Human Anatomy and Physiology Eleventh Edition - Lecture Notes - PDF

Human Anatomy and Physiology Eleventh Edition Chapter 12 Part A The Central Nervous System PowerPoint® Lectures Slid...

Human Anatomy and Physiology Eleventh Edition Chapter 12 Part A The Central Nervous System PowerPoint® Lectures Slides prepared by Karen Dunbar Kareiva, Ivy Tech Community College Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Brain Regions and Organization Adult brains have four regions: 1. Cerebral hemispheres 2. Diencephalon 3. Brain stem, consisting of: ▪ Midbrain ▪ Pons ▪ Medulla 4. Cerebellum Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Brain Anatomy Figure 12.2c Brain development. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Brain Regions and Organization Gray matter: short, nonmyelinated neurons and cell bodies White matter: myelinated and nonmyelinated axons Basic pattern found in CNS: central cavity surrounded by gray matter, with white matter external to gray matter Features and changes of pattern: 1. Spinal cord exhibits this basic pattern; however, pattern changes with ascent into brain stem Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Pattern of Distribution of Gray and White Matter in the CNS – spinal cord Figure 12.3 Pattern of distribution of gray and white matter in the CNS. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Brain Regions and Organization 2. Brain stem has additional gray matter nuclei scattered within white matter 3. Cerebral hemispheres (cerebrum) and cerebellum contain outer layer of gray matter called the cortex ▪ Cerebrum and cerebellum also have scattered areas of gray matter nuclei amid white matter Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Pattern of Distribution of Gray and White Matter in the CNS – brain stem Figure 12.3 Pattern of distribution of gray and white matter in the CNS. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Pattern of Distribution of Gray and White Matter in the CNS – cerebrum and cerebellum Figure 12.3 Pattern of distribution of gray and white matter in the CNS. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Ventricles Fluid-filled chambers that are continuous to one another and to central canal of spinal cord – Filled with cerebrospinal fluid (CSF) – Lined by ependymal cells (neuroglial cells) Paired lateral ventricles are large, C-shaped chambers located deep in each hemisphere – Pair is separated by membranous septum pellucidum Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Ventricles Each lateral ventricle is connected to the third ventricle via interventricular foramen – Third ventricle lies in diencephalon Third ventricle is connected to the fourth ventricle via cerebral aqueduct – Fourth ventricle lies in hindbrain – Continuous with central canal of spinal cord Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  12.2 Cerebral Hemispheres Cerebral hemispheres form superior part of brain – Account for 83% of brain mass Surface markings: – Gyri: ridges – Sulci: shallow grooves – Fissures: deep grooves ▪ Longitudinal fissure – Separates two hemispheres ▪ Transverse cerebral fissure – Separates cerebrum and cerebellum Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Lobes, Sulci, and Fissures of the Cerebral Hemispheres Several sulci divide each hemisphere into five lobes – Frontal – Parietal – Temporal – Occipital – Insula Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Animation – Rotatable Brain Click here to view ADA compliant Animation: Rotatable Brain https://mediaplayer.pearsoncmg.com/assets/rotating-model-brain Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 12.2 Cerebral Hemispheres Major sulci that divide lobes: – Central sulcus separates precentral gyrus of frontal lobe and postcentral gyrus of parietal lobe – Parieto-occipital sulcus separates occipital and parietal lobes – Lateral sulcus outlines temporal lobes Each hemisphere has three basic regions: – Cerebral cortex of gray matter superficially – White matter internally – Basal nuclei deep within white matter Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cerebral Cortex Cerebral cortex is “executive suite” of brain Site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding Thin (2–4 mm) superficial layer of gray matter – Composed of neuron cell bodies, dendrites, glial cells, and blood vessels, but no axons 40% of mass of brain Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cerebral Cortex Functional imaging (PET and MRI) of brain show specific motor and sensory functions are located in discrete cortical areas called domains – Higher functions are spread over many areas Figure 12.6 Functional neuroimaging (fMRI) of the cerebral cortex. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cerebral Cortex Four general considerations of cerebral cortex: 1. Contains three types of functional areas: ▪ Motor areas: control voluntary movement ▪ Sensory areas: conscious awareness of sensation ▪ Association areas: integrate diverse information 2. Each hemisphere is concerned with contralateral (opposite) side of body 3. Not entirely symmetrical - Lateralization (specialization) of cortical function can occur in only one hemisphere 4. Conscious behavior involves entire cortex in one way or another Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cerebral Cortex Motor areas – Located in frontal lobe, motor areas act to control voluntary movement – Primary motor cortex in precentral gyrus – Premotor cortex anterior to precentral gyrus – Broca’s area anterior to inferior premotor area – Frontal eye field within and anterior to premotor cortex; superior to Broca’s area Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Functional and Structural Areas of the Cerebral Cortex Figure 12.7a Functional and structural areas of the cerebral cortex. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cerebral Cortex – Primary (somatic) motor cortex ▪ Located in precentral gyrus of frontal lobe ▪ Pyramidal cells: large neurons that allow conscious control of precise, skilled, skeletal muscle movements ▪ Pyramidal (corticospinal) tracts: formed from long axons that project down spinal cord ▪ Somatotopy: all muscles of body can be mapped to area on primary motor cortex – Motor homunculi: upside-down caricatures represent contralateral motor innervation of body regions Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Body Maps in the Primary Motor Cortex and Somatosensory Cortex of the Cerebrum Figure 12.8 Body maps in the primary motor cortex and somatosensory cortex of the cerebrum. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cerebral Cortex – Premotor cortex ▪ Helps plan movements – Staging area for skilled motor activities ▪ Controls learned, repetitious, or patterned motor skills ▪ Coordinates simultaneous or sequential actions ▪ Controls voluntary actions that depend on sensory feedback Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cerebral Cortex – Broca’s area ▪ Present in one hemisphere (usually the left) ▪ Motor speech area that directs muscles of speech production ▪ Active in planning speech and voluntary motor activities – Frontal eye field ▪ Controls voluntary eye movements Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Clinical – Homeostatic Imbalance 12.1 Damage to areas of primary motor cortex, as seen in a stroke, paralyzes muscles controlled by those areas Paralysis occurs on opposite side of body from damage Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cerebral Cortex Sensory areas – Areas of cortex concerned with conscious awareness of sensation – Occur in parietal, insular, temporal, and occipital lobes – Eight main areas include primary somatosensory cortex, somatosensory association cortex, visual areas, auditory areas, vestibular cortex, olfactory cortex, gustatory cortex, and visceral sensory area Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cerebral Cortex – Primary somatosensory cortex ▪ Located in postcentral gyri of parietal lobe ▪ Receives general sensory information from skin and proprioceptors of skeletal muscle, joints, and tendons ▪ Capable of spatial discrimination: identification of body region being stimulated ▪ Somatosensory homunculus: upside-down caricatures represent contralateral sensory input from body regions Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Body Maps in the Primary Motor Cortex and Somatosensory Cortex of the Cerebrum Figure 12.8 Body maps in the primary motor cortex and somatosensory cortex of the cerebrum. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cerebral Cortex – Somatosensory association cortex ▪ Posterior to primary somatosensory cortex ▪ Integrates sensory input from primary somatosensory cortex for understanding of object ▪ Determines size, texture, and relationship of parts of objects being felt Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cerebral Cortex – Visual areas ▪ Primary visual (striate) cortex located on extreme posterior tip of occipital lobe – Most buried in calcarine sulcus – Receives visual information from retinas ▪ Visual association area surrounds primary visual cortex – Uses past visual experiences to interpret visual stimuli (color, form, or movement) Example: ability to recognize faces – Complex processing involves entire posterior half of cerebral hemispheres Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cerebral Cortex – Auditory areas ▪ Primary auditory cortex – Superior margin of temporal lobes – Interprets information from inner ear as pitch, loudness, and location ▪ Auditory association area – Located posterior to primary auditory cortex – Stores memories of sounds and permits perception of sound stimulus Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cerebral Cortex – Vestibular cortex ▪ Posterior part of insula and adjacent parietal cortex ▪ Responsible for conscious awareness of balance (position of head in space) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cerebral Cortex – OIfactory cortex ▪ Primary olfactory (smell) cortex – Medial aspect of temporal lobes (in piriform lobes) – Part of primitive rhinencephalon, along with olfactory bulbs and tracts – Remainder of rhinencephalon in humans becomes part of limbic system – Involved in conscious awareness of odors Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cerebral Cortex – Gustatory cortex ▪ In insula just deep to temporal lobe ▪ Involved in perception of taste – Visceral sensory area ▪ Posterior to gustatory cortex ▪ Conscious perception of visceral sensations, such as upset stomach or full bladder Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Functional and Structural Areas of the Cerebral Cortex Figure 12.7b Functional and structural areas of the cerebral cortex. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cerebral Cortex Multimodal association areas – Receive inputs from multiple sensory areas – Send outputs to multiple areas – Allows us to give meaning to information received, store in memory, tie to previous experience, and decide on actions – Sensations, thoughts, emotions become conscious: makes us who we are – Broadly divided into three parts: anterior association area, posterior association area, and limbic association area Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Human Anatomy and Physiology Eleventh Edition Chapter 12 Part B The Central Nervous System PowerPoint® Lectures Slides prepared by Karen Dunbar Kareiva, Ivy Tech Community College Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 12.3 The Diencephalon Consists of three paired gray-matter structures: – Thalamus – Hypothalamus – Epithalamus All three enclose third ventricle Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Click here to view ADA compliant Animation: Rotatable Brain (Sectioned) https://mediaplayer.pearsoncmg.com/assets/rotating-model-brain-sectioned Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Midsagittal Section of the Brain Figure 12.11a Midsagittal section of the brain. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Thalamus Bilateral egg-shaped nuclei that form superolateral walls of third ventricle Makes up 80% of diencephalon Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Selected Structures of the Diencephalon No need to memorize nuclei Figure 12.12a Selected structures of the diencephalon. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Thalamus Main thalamic function is to act as relay station for information coming into cortex – Sorts, edits, and relays ascending input such as: ▪ Impulses from hypothalamus for regulating emotion and visceral function ▪ Impulses from cerebellum and basal nuclei to help direct motor cortices ▪ Impulses for memory or sensory integration Overall, it acts to mediate sensation, motor activities, cortical arousal, learning, and memory Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Hypothalamus Located below thalamus Forms cap over brain stem and forms inferolateral walls of third ventricle Contains many important nuclei such as: – Mammillary bodies: paired anterior nuclei that act as olfactory relay stations Infundibulum: stalk that connects to pituitary gland No need to memorize nuclei Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Hypothalamus The hypothalamus is the main visceral control and regulating center that is vital to homeostasis Chief homeostasis controls: – Controls autonomic nervous system ▪ Examples: blood pressure, rate and force of heartbeat, digestive tract motility, pupil size – Initiates physical responses to emotions ▪ Part of limbic system: perceives pleasure, fear, rage, biological rhythms, and drives (sex drive) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Hypothalamus The hypothalamus also: – Regulates body temperature: sweating or shivering – Regulates hunger and satiety in response to nutrient blood levels or hormones – Regulates water balance and thirst – Regulates sleep-wake cycles ▪ Suprachiasmatic nucleus of thalamus sets our biological clock Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Hypothalamus – Controls endocrine system functions such as: ▪ Secretions of anterior pituitary gland ▪ Production of posterior pituitary hormones Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Epithalamus Most dorsal portion of diencephalon Forms roof of third ventricle Contains pineal gland (body) – Extends from posterior border – Secretes melatonin that helps regulate sleep-wake cycle Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 12.4 Brain Stem Consists of three regions: midbrain, pons, medulla oblongata Similar in structure to spinal cord but contains nuclei embedded in white matter Controls automatic behaviors necessary for survival Contains fiber tracts connecting higher and lower neural centers Nuclei are associated with 10 of the 12 pairs of cranial nerves Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Views of the Brain Stem (Green) and the Diencephalon (Purple) Figure 12.13c View of the brain stem (green) and the diencephalon (purple). Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 12.5 Cerebellum 11% of brain mass Located dorsal to pons and medulla Processes input from cortex, brain stem, and sensory receptors to provide precise, coordinated movements of skeletal muscles Also plays a major role in balance Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cerebellar Processing Cerebellum fine-tunes motor activity as follows: 1. Receives impulses from cerebral cortex of intent to initiate voluntary muscle contraction 2. Receives signals from proprioceptors throughout body, as well as visual and equilibrium pathways that: ▪ Pathways continuously “inform” cerebellum of body’s position and momentum 3. Cerebellar cortex calculates the best way to smoothly coordinate muscle contraction 4. Sends “blueprint” of coordinated movement to cerebral motor cortex and brain stem nuclei Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Cognitive Functions of Cerebellum As it does for motor processes, it may compare actual output of higher functions with expected output and adjust accordingly Neuroimaging suggests that cerebellum plays role in thinking, language, and emotion Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 12.8 Protection of Brain Meninges Function of meninges: – Cover and protect CNS – Protect blood vessels and enclose venous sinuses – Contain cerebrospinal fluid (CSF) – Form partitions in skull Consists of three layers (from external to internal): dura mater, arachnoid mater, and pia mater Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Meninges: Dura Mater, Arachnoid Mater, and Pia Mater Figure 12.22 Meninges: dura mater, arachnoid mater, and pia mater. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Meninges Dura mater – Strongest meninx – Made up of two layers of fibrous connective tissue ▪ Periosteal layer attaches to inner surface of skull – Found only in brain, not spinal cord ▪ Meningeal layer: true external covering of brain – Extends into vertebral canal as spinal dura mater Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Meninges Arachnoid mater – Middle layer with spiderweb-like extensions – Separated from dura mater by subdural space – Subarachnoid space contains CSF and largest blood vessels of brain – Arachnoid granulations protrude through dura mater into superior sagittal sinus ▪ Permit reabsorption of CSF back into venous blood Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Meninges Pia mater – Delicate connective tissue that clings tightly to brain, following every convolution ▪ Contains many tiny blood vessels that feed brain Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Clinical – Homeostatic Imbalance 12.9 Meningitis: inflammation of the meninges due to bacterial, viral, fungal or parasitic infection May spread to CNS, which would lead to inflammation of the brain, referred to as encephalitis Meningitis is usually diagnosed by observing microbes in a sample of CSF obtained via lumbar puncture Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Blood Brain Barrier Helps maintain stable environment for brain – Chemical variations could lead to uncontrollable neuron firings Substances from blood must first pass through continuous endothelium of capillary walls before gaining entry into neurons – Tight junctions ensure substances pass through, not around endothelial cells – Feet of astrocytes and smooth muscle-like pericytes surround endothelial cells ▪ Help to promote tight junction formation in endothelial cells Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Blood Brain Barrier Figure 12.26 The blood brain barrier. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Blood Brain Barrier Substances move through endothelial cells via: – Simple diffusion – allows lipid-soluble substances, as well as blood gases to pass freely through cell membrane – Specific transport mechanisms – facilitated diffusion moves substances important to the brain such as glucose, amino acids and specific ions ▪ Transcytosis moves larger substances into and out of brain Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Blood Brain Barrier Thick basement membrane surrounding capillaries is last part of barrier substances must pass through – Contains enzymes that destroy certain chemicals that would activate brain neurons Absent in some areas, such as vomiting center and hypothalamus – Necessary to monitor chemical composition and temperature of blood Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Human Anatomy and Physiology Eleventh Edition Chapter 12 Part D The Central Nervous System PowerPoint® Lectures Slides prepared by Karen Dunbar Kareiva, Ivy Tech Community College Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Gross Anatomy and Protection Spinal cord is enclosed in vertebral column – Begins at the foramen magnum – Ends at L1 or L2 vertebra Functions – Provides two-way communication to and from brain and body – Major reflex center: reflexes are initiated and completed at spinal cord Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Gross Structure of the Spinal Cord, Dorsal View Figure 12.28a Gross structure of the spinal cord, dorsal view. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Spinal Cord Segments Figure 12.30 Spinal cord segments. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Spinal Cord Cross-sectional Anatomy Two lengthwise grooves that run length of cord partially divide it into right and left halves – Ventral (anterior) median fissure – Dorsal (posterior) median sulcus Gray matter is located in core, white matter outside Central canal runs length of cord – Filled with CSF Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Spinal Cord Cross-Sectional Anatomy Gray matter and spinal roots – Cross section of cord resembles butterfly or letter “H” – Three areas of gray matter are found on each side of center and are mirror images: ▪ Dorsal horns: interneurons that receive somatic and visceral sensory input ▪ Ventral horns: some interneurons; somatic motor neurons ▪ Lateral horns (only in thoracic and superior lumbar regions): sympathetic neurons Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Spinal Cord Cross-Sectional Anatomy Gray matter and spinal roots (cont.) – Gray commissure: bridge of gray matter that connects masses of gray matter on either side ▪ Encloses central canal – Ventral roots: bundle of motor neuron axons that exit the spinal cord – Dorsal roots: sensory input to cord – Dorsal root (spinal) ganglia: cell bodies of sensory neurons – Spinal nerves: formed by fusion of dorsal and ventral roots Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Spinal Cord Cross-Sectional Anatomy Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Spinal Cord Cross-Sectional Anatomy White matter – Myelinated and nonmyelinated nerve fibers allow communication between parts of spinal cord, and spinal cord and brain – Run in three directions ▪ Ascending: up to higher centers (sensory inputs) ▪ Descending: from brain to cord or lower cord levels (motor outputs) ▪ Transverse: from one side to other (commissural fibers) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Spinal Cord Cross-Sectional Anatomy White matter (cont.) White matter is divided into three white columns (funiculi) on each side – Dorsal (posterior) – Lateral – Ventral (anterior) Each spinal tract is composed of axons with similar destinations and functions Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Human Anatomy and Physiology Eleventh Edition Chapter 13 Part A Peripheral Nervous System PowerPoint® Lectures Slides prepared by Karen Dunbar Kareiva, Ivy Tech Community College Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Peripheral Nervous System PNS provides links from and to world outside our body Consists of all neural structures outside brain and spinal cord that can be broken down into four parts: Part 1 – Sensory Receptors Part 2 – Transmission Lines: Nerves and Their Structure and Repair Part 3 – Motor Endings and Motor Activity Part 4 – Reflex Activity Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Place of the PNS in the Structural Organization of the Nervous System Figure 13.1 Place of the PNS in the structural organization of the nervous system. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Part 1 – Sensory Receptors and Sensation Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 13.1 Sensory Receptors Sensory receptors: specialized to respond to changes in environment (stimuli) – Activation results in graded potentials that trigger nerve impulses Awareness of stimulus (sensation) and interpretation of meaning of stimulus (perception) occur in brain Three ways to classify receptors: by type of stimulus, body location, and structural complexity Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Classification by Stimulus Type Mechanoreceptors—respond to touch, pressure, vibration, and stretch Thermoreceptors—sensitive to changes in temperature Photoreceptors—respond to light energy (example: retina) Chemoreceptors—respond to chemicals (examples: smell, taste, changes in blood chemistry) Nociceptors—sensitive to pain-causing stimuli (examples: extreme heat or cold, excessive pressure, inflammatory chemicals) – These signals stimulate subtypes of thermoreceptors, mechanoreceptors, and chemoreceptors Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Classification by Location Exteroceptors – Respond to stimuli arising outside body – Receptors in skin for touch, pressure, pain, and temperature – Most special sense organs Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Classification by Location Interoceptors (visceroceptors) – Respond to stimuli arising in internal viscera and blood vessels – Sensitive to chemical changes, tissue stretch, and temperature changes – Sometimes cause discomfort but usually person is unaware of their workings Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Classification by Location Proprioceptors – Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles – Inform brain of one's movements Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Classification by Receptor Structure Majority of sensory receptors belong to one of two categories: – Simple receptors of the general senses ▪ Modified dendritic endings of sensory neurons ▪ Are found throughout body and monitor most types of general sensory information – Receptors for special senses ▪ Vision, hearing, equilibrium, smell, and taste ▪ All are housed in complex sense organs ▪ Covered in Chapter 15 Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Classification by Receptor Structure Simple receptors of the general senses – General senses include tactile sensations (touch, pressure, stretch, vibration), temperature, pain, and muscle sense ▪ No “one-receptor-one-function” relationship – Receptors can respond to multiple stimuli e.g. heat and chemicals – Receptors have either: ▪ Nonencapsulated (free) nerve endings or ▪ Encapsulated nerve endings Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Classification by Receptor Structure – Nonencapsulated (free) nerve endings ▪ Abundant in epithelia and connective tissues ▪ Most are nonmyelinated, small-diameter group C fibers; distal terminals have knoblike swellings ▪ Respond mostly to temperature, pain, or light touch Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Classification by Receptor Structure – Nonencapsulated (free) nerve endings (cont.) ▪ Thermoreceptors – Cold receptors are activated by temps from 10 to 40ºC – Located in superficial dermis – Heat receptors are activated from 32 to 48ºC located in in deeper dermis – Outside those temperature ranges, nociceptors are activated and interpreted as pain Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Classification by Receptor Structure – Nonencapsulated (free) nerve endings (cont.) ▪ Nociceptors: pain receptors triggered by extreme temperature changes, pinch, or release of chemicals from damaged tissue – Vanilloid receptor: protein in nerve membrane is main player Acts as ion channel that is opened by heat, low pH, chemicals (example: capsaicin in red peppers) Itch receptors in dermis: can be triggered by chemicals such as histamine Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Classification by Receptor Structure – Nonencapsulated (free) nerve endings (cont.) ▪ Tactile (Merkel) discs: function as light touch receptors – Located in deeper layers of epidermis ▪ Hair follicle receptors: free nerve endings that wrap around hair follicles – Act as light touch receptors that detect bending of hairs Example: Allows you to feel a mosquito landing on your skin Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Table 13.1-1 General Sensory Receptors Classified by Structure and Function Table 13.1 General Sensory Receptors Classified by Structure and Function. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Classification by Receptor Structure – Encapsulated dendritic endings ▪ Almost all are mechanoreceptors whose terminal endings are encased in connective tissue capsule ▪ Vary greatly in shape and include: – Tactile (Meissner’s) corpuscles: small receptors involved in discriminative touch Found just below skin, mostly in sensitive and hairless areas (fingertips) – Lamellar (Pacinian) corpuscles: large receptors respond to deep pressure and vibration when first applied (then turn off) Located in deep dermis Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Classification by Receptor Structure – Bulbous corpuscles (Ruffini endings): respond to deep and continuous pressure Located in dermis – Muscle spindles: spindle-shaped proprioceptors that respond to muscle stretch – Tendon organ: proprioceptors located in tendons that detect stretch – Joint kinesthetic receptors: proprioceptors that monitor joint position and motion Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Table 13.1-2 General Sensory Receptors Classified by Structure and Function Table 13.1 General Sensory Receptors Classified by Structure and Function. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Reflex Activity Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 13.6 Peripheral Motor Endings Inborn (intrinsic) reflex: rapid, involuntary, predictable motor response to stimulus – Examples: maintain posture, control visceral activities – Can be modified by learning and conscious effort Learned (acquired) reflexes result from practice or repetition – Example: driving skills Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Components of a Reflex Arc Components of a reflex arc (neural path) 1. Receptor: site of stimulus action 2. Sensory neuron: transmits afferent impulses to CNS 3. Integration center: either monosynaptic or polysynaptic region within CNS 4. Motor neuron: conducts efferent impulses from integration center to effector organ 5. Effector: muscle fiber or gland cell that responds to efferent impulses by contracting or secreting Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Components of a Reflex Arc Reflexes are classified functionally as: – Somatic reflexes ▪ Activate skeletal muscle – Autonomic (visceral) reflexes ▪ Activate visceral effectors (smooth or cardiac muscle or glands) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved The Five Basic Components of all Reflex Arcs Figure 13.15 The five basic components of all reflex arcs. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 13.9 Spinal Reflexes Spinal reflexes occur without direct involvement of higher brain centers – Brain is still advised of spinal reflex activity and may have an effect on the reflex Testing of somatic reflexes important clinically to assess condition of nervous system – If exaggerated, distorted, or absent, may indicate degeneration or pathology of specific nervous system regions – Most commonly assessed reflexes are stretch, flexor, and superficial reflexes Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Stretch and Tendon Reflexes To smoothly coordinate skeletal muscle, nervous system must receive proprioceptor input regarding: – Length of muscle ▪ Information sent from muscle spindles – Amount of tension in muscle ▪ Information sent from tendon organs Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Stretch and Tendon Reflexes Functional anatomy of muscle spindles – Composed of 3–10 modified skeletal muscle fibers called intrafusal muscle fibers that are enclosed in a connective tissue capsule ▪ Central regions of intrafusal fibers lack myofilaments and are noncontractile ▪ End regions contain actin and myosin myofilaments and can contract – Regular effector fibers of muscle referred to as extrafusal muscle fibers Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Stretch and Tendon Reflexes Functional anatomy of muscle spindles (cont.) Two types of afferent endings in muscle spindle send sensory inputs to CNS: – Anulospiral endings (primary sensory endings) ▪ Endings wrap around spindle – Stimulated by rate and degree of stretch – Flower spray endings (secondary sensory endings) ▪ Small axons at spindle ends – Stimulated by degree of stretch only Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Stretch and Tendon Reflexes Functional anatomy of muscle spindles (cont.) Contractile end regions of spindle are innervated by gamma (γ) efferent fibers – Help maintain spindle sensitivity – Note: Extrafusal fibers (contractile muscle fibers) are innervated by alpha (α) efferent fibers of large alpha (α) motor neurons Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Stretch and Tendon Reflexes Functional anatomy of muscle spindles (cont.) Muscle spindles are stretched (and excited) in two ways – External stretch: external force lengthens entire muscle – Internal stretch: γ motor neurons stimulate spindle ends to contract, thereby stretching spindle Stretching results in increased rate of impulses to spinal cord Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Operation of the Muscle Spindle Figure 13.17a Operation of the muscle spindle. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Stretch and Tendon Reflexes Functional anatomy of muscle spindles (cont.) Contracting muscle could reduce tension on muscle spindle, and sensitivity would be lost Situation avoided by muscle spindle also shortening by impulses from γ motor neurons that fire when α neurons fire α−γ coactivation maintains tension and sensitivity of spindle during muscle contraction Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Copyright Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved