Physiology Exam 1 (Modules 5-9)

nervous system functions

regulate and control other systems of the body by communicating via electrochemical impulses (action potentials)

the number of processes

what are the structural classes of neurons based on?

parts of a neuron

• cell body (soma)

• dendrites

• axon

• axon hillock/initial segment

• axon terminal

the direction of impulse

what are the functional classes of neurons based on?

central nervous system

brain & spinal cord

glial cells in CNS

• astrocytes

• oligodendrocytes

• microglia

• ependymal cells

glial cells of PNS

• schwann cells

• satellite cells

schwann cells

PNS; forms myelin sheath in PNS, same function as oligodendrocytes

oligodendrocytes

CNS; forms myelin sheaths which insulates and covers axons and speeds up the conduction of electrical signals along axon

peripheral nervous system

afferent division

• somatic sensory

• visceral sensory

• special sensory

efferent division

• somatic motor

• autonomic motor

neuron

responds to stimuli; conduct electrical activity, release chemical regulators

does the strength of stimulus have an affect on action potential?

no, the stimulus strength doesn’t matter after passing the approximate value. the strength of the stimulus affects the FREQUENCY of AP and may recruit more neurons to have an AP.

Why does the AP peak stop at +30mV?

this is where the K+ gates open and Na+ gates close

association/interneurons

located completely within the CNS and integrate functions of the nervous system.

motor neurons

efferent neurons; conduct impulses from the CNS (brain & spinal cord) to target organs (muscles or glands)

sensory neurons

afferent neurons; conduct impulses from sensory receptors to the CNS

glial cells

• constitute about half of the cells in the CNS

• can divide by mitosis unlike neurons

• provide physical and metabolic support

myelin sheath

speed up conduction of electrical signals along axon

oligodendrocytes

insulates and covers axon; forms myelin sheaths

resting potential of membranes

-70 mV

ligand gates channels

specified by an ion, opening in response to binding (stimulus) of a chemical ligand to its receptors

voltage gated channel

protein channel that when stimulated depolarizes membrane to threshold, specific to an ion

mechanical gated channel

open when physical deformation to membrane occurs (like stretching)

where are ion gated channels located on neuron?

on receptive segment, dendrites & cell body

where are voltage gated channels located on neuron?

axon hillock/initial segment

where are mechanically gated channels located on neurons?

found in sensory receptors (touch, pressure, vibration)

threshold

approximate value needed for an action potential to occur. there is enough positive ions flowing in to move the membrane potential from -70mV to -55mV

action potential

• all or nothing electrical event in a single cell where the membrane potential quickly becomes positive and returns to resting potential (-70)

• used to communicated over large distances

• channels: v-gated Na+ and v-gated K+

• large, fast change in membrane potential: -70 to +30mV in approx. 3msec

location of AP

axon hillock (initial segment)

AP threshold

-55 mV

membrane potential of neurons

resting potential = -70 mV

established by large negative molecules inside the cell,, Na+/K+ pumps, and permeability of the membrane; ions are constantly moving to maintain concentration gradients

channels in the membrane of a neuron

• ligand gated

• voltage gated

• mechanical gated

why does absolute refractory period occur?

during this period, the neurons have to wait for the 1st AP to complete b/c since all Na+ channels are opening up another AP can’t start.

• Na+ channels are inactivated

• as soon as inactivation is removed and Na+ are closed, the channel can reopen to the 2nd stimulus

V-gated K+ channels

• stimulated: open at +30mV

• slower to open and close

• closed at resting potential of -70mV

v-gated Na+ channels

• open at negative values

• respond faster at threshold

• inactive at 30mV, breaking positive feedback loop

• closed at resting potential of -70mV

Absolute Refractory Period

a second stimulus will not produce an action potential because Na+ channels are inactivated.

relative refractory period

second action potential can happen only if stimulus strength is greater than usual because some K+ channels are still open.

synapses

a junction where impulses are transmitted from neurons and in the PNS target muscle or gland

presynaptic

conducting signal towards synapse

postsynaptic

conducting signals away from synapse

electrical synapse

• pre- and post- synaptic cells are connected by gap junctions

• current flow continues quickly across the gaps

• found in cardiac, smooth to allow contraction as a unit to occur

chemical synapses

• the majority

• axon terminals hold synaptic vesicles

• pre-synaptic neurons release neurotransmitter

neurotransmitter

chemical messenger that travels across the synaptic cleft and binds to receptors on post-synaptic neurons

SNARE complex

proteins loosely dock vesicles

excitatory postsynaptic potential (EPSP)

• opening Na+ or Ca2+ channels results in a graded depolarization called an ______

• brings postsynaptic membrane closer to threshold (depolarizing)

• is a graded potential

inhibitory postsynaptic potential (IPSP)

• opening K+ or Cl- channels results in a grader hyperpolarization called ________

• brings postsynaptic membrane further from threshold (hyperpolarizing)

• decreasing likelihood of an AP

graded potentials

amplitude decreases as singla moves toward axon hillock

Characteristics:

• summation and lack of a refractory period

• may lead to APs

acetylcholine

a neurotransmitter involved in muscle action and memory. Can cause increase arousal and enhanced cognition

norepinephrine

neurotransmitter involved in heart, intestines, and alertness. can cause increased arousal, and suppress appetite.

nicotinic Ach receptors

• Ach binds at post synaptic cell

• ex: skeletal muscle cells (how muscles contract)

• binding of 2 acetylcholine molecules opens a channel

muscarinic Ach Receptors

• Ach binds at postsynaptic cell

• ex: digestive cells or cardio

• binding at the receptor opens ion channels indirectly by using a G-protein

  • dopamine and norepinephrine receptors do this too!

sensory neurons

neurons that have an end to receive sensory stimuli and produce the nerve impulse and the other delivers impulse to synaps in the CNS.

sensory receptors

specialized cells that generate graded potentials called receptor potentials in response to a stimulus.

stimulus

energy or chemical activating a sensory receptor

photoreceptor

receptors that respond to light

thermoreceptor

receptors that respond to temperatures

chemoreceptor

receptors that interpret chemical stimuli, such as objects taste or smell

mechanoreceptor

receptors that respond to pressure, mechanical deformation

nociceptors

receptors that respond to intense stimuli through pain or tissue damage.

cortical association

• where complex integration occurs

• also where perception occurs along w/emotional or varying factors that will affect perception

Cutaneous Sensation & proprioceptors

sensation from skin, muscles, bones, tendons and joints. respond to

• touch and pressure

• temp

• pain

phasic receptors

respond quickly but just as quickly adapt to stimulus (fast-adapating) ex: smell

tonic receptors

maintain response to stimulus; slow-adapting; ex: pain

adaptation

a decrease in receptor sensitivity

transient receptor potential channels

a whole different set of channels open in the membrane because they are stimulated by painful heat or painful cold.

beta-endorphin

neurotransmitter involved in pain and pleasure. can result in decreased anxiety and decreased tension

glutamate

neurotransmitter involved in memory and learning; can increase learning and enhance memory

location of photoreceptor cells

retina

rods

respond to low levels of light

cones

respond to bright light signals (red, blue, green)

tympanic membrane

air molecules push against it at same frequency as sound waves

pitch & volume

indicated by pressure and movement of the membrane in the ear

Malleus, Incus, & Stapes

transduce sound by amplifying it via middle ear to the oval window

organ of corti

receptor cells called hair cells (mechanoreceptors)

stereocilia

hairs on the cell called ______ are bent back and forth as sound waves vibrate

glutamate in ear

a neurotransmitter that bind and causes APs in neurons making up the vestibulocochlear nerve

neural pathways in hearing

vestibulocochlear nerve —> brainstem (medulla oblongata) —> thalamus —> auditory cortex

microvilli

increase SA of taste receptor cells. come into contact with chemicals

Na+ (transduction mechanism)

salt (taste)

H+ (transduction mechanism)

acidic / sour (taste)

glucose (transduction mechanism)

sweet (taste)

quinine (transduction mechanism)

bitter (taste)

umami

glucose (transduction mechanism)

umami (taste)

pathways for taste

glossopharyngeal nerve —> medulla (brainstem) —> thalamus —> gustatory cortex

olfactory receptor neurons

lie in the olfactory epithelium in the upper part of the nala cavity

association/interneurons

form a network of communication from one area of the brain to another

central nervous system

composed of brain & spinal cord

CNS Functions

• receives input from sensory neurons and directs activity of motor neurons

• association neurons integrate sensory info and help direct the appropriate response to maintain homeostasis and respond to environment

• humans are capable of learning and memory adding a layer of modification to our behaviors

cerebrum

• higher mental functions

• largest portion of brain

• consists of cerebral cortex and corpus callosum

cerebral cortex

outer grey matter of cerebrum

corpus callosum

bundle of nerves that connects the cortex layers of the left and right hemispheres

limbic system

• controls emotions

• physically linked to thalamus, hippocampus, amygdala, and hypothalamus

aggression

controlled by amygdala and hypothalamus

fear

controlled by amygdala and hypothalamus

hunger/satiety

controlled by hypothalamus

sex drive

controlled by the whole limbic system

hippocampus

formation and retrieval of memory; helps form cognitive maps that help make mental models of our world; stress and emotion (via the limbic system) can affect memory