Ch 11: Nervous System & Nervous Tissue - PowerPoint Presentation

Slide1

Ch 11: Nervous System & Nervous Tissue

Section 1 – Functions & Divisions of the Nervous System (pp. 386-387)Slide2

This is your brain…The Nervous SystemSlide3

And this is your brain – IN ANATOMY!!

Or better yet…

The Nervous SystemSlide4

Functions of the Nervous System 1) Sensory input

- information about internal/external

changes

gathered by

sensory receptors 2)

Integration

- interpretation of sensory input 3) Motor output - activation of effector organs (muscles, glands, etc.) - production of response

The Nervous SystemSlide5

Divisions of the Nervous System 1) Central nervous system (

CNS

)

-

brain & spinal cord

-

integration & command center The Nervous SystemSlide6

Divisions of the Nervous System 2) Peripheral nervous system (PNS

)

-

spinal

&

cranial nerves - carry messages to & from

CNS

Functional divisions of PNS: a) Sensory (afferent) division - carry information to the CNS from effector organs

b) Motor (efferent) division

-

carry

information

away

from CNS to

effector organs

The Nervous SystemSlide7

Divisions of the Nervous System 2) Peripheral nervous system (PNS) - spinal & cranial nerves

- carry messages to & from CNS

Motor

divisions of PNS:

a) Somatic (

voluntary

) nervous system - provides conscious control of skeletal muscles b) Autonomic (involuntary) nervous system - regulates smooth muscle, cardiac muscle, & glands

- divided into sympathetic & parasympathetic

systems

The Nervous SystemSlide8

Ch 11: Nervous System & Nervous Tissue

Section 2 – Histology of Nervous Tissue

(pp. 388-395)Slide9

Neurons (aka “Nerve Cells”) - Fundamental units of the

nervous system

- Cells that are capable of carrying

electrical signals

Special characteristics

:

1) long-lived (capable of living

100

years or more)

2) amitotic…cannot divide (with a few exceptions) 3) high metabolic rate (require continuous O2 & sugar supply) 4) plasma membrane designed for electrical signalingNeuronsSlide10

Typical neurons have 4 distinct regions: 1) Dendrites - Receive

&

respond

to signals from other neurons

- Use special

receptors

to respond to neurotransmitters - Deliver electrical

signal

to cell body

2) Cell body (aka “perikaryon” or “soma”) - Neuron’s integration center - Combines all incoming electrical signals - If incoming signals are positive enough, cell body allows signal to continue to axon

NeuronsSlide11

Typical neurons have 4 distinct regions: 3) Axon - Long, thin fiber

…makes neurons

longest

cells in body

- Carries

electrical

signal away from cell body - Allows signals to be carried

large

distances

- Multiple axons are bundled together to form “nerves” 4) Synaptic terminals - Endings of the axons - Contain neurotransmitters (NTMs) - Release NTMs to other neurons, glands

, or muscles

NeuronsSlide12

Neuroglia - Literally means “nerve glue”

- Cells that

support

the

function

of the nervous system

- Are not capable of carrying electrical impulsesExamples found only in Central

Nervous System

:

1) Astrocytes - Abundant, star-shaped cells that brace neurons - Control chemical environment of brain - Form barrier between capillaries &

neurons

Other Cells of Nervous SystemSlide13

Other Cells of Nervous System

AstrocyteSlide14

2) Microglia - Spider-like phagocytes

that dispose of

debris

3)

Ependymal

cells

- Line

cavities

of the brain & spinal cord - Circulate cerebrospinal fluid

Other Cells of Nervous SystemSlide15

4) Oligodendrocytes - Produce myelin sheath

around

nerve

fibers

in

central nervous system

*Myelin

sheath

- Acts like insulation - Prevents short circuitsOther Cells of Nervous SystemSlide16

Other Cells of Nervous SystemSlide17

Examples of Neuroglia in the Peripheral Nervous System: 1)

Satellite

cells

- protect neuron

cell

bodies in PNS 2)

Schwann cells

-

form myelin sheath around axons in PNS - vital to regeneration of damaged peripheral nervesOther Cells of Nervous SystemSlide18

More on Myelin Sheath of PNS: - formed in a “Jelly roll”-like fashion

-

insulates

the axons

- enhances

& increases speed of the electrical signal

Nodes of

Ranvier

- Gaps in the myelin sheath formed by spaces between Schwann cellsOther Cells of Nervous SystemSlide19

Multipolar Neurons - Characterized by many

extensions

from cell body

- All of the

motor

neurons

Structural Classification of NeuronsSlide20

Bipolar Neurons - Consist of only one dendrite & one

axon

- Found only in

nose

(

smell

) & eyes (

vision)

Structural Classification of NeuronsSlide21

Unipolar Neurons - Consist of a single,

short

extension

leaving the cell body

- All

sensory neurons

Structural Classification of NeuronsSlide22

Ch 11: Nervous System & Nervous Tissue

Section 3 – Neuron Function

& Action Potentials

(pp. 399-404)Slide23

Information Processing Requires 4 Basic Operations:Determine the type of stimulus

- Distinguished by

various

wiring

patterns in the brainDetermine the

intensity

of the stimulus

- Either by the number of times a single neuron “fires” or the total number of neurons “firing” at onceIntegrate information from many different sources

Initiate & direct a response

Information ProcessingSlide24

Basic Neuron Function: - Neurons are highly irritable (responsive to stimuli

)

- Send

signals

over long distances by generating “

action potentials

” Action Potential

- “nerve impulse

”

- a brief change in the electrical charges found on either side of the nerve cell membrane - travels from the cell body to the end of the axon - always the same strength regardless of stimulus

Neuron FunctionSlide25

More on Action Potential: - created by the movement of positively charged

sodium

&

potassium

ions across the cell membrane of the

axon

- as charged particles move, they create electrical

impulses

- considered “

all-or-none phenomenon”…either happen completely or not at allThreshold stimulus - minimum stimulus required to create an action potential

Neuron FunctionSlide26

Conduction velocity: - the speed

action potentials travel

- vary widely…some

faster

than others

- fastest occur at 100

meters/sec or more!

Rate determined by…

1) Axon diameter - larger diameter = faster conduction velocities 2) Degree of myelination - more myelin = faster conduction velocitiesNeuron FunctionSlide27

Ch 11: Nervous System & Nervous Tissue

Section 4 – The Synapse & Neurotransmitters (pp. 406-421)Slide28

Synapses: - junctions

that

regulate

information between two neurons

- also found between

neurons & effector cells/organs

Presynaptic

neuron

- conduct impulses toward synapsePostsynaptic neuron - conduct impulses away from synapseThe SynapseSlide29

Two most common types of synapses:

1)

Axodendritic

synapse

- between the axon of one neuron & the

dendrite of another

2) Axosomatic synapse - between the axon of one neuron & the cell body of another*These may be either “electrical” or “chemical” synapses…

Types of Synapses

Animation

:

SynapsesSlide30

Electrical Synapses: - not as common as

chemical synapses

- neurons are

physically

connected by

gap junctions

-

electrical

signal travels directly through the gap junction - very rapid; utilized in very fast events…reflexesElectrical SynapsesSlide31

Chemical Synapses: - specialized for releasing

&

receiving

neurotransmitters

Typically composed of two parts: 1) Axon

terminal

- found on presynaptic neuron - contains synaptic vesicles w/ neurotransmitters 2) Receptor region - found on postsynaptic neuron - has special receptors that

receive neurotransmitters

Chemical SynapsesSlide32

Synaptic Cleft: - fluid

-filled space between pre- & post-synaptic neurons

- prevents

nerve impulses

from

directly passing from one neuron to the next

Synaptic CleftSlide33

Transmission of Electrical Impulse Between Neurons: - Electrical signal reaches end of axon

-

Neurotransmitters

are

released

from

synaptic terminals

- Neurotransmitters diffuse

through synaptic

cleft - Neurotransmitters bind to receptor sites on adjacent dendritesSynaptic CleftAnimation: NeurotransmittersSlide34

Terminating effects of neurotransmitters: - occurs within a few

milliseconds of NTM

release

- happens as a result of either the…

1) NTMs being broken

down by enzymes

2) NTMs being reabsorbed into the axon terminal 3) NTMs diffusing away from synaptic cleftSynaptic CleftSlide35

Types of neurotransmitters: - most neurons make 2

or

more

NTMs

- the number of

times per second that a neuron “

fires” determines which NTM is actually

released

- over 50 different NTMs have been identifiedNeurotransmittersSlide36

Specific Neurotransmitters

Neurotransmitters & Functions

:

1)

Acetylcholine

-

Activate skeletal muscles

2) Dopamine

-

Important in general movement 3) Epinephrine - Activates organs of sympathetic nervous system 4) Serotonin - Influences mood (“

mellow”) & sleep

5)

Endorphins

-

Influences

mood

(“feel good”), reduces

pain 6)

Nitric

oxide

-

Important in forming

memoriesSlide37

Ch 11: Nervous System & Nervous Tissue

Section 5 – Neural Integration…Circuits

(pp. 422-423)Slide38

Organization of Neurons

Types of circuits

:

1)

Diverging

circuits

- one incoming nerve fiber stimulates

multiple fibers

- often acts as an “amplifying” circuit Ex = single neuron in brain can activate hundreds of motor neurons in spinal cord and ultimately thousands of skeletal muscle fibersSlide39

Organization of Neurons

Types of circuits

:

2)

Converging

circuits

- multiple nerve fibers in different areas combine signals into

one fiber

- often have a “concentrating” effect; strong stimulation or strong inhibition Ex = seeing a baby smile, smelling baby powder, hearing baby laugh all combine to trigger “warm/fuzzy” feelings in parentsSlide40

Organization of Neurons

Types of circuits

:

3)

Reverberating

(oscillating) circuits

- chain of neurons arranged in a loop

- results in signal that is sent through the circuit over

&

over in a rhythmic pattern Ex = sleep-wake cycles, breathing, arms swinging when walkingSlide41

Organization of Neurons

Processing information in the nervous system

:

1)

Serial

processing

- input travels along one

path to a

specific

destination - works in all-or-none manner producing specific response Ex = spinal reflexesSlide42

Reflex - Simplest behavior -

Involuntary

movement of body part in

response

to stimulus

- Occur without involving the

conscious portions of the brain - Signal sent to

spinal

cord

& immediately back to source - Usually help keep you from being hurtNeural Pathways Direct BehaviorSlide43

Organization of Neurons

Processing information in the nervous system

:

2)

Parallel

processing

- input travels along several

pathways

- one

stimulus promotes many responses - crucial for higher-level mental functioning Ex = a smell usually isn’t processed as just an odor; also usually triggers memories of experiences associated w/ the

smellSlide44

Ch 11: Nervous System & Nervous Tissue

Section 6 – Homeostatic Imbalances

(pp. 422-423)Slide45

Homeostatic Imbalances

Multiple

Sclerosis

(MS)

:

-

autoimmune disease; mainly affects young adults

-

myelin

sheaths in the CNS become destroyed - sheaths turn into nonfunctional, hardened lesions - leads to short-circuiting of nerve impulses - eventually impulse conduction ceases Symptoms - visual/speech

disturbances, weakness, loss of muscle control, & loss of bladder

controlSlide46

Homeostatic Imbalances

Neuroblastoma

:

-

malignant

tumor that occurs in the

peripheral nervous system of childrenRabies

:

-

viral infection of nervous system - transmitted through bites from infected animals - causes inflammation of brain, delirium, & deathSlide47

Homeostatic Imbalances

Shingles

:

- viral infection of the

sensory

neurons found in the

skin - scaly, painful blisters

; similar to chickenpox

but w/ pain

- seen mostly in adults over 50 years old