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I. Nervous system Introduction A. Functions of the Nervous System a. Sensory input- information gathered by sensory receptors about internal and external changes b. ______________- interpretation of sensory input c. Motor output- activation of ______________ (muscles & glands) produces a response B. Divisions of the Nervous System a. Central Nervous System (_____) i. ___________ and spinal cord ii. Integration and command center b. Peripheral nervous system (_____) i. Paired ____________ and cranial nerves carry messages to and from the CNS C. Peripheral Nervous System a. Functions i. Sensory (___________) division 1. Somatic afferent fibers- convey impulses from skin, skeletal muscles, and joints 2. Visceral afferent fibers- convey impulses from visceral organs ii. Motor (___________) division 1. Transmits impulses from the CNS to effector organs 2. Somatic (___________) nervous system a. Conscious control of skeletal muscles 3. Autonomic (___________) nervous system (ANS) a. Visceral motor nerve fibers b. Regulated smooth muscle, cardiac muscle, and glands c. Functional divisions i. Sympathetic ii. Parasympathetic D. Histology of nervous system a. Two cell types i. ___________ - excitable cells that transmit electrical signals 1. Characteristics a. Long lived, amitotic, high metabolic rate, electrical signaling and cell-to-cell interactions during development 2. Parts of a neuron a. ___________ - biosynthetic center of a neuron, network of neurofibrils (neurofilaments) i. Axon hillock- cone shaped area where the axon arises ii. Clusters of cell bodies in the CNS are called nuclei, and in the PNS are called ganglia b. Processes- bundles are classed tracts (CNS) and nerves (PNS) i. Dendrites 1. Short, tapering and diffusely branched 2. Receptive (input) region of the neuron 3. Convey electrical signals ___________ the cell body ii. Axons 1. One long axon per cell body 2. Long axons are called nerve fibers 3. Knoblike axon terminals a. Secretory region of the neuron b. Release neurotransmitters to excite or inhibit other cells 4. Conducting region of the neuron, generates and transmits nerve impulses ___________ from the cell body 5. Unmyelinated axons are thin nerve fibers and one Schwann cell can incompletely enclose 15 or more unmyelinated axons 3. Structural classifications of neurons a. ___________ - 1 axon and several dendrites (most abundant) b. Bipolar- 1 axon and 1 dendrite (______) c. ___________ (pseudounipolar)- single, short process that has two branches i. Peripheral process- most distal branch ii. Central process- branch entering the CNS 4. Functional classification of neurons a. Sensory (___________)- transmit impulses from sensory receptors toward the CNS b. Motor (___________)- carries impulses from the CNS to effectors c. Interneurons (association neurons)- Shuttle signals through CNS pathways ii. Neuroglia (glial cells)- supporting cells 1. ___________ (CNS) a. Most abundant, versatile, and highly branched glial cells b. Cling to neurons, synaptic endings, and capillaries c. Support and brace neurons d. Determine capillary permeability e. Guide migration of young neurons f. Control chemical environment g. Information processing in the brain 2. ___________ (CNS) a. Migrate toward injured neurons b. Phagocytize microorganisms and neuronal debris 3. ___________ cells (CNS) a. May be ciliated b. Line the central cavities of the brain and spinal column c. Separate the CNS interstitial fluid from the cerebrospinal fluid in the cavities 4. ___________ (CNS) a. Branched cells b. Processes wrap CNS nerve fibers, forming insulating myelin sheaths i. Myelin sheath- concentric ________ of Schwann cell membrane ii. Neurilemmal- peripheral bulge of Schwann cell cytoplasm iii. Nodes of Ranvier-myelin sheath gaps between Schwann cells, sites where axon collaterals can emerge iv. CNS 1. Formed by processes of oligodendrocytes, Nodes of Ranvier not present, no ___________, thinnest fibers are unmyelinated v. _______ matter 1. Dense collections of myelinated fibers vi. _______ matter 1. Mostly neuron cell bodies and unmyelinated fibers 5. ___________ cells (PNS) a. Surround neuron cell bodies in the PNS 6. ___________ cells (PNS) a. Surround peripheral nerve fibers and form myelin sheaths b. Vital to regeneration of damaged peripheral nerve fibers E. Membrane potentials a. Role of membrane ion channels i. Proteins serve as membrane ion channels ii. Two main types of channels 1. Leakage (___________) channels- always open 2. ___________ channels a. Three types i. Chemical gated (ligand-gated) channels- open with binding of a specific neurotransmitter ii. ________-gated channels- open and close in response to changes in membrane potentials iii. Mechanically gated channel- open and close in response to physical deformation of receptors b. When gated channels are _______ i. Ions diffuse quickly across the membrane along their electrochemical gradients 1. Chemical gradients go from high to low 2. Electrical gradients go from low to high ii. Ion flow creates an electrical current and voltage changes across the membrane b. Resting membrane potential i. Potential difference across the membrane of a resting cell 1. Approximately -_______ in neurons ii. Generated by 1. Differences in ____ (intracellular fluid) and ____ (extracellular fluid) 2. Differential permeability of the plasma membrane iii. Differences in ionic makeup 1. ICF has _______ concentration of Na+ and Cl- than ECF 2. ICF has _______ concentration of K+ and negatively charged proteins (A-) than ECF iv. Sodium-potassium pump stabilizes the resting membrane potential by maintaining the concentration gradients for Na+ and K+ c. Membrane potentials act as signals i. Changes when concentrations of _______ across the membrane change and permeability of membrane to ions changes ii. Signals used to receive, ___________, and send information iii. Two types of signals 1. Graded potentials- incoming short-distance signals a. ___________ i. Reduction in membrane potential ii. Inside of the membrane becomes less negative than the resting potential iii. Increases the probability of producing a nerve impulse b. ___________ i. An increase in membrane potential ii. Inside of the membrane becomes more negative than the resting potential iii. Reduces the probability of producing a nerve impulse c. Occur when a stimulus causes gated ion channels to open d. Decrease in magnitude with distance as ions flow and diffuse through leakage channels 2. __________________ - long-distance signals of axons a. Brief reversal of membrane potential with an amplitude of ~100mV b. Occur in muscle cells and axons of neurons c. Does not decrease in magnitude over distance F. Nerve fiber classification a. Group ___ fibers i. Large diameter, myelinated somatic sensory and motor fibers b. Group ___ fibers i. Intermediate diameter, lightly myelinated ANS fibers c. Group ___ fibers i. Smallest diameter, unmyelinated ANS fibers G. The synapse a. A ___________ that mediated information transfer form one neuron to another neuron or an effector cell b. Presynaptic neuron- conducts impulses ___________ the synapse c. Postsynaptic neuron- transmits impulses ________ from the synapse d. Types of synapses i. Axodendritic- between the axon of one neuron and the ___________ of another ii. Axosomatic- between the axon of one neuron and the _______ of another iii. Less common 1. Axoaxonic (axon to axon) 2. Dendrodendritic (dendrite to dendrite) 3. Dendrosomatic (dendrite to soma) e. Electrical ___________ i. Less common than chemical synapses ii. Neurons are electrically coupled (joined by gap junctions) iii. Communication is very _________ and may be unidirectional or bidirectional iv. Important in embryonic nervous tissue and some brain regions f. Chemical synapses i. Specialized in the ___________ of neurotransmitters ii. Composed of two parts 1. ________ terminal of the presynaptic neuron 2. ___________ region on the postsynaptic neuron g. Synaptic cleft i. Fluid-filled space separating the presynaptic and postsynaptic neurons ii. Prevents nerve impulses from ___________ passing from one neuron to the next iii. Transmission across the synaptic cleft 1. Is a chemical event that involves the release, ___________, and binding of neurotransmitters that ensures unidirectional communication between neurons H. Neurotransmitters and their receptors a. Most neurons make two or more neurotransmitters, which are released at different stimulation frequencies b. _____ or more neurotransmitters have been identified c. Classified by ___________ Structure and by Function i. Acetylcholine (Ach) 1. Released at neuromuscular ___________ and some ANS neurons 2. Synthesized by enzyme choline acetyltransferase 3. Degraded by the ___________ acetylcholinesterase (AChE) ii. Biogenic amines include 1. Catecholamines a. ___________, norepinephrine (NE), and epinephrine 2. Indolamines a. Serotonin and hisamine 3. Broadly distributed in the ___________ 4. Play roles in ___________ behaviors and the biological clock iii. Amino acids 1. GABA (Gamma-aminobutyric acid) I. 2. Glycine 3. ___________ 4. Glutamate iv. Peptides (neuropeptides) 1. Substance P a. Mediator of _______ signals 2. Endorphins a. Act as natural opiates; ________ pain perception 3. Gut-brain peptides a. Somatostatin and cholecystokinin v. Purines such as ATP 1. Act in both the CNS and PNS 2. Provoke ________ sensation vi. Gases and lipids 1. Nitric oxide (NO) a. Involved in _________ and memory 2. Carbon monoxide (CO) a. Regulator of cGMP in the brain 3. Endocannabinoids a. Lipid soluble and involved in learning and _________ d. Direct action i. Neurotransmitter binds to channel-linked receptor and opens ion channels ii. Promotes ___________ responses 1. Ach and amino acids e. Indirect action i. Neurotransmitter binds to a G-protein-linked receptor and acts through an intracellular second messenger ii. Promotes long –lasting effects 1. Biogenic amines, neuropeptides, and dissolved gases f. Types of ___________ receptors i. Channel-linked receptors ii. G protein-linked receptors Basic concepts of neural integration a. Neuronal pools ___________ incoming information and forward the processes information to other destinations b. Simple neuronal pool i. Single presynaptic fiber branches and synapses with ___________ neurons in the pool ii. Discharge zone- neurons most ___________ associated with the incoming fiber iii. Facilitated zone- neurons ___________ away from incoming fiber c. Types of circuits in neuronal pools i. ___________ circuit 1. One incoming fiber stimulated an ever-increasing number of fibers, often amplifying circuits 2. May affect a single pathway or several 3. Common in both sensory and motor systems ii. ___________ circuit 1. Opposite of diverging circuits; strong stimulation or inhibition 2. Also common in sensory and motor systems iii. Reverberating (___________) circuit 1. Chain of neurons containing collateral synapses with previous neurons in the chain iv. Parallel after-discharge circuit 1. Incoming fiber stimulates several neurons in parallel arrays to stimulate a common output cell d. Neural processing i. Serial processing 1. Input travels along one pathway to a ___________ destination 2. Works in all-or-none manner to produce a specific response 3. Ex. reflexes ii. Parallel processing 1. Input travels along ___________ pathways 2. Important in higher-level mental functioning 3. Ex. Smell reminds you of an odor and associated experience J. Developmental aspects of neurons a. Originates from the neural ________ and neural _________ formed from ectoderm b. Neural tube becomes the CNS c. Cell ___________ i. About 2/3 of neurons die before birth ii. Death results in cells that fail to make functional synaptic contacts iii. Many cells also die due to ___________ (programmed cell death) during development K. Multiple Sclerosis (MS) a. An autoimmune disease that mainly affects __________ adults b. Myelin sheaths in the CNS become nonfunctional scleroses c. Shunting and short-circuiting of nerve __________ occurs, impulse condition slows and eventually ceases d. Symptoms: visual disturbances, ___________, loss of muscular control, speech disturbances, and urinary incontinence. II. Central Nervous System (CNS) A. Cephalization a. Evolutionary development of the anterior portion of the CNS b. Increases the number of neurons in the head c. Highest level is reached in the human brain B. The brain a. Embryonic development i. Neural plate forms from ectoderm ii. Neural plate invaginates to form a neural groove and neural folds iii. Neural groove fuses dorsally to form the neural tube 1. Anterior portion of the neural tube becomes three primary brain vesicles a. Prosencephalon-forebrain i. Gives rise to the telencephalon (cerebrum) and diencephalon (thalamus, hypothalamus, epithalamus, and retina) b. Mesencephalon- midbrain c. Rhombencephalon- hindbrain i. Gives rise to the metencephalon (pons and cerebellum) and myelencephalon (medulla oblongata) iv. Effect of space restriction on brain development 1. Midbrain flexure and cervical flexure cause forebrain to move toward the brain stem 2. Cerebral hemispheres grow posteriorly and laterally 3. Cerebral hemisphere surfaces crease and fold into convolutions b. Regions and organization i. Adult brain regions 1. Cerebral hemispheres 2. Diencephalon 3. Brain stem (midbrain, pons, and medulla) 4. Cerebellum ii. Spinal cord 1. Central cavity surrounded by a gray matter core 2. External white matter composed of myelinated fiber tracts iii. Brain 1. Similar pattern with additional areas of gray matter 2. Nuclei in cerebellum and cerebrum 3. Cortex of cerebellum and cerebrum c. Ventricles of the brain i. Contain cerebrospinal fluid 1. Two C-shaped lateral ventricles in the cerebral hemispheres 2. Third ventricle in the diencephalon 3. Fourth ventricle in the hindbrain, dorsal to the pons d. Cerebral hemispheres i. Surface markings: ridges (gyri), shallow grooves (sulci), and deep grooves (fissures) 1. Central sulcus- separates the precentral gyrus of the frontal lobe and the postcentral gyrus of the parietal lobe 2. Longitudinal fissure- separates the two hemispheres 3. Transverse cerebral fissure- separates the cerebrum and the cerebellum ii. Lobes 1. Frontal 2. Parietal 3. Temporal 4. Occipital 5. Insula iii. Cerebral cortex 1. Thin superficial layer of gray matter 2. 40% of the mass of the brain 3. Site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding 4. Each hemisphere connects to the contralateral side of the body a. Left controls language, math, and logic b. Right controls insight, visual-spacial skills, intuition, and artistic skill 5. Lateralization of cortical function in the hemispheres 6. Functional areas a. Motor areas- control voluntary movement i. Primary motor cortex- conscious control of precise, skilled, voluntary movements ii. Premotor cortex- controls learned, repetitious, or patterned motor skills iii. Broca’s area- motor speech area the directs muscle of the tongue iv. Frontal eye fold- controls voluntary eye movement b. Sensory areas- conscious awareness of sensation i. Primary somatosensory cortex- Capable of spatial discrimination: identification of body region being stimulated ii. Somatosensory association cortex- Determines size, texture, and relationship of parts of objects being felt iii. Visual areas- Receives visual information from the retinas iv. Auditory areas- Interprets information from inner ear as pitch, loudness, and location, stores memories of sounds and permits perception of sounds v. Olfactory cortex- Region of conscious awareness of odors vi. Gustatory cortex- Involved in the perception of taste vii. Visceral sensory area- Conscious perception of visceral sensations, e.g., upset stomach or full bladder viii. Vestibular cortex- Responsible for conscious awareness of balance (position of the head in space) c. Association areas- integrate diverse information i. Multimodal association area- receive input from multiple sensory areas, and sends output to multiple areas 1. Anterior association area- Involved with intellect, cognition, recall, and personality, contains working memory needed for judgment, reasoning, persistence, and conscience, development depends on feedback from social environment 2. Posterior association area- Plays a role in recognizing patterns and faces and localizing us in space, involved in understanding written and spoken language (Wernicke’s area) 3. Limbic association area- Provides emotional impact that helps establish memories e. Diencephalon i. Encloses the third ventricle ii. Three parts 1. Thalamus- 80% of the diencephalon, sorts, edits, and relays information 2. Hypothalamus- autonomic control center for many visceral functions: blood pressure, rate and force of heartbeat, digestive tract motility. Center of emotional response. Regulates body temperature, food intake, water balance, and thirst. Regulated sleep and sleep cycle, controls release of hormones from the pituitary gland 3. Epithalamus- secretes melatonin that regulates sleep cycle f. Brain stem i. Midbrain- control cranial nerves III (oculomotor) and IV (trochlear) ii. Pons- Connect higher brain centers and the spinal cord, Relay impulses between the motor cortex and the cerebellum iii. Medulla oblongata- Autonomic reflex centers, adjusts force and rate of heart contraction, adjusts blood vessel diameter for blood pressure regulation, generate respiratory rhythm, control rate and depth of breathing, regulate, vomiting, hiccupping, swallowing, coughing, sneezing g. Cerebellum i. Subconsciously provides precise timing and appropriate patterns of skeletal muscle contraction ii. Receives impulses from the cerebral cortex of the intent to initiate voluntary muscle contraction iii. Recognizes and predicts sequences of events during complex movements iv. Plays a role in non-motor functions such as word association and puzzle solving h. Functional brain systems i. Limbic system 1. Emotional or affective brain a. Amygdala—recognizes angry or fearful facial expressions, assesses danger, and elicits the fear response b. Cingulate gyrus—plays a role in expressing emotions via gestures, and resolves mental conflict 2. Puts emotional responses to odors- Example: skunks smell bad 3. The limbic system interacts with the prefrontal lobes, therefore: a. We can react emotionally to things we consciously understand to be happening b. We are consciously aware of emotional richness in our lives 4. Hippocampus and amygdala—play a role in memory ii. Reticular formation 1. RAS (reticular activating system) a. Sends impulses to the cerebral cortex to keep it conscious and alert b. Filters out repetitive and weak stimuli (~99% of all stimuli!) c. Severe injury results in permanent unconsciousness (coma) 2. Motor function a. Helps control coarse limb movements b. Reticular autonomic centers regulate visceral motor functions: Vasomotor, Cardiac, Respiratory centers C. Higher mental functions a. Brian wave patterns and the EEG i. EEG- record electrical activity that accompanies brain function and measures electrical potential differences between cortical areas. Used to diagnose and localize brain lesions, tumors, infracts, infections, abscesses, and epileptic lesions 1. Flat EEG is clinical evidence of death ii. Brain waves-patterns of neurological activity. Each persons’ brain waves are unique 1. Alpha waves (8–13 Hz)—regular and rhythmic, low-amplitude, synchronous waves indicating an “idling” brain 2. Beta waves (14–30 Hz)—rhythmic, less regular waves occurring when mentally alert 3. Theta waves (4–7 Hz)—more irregular; common in children and uncommon in adults 4. Delta waves (4 Hz or less)—high-amplitude waves seen in deep sleep and when reticular activating system is damped, or during anesthesia; may indicate brain damage iii. Brain waves change with age, sensory stimuli, brain disease, and the chemical state of the body b. c. d. e. iv. Epilepsy 1. A victim of epilepsy may lose consciousness, fall stiffly, and have uncontrollable jerking 2. Not associated with intellectual impairments 3. Occurs in 1% of the population 4. Absence seizures, or petit mal- Mild seizures seen in young children where the expression goes blank 5. Tonic-clonic (grand mal) seizures- Victim loses consciousness, bones are often broken due to intense contractions, may experience loss of bowel and bladder control, and severe biting of the tongue Consciousness i. Conscious perception of sensation ii. Voluntary initiation and control of movement iii. Capabilities associated with higher mental processing (memory, logic, judgment, etc.) iv. Loss of consciousness (e.g., fainting or syncopy) is a signal that brain function is impaired v. Clinically defined on a continuum that grades behavior in response to stimuli: Alertness, Drowsiness (lethargy), Stupor, Coma Sleep and sleep-wake cycles i. State of partial unconsciousness from which a person can be aroused by stimulation ii. Two major types of sleep (defined by EEG patterns) 1. Nonrapid eye movement (NREM): State of partial unconsciousness from which a person can be aroused by stimulation 2. Rapid eye movement (REM)- People deprived of REM sleep become moody and depressed, REM sleep may be a reverse learning process where superfluous information is purged from the brain iii. Sleep disorders 1. Narcolepsy- Lapsing abruptly into sleep from the awake state 2. Insomnia- Chronic inability to obtain the amount or quality of sleep needed 3. Sleep apnea- Temporary cessation of breathing during sleep Language i. Language implementation system 1. Basal nuclei 2. Broca’s area and Wernicke’s area (in the association cortex on the left side) 3. Analyzes incoming word sounds 4. Produces outgoing word sounds and grammatical structures ii. Corresponding areas on the right side are involved with nonverbal language components Memory i. Storage and retrieval of information ii. Two stages of storage 1. Short-term memory (STM, or working memory)—temporary holding of information; limited to seven or eight pieces of information 2. Long-term memory (LTM) has limitless capacity iii. Factors that affect transfer from STM to LTM 1. Emotional state—best if alert, motivated, surprised, and aroused 2. Rehearsal—repetition and practice 3. Association—tying new information with old memories 4. Automatic memory—subconscious information stored in LTM iv. Declarative memory (factual knowledge) 1. Explicit information 2. Related to our conscious thoughts and our language ability 3. Stored in LTM with context in which it was learned v. Nondeclarative memory 1. Less conscious or unconscious 2. Acquired through experience and repetition 3. Best remembered by doing; hard to unlearn 4. Includes procedural (skills) memory, motor memory, and emotional memory 5. Procedural memory 6. Motor memory 7. Emotional memory D. Protection of brain a. Bone (skull) b. Membranes (Meninges) i. Cover and protect the CNS ii. Protect blood vessels and enclose venous sinuses iii. Contain cerebrospinal fluid (CSF) iv. Form partitions in the skull v. Three layers 1. Dura mater, Arachnoid mater, Pia mater c. Watery cushion (Cerebrospinal fluid) i. Composition: Watery solution, less protein and different ion concentrations than plasma, constant volume ii. Functions 1. Gives buoyancy to the CNS organs 2. Protects the CNS from blows and other trauma 3. Nourishes the brain and carries chemical signals d. Blood-brain barrier i. Helps maintain a stable environment for the brain ii. Separates neurons from some blood borne substances iii. Absent in some areas, e.g., vomiting center and the hypothalamus, where it is necessary to monitor the chemical composition of the blood E. Homeostatic imbalances in the brain a. Traumatic brain injuries i. Concussion—temporary alteration in function ii. Contusion—permanent damage iii. Subdural or subarachnoid hemorrhage—may force brain stem through the foramen magnum, resulting in death iv. Cerebral edema—swelling of the brain associated with traumatic head injury b. Cerebrovascular accidents (CVAs)(strokes) i. Blood circulation is blocked and brain tissue dies, e.g., blockage of a cerebral artery by a blood clot ii. Typically leads to hemiplegia, or sensory and speed deficits iii. Transient ischemic attacks (TIAs)—temporary episodes of reversible cerebral ischemia iv. Tissue plasminogen activator (TPA) is the only approved treatment for stroke c. Degenerative brain disorders i. Alzheimer’s disease (AD): a progressive degenerative disease of the brain that results in dementia ii. Parkinson’s disease: degeneration of the dopamine-releasing neurons of the substantia nigra iii. Huntington’s disease: a fatal hereditary disorder caused by accumulation of the protein huntingtin that leads to degeneration of the basal nuclei and cerebral cortex F. The spinal cord a. Embryonic development i. By week 6, there are two clusters of neuroblasts 1. Alar plate—will become interneurons; axons form white matter of cord 2. Basal plate—will become motor neurons; axons will grow to effectors ii. Neural crest cells form the dorsal root ganglia sensory neurons; axons grow into the dorsal aspect of the cord b. Gross anatomy and protection i. Location 1. Begins at the foramen magnum 2. Ends as conus medullaris at L1 vertebra ii. Functions 1. Provides two-way communication to and from the brain 2. Contains spinal reflex centers iii. Protections 1. Bone, meninges, and CSF 2. Cushion of fat and a network of veins in the epidural space between the vertebrae and spinal dura mater 3. CSF in subarachnoid space iv. Spinal nerves 1. 31 pairs v. Cervical and lumbar enlargements 1. The nerves serving the upper and lower limbs emerge here vi. Cauda equina 1. The collection of nerve roots at the inferior end of the vertebral canal c. Cross –sectional anatomy i. Two lengthwise grooves divide cord into right and left halves 1. Ventral (anterior) median fissure 2. Dorsal (posterior) median sulcus ii. Pathway Generalizations 1. Pathways decussate (cross over) 2. Most consist of two or three neurons (a relay) 3. Most exhibit somatotopy (precise spatial relationships) 4. Pathways are paired symmetrically (one on each side of the spinal cord or brain) iii. Ascending Pathways 1. Consist of three neurons 2. First-order neuron a. Conducts impulses from cutaneous receptors and proprioceptors, Branches diffusely as it enters the spinal cord or medulla, Synapses with second-order neuron 3. Second-order neuron a. Interneuron, Cell body in dorsal horn of spinal cord or medullary nuclei, Axons extend to thalamus or cerebellum 4. Third-order neuron a. Interneuron, Cell body in thalamus, Axon extends to somatosensory cortex iv. Dorsal Column-Medial Lemniscal Pathways 1. Transmit input to the somatosensory cortex for discriminative touch and vibrations v. Anterolateral Pathways 1. Transmit pain, temperature, and coarse touch impulses within the lateral spinothalamic tract vi. Spinocerebellar Tracts 1. Convey information about muscle or tendon stretch to the cerebellum vii. Descending Pathways and Tracts 1. Deliver efferent impulses from the brain to the spinal cord a. Direct pathways—pyramidal tracts b. Indirect pathways—all others 2. Involve two neurons: a. Upper motor neurons i. Pyramidal cells in primary motor cortex b. Lower motor neurons i. Ventral horn motor neurons ii. Innervate skeletal muscles d. Spinal cord trauma and disorders i. Functional losses 1. Parasthesias- Sensory loss 2. Paralysis- Loss of motor function a. Flaccid paralysis—severe damage to the ventral root or ventral horn cells i. Impulses do not reach muscles; there is no voluntary or involuntary control of muscles. Muscles atrophy b. Spastic paralysis—damage to upper motor neurons of the primary motor cortex i. Spinal neurons remain intact; muscles are stimulated by reflex activity. No voluntary control of muscles 3. Transection a. Cross sectioning of the spinal cord at any level b. Results in total motor and sensory loss in regions inferior to the cut c. Paraplegia—transection between T1 and L1 d. Quadriplegia—transection in the cervical region 4. Poliomyelitis a. Destruction of the ventral horn motor neurons by the poliovirus b. Muscles atrophy c. Death may occur due to paralysis of respiratory muscles or cardiac arrest d. Survivors often develop postpolio syndrome many years later, as neurons are lost 5. Amyotrophic Lateral Sclerosis (ALS) a. Also called Lou Gehrig’s disease b. Involves progressive destruction of ventral horn motor neurons and fibers of the pyramidal tract c. Symptoms—loss of the ability to speak, swallow, and breathe d. Death typically occurs within five years e. Linked to glutamate excitotoxicity, attack by the immune system, or both G. Developmental aspects of CNS a. CNS is established during the first month of development b. Gender-specific areas appear in both brain and spinal cord, depending on presence or absence of fetal testosterone c. Maternal exposure to radiation, drugs (e.g., alcohol and opiates), or infection can harm the developing CNS d. Smoking decreases oxygen in the blood, which can lead to neuron death and fetal brain damage e. The hypothalamus is one of the last areas of the CNS to develop f. Visual cortex develops slowly over the first 11 weeks g. Neuromuscular coordination progresses in superior-to-inferior and proximal-to-distal directions along with myelination h. Age brings some cognitive declines, but these are not significant in healthy individuals until they reach their 80s i. Shrinkage of brain accelerates in old age j. Excessive use of alcohol causes signs of senility unrelated to the aging process III. Peripheral Nervous System (PNS) A. Sensory receptors and sensation a. Sensory receptors b. Sensory integration: from sensation to perception B. Transmission lines: Nerves and their structure and repair a. Nerves and associated ganglia b. Cranial nerves C. Motor endings and motor activity a. Peripheral motor endings b. Motor integration: from intention to effect D. Reflex activity a. The reflex arc b. Spinal reflexes c. Developmental aspects of the peripheral nervous system IV. Autonomic Nervous System (ANS) A. Introduction a. Comparison of somatic and autonomic nervous systems b. ANS divisons B. ANS anatomy a. C. ANS physiology D. Homeostatic imbalances of the ANS E. Developmental aspects of ANS V. Special Senses A. Eye and Vision B. Chemical senses: Taste and Smell C. The Ear: Hearing and Balancing D. Developmental aspects