The Nervous System Chapter 5 Section 1

Objectives Describe the basic structure of a neuron and how impulses move across a synapse. Compare the central and peripheral nervous systems. Explain how drugs affect the body.

Responding to Stimuli Stimulus Any internal or external change that brings about a response. Your body adjusts to changing stimuli with the help of the nervous system. The regulation of steady, life maintaining conditions inside an organism, despite changes in the environment is called homeostasis.

Nerve Cells Neurons The basic functioning units of the nervous system. Made up of Cell body Dendrites Receive messages from other neurons and send them to the cell body Axons Carry messages away from the cell body.

Types of Nerve Cells Sensory Neurons Motor Neurons Receive information and send impulses to the brain or spinal cord. Motor Neurons Interneuron’s relay impulses to motor neurons. Motor neurons then conduct impulses from the brain and spinal cord to muscles and glands throughout the body.

Sensory Neuron Interneuron's Motor Neurons

Facts Neurons do not touch one another. An impulse crosses a small space called a synapse. When a nerve impulse reaches the end of an axon, the axon releases a chemical. The chemical flows across the synapse and stimulates the impulse in the dendrite of the next neuron. Impulses only move in one direction.

The Path of an Impulse

Central Nervous System Made up of the brain and the spinal cord. Peripheral Nervous System Made up of all of the nerves outside of the central nervous system. Connects the brain and spinal cord to other body parts.

Central Nervous System Brain Coordinates all body activities 100 billion neurons Cerebrum Largest part of the brain Thinking takes place Movements are controlled Memories are stored Cerebellum Stimuli from the eyes and ears and from muscles and tendons are interpreted here. Help maintain balance Coordinate voluntary muscle movements

Central Nervous System Brain Stem Extends from the cerebrum and connects the brain to the spinal cord. Midbrain Provide pathways connecting various parts of the brain to each other. Pons Same as above medulla Controls involuntary actions such as heartbeat

Spinal Cord This is an extension of the brain stem About the width of the human thumb About 43 cm

Peripheral Nervous System Somatic Controls voluntary actions Cranial and spinal nerves that go from the CNS to the skeletal muscles. Autonomic Controls involuntary actions

Reflexes Spinal Pain Cord Withdrawal Reflex Is a involuntary, automatic response to a stimulus. Spinal Cord Pain Interneuron Impulse Withdrawal Reflex Motor Neuron Reflex responses are controlled in the spinal cord not the brain

How do Drugs Affect the Nervous System? Alcohol Absorbed directly into the stomach and small intestine into the circulatory system. Disrupts the functions of cells Depressant Caffeine Stimulant Can increase heart rate, cause insomnia

Alzeimer’s http://www.nia.nih.gov/alzheimers/publication/alzheimers-disease-fact-sheet#changes