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)