The Peripheral Nervous System and Reflex Activity: Part A 13 The Peripheral Nervous System and Reflex Activity: Part A

Peripheral Nervous System (PNS) What is the peripheral nervous system? How do we sense stuff?

Peripheral Nervous System (PNS) What is the peripheral nervous system? Everything except the brain and spinal cord How do we sense stuff?

Peripheral Nervous System (PNS) What is the peripheral nervous system? Everything except the brain and spinal cord How do we sense stuff? Sensory receptors Peripheral nerves and associated ganglia Motor endings

Review: what was the difference? Afferent vs efferent? Somatic vs autonomic? Symp vs parasymp? Central nervous system (CNS) Peripheral nervous system (PNS) Sensory (afferent) division Motor (efferent) division Somatic nervous system Autonomic nervous system (ANS) Sympathetic division Parasympathetic division Figure 13.1

Sensory Receptors Why do we need sensory receptors? These receptors communicate graded potentials  trigger nerve impulses WIDB: sensation vs perception?

Sensory Receptors Why do we need sensory receptors? Responding to changes in environment These receptors communicate graded potentials  trigger nerve impulses WIDB: sensation vs perception?

Sensory Receptors Why do we need sensory receptors? Responding to changes in environment Why do we need to do this? These receptors communicate graded potentials  trigger nerve impulses WIDB: sensation vs perception?

Sensory Receptors Why do we need sensory receptors? Responding to changes in environment Why do we need to do this? Homeostasis These receptors communicate graded potentials  trigger nerve impulses WIDB: sensation vs perception?

Sensory Receptors Why do we need sensory receptors? Responding to changes in environment Why do we need to do this? Homeostasis These receptors communicate graded potentials  trigger nerve impulses WIDB: sensation vs perception? Sensation sensing (unconscious interpretation) Perception “sensing the sense” (conscious interpretation)

Classification of Receptors How are the receptors classified?

Classification of Receptors How are the receptors classified? Stimulus type what you sense Location where you sense Structural complexity structure to help sense

Classification by Stimulus Type What are the five types of stimuli we need to sense?

Classification by Stimulus Type What are the five types of stimuli we need to sense? Touch, vibration Temperature Light Chemicals Pain

Classification by Stimulus Type What are the five types of classifications that go with these types of stimuli?

Classification by Stimulus Type What are the five types of classifications that go with these types of stimuli? Mechanoreceptors touch, pressure, vibration, stretch, and itch Thermoreceptors changes in temperature Photoreceptors light energy Chemoreceptors chemicals Nociceptors pain-causing stimuli What are some examples of areas or scenarios where these are important?

Classification by Location What are some simplified locations where you think that certain receptors may be needed?

Classification by Location What are some simplified locations where you think that certain receptors may be needed? Externally Internally “Middle” (Remember this as the orientation)

Classification by Location Exteroceptors Where are the receptors? Where are the stimuli? What will they sense?

Classification by Location Exteroceptors Where are the receptors? Skin, most special organs Where are the stimuli? What will they sense?

Classification by Location Exteroceptors Where are the receptors? Skin, most special organs Where are the stimuli? Outside of body What will they sense?

Classification by Location Exteroceptors Where are the receptors? Skin, most special organs Where are the stimuli? Outside of body What will they sense? touch, pain, temp

Classification by Location Exteroceptors Where are the receptors? Skin, most special organs Where are the stimuli? Outside of body What will they sense? touch, pain, temp Remember: what are the different forms of touch?

Classification by Location Exteroceptors Where are the receptors? Skin, most special organs Where are the stimuli? Outside of body What will they sense? touch, pain, temp Remember: what are the different forms of touch? Light Pressure Vibration Deep

Classification by Location Interoceptors (visceroceptors) Where are the receptors? Where are the stimuli? What will they sense?

Classification by Location Interoceptors (visceroceptors) Where are the receptors? Visceral organs, BV Where are the stimuli? What will they sense?

Classification by Location Interoceptors (visceroceptors) Where are the receptors? Visceral organs, BV Where are the stimuli? Internally What will they sense?

Classification by Location Interoceptors (visceroceptors) Where are the receptors? Visceral organs, BV Where are the stimuli? Internally What will they sense? Chemical, temp, stretch

Classification by Location Interoceptors (visceroceptors) Where are the receptors? Visceral organs, BV Where are the stimuli? Internally What will they sense? Chemical, temp, stretch What are some examples of when this would be important?

Classification by Location Interoceptors (visceroceptors) Where are the receptors? Visceral organs, BV Where are the stimuli? Internally What will they sense? Chemical, temp, stretch What are some examples of when this would be important? Blood concentrations Monitoring HCl production in stomach Find some others while you study!*

Classification by Location Proprioceptors Where are the receptors? Where are the stimuli? What will they sense?

Classification by Location Proprioceptors Where are the receptors? Skeletal muscles tissues Where are the stimuli? What will they sense?

Classification by Location Proprioceptors Where are the receptors? Skeletal muscles tissues Where are the stimuli? Skeletal system What will they sense?

Classification by Location Proprioceptors Where are the receptors? Skeletal muscles tissues Where are the stimuli? Skeletal system What will they sense? Orientation, stretch

Classification by Structural Complexity What are the classifications based on complexity?

Classification by Structural Complexity What are the classifications based on complexity? Complex Simple

Classification by Structural Complexity What are the classifications based on complexity? Complex special; specific Simple not so special; specific

Classification by Structural Complexity Complex receptors Function: special sense Vision, hearing, equilibrium, smell, and taste Simple receptors Function: general senses Tactile, temp, pain, and muscle sense Structure: unencapsulated or encapsulated When have we talked about these before?

Unencapsulated Dendritic Endings Thermoreceptors Cold receptors (10–40ºC); in superficial dermis Heat receptors (32–48ºC); in deeper dermis Interesting thought: why do you think that the cold receptors are superficial and that heat receptors are deeper? Also, why would these need to be unencapsulated?

Unencapsulated Dendritic Endings Nociceptors Respond to: Pinching Chemicals from damaged tissue Temperatures outside the range of thermoreceptors Capsaicin Why would these need to be unencapsulated?

Unencapsulated Dendritic Endings Light touch receptors Tactile (Merkel) discs Where are these? Hair follicle receptors Why would these need to be unencapsulated?

Table 13.1

Encapsulated Dendritic Endings Mechanoreceptors Meissner’s (tactile) corp. discriminative touch* Pacinian (lamellated) corp. deep and vibration* Ruffini endings deep (cont.) pressure* Muscle spindles muscle stretch^ Golgi tendon organs stretch in tendons^ Joint kinesthetic receptors stretch in articular capsules^ *All of these are specific receptors which can be found in the skin ^All of these can be found in musculoskeletal systems

Table 13.1

From Sensation to Perception Remember: what is the difference between sensation and perception? Sensation Perception

From Sensation to Perception Remember: what is the difference between sensation and perception? Sensation awareness of changes Perception conscious interpretation of stimuli

Sensory Integration All the input comes from various receptors Exteroceptors Proprioceptors Interoceptors Where is the input relayed?

Sensory Integration All the input comes from various receptors Exteroceptors Proprioceptors Interoceptors Where is the input relayed? CNS, the brain However, it is processed along the way!

Sensory Integration We have different levels of integration Receptor level sensor receptors Circuit level ascending pathways Perceptual level circuits in the cerebral cortex What is an analogy for these different levels of integration?

Remember that this is a very simplified explanation of this concept. 1 2 3 Receptor level (sensory reception and transmission to CNS) Circuit level (processing in ascending pathways) Spinal cord Cerebellum Reticular formation Pons Muscle spindle Joint kinesthetic receptor Free nerve endings (pain, cold, warmth) Medulla Perceptual level (processing in cortical sensory centers) Motor cortex Somatosensory Thalamus Figure 13.2 Remember that this is a very simplified explanation of this concept.

Processing at the Receptor Level What is transduction? The process by which a stimulus energy is converted into a graded potential. This potential is called a receptor potential

Adaptation of Sensory Receptors What is adaptation in terms of stimuli?

Adaptation of Sensory Receptors What is adaptation in terms of stimuli? Adaptation is a change in sensitivity in the presence of a constant stimulus Receptor membranes become less responsive Receptor potentials decline in frequency or stop What are some examples where our sensory receptors might need to adapt to a situation?

Adaptation of Sensory Receptors WIDB: the types of adaptation? Phasic Tonic

Adaptation of Sensory Receptors WIDB: the types of adaptation? Phasic fast-adapting receptors Signal the beginning or end of a stimulus Examples: receptors for pressure, touch, and smell Tonic

Adaptation of Sensory Receptors WIDB: the types of adaptation? Phasic fast-adapting receptors Signal the beginning or end of a stimulus Examples: receptors for pressure, touch, and smell Tonic slow-adapting receptors Can be slow or not at all Examples: nociceptors and most proprioceptors Why might you need both?

Processing at the Circuit Level Pathways of three neurons conduct sensory impulses upward to the appropriate brain regions First-order neurons Second-order neurons Third-order neurons

Processing at the Circuit Level Pathways of three neurons conduct sensory impulses upward to the appropriate brain regions First-order neurons Signals from receptor level  second-order neurons Second-order neurons Third-order neurons

Processing at the Circuit Level Pathways of three neurons conduct sensory impulses upward to the appropriate brain regions First-order neurons Signals from receptor level  second-order neurons Second-order neurons Found in CNS: thalamus or cerebellum Third-order neurons

Processing at the Circuit Level Pathways of three neurons conduct sensory impulses upward to the appropriate brain regions First-order neurons Signals from receptor level  second-order neurons Second-order neurons Found in CNS: thalamus or cerebellum Third-order neurons Impulse from thalamus  somatosensory cortex Perceptual level Remember: what does the somatosensory cortex do?

Processing at the Perceptual Level Perception of stimuli depends on the location of the target neurons in the sensory cortex Aspects of sensory perception: Perceptual detection detect a stimulus Requires summation of impulses Magnitude estimation intensity Coded in frequency of impulses Spatial discrimination site or pattern Two-point discrimination test

Main Aspects of Sensory Perception Feature abstraction complex aspects Understanding several stimulus properties Quality discrimination submodalities Categories of sensation Pattern recognition familiar/sig. patterns What could be an example of this????

Perception of Pain Why do we feel pain?

Perception of Pain Why do we feel pain? Stimuli include Warns of actual or impending tissue damage Stimuli include extreme pressure and temperature Compounds: histamine, K+, ATP, acids, and bradykinin Impulses travel on fibers that release neurotransmitters Examples: glutamate and substance P Some pain impulses are blocked by inhibitory endogenous opioids

Structure of a Nerve What is the structure of a nerve?

Structure of a Nerve What is the structure of a nerve? Cordlike organ of the PNS Bundle of myelinated and unmyelinated peripheral axons enclosed by connective tissue

Structure of a Nerve Connective tissue coverings include: Endoneurium Perineurium Epineurium

Structure of a Nerve Connective tissue coverings include: Endoneurium loose connective tissue encloses axons and their myelin sheaths Perineurium coarse connective tissue bundles fibers into fascicles Epineurium tough fibrous sheath around a nerve

Axon Myelin sheath Endoneurium Perineurium Epineurium Fascicle Blood vessels (b) Figure 13.3b

Classification of Nerves Most nerves are mixtures of afferent and efferent fibers and somatic and autonomic (visceral) fibers Pure sensory (afferent) or motor (efferent) nerves are rare Types of fibers in mixed nerves: Somatic afferent and somatic efferent Visceral afferent and visceral efferent Peripheral nerves classified as cranial or spinal nerves

Ganglia Contain neuron cell bodies associated with nerves Dorsal root ganglia (sensory, somatic) (Chapter 12) Autonomic ganglia (motor, visceral) (Chapter 14)

Regeneration of Nerve Fibers Mature neurons are amitotic What does this mean? Damaged soma can regenerate new axon Involves coordinated activity among: Macrophages Schwann cells Form regeneration tube and secrete growth factors Axons—regenerate damaged part Oligodendrocytes have growth-inhibiting proteins Prevent CNS fiber regeneration

Endoneurium Schwann cells The axon becomes fragmented at 1 The axon becomes fragmented at the injury site. Droplets of myelin Fragmented axon Site of nerve damage Figure 13.4 (1 of 4)

Macrophages clean out the dead axon distal to the injury. Schwann cell 2 Schwann cell Macrophage Figure 13.4 (2 of 4)

Aligning Schwann cells form regeneration tube Axon sprouts, or filaments, grow through a regeneration tube formed by Schwann cells. 3 Fine axon sprouts or filaments Figure 13.4 (3 of 4)

The axon Schwann cell Site of new regenerates and myelin sheath a new myelin sheath forms. Schwann cell Site of new myelin sheath formation 4 Single enlarging axon filament Figure 13.4 (4 of 4)