Neuro 400FT Chapter 16-3 PDF

Sensory, Motor & Integrative Systems 1  Synapses  Synapse: The point of connection between a nerve cell and another cell Specifically, a synapse is a specialized junction at which a nerve cell...

Sensory, Motor & Integrative Systems 1  Synapses  Synapse: The point of connection between a nerve cell and another cell Specifically, a synapse is a specialized junction at which a nerve cell (a neuron) communicates with a target cell. Target cells include Nerves Muscles Glands 2 3  Synapses  At electrical synapses, which are relatively rare in vertebrates, the membranes of the two cells are in tight contact, producing electrical coupling, which enables a nerve impulse (or action potential) arriving at the presynaptic nerve ending to pass swiftly and reliably to the next cell.  What effect does this have?  Chemical synapses are more complex, because the presynaptic and postsynaptic cells are physically separated by a gap roughly 10-15 times larger than an electrical synapse (the synaptic cleft). This prevents simple electrical transmission of the action potential to the postsynaptic cell. Instead, transmission is accomplished by 4  Synapses  The cytoplasm of the presynaptic nerve terminal (in a chemical synapse) is packed full of small vesicles, each containing a few thousand molecules of neurotransmitter.  When an action potential arrives in the terminal it stimulates the opening of voltage gated calcium channels in the terminal membrane.  As a consequence, calcium ions flood into the cell and trigger the synaptic vesicles to release their contents into the synaptic cleft.  The neurotransmitter molecules that are liberated diffuse across the cleft and interact with specialized protein receptor 5 6  Neurotransm  itters The molecular structure of the neurotransmitter and its receptor are matched, so that they fit one another like a lock and key (mostly)  At nerve-muscle synapses, and in many nerve-nerve synapses, the receptors have a double function, since they can also serve as ion channels.  Binding of a neurotransmitter produces a change in the three-dimensional shape of the receptor that opens a tiny intrinsic pore in the protein. 7  Neurotransm  In the case itters of neurotransmitters that excite the postsynaptic membrane, the pore permits positively-charged sodium ions to move into the cell, making the potential across its membrane less negative.  This local depolarization is known as an excitatory post-synaptic potential (EPSP), and its amplitude is determined (roughly) by the number of vesicles released from the presynaptic cell.  If it is sufficiently large, the synaptic potential reaches threshold and initiates an action potential in the cell.  If the target cell is a neuron the action potential sweeps along its fibre.  If it is a muscle, it also propagates over the 8 9 10 11 Neurotransmitters  Not all synaptic transmission is excitatory.  Inhibitory transmitters also exist which render the post-synaptic cell less excitable and thus less likely to generate an action potential.  They often act on receptors that act as channels for chloride or potassium ions, and generally make the interior of the postsynaptic cell even more negative (hyperpolarization).  Acetylcholine is the excitatory transmitter at nerve-skeletal muscle synapses, and glutamate is the main excitatory 12 13 14 15  Synaptic Transmission  Step 1: The action potential reaches an axon bulb and causes calcium ion gates to open and calcium ions move into the axon bulb.  Step 2: The rise in calcium ions in the axon bulb causes synaptic vesicles containing neurotransmitter to move towards the presynaptic membrane.  Step 3: Synaptic vesicles merge with the presynaptic membrane and exocytosis of neurotransmitters into the synaptic cleft occurs. Recall that exocytosis requires ATP energy. The axon bulb contains many mitochondria to produce ATP. 16  Step 4: Neurotransmitters diffuse across the synaptic cleft (a very short distance) and bind to receptor proteins on the postsynaptic membrane. Excitatory neurotransmitters cause sodium ions to move through receptor proteins depolarizing the membrane. Inhibitory neurotransmitters do not depolarize the postsynaptic membrane.  Step 5: If sufficient excitatory neurotransmitter binds to receptors, an action potential is produced in the postsynaptic membrane and travels along the length of the second neuron.  Step 6: To prevent continuous stimulation or inhibition of the postsynaptic membrane, neurotransmitters are broken down by 17 18  Serotonin 1) The presynaptic cell makes serotonin (5- hydroxytryptamine, 5HT) from the amino acid tryptophan and packages it in vesicles in the end terminals. Vitamin _____ helps this process. 2) An action potential passes down the presynaptic cell into its end terminals. 3) The action potential stimulates the vesicles containing serotonin to fuse with the cell membrane and exocytose serotonin into the synaptic cleft. 4) Serotonin passes across the synaptic cleft, binds with specialized proteins receptors on the membrane of the postsynaptic cell and depolarizes the postsynaptic cell. If the depolarization reaches the threshold level, a new action potential will be propagated in that cell. 19  Serotonin The remaining serotonin molecules in the cleft and those released by the receptors after use get degraded by the enzyme monoamine oxidase (MAO) In the presynaptic cell MAO destroys the reabsorbed serotonin molecules. This enables the nerve signal to be turned "off" and readies the synapse to receive another action potential. Catechol-o-methyl transferase (COMT) is a similar enzyme that targets catecholamines (dopamine, epinephrine, norepinephrine), but not serotonin. Whereas MAO will target catecholamines. 20 21  Modulation  The action of ‘fast’ neurotransmitters is brief, because they unbind quickly from their receptors and are then rapidly cleared from the synaptic cleft, usually by breakdown into inactive substances or reuptake into the cell.  Because the receptor channels remain open only as long as a neurotransmitter is bound, and because binding is only transient, the synaptic potential is also brief and the membrane potential returns rapidly to its resting level.  Many other transmitters, sometimes called modulators (including serotonin, dopamine, noradrenaline, and many small peptide molecules), act more slowly and for much longer periods of time. 22  Modulation  In general, their receptors do not act as channels but instead activate messenger molecules inside the cell, which can initiate a variety of responses, even including the switching-on/off of genes  It used to be thought that each nerve fibre releases only one neurotransmitter (‘Dale's principle’, after the British pharmacologist, Henry Dale), but it is now known that two or more transmitters and/or modulators can be produced by individual nerve terminals. 23 Name Type Postsynapti Location(s) Function(s) c Effect Brain, Control Dopamine Amine Excitatory smooth arousal muscle levels Brain, Effects on Serotonin Amine Excitatory smooth mood, sleep, muscle pain, appetite Brain, Induce Noradrenalin Amine Excitatory smooth arousal, e muscle heighten mood Parasymathe Role in Acetylecholin Acetic acid Excitatory & tic nervous memory, e (Ach) Inhibitory system, vasodilation brainstem GABA amino acid Inhibitory Brain Control anxiety level Reduce Enkephalin Neuropeptid Brain, spinal stress, 24  Each skeletal muscle fibre is innervated by a single excitatory nerve fibre, which discharges 100-300 vesicles for each arriving nerve impulse (enough to produce an action potential in the muscle cell).  In contrast, a single nerve cell may have tens, hundreds, or even thousands of synapses.  These are not only inhibitory/excitatory, but may involve many different type of transmitters and post-synaptic receptors 25  Each pre-synaptic input may release just a few vesicles in response to a nerve impulse, so that the synaptic potential may be far smaller than that of a muscle fibre and many simultaneous or closely-successive inputs are needed to elicit one action potential. The output of the post- synaptic neuron will therefore be an integrated response to all of its 26  Synapse Abuse  Most drugs that work on the brain, as well as drugs of abuse, act on synapses.  One of the best known is nicotine, which activates nicotinic acetylcholine receptors (especially in the brain) causing dopamine release (euphoria).  Curare, traditionally used by South American natives as an arrow poison, paralyzes prey because it acts antagonistically on the acetylcholine receptor and therefore blocks 27  Synapse Abuse  Morphine and heroin act on opiate receptors, and cannabis (unsurprisingly) on cannabinoid receptors.  Cocaine works differently. It blocks the reuptake system that clears the neurotransmitter dopamine from the synaptic cleft. Consequently, dopamine stays within the synaptic cleft for longer, which explains why cocaine acts as a stimulant.  Some nerve gas (ie. sarin) agents work 28  Synapse Abuse  A range of human diseases result from disorders of synaptic function.  For example, the inherited neuromuscular disorder myasthenia gravis occurs when the body produces antibodies which act antagonistically to the acetylcholine receptors on muscle fibres. This causes them to be bound to the cell, and the reduced number of receptors at the cell surface means that neurotransmission is compromised. Consequently, the patient is easily fatigued.  Graves disease is another classic example of disease related synapse dysfunction. Auto- antibodies are agonistically bound to the thyroid gland, causing an increase in thyroid hormone. 29  Synapse Abuse  Epilepsy is sometimes linked to a decrease in the efficiency of inhibitory transmission (GABA) in the brain, leading to over-excitability of networks of neurons.  There is some evidence that the major psychiatric conditions, depression and schizophrenia, involve disorders of synapses in which serotonin and dopamine, respectively, act as neurotransmitters. 30 31 32 Neural Circuits  Neurons never function in isolation; they are organized into ensembles or circuits that process specific kinds of information. Although the arrangement of neural circuits varies greatly according to the intended function, some features are characteristic of all such ensembles.  The synaptic connections that define a circuit are typically made in a dense tangle of dendrites, axons terminals, and glial cell processes that together constitute a neuropil. Few cell bodies are found here. 33 Neural Circuits  Thus, the neuropil between nerve cell bodies is the region where most synaptic connectivity occurs. The direction of information flow in any particular circuit is essential to understanding its function.  Nerves that carry information toward the central nervous system (or more centrally within the spinal cord/brain) are called afferent neurons. Nerves that carry information away from the brain or spinal cord are called efferent neurons.  Nerve cells that only participate in the local aspects of a circuit are called interneurons or local circuit neurons. These three classes— afferent neurons, efferent neurons, and interneurons—are the basic constituents of all 34 (A) Diagram of nerve cells and their component parts. (B) Axon initial segment (blue) entering a myelin sheath (gold). (C) Terminal boutons (blue) loaded with synaptic vesicles (arrowheads) forming synapses (arrows) with a dendrite (purple). (D) Transverse section of axons (blue) ensheathed by the processes of oligodendrocytes (gold). (E) Apical dendrites (purple) of cortical pyramidal cells. (F) Nerve cell bodies (purple) occupied by large round nuclei. (G) Portion of a myelinated axon (blue) illustrating the intervals between adjacent segments of myelin (gold) referred to as nodes of Ranvier (arrows). (Micrographs from Peters et al., 1991.) 35 36 Neural Circuits  Neural circuits are both anatomical and functional entities. A simple example is the circuit that controls the myotatic (or “knee- jerk”) spinal reflex (see above).  The afferent limb of the reflex is sensory neurons of the dorsal root ganglion in the periphery. These afferents target neurons in the spinal cord.  The efferent limb comprises motor neurons in the ventral horn of the spinal cord with different peripheral targets: One efferent group projects to flexor muscles in the limb, and the other to extensor muscles.  The third element is interneurons in the ventral horn of the spinal cord. The interneurons receive synaptic contacts from the sensory 37 Neural Circuits  The synaptic connections between the sensory afferents and the extensor efferents are excitatory, causing the extensor muscles to contract. Conversely, the interneurons activated by the afferents are inhibitory, and their activation by the afferents diminishes electrical activity in motor neurons and causes the flexor muscles to become less active.  The result is a complementary activation and inactivation of the synergist and antagonist muscles that control the position of the leg.  More complex circuits involve processes such as addiction 38 39  Neuronal Pools  The human body has about 10 million sensory neurons, 20 billion interneurons, and one-half million motor neurons. The interneurons are organized into a smaller number of neuronal pools.  A neuronal pool is a group of interconnected neurons with specific functions. Neuronal pools are defined on the basis of function. A pool may be diffuse, involving neurons in several regions of the brain, or localized, with 40  Neuronal Pools  Estimates of the actual number of pools range between a few hundred and a few thousand.  Each pool has a limited number of input sources and output destinations, and each may contain both excitatory and inhibitory neurons. The output of the entire pool may stimulate or depress the activity of other pools, or it may exert direct control over motor neurons or peripheral effectors.  The pattern of interaction among neurons provides clues to the functional characteristics of a neuronal pool. It is customary to refer to such a "wiring diagram" as a neural circuit, just as we refer to electrical circuits in the wiring of a 41  Divergence is the spread of information from one neuron to several neurons (see left) or from one pool to multiple pools. Divergence permits the broad distribution of a specific input. Considerable divergence occurs when sensory neurons bring information into the CNS, for the information is distributed to neuronal pools throughout the spinal cord and brain. For example, visual information arriving from the eyes reaches your conscious awareness at the same time it is distributed to areas of the brain that control posture and balance at the 42  In convergence, several neurons synapse on the same postsynaptic neuron (see left). Several patterns of activity in the presynaptic neurons can therefore have the same effect on the postsynaptic neuron. Through convergence, the same motor neurons can be subject to both conscious and subconscious control. For example, the movements of your diaphragm and ribs are now being controlled by your brain at the subconscious level. But the same motor neurons can also be controlled consciously, as when you take a deep breath and hold it. Two neuronal pools are 43  Information may be relayed in a stepwise fashion, from one neuron to another or from one neuronal pool to the next. This pattern is called serial processing (see left). Serial processing occurs as sensory information is relayed from one part of the brain to another. For example, when your brain wants to send information from one hemisphere to the other, it 44  Parallel processing occurs when several neurons or neuronal pools process the same information at one time (see left). Divergence must take place before parallel processing can occur. Thanks to parallel processing, many responses can occur simultaneously. For example, when you step on a sharp object, sensory neurons that distribute the information to a number of neuronal pools are stimulated. As a result of parallel processing, you might withdraw your foot, shift your weight, move your arms, feel 45  Some neural circuits utilize feedback to produce reverberation. This can be positive OR negative  In this arrangement, collateral branches of axons somewhere along the sequence extend back toward the source of an impulse and further affect the presynaptic neurons.  Reverberation is like a feedback loop involving neurons; once the circuit is activated, it may continue to stimulate itself or shut itself off. Very complicated examples of reverberation among neuronal pools in the brain may help maintain consciousness, muscular coordination, and normal breathing. 46  Chapter 16 Sensory, Motor & Integrative  Levels and components of sensation Systems  Pathways for sensations from body to brain  Pathways for motor signals from brain to body  Integration Process  wakefulness and sleep  learning and memory 47  Sensation  The components of the brain interact to receive sensory input, integrate and store the information, and transmit motor responses.  To accomplish the primary functions of the nervous system there are neural pathways to transmit impulses from receptors to the circuitry of the brain, which manipulates the circuitry to form directives that are transmitted via neural pathways to effectors as a response. 48  Sensation  Sensation is a conscious or unconscious awareness of external or internal stimuli.  The nature of the sensation and the type of reaction generated vary according to the destination of the impulses in the CNS and the types of receptors stimulated.  Sensory impulses relayed to the spinal cord may serve as input for spinal reflexes, such as the stretch 49  Sensation  When sensory impulses reach the lower brain stem, it can elicit more complex reflexes such as changes in heart rate and breathing rate.  When sensory impulses reach the cerebral cortex, the brain can precisely locate and identify specific sensations such as touch, pain, hearing or taste 50  Is sensation different   than Sensation is any stimulus the body is aware of If we have the receptor, our brain is aware of the sensation  perception? What are we aware of?  Heat, pain, touch, smells.  We are aware of these because we have receptors that pick up these types of stimuli  What are we not aware of?  X-rays, ultra high frequency sound waves, UV light 51  Is sensation different  than Perception is the conscious awareness & interpretation of a sensation.  perception? Localization and identification  Memories of perception are stored in the cortex  Can we sense something without perceiving it?  Can you feel your [blood sugar] right now?  Sensation  A Sensory Modality is the property by which one sensation is distinguished from another.  Ie. The different senses  Different types of sensations include  touch, pain, temperature, vibration, hearing, vision  Often, a single receptor can only detect one of these types of stimuli, but there are exceptions  Two classes of sensory modalities 53  Sensation General Senses include both somatic and visceral senses, the latter of which provide information about conditions within internal organs  Somatic sensory modalities include tactile sensations (touch, pressure, vibration, tickle and itch), thermal sensations (warm and cold), pain sensations and proprioceptive sensations 54  Sensation  Proprioceptive sensations can be both conscious and unconscious. They allow perception of both the static positions of limbs and body parts (joint and muscle position sense) and movements of the limbs and head.  Visceral senses provide information about conditions within internal organs The special senses include the modalities of smell, taste, vision, 55  Sensation The process of sensation begins in a sensory receptor, which can be either a specialized cell or the dendrites of a sensory neuron  For a sensation to arise, 4 events typically occur 1) Stimulation of the sensory receptor: an appropriate receptor must be present in the area of the stimulus 56  Sensation 2) Transduction of the stimulus: a sensory receptor transduces (converts) energy from a stimulus into a graded potential  e.g. odorant molecules in the air stimulate olfactory receptors in the nose, which transduce the molecules chemical energy into electrical energy in the form of a graded potential  vary in amplitude and are not propagated 57  Sensation 3) Generation of impulses when graded potentials reach threshold  impulses then propagated towards the CNS  Sensory neurons that conduct impulses from the PNS into the CNS are called first order neurons (1°) 4) Integration of sensory input by the CNS  A particular region of the CNS receives and integrates the sensory nerve impulses  Conscious sensations or perceptions are integrated in the cerebral cortex If any of these 4 steps are missing, no 58  Sensory  Receptors Receptor Structure may be simple or complex  General Sensory Receptors (Somatic Receptors)  no structural specializations in free nerve endings that provide us with pain, tickle, itch, temperatures  some structural specializations in receptors for touch, pressure & vibration  Special Sensory Receptors (Special Sense Receptors)  very complex structures---vision, hearing, 59  Classifying Sensory  Structural classification Receptors  Type of stimuli they detect  Type of response to a stimulus  Location of receptors & origin of stimuli 60  Structural  Classificatio Free nerve endings bare dendrites  nspecializations lack any structural  pain, temperature, tickle, itch & light touch  the terminal branches of the neuron are unmyelinated and spread throughout the dermis and epidermis.  Encapsulated nerve endings  dendrites enclosed in connective tissue capsule 61  Structural  Classificatio Separate sensory cells Sensory receptors for most special senses n  Specialized/separate cells that respond to stimuli by synapsing with first order neurons  vision, taste, hearing, balance 62 63  Stimuli  Detected Mechanoreceptors  detect physical or mechanical stress  touch, pressure, vibration, hearing, proprioception, equilibrium  Thermoreceptors are of two types, one that responds to an increase and the other that responds to a decrease in temperature 64  Stimuli  Detected Nociceptors detect potential damage to tissues  Nociceptors respond to intense mechanical deformation, excessive heat or chemical signals  Tissue damage releases chemicals which stimulate nociceptors 65  Stimuli  If the Detected initial stimulus of pain leads to an increased sensitivity to subsequent painful stimuli it is called hyperalgesia.  If descending pathways inhibit the transmission of pain stimuli, it leads to a suppression of pain and this is called stimulation-produced analgesia.  Opioids are involved in this mechanism. 66  Stimuli  Detected If both visceral and somatic afferent converge on the same interneuron, excitation of one can lead to excitation of the other, leading to the pain being felt at a site different from the actual injured part. This is called referred pain.  We aren’t sure how exactly this works.  Stimulating non-pain afferent fibers can inhibit neurons in the pain pathway. This is called the pain-gate theory.  This concept is used in transcutaneous 67  Stimuli  Detected Chemoreceptors detect chemicals.  Chemicals that we taste and smell, [arterial oxygen], blood osmolality, [blood CO2], [Blood glucose], amino acids, fatty acids, pH  Photoreceptors detect visible light  Rods - very sensitive, but doesn’t distinguish colour  Cones - less sensitive. There are three kinds of cones containing red, green, or blue sensitive pigment. 68  Stimuli  Detected Other receptors:  Ampullae of Lorenzini respond to electric fields, salinity, and to temperature, but function primarily as electroreceptors  Baroreceptors (specialized mechanoreceptors that respond to pressure)  Electromagnetic receptors respond to electromagnetic waves 69  Response to Stimuli  Generator potential (a type of graded potential)  free nerve endings, encapsulated nerve endings & olfactory receptors produce generator potentials  when large enough, it generates a nerve impulse in a first-order neuron 70  Response to  Stimuli Receptor potential (a type of graded potential)  vision, hearing, equilibrium and taste receptors produce receptor potentials  receptor cells release neurotransmitter molecules on first-order neurons producing postsynaptic potentials  PSP may trigger a nerve impulse  Amplitude of potentials vary with stimulus intensity 71  Location of  Exteroceptors near Receptor surface of body  receive external stimuli  hearing, vision, smell, taste, touch, pressure, pain, vibration & temperature  Interoceptors  monitors internal environment (BV or viscera)  receive internal stimuli  concentrations in blood, blood pressure. etc  not conscious except for pain or pressure  Proprioceptors  In muscles, tendons, and joint 72 BASIS OF CLASSIFICATION DESCRIPTION MICROSCOPIC FEATURES Free nerve endings Bare dendrites associated with pain, thermal, tickle, itch, and some touch sensations. Encapsulated nerve Dendrites enclosed in a connective tissue capsule for pressure, vibration, and some touch sensations. endings Separate cells Receptor cells synapse with first-order sensory neurons; located in the retina of the eye (photoreceptors), inner ear (hair cells), and taste buds of the tongue (gustatory receptor cells). RECEPTOR LOCATION AND ACTIVATING STIMULI Exteroceptors Located at or near body surface; sensitive to stimuli originating outside body; provide information about external environment; convey visual, smell, taste, touch, pressure, vibration, thermal, and pain sensations. Interoceptors Located in blood vessels, visceral organs, and nervous system; provide information about internal environment; impulses produced usually are not consciously perceived but occasionally may be felt as pain or pressure. Proprioceptors Located in muscles, tendons, joints, and inner ear; provide information about body position, muscle length and tension, position and motion of joints, and equilibrium (balance). TYPE OF STIMULUS DETECTED Mechanoreceptors Detect mechanical stimuli, provide sensations of touch, pressure, vibration, proprioception, and hearing and equilibrium; also monitor stretching of blood vessels and internal organs. Thermoreceptors Detect changes in temperature. Nociceptors Respond to painful stimuli resulting from physical or chemical damage to tissue. Photoreceptors Detect light that strikes the retina of the eye. Chemoreceptors Detect chemicals in mouth (taste), nose (smell), and body fluids. Osmoreceptors Sense the osmotic pressure of body fluids.  Adaptation  Most sensory receptors exhibit adaptation – the tendency for the generator or receptor potential to decrease in amplitude during a maintained constant stimulus.  Receptors may adapt rapidly or slowly  Decrease in sensitivity to long- lasting stimuli  leads to a decrease in responsiveness of a 74  Adaptation  A tonic receptor is a sensory receptor that adapts slowly to a stimulus and continues to produce action potentials over the duration of the stimulus. In this way it conveys information about the duration of the stimulus.  Some tonic receptors are permanently active and indicate a background level stimulus. Examples of such tonic receptors are nociceptors and 75  Adaptation  A phasic receptor is a sensory receptor that adapts rapidly to a stimulus. The response of the cell diminishes very quickly and then stops. It does not provide information on the duration of the stimulus; instead some of them convey information on rapid changes in stimulus intensity and rate.  An example of a phasic receptor is the 76  Adaptation  Variability in tendency to adapt:  Rapidly adapting receptors (smell, pressure, touch)  specialized for detecting changes  Slowly adapting receptors (pain, body position)  specialized for detecting duration 77 RECEPTOR TYPE RECEPTOR STRUCTURE AND LOCATION SENSATIONS ADAPTATION RATE TACTILE RECEPTORS Corpuscles of touch (Meissner Capsule surrounds mass of dendrites in dermal papillae of hairless skin. Onset of touch and low-frequency vibrations. Rapid. corpuscles) Hair root plexuses Free nerve endings wrapped around hair follicles in skin. Movements on skin surface that disturb hairs. Rapid. Type I cutaneous Saucer-shaped free nerve endings make contact with tactile epithelial Continuous touch and pressure. Slow. mechanoreceptors (tactile discs) cells in epidermis. Type II cutaneous Elongated capsule surrounds dendrites deep in dermis and in mechanoreceptors (Ruffini Skin stretching and pressure. Slow. ligaments and tendons. corpuscles) Oval, layered capsule surrounds dendrites; present in dermis and Lamellated (pacinian) subcutaneous layer, submucosal tissues, joints, periosteum, and some High-frequency vibrations. Rapid. corpuscles viscera. Itch and tickle receptors Free nerve endings in skin and mucous membranes. Itching and tickling. Both slow and rapid. THERMORECEPTORS Warm receptors and cold Free nerve endings in skin and mucous membranes of mouth, vagina, Warmth or cold. Initially rapid, then slow. receptors and anus. PAIN RECEPTORS Nociceptors Free nerve endings in every body tissue except brain. Pain. Slow. PROPRIOCEPTORS Sensory nerve endings wrap around central area of encapsulated Muscle spindles intrafusal muscle fibers within most skeletal muscles. Muscle length. Slow. Capsule encloses collagen fibers and sensory nerve endings at Muscle tension. Slow. Tendon organs junction of tendon and muscle. Lamellated corpuscles, type II cutaneous mechanoreceptors, tendon Joint position and movement. Rapid. Joint kinesthetic receptors organs, and free nerve endings.  Tactile  Sensations Tactile sensations are touch, pressure, and vibration plus itch and tickle.  Perceive differences among these sensations, but arise by activation of some of the same types of receptors.  Also, some receptors sense multiple stimuli 79  Tactile  Sensations Touch  crude touch is ability to perceive something has touched the skin, even though its exact location, shape, size or texture cannot be determined  discriminative touch provides specific information about a touch sensation, such as exactly what point on the body is touched plus the shape, size and texture of the source of stimulation 80  Touch  Two types of rapidly adapting touch receptors  Corpuscles of touch aka Meissner corpuscles  Receptors for touch located in the dermal papillae of glabrous skin  Abundant in the fingertips, hands, eyelids, tip of the tongue, lips, nipples, soles, clitoris, and tip of the penis.  Each corpuscle is an egg-shaped mass of dendrites enclosed by a capsule of 81  Touch  Hair root plexuses  Found in hairy skin  Consist of free nerve endings wrapped around hair follicles.  Detect movements on the skin surface that disturb hairs.  E.g., an insect landing on a hair causes movement of the hair shaft that stimulates the free nerve endings.  Touch  Two types of slowly adapting touch receptors  Type I Cutaneous mechanoreceptors aka Merkel discs  Saucer-shaped, flattened free nerve endings that make contact with Merkel cells of the stratum basale  Function in touch and pressure  Most abundant in fingertips, hands, lips and external genitalia 83  Touch  Type II cutaneous mechanoreceptors aka Ruffini corpuscles  Elongated, encapsulated receptors located deep in the dermis, and in ligaments and tendons.  Abundant in hands (especially fingers) and the soles, but found all over the body  Sensitive to stretching of skin that occurs as digits or limbs are moved. Also helps detect pressure  Pressure  Pressure is sustained sensation over a large area  Receptors that contribute to sensations of pressure include Type I and Type II cutaneous mechanoreceptors 85  Vibration  Sensations of vibration result from rapidly repetitive sensory signals from tactile receptors.  Receptors for vibration sensations are Meissner corpuscles and pacinian corpuscles.  Meissner corpuscles can detect lower-frequency vibrations, and pacinian corpuscles detect higher- frequency vibrations. 86  Vibration Lamellar corpuscles adapt rapidly – distributed throughout the body (in dermis, and SubQ; submucosal tissues that underlie mucous and serous membranes; around joints, tendons and muscles; in periosteum; in mammary glands, external genitalia; certain viscera such as pancreas and urinary bladder.  Itch Itch is a bit of a mystery  Triggers include mechanical stimulus, electricity, temperature and certain chemicals  Bradykinin and histamine are well known itch stimulators. When do we see these?  There is no agreed upon theory as to what the functionality of itch is in humans 89  Tickle Tickle is also a bit of a mystery  Tickle is stimulation of free nerve endings only by someone else We aren’t sure why we can’t tickle ourselves, but many ideas have been presented  Tickle can be divided into 2 categories  one of these evokes laughter and the other is considered annoying  Like itch, we aren’t certain why the sensation of tickle exists  Pacinian corpuscles also thought to mediate tickle response Phantom Limb Sensation Patients with a limb amputated may still experience sensations such as itching, pressure, tingling, or pain as if the limb were still there.  75% of amputees experience this, the majority of these experience painful sensations  One older explanation: cerebral cortex interprets impulses arising from the distal portions of damaged sensory neurons that previously carried impulses from the limb as coming from the nonexistent (phantom) Phantom Limb Sensation  Another newer explanation : the brain contains networks of neurons that generate sensations of body awareness.  neurons in the brain that previously received sensory impulses from the missing limb are reorganized (plasticity), and now sensations from other areas of the body create a phantom sensation from the former limb  Very distressing to an amputee – most report that the pain is severe, and that it often does not respond to traditional pain medication therapy. Thermal Sensations  Free nerve endings with 1mm diameter receptive fields on the skin surface  Cold receptors  Located in the stratum basale of the epidermis  Attached to medium-diameter, myelinated A fibers (few connect to small-diameter, unmyelinated C fibers)  Temperatures between 10° and 35°C (50– 95°F) activate cold receptors. 93 Thermal Sensations  Warm receptors  Not as abundant as cold receptors  Located in the dermis  Attached to small-diameter, unmyelinated C fibers  Activated by temperatures between 30° and 45°C (86–113°F).  Both adapt rapidly at first, but continue to generate impulses at a low frequency  Pain is produced below 10 deg C and over 45 deg C. Pain Sensations  Free nerve endings found in almost every tissue of the body (not found in the brain)  Activated by intense thermal, mechanical, or chemical stimuli  Tissue irritation or injury releases chemicals such as prostaglandins, substance p, kinins, and potassium ions (K+) that stimulate nociceptors. 95 Pain Sensations  May persist even after a pain- producing stimulus is removed because pain-mediating chemicals linger  Exhibit very little (if any) adaptation (tonic)  Conditions that can elicit pain include (massage related)  excessive distention (stretching) of a structure  prolonged muscular contractions Pain Sensations  Fast pain (acute)  occurs rapidly after stimuli (0.1 second)  pain is often felt as acute, sharp, or pricking pain  pain felt from a needle puncture or knife cut to the skin  not felt in deeper tissues  nerve impulses propagate along medium-diameter, myelinated A fibers. 97 Pain Sensations  Slow pain (chronic)  begins more slowly & increases in intensity  may be excruciating – felt as chronic, burning, aching, or throbbing pain  pain associated with a toothache  can occur both in the skin and in deeper tissues or internal organs  pain conducted along small-diameter, unmyelinated C fibers 98 Pain Sensations  You can perceive the difference in onset of these two types of pain best when you injure a body part that is far from the brain because the conduction distance is long.  When you stub your toe, you feel the sharp sensation of fast pain and then feel the slower, aching sensation of slow pain.  Somatic pain that arises from the stimulation of receptors in the skin is superficial somatic pain, 99 Pain Sensations  Visceral pain, unlike somatic pain, is usually felt in or just under the skin that overlies the stimulated organ  localized damage (cutting) intestines may cause no pain, but diffuse visceral stimulation can be severe  distension of a bile duct from a gallstone  distension of the ureter from a kidney stone  pain may also be felt in a surface area far from the stimulated organ in a phenomenon known as referred pain (Figure 16.3). 100  Referred Pain  Visceral pain that is felt just deep to the skin overlying the stimulated organ or in a surface area far from the organ.  Skin area & organ are served by the same segment of the spinal cord.  Heart attack is felt in skin along left arm since both are supplied by spinal cord segment T1-T5 101 ain Threshold vs Toleran  Pain threshold: How strong does the stimulation have to be before it elicits a pain response?  Ie. Before the stimulus reaches receptor threshold  Involves only the PNS  Constant among population  Pain tolerance: How much pain an individual can take?  Involves the CNS  varies widely among population 102  Drugs for Pain  Analgesic drugs such as aspirin, ibuprofen and naproxen block formation of prostaglandin and thromboxane, which stimulate nociceptors.  Inhibit the cyclooxygenase enzyme  Local anesthetics, such as Novocaine® or Lidocaine, are sodium channel blockers. They provide short-term pain relief by inhibiting 103  Drugs for Pain  Morphine and other opiates alter the quality of pain perception in the brain; pain is still sensed in the PNS, but the signal is affected in the CNS to either be blocked or perceived differently.  Causes euphoria  Many pain clinics use anticonvulsant and antidepressant medications to treat those suffering from chronic 104 Proprioception  Proprioceptive sensations allow us to know where our head and limbs are located and how they are moving even if we are not looking at them, so that we can walk, type, or dress without using our eyes.  Kinesthesia is the perception of body movements. 105 Proprioception  Proprioceptors  embedded in muscles (especially postural muscles) tendons and joints, inform us of the degree to which muscles are contracted, the amount of tension on tendons, and the positions of joints.  This awareness of the activities of muscles, tendons, and joints and of balance or equilibrium is known as the proprioceptive or kinesthetic sense. 106 Proprioception  Proprioceptors adapt slowly and only slightly (tonic)  brain continually receives nerve impulses related to the position of different body parts and makes adjustments to ensure coordination.  Proprioceptors allow weight discrimination, the ability to assess the weight of an object.  helps to determine the muscular effort necessary to perform a task.  E.g., as you pick up an object you 107 Proprioception  Proprioceptive information is sent to both the cerebellum & cerebral cortex  Cortical information is conscious  Cerebellar information is unconscious  3 types of proprioceptors:  muscle spindles within skeletal muscles  tendon organs within tendons  joint kinesthetic receptors in or around joint capsules. 108 Muscle Spindle  Proprioceptors in skeletal muscles that monitor changes in the length of skeletal muscles and participate in the stretch reflex  Each muscle spindle consists of several slowly adapting sensory nerve endings that wrap around 3 to 10 specialized muscle fibers, called intrafusal muscle fibers. 109 Muscle Spindle  Main function of muscle spindles is to measure muscle length—how much a muscle is being stretched.  Either sudden or prolonged stretching of the central areas of the intrafusal muscle fibers stimulates the sensory nerve endings.  The resulting nerve impulses propagate into the CNS – to the somatic sensory areas of the cerebral cortex, which allows conscious perception of limb positions and movements. 110 Muscle Spindle  In addition to their sensory nerve endings near the middle of intrafusal fibers, muscle spindles contain motor neurons called gamma motor neurons.  These terminate near both ends of the intrafusal fibers and adjust the tension in a muscle spindle to variations in the length of the whole muscle. 111 Muscle Spindle  E.g., when a muscle shortens, gamma motor neurons stimulate the ends of the intrafusal fibers to contract slightly.  Keeps the intrafusal fibers taut and maintains the sensitivity of the muscle spindle to stretching of the muscle.  As the frequency of impulses in its gamma motor neuron increases, a muscle spindle becomes more sensitive to stretching of its mid-region. 112 Muscle Spindle  Surrounding the muscle spindles are muscles fibers called extrafusal muscle fibers  supplied by large-diameter A fibers called alpha motor neurons.  cell bodies of both γ and α motor neurons are located in the anterior gray horn of the spinal cord (or in the brain stem for muscles in the head). 113 Muscle Spindle  During the stretch reflex, impulses in muscle spindle sensory axons propagate into the spinal cord and brain stem and activate alpha motor neurons that connect to extrafusal muscle fibers in the same muscle.  Activation of its muscle spindles causes contraction of a skeletal muscle, which relieves the stretching. 114 Muscle Spindle  Specialized intrafusal muscle fibers enclosed in a CT capsule and innervated by gamma motor neurons  Stretching of the muscle stretches the muscle spindles sending sensory information back to the CNS  Spindle sensory fiber monitor changes in muscle length  Brain regulates muscle tone by controlling alpha motor neuronss 115 Golgi Tendon Organ  Protect tendons and their associated muscles from damage due to excessive tension.  Penetrating the capsule s one sensory nerve ending that entwines among and around the collagen fibers of the tendon.  When tension is applied to a muscle, the GTO generate nerve impulses that propagate into the CNS, providing information about changes in muscle 116 Golgi Tendon Organ  Found at junction of tendon & muscle  Consists of an encapsulated bundle of collagen fibers laced with sensory fibers  When the tendon is overly stretched, sensory signals propagate toward the CNS & result in muscle relaxation 117 int Kinesthetic Recepto  Present within and around the articular capsules of synovial joints.  Free nerve endings and Ruffini corpuscles in the capsules of joints respond to pressure.  Small pacinian corpuscles in the connective tissue outside articular capsules respond to changes of speed of joints during movement. 118 RECEPTOR TYPE RECEPTOR STRUCTURE AND LOCATION SENSATIONS ADAPTATION RATE TACTILE RECEPTORS Corpuscles of touch (Meissner Capsule surrounds mass of dendrites in dermal papillae of hairless skin. Onset of touch and low-frequency vibrations. Rapid. corpuscles) Hair root plexuses Free nerve endings wrapped around hair follicles in skin. Movements on skin surface that disturb hairs. Rapid. Type I cutaneous Saucer-shaped free nerve endings make contact with tactile epithelial Continuous touch and pressure. Slow. mechanoreceptors (tactile discs) cells in epidermis. Type II cutaneous Elongated capsule surrounds dendrites deep in dermis and in mechanoreceptors (Ruffini Skin stretching and pressure. Slow. ligaments and tendons. corpuscles) Oval, layered capsule surrounds dendrites; present in dermis and Lamellated (pacinian) subcutaneous layer, submucosal tissues, joints, periosteum, and some High-frequency vibrations. Rapid. corpuscles viscera. Itch and tickle receptors Free nerve endings in skin and mucous membranes. Itching and tickling. Both slow and rapid. THERMORECEPTORS Warm receptors and cold Free nerve endings in skin and mucous membranes of mouth, vagina, Warmth or cold. Initially rapid, then slow. receptors and anus. PAIN RECEPTORS Nociceptors Free nerve endings in every body tissue except brain. Pain. Slow. PROPRIOCEPTORS Sensory nerve endings wrap around central area of encapsulated Muscle spindles intrafusal muscle fibers within most skeletal muscles. Muscle length. Slow. Capsule encloses collagen fibers and sensory nerve endings at Muscle tension. Slow. Tendon organs junction of tendon and muscle. Lamellated corpuscles, type II cutaneous mechanoreceptors, tendon Joint position and movement. Rapid. Joint kinesthetic receptors organs, and free nerve endings. Somatic Sensory  Pathways Somatic sensory pathways relay information from somatic receptors to the primary somatosensory area in the cerebral cortex and to the cerebellum.  The pathways consist (usually) of three neurons  first-order  second-order  third-order  Axon collaterals of somatic sensory neurons simultaneously carry signals into 120  Somatic Sensory  Pathways First-order neurons conduct impulses from the somatic receptors into the CNS (brainstem or spinal cord)  From the face, mouth, teeth and eyes, somatic sensory impulses propagate along cranial nerves to the brain stem  From the body, neck and posterior head, somatic sensory impulses propagate along spinal nerves into the spinal cord. 121 Somatic Sensory  Pathways Second-order neurons conducts impulses from CNS to the thalamus  cross over to opposite side of body in the brainstem or spinal cord before ascending to the thalamus  Sensory information from one side of the body reaches the contralateral half of the thalamus  Third-order neurons conduct impulses from the thalamus to the primary somatosensory area 122 Somatic Sensory  SomaticPathways sensory impulses entering the spinal cord ascend to the cerebral cortex via two general pathways  The posterior column pathway  The anterolateral pathways aka spinothalamic pathways  Also have the pathways to reach the cerebellum via the spinocerebellar tracts 123  Posterior Column – Medial  Nerve impulses for touch, pressure, Lemniscus vibration, and conscious proprioception from the limbs, trunk, neck, and posterior Pathway head ascend to the cerebral cortex via the PCML  Name of the pathway comes from the names of two white-matter tracts that convey the impulses: the posterior column of the spinal cord and the medial lemniscus of the brain stem. 124  Posterior Column – Medial  Impulses conducted along this pathway  Lemniscus Discriminative touch – ability to recognize specific information about a touch sensation, Pathway such as point of touch, shape, size and texture of source aka Stereognosis (the ability to perceive the form of an object by using sense).  Proprioception – awareness of the precise position of body parts  Kinesthesia – awareness of directions of movement  Weight discrimination – ability to assess weight of an object 125  Posterior Column – Medial Lemniscus  First-order neurons Pathway extend from sensory receptors in the limbs, trunk, neck, and posterior head into the spinal cord and ascend to the ipsilateral medulla oblongata  The cell bodies of these first-order neurons are in the posterior (dorsal) root ganglia of spinal nerves. 126  Posterior Column – Medial In the spinal cord, their axons form  Lemniscus the posterior (dorsal) columns, Pathway which consist of two parts: the gracile fasciculus and the cuneate fasciculus.  First-order neurons synapse with second-order neurons whose cell bodies are located in the gracile nucleus or cuneate nucleus of the 127  Posterior Column – Medial  Nerve impulses for touch, pressure, Lemniscus vibration and conscious proprioception from the upper limbs, upper trunk, neck, Pathway and posterior head propagate along axons in the cuneate fasciculus and arrive at the cuneate nucleus.  Nerve impulses for touch, pressure, vibration and conscious proprioception from the lower limbs and lower trunk propagate along axons in the gracile 128  Posterior Column – Medial  Lemniscus The axons of the second-order neurons cross to the opposite side of the medulla and enter the medial lemniscus  Pathway Thin ribbon-like tract that extends from the medulla to the ventral posterior nucleus (VPN) of the thalamus  In the thalamus the axon terminals of second-order neurons synapse with third- order neurons, which project their axons to the primary somatosensory area of the 129 130  Anterolateral or  3-neuron pathway  Spinothalamic The anterolateral or spinothalamic pathways carry mainly pain and Pathways temperature impulses, but also tickle and itch sensations, crude poorly localized touch, pressure and vibration  Touch, pressure and vibration are all poorly localized on these tracts 131  Spinothalam ic Pathways  First-order neurons travel through the posterior (dorsal) roots of spinal nerves to connect to second order nerves at the level of the spine in which they entered  Synapse with second- order neurons in the posterior gray horn of 132  Spinothalamic  Pathways Second-order neurons cross to the opposite side of SC – continue upward via either the lateral spinothalamic tract or the anterior spinothalamic tract  Lateral spinothalamic tract carries pain & temperature  Anterior tract carries tickle, itch, crude touch, pressure and vibrations  Axons of second order neurons synapse with third-order neurons in the thalamus (VPN) –  Third-order neurons project into the 133 134 Trigeminothala  mic Nerve Pathway impulses for most somatic sensations (tactile, thermal, pain, proprioception) from the face, nasal cavity, oral cavity ascend to the cerebral cortex along the trigeminothalamic pathways  Consists of a 3-neuron set  First order neurons extend from somatic sensory receptors in the face, nasal cavity, oral cavity and 135 Trigeminothala  mic The cell bodiesPathway of these first order neurons are in the trigeminal ganglia  Axon terminals of some 1st order neurons synapse with second order neurons in the pons.  Axons of other 1st order neurons descend into the medulla to synapse with second order neurons  Axons of second order neurons cross to the opposite side of the pons and medulla (some do not) and then ascend 136 Trigeminothala  mic Go to Pathway the ventral posterior nucleus of the thalamus and synapse with third order neurons  Third order neurons project axons to the primary somatosensory area on the same side of the cerebral cortex as the thalamus 137 138 Which cranial nerve conveys impulses for most somatic sensations from the left side of the face into the pons? 139 Spinocerebellar  Pathways Two tracts in spinal cord - posterior spinocerebellar tract and anterior spinocerebellar tract – major proprioceptive impulses from trunk and limbs of one side of the body to the ipsilateral cerebellum  These pathways are critical for maintenance of posture and balance and to coordinate, smooth and refine skilled movements. 140 Spinocerebellar Pathways 141  Primary  Somatosensory Occupies the postcentral gyri of the parietal lobes  Area Somatic sensory signals from the left side of the body to the right cerebral hemisphere and vice versa  The lips, face, tongue and thumb provide input to large regions in the somatosensory area  Relative sizes of cortical areas are presented as the homunculus  proportional to number of sensory 142  Primary Can be modified with Somatosensory learning (plasticity) Arealearn to read Braille  & will have larger area representing fingertips 143  Syphilis Bacterial infection caused by treponema pallidum Late stage syphilis can show neurological signs and symptoms at which point it is known as neurosyphilis One such sign is progressive degeneration of the posterior portion of the spinal cord As the posterior column takes up most of the posterior spinal cord, symptoms will mainly include a loss of the sensory information carried on this tract 144 OVERAL L 145  Somatic Motor Lower motor neurons extend from the Pathways  CNS to skeletal muscles (PNS)  Lower motor neurons are peripheral nerves  These lower motor neurons are also called the final common pathway because many regulatory mechanisms summate before a single signal is sent on these peripheral neurons  LMNs extend as cranial nerves to skeletal muscles of the face and head, and as spinal nerves to skeletal muscles of the 146  Somatic Motor  Pathways Control of body movement  motor portions of cerebral cortex (where?)  initiate & control precise movements  basal ganglia help establish muscle tone, integrate semi-voluntary automatic movements, inhibit excess movement  cerebellum coordinates smooth movement & helps maintain posture and balance 147 Somatic Motor Pathways Local circuit neurons (AKA interneurons)  located close to lower motor neuron cell bodies in the brain stem and spinal cord. Receive input from somatic sensory receptors (e.g. nociceptors and muscle spindles) and higher centres in brain. Help coordinate rhythmic activity in specific muscle groups (e.g. alternating flexion and extension of lower limbs during walking) 148 Somatic Motor Local Pathways circuit neurons and lower motor neurons receive input from upper motor neurons.  UMNs from the cerebral cortex are essential for planning, initiating and directing sequences of voluntary movements.  Other UMNs originate in motor centres of the brain stem and regulate mm tone, control postural muscles and help maintain balance and orientation of head and body (influenced by basal ganglia and cerebellum) 149 Neurons of the basal ganglia provide input to UMNs  Assist movement by initiating and terminating movements, suppress unwanted movements and establish normal level of mm tone. Cerebellar neurons also control activity of UMNs  Interconnect the cerebellum with motor areas of the cerebral cortex (via the thalamus) and the brain stem  Prime f(x) is to monitor differences between intended movements and movements actually performed  Then issues commands to UMN to reduce errors in movement  This coordinates body movements and helps 150  Somatic Motor Axons of UMN extend from brain to  Pathways LMNs via two types of descending somatic motor pathways:  direct pathways from cerebral cortex to spinal cord & out to muscles via LMN  indirect pathways includes synapses in motor centres in brain stem from basal ganglia, thalamus, reticular formation & cerebellum – then to the LMNs Paralysis: damage of lower motor neurons produces flaccid paralysis while damage to upper motor neurons 151  Direct Motor  Pathways Axons from UMN extend from the brain to LMNs via 2 descending somatic direct motor pathways  Direct Motor Pathway - provide input to LMNs via axons that extend directly from cerebral cortex. The direct (pyramidal) pathways include  lateral and anterior corticospinal tracts  corticobulbar tracts 152  Direct Motor  Pathways Aka Pyramidal pathways  1 million upper motor neurons in cerebral cortex  Nerve impulses for voluntary movements propagate from UMN in primary motor area and premotor area of cerebral cortex to LMNs  Axons descend from the cerebral cortex to the medulla oblongata where axon bundles form the ventral bulges known as pyramids 153  Direct Motor  90% of Pathways UMN fibers decussate (cross over) in the medulla  right side of brain controls left side muscles  10% remain on same side. They will eventually decussate at the SC where they synapse with interneurons or LMNs in either:  nuclei of cranial nerves  anterior horns of spinal cord 154 Direct Motor Pathways  Lateral corticospinal tract  Anterior corticospinal tract  Corticobulbar tract 155 Direct Motor Pathways Lateral corticospinal tracts  The 90% of the fibers that decussate in the medulla make up this tract  Control muscles in limbs for precise, agile, and highly skilled movements (hands & feet)  e.g. button a shirt or play piano  More muscles allows for finer movement, but also requires more nervous 156  Direct Motor Pathways Anterior corticospinal tracts  the 10% of axons that do not cross in the medulla  Decussate in the SC and then synapse with interneurons or LMN in anterior gray horn  Axons of LMNs exit cervical and upper thoracic segments of SC in the anterior roots of spinal nerves  controls movement of neck, trunk and girdle muscles 157  Direct Motor Pathways Corticobulbar tracts  Control skeletal muscles of head  Form in L and R cerebral peduncles – descend from cerebral cortex to brain stem  Some decussate, some do not  UMNs synapse with LMNs of CNs exiting brain stem  cortex to nuclei of CNs  III, IV, V, VI, VII, IX, X, XI & XII  Control precise and voluntary movements of 158  Primary  The primary motor area is Motor Cortex located in the precentral gyrus of the frontal lobe  upper motor neurons plan and initiate voluntary movements  Different muscles are represented unequally in the primary motor area  The cortical area devoted to a muscle is proportional to the number of motor units.  More cortical area is needed if thenumber of motor units in a muscle is high  vocal cords, tongue, lips, fingers & thumb 159  Paralysis  LMN damage = flaccid paralysis  no voluntary movement on same side as damage  no reflex actions  muscle limp & flaccid  decreased muscle tone  UMN damage = variable, but often spastic paralysis  paralysis on opposite side from injury (always?)  increased muscle tone  160  Indirect Motor  Indirect Pathways or extrapyramidal pathways include all somatic motor tracts other than the corticospinal and corticobulbar tracts.  involve the motor cortex, basal ganglia, thalamus, cerebellum, reticular formation, and nuclei in the brain stem  indirect tracts are the rubrospinal, tectospinal, vestibulospinal, lateral reticulospinal and medial reticulospinal tracts 161  Indirect Motor  circuits Pathways Complex polysynaptic  include basal ganglia, thalamus, cerebellum, reticular formation  Descend in spinal cord as 5 major tracts  All 5 tracts end upon interneurons or lower motor neurons 162  Indirect Motor  Pathways Rubrospinal: Conveys nerve impulses from the red nucleus to contralateral skeletal muscle for gross and precise movements of the upper limbs  Tectospinal: Conveys nerve impulses from the superior colliculus to contralateral skeletal muscles that move the head and eyes in response to visual stimuli.  Vestibulospinal: Conveys nerve impulses from the vestibular nucleus in the pons and medulla to regulate ipsilateral muscle tone for maintaining balance in response 163  Indirect Motor  Pathways Lateral reticulospinal: Conveys nerve impulses from the reticular formation to facilitate flexor reflexes, inhibit extensor reflexes, and decrease muscle tone in muscles of the axial skeleton and proximal parts of the limbs.  Medial reticulospinal: Conveys nerve impulses from the reticular formation to facilitate extensor reflexes, inhibit flexor reflexes, and increase muscle tone in muscles of the axial skeleton and proximal parts of the limbs. 164  Final Common  Lower motor Pathway neurons receive signals from both direct & indirect upper motor neurons  Sum total of all inhibitory & excitatory signals determines the final response of the lower motor 165  Integrative Functions of  the Cerebrum The integrative functions include  sleep  wakefulness  memory. 166  Sleep and RoleWakefulness of the Reticular Activating System (RAS)  Sleep and wakefulness are integrative functions that are controlled by the reticular activating system  Arousal, or awakening from a sleep, involves increased activity of the RAS.  When the RAS is activated, the 167  Sleep and  RAS has Wakefulness connections to cortex & spinal cord  Many types of inputs can activate the RAS  pain, light, noise, muscle activity, touch  Coma is sleep-like state  Defined in a 168  Sleep and Circadian rhythm   Wakefulness Any biological process that cycles on a daily schedule  ~24 hour biological clock  Some evidence suggests it’s longer than 24 hours  Established by the hypothalamus  EEG recordings show large amount of activity in cerebral cortex when awake 169  Sleep  Sleep: a state of altered consciousness or partial unconsciousness from which an individual can be aroused by different stimuli  During sleep activity in the RAS is very low  There are two types of sleep  non-rapid eye movement sleep (NREM)  rapid eye movement sleep (REM) 170  Sleep  Non-rapid eye movement (NREM) consists of four stages, each defined by the activity on an EEG  A regular night consists of phasing from one stage to the next in a typical sleep cycle 171  NREM  Stage 1  Sleep person drifting off with eyes closed (first few minutes)  Hypnic jerk occurs here  Stage 2  fragments of dreams  eyes may roll side to side  Stage 3  very relaxed, moderately deep  20 minutes after stage 1, body temperature & BP drop  Stage 4 = deep sleep  Parasomnia occurs here  172  REM Sleep  Most dreams occur during REM sleep (lucid dreams?)  Sleep cycles occur over ~90 minutes (depending on text)  go from stage 1 to 4 of NREM  go up to stage 2 of NREM  to REM sleep  The first REM of the night is very short  Every time REM sleep is entered, it lasts longer  Cycles repeat until REM sleep totals 90 to 173 Sleep Problems Parasomnia Delayed sleep phase disorder REM sleep behaviour disorder Narcolepsy 174  Learning and  Learning isMemory the ability to acquire new knowledge or skills through instruction or experience.  Memory is the process by which that knowledge is retained over time.  For an experience to become part of memory, it must produce persistent functional changes that represent the experience in the brain.  The capability for change with learning 175  Learning and  Memory Memory occurs in stages over a period and is described as immediate memory, short term memory, or long term memory  Immediate memory is the ability to recall for a few seconds  Short-term memory lasts only seconds or hours and is the ability to recall bits of information; it is related to electrical and chemical events.  Long-term memory lasts from days to 176  Amnesia  Amnesia refers to the loss of memory  Anterograde amnesia is the loss of memory for events that occur after the trauma (ie. the inability to form new memories)  Retrograde amnesia is the loss of memory for events that occurred before the trauma; the inability to recall past events. 177