the presence of a missing limb or other parts of the body - To help patients who suffer from phantom paralysis or vivid sensations, create a mirror box which will cause sensory conflict that tricks the brain into thinking the phantom part is there and moving - that phantom limb pain might be generated by changes in the brain - **Synesthesia** - Mingling of senses, people muddle up their senses and its genetic - Common in creative individuals - An abnormal gene which causes abnormal cross wiring of the color are and number area which are next to each other in the fusiform gyrus - Used various tests to explore the nature of synesthesia, including asking individuals to describe the colors they see when hearing words or sounds, and examining the consistency of their synesthetic experiences Lecture22: imaging brain rhythms and epilepsy **Imaging Techniques in Neuroscience** - **CLARITY Method:** - A technique that makes brain tissue transparent by replacing light-absorbing lipids with a water-soluble gel. - Enables visualization of deep brain structures using fluorescent proteins like GFP (green fluorescent protein). - **Magnetic Resonance Imaging (MRI):** - Non-invasive imaging technique used to visualize internal structures of the brain. - Detects changes in regional blood flow and metabolism. - **Positron Emission Tomography (PET):** - Functional imaging technique that measures metabolic processes in the brain. - Utilizes radioactive tracers to visualize areas of high glucose consumption. - **Functional MRI (fMRI):** - Measures brain activity by detecting changes associated with blood flow. - Active neurons consume more oxygen, leading to detectable changes in blood flow. - **Diffusion Tensor Imaging:** - An MRI-based technique that maps the diffusion of water molecules in brain tissue. - Useful for visualizing white matter tracts and understanding connectivity within the brain. - **Optical Imaging:** - Involves recording changes in light reflection from brain tissue to assess neural activity. - Can utilize voltage-sensitive dyes or intrinsic signals related to blood volume and oxygenation. - **Voltage-Sensitive Dye Imaging:** - Uses dyes that bind to cell membranes to record changes in membrane potential. - Provides precise information about the electrical activity of neurons at cellular resolution. **Neuroscience Applications** - **Overview:** Neuroscience applications encompass various techniques and studies aimed at understanding brain function and treating neurological disorders. Key methods include deep brain stimulation (DBS), neural coding, and the analysis of cortical dynamics through clinical case studies and imaging technologies. - **Deep Brain Stimulation (DBS):** - A neurosurgical procedure used to treat movement disorders like Parkinson\'s disease. - Involves implanting electrodes in specific brain regions to modulate abnormal activity. - Effective in reducing symptoms such as tremors and rigidity. - Utilizes imaging techniques (e.g., PET, MRI) for precise electrode placement. - **Clinical Case Studies:** - Provide insights into individual patient responses to treatments like DBS. - Highlight variations in brain activity patterns across different conditions (e.g., depression). - Use advanced imaging techniques to visualize changes in brain function pre- and post-intervention. - **Neural Coding:** - Refers to how information is represented in the brain by neuronal activity. - Investigates the relationship between stimulus features and neural responses. - Essential for understanding sensory processing and cognitive functions. - **Cortical Dynamics:** - Examines the temporal and spatial patterns of neural activity in the cortex. - Explores how networks of neurons interact during various tasks. - Techniques like voltage-sensitive dye imaging and fMRI are employed to study these dynamics. **Challenges in Brain Imaging** - **Overview:** Brain imaging techniques, particularly functional MRI (fMRI), face several challenges including limitations in spatial and temporal resolution, patient experience during procedures, and the need for non-invasive methods. These factors impact the effectiveness and applicability of brain imaging in clinical and research settings. - **Spatial Resolution:** - Current fMRI resolution is approximately 3mm³. - Need for improved spatial resolution to capture finer details of brain activity. - Techniques like genetically encoded voltage indicators (GEVIs) can provide insights at multiple spatial scales. - **Temporal Resolution:** - Single images from fMRI can be obtained in seconds, but capturing rapid neural events remains challenging. - The ability to track changes over time is crucial for understanding dynamic brain processes. - **Patient Experience:** - Comfort and anxiety levels during imaging can affect data quality. - Non-invasive techniques are preferred to minimize discomfort and risk. - Enhancements in patient experience can lead to better cooperation and more reliable results. - **Non-Invasiveness:** - fMRI is a non-invasive and non-irradiating technique, making it suitable for repeated use. - Importance of developing additional non-invasive methods to study brain function without surgical intervention or exposure to harmful radiation. **Brain Activity Measurement** - **Overview:** Brain activity measurement involves various imaging techniques to assess neuronal function and metabolism. These methods detect changes in blood flow, oxygen consumption, and intrinsic signals related to neural activity, providing insights into brain function during different tasks or stimuli. - **Static vs Functional Imaging:** - **Static Imaging:** Provides a snapshot of brain structure. - **Functional Imaging:** Measures dynamic processes like blood flow and metabolic changes associated with neuronal activity. - **Intrinsic Activity Imaging:** - Measures changes in: - Oxygen levels - Blood flow - Metabolism - Ions (e.g., calcium in neurons vs glia) - Voltage and receptor movement - **Neuronal Activity:** - Active neurons require more glucose and oxygen, leading to increased blood flow to active regions. - Techniques used to detect these changes include optical imaging and electrophysiological recordings. - **Blood Flow and Metabolism:** - Changes in blood flow and oxygenation can be assessed through light reflection from brain tissue. - Optical imaging captures reflectance changes correlated with neural activity, allowing for indirect assessment of membrane potentials. - **Oxygen Consumption:** - Reflects the metabolic demands of active neurons. - Important for understanding energy utilization in the brain during various activities. - **Techniques Overview:** - **Optical Imaging:** Uses voltage-sensitive dyes to measure changes in optical properties related to membrane potential. - **Positron Emission Tomography (PET):** - Utilizes radioactively labeled 2-Deoxyglucose (2-DG) to track glucose consumption by active neurons. - Limitations include radioactivity exposure and spatial resolution of 5-10 mm³. Lecture: Epilepsy and brain rhythms **Electroencephalogram (EEG)** - **Overview:** An electroencephalogram (EEG) is a noninvasive and painless method for recording electrical activity in the brain. It uses electrodes placed on the scalp to measure voltage fluctuations, helping diagnose neurological conditions and study brain rhythms. - **Recording Techniques:** - Electrodes are placed on the scalp with low-resistance connections. - Connected to amplifiers and recording devices to capture brain activity. - Measures voltage fluctuations in the range of tens of microvolts. - **Voltage Fluctuations:** - Reflect synchronous activity of underlying neurons. - Electrode pairs measure different brain regions\' activities. - **Amplitude Measurement:** - The amplitude of EEG signals indicates the level of neuronal synchronization. - Higher amplitudes suggest greater synchronized activity among neurons. - **Categorization of Rhythms:** - EEG patterns categorized by frequency (Hz) and amplitude: - **Alpha Waves (8-10 Hz):** Associated with relaxed wakefulness. - **Beta Waves (13-30 Hz):** Indicate intense mental activity. - **Delta Waves (0.5-4 Hz):** Present during deep sleep or drowsiness. - **Theta Waves (4-7 Hz):** Linked to drowsiness or potential pathology. - **Gamma Waves (40 Hz):** Associated with higher cognitive functions. - **EEG Patterns:** - Characterized by specific frequencies and amplitudes. - Essential for studying various states of consciousness, including sleep and wakefulness. - Useful in diagnosing conditions like epilepsy and sleep disorders. **Brain Rhythms** - **Overview:** Brain rhythms are the electrical oscillations produced by neuronal activity in the brain, reflecting various states of consciousness and behavior. They play a crucial role in processes such as sleep, attention, and cognitive functions, and can be measured using techniques like EEG. - **Electrical Rhythms:** - Range of frequencies categorized into different types (e.g., alpha, beta, theta, delta). - Each rhythm correlates with specific behavioral states or cognitive functions. - **EEG Recording:** - Electroencephalogram (EEG) is the classical method for recording brain rhythms. - Essential for studying sleep patterns and diagnosing neurological conditions like epilepsy. - Characterized by amplitude and frequency patterns associated with different mental states. - **Circadian Rhythms:** - Biological processes that follow a roughly 24-hour cycle influenced by the brain\'s internal clock. - Regulate physiological functions such as sleep-wake cycles, hormone release, and body temperature. - **Functions of Brain Rhythms:** - Correlate with particular behavioral states (e.g., relaxation, alertness). - May facilitate coordination among different brain regions, enhancing perceptual integration. - Some rhythms may not have direct functions but could be by-products of neural connectivity. - **Measurement Techniques:** - EEG provides generalized activity measurement of the cerebral cortex. - Useful for research and clinical diagnosis of sleep disorders and other neurological issues. **Neural Mechanisms** - **Overview:** Neural mechanisms refer to the processes and activities within the brain that govern rhythmic behaviors and functions. These include synchronous rhythms, pacemaker activity, and collective behavior in neural networks, which are essential for various physiological states and cognitive functions. - **Synchronous Rhythms:** - Rhythmic activities can be led by a pacemaker or arise from collective behavior. - Important for coordinating activity across different regions of the nervous system. - Facilitate binding together perceptual experiences through synchronized oscillations. - **Pacemaker Activity:** - Certain neurons act as pacemakers, generating rhythmic electrical impulses. - Essential for maintaining consistent brain rhythms during various states (e.g., sleep, wakefulness). - Contributes to the regulation of circadian rhythms and other physiological functions. - **Collective Behavior in Neural Networks:** - Rhythms emerge from interactions among large groups of interconnected neurons. - Can lead to complex behaviors and processing capabilities. - May result in rhythms that do not have direct functions but are by-products of network dynamics. - **Functions of Brain Rhythms:** - Correlate with specific behavioral states (e.g., attention, relaxation, deep sleep). - Different frequency bands associated with distinct mental states: - **Beta (15--30 Hz):** Activated or attentive cortex. - **Alpha (8--13 Hz):** Quiet, waking state. - **Theta (4--7 Hz):** Some sleep and waking states. - **Delta (\< 4 Hz):** Deep sleep. - High synchrony and amplitude observed during deep sleep phases. - **EEG Rhythms:** - Electroencephalography (EEG) is used to record brain rhythms. - Provides insights into the electrical activity of the cerebral cortex. - Various patterns such as alpha rhythms, spindles, and ripples indicate different states of consciousness and cognitive processes. Lecture: Epilepsy and endocannabinoids **Cannabis and Epilepsy** - **Overview:** Cannabis, particularly cannabidiol (CBD), has emerged as a potential treatment for epilepsy, especially in severe forms like Dravet syndrome. Research indicates that CBD can significantly reduce seizure frequency in treatment-resistant cases, prompting interest in medical marijuana as an adjunct therapy. - **Dravet Syndrome:** - A severe form of childhood epilepsy characterized by frequent seizures. - Often resistant to conventional antiepileptic drugs (AEDs). - Patients may benefit from cannabis-derived treatments, specifically high-CBD strains. - **Cannabidiol Use:** - Cannabidiol (CBD) is a non-psychoactive compound found in cannabis. - Used in conjunction with existing AED regimens to enhance seizure control. - Charlotte\'s Web strain exemplifies successful use in reducing seizures. - **Seizure Frequency Reduction:** - Significant reductions reported in patients using CBD-enriched cannabis. - In one study, 84% of parents noted decreased seizure frequency; some reported complete seizure freedom. - Benefits also included improved mood, alertness, and sleep quality. - **Medical Marijuana Research:** - Ongoing studies are needed to understand the mechanisms of action and efficacy of cannabinoids in epilepsy. - Safety and tolerability data for pediatric populations remain limited. - Standardized preparations of pure CBD are necessary for further research and clinical application. **Homeostatic Regulation** - **Overview:** Homeostatic regulation refers to the processes that maintain internal stability in the body despite external changes. It involves various systems and mechanisms that control physiological functions such as temperature, appetite, immune response, and pain modulation. - **Human Milk:** - Contains anandamide, which plays a role in newborn suckling. - Influences pain and stress modulation. - **Pain Modulation:** - Involves brain regions like the periaqueductal gray for analgesia. - Cannabinoid receptors (CB1) are involved in regulating pain perception. - **Immune Function:** - CB2 receptors primarily expressed in the immune system. - Anandamide influences immune responses and inflammation. - **Appetite Control:** - Hypothalamus regulates energy balance and appetite through cannabinoid signaling. - **Memory:** - Hippocampus is crucial for learning and memory; influenced by endocannabinoids. - **Inflammation:** - Endocannabinoids modulate inflammatory responses throughout the body. - Cannabinoid receptors play a role in managing inflammation in various organs. - **Thermoregulation:** - Hypothalamus also responsible for temperature regulation. - Endocannabinoids can influence thermoregulatory processes. **Cannabis Plant Components** - **Overview:** The cannabis plant consists of various components that contribute to its unique properties, including cannabinoids and terpenes. Understanding these components is essential for exploring the plant\'s medicinal and recreational uses. - **Parts of the Cannabis Plant:** - **Pistil:** Female reproductive part; crucial for flower development. - **Calyx:** Protective structure surrounding the ovary; contributes to flower formation. - **Trichomes:** Hair-like structures on the plant surface; produce cannabinoids and terpenes. - **Cola:** Cluster of buds at the top of the plant; high concentration of flowers. - **Fan Leaves:** Large leaves that support photosynthesis; not directly involved in cannabinoid production. - **Male Flowers:** Produce pollen; do not develop into buds. - **Trichomes:** - Specialized glandular structures found primarily on female plants. - Responsible for producing and storing cannabinoids (e.g., THC, CBD) and terpenes. - Types include capitate stalked, capitate sessile, and bulbous trichomes, each with varying functions and potency. - **Cannabinoid Profiles:** - **Tetrahydrocannabinol (THC):** Primary psychoactive compound; binds to CB1 receptors in the brain. - **Cannabidiol (CBD):** Non-psychoactive compound; known for therapeutic effects without intoxication. - Other cannabinoids include THCP, Delta-8 THC, and more, each with distinct effects and binding affinities. - **Terpene Profiles:** - Aromatic compounds contributing to the scent and flavor of cannabis. - Examples include myrcene, limonene, and pinene, which may also influence the effects of cannabinoids through the entourage effect. - Terpenes play a role in the plant\'s defense mechanisms and can have therapeutic benefits. **Cannabinoid Receptors** - **Overview:** Cannabinoid receptors are part of the endocannabinoid system, which plays a crucial role in regulating various physiological processes. The two main types, CB1 and CB2 receptors, interact with cannabinoids like anandamide and THC to influence brain function, immune response, and more. - **CB1 Receptors:** - Primarily located in the brain. - Bind to anandamide and THC. - Responsible for the psychoactive effects (the \'high\') associated with cannabis. - Involved in neural regulation, memory, and various bodily responses including nausea and appetite. - **CB2 Receptors:** - Found mainly in the immune system and immune-derived cells. - Greatest density in the spleen. - Play a role in modulating inflammation and immune responses. - **Anandamide:** - An endogenous cannabinoid (endocannabinoid) produced by the body. - Binds primarily to CB1 receptors, influencing mood, pain sensation, and memory. - **THC Effects:** - Tetrahydrocannabinol (THC) is the primary psychoactive component of cannabis. - Produces effects such as euphoria, altered perception, and increased appetite through its action on CB1 receptors. - Can also affect other systems, including respiratory and digestive functions. **Cannabinoids and Terpenes** - **Overview:** Cannabinoids and terpenes are compounds found in the cannabis plant that contribute to its medicinal properties. Cannabinoids interact with the endocannabinoid system, while terpenes provide unique therapeutic benefits, enhancing the overall effects of cannabinoids through synergy. - **Phytocannabinoids:** - Naturally occurring cannabinoids derived from the cannabis plant. - Key examples include THC (tetrahydrocannabinol) and CBD (cannabidiol). - Known for their psychoactive and therapeutic effects. - **Terpene Medicinal Properties:** - Aromatic compounds found in many plants, including cannabis. - Exhibit various medicinal properties such as anti-inflammatory, analgesic, and anxiolytic effects. - Contribute to the entourage effect, enhancing cannabinoid efficacy. - **Synthetic Cannabinoids:** - Man-made chemicals designed to mimic natural cannabinoids. - Often used in research and medical applications but can have unpredictable effects. - Examples include synthetic THC analogs. - **Cannabinoid Receptors:** - Two main types: CB1 and CB2 receptors. - CB1 receptors are primarily located in the brain and central nervous system, influencing mood and perception. - CB2 receptors are mainly found in the immune system, affecting inflammation and pain response. - **Endocannabinoid System:** - A complex cell-signaling system involved in regulating various physiological processes. - Composed of endocannabinoids, receptors, and enzymes. - Plays a crucial role in maintaining homeostasis and mediating the effects of cannabinoids and terpenes.