Regents Biology2003-2004

The Nervous System

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Structure and Function of the Neuron• Neuron is the scientific name for a Nerve

Cell.• Neurons consist of 3 basic structures:

Cyton, or cell body. Dendrites- receive messages, impulses, and

send them to the cell body. Axons- send messages away from the cell

body.• Nerve impulses travel from one neuron to

another across synapses, or spaces in between the cells.

• The “jumping across” the synapse is facilitated (helped) by chemicals called Neurotransmitters.2003-2004

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Parts of the Cell• Dendrites – Branched

parts of a neuron that receive impulses from other neurons.

• Cyton- Contains cytoplasm and the nucleus. Impulses pass through here to the axon.

• Axon- Single long fiber that carries impulses away from the cell body.

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• A Neuron

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Myelin coating

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signaldirection

myelin coating

Axon coated with insulation made of myelin cells speeds signal

signal hops from node to node 330 mph vs. 11 mph

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

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SynapseJunction between nerve cells

– 1st cell releases chemical to trigger next cell

– where drugs affect nervous system

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synapse

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Propagation of Nerve Impulses

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Image: A02484-12-15   

 

 

 

Fig. 12-15 Depolarization and repolarization. A, RMP results from an excess of positive ions on the outer surface of the plasma membrane. More Na+ ions are on the outside of the membrane than K+ ions are on the inside of the membrane. B, Depolarization of a membrane occurs when Na+ channels open, allowing Na+ to move to an area of lower concentration (and more negative charge) inside the cell-reversing the polarity to an inside-positive state. C, Repolarization of a membrane occurs when K+ channels then open, allowing K+ to move to an area of lower concentration (and more negative charge) outside the cell-reversing the polarity back to an inside-negative state. Each voltmeter records the changing membrane potential as a red line.

 

 

    

Copyright © 2003, Mosby, Inc. All Rights Reserved.

 

Depolarization and repolarization. A, RMP results from an excess of positive ions

on the outer surface of the plasma membrane. More Na+ ions are on the outside of the

membrane than K+ ions are on the inside of the membrane. B, Depolarization of a membrane

occurs when Na+ channels open, allowing Na+ to move to an area of lower concentration

(and more negative charge) inside the cell-reversing the polarity to an inside-positive state. C, Repolarization of a membrane occurs when K+

channels then open, allowing K+ to move to an area of lower

concentration (and more negative charge) outside the

cell-reversing the polarity back to an inside-negative state. Each voltmeter records the changing membrane potential as a red

line.

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Role of ion channels in maintaining the resting membrane potential (RMP). Some K+ channels are open in a "resting" membrane, allowing K+ to diffuse down its concentration gradient (out of the

cell) and thus add to the excess of positive ions on the outer surface of the plasma membrane. Diffusion of Na+ in the opposite direction would counteract this effect but is prevented from doing so

by closed Na+ channels.

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And the answer to how a nerve impulse is conducted…

In the nervous system, signals are propagated by action potentials. An action potential is initiated when the dendrites are stimulated,

and membrane potential decreases. As the signal moves down the axon of the neuron the voltage-gated sodium channels open,

allowing an influx of positive ions. Next, the voltage-gated potassium channels open allowing less positive ions to exit the cell,

thus restoring the cell’s negative charge behind the action potential.

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Continued…

The sodium-potassium pump works all the while to keep the interior of the cell negative by pumping 3 sodium ions out for every 2 potassium ions it pumps in. When the action potential reaches the end of the neuron, the neuron releases neurotransmitters into the synapse. These tiny particles exert their effect on the target cells in one of two ways: They can act to open voltage-gated ion channels by binding directly to the channel, or they can trigger a second messenger when they bind to a cell with a receptor-mediated ion channel.

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Types of Neurons

Neurons can also be classified by the direction that they send information:･ Sensory (or afferent) neurons: send information from sensory receptors (e.g., in skin, eyes, nose, tongue, ears) TOWARD the central nervous system.･Motor (or efferent) neurons: send information AWAY from the central nervous system to muscles or glands.･ Interneurons: send information BETWEEN sensory neurons and motor neurons. Most interneurons are located in the central nervous system.

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Reflexes Stimulus- a change

in the environment. Response/Reaction-

how the body reacts to a stimulus.

Reflex Arc- the pathway that an impulse follows to illicit a response to a stimulus.

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What is a reflex?

• A reflex is defined as an automatic, involuntary reaction to a stimulus resulting from a nerve impulse passing over a reflex arc.– The reflex arc is an impulse conduction route to

and from the central nervous system; it is the smallest part of the nervous system that can receive a stimulus and generate a response.

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Types of Reflex Arcs

• Ipsilateral– Reflex arc whose receptors and effectors are

located on the same side of the body.• Contralateral

– Reflex arc whose receptors and efectors are located on opposite sides of the body.

• Intersegmental Contralateral– Different sensory receptors deliver stimuli at the

same time, and the motor information leaves each segment on the opposite side of the CNS.

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With your group…

• Think up one scenario that might elicit each type of reflex arc:– Ipsilateral– Contralateral– Intersegmental contralateral

Structure of the Nervous System

• Major division - Central vs. Peripheral– Central or CNS- brain and

spinal cord

– Peripheral- nerves connecting CNS to muscles and organs

Central Nervous System

Peripheral Nervous System

Divisions of the Peripheral Nervous System

Skeletal(Somatic)

Sympathetic Parasympathetic

Autonomic

Peripheral Nervous System

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Peripheral Nervous System• Connects body to brain & spinal cord• 12 pairs of nerves from your brain (cranial

nerves)• 31 pairs from your spinal cord (spinal nerves)

– Bundles of sensory and motor neurons held together by connective tissue

• Two divisions– Somatic– Autonomic

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Divisions of the PNS:Somatic Nervous System• Controls voluntary actions• Made up of the cranial and spinal nerves

that go from the central nervous system to your skeletal muscles

Autonomic Nervous System• Controls involuntary actions-those not

under conscious control-such as your heart rate, breathing, digestion, and glandular functions

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Somatic System

Nerves to/from spinal cord control muscle

movements somatosensory inputs

Both Voluntary and reflex movements

Skeletal Reflexes simplest is spinal

reflex arcMuscle

MotorNeuron

InterneuronSkin receptors

SensoryNeuron

Brain

Autonomic System

• Two divisions: – sympathetic– Parasympatheitic

• Control involuntary functions– heartbeat– blood pressure– respiration– perspiration– digestion

• Can be influenced by thought and emotion

Sympathetic

“ Fight or flight” response Release adrenaline and

noradrenaline Increases heart rate and

blood pressure Increases blood flow to

skeletal muscles Inhibits digestive

functions

CENTRAL NERVOUS SYSTEMBrain

Spinalcord

SYMPATHETIC

Dilates pupilStimulates salivation

Relaxes bronchi

Accelerates heartbeat

Inhibits activity

Stimulates glucose

Secretion of adrenaline,nonadrenaline

Relaxes bladder

Stimulates ejaculationin male

Sympatheticganglia

Salivaryglands

Lungs

Heart

Stomach

PancreasLiver

Adrenalgland

Kidney

Parasympathetic

• “ Rest and digest ” system

• Calms body to conserve and maintain energy

• Lowers heartbeat, breathing rate, blood pressure

Sympathetic vs. Parasympathetic

Autonomic nervous system controls physiological arousalSympathetic

division (arousing)Parasympatheticdivision (calming)

Pupils dilate EYES Pupils contract

Decreases SALVATION Increases

Perspires SKIN Dries

Increases RESPERATION Decreases

Accelerates HEART Slows

Inhibits DIGESTION Activates

Secrete stresshormones

ADRENALGLANDS

Decrease secretionof stress hormones

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Central Nervous System

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Central Nervous System

• Consists of the Brain and Spinal Cord

SpinalCord

Brain

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Central Nervous System

• Brain• Spinal cord

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Protections1. Skull and Vertebrae2. 3 protective layers called meninges3. Dura Mater (outer layer): consists of connective tissues,

blood vessels, and nerves.4. Arachnoid Layer (middle layer): elastic and weblike5. Pia Mater (inner layer): contains nerves and blood vessels.6. Cerebrospinal fluid

– a clear watery liquid– separates the middle and inner layers – Acts as shock absorber– exchange of nutrients between blood and nervous system

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The Brain

• Coordinates body activities • Made up of approximately 100 billion neurons• Uses 20% of bodies oxygen and energy • Divided into three major parts-

– the Cerebrum– the Cerebellum– the Brain Stem (Medulla Oblongata, Pons)

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Brain has 2 Hemispheres

• Left & Right sides are separate

• Corpus Callosum : major pathway between hemispheres

• Some functions are ‘lateralized’– language on left– math, music on right

• Lateralization is never 100%

LeftHemisphere

Corpus CallosumRight

Hemisphere

Each hemisphere is divided into 4 lobes

Frontal

Parietal

Occipital

Temporal

Sensory Information sent to opposite hemisphere

• Principle is Contralateral Organization

• Sensory data crosses over in pathways leading to the cortex

• Visual Crossover– left visual field to right hemisphere– right field to left

• Other senses similar

Left visualfield

Right visualfield

Opticnerves

CorpusCallosum

Left VisualCortex

Right VisualCortex

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Contralateral Motor Control

Movements controled by motor area

Right hemisphere controls left side of body

Left hemisphere controls right side

Motor nerves cross sides in spinal cord

Somatosensory CortexMotor Cortex

Corpus Callosum

Major ( but not only) pathway between sides

Connects comparable structures on each side

Permits data received on one side to be processed in both hemispheres

Aids motor coordination of left and right side

Corpus Callosum

Medial surface of right hemisphere

Corpus Callosum

• What happens when the corpus callosum is cut?

• Sensory inputs are still crossed• Motor outputs are still crossed• Hemispheres can’t exchange data

The ‘Split Brain’ studies

• Surgery for epilepsy : cut the corpus callosum

• Roger Sperry, 1960’s• Special apparatus

– picture input to just one side of brain

– screen blocks objects on table from view

Nonverbalright

hemisphere

Verballeft

hemisphere

Nonverbalright

hemisphere

Verballeft

hemisphere

??

“What didyou see?”

The ‘Split Brain’ studies

• Picture to left brain– can name the object– left hand cannot identify by

touch

Picture to right brain can’t name the object left hand can identify

by touch

“Using your left hand,Pick up what you saw.”

I saw anapple.

“What didyou see?”

Nonverbalright

hemisphere

Verballeft

hemisphere

Localization of Function

Frontal

Parietal

Occipital

Temporal

Occipital Lobe

• Input from Optic nerve• Contains primary visual

cortex– most is on surface

inside central fissure• Outputs to parietal and

temporal lobes

OccipitalLobe

VisualLobe

Temporal Lobe

Inputs are auditory, visual patterns speech recognition face recognition word recognition memory formation

Outputs to limbic System, basal Ganglia, and brainstem

Contains primary auditory cortex

TemporalLobe

TemporalLobe

AuditoryCortex

ParietalLobe

SomatosensoryCortex

Parietal Lobe

Receives inputs from multiple senses

contains primary somatosensory cortex borders visual &

auditory cortex Outputs to Frontal lobe hand-eye coordination

eye movements attention

FrontalLobe

Frontal Lobe

Contains primary motor cortex

MotorCortexMotorCortexBroca’s

Area

MotorCortex

WorkingMemory

No direct sensory input Important planning and

sequencing areas Broca’s area for speech

Prefrontal area for working memory

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Parts of the Brain

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Functions of Different Parts of the Brain

• Brainstem– Integration of respiratory

and cardiovascular function

• Cerebellum– Coordinates Movement

• Cerebral Hemispheres– Skilled movement,

reason, learning, memory

• Thalamus– Control of skeletal-

muscle coordination– Awareness

• Hypothalamus– Hormones– Balance– Emotions– Thermoregulation

• Limbic System– Emotions– Learning

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Cerebrum

• Largest part of the brain• Thinking• Memory is stored• Movements are controlled• Impulses from the senses are interpreted.

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Cerebrum specialization• Regions specialized for different functions• Lobes

– frontal• speech,

control of emotions– temporal

• smell, hearing– occipital

• vision– parietal

• speech, tastereading

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frontal

temporal occipital

parietal

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Gray Matter vs. White Matter

• Gray Matter – Absence of myelin in masses of neurons accounts for the gray matter of the brain – Cerebral Cortex

• White Matter - Myelinated neurons gives neurons a white appearance – inner layer of cerebrum

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Cerebellum• Responsible for the

coordination of muscles and is the center of balance

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Medulla• Center of heart beat,

respiration, and other involuntary actions

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Other Structures inside the Brain• Thalamus – receives messages from

sensory receptors; relays information to proper regions of cerebrum

• Hypothalamus - Regulates hunger, thirst, fatigue, anger, etc… – Control of pituitary for endocrine function

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Pons

Pituitary gland

Hypothalamus

Cerebrum

Medulla oblongata Spinal cord

Cerebellum

Pineal gland

Thalamus

Section 35-3

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The Spinal Cord

• Extension of the brain stem• Bundles of neurons that carry impulses

from all parts of the body to the brain and from the brain to all parts of your body

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                                                                                                                                                                                                                                                                           Research Visit the Glencoe Science Web site at tx.science.glencoe.com for more information about the nervous system. Make a brochure outlining recent medical advances.

The Peripheral Nervous System Your brain and spinal cord are connected to the rest of your body by the peripheral nervous system. The PNS is made up of 12 pairs of nerves from your brain called cranial nerves, and 31 pairs from your spinal cord called spinal nerves. Spinal nerves are made up of bundles of sensory and motor neurons bound together by connective tissue. For this reason, a single spinal nerve can have impulses going to and from the brain at the same time. Some nerves contain only sensory neurons, and some contain only motor neurons, but most nerves contain both types of neurons.

Somatic and Autonomic Systems The peripheral nervous system has two major divisions. The somatic system controls voluntary actions. It is made up of the cranial and spinal nerves that go from the central nervous system to your skeletal muscles. The autonomic system controls involuntary actions-those not under conscious control-such as your heart rate, breathing, digestion, and glandular functions. These two divisions, along with the central nervous system, make up your body's nervous system.

Cranial and Facial Nerves

• How the sensory input from the world around us reaches our brain…

• And how our brain sends information to our face and sensory organs…

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Cranial Nerves