Nervous System Part II

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Types of Neurons 1. Motor Neurons 2. Sensory Neurons 3. Interneurons 176

Motor (Efferent) Neurons take information from the CNS to effectors (muscles or glands). Characterized by short dendrites, a central cell body and fairly long axons. Axons are often covered with a myelin sheath to carry impulse faster and to protect the long nerve fiber. 177

Sensory (Afferent) Neurons take information from sensory receptors to the CNS. Characterized by longer dendrite fiber, shorter axon fiber and a peripheral cell body. Both axon and dendrite fibers may be myelinated. 178

Interneurons (Connector/Association) occur within the CNS and integrate input. Characterized by short dendrites as well as short axon. Central cell body, but very seldom shows myelination along nerve fibers. They are found within brain and spine and act like Head Coordinator (Prewired Circuit Board) to receive and relay incoming impulses to the appropriate pathways. 179

Types of neurons All Three Work Together 1710

Myelin Sheath Long axons are covered by a protective myelin sheath formed by neuroglial cells called Schwann cells. The sheath contains lipid myelin which gives nerve fibers their white, glistening appearance. The sheath is interrupted by gaps called nodes of Ranvier. 1711

Myelin sheath SCHWANN Cells are a type of NEUROGLIAL cell. Myelination serves two purposes, it protects long fragile nerve fibers and it also speeds up a nerve impulse. It speeds up impulse by allowing action potential of nerve impulse to skip from node to node. 1712

Multiple sclerosis is a disease of the myelin sheath. 1713

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1. Give two separate names for the type of neuron shown here. A C B H G Name for branched endings D F Name for gaps in myelin sheath E Name of Cells that form Myelin 1715 Sheath

Reflex Arc Reflexive Actions are automatic responses to environmental stimuli Pain receptor detects stimulus that surpasses threshold>initiates impulse>travels along dendrite of sensory neuron>onto axon of sensory neuron>dendrite of interneuron>cell body of interneuron>interneuron axon> motor neuron>effector

Brain is not involved with reflexive actions; it is an advantage because reflexive actions are protective mechanisms Other interneurons conduct impulses to the brain to alert the mind that a reflexive action has taken place

https://www.youtube.com/watch?v=y5nj3zfe YDQ https://www.youtube.com/watch?v=wlrhyzdb bpe

Impulse Transmission Saltatory Impulse Transmission Comes from the latin term, saltare: to hop or leap Propagation of action potentials along myleinated axons from one node of Ranvier to the next node Animation: https://www.youtube.com/watch?v=i30bv_e0qau

LABEL. What type of neuron is this? A. F. G. B. C. E. D.

LABEL. What type of neuron is this? A. Dendrite Axon bulb F. Effector G. B. Cell Body C. Nucleus E. Axon Shwann D. cell (myelin sheath)

A. B. C.

Motor. A. B. Interneuron Sensory. C.

How are they arranged in the nervous system?

How were Action Potentials Discovered?

1 mm diameter

Axon Fibre is large enough that one electrode could be manually placed inside the axon fibre and one outside. Allowing them to measure the relative charge IN vs OUT.

Resting Potential in a Neuron OUTSIDE the cell INSIDE the cell Protein Protein Protein Protein

Resting Potential in a Neuron OUTSIDE the cell INSIDE the cell Protein Sodium/ Potassium Pump K + Protein Protein Protein

Resting Potential in a Neuron OUTSIDE the cell INSIDE the cell K + Protein Sodium/ /K Potassium + Pump Pump K + K + K + K + Protein Protein Protein K + K +

Resting Potential in a Neuron POSITIVE OUTSIDE the cell INSIDE the cell NEGATIVE 65 mv + + + + + + + + + + + + + + + Protein K +

Resting Potential Draw the steps of an Action Potential

https://www.youtube.com/watch?v=naecv3h868c MS Video: https://www.youtube.com/watch?v=m7o78lvrnsq

Stages of Action potential

https://www.youtube.com/watch?v=fhrc8sll ch0

Synaptic Transmission Introduction Video: https://www.youtube.com/watch?v=xf2ufv6 EKt0 We will finish this tomorrow!

Note Taking Time