Human Physiology BIOL3205 PDF

Human Physiology BIOL3205 Sensory and motor nervous systems Prof. Chi Bun Chan School of Biological Sciences 5N10 Kadoorie Biological Sciences Building [email protected] 39173823  Lecture outline General p...

Human Physiology BIOL3205 Sensory and motor nervous systems Prof. Chi Bun Chan School of Biological Sciences 5N10 Kadoorie Biological Sciences Building [email protected] 39173823  Lecture outline General properties of the sensory and motor nervous system Sensory receptors Sensory coding Pain and analgesic systems Structure of the peripheral nervous system (Para)Sympathetic nervous system Reflex  Why we can sense the world? Achieve through the functioning of sensory systems Depends on special receptors that can detect specific forms of energy (e.g. light vs X-ray) Perception – the conscious interpretation of the world based on the sensory system, memory, and other neural processes Perceptions of the stimuli are not absolute (e.g. water temperature of the swimming pool)  General properties of sensory system Sense – a detection of stimulus (in the form of physical energy) Special senses – vision, hearing, taste, smell, and body balance (special sensory system) Somatic senses – touch, temperature, pain, itch, and proprioception (Somatosensoty system) Proprioception – awareness of body movement and position in space Sensory system can either be complex or simple Single sensory neurons (pain) Sense organs (ear and eye) Sensory receptor (action potential firing) → integration center (CNS) → conscious perception or subconscious (without awareness)  Classification of neurons Classification according to functions Afferent neurons Somatic afferent Visceral afferent Interneuron 99% All in CNS Efferent neuron  Sensory receptors and unit Sensory receptors – specialized structures that detect a specific form of energy from the Temperature Pressure Light environment Sensory receptor vs protein receptor Can be nerve ending or separated cells Sensory unit - single afferent neuron + receptor Receptor field – an area over which an adequate Sensory unit stimulus can produce a response in the afferent neuron Types of receptors Photoreceptor (light) Chemoreceptor (chemical) Thermoreceptor (temperature) Mechanoreceptor (pressure) Proprioceptor (gesture) Simple Complex Special sense receptor receptor receptor Nociceptor (damage/pain)  Sensory transduction in neural Sensory transduction – converts pathways a sensory stimulus (modality) into changes in member potential (receptor potential) Nerve ending → threshold → AP action potential → CNS Cells → transmitter → threshold of AP GP neuron → action potential → CNS Started as graded potential Receptor adaption – a decrease over time in the magnitude of GP the receptor potential in the presence of a constant stimulus 1st, 2nd, and 3rd-order neurons  Sensory coding Sensory coding is an information processing that differentiates the type, strength, and location of the sensory stimulus 3rd order 3rd order 3rd order Sensory type is coded by the activated neuron neuron neuron receptor and pathway when the stimulus is applied. 2nd order 2nd order 2nd order Misperception will be formed if a pathway is neuron neuron neuron activated by non-specific stimuli Perception of stimuli is not necessarily 1st order 1st order 1st order based on a single sensory pathway but on neuron neuron neuron a combination of pathway Combination of pathways Stimulus intensity Stimulus location (acuity)  Sensory coding Frequency coding Sensory coding differentiates the type, strength, and location of the stimulus Stimulus type Misperception Combination of pathways Stimulus intensity Population coding Frequency coding – frequency of AP Population coding – no. of receptors activated Stimulus location (acuity)  Sensory coding Sensory coding differentiates type, No. of mechanoreceptors strength and location of the stimulus ~ 400 ~ 17,000 Stimulus type (1 mm) (5 cm) Misperception Combination of pathways Stimulus intensity Frequency coding – frequency of AP Population coding – no. of receptors activated Stimulus location (acuity) Receptive field – area over which an adequate stimulus can produce a response in the afferent neuron in a region Time difference in generating action potential  Sensory coding Sensory coding differentiates type, strength and location of the stimulus Stimulus type Receptors and pathway Misperception Combination of pathways Stimulus intensity Frequency coding – frequency of AP Population coding – no. of receptors activated Stimulus location (acuity) Receptive field – area over which an adequate stimulus can produce a response in the afferent neuron Size of receptive field – size α 1/acuity Time difference in generating an action potential  Thalamus Thalamus is the “relay station” for preliminary processing of sensory input Screens out insignificant signals and routes the important sensory impulses to appropriate areas of the somatosensory cortex E.g. Parents in response to a crying baby Cannot distinguish the signal intensity and location  Physiology of pain Classified according to Duration - Fast pain (sharp pricking sensation) vs slow pain (poorly localized, dull aching sensation) Location – referred pain Indicates tissue damage Avoids subsequent encounters with potential damaging stimuli Initiated by nociceptors Mechanical nociceptors - cutting Thermal nociceptors - temperature Polymodal nociceptors - chemicals  Endogenous analgesic pathway Pain pathways have different destinations in the cortex, thalamus, and reticular formation → not a single “pain center” Substance P is the major neurotransmitter for the pain pathway Built-in pain suppressing (analgesic) system Interneruons in the spinal cord releases endogenous opioid (endorphins), which acts on the opiate receptors to inhibit the release of substance P Morphine is a powerful analgesic  Morphine as an analgesic Morphine Opioid Opium poppy Opium Opioids are substances that act on opioid receptors Morphine is a type of opioid Pain killer Why rubbing the hurt site? Sensory information can be modulated to affect the final perception Done at the synapse of neural pathway Gate-control theory – Somatic signals of nonpainful sources can inhibit signals of pain at the spinal level Inhibitory interneuron modulates the signal transmission along the nociceptor pathway Simultaneous nonpainful mechanical stimulation activates the inhibitory pathway Transcutaneous electrical nerve stimulation (TENS)  2nd Can we sense the damage neuron of internal organ? Referred pain – activation of nociceptors in the viscera 1st order pain perceived at a location other than the site neuron of the painful stimulus/ origin Misinterpreted as pain from the body surface (‘referred”) E.g. Heart attack Caused by the common 2nd order neuron that receives the same input from two 1st order neurons Mixed with past-experience  Classification of neurons Classification according to function Afferent neurons Inhibitory neuron Somatic afferent Visceral afferent Interneuron 99% All in CNS Efferent neuron  Peripheral nervous system (PNS) PNS controls muscle and glands Somatic nervous system – voluntary action (muscle) Autonomic nervous system – involuntary actions (smooth muscle, glands) Sympathetic nervous system (thoracic and lumbar origin) Parasympathetic nervous system (cranial and sacral) Dual innervation – exert opposite effects in a particular organ Systemic level – increases the activity of one organ but reduces the activity of the other organ Two-neuron chain – Preganglionic fiber, postganglionic fiber Ganglion – a cluster of neuronal cell bodies outside the CNS Organization of PNS Locations of sympathetic and parasympathetic ganglion Parasympathetic ganglion  Anatomical comparison of sympathetic and parasympathetic system Origin Location of ganglion Length of pre- and Thoracic and Lumbar post-ganglionic fiber Neurotransmitter Cranial and sacral  Functional characteristics of autonomous nervous system Both systems are partially active (sympathetic or sympathetic tone) under the basal status The two systems are reciprocally controlled (increase of one system, decrease of another) Sympathetic fiber firing ↑ - sympathetic dominance Parasympathetic fiber firing ↑ - parasympathetic dominance Sympathetic dominance – prepare for an emergency or stressful situations (Fight-or-flight) Parasympathertic dominance – for general housekeeping (rest-and-digest) Precise control of the organ’s activity (accelerator and brake) Comparison of types of neurons (https://www.slideshare.net/ShubhamRoy10/ans-sympathetic-and- parasympathetic)  Control of autonomous nervous system Prefrontal cortex (Fight or flight) Hypothalamus is a collection of nuclei that integrates the homeostatic functions (internal environment) Links autonomous system and the endocrine system Controls – body temp, thirst and urine, food intake, pituitary hormone secretion, uterine contraction, and milk production, smooth muscle contraction, emotion, sleep-wake cycle Limbic system (cortex, basal nuclei, thalamus, hypothalamus) - emotion Medulla Pons Limbic system Spinal cord  Consistent and predictable Reflex Withdrawal reflex Response that occurs automatically without conscious effort Cranial reflex (integrated by the brain) Hypothalamus/brain stem-initiated response (e.g. pupil dilation) Spinal reflex (integrated by spinal cord) withdraw reflex Can be overrided by the cortex Innate (simple or basic) vs conditioned (a result of learning) reflex Stretch reflex Reflex arc – the neuronal pathway that controls reflex Somatic reflex arc (motor neurons to skeletal muscle) Visceral reflex arc (autonomic nervous system to smooth muscle) Monosynaptic vs polysynaptic reflex Not every reflex activity involves a reflex arc Hormone response Local response: blood pressure  Basal nuclei Voluntary movement involves the cortex, thalamus, basal nuclei, and cerebellum Basal nuclei masses of grey matter located deep within the cerebral white matter Functions Inhibiting the muscle tone throughout the body Suppressing the useless, unwanted patterns of movement Helping and monitoring slow and sustained muscle contractions related to posture and support Network of the motor cortex, thalamus, and basal nuclei Cortex – initiates the movement Thalamus - reinforces the motor behavior Basal nuclei – exerting inhibitor effect on the thalamus Cerebellum - posture Parkinson’s disease - gradual destruction of neurons that release dopamine in the basal nuclei  Summary General components of sensory and motor nervous systems Sensory signal transduction and integration Pain and analgesic systems Structural and functional differentiation of the sympathetic and parasympathetic nervous system Reflex actions Neural pathway of voluntary movement