Section 33.1: Structure of the Nervous System

A. Neurons Neurons  specialized cells that help you gather info about your environment, interpret the info, and react to it Neurons  specialized cells that help you gather info about your environment, interpret the info, and react to it Dendrites  receive signals called impulses from other neurons and conduct the impulses to the cell body Dendrites  receive signals called impulses from other neurons and conduct the impulses to the cell body Cell Body  houses the nucleus of the neuron and many of the cell organelles Cell Body  houses the nucleus of the neuron and many of the cell organelles

A. Neurons cont. Axon  carries the nerve impulse from the cell body to other neurons and muscles Axon  carries the nerve impulse from the cell body to other neurons and muscles

A. Neurons cont. 3 types of neurons 3 types of neurons –Sensory neurons  send impulses from receptors in the skin to the brain and spinal cord –Inter neurons  carry the impulse to motor neurons –Motor neurons  carry the impulse away from the brain to a gland or muscle  results in the response Reflex Arc  a nerve pathway that consists of a sensory neuron, an inter neuron, and a motor neuron (the brain is not involved) Reflex Arc  a nerve pathway that consists of a sensory neuron, an inter neuron, and a motor neuron (the brain is not involved)

B. A Nerve Impulse A Neuron at Rest: A Neuron at Rest: –It is not conducting an impulse –There are more sodium ions outside the cell –There are more potassium ions inside the cell –The ions will diffuse from high concentration to low concentration

B. A Nerve Impulse cont. An Action Potential An Action Potential –It’s an all or nothing impulse (response) –Threshold  the minimum stimulus that causes an action potential to be produced –When a stimulus reaches threshold, channels in the plasma membrane open –Sodium moves inside the cell, which causes channels to open up and allow potassium to move outside the cell

B. A Nerve Impulse Speed of the Action Potential Speed of the Action Potential –The speed varies –The axons are covered with myelin (insulation) –The myelin helps to transmit the signals from one neuron to the next  The more myelin, the faster the signal gets sent

B. A Nerve Impulse

The Synapse: The Synapse: –Synapse  a small gap between the axon of one neuron and the dendrite of another neuron  when an action potential reaches the end of an axon, vesicles carry the neurotransmitter across the synapse to the next –Neurotransmitter  a chemical that diffuses across a synapse and binds to the receptors on the dendrite of a neighboring neuron

B. A Nerve Impulse