This review will cover
1. The basic parts and functions of the nervous system including; The central nervous system and The peripheral nervous system, how nervous impulses are sent throughout the body and how the reflex arc works
2. A basic overview of our senses
a. Taste and smell
b. Vision
c. Hearing
d. Equilibrium
1. The nervous system is actually composed of two systems that work in conjunction with one another. The central nervous system (CNS) is made up of the spinal cord and the brain. The CNS takes in sensory information and then in some way decides what action will be taken. Both brain and spinal cord are heavily protected by bone and membrane. The spinal cord contains nerves going to and from it that act as a means of communication between the brain and the peripheral nerves that extend from the cord. Nerve impulses transmit messages within the nervous system. When axons (portions of neurons that conduct nerve impulses) are inactive, meaning that they are not conducting an impulse, it is known as the resting potential. At this state the membrane potential of an axon is about -65 mV. When a nerve impulse occurs a rapid change in the polarity across the axonal membrane it is known as the action potential. When this action potential occurs two gated channels are involved. First the sodium gates open and let sodium into the axon and this action changes the polarity to +40 mV. Then the potassium gates open and potassium exits the axon returning the axon to its resting potential. Some axons (mainly long ones) are covered in a lipid based substance known as myelin, these myelinated axons are capable of sending messages much faster than they would be otherwise because the nerve impulse is able to jump from node to node very quickly. The nervous system can be seriously dysfunctional when demyelination occurs and causes what are known as leukodystrophies as well as MS. All axons branch out with many fine endings at the end of which are small swellings known as axon terminals. These axon terminals are in very close proximity to the dendrite or cell body of another neuron. This close proximity is called the synapse. At these synapses transmission of nerve impulses occurs in this manner; nerve impulses reach the axon terminal, calcium ions enter the terminal and stimulate synaptic vesicles to merge with the sending membrane, and neurotransmitter molecules diffuse into the receiving membrane. The brain is referred to in four sections, cerebrum, diencephalon, cerebellum, and the brain stem. The cerebrum is the largest portion of the brain and is split into halves and then even further into four lobes which have very specific functions. The cerebral cortex is the outer layer of the cerebral hemispheres and is responsible processing sensation, voluntary movement, and all the thought processes of consciousness. The primary motor area begins the process of voluntary commands to skeletal muscles. Sensory information such as taste, sight and hearing are sent to the primary somatosensory area of the brain. Integration occurs at the association areas of the brain. Also in the cerebrum are processing centers, where information is received, actions are planned, and critical thinking is performed and appropriate behaviors are formulated. The remainder of the cerebrum is composed of white matter (myelinated neurons). The diencephalon is composed of the hypothalamus and the thalamus. The thalamus receives all sensory information except smell. The information is integrated here and sent to the appropriate place. The thalamus is also involved in memory and emotion. The hypothalamus is involved in homeostasis by regulating hunger, thirst, sleep etc. The cerebellum portion of the brain is where sensory information from the eyes, ears, joints and muscles is received and posture and balance are maintained. The brain stem contains the midbrain, pons and the medulla oblongata. The midbrain relays information from the cerebrum and spinal cord or cerebellum. The pons contains axons bridging between the cerebellum and the rest of the Central nervous system. The medulla oblongata ensures homeostasis by regulating the heartbeat, breathing and blood pressure. The peripheral nervous system contains the nerves, cranial nerves extend from the brain and spinal nerves extend from the spinal cord. Cranial nerves come in 12 pairs in humans some pairs contain sensory nerves, some motor nerves and some a mix of both. Spinal nerves also come in pairs emerging from either side of the spinal cord and contain both sensory and motor fibers. The PNS is in two divisions, the somatic system which contains the nerves for the skin skeletal muscles and tendons. The somatic system takes information from the external sensory receptors to the CNS and motor commands from the CNS to skeletal muscles. Reflexes are when response to a stimulus is non voluntary. The reflex arc is when a reflex only involves the spinal cord. A stimulus happens, nerve impulses move toward the spinal cord, sensory neurons enter the cord and pass signals to interneurons. Interneurons then synapse with motor neurons, the impulse travels along the motor fibers to an effector, which initiates a response. The autonomic system regulates cardiac and smooth muscles as well as glands. The sympathetic division of the autonomic system helps in fight or flight situations by accelerating the heartbeat and dilating the bronchi. The parasympathetic division of the autonomic system promotes a state of relaxation by slowing down the heartbeat and initiates the digestion of food. A wide variety of natural and synthetic compounds affect the nervous system, these are called drugs and they are widely used in our society. The abuse of drugs is a growing problem and their effects can range from the lowering of inhibitions to death.
2. Certain types of stimuli are detected by sensory receptors, either exteroreceptors, which detect stimuli from outside the body, or, interoreceptors, which receive stimuli from within the body. There are four classifications of sensory receptors 1. Chemoreceptors respond to chemical substances close to the body. Taste and smell utilize chemoreceptors as well as some other internal organs. Pain receptors are chemoreceptors that respond to chemicals released by a damaged tissue. 2. Response to light is carried out by photoreceptors in our eyes. 3. Mechanoreceptors are stimulated by pressure. 3. Mechanoreceptors are in our ears as well as pressure receptors in our skin that are sensitive to light or strong pressures. 3. Thermoreceptors are present in the hypothalamus and the skin and respond to changes in temperature. The conscious perception of stimuli is sensation. All sensory receptors initiate nerve impulses, but depending on what part of the brain receives the impulse the sensation can be different. Within the muscles, joints, tendons, some internal organs and skin are three different types of general sensory receptors. Proprioceptors are a sub category of mechanoreceptors and are involved in balance and posture. Cuataneous receptors lie in the dermis of the skin and are involved in making the skin sensitive to touch, pressure, pain, and temperature. Pain receptors in the internal organs are sensitive to chemicals released by damaged tissue. The senses of taste and smell are chemical senses due to the fact that they are responsive to molecules in the food we eat and the air. Adult humans have 3000 taste buds that occur mainly in the mouth on the tongue. Taste can be categorized one of primary ways; sweet, sour, bitter, or salty. There are areas on the tongue that are sensitive to different tastes. Taste is a different sensation that actually works in correlation with smell. About 80-90% of what we know as taste is actually smell, which explains why it made it easier for me to choke down food I hated as a child by plugging my nose! The sense of smell is also connected with memory and emotion, which is why certain smells bring back specific memories. Vision is a very complex sense and involves both the eyes and the brain. The eyeball has three layers, the sclera, the choroid, and the retina. The outer layer, sclera, contains the cornea, which is the window of the eye. The middle layer, choroid, contains the iris and the pupil which allow light in to the eye. The choroid also contains the lens which divides the eye into two compartments. The third layer, the retina contains rod and cone cells. Rod cells respond to light and cone cells help with seeing color. Hearing is another sense that is very complex in the sense that the ear performs dual functions, hearing and balance. The ear is split up into 3 portions outer, middle and inner ear. The outer ear contains the pinna which is the external flap that we see, and the auditory canal which has fine hairs and glands that secrete earwax. The middle ear begins at the eardrum and contains three tiny bones called the ossicles, as well as the auditory canal and then it ends with a bony wall that has two openings covered by membranes called the oval and round window. The inner ear is filled with liquid and has 3 areas, the semicircular canal, vestibule and the cochlea. Sound waves enter the ear and vibrate the eardrum the waves are then passed from the inner part of the eardrum through the incus to the stapes. The stapes then strikes the membrane of the oval window and the waves are passed to the fluid within the cochlea. Different parts of the cochlea are responsive to different pitches of sound. After long periods of time of being exposed to loud noise, hearing loss can occur. Also in the ear as part of the cochlea there are three semicircular canals that are involved in the sense of balance, or equilibrium. The canals are formed in such a way that they cover all dimensions of space. The base of the canals is called the ampulla where tiny hairs are submerged in a gelatinous material known as cupula. When the head moves, the cupula is displaced and the feeling of unbalance results when a movement such as spinning occurs for a prolonged period of time.
1. The basic parts and functions of the nervous system including; The central nervous system and The peripheral nervous system, how nervous impulses are sent throughout the body and how the reflex arc works
2. A basic overview of our senses
a. Taste and smell
b. Vision
c. Hearing
d. Equilibrium
1. The nervous system is actually composed of two systems that work in conjunction with one another. The central nervous system (CNS) is made up of the spinal cord and the brain. The CNS takes in sensory information and then in some way decides what action will be taken. Both brain and spinal cord are heavily protected by bone and membrane. The spinal cord contains nerves going to and from it that act as a means of communication between the brain and the peripheral nerves that extend from the cord. Nerve impulses transmit messages within the nervous system. When axons (portions of neurons that conduct nerve impulses) are inactive, meaning that they are not conducting an impulse, it is known as the resting potential. At this state the membrane potential of an axon is about -65 mV. When a nerve impulse occurs a rapid change in the polarity across the axonal membrane it is known as the action potential. When this action potential occurs two gated channels are involved. First the sodium gates open and let sodium into the axon and this action changes the polarity to +40 mV. Then the potassium gates open and potassium exits the axon returning the axon to its resting potential. Some axons (mainly long ones) are covered in a lipid based substance known as myelin, these myelinated axons are capable of sending messages much faster than they would be otherwise because the nerve impulse is able to jump from node to node very quickly. The nervous system can be seriously dysfunctional when demyelination occurs and causes what are known as leukodystrophies as well as MS. All axons branch out with many fine endings at the end of which are small swellings known as axon terminals. These axon terminals are in very close proximity to the dendrite or cell body of another neuron. This close proximity is called the synapse. At these synapses transmission of nerve impulses occurs in this manner; nerve impulses reach the axon terminal, calcium ions enter the terminal and stimulate synaptic vesicles to merge with the sending membrane, and neurotransmitter molecules diffuse into the receiving membrane. The brain is referred to in four sections, cerebrum, diencephalon, cerebellum, and the brain stem. The cerebrum is the largest portion of the brain and is split into halves and then even further into four lobes which have very specific functions. The cerebral cortex is the outer layer of the cerebral hemispheres and is responsible processing sensation, voluntary movement, and all the thought processes of consciousness. The primary motor area begins the process of voluntary commands to skeletal muscles. Sensory information such as taste, sight and hearing are sent to the primary somatosensory area of the brain. Integration occurs at the association areas of the brain. Also in the cerebrum are processing centers, where information is received, actions are planned, and critical thinking is performed and appropriate behaviors are formulated. The remainder of the cerebrum is composed of white matter (myelinated neurons). The diencephalon is composed of the hypothalamus and the thalamus. The thalamus receives all sensory information except smell. The information is integrated here and sent to the appropriate place. The thalamus is also involved in memory and emotion. The hypothalamus is involved in homeostasis by regulating hunger, thirst, sleep etc. The cerebellum portion of the brain is where sensory information from the eyes, ears, joints and muscles is received and posture and balance are maintained. The brain stem contains the midbrain, pons and the medulla oblongata. The midbrain relays information from the cerebrum and spinal cord or cerebellum. The pons contains axons bridging between the cerebellum and the rest of the Central nervous system. The medulla oblongata ensures homeostasis by regulating the heartbeat, breathing and blood pressure. The peripheral nervous system contains the nerves, cranial nerves extend from the brain and spinal nerves extend from the spinal cord. Cranial nerves come in 12 pairs in humans some pairs contain sensory nerves, some motor nerves and some a mix of both. Spinal nerves also come in pairs emerging from either side of the spinal cord and contain both sensory and motor fibers. The PNS is in two divisions, the somatic system which contains the nerves for the skin skeletal muscles and tendons. The somatic system takes information from the external sensory receptors to the CNS and motor commands from the CNS to skeletal muscles. Reflexes are when response to a stimulus is non voluntary. The reflex arc is when a reflex only involves the spinal cord. A stimulus happens, nerve impulses move toward the spinal cord, sensory neurons enter the cord and pass signals to interneurons. Interneurons then synapse with motor neurons, the impulse travels along the motor fibers to an effector, which initiates a response. The autonomic system regulates cardiac and smooth muscles as well as glands. The sympathetic division of the autonomic system helps in fight or flight situations by accelerating the heartbeat and dilating the bronchi. The parasympathetic division of the autonomic system promotes a state of relaxation by slowing down the heartbeat and initiates the digestion of food. A wide variety of natural and synthetic compounds affect the nervous system, these are called drugs and they are widely used in our society. The abuse of drugs is a growing problem and their effects can range from the lowering of inhibitions to death.
2. Certain types of stimuli are detected by sensory receptors, either exteroreceptors, which detect stimuli from outside the body, or, interoreceptors, which receive stimuli from within the body. There are four classifications of sensory receptors 1. Chemoreceptors respond to chemical substances close to the body. Taste and smell utilize chemoreceptors as well as some other internal organs. Pain receptors are chemoreceptors that respond to chemicals released by a damaged tissue. 2. Response to light is carried out by photoreceptors in our eyes. 3. Mechanoreceptors are stimulated by pressure. 3. Mechanoreceptors are in our ears as well as pressure receptors in our skin that are sensitive to light or strong pressures. 3. Thermoreceptors are present in the hypothalamus and the skin and respond to changes in temperature. The conscious perception of stimuli is sensation. All sensory receptors initiate nerve impulses, but depending on what part of the brain receives the impulse the sensation can be different. Within the muscles, joints, tendons, some internal organs and skin are three different types of general sensory receptors. Proprioceptors are a sub category of mechanoreceptors and are involved in balance and posture. Cuataneous receptors lie in the dermis of the skin and are involved in making the skin sensitive to touch, pressure, pain, and temperature. Pain receptors in the internal organs are sensitive to chemicals released by damaged tissue. The senses of taste and smell are chemical senses due to the fact that they are responsive to molecules in the food we eat and the air. Adult humans have 3000 taste buds that occur mainly in the mouth on the tongue. Taste can be categorized one of primary ways; sweet, sour, bitter, or salty. There are areas on the tongue that are sensitive to different tastes. Taste is a different sensation that actually works in correlation with smell. About 80-90% of what we know as taste is actually smell, which explains why it made it easier for me to choke down food I hated as a child by plugging my nose! The sense of smell is also connected with memory and emotion, which is why certain smells bring back specific memories. Vision is a very complex sense and involves both the eyes and the brain. The eyeball has three layers, the sclera, the choroid, and the retina. The outer layer, sclera, contains the cornea, which is the window of the eye. The middle layer, choroid, contains the iris and the pupil which allow light in to the eye. The choroid also contains the lens which divides the eye into two compartments. The third layer, the retina contains rod and cone cells. Rod cells respond to light and cone cells help with seeing color. Hearing is another sense that is very complex in the sense that the ear performs dual functions, hearing and balance. The ear is split up into 3 portions outer, middle and inner ear. The outer ear contains the pinna which is the external flap that we see, and the auditory canal which has fine hairs and glands that secrete earwax. The middle ear begins at the eardrum and contains three tiny bones called the ossicles, as well as the auditory canal and then it ends with a bony wall that has two openings covered by membranes called the oval and round window. The inner ear is filled with liquid and has 3 areas, the semicircular canal, vestibule and the cochlea. Sound waves enter the ear and vibrate the eardrum the waves are then passed from the inner part of the eardrum through the incus to the stapes. The stapes then strikes the membrane of the oval window and the waves are passed to the fluid within the cochlea. Different parts of the cochlea are responsive to different pitches of sound. After long periods of time of being exposed to loud noise, hearing loss can occur. Also in the ear as part of the cochlea there are three semicircular canals that are involved in the sense of balance, or equilibrium. The canals are formed in such a way that they cover all dimensions of space. The base of the canals is called the ampulla where tiny hairs are submerged in a gelatinous material known as cupula. When the head moves, the cupula is displaced and the feeling of unbalance results when a movement such as spinning occurs for a prolonged period of time.
No comments:
Post a Comment