The Nervous System Dr. Smith Chapter 7 Pgs. 136-171.

The Nervous System

Dr. SmithChapter 7Pgs. 136-171

Systems for Communication and Control – Nervous System

Homeostasis the the balanced and controlled internal environment of the body that is basic to life itself – only possible if our physiological control and integration systems function properly.

Transmits info very rapidly by nerve impulses conducted from one body area to another.

Provide control that is rapid ands brief.

Systems for Communication and Control – Endocrine System

Transmits info more slowly by chemical secreted by ductless glands to other parts of the body.

Also provides longer lasting control through hormones.

Organs and Divisions of the Nervous System

Nervous System: Brain Spinal Cord Specialized Sense Organs

• Ex. Eyes,Ears, Microscopic sense organs found in skin

Three Divisions of the Nervous System: Central Nervous System (CNS) Peripheral Nervous System (PNS) Autonomic Nervous System (ANS)

Cells of the Nervous System - Neurons 3 Parts:

Cell body (main part) Dendrites – one or more branching projections Axon – one elongated projection

Axon – processes that transmit impulses away from the neuron cell bodies or dendrites.

Dendrites – processes or projections that transmit impulses to the neuron cell bodies or axons.

Cell Body – function is to receive and send messages

Neuron Classification Sensory Neurons/Afferent – transmits impulses to

the spinal cord and brain from all parts of the body.

Motor Neurons/Efferent – Transmits impulses in the opposite direction – away from the brain and spinal cord. Do not conduct impulses to all parts of the body, but only to two kind of tissue – muscle and glandular epithelial

Interneurons/Central or Connecting Neurons – Conduct impulses from sensory neurons to motor neurons

Neuroglia

Neuroglia (glia) are special types of tissue cells. Name is derived from Greek word glia meaning

“glue” Function – Holds functioning neurons together

and protects them. One of the most common types of brain tumor –

called glioma – develops from glia. Glia vary in shape and size – some are relatively

large – thread like extension make them look like stars.

Astrocytes

Means “star cells” Attached to neurons and small blood vessels

holding them close together. Form a 2 layer structure called a blood-brain

barrier (BBB). Separates blood tissue from harmful chemicals in

blood.

Microglias

Smaller than astrocytes. Usually stationary, but in inflamed or

degenerating brain tissues, they enlarge, move about, act as microbe-eaters.

Phagocytosis – surround microbes, drown into cytoplasm, and digests them.

Oligodendrocytes

Help to hold nerve fibers together and produce fatty myelin sheath that envelops nerve fibers located in the brain and spinal cord.

Nerves

A nerve is a group of peripheral nerve fibers bundled together like a cable.

Nerve fibers have myelin sheath, myelin is white Nerves are called white matter of PNS

Cross –section of myelin sheath

Reflex Arc

Nerve impulses or action potential travel routes made up of neurons because they are the cells that conduct impulses.

Paths are called neuron pathways. Reflex arc is specialized type of neuron pathway

– important to function of the nervous system. Receptors (impulse conduction starts)

beginnings of dendrites of sensory neurons. Causes muscle contraction of gland secretion

Two Neuron Type

Synapse – a microscopic space separates the axon ending of 1 neuron from dendrites of another neuron.

Has a sensory neuron and motor neuron with one synapse between them.

Most common two neuron effect is the “knee jerk”.

Nerve impulse is generated by stimulation of stretch receptors travels along length of sensory neuron’s dendrite to its cell body.

Three neuron reflex arc Sensory ,interneuron motor example: withdrawal reflex in contact with CNS, feel pain -

sometimes after

Nerve Impulses Self-propagating wave of electrical disturbance that travels

along the surface of a neuron’s plasma membrane. Initiated by a stimulus – a change in the neuron’s

environment, pressure, temp. and chemical changes are common stimuli.

Saltatory conduction – traveling impulse encounters a section of membrane covered with insulating myelin, this type of impulse is much faster in nonmyelinated sections

Synapse – place where impulses are transmitted from one neuron called presynaptic neuron to another neuron called the postsynaptic neuron.

Connects neurons and passes stimuli.

Neurotransmitters

Chemicals by which neurons communicate. Presynaptic neurons release neurotransmitters

that assist, stimulate or inhibit postsynaptic neurons.

Specific neurotransmitters are localized in discrete groups of neurons and released in specific pathways.

Acetylocholine, Serotonin, Dopamine

Acetylcholine – released at some synapses in spinal cord and neuromuscular junctions.

Serotonin and Dopamine belong to group of compounds called catecholamines – play a role in sleep, motor function, mood and pleasure recognition.

Morphine-Like Neurotransmitters

Endorphine and Enkephalins are released at various spinal cord and brain synapses in the pain conduction pathway.

Neurotranmitters inhibit conduction of pain impulses.

They are not pain killers.

Central Nervous System (CNS)

Consists of the brain and spinal cord which occupy a midline or central location in the body.

Brain - Stem

Stem – lowest part:medulla oblongata – immed. above pons above that midbrain origin of cranial nerves.

3 parts function as two way conduction paths: Sensory fibers conduct impulses up from the cord to

other parts of the brain. Motor fibers conduct impulses down from brain to cord. Cardiac, respiratory, and vasometer collectively called

the vital centers are located in the medulla. Impulses from these centers control heartbeat, respiration, and blood vessel diameter which is important in controlling blood pressure.

BRAIN STEM Medulla - - lowest part, enlarged

continuation of spinal cord, one inch in length, mylinated tracts, connects cranial nerve origin of craial nerves IX X XI XII

Pons connected to cerebellum, medulla and midbrain, nuclei of cranial nerves V VI VII VIII

Midbrain - Above pons - cranial nerves III IV originate

Diencephalon – between midbrain and cerebrum

HYPOTHALAMUS Located below thalamus –

controls all internal organs Heartbeat, constrictions of

blood vessels, contractions of blood vessels, contractions of stomach and intestines.

Maintains body temp. Involved in functions such as regulation of H2O balance, sleep cycles, and many emotions involved in pleasure, fear, anger, sexual arousal and pain.

THALAMUS Composed of dendrites

and cell bodies of neurons that have axons extending up toward the sensory areas of the cerebrum.

Functions: Helps produce sensations Emotions associated with

sensations Arousal or alerting

mechanism

Cerebrum

Cerebral cortex and thin layer of gray matter made up of neuron dendrites and cell bodies composes surface of the cerebrum.

Largest and uppermost part of brain – many ridges (gyris) and groves (sulci).

Two hemispheres (longitudinal fissure) seperates the two

4 major regions, temporal, parietal, frontal, occipital Functions:

Consciousness, thinking, memory, sensations, emotions, willed movements, smell (olfactory bulb.

Cerebellum

2nd largest brain part lies under occipital lobe of cerebrum.

Controls balance,movement, posture, and coordination.

Spinal Cord

Approx. 17-18 inches long at average ends at 2nd lumbar.

Lies inside spinal column in spinal cavity and extends from occipital bone down to the bottom of the 1st lumbar vertebra.

Core consists of gray matter and is composed of mainly dendrites and cell bodies of neurons.

White matter from outer portion of spinal cord descending tracts, which transmit impulses controlling many voluntary movements.

More Spinal Cord Meninges - tough fluid containing membrane

that protects nerve tissue, brain, and spinal cord. Dura Mater – tough outer layer that lines the

vertebral canal. Pia Mater – innermost membrane covering the

spinal cord itself. Arachnoid – membrane between dura and pia

mater. Resembles a cobweb with fluid in its spaces. Arachnoid – “cobweb like” Arachne – Greek for “spider”.

Cerebral Spinal Fluid (CSF) – fluid in the subarachnoid spaces between pia mater and arachnoid in brain and spinal cord.

Cross section - H -shaped or butterfly shaped Gray Matter – cell bodies and dendrites White Matter – axon bundles spinal tracts

Dura mater - adhere to cranial bones

arachnoid - w CSF pia mater - adhere to

brain Brain cavities - filled with

CSF lateral ventricles (I and

II) located in each half of cerebrum

third ventricle in center of deincephalon

fourth ventricle in fron of cerebellum

Peripheral Nervous System Cranial and Spinal nerves - connect

brain and spinal cord to skin and structures

Autonomic Nervous System - part of PNS that controls instinctive behavior

Spinal Nerves

31 pairs of Spinal Nerves attached to the spinal cord 8 pairs attached to cervical segment 12 pairs to the thoracic segment 5 pairs to the sacrospinal segment 1 pair to coccygeal segment

Spinal Nerves have no special name –identified by a letter and number C1 – indicated spinal nerves attached to 1st segment of

cervical part of cord T8 – attached to 8th segment of thoracic part of cord

Spinal Nerves

31 Pairs Total 8 pairs – Cervical segment 12 pairs – Thoracic segment 5 parts – Lumbar segment 5 Parts – Sacrospinal segment 1 Part – Coccygeal segment

Dermatome - surface area maps of nerves

Autonomic Nervous System (ANS)

A subdivision of the peripheral nervous system which controls the body’s involuntary actions such as the heart rate and stomach contractions.

Consists of two divisions called the sympathetic nervous system and parasympathetic nervous system.

Sympathetic vs Parasympathetic Sympathetic - fight or flight Parasympathetic - rest and digest Sympathetic - thoraculmbar Parasympathetic - craniosacral

Pre, Post ganglion In the ANS, there are two neurons - one

that comes from the CNS - preganglionic, (ganglion), and a post ganglion to a visceral effector