The Nervous System. The nervous system. A. Two organ systems, the nervous system and the endocrine system, coordinate organ system activities in response to changing environmental conditions.
A. Two organ systems, the nervous system and the endocrine system, coordinate organ system activities in response to changing environmental conditions.
2. The nervous system is the most complex organ system.
4. The functions of the two major anatomical subdivisions of the nervous system are shown in figure 8.1 pages 226.
6. All communication between the CNS and the rest of the body occurs over the peripheral nervous system (PNS). The PNS includes all the neural tissue OUTSIDE the CNS.
8. The efferent division carries motor commands AWAY from the CNS to the muscles and glands.
9. The PNS is divided into the somatic nervous system (SNS) and the autonomic nervous system (ANS)
11. The ANS provides automatic involuntary regulations of the smooth, cardiac muscles and glandular secretions.
12. The ANS includes a sympathetic and a parasympathetic division, which commonly have opposite effects.
1. Neural tissue consists of two kinds of cells, neurons and neuroglia.
2. Neurons are the basic unit of the nervous system. All neural functions involve the communication of neurons with one another and with other cells.
1. The “model” neuron as cell body, several branching dendrites which receive incoming signals, an elongate axon which carries outgoing signals toward the one or more synaptic terminals.
b. Spreading out from the cell body are short-branched extensions called dendrites. Dendrites carry impulses from the environment or from other neurons toward the cell body.
d. The axon ends in a series of small swellings called axon terminates.
1. A multipolar neuron has multiple processes extending away from the cell body. These are very common in the CNS.
1. Neurons are sorted into three functional groups: sensory, motor and interneurons.
F.Sensory neurons of the afferent division convey information from both external and internal environments to other neurons inside the CNS.
1. Receptors may be grouped into three categories based on the information they carry.
3. The external receptors provide information about the external environment in the form of touch, temperature and pressure sensations and more complex senses of sight, smell, hearing and touch.
5. The visceral receptors or internal receptors monitor activities of digestive, respiratory, cardiovascular, urinary and reproductive systems and provide sensation for taste deep pressure and pain.
1. The half million motor neurons of the efferent division carry instructions from the CNS to other tissues, organs or organ systems.
2. The peripheral targets are called effectors because they change their activities in response to the commands issued by the motor neurons.
1. The 20 billion interneurons are located entirely within the brain and the spinal cord.
2. Interneurons are responsible for the connection between sensory and motor activity.
I. Neuroglia-are both found in both CNS and PNS, but the CNS has the greatest diversity of glial cells. There are four types of glial cells in the CNS.
1. Astrocytes- largest and the most numerous neuroglia. They secrete chemicals vital to the maintenance of the blood-brain barrier, which isolates the CNS from the general circulation.
3. Microglia- are the smallest and rarest. They are phagocytic cells that eat cellular waste and pathogens.
1. The electrical activity in a nerve impulse is a flow of electrical charges along the cell membrane of a neuron.
3. Myelin improves the rate of impulses along an axon. Myelin is composed of 80 percent lipid and 20 percent protein forms an insulated sheath around the axon.
5. The minimum level of a stimulus that is required to activate a neuron is called a threshold. Any stimulus that is weaker than the threshold will produce no impulse. Any stimulus that is stronger than the threshold will have an impulse.
7. The points of contact at which the impulses are passed from one cell to another are known as synapses.
1.The adult brain has six major regions:
3. The brain is wrapped in three layers of connective tissue known as meninges
5. The outermost layer is called dura mater.
6. Between the pia mater and the dura mater is cobweb like layer called arachnoid. This area is filled with cerebrospinal fluid. The fluid protects the brain from injury. Acts like a shock absorber.
B. The cerebrum is the largest prominent part of the human brain. It is responsible for all the voluntary activities in the body. It is the site of intelligence. . Hearing and judgment.
1. Is divided into two hemispheres, the right and left. It is separated by a deep groove. The hemispheres are connected in a region known as the corpus callosum.
3. Each hemisphere of the cerebrum is divided into regions called lobes. These lobes are named for the skull bones.
5. It is thought that right hemisphere is associated with creativity and artistic ability, whereas the left hemisphere is associated with analytical and mathematical ability.
1. Its function is balance and coordination.
2. Major part of learning how to perform physical activities seems to be related to the cerebellum. Ex. Shooting a basketball.
2. The hypothalamus controls center for hunger, thirst, fatigue, and anger and body temperature.
F. Above the pons is the midbrain, the smallest division of the brainstem. This area involves hearing and vision.
1. Electroencephalogram (EEG) gives a general idea of the activity of the brain.
3. Rapid Eye movement (REM) is deep sleep this is when all systems are the slowest.
A. The PNS is the link between the neurons and the CNS and the rest of the body.
1. The PNS transmits impulses from sense organs (ears, taste buds) to the CNS. The motor division transmits impulses from the CNS to the muscles or glands. The motor division is further divided into the somatic nervous system and the autonomic nervous system.
3. See page 255- cranial nerves.
1. If you step on a tac, you will pull your foot up. The information is taken to your muscle before it is taken to your brain. This is called a reflex arc.
1. Vision the eye-is composed with three layers. The outer layer consists of the sclera and the cornea; the middle layer contains the chorioid, ciliary body and iris. The inner layer consists of the retina.
3. In the front of the eye is the cornea, the iris the part of the eye through which light enters.
5. The pupil appears as the small black disk in the center of the eye. Tiny muscles in the iris regulate the size of the pupil.
7. Rods and cones are photoreceptors. Rods will see black and white and cones will see color.
8. See page 293 for accommodation problems.
1. Sound vibrations strike the eardrum and the little bones in the ear, malleus, hammer, anvil and stapes vibrate.
2. The ears contain structures for detecting movements and allow us to maintain our balance. Located within the inner ear are semicircular canals filled with fluid. The movement of fluid will detect movement.
G. Taste-it is also chemical with chemoreceptors. The sense organs are taste buds. Taste is detected by sweet, salty, sour, and bitter.
1. Meningitis- is the inflammation of the meningeal membranes following a bacterial or a viral infection. Meningitis is dangerous because it can disrupt the normal circulatory and CSF fluid.
2. Seizure- a temporary cerebral disorder accompanied by abnormal, involuntary movements. This chronic condition is called epilepsy.
4. Cataract- when the lens loses its transparency. As aging proceeds, the lens becomes less elastic, takes on a yellowish hue and eventually begins to lose transparency.
6. Night blindness- The dim light proves insufficient to activate the rods. This can be treated with vitamin A. Carrots contain vitamin A.