Biology II - Chapter 9: The Nervous System (Part I)

brain, spinal cord, nerves

overall function - coordinate the body’s systems by receiving and sending information, maintaining homeostasis

• gathering information from receptors in the body

• to monitor changes occurring inside and outside the body

• changes = stimuli

to process and interpret sensory input and decide if action is needed and where the action will occur

• a response to integrated stimuli

• the response activates muscles or glands to maintain homeostasis

Central Nervous System (CNS), Peripheral Nervous System (PNS)

brain and spinal cord

• nerves throughout the body

  • 31 pairs of spinal nerves

  • 12 pairs of cranial nerves

sensory (afferent) division, motor (efferent) division

nerve fibers that carry information to the central nervous system

nerve fibers that carry impulses away from the central nervous system, two subdivisions (somatic nervous system, autonomic nervous system)

voluntary; ex. skeletal muscles

involuntary; ex. smooth and cardiac muscles, glands

support cells in the CNS are grouped together as “neuroglia"; functions: to support, insulate, and protect neurons

• microglia

• oligodendrocytes

• astrocytes

• ependymal cells

• schwann cells'

• satellite cells

immune function; spider-like phagocytes that digest debris and kill bacteria

make myelin sheath that provides insulation around the axons in the central nervous system

abundant; star-shaped cells; brace neurons; connect blood vessels to neurons; form barrier between capillaries and neurons; control the chemical environment of the brain

forms membranes around tissue; lines cavities of the brain and spinal cord; circulates cerebrospinal fluid

form the insulating myelin sheath around the neurons in the PNS (same function as oligodendrocytes, which are found only in the CNS)

insulate axons; schwann cells supply the myelin for peripheral neurons; oligodendrocytes myelinated the axons of the central nervous system

nodes of ranvier

protect neuron cell bodies

masses of nerve cells that transmit information (functional unit of the system); major regions are cell body and processes (dendrites and axons)

contains the nucleus and other cell organelles

shorter, more numerous, receive information, conducts information toward the cell body

single long fibers, conducts information away from the cell body

in axonal terminals

vesicles with neurotransmitters (different neurotransmitters for different muscles)

separated from the next neuron by a gap or a synapse

transport system

insulation surrounding axons (white, fatty material)

gaps in the insulation

fibers within the axon

carry impulses from the sensory receptors to the CNS

cutaneous sense organs; proprioceptors; other sensory organs (eyes, ears, nose, mouth)

naked nerve endings (temperature and pain); Meissner’s Corpuscle (light touch); Pacinian Corpuscle (deep touch)

detect stretch or tension in tendons, ligaments, or muscles

carry impulses from the CNS to viscera, muscles, or glands

found in neuro pathways in the CNS; connect sensory and motor neurons

white matter

grey matter

sensory, motor, interneurons

bipolar, unipolar, multipolar

• longevity - can live and function for lifetime

• do not divide - fetal neurons lose their ability to under go mitosis; neural stem cells are an exception

• high metabolic rate - require abundant oxygen and glucose

• the nerve fibers of newborns are unmyelinated - this causes their responses to stimuli to be cause and sometimes involve the whole body

resting potential, threshold potential, action potential

weak electric current, like a wave

1. neuron membrane maintains resting potential

2. threshold stimulus is received

3. sodium channels open

4. sodium ions diffuse inward, depolarizing the membrane

5. potassium channels open

6. potassium ions diffuse outward, repolarizing the membrane

7. the resulting action potential causes a local bioelectric current that stimulates the membrane

8. wave of action potentials travel the length of the axon as a nerve impulse

is the loss of the difference in charge between the inside and outside of the plasma membrane of a muscle or nerve cell due to a change in permeability and migration of sodium ions to the interior

• is when potassium ions rush out of the neuron after sodium ions rush in

• the sodium-potassium pump, using ATP, restores the original configuration

• potassium ions diffuse out of the cell as the membrane permeability changes again restoring the negative charge on the inside of the membrane and the positive charge on the outside surface

speed is proportional to the size of the axon (a greater diameter = faster impulse); myelinated axons conduct impulses faster than unmyelinated ones

is the junction between two communicating neurons; a nerve pathway is the path from which nerve impulses travels from neuron to neuron

dendrite, cell body, along axon, synapse, dendrite

a neurotransmitter is released from a nerve’s axon terminal; he dendrite of the next neuron has receptors that are stimulated by the neurotransmitter; an action potential is started in the dendrite

a neurotransmitter is released at the gap to signal the next neuron; receptors on the dendrite receive this chemical message

• A: Neuron (axon)

• B: Neuron (dendrite)

1. mitochondria

2. vesicles

3. receptor

4. synapse

5. receptor

6. calcium channel

7. release neurotransmitter

8. re-uptake

excitatory, inhibitory

increase membrane permeability, increases chance for threshold to be achieved

decrease membrane permeability, decrease chance for threshold to be achieved

• acetylcholine

• dopamine

• serotonin

• endorphins

• gaba (common)

stimulates muscles contraction

mood, makes happiness or some other emotion

sleepiness; mood

pain reduction; mood

reduces the activity of the neurons to which it binds (inhibitory); most common type of receptor; 40% of all synapses work with GABA; GABA has a tranquilising effect; low levels of GABA associated with anxiety and phobia

molecule that has the same effect on the postsynaptic neuron as the neurotransmitter itself does

molecule that blocks the effect that the neurotransmitter normally has on the postsynaptic neuron

groups of neurons that make hundred of synaptic connections and work together to perform a common function; these “pools” help us remember sequential tasks (ex. tying a shoe, riding a bike)

rapid, predictable, and involuntary response to a stimulus; occurs over pathways called reflex arcs

direct route from a receptor, to a sensory neuron, to a interneuron, to a motor neuron, to an effector

• somatic reflexes

• patellar, or knee-jerk, reflex

• autonomic reflexes

activation of skeletal muscles (ex. when you move your hand away from a hot stove)

is an example of a two-neuron reflex arc

smooth muscle regulation; heart and blood pressure regulation; regulation of glands; digestive system regulation

CNS develops from the embryonic neural tube

the brain and spinal cord

the ventricles

• cerebral hemispheres (cerebrum)

• diencephalon

• brain stem

• cerebellum

cerebrospinal fluid

inky large part of the brain (cerebral cortex); includes more than half of the brain’s mass; higher mental function, solving problems

dendrites, axon, axon terminal, cell body

motor neuron,

Excitatory and inhibitory; excitatory: increase membrane permeability, increases chance for threshold to be achieved; inhibitory: decrease membrane permeability, decrease chance for threshold to be achieved; why the body needs it: both are necessary for you to not be overstimulated (by too much excitatory) or have dulled senses (by too much inhibitory), Mr Ronnie says you need to have them, instead of not having any at all, because if you had none you “wouldn’t be able to feel anything.”