1. Nervous System
Chapter 31

2. Neurons and Nerve Impulses
Neurons Conduct Electrical Signals
Neuron:
Specialized cells that transmit information throughout the body.
Enable important functions
Movement
Perception
Thought
Emotion
Learning

3. Structure of Neurons Dendrites: Axon: Nerves:
Extend from the cell body
The antennae of the neuron
Receives information from other cells
Axon:
Long extension of the cytoplasm that conducts nerve impulses
Nerves:
Bundle of neurons that contain axons of many different neurons
Some neurons are insulated with myelin
Fatty outer layer which insulates the axon
Allows for faster nerve impulses

4. Neuron Function Depends on electrical activity Membrane potential:
The difference in electrical charge across the cell membrane
Measured in volts (V)
Depends on the movement of ions into and out of a cell
Ions diffuse across a neuron’s cell membrane through a special protein called
Voltage-gated ion channels

5. Resting Potential
When a neuron is not conducting a nerve impulse the neuron is at rest.
Resting potential:
The membrane potential of a neuron at rest.
-70 millivolts (mV)
The inside of the cell is neg. charged compared to the outside of the cell.

6. Action Potential
Changes occur in the cell membrane when a neuron is conducting a nerve impulse is called an..
Action potential:
Local reversal of polarity inside the neuron
Moves down an axon like a flame burns down a match.
Action potential events:
1. At the resting potential Na channels are closed and K channels are opened.
2. During an action potential, Na channels open, causing Na ions to move into the axon.

7. Neurons Use Neurotransmitters to Communicate
When a nerve impulse arrives at axon terminals, the impulse is then transmitted to other cells
Synapse:
The junction at which neuron meets another cell
Synaptic cleft:
Tiny gap between receiving cell and axon terminal
Transmission of a nerve impulse uses electrical energy. It then converts to chemical energy and then back to electrical energy.
Neurotransmitters:
Produced by neurons and stored inside vesicles
Signal molecule that transmits nerve impulses across the synaptic cleft.

8. Release of Neurotransmitters
Neurotransmitters are released from a presynaptic neuron and diffuse across the synaptic cleft, stimulating a postsynaptic cell.
They either excite or inhibit

9. Structure of the Nervous System
Central nervous system (CNS):
Consists of the brain and spinal cord
Peripheral nervous system (PNS):
Contains sensory and motor neurons
Sensory neurons:
Send information from sense organs
Ex. Skin to CNS
Motor neurons:
Send commands from the CNS to muscles and other organs

10. Brain Brain: Body’s main processing center Cerebrum: Cerebellum:
The largest part of the brain
Used for learning, memory, perception, and intellectual function
Cerebellum:
Located in the posterior base of the brain
Regulates balance, posture, and movement
Brain Stem:
Base of the brain
Leads to the spinal cord
Thalamus:
Critical site of sensory processing
Hypothalamus:
Regulates vital homeostatic functions like breathing

11. Spinal Cord Spinal Cord:
Dense cable of nervous tissue that runs through the vertebral column
Links the brain to the PNS
Functions in reflexes
Reflex:
Sudden, involuntary movement of muscles in response to a stimulus
Interneurons:
Within the spinal cord that links neutrons together

12. Peripheral Nervous System
Branches throughout the body
Somatic nervous system
Stimulate skeletal muscles under conscious control
Spinal reflexes are involuntary
Self-protective motor response
Extremely rapid
Ex. Knee-jerk reflex
Autonomic nervous system
Regulate smooth muscles not under conscious control
Ex. Heart rate and blood flow
Two divisions
Parasympathetic: Breathe when you sleep
Sympathetic: “fight or flight”

13. Sensory Systems Sensory systems enable perception
Sensory receptors:
Specialized neurons that detect sensory stimuli and convert it to electrical signals, in the form of nerve impulses, that are interpreted by the brain.
Specific areas of the brain control different regions and functions of the body
Processing information
Large % of neurons in the cerebral cortex are responsible for processing incoming sensory information from the sense organs.

14. Eyes
Eyes detect light
Light enters through the pupil and is focused on the retina.
Lining on the back inner surface of the eye that consists of photoreceptors and neurons.
Contains two types of photoreceptors
Rods:
Respond best to dim light
Cones:
Respond best to bright light and enable color vision
Optic Nerve:
Carries information from the retina to the brain

15. Ears Ears detect sound and help maintain equilibrium
Ears convert the energy in sound waves to electrical signals that can be interpreted by the brain.
Cochlea:
Coiled in the shape of a snail shell
Contains mechanoreceptors called hair cells that vibrate when waves enter.
Semicircular canals:
Fluid-filled chambers in the inner ear that contain hair cells that bend according to the magnitude and direction of the fluid’s movement.
Signals generated by hair cells enable the brain to determine orientation and position of the head.

16. Taste and Smell Related to chemical senses
Chemoreceptors for taste cells detect 4 basic chemical substances
Sugars
Acids
Alkaloids
Salts
Chemoreceptors for odor
Olfactory receptors
Located in the roof of the nasal passage

17. Drugs and the Nervous System
Psychoactive drugs:
Drugs that alter the functioning of the central nervous system
Ex. Alcohol, nicotine, cocaine, and heroine
Drug addiction
Involved changes in neuron function
Stimulant:
A drug that generally increases the activity of the central nervous system
Depressant:
A drug that generally decreases the activity of the central nervous system.