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

Peripheral Nervous System (PNS) All neural structures outside the brain Sensory receptors Peripheral nerves and associated ganglia Motor endings

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 Specialized to respond to changes in their environment (stimuli) Activation results in graded potentials that trigger nerve impulses Sensation (awareness of stimulus) and perception (interpretation of the meaning of the stimulus) occur in the brain

Classification of Receptors Based on: Stimulus type Body Location Structural complexity

Classification by Stimulus Type Chemoreceptors—respond to chemicals (e.g., smell, taste, changes in blood chemistry) Mechanoreceptors—respond to touch, pressure, vibration, stretch, and itch Nociceptors—sensitive to pain-causing stimuli (e.g. extreme heat or cold, excessive pressure, inflammatory chemicals) Photoreceptors—respond to light energy (e.g., retina) Thermoreceptors—sensitive to changes in temperature

Classification by Location Exteroceptors Respond to stimuli arising outside the body Receptors in the skin for touch, pressure, pain, and temperature Most special sense organs Interoceptors (visceroceptors) Respond to stimuli arising in internal viscera and blood vessels Sensitive to chemical changes, tissue stretch, and temperature changes Proprioceptors Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles Inform the brain of one’s movements

Classification by Structural Complexity Complex receptors (special sense organs) Vision, hearing, equilibrium, smell, and taste (Chapter 15) Simple receptors for general senses: Tactile sensations (touch, pressure, stretch, vibration), temperature, pain, and muscle sense Unencapsulated (free) or encapsulated dendritic endings

Structure of a Nerve Cordlike organ of the PNS Bundle of myelinated and unmyelinated peripheral axons enclosed by connective tissue

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

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

Twelve pairs of nerves associated with the brain Cranial Nerves Twelve pairs of nerves associated with the brain Most are mixed in function; two pairs are purely sensory Each nerve is identified by a number (I through XII) and a name “On occasion, our trusty truck acts funny—very good vehicle anyhow” On Old Olympus' Towering Top, A Fine Vocal German Viewed Some Hops

Hypoglossal nerve (XII) Filaments of olfactory nerve (I) Frontal lobe Olfactory bulb Olfactory tract Optic nerve (II) Temporal lobe Optic chiasma Infundibulum Optic tract Facial nerve (VII) Oculomotor nerve (III) Vestibulo- cochlear nerve (VIII) Trochlear nerve (IV) Trigeminal nerve (V) Glossopharyngeal nerve (IX) Abducens nerve (VI) Vagus nerve (X) Cerebellum Accessory nerve (XI) Medulla oblongata Hypoglossal nerve (XII) (a) Figure 13.5 (a)

(One) smells first, olfactory. (Two) optic for stuff we see. (Three) oculomotor tie (Four) with trochlear round the eye. (Five) trigeminal the great. (Six) abducens eyes rotate. (Seven) facial faces near. (Eight) vestibulocochlear. (Nine) glossopharyngeal. (Ten) vagus. lungs, guts, heart and all. (Eleven) accessory shoulders reach. (Twelve) hypoglossal tongue and speech.

a. Olfactory b. Optic c. Oculomotor d. Trochlear e. Trigeminal f a. Olfactory b. Optic c. Oculomotor d. Trochlear e. Trigeminal f. Abducens g. Facial h. Vestibulocochlear i. Glossopharyngeal J. Vagus k. Spinal Accessory I. Hypoglossal

(XI) Spinal Accessory (I) Olfactory (III) Oculomotor (X) Vagus (VII) Facial (V) Trigeminal (VIII)Vestibulococchlear glossopharyngeal (IX) and facial (VII) (III) Oculomotor, (IV) Trochlear and (V) Trigeminal (II) Optic (I)Olfactory, (II) Optic, (VIII) vestibulocochlear

Afferent vs. Efferent D. Interneurons B. Motor (Efferent) A. Sensory (Afferent) C. Both

Delivers impulses from the CNS to muscles and glands Motor Division Delivers impulses from the CNS to muscles and glands Somatic Nervous System –regulates processes under voluntary control Autonomic Nervous System – regulates involuntary activities and is further divided into: Sympathetic Nervous system – “fight or flight” Parasympathetic –”Rest and Digest”

Reflex Arc Reflexes - actions of the somatic nervous system that occur automatically

R-SIM Reflex arc pathway . . . receptor neuron receives the stimuli S sensory neuron passes the impulse on I interneuron at the spinal cord processes M motor neuron acts

The Autonomic Nervous System