BIOL 3151: - PowerPoint Presentation

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BIOL 3151: Principles of Animal Physiology

ANIMAL PHYSIOLOGY

Dr. Tyler EvansEmail: tyler.evans@csueastbay.eduPhone: 510-885-3475Office Hours: M 8:30-11:30 or appointmentWebsite: http://evanslabcsueb.weebly.com/Slide2

LAST LECTURE

NEUROPHYSIOLOGY

each neuron has specialized regions that perform specific tasks:these tasks are: reception, integration, conduction or transmissione.g. VERTEBRATE MOTOR NEURON (Fig 4.2 pg. 145)Slide3

LAST LECTURE

NEUROPHYSIOLOGY

WHAT TYPES OF ELECTRICAL SIGNALS ARE SENT BY NEURONS?GRADED POTENTIALS: weak signals that occur in the soma and decrease in strength they get further away from the opened channele.g. Graded potential created by ligand gated sodium channel

s

everal

properties of the neuron influence why a graded potential decreases as it travels:

l

eakage of ions across membrane

e

lectrical resistance of cytoplasm

e

lectrical properties of membrane

t

extbook Fig 4.6 pg 151Slide4

LAST LECTURE

NEUROPHYSIOLOGY

more sodium outside of cells than inside. when ligand-gated Na channels open, sodium enters cells and intracellular regions become more positively charged.at +60mV there is no longer a gradient driving sodium inward.

t

extbook Fig 4.4 pg 148

WHAT TYPES OF ELECTRICAL SIGNALS ARE SENT BY NEURONS?

GRADED POTENTIALS

: weak signals that occur in the soma and decrease in strength they get further away from the opened

channel

e.g

. Graded potential created by ligand gated sodium channelSlide5

LAST LECTURE

NEUROPHYSIOLOGY

WHAT TYPES OF ELECTRICAL SIGNALS ARE SENT BY NEURONS?2. ACTION POTENTIALS: are stronger signals used to transmit information over longer distances without degrading

t

extbook Fig 4.10 pg 155Slide6

LAST LECTURE

NEUROPHYSIOLOGY

WHAT TYPES OF ELECTRICAL SIGNALS ARE SENT BY NEURONS?2. ACTION POTENTIALS: are stronger signals used to transmit information over longer distances without degradingthe three phases of an action potential are driven by the opening and closing of ion

channels

Na

+

channels open during depolarization and

Na

+

enters cell

K

+

channels open during repolarization and K

+

exits cells, making interior more negatively charged than exterior

K

+

channels close slowly which causes the hyperpolarization response

m

embrane returns to resting potential.

t

extbook Fig 4.10 pg 155Slide7

textbook Fig 4.2 pg 145

NEUROPHYSIOLOGY

TRANSMISSION ACROSS THE SYNAPSEonce the action potential reaches the AXON TERMINAL, the neuron must transmit the signal across the SYNPASE to the target cell

t

he cell that transmits the signal is called the

PRE-SYNAPTIC CELL

and the cell that receives the signal is referred to as the

POST-SYNAPTIC

CELL

t

he

space between the pre-synaptic and post-synaptic cell is the

SYNAPTIC CLEFT

.collectively, these three components make up the SYNPASESlide8

NEUROPHYSIOLOGY

TRANSMISSION ACROSS THE SYNAPSE

in the example we have been describing so far, the vertebrate motor neuron, the synapse forms at a

NEUROMUSCULAR JUNCTIONSlide9

NEUROPHYSIOLOGY

TRANSMISSION AT THE NEUROMUSCULAR JUNCTION

when an action potential reaches the axon terminal of the neuromuscular junction it triggers calcium (Ca+2) channels to openthe concentration of Ca+2 inside the neuron is much lower than outside, so Ca+2

moves into the neuron along its concentration gradient

this increase in internal

Ca

+2

concentration triggers the release of

SYNAPTIC VESICLES,

synaptic

vesicles contain neurotransmitters, which are then

released across the synapse

Textbook

Fig 4.16

p

g 162Slide10

NEUROPHYSIOLOGY

TRANSMISSION AT THE NEUROMUSCULAR JUNCTION

the main neurotransmitter released at vertebrate neuromuscular junctions is ACETYLCHOLINE acetylcholine is released from synaptic vesicles and binds to specific cell surface receptors in the membranes of post-synaptic cellsacetylcholine binds to receptors to induce muscle contraction

t

he enzyme

ACETYLCHOLINESTERASE

removes acetylcholine from its receptor to terminate the signal.

Textbook

Fig 4.17

p

g 163Slide11

NEUROPHYSIOLOGY

PATHOLOGIES THE NEUROMUSCULAR JUNCTION

strength of contraction is determined by two factors:1. amount of neurotransmitter released2. number of receptors on target cellsif the amount of neurotransmitter or density of receptors is high a strong muscle contraction

will result.

In contrast,

a

weak muscle contraction will

result when

amount of neurotransmitter or density of receptors is

low

disease

called

MYASTHENIA GRAVIS

occurs when muscles contain a reduced number of acetylcholine receptorsexperience muscle weakness and muscle fatigue

w

eakened

eye muscles can cause a drooping eyelid or

PTOSIS

, a common symptomSlide12

NEUROPHYSIOLOGY

Diversity in Neurophysiology

although all neurons have the same basic components, each of these components has been modified by evolution to better perform specific tasksall neurons have DENDRITES, a CELL BODY (SOMA) and an

AXON

, but details of each structure

are variable

EXAMPLES OF NEURON DIVERSITY

t

extbook Fig 4.18 pg 166Slide13

NEUROPHYSIOLOGY

Diversity in Neurophysiology

Brain, Sensory or Muscle?Slide14

NEUROPHYSIOLOGY

Diversity in Neurophysiology

1. SENSORY NEURONS

s

ensory neurons are found in animal senses: sight, hearing, touch, taste, smell

a

t one end of the neuron is a receptor that is associated with that particular sense

f

or example, olfactory receptors involved in smell are activated by airborne chemicals

a

t the other end are lots of dendrites that allow sensory neuron to connect to the brain for processing

dendrites

receptorsSlide15

NEUORPHYSIOLOGY

Diversity in Neurophysiology

2. BRAIN NEURONSthis type of neuron is called an INTERNEURON

have

large numbers of

dendrites on both ends

to maximize connections with other

neurons

often

lack an obvious

axon

because are only transmitting signals over short distances between other

neurons densely packed in the brainSlide16

NEUROPHYSIOLOGY

Diversity in Neurophysiology

3. VERTEBRATE MOTOR NEURONS

h

ave long axons covered in

MYELIN SHEATH

that allows signals to travel long distances

o

ne end branches into

NEUROMUSCULAR JUNCTIONS

o

ther end has lots of dendrites for connecting muscle to brain or spinal cordSlide17

diversity in neural signaling can also be achieved by varying cells associated with each

neuron. These accessory cells are called GLIAL CELLSi

n vertebrates, there are five types of glial cells:SCHWANN CELLS: form MYELIN SHEATHS and are associated with neurons with long axons. Increase the conduction speed and prevent the decay of action

potentials.

OLIGODENDROCYTES

: form myelin sheaths in the central nervous system.

ASTROCYTES

: found in central nervous system and have a number of functions including transport of nutrients and neuron development.

MICROGLIA

: are the smallest glial cells and are involved in neuron maintenance (e.g. removes debris and dead cells)

EPENDYMAL CELLS

: found in fluid-filled cavities of central nervous system. They are often

CILIATED

(tiny-hairs) and circulate spinal fluid.NEUROPHYSIOLOGY

Diversity in NeurophysiologySlide18

NEUROPHYSIOLOGY

Diversity in Neurophysiology

SCHWANN CELLS: form MYELIN SHEATHS and are associated with neurons with long axons. myelin increases the conduction speed and prevent the decay of action potentials.

Schwann cells wrap around an axon many times to form the myelin sheath

Fig 4.14 pg. 160Slide19

invertebrates lack a true myelin sheath, but are instead wrapped in membranes of glial cells called

GLIOCYTES

THE EVOLUTION OF MYELIN SHEATHScertain invertebrate neurons are wrapped in multiple layers of cell membrane similar in appearance to vertebrate myelin sheathsincludes nerve fibers in the ventral nerve cords of shrimp, crabs and earthworms.

t

extbook Box 4.2 pg 170

NEUROPHYSIOLOGY

Diversity in NeurophysiologySlide20

THE EVOLUTION OF MYELIN SHEATHS

protein complexes called SEPTATE JUNCTIONS

hold cells in place as they wrap around invertebrate axons.this structure suggests invertebrate wrappings play a similar role to vertebrate myelin sheaths, but evolved independently

INVERTEBRATE

VERTEBRATE

NEUROPHYSIOLOGYSlide21

THE EVOLUTION OF MYELIN SHEATHS

Invertebrate vs. Vertebrate Axon Wrappings

the layers of membrane in the invertebrate wrappings are not as closely stacked as vertebrate layers of myelin sheathprotein composition of myelin sheath is differentproteins critically important forming myelin sheath are largely missing from invertebrate axon wrappings

e.g. wings of birds, reptiles and mammals are all used for flying, but evolved independently and thus have different structures

t

extbook Box 4.2 pg 170

w

rappings

likely evolved separately by

CONVERGENT EVOLUTION

NEUROPHYSIOLOGYSlide22

neurons also differ in the speed at which signals are transmitted

axons conduct action potentials at different speeds: some quickly, some slowly

speed of action potentials are influenced by two variables: 1. PRESENCE OF MYELIN 2. AXON DIAMETER

t

extbook Table 4.3 pg. 172

NEUROPHYSIOLOGY

Diversity in NeurophysiologySlide23

OHM’S LAW describes the speed of an action potential traveling down an axon

speed or CURRENT (I) of the signal depends on two variables:

voltage and resistanceI=

V

R

I

=

V

R

or

voltage

current

resistance

e

ssentially, the strength of the signal along an axon (current) is greatest when voltage (input energy) is high and resistance is low

NEUROPHYSIOLOGY

Diversity in NeurophysiologySlide24

NEUROPHYSIOLOGY

Diversity in Neurophysiology

resistance (the force opposing conduction) is applied by different components of the cell

t

extbook Fig 4.20

pg. 173

e

ach component is has a different resistance value, which will reduce the strength of the signal over spaceSlide25

NEUROPHYSIOLOGY

Diversity in Neurophysiology

MYELIN SHEATH

prevents the signal from traveling through these areas of high resistance

a

s a result, current or conduction speed increasesSlide26

NEUROPHYSIOLOGY

Diversity in Neurophysiology

the same can be said for large diameter axonsless of the axon surface area is exposed to the membrane and cytoplasm that slows down the signal, so resistance is lowas a result, current or conduction speed increasesSlide27

LECTURE SUMMARY

once the action potential reaches the AXON TERMINAL, the neuron must transmit the signal across the

SYNPASE to the target cellin muscles involves the flow of calcium and the neurotransmitter ACETYLCHOLINEall neurons have DENDRITES, a CELL BODY (SOMA) and an

AXON

, but details of each structure are

variable

i

nterneurons in the brain have very short axons and many dendrites

s

ensory neurons have a receptor on one end and dendrites on the other

m

otor neurons have neuromuscular junctions

SCHWANN CELLS

form MYELIN SHEATHS that prevent the decay of action potentials when traveling down the axon

OHM’S

LAW

describes the speed of an action potential traveling down an axon

s

ignals travel fastest down myelinated and large diameter axons because resistance is lowered