Chapter 22:The Nervous

and Endocrine Systems

22.1 The Nervous System

• Functions of the nervous system:– Body’s control system.– Processes and stores information.– Communicates information throughout the body.– Controls the body’s response to stimulus.– Allows for feelings, emotions, dreams…

Organization of the Nervous System:

• Organs:– Brain– Spinal cord– Sensory organs• Eyes• Ears• Nose• Tongue• Skin

Neuron: nerve cell

• Parts of a neuron:– Cell body– Dendrites: Short branches off the neuron. Takes

in information from the environment or other cells.

– Axon: Long branch. Transmits information to other cells

Myelin sheath:

• “Pillows” that wrap around the axon, insulating it and making nerve signals travel faster.

Synapse: Gap between neurons.

Three classes of neurons:

• Sensory neurons: Carry information from the body or environment to the brain and spinal cord.

• Motor neurons: Carry information from the brain and spinal cord to the muscles and glands.

• Interneurons: Relay information between sensory and motor neurons.

Sending signals

• Nerve impulses travel in one direction only.

Path of a nerve impulse:1) Stimulus triggers electrical impulse in

dendrite of sensory organ.

2) Electrical impulse travels through the cell body and down the axon, “leaping” between the gaps in the myelin.

3) Electrical impulse causes end of axon to release neurotransmitters (chemical messengers) into the synapse.

4) Neurotransmitters move across synapse.

5) Neurotransmitters bind to dendrites of second neuron.

6) Binding triggers an electrical impulse in the second neuron.

Two divisions of the nervous system:

• Central nervous system (CNS):– The brain and spinal cord– Communication, memory, thought.

• Peripheral nervous system (PNS):– Connects brain and spinal cord to the rest of the

body.– Divided into:• Somatic nervous system–Voluntary actions

• Autonomic nervous system– Involuntary actions

22.2 Brain and Spinal Cord

• Brain: Allows for reasoning, intelligence, analysis of situations, communication, creation, feeling, and learning.

The brain is divided into three major parts:

• Cerebrum• Cerebellum• Brain stem

Cerebrum:

• Largest part of the brain.• Memory storage.• Thinking.• Processes information from sensory organs.• Communication and learning.

Cerebellum

• Coordination of voluntary actions.• Regulates skeletal muscle and maintains

muscle tone.• Balance.

Cerebellum

Brain stem

• Connects brain to spinal cord.• Three parts:– Midbrain– Pons– Medulla oblongata: Controls involuntary actions.

Brain stem

• The skull and the cerebrospinal fluid help protect the brain from injury.

Spinal Cord

• Connects brain to the rest of the body.

• Contains bundles of neurons held together by connective tissue, plus blood vessels to supply nutrients and oxygen.

Cross section of spinal cord

Vertebrae

• (singular: vertebra)• 33 irregularly-shaped

bones that protect the spinal cord.

• Fluid in the spine also helps protect the spinal cord.

Paralysis:

• Damage to the spinal cord can cause paralysis, because the brain cannot communicate with the body beyond the damaged area.

Reflexes:

• Automatic, involuntary response to a stimulus.

Reflex arc:

1) Stimulus triggers impulse in sensory neuron to interneuron in the spinal cord.

2) Interneuron sends impulse to motor neuron.3) Motor neuron causes muscles to move.

*Controlled in the spinal cord, not the brain.

22.3 The Senses

• Sensory receptors: Special cells in sensory organs that can detect light, mechanical, chemical, or thermal energy.

• Sensory receptors change these energies into electrical impulses that are sent to the brain to be processed.

Sight:

• Light energy is detected and turned into images.

• Two kinds of photoreceptors:– Cones: Day vision. Sensitive to red, blue, and

green light.– Rods: Night vision. Not sensitive to colors.

• Retina: Thin layer of tissue on the back of the eye that contains rods and cones.

Rods and cones

Hearing:

• Detection of sound waves (vibration).• Cilia: tiny hairs on receptor cells that change

the vibrations into an electrical impulse.• Cochlea: Contains the receptor cells.

Balance:

• Sensed in the ears.• Semicircular canals contain tiny hair cells, jelly-

like fluid, and ear stones (otoliths).• Ear stones move around and bend hair cells when

the body moves.• Hair cells send impulse to the brain.• Brain interprets the impulse, and if the body is

losing balance, contracts or relaxes muscles to restore balance.

Smell:

• Chemical enters the nose and binds with sensory receptors.

• This triggers an electrical impulse, which the brain interprets as smell.

Taste:

• Sensory receptors on the tongue (especially in the taste buds) detect different chemicals.– Sweet– Salty– Bitter– Sour– Umami (meaty, savory)

Touch:

• Different receptors detect pressure, temperature, and pain.

• Sensory receptors in the skin detect chemicals, heat, and mechanical energy.

22.4 The Endocrine System

• Messenger system.• Works with the nervous system to control the

body.• Sends mass messages throughout the body.

Hormones:

• Chemicals released into the bloodstream and generally regulate slow body processes:– Cell growth and development– Metabolism– Sexual function– Reproduction– Response to danger or stress

Gland

• Organ the produces and releases a substance.• Endocrine glands: Release hormones into the

bloodstream.

1) Gland is triggered.2) Gland releases hormone.3) Hormone attaches to receptor on target cell.4) Cell carries out a specific task.

Major glands in the body:

Hypothalamus:

• In the brain.• Connects nervous and endocrine systems.• Controls the pituitary gland.

Pituitary gland:

• Connected to the hypothalamus.• Secretes 9 different hormones.– Examples:• Growth hormone: Protein production, cell growth and

regulation.• Follicle-stimulating hormone: Sperm production or

egg cell release.• Prolactin: Milk production.• Thyroid-stimulating hormone: Triggers thyroid to

produce and release thyroxine.

Pineal gland:

• Tiny gland deep in the brain (size of a bean).• Produces melatonin: controls body rhythms,

such as the sleep-wake cycle.

Thyroid gland:

• Located at the base of the neck.• Produces thyroxine: controls cell break down

of chemicals and energy release.

Parathyroid glands:

• Four glands located on the back of the thyroid.• Regulates calcium.

Pancreas:

• Found in the abdomen. Also part of the digestive system.

• Produces insulin and glucagon, which regulate the sugar in the blood.

Thymus gland:

• Located in the upper chest.• Helps the body fight disease.– Helps form T-cells in the blood that fight infection.

Adrenal glands:

• Two glands, one located above each kidney.• Produce adrenaline, which cause the “rush”

you feel when nervous, excited, or coping with stress.

• Also produces 24 other hormones.

Reproductive glands:

• Control secondary sexual characteristics.• Male: Testes– Produce testosterone: Sperm production.

• Female: Ovaries– Produce estrogen and progesterone • Development of egg cells, control the

menstrual cycle

Controlling the endocrine system:

• Negative feedback system: Hormones or products of their effects feed back to stop original signal. Maintains homeostasis.

• Like a thermostat in a house.

Example: Controlling blood sugar.

1) Hypothalamus detects low blood sugar.2) Hypothalamus stimulates pituitary gland to

release growth hormone.3) Growth hormone travels through bloodstream to

liver.4) Liver cells are triggered to release glucose.5) Increased glucose in the blood is detected by the

hypothalamus, which triggers the pituitary gland to stop releasing growth hormone.