Nervous System

The
TheNervous
NervousSystem
System
Prof. Melvin Carreon
Physiological Psychology
University of the East

Anatomical Directions
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Rostral/Anterior – toward the head of a fourlegged animal
Caudal/Posterior – toward the tail
Inferior/Ventral – toward the belly
Superior/Dorsal – toward the back
Neuraxis – an imaginary line that runs the length of the spinal cord to the front of the brain
Midline – an imaginary line dividing the body into two equal halves
Ipsilateral – directional term referring to structures on the same side of midline

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Contralateral – opposite side of the midline
Medial – toward the midline
Lateral – away from the midline
Proximal – closer to center
Distal – opposite of proximal
Coronal section – anatomical section dividing the brain front to back, parallel to the face
Sagittal section – parallel to the midline
Midsagittal section – sagittal section that divides the brain into two equal halves
Horizontal/axial section – divides the brain from top to bottom

Meninges (singular: meninx )
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The protective sheaths around the brain & the spinal cord

The meninges consist of three layers: the dura mater, the arachnoid mater, and the pia mater. The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system. Layers of Meninges
Dura Mater – means hard mother, the outermost w/c is tough & flexible. It surrounds & supports the large venous channels carrying blood from the brain toward the heart.
Arachnoid membrane – the middle layer, so named because of its spider web-like appearance. It provides a cushioning effect for the CNS.
Pia Mater - very thin membrane composed of fibrous tissue covered on its outer surface by a sheet of flat cells thought to be impermeable to fluid. It is pierced by blood vessels which travel to CNS, and its capillaries are responsible for nourishing the brain.

Cerebrospinal Fluid
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occupies the space between the arachnoid mater & the pia mater. produced by Choroid plexus

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It acts as a "cushion" or buffer for the cortex, providing a basic mechanical and immunological protection to the brain inside the skull.

CSF serves four primary purposes
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Buoyancy: The actual mass of the human brain is about
1400 grams; however, the net weight of the brain suspended in the
CSF is equivalent to a mass of 25 grams. It allows the brain to maintain its density w/o being impaired by its own weight, which would cut off blood supply & kill neurons in the lower section.

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Protection: CSF protects the brain tissue from injury when jolted or hit. In certain situations such as auto accidents or sports injuries, the CSF cannot protect the brain from forced contact with the skull case, causing hemorrhaging, brain damage, and sometimes death.

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Chemical stability: CSF flows throughout the inner ventricular system in the brain and this allows for homeostatic regulation of the distribution of neuroendocrine factors, to which slight changes can cause problems or damage to the nervous system.

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Prevention of brain ischemia w/c is made by decreasing the amount of CSF in the limited space inside the skull.

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The brain contains a series of hollow interconnected chambers: ventricles
(little bellies) w/c are filled w/ CSF.
The largest chambers are the lateral ventricles w/c are connected to the third ventricles. The cerebral aqueduct (a long tube) connects the third ventricle to the fourth ventricle. Human Brain
Development
The brain emerges during embryonic development from the neural tube. The most anterior part of the neural tube is called the telencephalon, w/c expands rapidly due to cell proliferation, and eventually gives rise to the brain.
 Gradually some of the cells stop dividing and differentiate into neurons and glial cells. The newly generated neurons migrate to different parts of the developing brain to self-organize into different brain structures. Once the neurons have reached their regional positions, they extend axons and dendrites, which allow them to communicate with other neurons via synapses.
 Synaptic communication between neurons leads to the establishment of functional neural circuits that mediate sensory and motor processing, and underlie behavior. The brain does most of its development with in the first 20 years of life. 

Development of NS begins around 18th days after conception . Part of the embryo thickens & forms a plate w/c forms ridges. By the 21st day, these ridges fuse together to form neural tube w/c gives rise to the brain & spinal cord. The ridges’ top part break away & become the ganglia of ANS.
By the 28th day, neural tube is closed and develops into three interconnected chambers (ventricles), and the tissue surrounds them become the forebrain, midbrain & hindbrain.

cerebrum or telencephalon
Telencephalon refers to the embryonic structure, from which the mature
"cerebrum" develops. The dorsal telencephalon, or pallium, develops into the cerebral cortex, and the ventral telencephalon, or subpallium, becomes the basal ganglia. The cerebrum is also divided into symmetric left and right cerebral hemispheres.

Cerebral Cortex
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a sheet of neural tissue that is outermost to the cerebrum. 

It is constituted of up to six horizontal layers, each of which has a different composition in terms of neurons and connectivity. The human cerebral cortex is 2–4 mm (0.08–0.16 inches) thick. 

It has gray matter (formed from neurons and their unmyelinated fibers) & white matter
(formed predominantly by myelinated axons interconnecting neurons in different regions)

Cerebral Cortex
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Has convolutions, consisting of sulci (small grooves), fissures (large grooves), & gyri
(bulges bet. adjacent sulci or fissures)

Cortical Areas
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Sensory

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Motor

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Association

Sensory Areas
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receive and process information from the senses. Parts of the cortex that receive sensory inputs from the thalamus are called primary sensory areas. The senses of vision, audition, and touch are served by the primary visual cortex, primary auditory cortex and primary somatosensory cortex.

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In general, the two hemispheres receive information from the opposite (contralateral) side of the body except for olfaction & gustation

Motor Area
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located in both hemispheres of the cortex. The motor areas are very closely related to the control of voluntary movements, especially fine fragmented movements performed by the hand. The right half of the motor area controls the left side of the body, and vice versa.
Two areas of the cortex are commonly referred to as motor:
Primary motor cortex , which executes voluntary movements
Supplementary motor areas and premotor cortex, which select voluntary movements.
In addition, motor functions have been described for:
Posterior parietal cortex , which guides voluntary movements in space
Dorsolateral prefrontal cortex, which decides which voluntary movements to make according to higher-order instructions, rules, and self-generated thoughts.

Association areas
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function to produce a meaningful perceptual experience of the world, enable us to interact effectively, and support abstract thinking and language. The parietal, temporal, and occipital lobes all located in the posterior part of the cortex - organize sensory information into a coherent perceptual model of our environment centered on our body image. The frontal lobe or prefrontal association complex is involved in planning actions and movement, as well as abstract thought.
Broca's area - language expression
Wernicke's area - for language comprehension.

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Corpus Callosum – a large band of axons that connects corresponding parts of the association cortex of the left & right hemispheres. Thus, we know what is happening in the corresponding region of the opposite side of the brain.

Basal Ganglia
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group of nuclei in the brains are situated at the base of the forebrain. They are associated with a variety of functions, including motor control and learning.

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Currently popular theories implicate the basal ganglia primarily in action selection, that is, the decision of which of several possible behaviors to execute at a given time.

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Experimental studies show that the basal ganglia exert an inhibitory influence on a number of motor systems, and that a release of this inhibition permits a motor system to become active. The "behavior switching" that takes place within the basal ganglia is influenced by signals from many parts of the brain, including the prefrontal cortex, which is widely believed to play a key role in executive functions.

The main components of the basal ganglia
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The largest component, the striatum, receives input from many brain areas but sends output only to other components of the basal ganglia.

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The globus pallidus receives its most important input from the striatum
(either directly or indirectly), and sends inhibitory output to a number of motor-related areas, including the part of the thalamus that projects to the motor-related areas of the cortex.

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The substantia nigra consists of two parts, one that functions similarly to the globus pallidus, and another that provides the source of dopamine input to the striatum.

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The subthalamic nucleus receives input mainly from the striatum and cortex, and projects to the pallidus.

The basal ganglia play a central role in a number of neurological conditions, including several movement disorders. The most notable are, first, Parkinson's disease, involving degeneration of the melaninpigmented dopamine-producing cells in the substantia nigra, and secondly,
Huntington's disease, which primarily involves damage to the striatum. Basal ganglia dysfunction is also implicated in some other disorders of behavior control such as Tourette's syndrome and obsessive–compulsive disorder

Limbic System
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Amygdala - Involved in signaling the cortex of motivationally significant stimuli such as those related to reward and fear in addition to social functions such as mating.

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Hippocampus - Required for the formation of long-term memories and implicated in maintenance of cognitive maps for navigation.

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Parahippocampal gyrus - Plays a role in the formation of spatial memory 

Cingulate gyrus - Autonomic functions regulating heartrate, blood pressure and cognitive and attentionalprocessing

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Fornix - carries signals from the hippocampus to the mammillary bodies and septal nuclei.

Diencephalon
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Situated between telencephalon & mesencephalon 

It surrounds the 3rd ventricle.

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Important structures:
◦ Thalamus
◦ Hypothalamus

Thalamus

(Greek:THALAMOS

“inner chamber”)

receives all sensory messages from the spinal cord (except those from the olfactory receptors) prior to being directed to the cerebrum's sensory areas. The function of the thalamus is to sort and interpret these messages before relaying them to the appropriate neurons in the cerebrum

Thalamus bridge has 2 lobes connected by a of gray matter: massa intermedia

Thalamic Nuclei
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Lateral Geniculate – receives info from the eyes & sends axons to the primary visual cortex. 

Medial Geniculate – info from the inner ear
& sends to the primary auditory cortex

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Ventrolateral – info from cerebellum & projects it to the primary motor cortex.

Hypothalamus
Lies at the base of the brain, under the thalamus.
It contains olfactory centers and is the main integration hub for controlling the viscera (internal organs).
It supplies input to areas in the medulla and spinal cord that control activities such as heart rate, respiration, and fat metabolism. It regulates body temperature.
It also controls appetite and water balance and plays a part in emotional and sexual responses.
It is the bridge between the nervous and endocrine systems. It produces various hormones and regulates the pituitary gland.

Mesencephalon (Midbrain)
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the cerebral

aqueduct
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of:
◦1. Tectum – structures are superior & inferior colliculi. ◦2. Tegmentum

Tegmentum parts
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Reticular Formation – receives sensory info by means of various pathways; plays a role in sleep & arousal, attention, muscle tone.

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Periaqueductal Gray matter – consists neural circuits that control sequences of movements

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Substantia Nigra – contain neurons that project to the caudate nucleus & putamen, degeneration of these neurons causes
Parkinson’s disease.

Hindbrain
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Surrounds the 4th ventricle ; it consists of metencephalon & myelencephalon

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Metencephalon consists of the pons and the cerebellum. Cerebellum

(little brain)

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plays an important role in motor control. It is also involved in some cognitive functions such as attention & language, and probably in some emotional functions such as regulating fear and pleasure responses.

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It does not initiate movement, but it contributes to coordination, precision, and accurate timing. It receives input from sensory systems and from other parts of CNS, & integrates these inputs to fine tune motor activity.

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Because of this fine-tuning function, damage to the cerebellum does not cause paralysis, but instead produces disorders in fine movement, equilibrium, posture, and motor learning.

Myelencephalon
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It contains medulla oblongata (oblong marrow) which plays vital functions such as regulation of the cardiovascular system, respiration & skeletal muscle tonus.

The Spinal Cord
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extends down to the space between the 1st
& 2nd lumbar vertebrae; it does not extend the entire length of the vertebral column. It is around 45 cm (18 in) in men and around 43 cm
(17 in) long in women.
The enclosing bony vertebral column protects the relatively shorter spinal cord.

Spinal Cord
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The spinal cord functions primarily in the transmission of neural signals between the brain and the rest of the body but also contains neural circuits that can independently control numerous reflexes and central pattern generators.

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The spinal cord has three major functions: A. Serve as a conduit for motor information, which travels down the spinal cord. B. Serve as a conduit for sensory information, which travels up the spinal cord.
C. Serve as a center for coordinating certain reflexes.

Peripheral nervous system consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the CNS to the limbs and organs.
 Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood-brain barrier, leaving it exposed to toxins and mechanical injuries.
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The peripheral nervous system is divided into the somatic nervous system and the autonomic nervous system

Spinal Nerves
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carry motor, sensory, and autonomic signals between the spinal cord and the body. Humans have 31 left-right pairs of spinal nerves, each roughly corresponding to a segment of the vertebral column: 8 cervical spinal nerve pairs, 12 thoracic pairs, 5 lumbar pairs, and 5 sacral pairs and 1 coccygeal pair

Cranial Nerves
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emerge directly from the brain, in contrast to spinal nerves which emerge from segments of the spinal cord. In humans, there are 12 pairs of cranial nerves.
Only the first and the second pair emerge from the cerebrum; the remaining 10 pairs emerge from the brainstem. Autonomic Nervous
System
acts as a control system functioning largely below the level of consciousness, and controls visceral functions.
 The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils, micturition
(urination), and sexual arousal. Whereas most of its actions are involuntary, some, such as breathing, work in tandem with the conscious mind.
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Divisions of ANS
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Sympathetic and parasympathetic divisions typically function in opposition to each other. But this opposition is better termed complementary in nature rather than antagonistic. The sympathetic division typically functions in actions requiring quick responses. The parasympathetic division functions with actions that do not require immediate reaction. Consider sympathetic as
"fight or flight" and parasympathetic as "rest and digest".

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However, many instances of sympathetic and parasympathetic activity cannot be ascribed to "fight" or "rest" situations. For example, standing up from a reclining or sitting position would entail an unsustainable drop in blood pressure if not for a compensatory increase in the arterial sympathetic tonus.
Another example is the constant, second to second modulation of heart rate by sympathetic and parasympathetic influences, as a function of the respiratory cycles.

◦Thank you for listening…