NERVOUS SYSTEM
Nervous systems aid in the regulation and maintenance of homeostasis of an organism
NEURON - THE BASIC CELL WHICH ALL NERVOUS SYSTEM ARE MADE OF
drawing by Robert Turner
Parts and Function of a Neuron
Cell Body (2)- portion of a neuron most resembling other cell, contains a nucleus and cytoplasm, receives impulses from dendrite
axon (5)- long part of a neuron leading away from the cell body, transmits impulses away from the cell body
dendrite (1)- highly branched structures at one end of a neuron, impulses are conducted toward the cell body
Schwann cell (3)- aid in the nutrition and regeneration of axon
end brush (4)- filaments forming the end of a axon, release neurotransmitters
synapse- gap between two neurons receives impulse from one neuron and then sends then to the other neuron by releasing a neurotransmitter
myelin sheath- fatty outer layer that encloses the axon of many neurons, acts as an insulating layer to keep impulses from jumping to other neurons (shorting out)
neurolemma- thin membrane covering sounding the myelin sheath
terminal branch- branching out of the axon
Impulses are transmitted electrochemically throughout the neuron as an action potential, impulses cross the synapse as a chemical message called a neurotransmitter
All or None Response
all or none response- nerve impulse either fires or does not fire in a neuron
Threshold- nerve stimulus must have a certain intensity for an impulse to result
that is : there must be a certain strength stimulus to cause a response to occur
Reflex Arc
Reflex arc- path of an impulse takes during a reflex
includes 5 parts (in order of occurrence)
1. receptor (stimulus)
2. sensory neurons
3. interneurons
4. motor neurons
5. effector (response)
Drawn by Robert Turner
3 things necessary for a nervous response:
1. must be a means of detecting a change in environment (stimulus)
2. a stimulus is transmitted as an impulse along a network of neurons
3. an effector, which carries out the necessary response to the stimulus
Vertebrate nervous systems
The two major portion of a
vertebrate nervous system are the central nervous system (CNS),
and the peripheral nervous system. The cns consists of a brain
and one or more nerve cords. The peripheral nervous system is
made up of sensory and motor neurons connected to the cns. It
also has nerves that are connected to the cns with receptors, a
sense organ and effectors( a muscle or gland).
Central nervous system
Brain
Parts of the brain and their functions
Fore brain
Cerebrum - senses, cognitive abilities, memory
Consists of:
temporal lobe- learning and memory, senses of taste, smell, and hearing
parietal lobe- sensory input, touch
occipital lobe- vision, motor input, speech
frontal lobe- personality, learning, thought and speech
midbrain- relay center for impulses traveling to and through the brain
Consists of :
Thalmus - directs incoming impulses to the correct part of the cerebrum
Hypothalmus - produces hormones, controls body activities related to homeostasis
cerebellum- coordinating impulses posture and balance motor coordination muscle tone
Hind brain- heart rate, breathing and other internal organ control
Medulla - regulates heart rate
Pons - regulates breathing by monitoring the carbon dioxide level of the blood
meninges- 3 thin layers of fluid filled tissue that cover the brain and spinal cord for protection
Spinal cord
Functions of the Spinal Cord
1. controls reflexes
2. relays messages from the brain to the body and from the body to the brain
Peripheral Nervous System
Contains two pathways for nerve impulses to travel
The afferent pathway consists of nerve cells that convey information from receptors in the periphery of the body to the central nervous system
The efferent pathway consists of nerve cells that convey information from the central nervous system to muscles on glands.
And consists of two parts:
1. Autonomic nervous system-
carries messages to and from the " automatically functioning" or involuntary muscles and sense organs like the heart, lungs, digestive system, etc.
The parts of the autonomic nervous system are the parasympathetic system and the sympathetic system.
Sympathetic system - responds during times of stress
( increases heart rate, breathing, etc. while slowing digestion etc.)
Parasympathetic system- returns the body to normal conditions after a period of stress.
2. Sensory somatic System-
Carries messages to and from the voluntary muscles and sense organs like skeletal muscles
The five senses
1. sight
The part of the brain that is sight occurs in is occipital lobe. Information is transmitted through bipolar neurons to ganglion cells. The cell bodies of the ganglion cells lie in the retina of the eye and their axons pass through the optic nerve to the occipital lobe.
2. hearing
Sound was vibrations in the air enter the outer ear, the vibrations are picked up by the middle ear bones and transmitted to the inner ear where the auditory nerves are stimulated and transmit impulses to the temporal lobe.
3. taste
The surface of the tongue is not smooth, in fact it's sandpapery surface is made by the presence of thousands of tiny papillae, or taste buds.
Their are four kinds of taste buds. Each have a different function. They're arranged in bitter, sweet, salty, and sour.
Salty and sweet cells are found in the front of the tongue. Sour cells are in the middle, and the bitter cells are found in the back.
Taste buds are connected to neurons, which transmit messages to the brain.
These neurons are called sensory neurons, the message are sent to the temporal lobe of the brain.
4. smell
Olfactory receptor cells are located in the nasal epithelium within the roof of the nasal cavity on both sides of the nasal septum.
The free end of each olfactory cell contains several dendrites with olfactory hairs which are the chemically sensitive portion of receptor cell.
Sensory impulses are conveyed along the olfactory tract and into the olfactory portion of the temporal lobe, where they are interpreted as smell.
5. touch
Touch is a general term that includes several related senses such as pain, pressure, heat and cold. Each of these "touch" senses is defected by separate skin receptors. Each kind of receptor detects only one sense. The number of location of touch receptors around the body varies. For example, there are more touch receptors in the finger tips than in the legs. Whether detected by a simple nerve ending or special cells in a complex organ, sensory information causes action potentials in neurons. Each receptor or sense organ sends impulse to particular parts of the brain where they are interpreted and correct responses can be made.
Disorders of the Nervous System
Stroke
Stroke- occurs when the blood supply to a part of the brain tissue is cut off
Result- the nerve cells in that part of the brain die and thus cannot function
When this happens the part of the body controlled by these nerve cells can not function either.
Treatments- steroids (to decrease swelling), physical therapy, ventilators, tube feeding, and Hospice Care (for comfort measures)
Preventions- No smoking, controlled anxiety, controlled blood pressure, normal weight, low fat and low cholesterol diet to prevent clogging of arteries of the brain
Meningitis
Meningitis- inflammation (swelling ) of the meninges
Causes- a virus or bacterial infection
Treatments- antibiotics for bacterial infection, but there is no known specific treatment for viral meningitis
Adrenleukodystrophy ( ALD)
ALD - occurs when the Myelin sheath around the axons of the nerve cells of the brain degenerate and allow nerve impulses to jump from one neuron to surrounding neurons causing a kind of short circuiting of the brain and its functions resulting in a progressive degeneration of abilities resulting in coma then death if untreated. Usually affects young male children.
Treatments - diet high in the type of fat needed to maintain the Myelin
Effects of drugs and Alcohol
Stimulants
stimulants-increases activity of the nervous system,works on CNS (central nervous system)
Examples- Caffeine, cocaine,
Effects- increases activity of involuntary organs, making the person hyper
Where and How- increases stimulation of the autonomic nervous system in the brainstem, arousal system and cerebral cortex
Depressant
Depressant- "downer"
Examples- Sleeping pills, Valium, Barbiturates, and certain pain medication
Effect- depress body function or nerve activity making person dull or less active
Where and How- works on the thalamus and hypothalamus causing calming effects
Hallucinogen
hallucinogen- drugs that effect the way the brain interprets sensory input
Examples- LSD (lysergic Acid Diethylamide), peyto, and sometimes alcohol
Effects- produces hallucinations ; maybe visual, auditory, or olfactory
judgement maybe impaired, can't tell the difference between what is real or imaginary
Alcohol
BAC- Blood Alcohol Content
Effects as BAC levels rise- in general alcohol being a depressant causes your brain to shut off one part at a time, starting with the parts least necessary to maintain life
low BAC level - Affects the cerebrum by impairing senses and thinking, depresses inhibitions, this definitely affects your ability to drive!
moderate BAC level - Begins to affect the cerebellum as well, causing slurred speech and staggering, will shut off cerebrum all together causing one to pass out
high BAC level - Begins by causing vomiting, progresses by shutting off cerebellum functioning and then affects the medulla (brain stem) by causing alcohol induced heart attack or coma.
Legal intoxication for adults is a BAC of .1
Legal intoxication for minors is a BAC of .01
Both levels are consider to be in the low BAC range
Pain Killers
Pain Killers- naturally occurring or man made copies of endorphins and enkelphins
Effects- they stop the pain "message" impulse from reaching the brain
Where and How- pain killers act like neurotransmitters and act in the synapses
Endorphins- effect emotions
Enkelpahins- also reduce the pain feeling and are known as natural opiates