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PNS • Assumption that chapter has already been read • If you have not read the chapter I strongly suggest you get your book out now. If you have already read the chapter, use this PowerPoint as a test for understanding. Neuron • Draw and label a typical myelinated neuron. Schwann Cells • What are Schwann Cells? Schwann Cells • Special cells that wrap around axons forming the myelin sheath in neurons in the PNS. • What is the name of the spaces in the myelin sheath? • Node of Ranvier Myelin Sheath • What are the three major functions of the myelin sheath? Myelin Sheath • Insulator • Protection • Increase speed of transmission Types of Neurons • Sensory • Motor • Interneuron's Give a definition of each of the three types. Types of Neurons • Sensory- carry messages from receptors in sense organs, or in the skin, TO CNS • Motor- carry messages FROM CNS to muscles and glands • Interneuron- located in CNS, links between sensory and motor neurons. Structures of Neurons • Why are the neurons below classified as multipolar neurons? Structures of Neurons • Why are the neurons below classified as bipolar neurons? Structures of Neurons • Why is the neuron below classified as a unipolar neuron? Structures of Neurons • One axon and multiple dendrites • Most common type- interneurons and motor neurons to skeletal muscle Structures of Neurons • One axon and one dendrite- axon and dendrite have many branches • Eye, ear and nose- take impulses from receptor cells to other neurons Structures of Neurons • One extension- an axon • Cell body to one side • Most sensory neurons that carry messages to spinal cord are this type Neurons, Nerve fibre and Nerves • Neuron- a nerve cell • Nerve Fibre- any long extension of cytoplasm of a nerve cell body, although the term usually refers to an axon • Nerve- a bundle of fivres held together by connective tissue Synapses • What are they and what do they do? Synapses • Junction between branches of adjacent neurons • Occur between end branches of one neuron and a dendrite or cell body of another neuron • Messages carried across synapse • Where nerve attaches to muscle synapse called neuromuscular junction Synapse Divisions of Nervous system • CNS- Brain + spinal cord • PNS- nerves that connect body to CNS • PNS- Ganglia (groups of nerve bodies) outside CNS • 12 Cranial nerves • 31 spinal nerves – Joined to spinal cord by 2 roots- ventral and dorsal • Ventral- motor, cell bodies in grey matter • Dorsal- sensory, cell body in dorsal root ganglion Peripheral Division • Afferent- sensory – Somatic sensory neurons- impulses into nervous system from receptors in skin, muscles and joints – Visceral sensory neurons- impulses from internal organs • Efferent- motor – Somatic- impulses from CNS to skeltal system – Autonomic- impulses from CNS to heart muscle, involuntary muscle and glands – Divided into sympathetic and parasympathetic nervous systems Reflexes • What is a reflex? Reflexes • A reflex is a rapid, automatic response to a change in the external or internal environment. Reflexes • What are the four important properties of reflexes? Refelxes • A stimulus is required to trigger off a reflex, it is not spontaneous • A reflex is involuntary- it occurs without any conscious through • A reflex response is rapid- only a small number of neurons are involved • A reflex response is stereotyped- it occurs in the same way each time Reflexes • Most coordinated by spinal cord- spinal reflex – involuntary • Awareness does not occur until after the response has been initiated Reflex arc • Path an impulse follows from receptor to effector • 5 basic components 1. Receptor- ending of sensory neuron or specialised cell associated with sensonry neuron, reacts to change 2. Sensory neuron- carries impulse to CNS 3. Synapse- at least one 4. Motor Neuron- carries impulse to effector 5. Effector- receives impulse and carries out response, muscle or secretory cell. Reflexes • Eg – Blinking – Sneezing – Coughing – Constriction of pupil Learned Reflexes • Suckling, chewing, tracking with eyes • Acquired reflexes- adjustments required to maintain balance when riding a bike, jamming the brakes of a car or catching a ball- learned through repetition.
