Nervous System.pptx

Do Now

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_{Collect a notes package from the front.}

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_{If you haven’t handed in your student}

survey/course outline signature sheet,

please do so now.

Nervous System

•

_{Living cells can only survive and function}

within a very narrow range of conditions.

Homeostasis

is the body’s ability to keep

normal body functions (the internal

environment) in the same stable state or

order despite variation in the external

environment.

•

_{Human survival depends on a system of}

communication between the internal

environment and the external environment

.

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_{Both the nervous system and the endocrine}

system (hormones) perform this function

.

Responses to internal/external environments

are made possible by the electrochemical

messages relayed from the brain (nervous

system) or by chemical messengers

The main functions of the nervous

system:

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_{Receive information and carry it to the}

central nervous system

•

_Interpret

_{impulses and make decisions}

about the response

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_{Sorts impulses and sets priorities for}

action

i.e. walking across the street – eat a bug or get hit by a car

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_{Transmit impulses to the motor units}

(muscles) which carry out appropriate

action

Nerves

There are two main types of nerve

cells found in the nervous system:

•

_{Glial cells – neurological}

cells which are

non-conducting and used for

structural and nutritional

support

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_{Neurons – neurological}

cells that conduct (carry

nerve impulses)

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_{neurons are the basic}

unit of the nervous

system

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_{a nerve is actually a}

bundle of individual

neurons

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_{neurons are composed of}

a cell body and a number

of “branch-like”

Components of a neuron

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_{Dendrites are short thread-like branches that}

surround the cell body of the neuron.

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_{Dendrites carry received nerve}

impulses towards the cell body

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_{Axons are longer branches that carry}

impulses away from the cell body

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_{Axons may be enclosed in a fatty}

sheath called myelin sheath

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_{The myelin acts as insulation for neurons by}

preventing the loss of charged ions.

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_{Because of this, the myelin sheath increases}

the speed of nerve transmission.

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_{Myelin makes up Schwann cells, with}

small gaps between each Schwann cell

called the nodes of Ranvier.

Myelin acts as an insulator and

inhibits ion

movement in the axonal membrane that it surrounds.

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_{myelinated neurons form}

white matter in the brain

and spinal cord, while the

cell bodies and

unmyelinated neurons

form grey matter

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_{myelinated nerve fibers are covered by}

neurilemma which, along with the Schwann

cell, promotes the regeneration of the nerve

fiber after trauma

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_{Unmyelinated nerves lack a myelin sheath.}

These will not be regenerated after injury.

Multiple Sclerosis

•

_{The disease multiple}

sclerosis (MS) causes

hardened tissue to

form on top of the

myelin, affecting the

nerve transmission.

The more scar tissue

there is, the worse the

symptoms of MS

Neurons are classified into four types:

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_{Anaxonic neurons:}

–

_{found in the CNS}

–

_{No axons}

–

_{Unknown function}

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_{Unipolar neurons:}

-have a cell body off to one side

-axons and dendrites are continuous

-associated with receptors sensing

environment

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_{Bipolar neurons}

-single dendrite and axon with cell

-body of cell found in middle of axon

-rare i.e. rods and cones found in the

eye

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_{Multipolar neurons:}

-several short dendrites and a single long

axon with one or more branches

-most common

-activate glands or muscles

Do Now

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_{Answer the following questions:}

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_{Draw a simple picture of the neuron and}

label all the important parts we learned

about yesterday.

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_{What are the 4 main functions of the}

nervous system?

-a resting nerve is said to be polarized

- it has a relatively negative charge inside and

a relatively positive charge on the outside

Conduction of Nerve Impulses

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_{a nerve impulse (AKA action potential) has}

both a chemical and electrical component:

- the difference in this charge is called the

resting potential or membrane potential

- this charge difference is caused by the

relative concentrations of sodium ions

(Na

) and potassium ions (K

).

Polarization

–

_{in a resting membrane, the neuron is positive}

on the outside relative to the inside (or

negative on the inside relative to the outside)

– a resting membrane is said to be

polarized

- a resting membrane has a potential difference of

-70mV (compared to a AA battery 1500mV)

- a polarized membrane has more Na

on

the outside of the axon than K

on the

inside

outside + + + + + + + + + + + + inside - - -

Sodium/Potassium Channel and

Sodium-Potassium Pump

Depolarization

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_{stimulation of the neuron by electrical}

discharge (or by application of certain

chemicals) causes sodium “gates” to open

and therefore the axon membrane allows

Na

to pass through

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_Na

rush into the axon

(down their

concentration gradient)

which causes there to

be a positive charge on

the inside of the axon

relative to the outside.

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_{once the Na}

have rushed in, to it’s

equilibrium, the membrane becomes

impermeable to them again as the “gates” in

the membrane close.

•

the membrane is said to be depolarized.

outside - - - + + + + + + +  (direction of impulse) inside + + + + - - -

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_{this reverses the membrane potential from}

-70mV to +40mV with respect to the outside.

Repolarization

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_{Once the action potential has peaked,}

the Na

“gates” close , and the K

“gates” open.

•

_{this has the effect of making the outside of the}

membrane more positive again, but with the Na

and K

on the wrong sides of the membrane

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_{the sodium-potassium pumps will then kick}

in and exchange the Na

and K

to restore

the resting potential.

This is called repolarization.

 the process of polarization, depolarization and repolarization takes about 2ms!!!

Within milliseconds the membrane then

actively pumps out the Na

to restore

Refractory Period

remember that nerves are bundles of neurons, so when one neuron “fires” an impulse it causes the neurons around it to fire as well

this “wave” of depolarization, the action potential,

moves along the axon away from the stimulus – this is the nerve impulse

until the resting potential has been properly restored, a second action potential cannot be conducted along the axon – the time for this to occur is called the refractory period

it is at least 1ms long due to the fact that for this time, the membrane cannot be made permeable to Na+ , so

these ions cannot cause depolarization

the stronger the impulse, the longer it takes for the nerve to recover

In nerves wrapped with Schwann cells

(myelin sheath) the nerve impulse jumps from

one Node of Ranvier to another, greatly

Chemical Event:

• _{once the impulse has traveled through the entire length}

of the axon, it reaches the axon terminal

the axon terminal is in close contact with the dendrites of another neuron

the space between the axon terminal of the presynaptic neuron and the dendrites of the postsynaptic neuron is called the synapse

the axon terminal contains numerous synaptic vesicles and mitochondria (to provide energy). These vesicles store

chemical transmitters (neurotransmitters) which act as messengers that move through the synapse to help

Synapse

- tiny gap

between

neuron and the

next cell

(neuron or

effector cell)

Do Now

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_{Draw a picture or describe how one neuron}

passes an action potential to another neuron.

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_{What is an excitatory neurotransmitter?}

it causes the sodium channels of the post-synaptic membrane to

open the enzyme cholinesterase (or acetylcholinesterase) is released after ACh to break it down so that the ACh doesn’t continually try to stimulate the post-synaptic neuron

There are two types of neurotransmitters:

1)

Excitatory

an excitatory neurotransmitter

some of the ACh is also taken back up into the presynaptic neuron to help clear it out of the synapse i.e. insecticides block cholinesterase

acetylcholine is responsible for alertness, learning and memory and is being research in it’s possible role in Alzheimer’s disease norepinephrine (epinephrine) is also an excitatory

neurotransmitter that upon release (and stimulation of the post-synaptic neuron) is removed from the synapse through reuptake

Inhibitory

• _{inhibitory neurotransmitters (like GABA -}

Gamma-aminobutyric acid) have hyperpolarizing effect

these neurotransmitters make the post synaptic membrane more permeable to K+, rather than Na+. By opening more

K+ gates and letting K+ out of the cell membrane

increasing the number of + ions outside the cell relative to the inside

this makes it even more difficult to generate an action potential in the postsynaptic neuron and so it has an inhibitory effect on its activity

problems with GABA are often found in people with epilepsy, Huntington’s disease and some people with sleep disorders

speed of nerve impulses

different nerves can move at different speed, depending on their function/location in the body, and their axon diameter

myelinated neurons (insulated) have a faster transmission speed than unmyelinated neurons

C-nerve fibers are unmyelinated and have a small diameter, and they move the slowest

A-delta and A-beta nerve fibers are both myelinated, but A-beta nerve fibers have a larger diameter

beta nerve fibers carry impulses related to touch, A-delta nerve fibers carry impulses related to initial pain, temperature and C-nerve fibers carry impulses related to pain, temperature and itch

all-or-none response/threshold:

– _{a stimulus must be large enough to start an impulse}

(must reach a threshold level ) minimum stimulus to produce a response

Each axon will have its own threshold level

Increasing the stimulus strength does not increase the impulse strength – a neuron will either fire or not fire (called the All or None response) Fig. 15.12 Page 361

The intensity of a stimulus is instead detected by

increases in the frequency of the nerve impulses. Ex. Warm glass rod –slow rate; hot glass rod frequency of impulses is greatly increased

In the diagram above, neurons A and B are excitatory neurons and neuron C is an inhibitory neuron

In order to stimulate neuron D, A and B must be fired at the same time, and C must not be fired at all (C has the effect of canceling out A or B) since it is inhibitory.

Summation

some neurons require impulses from many other neurons in order to fire – this is called summation

Factors influencing the speed of

conduction:

1) Diameter of axon: The larger the diameter

the faster the rate of conduction

2) Myelinated axons: myelin stops ion movement

across it, therefore action potentials are only

generated at the nodes of Ranvier. This is called

saltatory conduction

Reflex arc:

Simplest neural pathway since reflexes are

automatic responses to sensory stimuli that

occur without brain stimulation.

reflexes are involuntary (autonomic) rather than

voluntary (somatic)

they involve parts of the central nervous system

(CNS) and peripheral nervous system (PNS)

the pathway of neurons that are involved is

called the reflex arc

Do Now

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_{How do excitatory/ inhibitory}

neurotransmitters work?

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_{What is a reflex? Give an example.}

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_{What factors affect the speed of a neural}

transmission?

The knee jerk reflex: (7 essential

components)

receptor – the stretch receptor in the quadricep muscle

sensory neuron – a unipolar neuron attached to the stretch receptor takes info to the CNS

interneuron – passes message to the motor neuron from the associated sensory neuron stimulus – the rubber hammer strikes the tendon just below the knee (infrapateller tendon)

motor neuron – the sensory neuron synapses with interneron in the CNS. This motor neuron takes the info away from the CNS to PNS (multipolar)

effector – a muscle or quadracep that

contracts in response to the info

no neurons are connected to the brain so the brain has no role in this response

the brain only “finds out about it” after it has occurred, through other sources. Ex. Kinetic response

you don’t notice that you brain wasn’t involved because these type of reflexes occur at such a fast rate – the command to kick the knee is given

BEFORE the blow is felt by the patient

this type of reflex is a protective response (eg. burning yourself)

The central nervous system (CNS) is

divided into two parts:

The Spinal Cord

Grey matter in center; white matter on outside. (Page 368)

the spinal cord connects the peripheral nervous system to the brain

the spinal cord receives sensory information through its dorsal root at the back of the cord and transfers

information through the ventral root at the front of the cord

sensory nerves entering the spinal column have their cell bodies localized in a mass outside the spinal cord called a ganglion

Basic Nervous Pathway

2. Forward (ventral)

nerves are motor

neurons

1. Rear (dorsal) nerves are

sensory neurons

Back

Tummy

A. Pairs of nerve bundles exit at

each vertebra - one pair for

The cell bodies of motor neurons are in the spinal cord (motor neurons are multipolar)

The spinal cord & brain are covered by membranes

called meninges. These prevent the exposure of brain & spinal cord cells against bone.

A fluid called cerebral spinal fluid bathes the spinal cord & brain. This acts as a shock absorber & transports

nutrients & wastes to and from the brain.

The brain has spaces called fissures. These are filled with cerebral spinal fluid

The Brain

The brain is made up of three main sections:

THE HINDBRAIN

consists of the cerebellum, medulla oblongata and the pons

a) cerebellum

the cerebellum is responsible for limb movement, balance and coordination

b) medulla oblongata

The medulla oblongata lies just above the spinal cord and it controls breathing, digestion,

peristalsis, heart rate, blood pressure

the pons is the bridge between the cerebellum and medulla oblongata

C. Brain Parts

1. Hindbrain -

includes:

pons

cerebellum

medulla

i. Responsible for ANS

activities like stimulation of

diaphragm, breathing

muscles, heartbeat, artery

diameter

ii. Pathway for impulses

moving from higher parts of

brain to motor nerves

and

muscles

a. Medulla Oblongata - swollen extension of

the spinal cord.

ii. Resp. for

coordination of

muscle movement,

balance, and muscle

tone

iii. Organizes,

integrates impulses

b. Cerebellum - located just above

medulla.

i. Grey/white matter, furrowed

appearance

c. Pons

i. Bridges medulla and mid-brain

ii. Transmits between two sides of

the

cerebellum

THE MIDBRAIN

Forms part of the brain stem

Acts as a relay center between hind &

forebrain

2. Midbrain - located above the pons

a. Relay centre for some eye

and ear reflexes

b. Contains network of

neurons known as the

Reticular Formation that

activates the forebrain

c. Allows you to concentrate

on specific stimuli and ignore

the rest.

Do Now

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_{What are the three major sections of the}

brain?

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_{What is responsible for breathing, heart}

rate, and many other autonomic systems?

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_{What part of the brain is responsible for}

THE FOREBRAIN

consists of the thalamus,

hypothalamus and cerebrum

a) Thalamus

The thalamus is a sensory relay center – it

directs incoming sensory signals

The thalamus has a large degree to do with

sleep, wakefulness, sensation of temperature

and degree of pain

3. Forebrain - contains the

a. Thalamus - located between the

midbrain and cerebrum.

i. Sensory relay for impulses on the

way to cerebrum (relay station)

ii. Affects consciousness and

awareness of pain

Hypothalamus

The hypothalamus connects to a special

structure called the pituitary gland

The major center for the integration of the

nervous & endocrine systems

The hypothalamus controls blood pressure,

urine production, water balance (produces

ADH), hunger, body temperature, internal

organs, autonomic nervous system

The hypothalamus also affects behavioral and

emotional responses

i. Control of ANS - internal

organs, blood pressure, temp.,

heart rate, water balance

(osmoreceptors) (sympathetic

and parasympathetic)

ii. Controls basic drives such as

hunger, thirst, sex and rage.

iii. The pituitary produces and

stores hormones

b. Hypothalamus - connected to and controls

function of the pituitary gland

Cerebrum

The cerebrum is the largest part of the human

brain (80% 0f mass)

The cerebral cortex surrounds the cerebrum

and is composed of grey matter, the inside of

the cerebrum is composed of white matter

The cerebrum is folded, which increases the

surface area

The cerebrum is divided into two cerebral

hemispheres, the left and right hemispheres

The right side of the brain controls the left side of

the body and the left side of the brain controls the

right side of the body.

c. Cerebrum - uppermost and outermost and

largest portion of the human brain. Highest

centre of nervous control.

Phineas Gage

“Improvised

Cerebral

CORPUS CALLOSUM

The corpus callosum is a bundle of nerve

fibers that connects these hemispheres

The hemispheres can be further

divided into 4 lobes:

2. Fissures - surface of the brain has many

folds

a. Results in more surface area --->

more synapses ---> more thinking

b. 2 main fissures separate brain into

regions

a. Hemispheres

connected internally

by

corpus callosum

white

matter.

b.Hemispheres seem

resp. for different

tasks

3. Longitudinal fissure -

separates brain into 2

hemispheres

Right Brain Left Brain

facial

speech areas

spatial sense verbal

artistic mathematical

creative

rational

LOBES OF THE BRAIN

FRONTAL LOBE –at the front of the cerebrum and controls voluntary muscles (walking, speech) and intelligence

TEMPORAL LOBE –located at the temples; controls part of vision, hearing, memory and interpretation of sensory

information like smell

PAREITAL LOBE –located at the top and back of the

cerebrum and monitors senses such as touch and temperature. Responsible for emotion and helps interprets speech and

pressure

OCCIPITAL LOBE –located in the lower back of the cerebrum and interprets visual information

Cerebrum

Association areas = integration and direction of voluntary behaviors

a. Frontal - greatly

developed in humans

i. Controls speech,

intelligence, personality

and

all voluntary

movements

(motor cortex)

ii. Sorting site for sensory

info.

4. Central fissure - divides brain into 4 lobes

named for bones of skull

c. Temporal -

hearing, smell

b. Parietal - sensory

receptors of skin,

body position detectors

(sensory cortex)

1. Motor cortex

-D. Sensory and Motors Regions of the

Cerebrum

b. Generally control of right side

of body comes from left brain

and vice versa.

a. controls

voluntary motor

activities

MENINGITIS

The brain is enclosed in the skull, made out of bone The brain is also surround cerebrospinal fluid, like the

spinal cord, which is surrounded by the meninges.

Meningitis: Inflamation of the meninges

Recent research has shown that information

stored in one side of the brain is not necessarily

present in the other. The right side has been

associated with visual patterns or spatial

awareness; the left side is linked to verbal skills.

Your ability to learn may be linked to the

THE PNS & ANS

The peripheral nervous system (PNS) is made of

somatic and autonomic nerves which extend beyond

the brain and spinal cord – this allows the brain and

spinal cord to communicate with the rest of the body,

and vice versa

The autonomic nervous system (ANS) controls the

internal organs and is made up of two involuntary

“systems”:

B. Peripheral

nervous system

(PNS)- nerves

which extend

beyond the brain

and spinal cord.

1. Somatic Nerves - voluntary control of

skeletal muscle, bones and skin.

a. Motor nerves -

carry messages

from CNS to

effectors

(eg. glands or

muscles)

b. Sensory nerves

- carry messages

2. Autonomic Nervous System (ANS) -

controls involuntary body actions

b.Parasympathetic

division - returns it to

normal

a. Sympathetic

division - preps body

for emergencies

Sympathetic System

•

_{Generally stimulatory}

Prepares body for fight or flight

Causes the adrenal medulla to secrete adrenalin Adrenaline causes the following:

Increase heart rate and breathing rate Pupil dilation, decrease in saliva

Release of glucose

Decrease in digestion and relaxes sphincters

Increase in sweat production and look white as a ghost because blood is

Parasympathetic System

Generally inhibitory

Tries to maintain or restore homeostasis

Slows heart rate and breathing rate

Stimulates peristalsis

Constricts pupils

Contracts sphincter

Relaxes body