13. Structure Of The Nervous System Flashcards
Describe the anatomy and function of the cerebral cortex.
Cerebral cortex, also called gray matter, is our brain’s outermost layer of nerve cell tissue. It has a wrinkled appearance from its many folds and grooves. Cerebral cortex plays a key role in memory, thinking, learning, reasoning, problem-solving, emotions, consciousness and functions related to your senses.
The whole surface of the cerebral hemispheres has many ridges of tissue called gyri. Gyri are separated by shallow grooves called sulci.
In the cerebral cortex there are many different functions: speech, memory, logical and emotional responses etc are all functions of the neurons of the cerebral cortex.
In the parietal lobe posterior to the central sulcus, there is the primary somatic sensory area. Impulses traveling from the body’s sensory receptors are localized and interpreted in this area of the brain. it also allows you to recognize pain coldness or light touch.
Describe the anatomy and function of the cerebellum.
The cerebellum projects dorsaly from under the occipital lobe of the cerebrum. It has two hemispheres and a convoluted μπερδεμενη surface. In addition it has an outer cortex made up of gray matter and an inner region of white matter.
The cerebellum provides the precise timing for skeletal muscle activity and controls our balance and equilibrium. Because of its activity body movements are smooth and coordinated. Fibers reach the cerebellum from the equilibrium apparatus of the inner ear! the eye, the proprioceptors of the skeletal muscles and tendons and many other areas.
The cerebellum compares the brain’s “intentions” with actual body performance by monitoring body position and the amount of tension in various body parts. When needed it sends messages to initiate the appropriate corrective measures.
What do you know about the blood brain barrier which substances are able to enter the brain and which are not.
No other body organ is so absolutely dependent on a constant internal environment as the brain.
Other body tissues can withstand the small fluctuations in the concentration of hormones, ions, and nutrients which continually occur, particularly after eating or exercising. If the brain were exposed to such chemical changes, the result will be an uncontrolled neural activity.
As a consequence, neurons are kept separated from blood-borne substances by the so-called blood-brain barrier composed of the least permeable capillaries διαπερατά αγγεία in the whole body.
Of all water soluble substances only water, glucose and essential amino acids pass easily through the walls of this capillaries. Metabolic wastes such as urea, toxins, proteins and most drugs are prevented from entering the brain tissue.
Nonessential amino acids and potassium ions are prevented from entering the brain and they are actively pumped from the brain into the blood across capillary walls.
The blood-brain barrier is virtually useless against fats, respiratory gases, and other fat-soluble molecules that diffuse easily through all plasma membranes. For this reason alcohol,nicotine and anesthetics can affect the brain.
Neurophysiological mechanisms of language
Broca’s area is a specialized cortical area that is very involved in our ability to speak. it is located in the base of the precentral gyrus.
Damage to this area which is located in only one cerebral hemisphere, causes inability to say words properly.
It is believed that the areas involved in higher intellectual reasoning and socially acceptable behavior are in the anterior part of the frontal lobes, the anterior association area.
Complex memories seem to be stored in both temporal and frontal lobes.
The posterior association area encompasses part of the posterior cortex. This area plays a role in recognizing patterns and faces, and in blending several different inputs into an understanding of the whole situation.
Within the posterior association area there is the speech area located at the junction of the temporal, parietal, and occipital lobes. Also this area is usually in only one cerebral hemisphere. The frontal lobes house areas involved with language comprehension.
Describe and explain the structure and fuctions of the basal gaglia
Basal nuclei: they are several islands of gray matter buried deep within the white matter of the cerebral hemispheres.
The basal nuclei, also called basal ganglia, help regulate voluntary motor activities by modifying instructions sent to the skeletal muscles by the primary motor cortex. The internal capsule which is a tight band of projection fibers, passes between the thalamus and the basal nuclei.
So basal ganglia are near the center of the brainand form important connections. These connections allow different areas of the brain to work together. The basal ganglia manage the signals of the brain send to help us move our muscles.
Describe the functions of the limbic system and hypothalamus.
The diencephalon sits atop the brain stem and is enclosed by the cerebral hemispheres. The thalamus, the hippopotamus, and their epithalamus are the main structure of the diencephalon.
The hypothalamus is an important autonomic nervous system center because it plays a role in the regulation of body temperature, water balance, and metabolism. It is also the center for many drives and emotions. It is an important part of the so-called limbic system or “emotional visceral brain”.
Thirst, appetite, sex, pain and pleasure centers are in the hypothalamus. In addition it regulates the pituitary gland and produce two hormones of its own.
The pituitary gland hangs from the anterior floor of the hypothalamus by a slender stalk. The mammillary bodies bulge from the floor of the hypothalamus posterior to the pituitary gland.
The limbic system is the part of the brain involved in our behavioural and emotional responses, especially when it comes to behaviours we need for survival: feeding, reproduction and caring for our young, and fight or flight responses.
You can find the structures of the limbic system buried deep within the brain, underneath thecerebral cortexand above the brainstem. The thalamus, hypothalamus (production of important hormones and regulation of thirst, hunger, mood etc) and basal ganglia (reward processing, habit formation, movement and learning) are also involved in the actions of the limbic system, but two of the major structures are the hippocampus and the amygdala.
Describe the various kind of aphasia and explain them.
Cerebrovascular accidents (CVAs) also known as strokes occur when blood circulation to a brain area is blocked by either a blood clot or a raptured blood vessel and vital brain tissue dies. After a CVA, it is often possible to determine the area of brain damage by observing the patient’s symptoms.
If the patient has left-sided paralysis the right motor cortex of the frontal lobe is most likely involved. Aphasia is a common result of damage to the left cerebral hemisphere where the language areas are located.
There are many types of aphasia, but the most common are: motor aphasia and sensory aphasia. Motor aphasia involves damage to Broca’s area and a loss of ability to speak, in sensory aphasia there is a loss of the ability to understand written or spoken language.
Aphasia is maddening to the victims because as a rule their intellect is unimpaired. Brain lesions can also cause Marked changes in a person’s disposition. In such cases a tumor as well as a CVA might be suspected.
Fewer than a third of those surviving a CVA are alive 3 years later. Some patients recover at least part of their lost faculties because undamaged neurons spread into areas where neurons have died and take over some lost functions. Indeed most of the recovery seen after brain injury is due to this phenomenon.
What is a nerve? Describe a nerve.
What is a nerve? A nerve is a bundle of neuron fibers found outside the central nervous system. Within a nerve neuron fibers or processes, are wrapped in protective connective tissue coverings. Each fiber is surrounded by a delicate connective tissue sheath θήκη, and endoneurium.
Groups of fibers are bound by a coarser connective tissue wrapping, the perineurium, to form fiber bundles or fascicles. Finally all the fascicles are bound together by a tough fibrous sheath, the epineurium, to form the cord like nerve.
Nerves, are classified according to the direction in which the transmit impulses. Nerves carrying both sensory and motor fibers are called mixed nerves, all spinal nerves are mixed nerves. Nerves that carry impulses only towards the CNS are called sensory or afferent nerves, whereas those that carry only motor fibers are motor or efferent nerves.
Describe the structure and functions of the autonomic nervous system
That autonomic nervous system (ANS) is a motor subdivision of the peripheral nervous system PNS that controls body activities automatically. It is composed of a specialized group of neurons that regulate cardiac muscle, smooth muscles and glands. Even though all body systems contribute to homeostasis, the relative stability of our internal environment depends largely of the working of the ANS.
At every moment signals flood from the visceral organs into the CNS, and the autonomic nervous system makes adjustments as necessary to best support body activities.
Blood flow for instance may be shunted to more “needy” areas, heart and breathing rate may be speeded up or slowed down, blood pressure may be adjust and stomach secretions may be increased or decreased. Most of these fine tuning occurs without our awareness or attention, few of us realize when our pupils dilate or arteries constrict. Hence the ANS is also called the involuntary nervous system.
There are some important differences between the somatic and the autonomic subdivision of the PNS. Besides differences in their effector organs and in the neurotransmitters they release, the patterns of their motor pathways differ. In the somatic division the cell bodies of the motor neurons are inside the CNS and their axons in spinal nerves extend all the way to the skeletal muscles they serve.
The autonomic nervous system has a chain of two motor neurons. The first motor neuron of each pair, the preganglionic neuron, is in the brain or spinal cord. Its axon, the preganglionic axon, leaves the CNS to synapse with the second motor neuron in a gaglion outside the CNS. The axon of this ganglionic neuron the postganglionic axon, then extends to the organ it serves.
The autonomic nervous system has two arms, the sympathetic and the parasympathetic. Both serve the same organs but cause essentially opposite effects, counterbalancing each other’s activities to keep body systems running smoothly. The sympathetic division mobilizes the body during extreme situations, for example fear, exercise or rage whereas the parasympathetic division allows us to “unwind” and conserve energy.
