Presentation 16 - Nervous System

The Nervous System

Coordination, Integration, Control

Key Concepts and Important Terms• Nervous systems function in sensory input, integration, and motor output.

• The nervous system is composed of neurons and supporting cells.• Membrane potentials arise from differences in ion concentrations between a

cell’s contents and the extracellular fluid.• An action potential is an all-or-none change in the membrane potential.• Action potentials travel along an axon because they are self-propagating.• Chemical or electrical communication between cells occurs at synapses.• One neurotransmitter can produce different effects on different types of cells. • The symmetry of the nervous system is correlated with body symmetry.• Vertebrate nervous systems are highly centralized and cephalized.• The vertebrate peripheral nervous system has several components differing in

organization and function.• The brainstem conducts data and controls automatic activities essential for

survival.• The cerebellum controls movement and balance.• The thalamus and hypothalamus are prominent integrating centers of the

forebrain.• The cerebrum contains the most sophisticated integrating centers.

Functions of Nervous Systems

Cells of the Nervous System

1. Neurons• Functional unit of the NS• Transmit signals from one

location to another• Structure• Large cell body• Processes that conduct

signals• Dendrites• Axons

2. Glia• Supporting cells• Protect

neurons• Insulate

neurons• Provide structure• Ex: astrocytes, microglia,

ependymal cells, oligodendrocytes, satellite and Schwann cells

The Dendrite Song!(sung to the tune of "Clementine" sent in by Leah B., a

graduate student in elementary education at Long Island Univ. Leah gives credit to Bruce Campbell for composing this song.)

Use your dendrites,Use your dendrites,To connect throughout your brain.Take in info, analyze it,Grow some new onesUnrestrained.

Axons send outNeurotransmittersTo the dendrites all aroundAcross the synapseJumps the impulseNew ideas can now abound.

StimulationIs what the brain needsTo make dendrites stretch and grow. New connectionsMake us smarterIn what we think and what we know.

Use your dendrites,Use your dendrites,To connect throughout your brainTake in info, analyze it,Grow some new onesUnrestrained.

How are neurons organized?• Three types of neurons1. Sensory neurons2. Interneurons3. Motor neurons

• Neural circuits form from any combination of two or more of these

1. Convergent: (many to one)2. Divergent: (one to many)3. Reverberating: (circular)

• Simplest: Sensory and motor neurons – reflex arc

Quiz 1(8 pts.)

1. What is the main function of the nervous system?

2. Draw two neurons and label the following parts:a. axonb. dendritec. cell bodyd. myelin sheathe. synapse

3. Diffentiate between a sensory neuron and a motor neuron in terms of structure and function.

Electrical conduction of information

• Membrane potential – Difference of charges across the

plasma membrane

• Resting potential– Resting cells are (-) inside and (+)

outside– Large amounts of Na+ outside the

cell and K+ inside

• Action potential/impulse– Rapid reversals in charges across

the plasma membrane– Caused by the exchange of ions

across the membrane of the neuron

– Threshold level (-55mV) needed to stimulate neurons ALL-OR-NONE principle

RESTING• Na+, K+ channels

closed• + outside, - inside• Resting potential

maintained

DEPOLARIZATION•Action potential

generated•Na+ channels open,

K+ channels close•+ inside, - outside•Rise in membrane

potential

REPOLARIZATION•Na+ channels close, K+ channels open•- inside, + outside•Drop in membrane potential

UNDERSHOOT/HYPERPOLARIZATION

•Na+ channels close, K+ channels remain open longer•more - inside, + outside•further drop in membrane potential• refractory period of neuron

Saltatory conduction – a faster way• Depends on myelin

sheaths coating an axon

• Impulses carried from node to node

• Advantages– Saves on ATP/energy– Increases the speed of

conduction

• Multiple sclerosis –demyelination of axons in the CNS

Gap junctions and neurotransmittersCommunication between neurons• Gap junctions form

continuous passages between some neurons

• Neurotransmitters cross the synapse to relay the impulse to another neuron or an effector

Diversity of nervous systems

• Nerve cord – thick bundle of nerves from the brain• Ganglion – mass of neurons in the PNS

Vertebrate nervous systems

Evolutionary trends1. Increase in overall brain

size2. Compartmentalization of

functions3. Increased development

of the forebrain

Vertebrate CNS

• Cephalized• Centralized

• Integration and processing of information

• White matter – axons in the CNS• Gray matter – cell bodies, dendrites,

unmyelinated axons

• Central canal of the spinal cord• Ventricles of the brain• Cerebrospinal fluid (CSF)

• Meninges – protective connective tissue

Vertebrate PNS

• Transmits information to and from the CNS

• Components– Both sensory and motor functions– Paired cranial nerves (12)– Paired spinal nerves (31)– Ganglia

• Motor division– Somatic nervous system

• Voluntary - signals to and from skeletal muscles

• Respond to external stimuli

– Autonomic nervous system• Involuntary - Internal

environment, smooth and cardiac muscles

• Sympathetic and parasympathetic divisions

Actions of the parasympathetic and sympathetic divisions of the ANS

• Sympathetic division– Stimulation– Energy generation

• Parasympathetic division– Calming– Rest and repair

• Often have antagonistic actions

• Cooperate to maintain homeostasis

Structure and function of the vertebrate brain

Integrating centers in the cerebrumRight and left cerebral

hemispheres• Cerebral cortex – Highly developed and

convoluted in mammals– Lobes with sensory areas

and association areas, frontal lobe with motor cortex

• Basal nuclei – planning and learning movement sequences

Other roles of the cerebral cortex

• Language and speech– Broca’s area– Wernicke’s area

• Emotions– Limbic system – amygdala,

hippocampus, and olfactory bulb– Laughing, crying, aggression,

feeding, and sexuality• Memory and learning

– Short-term: frontal lobe– Long-term: amygdala and

hippocampus– Neurons may make new

connections• Consciousness

– Emergent property based on activity in many areas of the cortex

Drugs and the Nervous SystemDrug Effect on the NS Effect on the Body

Alcohol (ethanol) CNS depressant Depends on dosage, FAS in babies

Stimulants Amphetamines Cocaine Caffeine Nicotine

CNS and Sym division stimulant, more dopamine / adenosine/ norepinephrine / serotonin in the synapse

Feelings of happiness and power, reduced fatigue, insomnia, psychosis, hallucinations, violent and aggressive behavior, tremors

Depressants Barbiturates

CNS depressant, action potentials cannot be produced

Reduce respiration, bp, heart rate, anesthetic

Opiates Heroin

CNS depressant, mimics the effects of endorphins, stimulate pleasure center

Analgesia, sedation, reduced respiration,

Hallucinogens/psychedelics

Mimics the effects of serotonin Vivid colors, heightened emotions, increase in heart rate and bp

Marijuana Acts on cannabinoid receptors in the brain

Altered sense of time and space, hallucinations