what do we mean by reflexes
they are simple, stereotyped movements made in response to sensory stimuli.
what are the types of reflexes
a. monosynaptic: In the stretch reflex, receptors of sensory neurons (muscle spindles) transmit impulses to the spinal cord where direct synapses with motor neurons occur.
b. polysynaptic: In the withdrawal reflex, interneurons in the spinal cord can activate or suppress motor neurons as necessary for a coordinated response.
what are the functional Divisions of the Nervous System
1. The central nervous system includes the brain and spinal cord.
a. The communication lines within the brain and spinal cord are called tracts; those in the white matter contain axons with glistening myelin sheaths and specialize in rapid transmission of impulses.
b. Gray matter consists of unmyelinated axons, dendrites, nerve cell bodies, and neuroglia cells, that protect and support neurons.
2. The peripheral nervous system includes all of the nerves carrying signals to and from the brain and spinal cord.
what are the parts of peripheral nervous system
Peripheral Nervous System
1. Somatic and Autonomic Subdivisions
a. The human peripheral system has two types of nerves based on location:
1) Spinal nerves (31 pairs) connect with the spinal cord and innervate most areas of the body.
2) Cranial nerves (12 pairs) connect vital organs directly to the brain.
b. Spinal and cranial nerves can also be classified on the basis of function:
1) The somatic nerves relay sensory information from receptors in the skin and muscles and motor commands to skeletal muscles (voluntary control).
2) The autonomic nerves sends signals to and from smooth muscles, cardiac muscle, and glands (involuntary control).
2. Sympathetic and Parasympathetic Nerves
a. Parasympathetic nerves tend to slow down body activity when the body is not under stress.
b. Sympathetic nerves increase overall body activity during times of stress, excitement, or danger; they also call on the hormone epinephrine to increase the “fight-flight” response.
what are the functional divisions of the brain
Functional Divisions of the Brain
A. The body’s master control panel, the brain, is a continuation of the anterior end of the spinal cord, and is also protected by meninges and bones.
1. The forebrain, midbrain, and hindbrain form from three successive portions of the neural tube.
2. The most primitive of the tissue is the brain stem, which contains simple, basic reflex centers.
B. Hindbrain
1. The medulla oblongata has influence over respiration, blood circulation, motor response coordination, and sleep/wake responses.
2. The cerebellum acts as reflex center for maintaining posture and coordinating limbs.
3. The pons (“bridge”) possesses bands of axons that pass between brain centers.
C. Midbrain
1. The midbrain originally coordinated reflex responses to visual input; the tectum still integrates visual and auditory signals in vertebrates.
2. In mammals it is now mostly a pathway switching center.
D. Forebrain
1. The large olfactory lobes dominated early vertebrate forebrains.
2. The cerebrum integrates sensory input and selected motor responses.
3. The thalamus (below cerebrum) relays and coordinates sensory signals.
4. The hypothalamus monitors internal organs and influences responses to thirst, hunger, and sex.
E. The Reticular Formation
1. The reticular formation is an ancient mesh of interneurons that extends from the uppermost part of the spinal cord, through the brain stem, and into the cerebral cortex.
2. It serves as a pathway and activates centers in the cerebral cortex.
F. Brain Cavities and Canals
1. The brain and spinal cord are bathed with cerebrospinal fluid that exists within a system of cavities and canals.
2. The fluid cushions vital nervous tissue from sudden, jarring movements.
3. The blood-brain barrier operates at the plasma membranes of cells forming the capillaries that service the brain.
a. Tight junctions fuse the capillary cells together forcing substances to move through the cells to reach the brain.
b. Membrane transport proteins allow essential nutrients (glucose) to move through but bar wastes (urea) and certain toxins.
what is memory
A. “Memory” is the storage and retrieval of information about previous experiences.
1. Association is the linkage of information into larger packages that can be sent to other brain regions for storage.
2. Information becomes stored in “memory traces”—chemical and structural changes in brain regions.
a. Short-term memory lasts from seconds to hours and is limited to seven to eight bits of information.
b. Long-term memory is more permanent and seems to be limitless.
3. Persons suffering from retrograde amnesia lose short-term memory, but long-term memory remains intact.
B. Information is moved into long-term storage with the cooperation of epinephrine, which increases a person’s state of arousal.
what are the components of the sensory system
Each sensory system has three component parts:
1. Sensory receptors are the branched endings of sensory neurons or specialized cells adja¬cent to them that detect specific stimuli.
2. Nerve pathways lead to the brain.
3. Brain regions process the information into a sensation; later, perhaps, a perception (understanding) of the sensation will be made.
what are the types of sensory receptors
Types of Sensory Receptors
1. Mechanoreceptors detect changes in pressure, position, or acceleration; they include receptors for touch, stretch, hearing, and equilibrium.
2. Thermoreceptors detect radiant energy, including infrared.
3. Pain receptors (nociceptors) detect tissue damage.
4. Chemoreceptors detect ions or molecules; they include olfactory and taste receptors.
5. Osmoreceptors detect changes in water volume (solute concentration) in the surrounding fluid.
6. Photoreceptors detect the energy of visible and ultraviolet light.
what are the types of receptors near the body surface
Receptors Near the Body Surface
1. Free nerve endings are simply branched endings of sensory neurons in the skin that function as mechanoreceptors, thermoreceptors, and pain receptors.
2. Encapsulated receptors are of several types:
a. Meissner corpuscles adapt slowly to vibrations of low frequencies.
b. The bulb of Krause is a thermoreceptor that is sensitive to temperatures below 20 degrees C.
c. Ruffini endings are sensitive to steady touching and pressure, and to temperatures above 45 degrees C.
d. Pacinian corpuscles are located both in the dermis and near joints; they are able to detect rapid pressure changes associated with touch and vibrations.
what is phantom pain
Phantom pain is the sensation that amputees may feel from a limb that is no longer a part of the body.
السبت سبتمبر 25, 2010 6:56 pm
