Nervous System

Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.

• The nervous system is the communication and control system of an animal’s body.

• Composed of two main divisions:• ____________ Nervous System (CNS)

• Composed of brain and spinal cord• _______________ Nervous System (PNS)

• Consist of nerves that come off of the CNS and innervate rest of body

• Function of nervous system activities:• _____________ (sense changes within or outside the body and sends it

to the spinal cord and brain)• _____________ (brain and spinal cord receive, analyze, store, and

integrate the info to produce a response)• _____________ (an instruction of the body to do something)

Introduction

Mosby items and derived items © 2008 by Mosby, Inc., an affiliate of Elsevier Inc.

• Neuron: basic functional units of nervous system• High requirement for ____________.

• Brain must always have O2 supply

• Cannot ___________ but can _____________ cell processes if the cell body remains intact

• Neuroglia (glial cells; these are not neurons): provide structural and functional support and protection to neurons

Neuron•Soma/Perikaryon• Central cell body

•Cell processes• _____________ – receive stimuli/impulses from other

neurons and transmit information_____soma.• Can also be sensory receptors for heat, cold, touch,

pressure, stretch or other physical changes inside or outside the body

• Short and branched

• ________ - conducts nerve impulses _______ from soma towards another neuron or an effector cell (muscle, gland)• Long, single process

Myelin

• Axons are often covered in myelin (fatty/protein substance)• Nervous tissue containing myelinated

axons is called ___________ matter.

• Myelin sheath: cell membrane of glial cells tightly wrapped around the axon• _____________________ in the brain

and spinal cord • ____________ ______ in the nerves

outside the brain and spinal cord

• Myelinated axons conduct impulses

faster than unmyelinated ones

Nodes of Ranvier

• Multiple Schwann cells or oligodendrocytes cover the entire length of the axon

• _____________________: gaps in the myelin sheath between adjacent glial cells

• Myelin sheath and nodes of Ranvier work together to enhance the ___________ of conduction of nerve impulses along the axon.

Organization of Nervous System

1. Anatomical

• _________ nervous system (CNS)• Brain and spinal cord

• ___________ nervous system (PNS)• Extends outward from the central axis

toward the periphery of the body• Cranial nerves originate directly from the

brain• Spinal nerves emerge from the spinal cord

Organization of Nervous System

2. Direction of Impulses

• _____________ nerves - conduct impulses TOWARD CNS

• a.k.a. sensory nerves - conduct sensations from sensory receptors in skin and other locations to CNS

• ______________ nerves - conduct impulses AWAY from CNS

• a.k.a. motor nerves - cause skeletal muscle contraction/movement

• Some nerve fibers are sensory (optic), motor (oculomotor), or both (glossopharyngeal)

Organization of Nervous System3. Function: Autonomic vs. Somatic

• _________________ nervous system - actions under conscious, or voluntary, control• Motor nerves lead to skeletal muscle and cause limb or body movement• Example: turning your head when your name is called

• _________________ nervous system - controls and coordinates automatic functions• Motor nerves lead to smooth muscle, cardiac muscle, and glands• Example: slowing of the heart rate in response to an increased blood

pressure, stomach releasing HCl when food is present

3.______________________ Division (fight or flight)

4.______________________ Division (feed or breed)

Neuron Function: DEPOLARIZATION AND REPOLARIZATION

• Resting __________ - when neuron is not stimulated• But, it’s still working to maintain a resting state (Na/K pump)

• Resting __________ ____________- difference in electrical charge across neuronal membrane• Due to differences in distribution of positive and negative charges from

sodium, potassium, proteins, and other charged ions on either side of neuronal membrane

• Inside of the neuron ends up having a more negative charge than the outside• Resting membrane potential is a negative number (-70 mV), indicating the

negative charge inside the cell• The Na/K pump maintains a negatively charges resting membrane potential

Neuron Function• Na+/K+ pump: specialized molecules located in the neuron’s cell

membrane that maintains cell resting state.• Pumps ____ (Na+) out of neuron• Pumps ____(K+) into neuron Cell membrane becomes ________________

DepolarizationSTEPS: •Neuron receives external stimulus•______ channel opens on cell membrane•Na+ flow into cell by passive _____________

• Down the concentration gradient• Electrical gradient (opposites attract)

DepolarizationSTEPS:• During depolarization, inside of neuron goes from being

__________ to _________ charged due to inflow of Na+ ions• ACTION POTENTIAL = significant change in electrical charge

Neuron Function: Depolarization

RepolarizationSTEPS:•Na+ channels close•______ channels open•K+ diffuses out of cell

• Electrical and concentration gradient, just like Na

•Resting potential (charge) restored• Cell is ___________________• But, Na+ is inside, K+ outside

Repolarization

AFTER Repolarization

• Na+/K+ pump moves ions back to their original sides

• Resting state restored