Nervous System Biology Ch. 42 Ms. Haut

Function of Nervous System Sensory Input – Signals received by sensory receptors in dermis of skin or internal organ systems Integration – Carried out by Central Nervous System (CNS) Brain and spinal cord Motor Output – Carried out by Peripheral Nervous System (PNS) – Signals are sent to muscle or gland cells – Carry out body’s responses to stimuli

Animal Nerve Cells Nerves: rope-like bundles of extensions of neurons, tightly wrapped in connective tissue Neurons: functional unit of the nervous system

Functional Organization of Neurons Sensory Neurons: relay information (stimuli) from the external and internal environments to CNS Motor Neurons: convey impulses from CNS to cells in muscles or glands

Overview of Vertebrate Nervous System

Neural Signals Nerve impulse is an electrical signal that depends on the flow of ions across the plasma membrane of a neuron

Membrane Resting Potential Cell is said to be polarized

Action Potential A nerve impulse is generated when the difference in electrical charge disappears Occurs when a stimulus contacts the tip of a dendrite and increases the permeability of the cell membrane to Na+ ions Cell is said to be depolarized

Regulation of Action Potential

Propagation of the Action Potential After the wave of depolarization has passed, the neuron reestablishes the difference in charges by pumping K+ out of the cytoplasm

Action Potential

Nerve Impulse

Saltatory Conduction

Synapses Nerve impulses pass down the dendrite, through the cell body, and down the axon. At the end of the axon, the signal reaches a fluid-filled space (synapse) separating the end of the axon from the dendrite of the next neuron. Neuromuscular junction: synapse located at the junction of a neuron and muscle fiber

Neuron Circuitry Simplest neural circuit involves synapses between 2 neurons, a sensory neuron and a motor neuron Result is often an automatic response called a reflex

The Knee-jerk Reflex

Chemical Synapse

MAJOR NEUROTRANSMITTERS AND THEIR EFFECTS Acetylcholine (ACh) Generally excitatory Affects arousal, attention, memory, motivation, movement. Too much: spasms, tremors. Too little: paralysis, torpor. DopamineInhibitoryInhibits wide range of behavior and emotions, including pleasure. Implicated in schizophrenia and Parkinson's disease. SerotoninInhibitoryInhibits virtually all activities. Important for sleep onset, mood, eating behavior. Norepinephrine Generally excitatory Affects arousal, wakefulness, learning, memory, mood. EndorphinsInhibitoryInhibit transmission of pain messages.

Vertebrate Nervous System

Autonomic Nervous System Works on an involuntary basis 2 subdivisions ParasympatheticSympathetic Return body to normal after an emergency Prepare body for emergency Heart rate slows, pupils constrict, blood vessels dilate Increase heart rate, constricted blood vessels, pupils dilate

Roles of Parasympathetic and Sympathetic Divisions of the Autonomic Nervous System

Structure of Brain

Brainstem Medulla oblongata – Contains centers that control autonomic, homeostatic functions Breathing, heart and blood vessel activity, swallowing, vomiting, and digestion Pons – Have nuclei in the medulla that regulate breathing centers Midbrain – Centers for receipt and integration of sensory information Coordinates large-scale body movements such as walking

Cerebellum Primary function is coordination of movement Receives information about position from joints and length of muscles, as well as auditory and visual systems Plays role in learning and remembering motor responses (hand-eye coordination)

Thalamus and Hypothalamus Thalamus – Main input center for sensory information going to cerebrum – Receives input from cerebrum to regulate emotion and arousal Hypothalamus – Source of posterior pituitary hormones and releasing hormones that act on anterior pituitary – Regulates body temp, thirst, hunger, other basic survival mechanisms – Plays role in sexual response and mating behaviors, fight-or-flight response, and pleasure

Structure and Function of Cerebrum

Drug Affects Cocaine binds to the dopamine transporter and prevents re-uptake of dopamine. By inhibiting dopamine re- uptake, it increases dopamine and the pleasure sensation

Drug Affects Nicotine – Addictive stimulant – Mimics action of acetylcholine which controls central functions of brain – Continued smoking, smoker’s brain adjusts – Withdraw nicotine and body becomes out of balance (“shakes”) – Smoking associated with lung cancer, heart disease, and respiratory disorders

Drug Affects Alcohol – Depressant – Changes shape of receptor proteins of neurons Become more or less sensitive to regular stimuli – Effects normal brain function Slows motor skills and coordination – Excessive drinking can lead to malnutrition, abnormalities in circulatory system, liver damage (cirrhosis)