Nervous System

THE NERVOUS SYTEM

NERVOUS SYSTEM• Tasting, smelling, seeing,

hearing, thinking, dreaming, breathing, heart beating, moving, running, sleeping, laughing, singing, remembering, feeling pain or pleasure, painting, writing...you couldn't do any of these things without your nervous system!

• The neuron is the functional unit of the nervous system1

http://www.fulton.edzone.net/winkler/chapter08/chapter08.html

1 Higashida. “Ciencias de la Salud” Mc. Graw Hill, 2001

THE NEURONThree basic functions are performed by nervous systems:

1. Receive sensory input from internal and external environments. Sensory input can be in many forms, including pressure, taste, sound, light, blood pH, or hormone levels, that are converted to a signal and sent to the brain or spinal cord.

2. Integrate the input. In the sensory centers of the brain or in the spinal cord, the barrage of input is integrated and a response is generated.

3. Respond to stimuli. The response, a motor output, is a signal transmitted to organs than can convert the signal into some form of action, such as movement, changes in heart rate, release of hormones, etc.

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookNERV.html

Estructure of a NeuronCell BodyCell BodyDendritesDendrites

Axon from other neurons

Axon from other neurons AxonAxon

MyelinMyelin

Dendrites from other neurons

Dendrites from other neurons

Audesirk Audesirk Byers Sixth Ed.Audesirk Audesirk Byers Sixth Ed.Biology Life on earth, Instructions Resource CD-ROM, Biology Life on earth, Instructions Resource CD-ROM, 2002 Prentice Hall2002 Prentice Hall

SynapticTerminalsSynaptic

Terminals

NEURON• Humans have about 100 billion neurons

in their brain alone! While variable in size and shape, all neurons have three parts.

• Dendrites receive information from another cell and transmit the message to the cell body.

• The cell body contains the nucleus, mitochondria and other organelles typical of eukaryotic cells.

• The axon conducts messages away from the cell body. 2

• Some axons are wrapped in a myelin sheath formed from the plasma membranes of specialized glial cells known as Schwann cells which serve as supportive, nutritive, and service facilities for neurons.3

2 Audersirk T., Audersirk T., Byers B. “Biología, Ciencia y naturaleza” Pearson, Prentice Hall, 2004

3 Pruitt, Crumpler, Prothrow-Stith, “Salud: destrezas para el bienestar”, Prentice Hall, 2000

http://www.morphonix.com/software/education/science/brain/game/specimens/neuron_parts.html

NEURON

The junction between a nerve cell and another cell is called a synapse. Messages travel within the neuron as an electrical action potential. The space between two cells is known as the synaptic cleft. To cross the synaptic cleft requires the actions of neurotransmitters which are stored in small synaptic vessicles clustered at the tip of the axon.


TYPES OF NEURONS• Three types of neurons occur. • Sensory neurons typically

have a long dendrite and short axon, and carry messages from sensory receptors to the central nervous system.

• Motor neurons have a long axon and short dendrites and transmit messages from the central nervous system to the muscles (or to glands).

• Interneurons are found only in the central nervous system where they connect neuron to neuron.

3 Pruitt, Crumpler, Prothrow-Stith, “Salud: destrezas para el bienestar”, Prentice Hall, 2000

NERVOUS IMPULSEThe plasma membrane of neurons, has an unequal distribution of ions and electrical charges between the two sides of the membrane. The outside of the membrane has a positive charge, inside has a negative charge. This charge difference is a resting potential and is measured in millivolts. Passage of ions across the cell membrane passes the electrical charge along the cell. The voltage potential is -65mV (millivolts) of a cell at rest. Sodium ions are more concentrated outside the membrane, while potassium ions are more concentrated inside the membrane. This imbalance is maintained by the active transport of ions to reset the membrane known as the sodium potassium pump.


OrgOrg --

OrgOrg --

OrgOrg --

Org

Org -- O

rgO

rg--

Org

Org--

OrgOrg--

Org

Org

--OrgOrg

--

ION GADIENT

KK++

KK++

KK++KK++

KK++

KK++

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NaNa++

NaNa++

NaNa++

NaNa++

NaNa++NaNa++

ClCl--

ClCl--

ClCl--

ClCl--

ClCl--

ClCl--

The sodium potassium pump keeps some ions in:

•K+•Org-

Other ions are kept outside:

•Na+•Cl-

Audesirk Audesirk Byers Sixth Ed.Audesirk Audesirk Byers Sixth Ed.Biology Life on earth, Instructions Resource CD-ROBiology Life on earth, Instructions Resource CD-ROM, 2002 Prentice HallM, 2002 Prentice Hall

NERVOUS IMPULSE• An action potential is a

temporary reversal of the electrical potential along the membrane for a few milliseconds.

• Sodium gates and potassium gates open in the membrane to allow their respective ions to cross.

• Sodium and potassium ions reverse positions by passing through membrane protein channel gates that can be opened or closed to control ion passage.


NERVOUS IMPULSESteps in an Action PotentialAt rest the outside of the

membrane is more positive than the inside.

1. Sodium moves inside the cell causing an action potential, the influx of positive sodium ions makes the inside of the membrane more positive than the outside. (DEPOLARIZED)

2. Potassium ions flow out of the cell, restoring the resting potential net charges. (REPOLARIZED)

3. Sodium ions are pumped out of the cell and potassium ions are pumped into the cell, restoring the original distribution of ions.


RESTING POTENTIAL((Extracellular fluidExtracellular fluid))

(Negatively charge(Negatively chargedd neuron cytoplasm) neuron cytoplasm)

((Neuronal MembraneNeuronal Membrane) )

((Neuronal MembraneNeuronal Membrane) )

OrgOrg--

NaNa++

OrgOrg--

OrgOrg--

OrgOrg--

OrgOrg--

KK++

KK++ KK++

KK++

KK++ClCl--

ClCl--

ClCl--ClCl--

NaNa++

NaNa++

NaNa++

Potassium Chanel

Potassium Chanel

Sodium chanel(closed)

Sodium chanel(closed)

Audesirk Audesirk Byers Sixth Ed.Audesirk Audesirk Byers Sixth Ed.Biology Life on earth, Instructions Resource CD-ROM, 2002 Prentice HallBiology Life on earth, Instructions Resource CD-ROM, 2002 Prentice Hall

OrgOrg--

NaNa++

OrgOrg--OrgOrg--

KK++KK++

ClCl--

NaNa++

KK++

KK++KK++ KK++

NaNa++

NaNa++

ClCl--

BEGINING OF ACTION POTENTIAL

OrgOrg--

KK++

KK++

KK++

ClCl--

NaNa++

NaNa++KK++

NaNa++

NaNa++

NaNa++

((Extracellular fluid)Extracellular fluid)

((Positive chargePositive charge)) ((Negative chargeNegative charge))((Negative chargeNegative charge))


BEGINING OF ACTION POTENTIAL


PROPAGATION OF ACTION POTENTIAL


OTHER NERVOUS CELLS

There are other type of nervous cells call GLIAL CELLS, which are classified as :

a) Astrocyte.- They functions as support cells for neurons and correlate blood vessels with neurons

b) Oligodendrocytes.- They are smaller and also have supportive function

c) Microglial Cells.- They give immune protection to the nervous system, attacking microorganisms and dead tissue.

http://www.tarleton.edu/~anatomy/nervepix3.html

1 Higashida. “Ciencias de la Salud” Mc. Graw Hill, 2001

CENTRAL NERVOUS SYSTEM (CNS)• Receives and process

information;• Initiates response actions

CENTRAL NERVOUS SYSTEM (CNS)• Receives and process

information;• Initiates response actions

BRAIN• Receives and process

sensory information;• Initiates response;• Memorizes;• Generates touts and

emotions

BRAIN• Receives and process

sensory information;• Initiates response;• Memorizes;• Generates touts and

emotions

SPINAL CORD• Conducts signals from

and to the brain• Controls reflex activities

SPINAL CORD• Conducts signals from

and to the brain• Controls reflex activities

PERIPHERAL NERVOUS SYSTEM (PNS)• Transmits signals from the CNS to the rest

of the body. It is composed by nerves.

PERIPHERAL NERVOUS SYSTEM (PNS)• Transmits signals from the CNS to the rest

of the body. It is composed by nerves.

SENSORY NEURONS• Take signals from

organs to the CNS

SENSORY NEURONS• Take signals from

organs to the CNS

MOTOR NEURONS• Take signals from CNS• Control muscular and endocrine

activities

MOTOR NEURONS• Take signals from CNS• Control muscular and endocrine

activities

SOMATIC NERVOUS SYSTEM (SNS)• Control voluntary movement• Activate skeleton muscle

SOMATIC NERVOUS SYSTEM (SNS)• Control voluntary movement• Activate skeleton muscle

AUTONOMIC NERVOUS SYSTEM• Control internal organs, smooth

muscle and glands

AUTONOMIC NERVOUS SYSTEM• Control internal organs, smooth

muscle and glands

SYMPATHETIC NERVOUS SYSTEM• Prepares the body to stressfull

situations• is involved in the fight or run

response

SYMPATHETIC NERVOUS SYSTEM• Prepares the body to stressfull

situations• is involved in the fight or run

response

PARASYMPATHETIC NERVOUS SYSTEM• is involved in relaxation • Participates in basal activities

PARASYMPATHETIC NERVOUS SYSTEM• is involved in relaxation • Participates in basal activities

ORGANIZATION AND FUNCTIONS

NERVOUS SYSTEMNERVOUS SYSTEM

CENTRAL NERVOUS SYSTEM

Formed by• The brain: is

composed of three parts:

• the cerebrum (seat of consciousness),

• the cerebellum, and • the brain steam

(these latter two are "part of the unconscious brain")

• The Spinal Cordhttp://health.allrefer.com/pictures-images/central-nervous-system.html


The Brain

• The human brain has been called the last great frontier of biology– Cerebrum– Diencephalon– Cerebellum – Brain stem

• Contains 4 ventricles– Two lateral, third,

and fourth

Cerebrum

• The cerebrum is the largest portion of the brain in humans

• Final area to receive sensory input and carry out integration

• Responsible for learning, memory, language and speech

Cerebrum• The cerebral cortex

is a thin but highly convoluted outer layer of gray matter that covers the cerebral hemispheres

• Sensation, voluntary movement, and all thought processes that we associate with consciousness

The Diencephalons• Contains the

hypothalamus and the thalamus

• Thalamus is receiving end for all sensory output except smell– Info integrated and

sent to the cerebrum• Pineal gland

– Secretes melatonin– Sleep, puberty

onset?

The Cerebellum• Primarily white matter

overlain by thin layer of gray matter

• Receives sensory input from the eyes, ears, joints, and muscles about the present position of body parts, and motor inputs from the cerebral cortex

• Integrates and sends out messages

• Ensures coordinated movement

The Brain Stem• The brain stem contains the

midbrain, the pons, and the medulla oblongata

• The midbrain acts as a relay station from cerebrum to spinal cord

• Contains reflex centers for visual, auditory, and tactile responses– Works with the medulla to

regulate breathing rate and has reflex centers for head to smell or sight

– Also vomiting, coughing, sneezing, hiccupping, and swallowing

Spinal Cord

• The spinal cord extends from the base of the brain through a large opening in the skull called the foramen magnum and into the vertebral canal formed by openings in the vertebrae

Functions of Spinal Cord

• Communication between brain and PNS

• Is organized in levels that correspond to body levels

• Sometimes the spinal cord is a relay site and a message from a sensory neuron stimulates a motor neuron via an interneuron

• Reflex actions• Sensory, motor and

interneurons are located here

PERIPHERAL NERVOUS SYSTEM• The PNS consists of • sensory neurons running

from stimulus receptors that inform the CNS of the stimuli

• motor neurons running from the CNS to the muscles and glands - called effectors - that take action.

• The peripheral nervous system is subdivided into – The sensory-somatic

nervous system and – the autonomic nervous

system http://www.sirinet.net/~jgjohnso/periperalns.html

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/PNS.html

PERIPHERAL NERVOUS SYSTEM• The somatic nervous system is connected to

skeletal muscle, voluntary movement and skin sensation. The sensory-somatic system consists of – 12 pairs of cranial nerves and – 31 pairs of spinal nerves

• The autonomic nervous system (ANS) which regulates individual organ function and homeostasis, and for the most part is not subject to voluntary control. It is also known as the visceral or automatic system. The autonomic nervous system has two subdivisions, the

• sympathetic nervous system and the • parasympathetic nervous system.

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/PNS.html#sensory-somatic

The Sympathetic Nervous System

• the sympathetic system enables the body to be prepared for fear, flight or fight. Sympathetic responses include an increase in heart rate, blood pressure and cardiac output, a diversion of blood flow from the skin and splanchnic vessels to those supplying skeletal muscle, increased pupil size, bronchiolar dilation, contraction of sphincters and metabolic changes such as the mobilization of fat and glycogen. http://www.nda.ox.ac.uk/wfsa/html/u05/u05_011.htm

http://faculty.washington.edu/chudler/auto.html

The Parasympathetic Nervous System

• In physiological terms, the parasympathetic system is concerned with conservation and restoration of energy, as it causes a reduction in heart rate and blood pressure, and facilitates digestion and absorption of nutrients, and consequently the excretion of waste products.

http://www.nda.ox.ac.uk/wfsa/html/u05/u05_011.htmhttp://faculty.washington.edu/chudler/auto.html

http://www.nda.ox.ac.uk/wfsa/html/u05/u05_011.htm

The Central Nervous System Disorders

• Meningitis– Is an infection of the

meninges– Can be caused by

virus, bacteria, or fungi

– Symptoms of stiffness, drowsiness, head ache and light sensitivity

– Can be deadly– Outbreaks more

common

Brain Injury• Can be caused by

– Physical force– Anoxia (no O2)

• Stroke (blockage)• Disease • Tumor

• Concussion – Caused by brain

bouncing off the skull• Contusion

– More serious– Bruising to the brain

Brain Injury

• Damage by– Crushing– Tearing– Bleeding– Swelling– Bruising

• The brain is complex and each injury if unique but these are reasons to wear a helmet when head injury is possible

Spinal Cord Damage

• If a disc slips and pinches the spinal cord you have a “slipped disk” and it hurts

Technology

Nervous System