The Nervous System

The Nervous System Page 897

• The nervous system is an intricate communication network that coordinates and controls functions throughout the body, responding to internal and external stimuli.

• Tiny jolts of energy called impulses travel along this network at tremendous speeds. (243 mph recorded between cells.)

• Messages travel over many routes carrying information about both the external environment and the internal environment.

Location of receptor Stimulus

eye light

ear sound

skin touch, temperature

Chemical reaction on Produces

tongue tastes

nose smell

All vertebrates have a nervous system (NS) made up of a:- central nervous system (CNS) and a - peripheral nervous system (PNS).

Central nervous system (CNS)1. CNS:

- consists of nerves of the brain and the spinal cord.

- coordination center for ingoing and outgoing information.

- covered by three protective membranes. These membranes are called the meninges. (With meningitis, these membranes swell.)

- Between the inner two layers is a clear fluid called cerebrospinal fluid which:- absorbs shock- transfers nutrients to the brain- removes wastes from the brain

CNS is composed of:a. Brain:

- control center- covered in grey matter (cerebral

cortex) which has many deep folds in it called fissures. (These increase the surface area.)

- also protected by skull

The Brain

• There are over 100 billion nerve cells in the brain.

b. Spinal cord: - carries sensory messages from

receptors to the brain and motor messages from brain to muscles and glands

- also controls many reflex responses - white matter on the outside; grey on

the inside - protected by the vertebrae

Developing fetus at 10.5 mm

Parts of the brain• Cerebrum (p. 902):

- largest and most highly developed- intelligence, thinking,creativity, reasoning, memory- voluntary activities of the body

Each hemisphere has 4 lobes:

• Frontal lobe: controls speech, motor activities (muscles), learning, judgement, creativity, organization

• Parietal lobe: perception, recognition, touch, temperature, memory

• Occipital lobe: vision, interpretation

• Temporal lobe: senses (smell, taste, hearing), some memory

THE CEREBRUM IS ALSO DIVIDED INTO TWO LAYERS:– Outer, cerebral cortex, gray matter which consists

of tightly packed nerve cell bodies.

– Inner, white matter, consists of bundles of axons with myelin sheaths.

– Connects the cerebral cortex and the brain stem.

The cerebrum is divided into two hemispheres (right and left, each controlling and receiving information from the opposite side of the body)

• Corpus callosum: - Connects the two hemispheres

• Brain stem:- Consists of the medulla oblongata, pons Varolii, and midbrain, that connect the spinal cord to the cerebrum.

• Pons:– Bridge between the

cerebrum and the cerebellum

• Cerebellum:– Balance, muscle tone

• Medulla Oblongata– Involuntary muscles– Internal organs– Heart rate,

respiration

• Thalamus:-Part of the brain that lies just below the cerebrum- Acts as a relay station by receiving impulses from most of the sensory neurons and directing these impulses to the part of the brain where each will be interpreted. -Screens out less significant stimuli (prevents sensory overload)

• Hypothalamus:– Coordinates NS and endocrine system

The Spinal Cord

• Carries thousands of messages at once• Main communication link between brain and

the rest of the body• Thirty-one pairs of spinal nerves branch out

from the spinal cord• Certain kinds of information, including some

reflexes, are processed directly in the spinal cord.

Peripheral Nervous System

• Consists of all the nerves and associated cells which are not part of the central nervous system.

• Is divided into the:– Sensory division: transmits impulses from sense

organs to the CNS– Motor division: transmits impulses from the CNS

to the muscles or glands.

Somatic and Autonomic Nervous Systems

The motor division is further divided into the somatic nervous system and the autonomic nervous system.

• The somatic nervous system regulates activities that are under conscious control (ie. the movement of the skeletal muscles)

(Some somatic nerves are also involved with reflexes and can act without conscious control.)

Autonomic Nervous System

• The autonomic nervous system regulates body activities that are automatic or involuntary.

(ex. When a person is running, the autonomic nervous system speeds up heart rate and blood flow, stimulates sweat and adrenal glands, and slows down the contractions of the smooth muscles of the digestive system.)

The autonomic nervous system is further subdivided into two parts:

–sympathetic nervous system

–parasympathetic nervous system

which have opposite effects on the same organ system. (Think gas and brake when driving a car.) (Sympathetic nervous system speeds up heart rate; parasympathetic slows it down.)

• http://www.youtube.com/watch?v=i-NgGKSNiNw

Neurons• The messages carried by the nervous system are

called impulses.• Neurons (the cells that carry these impulses)

are classified into three types, depending on the direction the nerve impulse travels along them:– Sensory neurons - sense organs (receptors) carry

impulse to spinal cord and brain– Motor neurons - carry impulse from brain and

spinal cord to muscles and glands– Interneurons - connect sensory and motor neurons

and carry impulses between the two of them

The Nervous System - page 897

Draw and label the diagram of neuron from the board.

• All organisms respond to changes in their environment. A reaction to stimulus is called a response.

• A stimulus is a change in the environment that induces a response. These stimuli are received through specialized receptors.

Receptors are classified in many different ways. One way is by the type of stimulus detected.

• Mechanoreceptors respond to physical force such as pressure (touch or blood pressure) and stretch.

• Photoreceptors respond to light.• Thermoreceptors respond to temperature

changes.• Chemoreceptors respond to dissolved chemicals

during sensations of taste and smell and to changes in internal body chemistry such as variations of O 2, CO 2, or H + in the blood.

• Nociceptors respond to a variety of stimuli associated with tissue damage. The brain interprets the pain.

• The parts of the body that respond to messages coming from the brain and spinal column (muscles, glands) are called effectors.