I. The Nervous System
A. Overview
B. Central Nervous system
C. Limbic System
D. Peripheral System
E. Drug Abuse
II. Senses
A. Sensory Receptors
B. Proprioceptors and Cutaneous Receptors
C. Taste and Smell
D. Vision
E. Hearing
F. Equilibrium
I. The Nervous System
A. Overview
There are two major parts of the nervous system: the central nervous system and t he peripheral system. The central nervous system encompasses the brain and the spinal cord. The peripheral consists of nerves. Those these systems are labeled separately, they work together as one system. The functions of the nervous system are: receiving sensory input, integrates the input and generates reactions through motor response. Nervous tissue is made up of nuerons which send nerve impulses to the different parts of the system. Neuroglia support the neurons.
There are three different types of neurons. Sensory neurons take impulses from receptors to the central nervous system (CNS). Interneurons, in the CNS, take in all the impulses from sensory neurons and other internuerons. Then motor neurons take a reactionary impulse to an effector, which can be muscles or glands. Neurons have three parts: the cell body, dendrites and an axon. Axons generate impulses while dendrites receive them. Myelin sheaths are a protective lipid-containing substance that are found around some axons. These protect and help in the regeneration of damaged axons.
Nervous information is conveyed in nerve impulses. Measuring these is done using a voltmeter on an axon. When an impulse is not being conducted the voltmeter reads the resting potential of an axon. The charge of the inside of the neuron is more negative than positive at this point. The action potential is the measurement of a neuron when an impulse is being conducted. The change of polarity is very quick. Conduction in myelinated axons is much quicker than in axons without myelin during an impulse. Action potential is always the same in an axon. Intensity depends on how many impulses are fired, because the action potential is the same every time. After an impulse is conducted the sodium gates on an impulse stay shut, called the refractory period, ensuring that the impulse travels in one direction and never backward.
The synapse is the small space between a sending axon and the receiving neuron. The transmission must be carried out by neurotransmitters. These molecules are release when an impulse reaches the axon terminal at the end of an axon. They diffuse through the synaptic cleft and bind to receptors on the receiving neuron or dendrite. Neurotransmitters are then either reabsorbed or destroyed. A neuron then receives either an excitatory or an inhibitory signal. These signals tell a neuron whether to move toward active potential or to move from it.
B. The central nervous system
Sensory information is received and motor response is conducted in the CNS. The brain and the spinal cord make up the CNS. They are both protected my bone and by membrane called meninges. Cerebrospinal fluid fills in the membrane which protects the CNS. There are four ventricles that hold cerebrospinal fluid in the brain. Excesses fluid drains into the cardiovascular system. There are two types of nervous tissue in the CNS. Gray matter is made up of nonmyelinated fibers. Whiter matter is made up of myelinated axons running in tracts.
The spinal cord starts at the base of the brain and runs through the vertebrae. The spinal cord is made up of a central canal, gray matter and white matter. The central canal has cerebrospinal fluid. Sensory and motor neurons are found somewhat in the the gray matter. The white matter contains ascending tracts to the brain and descending tracts from the brain. The spinal cord transmits information between the brain and the peripheral system. Sensory messages are sent to the brain from receptors to the brain. These can be blocked by endorphins. Reflex actions are caused as motor neurons send a response after being stimulated by interneurons who have processed an impulse from sensory neurons.
The brain contains four major parts: the cerebrum, the diencephalon, the cerebellum and the brain stem. The cerebrum is the largest part of the brain. There are two hemispheres of the cerebrum. Sulci are shallow grooves that divide the hemisphere into lobes. The lobes are: the frontal, the parietal, the occipital and the temporal. each lobe has different functional control. The cerebral cortex is a thin, dense layer that covers the lobes. It contains the functions of sensation, voluntary movement, and conscious thought. Most motor sensory is con
tained within the frontal lobe. Sensory information from the skin and muscles goes to the parietal lobe. Vision is processed in the occipital lobe. Hearing is processed in the temporal lobe.
Homeostasis is in part maintained by the hypothalamus in the diencephalon. It regulates things like sleep, hunger, thirst, body temperature and water balance. The thalamus first receives all sensory input except for smell. It integrates the input and then sends it out to the correct area of the brain. The cerebellum is found directly below the occipital lobe. The cerebellum receives sensory input and motor output from the cerebral cortex. It then sends motor impulses to skeletal muscles. It maintains posture in balance in one regard. The brain stem contains the midbrain, the pons and the medulla oblongata. The midbrain receives input from the tracts and also sends out reflexes. The pons contains axons that bridge the cerebellum and the rest of the CNS. It also works in conjunction with the medulla oblongata. The medulla oblongata contains many reflex centers for involuntary actions, such as breathing and heartbeat.
A. Overview
B. Central Nervous system
C. Limbic System
D. Peripheral System
E. Drug Abuse
II. Senses
A. Sensory Receptors
B. Proprioceptors and Cutaneous Receptors
C. Taste and Smell
D. Vision
E. Hearing
F. Equilibrium
I. The Nervous System
A. Overview
There are two major parts of the nervous system: the central nervous system and t he peripheral system. The central nervous system encompasses the brain and the spinal cord. The peripheral consists of nerves. Those these systems are labeled separately, they work together as one system. The functions of the nervous system are: receiving sensory input, integrates the input and generates reactions through motor response. Nervous tissue is made up of nuerons which send nerve impulses to the different parts of the system. Neuroglia support the neurons.
There are three different types of neurons. Sensory neurons take impulses from receptors to the central nervous system (CNS). Interneurons, in the CNS, take in all the impulses from sensory neurons and other internuerons. Then motor neurons take a reactionary impulse to an effector, which can be muscles or glands. Neurons have three parts: the cell body, dendrites and an axon. Axons generate impulses while dendrites receive them. Myelin sheaths are a protective lipid-containing substance that are found around some axons. These protect and help in the regeneration of damaged axons.
Nervous information is conveyed in nerve impulses. Measuring these is done using a voltmeter on an axon. When an impulse is not being conducted the voltmeter reads the resting potential of an axon. The charge of the inside of the neuron is more negative than positive at this point. The action potential is the measurement of a neuron when an impulse is being conducted. The change of polarity is very quick. Conduction in myelinated axons is much quicker than in axons without myelin during an impulse. Action potential is always the same in an axon. Intensity depends on how many impulses are fired, because the action potential is the same every time. After an impulse is conducted the sodium gates on an impulse stay shut, called the refractory period, ensuring that the impulse travels in one direction and never backward.
The synapse is the small space between a sending axon and the receiving neuron. The transmission must be carried out by neurotransmitters. These molecules are release when an impulse reaches the axon terminal at the end of an axon. They diffuse through the synaptic cleft and bind to receptors on the receiving neuron or dendrite. Neurotransmitters are then either reabsorbed or destroyed. A neuron then receives either an excitatory or an inhibitory signal. These signals tell a neuron whether to move toward active potential or to move from it.
B. The central nervous system
Sensory information is received and motor response is conducted in the CNS. The brain and the spinal cord make up the CNS. They are both protected my bone and by membrane called meninges. Cerebrospinal fluid fills in the membrane which protects the CNS. There are four ventricles that hold cerebrospinal fluid in the brain. Excesses fluid drains into the cardiovascular system. There are two types of nervous tissue in the CNS. Gray matter is made up of nonmyelinated fibers. Whiter matter is made up of myelinated axons running in tracts.
The spinal cord starts at the base of the brain and runs through the vertebrae. The spinal cord is made up of a central canal, gray matter and white matter. The central canal has cerebrospinal fluid. Sensory and motor neurons are found somewhat in the the gray matter. The white matter contains ascending tracts to the brain and descending tracts from the brain. The spinal cord transmits information between the brain and the peripheral system. Sensory messages are sent to the brain from receptors to the brain. These can be blocked by endorphins. Reflex actions are caused as motor neurons send a response after being stimulated by interneurons who have processed an impulse from sensory neurons.
The brain contains four major parts: the cerebrum, the diencephalon, the cerebellum and the brain stem. The cerebrum is the largest part of the brain. There are two hemispheres of the cerebrum. Sulci are shallow grooves that divide the hemisphere into lobes. The lobes are: the frontal, the parietal, the occipital and the temporal. each lobe has different functional control. The cerebral cortex is a thin, dense layer that covers the lobes. It contains the functions of sensation, voluntary movement, and conscious thought. Most motor sensory is con
tained within the frontal lobe. Sensory information from the skin and muscles goes to the parietal lobe. Vision is processed in the occipital lobe. Hearing is processed in the temporal lobe.Homeostasis is in part maintained by the hypothalamus in the diencephalon. It regulates things like sleep, hunger, thirst, body temperature and water balance. The thalamus first receives all sensory input except for smell. It integrates the input and then sends it out to the correct area of the brain. The cerebellum is found directly below the occipital lobe. The cerebellum receives sensory input and motor output from the cerebral cortex. It then sends motor impulses to skeletal muscles. It maintains posture in balance in one regard. The brain stem contains the midbrain, the pons and the medulla oblongata. The midbrain receives input from the tracts and also sends out reflexes. The pons contains axons that bridge the cerebellum and the rest of the CNS. It also works in conjunction with the medulla oblongata. The medulla oblongata contains many reflex centers for involuntary actions, such as breathing and heartbeat.
The central nervous system consists of the brain
and spinal cord.
C. Limbic system
The limbic system contains much including primitive emotion and high
er mental function. It blends and integrates these systems. The hippocampus, contained in the limbic system is thought to be very much integral to the learning process. It determines which information should be stored as memory and how to encode it. It most likely communicates with the frontal lobe. Memory is one function of learning. There are different types of learning. Short term memory is associated with the prefrontal area of the brain. Long term memory is a mixture of semantic memory and episodic memory. This is why we easily associate a phone number with a person, place and/or event. Skill memory is the memory of motor ability. Long term memory is apparently stored throughout the cerebral cortex. It appears as though the different hemispheres process the same information differently. Whereas it was believed that the left side of the brain was more rational and logical and the right was more creative and intuitive, it is now believed that the left side is more global and the right side is more specific.A view of the deep-lying limbic system.
D. Peripheral System
The peripheral system(PNS) contains all the nerves. All nerves take impulses to and from the CNS. Nerves that come from the brain are cranial and those from the spinal cord are spinal. There are 12 pairs of cranial nerves in humans. Cranial nerves are, for the most part, used for the face, head and neck. There are 31 pairs of spinal nerves on either side of the spine. All spinal nerves are "mixed" in that they have sensory and motor fibers. The somatic system is a division of the PNS that tends to the skeletal system, skin and tendons. This system contains the receptors that sense outer stimulus. Reflexes are automatic responses to certain stimuli. When reflexes occur much is involved. Outer stimulus is received by a receptor. The sensory neuron sends the information to interneurons in the spinal cord. These send a response impulse through motor neurons that react quickly. The interneurons also send an impulse to the brain. So the reflex is automatic, but also conducts brain activity. The pain is only felt after the brain processes the impulses. The autonomic system is the other major division of the PNS> This controls smooth muscles, breathing and glands. There are two types of autonomic division: sympathetic (urgent) and parasympathetic (relaxed.)
E. Drug Abuse
Drugs, whether natural or synthetic affect the nervous system to either increase the likelihood of excitation (stimulants) or decrease the likelihood of excitation (depressants) of neurons. Drugs artificially stimulate the reward circuit (collection of neurons that promote healthy pleasurable activities, like eating.) Drug abuse is characterized by a physical or psychological dependence and use that is potentially harmful. Alcohol is the most readily available and socially acceptable drug. It can be very harmful when abused. It causes damage to the liver and extensive damage to the brain. It can cause death or coma when used heavily at one time. Nicotine is also highly accepted. Addiction rate in American smokers is about 70%. Cocaine is highly addictive and is pleasurable to users because it keeps dopamine in "rotation" in the system without reabsorbing it quickly. It is a very dangerous drug with many side effects. Methamphetamine works similarly to cocaine in the way that it binds to dopamine keeping it in the system longer.
Its characteristics as well as its side effects are incredibly dangerous. Heroin is a depressant that is incredibly strong. It is pleasurable to users because it is converted to morphine which blocks pain and stimulates the reward circuit. It is highly addictive and its intravenous popularity can lead to hepatitis, HIV and bacterial infection. Marijuana is the most commonly used illegal drug. Its mild euphoria and depressant affects make it very popular. It affects the areas of the brain that maintain memory, balance, coordination and perception.Though not physically addictive, frequent use can make one psychologically dependant.The popularity of "shooting up" (intravenous injection)
has caused many cases of Hepatitis and HIV in heroin users.
II. Senses
A. Sensory receptors
Dendrites that detect specific stimuli are called sensory receptors. When they detect outer sensations they are called exteroceptors. When they detect inner changes they are called interoceptors. Interoceptors are integral to homeostasis. Exteroceptors are integral to detecting environmental changes. Chemoreceptors respond to chemicals nearby. These can be either interoceptors or exteroceptors. Pain receptors, which are protective, sense chemicals that have been released by damaged tissue, to alert the body to damage. Photoreceptors respond to light giving us a sense of vision. Mechanoreceptors respond to pressure. This gives us hearing as well as equilibrium. Thermoreceptors respond to changes of temperature respectively. Sensation is the perception of stimuli. Some sensory receptors are just nerve endings. Others contain specialized cells. Still others have receptor proteins that reacts to chemicals. Perception of stimuli happens in the cerebral cortex. No sensation is felt until the impulse has made it to the cerebral cortex. Integration, however, occurs in sensory receptors. This can cause sensory adaptation, which can cause a stimuli to either be ignored or filtered out.
B. Proprioceptors and cutaneous receptors
The three types of receptors found in the muscles, joints, tendons, skin and some internal organs. These are the proprioreceptors, cutaneous receptors and pain receptors. As reflexive mechanoreceptors, proprioreceptors help maintain poster and balance. Th
ey sense the amount of tension in a muscle and the stretch of tendons to pinpoint the location of a limb. Cutaneous receptors are many different types of receptors in the skin that determine touch, size, temperature and texture of an objects.Meissner corpuscles, Merkel disks and root hair plexuses are the "touch sensitive." Pacinian corpuscles and Ruffini endings are pressure sensitive. There are are many pain receptors, or nociceptors that detect chemical release at the sight of damage.meissner corpuscles.
C. Taste and Smell
Taste and smell are chemical senses. They respond to molecules in t
he food we eat as well as those in the air. Olfactory cells (smell) act from a distance and taste cells act directly. In humans taste buds are found on the tongue, the hard palate, the pharynx and the epiglottis. Taste buds open at a taste pore. These lead to supporting cells which eventually lead down into the sensory nerve. They are then carried to the gustatory cortex where they are interpereted. 80-90% of what is perceived as taste is actually smell. which is sensed by olfactory cells. Certain odor molecules bind to certain smell receptors which is what determines the interpretation of the smell. Smell is very connected to the limbic system and can, therefore, trigger memory.an illustration of a taste bud.
D. Vision
There is a very complex process to sight that involves the brain and the eye. There are three layers to the eye: the sclera, the choroid, and the retina. The cornea is the only transparent part of the sclera, the rest is fiberous and white. The iris is found at the front of the choroid. This determines the size of the pupil, which is the center of the iris and allows in light for vision process. The ciliary body of the choroid determines the shape of the lense for distance of viewing. The retina contains photo receptors. There are two types: rod and cone. Rods are very sensitive to light but only perceive black and white. Cones perceive colors but need much more light and that is why it is much easier to detect color the more light there is. The optic nerve runs from the retina to the visual cortex. An image is focused, through the lens, on the retina. Photoreceptors in the retina recieve light and break down the refraction chemically. The signals are passed to ganglion cells and then to the optic nerve where they are carried to the optic chiasma. The image is crossed and split. Then it goes on to be processed in the visual cortex. Color blindness and distance vision are the most common eye problems.
E. Hearing
The inner ear has to sensory jobs: balance and hearing. There are three parts to the ear. The outer ear contains the pinna and the auditory canal. The middle ear contains the tympanic membrane (eardrum) It ends at a bony wall with two small openings called the oval and round windows. It also contains the auditory tube, which runs to the nasopharynx. This is mimportant to air balance and equilibrium. The inner ear is filled with fluid. There are three areas: the semicircular canals, the vestibule and the cochlea. The first two are important to equilibrium and the last to hearing. When sound waves hit the tympanic membrane it vibra
tes. The pressure is multiplied by the maleus and sent to the stapes. The pressure strikes the oval window. This makes the vibration pressure to pass into the fluid in the inner ear. This stimulates the cochlear nerve which sends the signal to the auditory cortex and is interpreted as sound. Different parts of the nerve are sensitive to different frequencies. Volume is determined by the amount of pressure wsound waves place upon the inner fluid.The inner ear senses hearing and contributes to equilibrium.
F. Equilibrium
Also within the ear are the parts that maintain equilibrium. The vestibular nerve carries pressure signals from the semicircular canals, saccule and utricle to the brain stem and cerebellum. The mechanoreceptors in the semicircular canals are responsible for detecting rotational movement. The reaction of the cupula on the end of vestibular nerve sends a signal of pressure that tells position. Dizziness occurs when the cupula gets used to rotational movement and when the movement stops the cupula slowly comes back to normal throwing off our true rotational balance. Mechanoreceptors in the utricle and saccule dtect movement in the horizontal/vertical planes. These membranous sacs contain little hair cells which are stimulated by the movement of the otolithic membrane they are suspended in. This gel moves with the movement of the head. Impulses are increased or decreased dpending on the direction of the flow. When this data reaches the brain it determine the correct motor output for the gravitational positioning.
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