physiology exam 1

nervous system (NS)

• one of two main control systems in body

• NS responds to stimulus from inside or outside the body

  • inside ex: felling full

  • outside ex: stepping on a pin

NS functions

• sensory function

• integrative function (carried out by CNS)

• motor function

NS sensory function

• detection of internal and external stimuli by sensory receptors

• nerve impulses travel toward CNA along sensory neurons

NS integrative function

• carried out by CNS

• processing of sensory information, sending messages to appropriate effector

  • effectors - targets (ex: muscles, glands)

NS motor function

• generation of responses to initial stimulus

• nerve impulses travel away from CNS along motor neurons which lead to effectors throughout the body

• effectors carry out the response

CNS-PNS neuron organization

• sensory and motor neurons — peripheral NS

• interneurons — central NS

CNS

• brain and spinal cord

• integrative and control centers

PNS

• cranial nerves, spinal nerves, sensory receptors in skin

• communication lines between CNS and rest of body

PNS organization

sensory (afferent) division

• somatic and visceral sensory nerve fibers

• conducts impulses from receptors to the CNS

motor (efferent) division

• motor nerve fibers

• conducts impulses from the CNS to effectors (muscles and glands)

somatic ns

• somatic motor (voluntary)

• conducts impulses from the CNS to skeletal muscles

• skin, skeletal muscles, joints

autonomic ns

• visceral motor (involuntary)

• conducts impulses from the CNS to cardiac muscles, smooth muscles, and glands

• coming from internal organs

sympathetic divison

mobilizes body systems during activity

parasympathetic division

• conserves energy

• promotes house-keeping functions during rest

neuron

• nerve cell

• conducts electrical impulses and releases chemical messengers (neurotransmitters) to communicate with other cells

neuron parts

• cell body (soma)

• dendrites

• axon

• axon hillock

• axon terminals/synaptic bulbs

cell body (soma)

• contains organelles, makes NT

• cluster of cell bodies in PNS - ganglia

• cluster of cell bodies in CNS - nuclei

dentrites

• receiving end of a neuron

• receive signals from other neurons or from stimuli in the environment

axon

• transmits impulses away from cell body

• <1mm to >1m in length

• bundle of axons in PNS - nerve

• bundle of axons in CNS - tract

axon hillock

• area where impulses (action potentials) are initiated

mixed/single nerves

• contain both sensory and motor fibers (axons)

referred pain

• pain stimuli from visceral organs are perceived at a site other than the place of origin

axon terminals/synaptic bulbs

• store NT molecules in synaptic vesicles

• secrete NT via exocytosis

synapse

where a neuron meets its target

cells in neuroglia

• nourish, protect, and support neurons

• maintain homeostasis of cerebrospinal fluid\

• oligodendrocytes - surround CNS axons, form myelin sheaths

• schwann cells - surrounds PSN axons, form myelin sheaths

myelin

lipid and protein wrapping that surrounds the axon

myelin functions

• electrically insulates the axon

• increases speed of nerve impulse conduction

  • nodes of ranvier - areas without myelin

myelin - faster conduction

• occurs along myelinated, larger diameter axons

myelin - slower conduction

occurs along unmyelinated, smaller diameter axons

opening of ion channels (integral membrane protiens)

allows charge flow across membrane

type of ion channel - leak channel

transiently open and close

type of ion channel - gated channel

open in response to a stimulus

gated ion channels - chemically gated ion channels

open in response to binding of the appropriate neurotransmitter (facilitated diffusion)

gated ion channels - voltage gated ion channels

open in response to changes in membrane potential (facilitated diffusion)

other types of gated ion channels

• mechanically gated

• thermally gated

graded potentials

• occurs mainly in cell bodies and dendrites

• types of graded potentials:

  • depolarizing and hyperpolarizing

• vary in size/amplitude according to the strength of the stimulus

  • stronger stimuli open more ion channels, leading to a larger graded potential

• can summate (they can add together)

• names according to their location

  • on motor end plate of skeletal muscle = end plate potential

  • after a synapse on a postsynaptic cell/target = postsynaptic potential

depolarizing graded potential

• potential becomes less negative compared to resting potential

  • > -55mV

• are excitatory and are essential for triggering action potential

  • more likely to fire impulse

hyperpolarizing graded potential

• potential becomes more negative compared to resting potential

• < -55mV

• are inhibitory and neuron are less likely to fire impulse (AP)

EPSP

• excitatory postsynaptic potential

• depolarizing

• bring the neuron closer to AP threshold (-55mV)

IPSP

• inhibitory postsynaptic potential

• polarizing

• drive the neuron away from AP threshold (-55mV)

action potential

• series of rapidly occurring events that cause a large change in membrane potential

  • always same size/amp regardless of stimulus strength

  • has refractory periods

  • always begins as an excitatory (depolarizing) graded potential

  • occurs if depolarization brings membrane potential to threshold potential

What are the differences/ similarities between graded and action potentials?

action potential diagram

AP voltage changes occur as a result of the opening and closing of voltage-gated Na+ and K+ channels in the neuronal membrane

voltage grated Na+ channels during AP

Na+ down its gradient (into cell) - facilitated diffusion

1. closed - not crossing; activation gate is closed

2. opened - crossing; activation gate is open

3. inactivated - prevents Na+ from crossing; inactivation gate blocking

• inactivation will switch back to closed when potential returns to -70mV

voltage grated K+ channels during AP

K+ down its gradient (out of cell) - facilitated diffusion

1. closed - not crossing; activation gate is closed

2. opened - crossing; activation gate is open

action potential - #1

• resting state / resting potential

  • -70mV

• gated channels closed

action potential - #1a

• stimulus has opened gated channels (not voltage; either chemical or mechanical) 

• depolarization occurs and spreads to axon hillock (current flow)

• threshold potential = -55mV

• once threshold potential is reached, AP will occur

• if stimulus isn’t powerful enough to get membrane to -55mV, it returns to rest (no AP)

Action potential - #2

• depolarization

• voltage gated Na+ channels open

• Na+ rushes in > rapid depolarization

• positives are getting added inside so it gets less negative

action potential - #3

• voltage gated Na+ channels inactive

• voltage gated K+ channels open

• K+ flows out of neuron > rapid repolarization

  • positives are leaving the neuron

repolarization

returning to resting potential

action potential - #4

• K+ channels are still open > hyperpolarization

  • positives still leaving neuron; getting even more negative

• once K+ channels close, resting membrane potential is re-established (-70mV)

  • at resting membrane potential > unequal leakage of Na+/K+ pumps

absolute refractory period

excited neuron cannot generate a second action potential

• from -55mV until membrane is back down to -70mV

relative refractory periods

AP can be initiated by a suprathreshold stimulus during period of hyperpolarization

• would need an extremely strong stimulus to bring the membrane potential from below -70mV back up to -50mV

how do neurons communicate with their targets?

stimulus > AP initiated at axon hillock > electrical signal across axon > neurotransmitter > effector/target

propagation of an action potential along unmyelinated axons

• continuous conduction

• wave of depolarization spreads one-way down axon

  • voltage gated Na+ channels are opened in succession all along the membrane

    • APs occur all along the axon

• have leakage through leak channels

  • slows down conduction

propagation of an action potential along unmyelinated axons

• saltatory conduction

• APs only occur at nodes of Ranvier

• current passes quickly inside myelinated areas of axon

  • faster conduction

How are action potentials propagated down the axon?

what events occur when the impulse reaches the axon terminal?

removal of neurotransmitter from cleft

• diffusion

• enzyme degradation of neurotransmitter

  • ex: acetylcholinesterase enzyme breaks down the neurotransmitter acetylcholine

• reuptake into presynaptic neuron

  • neurotransmitter is actively pumped back into the presynaptic axon terminal that released it

summation

• ability of postsynaptic neuron to “add up” EPSPs and IPSPs and generate an appropriate response

  • if the net summation of EPSP and IPSP brings the membrane to threshold, neuron will fire

brain - cerebrum

• divided into right and left cerebral hemispheres

  • connected via corpus callosum

brain - 5 cerebral hemisphere lobes

• frontal

• parietal

• temporal

• occipital

• insula (sensing emotions)

frontal lobe

motor function, conscious, thought; short term memory

parietal lobe

somatosensory (touch, temperature)

temporal lobe

hearing, language

occipital lobe

vision

cerebrum three main regions

• cerebral cortex (outer surface)

  • highly convoluted gray matter

  • most complex integrating area of the brain

  • site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, understanding

• internal white matter

• basal nuclei

gray matter

• darker

• cell bodies, dendrites, glial cells

• integration of sensory input and motor output occurs via synapse

white matter

• white

• tracts of myelinated and unmyelinated axons

• signal transmission between parts of cortex and between cortex and other regions of CNS

cerebral cortex

• highly convoluted gray matter

• most complex integrating area of the brain

• site of conscious mind: awareness, sensory perception, voluntary motor initiation, communication, understanding

• three types of functional areas

  • motor areas - controls voluntary movement

  • sensory areas - conscious awareness of sensation

  • association areas - integrate diverse information (making sense of stimulus)

language - broca’s area

• present in left hemisphere

• motor speech areas that directs muscles of speech production

• active in planning speech and voluntary motor activities

language - wernicke’s area

• left cortex at the juncture of parietal, temporal, and occipital lobes

• associated with language comprehension of spoken and written messages

aphasia

• language disorder due to damage in cortical areas

• expressive aphasia (broca’s aphasia)

  • “non fluent” aphasia

  • difficulty producing words, saying the correct words

• receptive aphasia (wernicke’s aphasia)

  • “fluent” aphasia

  • language comprehension and understanding the meaning of words is impaired but speech production is not impaired

brain stem

• consists of midbrain, pons and medulla

• contains centers that control cardiovascular and respiratory functions

cerebellum

• coordination

• smoothing out movement

• balance

• important in coordinating thought and emotions

thalamus

• afferent fibers from all parts of body synapse onto one or more nuclei in thalamus

• “grand central station”

• “screens out” insignificant signals

cerebrum - basal nuclei

• “islands of gray matter” within cerebral white matter

• influence muscle movements

  • select and maintain purposeful motor activity

  • control voluntary and habitual movements

  • inhibit antagonistic/unnecessary movement

limbic system

• functional brain system

  • network of neurons that function together

• associated with emotions, inborn survival patterns, motivation, learning, memory

• include amygdala and hippocampus

amygdala

important in emotions of all types

hippocampus

important in consolidation of memories from short-term to long term

meninges

• protect CNS

• three connective tissue layers

  • dura mater - outermost

  • arachnoid mater - middle

  • pia mater - innermost

blood-brain barrier

• protect CNS

• refers to impermeable capillaries in brain

  • only allow certain substances to cross

• limits access of blood-borne materials into brain tissue

  • O2, CO2, water, lipid-soluble substances can cross via simple diffusion

  • glucose crosses via facilitated diffusion

• maintained by astrocytes

importance of blood, glucose, oxygen to the brain

• brain depends on constant blood supply

• brain metabolizes exclusively aerobically (required O2)

• preferred fuel for brain: glucose

  • body exhibits “glucose sparing” activities to ensure adequate glucose supply for brain

    • “glucose sparing” helps the body spare (conserve) glucose for tissues that need it most

stoke (cerebrovascular accicent)

part of the brain deprived of O2 and nutrients

causes of stoke

• clot in blood vessels within brain or leading to brain

  • leads to impaired blood flow to a tissue = ischemia

• hemorrhage = blood loss, “brain bleed”

divisions of autonomic nervous system

parasympathetic and sympathetic

parasympathetic division

• dominates in quiet and relaxed situations

• “rest and digest” division

  • activities support body functions that conserve energy, restore energy during recovery and/or rest periods

• main parasympathetic responses/actions: (3 decreases and 3 Ds)

  • 3 decreases

    • heat rate

    • airway diameter

    • pupil diameter

  • 3 Ds

    • digestion (increased GI smooth muscle contraction, increased secretory activity in GI tract)

    • defecation

    • diuresis (urination - bladder smooth muscle contracts)

sympathetic division

• most active in stressful situations

• “fight or flight” system

• exercise, excitement, emergency, embarrassment

  • increased heart rate, increased force of heart contraction (contractility)

  • blood vessels supplying skeletal muscles and heart dilate (vasodilation)

  • blood vessels supplying GI tract and kidneys constrict (vasoconstriction)

  • respiratory airways dilate (via relaxation of airway smooth muscle)

  • smooth muscle of GI tract relaxes (digest activity slows)

  • bladder smooth muscle relaxes (no urination)

  • pupils dilate

receptors ACh binds to

cholinergic receptors 

types of cholinergic receptors

• nicotinic receptors (N1-N2)

  • found on skeletal muscle and on all postganglionic neurons

• muscarinic receptors (M1-M5)

  • found on all parasympathetic targets

receptors norepi and epi binds to

adrenergic recepetors

types of adrenergic receptors

• alpha-1

• beta-1

• beta-2

(all found on many organs throughout the body)

autonomic nervous system

system of motor neurons that innervates cardiac muscle, smooth muscle, glands; involuntary

neurotransmitters - acetylcholine (ACh)

• neuron that releases ACh = cholinergic neurons

• receptors that binds ACh = cholinergic receptors

neurotransmitters - biogenic amines (from amino acids)

• serotonin

• catecholamines

  • dopamine

  • norepinephrine - main NT of sympathetic branch of autonomic NS

  • epinephrine (adrenaline) - mainly released by adrenal glands

    • neuron that releases norepi/epi = adrenergic neuron

    • receptor that binds to norepi/epi = adrenergic receptor

neurotransmitter - amino acids

• glutamate - main excitatory NT in CNS

• gaba - main inhibitory NT in CNS

• aspartate

• glycine

CNS and PNS contain?

CNS : contains many types of neurotransmitters

PNS : contains mainly ACh, norepi, epi