Anatomy and Physiology nervous system PDF

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Anatomy and Physiology lecture notes -> review notes of the nervous system...

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ANAPHY REVIEWER

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NERVOUS SYSTEM  Master control and communication system of the body  Communicates with body cells using electrical impulses which are rapid and specific and cause almost immediate responses FUNCTION OF THE NERVOUS SYSTEM 1. Sensory Input  Gathering information  To monitor changes occurring inside and outside the body  Changes: stimuli  Sensory organs 2.   3.  

Integration To process and interpret sensory input and decide whether action is needed Occurs in the CNS (brain) Motor Output A response to integrated stimuli Activates muscles or glands (effectors)

Cranial nerves: carry impulses to and from the brain

b) Functions  These nerves serve as communication lines among sensory organs, the brain and spinal cord, and glands/muscles  Link all parts of the body by carting impulses from the sensory receptors to the CNS and from the CNS to the appropriate glands or muscles NERVOUS SYSTEM BASED ON FUNCTIONAL CLASSIFICATION 1. Sensory (Afferent) Division  Afferent: towards the CNS  Consists of nerves (composed of many individual nerve fibers) that convey impulses to the CNS from sensory receptors located in various parts of the body  Keeps the body constantly informed of events going on both inside and outside the body  Acts as spy that detects different changes happening in and out the body

ORGANIZATION OF THE NERVOUS SYSTEM

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NERVOUS SYSTEM BASED ON STRUCTURAL CLASSIFICATION 1. Central Nervous System a) Organs  Brain and spinal cord b)    2.

Functions Integration; command center Interpret incoming sensory information Issue instructions based on past experience and current conditions

Peripheral Nervous System a) Nerves extending from the brain and spinal cord  Spinal nerves: carry impulses to and from the spinal cord

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Somatic Sensory Fibers  soma = body  Sensory fibers delivering impulses from the skin, skeletal muscles, and joints

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Visceral Sensory Fibers  Transmitting impulses from the visceral organs

Motor (Efferent) Division Carries impulses from the CNS to effector organs, the muscles and glands; that is, they effect (bring about or cause) a motor response Output to the integrated NS Issue fibers that carry impulses away from the CNS organs a) Somatic Nervous System  Allows us to consciously, or voluntarily, control our skeletal muscles  Voluntary nervous system  Not all skeletal muscle activity controlled by this motor division is voluntary – stretch reflex b)

Autonomic Nervous System  Regulates events that are automatic, or involuntary, such as the activity of smooth muscle, cardiac muscle, and glands  Involuntary nervous system which has two parts – what one stimulates, the other inhibits o Sympathetic  vigorous and strenuous acts o Parasympathetic  Inhibit certain stimulus

NERVE TISSUE: STRUCTURE AND FUNCTION

TWO PRINCIPAL TYPES OF CELLS  Supporting Cells: mainly for support  Neurons: send electrical impulses SUPPORTING CELLS  Are lumped or grouped together in the CNS as neuroglia (nerve glue, glial cells / glia)  General Functions of Neuroglia: support, insulate, and protect delicate neurons 1. Astrocytes 2. Microglia 3. Ependymal 4. Oligodendrocytes 1.   

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ASTROCYTES Abundant star-shaped cells that account nearly half of neural tissue Their numerous projections have swollen ends that cling to neurons, bracing them and anchoring them to their nutrient supply lines – blood capillaries Form a living barrier between capillaries and neurons, help determine capillary permeability, and play a role in making exchanges between the two  Help protect the neurons from harmful substances that might be in the blood Help control the chemical environment in the brain by “mopping up” leaked potassium ions, which are involved in generating a nerve impulse, and recapturing chemicals released for communication purposes

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OLIGODENDROCYTES Wrap their flat extensions (processes) tightly around the nerve fibers, producing fatty insulating coverings called myelin sheaths Exclusive to CNS only

The glial cells are said to be mitotic. They divide rapidly, while neurons don’t divide. Consequently, most brain tumors are gliomas – tumors formed by neuroglia

PNS GLIAL CELLS 1. Satellite Cells  Protect neuron cell bodies

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MICROGLIA Spiderlike phagocytes that monitor the health of nearby neurons and dispose debris, such as dead brain cells and bacteria Immunity and self-defense

EPENDYMAL Line the central cavities of the brain and the spinal cord The beating of their cilia helps to circulate the cerebrospinal fluid that fills those cavities and forms a protective watery cushion around the CNS

2. Schwann Cells  Form myelin sheaths in the PNS NERVOUS TISSUE: NEURONS  Nerve cells  Highly specialized to transmit messages (nerve impulses) from one part of the body to another  Neurons differ structurally from one another, but they have many common features  Have a cell body that contains the nucleus and one or more slender processes extending from the cell body MAJOR REGIONS OF NEURONS 1. Cell Body  Is the metabolic center of the neuron  Its transparent nucleus contains a large nucleolus  The cytoplasm surrounding the nucleus contains the usual organelles, except that it lacks centrioles – amitotic  Contains Rough ER or Nissl Bodies and neurofibrils  Neurofibirils: intermediate filaments that are important in maintaining cell shape and are abundant in the cell body

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Processes Armlike processes or fibers, vary in length from microscopic to about 7ft in the tallest humans  The longest ones reach from the lumbar region of the spine to the great toe a) Dendrites  Neuron processes that convey incoming messages (electrical signals) toward the cell body  Neurons may have hundreds of branching dendrites (dendr = tree), depending on the neuron type b)   

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Axons Generate nerve impulses and typically conduct them away from the cell body Each neuron has only one axon, which arises from a conelike region of the cell body called the axon hillock An occasional axon gives off a collateral branch along its length, but all axons branch profusely at their terminal end, forming hundreds to thousands of axon terminals Axon terminals: contain hundreds of tiny vesicles, or membranous sacs, that contain chemicals called neurotransmitters When impulses reach the axon terminals, they stimulate the release of neurotransmitters into the extracellular space between neurons, or between a neuron and its target cell. Synaptic Cleft: a tiny gap that separates each axon terminal to the next neuron . Synapse: junction between nerves Synapse: where an impulse is transmitted from one neuron to another (syn = to clasp or join) Myelin sheaths Whitish, fatty material covering axons Has waxy appearance Protects and insulates the fibers and increases the transmission rate of nerve impulses. a) Axons outside the CNS are myelinated by Schwann Cells which wrap themselves around axons in a jelly-roll fashion (nodes of Ranvier: gaps or indentations at regular intervals)  Neurilemma: outermost part of plasma membrane external to the myelin sheath  Neurilemma: important role in fiber regeneration where peripheral nerve is damaged b) 

Oligodendrocytes Produce myelin sheaths around axons of the CNS

NEURON CELL BODY LOCATIONS  Most neuron cell bodies are found in the CNS  Nuclei: cluster of cell bodies within the bony skull or vertebral column  Ganglia: small collections of cell bodies outside the CNS; associated with PNS (can be found in a few sites outside the CNS in the PNS)  Ganglion: relay station for the ganglia signals  Interneurons: connect sensory and motor neurons

1.  2.  3.  4. 

Tracts Bundles of nerve fibers (neuron processes) running through the CNS Nerves Bundles of nerve fibers (neuron processes) running through the PNS White Matter Collections of myelinated fibers (tracts) Gray Matter Collections of mostly unmyelinated fibers and cell bodies

CENTRAL NERVOUS SYSTEM  Develops from the embryonic neutral tube    

NEURAL TUBE Becomes the brain and the spinal cord It extends the dorsal median plane Its opening becomes the ventricles  Four chambers within the brain  Filled with cerebrospinal fluid which used for cushioning and lubrication

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FOUR MAJOR REGIONS OF THE BRAIN 1. Cerebral Hemispheres 2. Diencephalon 3. Brain Stem 4. Cerebellum I.    

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CEREBRAL HEMISPHERES (PAIRED) Collectively called the cerebrum Most superior part of the brain Larger than the other three brain regions combined As they develop and grow, they enclose and obscure most of the brain stem (so many brain stem structures cannot be normally seen unless a sagittal region is made) The right and left hemisphere performs higher functions (interpret, touch, hear, speak) – sense organs for cognitive reasoning Have three basic regions:  a superficial cortex of gray matter  an internal are of white matter  basal nuclei – islands of matter situated deep within the white matter (innermost)

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GYRI Elevated ridges of tissue exhibited by the entire surface of the cerebral hemispheres Singular; twisters

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SULCI Shallow grooves separating gyri

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LOBES OF THE CEREBRUM Other fissures or sulci divide each cerebral hemisphere into these Named for the cranial bones that lie over them

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 FISSURES  Deeper grooves which are less numerous  Separates the right and left hemisphere - large regions of the brain  Longitudinal Fissure: single deep fissures that separates the cerebral hemisphere

 “little man”  Is a spatial map that has been used to show how much tissue in the primary somatic area is developed to sensory functions various 2. Cerebral Area Involved in Special Areas  Impulses from the special sense organs are interpreted in other cortical areas  Visual area is located in the posterior part of the occipital lobe bordering the lateral sulcus  Olfactory area us deep inside the temporal lobe     

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SURFACE LOBES OF THE CEREBRUM 1. Frontal Lobe  Recognizing  Motor skills  Higher level of recognition  Expressive language  Damage results to behavioral changes 2. Parietal Lobe  Tactile sensory information  Pressure  Pain  Touch  Process information corresponding to pressure and touch  Damage results to numbness 3. Occipital Lobe  Visual stimuli and information  Damage results to blindness and dyslexia

 PYRAMIDAL TRACT / CORTICOSPINAL TRACT  Major voluntary tract formed by the primary motor area which descends to the cord  Most of the neurons located here control body areas having the finest motor control – face, mouth, and hands  Motor homunculus is the body map on the motor cortex; spatial map 3. Broca’s Area  Motor Speech Area  Specialized cortical area involved in our ability to speak  Found at the base of the precentral gyrus (anterior to the central sulcus)  Base of the primary motor cortex  Damage to this area, which is only located in one hemisphere (usually left), causes the inability to say words properly 

4. Temporal Lobe  Interpreting sounds and language that we hear SPECIALIZED AREAS OF THE CEREBRUM 1. Primary Somatic Area  Located in the parietal lobe posterior to the central sulcus  Receives, localizes, and interprets impulses traveling from the body’s sensory receptors (except for the special senses)  Allows you to recognize pain, coldness (temperature), or light touch  Body regions with the most sensory receptors – the lips and fingertips – send impulses to neurons that make up a large part of the sensory area  Left side of the primary somatic sensory area receives impulses from the right side (vice versa) – Sensory pathways are crossed-pathways 

SENSORY HOMUNCULUS

PRIMARY MOTOR AREA Anterior to the central sulcus in the frontal lobe Sends impulses to skeletal muscles Allows us to consciously move our skeletal muscles The axons of these motor neurons form the pyramidal tract

OTHER SPECIALIZED AREAS  Intellectual reasoning and socially acceptable behavior  Posterior: recognize patterns and faces and blending of several inputs to understand the whole situation; abstract reasoning  Anterior and posterior association area 

Speech area (Wernicke’s): located at the junction of frontal, parietal, and occipital lobe

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REGIONS OF THE BRAIN: CEREBRUM 1. GRAY MATTER  Outer layer in the cerebral cortex  Composed mostly of neuron cell bodies 2.    

WHITE MATTER Fiber tracts deep to the gray matter Corpus callosum connect hemisphere Most of the remaining cerebral hemisphere tissue Composed of fiber tracts carrying impulses to, from, or within the cortex     

CORPUS CALLOSUM Very large fiber tract Connects the cerebral hemispheres Fiber tracts: commissures Arches above the structures of the brain stem and allow the cerebral hemispheres to communicate with one another  Important because some of the cortical functional areas are in only one hemisphere  Association fiber tracts connect areas within hemisphere  Protection fiber tracts connect the cerebrum with lower CNS centers – brain stem

1. THALAMUS  Encloses the third ventricle the brain  Relay station for sensory impulses passing upward sensory cortex  Transfers impulses to the correct part of the cortex for localization and interpretation – primary somatic sensory area  As impulses surge through it, crude recognition of whether the sensation is pleasant or unpleasant  Judgement center of the brain because it interprets 2.          

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BASAL NUCLEI Innermost portion Several islands of gray matter Buried deep within the white matter of the cerebral hemispheres Help regulate voluntary activities (skeletal muscles) Modify instruction sent into the skeletal muscle by primary motor cortex A tight band of projection fibers called the internal capsule, passes between the thalamus and the basal nuclei Damage: unable to walk/move properly because it mainly affects skeletal system  Parkinson’s Disease  Hereditary  All ages  Males are prone  New degenerative disorder  Neurons undergo degeneration  Tremors, stiffness, and slow movement  Huntington’s Disease  Both genders are affected  Younger are more vulnerable  Primarily affect our brain with a gradual loss in control of movement and memory, mental ability

REGIONS OF THE BRAIN: DIENCEPHALON

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DIENCEPHALON Interbrain Sits atop the brain stem and is enclosed by the cerebral hemispheres Made of three parts (major strucures):  Thalamus  Hypothalamus

Epithalamus

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HYPOTHALAMUS Under the thalamus Makes up the floor of the diencephalon Regulates temperature, water balance, metabolism Center for many drives and emotions Ex. Thirst, appetite, sex, pain, and pleasure Limbic System “emotional-visceral brain” Regulates the pituitary gland (an endocrine organ) and produces two hormones of its own Two hormones:  Thyrotropin  Corticotropin Pituitary Gland: hangs from the anterior floor of the hypothalamus by a slender stalk Mamillary bodies: reflex centers involved in olfaction (the sense of smell), bulge from the floor of the hypothalamus posterior to the pituitary gland Important autonomic nervous system – involuntary EPITHALAMUS Forms the roof of the third ventricle Important parts are the pineal gland (endocrine) and choroid plexus of the third ventricle Choroid plexus: knots of capillaries within each of the four ventricles, form the cerebrospinal fluid Ependymal cells possess tiny hairlike structures called cilia The layer of ependymal-derived cells surrounding the blood vessels of the choroid plexus functions mainly to produce cerebrospinal fluid Cilia regulates CSF Involved in melatonin secretion  Melatonin – sleep hormone and produced by pineal gland  Which type of functional classes of globular proteins ---- to diencephalon  Hormones maintain body homeostasis

III. BRAIN STEM  Is about the size of a thumb in diameter and approximately 3 inches (7.5 cm) long  Major structures:  Midbrain  Pons  Medulla Oblongata  Provides a pathway for ascending and descending tracts  Has many small gray matter areas  Produce the rigidly programmed autonomic behaviors necessary for survival.

 Some are associated with the cranial nerves and control vital activities such as breathing and blood pressure

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1. MIDBRAIN  A relatively small part of the brain stem  Extends from thee mammillary bodies to the pons inferiorly  Cerebral Aqueduct: tiny canal that travels through the midbrain, connects the third ventricle of the diencephalon to the fourth ventricle  Forms a canal between the ventricles located in third and fourth ventricles where cerebrospinal fluid will be located  Cerebral Peduncles: two bulging fiber tracts located in the midbrain, anteriorly that convey ascending and descending impulses  Little feet of the cerebrum  Cerebral Quadrigemina: four rounded protrusions that are dorsally located.  They reminded some anatomist of two pairs of twins (gemini).  These bulging nuclei are reflecx centers involves with vision and hearing.  Pupillary and auditory reflex  Smallest muscle that can be found in human body responsible for auditory reflex – stapes / stapedius muscle 2.    3.        

PONS Is the rounded structure that protrudes just below the midbrain Means “bridge” and this area of the brain stem is mostly fiber tracts (bundle of nerve fibers in the CNS). However, it does have important nuclei involved in the control of breathing. MEDULLA OBLONGATA Most inferior part of the brain stem Below the brain Merges into the spinal cord below without any obvious change in structure Like the pons, it is an important fiber tract area. Area where the pyramidal tracts (motor fibers) cross over to the opposite side Also contains many nuclei that regulate vistal visceral activities Contains centers that control heart rate, blood pressure, breathing, swallowing, and vomiting, among others. Fourth Ventricle lies posterior to the pons and medulla and anterior to the cerebellum

RETICULAR FORMATION  Extends to the entire length of the brain stem  Diffuse mass of gray matter along the brain stem  Its neurons are involved in motor control of the visceral organs  Controlling smooth muscle in the digestive tract 

RETICULAR ACTIVATING SYSTEM (RAS)  Plays a role in consciousness and the awake/sleep cycle

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Acts as a filter for the flood of sensory inputs that streams up the spinal cord and brain stem daily Filters weak or repetitive signals, but unusual or strong impulses do reach consciousness. Damage to this area can result in prolonged unconsciousness or coma

RADIATIONS TO CEREBRAL CORTEX  Wakes up consciousness  Will produce motor – efferent output  Descending motor projections to spinal cord  Ascending sensory tracts – touch, pain, temperature REGIONS OF THE BRAIN: CEREBELLUM  Large, cauliflower-like  Projects dorsally from under the occipital lobe of the cerebrum  Has two hemispheres and a convoluted surface  Also has an outer cortex made up of gray matter and an inner region of white matter  Difference to cerebrum, it does not have basal nuclei  Provides precise timing for skeletal muscle activity and controls our balance  Because of its activity, body movements are smooth and coordinated  It plays its role less well when it is sedated by alcohol  Fibers reach the cerebellum from the equilibrium apparatus of the inner ear, the eye, t...