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Central Nervous System

The Central Nervous System
by

Curtus Bigelow

on 5 March 2012

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Transcript of Central Nervous System

CENTRAL NERVOUS SYSTEM BRAIN Spinal Cord Efferent Nerves Somatic Nervous System Automomic Nervous System Afferent Nerves- are concerned with conveying impulses to the brain and spinal cord
from tissues and organs any place in the body , eg, fingers,toes. Sympathetic
Nervous System Parasympathetic
Nervous System Spinal Nerves Cranial Nerves The Somatic Nervous System involves the Skeletal muscles and are under our concious control. Afferent Nerves Somatic nerves are studied in two convenient anatomic groups : spinal nerves and cranial nerves The brain is the largest and most complex mass of nervous tissue, and is housed inside the 'closed box' structure made of bone called the skull. Transmit impulses to and from skeletal muscles. There are 31 pairs of spinal nerves which correspond to the segments of the spinal cord. 8 cervical 12 Thoracic 5 Lumbar 5 Sacral 1 coccygeal When the spinal cord is cut transversely the tissue will show two different colours. There is a central "H" shaped area which is mainly made of nerve cell bodies, while the outer white matter is made of nerve fibres. 12 Thoracic 8 Cervical


12 Thoracic



5 Lumbar

5 Sacral

1 Coccygeal The largest and most complex part of the brain is the Cerebrum. The Cerebrum is divided into hemispheres, and then refined into different portions, each portion controlling a different function. Voluntary actions are controlled by the Somatic nervous system and can be divided up into two major nerves: Spinal Nerves and Cranial Nerves. There are 31 pairs of
spinal nerves which
correspond to segments
of the spinal cord. 8 Cervical


12 Thoracic


5 Lumbar


5 Sacral
1 Coccygeal When the spinal cord is cut transveresly, the tissue will show two different colours. There is a central "H" shaped dark area and an outer white area. The darker area is made of nerve cell bodies while the white matter is made of mostly nerve fibres.

The major difference between white and gray matter within the spinal cord is that white matter is primarily composed of myelinated nerve fibers, while the nerve fibers of gray matter are not. Myelinated nerve cells tremendously increase the speed at which the action potential (nerve impulse) moves along the neurons axon.
P
N
S are concerned with
conveying impulses to the
brain and spinal cord from tissues
and organs any place in the body. e.g. fingers,toes
Dermatones indicate areas of the body innervated by specifig spinal cord segments. are concerned with carrying
impluses away from the brain and
spinal cord to all structures in the body Anterior Aspect of the Frontal Lobe: responsable for elaboration of thought
Posterior Aspect of the Frontal Lobe: responsable for the initiation of voluntary movement
Parietal Lobe: reponsable for processing of stimuli/ stimuli redirection
Temporal Lobe: responsable for the primary part of hearing
Occipital Lobe: concerned with sight Pain Pain is a protective bodily function that works by informing the brain of any damaging proces. Pain receptors are activated when bodily tissues are being stimulated. Stimulation of pain receptors occurs not only from the initial damage, but also from the after effects: swelling, releasing of chemicals, clotting, other stimuli/ repairative functions. The Central Nervous System The Central Nervous System, CNS, is the control centre of all body function. It is responsable for the reception of many bodily impulses, and making sure the proper actions are carried out for each function. While the Central Nervous System only consists of two main parts: the Brain and the Spinal Cord, they both play an important role in the operation of the entire Nervous System as well. Important things to remember about the Central Nervous System Injuries: The effects of CNS injuries depend on the location and extent of the damage sustained
It may be possible to deduce the nature of an injury by observing what abilities are missing or compromised
Functional losses due to injury may be permanent due to the fact that CNS tissue is unable to regenerate
Both the Brain and the Spinal Cord are surrounded by a protective barrier called 'the meninges' that helps to shield them from injury. 12 pairs of nerves that come from the base of the brain. Important for such functions as: Heart Actions Hearing Sight Vision Digestion Respirations Note: Sight is the process of the
eyes to focus on an image on the
retina and vision is the ability of the brain
to give this image meaning Parasympethic or craniosacrel division
of the autonomic nervous system accompanies the cranial nerves The Medulla Oblongata: The Medulla Oblongata serves as a control centre for visceral activities which include
Cardiac Vital Centre- controls heart rate
Vasomotor Vital Centre- controls impulses of smooth muscles in the walls of blood vessels
Respiratory Vital Centre- works with Pons to regulate the rhythm, rate and depth of breathing The Peripheral Nervous system is Classified as either
1.Somatic(Voluntary)
2.Autonomic(Involuntary)



Peripherial Nerves consist of
long axons running the full length
of the nerve.
-the bodies of motor nerves are located inside the spinal cord while those of the sensory are located outside the spinal cord in groups called ganglia .
-Autonomic nerves are connected to each other by a chain of gangila lying adjacent to the spinal column in the throracic and abdominal cavity .

Ganglion are a maass of nerve tissue; a group of nerve cell bodies, especially nerve cells external to the brain or spinal cord.
Important things to know about the Peripheral nervous system Activities such as heart contractions, digestive processes, dilation and constriction of blood vessels and pupil size are all done automatically, or involuntarily. Some of the nerves belong to the autonomic nervous system. The parasympathetic division of the Autonomic nervous system (ANS) accompanies cranial nerves from the brain and the spinal nerves at the lower end of the spinal cord. How pain is felt: In general the sympatheic and parasympathetic nervous systems of the ANS have opposing actions. Sympathetic prepares the body for stressful situations requiring fast action and great exertion. While Parasympathetic restores the body to normal conditions when the emergency has diminshed. Painful stimuli is felt at open/ exposed nerve ending(s) through the central affected area (damaged area), as well as through any major organs in any of the body cavities in any of the surrounding areas. Functionally, the Sympathetic Nervous System (SNS) controls blood vessels. Most of these vessels are constricted by SNS stimulation of the smooth muscle layer within the vessel. To increase blood flow under stressful conditions to the areas they serve, coronary and skeletal muscle vessels are dialated. Examples of tissue damaging stimuli: Intense Heat
Extreme Cold
Chemical Irritation
Trauma By controlling peripheral vessel diameter, the SNS is capable of regulating both cardiac output and arterial pressure. Other autonomic effects from SNS stimulation where Parasympathetic nervous system have no effects are :
Increased glucose released into the blood
Decreased urinary output from kidneys
50% increase in basal metabolism
Increased cortical secretion
Increased mental activity

All nerve impulses are carried by the same matter the impulse travels from the dendrite end of the neuron to the synapse of the neuron. Reactions to pain: Skin- cutting or burning feeling
Digestive Tract- distension or spasm
Skeletal or Muscle- ischemia
Heart- ischemia NERVE IMPULSES
Nervous tissues have the ability to respond to a change in the environment. when stimulated, the tissue is conductive which is the ability to transfer impulses to the CNS. Those messages are conveyed back to various effectors to make adjustments. The Spinal Cord: -a resting neuron is in a non-conducting state. The semi-permeable membrane is polarized through the active transport of Na+(sodium pump) When the outside is more positive relative to the inside, the neuron is said to have a resting potential. The spinal cord is actually a continuation of the Medulla Oblongata that extends out of the skull. THe spinal cord is a long band of nervous tissue that reaches 45cm in length by adulthood. The spinal cord ends in the lower portion of the back, as the Conus Medullaris. It is of vital importance that the brain and all of its components recieve an uninterrupted supply of blood. The brain recieves 16% of cardiac output, and accounts for 20% of oxygen usage by the body. The reversal of polarization results in an action
potential which allows the stimulus to be carried along the nerve fibre. Action potentials are said to be "all-or-nothing" since they either occur fully or they do not occur at all. Action potential travels along the membrane while "behind" it occurs the recovery of resting potential. A synapse is a very small cleft located
between the end of the presynaptic neuron
and the dendrite end of the postsynaptic
neuron When the action potential reaches the end of the presynaptic neuron, the vesicles move to the surface of the axon membrane. These then fuse with the terminal surface and release their contents into the synaptic cleft. The neurotransmitter molecules diffuse across the synapse and contact the membrane of the post synaptic neuron. Neurotransmitter receptors create a site of depolarization. Electrochemical process is the nerve impulse that occurs along a series of neurons. The wave of depolarization continues over succeeding neurons, until the message reaches the brain, where interpretation occurs.
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