BMD 251 - Exam 4 (Final Exam)

Refractory Periods

1. Absolute Refractory Period: Time from opening of Na+ activation gates until closing of Na+ inactivation gates. • Prevents neuron from generating another action potential. • Ensures that each action potential is a separate, all‐or‐none event. • Enforces one‐way transmission of nerve impulses. 2. Relative Refractory Period: Interval following absolute refractory period. • Most Na+ channels have reset. • Repolarization is occurring. • Axon's threshold for AP generation is elevated. • Strong stimuli can reopen Na+ activation gates generating a new AP.

Muscles Crossing the Hip & Knee Joints: thigh adduction (five adductor muscles)

1. Adductor Magnus: Adducts, flexes, and medially rotates the thigh. 2. Adductor Longus: Adducts, flexes, and medially rotates the thigh. 3. Adductor Brevis: Adducts, flexes, and medially rotates the thigh. 4. Pectineus: Adducts, flexes, and medially rotates the thigh. 5. Gracilis: Adducts, flexes, and medially rotates the thigh.

Types of Neuroglia in the CNS and their Functions.

1. Astrocytes ("star cells"): • Most abundant, most versatile, highly‐branched glial cells. • Cling to neurons & their synaptic endings; cover capillaries. Functions of Astrocytes: •Support & brace neurons. • Anchor neurons to their nutrient supplies (capillaries). • Guide migration of young neurons & formation of synapses between neurons. • Control chemical environment around neurons. 2. Microglial Cells: Small, ovoid cells with spiny processes. • Processes touch neurons, monitoring their health. • Transform into special macrophages that phagocytize neuronal debris & bacteria. 3. Ependymal Cells: Range in shape from cuboidal to columnar; many are ciliated. • Line central cavities of brain & spinal cord. • Beating cilia help spinal fluid circulate. 4. Oligodendrocytes: Branched cells that wrap their processes around CNS nerve fibers. • Fewer processes than astrocytes. • Produce insulated coverings called myelin sheaths.

Muscles Crossing the Elbow Joint: anterior muscles Forearm flexion

1. Biceps Brachii: Flexes elbow & supinates forearm. • long head • short head 2. Brachialis: Deep to biceps; prime mover of forearm flexion. 3. Brachioradialis: Synergist in forearm flexion.

Muscles Crossing the Hip & Knee Joints: primary thigh extensors - hamstring muscles

1. Biceps Femoris: Extends thigh and flexes leg. 2. Semitendinosus: Extends thigh and flexes leg. 3. Semimembranosus: Extends thigh and flexes leg.

Neurons: Structure & Function

1. Cell Body: • Neuron Cell Body (a.k.a perikaryon, or soma): Consists of a spherical nucleus with a conspicuous nucleolus surrounded by cytoplasm. - Major biosynthetic center of neuron. - Chromatophilic Substance (Nissl Bodies): Most active & best developed rough endoplasmic reticulum in the body. - Microtubules & Neurofibrils: Maintain cell shape. - Plasma Membrane of Cell Body: Part of receptive region. • Location of Cell Bodies: - Nuclei: Clusters of cell bodies in the CNS; most common. - Ganglia: Clusters of cell bodies along the nerves in the PNS. 2. Processes (dendrites & axons): Arm‐like extensions from the cell body of all neurons. • CNS : Contains neuron bodies & processes. - Tracts: Bundles of neuron processes in the CNS. • PNS: Contains mostly neuron processes. - Nerves: Bundles of neuron processes in the PNS. • Dendrites: Short, tapering, diffusely branching processes. - Main receptive or input regions of neuron. - Dendritic Spines: Points of close contact (synapses) with other neurons. - Move incoming signals towards the cell body using short‐distance signals called graded potentials (not action potentials). • Axons - Structure: Slender process extending from neuron. - Each neuron has a single axon. - Nerve fibers: Long axons. - Axon collaterals: Occasional axon branches, if present. - Axon hillock: Cone‐shaped area of neuron where axon arises. - Terminal branches: Profuse branches at axon's end; 10,000+. - Axon terminal (terminal boutons, synaptic bulb, synaptic knob): Knoblike distal endings of the terminal branches. • Axons - Function: 1. Conduction of Nerve Impulses: • Axon: Conducting region of the neuron. - Generates nerve impulses & transmits them typically away from the cell body along the plasma membrane. ○ Axolemma ‐ Plasma membrane of axon. - Trigger zone: Junction of axon hillock & axon where nerve impulses are generated. - Nerve impulses are conducted along axon to axon terminals. - Secretory region: The axon terminals; where neurotransmitters are released. - Neurotransmitters: Signaling chemicals stored in vesicles; released into extracellular space. ○ Inhibit or excite neurons or effector cells. 2. Movement of Molecules: • Axon: Lacks chromatophilic substance (rER) & a Golgi apparatus. • Axon depends on: - Cell body to renew necessary proteins & membrane components. - Efficient transport mechanisms to distribute them. • Types of Axonal Movement: - Anterograde Movement: Toward axon terminal. ○ Mitochondria, cytoskeletal elements, plasma membrane components, enzymes. - Retrograde Movement: Away from axon terminal. ○ Mostly organelles for removal or recycling.

Principal Parts of Nervous System

1. Central Nervous System (CNS): Brain & spinal cord. • Integration & command center. • Interprets sensory input & dictates motor output responses. 2. Peripheral Nervous System (PNS): Part of nervous system outside CNS; primarily paired cranial & spinal nerves. • Nerves: Bundles of axons that extend from the brain & spinal cord. • Cranial Nerves: Carry impulses to & from the brain. • Spinal Nerves: Carry impulses to & from the spinal cord.

Muscles of the Head: muscles of the face Innervated by cranial nerve VII (facial nerve)

1. Corrugator Supercilii: Pulls eyebrows medially and inferiorly. 2. Orbicularis Oculi: Closes eye. 3. Levator Labii Superioris: Opens lips. 4. Zygomaticus (minor and major): Raises lateral corners of mouth upwards (smiling muscle). 5. Buccinator: Compresses cheek. 6. Risorius: Pulls corner of lip laterally (synergist of zygomaticus). 7. Orbicularis Oris: Closes lips. 8. Mentalis: Wrinkles chin. 9. Depressor Labii Inferioris: Pulls lower lip inferiorly. 10. Depressor Anguli Oris: Pulls corners of lip downwards & laterally. 11. Platysma: Tenses skin of neck.

Muscles Crossing the Shoulder Joint

1. Deltoid: Prime mover of arm abduction when all its fibers contract simultaneously. 2. Pectoralis Major: Prime mover of arm flexion; adducts and medially rotates the arm. 3. Latissimus Dorsi: Prime mover of arm extension; powerful arm adductor; medially rotates arm. • Rotator Cuff Muscles (4): Reinforce shoulder capsule; act as synergists & fixators for arm movements. 4. Subscapularis: Rotates arm medially; prime mover. 5. Supraspinatus: Initiates abduction of arm. 6. Infraspinatus: Rotates arm laterally. 7. Teres Minor: Same action as infraspinatus muscle. 8. Coracobrachialis: Synergist; doesn't contribute to shoulder joint reinforcement; flexes and adducts humerus. 9. Teres Major: Extends, medially rotates, and adducts humerus.

Muscles of the Anterior Neck and Throat: suprahyoid muscles Above (superior to) the hyoid bone

1. Digastric: Consists of anterior & posterior bellies united by a central tendon connected to hyoid bone; open mouth and depress mandible. 2. Mylohyoid: Elevates hyoid bone & floor of mouth. 3. Stylohyoid: Elevates & retracts hyoid bone. 4. Geniohyoid: Elevates and protracts the hyoid bone by pulling it superiorly & anteriorly.

Muscles of the Head: muscles of the scalp Innervated by cranial nerve VII (facial nerve)

1. Epicranius (occipitofrontalis): Two-part muscle consisting of the frontal and occipital bellies connected by the epicranial aponeurosis. • Frontal Belly (frontalis): raises eyebrow. • Occipital Belly (occipitalis): fixes aponeurosis and pulls scalp posteriorly. • Epicranial Aponeurosis: connective tissue sheet connecting the frontal belly & occipital belly.

Deep Muscles of the Thorax

1. External Intercostals: Superficial layer of muscles between ribs. • With first ribs fixed by scalene muscles, pull ribs toward one another to elevate rib cage. • Increases thoracic volume to allow inspiration (inhalation). • Innervated by intercostal nerves. 2. Internal Intercostals: • With 12th ribs fixed by quadratus lumborum muscles, pull ribs together and depress rib cage. • Aiding in forced expiration (exhalation). • Innervated by intercostal nerves. 3. Diaphragm: • Prime mover of inspiration • Broad, dome‐shaped structure • Flattens on contraction • Increases thoracic volume vertically when contracted • Large central tendon • Openings for aorta, inferior vena cava, & esophagus • Innervated by phrenic nerves

Muscles of the Abdominal Wall

1. External Oblique: Largest, most superficial of the 3 lateral muscles; flexes vertebral column & compresses abdominal wall. 2. Internal Oblique: Most fibers run upward & medially; same action as external oblique. 3. Transversus Abdominis: Deepest, horizontal fibers; compresses abdominal contents. 4. Rectus Abdominis: Medial superficial muscle; "six pack"/"washboard" abs; flexes & rotates lumbar region of vertebral column. • Linea Alba ("white line") : Fused rectus abdominis aponeuroses.

Muscles of the Leg: posterior compartment Primarily plantar flex the foot and flex the toes (curl toes)

1. Gastrocnemius: Superficial muscle of calf; plantar flexes the foot. • Achilles (calcaneal) tendon inserts into calcaneus bone of ankle. 2. Soleus: Deep muscle of calf; plantar flexes the foot. • Useful for walking and running (fatigue resistant). • Also uses calcaneal tendon. 3. Popliteus: Unlocks extended knee when flexion begins.

Muscles of the Head: muscles promoting tongue movement Innervated by cranial nerve XII (hypoglossal nerve)

1. Genioglossus: Protracts tongue. 2. Styloglossus: Retracts & elevates tongue. 3. Hyoglossus: Depresses tongue.

Muscles Crossing the Hip & Knee Joints: forceful thigh extension

1. Gluteus Maximus: Largest buttocks muscle.

Muscles Crossing the Hip & Knee Joints: thigh abduction and rotation

1. Gluteus Medius: Abducts and medially rotates the thigh. 2. Gluteus Minimus: Abducts and medially rotates the thigh.

Muscles Crossing the Hip & Knee Joints: primary thigh flexors

1. Iliopsoas (Psoas Major & Iliacus): Prime mover of thigh flexion or flexing trunk on thigh. 2. Tensor Fasciae Latae: Steadies the leg and trunk on thigh by tightening iliotibial tract; flexes and abducts thigh. 3. Rectus Femoris: One of the 4 heads of the quadriceps femoris muscle; flexes thigh and extends knee.

Types of Membrane Ion Channels

1. Leak (Nongated) Channels: Channels that are always open. 2. Gated Channels: Part of the protein forms a molecular "gate" that changes shape to open and close the channel in response to specific signals. • Chemically gated (ligand‐gated) channels • Voltage‐gated channels • Mechanically gated channels

Criteria used in naming muscles

1. Muscle Location: Some muscle names indicate the bone or body region with which the muscle is associated. • Example: The temporalis muscle overlies the temporal bone. • Example: The brachialis muscle is in the arm. 2. Muscle Shape: Some muscles are named for their distinctive shapes. • Example: The deltoid muscle is roughly triangular (Greek letter delta = Δ). • Example: The right and left trapezius muscles together form a trapezoid. 3. Muscle Size: Terms such as maximus (largest), minimus (smallest), longus (long), and brevis (short) are often used in muscle names. • Example: The gluteus maximus and gluteus minimus are the large and small gluteus muscles. 4. Direction of Muscle Fibers: The names of some muscles reveal the direction in which their fibers and fascicles run in reference to some imaginary line, usually the midline of the body or the longitudinal axis of a limb bone. • Rectus (straight): The fibers run parallel to the imaginary line. - Example: Rectus abdominis & rectus femoris • Transversus (right angle): The fibers run at right angles to the imaginary line. - Example: Transverse abdominis • Oblique (oblique): The fibers run obliquely to the imaginary line. - Example: Internal oblique 5. Number of Origins: When biceps, triceps, or quadriceps forms part of a muscle's name, you can assume that the muscle has two (biceps), three (triceps), or four (quadriceps) heads, each attached to a different origin. • Example: The biceps brachii muscle of the arm has two origins. 6. Location of the Attachments: Some muscles are named according to their points of origin and insertion. The origin is always named first. • Example: The sternocleidomastoid muscle of the neck has a dual origin on the sternum (sterno) and the clavicle (cleido), and it inserts on the mastoid process of the temporal bone (mastoid). 7. Muscle Action: Some muscles are named for the movement they produce; such as flexor (flexion, decreasing the angle of a joint), extensor (extension, increasing the angle of a joint), adductor (adduction, movement of a limb toward the body's midline), or supinator (supination, palm forward). • Example: The adductor longus, located on the medial thigh, brings about thigh adduction.

Muscle Functional Classification

1. Prime Movers (Agonists): A muscle that has the major responsibility for producing a specific movement. • Example: Brachialis (or biceps brachii) is prime mover of elbow flexion. 2. Antagonists: Muscles that oppose or reverse a particular movement. • Example: Triceps brachii extends the elbow. • When a prime mover is active, its antagonist is usually slightly contracted. - Prevents prime mover from overshooting the mark. - Slows or stops movement. • Prime mover & its antagonist are located on opposite sides of a joint. 3. Synergists: Assist prime movers. • Add force to a movement. • Reduce undesirable or unnecessary movement. - Example: When a muscle crosses two or more joints, its contraction affects all the spanned joints unless other muscles act as joint stabilizers. 4. Fixators: Synergists that immobilize a bone, or a muscle's origin. • Give prime mover a stable base on which to act. • Example: Scapula is held to the axial skeleton only by muscles; fixator muscles immobilize the scapula. • The same muscle can perform different functions for different movements ‐ prime mover, antagonist, & synergist

Muscles Crossing the Hip & Knee Joints: knee movement - extension

1. Quadriceps Femoris: • Four separate heads form flesh of front & sides of thigh. • Quadriceps tendon: common insertion tendon of the four heads. • Sole knee extensor. • Most powerful muscle in body. • Muscle tone contributes to strength of knee joint. • Hamstring muscles are antagonists; flex knee.

Muscles Crossing the Hip & Knee Joints: assists in thigh flexion

1. Sartorius (tailor's muscle): Longest muscle in body; produces cross‐legged position.

Types of Neuroglia in the PNS and their Functions.

1. Satellite Cells: Surround neuron cell bodies located in PNS. • Functionally similar to astrocytes. • Name comes from their resemblance to moons (satellites) around a planet. 2. Schwann Cells (neurolemmocytes): Surround all nerve fibers in the PNS; form myelin sheaths around thicker nerve fibers. • Functionally similar to oligodendrocytes. • Vital to regeneration of damaged peripheral nerves.

Functional Subdivisions of PNS

1. Sensory (Afferent) Division: Consists of nerve fibers (axons) that carry impulses from sensory receptors to the CNS. • Somatic Sensory Fibers: Carry impulses from skin, skeletal muscles, & joints to the brain. • Visceral Sensory Fibers: Transmit impulses from visceral organs to the brain. 2. Motor (Efferent) Division: Transmits impulses from CNS to effector organs. • Effector Organs: muscles & glands • Activates muscles to contract & glands to secrete Learning tip!!! • Afferent Approaches CNS • Efferent Exits CNS

Basic Functions of the Nervous System

1. Sensory Input: The nervous system uses its millions of sensory receptors to monitor changes occurring both inside and outside the body. The gathered information is called sensory input. 2. Integration: The nervous system processes and interprets sensory input and decides what should be done at each moment. 3. Motor Output: The nervous system activates effector organs (the muscles and glands) to cause a response.

Main Parts of Motor (Efferent) Division

1. Somatic Nervous System: Composed of somatic motor nerve fibers that conduct impulses from CNS to skeletal muscles. • Also called voluntary nervous system. • Conscious (voluntary) control of skeletal muscles. 2. Autonomic Nervous System (ANS): Composed of visceral nerve fibers that regulate the activity of smooth muscles, cardiac muscles, and glands. • Also called involuntary nervous system. • Functional subdivisions: ○ Sympathetic Division: Mobilization; "fight or flight" ○ Parasympathetic Division: Housekeeping; "rest and digest"

Muscles of the Neck and Vertebral Column: intrinsic muscles of the back Involved in head movements and trunk extension

1. Splenius (capitis & cervicis): Extends or hyperextends head. 2. Erector Spinae: Prime mover of back extension; consists of three columns on each side of vertebral column. • Iliocostalis: Lateral • Longissimus: Intermediate • Spinalis: Medial 3. Semispinalis: Composite muscle (capitis, cervicis, thoracis); extends vertebral column & head and rotates them to opposite side. 4. Quadratus Lumborum: Laterally flexes vertebral cloumn. • Unilateral Contraction: lateral flexion • Bilateral Contraction: extension of lumbar vertebrae

Muscles of the Neck and Vertebral Column: anterolateral neck muscles Involved in head movements and trunk extension

1. Sternocleidomastoid: Two-headed muscle; flexes and laterally rotates the head. • Bilateral Contraction: neck flexion• Unilateral Contraction: contralateral rotation 2. Scalenes: Anterior, middle, posterior; elevate first two ribs to aid in inspiration; lateral flexion of neck.

Superficial Muscles of the Anterior Thorax

1. Subclavius: Helps stabilize & depress pectoral girdle. 2. Pectoralis Minor: With ribs fixed, pulls scapula forward and downward. 3. Serratus Anterior: Medially rotates scapula.

Muscles of the Head: muscles of mastication (chewing) Innervated by cranial nerve V (trigeminal nerve)

1. Temporalis: Closes jaw; elevates & retracts mandible. 2. Masseter: Prime mover of jaw closure; elevates mandible. 3. Lateral Pterygoid: Provides forward sliding & side-to-side grinding movements of lower teeth. 4. Medial Pterygoid: Acts with the lateral pterygoid muscle to protract (pull anteriorly) the mandible and promote side-to-side grinding movements. • Buccinator Muscle: Aids muscles of mastication by compressing the cheek and keeping food between the grinding surfaces of the teeth during chewing.

Muscles of the Anterior Neck and Throat: infrahyoid muscles Below (inferior to) the hyoid bone

1. Thyrohyoid: Superior continuation of sternohyoid muscle; depresses hyoid; elevates larynx if hyoid is fixed. 2. Sternothyroid: Depresses larynx and hyoid bone by pulling them inferiorly. 3. Omohyoid: Superior & inferior bellies originate at scapula; depresses & retracts hyoid. 4. Sternohyoid: Depresses larynx & hyoid bone if mandible is fixed by pulling them inferiorly. 5. Pharyngeal Constrictor Muscles: superior, middle, & inferior muscles; constricts pharynx during swallowing.

Superficial Muscles of the Posterior Thorax

1. Trapezius: Extension of neck; stabilizes, elevates, retracts, and rotates scapula. 2. Rhomboids: Minor and major; stabilize and retract scapula. 3. Levator Scapulae: Elevates and adducts scapula.

Muscles Crossing the Elbow Joint: posterior muscles Forearm extension

1. Triceps Brachii: Prime mover of forearm extension. • lateral head • long head • medial head (deep to long head)

Synapse

A junction that mediates information transfer from one neuron to the next neuron or from a neuron to an effector cell.

Action Potential Propagation

Action Potential Propagation: The transmission of an action potential along the axon's entire length. • APs are initiated at one end of axon (usually axon hillock) & are conducted toward the axon terminals. • AP propagates away from its point of origin. • Self‐propagates at a constant velocity. • Repolarization wave follows the depolarization wave down the length of the axon. • Not all local depolarization events produce action potentials; stimulus must be strong enough and/or last long enough to reach threshold. • All‐or‐None Phenomenon: APs either happen completely or not at all; must achieve threshold to propagate.

Continuous Conduction

Action potential propagation in nonmyelinated axons occurs by continuous conduction because the voltage-gated channels in the membrane are immediately adjacent to each other. Continuous conduction is relatively slow.

Superficial Muscles of the Ant. & Post. Thorax: actions

Actions: • Fix or move scapula to increase range of arm movements. • Involved with scapular movements: elevation/depression, rotation, & lateral/medial movements.

Second-Class Levers

Arrangement: Fulcrum-Load-Effort • All second class levers in the body work at a mechanical advantage because the muscle insertion is always farther from the fulcrum than is the load. • Second class levers are levers of strength, but speed and range of motion are sacrificed for that strength. • Second class levers are uncommon in the body. • Example: Wheelbarrow • Example in the body: The act of standing on your toes

Third-Class Levers

Arrangement: Load-Effort-Fulcrum • Third class levers always operate at a mechanical disadvantage. • Most skeletal muscles of the body act in third class lever systems. • Third class lever systems permit a muscle to be inserted very close to the joint across which movement occurs, which allows rapid extensive movements (as in throwing) with relatively little shortening of the muscle. • Muscles involved in third class lever systems tend to be thicker and more powerful. • Example: Tweezers • Example in the body: Flexing the forearm by the biceps brachii muscle

First-Class Levers

Arrangement: Load-Fulcrum-Effort • Some first class levers in the body operate at a mechanical advantage (for strength), but others operate at a mechanical disadvantage (for speed and distance). • Example: Seesaws and scissors • Example in the body: When you lift your head off your chest

Myelin Sheath in CNS

Cells that form myelin sheaths: • CNS: Oligodendrocytes CNS Myelin Sheaths: • CNS has both myelinated and unmyelinated axons. • Oligodendrocytes: Form myelin sheaths in CNS. - Have multiple flat processes that can coil around as many as 60 axons at once. • CNS Myelin Sheaths: Lack a neurilemma. Myelination in the CNS: • White Matter: Regions with dense collections of myelinated fibers; primarily fiber tracts. • Gray Matter: Contains mostly nerve cell bodies & unmyelinated fibers.

Myelin Sheath in PNS

Cells that form myelin sheaths: • PNS: Schwann cells PNS: Myelin Sheath Formation 1. A Schwann cell envelopes and axon. 2. The Schwann cell then rotates around the axon, wrapping its plasma membrane loosely around it in successive layers. 3. The Schwann cell cytoplasma is forced from between the membranes. The tight membrane wrappings surrounding the axon form the myelin sheath. PNS: Myelinated & Unmyelinated Axons • Myelin Sheath Gaps (Nodes of Ranvier): Gaps in myelin sheath that occur between adjacent Schwann cells. - Occur at regular intervals (1 mm apart) along myelinated axon. - Sites where axon collaterals can emerge.

Muscles of the Abdominal Wall: characteristics & actions

Characteristics: • Anterior & lateral abdominal walls made up of 4 paired muscles, their fasciae, and aponeuroses. • Muscle fascicles run at right & oblique angles giving added strength. Actions: • Flex vertebral column. • Also involved with lateral flexion and trunk rotation. • Increase intra‐abdominal pressure, aiding urination, defecation, childbirth, vomiting, coughing, screaming, sneezing, burping, & nose blowing.

Chemical Synapses

Chemical Synapses: Specialized for release & reception of neurotransmitters. • Parts of Chemical Synapse: - Axon Terminal of presynaptic neuron: Contains synaptic vesicles; each vesicle contains 1000s of neurotransmitter molecules. - Receptor region of postsynaptic neuron : Region on the membrane of dendrite or cell body that contains receptor proteins. • Synaptic Cleft: Fluid‐filled space separating presynaptic & postsynaptic membranes. - Prevents direct transmission of nerve impulses from one neuron to next one. - Transmission is a chemical event (not electrical). - Results in unidirectional communication between neurons. • Synaptic Delay: Time needed for neurotransmitter's release, diffusion across synaptic cleft, & binding to receptors. - 0.3‐5.0 milliseconds - Rate‐limiting (slowest) step of neural transmission. Information Transfer Across Chemical Synapses: • Step 1: Action potential arrives at axon terminal. - Neurotransmission at a chemical synapse begins with arrival of an action potential (nerve impulse) at the presynaptic axon terminal. • Step 2: Voltage‐gated Ca2+ channels open & Ca2+ enters the axon terminal. - The action potential opens voltage‐gated Ca2+ channels. - Ca2+ flows down its electrochemical gradient from the extracellular fluid into the axon terminal. • Step 3: Ca2+ entry causes synaptic vesicles to release neurotransmitter by exocytosis. - Ca2+ acts as an intracellular messenger, causing synaptic vesicles to fuse with the axon membrane. - Vesicles empty their contents (neurotransmitters) by exocytosis into the synaptic cleft. - Ca2+ is quickly removed from the axon terminal. ○ Taken into mitochondria. ○ Ejected from neuron by an active Ca2+ pump. • Step 4: Neurotransmitter diffuses across the synaptic cleft & binds to specific receptors on the postsynaptic membrane. • Step 5: Binding of neurotransmitter opens ion channels, creating graded potentials. - When the neurotransmitter binds to the receptor protein, it changes the receptor's three‐dimensional shape. - Ion channels (in the plasma membrane of a dendrite or neuron cell body) open, creating graded potentials. - Receptor proteins & ion channels are often packaged together as chemically‐gated ion channel. - Depending on receptor protein & type of channel, the postsynaptic neuron may be either excited or inhibited. • Step 6: Neurotransmitter effects are terminated. - As long as neurotransmitter is bound to receptor, it continues to affect membrane permeability & block additional signals. - Effects of the neurotransmitter need to be stopped. -Processes terminating the effects of neurotransmitters: 1. Reuptake by astrocytes or the presynaptic terminal; either stored or destroyed by enzymes. 2. Degradation by enzymes present in postsynaptic membrane or synapse. 3. Diffusion away from synapse.

Chemically Gated Ion Channels

Chemically Gated (Ligand‐ Gated) Channels: Open when the appropriate chemical binds (in this case, neurotransmitter). • Example: ACh receptors at motor end plate (skel. muscle). - Closed: ACh is not bound to receptor. ○ Na+ cannot enter cell & K+ cannot exit cell. - Open: ACh is attached to receptor. ○ Na+ enters cell & K+ exits cell

Electrical Synapses

Electrical Synapses: Specialized to allow the flow of ions between neurons; less common type. • Neurons are connected by gap junctions. • Ions & small molecules can flow from one neuron to the next. • Neurons joined this way are electrically coupled. • Rapidly synchronize activity of connected neurons. • Found in parts of the brain involved in emotions & memory.

EPSPs & IPSP's

Excitatory Postsynaptic Potential (EPSP): Local graded depolarization event that helps trigger an AP at the axon hillock of the postsynaptic neuron. Inhibitory Postsynaptic Potentials (IPSP): Local graded hyperpolarization event that reduces the ability of the postsynaptic neuron to generate an AP.

Neuron Classification: Functional

Functional Classification: Based on direction nerve impulse travels relative to CNS. • Sensory (Afferent) Neurons: Transmit impulses from sensory receptors in skin or internal organs toward or into CNS. - Mostly unipolar with cell bodies in sensory ganglia outside CNS. - Some neurons associated with the special senses (retinal cells, for example) are bipolar. • Motor (Efferent) Neurons: Carry impulses away from CNS to the effector organs (muscles & glands) of the body periphery. - Multipolar - Cell bodies usually in CNS. • Interneurons (association neurons): Lie between motor & sensory neurons in neural pathways; shuttle signals through CNS pathways where integration occurs. - May be one of a chain of CNS neurons, or a single neuron connecting sensory & motor neurons. - 99% of neurons are this type. - Almost all are multipolar.

Muscles of the Neck and Vertebral Column: head movements & trunk extension

Head movements: • Effected by muscles originating in the axial skeleton. • Lateral head movements occur when muscles contract on only one side of the neck. Trunk Extension: • Effected by the deep or intrinsic back muscles associated with the bony vertebral column. - A broad, thick column of muscles extending from the sacrum to the skull. - Muscles are of different lengths and have overlapping origins & insertions. • Vertebrae short muscles: synergists in spinal extension & rotation

Levers: Mechanical Advantage VS. Mechanical Disadvantage

Lever: A rigid bar that moves on a fixed point called a fulcrum when a force is applied to it. • Levers allow a given effort to: - move a heavier load - or move a load farther or faster Mechanical Advantage: • Load is close to fulcrum • Effort is applied far from fulcrum • A small effort can move a large load • Power lever: A lever that operates at a mechanical advantage - A large load is moved only a small distance, but the effort required is also small. Mechanical Disadvantage: • Load is far from fulcrum • Effort is applied close to the fulcrum • Large effort is required to move a small load • Speed lever: A lever that operates at a mechanical disadvantage. - Allows for a load to be moved over a greater distance and at a greater speed. • Regardless of type, all levers follow the same basic principle: - Effort farther than load from fulcrum = lever operates at a mechanical advantage - Effort nearer than load to fulcrum = lever operates at a mechanical disadvantage

Graded Potentials VS. Action Potentials

Location of Event: • Graded Potential: Cell body & dendrites, typically. • Action Potential: Axon hillock & axon. Distance Traveled: • Graded Potential: Short distance - typically within cell body to axon hillock. • Action Potential: Long distance - axon hillock through entire length of axon. Amplitude (Size): • Graded Potential: Various sizes (graded); decays with distance. • Action Potential: Always same size; does not decay with distance. Stimulus for Opening of Ion Channels: • Graded Potential: Chemical (neurotransmitter) or sensory stimulus (e.g., light, pressure, temperature). • Action Potential: Voltage (depolarization; triggered by graded potential reaching threshold). Positive Feedback Cycle: • Graded Potential: Absent • Action Potential: Present Repolarization: • Graded Potential: Voltage independent; occurs when stimulus is no longer present. • Action Potential: Voltage regulated; occurs when Na+ channels inactivate and K+ channels open.

Mechanically Gated Ion Channels

Mechanically Gated Channels: Open in response to physical deformation of the receptor. • Associated with sensory receptors. - Closed: No stimulus (e.g. pressure, touch). - Open: Pressure or touch physically deforms the sensory receptor.

Myelin Sheath

Myelin Sheath: A fatty protein segment that covers nerve fibers, particularly those that are long or large in diameter. • Protects and electrically insulates fibers. • Increases transmission speed of nerve impulses. - Myelinated fibers: Conduct nerve impulses rapidly. - Nonmyelinated fibers: Conduct nerve impulses more slowly. - Myelin sheaths are associated with only axons; dendrites are nonmyelinated.

Neuroglia

Neuroglia (a.k.a glial cells): Supporting cells that surround & wrap neurons. They are smaller than neurons and do not carry electrical signals. • 6 types of neuroglia: 4 in CNS; 2 in PNS General Functions of Neuroglia: • Provide a supportive scaffolding for neurons. • Guide young neurons to proper connections. • Promote neuron health & growth. • Wrap around & insulate neuronal processes to speed up action potential conduction.

Neurons

Neurons, also called nerve cells, are the structural units of the nervous system. Each neuron is a large, highly specialized cell that conducts messages in the form of nerve impulses from one part of the body to another. Special Characteristics of Neurons: • Extreme Longevity: Over 100 years with good nutrition. • Amitotic: Most neurons don't divide and can't be replaced. - As neurons form a communicating network with other neurons, they lose their ability to divide. - Exception: Olfactory epithelium & hippocampus. • Exceptionally high metabolic rate. - Require continuous supplies of oxygen & glucose. - Cannot survive more than a few minutes without oxygen.

Resting Membrane Potential

Resting Membrane Potential: Potential difference across the plasma membrane of a resting neuron. • Approximately ‐70 mV. • Membrane is polarized (negative inside). • Generated by different concentrations of Na+, K+, Cl-, & protein anions (A-). • Ionic differences result from differences in plasma membrane permeability to Na+ (slightly permeable) & K+ (25x more permeable); due to leak channels. • Na+‐K+ pump maintains concentration gradients. • Neurons use changes in their membrane potentials as communication signals to receive, integrate, & send information (sensory input, integration, motor output). • Change in membrane potential produced by anything that: - Alters ion concentrations on the two sides of the membrane. - Changes membrane permeability to any ion. • Signal Types: - Graded potentials: Incoming signals operating over short distances; occur on dendritic and neuron cell body membranes. - Action Potentials: Outgoing signals operating over long distances; occur on axon membranes.

Action Potential Generation

Step 1. Resting state: All gated Na+ and K+ channels are closed; leak (ungated) channels are always open. • Na+ channel: Has 2 voltage‐sensitive gates. - Activation Gate: Closed at rest; opens quickly to depolarization. - Inactivation Gate: Opened at rest; closes slowly to depolarization. • K+ channel: Closed at rest; opens slowly to depolarization. Step 2. Depolarization: Na+ channels open. • Axon membrane is depolarized by graded potentials, opening fast activation gates of Na+ channels. • Na+ rushes into cell, depolarizing it further & opening more Na+ channels; cell interior becomes progressively less negative. • When threshold (‐55 to ‐50 mV) is reached, depolarization becomes self‐generating. Step 3. Repolarization: Na+ channels are inactivating (inactivation gate) & K+ channels open. • Slow inactivation gates of Na+ channels begin to close; membrane permeability to Na+ declines to resting levels & influx of Na+ stops. • Slow voltage‐gated K+ channels open; K+ rushes out of cell restoring internal negativity. Step 4. Hyperpolarization: Some K+ channels remain open & Na+ channels reset. • Increased K+ permeability lasts longer than needed. • Hyperpolarization: Excessive K+ efflux (outward flow) causes a slight dip in action potential curve. • Na+ channels reset; reopen inactivation gates & close activation gates.

Neuron Classification: Structural

Structural Classification: Based on number of processes. • Multipolar Neurons: Three or more processes. - One axon and the multiple dendrites. - Most common type of human neuron (99%). • Bipolar Neurons: Two processes. - One axon & one dendrite on opposite sides. - Rare neurons in some special sense organs. • Unipolar Neurons: Single, short process that emerges from cell body & divides T‐ like into proximal & distal branches. - Peripheral process: Distal; associated with sensory receptor. - Central process: Proximal; enters CNS. - Found mainly in ganglia in PNS; sensory neurons.

Voltage Gated Ion Channels

Voltage‐Gated Channels: Open & close in response to changes in the membrane potential. • Example: Na+ channel - Closed: Membrane potential is negative. ○ Na+ cannot enter cell. - Open: Membrane potential is less negative (depolarization). ○ Na+ can enter cell. ○ Membrane interior changes from negative to positive.

Saltatory Conduction

When an AP is generated in a myelinated fiber, the local depolarizing current does not dissipate through the adjacent membrane regions, which are nonexcitable. Instead, the current is maintained and moves rapidly to the next myelin sheath gap, a distance of approximately 1mm, where it triggers another AP. Consequently, AP's are triggered only at the gaps. This type of conduction is called saltatory conduction because the electrical signal appears to jump from gap to gap along the axon. Saltatory conduction is about 30 times faster than continuous conduction.

A muscle's position relative to a joint affects its action.

• A muscle that crosses on the ANTERIOR SIDE of a joint produces FLEXION. - Example: Pectoralis major • A muscle that crosses on the POSTERIOR SIDE of a joint produces EXTENSION. - Example: Latissimus dorsi • A muscle that crosses on the LATERAL SIDE of a joint produces ABDUCTION. - Example: Deltoid middle fibers • A muscle that crosses on the MEDIAL SIDE of a joint produces ADDUCTION. - Example: Teres major

Integration & Modification of Synaptic Events

• EPSPs & IPSPs summate to determine if threshold is reached. Types of summation: • Temporal (time) • Spatial (location) Integration & Modification of Synaptic Events: A. No Summation: A slowly firing presynaptic neuron causes EPSP's that are far apart in time. - Threshold is not reached, so no AP is generated. B. Temporal Summation: A rapidly firing presynaptic neuron causes EPSP's that are close in time. - Summation brings the axon's initial segment to threshold and an AP fires. C. Spatial Summation: If more than one presynaptic neuron fires at the same time, EPSP's are generated at different locations on the neuron. - Summation brings the axon's initial segment to threshold and an AP fires. D. Spatial Summation of EPSP's & IPSP's: If a presynaptic neuron creates an IPSP, it can override the EPSP created by another neuron. - An IPSP brings the neuron farther form the threshold. - Together, they (nearly) cancel each other out.

Graded Potentials

• Graded Potential: Short‐lived, localized change in membrane potential; depolarization or hyperpolarization. - Triggered by change (a stimulus) in neuron's environment that causes gated ion channels to open. - "Graded": Magnitude (strength, amplitude) of graded potential varies directly with stimulus strength. - Decreases in intensity with distance; current dissipates quickly due to leaky plasma membrane (leak channels). - Graded potentials usually occur along the dendritic and neuron cell body membranes and travel towards the axon hillock. - Sufficiently strong graded potentials can initiate an axon AP • Examples of Graded Potentials: 1. Depolarization: Decrease in membrane potential; inside of the membrane becomes less negative than resting membrane potential. • Moves closer to zero (Example: ‐70 mV to ‐65 mV). • Also includes events in which the membrane potential reverses & moves above zero to become positive. • Promotes generation of action potentials; moves toward threshold. 2. Hyperpolarization: Increase in membrane potential; inside of the membrane becomes more negative than resting membrane potential. • Example: ‐70 mV to ‐75 mV. • Inhibits generation of AP's; moves away from threshold.

Current, Voltage, & Resistance

• Ohm's Law: Relationship between voltage, current, & resistance. Current (I) = Voltage (V) / Resistance (R) • Current and voltage are directly proportional. • Current and resistance are inversely proportional.