• skeletal - attached to bone & skin, striated, voluntary, powerful
• cardiac - only in the heart, striated, involuntary
• smooth - walls of hollow organs, not striated, involuntary

• Excitability (responsiveness or irritability): ability to receive and respond to stimuli
• Contractility: ability to shorten when stimulated
• Extensibility: ability to be stretched
• Elasticity: ability to recoil to resting length

• Produces movement of bones or fluids (eg blood)
• Maintains posture and body position
• Stabilizes joints
• Generates heat (especially skeletal muscle)

• Each muscle is served by one artery, one nerve and one or more veins
• Each skeletal muscle fiber (cell) is supplied with a nerve ending which controls its activity
• The nerve cells that acivate skeletal muscle fibers are called somatic motor neurons. The axon of each motor neuron divides as it enters the muscle. The neuromuscular junction is the location where a motor neuron innervates a muscle cell (fiber)

• Epimysium: dense regular connective tissue surrounding entire muscle
• Perimysium: fibrous connective tissue surrounding fascicles (groups of muscle fibers)
• Endomysium: fine areolar connective tissue surrounding each muscle fiber

Muscles attach:

• Directly - epimysium of muscle is fused to the periosteum of bone or perichondrium of caritlage
• Indirectly - connective tissue wrappings extend beyond the muscle as a ropelike tendon or sheetlike aponeurosis

• Cylindrical cell 10 to 100 μm in diameter, up to 30 cm long
• Multiple peripheral nuclei
• Many mitochondria
• Also contain myofibrils, sacroplasmic reticulum, and T tubules

• Network of smooth endoplasmic reticulum surrounding each myofibril
• Pairs of terminal cisternae form perpendicular cross channels
• Functions in the regulation of intracellular Ca²⁺ levels

• Continuous with the sarcolemma
• Penetrate the cell's interior at each A band - I band junction
• Associate with the paired terminal cisternae to form triads that encircle each sacromere

• Densely packed, rodlike elements
• ~80% of cell volume
• Exhibit striations: perfectly aligned repeating series of dark A bands and light I bands
• (A = dark, I = light)

• smallest contractile unit (functional unit) of a muscle fiber
• The region of a myofibril between two successive Z discs
• Comprised of thick and thin myofilaments made of contractile proteins

• Thick filaments: run the entire length of an A band
• Thin filaments: run the length of the I band and partway into the A band
• Z disc: coin-shaped sheet of proteins that anchors the thin filaments and connects myofibrils to one another
• H zone: lighter mid-region where filaments do not overlap
• M line: line of protein that holds adjacent thick filaments together

• Composed of the protein myosin
• Myosin tail
• Myosin heads
• Binding sites for actin of thin filaments
• Binding sites for ATP

• Twisted double strand of fibrous protein actin
• Actin bears active sites for myosin head attachment during contraction
• Tropomyosin and troponin: regulatory proteins bound to actin

• In the relaxed state, thin and thick filaments overlap only slightly
• During contraction, myosin heads bind to actin, detach, and bind again, to propel the thin filments toward the M line
• As H zones shorten and disappear, sacromeres shorten, muscle cells shorten, and the whole muscle shortens

1. Excitation: neural stimulation at a neuromuscular junction (neurotransmitter: acetylcholine (ACh))
2. Excitation-contraction coupling: Links exciation of a muscle by the motor neuron to muscle contraction through the sacrolemma, T-tubules, and sacroplasmic reticulum
3. Cross-bridge cycling: Initiated by release of calcium from sarcoplasmic reticulum. Results in sliding of filaments

• Neuromuscular junction has 3 parts:
• Synaptic knob: expanded tip of an axon. Has vesicles which contain the neurotransmitter acetylcholine (ACh)
• Synaptic cleft narrow space between synaptic knob and endplate
• Motor endplate specialized region of the sacrolemma of a muscle fiber. Has many acetylcholine receptors

• Nerve impulse arrives at axon terminal
• ACh is released and binds with receptors on the sarcolemma
• This leads to the generation of an action potential (electrical current)
• ACh effects are quickly terminated by the enzyme acetylcholinesterase
• Prevents continued muscle fiber contraction in the absence of additional stimulation

• Action potential is propagated along sacrolemma to T tubules
• This stimulates Ca²⁺ release from sacroplasmic reticulum
• Ca²⁺ is necessary for contraction

• Role of calcium:
• Low intracellular calcium: active sites on actin are blocked by tropomyosin (myosin head cannot attach, muscle is relaxed)
• At high calcium, Ca²⁺ binds to troponin which changes shape and moves tropomyosin away from active site
• Events of the cross bridge cycle occur

• Continues as long as the Ca²⁺ signal and adequate ATP are present
• 4 steps
• Cross bridge formation: high-energy myosin head attaches to thin filament
• Power stroke: Myosin head pivots and pulls tin filament. ADP and Pi are released
• Cross bridge detachment: New ATP attaches to myosin head and the cross bridge detaches
• Reset of myosin head: as ATP is hydrolyzed to ADP + Pi, the myosin head returns to its pre-stroke high-energy position

• Contraction produces tension, the force exerted on the load or object to be moved
• Contraction does not always shorten a muscle:
• Isometric cotnraction: no shortening; muscle tension increases but does not exceed the load
• Isotonic contraction: muscle shortens because muscle tension exceeds the load

• Motor unit = a motor neuron and all (four to several hundred) muscle fibers it supplies
• Small motor units in muscles that control fine movements (figers, eyes)
• Large motor units in large weight-bearing muscles (thighs, hips)

• Constant, slightly contracted state of all muscles
• Due to spinal reflexes that activated groups of motor units alternately in response to input from stretch receptors in muscles
• Keeps muscles firm, healthy, and ready to respond

• Muscular dystrophy - inherited diease that destroys muscles, usually happens during childhood, most serious Duchenne's MD (recessive sex-linked)
• Tetanus - spastic (tight) paralysis, toxins from bacteria (Clostridium tetani), over excessive contraction of muscle, from wounds that are contaminated
• Botulism - potentially fatal muscle paralysis, due to toxin from bacterial (Clostridium botulinum), prevents release of ACh from synaptic knob, toxin produced under anaerobic conditions (such as poor canning)

• Sensory input
• Information gathered by sensory receptors about internal and external change
• Integration
• Interpretation of sensory input
• Motor output
• Activation of effector organs (muslces and glands) produces a response

• Central nervous system (CNS)
• Brain and spinal cord
• Integration and command center
• Peripheral nervous system (PNS)
• Paired spinal and cranial nerves
• 2 functional divisions
• carry message to [afferent]
• and from the CNS [efferent]

• Sensory (afferent) division
• Somatic afferent fibers - convey impulses from skin, skeletal muscles, and joints
• Visceral afferent fibers - convey impulses from visceral organs
• Motor (efferent) division
• Transmits impulses from the CNS to effector organs

• Somatic nervous system [voluntary]
• Conscious control of skeletal muscles
• Autonomic nervous system (ANS) [involuntary]
• Regulates smooth muscle, cardiac muscle, and glands
• 2 Divisions-
• Sympathetic 
• Parasymapthetic

• Neurons - excitable cells that transmit electrical signals
• Neuroglia (glial cells) - supporting cells: 6 types

• Provide a supportive scaffolding for neurons
• Segregate and insulate neurons
• Guide young neuorns to the proper connections
• Promote health and growth
• CNS: astrocytes, microglia, ependymal cells, oligodendrocytes
• PNS: satellite cells, Schwann cells

• Most abundant, veratile, and highly branched glial cells
• Cling to neurons, synaptic endings, and capillaries
• Support and brace neurons
• Guid migration of young neurons
• Control the chemical environment
• Participate in information processing in the brain

• Small, ovoid cells with throny processes
• Defensive cells of the CNS: Migrate toward injured neurons and phagotize microorganisms and neuronal debris
• Monitor health of neurons, provide defense function for neurons

• Range in shape and may be ciliated
• Line the central cavities of the brain and spinal column
• Help circulate cerebrospinal fluid (CSF)

• Branched cells
• Processes wrap CNS nerve fibers, forming insulating myelin sheaths

• Schwann cells (neurolemmocytes)
• Surround peripheral nerve fibers and form myelin sheaths
• Vital to regeneration of damaged peripheral nerve fibers
• Satellite cells
• Surround neuron cell bodies in the PNS
• Function not well known

• Special characteristics:
• Long-lived (→ 100 years or more)
• Amitotic (do not divide, have to live long) - with few exceptions
• High metabolic rate - depends on continuous supply of oxygen and glucose
• Plasma membrane function in:
• Electrical signaling
• Cell-to-cell interactions during development
• 3 parts
• Body, axon, and dendrites

• Contains the nucleus
• No centrioles (hence its amiotic nature)
• Well-developed Nissl bodies (rough ER)
• Contains an axon hillock - cone-shaped area from which axon arises
• Most neuron cell bodies are located in CNS for protection
• Clusters of cell bodies in the CNS=NUCLEUS
• Clusters of cell bodies in the PNS =GANGLIA

• Dendrites and axons
• Bundles of processes are called
• Tracts in the CNS
• Nerves in the PNS

• Short, tapering, and diffusely branched
• Receptive (input) region of a neuron ("antenna")
• Convey electrical signals toward the cell body as graded potentials

• One axon per cell arising from the axon hillock
• Long axons (nerve fibers)
• Occasional branches (axon collaterals)
• Numerous terminal branches (telodendria)
• Knoblike axon terminals (synaptic knobs or boutons)
• Secretory region of neuron
• Release neurotransmitters to excite or inhibit other cells

• Conducting region of a neuron
• Generates and transmits nerve impulses (=action potentials) away from the cell body
• Molecules and organelles are moved along axons in 2 directions:
• Anterograde - toward axonal terminal
• Examples: mitochondria, membrane components, enzymes
• Retrograde - toward the cell body
• Examples: organelles to be degraded, signal molecules, viruses, and bacterial toxins

• Segmented protein-lipoid sheath around most long or large-diameter axons
• It functions to:
• Protect and electrically insulate the axon
• Increase speed of nerve impule transmission

• Schwann cells wraps many times around the axon
• Myelin sheath-concentric layers of Schwann cell membrane
• Neurilemma - peripheral bulge of Schawnn cell cytoplasm
• Nodes of Ranvier
• Myelin sheath gaps between adjacent Schwann cells
• Sites where axon collaterals can emerge

• Thin nerve fibers are unmyelinated
• One Schwann cell may incompletely enclose 15 or more unmyelinated axons

• Formed by processes of oligodendrocytes, not the whole cells
• Nodes of Ranvier are present
• No neurilemma
• Thinnest fibers are unmyelinated

• White matter
• Dense collections of myelinated fibers
• Gray matter
• Mostly neuron cell bodies and unmyelinated fibers

1. Multipolar - 1 axon and several dendrites
• Most abundant
• Motor neurons and interneurons
2. Bipolar - 1 axon and 1 dendrite
• Rare, eg retinal neurons
3. Unipolar (pseudounipolar) - single, short process that has two branches
• Peripheral process - most distal branch, often associated with a sensory receptor
• Central process - branch entering the CNS

1. Sensory (afferent)
• Transmit impulses from sensory receptors toward the CNS
2. Motor (efferent)
• Carry impulses from the CNS to effectors
3. Interneurons (association neurons)
• Shuttle signals through CNS pathways; most are entirely within the CNS

• Neuron are highly excitable
• Respond to adequate stiumulus by generating an action potential (nerve impulse)
• Impulse is always the same regardless of stimulus

• If opposite electrical charges are separated, the system has potential energy
• Voltage (V): measure of potential energy generated by separated charge = Voltage (V)

1. Leakage (nongated) channels - always open
2. Gated channels (3 types):
• Chemically gated (ligand-gated) channels - open with binding of a specific neurotransmitter
• Voltage-gated channels - open and close in response to changes in membrane potential
• Mechanicallhy gated channels - open and close in response to physical deformation of receptors

• When gated channels are open:
• Ions move quickly across the membrane
• Movement is along their electrochemical gradients
• An electrical current is created
• Voltage changes accross the membrane

• Ions flow along their chemical gradient when they move passively from an area of high concentration to an area of low concentration
• Ions flow along their electrical gradient when they move toward an area of opposite charge
• Electrochemical gradient - the electrical and chemical gradients taken together
• Ion flow along electro chemical gradients underlies all electrical phenomena in neurons

• Potential difference across the membrane (only) of a resting cell
• Approximately -70 mV in neurons (cytoplasmic side of membrane is negatively charged relative to outside)
• Generated by:
• Differences in ionic makeup of ICF and ECF
• Differential permeability of the plasma membrane

• Differences in ionic makeup
• ICF has lower concentration of Na⁺ and Cl^- than ECF
• ICF has higher concentration of K⁺ and negatively charged proteins (A^-) than ECF
• Differential permeability of membrane
• Negative interior of the cell is due to much greater diffusion of K⁺ out of the cell than Na⁺ diffusion into the cell (Via leakage channels)
• Sodium-potassium pump stabilizes the resting membrane potential by maintaining the concentration gradients for Na⁺ and K⁺

• Neurons use changes in membrane potential as communication signals
• Membrane potential changes when:
• Concentrations of ions across the membrane change
• Permeabilityof membrane to ions changes
• Types of signals -
• Graded potentials (signal over short distances)
• Action potentials (signal over long distances)

• Depolarization
• A reduction in membrane potential (toward zero)
• Inside of the membrane becomes less negative than the resting potential
• Increase the probability of producing a nerve impulse
• Repolarization
• Membrane returns to its resting potential
• Hyperpolarization
• Inside of the membrane becomes more negative than the resting potential
• Reduces the probability of producing a nerve impulse

• Two types of signals
• Graded potential
• Incoming short-distance signals
• Action potentials
• Long-distance signals of axons

• Short-lived, localized changes in membrane potential
• Occur when a stimulus causes gated ion channels to open
• Can only travel short distances: local currents
• Magnitude varies directly ("graded") with sterngth of stimulus
• Decrease in magnitude with distance as ions flow and diffuse through leakage channels
• Sufficiently strong graded potential can initiate an action potential

• Brief reversal of membrane potential with a total amplitude of ~100 mV
• Only occurs in muscle cells and axons of neurons
• Does not decrease in magnitude over distance
• Principals means of long-distance neural communication
• An action potential in the axon of a neuron is a nerve impulse

• Depolarizing local currents open voltage-gated Na⁺ channels
• Na⁺ influx causes more depolarization
• At threshold (-55 to -50 mV) positive feedback leads to opening of all Na⁺ channels, and a reversal of membrane polarity to +30mV (spike of action potential)

• Na⁺ channel slow inactivation gates close
• Membrane permeability to Na⁺ declines to resting levels
• Slow voltage-sensitive K⁺ gates open
• K⁺ exits the cell and internal negativity is restored

• Some K⁺ channels remain open, allowing excessive K⁺ efflux
• This causes after-hyperpolarization of the membrane (undershoot)

• Self propagating and continues along axon at constant velocity:
• Each AP provides the depolarization stimulus for triggering an AP in the next patch of membrane (~domino effect)
• Region that just generated an AP becomes refractory: that is why the AP propagates only in one direction (awy from stimulus)
• Saltatory (to leap) Conduction = propagation of AP along a myelinated axon
• Continuous Conduction - propagation of AP along an unmyelinated axon

• Threshold: typically when membrane is depolaized by 15 to 20 mV from resting value
• Only if threshold is reached will an AP be generated
• All-or-none phenomenon - action potentials either happen completely, or not at all

• All action potentials are alike and are independent of stimulus intensity
• Strong stimuli can generate an action potenital more often than weaker stimuli

• Conduction velocities of neurons vary widely
• Effector of axon diameter
• Larger diameter fibers: faster
• Effect of myelination
• Myelinated: faster vs unmyelinated

• An autoimmune disease that mainly affects young adults
• Symptoms: visual disturbances, weakness, loss of muscular control, speech disturbances, and urinary incontinence
• Myelin sheaths in the CNS become nonfunctional scleroses
• Shunting and short-circuiting of nerve impulses occurs
• Impulse conduction slows and eventually ceases

• A junction that mediates information transfer from one neuron:
• To another neuron, or
• To an effector cell
• Presynaptic neuron - conducts impulses toward the synapse
• Postsynaptic neuron - transmits impulses away from the synapse

• Electrical synapses
• Chemical synapses

• Less common than chemical synapses
• Neurons are electrical coupled (joined by gap junctions)
• Communication is very rapid
• Are important in:
• Embryonic nervous tissue
• Some brain regions

• Use neurotransmitters
• Typically composed of two parts
• Axon terminal of the presynaptic neuron, which contains synaptic vesicles
• Receptor region on the postsynaptic neuron
• Synaptic Cleft
• Fluid-filled space separating the presynaptic and postsynaptic neurons
• Prevents nerve impulses from directly passing from one neuron to the next

• Transmission across the synaptic cleft:
• Is a chemical event (as opposed to an electrical one)
• Involves release, diffucion, and binding of neurotransmitters
• Ensures unidirectional communication between neurons

1. AP arrives at axon terminal of the presynaptic neuron
2. Exocytosis of neurotransmitter occurs
3. Neurotransmitter diffuses and binds to receptors (often chemically gated ion channels) on the postsynaptic neuron
4. Ion channels are opened, causing an excitatory or inhibitory event (graded potential)
5. Within a few milliseconds, the neurotransmitter effect is terminated
1. Degradation by enzymes
2. Reuptake by astrocytes or axon terminal
3. Diffusion away from the synaptic cleft

• Graded potentials
• Strength determined by:
• Amount of neurotransmitter released
• Time the neurotransmitter is in the area
• Types of postsynaptic potentials
1. EPSP - excitatory postsynaptic potentials
2. IPSP - inhibitory postsynaptic potentials

• A single EPSP cannot induce an action potential
• EPSPs can summate to reach threshold
• IPSPs can also summate with EPSPs, canceling each other out
• Temporal summation
• One or more presynaptic neurons transmit impulses in rapid-fire order
• Spatial summation
• Postsynaptic neuron is stimulated by a large number of terminals at the same time

• Most neurons make two or more neurotransmitters, which are released at different stimulation frequencies
• 50 or more neurotransmitters have been identified
• Classified by chemical structure and by function (i.e. excitatory or inhibitory)

• Acetylcholine (Ach): neuromuscular junctions & some ANS nurons; degraded by acetylcholinesterase (AChE)
• Amines:
• Catcholamines (Dopamine, norepinephrine (NE), and epinephrine)
• Serotonin, histamine
• Amino acids: GABA-Gamma-amniobutyric acid; Glycine; Aspartate; Glutamate
• Peptides (neuropeptides): Substance P (Mediator of pain signals); Endorphins: act as natural opiates, reduces pain perception
• Other: ATP, nitric oxide (NO), carbon monoxide (CO)

• Functional groups of neurons that:
• Integrate incoming information
• Forward the processed information to other destinations

• Composed of wrinkled, pinkish grey tissue
• Brain mass: male > female
• but brain mass per body mass is the same in males and females
• Encephalo: from Greek enkephalo (in the head)
• During embryonic development a neural tube is formed that gives rise to the brain and spinal cord

1. Cerebal hemispheres (=cerebrum)
• Cerebral cortex, white matter, basal nuclei
2. Diencephalon
• thalamus, hypothalamus, epithalamus
3. Brain stem
• midbrain, pons, medulla oblongata
4. Cerebellum

• Basic patterns of the CNS:
• central cavity surrounded by grey matter (mostly neuron cell bodies), external to which is the white matter (myelinated fiber tracts)
• Brain: the cerebrum and cerebellum have an outer grey matter layer = cortex ("bark")

• Connected to one another and to the central canal of the spinal cord 
• Lined by ependymal cells
• Contain cerebrospinal fluid
• Two C-shaped lateral ventricles in the cerebral hemispheres
• Third ventricle in the diencephalon
• Fouth ventricle dorsal to the pons

• Surface markings
• Ridges (gyri), shallow ridges (sulci), and deep groves (fissures)
• Several sulci divide each hemisphere into lobes
• Frontal
• Temporal
• Parietal
• Occipital
• A 5th lobe (insula) is buried within

• Thin (2-4 mm) superficial layer of grey matter
• Site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, memory storage, understanding
• Each hemisphere controls contralateral side of the body

• Lateralization - each hemisphere has abilities not shared with its partner
• Cerebral dominance - designates the hemisphere dominant for language
• Left hemisphere - controls lanaguage, math, and logic (for 90% of people)
• Right hemisphere - controls visual-spatial skills, emotions, artistic skills

• The three types of functional areas are:
• Motor areas - control voluntary movement
• Sensory areas - conscious awareness of sensation
• Association areas - integrate diverse information
• Conscious behavior involves the entire cortex

• Primary (somatic) motor cortex
• Precise or skilled vocabulary movements
• Premotor cortex
• Skilled motor activities: repetitious, or patterned motor skills (eg typing)
• Broca's Area  (usually only in the L hemisphere)
• Directs muscle involved in speech
• Frontal eye field
• Controls voluntary eye movement

• Primary somatosensory cortex
• Receives information from the skin and skeletal muscles and provides spatial discrimination (identifies body regions being stimulated)
• Somasensory association cortex 
• Integrates sensory inputs (temp, pressure, etc.) [can tell what you feel when reaching in pocket]
• Visual ("eyes in the back of your head") and auditory cortices
• Oflactory cortex (smell), gustatory cortex (taste)
• Visceral sensory area (sensation of visceral organs)
• Vestibular cortex (balance and equilibrium)

• Receive inputs from multiple sensory areas
• Send outputs to multiple areas, including the premotor cortex
• Allow us to give meaning to information received, store it as memory, compare it to previous experience, and decide on action to take

• Anterior association areas = prefrontal cortex
• most complicated region of cortex, involved with intellect, cognition, memory personality
• Posterior association area
• eg. language areas (Wernicke's area)
• Limbic association area
• Emotional impact that makes a scene important to use

• Myelinated fibers and their tracts
• Responsible for communication
• Commisures (in corpus callosum) - connect gray matter of the two hemispheres
• Association fibers - connect different parts of the same hemisphere
• Projection fibers - (corona radiata) connect the hemisphere with lower brain or spinal cord

• Masses of gray matter found deep within the cortical white matter
• Consists of the corpus striatum
• Influence movement
• Eg. Regulate intensity of slow or stereotyped movements (eg. arm swinging during walking)
• Inhibits antagonistic and unnecessary movements

• Three paired structures
• Thalamus
• Hypothalamus
• Epithalamus
• Encloses the third ventricle

• Gateway to the cerebral cortex = sorts, edits, and relays information
• Afferent impulses from all senses and all parts of the body
• Mediates sensation, motor activities, cortical arousal, learning, and memory

• Below thalamus (caps the brain stem)
• Infundibulum - stalk that connects the pituitary gland
• Functions:
• ANS control (blood pressure, rate/force of heartbeat, digestive tract motility)
• Center for emotional response: eg perception of pleasure, fear and rage and in biological rhythms and drives
• Regulates body temperature, hunger, water balance, and thirst
• Regulates sleep and wake cycle
• Part of the endocrine system (regulates hormones)

• Most dorsal portion of the diencephalon; forms roof of third ventricle
• Pineal gland - extends from posterior border and secretes melatonin
• Melatonin - helps regulate sleep wake cycles

• Midbrain
• Pons
• Medulla oblongata

• Similar structure to spinal cord but contains embedded nuclei
• Controls automatic behaviors necessary for survival
• Contains fiber tracts connecting higher and lower neural centers
• Associated with 10 of the 12 pairs of cranial nerves

• Cerebral peduncles - two bulging structures that contain descending pyramidal motor tracts
• Cerebral aquaduct - hollow tube that connects the thrid and fourth ventricles
• Various nuclei:
• Corpora quadrigema - visual and auditory reflex centers
• Substantia nigra - involved in movement (degeneration causes Parkinson's disease)

• Forms part of the anterior wall of the fourth ventricle
• Fibers of the pons
• Connect higher brain centers and the spinal cord
• Part of the reticular formation
• Nuclei that help retain the normal rhythm of breathing

• Joins spinal cord at the foramen magnum
• Forms part of the ventral wall of the fourth ventricle
• Decussation of the pyramids - crossover of the corticospinal tracts
• Relay sensory information from muscles and joints to cerebellum

• Autonomic reflex centers:
• Cardiovascular center:
• adjusts force and rate of heart contraction, blood vessel diameter
• Respiratory center:
• generate respiratory rhythm, rate and depth of breathing
• Other: regulates vomiting, hiccuping, swallowing, coughing, sneezing

• Dorsal to the pons and medulla
• Two hemispheres connected by vermis
• 3 lobes per hemisphere
• Arbor vitae ("tree of life") - distinctive tree-like pattern of the cerebellar white matter
• Subconsciously provides precise timing and appropriate patters of skeletal muscle contraction 
• All fibers in the cerebellum are ipsilateral (controls same side)

• Networks of neurons that work together and span wide area of the brain
• Limbic system
• Emotional or affective brain
• eg puts emotional responses to odors (skunks smell bad)
• Reticular formation (along length of brain stem)
• Sends impulses to cerebral cortex to keep it conscious and alert
• Filters out weak and repetitive stimuli (~90% of all stimuli!)
• Severe injury results in permanent unconsciousness (coma)

• Records electrical activity that accompanies brain function
• Each person's brain waves are unique
• A flat EEG (no electrical activity) is clinical evidence of death

• Clinically defined on a continuum that grades behavior in response to stimuli
• Alertness
• Drowsiness (Lethargy)
• Stupor
• Coma

• State of partial unconsciousness from which a person can be aroused by stimulation
• Two major types of sleep (defined by EEG patterns)
• Nonrapid eye movement (NREM)
• Rapid Eye Movement (REM) (dreams occur here)

• Narcolepsy
• Lapsing abruptly into sleep from the awake state
• Insomnia
• Chronic inability to obtain the amount or quality of sleep needed
• Sleep apnea
• Temporary cessation of breathing during sleep

• Storage and retrieval of information 
• Two stages of storage
• Short-term memory (STM, or working memory) - temporary holding of information; limited to seven or eight pieces of information
• Long-term memory (LTM) has limitless capacity

• Bone (skull)
• Membranes (meninges)
• Watery cushion (cerebrospinal fluid)
• Blood-brain barrier

• Cover and protect the CNS
• Protect blood vessels and enclose venous sinuses
• Contain cerebrospinal fluid (CSF)
• Form partitions in the skull

• Dura mater
• Arachnoid mater
• Pia mater

• strongest menix
• two layers of fibrous connective tissue (around the brain) separate to form dural sinuses (collect venous  blood)

• middle layer with weblike extensions
• separated from dura mater by subdural space
• subarachnoid space contains CSF and blood vessels

• layer of delicate vascularized connective tissue that clings tightly to the brain

• Composition
• Watery solution
• Less protein & different ion concentration vs. plasma
• Constant volume
• Functions
• Gives buoyancy to the CNS organs
• Protects the CNS from blows and other trauma
• Nourishes the brain and carries chemical signals
• Produces by the choroid plexus (network of capillaries) of each ventricle

• Composition
• Continuous endothelium of capillary walls, basal lamina, and "feet" of astrocytes
• Function
• Helps maintain a stable environment for the brain
• Selective barrier
• Allows nutrients to pass while metabolic wastes, toxins, drugs excluded
• Fat-soluble substances can pass, including alcohol, nicotine, and anesthetics
• Absent in areas where it is necessary to monitor the chemical composition of the blood (eg hypothalamus)

• Concussion - temporary alteration in function
• Contusion - permanent damage
• Cerebral edema - swelling of the brain associated with traumatic head injury

• Blood circulation is blocked and brain tissue dies, eg blockage of a cerebal artery by a blood clot
• Typically leads to hemiplegia (one side of body paralyzed), or sensory and speed deficits

• Alzheimer's Disease (AD) - a progressive degenerative disease of the brain that results in dementia
• Parkinson's Disease - degeneration of the dopamine-releasing neurons of the substantia nigra
• Huntington's Disease - a fatal hereditary disorder caued by accumulation of the protein huntingtin that leads to degeneration of the basal nuclei and cerebral cortex

• Location
• Begins at the foramen magnum
• Ends at conus medullaris at L₁ vertebrae
• Functions
• Provides two-way communication to and from the brain
• Contains spinal reflex centers

• Bone, meninges, and CSF (in subarachnoid space)
• Cushion of fat and network of veins in the epidural space between the vertebrae and spinal dura mater

• Filum terminale: fibrous extension from conus medullaris; anchors the spinal cord to the coccyx
• Spinal cord ends at the L1 (or L2) [=conus medullaris] but dura and arachnoid extend to S2 (well beyond SC, so ideal spot for lumbar puncture)

• 31 pairs of spinal nerves in humans
• Cervical and lumbar enlargements
• The nerves serving the upper and lower limbs emerge here
• Cauda equina
• The collection of nerve roots at the end of the vertebral canal

• Two lengthwise grooves divide the cord into right and left halves
• Ventral (anterior) median fissure
• Dorsal (posterior) median sulcus
• Gray commissure - connects masses of gray matter; encloses central canal

4 zones are evident in the gray matter -

somatic sensory (SS)

visceral sensory (VS)

visceral motor (VM)

somatic motor (SM)

• Fibers run in 3 directions - Ascending, Descending, Transversely (most of the white matter made up of ascending and descending fibers)
• Divided into three funiculi (columns) - Posterior, Lateral, and Anterior
• Each funiculus contains several fiber tracts
• Fiber tract names reveal their origin (1st) and destination (2nd)

• Pathways decussate (cross over)
• Most consist of two or three neurons (a relay)
• Pathways are paired symmetrically (one on each side of the spinal cord or brain)

• First-order neuron
• Conducts from cutaneous receptors and proprioceptors 
• Cell bodies in dorsal root ganglia (or cranial ganglia)
• Second-order neuron
• Interneuron with cell body in dorsal horn of spinal cord (or medullary nuclei)
• Axons extend to thalamus (or cerebellum)
• Third-order neuron
• Interneuron with cell body in thalamus
• Axon extends to somatosensory cortex

• Deliver efferent impulses from the brain to the spinal cord and involve 2 neurons:
• Upper motor neurons: cell body in primary motor cortex (=pyramidal cells). Synapses with:
• Lower motor neurons: cell body in ventral horn
• Innervate skeletal muscles

• Any localized damage to the spinal cord or its roots lead to paralysis (loss of motor function) or paresthesia (loss of sensory function)
• Damage to upper motor neurons lead to spastic paralysis (voluntary control over skeletal muscle is lost)
• Severe damage to ventral root or ventral horn results in flaccid paralysis (since nerve impulses not transmitted)
• Paralysis of lower limbs: paraplegia (when damage is between T1 and L1)
• Paralysis of all four limbs: quadriplegia (when damage is in the cervical region)
• Polyomyelitis: due to destruction of motor neurons from ventral horn
• Amylotrophic lateral sclerosis (ALS) or Lou Gehrig's disease involves progressive destruction of ventral horn motor neurons and fibers of the corticospinal tract