Nervous System

Unit 5: Nervous System & Senses3a. Interpret interactions among hormones,

senses, and nerves which make possible the coordination of functions of the body.

3b. Investigate the physiology of electrochemical impulses and neural integration and trace the pathway of an impulse, relating biochemical changes involved in the conduction of the impulse.

3c. Describe how the body perceives internal and external stimuli and responds to maintain a stable internal environment, as it relates to biofeedback.

p. 35

electrochemical

biochemical

functionssenses nerves

internal external

internal (homeostasis)

I. Function of the Nervous System

Control & coordination of body systems

Three basic functions to accomplish this mission:

A.Sensory input

B.Integration

C.Motor output

The three functions… visualized:

Sensory input

Integration

Motor outputInformation IN

Evaluate the info

Send response instruction(s)

Comp Book:

-p. 38 Flow Map:

From Stimulus to Nervous Response

II. General Overview

A. Structural Classification

There are 2 major structural divisions of the nervous system:

the central nervous system (CNS)

the peripheral nervous system (PNS)

1. Central Nervous System (CNS) – is made up of the brain & spinal cord

a. Brain – contains about 100 billion neurons

Click here for intro to the brain video

The brain can be divided into 4 major regions: i. Cerebrum

ii. Diencephalon

iii. Cerebellumiv. Brain stem

(midbrain)

i. The cerebrum governs:• interpretation of

sensory info. (smell,taste, sight, hearing)

• intelligence• memory• language

• motor functions (activity of muscles and glands)

ii. The diencephalon is found beneath / within the cerebrum

The diencephalon contains:

• Thalamus: conducts information between the spinal cord & cerebrum

• Hypothalamus (below the thalamus):

center for homeostasis in the body (temperature, appetite, & water balance)

iii. Cerebellum: below the cerebrum & behind the brain stem

Cerebellum

• smooth, coordinated movements

• helps maintain posture, muscle tone, and equilibrium (balance)

(you lose your equilibrium when you drink because the alcohol inhibits the function of the cerebellum)

iii. Cerebellum governs:

iv. brain stem: connects brain to spinal cord—it regulates:

• heartbeat

• respiration

• blood pressure

• swallowing

• coughing

• hiccupping

• sneezing

• vomiting

Neurons passing through the brain stem cross from one side of the body to the other.

(In other words, if your right hand was burned, the pain signals would travel to the left side of the cerebrum to be interpreted)

(Also, if you wanted to lift your left arm, the signal would be sent to your left arm from the right side of your cerebrum)

b. Spinal cord – extends from the brain stem, through the vertebrae to the 2nd lumbar vertebra

• Notice: the spinal cord does not extend to the tip of the vertebral column

• information traveling to and from the brain must pass through the spinal cord to reach other parts of the body

• often called the “information highway” of the CNS

• made of 2 layers: “gray” & “white” matter

2. Peripheral Nervous System (PNS) the cranial & spinal nerves

Humans have:

• 12 pairs of cranial nerves ex. optic nerves,

olfactory nerves,

facial nerves

• 31 pairs of spinal nerves

One of the most important functions of the PNS is to perform reflex actions, which do not involve the brain

A reflex is a sudden, rapid, involuntary response to a stimulus

Reflex examples:

• knee jerk reflex (lower leg kicks when tendon is tapped)

• withdrawal reflex (hand withdraws if it touches something hot)

• papillary reflex (pupil constricts if a bright light is shown in your eyes)

Knee jerk reflex: the patellar tendon is tapped

• this generates nerve impulses which travel along sensory neurons to the spinal cord

How do reflexes work?

• the spinal cord then transmits impulses through motor neurons

• the rectus femoris muscle is instructed to contract, causing extension of the lower leg

• the brain is not involved in the response

• information travels over a shorter distance – producing faster reaction times

• the reflex is completed before your brain is aware of what happened

• you will typically withdraw your hand from something hot before you recognize the pain of the burn

Comp Book:

-set it up

-back of p. 35 structural classification

II. General Overview (continued)

B. Functional Classification of PNS: categorizing parts of the nervous system based on the nerve function in the overall nerve pathway; in this way, there are 2 types of nerves:

Sometimes it is simpler to address each part of the nervous system based on the general role it plays in the nerve pathway…

Remember the nerve pathway?

Sensory integration motor output(brain)

1. Sensory2. Motor

1. Sensory Nerves = Afferent Division: The body’s receptive nerves taking info from both the internal and external environment toward the CNS:

a. Somatic sensory fibers—nerve endings & receptors in skin, skeletal muscles & joints

b. visceral sensory fibers—nerve endings and receptors in abdominal & pelvic organs

c. Vision from the eyes

d. Hearing & balance from the ears

e. Smelling from the nose

(chemoreceptors)

f. Taste from the tongue

(chemoreceptors)

Plus all your special senses… ch. 9

2. Motor Nerves = Efferent Division

After the brain integrates the sensory input, outgoing response is sent through the efferent nerves

The motor or efferent portion of the PNS is typically divided into 2 subsystems:

a. Somatic Nervous System

b. Autonomic Nervous System

a. Somatic Nervous System – includes the cranial & spinal nerves that regulate voluntary actions

b. Autonomic Nervous System – includes the cranial & spinal nerves that regulate involuntary actions

ex. cardiac muscle

smooth muscle

gland activity

Keep in mind that although the ANS functions “automatically”, you can consciously control it for a short period of time

When you hold your breath, you are overriding your ANS – however, you cannot override it indefinitely

The Autonomic Nervous System can be further subdivided into:

i. Sympathetic Division

ii. Parasympathetic Division

i. Sympathetic Division: regulates involuntary actions during periods of high stress or increased activity

• increases blood pressure

• heart rate

• breathing rate

• blood flow to muscles

• dilates the pupils of your eyes (increases amount of light; see better)

• decreases digestion of food & blood flow to the skin

All of these changes prepare your body for action (“fight or flight”)

ii. Parasympathetic Division: regulates involuntary actions during periods of rest or relaxation

• decreases blood pressure

• decreases heart & respiratory rates

• decreases blood flow to muscles

ii. Parasympathetic Division (cont.’d):

• constricts the pupils of your eyes

• increases digestion of food and blood flow to the skin

*** Most internal organs are regulated by both the sympathetic and parasympathetic divisions.***

• the parasympathetic division dominates when you are relaxed

• the sympathetic division dominates when you are under stress

Comp Book:

-p. 36 functional classification-back of p. 37 Venn:

Autonomic vs. Somatic

III. The Electrochemical Impulse

A. Anatomy of a neuron

Click here for intro to nerve cells video

Neuron structure – 3 basic parts

1. One or more dendrites

• Short, highly branched extensions

• Receive impulses from receptors or other neurons

• transmit impulses toward the cell body

dendrites

2. Cell body – main portion of the neuron

• processes information sent by the dendrites

cell body

3. One axon –

• axon tip usually branched forming axon terminals

• long extension that transmits impulses away from the cell body

axon

Impulses always travel in this direction:

Dendrites

cell body

axon

axon terminals

• Schwann cells produce a myelin sheath that functions to protect the axon and speed up impulse conduction

myelin sheath

Many axons are surrounded by specialized cells called Schwann cells

• Similar to the coating on electrical cords

A disease that involves the destruction of the myelin sheath – multiple sclerosis

• destruction of the sheath impairs the transmission of nerve impulses

• this causes muscular weakness, loss of memory, double vision, and paralysis

Comp Book:

p. 37 Frayer: neuron

III. The Electrochemical Impulse

B. Physiology of a nerve impulse

A. Anatomy of a neuron

Nerves are the functional units of the nervous system

Electrical signals called nerve impulses are transmitted by neurons

III. The Electrochemical Impulse

B. Physiology of a nerve impulse

1. Resting Conditions

2. Stimulus & Local Depolarization

3. Depolarization & Action Potential

5. Repolarization

6. Initial Ionic Conditions Restored

4. Propagation

Click here for animation about resting potential

Neurons that are not conducting an impulse are called “resting” neurons

http://www.youtube.com/watch?v=nIojqRFJWbM&feature=related (basic)

A resting neuron has:

• a high concentration of sodium ions (Na+) to its outside

• a high concentration of potassium ions (K+) and negatively charged organic molecules on its inside

• a resting neuron is disturbed (by pressure or other stimulus)

• Na+ diffuses into the cell in one, local spot

2. Stimulus & Local Depolarization

3. Depolarization & Action Potential

• If enough stimulus is present, the whole membrane’s polarity is completely reversed, generating an action potential

• this sudden reversal of voltage across the neuron membrane is called an action potential

4. Propagation

Depolarization of the local patch changes the membrane beside it…

And the same repeats on the patch beside that…

This sends the signal down the length of the neuron.

5. Repolarization

Membrane changes cause K+ to diffuse and re-establish the initial charges.

6. Restoration

The sodium-potassium pump restores the resting state

The sodium/potassium pumps located within the cell membrane of the neuron maintains the high concentration of Na+ on the outside and K+ on the inside

All of these events travel down the entire length of the neuron (like the falling of dominoes) until the action potential reaches the axon terminals

The neuron cannot transmit another action potential until the recovery period is completed

More Action Potential Videoshttp://www.youtube.com/watch?v=R0TdXkxBOkE&feature=related

http://www.youtube.com/watch?v=ifD1YG07fB8&feature=related

Comp Book:

-back of p. 36 Flow Map: Conduction of a Nerve Impulse-Frayer Model: action potential

The action potential when it reaches the axon terminals must be transmitted to either:

—another neuron

— an effector (muscle or gland)

C. After the axon terminal

Action potentials transferring to another neuron must cross the space between the two cells.

The gap between the 2 neurons or a neuron and its effector is called the synapse

Conduction of Impulses Across a Synapse:

An action potential is transmitted across a synapse by chemical messengers called neurotransmitters

Click here for intro video about synapses

Neurotransmitters are found in tiny sacs at the end of axon terminals

When impulses reach the axon terminal, they:

1. the tiny sacs release the neurotransmitters into the synapse

2. The neurotransmitters diffuse across the synapse

3. neurotransmitters bind to receptor proteins on the effector (muscle or gland) or dendrite of another neuron

4. the muscle, gland or neuron responds

Over 60 different neurotransmitters have been identified

• the response observed depends upon which neurotransmitter was released

Some neurotransmitters are stimulators, causing:

•muscles to contract,

• glands to secrete, or the generation of another action potential

Other neurotransmitters are inhibitors, making:

• muscles more difficult to contract,

• reduced secretion of the gland,

• or inhibiting the transfer of the action potential in the adjacent neuron

IV. Perception

Can be internal or external

Internal = nerve endings or receptors

External = sensory organs

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Comp Book:

Back of p. 38 and p. 39 Visual and Auditory Perception