Nervous System

Communication, control and Integration

All functions are Linked.

• Communication makes control possible

• Control makes integration possible• Integration leads to homeostasis

which makes survival possible

Nervous system does not work alone.To maintain homeostasis the body must have

the ability to monitor and then respond appropriately to changes that may occur in either the internal or external environment.

• Sense organs such as the eye and simple receptors in the skin or other tissues provide input.

• The Endocrine system produces hormones that also regulate body functions and maintain homeostasis working with the nervous system.

• Nervous systems is rapid and Endocrine systems is slower.

Parts of the Nervou System

2 Divisions of Nervous System• Central Nervous System - CNS BRAIN and SPINAL CORD• Peripheral Nervous System - PNS NERVES

cranial nerves – carry impulses to and from the brain.

Spinal nerves – carry impulses to and from the spine.

Brain, Spinal cord and Nerves

CNS integrates incomingPieces of info and Initiates outgoing responses

PNS – Nerves that lie in the Periphery or outer regions(Cranial and Spinal Nerves)

PNS

• Incoming – Afferent nerves – Sensory nerves –carry toward CNS from somatic or visceral sensory fibers.

• Outgoing – Efferent nerves – Motor nerves – carry away from CNS to somatic effectors (muscles and glands)

ANS – Autonomic Nervous SystemPart of the PNS 2 partsSympathetic Parasympathetic exits the spine exits the brain Fight or Flight Rest & Repair

response response

Activity Normal resting AKA Involuntary nervous system

Nervous Tissue

Neurons (Nerve Cells) and Neuroglia (Supporting Cells)

NeurogliaAstrocytes, Microglia, Ependymal cells, Oligodendrocytes and Schwann Cells

STAR shaped, largest, most numerous and form a sheath around the brain blood capillaries (BBB) Blood-Brain Barrier Form the living barrier between capillaries and neurons to allow exchange between them. Protects neurons from harmful substances that might be in the blood. Pick up excess ions and recaptures neurotransmitters.

Astrocytes

Microglia

• Spiderlike Phagocytes -Enlarge and Engulf and Destroy microbes and cellular debris

Ependymal Cells

• Form thin sheets that line fluid filled cavities in the brain and spinal cord.

• Their cilia help circulate cerebrospinal fluid.

Oligodendrocytes• Produce the fatty myelin sheet around

nerve fibers like insulation around a wire.

Neuroglia cannot conduct impulses!

Schwann Cells

• Form the myelin sheaths around nerve fibers that are found in the PNS

Contain the fatty white substance myelin

Schwann Cells

Neurons

• Cell body• Dendrites• Axons• Synaptic knobs

3 types of Neurons

“The big dogs” of the Nervous system

Unipolar Bipolar Multipolar Neurons

One axon several dendrites

Two processes becomefused as one then separate into axon and dendrite.

One axon andone dendrite

White matter vs. Gray matter• White matter is

myelinated - faster• Gray matter is

unmyelinated - slower

Physiology of an impulse

• Resting Membrane Potential -70mV

• Depolarization• Threshold -56mV• Action Potential -30mV• Repolarization• Depolarization/repolar-

ization repeats down the neuron until it reaches the end. Either at a motor end plate or the next neuron.

Synaptic Cleft and transmission of an impulse

Neurotransmitters bridge the gap at the synaptic clefts.

Acetylcholine – the main neurotransmitterAmines – Serotonin and histamine subclass- dopamine, epinephrine,

norepinephrine Affect learning, emotions, motor control and

other activities.Amino Acids – Most important common

neurotransmitters. Ex. Glutamate -75% of signals in the brain.Neuropeptides – act as hormones and pain relievers

subclass- enkephalins and endorphinsNeuromodulators AKA cotransmitters -regulate the

effects of neurotransmitters.

Which parts Control What?

(another view)

12(pairs) Cranial Nerves

Spinal Nerves (31 Pairs)

Coverings of the Brain and Spinal Cord

Meninges or membranous coverings • Dura mater – Outer covering Tough, leathery – forms a large cavity of

blood along the top of the brain called the sagittal sinus.

• Arachnoid – thin, translucent middle layer – contains cerebrospinal fluid (CSF)

• Pia mater – Inner most covering – Thin, vascular membrane covering the brain.

Meninges of the Brain

HOMEOSTASIS

NO OTHER BODY ORGAN IS SO ABSOLUTELY DEPENDENT ON A CONSTANT INTERNAL

ENVIRONMENT AS THE BRAIN.Other tissues can withstand the small

fluctuations in the concentrations of hormones, ions, and nutrients that continually occur after eating or exercising.

If these changes occurred in the brain, uncontrolled neural activity might result.

Blood-Brain Barrier• The BBB is composed of the least permeable

capillaries in the body.• Only water, glucose and essential amino acids pass

easily through the walls of these capillaries.• Wastes, toxins, proteins, and most drugs are

prevented from entering the brain tissue.• Potassium ions are actively pumped from the brain to

the capillaries.• Fats, respiratory gases, and other fat-soluble

molecules diffuse easily through the BBB.(Thus, alcohol, nicotine, and anesthetics can affect the

brain)

Circulation of CSF

• CSF is continually moving from the 2 lateral ventricles to the 3rd ventricle in the diencephalon and then through the cerebral aqueduct of the midbrain to the 4th ventricle to the pons and medulla oblongata.

• Normal drainage should maintain a volume of about 150mL or ½ a cup

Problems with the Nevous System• Tumors may obstruct drainage of CSF or

interfere with normal function.• Meningitis – inflammation of the meninges bacterial or viral infections• Encephalitis- inflammation of the brain. • Multiple sclerosis

Lumbar (Spinal) Tap – CSF sampling

Brain Dysfunctions• Huntington’s disease is genetic– loss of

coordination of muscle movements - After 40 usually. - Benefit from drugs that block dopamine

• Parkinson’s disease – neurotransmitter deficiency – deficient dopamine

• Concussion – brain injury is slight- dizziness, seeing stars, or unconscious briefly.

• Contusion – marked tissue destruction –severe brain stem contusions result in comas that may last from hours to a lifetime.

• Intracranial hemorrhage – death• Cerebral Edema – Swelling of the brain

Degenerative Brain Diseases• Stroke AKA Cerebrovascular Accident CVAs - 3rd leading

cause of death in the US.• Transient ischemic attack –TIA- temporary 5 to 50

minutes• Alzheimer’s Disease originally called Senile dementia –

structural damage occurs in the brain, abnormal protein deposits and twisted fibers appear within the neurons and localized brain atrophy.

• Half of Nursing Home Patients are stroke victims most of the other half are Alzheimer’s patients.

• Cerebral palsy- during deliveries a temporary lack of oxygen can result in CP - A neuromuscular disability in which the voluntary muscles are poorly controlled and spastic due to brain damage.

• Spina bifida- occurs when vertebrae form incompletely

• Hydrocephalus- Failure of the cerebrum to develop - water on the brain.

Spinal Cord Injuries• IF the spinal cord is transected or

crushed Spastic Paralysis results.Quadraplegic – all four limbs

affected.Paraplegic – only the legs affected.Swelling may cause temporary

paralysis.

Identify the types of neurons below

Identify the parts of this cell.

1.

2 3

4

5 6

7 8 9

10. What are the support cells of the nervous system called?

Place these in order of the 12 cranial nerves as they exit the brain. Then ID the nerve type. (S,M, or B)

• Vestibulocochlear• Trochlear• Oculomotor• Glossopharyngeal• Accessory• Olfactory• Abducens• Vagus• Hypoglossal• Optic• Trigeminal• Facial