Download Symptoms: visual disturbances, ______, loss of

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