9th Biology The Nervous System
Structure of the Nervous System Central Nervous System: CNS Brain and Spinal Cord Peripheral Nervous System: PNS Everything else: peripheral nerves from the spinal cord to the limbs
Neurons Neurons are specialized cells that help you gather information and react to it.
3 Kinds of Neurons: 1. Sensory neurons- involuntary Send impulses from receptors in skin and sense organs to brain and spinal cord 2. Interneurons- involuntary carry impulse to motor neurons, which results in a response. 3. Motor neurons- voluntary respond to stimulus; skeletal muscle
Neurons
Reflex Arc
Nerve Impulse: Action Potential Electrical charge, traveling the length of the neuron. Causes a message to be sent to other neurons to elicit a response Neuron at rest: Resting potential
Action Potential Na+ rushes into cell, changes charge from negative to positive. Causes neurotransmitters(chemicals) to be released at the terminal, to stimulate the next neuron in the chain.
Action Potential: One way only Myelin- insulation on axon that helps signal’s rapid response Multiple Sclerosis- disease where part of myelin sheath is worn away- nerve conduction no longer works properly
Synapse Space between axon terminal of one neuron and dendrites of another. Neurotransmitters in vesicles released in cleft either cause the cell to fire (excitatory) or not fire (inhibitory).
ORGANIZATION OF THE NERVOUS SYSTEM 1. Central nervous system: CNS Brain and spinal cord Relays messages, processes information, analyzes responses The brain: 100 billion neurons Cerebrum- Cognitive function Cerebellum- balance, movement Medulla oblongata- breathing rate, heart rate, blood pressure Pons- breathing rate
ORGANIZATION, cont. 2. Peripheral nervous system: PNS Everything outside the brain and spinal cord A. Somatic nervous system: Relays info to motor neurons All voluntary except reflexes
ORGANIZATION, cont. B. Autonomic nervous system Carries impulses from CNS to heart and other organs. Fight or flight Business as usual Sympathetic branch- Active in times of emergency Parasympathetic branch- Active when body is at rest