Download Nervous System = communication conduit b/w brain

Nervous System = communication conduit b/w brain and body
Because neurons do not regenerate, spinal cord injuries can result in:
a) paraplegia = paralysis of lower half of body
b) quadriplegia = paralysis from neck down
Neuron = nerve cell
Three Main Regions of a Neuron:
a) dendrites = receive impulses from other neurons & conduct them to cell body
b) cell body = contains nucleus/organelles
c) axon = carries impulses from cell body to other neurons & muscles
Neuron Sketch (see textbook)
Three Types of Neurons:
a) sensory neurons = send impulses from receptors in skin & sense organs to
interneurons
b) interneurons = found in CNS – take impulse from sensory neuron & transmit to
motor neuron
c) motor neurons = carry impulse away from CNS to a gland or muscle, which
results in a response
Reflex Arc = nerve pathway that consists of a sensory neuron, an interneuron, and a
motor neuron
Nerve Impulse = electrical charge traveling length of a neuron (results from a stimulus –
ex: touch)
Neuron At Rest:
 There are more Na+ ions outside of neuron than inside, more K+ ions inside than
out.
 Negatively charged proteins in neuron act as a Na+/K+ pump – working to
counteract diffusion. Pumps Na+ out & K+ in. For every 2 K+ pumped into
neuron, three Na+ are pumped out. This creates unequal distribution of (+)
charged ions, resulting in a (+) charge outside neuron and a (-) charge inside
neuron.
Action Potential = another name for nerve impulse
Threshold = minimum stimulus to cause an action potential
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When a stimulus reaches threshold, channels in plasma membrane open.
Na+ rush into neuron’s cytoplasm through these channels.
This causes a temporary reversal in electrical charge.
Inside is now (+).
This causes other channels to open.
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K+ leaves cell through these channels, restoring (+) charge outside of cell.
This change in charge moves like a wave along the length of the axon.
Speed Of An Action Potential:
 Some axons have myelin sheath (insulating layer)
 Myelin sheath has gaps (nodes of Ranvier) along axon
 Na+/K+ cannot diffuse through myelin but they can reach plasma membrane at
these nodes
 This allows action potential to jump from node to node, increasing speed of
impulse as it travels length of axon.
 Some neurons have myelin, some do not
 Neurons with myelin carry impulses associated with sharp pain.
 Neurons that lack myelin carry impulses associated with dull, throbbing pain.
 Action potential in these neurons travels much more slowly than they do in
neurons with myelin.
Synapse = small gap between axon of 1 neuron & dendrite of another neuron.
 When an action potential reaches the end of an axon, vesicles (small sacs)
carrying neurotransmitters fuse with plasma membrane and release
neurotransmitter by exocytosis.
 When a motor neuron synapses with a muscle cell, the released neurotransmitter
crosses synapse and causes muscle to contract.
 Neutrotransmitter = chemical that diffuses across synapse and binds to receptors
on the dendrite of a neighboring neuron.
 This causes channels to open up on the neighboring cell and creates a new action
potential.
 Two most common neurotransmitters in human body: acetylcholine, epinephrine
Two Major Divisions of Nervous System:
1) Central Nervous System (CNS)
2) Peripheral Nervous System (PNS)
CNS = brain & spinal cord
PNS = sensory neurons & motor neurons (carry info to and from CNS)
CNS:
 made up mainly of interneurons.
 CNS relays messages, processes info., and analyzes responses
Brain = control center of body
 100 billion + neurons
 major sections (cerebrum, cerebellum, brain stem)
Cerebrum = largest part of brain
 divided into two hemispheres
 two hemispheres connected by bundle of nerves
 cerebrum carries out thought processes involved with learning, memory,
language, speech, voluntary body movements, & sensory perception.
 Folds/grooves increase surface area – allowing more complicated thought
processes.
Cerebellum = located at back of brain
 controls balance, posture, and coordination
 controls smooth & coordinated movement of skeletal muscles and is involved
with motor skills (ex: riding bike)
Brain Stem = connects brain to spinal cord
 Two regions of brain stem:
 Medulla oblongata = relays signals b/w brain & spinal cord
 Controls breathing, heart rate, BP
 Pons = relays signals b/w cerebrum & cerebellum, also helps control breathing
rate
Hypothalamus = located b/w brain stem & cerebrum
 maintaining homeostasis
 regulates body temp, thirst, appetite, and water balance.
 Partially regulates BP, sleep, aggression, fear, & sexual behavior.
Spinal Cord:
 nerve column extending from brain to lower back
 protected by vertebrae
 spinal nerves extend from spinal cord to parts of body
Nerve = bundle of neurons
 12 cranial nerves = lead to and from brain
 31 spinal nerves = lead to and from spinal cord
Peripheral Nervous System (PNS):
 all neurons not part of CNS including sensory neurons & motor neurons
 classified as part of somatic nervous system or autonomic nervous system
Somatic Nervous System (Voluntary)
 relays info. from sensory receptors to CNS & from CNS to skeletal muscle
Autonomic Nervous System (Involuntary) (not under conscious control)
 carries impulses from CNS to internal organs (ex: heart)
 fight or flight response ex: scary nightmare – heart rate quickens
Two Branches of Autonomic Nervous System:
 Sympathetic Nervous System (active in stressful times when heart rate/breathing
rate increase)
 Parasympathetic Nervous System (most active when body is relaxed,
counterbalances effects of sympathetic nervous system and restores body to a
resting state after a stressful situation)