Sensory, Motor, & Integrative Systems (Biology 1191) - Chapter 16 PDF

Sensory, Motor, & Integrative Systems BIOLOGY 1191 - CHAPTER 16 JANAINA BRUSCO PHD Outline Sensation Somatic Sensations Somatic Sensory Pathways Somatic Motor Pathways Integrative Functions of the Cerebrum Intended Learning Outcomes Sensation vs Perception Perception is the conscious awarene...

Sensory, Motor, & Integrative Systems BIOLOGY 1191 - CHAPTER 16 JANAINA BRUSCO PHD Outline Sensation Somatic Sensations Somatic Sensory Pathways Somatic Motor Pathways Integrative Functions of the Cerebrum Intended Learning Outcomes Sensation vs Perception Perception is the conscious awareness & interpretation of a sensation ◦ Perception of a sensation involves the cortex ◦ precise localization & identification ◦ memories of sensations are stored in cortex Sensation is any stimuli the body is aware of (consciously or not) ◦ Chemoreceptors, thermoreceptors, nociceptors, baroreceptors ◦ What are we not aware of? ◦ X-rays, ultra high-frequency sound waves, UV light ◦ We have no sensory receptors for those stimuli 4 Sensory Modalities Sensory Modality is a type of sensation ◦ a given sensory neuron carries information for only one sensory modality ◦ touch, pain, temperature, hearing, vision, are all different sensory modalities Two classes of sensory modalities ◦ general senses (somatic and visceral senses) ◦ special senses (smell, taste, vision, hearing, and equilibrium) 5 Process of Sensation 4. Integration of sensory 3. Generation of nerve impulses information when the graded potential reaches threshold, A specific part of CNS an action potential is triggered receives and integrates the neurons that conduct nerve impulses from PNS sensory nerve impulses directly to CNS are called first-order neurons 2. Transduction of the stimulus = conversion into a graded potential Graded potentials vary in amplitude depending on the strength of the stimulus and are not propagated 1. Stimulation of sensory receptors - Each receptor only responds to one type of stimulus 6 Free nerve endings Free nerve endings are the For the sensations of pain, dendrites of first-order neurons temperature, tickle, itch & light touch, and smell Cold stimulus Triggers Propagate into CNS Nerve impulses The graded potential triggered in a neuron with free nerve endings is called a generator potential 7 Encapsulated nerve endings Dendrites of first-order For the sensations of pressure, neuron enclosed in vibration and deep touch connective tissue capsule Pressure stimulus Triggers Propagate into CNS Nerve impulses The graded potential triggered in a neuron with encapsulated nerve endings is called a generator potential 8 Separate Sensory cells Separate sensory cells synapse For vision (photoreceptors), taste with first-order neurons (gustatory receptor cells), hearing and equilibrium (hair cells) Synaptic vesicle Sugar molecule Dendrite Release Triggers Propagate of NT into CNS Nerve impulses The graded potential triggered in a sensory cell is The receptor potential triggers the release of called a receptor potential neurotransmitters onto the first-order neuron 9 Generator vs Receptor Potential Generator potential ◦ Triggers an AP in the 1st order neuron ◦ E.g., Free nerve endings, encapsulated nerve endings & olfactory receptors Receptor potential ◦ Receptor cells release neurotransmitter molecules on first-order neurons producing postsynaptic potentials → PSP may trigger a nerve impulse ◦ E.g., Vision, hearing, equilibrium and taste receptors produce receptor potentials Both are GRADED → Amplitude of potentials vary with stimulus intensity A generator potential produces action potentials and a receptor potential causes release of neurotransmitters. a) True b) False Separate sensory cells are different from other sensory receptors in that a) Separate sensory cells are part of the first-order neuron b) Separate sensory cells are part of the dendrites of first-order neurons c) When separate sensory cells are involved, first-order neurons are not required d) Separate sensory cells synapse onto first-order neurons 12 Classification of receptors by Location Exteroceptors ◦ Located near the surface of the body ◦ receive external stimuli ◦ hearing, vision, smell, taste, touch, pressure, pain, vibration & temperature Interoceptors ◦ Located in and monitor the internal environment (BV, viscera, muscles, nervous system) ◦ not consciously perceived except for pain or pressure Proprioceptors ◦ Located in muscles, tendons, joints & inner ear ◦ sense body position & movement 13 Classification of receptors by Stimuli Detected Mechanoreceptors ◦ detect mechanical stimuli (e.g. deformation, stretching, bending) ◦ touch, pressure, blood pressure, vibration, proprioception, hearing, and equilibrium Thermoreceptors ◦ detect changes in temperature Chemoreceptors Nociceptors detect molecules ◦ detect damage to tissues = pain taste, smell & changes in body fluid chemistry Photoreceptors Osmoreceptors ◦ detect light detect osmotic pressure in fluids 14 Adaptation in Sensory Receptors Most sensory receptors exhibit adaptation ◦ the tendency for the generator or receptor potential to decrease in amplitude during a maintained constant stimulus ◦ because of adaptation, the perception of a sensation may fade or disappear even though the stimulus persists There is a variability in the tendency to adapt: ◦ Rapidly adapting receptors (e.g. smell, pressure, touch) ◦ specialized for detecting changes in a stimulus ◦ Slowly adapting receptors (e.g. pain, body position) ◦ nerve impulses continue if the stimulus persists – Pain is not easily ignored 15 Which of the following primarily consists of slowly adapting sensory receptors? a) Body position b) Touch c) Pressure d) Smell 16 Which of the following somatic sensations has an encapsulated nerve ending as its sensory receptor? a) tickle b) pain c) heat or cold d) pressure e) itch Somatic Sensations 1. TACTILE SENSATIONS 2. THERMAL SENSATIONS 3. PAIN SENSATIONS 4. PROPRIOCEPTIVE SENSATIONS 18 1. Tactile Sensations TOUCH, PRESSURE, VIBRATION, TICKLE AND ITCH 19 Touch Merkel (tactile) disc (type I cutaneous mechanoreceptor) Nociceptor (pain receptor) Corpuscle of touch (Meissner corpuscle) are Epidermis encapsulated nerve endings located in the dermal papilla of hairless skin (fingertips, hands, eyelids, tip of tongue, lips, nipples, soles, clitoris and tip of penis). They are sensitive and rapidly adapting Dermis Ruffini corpuscle (type II cutaneous mechanoreceptor) Hair root plexuses are rapidly adapting free nerve endings wrapped around hair follicles (dermis). They detect hair movements Subcutaneous layer Pacinian (lamellated) corpuscle 20  Type I cutaneous mechanoreceptors (Merkel Touch tactile discs) are slowly adapting free nerve endings located in the dermal papilla (fingertips, Nociceptor (pain receptor) hands, lips, external genitalia). They contact Merkel cells from the stratum basale. Epidermis Corpuscle of touch Type II cutaneous mechanoreceptors (Ruffini Dermis corpuscles) are slowly adapting encapsulated nerve endings located deep in the dermis, ligaments and tendons. Sensitive to stretching as digits and limbs move. Subcutaneous Hair Root Plexus layer Pacinian (lamellated) corpuscle 21 Pressure: involves sustained deformation in deep tissues felt over larger area than touch Nociceptor Type I cutaneous mechanoreceptors detect pressure (pain receptor) Epidermis Corpuscles of touch detect pressure Ruffini corpuscle (type II cutaneous mechanoreceptor) Hair Root Plexus Dermis Lamellated (Pacinian) corpuscles are encapsulated nerve endings widely distributed in the body (deep in the dermis and subQ layer; mucous and serous Subcutaneous membranes; joints, tendons, muscles; periosteum; layer mammary glands, external genitalia, and some viscera 22 Vibration: involves rapidly repetitive sensory signals from tactile receptors Merkel (tactile) disc (type I cutaneous mechanoreceptor) Nociceptor (pain receptor) Epidermis Corpuscle of touch (Meissner corpuscle) detect lower-frequency vibrations Ruffini corpuscle (type II Dermis cutaneous mechanoreceptor) Hair Root Plexus Lamellated (Pacinian) corpuscles Subcutaneous detect higher-frequency vibrations layer 23 Itch: stimulation of free nerve endings by certain chemicals (often released during an inflammatory response) Nociceptor (pain receptor) Type I cutaneous mechanoreceptors detect itch Epidermis Corpuscle of touch Ruffini corpuscle (type II cutaneous mechanoreceptor) Dermis Hair root plexuses detect itch Pacinian (lamellated) Subcutaneous corpuscle layer 24 Tickle: stimulation of free nerve endings that occurs only when someone else touches you Nociceptor (pain receptor) Type I cutaneous mechanoreceptors are involved in tickle sensations Epidermis Corpuscle of touch Ruffini corpuscle (type II cutaneous mechanoreceptor) Dermis Hair root plexuses are involved in tickle sensations Pacinian (lamellated) Subcutaneous corpuscle layer 25 Phantom limb sensations When sensations (often pain) are coming from an amputated limb (which, obviously, isn’t there) Could be due to sectioned neurons remaining in the stump, which get activated Could be due to rewiring of the brain, leading to stimulations from other parts of the body being perceived as coming from the amputated limb Traditional pain medicine ineffective Alternative therapies more promising (mirror therapy, electrical nerve stimulation, acupuncture, biofeedback) 26 Which somatic sensory receptor is rapidly adapting and responsible for fine touch? a) type I cutaneous mechanoreceptor b) lamellated corpuscle c) nociceptor d) corpuscle of touch e) type II cutaneous mechanoreceptor 2. Thermal Sensations 28 Thermal Sensations Free nerve ending receptors on the skin surface ◦ Cold receptors in the stratum basale (100C to 400C) ◦ Warm receptors in the dermis (320C to 480C) Both adapt rapidly at first, but continue to generate impulses at a low frequency Pain receptors rather than thermoreceptors are activated below 100C and over 480C 29 3. Pain Sensations 30 Pain Sensations Pain is a sensation necessary for survival – signals the presence of tissue- damaging conditions ◦ stretching, prolonged muscular contractions, muscle spasms, ischemia Pain receptors (nociceptors) are free endings that are located in nearly every body tissue (except brain) ◦ adaptation is slight if it occurs at all Tissue injury releases chemicals that stimulate nociceptors ◦ e.g. prostaglandins, kinins, potassium ◦ pain may remain even after stimulus is removed because chemicals are still present 31 Types of Pain Fast pain ◦ sharp, acute, pricking pain (needle puncture or cut) ◦ occurs rapidly after stimulus (.1 second) ◦ not felt in deeper tissues ◦ travels through large, fast-conducting nerve fibers Slow pain ◦ chronic, aching, burning or throbbing pain (eg. toothache) ◦ begins more slowly (1 sec) & increases in intensity ◦ in both superficial and deeper tissues ◦ travels through small, slow-conducting nerve fibers 32 Types of Pain – based on location Superficial somatic pain ◦ Involves the stimulation of pain receptors in the skin Deep somatic pain ◦ Involves the stimulation of receptors in skeletal muscles, joints, and tendons Visceral pain ◦ Involves the stimulation of pain receptors in visceral organs; if stimulation is diffuse (involves large areas), visceral pain can be severe. Can be due to pressure, tears, ischemia, stretching, rubbing… 33 Referred Pain Visceral pain is usually felt in specific skin or surface areas; skin area and organ are usually served by the same spinal cord segment Heart e.g., heart attack can Liver and Lung and Liver and gallbladder diaphragm gallbladder be felt in skin along Heart Stomach left arm since both Gallbladder Liver and gallbladder Pancreas are supplied by spinal Small intestine Stomach cord segment T1-T5) Ovary Ovary Kidney Urinary Kidney bladder Ureter (a) Anterior view (b) Posterior view 34 The best example of referred pain is: a) Shoulder pain while throwing a baseball b) Pain still present several minutes after stubbing your toe c) “Brain freeze” (sharp headache upon eating or drinking something cold) d) Pain down your leg from a pinched nerve in your back 35 Pain Relief ▪can block formation of chemicals that stimulate nociceptors (aspirin and ibuprofen) ▪can block conduction of nerve impulses along pain fibers (Novocaine = local anesthetic) ▪can lessen the perception of pain in the brain – pain is still sensed, but is not perceived as noxious (Morphine) 36 4. Proprioceptive Sensations 37 Proprioception Awareness of body position & movement ◦ walking or getting dressed without looking ◦ estimate weight of objects (so can adjust necessary force) Proprioceptors adapt only slightly Sensory information is continuously sent to cerebellum & cerebral cortex ◦ Receptors located in muscle, tendon, joint capsules & hair cells in the vestibular apparatus ◦ Receptors include 1. Muscle spindles, 2. Tendon organs (Golgi tendon organs), 3. Joint kinesthetic receptors 38 Proprioceptors: muscle spindles Muscle spindles are proprioceptors Stretching in skeletal muscles that monitor the 1 stimulates 2 SENSORY NEURON muscle spindle length of muscle fibers (participate excited in stretch reflex) MOTOR NEURON excited 3 Within INTEGRATING CENTER (spinal Based on the input from cord) muscle spindles, the brain also sets muscle tone EFFECTOR (same muscle) contracts and relieves the stretching 39 Components of a muscle spindle 2. Alpha motor neurons innervate extrafusal muscle fibers to cause 3. Gamma motor neurons To CNS innervate intrafusal fibers to contraction of the muscle in From CNS response to stretching keep tension and maintain Sensory neurons sensitivity of the muscle spindle even when muscle is contracted Muscle spindle capsule (connective tissue) 1. Sensory nerve endings wrap around 3-10 specialized muscle fibers Extrafusal (intrafusal fibers) muscle fibers 40 How a muscle spindle works 3. Motor neurons cause same muscle 2. Impulses are sent to the cerebral to contract in response to stretching cortex (primary somatosensory (remember stretch reflex) area) for conscious perception of position and movement; impulses To CNS also sent to cerebellum for From CNS movement coordination 1. Sensory neurons monitor the degree of stretching Extrafusal muscle fibers 41 Muscle spindles a) Are found in tendons b) Are responsible for the stretch reflex c) When stretched, lead to relaxation of the muscle d) A and B e) A, B and C 42 Proprioceptors: tendon organs Tendon organs are MOTOR Increased tension 4 proprioceptors located at stimulates NEURON inhibited 2 SENSORY NEURON 1 the junction of tendons and SENSORY excited muscles (involved in tendon RECEPTOR (tendon organ) reflex) 3 INTEGRATING center (spinal cord) 5 EFFECTOR (muscle attached to same Motor neuron to tendon) relaxes and antagonistic muscles is relieves excess tension excited 43 Components of a tendon organ To CNS From CNS Muscle spindle Tendon Tendon fascicles organ (bundles of collagen fibers) laced with sensory nerve endings Extrafusal Capsule of muscle fibers connective tissue 44 How a tendon organ works 3. Motor neuron is inhibited so muscle can relax (remember To CNS From CNS 2. Impulses are sent to the cerebral tendon reflex) cortex for conscious perception of position and movement; impulses also sent to cerebellum for movement coordination 1. Sensory nerve endings detect overstretching in the tendon (too much tension in muscle) Extrafusal muscle fibers 45 Proprioceptors: Joint Kinesthetic Receptors Type II cutaneous mechanoreceptors (Ruffini corpuscles) ◦ found in joint capsule ◦ respond to pressure Small lamellated (Pacinian) corpuscles ◦ found in connective tissue around the joint ◦ respond to acceleration & deceleration of joints 46 Somatic Sensory Pathways POSTERIOR COLUMN-MEDIAL LEMNISCUS PATHWAY ANTEROLATERAL (SPINOTHALAMIC) PATHWAY TRIGEMINOTHALAMIC PATHWAY ANTERIOR AND POSTERIOR SPINOCEREBELLAR PATHWAY 47 Sensory, Motor & Integrative Systems In general, pathways are: 1. Paired - located bilaterally 2. Axons are grouped based on body region innervated (recall nerves) 3. All tracts involve the Brain and the Spinal cord 4. The name of a pathway indicates its origin and its destination: e.g., spinothalamic e.g., vestibulospinal Recall… Sensory information ascends Motor information ____________ Pathways are made of __________and nuclei Synapses are the site at which _______________ of information will occur How many synapses a pathway has will depend on the type of pathway ◦ Examples: ◦ Sensory pathways that end in the cortex have three neurons ◦ Sensory pathways that end in the cerebellum have two neurons Somatic Sensory Pathways Somatic sensory pathways relay information from somatic receptors to the primary somatosensory area in the cerebral cortex. The pathways consist of three neurons ◦ first-order neuron – from somatic receptor to spinal cord or brain stem ◦ second-order neuron – from spinal cord or brain stem to thalamus (opposite side because of decussation) ◦ third-order neuron – from the thalamus to the primary somatosensory area of the cortex (on the same side as the thalamus) 50  RIGHT SIDE Information is sent to primary OF BODY Second-order neurons somatosensory area of cortex and third-order neurons synapse in THIRD-ORDER the thalamus NEURONS Posterior First-order neurons and second- order neurons from the lower Medial lemniscus (in Column- body synapse in the Gracile midbrain) nucleus of the medulla. Same side SECOND-ORDER Medial NEURONS Lemniscus First-order neurons and second- order neurons from the upper Midbrain Second-order neurons decussate Pathway body synapse in the Cuneate nucleus of the medulla. Same side to the other side of the medulla POSTERIOR Medulla COLUMN: FIRST-ORDER NEURONS Gracile fasciculus lower body Cuneate fasciculus upper body Receptors for touch, pressure, vibration, and proprioception Cervical Receptors for touch, spinal cord in the upper limbs, upper pressure, and vibration in the trunk, neck, and posterior head lower limbs and lower trunk Lumbar spinal cord Somatosensory Map of Postcentral Gyrus from lower body from upper body 52 In the posterior column medial lemniscus pathway, first-order neurons… a) synapse with second-order neurons in the thalamus b) synapse with third-order neurons in the thalamus c) synapse with second-order neurons in the pons d) synapse with second-order neurons in the medulla 53 Which sensation is not carried by the posterior column-medial lemniscus pathway? a) Proprioception b) Vibration c) Temperature d) Fine touch 54  RIGHT SIDE LEFT SIDE OF BODY Information is sent to OF BODY primary somatosensory area of cortex Anterolateral THIRD-ORDER NEURON (Spinothalamic) Pathway to the Second-order neurons and third-order Cortex neurons synapse in First-order neurons and the thalamus second-order neurons Midbrain synapse in the posterior gray horn of the spinal cord FIRST-ORDER NEURON Medulla Second-order neurons Receptors for pain, decussate to the other side of cold, warmth, the spinal cord tickle, and itch SPINOTHALAMIC Spinal cord TRACT 55  RIGHT SIDE LEFT SIDE OF BODY Information is sent to OF BODY primary somatosensory Second-order neurons area of cortex and third-order THIRD-ORDER Trigemino- neurons synapse in the thalamus NEURON thalamic SECOND-ORDER First-order neurons Pathway to and second-order NEURONS the Cortex neurons synapse in the pons or medulla Midbrain TRIGEMINOTHALAMIC TRACT Trigeminal (V) nerve FIRST-ORDER Receptors for touch, pressure, NEURON Pons vibration, pain, cold, warmth, Second-order neurons decussate itch, and tickle in the face, nasal to the other side of the brain stem cavity, oral cavity, and teeth 56 Medulla Sensory Pathways to the Cerebellum Axon collaterals of proprioceptive sensory neurons use the posterior and anterior Posterior spinocerebellar tract spinocerebellar tracts to carry signals into the cerebellum (not consciously perceived) Essential for posture, balance and coordination of skilled movements Two neuron pathway Receptor → 1st order neuron → posterior grey horn → 2nd order neuron Spinal cord The signal travels up to the same side of body Anterior spinocerebellar tract (no decussation) 57  Posterior column: Gracile fasciculus See table 16.3 for a Cuneate fasciculus summary for the major somatic sensory tracts and pathways Spinal cord Spinothalamic tract Spinal cord Trigeminothalamic tract Pons Posterior spinocerebellar tract Anterior spinocerebellar tract Spinal cord 58 In sensory pathways to the cortex… a) the second-order neuron is always the one that decussates b) decussation always takes place in the medulla c) decussation always takes place in the thalamus d) A and B e) A, B and C 59 Somatic Motor Pathways 60 Somatic Motor Pathways Always involve 2 motor neurons in series Upper Motor Neuron (UMN): cell body in the CNS motor area (80% in cortex; 20% in brainstem) Lower Motor Neuron (LMN): extends from the brain stem or spinal cord to innervate skeletal muscles FINAL COMMON PATHWAY From brainstem through cranial nerves to innervate muscles of face and head From spinal cord through spinal nerves to innervate muscles of limbs and trunk  Right side of brain Left side of brain 5 Cerebral cortex Brain Interneuron 4 Upper motor neuron 6 Thalamus 3 Interneuron Sensory neuron Lower Motor Neurons (LMN) 7 Sensory 2 Spinal cord extend directly from the CNS receptor (where their cell bodies are) 1 Key: to skeletal muscles 8 Neuromuscular junction Skeletal muscles 62 Somatic Motor Pathways ◦ Control of body movement involves: ◦ Motor portions of cerebral cortex ◦ Initiate & control precise movements Basal nuclei help establish muscle tone & integrate semi-voluntary automatic movements Cerebellum helps make movements smooth & helps maintain posture & balance Basal Nuclei Frontal plane Corpus callosum The basal nuclei are 3 nuclei deep within each View hemisphere: Longitudinal fissure Caudate Lateral ventricle nucleus Insula Thalamus Putamen Hypothalamus and associated nuclei Globus pallidus Third ventricle Somatic Motor Pathways Four distinct neural circuits (somatic motor pathways) participate in control of movement by providing input to lower and upper motor neurons 1. Local circuit neurons are located close to lower motor neuron cell bodies in the brain stem and spinal cord. 2. Local circuit neurons and lower motor neurons receive input from upper motor neurons. 3. Neurons of the basal ganglia provide input to upper motor neurons. 4. Cerebellar neurons also control activity of upper motor neurons. In somatic motor pathways… a) all pathways ultimately lead to the activation of the basal nuclei b) all pathways ultimately lead to the activation of the cerebellum c) all pathways ultimately lead to the activation of lower motor neurons 66  Sensory, motor, and 2 Upper motor association cortex neurons from cerebral cortex 3 Basal nuclei neurons Thalamus Local circuit neurons are located close 4 Cerebellar neurons to LMN cell bodies (in the spinal cord or brain stem); they coordinate Motor centers in rhythmic activities (like alternating brainstem flexion and extension of lower limb 2 Upper motor muscles when walking). They receive neurons from 1 Local circuit neurons brain stem in brain stem and input from sensory neurons and from spinal cord higher centers in the brain. Lower motor neurons (final common pathway) Skeletal muscles 67 Local circuit neurons… a) are neurons located in the basal nuclei b) are neurons located in the cerebral cortex c) are neurons located near lower motor neurons 68  Sensory, motor, and 2 Upper motor association cortex neurons from cerebral cortex 3 Basal nuclei UMN from cortex are neurons Thalamus involved in planning, initiating and 4 Cerebellar neurons directing movements. Motor centers in brain stem 2 Upper motor neurons from Most UMN synapse onto 1 Local circuit neurons brainstem in brain stem and local circuit neurons, and UMN from brain spinal cord some of them synapse stem regulate directly onto LMN. They Lower motor muscle tone, neurons (final receive input from the common pathway) posture, orientation basal nuclei and the of head and body cerebellum. Skeletal muscles Upper motor neurons… a) can descend from the brainstem or from the cerebral cortex b) can synapse onto local circuit neurons or onto lower motor neurons c) a and b 70  Sensory, motor, and 2 Upper motor association cortex neurons from cerebral cortex Basal nuclei neurons provide 3 Basal nuclei neurons Thalamus input to UMN (in cortex or brain stem); neural circuits 4 Cerebellar neurons interconnect the basal nuclei, the cerebral cortex and the Motor centers in brainstem. Help initiate and brain stem terminate movements, 2 Upper motor neurons from 1 Local circuit neurons suppress unwanted brainstem in brain stem and movements and set normal spinal cord level of muscle tone Lower motor neurons (final common pathway) Skeletal muscles The basal nuclei… a) influence upper motor neurons in the cortex or brain stem b) communicate directly with lower motor neurons c) a and b 72  Sensory, motor, and 2 Upper motor association cortex neurons from cerebral cortex 3 Basal nuclei neurons Thalamus 4 Cerebellar neurons Cerebellar neurons provide input to UMN (in cortex or brain stem); Motor centers in brain stem neural circuits interconnect the 2 Upper motor cerebellum, the cerebral cortex neurons from brain stem 1 Local circuit neurons and the brain stem. Functions in in brain stem and spinal cord monitoring the difference between intended movement and Lower motor movement actually performed. neurons (final common pathway) Skeletal muscles 73 The cerebellum… a) influences upper motor neurons in the cortex or brain stem b) communicates directly with lower motor neurons c) a and b 74  Sensory, motor, and 2 Upper motor association cortex neurons from cerebral cortex 3 Basal nuclei neurons Thalamus 4 Cerebellar neurons Motor centers in UMN from Direct brainstem Motor Pathways extend 2 Upper motor directly from the neurons from UMN from Indirect brainstem 1 Local circuit neurons cerebral cortex to LMN. in brain stem and Motor Pathways extend spinal cord from various nuclei of the brainstem and will Lower motor In both direct and indirect neurons (final use various tracts before common pathway) motor pathways, the basal they connect with LMN. nuclei and the cerebellum Skeletal muscles influence the UMN. Direct Motor Pathways: LATERAL CORTICOSPINAL PATHWAY ANTERIOR CORTICOSPINAL PATHWAY CORTICOBULBAR PATHWAY 76  RIGHT SIDE Primary motor area of OF BODY cerebral cortex The lateral corticospinal pathway is for movements of hands and feet (highly skilled movements) from cortex, through cerebral peduncles, 90% of UMN decussate Midbrain in the pyramids of medulla UPPER MOTOR Cerebral NEURON peduncle Pons The lateral corticospinal tract forms in the lateral part of the SC Medulla Pyramid UMN synapse either with local circuit neurons Spinal cord or with LMN in anterior gray horn of SC Spinal nerve LMN exit through anterior root of spinal nerve LOWER MOTOR NEURON Spinal cord 77  RIGHT SIDE Primary motor area of LEFT SIDE OF BODY cerebral cortex OF BODY The anterior corticospinal pathway is for movements of the trunk and proximal parts of limbs Midbrain Cerebral peduncle UPPER MOTOR NEURON The remaining 10% of UMN that Pons do NOT decussate in the pyramids use this tract Medulla Pyramid ANTERIOR Decussation occurs in the spinal cord, just CORTICOSPINAL before synapsing with local circuit neurons TRACT or LMN in anterior gray horn of SC Spinal nerve LOWER MOTOR NEURON Spinal cord 78  RIGHT SIDE Primary motor area of LEFT SIDE OF BODY cerebral cortex OF BODY The corticobulbar pathway is for movements of skeletal muscles in head: eyes, tongue, neck, UPPER MOTOR NEURON chewing, expression & speech CORTICOBULBAR TRACT from cortex to nuclei in brain stem, Cerebral peduncle then cranial nerves: all but I, II and VIII (because these are sensory nerves) Facial (VII) nerve Midbrain Some decussate, To skeletal muscles of LOWER MOTOR facial expression others don’t NEURON Pons Hypoglossal (XII) nerve LOWER MOTOR NEURON Medulla To skeletal muscles of the tongue 79 Summary: Location of Direct Pathways Lateral corticospinal tract Anterior corticospinal tract Corticobulbar tract Most motor neurons from direct motor pathways are dedicated to… a) Movement of hands and feet b) Movements of facial muscles c) Movements of the trunk and proximal part of limbs 81 Indirect Motor Pathways 82 Indirect Pathways All motor pathways other than the Rubrospinal Tectospinal corticospinal and corticobulbar tracts tract tract Axons from UMNs descend from various nuclei in brainstem into 5 major tracts of spinal cord synapse w/ local circuit neurons or LMNs Lateral reticulospinal Medial tract reticulospinal tract Vestibulospinal tract Spinal cord 83 Indirect Pathways Rubrospinal: from red nucleus (midbrain). Precise movements from distal part of limb Tectospinal: from superior colliculi (midbrain). Move head and eye in response to visual stimuli Vestibulospinal: from vestibular nucleus (CN VIII; pons). Maintain balance in response to head movements Lateral reticulospinal: from reticular formation. Facilitate flexor reflexes, inhibit extensor reflexes, decrease muscle tone (axial sk. & prox. limb) Medial reticulospinal: from reticular formation. Facilitate extensor reflexes, inhibit flexor reflexes, increase muscle tone (axial sk. & prox. limb) 84 Somatic Motor Pathways: Summary Table 16.4 Basal Nuclei connections UMN in cortex Sensory, motor, and 1. Basal nuclei influence movements through association cortex their effect on UMN ◦ Input from cortex (sensory, motor, Basal nuclei neurons Thalamus association) and substantia nigra (midbrain) ◦ Output to cortex via thalamus Cerebellar neurons ◦ Cortex to basal nuclei to thalamus to cortex – involved in initiating and terminating Motor centers in movements UMN in brain stem brain stem 2. Basal nuclei reduce muscle tone – damage causes a generalized increase in muscle tone 3. Basal nuclei suppress unwanted movements 86 Modulation of Movement by the Cerebellum The cerebellum is active in both learning and performing rapid, coordinated, highly skilled movements and in maintaining proper posture and equilibrium. The four aspects of cerebellar function ◦ Monitoring intention for movement ◦ Monitoring actual movement ◦ Comparing intention with actual performance ◦ Sending out corrective feedback  The cerebellum receives sensory information to help it with monitoring Input from Output to Proprioception Sensation Spinocerebellar tract (position) Vestibular sensation UMN on the Vestibular Nuclei corticospinal medial and (Balance) lateral pathways Visual information Superior colliculi 1 2 Cerebellum receives Sagittal plane Cerebellum receives input Motor input from motor area areas of from proprioceptors cerebral of cortex and basal cortex which report on what nuclei about intention movement is actually Corrective of movement (via pons) feedback Thalamus happening (via Motor centers spinocerebellar tracts) in brain stem Cortex of cerebellum 3 Pons 4 4 Cerebellum compares 1 Cerebellum sends 3 Pontine nuclei the intention of out corrective 2 movement with the Direct motor pathways feedback to UMN in actual movement Indirect motor cortex (via thalamus) Sensory signals performed (integration from proprioceptors pathways or in brain stem in muscles and in gray matter of joints, vestibular Signals to lower motor neurons cerebellum) apparatus, and eyes Sagittal section through brain and spinal cord Integrative functions of the cerebrum SLEEP & WAKEFULNESS LEARNING AND MEMORY 90 Sleep and Wakefulness Sleep - a state of altered consciousness or partial unconsciousness from which an individual can be aroused by different stimuli During wakefulness, the cerebral cortex is very active During most stages of sleep, less activity is seen in the cerebral cortex 91  Sleep and wakefulness are controlled by the reticular RAS has numerous connections to activating system (RAS), found the cortex; Arousal involves in the reticular formation increased activity in the RAS, which increases activity in the cortex Cerebral cortex Visual impulses from eyes Auditory and equilibrium impulses Many types of inputs can activate from ears the RAS: pain, light, noise, muscle Somatic sensory impulses (from nociceptors, proprioceptors, and touch receptors) activity, touch (but not smell) 92 Sleep During sleep, activity in the RAS is very low ◦ Adenosine is a sleep-inducing chemical in the brain that inhibits activity in RAS ◦ caffeine binds to adenosine receptors, thereby preventing adenosine from binding and inducing sleep Normal sleep consists of two types: ◦ non-rapid eye movement sleep (NREM) ◦ inactive brain, active body ◦ rapid eye movement sleep (REM) ◦ active brain, inactive body 93 NREM Sleep Stage 1 ◦ person is drifting off with eyes closed (first few minutes) Stage 2 ◦ person becomes increasingly harder to awaken Stage 3 ◦ relaxed, deep sleep, body temperature & BP drop, reflexes and muscle tone are intact ◦ bed-wetting & sleepwalking occur in this phase Note: stages 3 used to be separated into stages 3 and 4 94  REM Sleep Most dreams occur during REM sleep 3-5 episodes of REM in a 7–8-hour sleep, increasing in length (first ~10min, last ~50min) ◦ total REM sleep = 90 to 120 minutes Total REM & dreaming time decreases with age ◦ ~80% REM in newborns ◦ ~50% REM in infants Neuronal activity & oxygen use is highest in REM sleep ◦ ~35% REM in 2yo (higher than during intense mental or physical activity!) ◦ ~25% REM in adults Motor neurons are inhibited (except for breathing and eye movements) = paralysis of skeletal muscles REM thought to be important for proper brain development and function 95  Cycles of N1 → N2 → N3 → N2 → REM. There is a greater amount of deep sleep (stage N3) earlier in the night, while the proportion of REM sleep increases later in the night, in the cycles before natural awakening 96 Learning and Memory Learning is the ability to acquire new information or skills through instruction or experience Memory is the process by which that information is stored and retrieved For an experience to become part of memory, it must produce persistent structural and functional changes that represent the experience in the brain ◦ The capability for change with learning is called PLASTICITY 97 Types of memory Declarative memory vs Procedural memory Short-term memory lasts only seconds or minutes and is the ability to recall bits of information; changes in synapses Long-term memory lasts from hours, days to years and is related; anatomical and biochemical changes at synapses ◦ Long-term memory for information that can be verbalized is stored in cerebral cortex ◦ Long-term memory for motor functions stored in basal ganglia, cerebellum and cortex 98 Sleepwalking occurs in which stage of non- rapid eye movement (NREM) sleep? a) stage 1 b) stage 2 c) stage 3 d) None of these – it occurs during REM sleep 99