Nervous System The Nerve Cell What is the

Nervous System The Nerve Cell

What is the nervous system? What are impulses? • The nervous system is a network of nerve cells that carry messages called impulses.

Receptor • Receptor – the specialized structures sensitive to certain types of stimuli • An example of a receptor is a sense organ

Effector • Effector – responds to a stimulus • An example of an effector is a muscle or a gland

Stimulus • Stimulus – is anything that causes a receptor to start impulses in a nerve pathway • Examples: • Heat • Cold • Pain • Pressure

What are nerves? • Nerves – are bundles of axons or dendrites bound together by connective tissue

Sensory neurons • Sensory neurons – carry impulses from receptors to the spinal cord and brain

Motor neurons • Motor neurons – carry impulses from the brain and spinal cord to effectors

Interneurons • Interneurons – relay impulses from one neuron to another in the brain and spinal cord

The Reflex Arc • Receptor (sense organ) • Sensory neuron • Interneuron • Motor neuron • Effector (muscle)

The Reflex Arc

Structure of a neuron

Neuron • Neuron – is a nerve cell

Cell Body • Cell Body – contains the nucleus and cell organelles

Dendrites • Dendrites – short, highly branched fibers that receive impulses - conduct impulses toward the cell body

Axons • Axons – are long, thin fibers that extend from the cell body - carry impulses away from the cell body - send impulses to other neurons or effectors

Schwann cells • Schwann cells – surround the axon

Myelin • Myelin – is the fatty substance that covers the axon

Nodes of Ranvier • Nodes of Ranvier – are the gaps between Schwann cells where there is no myelin

Synapse • Synapse – is the region where nerve impulses pass from one neuron to another