Download Chapter 48: The Nervous System

Chapter 48: The Nervous System
The nervous system & endocrine system work to
regulate the organism & maintain homeostasis.
Nervous system
Involves:
Sensory
reception
Stimulus
(change in environment) triggers a response
concentrated in sense organs
Sensitivity determined by density of receptors
Integration
Interneurons
Motor
A
or associative neurons within the CNS relay message
response
reaction or behavior resulting in response to a stimulus
Effecter- muscle or gland which carries out a response

Neurons

Nerve cells



Structure similar in all organisms
Organization of cells varies among organisms
Parts

Dendrites

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Cell body

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Axon

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transmits signal
encloses axon, insulating signal
aids in speed of action potential
Terminal branches

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contains nucleus & other organelles
Myelin sheath


receive signal
may contain neurotransmitters
Synaptic gap

site of communication between 2 neurons via neurotransmitters
*Impulse enters via dendrites & exits via terminal branches

Glia= supporting cells

Types

Astrocytes


Radial glia


regulate ion & neurotransmitter concentration; dilation of blood vessels
act as stem cells
Oligodendrocytes (CNS) & Schwann cells (PNS)

form myelin sheath

Reflexes
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Automatic, inborn, unlearned
Protective responses to stimulation
Examples: blinking, sneezing, coughing
Reflex arc
Stimulus (receptors on sense organ) sensory neuron interneuron within CNS (analyze
& interpret) motor neuron effectors at neuromuscular junction


Instincts- automatic & inborn like reflexes but
not necessarily protective in function
Habits


Automatic, learned behaviors
Examples: smoking, tying shoe laces, using
profanity, writing

Response of neurons

Graded potentials

Magnitude of depolarization or hyper-polarization varies with stimulus
strength


Action potentials


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Bigger stimuli= bigger change
All or none depolarization
Same strength regardless of stimulus
Nerve impulse


Electrochemical signal; speeds of 100 meters/second
Resting state




both Na+ & K+ activation gate channels are closed
Resting potential- membrane more permeable to K+ so more K+ moves
out than Na+ moves in.
Ion permeability must change to send an impulse
Threshold must be achieved to depolarize neuron membrane &
produce an action potential



Depolarization: Na+ channels open & Na+ flows into neuron reversing
polarity
Re-polarization: K+ ions allowed into neuron as Na+ is blocked
Refractory: brief period of time when cell can not be stimulated to carry
an impulse

The Synapse

Types

Electrical synapses


Gap junctions allow action potential to travel cell to cell
Chemical synapses
Neurotransmitters released from synaptic vesicles & bind to dendrites of
next neuron to start a new action potential
**Majority of synapses


Neurotransmitters



Chemicals released into synaptic gap that diffuse & bind to next
neuron
Ca+2 required for release
Excitatory neurotransmitters


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Transmit impulses
Examples: acetylcholine (to skeletal muscle), norepinephrine, dopamine,
glutamate, aspartate
Inhibitory neurotransmitters


Block impulse transmission
Examples: acetylcholine (to cardiac muscle), serotonin, epinephrine,
glycine, GABA, endorphins

Regulation in invertebrates

Protists


Sensitive to light, chemicals, temperature
Cnideria (hydra)
Nerve net
 Whole organism responds to stimulus


Annelida (earthworm)
Ventral nerve cord
 Fused ganglia (clusters of neurons) acting as brain


Arthropoda (insects)
Ventral nerve cord
 Sensory organs

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Antennae
Tympanum
Compound eyes
Mammalian Nervous System
 Central Nervous System

Cerebrospinal fluid




helps supply nutrients & hormones to brain & removes waste
cushions brain & spinal cord
Meninges- protective layers surrounding brain & spinal cord
Brain

Cerebrum

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Largest, upper portion of brain
thinking, memory, body awareness, social behavior, language
EEG (electroencephalogram) detects brain wave activity
Convolutions- folds in brain
Limbic system- lower part of brain that interacts with cerebral cortex to produce
emotions, complex reasoning, & personality
 Includes:
 Amygdala- emotional memories
 Hippocampus- emotional events, long term memories
 Olfactory bulb
Corpus callosum- axons that enable communication between hemispheres of
cerebrum
Lobes:
 Frontal- speech, motor function
 Temporal- smell, hearing, auditory association
 Occipital- vision
 Parietal- reading, somatosensory association, speech, taste

Cerebellum


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Brainstem



Lower, posterior portion of brain
Regulates muscle balance, tone, coordination, & error checking
during motor, perceptual, & cognitive functions
Primitive brain controlling involuntary activities includes:
 Midbrain
 Pons- heart beat, swallowing, vomiting, digestion
 Medulla oblongata- breathing
Reticular formation
 network of neurons in the brainstem which selects
information being sent to cerebral cortex
 affects alertness
Diencephalon

Includes
 Epithalamus- pineal gland & choroid plexus
 Thalamus- input center for sensory info & output center for
motor info & emotions
 Hypothalamus- homeostatic regulation; connection between
nervous & endocrine systems; regulates circadian rhythms


Spinal cord- connects the brain to the peripheral nervous
system
Peripheral nervous system


System of branching nerves linking CNS to body tissues &
organs
Consists of:

Somatic nervous system

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
Voluntary control or awareness of muscles, sense organs, & skin
Allows for conscious control in response to external stimulation
Autonomic nervous system


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Automatic, unconscious or involuntary regulation
Regulates internal environment by controlling smooth & cardiac muscle
& organs
Includes
 Sympathetic nervous system- increased heart beat, blood vessel
constriction, bronchi open, pupils dilate, peristalsis slows, bladder
relaxes
 Parasympatheic nervous system- reverse reactions of sympathetic
nervous system
 Enteric nervous system- network of neurons to control organ
secretions & smooth muscles; regulated through the sympathetic &
parasympatheic nervous systems
Diseases & Disorders
 Schizophrenia
 Bipolar disorder/Manic depressive disorder
 Major depression
 Alzheimer’s disease
 Parkinson’s disease