the nervous & endocrine systems - bio 006 1 the nervous system (rev 6/10) control of the cells...

The Nervous & Endocrine Systems - BIO 006

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The Nervous System (rev 6/10) The Nervous System (rev 6/10) Control of the cells of our body is carried out by

2 communication systems, the nervous system and the endocrine system.

Both systems transmit information from one part of the body to another, but they do it differently.

• Nervous System: transmits information very rapidly by nerves which send impulses from one part of the body to another.

• Endocrine System: transmits information through chemicals secreted into the blood; glands without ducts secrete the chemicals.


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Divisions of the Nervous System

Central nervous system (CNS)—brain and spinal cord– is the integrating and command center of the nervous system

– it interprets incoming sensory information and produces motor responses

Peripheral nervous system (PNS) —all nerves which extend from the CNS to all parts of the body

Subdivisions: – Autonomic nervous system (ANS) ---

controls involuntary functions of the body: heart rate, stomach and intestine contractions, gland secretions

– Is further sub-divided into the• SYMPATHETIC NERVOUS SYSTEM which

mobilizes body systems during emergency situations

• the PARASYMPATHETIC NERVOUS SYSTEM which primarily conserves our energy


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Lab 5-Nervous System I 4

• the PNS has 2 functional subdivisions– the sensory or afferent division carries

impulses TO the CNS and keeps the CNS informed of events going on inside and outside of the body

– The motor or efferent division carries impulses FROM the CNS

• this division enables us to respond to stimuli


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Cells of the Nervous SystemCells of the Nervous System

2 types of cells: Neurons and Glia (also called Neuroglia)

Neurons Consist of three main parts

dendrites, which conduct impulses to the cell body of neuron;

cell body; and axon, which conducts impulses away

from cell body of neuron


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Myelin Sheath: wrapping around axon; formed by Schwann Cells; called Myelinated Fibers. Myelin is white in color.

Nodes of Ranvier

Saltatory Conduction


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Neurons are classified according to function:

• Sensory or afferent: conduct impulses TO the spinal cord and brain;

• Motor or efferent: conduct impulses AWAY FROM the brain and spinal cord to muscles and glands;

• Interneurons: conduct impulses from sensory neurons to motor neurons


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Glia (neuroglia) Support cells;

Attaches neurons to nearby structures protects them

Three main types of glial cells Astrocytes—anchor small blood vessels to

neurons Microglia—in inflamed or degenerating

brain tissue they act as phagocytes and remove this tissue

Oligodendrocytes—form myelin sheaths on axons in the CNS

Schwann cells form myelin sheaths of axons in the PNS


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NervesNerves

• Nerve —group of peripheral axons bundled together. The bundles are usually called “tracts”.• In the CNS, these bundles of axons

are called “tracts”.• White matter —tissue composed

primarily of myelinated axons (nerves or tracts)

Gray matter —tissue composed primarily of cell bodies, dendrites and unmyelinated fibers


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Nerve coverings—fibrous connective tissue Endoneurium—surrounds

individual fibers within a nerve Perineurium—surrounds a

group (fascicle) of nerve fibers Epineurium—surrounds the

entire nerve

Lab 5-Nervous System I 11

The Reflex Arc

Many of the body’s control systems belong to a general category known as reflexes.

• A reflex is a rapid, predictable motor response to a stimulus. – It is automatic, involuntary, and protective.– Both the spinal cord and the brain are reflex

centers.


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ReflexesReflexes• Nerve impulses are conducted from RECEPTORS

(receive stimulus)• to EFFECTORS (muscle or gland) over neuron

pathways (specific route frequently traveled by nerve impulses);

• The simplest reflexes are two-neuron arcs-- consist of sensory neurons synapsing in the spinal cord with an interneuron and then a motor neuron;

• • Complex or three-neuron reflexes consist of

sensory neurons synapsing in the spinal cord with interneurons that synapse with motor neurons and send a signal to the spinal cord and the brain.


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Nerve Impulse ConductionNerve Impulse Conduction

Definition—self-generating wave of electrical impulses that travel along the surface of a neuron

Mechanism: • The plasma membrane of a resting neuron has a slight

positive charge on the outside and a negative charge on the inside.• A stimulus triggers the opening of sodium (Na+)

channels in the plasma membrane of the neuron. • Positively charged sodium ions move into the cell

leaving a more negative charge outside the cell. • This causes an electrical impulse to start moving

down the nerve cell (neuron).


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Nerve signals need to jump across a space, called a synapse or a synaptic cleft, between the neurons.

The first neuron is called the pre-synaptic neuron and the neuron after the synapse is called the postsynaptic neuron.

When a nerve impulse arrives at the end of the neuron to an area called the synaptic knob (a tiny bulge at the axon terminals), it releases a neurotransmitter (chemicals by which neurons communicate) into the synaptic cleft (the space between the first and second neuron).

The second, or postsynaptic neuron, has protein molecules embedded in it opposite each synaptic knob. These are receptors and the neurotransmitter binds to them. The binding begins an impulse in the postsynaptic neuron.


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• Names of neurotransmitters: Acetylcholine, catecholamines

(epinephrine, norepinephrine, dopamine, and serotonin), and other compounds


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Central Nervous SystemCentral Nervous System

Divisions of the brainI. Brainstem:

Consists of the medulla oblongata, pons, and midbrain


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A. Medulla1. Two way conduction pathway between the spinal cord

and higher brain centers

2. contains the cardiac, respiratory, and vasomotor (blood vessels) control centers

B. Pons1. Two way conduction pathway between areas of

the brain and other areas of the body; Aids information flow--coordinates information flow between cerebellum and higher brain centers

2. Works with the medulla in regulating respiration

C. Midbrain1. Two way conduction pathway—relay for visual and

auditory pathways


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II. Cerebellum

A. Helps control coordinated movements, balance, and normal posture

III.Diencephalon A. Hypothalamus

1. Consists mainly of the posterior pituitary gland and gray matter

2. Acts as the major center for control of the Autonomic Nervous System (ANS---the ANS controls the functioning of most internal organs)


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3. Controls hormone secretion by anterior and posterior pituitary gland and therefore helps control hormone secretion by most other endocrine glands

4. Contains centers for controlling body temperature, water balance, appetite, wakefulness, pleasure, and many other body emotions


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B. Thalamus

1. Dumbbell-shaped mass of gray matter in each cerebral hemisphere

2. Produces sensations by relaying sensory impulses to the cerebral cortex

3. Associates sensations with the emotions of pleasantness or unpleasantness

4. Plays a part in the arousal or alerting mechanism


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Central Nervous SystemCentral Nervous System

IV. Cerebrum

A. Largest part of the human brain

B. Outer layer of gray matter is the cerebral cortex;

1. composed mainly of dendrites and cell bodies of neurons

2. made up of lobes as well as gyri (ridges) and sulci (grooves);

3. Interior of the cerebrum composed mainly of white matter

4. Functions—


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a. Frontal lobes initiate motor activity and are responsible for speech, conscious thought, and personality

b. Parietal lobes contain the somatosensory cortex; interpretation of sensory information from the skin and from the muscles and joints.

c. Occipital lobes contain the primary visual cortex and the visual association area

• association areas allow us to interpret/understand information

d. Temporal lobes interpret auditory information and are responsible for perceptual

judgment


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• Spinal cord Is the center for all spinal cord reflexes Outer part is composed of white matter made

up of many nerve tracts (bundles of axons); Interior composed of gray matter made up

mainly of dendrites and cell bodies Sensory tracts conduct impulses TO the brain Motor tracts conduct impulses FROM the

brain


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Coverings and fluid spaces of the brain and spinal cord Coverings

Skull and vertebraeCerebral and spinal meninges—the dura

mater, the arachnoid mater, and the pia mater

Form protective covering for the brain and the spinal cord

Cerebrospinal FluidBlood-brain barrierHydrocephalus


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Autonomic Nervous SystemAutonomic Nervous System

• Composed of two divisions— • the sympathetic system —the “fight or flight”

system and • the parasympathetic system —the “normal

functioning” system• regulates the body’s automatic or involuntary

functions • conducts impulses from the central nervous

system to cardiac muscle, smooth muscle, and glandular epithelial tissue


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• Sympathetic nervous system Sympathetic preganglionic neurons are

located in the thoracic and upper lumbar segments of the spinal cord

Parasympathetic nervous system Parasympathetic preganglionic neurons are

located in the brainstem and in the sacral segments of the spinal cord

Nervous System Disorders--Psychoactive Drugs

• Action: affects higher brain functions; work by influencing the actions of brain neurotransmitters; can cross the blood brain barrier

• Psychological dependence: user craves the feeling associated with the drug

• Tolerance: takes more of the substance to achieve the same affect

• Addiction: the need to continue obtaining and using a substance; no free choice

• Withdrawal: physical symptoms that occur upon stopping the drug

Autoimmune Disorders:Multiple Sclerosis (MS):

• An autoimmune disease that mainly affects young adults– The sheaths of myelinated neurons in the brain

and spinal cord become progressively damaged until they form hardened (sclerotic) scar tissue. These areas can’t effectively insulate the neurons and so impulse transmission is slowed and disrupted.

– People with MS experience a variety of symptoms depending on which area of the CNS are damaged.

Disorders of the Nervous System

• Symptoms include visual disturbances, weakness, loss of muscular control, and urinary incontinence

TREATMENT• The advent of disease-modifying drugs

including interferon beta-1a and -1b, Avonex, Betaseran, and Copazone:– Hold symptoms at bay– Reduce complications– Reduce disability

Multiple Sclerosis

Amyotrophic Lateral Sclerosis (ALS)• Similar to MS but the sclerotic areas

begin in areas of the spinal cord involved in the motor control of skeletal muscles

• Primary symptom is progressive weakening and wasting of skeletal muscles, especially those responsible for breathing

Trauma: • Concussion: caused by a violent blow to the head

or neck– Usually see a short loss of consciousness due to

a disruption of the electrical activity of brain neurons.

– After regaining consciousness, person may have blurred vision, confusion, nausea and vomiting

– Typically concussions don’t have permanent damage unless there is a subdural hematoma: bleeding into the space between the meninges

• Bleeding increases pressure within headsquashes brain tissue and disrupts function of brain

–Symptoms: drowsiness, headache and weakness of 1 side of body

• Treatment: surgery for immediate relief of pressure and repair of bleeding blood vessels

• Spinal cord injuries: will impair sensation and function below the level of injury– Paraplegia or quadriplegia; can be fatal; will

always cause problems with bladder and bowel control

Infections: Brain and spinal cord typically do not get infected due to the blood-brain barrier.

• Encephalitis: inflammation of the brain; typically caused by a virus– Symptoms: headache, fever, fatigue,

hallucinations, confusion, disturbances in speech, memory or behavior, epileptic seizures

– Treatment: Hospitalization with IV medications

• Meningitis: Inflammation of the meninges; can be viral or bacterial– Symptoms: headache, fever, nausea and

vomiting, light sensitivity, stiff neck– Treatment: hospitalization. If viral, mild

symptoms and will improve in few weeks–If bacterial, can be fatal; IV antibiotics

needed ASAP

• Rabies: infectious viral brain disease – Transmitted to humans by direct contact, either bite or

lick over broken skin• Virus attacks the sensory neurons in the bite region then

travels to the spinal cord, then to the brain where it multiplies and kills cells

– Symptoms: swollen lymph glands, painful swallowing, vomiting, choking, spasms of throat and chest muscles, fever, becomes irrational. Death within 2-20 days

– Treatment: wash wound thoroughly ASAP, go to emergency room or doctor, have animal tested, receive rabies immunization ASAP

Neural and synaptic transmission disorders: action potentials can’t be properly sent. Symptoms depend on which nerves are affected

• Epilepsy: recurring episodes of abnormal electrical activity in brain– Seizure triggers: fatigue, stress, flashing lights – Seizures vary widely due to which part of brain

is affected– Treatment: EEG, medications

• Parkinson’s disease: progressive degenerative illness; loss of dopamine releasing neurons in the area of the midbrain that coordinates muscle movements; can’t perform smooth, coordinated movement– Symptoms: stiff joints, muscle tremors in

hand, loss of mobility, depression and other mental impairments

– Treatment: L-dopa, a drug which the body converts to dopamine. Will become ineffective eventually

• Alzheimer’s disease: disorder of mental impairment, especially memory due to a shortage of the neurotransmitter acetylcholine. Primarily affects neurons in the limbic system and frontal lobe. See plaques (beta amyloid) in brain tissue and abnormal, tangled neurons.

– Symptoms: Progresses from memory lapses to severe memory loss, especially of STM. LTM affected very slowly. Disorientation, dementia, personality changes, loss of ability to function independently

– Treatment: medications which increase the brain’s production of acetylcholine

Brain tumors: abnormal growth in or on the brain

• Can be cancerous or benign– Problems due to increased pressure within

the brain– Symptoms: headache, vomiting, visual

impairment, confusion, muscle weakness, difficulty speaking, seizures

– Treatment: Surgical removal, radiation and chemotherapy to try to shrink the tumor.

the nervous & endocrine systems - bio 006 1 the nervous system (rev 6/10) control of the cells...

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