The Nervous System

Homework Handout

Division of the Nervous System

• Central Nervous System (CNS)– Consists of the brain

and spinal cord– The central nervous

system relays messages, processes information, and analyzes information.

• Peripheral Nervous System (PNS)– Consists of all the

nerves outside the CNS

– Senses and movement; Relays information from the external environment to the central nervous system.

• Somatic Nervous System  • Autonomic Nervous

System 

Peripheral Nervous System

• Sensory – Conveys information from sensory receptors or nerve endings

• Motor – Stimulates voluntary and involuntary muscles

• Consists of two systems– Somatic Nervous System

• regulates activities that are under conscious control, such as the movement of the skeletal muscles

– Autonomic Nervous System• Controls involuntary muscles

Autonomic System

• Further divided into two parts:• Sympathetic

– Fight-or-flight response– Increases heart and breathing rate– Liver converts glycogen to glucose– Bronchi of lungs dilate and increase gas exchange– Adrenaline raises blood glucose levels

• Parasympathetic– Opposes the sympathetic system– Calms the body down– Decreases heart/breathing rate– Enhances digestion

Neurons (Nerve Cells)

• Neuron - cell that carries messages throughout the nervous system– cell body - largest part of a typical neuron; contains the nucleus

and much of the cytoplasm.– Dendrites – sensory parts of neuron. Messages are received

here and transmitted to the rest of the cell by electrical impulses. (Neurons can have numerous dendrites)

– Axon - long fiber that carries impulses away from the cell body of a neuron. Neurons only have one axon, but it can be several feet long.

– Myelin sheath - insulating membrane surrounding the axon in some neurons. Protects and aid in transfer of electrical impulse. Formed by Schwann Cells.

Neuron

The Reflex Arc

• The simplest nerve response

• Notice that the loop is completely independent, it is not necessary to have CNS involvement beyond the relay with the interneuron.

Nerve Impulse• A nerve impulse begins

when a neuron is stimulated by another neuron or by its environment.

• resting potential - difference in electrical charge across the cell membrane of a resting neuron

• action potential - reversal of charges across the cell membrane of a neuron

Nerve Impulse - (Resting Potential)

• All living cells have a membrane potential between the cytoplasm and extracellular fluid. (-50mV to -100mV)

• A resting Neuron is polarized (-70mV)– Sodium-potassium pump maintains this state

by pumping out + ions– Stimulus must overcome resting potential (-

70mV or possible more)

How a Neuron Functions (Resting

Potential)

Nerve Impulse - Action Potential

• Action Potential or impulse can only be generated in the Axon.– Stimulus overcomes

threshold– Membrane become

more permeable• Allowing Na+ to rush in.• Like a wave or domino

affect

Nerve Impulse - Action Potential

Nerve Impulse - Action Potential

Nerve Pulse transfer

• Synapse – Location where the axon terminals meet the dendrite of an adjacent neuron– Synaptic cleft is the

space between• Neurotransmitter -

chemical used by a neuron to transmit an impulse across a synapse to another cell

Action Potential

Central Nervous System• Cerebrum - area of the brain responsible for all

voluntary activities of the body• Cerebellum - region of the brain that coordinates body

movements• brain stem - structure that connects the brain and

spinal cord; includes the medulla oblongata and the pons “Switchboard”

• Thalamus - brain structure that receives messages from the sense organs and relays the information to the proper region of the cerebrum for further processing

• Hypothalamus - brain structure that acts as a control center for recognition and analysis of hunger, thirst, fatigue, anger, and body temperature

Central Nervous System

The Senses of the Nervous System

There are five general categories of sensory receptors: pain

receptors, thermoreceptors, mechanoreceptors,

chemoreceptors, and photoreceptors.

The Eye

• Pupil - small opening in the middle of the iris through which light enters the eye

• Lens - transparent object behind the iris that changes shape to help adjust the eye’s focus to see near or distant objects

• Retina - innermost layer of the eye• Cornea – tough, clear covering that protects the eye and

allows light to pass through• Humor – fluids that maintain the shape of the eye• Iris – colored part of the eye that controls how much light

enters• Rod - photoreceptor in eye that is extremely sensitive to light• Cones - in the retina of the eye, a photoreceptor that responds

to light of different colors, producing color vision

Eye

The Ear (Hearing and Balance)• Hearing

– Auditory Canal – ear canal, where sound enters– Tympanum – Ear Drum, vibrates as sound wave hit it– Cochlea - fluid-filled part of the inner ear; sends nerve impulses to the

brain through the cochlear nerve– Ear bones

• Hammer• Anvil • Stirrup

– Eustachian tube – equalizes pressure between environment and inner ear

– Oval window – sends waves of pressure to cochlea• Balance

– semicircular canal - one of three structures within the inner ear that help an organism maintain balance (oriented perpendicular to each other)

Ear

Semicircular Canals

Smell and Taste

• Chemoreceptors – receptors which sense different Chemicals

• Taste and smell are linked closely together

• “Hold your Nose”• taste bud - sense organ

that detects the flavor of a substance

Touch Related Senses

• Touch – Mechanoreceptors

• Temperature – Thermoreceptors

• Pain – Pain Receptors

Questions

1. Name the five types of sensory receptors and list where they are found in the body.

2. Identify the parts of the eye and the function of each part.

3. What parts of the ear are responsible for hearing? For balance?

4. Explain why you can’t “taste” food when you have a bad cold.

5. Why do you feel dizzy after spinning around? How can a dancer or ice skater do lengthy spins?