The Human Nervous System

Regulation

the life process by which cells and organisms respond to changes within and around them

Central Nervous System

consists of the brain and the spinal cord (CNS)

Peripheral Nervous System

consists of nerves outside of the brain and spinal cord (PNS)

Stimulus

a change in the environment

Receptors

special cells sensitive to stimuli

Sense organs

eyes, ears, nose, tongue, skin

Impulse

an electrical/chemical message that is carried by a nerve cell

response

a reaction to a stimulus

Effectors

muscles and glands

Neuron

nerve cells that conducts impulses

neuroglia

non-conducting connective tissue cells that support neurons

Characteristics of neuroglia

smaller, but more numerous than neurons

consists more than half the volume of the brain

they regularly divide via mitosis

6 Types of Neuroglia

1. Microglia

2. Astrocytes

3. Ependymal Cell

4. Oligodendrocytes

5. Schwann Cells

6. Satellite Cells

Microglia

small, phagocytic cells that protect neurons from microbes and debris

Astrocytes

star shaped cells that cling to neurons and capillaries; help form the blood brain barrier and help transport substances from blood.

Ependymal Cells

lines the brain and spinal cord; produce cerebrospinal fluid (CSF)

Oligodendrocytes

most common cells in the CNS; provide the myelin sheath

Myelin Sheath

lipid/protein substances that wrap around neurons

Schwann Cells

produce myelin sheath around the PNS neurons

Satellite Cells

support neurons in ganglia

Characteristics of Neurons

Excitability = respond to stimuli

Conductivity = conduct impulses

Integration = interpret and respond to impulses

Range

Speed

Longevity

high metabolic rate

Cell Body

contains the nucleus and cytoplasm

nissl bodies

pieces of the ER that produce protein

Neurofibrils

filaments that form the cytoskeleton

dendrites

receives impulses from other neurons

Axon

carries impulses to the next neuron

axon hillock

area where cell body meets the axon

axon collateral

branches of axon

terminal branches

branches at the end of the axon

axon terminal

end bulbs of terminal branches that contain neurotransmitters

schwann cells/oligodendrocytes

surrounds axon producing myelin

Neurilemma

membrane that covers the myelin formed by schwann cells

nodes of ranvier

gaps between schwann cells along axon

synapse

space between neurons

neurotransmitters

chemicals that cross the synapse

Three Types of Neurons

1. sensory

2. interneurons

3. Motor

Sensory Neuron

carries impulses from receptors to brain

interneurons

brain processing neurons

motor neurons

carries impulses from brain to effectors

Nerves

bundles of neurons within the PNS

Transmission of nerve impulses

a change in the electrical charge along the cell membrane of a neuron caused by the movement of ions across the cell membrane

Resting state of a neuron

no impulse conduction; positive charge outside membrane, negative charge inside the membrane.

Impulse Conduction

reversal of polarity along the membrane as the voltage charge reaches threshold

Action potential

a rapid rise and subsequent fall in voltage or membrane potential.

depolarization

the membrane charge becomes negative outside and positive inside

repolarization

the membrane charge returns to positive outside and negative inside.

refractory period

resting period before next impulse (action potential)

Two factors effecting the rate of an impulse

1. Thicker the nerve fiber = faster impulse

2. myelinated axons are 50x faster than unmyelinated axons

Nerve threshold

minimum strength to start an impulse

Distinguishing strength and type of stimulus

1. Stronger stimuli create more impulses; hot = many impulses; warm = few impulses

2. different neurons have different thresholds; hot = thresholds 80 mV; warm = thresholds 30 mV

types of receptors

each receptor is sensitive to only a certain type of stimulus; eyes are sensitive to light, not sound

transmission of a synapse

1. electrical impulses stimulate the release of neurotransmitters

2. neurotransmitters bind to receptors

3. if enough neurotransmitters bind to reach the threshold (action potential), impulse continues

neuromuscular junction

space between nerve cells and muscle fibers

the brain is made up of:

100 billion neurons, 1 trillion neuroglia

Cranial Meninges

tough fluid filled membrane covering the brain

3 layers of cranial meninges

Dura mater - outer

Arachnoid - middle

pia mater - inner

Cerebrospinal Fluid (CSF)

contains glucose, proteins, lactic acid, urea, electrolytes, and lymphocytes; Functions:

1. provides shock absorption, floats brain

2. provides optimal chemical environment for neurons

3. Allows for exchange of nutrients and waste between blood and brain tissue

Ventricles

cavities in the brain filled with CSF

Blood-Cerebrospinal fluid barrier

tight junctions between ependymal cells prevent leaking; protects brain and spinal cord from harmful substances

blood-brain barrier

tight junctions in endothelial cells of brain capillaries

brain stem

consists of white matter and scattered bits of gray matter; consists of medulla, pons, and midbrain

Medulla Oblongata

controls involuntary activities; controls swallowing, vomiting, coughing, sneezing, and hiccupping.

Diencephalon

consists of thalamus and hypothalamus

Thalamus

relay center between impulses and cerebrum; interprets pain and pressure impulses

Hypothalamus

maintains homeostasis; relay center between brain and endocrine system

Cerebellum

2nd largest portion of brain; white matter outer layer, gray matter inner layer.

functions:

produces smooth muscle coordinated movements.

maintains posture, muscle tone, balance, and equilibrium

Cerebrum

largest portion of the brain; functions:

interprets sensory impulses from sense organs

initiates impulses for voluntary responses

associated with memory, learning, thought, emotions, and personality.

cerebral cortex

thin outer layer of gray matter

convolutions (gyri)

folds that increase the surface of the cortex

corpus callusom

connects the 2 cerebral hemispheres

sulcus

shallow grooves

fissures

deep grooves that separate the cerebrum into distinct lobes

Spinal Cord

extension of the brain stem that runs down the spinal canal protected by the vertebrae, spinal meninges, and cerebrospinal fluid; “cauda equina”;

functions:

connects the CNS to the PNS

controls spinal reflexes

Reflex

an involuntary response such as a sneeze, blink, or hiccup; goal: speed up response; does not involve the brain = less neurons; automatic or unconscious response

reflex arc

receptor → sensory neuron → spinal cord interneuron → motor neuron → effector

Two types of nerves

Spinal Nerves, Cranial nerves

Spinal Nerves

31 pairs that stem from spinal cord- cauda equina

cranial nerves

12 pairs that stem from brain

Divisions of the PNS

1. Somatic Nervous System

2. Autonomic Nervous System

   1. Sympathetic Nervous System

   2. Parasympathetic Nervous System

Somatic Nervous System

Controls voluntary activities; serves skeletal muscles

Autonomic Nervous System

controls involuntary activities to control homeostasis; stimulates/inhibits actions of involuntary muscles/glands; heart and breathing rate, blood pressure, body temp.

Sympathetic nervous system

prepares body for energy-expending, stressful, or emergency situations; increases and decreases rates

Parasympathetic nervous system

restores body to resting state following a stressful experience; goes back to rest from Sympathetic nervous system

Stroke

a blockage or rupture of a blood vessel in the brain causing death of brain cells

Parkinson’s

a slowly progressive degenerative disorder of the nervous system characterized by muscle tremors caused by low dopamine levels

Meningitis

an inflammation of membrane surrounding brain and spinal cord caused by bacterial infection/severe headache and stiffness in the neck

Alzheimers

a progressive loss of mental function, characterized by degeneration of brain tissue, including loss of nerve cells and the development

Epilepsy

seizures caused by periodic disturbances of the brain’s electrical activity resulting in some degree of temporary brain dysfunction

Multiple Sclerosis

destruction of myelin causing scarring of brain tissue

Cerebral Palsy

birth disorder affecting motor functions, crippling disorder with no cure

Polio

viral disease causing paralysis/prevented by vaccine