NERVOUS SYSTEM

CHAPTER 7

ORGANS AND DIVISIONS OF THE NERVOUS SYSTEM

Central Nervous System (CNS): Organs: Brain and spinal cord

Peripheral Nervous System (PNS):

Organs: All Nerves Autonomic Nervous System

(ANS): Organs: Motor neurons

CELLS OF THE NERVOUS SYSTEM

2 Types of cells found in the nervous system:1. NEURONS: nerve cells

Parts: cell body, dendrites and axon 3 types: sensory, motor and interneurons

2. GLIA: specialized connective tissue

Glia means glue. Holds the functioning neurons together to protect them.

NEURONSMotor neurons transmit impulses away

from the spinal cord and brain to muscle and glandular epithelial tissue.Also called efferent neurons.

Interneurons conduct impulses form sensory neurons to motor neurons. Also called central or connecting

neurons.Sensory neurons transmit impulses to the

spinal cord and brain from all parts of the bodyAlso called afferent neurons.

STRUCTURE OF NEURON

AXON: is surrounded by segmented wrapping called myelin.

- Myelin is a white, fatty substance by Schwann cells that wrap around some axons outside the CNS.

- These fibers are called myelinated fibers

GLIAGlia or neuroglia: They are special types of

supporting cells - Function: is to hold neurons together and

protect them. - Vary in size and shape: * Large cells look like stars: astrocytes * Smaller cells are Microglia * Oligodendrocytes: helps hold fibers together,

produce the fatty myelin sheath that envelops nerve fibers in the brain and spinal cord

NERVESNerve is a group of peripheral nerve fibers (axons) bundled together like the strands of a cable.

Myelin is found on nerves and is white.Nerves are called white matter of the PNS and also the CNS.

Unmyelinated axons and dendrites are called gray matter. (because of gray color)

WHITE AND GRAY MATTER

REFLEX ARCNerve impulses are conducted from

receptors to effectors over neuron pathways known as Reflex arcs.

This results in a reflex. (a contracted muscle or secretion from a gland)

2 types of reflex arcs: - two-neuron arcs: spinal cord and motor

neuron - three-neuron arcs: sensory neurons,

interneurons and motor neurons

RECEPTORS

Impulse conduction normally starts in the receptors.

Found at the beginning of the dendrites of sensory neurons

Located in the tendons, skin or mucous membranes.

MS (MULTIPLE Sclerosis) DAMAGE TO MYELIN

Hard lesions replace the destroyed Myelin

As the myelin is lost, nerve conduction is impaired

Causing weakness, loss in coordination, visual impairment, speech disturbances

No known cure, occurs most in women ages 20-40.

SynapseA microscopic space from the axon ending

of one neuron to the dendrite of another neuron.

The nerve impulse stops, chemicals are sent across the gap, the impulse continues alone the dendrites.

Neurotransmitters

Chemicals by which neurons communicate.Specific neurotransmitters are released in

specific pathways.Some help us sleep, make us happy, make us

more energetic, some inhibit pain

CNS (CENTRAL NERVOUS SYSTEM)Spinal Cord and Brain

4 Divisions of the brain:Brainstem

Medulla Oblongata Pons Midbrain

CerebellumDiencephalon

Hypothalamus Thalamus

Cerebrum

                     

.

BRAINSTEM

* Medulla Oblongata: largest part of the brainstem.

- extension of the spinal cord - Location: lies below the pons and the midbrain

- Functions: reflex center (control heartbeat, respiration and blood vessel diameter)

DIENCEPHALONHypothalamus: - Structure: consists mainly of the posterior

pituitary gland, pituitary stalk and gray matter. - Function: Acts as the major center for controlling the ANS. (function of internal organs) - Controls hormone secretion - Centers for controlling appetite,

wakefullness and pleasure

DIENCEPHALONTHALAMUS: - Structure: dumbbell shaped mass of gray matter in each cerebral hemisphere

- Function: relays sensory impulses to cerebral cortex

- Produces emotions of pleasantness and unpleasantness associated with sensation

CEREBELLUMSecond largest part of the brainStructure: Lies under the occipital lobe of the cerebrum

- composed of gray matter in outer layer and white matter in the inner layer

•Function: helps control muscle contractions to produce coordinated movements.

• Also, maintain balance, move smoothly and sustain normal posture

CEREBRUMLargest part of the brainStructure: Structures: Series of ridges and

grooves -Ridges are called convolutions or Gyri -Grooves are called Sulci (deepest sulci

are called fissures) -Divided into two halves- Hemispheres -Hemispheres connected by the Corpus

callosum

CEREBRUM

HEMISPHERES: Divided into lobesLobes are named after bones that lie over

them.

CEREBRUM

Function: mental process of all types Sensations Consciousness Thinking Memory Willed Movements

Page 177, second paragraph

Cerebrum

Specific areas have specific functions Temporal lobe’s auditory areas interpret incoming

nervous signals as specific sounds Visual area of the occipital lobe helps you understand

and identify images

If a specific part of the brain is damaged, for example the Primary Taste Area, you would not be able to taste things.

__________CEREBRUM

SPINAL CORD

Structure: Outer part composed of white matter

- Interior part composed of gray matter

Function: center of all spinal cord reflexes

- sensory tracts conduct impulses to the brain.

- motor tracts conducts impulses from the brain

Cutting the Cord

Completely severing the spinal cord produces a loss of sensation for all areas below the cut, called anesthesia.

It also produces a loss of the ability to make voluntary movements, called paralysis.

Peripheral Nervous System (PNS)

Cranial and Spinal Nerves

Connect the Brain and Spinal Cord to Peripheral structures like skin and muscles.

Cranial Nerves: - 12 pairs of cranial nerves - Functions vary - see diagram on page 187 and chart on

188 for function and location (you will need to know number, name, function)

SPINAL NERVES

Structure: contain dendrites of sensory neurons and axons of motor neurons

Function: conduct impulses necessary for sensations and voluntary movements

Dermatones: skin areas that are supplied by a single spinal nerve

Autonomic Nervous System (ANS)

Structure: Consists of motor neurons that conduct impulses from spinal cord or brainstem to:

1. Cardiac Muscle tissue2. Smooth muscle tissue3. Glandular epithelial tissueFunction: regulate involuntary functions - heartbeat, contractions of the stomach

and intestines and secretions by glands

2 Divisions of ANS1. Sympathetic nervous system: -Structure: dendrites and cell bodies located in gray matter of the thoracic and upper lumbar segments of the spinal cord

-Function: serves as the emergency or stress system during strenuous exercise and strong emotions (hate, anger, fear or anxiety)

- controls the “ fight or flight” response

2 Divisions of ANS2. Parasympathetic Nervous System:

Structure: Neurons are located in gray matter of the brainstem and sacral segments of the spinal cord.

Function: dominates control of many visceral effectors under normal everyday conditions (bladder, intestines, lung)

Autonomic Neurotransmitters

Each division of the ANS signals its effectors with a different neurotransmitter.

This is how an organ can tell which division is stimulating it. Ex. The heart responds to acetylcholine from the

parasympathetic division by slowing down. If norepinephrine, from the sympathetic division, is present, the heart speeds up.

ANS as a Whole

Regulates the body’s autonomic functions in ways that maintain HOMEOSTASIS

Many visceral effectors are effected by both sympathetic and parasympathetic divisions.