CHAPTER 28Nervous System

28.1 Nervous systems receive sensory input, interpret it, and send

out appropriate commands

• The nervous system has three interconnected functions– Sensory input: receptors-structures

specialized to detect certain stimuli– Integration: through the spinal cord & brain– Motor output: effectors-respond to a

stimulus such as muscles or glands

28.1 Nervous systems receive sensory input, interpret it, and send out appropriate commands

II

2003-2004

Nervous System

• Central nervous system– brain & spinal chord

• Peripheral nervous system– nerves from senses– nerves to muscles

cerebrum

cerebellum

spinal cord cervicalnerves

thoracicnerves

lumbarnerves

femoral nerve

sciatic nerve

tibialnerve

Three types of neurons correspond to the nervous system’s three main

functions

– Sensory neurons convey signals from sensory receptors into the CNS

– Interneurons integrate data and relay signals

– Motor neurons convey signals to effectors

2003-2004

Types of neuronssensory neuron(from senses)

interneuron(brain & spinal chord)

motor neuron(to muscle)

28.2 Neurons are the functional units of nervous systems

• Neurons are cells specialized to transmit nervous impulses

• They consist of– a cell body ~contains the nucleus– dendrites (highly branched fibers) stimulus toward cell body– an axon (long fiber) carries impulses away from cell body

2003-2004

signaldirection

myelin coating

Myelin coating Axon coated with insulation

made of myelin cells speeds signal

signal hops from node to node (Nodes of Ranvier)

330 mph vs. 11 mph

Multiple Sclerosis immune system (T cells) attacks myelin coating loss of signal

Multiple Sclerosis immune system (T cells) attacks myelin coating loss of signal

Supporting cells protect, insulate, and reinforce neurons

• The myelin sheath is the insulating material in vertebrates– It is composed of a chain of Schwann cells linked by nodes of

Ranvier– It speeds up signal transmission– Multiple sclerosis (MS) involves the destruction of myelin sheaths

by the immune system

NERVE SIGNALS AND THEIR TRANSMISSION 28.3 A neuron maintains a membrane

potential across its membrane• The resting potential of a

neuron’s plasma membrane is caused by the cell membrane’s ability to maintain – Polarity– outside axon membrane +– Inside axon membrane -

• Resting potential is generated and maintained with help from sodium-potassium pumps– These pump K+ into the cell

and Na+ out of the cell

28.4 A nerve signal begins as a change in the membrane potential

• A stimulus alters the permeability of a portion of the plasma membrane

– Ions pass through the plasma membrane, changing the membrane’s voltage

– It causes a nerve signal to be generated• An action potential is a nerve signal

– It is an electrical change in the plasma membrane voltage from the resting potential to a maximum level and back to the resting potential

28.5 The action potential propagates itself along the neuron

• An action potential is an all-or-none event

28.6 Neurons communicate at synapses

– It is a junction or relay point between two neurons or between a neuron and an effector cell

• Synapses are either electrical or chemical – Action potentials pass

between cells at electrical synapses

– At chemical synapses, neurotransmitters cross the synaptic cleft to bind to receptors on the surface of the receiving cell

28.9 Connection: Many drugs act at chemical synapses

• Drugs act at synapses and may increase or decrease the normal effect of neurotransmitters– Caffeine– Nicotine– Alcohol– Prescription

and illegal drugs

28.12 The peripheral nervous system of vertebrates is a functional hierarchy

Peripheralnervous system

Sensorydivision

Motordivision

Autonomicnervous system(involuntary

Somaticnervous system(voluntary

Sympatheticdivision

Parasympatheticdivision

Sensingexternalenvironment

Sensinginternalenvironment

28.13 Opposing actions of sympathetic and parasympathetic neurons regulate the internal

environment– The

parasympathetic division primes the body for activities that gain and conserve energy

– The sympathetic division prepares the body for intense, energy-consuming activities

28.15 The structure of a living supercomputer: The human brain

28.15 The structure of a living supercomputer: The human brain II

2003-2004

Primitive brain • The “lower brain”

– medulla oblongata– pons– cerebellum

• Functions– basic body functions

• breathing, heart, digestion, swallowing, vomiting (medulla)

– homeostasis– coordination of movement (cerebellum)

2003-2004

Higher brain • Cerebrum

– 2 hemispheres– left = right side of

body– right = left side of

body• Corpus callosum

– connection between 2 hemispheres

2003-2004

Division of Brain Function• Left hemisphere

– “logic side”– language, math, logic operations, vision &

hearing details– fine motor control

• Right hemisphere – “creative side”– pattern recognition, spatial

relationships, non-verbal ideas, emotions, multi-tasking

2003-2004

Cerebrum specialization

frontal

temporal

• Regions specialized for different functions• Lobes

– frontal• speech,

control of emotions

– temporal• smell, hearing

– occipital• vision

– parietal• speech, taste

reading occipital

parietal

2003-2004

Limbic systemControls basic emotions (fear, anger), involved in emotional bonding, establishes emotional memory

2003-2004

Simplest Nerve Circuit Reflex, or automatic response

rapid response automated

signal only goes to spinal cord no higher level

processingadvantage

essential actions don’t need to think or

make decisions about blinking balance pupil dilation startle

2003-2004

cerebrum

cerebellum

spinal cord cervicalnerves

thoracicnerves

lumbarnerves

femoral nerve

sciatic nerve

tibialnerve

Any Questions??