Nervous System Chapter 31

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

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

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

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.

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.

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.

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

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

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

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

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”

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.

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

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.

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

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.