Nervous System

Chapter 7

Three Basic Functions:

Sensory Input Uses millions of sensory receptors to monitor

changes occurring both inside and outside the body…these changes are called stimuli and the gathered information is called sensory input

Integration Processes and interprets the sensory input and

makes decisions about what should be done at each moment…a process called integration

Motor Output Effects a response by activating muscles or glandes

(effectors) through motor output

Organization of Nervous System:

Structural Structures

Functional Activities

Structural Organization: Includes all nervous

system organs 2 subdivisions:

Central Nervous System (CNS)

Peripheral Nervous System (PNS)

Central Nervous System (CNS): Consists of the brain and spinal cord

Peripheral Nervous System (PNS): Consists mainly of nerves that

extend from the brain and spinal cord

Spinal nerves: carry impulses to and from the spinal cord (31 pairs)

Cranial nerves: carry impulses to and from the brain (12 pairs)

These are the communication lines…linking all parts of the body by carrying impulses from sensory receptors to the CNS and from the CNS to appropriate glands/muscles

Cranial Nerves: Listed on pages 250-251 and picture on

page 252 12 pairs Serve the head and neck Most are mixed nerves (send impulses both

ways…to and from CNS) Only 1 pair-the vagus nerve-extends to the

thoracic and abdominal cavities

Giraffe Vagus Nerve Dissection

Spinal Nerves: Listed on page 255 31 pairs of human spinal nerves are formed by the combination

of the ventral and dorsal roots of the spinal cord Each spinal nerve is only about ½ inch long and almost

immediately after being formed divides into dorsal and ventral “rami”

The rami contain both motor and sensory fibers…thus damage to a spinal nerve or its “rami” results in loss of sensation and paralysis of area of body served

Smaller dorsal rami serve the skin and muscles of the posterior body trunk

Ventral rami of spinal nerves T1-T12 supply the muscles between the ribs and skin and muscles of the anterior and lateral trunk

The ventral rami of all other spinal nerves form the complex networks or nerves called plexuses, which serves the motor and sensory needs of the limbs.

Functional Classification: Concerns only PNS structures Divides them into 2 principal

subdivisions Sensory (or afferent) division Motor (or efferent) division

Functional Subdivisions:Sensory (Afferent):

Consists of nerve fibers that convey impulses to the CNS from sensory receptors

Motor (Efferent):

Carry impulses from the CNS to effector organs, muscles, and glands

These impulses activate muscles and glands…they “effect” a motor response

Has 2 subdivisions…

2 subdivisions of Motor division:

Somatic Nervous System Allows us to consciously,

or voluntarily, control our skeletal muscles

Often referred to as “voluntary nervous system”

Autonomic Nervous System Regulates events that

are automatic or involuntary such as the activity of smooth and cardiac muscles and glands

Referred to as “involuntary nervous system”

Has 2 parts: Sympathetic &

Parasympathetic: Bring about opposite

effects…one stimulates while one inhibits

Nervous Tissue: Structure & Function Nervous tissue is made up of just 2

types of cells…supporting cells and neurons

You should remember neurons from the tissue chapter….probably easiest slide to ID!

“Neuroglia” (supporting cells) Neuroglia literally

means “nerve glue” 6 types:

1. Astrocytes2. Microglia3. Ependymal cells4. Oligodendrocytes5. Schwann cells6. Satellite cells

Neurons (nerve cells) Highly specialized to

transmit messages (nerve impulses) from one part of the body to another

Neurons can differ structurally, but have many common features like the cell body (that includes the nucleus and is metabolic center of cell)and one or more processes (or fibers)…

Processes: Vary in length from microscopic to 3

or 4 feet…longest ones in humans reach from lumbar region of the spine to the great toe!

Processes that convey incoming messages toward the cell body are dendrites (dendr=tree)

Processes that generate nerve impulses and conduct them away from the cell body are axons (a&a)

Neurons may have hundreds of the branching dendrites, depending of the neuron types, but each neuron has only one axon…all axons branch profusely at their terminal end…forming hundreds to thousands of axon terminals!

Axons continued…. Axon terminals contain hundreds of tiny vesicles, or

membranous sacs that contain chemicals called neurotransmitters

As said earlier, axons transmit nerve impulses away from the cell body…when these impulses reach the axon terminals, they stimulate the release of neurotransmitters into extracellular space

Each axon terminal is separated from the next neuron y a tiny gap called the synapse

Although they are close, neurons never actually touch other neurons!

More Neuron Anatomy: Myelin:

Whitish, fatty material that covers long nerve fibers Protects and insulates the fibers and increases the

transmission rate of nerve impulses Schwann cells:

Specialized supporting cells that wrap themselves tightly around the axon jelly-roll fashion

When the wrapping process is done, a tight coil of wrapped membranes, the myelin sheath, encloses the axon

Nodes of Ranvier: Since the myelin sheath is formed by many

individual Schwann cells, it has gaps or indentations, called nodes of Ranvier at regular internals

Nerve Impulses: 2 major functions:

1. irritability The ability to respond to a stimulus and convert it into a

nerve impulse 2. conductivity

The ability to transmit the impulse to other neurons, muscles or glands.

*Figure 7.9, pg.232 describes how nerve impulses work in a step by step manner. Here are some videos:

Nerve Impulse Animation Animation: Transmission Across a Synapse Nerve impulse Animation - YouTube

Reflexes Rapid, predictable, and involuntary

responses to stimuli Like one way streets-once it begins,

always goes in the same direction Occur over neural pathways called

reflex arcs Involve both CNS and PNS

Types of Reflexes:Somatic

All reflexes that stimulate skeletal system Ex: When you pull your hand away from hot

object

Autonomic Regulate activity of smooth muscles, heart, and

glands Regulate digestion, elimination, blood pressure,

and sweating Ex: Changes in size of pupil

Reflex Arcs 5 Elements:1. Receptor2. Effector organ3. Sensory neuron4. Integration center5. Motor neuron

Brain Anatomy:4 major regions:

1. Cerebral hemispheres2. Diencephalon3. Brain stem4. Cerebellum

Cerebral Hemispheres “cerebrum”

Most superior part of brain and together are larger than the other 3 brain regions combined!

Controls sensory and motor functions and higher mental function like memory and reasoning and higher mental function (like memory and reasoning).

Diencephalon (interbrain):

Sits atop the brain stem and is enclosed by the cerebral hemispheres

Includes: Thalamus,

hypothalamus, and epithalamus

Brain Stem: About the size of a thumb

in diameter and about 3 inches long

Includes:1. Midbrain: reflex centers

involved with vision and hearing

2. Pons: nuclei involved in the control of breathing

3. Medulla oblongata: contains centers that control heart rate, blood pressure, breathing, swallowing, vomiting, and others.

Cerebellum: Large, cauliflower-like

structure that projects dorsally

Has 2 hemispheres (like cerebrum)

Provides the precise timing for skeletal muscle activity and controls our balance and equilibrium…Because of its activity, body movements are smooth and coordinated

Meninges (Protection of CNS) 3 connective tissue membranes that

cover and protect the CNS Dura mater

Outermost layer “tough or hard mother” Arachnoid mater

“spider” some think it looks like web Pia mater

Innermost layer “gentle mother”-clings tightly to surface of brain and spinal chord

Spinal Cord: About 17in, glistening white

continuation of brain stem Provides a 2-way conduction

pathway to and from the brain Major reflex center Is enclosed within the vertebral

column Extends from the foramen

magnum of the skull to the first or second lumbar vertebra, where it ends just below the ribs

Also protected by meninges In humans, 31 pairs of spinal

nerves arise from the cord and exit from the vertebral column to serve the body area close by!