Physiology Chp 10 Part A PDF

Physiology: Chp 10 Part A Central Nervous System Juan J. Bustamante, Ph.D. Assistant Professor Pharmaceutical Science Phone (361) 221-0643 Email: [email protected] Office: Room 223 © 2016 Pearson Education, Inc.  A...

Physiology: Chp 10 Part A Central Nervous System Juan J. Bustamante, Ph.D. Assistant Professor Pharmaceutical Science Phone (361) 221-0643 Email: [email protected] Office: Room 223 © 2016 Pearson Education, Inc.  About This Chapter General properties of sensory systems Somatic senses Chemoreception: smell and taste The ear: hearing The ear: equilibrium The eye and vision © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc.  Sensory Pathways Stimulus as physical energy sensory receptor – Receptor acts as a transducer Intracellular signal usually change in membrane potential Stimulus threshold action potential to CNS Integration in CNS cerebral cortex, where they reach conscious perception, or acted on subconsciously © 2016 Pearson Education, Inc. Figure 10.1 Simple, complex, and nonneural sensory receptors Simple receptors are neurons Complex neural receptors have nerve Most special senses receptors are cells with free nerve endings. They endings enclosed in connective tissue capsules. that release neurotransmitter onto sensory may have myelinated or This illustration shows a Pacinian corpuscle, neurons, initiating an action potential. The unmyelinated axons. which senses touch. cell illustrated is a hair cell, found in the ear. Stimulus Stimulus Stimulus Free nerve endings Enclosed nerve Specialized receptor ending cell (hair cell) Layers of connective tissue Synaptic vesicles Synapse Unmyelinated axon Myelinated axon Myelinated axon Cell body Cell body Cell body of sensory neuron © 2016 Pearson Education, Inc. Figure 10.1a Simple, complex, and nonneural sensory receptors Simple receptors are neurons with free nerve endings. They may have myelinated or unmyelinated axons. Stimulus Pain and itch Free nerve endings Unmyelinated axon Cell body © 2016 Pearson Education, Inc. Figure 10.1c Simple, complex, and nonneural sensory receptors Most special senses receptors are cells that release neurotransmitter onto sensory neurons, initiating an action potential. The cell illustrated is a hair cell, found in the ear. Stimulus Specialized receptor cell (hair cell) Synaptic vesicles Synapse Myelinated axon Cell body of sensory neuron © 2016 Pearson Education, Inc.  Receptors to Particular Forms of Energy are Divided into 4 Main Groups Chemoreceptors respond to chemical ligands: taste, smell Mechanoreceptors respond to mechanical energy pressure and sound: hearing Thermoreceptors respond to temperature Photoreceptors for vision respond to light © 2016 Pearson Education, Inc. © 2016 Pearson Education, Inc. Figure 10.2 Receptive fields of sensory neurons Convergence creates large receptive fields. Small receptive fields are found in more sensitive areas. Compass with points separated by 20 mm The receptive fields of three When fewer neurons converge, primary sensory neurons secondary receptive fields are overlap to form one large much smaller. secondary receptive field. Skin surface Skin surface Primary sensory neurons Convergence of primary neurons allows simultaneous Secondary subthreshold stimuli to sum sensory at the secondary sensory neurons neuron and initiate an action potential. Two stimuli that fall within the same The two stimuli activate separate secondary receptive field are perceived pathways to the brain. The two as a single point, because only one points are perceived as distinct signal goes to the brain. Therefore, stimuli and hence there is there is no two-point discrimination. two-point discrimination. © 2016 Pearson Education, Inc. Figure 10.2a Receptive fields of sensory neurons Convergence creates large receptive fields. Compass with points separated by 20 mm The receptive fields of three primary sensory neurons overlap to form one large secondary receptive field. Skin surface Primary Example: arm/leg sensory neurons Convergence of primary Secondary neurons allows simultaneous sensory subthreshold stimuli to sum neurons at the secondary sensory neuron and initiate an action potential. Two stimuli that fall within the same secondary receptive field are perceived as a single point, because only one signal goes to the brain. Therefore, there is no two-point discrimination. © 2016 Pearson Education, Inc. Figure 10.2b Receptive fields of sensory neurons Small receptive fields are found in more sensitive areas. Compass with points separated by 20 mm When fewer neurons converge, secondary receptive fields are much smaller. Skin surface Primary sensory neurons Secondary sensory neurons Example: fingertip The two stimuli activate separate pathways to the brain. The two points are perceived as distinct stimuli and hence there is two-point discrimination. © 2016 Pearson Education, Inc.  Sensory Transduction Stimulus energy converted into information processed by CNS – Ion channels or second messengers initiate membrane potential change Adequate stimulus: form of energy to which a receptor is most responsive Threshold: minimum stimulus Receptor potential: change in sensory receptor membrane potential © 2016 Pearson Education, Inc.  Integration by CNS Sensory information – Spinal cord to brain by ascending pathways – Directly to brain stem via cranial nerves Visceral reflexes integrated in brain stem or spinal cord usually do not reach conscious perception. © 2016 Pearson Education, Inc.  Integration by CNS Perceptual threshold: level of stimulus necessary to be aware of particular sensation – brain can filter out “turn off” or “tune out”- neurons higher in the pathway dampen the perceived signal so that it does not reach the conscious brain Habituation: decreased perception through inhibitory modulation – Falls below perceptual threshold © 2016 Pearson Education, Inc.  Properties of Stimulus: Modality Four properties of a stimulus – Modality – Location – Intensity – Duration © 2016 Pearson Education, Inc.  Properties of Stimulus: Modality Modality indicated by – Which sensory neurons are activated – Where neurons terminate in brain Each receptor type is most sensitive to a particular modality of stimulus Labeled line coding – 1:1 association of receptor with sensation – Example: Stimulation of a cold receptor is always perceived as cold, whether the actual stimulus was cold or an artificial depolarization of the receptor © 2016 Pearson Education, Inc.  Properties of Stimulus: Location According to which receptive fields are activated Auditory information is an exception – Ear neurons sensitive to different frequencies – Brain uses timing to locate © 2016 Pearson Education, Inc. Figure 10.4 Localization of sound Source of sound Sound takes longer to reach left ear. Signals coming Left from the right reach Right the brain first. Top view of head © 2016 Pearson Education, Inc.  Properties of Stimulus: Location Lateral inhibition – Increases contrast between activated receptive fields and inactive neighbors Population coding – Multiple receptors functioning together © 2016 Pearson Education, Inc. Figure 10.5 Lateral inhibition Stimulus Stimulus Frequency of action potentials Pin Skin A B C Tonic level Primary neuron A B C response is proportional to stimulus strength. Primary sensory neurons Pathway closest to Secondary the stimulus inhibits neurons neighbors. Frequency of action potentials A B C Inhibition of lateral Tonic level Tertiary neurons enhances neurons perception of stimulus. A B C © 2016 Pearson Education, Inc.  Properties of Stimulus: Intensity and Duration Intensity – Coded by number of receptors activated and frequency of action potentials called frequency coding Duration – Coded by duration of action potentials – Some receptors can adapt, or cease to respond Tonic receptors versus phasic receptors © 2016 Pearson Education, Inc. Figure 10.6 Coding for stimulus intensity and duration Cell body Axon terminal Transduction site Trigger zone Myelinated axon Stimulus Moderate Stimulus Membrane potential (mV) 20 0 Amplitude 20 40 Threshold 60 80 0 5 10 0 5 10 0 5 10 Duration Time (sec) Membrane potential (mV) Longer and 20 Stronger Stimulus 0 20 40 60 80 0 5 10 0 5 10 0 5 10 Frequency of action Receptor potential Receptor potential Neurotransmitter potentials is proportional strength and is integrated at the release varies to stimulus intensity. duration vary with trigger zone. with the pattern Duration of a series of the stimulus. of action potentials action potentials is arriving at the axon proportional to stimulus terminal. duration. © 2016 Pearson Education, Inc. Figure 10.7a Receptor adaptation In general, the stimuli that activate tonic receptors are parameters that must be monitored continuously by the body such as baroreceptor. © 2016 Pearson Education, Inc. Figure 10.7b Receptor adaptation This type of response allow the body to ignore information that have evaluated and found not to threaten homeostasis or well-being for example smell – cologne © 2016 Pearson Education, Inc.  Somatic Senses: Modalities Touch Proprioception Temperature Nociception – Pain – Itch © 2016 Pearson Education, Inc. Figure 10.8 Somatosensory pathways Slide 1 Sensations are perceived in the primary somatic sensory cortex. KEY Primary sensory neuron Secondary sensory neuron Tertiary neuron Sensory pathways synapse in the THALAMUS thalamus. MEDULLA Fine touch, vibration, and proprioception pathways cross the midline in the medulla. Fine touch, proprioception, vibration Pain, temperature, and coarse touch Nociception, cross the midline in temperature, the spinal cord. coarse touch SPINAL CORD © 2016 Pearson Education, Inc. Figure 10.8 Somatosensory pathways Slide 2 KEY Primary sensory neuron Secondary sensory neuron Tertiary neuron THALAMUS MEDULLA Pain, temperature, and coarse touch Nociception, cross the midline in temperature, the spinal cord. coarse touch SPINAL CORD © 2016 Pearson Education, Inc. Figure 10.8 Somatosensory pathways Slide 3 KEY Primary sensory neuron Secondary sensory neuron Tertiary neuron THALAMUS MEDULLA Fine touch, vibration, and proprioception pathways cross the midline in the medulla. Fine touch, proprioception, vibration SPINAL CORD © 2016 Pearson Education, Inc. Figure 10.8 Somatosensory pathways Slide 4 KEY Primary sensory neuron Secondary sensory neuron Tertiary neuron Sensory pathways synapse in the THALAMUS thalamus. MEDULLA Fine touch, vibration, and proprioception pathways cross the midline in the medulla. Fine touch, proprioception, vibration Pain, temperature, and coarse touch Nociception, cross the midline in temperature, the spinal cord. coarse touch SPINAL CORD © 2016 Pearson Education, Inc. Figure 10.8 Somatosensory pathways Slide 5 Sensations are perceived in the primary somatic sensory cortex. KEY Primary sensory neuron Secondary sensory neuron Tertiary neuron Sensory pathways synapse in the THALAMUS thalamus. MEDULLA Fine touch, vibration, and proprioception pathways cross the midline in the medulla. Fine touch, proprioception, vibration Pain, temperature, and coarse touch Nociception, cross the midline in temperature, the spinal cord. coarse touch SPINAL CORD © 2016 Pearson Education, Inc. Figure 10.9 The somatosensory cortex No pain fiber in the brain The amount of space Posterior on the somatosensory view cortex devoted to Size of region not fix. each body part is proportional to the sensitivity of that part. Reading braille enlarge region devoted to fingertips Lost of a finger – area take over by adjacent Thalamus structure Cross section of the right cerebral hemisphere and sensory areas of the Sensory signals cerebral cortex from left side of body © 2016 Pearson Education, Inc. Figure 10.10-1 Sensory receptors in the skin Merkel receptors Meissner's corpuscle sense steady pressure responds to flutter and and texture. stroking movements. Hair Free nerve ending Free nerve ending of Free nerve ending nociceptor responds of hair root senses Hair root to noxious stimuli. hair movement. Sensory nerves Pacinian corpuscle carry signals to senses vibration. spinal cord. Ruffini corpuscle responds to skin stretch. © 2016 Pearson Education, Inc.  Temperature Receptors Free nerve endings Terminate in subcutaneous layers Cold receptors – Lower than body temperature Warm receptors – Above body temperature to about 45°C – Pain receptors activated above 45°C Thermoreceptors use cation channels called transient receptor potential (TRP) channels © 2016 Pearson Education, Inc.