Chapter 35: The Nervous System

4 levels of organization

4.organ systems

muscle tissue

-controls internal movement of materials

epithelial tissue

-covers body surface
-lines internal organs and body cavities
-makes up glands that secrete products

connective tissue

-provides support to other tissues
-holds organs in place
-binds body parts together


in connective tissue, holds muscle to bone


in connective tissue, joins bone to bone

nervous tissue

receives messages from internal/external environment


process by which an organism maintains a stable internal environment

feedback inhibition

The product of a system shuts down or limits that system; helps to maintain homeostasis


-brain region where skin and core body temp is monitored
-regulates activity that controls body temp such as shivering/sweating

nervous system

controls and coordinates functions throughout the body and responds to internal and external stimuli


-cell that transmits electrical impulses throughout the body
-basic unit of the nervous system

Three types of neurons

sensory, motor, and interneurons

sensory neurons

sense organs--->spinal cord and brain

motor neurons

brain and spinal cord--->muscles and glands


sensory neurons<--->motor neurons

cell body

-contains nucleus and most cytoplasm
-largest part of neuron
-most metabolic activity occurs here


-short branched extension from cell body
-carry impulses from environment to the cell body
-many per neuron


-long fiber that carries impulses away from cell body
-ends with many axon terminals

myelin sheath

-insulating membrane around axon
-exposed Nodes of Ranvier
-Myelin speeds transmissions of impulse from node to node


-bundles of neuron; can be very long

nerve impulse

when a nerve cell fires

what does production of a nerve impulse depend on?

movement of positive ions across a membrane

how do nerve impulses travel?

travel along cell membrane from dendrites to axons

resting potential

-the difference in electrical charge across the membrane of a resting axon

how is the diff. in concentration of these ions maintained?

Active Transport via the Na+-K+ pump

What is the result of the Na+-K+ pump?

-K+ diffuses out of the cell (because there is more K+ in cell)
-Na+ diffuses into the cell easily (because more Na+ out of the cell)

Action Potential

-reversal of charges across the cell membrane during transmission of an impulse


minimum level of a stimulus required to activate a neuron


Any stimulus stronger than threshold will trigger an impulse

No impulse

Any stimulus weaker than threshold will NOT trigger an impulse

The Synapse

space between axon terminal and their target cells


-chemical used to transmit impulses across synapses to other cells
-Contained in vesicles within axon terminals

Central Nervous System

-Brain and Spinal Cord
-relays messages, processes information, analyzes information
-protected by skull and vertebrae
-covered by meninges


3 layers of connective tissue

cerebrospinal fluid(4)

-Found in spaces with meninges
-covers brain and spinal cord
-shock absorber
-allows exchange of nutrients and waste between blood and neurons

cerebrum's structure?(2)

-2 hemispheres
-connected by the corpus callosum

corpus callosum

holds the two hemispheres of cerebrum together and allows them to communicate to each other

4 lobes in each hemisphere

-frontal, parietal, temporal, occipital
-8 total

frontal lobe of cerebrum

memory, voluntary movements, speech

parietal lobe of cerebrum

taste, smell, texture, reading, math

temporal lobe of cerebrum

smell, hearing, memory integration

Occipital lobe of cerebrum

vision, visual memory

functions of cerebrum(3)

1. controls voluntary/conscious activities
2. site for intelligence, learning, judgement
3. each hemisphere controls function in the opposite side of the body

right hemispere

creativity, art and music

left hemisphere

logic, language, science and math

cerebral cortex(4)

-outer surface
-processes from sense organs
-controls body movements
-made up of gray matter

gray matter

cell bodies; what the cerebral cortex is made of

white matter

-bundles of axons w/ myelin sheaths
-central part of cerebrum


coordinates and balances actions of muscles so that the body moves gracefully and efficiently

brain stem(3)

-regulates flow of info between brain and body
-controls heart rate, blood pressure, breathing, swallowing
-consist of medulla oblongata, and pons


relays messages from sense organs to correct region of cerebrum


control center for hunger, thirst, fatigue, anger, body temp

pituitary gland(2)

-stores many hormones that control various body processes
-controlled by the hypothalamus

pineal gland

-secretes melatonin
-controls sleep

spinal cord

-31 pairs of nerves connected the brain to the body
-some info is processed directly here


-quick automatic response to a stimulus processed in the spinal cord
-allows immediate response to danger

peripheral nervous system

receives info from environment and sends it to the brain

sensory division (part of PNS)

receives info from organs and sends to brain

motor division (part of PNS)

relays command from brain back to organs

somatic nervous system

regulates conscious activites

how does somatic nervous system work?

moving limbs

reflex arc

message goes only to spinal cord and back

autonomic nervous system

-regulates involuntary activities
-examples: heartburn, digestion, blood vessel diameter

sympathetic nervous system "fight or flight"(2)

-2 diff sets of neurons
-analogy: gas pedal and brake

parasympathetic nervous system

-opposite effects on the same organs
-ex. heart rate