Exam 1: Modules 1 to 7


Module 1

--> study of function in living organisms

--> mechanisms which they control internal environment

--> explains physical & chemical factors of function and disease

Homeostasis <-- maintenance of internal environment

Internal environment <-- interstitial fluid & blood plasma

External environment <-- outside body, contents digestive, respiratory & urogenital tracts

--> maintains homeostasis via (+) & (-) feedback

Negative Feedback Control Systems

--> all of them contain same components

--> Ex. heat @ house

--> controlled variable (heat), detected by sensor, shuts off own production by effector (furnace)

Body Temperature (Set pt. 37°C)

--> temp. could drop to 35°C

--> detected by sensors in nervous systems

--> signals control centre in hypothalamus

--> activates organs & systems to generate heat

--> once back to set point , regulates

Positive Feedback Control Systems

--> controlled variable stimulates its own production

--> large amounts of controlled variable produced quickly

Ex. have impulses, ovulation

Positive and Negative Feedback Controlled by

1. Nervous System

--> rapid

2. Endocrine System

--> slow


Module 2

-> Internal environment bathed in fluids

Body Fluids Compartments

  1. Intracellular (ICF)
  2. Inside cells
  3. Extracellular (ECF)
  4. Interstitial fluid
  5. Plasma

Plasma - Pale yellow fluid, 92% H2O, 8% (proteins, ions, gas, nutrients & waste)

-> colloidal solution (suspended subs that doesn't settle)

Chemical Composition of Bodily Fluids

-> huge difference in ion concentrations between plasma & interstitial fluid vs intracellular fluid

-> small difference between plasma & interstitial fluid

-> composition maintained by selectively permeable membrane


Module 3

  1. Cell membrane selectively permeable

-> Carbohydrates for cell recognition

-> Cholesterol for stability & immune response

-> Associated enzyme act as catalysts for reactions

Carriers - Transport molecules across membrane

Identity Markers - Distinguish between self & foreign cells

Pores - Allows water soluble subs in cell

Enzyme - Chemical reactions, breakdown of molecules

Receptor - Attach hormones & neurotransmitters

Diffusion - Electrically charged molecules (Na+) tend to move toward areas of opposite charge (+) (-)

-> Down their electric current gradient

  1. Lipid soluble substances (O2, Co2, steroids) pass through cell membrane with ease
  2. Water soluble substances must use pores/carriers (K+, Na+)

Diffusion Factors

  1. Size of channels (sugar too big), approximately 0.8 nm
  2. Charge on molecule, (+) molecule won't go through (+) channel
  3. Greater the electrochemical gradient, greater its rate of movement down channel/membrane
  4. # channels in membranes, increase in channels, increase in ions in cell

Facilitated Diffusion

  1. Rate of transport limited by number of available proteins
  2. Shows chemical specificity (interact with specific shape)
  3. Shows competitive inhibition

Active Transport - Involves energy

  1. Works against concentration gradient
  2. Requires ATP
  3. Shows competitive inhibition & saturation


  1. Cell has osmolarity 300 milliosmoles (mOsm)
  2. Diffusion of H2O across membrane, net movement H2O down concentration gradient

Solute - Substance being dissolved (ice, sugar, Na+)

Solvent - Liquid doing dissolving (H2O)

Solution - When solute dissolves in solvent

Factors affecting Osmosis

  1. Permeability of membrane to solutes in intra & interstitial
  2. Concentration gradients of solutes in intra & interstitial
  3. Pressure gradient across cell membrane.

Units -> osmole <- # osmotically active particles in solution

  1. Osmolality= # osmoles/ Kg. H2O
  2. Osmolarity= # of osmoles/ L of solution

Tonicity - Ability solution to cause osmosis cross biomembrane

Isotonic (300 mOsm) Concentrations same on both sides (balance)

Hypotonic (260 mOsm) Low concentration compared cellular fluids so osmosis into cell (swells)

Hypertonic (360 mOsm) - High concentration compared to cell & osmosis out of cell (cell shrinks)

Concentration Gradients & Membrane Permeabilities

  1. Na+, Ca++, Cl- higher concentration outside cell

-> Concentration gradients make them inside cell

-> Just cause gradient doesn't mean it moves that way

-> All three have very few channels in membrane

  1. K+ higher concentration inside cell

-> Concentration gradient move out of cell

-> Membrane more permeable, some diffuse through

  1. These channels open due to a variety of stimuli

Membrane Potentials

-> Movement of charged particles (ions) affected by electrical gradients (+ & -) attract.

Electrical Potential - Charge difference between two points

Resting Membrane Potential (-70 mv)

  1. Nerves and muscles are excitable cells, they need resting potential
  2. Very minute excess of (-) ions accumulate inner
  3. Cations accumulate outside
  4. Establishment of electrical Potential
  5. All cells in body have one

Equilibrium Potentials

  1. When concentration gradient & electrical gradient are equal in magnitude in opposite directions no net movement

-> Called electrochemical equilibrium

Equilibrium Potential - electrical potential that must be applied to the inside of the cell in order stop concentration gradient movement

  1. Larger the concentration gradient, larger equilibrium potential needed to stop movement of ion

Vertebrate Neuron Equilibrium Potentials

  1. (K+) = -90mV
  2. (Na+) = +60 mV

-> Has pores otherwise would diffuse

  1. (Cl-)= -70mV
  2. Charge needed to keep ion from moving into cell

Sodium Potassium Pump

  1. Pumps 3Na+ ions out & 2K+ in
  2. Helps maintain resting potential -> Electrogenic pump
  3. Pumps against concentration gradient needs ATP
  4. Causes cell to become electronegative
  5. Without it most cells would swell & explode
  6. Cell volume kept constant
  7. Helps with osmosis & solute concentrations


Module 4

Excitable Cells - Can use resting potential to generate electrochemical impulse (action potential)

--> Ex. nerve & muscle cells

Action Potential--> rapid reversal of resting membrane

  1. Strong depolarization at axon hillock triggers of Na+
  2. Na+ rushes in
  3. Membrane depolarizes to +35mV
  4. Na+ channels inactivate, K+ open
  5. K+ rushes out
  6. Membrane re-polarizes +35mV --> 7-0mV
  7. K+ rushes out hyper polar -90mV
  8. K+ closes channel, slowly back to 7-0mV

Voltage Gated Na+ Channel V--> depolarization of membrane --> Na+ flow in cell ---> Na+ closes & returns to normal configuration ---> Channel won't open during absolute refractory period -

Voltage Gated K+ Channel

--> open when Na+ close

--> K+ flow out of cell

--> gate closes & returns to resting configuration

--> don't have an inactivation periodR

efractory Periods

Absolute --> Na+ channels can't be activated

Relative --> 1membrane yper polarized

2--> aused by K+ that slow to close

--> i is possible to fire stimulus but would need stronger stimulus

Threshold Staring Action Potential

--> initial depolarization must be strong enough to open almost all of the Na+ voltage gated channels

--> occurs when membrane potential depolarizes to -55mV -

-> once this reached will always have action potential

Action Potential Propagation

--> movement of action potential down axon

--> direction current flow (+) --> (-) (opposite attract)

Un myelinated Nerve

  1. inside membrane (+) (35mv) cause Na+ enter cell
  2. (+) charge attracted to (-) of near by resting membrane
  3. Nearby cell depolarizes, due to build up of (+) charge --> causes Na+ channels to open
  4. Na+ depolarizes, creates new action potential
  5. Repetition of this causes propagation along membrane

Ex. think of human wave at baseball game

Myelinated Nerve (Saltatory Conduction)

*Saltare - To jump*

--> much faster than Uu yelinated due to jumping

--> insulates axon to prevent ions leaking

--> voltage gated channels only at gaps (Nodes Ranvier)

  1. (+) charge from action potential attracted to adjacent node (-)
  2. Node depolarizes
  3. Triggers voltage-gated Na+ to open
  4. Na+ rushes in, depolarizes, starts new action potential
  5. Repeat & propagated

--> due to absolute refractory period, propagation can't & won't go backwards --> always forward


--> myelinated sheaths under attack

--> body's natural immune system attacks & damages myelin

--> can stop transmission of action potentials

--> if nerve damaged, connected to muscle, muscle won't contract --> causes paralysis

Synaptic Transmission

--> connection of nerve cell to other nerve, muscle or organ called chemical synapse

euromuscular Junction (NMJ)

  1. synapse between neuron & muscle cell
  2. leads to contraction of muscle cell
  3. membrane presynaptic axon terminal contains Ca2+ channel

--> open when cell membrane depolarizes

  1. axon terminal contains vesicles with acetylcholine (ACh)
  2. basement membrane of axon terminal contains enzyme acetylcholinesterase (AChE)

muscle cell membrane (sarcolemma) under axon terminal --> called end plate (has receptors for acetylcholine

--> associated with ligand-gated ion channels

Events at NMJ

  1. action potential triggers Ca2+ voltage gated channels open Ca2+ flows into cell
  2. Ca2+ triggers fusing synaptic vesicles to membrane & release of ACh into synaptic cleft via exocytosis
  3. ACh diffuses across synapse to receptors on muscle cell
  4. ligand-gated channels open, Na+ flows in, few K+ leave --> triggers local depolarization called end plate potential (EPP)
  5. depolarization EPP spreads to adjacent cells, channels open, large number of Na+ flows into muscle cell and triggers action potential
  6. ACh broken to acetic acid and choline by AChE --> choline back to axon terminal to recycle


Module 5

  1. Biological machines that utilize chemical energy from breakdown and metabolism of food to perform useful work
  2. 600+ muscles
  3. Perform 3 main functions
  4. Movement
  5. Heat production
  6. Body support, posture

Skeletal Muscle

  1. Whole muscles made up of bundles of fasciculi
  2. Each fascicle made up of groups cells or fibres
  3. Each muscle cell --> bundles myofibrils
  4. Each myofibril contains thick and thin myofilaments
  5. Thin <-- protein actin with troponin and tropomyosin
  6. Thick <-- myosin protein

--> interaction thin and thick = muscle contraction

--> fasciculi surrounded by white connective tissue called perimysium

Structure Skeletal Muscle

  1. Muscle cells surrounded by sarcolemma (muscle cell membrane)

--> action potential transmitted on

  1. Sarcolemma has small tube-like projections

--> called transverse tubules

--> extend down into cell

--> conduct action potential deep into cell where contractile proteins are located

  1. Within muscle cell are long cylindrical myofibrils that contain contractile proteins (thick and thin)
  2. Myofibrils surrounded by sarcoplasmic reticulum (SR)

--> mesh-like network of tubes containing calcium ions (Ca2+) (essential for contraction)

  1. Terminal cisternae (membranous enlargement of SR)

--> either end and continuous SR

--> its close to T-tubule (action potential travels)

Thin Myofilament

  1. Composed of predominately of globular protein --> actin
  2. Each actin has special binding site for myosin
  3. Actins strung together like beads on a necklace and then twisted to form a backbone of thin myofilaments
  4. Tropomyosin <-- long protein strands on thin myofilaments

--> muscle at rest, proteins cover binding sites of myosin

  1. Troponin <-- regulatory protein

A --> binds to actin

B --> binds to tropomyosin

C --> binds with Ca2+

  1. at rest troponin complex holds tropomyosin over myosin binding sites

Thick Myofilament

  1. Made of protein myosin
  2. Protein has long, bendable tail and two heads that can each attach to myosin binding sites on actin
  3. Heads have site that can bind and split ATP --> splitting of ATP that releases energy to myosin that powers contraction of the muscle
  4. Many myosin molecules arranged form one thick filament

Actin/Myosin Relationship

  1. Arranged in repeating pattern
  2. Each group thin myofilaments extends outward in opposite directions from central Z disc --> where they are anchored
  3. Groups thick myofilaments extend outward from central M line --> where they are attached
  4. Myofilament parallel to length of myofibril and muscle cell
  5. Sarcomere : region from one Z disc to another --> smallest functional contractile unit
  6. Under microscope gives striated appearance

A bands <-- thick filaments as dark bands

I bands <-- thin filaments with light bands

Muscle Contraction

  1. Interaction between actin and myosin leads to contraction
  2. Head myosin attaches binding site of actin --> forms cross-bridge, myosin undergoes change in shape
  3. Change in shape cause myosin head to swing --> producing power stroke
  4. Power stroke --> slides actin past myosin

*Thick/thin do NOT shorten during contraction*

Excitation Contraction Coupling & Muscle Contraction

  1. Process action potential excites muscle cell to produce muscle contraction
  2. Action potential at NMJ spread over sarcolemma and down T-tubules into core of muscle cell --> produce muscle contraction
  3. Action potential travels close to SR and opens Ca2+ channels --> releases Ca2+ from terminal cisternae of SR
  4. Ca2+ will bind to troponin C on thin myofilaments causing tropomyosin to uncover myosin binding sites on actin
  5. Myosin attaches to actin and power stroke occurs

Relaxation of Muscle

  1. Action potential stop, Ca2+ no longer diffuse out of SR
  2. Special Ca pumps, pumps Ca2+ back into SR (against concentration grad) --> requires ATP
  3. Tropomyosin covers myosin binding sites
  4. Myosin unable binds --> relax muscle no power strokes

Actin-Myosin and ATP cycle

  1. Splitting ATP to adenosine diphosphate (ADP) and inorganic phosphate releases energy to myosin and prepares myosin head for activity
  2. Formation cross-bridges occur when Ca2+:
  3. have been released from SR by Action Potential, binds Troponin C
  4. rolls tropomyosin off myosin binding sites
  5. Power stroke occurs when myosin heads bend and slides the thin myofilaments of actin over thick myofilaments of myosin
  6. ADP and P molecules released from head
  7. New molecule ATP binds to myosin heads

Two ways Muscles Alter Force Contraction

  1. Recruit Motor Units
  2. Summation Twitch Contractions

Motor Unit

  1. Is a motor neuron and all muscle cell/fibres causes contact
  2. One motor neuron contact several muscle cells --> ever muscle cell only one motor neuron

Large --> 200 cells

Small --> Few cells

Motor Unit Recruitment

--> Progressive activation of motor units resulting in more forceful contraction

Muscle Twitch

  1. Simplest and smallest contraction
  2. Result of an action potential in motor neuron
  3. Will cause excite cell and release Ca2+ from SR --> very small contraction
  4. Varies 10-100ms --> AP = 2ms
  5. Latent period due to all events at NMJ
  6. Can increase force contraction by increasing # action potential/second that travel down nerve (frequencies)
  7. High frequencies


Module 6

Central Nervous (CNS)

-> brain & spinal cord

Peripheral Nervous (PNS)

-> nerves that goes to muscles & organs

Basic Structure of the Brain

Left Hemisphere - Send signals to activate muscles on the right side of body

Right Hemisphere - Sensory information from right side goes to left hemisphere (vice versa)

Cerebellum - Responsible coordinated movement (above brain stem)

Brain Stem

-> controls basic functions like heart rate and respiration

-> made up of midbrain, pons & medula ablongata

Diencephalon - thalamus & hypothalamus


  1. Found in mammals divided in 3 types based on # of processes that emerge from cell body

1.Bipolar - two process from cell body

  1. specialized & found in retina of eye

2.Unipolar --> one process

  1. located in peripheral nerves → cell body middle axon
  2. usually sensory & transmit to & from spinal cord

3.Multipolar --> contain many branching dendrites 2 one axon

--> most common in CNS

Glial cells

--> support cells of brain

--> maintain delicate internal environment of CNS

--> there are 5 times as many glial cells as neurons

--> regulate nutrients & specific interstitial fluids

--> several types astrocytes, microglia, oligodendrocytes

Language Nervous System / Neural Coding

  1. action potentials are language of nervous system neural coding
  2. weight of object "coded" into action potential

--> heavier object, more action potentials per second

Chemical Synapse

--> presynaptic nerve releases neurotransmitter --> affects postsynaptic

1) Axon Terminal Presynaptic Cell

  1. voltage-gated Ca2+ channels
  2. synaptic vesicles containing
  3. neurotransmitters
  4. mitochondria

2) Synaptic Cleft

3) Postsynaptic Cell

  1. chemical receptors
  2. chemically gated channels
  3. chem = neurotransmitters

Event @ Chemical Synapse

--> neurotransmitters synthesized in presynaptic neuron → stored synaptic vesicles

--> action potential (AP) in presynaptic depolarizes membrane & activates Ca2+

--> Ca2+ cause synaptic vesicle to fuse to wall synaptic terminal

-> cause exocytosis & release neurotransmitter

--> neurotransmitter into cleft & acts on chemical receptors on postsynaptic

--> receptors cause opening chemically gated ion channels

--> postsynaptic membrane potential changes

-> causing depolarization/ hyperpolarization (depends on neurotransmitter)

--> depolarization increases probability of action potential on postsynaptic neuron

--> hyperpolarization decreases likelihood


--> are chemicals released by neurons @ axon terminal

--> synthesized in neuron stored synaptic vesicles released response to action potential

--> diffuses through synaptic cleft → produces response to post synaptic neuron

--> type of neurotransmitter --> 2 outcomes

1) excitatory (on) --> leading to depolarization of postsynaptic cell

-> it strong enough, may fire action potential

2) inhibitory (off) --> leading to hyperpolarization of postsynaptic

-> harder to generate action potential

Four main types of Neurotransmitters

1) Acethylcholine

2) Biogenic Amines

--> catecholamines

--> dopamine

--> norepinephrine

--> epinephrine

3) Amino Acids

--> Excitatory

--> Glutamate/ Aspartate

--> Inhibitory

--> GABA / Glycine

4) Neuropeptides

-> endogenous opioids (endorphine)

-> Vasoactive Intestinal Peptide (VIP)

Most Common Excitatory : Glutamate

Most Common Inhibitory : GABA, gamma-amino-butyric acid


--> excitatory potential neurotransmitter causes opening of chemically gated channels

--> EPSP & IPSP occur on dendrites of neutrons on CNS

--> gates selective (+) ions, mostly Na(+) flow in

--> cause local depolarization called --> EPSP

-> very local event that diminishes w time

-> called graded potential

--> influx Na+ will depolarize --> no AP

-> no AP cause no voltage gated channels

--> in order to genereate AP EPSP must depolarize axon Hillock

--> (+) current EPSP must be strong enough to spread from synapse where it originated to axon hillock

-> now can have action potential

Strength EPSP increases in Two Ways

1) Spatial Summation EPSP

--> when sufficient number voltage channels reach threshold fire

--> additive effect produced by many EPSPs that have been generated @ diff synapses on same post synaptic neuron @ same time

2) Temporal Summation EPSP

--> sufficient number of voltage channels reach threshold fire action potential

--> additive effect produced by many EPSPs that have been generated @ same synapse by series of high-frequency action potentials on presynapse


--> neurotransmitters in this situation hyperpolarize

-> called inhibitory post synaptic potential (IPSP)

--> do so by opening diff chemically gated channels

-> let Cl- into (making more (-))

-> let K+ leave (making more (-))

--> moves it further from threshold (less likely Action Potential)

-> will shut off nerve cells

--> spatial & temporal summation occur with IPSPs & EPSPs

-> for IPSP produce strong hyperpolarizations

Synaptic Integration

--> single postsynaptic nerve cell can receive hundred & synapse

--> battle between EPSPs & IPSPs

Basic Structures and Organization

  1. Motor system includes the
  2. Supplementary motor area
  3. Premotor area
  4. Primary motor cortex area
  5. Basal ganglia
  6. Spinal pathways
  7. Motor nerves going to the muscles
  8. Muscle receptors

Motor system

Premotor cortex --> located in front lobe

-> develops appropriate strategy for movements

Supplementary Cortex --> located frontal lobe

-> program motor sequences, more complex more this cortex used

-> important for repetitive movements (typing)

-> code has now been written & sent to primary motor cortex

Primary Motor Cortex (PMC)

--> located on precentral gyrus in frontal lobe

Motor Homunculus --> topographical representation body on surface of cortex

-> specific area motor cortex activates particular muscle

--> signals from primary motor cortex travel down spinal cord through corticospinal tract

Corticospinal Tract

--> major motor pathway from PMC to motor neurons

--> made of millions axons, cell bodies lie in PMC

--> tract begins in motor cortex descends down to brain stem

--> in medulla

-> 80 % nerve fibres cross to other side body (contralateral)

-> 20 % nerve fibres remain on same side (ipsilateral)

--> from brain stem fibres enter spinal cord

--> once fibres reach level spinal cord where they synapse with motor neurons

-> fibres previously on ipsilateral side cross to contralateral side

--> neurons cortical spinal tract synapse with motor neurons

-> which directly innervate muscle

Muscle Receptors

Proprioception --> "muscle sense", brain being aware of positions of limbs & extent of muscle contraction

Two Receptor Types :

1) Muscles Spindles :

-> detect muscle stretch/length & rate of change of muscle

2) Golgi Tendon Organs

-> detect muscle tension

Muscle Spindles

--> sense length & stretch

Gamma Motor Neurons

->two of them

-> activate intrafusual fibres

--> when whole muscle cell stretches sensory region of spindles also does

--> sensory region sensitive to change

-> depolarizes and triggers action potential sensory nerve

--> sends to brain

-> increase stretch muscle, increase Action Potential to brain

-> since muscle attached to limb brain knows

Alpha - Gamma Coactivation

--> ensures muscles spindle continues send brain signals

--> signals to whole muscles travel through alpha, intra not active

--> during muscle contraction command sent through gamma too

Reflex Arc

--> most basic type integrated neural activity

1) begins with receptor & receptor potential produces action potential afferent neuron

2) action potential enters spinal cord, produces action potentials on interneurons & eventually on efferent neuron

3) Efferent neuron activates effector (Ex. muscle)

--> reflex arc doesn't require output from brain to cause muscle to contract

  1. Sensory Receptor 2. Afferent neuron 3. Interneuron (spine) 4. Efferent Neuron 5. Efferent organ

Stretch Reflex

--> example of reflex arc

--> reflex found in every muscle

Stretch Reflex Quadriceps :

1) tap tendon makes small stretch quad muscle

2) muscle stretch = muscle spindle stretch

3) Muscle spindles trigger action potential in afferent neuron that enters spinal cord

4) Motor Nerve of quadriceps activated while muscles hamstring inhibited

5) Quadriceps contract & hamstring relaxes, lower leg kicks out

*brain not involved w contraction*

Cerebellum " little brain "

--> contains more neurons than rest of brain combined

Functions :

--> contributes generation accurate limb movements

--> correcting ongoing movements & modifying strength of some reflexes

--> involved with pavlovian conditioning

--> learning new muscle movements & vestibular <-- eye move occular reflex

How it Assists Accurate Limb movements

--> must recieve --> must receive same info from:

-> motor cortex <-- travelling out to muscles

-> proprioception <-- position muscle

--> cerebellum can make sure muscle doing right

--> if movement incorrect cerebellum modifies signals from the primary motor cortex

Limbic System

--> composed of hypothalamus, amygdala & hippocampus, cingulate cortex & septum

--> found deep in brain & form ring around brain stem

--> Key function: to link higher thought process with more primitive emotional responses (fear, rage, sex)

--> involved w feeding, drinking, pain, motivation, learning

--> allows respond changes in environment


(base of brain, anterior brain stem)

Major Functions:

--> temp control, H2O regulation, regulates food intake, cardiovascular regulation, circadian clock, emotion coordination

-> and controls release hormones from pituitary

--> does most functions through use of negative feedback

Ex. body @ 39°C instead 37°C

--> hypothalamus detects & starts sweating to cool body down

Effects of SYN and PSYN usually opposite, where one excites other will inhibit.

Automatic Nervous System (ans)

--> not under voluntary control "automatic" system


--> heart rate, pupils in eye, smooth muscle in walls of arteries, glands, many other organs

Two divisions of ANS:

1) sympathetic (SYN)

--> excites/inhibits

--> fight or flight response nerves

--> exist @ spinal cord in thoracic & lumber (center)

--> preganglionic neurons synapse in ganglia onto 2nd postganglic nerve

--> that travels to effector/ target organ

2) parasympathetic (PSYN)

--> storage & conservation

--> nerves exist @ brain stem & spinal cord very low sacral region

--> preganglionic nerves will synapse onto postganglionic nerve near effector organ

--> nerve will synapse onto target organ

--> every organ has SYN & PSYN

-> except adrenal only SYN

Neurotransmitters of ANS

--> preganglionic neurons that leave spinal cord in SYN & PSYN release neurotransmitters acetylcholine (ACh)

--> axons of PSYN preganglionic longer cause synapse occurs closer to effector organ

--> ACh will stimulate 2nd postganglionic neuron

--> sympathetic --> usually releases norepinephrine, sometimes ACh

--> parasynpathetic --> always ACh released

Sensory System

Module 7

Transduction Environment

--> how external stimuli detected by sensory receptors

Environmental Stimuli

  1. Stimulus must be detected by sensory receptor
  2. Different environmental stimuli, therefore different receptors needed

Mechanical Stimuli

--> Touch, pressure, vibration, sound, proprioception (muscle sense)

Chemical Stimuli

--> Taste, pain, odours

Electromagnetic Stimuli

--> Light

Other Stimuli

--> Gravity, motion, acceleration, heal

Adequate Stimulus

  1. Some receptors detect more than one stimulus

Adequate stimulus <-- Stimulus sensory receptor most sensitive to

--> Example: Rod & cone cells in eye adequate stimuli --> Light

Receptor Potentials

  1. Once sensory receptor stimulated by environmental stimulus
  2. Cause change in ion permeability, leading to local depolarization
  3. Called "generator/receptor potential"
  4. Receptor no voltage gated channels
  5. Therefore, receptor potential must spread to area on sensory neuron that contains voltage channel
  6. Usually at first node of ranvier on axon
  7. action potential then generated & propagated along axon & in spinal cord
  8. In receptors with no axons, depolarization spread & to synapse, results in release of neurotransmitters
  9. Hair cell in ear

Shared Characteristics between EPSP's & IPSP's

  1. Generally depolarizing but can be hyper-polarizing too
  2. Caused by increasing permeability to sodium ions -> increase permeability K+ for hyper-polarizing
  3. Are local, spread like EPSP, decrease with time and distance from stimulus
  4. Proportional strength stimulus, increase stimulus, increase receptor potential, increase action potential likeliness

Somatosensory System

  1. Detects & processes sensations of touch, vibration, temperature & pain <-- most originate in skin

Cutaneous Receptors (receptors in skin)

  1. Hair follicle: Sensitive to find touch and vibration
  2. Free Nerve Endings: Pain & temperature (hot/cold)
  3. Meissners Corpuscles: Detect touch low frequency vibrations (30 & 40 cycles)
  4. Ruffinis Corpuscles: Detect touch
  5. Pacinian Corpuscles: Detect high frequency vibrations & touch (250-300 cycles)

Receptive Field

  1. Area on surface of skin where adequate stimulus will activate particular receptor to fire an action potential in neuron
  2. Any stimulus applied outside receptor field will not generate action potential

Spinothalamic (anterolateral) Tract

  1. Somatosensory pathway
  2. Transmits information dealing with basic sensations (pain, temperature, touch)
  3. Information from sensory neuron (1st order) enters spinal cord
  4. Synapses with (2nd order) neuron
  5. This neuron crosses to opposite contralateral side of spinal cord & ascends to thalamus
  6. Thalamus: relay center all sensory (except smell)
  7. Synapse occurs with neuron (3rd order) then travels
  8. Travels to somatosensory cortex
  9. Sensory information from right side of body goes to left side of the brain

Dorsal Column Medial Lemniscal

  1. Somatosensory Pathway
  2. Transmits information: fine detail touch, proprioception & vibration
  3. Sensory neuron information (1st order) enters spinal cord & immediately travels up spinal cord -> Before crossing contralateral side
  4. Upper spinal cord sensory neuron synapses with (2nd order neuron) -> Then crosses to opposite side of spinal cord
  5. Continues to thalamus, synapses again onto (3rd order)
  6. Then travels to somatosensory cortex

Primary Somatosensory Cortex

  1. Once sensory information has reached the brain, travels to primary somatosensory cortex which is located

-> In parietal lobe on postcentral gyrus behind central sulcus

Somatosensory Homuncutus

  1. Organization of PSC in topographical Representation of body
  2. It is geographically preserved
  3. Some areas on cortex like hand, tongue, & lips require more of brain to process & get more sensory information
  4. They contain many more sensory receptors than any other part

The Visual System

  1. Detects light, converts into action potential & sends to primary visual areas for processing
  2. Once processed become aware visual environment

Consists of:

Eye: Contains photoreceptors that convert light to Action Potential

Visual Pathway: Transmits action potentials

Primary Visual Area: Process incoming signals (in occipital lobe)

The Eye

  1. Light Passes through Cornea
  2. Amount of light regulated by Iris
  3. Constricts bright light or dilates low light
  4. Lens flips light (upside down & backwards) & focuses it onto retina at back of eye
  5. Retina contains photoreceptors
  6. rods and cones (point at back of head)
  7. Fovea, part of retina with highest concentration of cone cells
  8. Center of vision focused here

Rod Cells & Cone Cells

  1. Don't have axons therefore no action potentials
  2. Generate receptor potentials that release inhibitory neurotransmitters from synaptic end

Rods - Extremely sensitive light

  1. Function best low light
  2. Contain one photopigment
  3. Don't detect colours
  4. Rods located mostly region of retina outside & around fovea

Cones - Function best bright light

  1. Ideal detecting detail
  2. 3 types each sensitive 1 primary colour
  3. Found in large concentrations on fovea

Other Cells Retina

  1. Retina contains pigment layer at very back of eye that observes & absorbs excess light
  2. Other cells: bipolar, ganglion, horizontal, amacrine
  3. Other cells responsible for integration of information from rod & cones & production of action potential (bipolar)

Transduction Light to Action Potential

  1. Light hyperpolarizes these cells & shuts them off
  2. These cells release inhibitory neurotransmitters when depolarized in dark
  3. Inhibit bipolar
  4. Light strikes photoreceptors, they hyper-polarize, shut off & stop releasing inhibitory neurotransmitters
  5. Bipolar cells depolarize (independently) & become activated
  6. Depolarization of bipolar cells may lead to action potential in ganglion cells

In dark

  1. Depolarize rod/cone - release inhibitory neurotransmitters

In light

  1. Hyperpolarize rod/cone - no inhibitory released
  2. Bipolar cells depolarizes

Types of Eye Movements

  1. Saccades -> Rapid, jerky eye movements -> Used to rapidly move eye to object of interest Example: Reading on computer
  2. Smooth Pursuit -> Smooth movement of eyes made to keep moving object focused on fovea Example: Watching bird fly keeping head still
  3. Vestibular Ocular Reflex (VOR) -> When you focus your attention on object & then move head back & forth or shake up/down Example: Agreeing/disagreeing & staring at someone
  4. Vergences -> When object of interest is approaching or moving away from you -> When object moving away - eyes diverge -> When object moves closer - eyes converge Example: Staring at pencil moving away from & toward face

The Auditory System

  1. Converts sound waves from external environment to action potentials that travel to auditory system of brain
  2. Human car 20 Hz to 20,000 Hz
  3. Most accurate hearing 1,000 - 3,000 Hz


  1. External ear contains auricle & external auditory canal
  2. Middle ear: eardrum (tympanic membrane), ear ossicles (made up 3 bones - malleus, incus & stapes) & Eustachian tube
  3. Inner ear consists of vestibular apparatus (balance) & cochlea (processing sound)


(Shape of shell of snail)

  1. Hollow area inside "shell" divided in 3 components
  2. Upper Scala Vestibuli (Vestibular duct)
  3. Middle cohclear duct
  4. Lower scala tympani
  5. Separating Cochlear duct & tympanic duct is basilar membrane
  6. Basilar Membrane contains organ of corti
  7. Organ of corti: Where sound converted to action potentials by special hair cells
  8. Hair cells embedded in tectorial membrane
  9. Sound waves cause basilar membrane vibrate, causes hair cell vibration

Frequency - Number of waves (cycles) per unit time

Intensity - (loudness) expressed height (amplitude) soundwave scala Vestibuli

Transfer & Amplification Sound

  1. Airways of sound travel through air & reach outer ear
  2. Waves funnelled into external auditory canal
  3. Strike tympanic membrane causing flex back and forth
  4. Levering action ear ossicles amplifies, pressure waves that strike tympanic membrane
  5. Ear ossicles cause oval window to vibrate
  6. Oval window underneath stapes
  7. Waves amplified 15-20 times original amount
  8. Cause oval window much smaller than tympanic membrane
  9. Fluid inside cochlea (perilymph) transmits waves to hair cells embedded in basilar membrane
  10. Basilar membrane detect vibrations & turn them into action potentials in auditory nerve
  11. Near different frequencies cause vibration basilar membrane
  12. Pressure waves in fluid created by vibrations of oval window produce travelling wave on basement membrane
  13. Reaches peak at different regions of membrane
  14. Happens cause membrane not consistent along its length

Basilar Membrane

  1. Tension varies along length
  2. Tight at base, loose at top
  3. Depending part of membrane thats vibrating only certain hair cells activated by certain sounds
  4. can also differ frequencies by length and stiffness of hair cell

Low Frequencies

  1. Stimulate hair cells at apex (top) of cochlea

High Frequencies

  1. Stimulate hair cells on membrane near oval window


  1. When basilar membrane vibrates hair cells are bent causing ion channels to open & depolarization of cells
  2. Depolarization causes release of neurotransmitters from hair cells
  3. Excites neurons of auditory nerve, which then fire action potentials
  4. Louder sound, stronger vibration of basilar membrane the more bent the hair cells, more neurotransmitters & higher frequency of action potentials produced
  5. Signals flow to auditory cortex located in temporal lobe of brain

Vestibular System

(Also VOR eye movement)

  1. Located inner ear next to cochlea
  2. Responsible for maintaining balance, equilibrium & reflexes
  3. Does this by detecting linear & rotational motion & position of head relative to rest of body
  4. Has two primary structures in apparatus
  5. Semicircular canals
  6. Otolith organs

Semicircular Canals

(Detect rotational/angular accelerations of head)

  1. Three canals, one for each plane of motion
  2. Filled with fluid called "Endolymph"
  3. End each canal swelling -> Ampula
  4. Inside ampula sensory region -> Crista Ampullaris
  5. Contains sensory hair cells
  6. Fixed at base, cilia embedded in gelatinous material - cupula
  7. When head bends endolymph lags behind & moves to the right (opposite side head tilt)
  8. Endolymph hits cupula & bends hair cells inside
  9. When hair cells bent certain way they depolarize & fire AP to brain
  10. When bent opposite direction hyper-polarize
  11. No signals to brain

Otolith Organ

  1. Detect linear accelerations & decelerations & position of head when its tilted
  2. Are two otolith organs in each vestibular apparatus

Utiricle - Detects horizontal accelerations & decelerations (in car)

Saccule - Detects vertical accelerations & decelerations (elevator)

  1. Each otolith organ contains many hair cells that are anchored at base & have their cilia embedded in gelatinous membrane
  2. Gelatinous membrane has otolith crystals embedded to give it weight & inertia during movements
  3. Utiricle and Saccule act together to detect head tilts

Body Accelerations

  1. Crystals lag & move opposite direction increase frequency of action potentials in nerve

Body Constant Velocity

  1. Hair cells resting state & frequency of action potential


  1. Hair cells bend in other direction which causes frequency of action potentials to go down from resting
  2. More rapid decelerate down AP frequency

Hair cell

  1. When at rest release small resting leveI neurotransmitters from base to sensory nerve (fires action potentials)

Acceleration - Smaller sterocilia bend toward larger kinocilium hair cell releases more neurotransmitters causing more action potentials on sensory nerve

Deceleration - Stereocilia bend away kinocilium hair cell less neurotransmitters = fewer action potentials

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