The Nervous System 1.Control center for all body activities 2.Responds and adapts to changes that occur both inside and outside the body (Ex: pain, temperature, pregnancy) (Ex: pain, temperature, pregnancy)

The Nervous System Homeostasis –The regulation of steady, life-sustaining conditions inside an organism, despite changes in the environment. Stimuli-an internal or external change that brings about a response

Structure of a Neuron Each neuron contains: - Cell body with nucleus - Cell body with nucleus - Dendrites : fibers that receive messages from other neurons - Dendrites : fibers that receive messages from other neurons - Axons : fibers that send messages to other neurons - Axons : fibers that send messages to other neurons

Neurons do NOT touch; there is a gap between them called a synapse Neurons do NOT touch; there is a gap between them called a synapse Messages are sent across the synapses by special chemicals that are released by the axon. The chemical flows across the synapse and stimulates the impulse in the dendrite of the next neuron Messages are sent across the synapses by special chemicals that are released by the axon. The chemical flows across the synapse and stimulates the impulse in the dendrite of the next neuron

3 main types of nerve cells sensory neuron Inter- neuron motor neuron

Sensory neurons Carries impulses from receptors e.g pain receptors in skin to the CNS( brain or spinal cord)

Interneuron Carries impulses from sensory nerves to motor nerves.

Motor neuron Carries impulses from CNS to muscle to bring about movement or gland to bring about secretion of hormone.

The Nervous System Two Major Divisions of the Nervous System Two Major Divisions of the Nervous System Central Nervous System(CNS) consists of the brain and the spinal cord. The peripheral Nervous System (PNS) is made up of all the nerves outside the CNS.

CNS - The Brain The brain coordinates all of your body activities a mass of 100 billion neurons located inside the skull Three major parts of the brain- cerebrum, cerebellum, and the brain stem

CNS --Brain Cerebrum Cerebrum : largest part of human brain - Responsible for: - Thought - Language - Senses - Memory - Voluntary movement

CNS --Brain Cerebellum Cerebellum : at base of brain -Responsible for: - Muscle coordination - Balance - Posture

CNS --Brain Brain Stem Brain Stem : connects brain to spinal cord -Responsible for: - Breathing - Swallowing - Heartbeat - Blood pressure

CNS –Spinal Cord Spinal Cord An extension of the brain stem Made up of bundles of neurons Carries impulses from all parts of the body to the brain and from the brain to all parts of the body

Two major Divisions of the PNS Somatic Controls voluntary action Made up of cranial and spinal nerves that go from the CNS to skeletal muscles Autonomic Controls involuntary actions Not under conscious control Examples-breathing, heartbeat and digestion

Reflexes Reflex An involuntary, automatic response to stimuli Involves a simple pathway called a reflex arc Reflex Arc Sensory Motor A reflex allows the body to respond Without having to think about it.

Drugs and the Nervous System Drugs: Chemicals that causes change in a person’s body or behavior. Depressants slow down the CNS. Alcohol is an example. Stimulants speed up the activities of the CNS. Caffeine is an example. Steroids are synthetic chemicals that some athletes use to improve performance. They cause mood changes and permanent physical damage.