Spinal Cord Tracts PDF

1 Spinal cord 1. The CNS is composed of the brain and spinal cord © 2019 McGraw-Hill Education  2...

1 Spinal cord 1. The CNS is composed of the brain and spinal cord © 2019 McGraw-Hill Education  2 Spinal cord 1. The CNS is composed of the brain and spinal cord Brain Gray matter White matter Spinal cord © 2019 McGraw-Hill Education  3 Introduction: Spinal Cord Tracts The white matter is composed of ascending and descending fiber tracts. Ascending tracts carry sensory impulses and are given the prefix spino- with a suffix that indicates the brain region it synapses on; example: lateral spinothalamic tract Descending tracts carry motor impulses and are given the suffix -spinal, and the prefix indicates the brain region they come from; example: anterior corticospinal tract el bialy, Safaa & Weng, Robin & Jalali, Alireza. (2019). Development of a 3D Printed Neuroanatomy Teaching Model. University of Ottawa Journal of Medicine. 9. 49-53. 10.18192/uojm.v9i1.4057. © 2019 McGraw-Hill Education  Ascending Tracts: anterolateral 4 spinothalamic Principal Ascending Tracts of the Spinal Cord Tract Origin Termination Function Anterolateral Posterior horn on one side Thalamus, then cerebral Conducts pain and temperature spinothalamic of cord but crosses to cortex impulses that are interpreted opposite side within cerebral cortex Dorsal horn spinal cord Dorsal horn spinal cord © 2019 McGraw-Hill Education  Ascending Tracts: anterolateral 5 spinothalamic Third order Neuron cell body First order Neuron cell body Second order Neuron cell body First order Neuron Second order cell body Neuron cell body © 2019 McGraw-Hill Education  Ascending Tracts: dorsal columns 6 medial lemniscus Principal Ascending Tracts of the Spinal Cord © 2019 McGraw-Hill Education  Ascending Tracts: dorsal column 7 medial lemniscus Third order Neuron cell body First order Neuron cell body Second order Neuron cell body First order Neuron Second order cell body Neuron cell body © 2019 McGraw-Hill Education  8 Descending Tracts 1.The descending tracts are the pathways by which motor signals are sent from upper motor neurons to lower motor neurons. The lower motor neurons then directly innervate muscles to produce movement. 2.Two major groups:. a.Pyramidal: originate from the cerebral cortex to the spinal cord and brain stem. They are responsible for the voluntary control of the musculature of the body and face. b.Extrapyramidal tracts: originate in the brain stem. They are responsible for 1)The involuntary and automatic control of all musculature, such as muscle tone, balance, posture and locomotion. 2)Refine and adjust movements initiated by the pyramidal tracts to ensure smooth execution. © 2019 McGraw-Hill Education  9 Pyramidal Tracts 1. Two major groups: a. Corticospinal: supplies the musculature of the body. b. Corticobulbar supplies the musculature of head and neck. Corticospinal Corticobulbar © 2019 McGraw-Hill Education  1 0 Pyramidal Tracts: corticospinal Tract Category Origin Crossed/Uncrossed Lateral corticospinal Pyramidal Cerebral cortex Crossed Anterior corticospinal Pyramidal Cerebral cortex Uncrossed/Crossed Cell bodies of the upper motor neurons are located in the precentral gyrus (Primary motor cortex). 80 to 90% cross in the medulla pyramids and descend as lateral corticospinal tracts. Those that do not cross in the medulla, descend as anterior corticospinal tracts and cross in the spinal cord at the level that the nerves leave the cord. Those that do cross in the medulla, descend as lateral corticospinal tracts. © 2019 McGraw-Hill Education  1 1 Extrapyramidal Tracts Tract Category Origin Crossed/Uncrossed Rubrospinal Extrapyramidal Red nucleus (midbrain) Crossed Tectospinal Extrapyramidal Superior colliculus (midbrain) Crossed Vestibulospinal Extrapyramidal Vestibular nuclei (medulla oblongata) Uncrossed Reticulospinal Extrapyramidal Reticular formation (medulla and pons) Crossed The extrapyramidal tracts originate in the brainstem, carrying motor fibers to the spinal cord. They are responsible for the involuntary and automatic control of all musculature. Reticulospinal tracts are the major descending extrapyramidal tracts. Vestibulospinal tracts arise from the vestibular nuclei in the medulla oblongata Rubrospinal tracts arise from the red nuclei. Tectospinal tracts arise from the tectum in the midbrain. © 2019 McGraw-Hill Education  1 2 I. The Peripheral Nervous System © 2019 McGraw-Hill Education  Peripheral Nervous System (PNS): 1 3 introduction Composed of: 1. Nerves: bundles of axons in the PNS are referred to as nerves. These structures in the periphery are different than the central counterpart, called a tract. 1. Cranial Nerves 2. Spinal Nerves 2. Ganglia: group of neuron cell bodies in the periphery. They can be categorized, for the most part, as either sensory ganglia or autonomic ganglia, referring to their primary functions. © 2019 McGraw-Hill Education  1 4 Cranial Nerves 1. Nerves that arise directly from nuclei in the brain 2. Twelve pairs 3. Most are mixed nerves with both sensory and motor fibers (i.e. the vagus nerve [cranial nerve X] ) 4. Those associated with vision, olfaction, and hearing are sensory only. https://co.pinterest.com/pin/55943220356399163/?lp=true Cranial Nerves © 2019 McGraw-Hill Education  1 5 Spinal Nerves 1. Nerves that arise directly from the spinal cord 2. 31 pairs: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal 3. Spinal Nerves are mixed nerve. 4. The sensory fibers enter the cord via the posterior/dorsal root, and the motor fibers exit by way of the anterior/ventral root © 2019 McGraw-Hill Education  Peripheral Nervous System (PNS): 1 6 introduction Composed of: 1. Nerves: bundles of axons in the PNS are referred to as nerves. These structures in the periphery are different than the central counterpart, called a tract. 1. Cranial Nerves 2. Spinal Nerves 2. Ganglia: group of neuron cell bodies in the periphery. They can be categorized, for the most part, as either sensory ganglia or autonomic ganglia, referring to their primary functions. © 2019 McGraw-Hill Education  1 7 Ganglia A ganglia is a group of neuron cell bodies in the periphery. They work as relay station for nerve signals. One nerve enters (preganglionic) and another nerve exits (postganglionic) from each ganglion. The cell bodies of the preganglionic neurons are in the brainstem or spinal cord of the central nervous system (CNS). The cell bodies of the postganglionic neurons are in the ganglia. Ganglia can be categorized, for the most part, as either sensory ganglia or autonomic ganglia, referring to their primary functions. © 2019 McGraw-Hill Education  1 8 Different part of the PNS 1. Somatic nervous system: serves the skin, skeletal muscles, and tendons. It includes nerves that take sensory information from external sensory receptors to the CNS and motor commands away from the CNS to the skeletal muscles. Sensory nerve fibers in the peripheral nerves are the peripheral axonal process of neurons in the dorsal root ganglion. 2. Autonomic nervous system: innervates all effector organs and tissues except for skeletal muscles. It is autonomic because it functions subconsciously and involuntarily. Somatic Nervous System Autonomic Nervous System © 2019 McGraw-Hill Education  1 9 Autonomic Nervous System Autonomic nervous system regulates: Activities of glands Smooth muscle function Function of heart and circulatory system Function of digestive system etc… Visceral organs innervated by the Autonomic Nervous system © 2019 McGraw-Hill Education  2 0 Autonomic Nervous System Sympatetic - fight or flight Involved in responses that would be associated with fighting or fleeing, such as increasing heart rate and blood pressure as well as constricting blood vessels in the skin and dilating them in muscles. The sympathetic division is most active during times of excitement and physical activity. Parasympatetic - rest and digest Involved in energy conservation functions and increases gastrointestinal motility and secretion. It also increases bladder contractility. The parasympathetic division is most active during rest and stimulates digestive activities. © 2019 McGraw-Hill Education  2 1 Sympathetic Division 1.The axons of preganglionic neurons come from the thoracic and lumbar regions of the Sympathetic is in red spinal cord. 2.Preganglionic neurons (not all of them…see point 3 below) synapse in sympathetic ganglia that run parallel to the spinal cord. 1. These are called the paravertebral ganglia. 2. Paravertebral ganglia are connected, forming a sympathetic chain of ganglia. 3.Many of the sympathetic neurons that exit the spinal cord below the diaphragm do not synapse in the sympathetic chain of ganglia. 1. Collateral ganglia include celiac, superior mesenteric, and inferior mesenteric ganglia © 2019 McGraw-Hill Education  2 2 Sympathetic Division: chain of ganglia It allows nerve fibers to travel to spinal nerves that are superior and inferior to the one in which they originated. Convergence and Divergence Because preganglionic neurons can branch and synapse in ganglia at any level, there is: 1) Divergence: One preganglionic neuron synapses on several postganglionic neurons at different levels. 2) Convergence: Several preganglionic neurons at different levels synapse on one postganglionic neuron. Allows the sympathetic division to act as a single unit through mass activation and to be tonically active © 2019 McGraw-Hill Education  2 3 Parasympathetic Division Preganglionic neurons come from the brain (brainstem) and sacral region of the spinal cord. a. Also called the craniosacral division. Some preganglionic neurons synapse on small terminal ganglia or intramural ganglia, so named because they lie near or within (respectively) the organs they innervate. 1) Exception are the four parasympathetic ganglia of the head and neck. © 2019 McGraw-Hill Education  Parasympathetic Division: the vagus 2 4 nerve The vagus nerve (X) represents the main Vagus Nerve Innervation component of the parasympathetic nervous system. The vagus nerve oversees a vast array of crucial bodily functions, including control of mood, immune response, digestion, and heart rate. It establishes one of the connections between the brain and the gastrointestinal tract and sends information about the state of the inner organs to the brain via afferent sensory fibers. © 2019 McGraw-Hill Education  2 5 III. Functions of the Autonomic Nervous System © 2019 McGraw-Hill Education  2 6 Autonomic Nervous System Sympatetic - fight or flight Involved in responses that would be associated with fighting or fleeing, such as increasing heart rate and blood pressure as well as constricting blood vessels in the skin and dilating them in muscles. The sympathetic division is most active during times of excitement and physical activity. Parasympatetic - rest and digest Involved in energy conservation functions and increases gastrointestinal motility and secretion. It also increases bladder contractility. The parasympathetic division is most active during rest and stimulates digestive activities. © 2019 McGraw-Hill Education  2 Adrenergic and Cholinergic Synaptic 7 Transmission 1. Cholinergic Synaptic Transmission a. Acetylcholine (ACh) is the neurotransmitter used by all preganglionic neurons (sympathetic and parasympathetic) a. Always excitatory - nicotinic receptors b. It is also the neurotransmitter released from most parasympathetic post ganglionic neurons. a. Can be excitatory or inhibitory - muscarinic receptors. 2. Adrenergic Synaptic Transmission a. Norepinephrine is the neurotransmitter released by most sympathetic postganglionic neurons. a. Can be excitatory or inhibitory - noradrenergic alpha or beta receptors. © 2019 McGraw-Hill Education  2 8 Other Autonomic Neurotransmitters 1. Some postganglionic autonomic neurons do not release ACh or norepinephrine. a. Called “nonadrenergic, noncholinergic fibers” b. Proposed neurotransmitters include ATP, vasoactive intestinal peptide (VIP), and nitric oxide (NO). © 2019 McGraw-Hill Education  2 9 Organs with Dual Innervation 1. Most visceral organs are innervated by both sympathetic and parasympathetic neurons. 2. The activity of the two divisions of the autonomic system can be: a. Antagonistic b. Complementary c. Cooperative © 2019 McGraw-Hill Education  3 Antagonistic action of sympathetic and parasympathetic 0 autonomic system a. Occur when both divisions produce opposite effects on the same target b. Example - a. Heart rate – sym increases, para decreases b. Digestive functions – sym decreases, para increases c. Pupil diameter – sym dilates, para constricts © 2019 McGraw-Hill Education  3 Complementary action of sympathetic and 1 parasympathetic autonomic system a. Occur when both divisions produce similar effects on the same target b. Example - Salivary gland secretion: parasympathetic division stimulates secretion of saliva; sympathetic constricts blood vessels so the secretion is thicker. © 2019 McGraw-Hill Education  3 Cooperative action of sympathetic and parasympathetic 2 autonomic system a. Occur when both divisions produce different effects that work together to promote a single action. b. Example - Urination: parasympathetic division aids in urinary bladder contraction; sympathetic helps with bladder muscle tone to promote/control urination reflex (triggered when the bladder fills with urine). © 2019 McGraw-Hill Education  3 3 Organs Without Dual Innervation 1. The following organs are innervated by the sympathetic division only: a. Adrenal medulla b. Arrector pili muscles in skin c. Sweat glands in skin d. Most blood vessels 2. Regulated by increase and decrease in sympathetic nerve activity 3. Important for body temperature regulation through blood vessels and sweat glands © 2019 McGraw-Hill Education  1 Different part of the PNS Divided in: 1. Somatic nervous system: sensory and motor nerves that innervate the limbs and body. 2. Autonomic nervous system: innervates all effector organs and tissues except for skeletal muscles. It is autonomic because it functions subconsciously and involuntarily. 1. Sympathetic 2. Parasympathetic Somatic Nervous System Autonomic Nervous System © 2019 McGraw-Hill Education  2 Introduction Ascending tracts and sensory component of cranial nerves are the neural pathways of sensory systems. © 2019 McGraw-Hill Education  Sensory physiology A sensory system is a part of the nervous system responsible for processing sensory information. It consists of : sensory receptors, neural pathways (slide before), and parts of the brain involved in sensory perception. In each sensory modality : 1- a specific type of stimulus energy is transformed into electrical signals by specialized receptors. 2- The sensory information is transmitted to the central nervous system by trains of action potentials (along the neural pathway) that represent aspects of the stimulus. © 2019 McGraw-Hill Education  I. Characteristics of Sensory 4 Receptors © 2019 McGraw-Hill Education  5 Introduction to Sensory Receptors 1. Sensory receptors are specialized cells, usually neurons, that detect and respond to physical and chemical stimuli. 2. Many sensory receptors cells are located at the surface to detect external stimuli, but others lie within body tissues to monitor internal organ functions and provide crucial homeostatic feedback regulation © 2019 McGraw-Hill Education  6 Introduction to Sensory Receptors Sensory receptors cells transduce (change) different forms of energy in the “real world” into nerve impulses. Different modalities of sensations (sound, light, pressure, taste, odor) arise from differences in neural pathways and synaptic connections a. If the optic nerve delivers an impulse, the brain interprets it as light even though the impulse (in the form of action potential) is the same as for hearing, taste, olfaction, etc… Sensory receptors cells Transduction Processing of sensory information Generation of action potential CNS © 2019 McGraw-Hill Education  7 Functional Categories of Sensory Receptors: Type of Signal a. According to the type of signal they transduce: 1) Chemoreceptors: sense chemicals in the external (taste, smell) or internal (CO2) environment 2) Photoreceptors: sense light. 3) Thermoreceptors: respond various degrees of heat. 4) Mechanoreceptors: stimulated by mechanical deformation of the receptor (touch, hearing). 5) Nociceptors: sense stimuli that accompany tissue damage (high heat, high pressure acid). b. According to the type of information they deliver to the brain: 1) Proprioceptors: found in muscles, tendons, and joints. Provide a sense of body position and allows fine muscle control. 2) Cutaneous (skin) receptors – touch, pressure, heat, cold, and pain 3) Special senses – vision, hearing, taste, smell, equilibrium © 2019 McGraw-Hill Education  8 Categories of Sensory Receptors c. According to the origin of the information: 1) Exteroceptors: respond to stimuli from outside the body; includes cutaneous receptors and special senses 2) Interoceptors: respond to internal stimuli; found in organs; monitor blood pressure, pH, and oxygen concentrations. d. According to how they respond to a stimulus. 1. Phasic receptors 2. Tonic receptors © 2019 McGraw-Hill Education  9 Generator (Receptor) Potential 1. Sensory receptors cells behave very similarly to dendrites of neurons. 2. Stimuli produce depolarizations called generator potentials. a. Similar to EPSPs: It is a graded response b. Light touch on a Pacinian corpuscle in the skin produces a small generator potential. c. Increasing the pressure increases the magnitude of the generator potential until threshold is met and an action potential occurs. © 2019 McGraw-Hill Education  1 0 Generator (Receptor) Potential The generator (receptor) potential is (like the EPSP) proportional to the intensity of the stimulus. Increased intensity results in increased frequency of action potential after threshold is reached. © 2019 McGraw-Hill Education  1 1 Generator (Receptor) Potential © 2019 McGraw-Hill Education  1 2 Categories of Sensory Receptors Tonic Maintain a high firing rate if the stimulus is applied (they can be no adapting or slow-adapting). Examples: no adapting: pain receptors, and proprioceptors. (A) slow adapting: Merkel’s discs and Ruffini corpuscles (touch and pressure), interoceptors. (B) Phasic: respond with a burst of activity when stimulus is first applied but quickly adapt to the stimulus by decreasing response (fast-adapting) (C) a) Allow sensory adaptation – cease to pay attention to constant stimuli b) May deliver another burst when stimulus is removed to provide on and off information c) Examples - smell, touch (Pacinian Corpuscles), temperature (actually this can occur with all senses) © 2019 McGraw-Hill Education  1 3 V. The Ears and Hearing © 2019 McGraw-Hill Education  1 4 The sense of Hearing 1. The human ear (and other animals) are sensitive detectors capable of detecting the fluctuations in air pressure that impinge upon the eardrum. 1) Capable of detecting sound waves with a wide range of frequencies, ranging between approximately 20 Hz to 20 000 Hz. 2) Cats can detect frequencies as low as approximately 45 Hz and as high as 85 000 Hz. 3) Dolphins can detect frequencies as high as 200 000 Hz. 2. Intensity or loudness, measured in decibels 1) Related to the amplitude of the wave 2) Human optimal range is 0 to 80 dB 3. Frequency or pitch 1) The frequency of sound waves is measured in hertz (Hz), or the number of waves that pass a fixed point in a second. © 2019 McGraw-Hill Education  1 5 The Ear 1.Outer ear (external ear): Pinna or auricle and external auditory canal – sound gathering 2.Middle ear: made of tiny bones – modulation of sound vibrations and transfer to the inner ear. 3.Inner ear: cochlea – transduction of sound vibration into electrical signals. https://www.britannica.com/science/ear/The-physiology-of-hearing © 2019 McGraw-Hill Education  1 6 The Outer Ear 1.Sound waves enter the outer ear and travel through a narrow passageway called the ear canal (external auditory meatus), which leads to the eardrum or tympanic membrane. 2.The eardrum vibrates from the incoming sound waves and sends these vibrations to three tiny bones in the middle ear. https://www.britannica.com/science/ear/The-physiology-of-hearing © 2019 McGraw-Hill Education  1 7 Medial View of the Middle Ear 1. Air-filled cavity between the tympanic membrane and the cochlea 2. Contains three bones called ossicles: a. Malleus → incus → stapes b. Vibrations are transmitted and amplified along the bones. c. The stapes is attached to the oval window, which transfers the vibrations into the cochlea in the inner ear. d. Stapedius muscle dampens the stapes if the sound is too intense © 2019 McGraw-Hill Education  1 8 The Cochlea 1.The cochlea is the hearing part of the inner ear. It has a characteristic snail-shaped structure. It is composed of three chambers: 1.The upper chamber is called the scala vestibuli. 2.The lower chamber called the scala tympani. Both chambers are filled with perilymph. 3.The cochlea also contains a portion of the membranous labyrinth called the scala media, or cochlear duct, filled with endolymph. This chamber contains the sensitive element in the inner ear the organ of Corti (Spiral organ). 4.Endolymph (High K+) and perilymph vary significantly in their concentration of ions. This difference is essential to the overall function of the cochlea. © 2019 McGraw-Hill Education  1 9 The Cochlea Journey of sound vibrations reaching The organ of Corti 1.Vibrations from the oval window of the middle ear displace perilymph in the scala vestibuli. 2.Vibrations pass through the vestibular membrane into the scala media (or cochlear duct) through the endolymph. 3.Next, vibrations pass through the basilar membrane into the perilymph of the scala tympani. 4.Vibrations leave the inner ear via the round window. © 2019 McGraw-Hill Education  2 0 The Cochlea: Organ of Corti © 2019 McGraw-Hill Education  2 1 Spiral Organ (Organ of Corti) 1. The organ of Corti is the sensitive element in the inner ear and can be thought of as the body's microphone 2. Sensory hair cells are located on the basilar membrane, projecting into the endolymph (High K+) of the cochlear duct a. Inner hair cells: they transform sound waves into nerve impulses. Each is innervated by 10 to 20 sensory neurons of cranial nerve VIII and relay sound. b. Outer hair cells: their role is mostly to amplify softer sound and sharpen pitch perception by changing their length. Such movement are believed to aid the sensory function of the inner hair cells © 2019 McGraw-Hill Education  2 2 How hearing works a. When sound waves enter the scala media, the tectorial membrane vibrates, bending stereocilia of the inner hair cells. 1) Opens mechanically-gated K+ channels that are facing the endolymph 2) K+ rushes in, depolarizing the cell….wait what? ionic gradients unique to the endolymph (High K+). 3) The hair cell itself does not fire an action potential. Instead, the influx of positive ions from the endolymph in the scala media depolarizes the cell, resulting in a receptor potential. 4) Releases glutamate onto sensory neurons 5) The greater the amount of basilar membrane displacement and bending the stereocilia, the more glutamate is released, producing a greater receptor potential. © 2019 McGraw-Hill Education  2 3 The Cochlea: tonotopic organization © 2019 McGraw-Hill Education  2 4 Neural Pathways 1. Vestibulocochlear nerve → 2. Cochlear nuclei in the medulla oblongata & pons→ 3. Inferior colliculus of midbrain → 4. Medial geniculate body of the thalamus → 5. Auditory cortex of temporal lobe; © 2019 McGraw-Hill Education  2 5 Hearing Impairment 1. Conduction deafness: Sound waves are not conducted from the outer to the inner ear. a. May be due to a buildup of earwax, too much fluid in the middle ear, damage to the eardrum, or overgrowth of bone in the middle ear b. Impairs hearing of all sound frequencies c. Can be helped by hearing aids 2. Sensorineural/perceptive deafness: Nerve impulses are not conducted from the cochlea to the auditory cortex. a. May be due to damaged hair cells (from loud noises) b. May only impair hearing of particular sound frequencies and not others c. May be helped by cochlear implants 3. Presbycusis – age-related hearing impairment © 2019 McGraw-Hill Education  1 II. Cutaneous Sensations © 2019 McGraw-Hill Education  2 Cutaneous Receptors 1.Pain, cold, and heat receptors are naked dendrites of sensory neurons. a. Free nerve endings 2.Touch and pressure receptors have special structures around their dendrites. a. Merkel’s disks b. Meissner’s corpuscles: c. Pacinian corpuscles: d. Ruffini corpuscles © 2019 McGraw-Hill Education  3 Cutaneous Receptors: temperature Cold Receptors: Transient receptor potential (TRP) channel a. There are many more receptors that respond to cold than to hot. b. Located close to the epidermis c. Stimulated by cold and inhibited by warm d. Some cold receptors also respond to menthol e. The temperature range of response is 8 to 28°C Warm Receptors: Transient receptor potential (TRP) channel a. Located deeper in the dermis b. Excited by warming and inhibited by cooling c. Different from receptors that detect painful heat (see below) Hot Receptors: Transient receptor potential (TRP) channel a. The pain experienced by a hot stimulus is sensed by a special nociceptor called a capsaicin receptor. b. Also a receptor for the chemical found in chili peppers (capsaicin) c. Activated at 43°C or higher © 2019 McGraw-Hill Education  4 Pain Receptors a. Nociceptors can be myelinated or unmyelinated. 1) Sudden, sharp pain is transmitted by myelinated neurons. 2) Dull, persistent pain is transmitted by unmyelinated neurons. b. Nociceptors may be activated by chemicals released by damaged tissues, such as ATP, or by pH change or mechanical stimuli. 7. Itch Sensation a. Acute itch stimulated by histamine release from mast cells and basophils. b. Chronic itch stimulated by other chemicals and does not respond to antihistamines c. Receptors stimulate unmyelinated sensory axons to the spinal cord © 2019 McGraw-Hill Education  5 Neural Pathway for Somesthetic Sensations Tract Origin Termination Function Anterolateral Posterior horn on one Thalamus, then Conducts pain and temperature impulses that spinothalamic side of cord but crosses cerebral are interpreted within cerebral cortex to opposite side cortex © 2019 McGraw-Hill Education  6 Receptive Fields and Sensory Acuity 1. The receptive field is the area of skin that, when stimulated, changes the firing rate of a neuron. a. The size of a receptive field depends on the density of receptors in that region of skin. b. There are few receptors in the back and legs, so the receptive fields are large. c. There are many receptors in the fingertips, so the receptive fields are small d. The more receptors, the smaller the field, the larger the area of the somatosensory cortex e. A small receptive field = greater tactile acuity – sharpness of the sensation © 2019 McGraw-Hill Education  7 Two-point touch threshold a. Receptive fields can be measured by seeing at what distance a person can perceive two separate points of touch. b. Measures tactile acuity c. Important in spacing the raised dots in Braille symbols © 2019 McGraw-Hill Education  8 Two-Point Touch Threshold TABLE 10.3 The Two-Point Touch Threshold for Different Regions of the Body Body Region Two-Point Touch Threshold (mm) Big toe 10 Sole of foot 22 Calf 48 Thigh 46 Back 42 Abdomen 36 Upper arm 47 Forehead 18 Palm of hand 13 Thumb 3 First finger 2 Source: Weinstein, S., and D.R. Kenshalo, editors, The Skin Senses. Springfield, Illinois: Charles C. Thomas, Publisher, Ltd., 1968. © 2019 McGraw-Hill Education  9 VI. The Eyes and Vision © 2019 McGraw-Hill Education  1 Introduction to Vision 0 1. Vision comes from light energy transduced into nerve impulses 2. Only a limited part of the electromagnetic spectrum can excite photoreceptors in the eye. © 2019 McGraw-Hill Education  1 1 Structure of the eye 1. Sclera: tough outer layer of the eyeball (the white of the eye). The slight bulge in the sclera at the front of the eye is the cornea. The cornea directs light rays into the eye and helps focus them on the retina. 2. Pupil: is the opening in the colored part of the eye (which is called iris). It allows light to pass to the lens. 3. Lens: normally clear and is located behind the iris. Small muscles attached to the lens can change its shape. This allows the eye to focus on near or far objects. 4. Retina: thin nerve tissue that lines the back of the eye. It detects light entering the eye and converts it into electrical impulses. 1. Fovea-Macula: is part of the retina provides the sharp, detailed, central vision that allows you to focus on what is directly in the line of sight. The rest of the retina provides side (peripheral) vision, which allows you to see shapes but not fine details. © 2019 McGraw-Hill Education  General Pathway of light through the 1 2 eye a. Light passes through the cornea and into the anterior chamber of the eye. b. Next, it passes through the pupil, which can change shape (due to the pigmented iris muscle) to allow more or less light in. c. Then it passes through the lens, which can change shape to focus the image. d. Then passes through the posterior chamber and the vitreous body e. Finally, it hits the retina, where photoreceptors are found. © 2019 McGraw-Hill Education  1 3 Structures of the Eye: Pupil and Iris a. The iris sphincter muscle (pupillary sphincter, pupillary dilator) can increase or decrease the diameter of the pupil. 1) Constriction: contraction of pupillary sphincter via parasympathetic stimulation 2) Dilation: contraction of pupillary dilator via sympathetic stimulation b. The iris also has pigmented epithelium for eye color © 2019 McGraw-Hill Education  1 4 VII. The Retina © 2019 McGraw-Hill Education  1 5 Introduction to the Retina 1. The retina is approximately 0.5 mm thick and lines the back of the eye. The retina consist of : 1. single cell pigmented epithelium, 2. photoreceptors neurons called rods and cones 3. and layer of other neurons. 2. The photosensors the rods and cone) lie outermost in the retina against the pigment epithelium. 3. The ganglion cells (the output neurons of the retina) lie innermost in the retina "closest" to the lens and the front of the eye. 4. The optic nerve contains the ganglion cell axons running to the brain © 2019 McGraw-Hill Education  1 6 Layers of the Retina: rods and cones © 2019 McGraw-Hill Education  1 7 Layers of the Retina: rods and cones 1. Photoreceptors (rods and cones) are in the inner layer (toward the vitreous body) © 2019 McGraw-Hill Education  1 8 Layers of the Retina: rods and cones 1. Photoreceptors (rods and cones) are in the inner layer (toward the vitreous body) 2. They synapse on a middle layer of bipolar cells, which synapse on the outer layer of ganglion cells. 3. There are also horizontal cells and amacrine cells within the layers © 2019 McGraw-Hill Education  1 9 Layers of the Retina: rods and cones © 2019 McGraw-Hill Education  Electrical Activity of the rods of the “On- 2 0 pathway” 1. Contain the pigment rhodopsin. Rhodopsin is extremely sensitive to light. When rhodopsin is exposed to light, it immediately photobleaches. Effects of Light on the Rods – “on pathway” © 2019 McGraw-Hill Education  Effects of Light on the Retina – “on 2 1 pathway” 1. When Light Hits Photoreceptors a. Dissociation of rhodopsin activates a G- protein/2nd messenger system, which closes Na+ channels. 1) G-proteins are called transducins. 2) Activation of the enzyme phosphodiesterase converts cGMP to GMP. 3) This closes Na+ channels. b. Photoreceptors are hyperpolarized, and inhibition on bipolar cells is lifted. c. Bipolar cells activate ganglion cells that transmit action potentials to the brain Inhibitory effect © 2019 McGraw-Hill Education  2 2 Glutamate receptors Receptors for glutamate fall into three major classes, known as 1. AMPA receptors (iGluR - ligand) 2. NMDA receptors (IGluR - ligand and voltage!) 3. Metabotropic glutamate receptors. 1. Metabotropic receptors act through second messenger systems to create slow, sustained effects on their targets. © 2019 McGraw-Hill Education  2 3 Neural Pathway for Vision Geniculostriate System a. Axons from ganglion cells synapse on the lateral geniculate nucleus of the thalamus by way of the optic chiasma b. Information from the lateral portion of the retinas does not cross sides, but information from the medial portion does. c. Neurons from the thalamus synapse on the visual cortex of the occipital lobe. d. Carries information of “what” is seen Tectal System a. 20 to 30% of the ganglion cell axons synapse on the superior colliculus of the midbrain, which helps with eye and body movements. b. Carries information about “where” the object is © 2019 McGraw-Hill Education  2 4 III. Taste and Smell © 2019 McGraw-Hill Education  2 5 Introduction: Taste and Smell 1. Chemoreceptors a. Interoceptors detect chemical changes within the body. b. Exteroceptors detect changes from outside the body; include taste and smell. 1) Taste responds to chemicals dissolved in food and drink. 2) Smell responds to chemical molecules from the air. 3) Olfaction greatly influences gustation © 2019 McGraw-Hill Education  2 6 Taste 1. Also called gustation: Sweet; Sour; Acid; Bitter Umami (Savory). Receptor cells are called “Taste cells” 2. Taste cells are specialized epithelial cells with long microvilli that extend out through the pore in the taste bud to the environment of the mouth 3. Taste cells are organized in taste buds – each taste bud consist of 50 to 100 taste cells. 4. Taste buds (and the taste cells) constantly regenerate throughout adult life - ever~2 weeks © 2019 McGraw-Hill Education  2 7 Location of Taste Buds a. Located in bumps on the tongue called papillae b. Types of papillae: 1) Fungiform: anterior surface a) Information travels via facial nerve. 2) Circumvallate: posterior surface a) Information travels via glossopharyngeal nerve. 3) Foliate: sides a) Information travels via glossopharyngeal nerve. © 2019 McGraw-Hill Education  2 8 Taste cells Specialized epithelial cells 1) They behave like neurons by depolarizing (receptor potential) and releasing neurotransmitters. 2) Microvilli are equipped with receptors (T1 and T2) and encounter chemicals; the binding of the taste chemical with the receptors lead to depolarization of the taste cell. 3) Cells release neurotransmitters (ATP and serotonin) onto sensory neurons. 4) Each taste bud has taste cells sensitive to each category of tastes. © 2019 McGraw-Hill Education  2 9 Taste pathways Facial and glossopharyngeal nerves → Medulla oblongata (NST) → Thalamus → Primary gustatory cortex of insula, somatosensory cortex of parietal lobe, and prefrontal cortex © 2019 McGraw-Hill Education  3 0 Smell 1. Olfactory Apparatus a. Smell is also called olfaction. b. Olfactory receptors are located in the olfactory epithelium of the nasal cavity. c. Basal stem cells replace receptors damaged by the environment. © 2019 McGraw-Hill Education  3 Smell: a mature OSN express only one OR 1 gene © 2019 McGraw-Hill Education  3 2 Smell How Smell Works a. G-protein coupled b. Odor binding activates adenylate cyclase to make cAMP and PPi (pyrophosphate) c. cAMP opens Na+ and Ca2+ channels d. Produces a graded depolarization which stimulates the action potential e. Up to 50 G-proteins may be associated with 1 receptor protein – gives great sensitivity through amplification © 2019 McGraw-Hill Education  3 3 Smell © 2019 McGraw-Hill Education  3 4 Smell b. The mitral and tufted neurons of the glomeruli in the olfactory bulb synapse on the primary olfactory cortex of the frontal and parietal lobes c. Interconnections are made with the amydgala, hippocampus, and limbic system through the piriform cortex © 2019 McGraw-Hill Education  1 III. Taste and Smell © 2019 McGraw-Hill Education  2 Introduction: Taste and Smell 1. Chemoreceptors a. Interoceptors detect chemical changes within the body. b. Exteroceptors detect changes from outside the body; include taste and smell. 1) Taste responds to chemicals dissolved in food and drink. 2) Smell responds to chemical molecules from the air. 3) Olfaction greatly influences gustation © 2019 McGraw-Hill Education  3 Taste 1. Also called gustation: Sweet; Sour; Acid; Bitter Umami (Savory). Receptor cells are called “Taste cells” 2. Taste cells are specialized epithelial cells with long microvilli that extend out through the pore in the taste bud to the environment of the mouth 3. Taste cells are organized in taste buds – each taste bud consist of 50 to 100 taste cells. 4. Taste buds (and the taste cells) constantly regenerate throughout adult life - ever~2 weeks © 2019 McGraw-Hill Education  4 Location of Taste Buds a. Located in bumps on the tongue called papillae b. Types of papillae: 1) Fungiform: anterior surface a) Information travels via facial nerve. 2) Circumvallate: posterior surface a) Information travels via glossopharyngeal nerve. 3) Foliate: sides a) Information travels via glossopharyngeal nerve. © 2019 McGraw-Hill Education  5 Taste cells Specialized epithelial cells 1) They behave like neurons by depolarizing (receptor potential) and releasing neurotransmitters. 2) Microvilli are equipped with receptors (T1 and T2) and encounter chemicals; the binding of the taste chemical with the receptors lead to depolarization of the taste cell. 3) Cells release neurotransmitters (ATP and serotonin) onto sensory neurons. 4) Each taste bud has taste cells sensitive to each category of tastes. © 2019 McGraw-Hill Education  6 Taste pathways Facial and glossopharyngeal nerves → Medulla oblongata (NST) → Thalamus → Primary gustatory cortex of insula, somatosensory cortex of parietal lobe, and prefrontal cortex © 2019 McGraw-Hill Education  7 Smell 1. Olfactory Apparatus a. Smell is also called olfaction. b. Olfactory receptors are located in the olfactory epithelium of the nasal cavity. c. Basal stem cells replace receptors damaged by the environment. © 2019 McGraw-Hill Education  8 Smell: a mature OSN express only one OR gene © 2019 McGraw-Hill Education  9 Smell How Smell Works a. G-protein coupled b. Odor binding activates adenylate cyclase to make cAMP and PPi (pyrophosphate) c. cAMP opens Na+ and Ca2+ channels d. Produces a graded depolarization which stimulates the action potential e. Up to 50 G-proteins may be associated with 1 receptor protein – gives great sensitivity through amplification © 2019 McGraw-Hill Education  1 0 Smell © 2019 McGraw-Hill Education  1 1 Smell b. The mitral and tufted neurons of the glomeruli in the olfactory bulb synapse on the primary olfactory cortex of the frontal and parietal lobes c. Interconnections are made with the amydgala, hippocampus, and limbic system through the piriform cortex © 2019 McGraw-Hill Education  1 2 Nervous system vs. endocrine system Electrical impulses are Information is the mode in which transmitted via the information is blood vessels. transmitted. Hormones are the Neurotransmitters are messenger in the the messenger in the endocrine system. nervous system. © 2019 McGraw-Hill Education  1 3 Common Aspects of Neural and Endocrine Regulation 1. Hormones and neurotransmitters both interact with specific receptors. 2. Binding to a receptor causes a change within the cell. 3. There are mechanisms to turn off target cell activity; the signal is either removed or inactivated. 4. Some hormones can also be neurotransmitters in the CNS 1. Noradrenaline (Norepinephrine) 2. Adrenaline (Epinephrine) © 2019 McGraw-Hill Education  1 4 Hormone Interactions 1. A target tissue is usually responsive to several different hormones. a. Hormones may be a. Synergistic i. Complementary ii. Addictive b. Antagonistic c. Permissive b. How a cell responds depends on the amount of hormone and the combination of all hormones. © 2019 McGraw-Hill Education  Hormone Interactions: Synergistic 1 5 Effects a. Occur when two or more hormones work together to produce a particular effect b. Effects may be additive, as when epinephrine and norepinephrine each affect the heart in the same way. c. Effects may be complementary, as when each hormone contributes a different piece of an overall outcome. 1) For example, lactation requires estrogen, prolactin, and oxytocin 1) Estrogen and progesterone prepare the breasts to make milk. 2) Prolactin helps the breasts make milk. 3) Oxytocin releases milk from the breasts. © 2019 McGraw-Hill Education  Hormone Interactions: Antagonistic 1 6 Effects a. Occur when hormones work in opposite directions. b. Insulin and glucagon affect both glucose blood- levels and adipose tissue. 1) Insulin stimulates cellular uptake of glucose and promote fat storage by inhibition of fat breakdown. 2) Glucagon stimulates glucose production (gluconeogenesis) and secretion in the blood, and stimulate fat breakdown (Lipolysis, ketogenesis). © 2019 McGraw-Hill Education  Hormone Interactions: Permissive 1 7 Effects a. Occur when one hormone makes the target cell more responsive to a second hormone 1) Exposure to estradiol makes the uterus more responsive to progesterone. 2) Increased secretion of parathyroid (PTH) hormone makes the intestines more responsive to Vit D3 in calcium absorption © 2019 McGraw-Hill Education  1 8 Effects of Hormone Concentrations on Tissue Response 1. Hormone Half-life a. The time required for the plasma concentration of a given amount of hormone to be reduced by half b. The half-life of hormones circulating in the blood ranges from minutes to hours to days. c. Most hormones are removed from the blood by the liver and converted to less active products 2. Hormone Concentration a. Tissues only respond when hormone concentrations are at a certain “normal” or physiological level. b. At higher pharmacological concentrations (when taken as drugs), effects may be different from normal. 1) High concentrations may result in binding to receptors of different (but closely related) hormones. 2) This can result in widespread side effects. © 2019 McGraw-Hill Education  1 9 Effects of Hormone Concentrations on Tissue Response 3. Priming Effects/Up-regulation a. Some target cells respond to a particular hormone by increasing the number of receptors it has for that hormone. b. This makes it more sensitive to subsequent hormone release and have a greater response 4. Desensitization and Downregulation a. Prolonged exposure to high concentrations of hormone may result in a decreased number of receptors for that hormone. b. To avoid desensitization, many hormones are released in spurts, called pulsatile secretion. © 2019 McGraw-Hill Education  2 0 II. Mechanisms of Hormone Action © 2019 McGraw-Hill Education  2 1 Introduction: Hormone Action 1. Hormones bind to receptors on or in target cells. a. Binding is highly specific (high affinity). b. Hormones bind to receptors with a low capacity; saturating the receptors with hormone molecules 2. Lipophilic hormone receptors are in the cytoplasm or nucleus 3. Water-soluble hormone receptors are on the outer surface of the plasma membrane © 2019 McGraw-Hill Education  2 2 Hormones That Bind to Nuclear Receptor Proteins Lipophilic steroid hormones and thyroid hormones: a. Travel (in the bloodstream) to target cells attached to carrier proteins b. At the target cell, dissociate from the carrier protein and diffuse across the plasma membrane c. Receptors are found within the nucleus or the cytoplasm and are called nuclear hormone receptors because they activate genetic transcription These hormone receptors serve as transcription factors (genomic action). a. They are activated by the binding of the hormone b. The effect of these hormones is therefore to produce new proteins, usually enzymes that change metabolism inside the cell. © 2019 McGraw-Hill Education  2 3 Hormones That Bind to Nuclear Receptor Proteins a. Two regions on the receptor: 1) Ligand-binding domain for the hormone 2) DNA-binding domain for DNA b. Binding of the hormone activates the DNA- binding domain, that binds to a hormone response element on the DNA © 2019 McGraw-Hill Education  2 4 Introduction: Hormone Action 1. Hormones bind to receptors on or in target cells. a. Binding is highly specific (high affinity). b. Hormones bind to receptors with a low capacity; saturating the receptors with hormone molecules 2. Lipophilic hormone receptors are in the cytoplasm or nucleus 3. Water-soluble hormone receptors are on the outer surface of the plasma membrane © 2019 McGraw-Hill Education  2 Water soluble hormones Use 2nd Messengers 5 1. These hormones cannot cross the plasma membrane, so they bind to receptors on the cell surface. 2. Activate an intracellular mediator called a second messenger 3. There are three possible 2nd messenger mechanisms: a. Adenylate cyclase b. Phospholipase C c. Tyrosine kinase © 2019 McGraw-Hill Education  2 6 Adenylate Cyclase (cAMP) System © 2019 McGraw-Hill Education  2 7 Phospholipase C System © 2019 McGraw-Hill Education  2 8 Tyrosine Kinase System © 2019 McGraw-Hill Education  2 Endocrine system 9 The endocrine system is composed of a network of endocrine glands Hypothalamus (in part) Pituitary gland Pineal gland Thyroid Parathyroid Thymus Adrenal Pancreas Ovaries Testes Placenta © 2019 McGraw-Hill Education  3 0 Hypothalamus and pituitary gland The pituitary gland is often referred to as the "master gland" of the body. The hypothalamus decides which hormones the pituitary should release…how?.... by sending either hormonal or electrical messages. © 2019 McGraw-Hill Education https://opentextbc.ca/anatomyandphysiology/chapter/17-3-the-pituitary-gland-and-hypothalamus/  Hypothalamus and posterior Pituitary 3 1 Gland The posterior pituitary (neurohypophysis) is an extension of the neurons of the paraventricular and supraoptic nuclei of the hypothalamus. The cell bodies of these regions rest in the hypothalamus, but their axons descend as the hypothalamic–hypophyseal tract and end in axon terminals that comprise the posterior pituitary The posterior pituitary gland does not produce hormones, but rather stores and secretes hormones produced by the hypothalamus. The paraventricular nuclei produce the hormone oxytocin, whereas the supraoptic nuclei produce ADH. These hormones travel along the axons and are stored the axon terminals of the posterior pituitary. In response to signals from the same Antidiuretic hormone (ADH) Peptide Stimulates water reabsorption by kidneys hypothalamic neurons, the hormones are released from the axon terminals into the Stimulates uterine contractions during bloodstream. Oxytocin Peptide childbirth © 2019 McGraw-Hill Education https://opentextbc.ca/anatomyandphysiology/chapter/17-3-the-pituitary-gland-and-hypothalamus/  Hypothalamus and anterior Pituitary 3 2 Gland The anterior pituitary does manufacture hormones. However, the production and secretion of hormones from the anterior pituitary is regulated by hormones released by the hypothalamus. Hypothalamic hormones are secreted by neurons, but enter the anterior pituitary through the hypophyseal portal system (primary capillary plexus; they don’t enter the systemic circulation at this point!) The hypothalamus can release the following hormones. Hormones produced by the anterior pituitary (in Thyrotropin-releasing hormone (TRH) response to releasing hypothalamic hormones) enter a Corticotropin-releasing hormone (CRH) secondary capillary plexus, and from there drain into Somatostatin the circulation. Gonadotropin-releasing hormone (GnRH) The anterior pituitary produces seven hormones. growth hormone (GH), Growth hormone (GH) Promotes growth of body tissues thyroid-stimulating hormone (TSH) adrenocorticotropic hormone (ACTH), Prolactin (PRL) Promotes milk production from mammary glands follicle-stimulating hormone (FSH), TSH Stimulates thyroid hormone release from thyroid luteinizing hormone (LH), beta endorphin, and prolactin (not in the graph). ACTH Stimulates hormone release by adrenal cortex