Nervous System Nervous System Biology Ch. 42 Ms. Haut
Jan 19, 2016
Nervous SystemNervous System
Biology
Ch. 42
Ms. Haut
Function of Nervous SystemFunction 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 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 Functional Organization of NeuronsNeurons
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 SystemOverview of Vertebrate Nervous System
Neural SignalsNeural Signals
Nerve impulse is an electrical signal that depends on the flow of ions across the plasma membrane of a neuron
Membrane Resting PotentialMembrane Resting Potential
Cell is said to be polarized
Action PotentialAction 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 PotentialRegulation of Action Potential
Propagation Propagation of the Action of the Action
PotentialPotential After the wave
of depolarization has passed, the neuron reestablishes the difference in charges by pumping K+ out of the cytoplasm
Action PotentialAction Potential
Nerve ImpulseNerve Impulse
Saltatory ConductionSaltatory Conduction
SynapsesSynapses
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 CircuitryNeuron 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 ReflexThe Knee-jerk Reflex
Chemical SynapseChemical Synapse
Chemical Chemical SynapseSynapse
MAJOR NEUROTRANSMITTERS AND THEIR EFFECTS
Acetylcholine (ACh)
Generally excitatory
Affects arousal, attention, memory, motivation, movement. Too much: spasms, tremors. Too little: paralysis, torpor.
Dopamine Inhibitory Inhibits wide range of behavior and emotions, including pleasure. Implicated in schizophrenia and Parkinson's disease.
Serotonin Inhibitory Inhibits virtually all activities. Important for sleep onset, mood, eating behavior.
Norepinephrine Generally excitatory
Affects arousal, wakefulness, learning, memory, mood.
Endorphins Inhibitory Inhibit transmission of pain messages.
Vertebrate Vertebrate Nervous Nervous SystemSystem
Autonomic Nervous SystemAutonomic Nervous System
Works on an involuntary basis2 subdivisions
Parasympathetic Sympathetic
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 Roles of Parasympathetic Parasympathetic and Sympathetic and Sympathetic Divisions of the Divisions of the Autonomic Autonomic Nervous SystemNervous System
Structure of BrainStructure of Brain
BrainstemBrainstem 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
CerebellumCerebellum
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 Thalamus and HypothalamusHypothalamus 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 Structure and Function of CerebrumCerebrum
Drug AffectsDrug 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 AffectsDrug 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 AffectsDrug 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)