The Nervous SystemChapter 48

By: Julia Moen

Evolution

• The ability of cells to respond to the environment has evolved over billions of years

• Plants use signal-transduction pathways to recognize environmental signals and create cellular responses; they have impulses called action potentials that resemble the nervous system messages in animals (Chapter 39)

• Embryonic development of the vertebrate brain reflects the evolution from three anterior bulges of the neural tube (forebrain, midbrain and hindbrain)

Why is the Nervous System Necessary?

• The Nervous System is responsible for picking up stimulus and signals, processing them and creating a reaction (either voluntary or involuntary)

• The Central Nervous System (CNS) processes information

• The Peripheral Nervous System (PNS) communicates sensory and motor signals between the CNS and the rest of the body

The Nervous SystemConsists of Two parts

A. Central Nervous System (CNS)B. Peripheral Nervous System (PNS)

I. SensoryII. Motora. Somatic Systemb. Autonomic Systemi. Sympatheticii. Parasympathetic

• In terms of function, Somatic NS voluntary muscles and reflexesvsAutonomic NS visceral/smooth and cardiac muscleSympathetic NS increases energy expenditureprepares for action

Parasympathetic NS decreases energy expendituregains stored energythese have the opposite effects on the same organs

--OR--

In terms of location, Peripheral NS sensory and motor neuronsvsCentral NS (CNS) interneurons: brain and spinecovered with three membranes, the meningesinflammation of these is called meningitisbrain has gray matter on outside and white in centerspine has white matter on outside and gray in center

Neuron

Terminal Branch

A. The Neuron• cell body with a nucleus and other organelles• cytoplasmic extensions• dendrites- can have hundreds; sensory; receive

incoming messages from other cells and carry the electrical signal to the cell body

• axons- only one, but can be several feet long in large mammals; transmits an impulse from the cell body outward to another cell

A. The Neuron

• Myelin Sheath- speeds the passage of an impulse– Glial cells are essential for the normal functioning of

neurons; there are many more glial cells than neurons• Schwann cells- glial cells that form the myelin sheath

• Nodes of Ranvier-between myelin sheaths• Terminal Branch-works with synapse to as the

final point the impulse is in one neuron before going to the next

B. Types of NeuronsI. Sensory neurons- receive an initial stimulus from

a sense organ or from another neuronII. Motor neuron- stimulates effectors (muscles or

glands)III. Interneuron or association neuron- within spinal

chord and brain; receives sensory stimuli and transfers the info directly to a motor neuron or to the brain for processing

Resting Potential

• Membrane potential---difference in electrical charge between the cytoplasm (negative ions) and extracellular fluid (positive ions)– Measured in microelectrodes– Potential should be between -50 mV and -100mV

• Polarized state (resting potential)--- neuron in an unstimulated state has a membrane potential of

-70mV• Nerves can only fire if the stimulus is large enough to

overcome the resting potential

Gated Channels• The sodium-potassium pump maintains the polarization by

actively pumping ions that leak across the membrane• Gated-ion channels- in neurons; open and close in

response to stimuli; help transmit electrical impulses• Sodium ion-gated channels---when opened, sodium flows

into the cytoplasm; decreases polarization (to about -60mV, usually); depolarized

• Potassium ion-gated channel----when opened, potassium levels are increased in the cell and the membrane becomes hyperpolarized and therefore harder for the neuron to fire

Action Potential• Impulse• Generated in axons• action potentials relay different intensities of information by

changing the frequency of the action potential– i.e. a strong stimulus sets up more action potentials than a weak

one• Wave of depolarization-reverses polarity of the membrane

(Na+ in, K+ out)• With this change, the message moves along the axon• Refractory period-quickly (a few milliseconds) reverts back

to correct potential

Synapse• Electrical– In crustaceans– Impulses travel from neuron to neuron with no delay– Much less common

• Chemical – Uses Ca2+– Synaptic vesicles contain thousands of

neurotransmitters (substance is released as an intercellular messenger) • Acetylcholine is a common example (see page 1037)

Synapse

The Nervous SystemConsists of Two parts

A. Central Nervous System (CNS)B. Peripheral Nervous System (PNS)

I. SensoryII. Motora. Somatic Systemb. Autonomic Systemi. Sympatheticii. Parasympathetic

Autonomic System

Sympathetic• Fight or flight response• Increases heart and

respiratory rate• Liver converts glycogen to

glucose• Bronchi of lungs dilate and

increase gas exchange• Adrenalin raises blood

glucose levels

Parasympathetic• Opposes the sympathetic

system• Calms the body• Decreases heart and

respiratory rate• Enhances digestion

See page 1041

The Brain• Brainstem-contains the Medulla and pons, and the

midbrain; control areas include movement of the eyes and mouth, relaying sensory messages, hunger, respirations, consciousness, cardiac function, body temperature, involuntary muscle movements, sneezing, coughing, vomiting, and swallowing– Pons-A deep part of the brain, located in the brainstem;

contains many of the control areas for eye and face movements

– Medulla- The lowest part of the brainstem; contains important control centers for the heart and lungs; extremely vital

The Brain con’t

• Thalamus- main input center for sensory information; incoming info sorted in thalamus

• Cerebellum- back of the head; coordinates voluntary muscle movements and maintains posture, balance, and equilibrium.

• Hypothalamus-posterior pituitary hormone and releasing hormones; regulates temperature, hunger, thirst and other basic survival mechanisms; circadian rhythms

Cerebrum• Frontal Lobe-The largest

section of the brain located in the front of the head; involved in personality characteristics and movement.

• Parietal lobe-The middle part of the brain; helps to identify objects and understand spatial relationships; also involved in interpreting pain and touch in the body.

• Occipital lobe-back part of the brain; involved with vision.

• Temporal lobe-The sides of the brain; involved in memory, speech, and sense of smell.

Cerebrum

• Different regions are specialized for different functions

• Main functions of Cerebrum include– Language and Speech, Emotions (Limbic System),

Memory and Learning, Human Consciousness etc.

Interdependence

• The nervous system often works with the endocrine and immune systems to regulate body functions and behavior

• In all systems many functions are started because of signals to either voluntary or involuntary systems– Respiratory, Muscular, Digestive

Main Points• Nervous systems gather, process and respond to information

from stimuli• Networks of neurons work together to form the nervous system• Every cell has a membrane potential that must be overcome to

transport a signal• The signal is passed as an impulse along axons• The same neurotransmitter can produce different effects on

different types of cells• The nervous system is composed of the CNS and the PNS• The separate parts of the peripheral nervous system interact in

maintaining homeostasis• The cerebrum is the most highly evolved structure in mammal’s

brains

Diseases and Disorders

• There are many common diseases and disorders because the nervous system is such a complex system- there is much that can go wrong

• The list of Neurological diseases and disorders include Parkinson’s Disease, Cerebral Palsy, Multiple Sclerosis, Alzheimer’s Disease, Stroke, Epilepsy/Seizures,

Multiple Sclerosis• A chronic disease of the nervous system that can affect young and middle-

aged adults.

• The myelin sheaths surrounding nerves in the brain and spinal cord are damaged, which affects the function of the nerves involved. The underlying cause of the nerve damage remains unknown.

• Multiple Scerosis affects different parts of the brain and spinal cord, resulting in typically scattered symptoms.– These can include:

• Unsteady walk and shaky movement of the limbs• Rapid involuntary movements of the eyes • Defects in speech pronunciation• Inflammed optic nerve

Cerebral Palsy• Non-progressive disorder• results from damage to the brain before , during or

directly after birth• The most common disability is a spastic paralysis.

Sensation is often affected, leading to a lack of balance and intelligence

• posture and speech are frequently impaired. • Other associated features include epilepsy, visual

impairment, squint, reduced hearing, and behavioral problems.

Sciatica

• Often refers to any pain in lower back, which is relatively common

• Caused by compression of, or damage to, a nerve or nerve root

• Stiff pain felt down the back and outer side of the thigh, leg and foot

• Numbness and weakness in the leg

• http://www.youtube.com/watch?v=AjxJabpjDGo&feature=related

• Really informational!

Nervous System

http://www.youtube.com/watch?v=xx--f9Y8wjg

Works Cited

• http://www.dsart.com/Gallery/brain.htm• Barron’s AP Biology Study Guide• Biology 6th Ed. Campbell and Reece• Google images• http://www.adam.com/ • http://familydoctor.org/online/famdocen/ho

me/common/brain.html