Chapter 4. Anatomy of the Nervous System
Essay Questions:
1. List the major divisions and subdivisions of nervous system
2. Describe the major structures and functions of medulla and pons
3. Describe the major structures and functions of midbrain
4. Describe the major functions of the hypothalamus, pituitary gland, and thalamus
5. Describe the major functions of different lobes of the cerebral hemispheres
Chapter 4. Anatomy of the Nervous System
1. The major divisions and subdivisions of the N.S.
Central N.S.:
Brain: hindbrain, midbrain, forebrain
Spinal cord: white matter and gray matter
Peripheral N.S.:
Somatic N.S.: sensory nerve (afferent)
motor nerve (efferent)
Autonomic N.S.: sensory nerve (afferent)
motor nerve: sympathetic division
parasympathetic division
2. The peripheral nervous system
2.1. Somatic nervous system
(1). Sensory nerves (afferent)
Functions: carrying sensory information from sensory receptors to the Central N.S.
Pathways: sensory receptor - sensory nerve axons - neurons in the ganglion dorsal root just outside of spinal cord - spinal cord - thalamus - sensory cortex
(2). Motor nerves (efferent)
Functions: carrying motor signals from central N.S. to muscles
Pathways: motor cortex (making decision) - thalamus - cerebellum - spinal cord - ventral root of spinal cord - motor nerve axons - muscles
2.2. Autonomic nervous system
(1). Sensory nerves
Functions: carrying sensory information from internal organs to central N.S.
Pathways: receptors in the internal organs - nerve axons - neurons in the ganglia (outside of the spinal cord) - dorsal root - spinal cord - thalamus - cortex
ex: drinking 70% alcohol induce burning feelings in stomach
(2). Motor nerves
1). Functions: regulation of activities of internal organs (smooth muscle, cardiac muscle, and glands)
2). Structures: two divisions
a. Sympathetic division:
Functions: mobilize and utilize energy during emergency situations.
Ex: the killer is chasing you
Neural pathways: neurons in the spinal cord (thoracic and lumbar regions) - exit via the ventral roots - neurons in the ganglia of the sympathetic chain - axons to the target organ - adrenal gland (medulla)
b. Parasympathetic division:
Functions: restore and conserve energy
ex: resting and relaxation
Neural pathways:
I. Neurons in the brain stem - vagus nerve - neurons in the ganglia near
the target organs - target organs
II. Neurons in the sacral region of the spinal cord - pelvic nerve
- ganglia near the target organ - target organ
3. Spinal cord
3.1. White matter and gray matter
(1). The white matter are axons and the gray matter are neurons
(2). The axons of the sensory nerves enter the spinal cord on the dorsal (back) side
(3). The axons of the motor nerves leave the spinal cord on the ventral (stomach) side
3.2. Segments of the spinal cord
(1). Cervical nerves: 8 pairs
(2). Thoracic nerves: 12 pairs
(3). Lumbar nerves: 5 pairs
(4). Sacral nerves: 5 pairs
(5). Coccygeal nerves: 1 pair
Total: 31 pairs
4. The hindbrain
(The brain consists of hindbrain, midbrain, and forebrain)
4.1. Medulla (myelencephalon)
(1). Structure: (Nucleus is a group of neurons)
1). The nuclei for cranial nerves 9, 10, 11, 12 are located in the medulla (Nuclei = group of nucleus)
2). Major ascending and descending tracts from spinal cord and brain
3). Reticular formation: the core network of nuclei
(2). Functions:
Controls a number of vital reflexes, such as breathing, heart beat, vomiting, salivation, coughing, sneezing
Ex: Car accident may damage medulla: fatal
Ex: Large doses of morphine and cocaine can inhibit medulla's activity, death follows
4.2. Pons (One of the two major divisions of the metencephalon)
(1). Structures:
1). Ascending and descending tracts
2). The nuclei for cranial nerves 5, 6, 7, 8
3). Reticular formation
(2). Major function: arousal and sleep
4.3. Cerebellum (One of the two major divisions of the metencephalon)
(1). Structures: fibers and nuclei
(2). Functions:
1). The control of movement
2). The speed and skills of movement
3). Language and learning
5. Midbrain (mesencephalon)
Midbrain's major structures and functions
5.1. Tectum:
(1). Superior colliculi - vision
(2). Inferior colliculi - audition
5.2. Tegmentum:
(1). Reticular formation - arousal and sleep
(2). Cerebral aqueduct - connect 3 - 4 ventricles
(3). Periaqueductal gray - secrete endorphins
(4). Substantia nigra - motor control
(5). Nuclei for cranial nerves 3 and 4
6. Forebrain
6.1. Hypothalamus (One of the two major divisions of the diencephalons)
(1). Structure: contains a number of distinct nuclei (dorsomedial nucleus, posterior nucleus, preoptic area, paraventricular nucleus, lateral hypothalamic area, ventralmedial nucleus, supraoptic nucleus, arcuate nucleus)
(2). Functions: feeding, drinking, temperature regulation, sexual behavior, fighting, control pituitary gland activity (hormone releasing process), and daily rhythms of activity and sleep
6.2. Pituitary gland
(1). Structures: anterior pituitary gland
posterior pituitary gland
(2). Functions:
1). Synthesizes and releases hormones into the blood stream
2). Controls the timing and amount of hormone secretion by the rest endocrine glands, such as thyroid, adrenal glands, gonads.
6.3. Thalamus (One of the two major divisions of the mesencephalon)
(1). Structures: including 9 major nuclei (anterior nucleus lateral dorsal n., lateral posterior n., lateral geniculate n. (vision), medial geniculate n. (audition), ventral posterior n. (somatosensory), ventral lateral n, ventral anterior n., pulvinar)
(2). Functions: relay stations for vision, audition, somatic senses. They receive signals from spinal cord and process them and then transmit them to cortex
Note: the following parts of the nervous system are named as telencephalon
6.4. Hippocampus
(1). Structures: located between the thalamus and cerebral cortex
(2). Functions: memory
6.5. Basal ganglia
Structures and functions
(1). Globus pallidus - movement
(2). Striatum: putamen and caudate nucleus - movement (receives major dopaminergic input from substantia nigra of the midbrain)
(3). Amygdala - aggression
6.6. Limbic system
(1). Structures: olfactory bulb, hypothalamus, hippocampus, amygdala, and cingulate gyrus of the cerebral cortex
(2). Functions: for motivated and emotional behavior: such as memory, emotion, learning, motivation, eating, drinking, sexual activity, anxiety, and aggression
6.7. The cerebral cortex
(1). Occipital lobe
1). Structure: neurons receive input from thalamus (lateral geniculate nuclei)
2). Function: vision perception
(2). Parietal lobe
1). Structure: neurons receive inputs from thalamus (ventral posterior nucleus)
2). Function: primary somatosensory cortex for touch sensation and skin and muscle information
(3). Temporal lobe
1). Structure: neurons receive inputs from ears and vestibular organs
2). Functions: auditory, balance and equilibrium, perception of complex patterns, such as faces, language comprehension, and emotion and motivation
(4). Frontal lobe
1). Structure: neurons receive inputs from all the sensory system
2). Functions: control of fine movement, planning, decision, monitoring, emotion, organizing sensory information and cognitive function (intelligence)
7. Ventricles and cerebralspinal fluid
7.1. Ventricles
(1). Two lateral ventricles
(2). The third ventricle
(3). The fourth ventricle
7.2. Cerebralspinal fluid (CSF)
Functions: supporting and cushioning the brain from injury, nutrition
8. Methods of visualizing the living brain
8.1. Contrast X rays = Angiography
Dye is injected into the carotid artery to show vascular damage
8.2. Magnetic Resonance Imaging
The images are constructed from the measurement of waves that hydrogen atoms emit when they are activated by radio-frequency waves in a magnetic field
The concentration of hydrogen atoms in different structures varies substantially
MRI shows abnormal structures clearly
8.3. Positron Emission Tomography (PET)
PET is a method of visualizing brain metabolic activity rather than brain structure
The patient is injected with radioactive 2-deoxyglucose (2-DG). Because of its similarity to glucose, the primary metabolic fuel of the brain, 2-DG is taken up more rapidly by active neurons than non active neurons. However, 2-DG cannot be metabolized, and it thus accumulates in active neurons until it can be gradually broken down and released. Thus, if PET is performed on a patient while he or she is engaged in an activity such as reading, the PET scan will indicate the areas of the brain most active during activity
8.4. Regional cerebral blood flow (rCBF)
(1). Xenon (a radioactive gas) is dissolved in the blood
(After the patient inhales xenon, it enters the bloodstream)
(2). The patent's head is put under a PET scanner
(3). A computer constructs a colored image of the brain
(4). Areas with a great deal of radioactivity appear red; less activity appear orange, yellow, green, blue, and violet
8.5. Functional magnetic resonance imaging (fMRI)
Functional magnetic resonance imaging (fMRI) is a recent MRI technique which provides an unprecedented window onto visualizing neuronal activity in variety of regions of human brain in a noninvasive way. It is a very safe method without harm to human subject. fMRI can identify brain regions that mediate specific aspects of human behavior. The mechanism of fMRI is based on measuring blood circulation activity of the brain. FMRI visualizes the physiological changes in oxy- and deoxyhemoglobin concentration changes in small cortical blood vessels upon neuronal activation. Unlike other brain imaging methods, such as positron emission tomography (PET), fMRI requires no exposure to ionizing-radiation, no injection of tracers, and no sampling of blood. fMRI is a revolutional technique for neuroscience. It is extensively used in exploring cognitive neurological process of learning, memory, and language processing.
fMRI has become the most powerful tool investigating variety human behaviors in a living brain. The followings are the topics and areas that fMRI technique has been used from the published studies: language processing, memory, learning, visual spatial tasks, motor learning, cognitive performance, physical and motor performance, mental disorder, imagery, speech communication, dyslexia, emotion, addictive drug effects, compulsive disorder, aging, music learning, physical pain, emotion, child development, human sexuality, etc... We think that the application of fMRI is a remarkable scientific breakthrough in brain research..
fMRI is fundamentally difference from anatomic MRI. fMRI measures two neurological states then computes the different between the two states. One common practice is use resting as one state (not performing a mental task), and the acting as another states (mentally performing a task, such as recall or solving a math question). This sequence is required to be repeated several times. A statistical comparison between two states, rest and active, to be conducted to see which areas of brain increased blood-oxygenation-level-dependent (BOLD) contrast.