1. Chapter 6: The Nervous System
Sect. 1: How the Nervous System Works
Sect. 2: Divisions of the Nervous System
Sect. 3: The Senses

2. Sect. 1: How the Nervous System Works
What are the functions of the Nervous System?
Receive information
Process information from both external (outside environment) & internal (inside the body) sources
Nerve impulse:
messages carried by nerve cells
Respond to information
Responses to stimuli can either be voluntary or involuntary.
Stimulus: any change or signal in the environment that can make an organism react.
Response: body’s reaction to a stimulus
Maintain homeostasis
Directs and coordinates the body’s response to the environment either chemically (release of hormones & other chemicals ) or mechanically (directing movement).

3. Neurons: nerve cells Structure of a neuron.
Soma
Cell body of a nerve cell
Dendrite
Carry impulses toward the cell body
Nucleus
Controls the direction of impulses
Axon
Carry impulses away from the cell
Axon tip
Connections at the end of an axon that delivers impulses to different cells
Nerve: bundle of nerve fibers

4. Types of Neurons Sensory neurons Interneuron Motor neuron
Pick up stimuli from the internal or external environment & converts it into a nerve impulse.
Interneuron
Connector neurons that pass nerve impulse from one neuron to another.
Synapse: junction where one neuron can transfer a nerve impulse to another nerve or structure.
Nerve impulses are passed across the synapse through the use of chemicals released by the axon tip.
Motor neuron
Neurons that carry the nerve impulse to a muscle or gland cause them to respond to the stimuli.

6. Sect. 2: Divisions of the Nervous System
The Nervous System is divided into 2 parts….
Central Nervous System
Peripheral Nervous System
The Central Nervous System consists of….
Brain
Spinal cord
The Peripheral Nervous System consists of….
The nerves that branch out from the brain & the spinal cord.

7. Central Nervous System
Brain
Control center for most of the body’s functions.
Regions of the brain
Cerebrum
Largest part of the brain.
Controls functions such as the senses, speech, memory, movement & abstract thought.
Divided into 2 half; right & left. Right half controls skeletal muscles on left side of body. Left half controls muscles on right side of body.
Right half associated with creativity & artistic ability.
Left half associated with logical & mathematical reasoning.

8. Spinal cord Cerebellum Brain stem
2nd largest part of the brain
Primarily responsible for sensory integration & coordination of movement & balance.
Brain stem
Smallest part of the brain
Responsible for controlling involuntary functions; i.e., breathing, heartbeat, etc.
Spinal cord
Thick column of nervous tissue that links the brain to most of the nerves of the peripheral nervous system.
Protected by vertebrae, layers of connective tissue, and spinal fluid.

9. Peripheral Nervous System
Divisions of the peripheral nervous system
Somatic Nervous System
Control voluntary actions
Autonomic Nervous System
Control involuntary actions
Components
Nerves that branch out from the brain & spinal cord
43 total pairs of nerves (right side body & left side body)
12 pairs extend from the brain; 31 extend from the spinal cord.
Spinal nerves contain both motor & sensory neurons
Sensory neurons: impulses from the body to the central nervous system
Motor neurons: impulses from the central nervous system to the body

10. Reflex
Automatic response that occurs very rapidly and without conscious control.
Reflexes are controlled by spinal cord not the brain
Steps to a reflex pathway
Sensory neuron detect stimulus
Nerve impulse travels to spinal cord
Spinal cord sends return impulse to direct immediate response.
Nerve impulse travels to brain where brain then interprets impulse.

11. Nervous System Injuries
Stroke
The arteries of the a part of the brain are damaged and blood flow to the area is affect.
Movement (paralysis) on the opposite side of the body in which the stroke took place is usually affected
Concussions
bruise like injury of the brain; soft tissue of the brain collides against the skull.
Symptoms of moderate to severe concussions
Headaches
Lose of consciousness, drowsiness
Confusion
Spinal cord injuries
Paralysis: complete loss of muscle function for one or more muscle groups
Paraplegia: loss of muscle function in the lower half of the body.
Quadriplegia: loss of muscle function in all 4 limbs.

12. Sect. 3: The Senses What happens to light that enters the eye?
Light enters through the cornea.
Cornea is the clear tissue that covers the front of the eye.
Light then enters the pupil.
Pupil is a hole located in the center of the iris of the eye that dilates & contracts to allow more (low light areas) or less (sunny areas) into the eye.
It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye.
In humans the pupil is round, but other species, such as some cats, have slit pupils
Iris is the colored portion of the eye that are actually muscles that control how much the pupil dilates or contracts.

13. Light then strikes the lens.
Lens is a flexible, translucent structure that focuses the light onto the retina.
Light then strikes the retina.
Retina is the row of a light-sensitive tissue lining the inner surface of the back of the eye.
Light striking the retina initiates a cascade of chemical and electrical events inside cells called rods & cones that ultimately trigger nerve impulses.
Rods are low light receptor cells; see black, white & shades of gray
Cones are high light receptor cells; see color, clarity & contrast.
Image created on back of the eye is upside down & backwards.

14. Optic nerves connects each eye to the cerebrum.
The cerebrum receives the nerve impulses from the optic nerves.
It flips the image.
It reverses the image.
It combines the images generated from both eyes to form the single image that you see.

15. Common eye problems Nearsightedness Farsightedness
Inability to see objects from a distance.
Eyeballs tend to be elongated.
Image focuses in front instead of on the retina.
Corrected by the use of a concave lens that focuses the light onto the retina.
Farsightedness
Inability to see objects up close.
Eyeballs tend to be shortened.
Image focuses behind instead of on the retina.
Corrected by the use of a convex lens that focuses the light onto the retina.

16. How do you hear? Outer Ear Middle Ear
Vibrations or sound waves are created by objects in the outside environment.
Those sound waves radiate or move toward your ear.
You outer ear is designed to funnel those sound waves into the ear canal.
Middle Ear
Those vibrations travel through the ear canal and hit the eardrum causing it to vibrate.
Those vibrations are then passed to the structures of the middle ear; hammer, anvil, & stirrup, causing them to vibrate.

17. Inner Ear
The stirrup cause vibrations to pass to the structures of the inner ear, primarily the cochlea; a fluid filled, snail shaped structure that also contains sensory neurons.
The sensory neurons change the vibrations into nerve impulses that are sent to the brain to be interpreted as sound.

18. Semicircular canals are structures within the ear that control you sense of balance.
Sense of Smell
Nose can distinguish between over 50 basic odors.
Nasal receptors react to the smell of a food before taste receptors on the tongue.
Sense of Taste
Taste receptors on the tongue can determine about 5 main “tastes.”
Sweet
Sour
Bitter
Salty
Umami: a “meatlike” or savory taste
Taste buds change about every 7 years.

19. Sense of Touch Skin is the largest sense organ.
Contains receptors that respond to…
Light pressure
Upper part of the dermis
Heavy pressure
Lower part of the dermis
Pain
Body’s early warning system for possible danger & damage to an area.
Temperature
Used to help regulate internal body temperature & the maintaining of homeostasis