BMS 302 Exam 1 Study Guide

Moving with the concentration gradient

materials moving from a high concentration to a lower concentration

Moving against a concentration gradient

materials moving from a low concentration to a higher concentration

Passive Membrane Transport

the movement of molecules across a cell membrane without the expenditure of energy

Diffusion

the net movement of molecules (solute) from an area of higher concentration to a lower concentration

Flicks Law of diffusion

think about how temperature, solubility, cross-sectional area and other factors affect the rate of diffusion

Selective permeability of the membrane

separates intracellular and extracellular environment, allows water and small non-polar molecules to pass freely

What are the types of diffusion?

1. Simple diffusion
2. Facilitated diffusion
3. Active Transport

What is simple diffusion?

high concentration to low concentration, energy is not required

What is facilitated diffusion?

high concentration to low concentration, uses the help of a carrier molecule, energy is not required

What is active transport?

low concentration to higher concentration, energy is required

Osmosis

movement of water through a selectively permeable membrane (moves down the concentration gradient)

What is an ion

any molecule or atom that is charged (positive and negative attract, two of the same charge repel)

Resting membrane potential

occurs due to an imbalance of charged particles between the extracellular and intracellular surfaces of the cell membrane

What is an ion channel?

channels that are selective to the type of ion they were made for

What are the two types of ion channels?

1. Leakage channels
2. Gated channels

Leakage channels

always open to the molecule they are specified for

Gated channels

have a mechanism to keep the gate closed until sufficient stimulus is presented

What are the two types of gated channels?

1. Voltage gated channels
2. Chemically gated channels

What are voltage gated channels?

open and close in response to changes in the membrane potential

What are chemically gated channels?

stimulated to open when the appropriate stimulus binds to a receptor associated with the channel

Inside of the cell compared to the outside

1. more potassium inside the cell (K+)
2. more sodium outside cell than inside (Na+)
Membrane is more permeable to potassium than sodium

What are the two properties that nerve and muscle cells have?

1. have the ability to form action potentials
2. are conductive

Neuron cells

1. soma-cell body
2. dendrites- ears
3. axon- mouth

What two forms do electronic signals take?

1. graded potentials
2. action potentials

Graded potentials

signal over short distances

Action potentials

signal over long distances

Graded potentials

changes in the membrane potential either above or below the resting membrane potential, they are called graded because the amplitude of the graded potential is directly proportional to the amplitude of the stimulus that initiates it

Action potentials

basic unit of electrical activity in the nervous system, described as the progression of an abrupt change in the resting potential along an excitable cell membrane

Sequence of Events leading to an action potential

1. an adequate stimulus of the membrane occurs altering the membrane potential via a graded potential
2. Voltage gated Na+ channels open creating an increases permeability for sodium at the point of stimulation
3. Sodium ions diffuse down concentration gradients
4. sodium ions moving inward causing the transmembrane potential to reach zero (0)
5. sodium ions continue to diffuse inward, inside of cell becomes positive in relation to outside of the cell (depolarization)
6. depolarization at stimulus site send stimulus to adjacent region of membrane and action potential is propagated along axonal membrane
7. at point of origination, decrease of membranes permeability to sodium occurs and channels are closed
8. Increased membrane permeability for potassium (+) as voltage gated potassium channels open
9. potassium ions diffuse outward, membrane becomes negative (repolarization)
10. membrane potential becomes more negative than resting membrane potential, hyperpolarized state results from K+ moving out of cell than necessary
11. cycle repeats from step 1
12. sodium potassium pumps transport Na+ out and K+ into the cell

All or none phenomenon

if a stimulus adequate to cause a membrane potential to reach the threshold potential, a maximal response is evoked

Absolute refractory period

period that cell is unresponsive after action potential

Relative refractory period

when a membrane will respond to a supra-maximal stimulus, period of less than normal responsiveness

What factors influence conduction velocity?

1. diameter of the conduction fiber- as diameter increases so does conduction speed
2. temperature of the cell- all temperature increases so does conduction speed
3. myelin sheath- presence of the myelin sheath increases conduction velocity
4. pharmacological agents- can go either way

Steps of the process of synaptic transmissions

1. action potential spreads over the axon terminal causing changes in membrane potential
2. Ca++ voltage gated channels open allowing influx of Ca++
3. Ca++ serves as intracellular messenger causes synaptic vesicles to fuse with membrane in axon terminal
4. Vesicles release neurotransmitters via exocytosis into synaptic cleft
5. neurotransmitters diffuse across synaptic cleft to post-synaptic membrane
6. neurotransmitter combines with specific receptor on chemically gated channels on post synaptic membrane
7. Permeability of post synaptic membrane is altered, allows for rapid Na+ influx into post synaptic cell
8. if enough transmitter binds, then action potential generated on post synaptic neuron
9. neurotransmitter removed from synapse by degrading from enzymes, taken back into pre-synaptic terminal or diffusing out of the synaptic region

Action potentials are complicated by two factors in compound nerves

1. compound nerve potential amplitude increases until until all the axons have been stimulated
2. action potential may show humps since difference axons conduct signals at different speeds due to temp, size, myelination etc.

What is the compound nerve action potential?

represents the sum of electrical activity occurring at any given time

What is the electrical potential

the relative voltage at a point in an electric field with respect to some reference point in the field

Skeletal muscle is also referred to as what?

voluntary muscle

Anatomy of the muscle cell

1.sarcolemma- cell membrane that surrounds the muscle fibers
2. Myofibrils- fine-like fibers that make of muscle fibers (striated due to mysosin)
3. Sarcomeres- makes of myofibrils, functional unit of contraction
4. Myofilaments- myosin and actin, functional units of myofibrils

What are the subunits of myosin myofilaments?

1. actin- has spherical globular units (G actin)
2. tropomyosin
3. troponin

Actin

spherical subunits (g-actin) are organized into a double chain of f-actin

Tropomyosin

long protein strand lying within the grooves of the F actin helix

Tropinin

found at various active sites along the helix of f-actin

Gap between actin and myosin myofilaments

myosin heads bridge the gap

Sarcoplasmic reticulum

part of striated muscles (skeletal and cardiac)

Transverse tubules (T-tubules)

function is to rapidly and efficiently conduct the wave of depolarization from the sarcolemma to the sarcoplasmic reticulum

Contraction of a skeletal muscle:

also known as excitation-contraction coupling

Excitation process

1. action potential travels to the muscle fiber along the axon of a somatic motor neuron to the neuromuscular junction
2. release of neurotransmitter acetylcholine from synaptic vesicles
3. acetylcholine binds to receptors on muscle membrane (sarcolemma)
4. chemically gated channels open which leads to depolarization
5. Na+ voltage gated channels open initiating the action potential which is propagated along the sarcolemma (occurs from membrane potential alteration)
6. wave of depolarization moves along sarcolemma into the t-tubules
7. sarcoplasmic reticulum releases large quantities of calcium ions into the cytoplasm or sarcoplasm

Steps of contraction (mechanical)

1. calcium ions diffuse into sarcoplasmic and bind to troponin subunit of actin molecule
2. calcium bound troponin causes tropomyosin subunit to be pulled deeper into the groove of the two strands of f actin helix, exposing myosin binding sites on actin filament
3. myosin heads in high energy state bind to myosin binding sites on actin molecule forming cross bridges which pulls actin filament like ratchet
4. after first power stroke, ATP combines with myosin head (now in low energy state), myosin head separates from binding site on actin molecule
5. ATPase found in myosin head hydrolyzes ATP on myosin head, energy released used for "cocking" of myosin head, head attaches to another binding point on actin filament, another power stroke occurs
6. shortly after release of calcium ions into sarcoplasm, calcium pump pumps them back into sarcoplasmic reticulum, when enough calcium has been pumped back into sarcoplasmic reticulum the interaction between actin and myosin ceases and the muscle relaxes (ATP needed to pump calcium back into sarcoplasmic reticulum)

Rigor mortis

occurs within a few hours of an organism dying, in the absence of ATP, myosin heads cannot be released from actin binding sites and calcium ions cannot be removes preventing relaxation from happening

Muscle Twitches

occurs from a brief stimulus to the fibers of a skeletal muscle, only a single contraction occurs before returning to relaxation

Myogram

recording of a muscle contraction

What is a latent period?

a brief period before the muscle begins to contract, following the application of a stimulus to a motor neuron innervating a muscle fiber

Motor Units

each single motor neuron and the muscle fibers it innervates

Threshold stimulus

stimulus of adequate strength to cause a reaction

What does a smooth, graded response by a muscle depend on?

1. number of motor units activated at any given time
2. the frequency of nerve impulses
3. asynchronous firing of different motor neurons

Summation

adding together the individual muscle twitches that make a strong and concerted useful muscle movement

What two ways does summation occur?

1. increasing the number of motor units contracting simultaneously
2. increasing the frequency of contraction (by increasing frequency of stimulus)

Multiple motor unit summation

1. occurs from increasing the number of motor units firing simultaneously
2. in theory, only one motor unit can be stimulated
3. maximal stimulus- recruits all motor units to fire
4. Supra-maximal stimulus- does not cause a more intense reaction as all motor units would be firing

Wave summation

1. occurs from increasing the frequency of contraction (by way of increase frequency of stimulation)
2. second stimulation is applied before motor unit is relaxed causing it to extend again

Tetanus

occurs when succeeding stimuli arrive so quickly that the preceding contractions cannot relax at all

Muscle Fatigue

inability of a muscle to maintain a particular strength of contraction or tension (underlying factor is muscle's inability to generate energy as ATP at a sufficient rate)

Muscle Tone

residual degree of muscle contraction even when the muscle is relaxed

Asynchronous firing of motor units

allows for contractions to be maintained for an extended period of time, motor units are firing at different times basically (think about the muscle motors in the neck)

Motor points

certain sensitive spots that can stimulate contraction through the skin into the nerve responsible for that muscle

Autonomic nervous system

responsible for involuntary actions such as heart beat, body temperature, blood pressure, gastrointestinal motility etc.

Smooth muscles

important for walls of blood vessels, viscera and airways

Functional differences between Autonomic and Somatic nervous systems

1. autonomic system usually increases or decreases organ activity (sympathetic and parasympathetic)

Anatomic differences between autonomic and somatic nervous systems

1. Efferent ANS neurons- pre-ganglionic and post-ganglionic neuron

Ganglion

collection of nerve cell bodies (somas) located outside the CNS, parasympathetic are usually close to their effector organ

Adrenal Medulla

no post-ganglionic neurons as the gland releases epinephrine directly into circulation

Receptor Physiology

distinctive small sites on the cell membranes of tissues in which neurotransmitters interact with to produce a response

Receptors for acetylcholine

cholinergic receptors, can be either of the two following
1. nicotinic- excitatory and rapid
2. muscrinic- can be excitatory or inhibitory, response is prolonged

Receptors for norepinephrine (neurotransmitter) or epinephrine (hormone)

divided into alpha and beta receptors (dont need to know)

Pharmacology

study of actions of drugs on living organisms

Types of Drugs

1. agonist- bind to receptor and mimic the effect of a neurotransmitter
2. antagonist- binds to a receptor and blocks the action of the agonist

Cholinergic drugs

1. cholinergic agonist- mimics effects of acetylcholine
2. cholinergic antagonist- block effects parasympathetic drugs

Adrenergic Drugs

1. adrenergic agonist- mimic the sympathetic system
2. adrenergic antagonist- do not stimulate or inhibit the tissue itself, but prevent the effect of adrenergic drugs

Differences between smooth and skeletal muscles

1. calcium enters in smooth muscle enters from extracellular fluid since its sarcoplasmic reticulum is not well developed
2. Latent period for smooth muscle is up to 50x longer than the latent period for skeletal muscle
3. contraction is measured in seconds for smooth muscle rather than milliseconds for skeletal muscles

What are the two major types of smooth muscle?

1. multi unit smooth muscle
2. visceral smooth muscle

Multi Unit muscle

1. each fiber operates independently of each other
2. one neuron innervates each fiber
3. do not exhibit inherent rhythmicity
4. controlled almost entirely by the autonomic nervous system
5. contractions are discrete and localized (think about fine tuned muscles such as the eye)

Visceral muscle characteristics

1. occur in large sheets and compose organ walls
2. tightly bound together via gap junctions to form continuous networks of fibers
3. when one fiber is stimulated, the action potential travels over adjacent fibers so that contractions move from cell to cell

What is inherent rhythmicity?

the ability of a muscle to contract spontaneously without being stimulated by the nervous system

How does inherent rhythmicity work?

1. pacemaker cells- some myogenic muscle cells are self- excitatory

Tonus

visceral smooth muscles are usually in a state of sustained partial contraction

Plasticity

within limits, the walls of hollow organs accommodate themselves by their level of tonus to the volume of their contents without any marked alteration in the tension on the wall of the organ ( think about when you "stuff" yourself on thanksgiving day)

Mechanisms involved with innervation of the gastrointestinal tract

Extrinsic mechanisms- autonomic nervous system
Intrinsic:
1. myenteric plexus- lies between the outer longitudinal and the middle circular muscle layers and is primarily involved in motility of the GI tract
2. submucosal plexus- lies between the middle circular layer and the mucosa, has a major role in secretory activities in GI tract

Enteric Nervous System

composed of over a million neurons, responsible for the coordination of smooth muscle contractions that occur in the absence of extrinsic innervation

What are the two major functions of smooth intestinal muscle?

1. to mix intestinal contents
2. to move intestinal contents slowly through the small intestine to the large intestine. Movement is slow to allow time for digestive enzymes to function and for absorption to take place

What are the two important movements of the small intestine?

1. Segmentation- "kneading" and "mixing" of contents due to alternating contractions and relaxations
2. peristalsis- wave-like contractions, occur due to circular muscle contractions constrict the area above a bolus of food in order to move it further down the GI tract

What are the three levels of control in terms of motility?

1. inherent rhythmicity-pacemaker cells
2. enteric nervous system- intrinsic innervation
3. autonomic nervous system- extrinsic innervation