B33 Lecture 6 - Nervous system 2 2024 PDF

BIOB33/HLTB33 Lecture 6 – Nervous System 2 (Chapter 16, 17, 18), Early Development of the Nervous System and Development of the Brain, Part I & Part II (Embryology Summary) Note the due date for the Homework Module & Lab Quiz for this material! Remember we are writing tests next week...

BIOB33/HLTB33 Lecture 6 – Nervous System 2 (Chapter 16, 17, 18), Early Development of the Nervous System and Development of the Brain, Part I & Part II (Embryology Summary) Note the due date for the Homework Module & Lab Quiz for this material! Remember we are writing tests next week The Eye - Salvador Dalí, 1945 Recall Subdivisions of the Nervous System Early Development of the Nervous System Development of the Brain Development of the Brain, cont’d Development of the Brain, cont’d  Major Regions of the Brain Cerebrum Landmark yourself! Brainstem is the structure connecting cerebrum to the spinal cord & cerebellum Major regions: Medulla oblongata Pons Cerebellum Diencephalon Mesencephalon Diencephalon (epithalamus, thalamus, hypothalamus) Mesencephalon Cerebellum (Midbrain) Cerebrum Pons Each area has a distinct function Medulla oblongata  Major Regions of the Brain, cont’d Four fluid-filled ventricles around located in the brain (Hint: Lateral ventricle count as two) Remember cerebrospinal fluid in central canal of spinal cord?  Protect the brain!!!! Bones of the skull Blood brain barrier Cranial meninges Dura mater (tough outer layer) Arachnoid mater (with subarachnoid space) Pia mater (attached to surface of the brain) Remember the anterior fontanelle? Dura mater made of two layers: periosteal cranial dura & meningeal cranial dura  Cerebrospinal Fluid (CSF) Remember ependymal cells? Choroid plexus in ventricles contain specialized ependymal cells CSF circulates through the ventricles and connecting spaces Some enters central canal of spinal cord Most flows into subarachnoid space Enters circulation via the arachnoid granulations (outpockets into venous sinuses in the dura mater)  Medulla oblongata Continuous with the spinal cord & brainstem; all communication between brain & spinal cord passes through this area Areas (called nuclei) in the medulla oblongata are: Relay stations Gracile nucleus Cuneate nucleus Solitary nucleus Olivary nucleus  Medulla oblongata, cont’d Areas (called nuclei) in the medulla oblongata are: Autonomic nuclei Reflex centres for cardiovascular centres (cardiac & vasomotor) & respiratory centres (rhythmic breathing) Cranial nerves Some sensory & motor nuclei of cranial nerves (CN): VIII, IX, X, XI, & XII  Pons Prominent bulge superior to medulla oblongata, consists of: More cranial nerves Some sensory & motor nuclei for CN V, VI, VII, & VIII More control centres for breathing Pneumotaxic centre Apneustic centre Tracts of nerves relaying commands to/from cerebellum  Mesencephalon Two bulges can be used to landmark this area: Inferior colliculi Superior colliculi The corpora quadrigemina (Latin: quadruplet bodies) form the “roof” over the cerebral aqueduct  Mesencephalon, cont’d Walls and floor consist of nuclei of reticular formation: Red nucleus Substantia niger Reticular formation composed of hundreds of nuclei. Information from the body to control sleep-wake cycle, fatigue, motivation, & pain sensitization Ventral surface contains cerebral peduncles (originate in cerebrum & ultimately the cerebellum or spinal cord)  Diencephalon Can be divided into epithalamus, thalamus, & hypothalamus Left & right sides of thalamus are connected at the interthalamic adhesion You might recognize the pineal gland of the epithalamus & the stalk (infundibulum) projecting from thalamus leading to the pituitary gland Lateral Third ventricle Interthalamic adhesion  Cerebellum Notice the distinct arbor vitae, connecting cerebellar cortex (outer layer) with cerebellar peduncles (stalks) Afferent & efferent fibers coordinate subconscious coordination of movement Notice the narrow bands of cortex, called vermis Remember Purkinje cells? Dendrites (grey matter) send information along to white matter in the cerebellum  Cerebrum Hint: Use your knowledge of skull bones to identify cerebral lobes Note bumps (gyrus) and grooves (sulcus & fissure) Special areas control higher order functions (speech, analytical ability) Watch out for the myth of being left-brained (analytical) or right-brained (creative). Brain scans suggest activity on BOTH sides – don’t use this as an excuse for not being able to be creative or able to do STEM Deep structures control movement (basal nuclei) & emotions/memory (limbic system)  Cranial Nerves HINT: If mnemonics work for you, use them. If not, just memorize! Numbering starts rostrally All have different roles, some are sensory, others motor, others mixed Hint: Revisit the skull to understand the roles of foramen Hint: Revisit the muscles to understand connection to brain Recall: Somatic Nervous System Involves things you consciously do Sensory information from the skin, skeletal muscles and joints (afferent nerves) Signals sent from CNS to periphery (efferent nerves) Somatic peripheral nervous system is a single-neuron system with the motor neurons in the brainstem or spinal cord and the sensory neurons in the dorsal root ganglia  Autonomic Nervous System Works without you thinking about it Motor fibers control visceral (internal organs) function Autonomic peripheral nervous system is a two-neuron system, with a neuron lying outside the CNS in the autonomic ganglia The nerve fibers have different sizes & degrees of myelination for different conduction velocities Two divisions (sympathetic & parasympathetic) have opposite BUT complementary roles Sympathetic Division * Know the ganglia & the vertebral region the come from; we’ll reinforce targets as we cover the systems  Adrenal Medulla Medulla – inside (of an organ or tissue) Preganglionic fibers (T5-T8) pass through sympathetic chain & celiac ganglion to go directly to the medulla of the adrenal gland Cells in this area are modified neurons and will release epinephrine & norepinephrine when stimulated These are neurotransmitters, but they act like hormones What are other names for epinephrine & norepinephrine? Fight or flight response Rest and digest response  Parasympathetic Division Note: Parasympathetic preganglionic fibers leave through cranial nerves & in sacral region Some synapse in ganglia while CN X synapse in visceral walls after forming weblike structures (plexus) in thoracic, abdominal, and pelvis regions Unlike somatic reflexes, visceral reflexes are polysynaptic – long reflex more widespread response & short more localized  How does an afferent signal start? Information is “picked up” by sensory receptors General senses Refers to temperature, pain, touch, pressure, vibration, and proprioception General sensory receptors are distributed throughout the body Special senses Refers to smell, taste, balance, hearing, and vision Special sense receptors are located in complex sense organs Activation of a sensory receptor produces electrical impulses in a corresponding sensory nerve  General Senses Exteroceptors Provide information about the external environment Proprioceptors Provide information about the position of the body Interoceptors Provide information about the inside of the body Nociceptors Respond to the sensation of pain Thermoreceptors Respond to changes in temperature Mechanoreceptors Sensitive to physical distortion of cell membranes Chemoreceptors Monitor the chemical composition of body fluids  Receptor Specificity Sensory receptors have specific modalities – free nerve ending (touch), baroreceptors (mechanoreceptors that stretch), photoreceptors (light) Each receptor monitors a specific area For touch, this can be demonstrated with the Weber two-point discrimination test In skin, some areas have larger (shin ~30 mm) and others have smaller fields (fingertips ~5 mm). The smaller the field, the more precise the location of stimulus  Special Senses – Olfaction (Smell) Special sense have specialized organs used only for perception of the appropriate sensory information (modality) Olfactory organs (olfactory epithelium, olfactory nerves, supporting cells) provide smell Dendrites of olfactory nerves form olfactory bulb while axons travel in olfactory tract. Dendrites extend into olfactory epithelium to be stimulated by airborne compounds trapped in the olfactory mucus Olfactory tract goes to the olfactory cortex, hypothalamus, & limbic system  Special Senses – Gustation (Taste) Taste receptors are found in taste buds Tongue surface has epithelial projections called lingula papillae, which contain the taste buds Taste buds contain gustatory epithelial cells and basal cells, with microvilli extending through a taste pore into surrounding fluid Sensations: sour, bitter, salty, sweet, umami  Special Senses – Vision The eye consists of: Three layers: Fibrous layer Vascular layer Inner Layer Anterior cavity Anterior chamber Posterior chamber Posterior cavity  Eye Orbit The orbits are bony structures of the skull that house the eye, extra-ocular muscles, nerves, blood vessels, lacrimal apparatus, and adipose tissue Lacrimal apparatus makes and removes tears to reduce friction, remove debris, and provide oxygen to epithelium covering the eye Path of light is affected as it passes through the eye, entering at cornea and then through lens and fluids of eye Intra-ocular muscles (ciliary muscle, sphincter pupillae & dilator pupillae that make up the iris) control optical properties of the eye  Retinal Organization Light is projected onto the back of the eye Retina contains a layer of photoreceptor cells that capture light and ganglion cells, latter extend axons to form optic nerve Two types of photoreceptors: cones are used for colour vision and rods are detect light in general Rods more numerous and at periphery of eye. Cones concentrated near fovea centralis in the macula Heavy pigmentation of choroid absorbs light Optic disc contains no ganglion cells and is called the blind spot. Why?  Visual Pathways Remember the optic chiasma? Optic nerves cross over to create cortical integration Each cerebral hemisphere receives information from the lateral half of the retina on the ipsilateral side, and from the medial half of the retina on the contralateral side Signals are relayed to cortex and brainstem by the lateral geniculate nuclei Information arrives at the visual cortex of the occipital lobes Visual association areas integrate the images to develop a composite of the entire visual field  Special Senses – Hearing Hearing is the detection of sound (pressure waves) Structures of the ear are involved in balance and hearing The ear is subdivided into three regions: External ear Middle ear Internal ear Middle ear contains auditory ossicles (remember malleus, incus, & stapes?) The receptor cells of hearing (hair cells) are located within the cochlea of the inner ear  Conduction of sound The scala vestibuli (vestibular duct) and scala tympani (tympanic duct) are connected at the apical end of the cochlea The oval window is at the base of the vestibular duct The round window is at the base of the tympanic duct Scala media (cochlear duct) contains endolymph Hair cells are in contact with an overlying tectorial membrane. Movement of hair cells cause electrical signal to be transferred along cochlear nerve  Special Senses – Balance The Vestibular Complex and Equilibrium The vestibular complex is the part of inner ear that provides equilibrium sensations by detecting rotation, gravity, and acceleration Consists of: Semicircular canals Utricle Saccule Sensory neurons located in vestibular ganglia Sensory fibers from these ganglia form the vestibular nerve (a branch of the vestibulocochlear nerve)  Special Senses – Balance Hair cells of the utricle and saccule are in clusters called maculae Processes of the hair cells are embedded in gelatinous material Surface of gelatinous material covered with otoliths (calcium carbonate crystals) Gelatinous material and otoliths are collectively the otolithic membrane Otoliths press down on the macular surface. Movement shifts these crystals distorts the hair cells, creating electrical signal for sensory neuron