The Nervous System

The Nervous System & Homeostasis

• The nervous system is the main _______ _____________________________of the body.

• Every thing we do, feel and think consciously or unconsciously is directed by the nervous system.

• The communication between the nervous system and the body is through ________ and __________ signals that move rapidly and to specific areas allowing for immediate response.

Three functions of the nervous system

1. ______________________ ___________________

• ________________- an organ having nerve endings that respond to stimulation.

Ex: in the skin, eye, ear, nose, mouth, or any internal organ

• These monitor changes occurring internally and externally of the body.

• The information gathered is called “_________________”.

2. The ____________ of this information. • The sensory input is _________________

which ___________on how to respond every bit of information it receives.

3. The third function is the actual ________ • This is called ________________

• The response ___________________ and/or _______(which release hormones) in the body.

• Effectors = any part of the body that carries out the response.

• Examples : A muscle contracting to move the arm

A muscle squeezing saliva from the salivary gland

A gland releasing a hormone into the blood.

– Hormones are ________________produced in glands and carried by the blood to specific organs in the body. The carry messages for specific body parts to ___________________ _______________

Some Helpful Definitions

• ____________= something that causes a receptor to trigger impulses in a nerve pathway

• __________= specialized sensing cells that respond to a particular type of stimulus

• _____________________= electrical message carried by the nerve cells

• ____________= a muscle or gland that responds to a particular stimulus

Neurons (Nerve cells) Types of Neurons:

1. _____________= carries impulses from receptors TO CNS (spinal cord / brain)

2. __________ = relay impulses from each neuron in the brain and spinal column

3. __________= carries responses AWAY from CNS to the effectors (muscles / glands)

Lets look at the anatomy of a neuron…

Interneuron

Cell body

•Integrates signals

•Coordinates metabolic activities

Dendrites

•Picks up impulses (from receptors or neurons and conducts it to the cell body)

Schwann cells

form a fatty material called myelin to insulate the axons

Nodes of Ranvier

• Gaps that aren‟t covered by sheath

• Speeds up AP because now it jumps from gap to gap

Myelin sheath

•White, fatty protein

•FXN: insulates, prevents loss of chemical ions (necessary for transmission of impulse), speeds up conduction

Axon

•Carries impulse

away and

passes it on to

other neurons

Sensory neuron Motor neuron

Synaptic terminals

• Transmit signals to other neurons (chemicals called neurotransmitters)

• Enzymes stop transfer of signals

Organization of the Nervous System

http://www.youtube.com/watch?v=i-NgGKSNiNw

Types of Neurons

Parts of a Neuron:

• ______________= pick up impulses (from receptors or other neurons) → conducts impulse to cell body

• ______________= integrates signal, coordinates metabolic activities

• __________= carries impulse away to other neurons/cells

• Note: The direction of an impulse ________ _________________________________

• Note: A neuron = ___________________ A “NERVE” = ______________________

• _______________= white, fatty, protein that insulates the axon and prevents the loss of chemical ions (necessary for transmission of impulse)

– forms when ________________wrap themselves around an axon

– Not on all neurons

• ________________= gaps on myelinated axons (not covered by the sheath)

– The AP moves down the axon, but ion-swapping across the membrane occurs only at ___________ ____________

– This makes the AP jump along the axon, from node to node, rather than continuously

– =FASTER

Myelin Sheath

• ____________________ – Bulbs at the end of an axon where _________

________________________________and released

– there is no contact b/w two neurons

– electrical impulse cannot jump the gap between neurons

– The microscopic gap b/w neurons is called the _____________

– ____________________are used to jump the synapse to signal the next neuron to „fire‟

Note: _______________will stop the transmission of the signal

Synapse Structure

http://www.youtube.com

/watch?v=HXx9qlJetSU

___________________(aka Nerve Impulses) • When a nerve cell is at ____(not stimulated)

it is ___________ – The negative charge is on the inside and positive

charge is on the outside of the neuron – allows potassium/sodium ions to move freely

across membrane

• _______________= as the action potential zooms down an axon, the polarity (charges on either side of the cell‟s membrane) rapidly switches (now negative charges on the outside and positive charges on the inside)

• _____________= restores resting position (negative charges inside/positive outside)

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Direction of Impulse

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K+ Na+

Depolarized Polarized = not stimulated (@rest)

Repolarization = restores resting potential

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http://www

.youtube.c

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Let’s take a closer look at what happens....

The Resting Potential (Nerve at Rest):

•The neuron needs to build up opposite charges across

the membrane and maintain them

•Neuron actively transports 3 sodium ions (Na+) OUT

and 2 potassium ions (K+) IN using active transport

(sodium potassium pump)

– therefore a positive charge builds up outside neuron

•Neuron’s cytoplasm already contains negative

molecules, primarily negatively charged proteins, and

some chloride ions (Cl-)

– This maintains a net negative charge inside the neuron

•Having different charges is called being POLARIZED

Let’s take a closer look at what happens....

Action Potential (nerve impulse)

•A stimulus from sensory input causes sodium

(Na+) channels in the neuron membrane to open

•Na+ rushes INTO the neuron by diffusion – Recall: Na+ was built up on outside using the sodium

potassium pump – it doesn’t like to be built up

•This influx of Na+ now makes the inside of the

neuron become positive compared to the outside – this is called DEPOLARIZATION

•Depolarization of one region of an axon causes the next

area on the axon to open up sodium channels, and thus

the action potential continues down the axon

• Sodium (Na+) channels then close

• Potassium (K+) channels open allowing potassium to flood OUT of the cell

– Recall: K+ was built up on inside using the sodium potassium pump – it doesn’t like to be built up. Plus now there is Na+ in there too (+ve charges repel)

• This resets the inside of the membrane back to being more negative than the outside – That is, back to it’s resting potential

– We call this process REPOLARIZATION

• Potassium (K+) channels now close – The neuron has now returned to it’s resting state in which the

inside is negative compared to the outside HOWEVER the ions are misplaced and must be switched. [ie: we have a build up of potassium (K+) on the outside of the neuron and sodium (Na+) on the inside...needs to be the other way around]

• The neuron uses the ‘sodium potassium pump’ to swap 3 Na+ OUT for every 2 K+ pumped IN until these ion concentrations are back to normal on their proper sides of the membrane

Two Divisions of the Nervous System:

1.Central nervous system (CNS)

– _________________________ – Function: controls ___________

2.Peripheral nervous system (PNS) – Everything else

– ____________________________________

– Function: ________to the world around you

Anatomy of Brain 1. Medulla oblongata

– Base of brain, top of spinal cord.

– Deep in brain, so hasn‟t changed much over millions of years, therefore has primitive functions:

• Controls:

2. Cerebellum • Contains 50% of brain‟s neurons

• Controls ____________________

– _________, position, contracting & relaxing muscles, ___________ upright, etc.

– Therefore, has a constant feedback system • As we get more used to physical activities, the

cerebellum slowly takes over. That‟s how you become more graceful at physical activities. Because you don‟t have to consciously think about it!!!

– Think about it...an infant learning to walk vs. an adult standing / walking

3. Thalamus • This is the „___________

_____________‟ – Like a post office!

• ___________sensations (touch, pain, heat, muscle info...) ___________the information to the appropriate part of the brain so the brain can ignore it or take action.

• Also controls ______ and ______________

4. Hypothalamus • Is the “_________________________”

because it controls the ___________and ___________________nervous systems (more on this later) – What do you think homeostatic control center

means?

• Controls ____________, thirst, appetite, sleeping

• Involved in “fight or flight” response and resetting the body back to normal – Via the sympathetic and parasympathetic

nervous systems

5. Cerebrum • Largest part of the brain

– Divided into left & right hemispheres

• A very ________________ of our brain – Highly developed in humans, underdeveloped in

primitive creatures...what makes humans humans

• Where all of our _________ are sorted out and interpreted

• Controls voluntary muscles (running, walking, etc)

• Controls speech • Responsible for __________, ________,

____________, and _______________

6. Cerebral Cortex – a layer of the cerebrum

• Each hemisphere of the cerebrum has an inside layer called the _____________and an outside layer of ____________called the cerebral cortex

• Whereas the inside of the cerebrum __________ sensations, the outer layer (cerebral cortex) _______________ them.

• The cerebral cortex also ___________________ __________________ like running and walking.

You taste, feel, and smell things in your BRAIN, not in your mouth, nose, and skin!!

7. Corpus Callosum

• A mass of fibres that ______________ _______________________________.

• Note: The right hemisphere controls the left side of the body and the left hemisphere controls

the right side of the

body.

• Almost every person

has one dominant

hemisphere

1. The CNS – b) the spinal cord

• Extends from the opening at the base of the skull, through the vertebral canal (the holes in your vertebrae)

to the lower back • ___________________ ____________________ ____________________ (sensory and motor neurons) • Controls ____________actions that do not require intervention from the brain

– Called the reflex arc

Human Reflexes and Reaction Time

The reflex arc

• it involves only 3 neurons

• by-passes the brain

• consists of: receptor, _________________, ____________in spine, ___________, effector

• a typical reflex arc is the response to pain

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Paralysis

Remember this slide??? Two Divisions of the Nervous System: 1.Central nervous system (CNS)

– the brain and spinal cord – Function: controls behavior

2.Peripheral nervous system

(PNS) – Everything else – Includes the nerves that lead

into and out of the CNS – Function: responds to the world

around you

Somatic and Autonomic

Nervous Systems

Somatic nervous system

• contains both ______________________ that connect the central nervous system to skeletal muscles, the skin, and the sense organs

• is responsible for body movements over which the individual has conscious awareness or _____________________

Autonomic nervous system • made up of motor fibres from the brain and

spinal cord that ____________________ of the body

• usually has _______________________ • controls functions like rate of heartbeat,

blood flow through __________, breathing movements, movements of the __________ system, and secretions of certain glands

• is made up of 2 systems: – ____________________ – ____________________

these work in opposite ways to counteract each other

• The parasympathetic system is responsible for „_____________________‟ activities,

• and the sympathetic is responsible for „____ ________________‟ responses – So…parasympathetic functions to return to

normal operations of the body that were shut down or slowed down by the sympathetic system in an emergency or stressful situation