Chapter 25Nervous and Endocrine Systems

Section 1: Objectives• Describe the relationship

between the central nervous system and the peripheral nervous system.

• Compare the somatic nervous system with the autonomic nervous system.

• List one function of each part of the brain.

The Nervous System• The central nervous system (CNS) is

your brain and spinal cord. • The CNS processes and responds to all

messages coming from the peripheral nervous system.

• The peripheral nervous system (PNS) is all of the parts of the nervous system except for the brain and the spinal cord.

• The PNS connects all parts of the body to the CNS.

The Nervous System• A neuron is a nerve cell that is specialized

to transfer messages in the form of fast-moving electrical energy. • The three parts of a neuron are the cell body,

the dendrites, and the axon.

• Sensory neurons gather information about what is happening in and around your body.

• Neurons that send impulses from the brain and spinal cord to other systems are called motor neurons.

The Nervous System

The Nervous System• The central nervous system is

connected to the rest of your body by nerves.

• A nerve is a collection of axons bundled together with blood vessels and connective tissue.

• Most nerves have axons of both sensory neurons and motor neurons.

The Nervous System• Somatic Nervous System Most of

the neurons that are part of the somatic nervous system are under your conscious control.

• Autonomic Nervous System Autonomic nerves do not need your conscious control. The autonomic nervous system controls body functions that you don’t think about, such as digestion and heart rate.

The Nervous System• The brain is the largest organ of

the nervous system.

• The brain is the main control center of the nervous system. Its controls both voluntary and involuntary processes.

• The brain is comprised of the cerebrum, the cerebellum, and the medulla.

The Nervous SystemThe cerebrum is where you think

and where most memories are stored. It controls voluntary movements and the senses.

The Nervous System• The cerebellum processes

sensory information from your body, such as from skeletal muscles and nerves.

• The medulla controls involuntary processes such as blood pressure, body temperature, heart rate, and involuntary breathing.

The Nervous System

The Nervous SystemThe spinal cord is made of

neurons and bundles of axons that pass impulses to and from the brain.

The spinal cord is surrounded by protective bones called vertebrae.

A spinal cord injury may block all information to and from the brain.

Each year, thousands of people are paralyzed by spinal cord injuries.

The Nervous System

Section 2: Objectives• List four sensations that are

detected by receptors in the skin.

• Describe how a feedback mechanism works.

• Describe how light relates to sight.

• Describe how the senses of hearing, taste, and smell work.

Sensory OrgansTouch is what you feel when

sensory receptors in the skin are stimulated. Each kind of receptor responds mainly to one kind of stimulus.

Sensory Organs• Pain receptors in your skin

activate immediate, involuntary actions called reflexes.

• Reflexes help you move quickly out of the way of danger.

• Feedback Mechanisms are cycles of events in which information from one step controls or affects a previous step.

Sensory OrgansYour pupil is an opening that lets light

enter the eye. The pupil is surrounded by the iris.

The iris is a ring of muscle that controls the amount of light that enters the eye.

Light travels in straight lines until it passes through the cornea and the lens. Muscles in the eye change the shape of the lens in order to focus light onto the retina.

Sensory OrgansEach ear has an outer, middle,

and inner portion. Sound waves reaching the outer ear are funneled into the middle ear and then into the inner ear before being interpreted by the brain.

Sensory Organs• Your tongue is covered with tiny

bumps called papillae. • Most papillae contain taste buds.

• Taste buds contain cluster of taste cells, or receptors for taste.

• Taste buds respond to sweetness, sourness, saltiness, and bitterness.

Sensory OrgansReceptors for smell are located on olfactory cells in the upper part of your nasal cavity. An olfactorycell is a nerve cell that responds to chemical molecules in the air.

Ch. 25 Sec. 1-2 Pop Quiz1) What is the difference between

the CNS and PNS?2) What is the function of sensory

neurons?3) What connects the CNS to the rest

of your body?4) What is the largest nervous

system organ?5) What are the functions of the

medulla, cerebrum, and cerebellum?

Section 3: Objectives• Explain why the endocrine system is

important to the body.

• Identify five glands of the endocrine system, and describe what their hormones do.

• Describe how feedback mechanisms stop and start hormone release.

• Name two hormone imbalances.

The Endocrine System• The endocrine system is a collection of

glands and groups of cells that secrete hormones.

• A gland is a group of cells that make special chemical messengers, called hormones, for your body.

• A hormone is a chemical messenger made in one cell or tissue that causes a change in another cell or tissue in another part of the body.

The Endocrine System• Your thyroid gland controls the

secretion of growth hormones for normal body growth.

• Your thymus gland produces killer T cells that help destroy or neutralize cells or substances that invade your body.

• Metabolism is the sum of all the chemical processes that take place in an organism.

The Endocrine SystemOccasionally, an endocrine gland

makes too much or not enough of a hormone.

For example, sometimes a child’s pituitary gland doesn’t make enough growth hormone. As a result, the child’s growth is stunted.

Endocrine glands control feedback mechanisms in the body.

Ch. 25 Sec. 2-3 Recap1) Why are reflexes important to

organisms?2) What is the iris and what is its

function?3) What is an olfactory cell?4)What is metabolism?5) What controls feedback

mechanisms in the body?

The Endocrine System