The Nervous System Ch. 36

Communication Center Central Nervous System (CNS): system of nerves, the spinal cord, and the brain that receives signals from environment and sends out responses to those signals Neurons: nerve cell; 3 sections Dendrites: fan like branches that receive impulses Cell body: main area of cell Axon: long extension that sends impulses on to other neurons or body cells

Types of Neurons Sensory neurons: receive signals from the environment and send impulses to the spinal cord and brain Interneurons: nerves that make up the brain and spinal cord; process impulses and send response impulses to motor neurons Motor neurons: react to impulses from brain and spinal cord; activate glands, muscles, etc..

How Neurons Send Impulses Ion channels allow the inward flow of K+ and limit the flow of Na+ Concentration difference between Na+/K+ is made greater by Na+/K+ Pump Membrane is polarized: Inside has negative charge Outside has positive charge About -70mV difference (resting potential) Impulse is sent as swift of K+ and Na+ across the membrane change the polarity of the cell (action potential)

Na+/K+ Pump Concentration gradient of Na+ and K+ most be large so the flow of ions is fast Na+/K+ Pump uses ATP to pull in K+ and push out Na+ 1 ATP= 2 K+ in; 3 Na+ out Also helps to repolarize membrane after impulse

Sending an Impulse Sending an impulse starts with an action potential Stimulus must be strong enough to start action potential; pass threshold Na+ channels in the nerve membrane open up; Na+ rush into cell down a concentration gradient Inside cell changes from – to + Shift causes other Na+ channels to open and signal moves like a wave down the axon

Sending an Impulse After impulse, the K+ channels open and K+ rush out, changing the inside of the cell from + to – Repolarizing (outside +; inside -) the area of nerve must happen to send another signal Signals can “jump” down axon by traveling to pockets between myelin sheaths

White and Gray Matter Myelin sheaths increase signal transmission Heavily myelinated nerves have a white color Inner areas of the brain Spinal cord nerves Regular nerves have gray color Outer areas of the brain Body nerves

Neuron to Neuron Signals Nerve cells don’t touch; signal “wave” has to be passed from cell to cell Synapse: small space (10-20 nm) between neurons Neurotransmitter: chemical signals that travel from axon of one neuron to the dendrite of the next neuron; triggered by Ca+ channels

Regions of the Brain 3 main sections: Cerebrum- main area of the brain; divided into two hemispheres; where language, memory, intelligence, personality, muscle movement come from Cerebellum- back of your brain; controls balance, senses, and coordination Brain stem- connection between brain and spinal cord Medulla oblongata- controls involuntary activities Pons- connects areas in the brain Midbrain- responds to signals and sends them to regions of the brain Hypothalamus- connection between nervous and endocrine system

Layers of the Nervous System Peripheral Nervous System (PNS): nerves that carry messages to and from the CNS Two system in the PNS: 1) Somatic Nervous System: - 12 nerves in the brain - 31 nerves in the spine - send information for all voluntary movement Reflex: automatic response to set stimuli so to quickly minimize damage - pulling back when burned

Layers of the Nervous System 2) Autonomic Nervous System: - send impulses to organs in the body - control involuntary movements Two systems in the ANS: Sympathetic Nervous System: - controls organs during times of stress - release of epinephrine Parasympathetic Nervous System: - controls organs during times at rest

Layers of the Nervous System