The Nervous System Nerve Cells (SEM x 2,250).. .

The Nervous System

Nerve Cells (SEM x 2,250).

• http://www.pbs.org/wgbh/nova/mind/probe.html

• http://www.pbs.org/wnet/brain/

http://science.howstuffworks.com/brain9.htm

Nervous System• the body's information gatherer,

storage center and control system

Neurons – specialized cells; functional unit of nervous system

The Neuronhttp://www.brainpop.com/health/nervoussystem/nervoussystem/

• basic unit of structure and function

• nerve cells – conduct impulses

.

Cell body

• contains nucleus & most organelles

Dendrites –branchlike extensions

• receive signals from other neurons

Axon – long fiber; transmits signals to other cells (neurons or effectors)– myelin sheath a lipid layer which covers some

axons• insulates • speeds up transmission through axon

• Neurons do not act alone as individual cells

• Neurons lie end to end with axons to dendrites (do not touch)

Neural Signaling

middle.

                                               Some types of neurons: motoneuron (a), sensory neuron (b), cortical pyramidal cell (c)

Neurons also vary with respect to their functions:

3 types of neurons • Sensory neurons – transmits info from sensors (receptors)to the CNS. – detect external or internal changes

• Interneurons –within the CNS. Analyze and interpret the sensory input

• Motor neurons – transmits motor output from the CNS to muscle cells or endocrine cells (effectors)

Nerve Impulses

• a flow of electrical charges along The cell membranes of a neuron.

• electrical activity causes the release of neurotransmitters (chemicals) into the synaptic cleft

• neurotransmitters trigger activity in the second neuron

• neurons have an electrical charge different from the fluid that surrounds them. 

– A difference in electrical charge between two locations is called a potential

Resting Potential

• neuron is not receiving or sending a signal

• inside of the neuron is negatively charged

– concentration of negatively charged proteins and K+ is greater inside the cell

• outside the cell is positively charged– Na+ is greater outside the cell

Action Potential

• when a neuron is stimulated it becomes permeable to Na+

• Na+ rapidly moves into the cell

• Results in a change in the charges inside and outside the cell or

depolarization

Repolarization

• K+ diffuse outward resulting in the inside of the neuron to become negatively charged again

Review

• A neuron at rest has a higher concentration of K+ inside the cell and a higher concentration of Na + outside the cell. Why?

The Nerve Impulsehttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter14/animation__the_nerve_impulse.html

• http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter45/animations.html#

• http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120107/anim0013.swf::Voltage Gated Channels and the Action Potential

• http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120107/bio_a.swf::Sodium-Potassium Exchange

• Chemical Synapse• http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter45/animations.html#

• http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120107/bio_c.swf::Function of the Neuromuscular Junction

2 Major Divisions

Central Nervous System (CNS) • consist of the brain and the spinal cord.

Peripheral Nervous System (PNS) • consists of the neurons NOT included in the brain and sp

cord. – afferent neurons - collect info and transmits it toward the CNS– efferent neurons – transmit info away from the CNS

Neuron Signal Transmission

2 major divisions of N. S.

• 1. Central Nervous System (CNS)– Control center of the body– Brain and spinal cord

• The spinal cord carries messages from the body to the brain

• Messages are analyzed and interpreted

• Response messages are passed from the brain through the spinal cord and to the rest of the body

The Brain http://www.brainpop.com/health/nervoussystem/brain/

• The brain is the main unit of the central nervous system

• It is the place to which impulses flow and from which impulses originate

3 main parts• Forebrain

– Cerebrum – the control center of the brain– Responsible for all the voluntary activies of the

body– The site of intelligence, learning and judgement– Functions in language, conscious thought,

memory, personality development, visions and other sensations.

• Cerebrum - divided into two hemispheres– The right and left– Each hemisphere is divided into regions called

lobes• Frontal, parietal, temporal and occipital lobes

– The left side of the body sends its sensations to the right hemisphere, and the right side of the body send its sensations to the left hemisphere

– The r. hem is associated with creativity and artistic ability

– The l. hem is associated with analytical and mathematical ability

– Thalamus - relay station for nerve impulses carrying sensory information into the brain

– Hypothalamus - regulates certain metabolic processes and other autonomic activities.

• Cerebellum – located at the back of the brain– Coordinated muscle movements– Controls balance, posture and coordination

• The brain stem – connects the brain to the spinal cord– controls the automatic functions (heart rate, blood

pressure), limb movements and organ functions (digestion, urination).

– every nerve impulse that passes between the brain and the spinal cord must pass through the brainstem

• Brain stem divided into 3 parts:– Midbrain– Pons– Medulla oblongata

The spinal cordhttp://www.brainpop.com/health/nervoussystem/spinalcord/

• communication link between the brain and the peripheral nervous system (PNS) – the rest of the body– Carries impulses to and from the brain

• Regulates reflexes– A reflex is a response to a stimulus

• Examples: sneezing , blinking

– Reflexes are very fast and most never reach the brain

• 2. Peripheral Nervous System (PNS) – Consists of nerves or neurons that extend

outside the CNS• connects the CNS to other parts of the body

• Example: serves the limbs and organs

2 divisions of PNS

Somatic nervous system

• regulates activities that are under conscious control– (movement of skeletal muscles)

• and external sensory receptors – reflexes

• Autonomic Nervous System - consists of motor neurons that control internal organs.

– The autonomic system controls muscles in the heart, the smooth muscle in internal organs such as the intestine, bladder, and uterus.

– involves the homeostasis of organs

• THE AUTONOMIC NERVOUS SYSTEM IS FURTHER SUBDIVIDED INTO TWO PARTS:

– THE SYMPATHETIC DIVISION– THE PARASYMPATHETIC DIVISION

• The TWO parts have OPPOSITE EFFECTS on the ORGANS they control.

Fight or Flight• When the brain perceives a threat or danger, messages are sent

to a section of your nerves called the autonomic nervous system (ANS) which then activates the adrenal glands in the kidneys to secrete chemicals, such as adrenaline and noradrenaline, which key up the body for fight or flight.

• The autonomic nervous system is divided into two sub-sections called the sympathetic nervous system and the parasympathetic nervous system. The sympathetic nervous system is the actual system that releases energy and prepares the body for action. The body then typically restores itself back to normal after a period of time by the parasympathetic nervous system, which acts as a kind of stabilizer.

• Destruction of large patches of Myelin characterize a disease called Multiple Sclerosis. 

• Normal nerve function is impaired, causing symptoms such as double vision, muscular weakness, loss of memory, and paralysis.

Stroke

• Blood vessels in the brain are blocked by blood clots

• Circulation to an area is blocked and the brain tissue dies– A severe stroke in one side of the brain may

cause paralysis of the other side of the body

• Meningitis – • inflammation of the membrane covering the

brain

• Epilepsy – - storms of electrical activity in the brain that can cause

seizures

• Shingles – - infection of sensory nerves caused by a virus